CHARACTERIZING WI-FI LINK IN OPEN OUT-DOOR NETWORK

BY:

SALAH AMEAN

OUTLINES

Summary of the paper

scope

Background

802.11n

literature

experiment / preparation

Results and discussion

Conclusion

BACKGROUND

Providing internet to remote areas in developed or developing countries

Unlicensed WiFi spectrum WiFi availability and low cost

These networks typically have long distance point-to-point wireless lin enabled by high-gain directional antennas Several KM

Low throughput

Infrastructure is installed on top of high areas Antennas on tall building or towers

BACKGROUND

Oil and gas exploration Sensors that are deployed to collect seismic data covering a huge geographic space

sensor data needs to be collected and delivered to a centralized command unit

Sensors are buried in the ground to capture seismic data

Access Point (AP) covers a space where the sensors in that space communicate to that AP

APs form aggregation layer

The APs of one aggregation layer communicates to an AP of the next higher layer, and vice versa

CONSECUTIVE SUMMARY

Characterizing Wi-Fi links in open space outdoor environment

A large scale wireless sensor network scenario of seismic data collection from sensors that are buried in ground and

a set of access points (APs) form the hierarchical aggregation layer and the backbone of the network

Oil and gas exploration

Evaluate the links between sensor nodes and a wireless AP using IEEE 802.11a/b/g and then IEEE 802.11n Ieee802.11n high gain directional antenna for high throughput and long distance

Characterize the long distance wireless backhaul links between the Aps 148 Mb/s throughput at 800 meter line-of-sight links

40.8 Mb/s for the 1800 m link

Showing how PHY and MAC enhancement of 802.11n impact performance in outdoor environment

OUTDOOR WIFI ADVANTAGES

Providing internet to remote places

Cheaper assets

Considering the amount of capital investment in developing countries Implement in some developed countries where the number of users are not dense

Variety of applications can used for wifi deployment in resorts, hotels, etc.

deploying service to distant locations in developing countries India(Aravind hospital), Ghana, malawi

802.11B LINKS: PERFORMANCE MEASUREMENT AND EXPERIENCE PAPER (RE-QUIREMENTS)

What are the packet error-rate seen on the long distance links? and how they vary with the RSS?

Is there any dependence of the packet error rate on the link length?

What is effect of packet size and transmit rate (modulation) on the packet error rate?

Is there any time-correlation in the packet errors seen? At what time scales?

What effect do weather conditions (rain/fog) have on the link performance?

Are there any MAC-level ACK timeouts on the long distance links? What effect does this have on the application throughput

What is the effect of inter-link or external interference?

Answers to the above questions have implications on the planning of long-distance links, protocol design, as well as application design.

THERE ARE TWO MAIN REASONS FOR THIS POORPERFORMANCE IN WILD NETWORKS

Shortcoming of Wi-Fi 802.11 that makes it ill-suited for WiLD networks Link recovery mechanism(stop-and-wait) cause low utilization

ACK or retransmit options

With long distance , sender waits for a longer time for the ACKs to return

long distances frequent collisions occur because of the failure of CSMA/CA

Interlink interference

Solution: Using adaptive link recovery mechanism

Using bulk acknowledgment

Application-based parameter configuration

LONG DISTANCE WIFI BASED NETWORKS

Developed countries Least occupied places

E.g., Norway

Developing countries Providing internet facility

India

Malaysia ( Kampung WiFi)

Zambia

Ghana

ARAVIND EYE HOSPITAL AT THENI

Providing eye care to rural areas

Only one nurse working in the clinic

Specialist at the Aravind eye hospital inTheni diagnose patients

RELATED WORK(1)B. Raman 2007 the first to deploy a WiFi based outdoor long

distance network consisting of approximately ten links and lengths ranging from 1 ~ 16 Km

-All these work have infrastructured APs on top of towers or high buildings to create LOS links.

-In addition, their main focus is to provide network connection over long-distance (up to 16 Km) point-to-point link and high throughput is not their major concern. -In contrast, our network requires high bandwidth and has relaying APs every 1~2 Km. -We evaluate 802.11n for long distance links in a rural environment where there is less multipath ef-fect than indoor and urban environments.

K. Chebrolu, 2006 -study of long distance 802.11b link performance-study the behavior of such long links for varying packet sizes, data rates, SNRs and weather conditions-modification to the MAC to

R. Patra 2007 a TDMA based MAC protocol in lossy conditions for long distance links

V. Shrivastava 2008 show that the throughput of an 802.11n link can be severely degraded in presence of an 802.11g link

Constantinos pelechinis

2010 -802.11n produces more loss in high transmission rate(outage) -wider channel are sensitive to interference

RELATED WORK(2)

Ece Gelal et al. 2010 -PHY layer gains due to MIMO diversity do not always carry over to the higher layers,-the use of other PHY layer features such as FEC codes significantly influence the gains due to MIMO diversity- routing metric used may impact the gains possible with MIMO.

-

Arslan et al. 2010 -Channel bonding (CB) exacerbates interference ef-fect-CB does not always provide benefits in interfer-ence-free settings, and can even degrade perfor-mance in some cases-ACORN integrates the functions of user association and channel allocation

-J. P. Kermoal, -I. Sarris and A. R. Nix. -J. M. G. Pardo,

2001,2007,2009 Reporting the gain of polarization antenna diversity on MIMO channel with LOS components-indoor environment -controlled & anechoic chamber -focusing on validating their theoretical model

-this paper is the first measurement report that shows the polarization diversity gain for long distance outdoor communication using commod-ity 802.11n devices

NETWORK ARCHITECTURE CONCEPTUAL DIAGRAM

Two link characterisation Sensor-to-AP

AP-to-AP

SENSOR-TO-AP The link between a sensor node and an AP

High throughput is not required for this link

Range is important for the network design

802.11a/b/g is used for this link

Because of the simplistic design of the sensor node,

it is not possible to use multiple antennas at the sensor node.

