WiMAX Possible Research Axis in Radio Resource Management

Transcription

1 WiMAX Possible Research Axis in Radio Resource Management Loutfi Nuaymi TELECOM Bretagne, Rennes (ex: ENST Bretagne) Lisbon, Feb 19, 2008

2 Presentation Plan WiMAX Framework Possible research in radio resource management Conclusions and Future works Discussion L. Nuaymi (c), Telecom Bretagne, NSM (RSM) Dept - v

3 1- The context: WiMAX technology, based on IEEE standard ([ ] and [802.16e]), has a very rich set of features. A technical introduction to WiMAX is proposed in [ ] IEEE , IEEE Standard for local and metropolitan area networks, Air Interface for Fixed Broadband Wireless Access Systems, Oct [802.16e] IEEE e, IEEE Standard for local and metropolitan area networks, Air Interface for Fixed Broadband Wireless Access Systems, Amendment 2: Physical and Medium Access Control Layers for Combined Fixed and Mobile Operation in Licensed Bands and Corrigendum 1, Feb 2006 (Approved: 7 dec 2005). L. Nuaymi (c), Telecom Bretagne, NSM (RSM) Dept - v

4 1- The context: WiMAX is: - OFDM Transmission; - Sophisticated MAC Layer: efficient use of the frequency AND QoS Management; The (expected?) result is: - High Data rates (order: 1, 5, 10, 20, Mb/s). - Different types of transmission services: voice, video, games, real-time, Best Effort, L. Nuaymi (c), Telecom Bretagne, NSM (RSM) Dept - v

5 Initially wireless DSL, 1- The context: and mobility was added WiMAX expected evolution is to be a complement or a competitor for cellular systems (such as UMTS and LTE) mobility (only up to 120 km/h?) Other possible use of WiMAX: telemetering Reporting of electricity, gas, water and other measurements L. Nuaymi (c), Telecom Bretagne, NSM (RSM) Dept - v

6 1- The context: Pre-WiMAX products: many companies had wireless broadband equipment using proprietary technology since the nineties and even before. Evidently these products were not interoperable. 2001: The first version of IEEE standard. 2004: IEEE : revises and consolidates previous Standards Fixed WiMAX dec 2005: approval of IEEE e amendment which (mainly) adds mobility Mobile WiMAX Other standards : f (MIB, SNMP), g (QoS management, radio resource management procedures, MIH), h (License-Exempt Operation), j (Mesh networks) and mainly: m : Higher data rates (> 100 Mb/s) for mobiles users (approval expected by 2009). Other (possible) names : WiMAX2, WiMagic,? L. Nuaymi (c), Telecom Bretagne, NSM (RSM) Dept - v

7 1- The context: Korean flavor of WiMAX: WiBro WiBro (Wireless Broadband): BWA System proposed in Korea by Samsung, KT (Korea Telecom) and other leading players. Standard approved in june 2004, by TTA (Telecommunications Technology Association) under the name TTA PG302. Agreement in the second half of 2004 to integrate WiBro in Mobile WiMAX (802.16e) 3 WiBro licences assigned in Korea in january Commercial offers (Mobile WiMAX) since june L. Nuaymi (c), Telecom Bretagne, NSM (RSM) Dept - v

8 1- The context: Evolution of BWA subscribers number Source: Accumulated WiMAX and proprietary subscribers, from: "WiMAX and Broadband Wireless (Sub- 11GHz) Worldwide Market Analysis and Trends ", Maravedis Report, Sept 2006 L. Nuaymi (c), Telecom Bretagne, NSM (RSM) Dept - v

9 1- The context: United States: The US operator Sprint-Nextel announced (august 2006) a wide scale deployment of Mobile WiMAX. First commercial services expected before end Update Joint network between Sprint and Clearwire announced in July 07. Abandoned since! Delays expected: 2009? many other expected Mobile WiMAX deployments L. Nuaymi (c), Telecom Bretagne, NSM (RSM) Dept - v

