energy efficient downlink transmission in wireless lans by...

Research ArticleEnergy Efficient Downlink Transmission in Wireless LANs byUsing Low-Power Wake-Up Radio

Suhua Tang and Sadao Obana

Graduate School of Informatics and Engineering The University of Electro-Communications Chofu Japan

Correspondence should be addressed to Suhua Tang shtanguecacjp

Received 26 August 2017 Accepted 28 November 2017 Published 24 December 2017

Academic Editor Zhi Liu

Copyright copy 2017 Suhua Tang and SadaoObanaThis is an open access article distributed under theCreative CommonsAttributionLicense which permits unrestricted use distribution and reproduction in anymedium provided the originalwork is properly cited

In the downlink of a wireless LAN power-save mode is a typical method to reduce power consumption However it usually causeslarge delay Recently remote wake-up control via a low-power wake-up radio (WuR) has been introduced to activate a node toinstantly receive packets from an access point (AP) But link quality is not taken into account and protocol overhead of wake-upper node is relatively large To solve these problems in this paper a broadcast-based wake-up control framework is proposed anda low-power WuR is used to receive traffic indication map from an AP monitor link quality and perform carrier sense Amongthe nodes which have packets buffered at the AP only those whose SNR is above a threshold will be activated contending via aproper contention window to receive packets from the AP Optimal SNR threshold deduced by theoretical analysis helps to reducetransmission collisions and false wake-ups (caused by wake-up latency) and improve transmission rate Extensive simulationsconfirm that the proposed method (i) effectively reduces power consumption of nodes compared with other methods (ii) hasless delay than power-save mode in times of light traffic and (iii) achieves higher throughput than other methods in the saturationstate

1 Introduction

Wireless local area network (WLAN) [1] is playing amore andmore important role in offloading the ever-increasing mobiletraffic from cellular networks Downlink traffic is themajorityin WLANs and its transmission usually faces two problems(i) First one is the energy waste due to idle waiting Becausethe arrival timing of a packet is not known in advance theWLAN module of each node has to stay awake so as toreceive any packet instantly This constant awake mode leadsto much energy waste Power-save mode [1] (and adaptivePSM [2]) is a typical method to reduce power consumptionIn this method WLAN modules of nodes periodically wakeup to receive from the AP (Access Point) beacons with trafficindication and if any packets have arrived they stay awake toreceive those packetsHowever in this duty-cyclingmode [3]saving more power requires a longer period which usuallyleads to larger delay (ii) Second one is the low transmissionrate or even packet loss due to multipath fading This isbecause an AP has no channel state information (CSI) aboutits nodes

As for (i) there has been much research on remote wake-up control [4 5] The basic idea is to equip each nodewith a low-power wake-up radio (WuR) which is alwaysactive to accept wake-up request [6ndash8] Then power-hungryparts of a node are put into sleep and remotely activated ondemand This was first studied for sensor networks [9ndash11]Because there is little traffic in sensor networks most existingwork adopted a loose integration of the WuR and the sensormodule

Recently the idea of wake-up control is also appliedto WLAN In the simple downlink wake-up control [12]an AP transmits a wake-up message (WuM) to a specificnode A WuR receiving a WuM matching its own addressactivates its colocated WLAN module on demand Howeverthis unicast wake-up per node generates much overhead andtransmissions may be conducted at a low rate or even packetloss occurs in the presence of multipath fading

As for (ii) many efforts have been devoted to applyingmultiuser scheduling to improve transmission rate and thereis still active research in this field [13 14] In the multipleaccess uplink many nodes contend to access the shared

HindawiWireless Communications and Mobile ComputingVolume 2017 Article ID 2405381 12 pageshttpsdoiorg10115520172405381

2 Wireless Communications and Mobile Computing

channel to transmit to the AP The performance dependson two important factors (i) collision probability and (ii)transmission rate Because each node experiences fadingindependently by limiting the contention to nodes withhigh link quality average transmission rate can be improvedand collision probability can be reduced There have beensome methods suggested for slotted ALOHA [15 16] andCSMA networks [17] This is also applied to the downlinktransmission by letting each node contend to initiate thereceiving from the AP based on their link quality [18] Buta WLAN module is kept awake to monitor the channelcontinuously to obtain fresh CSI which leads tomuch energywaste

Compared with previous works that separately solve theabove issues in this work we try to jointly solve these issuesapplying multiuser scheduling to improve transmission ratemeanwhile reducing both the protocol overhead of wake-upcontrol and the energy overhead of monitoring the channelall by using the low-power WuR To this end we proposea new framework broadcast-based wake-up control In thisframework an AP periodically broadcasts by its WLANmodule a WuM carrying a traffic indication map (TIM)[1] which is modulated by OOK (On-Off-Keying) on theenvelope of an OFDM signal [19] This WuM is received byenvelope detection at a low-power WuR equipped at eachnode AWuR is used tomonitor link quality performs carriersense and activates its colocated WLAN module via thedistributed contention

The broadcast-based wake-up control brings new issuesWhen more than two nodes contend there will be transmis-sion collisions and false wake-ups A WLAN module cannottransmit immediately after it receives wake-up instructionfrom its WuR in the presence of the wake-up latency Duringthe wake-up period of a node other WuRs sense the channelas idle and falsely activate their WLAN modules which leadto false wake-up [20] and power waste The false wake-up problem occurs because the initial values of backoffcounters of two or moreWuRs have a difference less than thelength of the wake-up period This problem is addressed in[20] by adjusting the contention window which uses largercontention window at the cost of more idle slots In thiswork this issue is solved by setting the SNR (signal to noiseratio) threshold and applying the distributed scheduling ofwake-up control and transmissionThis reduces transmissioncollisions as well

Main contributions of this paper are threefold as follows

(1) A new framework of broadcast-based wake-up con-trol enables distributed wake-up scheduling

(2) Broadcast-based wake-up control reduces protocoloverhead and improves channel efficiency comparedwith wake-up per node

(3) The three problems multipath fading transmissioncollisions and false wake-ups are solved simultane-ously by setting a proper SNR threshold

Optimal SNR threshold is deduced by theoretical analysisExtensive simulations verify that the proposed method (i)effectively reduces power consumption of nodes compared

with the other methods (ii) has less delay than power-save mode in times of light traffic and (iii) achieves higherthroughput than the other methods in the saturation state

The rest of this paper is organized as follows Section 2presents the proposed framework Section 3 gives the optimalparameter by theoretical analysis Section 4 shows the resultsof simulation evaluation and finally Section 5 concludes thispaper

2 Proposed Method

The framework of the proposed method is shown in Figure 1In this framework a low-power WuR is added to each nodefor activating its colocated WLAN module To suppresspower consumption a WuR instead of a power-hungryWLAN module is used to monitor the channel and performcarrier sense To this end a WuR shares the same channelwith WLAN modules and a WuM is transmitted from theWLANmodule of an AP to a WuR

21 Wake-Up Model Different methods can be used toconvey a WuM from a WLAN module (of an AP) to anon-WLAN WuR as follows (i) Frame length of WLANsignals can be modulated to deliver wake-up message froma WLAN module (transmitter) to a WuR [21ndash23] (ii) AWLAN module at a low clock rate can work as a WuR todetect a WuM embedded in the preamble of a WLAN signal[24] (iii) OOK modulation can be emulated to transmit aWuM by modulating the envelope of an OFDM signal [19]In this work we adopt (iii) because a WuR with envelopedetection can work with low-power consumption and OOKmodulation is more efficient than frame length modulation

A WuM carried in the envelope of a WLAN signal isdetected by a WuR using envelope detection It should benoted that emulating the OOK modulation has its own costFor example at the rate of 100 kbps transmitting aWuMwith40 bits will require 04ms which causes much overhead forwake-up per node To reduce protocol overhead a broadcastwake-up policy is adopted in this work instead of letting anAP separately activate each node to receive packets To thisend eachWuM carries a TIM which simultaneously notifiespacket availability tomultiple nodesThen it is nodes insteadof the AP that contend to initiate the data receiving [25] bytransmitting a CTS (clear to send) frame to the APThis CTStells the AP that the transmitting node has changed from thesleep mode to the active mode

Each WuM initiates the transmission of all packetsindicated by a WuM The frame control field in each dataframe carries a More Data flag [1] by which the AP notifiesa node whether any data remain for that node to receive(to ensure fair scheduling an AP can clear the More Dataflag to a node when the allocated time for that node hasrun out although actually there are still packets waiting fortransmission to that node) A node without any more datawill go to sleep after notifying the AP

A WuM has the same preamble as a WLAN signalTherefore a WuR can estimate SNRRSSI of a WuM and onthis basis performs carrier sense contending to activate its

Wireless Communications and Mobile Computing 3

CPUWLAN

AP

EmulatedOOK

CPU WLAN

Node

CS

OOK Dem SNR Det

WuR

Preamble OOK on top of OFDM

Fixed length Wake-up message

Envelopedetection

Transmitting a wake-up message by modulating envelope of an OFDM signal

Figure 1 Framework for remote wake-up control of a mobile node An AP transmits a wake-up message with a traffic indication map byapplying the OOK modulation on the envelope of an OFDM signal A node is equipped with a low-power WuR which conducts envelopedetection to receive a wake-up message detects SNR and performs carrier sense

colocated WLAN module If multiple nodes wake up simul-taneously their contention may cause collisions To reducecollisions onlyWuRs with high SNR above the threshold andpackets ready will participate in this contention Due to thewake-up latency the channel is continuously idle in thewake-up period of a node that has just won the channel contentionAs a result other WuRs sense the channel as idle and mayfalsely activate their colocated WLAN modules [20] Settinga SNR threshold helps to reduce false wake-up as well It isdesired that by proper control exactly one node with highSNR is activated so as to avoid false wake-up and collisionand improve transmission rate

Here normalized SNR [18] instead of absolute SNR isused and it is defined as the ratio of instantaneous SNR ofa node to its average Using normalized SNR helps to ensureproportional fair scheduling among nodes with different linkqualities in a long term But using a fixed SNR threshold mayprevent a node in deep fading from accessing the channel ina short term To alleviate this problem the SNR threshold isadapted to the number of contending nodes

The number of contending nodes with packets ready tobe received changes with time so does the SNR thresholdThe AP continues transmitting all packets to the same nodein a burst mode where frames are spaced by SIFS (ShortInterframe Space) The switch between nodes is indicated bya space of DIFS (DCF Interframe Space longer than SIFS)By checking this DIFS the number of contending nodes canbe updated Later in Section 3 optimal SNR threshold isobtained from the latest number of contending nodes Inthis way the SNR threshold decreases with the number ofcontending nodes which helps to alleviate the short-termfairness problem

As link quality changes dynamically the backoff counteris not resumed after each contention but initialized percontention round using a fixed contention window (CW)

22 Main Procedure The main procedure of the proposedmethod is described as follows

(1) An AP periodically broadcasts a WuM by applyingOOK modulation on the envelope of WLAN signalscarrying a TIM indicating the availability of packets

(2) A WuR measures RSSISNR on receiving a WuMgets TIM from this WuM and finds the numberof contending nodes Then based on the numberof contending nodes each WuR determines its SNRthreshold (based on a table)