Thus, there is no link range benefit by using 802.11n for this link.

BACKHAUL LINK BETWEEN TWO AP

high throughput & distance are required as it transmits the aggregated data from a large number of sensors towards a remote data collection & command center

Consideration of 802.11n for this link because the 802.11n MIMO technique support

Consideration of MAC enhancements provide high throughput without requiring stronger signal power than 802.11a/g

CONTRIBUTION

Studying how different modulation schemes and antenna heights at the sensor nodes af-fect the maximum communication distance

Evaluating the performance of 802.11n in an open outdoor environment , and showing its effectiveness in outdoor desert-like environment

Analyzing how several PHY/MAC enhancements of 802.11n improve the performance in an outdoor network

SET UP OF A WCB NODE ON THE GROUND

Sensor node-HP E-M111 Access point-HP E-MSM422 AP

ANTENNA SETUP AT ONE END OF THE LINK AP is connect to this antenna

12dBi gain antenna

The antenna is mounted on top of tripod 3 m high

Previous works of WiLD networks 24dBi to 14KM

TESTING AREA

SATELITE VIEW OF THE AREA

Nodes are shown in circles Green is fixed

MEASURED RECEIVED SIGNAL STRENGTH

RSS naturally decays over distance

Measured using

Pr power received , Pt is the transmitted power

K is constant depending

transmission frequency, antenna gains, and antenna height

α is 2 or 6 depending on the propagation environment

d transmitter-receiver distance

802.11N FEATURES

Frame Aggregation and Block Acknowledgement Allowing multiple frames to form an aggregated frame(A-MPDU and A-MSDU)

Block ACK for several frames received

Reduces overhead

Channel Bonding Wider channel 40MHz doubles data rate

Reduces the No. of channels

Prone to interferences

reduces received power at the receiver by 3 dB because the transmitted energy spreads over twice the channel widtd

802.11N FEATURES

Guard Interval Theoretically SGI provides 11% increase in PHY data rate

Reduction of inter OFDM symbols from 800ns to 400ns

PHY Layer Diversity MIMO antennas with spatial diversity and spatial multiplexing

Various modulation and coding schemes MCS

MAC and application throughput will be less than the specified PHY data rates mainly due to the

MAC layer overhead including back-off and retransmissions caused by packet losses

sa

PHY LAYER DATA RATES

3 × 3 MIMO streams

combination of channel width and guard interval.

MCS 0 to 7 indicate one data stream,

MCS 8 to 15 indicate two data streams

whereas MCS 16 to 23 indicate three data streams

THROUGHPUT FOR 300M LINK LENGTHS

Shows throughput when enabling/disabling aggregation

Huge improvement in throughput

could not establish link connectivity

for the high MCS rates(above 18)

THROUGHPUT IMPROVEMENT FOR FRAME AGGREGATION FOR 300M LINK

Frame aggregation reduces the MAC layer overhead

%450 through put improvement 40MHz Channel + SGI

Aggregation is necessary To notice significant improvement in throughput

THROUGHPUT IMPROVEMENT FOR CHANNEL BONDING FOR DIFFERENT LINK LENGTHS. FRAME AGGREGATION IS ENABLED AND LONG GI IS USED

Aggregation + SGI (300Meter) Aggregation and LGI

SNR AND ERROR

SNR Error (Aggregation and LGI)

This work is intended for the usage at oil and gas exploration wireless sensor network

This scenario is different from the traditional long distance WiFi network in the sense that nodes are placed closer to ground level and long links also require high bandwidth

present a measurement experimental study of two types of links of this network

First hop-link uses 8 02.11a/b/g to find the maximum link range and construct a path-loss model for our network

We use 802.11n for the backhaul link and evaluate different PHY/MAC layer features pro-vided in 802.11n

CONCLUSION

REFERENCES Paul, U.; Crepaldi, R.; Jeongkeun Lee; Sung-Ju Lee; Etkin, R., "Characterizing WiFi link performance in open outdoor

networks," Sensor, Mesh and Ad Hoc Communications and Networks (SECON), 2011 8th Annual IEEE Communications Society Conference on , vol., no., pp.251,259, 27-30 June 2011.

Kameswari Chebrolu, Bhaskaran Raman, and Sayandeep Sen. 2006. Long-distance 802.11b links: performance measurements and experience. In Proceedings of the 12th annual international conference on Mobile computing and networking (MobiCom '06). ACM, New York, NY, USA, 74-85. DOI=10.1145/1161089.1161099 http://doi.acm.org/10.1145/1161089.1161099

http://www.arubanetworks.com/wp-content/uploads/AP_OutdoorPointToPoint.pdf

http://www.niasat.com/q-what-is-the-difference-between-terrestrial-land-based-internet-and-satellite-internet-service/

Rabin Patra, Sergiu Nedevschi, Sonesh Surana, Anmol Sheth, Lakshminarayanan Subramanian, and Eric Brewer. 2007. WiLdnet: design and implementation of high performancewifi based long distance networks. In Proceedings of the 4th USENIX conference on Networked systems design \&\#38; implementation (NSDI'07). USENIX Association, Berkeley, CA, USA, 7-7.

http://www.berkeley.edu/news/media/releases/2006/06/06_telemedicine.shtml

P. Ermanno. Setting Long Distance WiFi Records: Proofing Solutions for Rural Connectivity. http://ci-journal.net/index.php/ciej/article/view/487/402

Antennas: http://www.tp-link.com/lk/products/details/?model=TL-ANT2412D#spec

Arvind case: http://www.youtube.com/watch?v=v-Jog34Ovco