Chapter 5: WMAN - IEEE 802.16 / WiMax - uni-bremen.de · FB 1 – Communication Networks ... •...

FB 1 – Communication Networks Andreas Könsgen – Summer Term 2013

Chapter 5: WMAN - IEEE 802.16 / WiMax

5.1 Introduction and Overview5.2 Deployment5.3 PHY layer5.4 MAC layer5.5 Network Entry5.6 Mobile WiMAX


5.1 Introduction and Overview


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IEEE 802.16 and WiMAX• IEEE Working Group on Broadband Wireless Access,

established 1999• “Wireless MAN”• Objective: Standardisation of Wireless Metropolitan Area

Network• WiMAX: industry consortium

– 802.16 provides standardised PHY and MAC– Interoperability between devices– Compatibility to higher protocol layers– Network architecture

• First published standard published in 2001– Fixed Mobile Broadband Wireless Access, Single Carrier (SC), 10-66

GHz


802.16-2004• Air interface for Fixed Broadband Wireless Access (FBWA)• Including several physical layer specifications (system profiles)

– Single Carrier (SC) 10-66 GHz– Single Carrier below 11 GHz (former 802.16a) – Orthogonal Frequency Division Multiplex below 11 GHz (OFDM)– Orthogonal Frequency Division Multiple Access below 11 GHz (OFDMA)

• Mesh Networks & Advanced Antenna Systems (AAS)

IEEE 802.16 evolution (1)

www.wirelessman.org

http://www.wirelessman.org/


802.16-2009• Air Interface for Fixed and Mobile Broadband Wireless Access

System• PHY and MAC Layers for Combined Fixed and Mobile

Operation in Licensed Bands (former 802.16e) • Network Management (NetMan): Management Information

Base (MIB), Management Plane Procedures and Services• Coexistence in license-exempt bands



Further developments• IEEE 802.16h: Improved coexistence mechanisms in license-

exempt operation (2010)• IEEE 802.16j: Multihop Relay (2009)

– PMP compliant, multihop operation for OFDMA PHY

• IEEE 802.16m: Advanced Air Interface with data rates of 100 Mbit/s mobile and 1 Gbit/s fixed (2011)– Also known as Mobile WiMAX Release 2 or WirelessMAN-

Advanced

– Aiming at fulfilling the ITU-R IMT-Advanced requirements on 4G systems

• IEEE 802.16n: Reliable Operation (2013)• IEEE 802.16p: Enhancements to Support Machine-to-

Machine Applications (2012)



IEEE 802.16 evolution (4)802.16 802.16a 802.16-

2004802.16e

Date Completed

December 2001

January 2003

June 2004 December 2005

Spectrum 10-66 GHz < 11 GHz < 11 GHz < 6 GHz

Operation LOS, only SC Non-LOS Non-LOS NLOS and Mobile

Bit Rate 32-134 Mbps Up to 75 Mbps

Up to 75 Mbps

Up to 15 Mbps

Cell Radius 2-4 km 5-8 km 5-8 km 2-4 km

Hussain, APRICOT 2006


• Fundamentally different MAC layer approaches:– 802.11: distributed control, contention based access– 802.16: centrally coordinated, frame based

• Similar OFDM based PHY modes• Quality of service (QoS) support

– Guaranteed multimedia QoS in 802.16– No QoS in 802.11a/b/g– Traffic classes in 802.11e

• Higher data rates due to reduced MAC overhead• Much longer distances due to allocated frequency band and higher

transmit power

802.16 vs. 802.11


5.2 Deployment


WiMax deployment: point-to-point backbone (LOS)

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WiMAX deployment: backhaul links

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point-to-multipoint, non-line-of-sight, stationary


WiMAX deployment: user access

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point-to-multipoint, non line-of-sight, mobile