(3) If there is a packet ready and its normalized SNR isgreater than the threshold a WuR initiates its backoffcounter by a random value drawn from a CW anddecreases its backoff counter per idle slot A WuRimmediately wakes up its WLAN module when itsbackoff counter reaches 0

(4) An activated WLAN module performs carrier senseagain If the channel remains idle a WLAN moduletransmits a CTS to initiate its receiving from the APOtherwise the channel is already busy and this is afalse wake-up and the WLAN module goes to sleepagain

(5) On receiving a CTS frame from a node the APtransmits all packets to the node in a burst with a SIFSbetween adjacent frames and notifies the end of thisburst by clearing the More Data flag

(6) When the transmission to a node finishes there willbe a space of DIFS after which other nodes willcontend to initiate their receiving from the AP Aspace of DIFS or longer indicates the decrease by 1in the number of contending nodes and the SNRthreshold is updated Then the procedures from step(3) are repeated


WuMAP

A

B

C

DIFS

7 6 5 4

3 2 1 0ACK

SIFS

WuM

WLAN active

CTS

SIFS

SLOT

3 2 1 0

WLAN false wake-up

TIM

TIM TIMACK

SIFS SIFS DIFS

2 1 0 WLAN active

CTS ACK

SIFS SIFS DIFS

TIMTIM

T７５

T７５

T７５

T３

T３

T３

PB1 PB2 PC1

Figure 2Wake-up control for the downlink transmission scheduling in aWLANwith an AP and 3 nodesThe AP broadcasts aWuM whichcarries a TIM The WuR of each node on receiving a TIM and detecting its normalized SNR above the threshold performs carrier sensecontending to activate its WLAN module An activated WLAN module initiates the receiving from the AP Packets to the same nodes arespaced by SIFS and packets to different nodes are spaced by DIFS and random backoff (119879WU = 5 slots)

Occasionally SNR of all remaining nodes (that have notreceived their packets yet) happen to be below the specifiedthreshold After DIFS no nodes transmit and the channelremains idle until the AP rebroadcasts a new WuM whichrecovers the contention among the nodes

A collision occurs when multiple nodes simultaneouslytransmit CTS In this case the AP failing to receive anexpected CTS transmits a newWuM to resynchronize all thenodes

A simple example is shown in Figure 2 where a WLANconsists of an AP and 3 nodes At first the AP sends a WuMindicating that there are packets ready for 119860 119861 and 119862 In thefirst contention round normalized SNR of 119861 and 119862 is abovethe threshold and WuRs 119861 and 119862 start to compete for thechannel WuR 119861 happens to initiate its backoff counter with asmall value of 3 and wins the contention Its WLAN moduleis activated to send a CTS frame to initiate the receivingof 1198751198611 and 1198751198612 from the AP Meanwhile in the wake-upperiod (with a length of 119879WU) of 119861 the channel is idle andWuR 119862 decreases its backoff counter It happens that WLANmodule of 119862 is also activated which is a false wake-up Toreduce power consumption a falsely activated node is putinto the sleep mode again and the probability of false wake-up will be controlled by adjusting the SNR threshold A DIFSspace indicates that the previous node (119861) has finished itsreceiving and the number of nodes is reduced by one Thenchannel access is repeated based on the latest SNR thresholdcorresponding to the number of remaining nodes that havenot received their packets yet

3 Performance Analysis

Here we analyze the performance of the proposed methodto deduce the optimal parameter In the analysis we usethe following notations 119873 is the CW value 120574 is normalizedSNR with a PDF (probability density function) 119891(120574) and aCDF (cumulative distribution function) 119865(120574) and 1205740 is SNRthreshold In the case of Rayleigh fading if instantaneous

Table 1 Main notations for the analysis

119905DIFS Time length of a DIFS119905SIFS Time length of an SIFS119905EIFS Time length of an EIFS119905WuM Time length of a wake-up message119905CTS Time length of a CTS frame119905Data Time length of a DATA frame119905ACK Time length of an ACK frame119864119879 Power consumption at transmission state (1 watt)119864119877 Power consumption at receiving state (1 watt)119864119868 Power consumption at idle state (1 watt)119864WR Power consumption of WuR (1mill-watt)119879119878 Time length of a contention slot119873 Amount of slots in a contention window119873WU Amount of slots corresponding to wake-up period119873SL Amount of slots corresponding to sleep period119898 Number of nodes participating in the contention119872 Number of nodes with packets ready119862119872119898 Number of combinations choosing119898 out of119872 elements

absolute SNR of a node (119894 = 1 2 119872) is 1205741015840119894 and its averagevalue is 1205741015840119894 its normalized SNR 120574119894 is defined as 120574119894 = 1205741015840119894 1205741015840119894 and119891(120574) = exp(minus120574) and 119865(120574) = 1 minus exp(minus120574) are the same for allnodes

The length of wake-up period 119879WU varies with devicesand mainly depends on the performance of high frequencyoscillator According to [24] it takes 139120583s to switch from 14clock rate to full clock rate and takes about 200 120583s to generatea stable carrier frequency within 50 kHz of the desiredvalue in MAX7032 (httpswwwmaximintegratedcomenproductscommswireless-rfMAX7032html) In the analy-sis the wake-up latency is assumed to be 119879WU = 200 120583sapproximately 119873WU = 22 slots with 119879119878 = 9 120583s Table 1 liststhe main notations


CTSCTS

j

WuM WuM

WuM CTS DATA ACK WuM

WuM CTS WuM

(a) Contention window

(b) No node transmits

(c) One node transmits

(d) A collision occurs due to concurrent transmissions

DIFS DIFSN slots

SIFS SIFS DIFS

EIFS

j-1 idle slots N７５ slots (wake-up latency)

t(E | N)

t(S | j mN)

t(C | k j mN)

T７５

T７５

Figure 3 Different cases of a transmission (a) A contention window with 119873 slots (b) No node transmits and the channel remains idleduring the whole contention window (c) Exactly one node transmits without a collision (d) A collision occurs because multiple nodessimultaneously transmit

31 Basic Analysis of Slotted Contention Among all nodesthere are119872 nodes with packets ready (119872 changes with time)Out of these119872 nodes with a probability

119875 (119898 | 1205740) = 119862119872119898 sdot 119865 (1205740)119872minus119898 sdot [1 minus 119865 (1205740)]119898 (1)

the normalized SNR of119898 nodes is above the threshold 1205740Consider the 119895th slot of the contention window where

multiple WLAN modules may be simultaneously activatedbecause their backoff counters are first decreased to 0 at thatslot It should be noted that anyWuR whose backoff counterreaches 0 in the 119873WU slots immediately after the 119895th slotalso falsely activates its WLAN module because no nodetransmits in this wake-up period Falsely activated nodes areput into sleep again

There are three possible cases after each channel con-tention

(i) All nodes have a normalized SNR below 1205740 and nonode transmits at all (Figure 3(b) denoted as 119864) which has aprobability

119875 (119864 | 1205740) = 119875 (0 | 1205740) (2)

and the channel is idle for a time

119905 (119864 | 119873) = 119905WuM + 119905DIFS + 119873 sdot 119879119878 + 119905DIFS

119905 (119864 | 1205740 119873) = 119905 (119864 | 119873) sdot 119875 (119864 | 1205740) (3)

Then theAP rebroadcasts aWuM to start the next contentionperiod

(ii)One node transmitswithout any collision (Figure 3(c)denoted as 119878) This happens if exactly one node chooses theleast timer value 119895 which has a probability

119875 (119878 | 119895 119898119873)

=

1119873 1 le 119895 le 119873 119898 = 1

1198621198981 sdot(119873 minus 119895)119898minus1

119873119898 1 le 119895 le 119873 minus 1 119898 ge 2

(4)

and the overall success probability is

119875 (119878 | 1205740 119873) =119872

sum119898=1

119873

sum119895=1

119875 (119878 | 119895 119898119873)119875 (119898 | 1205740) (5)

Each successful transmission consumes the time119905 (119878 | 119895 119898119873) = 119905WuM + 119905DIFS + 119895 sdot 119879119878 + 119879WU + 119905CTS

+ 119905SIFS + 119905Data + 119905SIFS + 119905ACK + 119905DIFS(6)

and its average is equal to

119905 (119878 | 1205740 119873)

=119872

sum119898=1

119873

sum119895=1

119905 (119878 | 119895 119898119873)119875 (119878 | 119895 119898119873)119875 (119898 | 1205740) (7)


And the number of successful transmissions per contentionround is equal to

119871 (119878 | 1205740 119873) = 1 sdot119875 (119878 | 1205740 119873)1 minus 119875 (119864 | 1205740)

(8)

Of the other 119898 minus 1 nodes whose backoff counters reach0 in the remaining 119873 minus 119895 slots the ones that reach 0 inthe subsequent 119873WU slots will experience false wake-upThis is equivalent to a binomial distribution [26] with 119901 =119873WU(119873minus119895) in the119898minus1 trialsTherefore the average numberof nodes that will experience false wake-ups is equal to

119871119865 (119878 | 119895 119898119873)

=

(119898 minus 1) 119873WU119873 minus 119895 1 le 119895 le 119873 minus 119873WU 119898 ge 2

(119898 minus 1) 119873 minus 119873WU lt 119895 le 119873 minus 1 119898 ge 2

(9)

The number of false wake-ups under a successful transmis-sion is equal to

119871119865 (119878 | 1205740 119873) =119872

sum119898=1

119871119865 (119878 | 119898119873) 119875 (119898 | 1205740)1 minus 119875 (119864 | 1205740)

119871119865 (119878 | 119898119873) =119873

sum119895=1

119875 (119878 | 119895 119898119873) sdot 119871119865 (119878 | 119895 119898119873) (10)

(iii) Two or more nodes transmit simultaneously whichleads to a collision (Figure 3(d) denoted as 119862) A collisionhappens when 119896 ge 2 nodes choose the same least timer value119895 which has a probability

119875 (119862 | 119896 119895 119898119873)

=

119862119898119896 sdot(119873 minus 119895)119898minus119896

119873119898 1 le 119895 le 119873 minus 1 119898 ge 21119873119898 119896 = 119898 119895 = 119873 119898 ge 2

(11)

A collision leads to the channel waste for a time

119905 (119862 | 119896 119895 119898119873) = 119905WuM + 119905DIFS + 119895 sdot 119879119878 + 119879WU

+ 119905CTS + 119905EIFS(12)


119905 (119862 | 1205740 119873) =119872

sum119898=2

119873

sum119895=1

119898

sum119896=2

119905 (119862 | 119896 119895 119898119873)

sdot 119875 (119862 | 119896 119895 119898119873)119875 (119898 | 1205740) (13)

The number of nodes simultaneously transmitting in acollision is equal to

119871 (119862 | 119896 119895 119898119873) =

119896 1 le 119895 le 119873 minus 1 119898 ge 2119898 119895 = 119873 119898 ge 2

(14)


119871 (119862 | 1205740 119873) =119872

sum119898=2

119871 (119862 | 119898119873) 119875 (119898 | 1205740)1 minus 119875 (119864 | 1205740)

