wman, part 1 contents

8/14/2019 WMAN, Part 1 Contents

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S-72.3240 Wireless Personal, Local, Metropolitan, and Wide Area Networks 1

WMAN, part 1

Contents

IEEE 802.16 family of standards

Protocol layering

TDD frame structure

MAC PDU structure

Part 1:

Part 2: Dynamic QoS management

OFDM PHY layer


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WMAN, part 1

IEEE 802.16

The standard IEEE 802.16 defines the air interface, includingthe MAC layer and multiple PHY layer options, for fixedBroadband Wireless Access (BWA) systems to be used in a

Wireless Metropolitan Area Network (WMAN) for residentialand enterprise use. IEEE 802.16 is also often referred to asWiMax. The WiMax Forum strives to ensure interoperabilitybetween different 802.16 implementations - a difficult taskdue to the large number of options in the standard.

IEEE 802.16 cannot be used in a mobile environment. For thispurpose, IEEE 802.16e is being developed. This standard willcompete with the IEEE 802.20 standard (still in early phase).


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WMAN, part 1

IEEE 802.16 standardization

The first version of the IEEE 802.16 standard was completedin 2001. It defined a single carrier (SC) physical layer for line-of-sight (LOS) transmission in the 10-66 GHz range.

IEEE 802.16a defined three physical layer options (SC, OFDM,and OFDMA) for the 2-11 GHz range.

IEEE 802.16c contained upgrades for the 10-66 GHz range.

IEEE 802.16d contained upgrades for the 2-11 GHz range.

In 2004, the original 802.16 standard, 16a, 16c and 16d werecombined into the massive IEEE 802.16-2004 standard.


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WMAN, part 1

Uplink / downlink separation

IEEE 802.16 offers both TDD (Time Division Duplexing) andFDD (Frequency Division Duplexing) alternatives.

Wireless devices should avoid transmitting and receiving atthe same time, since duplex filters increase the cost:

TDD: this problem is automatically avoided

FDD: IEEE 802.16 offers semi-duplex operation as anoption in Subscriber Stations.

(Note that expensive duplex filters are also the reason whyIEEE 802.11 WLAN technology is based on CSMA/CA insteadof CSMA/CD.)


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WMAN, part 1

Uplink / downlink separation

TDD

FDD

Semi-duplexFDD

Downlink

Uplink

Adaptive

Frequency 1

Frequency 2

Frame n-1 Frame n Frame n+1


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WMAN, part 1

IEEE 802.16 PHY

IEEE 802.16-2004 specifies three PHY options for the 2-11 GHzband, all supporting both TDD and FDD:

WirelessMAN-SCa(single carrier option), intended for a line-of-sight (LOS) radio environment where multipathpropagation is not a problem

WirelessMAN-OFDM with 256 subcarriers (mandatory forlicense-exempt bands) will be the most popular option inthe near future

WirelessMAN-OFDMA with 2048 subcarriers separates usersin the uplink in frequency domain (complex technology).


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WMAN, part 1

IEEE 802.16 basic architecture

BS SS

SS

SS

Point-to-multipointtransmission

AP

AP

802.11WLAN

BS = Base StationSS = Subscriber Station

Fixednetwork

Subscriber line

replacement


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WMAN, part 1

ATMtransport

IPtransport

Service Specific ConvergenceSublayer (CS)

IEEE 802.16 protocol layering

MAC Common Part Sublayer(MAC CPS)

Privacy sublayer

Physical Layer (PHY)

MA

C

Like IEEE 802.11, IEEE802.16 specifies the

Medium Access Control(MAC) and PHY layers ofthe wireless transmissionsystem.

The IEEE 802.16 MAClayer consists of three

sublayers.


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WMAN, part 1

ATMtransport

IPtransport




Privacy sublayer


MA

C

CS maps data (ATM cellsor IP packets) to acertain unidirectionalconnection identified bythe Connection Identifier(CID) and associated

with a certain QoS.

CS adapts higher layerprotocols to MAC CPS.

May also offer payloadheader suppression.


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WMAN, part 1

ATMtransport

IPtransport




Privacy sublayer


MA

C

MAC CPS provides thecore MAC functionality:

System access

Bandwidth allocation

Connection control

Note: QoS control is

applied dynamically toevery connectionindividually.


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WMAN, part 1

ATMtransport

IPtransport




Privacy sublayer


MA

C

The privacy sublayer

provides authentication,key management andencryption.