10 1- The context: WiMAX: a «swiss knife» technology! Oct 2007: Mobile WiMAX has been selected as a new IMT-2000 (3G) radio interface. Name: IMT-2000 OFDMA TDD WMAN Until then, only five IMT-2000 interfaces were defined. L. Nuaymi (c), Telecom Bretagne, NSM (RSM) Dept - v

11 2- WiMAX Standard basics: Two topologies (modes) can be used: PMP and Mesh PMP (Infrastrucure) Point-to-MultiPoint PDA PMP topology: the BS covers its SSs. All transmissions end or start at the BS Other WiMAX SS wireless terminal L. Nuaymi (c), Telecom Bretagne, NSM (RSM) Dept - v

12 2- WiMAX Standard basics: SS 1 SS 3 SS 2 Base station (BS) (Mesh) optional mode Traffic can be routed through other SSs until the BS. Also can take place only between SSs. L. Nuaymi (c), Telecom Bretagne, NSM (RSM) Dept - v

13 2- WiMAX Standard basics: Service-Specific Convergence Sublayer (CS) MAC Common Part Sublayer (CPS) WiMAX (common) MAC Layer Security Sublayer OFDM PHY Layer [Section 8.3 of the standard] OFDMA PHY Layer [Section 8.4 of the standard] Possible PHYsical layers of WiMAX L. Nuaymi (c), Telecom Bretagne, NSM (RSM) Dept - v

14 2- WiMAX Standard basics: Convergence Sublayer (CS) The Service-Specific Convergence Sublayer (CS) is in charge of mapping of data coming from an external network: IPv4, IPv6, Ethernet, ATM,... Received at the CS service access point (SAP) CS sublayer tasks include: - classification of SDUs; - association of each SDUs to the appropriate MAC SFID (service flow identifier) and CID (connection identifier); - (optional) PHS, Payload Header Suppression: suppression of repetitive header parts. External Network. Example: IP ou ATM CS SAP Service-Specific Convergence Sublayer (CS) MAC SAP MAC Common Part Sublayer (CPS) MSDU L. Nuaymi (c), Telecom Bretagne, NSM (RSM) Dept - v

15 Upper Layer Entity (e.g., bridge, router, host) 2- WiMAX Standard basics: Convergence Sublayer (CS) Upper Layer Entity (e.g., bridge, router, host) SDU SDU SAP SAP CID #1 CID #2 Reconstitution (e.g., undo PHS) Classifier CID #... {SDU, CID } CID #n {SDU, CID } SAP MAC CPS SAP MAC CPS (Packet) CS Classification MAC SDU are mapped on convenient CIDs before transmission between corresponding MAC entities. Figure: downlink Figure source: standard L. Nuaymi (c), Telecom Bretagne, NSM (RSM) Dept - v

16 2- WiMAX Standard basics: QoS Parameters Each connection is associated with a single data service. Each data service is associated with a set of QoS parameters* that quantify aspects of its behavior. WiMAX QoS parameters include: Traffic priority, QoS Class (Scheduling Service Type), minimum rate, maximim latency, etc. The QoS parameters are managed using the DSA (Dynamic Service Addition) and DSC (Dynamic Service Change) message dialogs. MAC Management Messages: DSA-REQ, DSA-RSP, * Detail of QoS parameters : Section of the standard. L. Nuaymi (c), Telecom Bretagne, NSM (RSM) Dept - v

17 2- WiMAX Standard basics: ARQ All flavors of ARQ included. Figure: Cumulative ARQ process (use of a sliding window) Transmitter Frame #1 Frame #2... Frame #k Cumulative ACK Acknowledgment for the previous block frames Frame #k+1... Frame #k+k Cumulative NACK No Acknowledgment for the previous block frames Frame #k+1 Sliding Window = K Receiver... Frame #k+k Cumulative ACK Acknowledgment for the previous block frames L. Nuaymi (c), Telecom Bretagne, NSM (RSM) Dept - v