119871 (119862 | 119898119873)

=119873

sum119895=1

119898

sum119896=2

119875 (119862 | 119896 119895 119898119873) sdot 119871 (119862 | 119896 119895 119898119873)

(15)

Of the other 119898 minus 119896 nodes whose backoff counters reach0 in the remaining 119873 minus 119895 slots the ones that reach 0 in thesubsequent 119873WU slots will experience false wake-up This isequivalent to a binomial distribution with 119901 = 119873WU(119873 minus 119895)in the 119898 minus 119896 trials Therefore the average number of nodesthat will experience false wake-ups is equal to

119871119865 (119862 | 119896 119895 119898119873)

=

(119898 minus 119896) sdot 119873WU119873 minus 119895 1 le 119895 le 119873 minus 119873WU 119898 ge 2

(119898 minus 119896) 119873 minus 119873WU lt 119895 lt 119873 119898 ge 2

(16)

The average number of false wake-ups under a collision isequal to

119871119865 (119862 | 1205740 119873) =119872

sum119898=2

119871119865 (119862 | 119898119873) 119875 (119898 | 1205740)1 minus 119875 (119864 | 1205740)

119871119865 (119862 | 119898119873)

=119873

sum119895=1

119898

sum119896=2

119875 (119862 | 119896 119895 119898119873) sdot 119871119865 (119862 | 119896 119895 119898119873)

(17)

32 Optimal Parameter The average time for each roundis the weighted sum of three parts (idle waiting successfultransmission and collision) as follows

119905 (1205740 119873) = 119905 (119864 | 1205740 119873) + 119905 (119878 | 1205740 119873)

+ 119905 (119862 | 1205740 119873) (18)

The average transmission rate is an average over all nodesThetransmission rate (119903119894 for the 119894th node) is estimated from theabsolute SNR (120574 sdot 1205741015840119894 ) based on the Shannon capacity and theoperator 119864(sdot) represents the computation of expectation

119864 (119903 | 120574 ge 1205740) =1119872119872

sum119894=1

119864 (119903119894 | 120574119894 ge 1205740)

119864 (119903119894 | 120574119894 ge 1205740) =intinfin1205740

log2 (1 + 120574 sdot 1205741015840119894) sdot 119891120574119894 (120574) 119889120574intinfin1205740119891120574119894 (120574) 119889120574

(19)


0

05

1

15

2

25En

ergy

effici

ency

0 1 2 3 4 5 6 7 8minus1

Normalized SNR threshold (dB)

SlotＭ = 50

SlotＭ = 40

SlotＭ = 30

SlotＭ = 20

SlotＭ = 10

(a) Energy efficiency 1205781015840(1205740119873)

= 50SlotＭ SlotＭ = 40

= 30

= 20

SlotＭ SlotＭ SlotＭ = 10

0

005

01

015

02

025

03

Ener

gy effi

cien

cy

0 1 2 3 4 5 6 7 8minus1


(b) Energy efficiency 120578(1205740119873)

Figure 4 Different definitions of energy efficiency (average absolute SNR is equal to 20 dB)

The average energy per round 120576(1205740 119873) is a sum of three parts120576119878(1205740 119873) for successful transmission 120576119862(1205740 119873) for collisionsand 120576119865(1205740 119873) for false wake-ups as follows

120576 (1205740 119873) = 120576119878 (1205740 119873) + 120576119862 (1205740 119873) + 120576119865 (1205740 119873)

120576119878 (1205740 119873) = ((119879WU + 119879SL + 2 sdot 119905SIFS) sdot 119864119868)

sdot 119871 (119878 | 1205740 119873)

+ ((119905CTS + 119905ACK) sdot 119864119879 + 119905Data sdot 119864119877)

sdot 119871 (119878 | 1205740 119873)

120576119862 (1205740 119873) = ((119879WU + 119879SL + 119905EIFS) sdot 119864119868 + 119905CTS sdot 119864119879)

sdot 119871 (119862 | 1205740 119873)

120576119865 (1205740 119873) = (119879WU + 119879SL) sdot 119864119868sdot (119871119865 (119878 | 1205740 119873) + 119871119865 (119862 | 1205740 119873))

(20)

where 120576119878(1205740 119873) is computed from 119871(119878 | 1205740 119873) the averagenumber of successful transmissions 120576119862(1205740 119873) is computedfrom 119871(119862 | 1205740 119873) the average number of nodes involved ina collision and 120576119865(1205740 119873) is computed from 119871119865(119878 | 1205740 119873) +119871119865(119862 | 1205740 119873) the average number of nodes experiencingfalse wake-up

First energy efficiency defined as the ratio of the numberof overall bits to the product of average transmission time andaverage energy is considered as follows

1205781015840 (1205740 119873) =119864 (119903 | 120574 ge 1205740) sdot 119905Data sdot 119875 (119878 | 1205740 119873)

119905 (1205740 119873) sdot 120576 (1205740 119873) (21)

Figure 4(a) shows the result which plots energy efficiencywith respect to normalized SNR threshold (1205740) Energyefficiency under different contention window sizes (119873) hasalmost the same peak value which indicates that themaximalenergy efficiency is not very sensitive to contention window

size A small contention window usually cannot well removethe false wake-up in that case a large SNR threshold needsto be used and the SNR range is narrow In contrast using arelatively large CWhelps to remove collisions and false wake-ups in part and a smaller SNR threshold can be used instead

A problem is that average transmission rate 119864(119903 | 120574 ge1205740) depends on the absolute SNR per link which is difficultto obtain in the distributed environment We notice thatSNR threshold helps to both improve transmission rate andremove false wake-up By separately considering the twoitems 119864(119903 | 120574 ge 1205740) and 120576(1205740 119873) in (21) that is keeping oneand removing the other we find that reducing false wake-upusually requires higher SNR threshold

Therefore we choose to remove 119864(119903 | 120574 ge 1205740) from (21)and use the following definition of energy efficiency

120578 (1205740 119873) =119905Data sdot 119875 (119878 | 1205740 119873)119905 (1205740 119873) sdot 120576 (1205740 119873)

(22)

Figure 4(b) shows the energy efficiency 120578(1205740 119873) which has asimilar trend as that in Figure 4(a) As will be explained latera high SNR threshold may increase the probability that nonodes have SNR above the threshold due to limit of channelcoherence time Therefore a low SNR threshold is preferredand a relatively large value is chosen for contention windowwhich is fixed to119873 = 50 when there are no less than 5 nodesThen (22) is used to compute the optimal SNR threshold

4 Performance Evaluation

In the simulation evaluation we compare the following 4methods (1) First is the PSM mode [1] without using WuRAWLANmodule periodically wakes up to receive TIM andif there are any packets buffered at the AP it stays awake inthe whole beacon period Later simulation results will showthat in this method a WLAN module will consume muchmore power than in othermethods due to the idle waiting (2)Second is the adaptive PSM mode (PSMAdapt) [2] without


Period of wake-up (ms)

Del

ay p

er p

acke

t (m

s)

10 nodes20 nodes

0

50

100

150

5 10 15 20 25 30

(a) Delay per packet (ms)

10 nodes20 nodes

0

005

01

015

02

025

03

Chan

nel u

tility

10 15 20 25 305


(b) Channel utilization

10 nodes20 nodes

0

5

10

15

20

25

30

Pow

er co

nsum

ptio

n (m

W)

10 15 20 25 305


(c) Power consumption (mW)

Figure 5 Performance of WuRMUS under different WuM periods (traffic rate 50 packetss per node)

WuR This is built on top of the PSM mode but a node thathas received all packets buffered at the AP will enter the sleepmode immediatelyThis helps to reducemost of the idle wait-ing in the PSM mode although it causes large delay becausepackets which arrive after the node sleeps will not be receiveduntil the next TIM timing (3) Third is the wake-up pernode (WuR) The AP activates each node separately withoutreferring to their link quality (4) Fourth is the wake-up withmultiuser scheduling (WuRMUS) the proposed method

We built a packet-level simulator in the MATLAB envi-ronment We consider a WLAN with an AP and a variablenumber of nodes (average absolute SNR is equal to 20 dB)and evaluate its performance with different traffic settingsPacket arrival follows the Poisson process In the evaluationwe will consider four metrics delay channel utilization (thepercentage of time that the channel is busy including SIFSDIFS and backoff slots) power consumption per node andthroughput The results are the average of 50 runs withdifferent seedsThe transmission rate is decided by SNR [27]IEEE 80211a is adopted and packet length is 1000 bytes Main

parameters are shown in Table 2 In all methods opportunis-tic packet aggregation [28] is used so that multiple packetsthat arrived before the transmission timing are transmittedtogether if they can be aggregated (with the constraint thatthe transmission time will not be larger than the one fortransmitting a packet at the lowest rate)

41 Effect of WuM Period In the proposed method theWuM period plays an important role Here we evaluate theperformance of the proposed method under different WuMperiods and the results are shown in Figure 5Unsurprisinglythe delay per packet increases with the WuM period (Fig-ure 5(a)) Figure 5(b) shows that channel utilization decreasesasWuMperiod increasesThis is because a largeWuMperiodincreases the opportunity of packet aggregation and improveschannel efficiency This will reduce the time that a node staysawake to receive its packets buffered at the AP As a resultpower consumption per node decreases as WuM periodincreases as shown in Figure 5(c) Because a very smallWuMperiod will increase the overhead and energy consumption


PSMPSMAdapt

WuRWuRMUS

0

50

100

150D

elay

per

pac

ket (

ms)

Number of nodes in a WLAN5 10 15 20 25 30


PSMPSMAdapt

WuRWuRMUS


0

005

01

015

02

025

03

Chan

nel u

tility


Number of nodes in a WLAN

Pow

er co

nsum

ptio

n (m

W)

PSMPSMAdapt

WuRWuRMUS

5 10 15 20 25 30

101

102


Figure 6 Performance of different methods under different numbers of nodes (overall traffic rate 500 packets)

Table 2 Main parameters for simulation

PHY IEEE 80211a propagation free-space amp two-rayMAC CSMA 119879SLOT = 9 120583119904 119879SIFS = 16 120583119904 119879DIFS = 34 120583119904Period Beacon 100ms TIM 200ms WuM 10msWuM 04ms in WuRMUS 01ms in WuRPacket 119871 = 1000 byteTraffic Packet arrival time follows Poisson processBit rate Decided by SNRCW 50 slotsLatency Wake-up latency 22 times 119879SLOT sleep 2 times 119879SLOT

Power WLAN receivingidle 1W transmission 1W WuR 1mW

while a very large WuM period will increase the delay in thefollowing the WuM period is chosen to be 10ms

42 Under Different Numbers of Nodes Here we evaluate theperformance of differentmethods with respect to the numberof nodes in a WLAN In this evaluation the overall traffic

is fixed to 500 packets and the amount of traffic per nodedecreases as the number of nodes increases Because packetsto different nodes arrive at different timing the number ofnodes that have packets buffered at the AP changes with time

