Chapter 5: WMAN - IEEE / WiMax. 5.1 Introduction and Overview 5.2 Deployment 5.3 PHY layer 5.4 MAC layer 5.5 Network Entry 5.

Transcription

1 Chapter 5: WMAN - IEEE / WiMax 5.1 Introduction and Overview 5.2 Deployment 5.3 PHY layer 5.4 MAC layer 5.5 Network Entry 5.6 Mobile WiMAX

2 5.1 Introduction and Overview

3 IEEE and WiMAX IEEE Working Group on Broadband Wireless Access, established 1999 Wireless MAN Objective: Standardisation of Wireless Metropolitan Area Network WiMAX: industry consortium 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), GHz 3

4 IEEE evolution (1) Air interface for Fixed Broadband Wireless Access (FBWA) Including several physical layer specifications (system profiles) Single Carrier (SC) GHz Single Carrier below 11 GHz (former a) Orthogonal Frequency Division Multiplex below 11 GHz (OFDM) Orthogonal Frequency Division Multiple Access below 11 GHz (OFDMA) Mesh Networks & Advanced Antenna Systems (AAS)

5 IEEE evolution (2) Air Interface for Fixed and Mobile Broadband Wireless Access System PHY and MAC Layers for Combined Fixed and Mobile Operation in Licensed Bands (former e) Network Management (NetMan): Management Information Base (MIB), Management Plane Procedures and Services Coexistence in license-exempt bands

6 IEEE evolution (3) Further developments IEEE h: Improved coexistence mechanisms in licenseexempt operation (2010) IEEE j: Multihop Relay (2009) PMP compliant, multihop operation for OFDMA PHY IEEE m: 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 n: Reliable Operation (2013) IEEE p: Enhancements to Support Machine-to- Machine Applications (2012)

7 IEEE evolution (4) a e Date Completed December 2001 January 2003 June 2004 December 2005 Spectrum GHz < 11 GHz < 11 GHz < 6 GHz Operation LOS, only SC Non-LOS Non-LOS NLOS and Mobile Bit Rate Mbps Up to 75 Mbps Up to 75 Mbps Cell Radius 2-4 km 5-8 km 5-8 km 2-4 km Up to 15 Mbps Hussain, APRICOT 2006

8 Fundamentally different MAC layer approaches: : distributed control, contention based access : centrally coordinated, frame based Similar OFDM based PHY modes Quality of service (QoS) support Guaranteed multimedia QoS in No QoS in a/b/g Traffic classes in e vs Higher data rates due to reduced MAC overhead Much longer distances due to allocated frequency band and higher transmit power

9 5.2 Deployment

10 WiMax deployment: point-to-point backbone (LOS) 10

11 WiMAX deployment: backhaul links point-to-multipoint, non-line-of-sight, stationary 11

12 WiMAX deployment: user access point-to-multipoint, non line-of-sight, mobile 12

13 5.3 PHY Layer Overview Protocol Stack, Profiles Single Carrier (SC) OFDM OFDMA

14 5.3.1 WiMAX Protocol Stack Handling higher layer protocols Channel access, connection handling, QoS Authentication, secure key exchange, encryption 14

15 Overview about profiles [BER] 15

16 PHY layer: SC TDD (1) 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 (RTG 1, TTG 2 ) necessary between DL and UL Most prominent in license-exempt bands 1 RTG: Receive/Transmit Transition Guard 2 TTG: Transmit/Receive Transition Guard

17 5.3.2 PHY layer: SC TDD (2)

18 PHY layer: SC FDD SS: Subscriber Station

19 PHY layer: SC downlink subframe In case of FDD to support half-duplex stations DIUC: Downlink Interval Usage Code 19

20 PHY layer: SC uplink subframe SS: Subscriber Station; UIUC: Uplink Interval Usage Code 20

21 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 21

22 PHY Layer: OFDM TDD frame (DL) DL UL map map DL burst: FCH: Frame Control Header TTG: Transmit Transition Gap RTG: Receive Transition Gap 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)

23 PHY Layer: OFDM TDD frame (UL) BW: bandwidth FCH: Frame Control Header TTG: Transmit Transition Gap RTG: 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

24 5.3.4 PHY layer: OFDMA profile example 24

25 PHY layer: OFDMA frame structure 25

26 5.4 MAC Layer

27 802.16: 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 27

28 Generic MAC header format bits HT EC Type ESF CI EKS Rsv LEN CID HCS HT header type Rsv reserved EC encryption control LEN length ESF extended subheader field CID connection identifier CI CRC indicator HCS header check sequence EKS Encryption Key Sequence CRC cyclic redundancy check From etutorials.org 28

29 Extended subheader format variable 1+7 variable 1+7 variable bits length Type 1 Body 1 Type 2 Body 2 Type n Body n Length length of extended sublayer group Type subheader type 1+7 MSB reserved, 7 LSBs valid Types for example: feedback request, uplink Tx power report 29

30 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 30

31 5.5 Network Entry

32 Network Entry Process 32

33 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 DCD 1 management messages 2. Obtain transmit parameters Network Entry Process Search for the UCD 2 management messages Extract a set of transmission parameters for a possible UL channel Wait for UL-MAP and look for initial ranging interval BS DL preamble DL-MAP / DLFP DCD UCD UL-MAP SS SS power on PHY synchronization & wait for UCD obtain UL parameters extract slot info For UL & wait for trans. opportunity 1/2 DCD/UCD: Downlink/Uplink Channel Description

34 3. Perform initial ranging Network Entry Process 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 UL-MAP RNG-REQ RNG-RSP UL-MAP RNG-REQ RNG-RSP Cyclically repeated SS transmit in contention mode with CID=0 (recognise MAC ID) store basic CID adjust TX param. (recognise basic CID) reply to initial ranging poll (recognise basic CID) adjust Tx param.

35 5.6 Mobile WiMAX

36 WiMAX vs. Mobile WiMAX Chang 2006 Lin 2006

37 IEEE e PHY (1) IEEE e-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 37

38 IEEE e 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 38

39 IEEE m 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