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WMAN, part 1

ATMtransport

IPtransport




Privacy sublayer


MA

C IEEE 802.16 offers threePHY options for the 2-11GHz band:

WirelessMAN-SCa

WirelessMAN-OFDM

WirelessMAN-OFDMA


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WMAN, part 1

WiMAX

The WiMax (WorldwideInteroperability for MicrowaveAccess) certification program of

the WiMax Forum addressescompatibility of IEEE 802.16equipment

=>

WiMax ensures interoperability

of equipment from differentvendors.

ATMtransport

IPtransport

Service Specific Convergence

Sublayer (CS)


Privacy sublayer


WiMax


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WMAN, part 1

Overall TDD frame structure (1)

Frame n-1 Frame n Frame n+1 Frame n+2

Frame length 0.5, 1 or 2 ms

The following slides present the overall IEEE 802.16 framestructure for TDD.

It is assumed that the PHY option is WirelessMAN-OFDM, sincethis presumably will be the most popular PHY option (in thenear future). The general frame structure is applicable also toother PHY options, but the details may be different.


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WMAN, part 1

Overall TDD frame structure (2)

Frame n-1 Frame n Frame n+1 Frame n+2

DL PHYPDU

Contentionslot A

Contentionslot B

UL PHYburst 1

UL PHYburst k

DL subframe UL subframe

TDMA bursts from

different subscriberstations (each withits own preamble)

TDM signal

in downlink

For initial

ranging

For BW

requests

Adaptive


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WMAN, part 1

UL PHYburst k

DL subframe structure (1)

DL PHYPDU

Contentionslot A

Contentionslot B

UL PHYburst 1

Preamble FCH DL burst 1 DL burst n

The DL subframe starts with a preamble (necessary for framesynchronization and equalization) and the Frame ControlHeader (FCH) that contains the location and burst profile ofthe first DL burst following the FCH. The FCH is one OFDMsymbol long and is transmitted using BPSK modulation.


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WMAN, part 1

UL PHYburst k


DL PHYPDU

Contentionslot A

Contentionslot B

UL PHYburst 1


The first burst in downlink contains the downlink and uplinkmaps (DL MAP & UL MAP) and downlink and uplink channel

descriptors (DCD & UCD). These are all contained in the firstMAC PDU of this burst. The burst may contain additional MACPDUs.


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WMAN, part 1

UL PHYburst k


DL PHYPDU

Contentionslot A

Contentionslot B

UL PHYburst 1


DL MAP

UL MAP

DCD

UCD

DL MAP

UL MAP

DCD

UCD

The downlink map (DL MAP) indicates thestarting times of the downlink bursts.


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WMAN, part 1

UL PHYburst k


DL PHYPDU

Contentionslot A

Contentionslot B

UL PHYburst 1


DL MAP

UL MAP

DCD

UCD

DL MAP

UL MAP

DCD

UCD

The uplink map (UL MAP) indicates thestarting times of the uplink bursts.


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UL PHYburst k


DL PHYPDU

Contentionslot A

Contentionslot B

UL PHYburst 1


DL MAP

UL MAP

DCD

UCD

DL MAP

UL MAP

DCD

UCD

The uplink channel descriptor (UCD)

describes the uplink burst profile (i.e.,modulation and coding combination)and preamble length for each UL burst.


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WMAN, part 1

Modulation and coding combinations

Modulation

BPSKQPSK

QPSK

16-QAM

16-QAM

64-QAM

64-QAM

Info bits /subcarrier

0.51

1.5

2

3

4

4.5

Info bits /symbol

88184

280

376

568

760

856

Peak datarate (Mbit/s)

1.893.95

6.00

8.06

12.18

16.30

18.36

Codingrate

1/21/2

3/4

1/2

3/4

2/3

3/4

Depends on chosen bandwidth (here 5 MHz is assumed)


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WMAN, part 1

UL PHYburst k


DL PHYPDU

Contentionslot A

Contentionslot B

UL PHYburst 1


Downlink bursts are transmitted in order of decreasing

robustness. For example, with the use of a single FEC typewith fixed parameters, data begins with BPSK modulation,followed by QPSK, 16-QAM, and 64-QAM.

BPSK 64 QAM


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WMAN, part 1

UL PHYburst k


DL PHYPDU

Contentionslot A

Contentionslot B

UL PHYburst 1


A subscriber station (SS) listens to all bursts it is capable of

receiving (this includes bursts with profiles ofequal orgreater robustness than has been negotiated with the basestation at connection setup time).

BPSK 64 QAM

Sorry, Icannotdecode


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WMAN, part 1

UL PHYburst k


DL PHYPDU

Contentionslot A

Contentionslot B

UL PHYburst 1


A subscriber station (SS) does not know which DL burst(s)

contain(s) information sended to it, since the Connection ID(CID) is located in the MAC header, not in the DL PHY PDUheader.