Figure 6(a) shows the delay per packet in different meth-ods WuRMUS lies between PSM and WuR and PSMAdapthas the largest delay In PSM each node wakes up per TIMtiming (period = 200ms) and shifts to the sleep state if nopacket is available Any packets arriving immediately aftera node sleeps will have a large delay As for PSMAdapt anode shifts to the sleep mode more aggressively which leadsto larger delay In WuRMUS the delay per packet increaseswith the number of nodes As the number of nodes increasesmore nodes have buffered packets and will participate in thetransmission scheduling Then a higher SNR threshold willbe selected But the channel does not change much withina short time (channel coherence time) and the probabilitythat no nodes have SNR above the specified SNR thresholdincreases which increases the delay in WuRMUS The delayper packet in WuR is almost always nearly 0 at the cost ofmore overhead and power consumption


PSMPSMAdapt

WuRWuRMUS

200 300 400 500 600 700 800 900 1000100Number of packets per second

0

50

100

150D

elay

per

pac

ket (

ms)


Pow

er co

nsum

ptio

n (m

W)

PSMPSMAdapt

WuRWuRMUS

101

102


(b) Power consumption (mW)

PSMPSMAdapt

WuRWuRMUS

5

10

15

20

25

Thro

ughp

ut (M

bps)

3000 4000 5000 60001000 2000Number of packets per second

(c) System throughput (Mbps)

Figure 7 Performance of different methods under different volumes of traffic (number of nodes = 20)

Figure 6(b) shows channel utilization in different meth-ods Channel utilization is the highest in WuR due toits transmission of WuM per node PSMAdapt has lowerchannel utilization compared with PSM because with moreaggressive sleep policy more packets are buffered at the TIMtiming which enablesmore chance of packet aggregation andreduces overhead InWuRMUS channel utilization decreasesas the number of nodes increases due to two reasons (i)The SNR threshold increases with the number of nodeswhich at the cost of delay increases the chance of packetaggregation ButWuRMUShasmuch smaller delay than PSMby using a smaller WuM period (ii) With more nodes theeffect of multiuser diversity becomes more obvious and thetransmission rate is improved

Figure 6(c) shows power consumption per node Unsur-prisingly power consumption is the highest in PSM becauseeach node once detecting that there is a packet ready to bereceived according to the TIM included in a beacon willwait until the next beacon announces that no packet remainsUsing a more aggressive power-save mode in PSMAdapteffectively reduces the power consumption compared with

PSM but power consumption is still nearly constant becausesome nodes that failed to capture the channel first have to stayawake waiting for other nodes to finish receiving In WuRandWuRMUS power consumption decreases as the numberof nodes increases this is because (i) the WLAN module ofa node is active only when receiving a packet and (ii) theoverall traffic is fixed and the amount of traffic per nodedecreases so does the active time per nodeWuRMUS furtherdecreases power consumption per node comparedwithWuRand its gain ranges from 40 to 43 This is achieved by(i) improving transmission rate by setting an SNR thresholdand (ii) increasing the opportunities of packet aggregation byperiodically transmitting WuMs

43 Under Different Traffic Volume Next we fix the numberof nodes to 20 and adjust the overall traffic to investigate thechanges in delay power consumption and system through-put

Figure 7(a) shows the delay per packet As the amountof overall traffic increases on average the delay decreasesin PSM But the delay in WuRMUS has a different trend


Although the number of overall nodes is fixed with moretraffic the number of nodes with buffered packets increasesso does the SNR threshold Then the probability that nonodes have SNR above the specified SNR threshold increaseswhich increases the delay in WuRMUS But the delay inWuRMUS is still less than that in PSM

Figure 7(b) shows that power consumption per nodeincreases with the amount of traffic as well Anyway powerconsumption is always the lowest inWuRMUSWhen there islittle traffic (le300 packets) the superiority ofWuRMUS overWuR is not very obvious But with more traffic WuRMUSreduces power consumption per node by 35 to 55compared with WuR

Figure 7(c) shows that throughput increases with theamount of overall traffic and finally approaches constantvalues in all methods when the network saturates AlthoughWuR and WuRMUS have relatively large overhead in timesof light traffic in the saturation state many packets areaggregated and the overhead of wake-up control is not veryobvious Therefore in the saturation state the throughput ofWuR is only a little lower than that of PSM and PSMAdaptWuRMUS achieves higher throughput than other methodsbecause it exploits multiuser scheduling to improve trans-mission rates It should be noted that WuRMUS does notrealize throughput fairness among nodes Instead it ensures aproportional fairness and interested readers may refer to [18]for more details

In summary WuRMUS reduces power consumptioncompared with other methods In times of light traffic WuR-MUS also reduces delay compared with PSM and PSMAdaptand reduces channel utilization compared with WuR Intimes of medium traffic or many nodes the number of nodesthat have buffered packets increases which increases the SNRthreshold But the channel does not change completely ran-domly due to the limit of channel coherence time ThereforeinWuRMUS the probability that no nodes have SNR greaterthan specified SNR increases which leads to large delay Howto solve this problem is left as a future work In times of heavytraffic the overhead of wake-up control in WuRMUS is notobvious after packet aggregation Instead applying multiuserscheduling helps to improve system throughput

5 Conclusion

This paper studies the transmission scheduling in the down-link of a WLAN by using a wake-up radio to remotelyactivate a WLAN module to receive packets on demandInstead of wake-up per node we proposed a broadcast-based wake-up control framework to reduce the overheadand improve the transmission rate This brings new issueslike transmission collisions and false wake-up These prob-lems are solved by setting a SNR threshold In this waythe proposed method reduces transmission collisions andfalse wake-ups and improves transmission rate Simulationevaluations verify that the proposed method (i) effectivelyreduces power consumption of nodes compared with state-of-the-art methods (ii) reduces delay compared with power-save mode in times of light traffic and (iii) improves systemthroughput compared with other methods in the saturation

state In the future we will also study how to further reducethe delay in the proposed method

Conflicts of Interest

The authors declare that there are no conflicts of interestregarding the publication of this paper

References

[1] ldquoWireless LAN Medium Access Control (MAC) and PhysicalLayer (PHY) Specificationrdquo IEEE Std 80211 2012

[2] YHe andR Yuan ldquoA novel scheduled power savingmechanismfor 80211 wireless LANsrdquo IEEE Transactions onMobile Comput-ing vol 8 no 10 pp 1368ndash1383 2009

[3] G Anastasi M Conti M Di Francesco and A PassarellaldquoEnergy conservation in wireless sensor networks a surveyrdquoAdHoc Networks vol 7 no 3 pp 537ndash568 2009

[4] S Tang H Yomo Y Kondo and S Obana ldquoWake-up receiverfor radio-on-demand wireless LANsrdquo EURASIP Journal onWireless Communications and Networking vol 2012 article no42 2012

[5] J Oller I Demirkol J Casademont J Paradells G Gammand L Reindl ldquoHas time come to switch from duty-cycledMACprotocols towake-up radio for wireless sensor networksrdquoIEEEACM Transactions on Networking vol 24 no 2 pp 674ndash687 2016

[6] I Demirkol C Ersoy and EOnur ldquoWake-up receivers for wire-less sensor networks benefits and challengesrdquo IEEE WirelessCommunications Magazine vol 16 no 4 pp 88ndash96 2009

[7] V Jelicic M Magno D Brunelli V Bilas and L Benini ldquoAna-lytic comparison of wake-up receivers for WSNs and benefitsover the wake-on radio schemerdquo in Proceedings of the 7thACM Workshop on Performance Monitoring and MeasurementofHeterogeneousWireless andWiredNetworks (PM2HW2N rsquo12)pp 99ndash106 ACM Paphos Cyprus October 2012

[8] D K McCormick ldquoIEEE technology report on wake-up radioan application market and technology impact analysis of low-powerlow-latency 80211 wireless LAN interfacesrdquo 80211baBattery Life Improvement IEEE Technology Report on Wake-UpRadio pp 1ndash56 Nov 2017

[9] S C Folea andGMois ldquoA low-power wireless sensor for onlineambient monitoringrdquo IEEE Sensors Journal vol 15 no 2 pp742ndash749 2015

[10] D Spenza M Magno S Basagni L Benini M Paoli and CPetrioli ldquoBeyond duty cycling wake-up radio with selectiveawakenings for long-lived wireless sensing systemsrdquo in Pro-ceedings of the IEEE Conference on Computer Communications(INFOCOM rsquo15) pp 522ndash530 KowloonHongKongApril 2015

[11] F Z Djiroun and D Djenouri ldquoMAC protocols with wake-upradio for wireless sensor networks a reviewrdquo IEEE Communi-cations Surveys amp Tutorials vol 19 no 1 pp 587ndash618 2017

[12] H Qin and W Zhang ldquoZigBee-assisted power saving man-agement for mobile devicesrdquo IEEE Transactions on MobileComputing vol 13 no 12 pp 2933ndash2947 2014

[13] J Guo Z Song Y Cui Z Liu and Y Ji ldquoEnergy-efficientresource allocation for multi-user mobile edge computingrdquoin Proceedings of the IEEE Global Communications Conference(GLOBECOM) IEEE 2017

[14] Y Cui W He C Ni C Guo and Z Liu ldquoEnergy-efficientresource allocation for cache-assisted mobile edge computingrdquo


in Proceedings of the 2017 IEEE 42nd Conference on LocalComputer Networks (LCN) pp 640ndash648 Singapore October2017

[15] X Qin and R A Berry ldquoDistributed approaches for exploitingmultiuser diversity in wireless networksrdquo IEEE Transactions onInformation Theory vol 52 no 2 pp 392ndash413 2006

[16] S Adireddy and L Tong ldquoExploiting decentralized channelstate information for random accessrdquo IEEE Transactions onInformation Theory vol 51 no 2 pp 537ndash561 2005

[17] C-S Hwang and J M Cioffi ldquoOpportunistic CSMACA forachieving multi-user diversity in wireless LANrdquo IEEE Transac-tions on Wireless Communications vol 8 no 6 pp 2972ndash29822009

[18] S Tang ldquoDistributed multiuser scheduling for improvingthroughput of wireless LANrdquo IEEE Transactions on WirelessCommunications vol 13 no 5 pp 2770ndash2781 2014

[19] M Park S Azizi R Stacey et al ldquoProposal for wake-up receiver(WUR) study grouprdquo Tech Rep IEEE 80211-160722r1 May2016

[20] S Tang and S Obana ldquoTight integration of wake-up radioin wireless LANs and the impact of wake-up latencyrdquo in Pro-ceedings of the 59th IEEE Global Communications ConferenceGLOBECOM 2016 USA December 2016

[21] K Chebrolu and A Dhekne ldquoEsense communication throughenergy sensingrdquo in Proceedings of the 15th Annual ACMInternational Conference on Mobile Computing and Networking(MobiCom rsquo09) pp 85ndash96 ACM Beijing China September2009

[22] Y Kondo H Yomo S Tang et al ldquoEnergy-efficient WLANwith on-demand AP wake-up using IEEE 80211 frame lengthmodulationrdquo Computer Communications vol 35 no 14 pp1725ndash1735 2012