18 2- WiMAX Standard basics: HARQ HARQ (Hybrid ARQ): can be used only with OFDMA PHYsical Layer The main difference between ARQ and HARQ is that in HARQ, subsequent retransmissions are combined with the previous erroneously-received transmissions in order to improve reliability. The two main variants of HARQ are supported: - Chase Combining, for all coding schemes; - Incremental Redundancy (IR), for CTC and CC. Each subpacket is uniquely identified by a SubPacket IDentifier (SPID). L. Nuaymi (c), Telecom Bretagne, NSM (RSM) Dept - v

19 2- WiMAX Standard basics: (OFDMA) Channel Quality Information CHannel For OFDMA PHY, the SS may send CINR (Carrier-to-Interferenceand-Noise Ratio) reports using one of these methods: - REP-RSP MAC Management message (Type = 37); - the fast-feedback channel (CQICH), see OFDMA f rame. - MAC Header (MAC header format without payload), see below. L. Nuaymi (c), Telecom Bretagne, NSM (RSM) Dept - v

20 2- WiMAX Standard basics: AAS, beamforming and smart antenna Smart antennas guarantee better performances: capacity (throughput) and range. co-channel user Figure Source : Schwarz, John, WiMAX Summit 06 passive mitigation user active mitigation coherent gain omni/sector reference L. Nuaymi (c), Telecom Bretagne, NSM (RSM) Dept - v

21 2- WiMAX Standard basics: MIMO MIMO: Multiple Input, Multiple Output The MIMO technique expected to be used in WiMAX is STC, Space-Time Coding. STC: redundant transmission of data, in time and space (antennes). Use of Alamouti Algorithm. The basic version, without MIMO, is sometimes known as SISO Figure: J. Andrews, Univ. of Texas at Austin L. Nuaymi (c), Telecom Bretagne, NSM (RSM) Dept - v

22 MIMO-STC performance 2- WiMAX Standard basics: MIMO - Link adaptation included - This type of figures is strongly dependent on the simulation environment (channel model, etc.) Figure: J. Andrews, Univ. of Texas at Austin L. Nuaymi (c), Telecom Bretagne, NSM (RSM) Dept - v

23 2- WiMAX Standard basics: MIMO SM, Spatial Multiplexing During a symbol interval, different information is sent in parallel on different antennas greater capacity. No diversity. Yet intelligent flow allocations allow better performances (see spacetime precoding theory); SM not included in present versions of WIMAX Figure: J. Andrews, Univ. of Texas at Austin L. Nuaymi (c), Telecom Bretagne, NSM (RSM) Dept - v

24 2- WiMAX Standard basics: Architecture IEEE standard defines only the PHY and MAC layers of a BWA System. The architecture of WiMAX System is defined by the WiMAX Forum, specifically by the NWG (Network Group) of the WiMAX Forum. R2 Visited NSP Home NSP Network Reference Model R2 SS/ MS R1 R3 ASN CSN CSN R5 Source: (Draft du NWG) WiMAX Forum, «WiMAX End-to-End Network Systems Architecture, (Stage 2: Architecture Tenets, Reference Model and Reference Points)», Draft, March 2006 R4 Another ASN ASP Network OR Internet ASP Network OR Internet NAP L. Nuaymi (c), Telecom Bretagne, NSM (RSM) Dept - v

25 2- WiMAX Standard basics: Handover In e, the 2 types of handover are defined: - hard handover: break-before-make; - soft handover (make-before-break): 2 types of soft handover are defined: - MDHO (Macro Diversity HandOver): transmissions are between the MS and more than one BS; - FBSS (Fast BS Switching) : a state where the MS may rapidly switch from one BS to another. Only the Hard Handover is mandatory L. Nuaymi (c), Telecom Bretagne, NSM (RSM) Dept - v

26 2- WiMAX Standard basics: Power-Save Modes Active Mode : the normal mode that exists in IEEE e defines two new modes: Sleep Mode and Idle Mode in order to have: - power-efficient MS operation, - a more efficient handover. L. Nuaymi (c), Telecom Bretagne, NSM (RSM) Dept - v