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WMAN, part 1

UL PHYburst k


DL PHYPDU

Contentionslot A

Contentionslot B

UL PHYburst 1


MAC PDU 1 MAC PDU k pad

IEEE 802.16 offers concatenation of severalMAC PDUs within a single transmission burst.


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UL PHYburst k

UL subframe structure (1)

DL PHYPDU

Contentionslot A

Contentionslot B

UL PHYburst 1

The uplink subframe starts with a contention slot that offerssubscriber stations the opportunity for sending initial rangingmessages to the base station (corresponding to RACHoperation in GSM).

A second contention slot offers subscriber stations theopportunity for sending bandwidth request messages to thebase station.


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WMAN, part 1

UL PHYburst k


DL PHYPDU

Contentionslot A

Contentionslot B

UL PHYburst 1

The usage ofbandwidth request messages in this contentionslot (and response messages in downlink bursts) offers amechanism for achieving extremely flexible and dynamicaloperation of IEEE 802.16 systems.

Bandwidth (corresponding to a certain modulation andcoding combination) can be adaptively adjusted for eachburst to/from each subscriber station on a per-frame basis.


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WMAN, part 1

Example: Efficiency vs. robustness trade-off

Large distance => high attenuation => low bit rate

BS64 QAM

16 QAM

QPSK

SS

SS

SS


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WMAN, part 1

UL PHYburst k


DL PHYPDU

Contentionslot A

Contentionslot B

UL PHYburst 1

MAC PDU k pad

IEEE 802.16 offers concatenation of severalMAC PDUs within a single transmission burstalso in uplink.

Preamble MAC PDU 1

Preamble ineach uplinkburst.

UL PHY burst = UL PHY PDU


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WMAN, part 1

MAC PDU structure

MAC Header MAC Payload CRC-32

6 bytes 0 - 2041 bytes 4 bytes

MAC payload containsmanagement messageor user data

For errorcontrol

Two MAC headerformats:

1. Generic MACheader (HT=0)

2. Bandwidthrequest header(HT=1)

No MAC payload, no CRC


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WMAN, part 1

Generic MAC header (1)

Length of MACPDU in bytes

(incl. header)

Connection ID(CID) is in MAC

header!


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WMAN, part 1

Generic MAC header (2)

CRC indicator

Encryption keysequence

Encryptioncontrol

Header checksequence


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WMAN, part 1

Bandwidth request header

Type (3) BR msb (11)The bandwidth

request (BR) field

indicates thenumber of uplinkbytes requested

000 - incremental001 - aggregate

bandwith request


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WMAN, part 1

Significance of Type field

MAC Header MAC PDU CRC-32

This field indicates if (and what kind of)MAC subheader(s) is (are) inserted inthe PDU payload after the MAC header.

MAC subheaders are used for: a) Fragmentationb) Packingc) Grant management

Subheader


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WMAN, part 1

Fragmentation

Fragmentation is the process by which a MAC SDU is dividedinto one or more MAC PDUs. This process allows efficient useof available bandwidth relative to the QoS requirements of aconnections service flow.

H

MAC SDU

Fragmentation subheaders

T H T H T

MAC PDUs


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WMAN, part 1

Fragmentation subheader (1 byte) format

FragmentationSequence Number(modulo 8)

Fragmentation Control

00 no fragmentation

01 last fragment10 first fragment11 middle fragment

Number values my be outdated


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WMAN, part 1

Packing

Packing means that several MAC SDUs are carried in a singleMAC PDU. When packing variable-length MAC SDUs, a packingsubheader is inserted before each MAC SDU.

Header

MAC SDUs

2-byte packing subheaders

CRC

MAC PDU


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WMAN, part 1

Packing subheader (2 byte) format

Length (in bytes) of the MAC SDU or SDU fragment,including the two byte packing subheader

This enablessimultaneousfragmentationand packing

Number values my be outdated


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WMAN, part 1

Difference between concatenation & packing

Packing = within MAC PDU

MAC PDUMAC PDU MAC PDUMAC PDU MAC PDUMAC PDU

MACSDU

MAC

SDUMACSDU

MAC

SDU

PreamblePreamble DL or UL burst (PHY layer)DL or UL burst (PHY layer)

Concatenation = within burst


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WMAN, part 1

Fragmentation & packing

If fragmentation or packing is enabled for a connection, it isalways the transmitting entity (base station in downlink orsubscriber station in uplink) that decides whether or not to

fragment/pack.Fragmentation and packing can be done at the same time(see packing subheader structure). In this way the channelutilisation can be optimised.

wman, part 1 contents

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