[23] S Tang H Yomo and Y Takeuchi ldquoOptimization of framelength modulation-based wake-up control for green WLANsrdquoIEEE Transactions on Vehicular Technology vol 64 no 2 pp768ndash780 2015

[24] X Zhang and K G Shin ldquoE-mili energy-minimizing idlelistening in wireless networksrdquo IEEE Transactions on MobileComputing vol 11 no 9 pp 1441ndash1454 2012

[25] F Talucci M Gerla and L Fratta ldquoMACA-BI (MACA byinvitation)-a receiver oriented access protocol for wirelessmultihop networksrdquo in Proceedings of the 1997 InternationalSymposium on Personal Indoor and Mobile Radio Communica-tions (PIMRC rsquo97) pp 435ndash439 September 1997

[26] D P Bertsekas and J N Tsitsiklis Introduction to ProbabilityAthena Scientific Belmont Mass USA 2002

[27] G Holland N Vaidya and P Bahl ldquoA rate-adaptive MACprotocol for multi-Hop wireless networksrdquo in Proceedings of the7th Annual International Conference on Mobile Computing andNetworking (MobiCom rsquo01) pp 236ndash251 Rome Italy 2001

[28] Y Lin and V W S Wong ldquoFrame aggregation and optimalframe size adaptation for IEEE 80211nWLANsrdquo in Proceedingsof the IEEE Global Telecommunications Conference (GLOBE-COM rsquo06) pp 1ndash6 San Francisco Calif USA November-December 2006

RoboticsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014


Active and Passive Electronic Components

Control Scienceand Engineering

Journal of


International Journal of

RotatingMachinery


Hindawi Publishing Corporation httpwwwhindawicom

Journal of

Volume 201

Submit your manuscripts athttpswwwhindawicom

VLSI Design



Shock and Vibration


Civil EngineeringAdvances in

Acoustics and VibrationAdvances in



Electrical and Computer Engineering

Journal of

Advances inOptoElectronics


Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of


Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014


Chemical EngineeringInternational Journal of Antennas and

Propagation




Navigation and Observation



DistributedSensor Networks



channel to transmit to the AP The performance dependson two important factors (i) collision probability and (ii)transmission rate Because each node experiences fadingindependently by limiting the contention to nodes withhigh link quality average transmission rate can be improvedand collision probability can be reduced There have beensome methods suggested for slotted ALOHA [15 16] andCSMA networks [17] This is also applied to the downlinktransmission by letting each node contend to initiate thereceiving from the AP based on their link quality [18] Buta WLAN module is kept awake to monitor the channelcontinuously to obtain fresh CSI which leads tomuch energywaste

Compared with previous works that separately solve theabove issues in this work we try to jointly solve these issuesapplying multiuser scheduling to improve transmission ratemeanwhile reducing both the protocol overhead of wake-upcontrol and the energy overhead of monitoring the channelall by using the low-power WuR To this end we proposea new framework broadcast-based wake-up control In thisframework an AP periodically broadcasts by its WLANmodule a WuM carrying a traffic indication map (TIM)[1] which is modulated by OOK (On-Off-Keying) on theenvelope of an OFDM signal [19] This WuM is received byenvelope detection at a low-power WuR equipped at eachnode AWuR is used tomonitor link quality performs carriersense and activates its colocated WLAN module via thedistributed contention

The broadcast-based wake-up control brings new issuesWhen more than two nodes contend there will be transmis-sion collisions and false wake-ups A WLAN module cannottransmit immediately after it receives wake-up instructionfrom its WuR in the presence of the wake-up latency Duringthe wake-up period of a node other WuRs sense the channelas idle and falsely activate their WLAN modules which leadto false wake-up [20] and power waste The false wake-up problem occurs because the initial values of backoffcounters of two or moreWuRs have a difference less than thelength of the wake-up period This problem is addressed in[20] by adjusting the contention window which uses largercontention window at the cost of more idle slots In thiswork this issue is solved by setting the SNR (signal to noiseratio) threshold and applying the distributed scheduling ofwake-up control and transmissionThis reduces transmissioncollisions as well

Main contributions of this paper are threefold as follows

(1) A new framework of broadcast-based wake-up con-trol enables distributed wake-up scheduling

(2) Broadcast-based wake-up control reduces protocoloverhead and improves channel efficiency comparedwith wake-up per node

(3) The three problems multipath fading transmissioncollisions and false wake-ups are solved simultane-ously by setting a proper SNR threshold

Optimal SNR threshold is deduced by theoretical analysisExtensive simulations verify that the proposed method (i)effectively reduces power consumption of nodes compared

with the other methods (ii) has less delay than power-save mode in times of light traffic and (iii) achieves higherthroughput than the other methods in the saturation state

The rest of this paper is organized as follows Section 2presents the proposed framework Section 3 gives the optimalparameter by theoretical analysis Section 4 shows the resultsof simulation evaluation and finally Section 5 concludes thispaper

2 Proposed Method

The framework of the proposed method is shown in Figure 1In this framework a low-power WuR is added to each nodefor activating its colocated WLAN module To suppresspower consumption a WuR instead of a power-hungryWLAN module is used to monitor the channel and performcarrier sense To this end a WuR shares the same channelwith WLAN modules and a WuM is transmitted from theWLANmodule of an AP to a WuR

21 Wake-Up Model Different methods can be used toconvey a WuM from a WLAN module (of an AP) to anon-WLAN WuR as follows (i) Frame length of WLANsignals can be modulated to deliver wake-up message froma WLAN module (transmitter) to a WuR [21ndash23] (ii) AWLAN module at a low clock rate can work as a WuR todetect a WuM embedded in the preamble of a WLAN signal[24] (iii) OOK modulation can be emulated to transmit aWuM by modulating the envelope of an OFDM signal [19]In this work we adopt (iii) because a WuR with envelopedetection can work with low-power consumption and OOKmodulation is more efficient than frame length modulation

A WuM carried in the envelope of a WLAN signal isdetected by a WuR using envelope detection It should benoted that emulating the OOK modulation has its own costFor example at the rate of 100 kbps transmitting aWuMwith40 bits will require 04ms which causes much overhead forwake-up per node To reduce protocol overhead a broadcastwake-up policy is adopted in this work instead of letting anAP separately activate each node to receive packets To thisend eachWuM carries a TIM which simultaneously notifiespacket availability tomultiple nodesThen it is nodes insteadof the AP that contend to initiate the data receiving [25] bytransmitting a CTS (clear to send) frame to the APThis CTStells the AP that the transmitting node has changed from thesleep mode to the active mode

Each WuM initiates the transmission of all packetsindicated by a WuM The frame control field in each dataframe carries a More Data flag [1] by which the AP notifiesa node whether any data remain for that node to receive(to ensure fair scheduling an AP can clear the More Dataflag to a node when the allocated time for that node hasrun out although actually there are still packets waiting fortransmission to that node) A node without any more datawill go to sleep after notifying the AP

A WuM has the same preamble as a WLAN signalTherefore a WuR can estimate SNRRSSI of a WuM and onthis basis performs carrier sense contending to activate its


CPUWLAN

AP

EmulatedOOK

CPU WLAN

Node

CS

OOK Dem SNR Det

WuR



Envelopedetection















WuMAP

A

B

C

DIFS

7 6 5 4

3 2 1 0ACK

SIFS

WuM

WLAN active

CTS

SIFS

SLOT

3 2 1 0

WLAN false wake-up

TIM

TIM TIMACK

SIFS SIFS DIFS

2 1 0 WLAN active

CTS ACK

SIFS SIFS DIFS

TIMTIM

T７５

T７５

T７５

T３

T３

T３

PB1 PB2 PC1












CTSCTS

j

WuM WuM


WuM CTS WuM





DIFS DIFSN slots

SIFS SIFS DIFS

EIFS


t(E | N)

t(S | j mN)

t(C | k j mN)

T７５

T７５








119875 (119864 | 1205740) = 119875 (0 | 1205740) (2)



119905 (119864 | 1205740 119873) = 119905 (119864 | 119873) sdot 119875 (119864 | 1205740) (3)



119875 (119878 | 119895 119898119873)

=

1119873 1 le 119895 le 119873 119898 = 1

1198621198981 sdot(119873 minus 119895)119898minus1

119873119898 1 le 119895 le 119873 minus 1 119898 ge 2

(4)


119875 (119878 | 1205740 119873) =119872

sum119898=1

119873

sum119895=1

119875 (119878 | 119895 119898119873)119875 (119898 | 1205740) (5)




119905 (119878 | 1205740 119873)

=119872

sum119898=1

119873

sum119895=1

119905 (119878 | 119895 119898119873)119875 (119878 | 119895 119898119873)119875 (119898 | 1205740) (7)



119871 (119878 | 1205740 119873) = 1 sdot119875 (119878 | 1205740 119873)1 minus 119875 (119864 | 1205740)

(8)


119871119865 (119878 | 119895 119898119873)

=



(9)


119871119865 (119878 | 1205740 119873) =119872

sum119898=1

119871119865 (119878 | 119898119873) 119875 (119898 | 1205740)1 minus 119875 (119864 | 1205740)

119871119865 (119878 | 119898119873) =119873

sum119895=1

119875 (119878 | 119895 119898119873) sdot 119871119865 (119878 | 119895 119898119873) (10)


119875 (119862 | 119896 119895 119898119873)

=

119862119898119896 sdot(119873 minus 119895)119898minus119896

119873119898 1 le 119895 le 119873 minus 1 119898 ge 21119873119898 119896 = 119898 119895 = 119873 119898 ge 2

(11)


119905 (119862 | 119896 119895 119898119873) = 119905WuM + 119905DIFS + 119895 sdot 119879119878 + 119879WU

+ 119905CTS + 119905EIFS(12)


119905 (119862 | 1205740 119873) =119872

sum119898=2

119873

sum119895=1

119898

sum119896=2

119905 (119862 | 119896 119895 119898119873)

sdot 119875 (119862 | 119896 119895 119898119873)119875 (119898 | 1205740) (13)


119871 (119862 | 119896 119895 119898119873) =

119896 1 le 119895 le 119873 minus 1 119898 ge 2119898 119895 = 119873 119898 ge 2

(14)


119871 (119862 | 1205740 119873) =119872

sum119898=2

119871 (119862 | 119898119873) 119875 (119898 | 1205740)1 minus 119875 (119864 | 1205740)

119871 (119862 | 119898119873)

=119873

sum119895=1

119898

sum119896=2

119875 (119862 | 119896 119895 119898119873) sdot 119871 (119862 | 119896 119895 119898119873)

(15)


119871119865 (119862 | 119896 119895 119898119873)

=



(16)


119871119865 (119862 | 1205740 119873) =119872

sum119898=2

119871119865 (119862 | 119898119873) 119875 (119898 | 1205740)1 minus 119875 (119864 | 1205740)

119871119865 (119862 | 119898119873)

=119873

sum119895=1

119898

sum119896=2

119875 (119862 | 119896 119895 119898119873) sdot 119871119865 (119862 | 119896 119895 119898119873)

(17)


119905 (1205740 119873) = 119905 (119864 | 1205740 119873) + 119905 (119878 | 1205740 119873)