5.3 PHY Layer

5.3.1 Overview Protocol Stack, Profiles5.3.2 Single Carrier (SC)5.3.3 OFDM5.3.4 OFDMA


5.3.1 WiMAX Protocol Stack

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Handling higher layer protocols

Channel access, connection handling, QoS

Authentication, secure key exchange, encryption


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Overview about profiles

[BER]


Time division duplex (TDD)• Downlink (DL) & uplink (UL) time-share the same channel• Dynamic asymmetry, i.e., variable allocation of UL and DL capacity • Stations do not transmit/receive simultaneously

(single RF filter, oscillator and synthesizer)+ Low cost+ Power saving– More complicated MAC scheduler

• Turnaround gaps (RTG1, TTG2) necessary between DL and UL• Most prominent in license-exempt bands

1 RTG: Receive/Transmit Transition Guard

2 TTG: Transmit/Receive Transition Guard

PHY layer: SC TDD (1)


5.3.2 PHY layer: SC TDD (2)


PHY layer: SC FDD

SS: Subscriber Station


PHY layer: SC downlink subframe

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In case of FDD to support half-duplex stations

DIUC: Downlink Interval Usage Code


PHY layer: SC uplink subframe

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SS: Subscriber Station; UIUC: Uplink Interval Usage Code


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5.3.3 PHY layer: OFDM profile

• Scalable OFDM• Channel bandwidth

– Fixed profile: 3.5 MHz, 5 MHz, 7 MHz, 10 MHz– Mobile profile: 5 MHz, 8.75 MHz, 10 MHz

• Up to 2048 subcarriers• Subcarrier modulation: BPSK, QPSK, 16 QAM, 64 QAM• MIMO (Multiple Input Multiple Output)• Max. TX power

– 30 W for base station– 4 W for mobile station


• DL burst: – Transmission of MAC PDUs having the same burst profile

(to simplify PHY modem)– Addressed to a broadcast, multicast or unicast address– Optional short preamble (1 OFDM symbol) preceding DL-burst– Padding up to an integer number of OFDM symbols

(padding bytes: 0xFF or padding PDU with padding CID)

PHY Layer: OFDM TDD frame (DL)

DLmap

ULmap

FCH: Frame Control HeaderTTG: Transmit Transition GapRTG: Receive Transition Gap


• Contention slots for initial ranging (network entry) and bandwidth request purposes

• Uplink (UL) burst:– Reception of MAC PDUs originated by one single sender– Short preamble preceding each UL burst – Optional (short) midambles repeated in periodic intervals – Padding up to an integer number of OFDM symbols

PHY Layer: OFDM TDD frame (UL)

BW: bandwidthFCH: Frame Control HeaderTTG: Transmit Transition GapRTG: Receive Transition Gap


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5.3.4 PHY layer: OFDMA profile example


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PHY layer: OFDMA frame structure


5.4 MAC Layer


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802.16: MAC layer• For data transport, base station controls channel• variable-length time slot in a superframe is assigned by

base station to each mobile station• Encapsulation of different (wired) packet formats on the

air interface: Ethernet, ATM, raw IP• Connection-oriented: station needs to register in order to

get a time slot allocated• Because of time slots, QoS provisioning easy • Connection setup by random access• DES/AES encryption


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Generic MAC header format

HT header type Rsv reservedEC encryption control LEN lengthESF extended subheader field CID connection identifierCI CRC indicator HCS header check sequenceEKS Encryption Key Sequence CRC cyclic redundancy check

HT EC Type CI LENEKS CID HCS

1 1 6 1 1 1 11 16 8 bits

ESF

2

Rsv

From etutorials.org


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Extended subheader format

Length length of extended sublayer groupType subheader type1+7 MSB reserved, 7 LSBs validTypes for example: feedback request, uplink Tx power report

length Body 1 Type 2 Body 2

8 1+7 1+7 variable variable1+7

Type 1

variable

Type n Body n

bits


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QoS classes

• Unsolicited Grant Service (UGS)– Periodic fixed-size packets, e.g. T1 transport