+ 119905 (119862 | 1205740 119873) (18)


119864 (119903 | 120574 ge 1205740) =1119872119872

sum119894=1

119864 (119903119894 | 120574119894 ge 1205740)

119864 (119903119894 | 120574119894 ge 1205740) =intinfin1205740


(19)


0

05

1

15

2

25En

ergy

effici

ency

0 1 2 3 4 5 6 7 8minus1


SlotＭ = 50

SlotＭ = 40

SlotＭ = 30

SlotＭ = 20

SlotＭ = 10



= 30

= 20


0

005

01

015

02

025

03

Ener

gy effi

cien

cy

0 1 2 3 4 5 6 7 8minus1





120576 (1205740 119873) = 120576119878 (1205740 119873) + 120576119862 (1205740 119873) + 120576119865 (1205740 119873)


sdot 119871 (119878 | 1205740 119873)


sdot 119871 (119878 | 1205740 119873)


sdot 119871 (119862 | 1205740 119873)

120576119865 (1205740 119873) = (119879WU + 119879SL) sdot 119864119868sdot (119871119865 (119878 | 1205740 119873) + 119871119865 (119862 | 1205740 119873))

(20)



1205781015840 (1205740 119873) =119864 (119903 | 120574 ge 1205740) sdot 119905Data sdot 119875 (119878 | 1205740 119873)

119905 (1205740 119873) sdot 120576 (1205740 119873) (21)





120578 (1205740 119873) =119905Data sdot 119875 (119878 | 1205740 119873)119905 (1205740 119873) sdot 120576 (1205740 119873)

(22)






Del

ay p

er p

acke

t (m

s)

10 nodes20 nodes

0

50

100

150

5 10 15 20 25 30


10 nodes20 nodes

0

005

01

015

02

025

03

Chan

nel u

tility

10 15 20 25 305



10 nodes20 nodes

0

5

10

15

20

25

30

Pow

er co

nsum

ptio

n (m

W)

10 15 20 25 305









PSMPSMAdapt

WuRWuRMUS

0

50

100

150D

elay

per

pac

ket (

ms)



PSMPSMAdapt

WuRWuRMUS


0

005

01

015

02

025

03

Chan

nel u

tility



Pow

er co

nsum

ptio

n (m

W)

PSMPSMAdapt

WuRWuRMUS

5 10 15 20 25 30

101

102











PSMPSMAdapt

WuRWuRMUS


0

50

100

150D

elay

per

pac

ket (

ms)


Pow

er co

nsum

ptio

n (m

W)

PSMPSMAdapt

WuRWuRMUS

101

102



PSMPSMAdapt

WuRWuRMUS

5

10

15

20

25

Thro

ughp

ut (M

bps)














5 Conclusion





References































RoboticsJournal of





Journal of



RotatingMachinery



Journal of

Volume 201


VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation










CPUWLAN

AP

EmulatedOOK

CPU WLAN

Node

CS

OOK Dem SNR Det

WuR



Envelopedetection















WuMAP

A

B

C

DIFS

7 6 5 4

3 2 1 0ACK

SIFS

WuM

WLAN active

CTS

SIFS

SLOT

3 2 1 0

WLAN false wake-up

TIM

TIM TIMACK

SIFS SIFS DIFS

2 1 0 WLAN active

CTS ACK

SIFS SIFS DIFS

TIMTIM

T７５

T７５

T７５

T３

T３

T３

PB1 PB2 PC1












CTSCTS

j

WuM WuM


WuM CTS WuM





DIFS DIFSN slots

SIFS SIFS DIFS

EIFS


t(E | N)

t(S | j mN)

t(C | k j mN)

T７５

T７５








119875 (119864 | 1205740) = 119875 (0 | 1205740) (2)



119905 (119864 | 1205740 119873) = 119905 (119864 | 119873) sdot 119875 (119864 | 1205740) (3)



119875 (119878 | 119895 119898119873)

=

1119873 1 le 119895 le 119873 119898 = 1

1198621198981 sdot(119873 minus 119895)119898minus1

119873119898 1 le 119895 le 119873 minus 1 119898 ge 2

(4)


119875 (119878 | 1205740 119873) =119872

sum119898=1

119873

sum119895=1

119875 (119878 | 119895 119898119873)119875 (119898 | 1205740) (5)




119905 (119878 | 1205740 119873)

=119872

sum119898=1

119873

sum119895=1

119905 (119878 | 119895 119898119873)119875 (119878 | 119895 119898119873)119875 (119898 | 1205740) (7)



119871 (119878 | 1205740 119873) = 1 sdot119875 (119878 | 1205740 119873)1 minus 119875 (119864 | 1205740)

(8)


119871119865 (119878 | 119895 119898119873)

=



(9)


119871119865 (119878 | 1205740 119873) =119872

sum119898=1

119871119865 (119878 | 119898119873) 119875 (119898 | 1205740)1 minus 119875 (119864 | 1205740)

119871119865 (119878 | 119898119873) =119873

sum119895=1

119875 (119878 | 119895 119898119873) sdot 119871119865 (119878 | 119895 119898119873) (10)


119875 (119862 | 119896 119895 119898119873)

=

119862119898119896 sdot(119873 minus 119895)119898minus119896

119873119898 1 le 119895 le 119873 minus 1 119898 ge 21119873119898 119896 = 119898 119895 = 119873 119898 ge 2

(11)


119905 (119862 | 119896 119895 119898119873) = 119905WuM + 119905DIFS + 119895 sdot 119879119878 + 119879WU

+ 119905CTS + 119905EIFS(12)


119905 (119862 | 1205740 119873) =119872

sum119898=2

119873

sum119895=1

119898

sum119896=2

119905 (119862 | 119896 119895 119898119873)

sdot 119875 (119862 | 119896 119895 119898119873)119875 (119898 | 1205740) (13)


119871 (119862 | 119896 119895 119898119873) =

119896 1 le 119895 le 119873 minus 1 119898 ge 2119898 119895 = 119873 119898 ge 2

(14)


119871 (119862 | 1205740 119873) =119872

sum119898=2

119871 (119862 | 119898119873) 119875 (119898 | 1205740)1 minus 119875 (119864 | 1205740)

119871 (119862 | 119898119873)

=119873

sum119895=1

119898

sum119896=2

119875 (119862 | 119896 119895 119898119873) sdot 119871 (119862 | 119896 119895 119898119873)

(15)


119871119865 (119862 | 119896 119895 119898119873)

=



(16)


119871119865 (119862 | 1205740 119873) =119872

sum119898=2

119871119865 (119862 | 119898119873) 119875 (119898 | 1205740)1 minus 119875 (119864 | 1205740)

119871119865 (119862 | 119898119873)

=119873

sum119895=1

119898

sum119896=2

119875 (119862 | 119896 119895 119898119873) sdot 119871119865 (119862 | 119896 119895 119898119873)

(17)


119905 (1205740 119873) = 119905 (119864 | 1205740 119873) + 119905 (119878 | 1205740 119873)

+ 119905 (119862 | 1205740 119873) (18)


119864 (119903 | 120574 ge 1205740) =1119872119872

sum119894=1

119864 (119903119894 | 120574119894 ge 1205740)

119864 (119903119894 | 120574119894 ge 1205740) =intinfin1205740


(19)


0

05

1

15

2

25En

ergy

effici

ency

0 1 2 3 4 5 6 7 8minus1


SlotＭ = 50

SlotＭ = 40

SlotＭ = 30

SlotＭ = 20

SlotＭ = 10



= 30

= 20


0

005

01

015

02

025

03

Ener

gy effi

cien

cy

0 1 2 3 4 5 6 7 8minus1





120576 (1205740 119873) = 120576119878 (1205740 119873) + 120576119862 (1205740 119873) + 120576119865 (1205740 119873)


sdot 119871 (119878 | 1205740 119873)


sdot 119871 (119878 | 1205740 119873)


sdot 119871 (119862 | 1205740 119873)

120576119865 (1205740 119873) = (119879WU + 119879SL) sdot 119864119868sdot (119871119865 (119878 | 1205740 119873) + 119871119865 (119862 | 1205740 119873))

(20)



1205781015840 (1205740 119873) =119864 (119903 | 120574 ge 1205740) sdot 119905Data sdot 119875 (119878 | 1205740 119873)

119905 (1205740 119873) sdot 120576 (1205740 119873) (21)





120578 (1205740 119873) =119905Data sdot 119875 (119878 | 1205740 119873)119905 (1205740 119873) sdot 120576 (1205740 119873)

(22)






Del

ay p

er p

acke

t (m

s)

10 nodes20 nodes

0

50

100

150

5 10 15 20 25 30


10 nodes20 nodes

0

005

01

015

02

025

03

Chan

nel u

tility

10 15 20 25 305



10 nodes20 nodes

0

5

10

15

20

25

30

Pow

er co

nsum

ptio

n (m

W)

10 15 20 25 305









PSMPSMAdapt

WuRWuRMUS

0

50

100

150D

elay

per

pac

ket (

ms)



PSMPSMAdapt

WuRWuRMUS


0

005

01

015

02

025

03

Chan

nel u

tility



Pow

er co

nsum

ptio

n (m

W)

PSMPSMAdapt

WuRWuRMUS

5 10 15 20 25 30

101

102











PSMPSMAdapt

WuRWuRMUS


0

50

100

150D

elay

per

pac

ket (

ms)


Pow

er co

nsum

ptio

n (m

W)

PSMPSMAdapt

WuRWuRMUS

101

102



PSMPSMAdapt

WuRWuRMUS

5

10

15

20

25

Thro

ughp

ut (M

bps)














5 Conclusion





References































RoboticsJournal of





Journal of



RotatingMachinery



Journal of

Volume 201


VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation










WuMAP

A

B

C

DIFS

7 6 5 4

3 2 1 0ACK

SIFS

WuM

WLAN active

CTS

SIFS

SLOT

3 2 1 0

WLAN false wake-up

TIM

TIM TIMACK

SIFS SIFS DIFS

2 1 0 WLAN active

CTS ACK

SIFS SIFS DIFS

TIMTIM

T７５

T７５

T７５

T３

T３

T３

PB1 PB2 PC1












CTSCTS

j

WuM WuM


WuM CTS WuM





DIFS DIFSN slots

SIFS SIFS DIFS

EIFS


t(E | N)

t(S | j mN)

t(C | k j mN)

T７５

T７５








119875 (119864 | 1205740) = 119875 (0 | 1205740) (2)



119905 (119864 | 1205740 119873) = 119905 (119864 | 119873) sdot 119875 (119864 | 1205740) (3)



119875 (119878 | 119895 119898119873)

=

1119873 1 le 119895 le 119873 119898 = 1

1198621198981 sdot(119873 minus 119895)119898minus1

119873119898 1 le 119895 le 119873 minus 1 119898 ge 2

(4)


119875 (119878 | 1205740 119873) =119872

sum119898=1

119873

sum119895=1

119875 (119878 | 119895 119898119873)119875 (119898 | 1205740) (5)




119905 (119878 | 1205740 119873)

=119872

sum119898=1

119873

sum119895=1

119905 (119878 | 119895 119898119873)119875 (119878 | 119895 119898119873)119875 (119898 | 1205740) (7)



119871 (119878 | 1205740 119873) = 1 sdot119875 (119878 | 1205740 119873)1 minus 119875 (119864 | 1205740)

(8)


119871119865 (119878 | 119895 119898119873)

=



(9)


119871119865 (119878 | 1205740 119873) =119872

sum119898=1

119871119865 (119878 | 119898119873) 119875 (119898 | 1205740)1 minus 119875 (119864 | 1205740)

119871119865 (119878 | 119898119873) =119873

sum119895=1

119875 (119878 | 119895 119898119873) sdot 119871119865 (119878 | 119895 119898119873) (10)


119875 (119862 | 119896 119895 119898119873)

=

119862119898119896 sdot(119873 minus 119895)119898minus119896

119873119898 1 le 119895 le 119873 minus 1 119898 ge 21119873119898 119896 = 119898 119895 = 119873 119898 ge 2

(11)


119905 (119862 | 119896 119895 119898119873) = 119905WuM + 119905DIFS + 119895 sdot 119879119878 + 119879WU

+ 119905CTS + 119905EIFS(12)


119905 (119862 | 1205740 119873) =119872

sum119898=2

119873

sum119895=1

119898

sum119896=2

119905 (119862 | 119896 119895 119898119873)

sdot 119875 (119862 | 119896 119895 119898119873)119875 (119898 | 1205740) (13)


119871 (119862 | 119896 119895 119898119873) =

119896 1 le 119895 le 119873 minus 1 119898 ge 2119898 119895 = 119873 119898 ge 2

(14)


119871 (119862 | 1205740 119873) =119872

sum119898=2

119871 (119862 | 119898119873) 119875 (119898 | 1205740)1 minus 119875 (119864 | 1205740)

119871 (119862 | 119898119873)

=119873

sum119895=1

119898

sum119896=2

119875 (119862 | 119896 119895 119898119873) sdot 119871 (119862 | 119896 119895 119898119873)

(15)


119871119865 (119862 | 119896 119895 119898119873)

=



(16)


119871119865 (119862 | 1205740 119873) =119872

sum119898=2

119871119865 (119862 | 119898119873) 119875 (119898 | 1205740)1 minus 119875 (119864 | 1205740)

119871119865 (119862 | 119898119873)

=119873

sum119895=1

119898

sum119896=2

119875 (119862 | 119896 119895 119898119873) sdot 119871119865 (119862 | 119896 119895 119898119873)

(17)


119905 (1205740 119873) = 119905 (119864 | 1205740 119873) + 119905 (119878 | 1205740 119873)

+ 119905 (119862 | 1205740 119873) (18)


119864 (119903 | 120574 ge 1205740) =1119872119872

sum119894=1

119864 (119903119894 | 120574119894 ge 1205740)

119864 (119903119894 | 120574119894 ge 1205740) =intinfin1205740


(19)


0

05

1

15

2

25En

ergy

effici

ency

0 1 2 3 4 5 6 7 8minus1


SlotＭ = 50

SlotＭ = 40

SlotＭ = 30

SlotＭ = 20

SlotＭ = 10



= 30

= 20


0

005

01

015

02

025

03

Ener

gy effi

cien

cy

0 1 2 3 4 5 6 7 8minus1





120576 (1205740 119873) = 120576119878 (1205740 119873) + 120576119862 (1205740 119873) + 120576119865 (1205740 119873)


sdot 119871 (119878 | 1205740 119873)


sdot 119871 (119878 | 1205740 119873)


sdot 119871 (119862 | 1205740 119873)

120576119865 (1205740 119873) = (119879WU + 119879SL) sdot 119864119868sdot (119871119865 (119878 | 1205740 119873) + 119871119865 (119862 | 1205740 119873))

(20)



1205781015840 (1205740 119873) =119864 (119903 | 120574 ge 1205740) sdot 119905Data sdot 119875 (119878 | 1205740 119873)

119905 (1205740 119873) sdot 120576 (1205740 119873) (21)





120578 (1205740 119873) =119905Data sdot 119875 (119878 | 1205740 119873)119905 (1205740 119873) sdot 120576 (1205740 119873)

(22)






Del

ay p

er p

acke

t (m

s)

10 nodes20 nodes

0

50

100

150

5 10 15 20 25 30


10 nodes20 nodes

0

005

01

015

02

025

03

Chan

nel u

tility

10 15 20 25 305



10 nodes20 nodes

0

5

10

15

20

25

30

Pow

er co

nsum

ptio

n (m

W)

10 15 20 25 305









PSMPSMAdapt

WuRWuRMUS

0

50

100

150D

elay

per

pac

ket (

ms)



PSMPSMAdapt

WuRWuRMUS


0

005

01

015

02

025

03

Chan

nel u

tility



Pow

er co

nsum

ptio

n (m

W)

PSMPSMAdapt

WuRWuRMUS

5 10 15 20 25 30

101

102











PSMPSMAdapt

WuRWuRMUS


0

50

100

150D

elay

per

pac

ket (

ms)


Pow

er co

nsum

ptio

n (m

W)

PSMPSMAdapt

WuRWuRMUS

101

102



PSMPSMAdapt

WuRWuRMUS

5

10

15

20

25

Thro

ughp

ut (M

bps)














5 Conclusion





References































RoboticsJournal of





Journal of



RotatingMachinery



Journal of

Volume 201


VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation










CTSCTS

j

WuM WuM


WuM CTS WuM





DIFS DIFSN slots

SIFS SIFS DIFS

EIFS


t(E | N)

t(S | j mN)

t(C | k j mN)

T７５

T７５








119875 (119864 | 1205740) = 119875 (0 | 1205740) (2)



119905 (119864 | 1205740 119873) = 119905 (119864 | 119873) sdot 119875 (119864 | 1205740) (3)



119875 (119878 | 119895 119898119873)

=

1119873 1 le 119895 le 119873 119898 = 1

1198621198981 sdot(119873 minus 119895)119898minus1

119873119898 1 le 119895 le 119873 minus 1 119898 ge 2

(4)


119875 (119878 | 1205740 119873) =119872

sum119898=1

119873

sum119895=1

119875 (119878 | 119895 119898119873)119875 (119898 | 1205740) (5)




119905 (119878 | 1205740 119873)

=119872

sum119898=1

119873

sum119895=1

119905 (119878 | 119895 119898119873)119875 (119878 | 119895 119898119873)119875 (119898 | 1205740) (7)



119871 (119878 | 1205740 119873) = 1 sdot119875 (119878 | 1205740 119873)1 minus 119875 (119864 | 1205740)

(8)


119871119865 (119878 | 119895 119898119873)

=



(9)


119871119865 (119878 | 1205740 119873) =119872

sum119898=1

119871119865 (119878 | 119898119873) 119875 (119898 | 1205740)1 minus 119875 (119864 | 1205740)

119871119865 (119878 | 119898119873) =119873

sum119895=1

119875 (119878 | 119895 119898119873) sdot 119871119865 (119878 | 119895 119898119873) (10)


119875 (119862 | 119896 119895 119898119873)

=

119862119898119896 sdot(119873 minus 119895)119898minus119896

119873119898 1 le 119895 le 119873 minus 1 119898 ge 21119873119898 119896 = 119898 119895 = 119873 119898 ge 2

(11)


119905 (119862 | 119896 119895 119898119873) = 119905WuM + 119905DIFS + 119895 sdot 119879119878 + 119879WU

+ 119905CTS + 119905EIFS(12)


119905 (119862 | 1205740 119873) =119872

sum119898=2

119873

sum119895=1

119898

sum119896=2

119905 (119862 | 119896 119895 119898119873)

sdot 119875 (119862 | 119896 119895 119898119873)119875 (119898 | 1205740) (13)


119871 (119862 | 119896 119895 119898119873) =

119896 1 le 119895 le 119873 minus 1 119898 ge 2119898 119895 = 119873 119898 ge 2

(14)


119871 (119862 | 1205740 119873) =119872

sum119898=2

119871 (119862 | 119898119873) 119875 (119898 | 1205740)1 minus 119875 (119864 | 1205740)

119871 (119862 | 119898119873)

=119873

sum119895=1

119898

sum119896=2

119875 (119862 | 119896 119895 119898119873) sdot 119871 (119862 | 119896 119895 119898119873)

(15)


119871119865 (119862 | 119896 119895 119898119873)

=



(16)


119871119865 (119862 | 1205740 119873) =119872

sum119898=2

119871119865 (119862 | 119898119873) 119875 (119898 | 1205740)1 minus 119875 (119864 | 1205740)

119871119865 (119862 | 119898119873)

=119873

sum119895=1

119898

sum119896=2

119875 (119862 | 119896 119895 119898119873) sdot 119871119865 (119862 | 119896 119895 119898119873)

(17)


119905 (1205740 119873) = 119905 (119864 | 1205740 119873) + 119905 (119878 | 1205740 119873)

+ 119905 (119862 | 1205740 119873) (18)


119864 (119903 | 120574 ge 1205740) =1119872119872

sum119894=1

119864 (119903119894 | 120574119894 ge 1205740)

119864 (119903119894 | 120574119894 ge 1205740) =intinfin1205740


(19)


0

05

1

15

2

25En

ergy

effici

ency

0 1 2 3 4 5 6 7 8minus1


SlotＭ = 50

SlotＭ = 40

SlotＭ = 30

SlotＭ = 20

SlotＭ = 10



= 30

= 20


0

005

01

015

02

025

03

Ener

gy effi

cien

cy

0 1 2 3 4 5 6 7 8minus1





120576 (1205740 119873) = 120576119878 (1205740 119873) + 120576119862 (1205740 119873) + 120576119865 (1205740 119873)


sdot 119871 (119878 | 1205740 119873)


sdot 119871 (119878 | 1205740 119873)


sdot 119871 (119862 | 1205740 119873)

120576119865 (1205740 119873) = (119879WU + 119879SL) sdot 119864119868sdot (119871119865 (119878 | 1205740 119873) + 119871119865 (119862 | 1205740 119873))

(20)



1205781015840 (1205740 119873) =119864 (119903 | 120574 ge 1205740) sdot 119905Data sdot 119875 (119878 | 1205740 119873)

119905 (1205740 119873) sdot 120576 (1205740 119873) (21)





120578 (1205740 119873) =119905Data sdot 119875 (119878 | 1205740 119873)119905 (1205740 119873) sdot 120576 (1205740 119873)

(22)






Del

ay p

er p

acke

t (m

s)

10 nodes20 nodes

0

50

100

150

5 10 15 20 25 30


10 nodes20 nodes

0

005

01

015

02

025

03

Chan

nel u

tility

10 15 20 25 305



10 nodes20 nodes

0

5

10

15

20

25

30

Pow

er co

nsum

ptio

n (m

W)

10 15 20 25 305









PSMPSMAdapt

WuRWuRMUS

0

50

100

150D

elay

per

pac

ket (

ms)



PSMPSMAdapt

WuRWuRMUS


0

005

01

015

02

025

03

Chan

nel u

tility



Pow

er co

nsum

ptio

n (m

W)