• Extended Real-Time Polling Service (ertPS)– Periodic variable-size packets, e.g. VoIP

• Real-time polling service (rtPS)– Periodic variable-size packets, e.g. MPEG stream

• Non-real-time polling service (nrtPS)– Delay-tolerant streams, minimum throughput, e.g. FTP

• Best Effort (BE)– No QoS requirements, e.g. HTTP


5.5 Network Entry


Network Entry Process

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1. Scan for downlink channel and establish synchronization with the BS

– Scan possible channels of the DL frequency band of operation until it finds a valid downlink signal

– Last operational parameters shall be stored to check them first

– Search for the DL-MAP and DCD1 management messages

2. Obtain transmit parameters– Search for the UCD2 management messages– Extract a set of transmission parameters for

a possible UL channel– Wait for UL-MAP and look for initial ranging

interval

1/2 DCD/UCD: Downlink/Uplink Channel Description

DL-MAP / DLFP

SS power on

PHY synchron-ization& wait for UCD

DCD

UCDobtain UL parameters

extract slot infoFor UL & waitfor trans.opportunity

UL-MAP

DL preamble


BS SS


3. Perform initial ranging

– Send ranging request (RNG-REQ)– Receive ranging response (RNG-RSP)

containing• Basic and primary management CID• RF power level and offset frequency

adjustment • timing offset corrections• Status of ranging

– Repeat cycle until RNG-RSP notifies a successful ranging, i.e. correct timing offset and power adjustments

– Using invited initial ranging intervals – If SS’s max. power level is not sufficient,

ranging can be performed on subchannels (1/16 BW)

– Periodic ranging during operation

BS SS

(recognise MAC ID)store basic CIDadjust TX param.

transmit in contentionmode with CID=0

(recognise basic CID)

UL-MAP

reply to initial ranging poll

RNG-REQ

RNG-RSP

UL-MAP

RNG-REQ

RNG-RSP (recognise basic CID)adjust Tx param.Cyclically

repeated



5.6 Mobile WiMAX


WiMAX vs. Mobile WiMAX

Chang 2006

Lin 2006


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IEEE 802.16e – PHY (1)

• IEEE 802.16e-2005 (Mobile WiMAX) ● Improvement on the modulation schemes

– stipulated in the original (fixed) WiMAX standard

– fixed wireless and mobile NLOS applications primarily by enhancing the OFDMA

– SOFDMA (Scalable OFDMA): selection of 128, 512, 1024, 2048 subcarriers for NLOS applications

● Improving NLOS coverage– advanced antenna diversity schemes

– hybrid-Automatic Retransmission Request (hARQ)● Increasing system gain by use of denser sub-channelization

– thereby improve indoor penetration


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IEEE 802.16e – PHY (2)● Turbo Coding and Low-Density Parity Check (LDPC)

– Enhance NLOS performance● Introducing downlink sub-channelization

– Allowing administrators to trade coverage for capacity or vice versa● Introducing Adaptive Antenna Systems (AAS) and Multiple Input

Multiple Output (MIMO) technology– Improve coverage

● Enhanced Fast Fourier transform (FFT) algorithm can tolerate larger delay spreads– Increasing resistance to multipath interference


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IEEE 802.16m● Part of ITU-R's IMT Advanced recommendation for supporting mobility

applications with high data rates● Multi-user MIMO● Multi-carrier operation (channel bundling up to 100 MHz bandwidth,

contiguous or non-contiguous)● Reduced guard bands between neighbouring channels● Fixed frame length and introduction of superframes for more efficient

implementation● Cooperative communication – stations can act as relays● Self-organising network (SON)● Femto cells● Targeting of new frequency bands● Together with other new extensions integrated into IEEE 802.16-2012

Chapter 5: WMAN - IEEE 802.16 / WiMax - uni-bremen.de · FB 1 – Communication Networks ... •...

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