PSMPSMAdapt

WuRWuRMUS

5 10 15 20 25 30

101

102











PSMPSMAdapt

WuRWuRMUS


0

50

100

150D

elay

per

pac

ket (

ms)


Pow

er co

nsum

ptio

n (m

W)

PSMPSMAdapt

WuRWuRMUS

101

102



PSMPSMAdapt

WuRWuRMUS

5

10

15

20

25

Thro

ughp

ut (M

bps)














5 Conclusion





References































RoboticsJournal of





Journal of



RotatingMachinery



Journal of

Volume 201


VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation











119871 (119878 | 1205740 119873) = 1 sdot119875 (119878 | 1205740 119873)1 minus 119875 (119864 | 1205740)

(8)


119871119865 (119878 | 119895 119898119873)

=



(9)


119871119865 (119878 | 1205740 119873) =119872

sum119898=1

119871119865 (119878 | 119898119873) 119875 (119898 | 1205740)1 minus 119875 (119864 | 1205740)

119871119865 (119878 | 119898119873) =119873

sum119895=1

119875 (119878 | 119895 119898119873) sdot 119871119865 (119878 | 119895 119898119873) (10)


119875 (119862 | 119896 119895 119898119873)

=

119862119898119896 sdot(119873 minus 119895)119898minus119896

119873119898 1 le 119895 le 119873 minus 1 119898 ge 21119873119898 119896 = 119898 119895 = 119873 119898 ge 2

(11)


119905 (119862 | 119896 119895 119898119873) = 119905WuM + 119905DIFS + 119895 sdot 119879119878 + 119879WU

+ 119905CTS + 119905EIFS(12)


119905 (119862 | 1205740 119873) =119872

sum119898=2

119873

sum119895=1

119898

sum119896=2

119905 (119862 | 119896 119895 119898119873)

sdot 119875 (119862 | 119896 119895 119898119873)119875 (119898 | 1205740) (13)


119871 (119862 | 119896 119895 119898119873) =

119896 1 le 119895 le 119873 minus 1 119898 ge 2119898 119895 = 119873 119898 ge 2

(14)


119871 (119862 | 1205740 119873) =119872

sum119898=2

119871 (119862 | 119898119873) 119875 (119898 | 1205740)1 minus 119875 (119864 | 1205740)

119871 (119862 | 119898119873)

=119873

sum119895=1

119898

sum119896=2

119875 (119862 | 119896 119895 119898119873) sdot 119871 (119862 | 119896 119895 119898119873)

(15)


119871119865 (119862 | 119896 119895 119898119873)

=



(16)


119871119865 (119862 | 1205740 119873) =119872

sum119898=2

119871119865 (119862 | 119898119873) 119875 (119898 | 1205740)1 minus 119875 (119864 | 1205740)

119871119865 (119862 | 119898119873)

=119873

sum119895=1

119898

sum119896=2

119875 (119862 | 119896 119895 119898119873) sdot 119871119865 (119862 | 119896 119895 119898119873)

(17)


119905 (1205740 119873) = 119905 (119864 | 1205740 119873) + 119905 (119878 | 1205740 119873)

+ 119905 (119862 | 1205740 119873) (18)


119864 (119903 | 120574 ge 1205740) =1119872119872

sum119894=1

119864 (119903119894 | 120574119894 ge 1205740)

119864 (119903119894 | 120574119894 ge 1205740) =intinfin1205740


(19)


0

05

1

15

2

25En

ergy

effici

ency

0 1 2 3 4 5 6 7 8minus1


SlotＭ = 50

SlotＭ = 40

SlotＭ = 30

SlotＭ = 20

SlotＭ = 10



= 30

= 20


0

005

01

015

02

025

03

Ener

gy effi

cien

cy

0 1 2 3 4 5 6 7 8minus1





120576 (1205740 119873) = 120576119878 (1205740 119873) + 120576119862 (1205740 119873) + 120576119865 (1205740 119873)


sdot 119871 (119878 | 1205740 119873)


sdot 119871 (119878 | 1205740 119873)


sdot 119871 (119862 | 1205740 119873)

120576119865 (1205740 119873) = (119879WU + 119879SL) sdot 119864119868sdot (119871119865 (119878 | 1205740 119873) + 119871119865 (119862 | 1205740 119873))

(20)



1205781015840 (1205740 119873) =119864 (119903 | 120574 ge 1205740) sdot 119905Data sdot 119875 (119878 | 1205740 119873)

119905 (1205740 119873) sdot 120576 (1205740 119873) (21)





120578 (1205740 119873) =119905Data sdot 119875 (119878 | 1205740 119873)119905 (1205740 119873) sdot 120576 (1205740 119873)

(22)






Del

ay p

er p

acke

t (m

s)

10 nodes20 nodes

0

50

100

150

5 10 15 20 25 30


10 nodes20 nodes

0

005

01

015

02

025

03

Chan

nel u

tility

10 15 20 25 305



10 nodes20 nodes

0

5

10

15

20

25

30

Pow

er co

nsum

ptio

n (m

W)

10 15 20 25 305









PSMPSMAdapt

WuRWuRMUS

0

50

100

150D

elay

per

pac

ket (

ms)



PSMPSMAdapt

WuRWuRMUS


0

005

01

015

02

025

03

Chan

nel u

tility



Pow

er co

nsum

ptio

n (m

W)

PSMPSMAdapt

WuRWuRMUS

5 10 15 20 25 30

101

102











PSMPSMAdapt

WuRWuRMUS


0

50

100

150D

elay

per

pac

ket (

ms)


Pow

er co

nsum

ptio

n (m

W)

PSMPSMAdapt

WuRWuRMUS

101

102



PSMPSMAdapt

WuRWuRMUS

5

10

15

20

25

Thro

ughp

ut (M

bps)














5 Conclusion





References































RoboticsJournal of





Journal of



RotatingMachinery



Journal of

Volume 201


VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation










0

05

1

15

2

25En

ergy

effici

ency

0 1 2 3 4 5 6 7 8minus1


SlotＭ = 50

SlotＭ = 40

SlotＭ = 30

SlotＭ = 20

SlotＭ = 10



= 30

= 20


0

005

01

015

02

025

03

Ener

gy effi

cien

cy

0 1 2 3 4 5 6 7 8minus1





120576 (1205740 119873) = 120576119878 (1205740 119873) + 120576119862 (1205740 119873) + 120576119865 (1205740 119873)


sdot 119871 (119878 | 1205740 119873)


sdot 119871 (119878 | 1205740 119873)


sdot 119871 (119862 | 1205740 119873)

120576119865 (1205740 119873) = (119879WU + 119879SL) sdot 119864119868sdot (119871119865 (119878 | 1205740 119873) + 119871119865 (119862 | 1205740 119873))

(20)



1205781015840 (1205740 119873) =119864 (119903 | 120574 ge 1205740) sdot 119905Data sdot 119875 (119878 | 1205740 119873)

119905 (1205740 119873) sdot 120576 (1205740 119873) (21)





120578 (1205740 119873) =119905Data sdot 119875 (119878 | 1205740 119873)119905 (1205740 119873) sdot 120576 (1205740 119873)

(22)






Del

ay p

er p

acke

t (m

s)

10 nodes20 nodes

0

50

100

150

5 10 15 20 25 30


10 nodes20 nodes

0

005

01

015

02

025

03

Chan

nel u

tility

10 15 20 25 305



10 nodes20 nodes

0

5

10

15

20

25

30

Pow

er co

nsum

ptio

n (m

W)

10 15 20 25 305









PSMPSMAdapt

WuRWuRMUS

0

50

100

150D

elay

per

pac

ket (

ms)



PSMPSMAdapt

WuRWuRMUS


0

005

01

015

02

025

03

Chan

nel u

tility



Pow

er co

nsum

ptio

n (m

W)

PSMPSMAdapt

WuRWuRMUS

5 10 15 20 25 30

101

102











PSMPSMAdapt

WuRWuRMUS


0

50

100

150D

elay

per

pac

ket (

ms)


Pow

er co

nsum

ptio

n (m

W)

PSMPSMAdapt

WuRWuRMUS

101

102



PSMPSMAdapt

WuRWuRMUS

5

10

15

20

25

Thro

ughp

ut (M

bps)














5 Conclusion





References































RoboticsJournal of





Journal of



RotatingMachinery



Journal of

Volume 201


VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation











Del

ay p

er p

acke

t (m

s)

10 nodes20 nodes

0

50

100

150

5 10 15 20 25 30


10 nodes20 nodes

0

005

01

015

02

025

03

Chan

nel u

tility

10 15 20 25 305



10 nodes20 nodes

0

5

10

15

20

25

30

Pow

er co

nsum

ptio

n (m

W)

10 15 20 25 305









PSMPSMAdapt

WuRWuRMUS

0

50

100

150D

elay

per

pac

ket (

ms)



PSMPSMAdapt

WuRWuRMUS


0

005

01

015

02

025

03

Chan

nel u

tility



Pow

er co

nsum

ptio

n (m

W)

PSMPSMAdapt

WuRWuRMUS

5 10 15 20 25 30

101

102











PSMPSMAdapt

WuRWuRMUS


0

50

100

150D

elay

per

pac

ket (

ms)


Pow

er co

nsum

ptio

n (m

W)

PSMPSMAdapt

WuRWuRMUS

101

102



PSMPSMAdapt

WuRWuRMUS

5

10

15

20

25

Thro

ughp

ut (M

bps)














5 Conclusion





References































RoboticsJournal of





Journal of



RotatingMachinery



Journal of

Volume 201


VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation










PSMPSMAdapt

WuRWuRMUS

0

50

100

150D

elay

per

pac

ket (

ms)



PSMPSMAdapt

WuRWuRMUS


0

005

01

015

02

025

03

Chan

nel u

tility



Pow

er co

nsum

ptio

n (m

W)

PSMPSMAdapt

WuRWuRMUS

5 10 15 20 25 30

101

102











PSMPSMAdapt

WuRWuRMUS


0

50

100

150D

elay

per

pac

ket (

ms)


Pow

er co

nsum

ptio

n (m

W)

PSMPSMAdapt

WuRWuRMUS

101

102



PSMPSMAdapt

WuRWuRMUS

5

10

15

20

25

Thro

ughp

ut (M

bps)














5 Conclusion





References































RoboticsJournal of





Journal of



RotatingMachinery



Journal of

Volume 201


VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation










PSMPSMAdapt

WuRWuRMUS


0

50

100

150D

elay

per

pac

ket (

ms)


Pow

er co

nsum

ptio

n (m

W)

PSMPSMAdapt

WuRWuRMUS

101

102



PSMPSMAdapt

WuRWuRMUS

5

10

15

20

25

Thro

ughp

ut (M

bps)














5 Conclusion





References































RoboticsJournal of





Journal of



RotatingMachinery



Journal of

Volume 201


VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation














5 Conclusion





References































RoboticsJournal of





Journal of



RotatingMachinery



Journal of

Volume 201


VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation

























RoboticsJournal of





Journal of



RotatingMachinery



Journal of

Volume 201


VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation









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