27 2- WiMAX Standard basics: Ranging The ranging process is defined in standard as the process which allows the SSs to: - acquire the correct timing offset of the network. - request power adjustments and/or downlink burst profile change. The SS can then be received within the appropriate reception thresholds. Two types of Ranging processes: - initial ranging: a loop between the SS and the BS until power and timing are ok ; - periodical ranging (see Power Control). power and timing is ok L. Nuaymi (c), Telecom Bretagne, NSM (RSM) Dept - v

28 2- WiMAX Standard basics: Mobile WiMAX (System) Profiles Release 1 of 16e profiles is divided in two waves: Wave 1: minimal set. Subset of Release 1: - TDD, 5 ms frame, CP=1/8, - Channel Coding modes (CC, CTC, H-ARQ-CC) - Mobility - Power Save modes (Sleep, Idle) - SISO GHz Wave 2: MIMO, AAS, MBS (Broadcast Service) (expected) Release 2: bandwidthes of 15 and 20 MHz. More ambitious services. L. Nuaymi (c), Telecom Bretagne, NSM (RSM) Dept - v

29 2- WiMAX Standard basics: Mobile WiMAX (System) Profiles!! Delays!! Update!! Source: WiMAX forum, white paper, Jan 07 L. Nuaymi (c), Telecom Bretagne, NSM (RSM) Dept - v

30 2- WiMAX Standard basics: The frequencies: Two types of frequency bands are defined: (< 11 GHz) : - Licensed bands; - License-Exempt bands. License-exempt bands have some drawbacks: more interference and more important power limits and an advantage: they are free! The license-exempt bands should have the same type of use as WiFi (limited coverage, associations, etc.). Operator revenues should be mainly from licensed-frequencies use, where the service can be guaranteed. Agnostic licences? For licensed bands, the initial trend was : 3.5 GHz in Europe and 2.5 GHz in the US L. Nuaymi (c), Telecom Bretagne, NSM (RSM) Dept - v

31 Example : Cluster Size: 1 ou 3 Tri-sectorisation 2- WiMAX Standard basics: Frequency reuse Fig Source : Dean Chung, Aperto Networks, WIMAX Summit, Feb 06 L. Nuaymi (c), Telecom Bretagne, NSM (RSM) Dept - v

32 3- Multiple Access and Scheduling Scheduling and link adaptation Objectives of scheduling and link adaptation: The purpose of scheduling is to allow every user, if possible, to have the (minimum?) QoS required for his application. This includes: - scheduling of uplink communications, between the SSs; - scheduling of individual packets for each SS and BS. For both uplink and downlink, the modulation and coding scheme can change for each burst flexible scheduling The link adaptation allows a fair performing for the different applications and a good optimization of using the radio resources (= frequency bandwidth), realizing the QoS required for the transmission of the data stream. L. Nuaymi (c), Telecom Bretagne, NSM (RSM) Dept - v

33 The MSDUs (MAC SDU) are: - received by the MAC CPS; - placed in MPDU(s); 3- Multiple Access and Scheduling Transmission of MAC PDU (MPDU) IEEE Standard scope External Network. Example: IP or ATM CS SAP Service-Specific Convergence Sublayer (CS) MAC SAP MAC Common Part Sublayer (CPS) Security Sublayer MSDU MAC layer OSI Layer 2: data link layer - transmitted on the radio interface. PHY SAP PHYsical Layer MPDU(s) OSI Layer 1: PHYsical layer L. Nuaymi (c), Telecom Bretagne, NSM (RSM) Dept - v

34 3- Multiple Access and Scheduling General principles Duplexing: FDD (and H-FDD, Half-duplex FDD) and TDD are in the standard Simultaneous access (both uplink and downlink) is: very flexible TDMA Resource allocation is centralised. Contention-based Grant- Request can be used. WiMAX is also a DAMA (Demand-Assigned Multiple Access). 5 classes of service (of QoS) are defined. L. Nuaymi (c), Telecom Bretagne, NSM (RSM) Dept - v

35 3- Multiple Access and Scheduling TDD and Frame durations Figure from the standard ( ) Possible frame durations (TDD or FDD): (OFDM PHY) 2.5; 4; 5; 8; 10; 12.5 and 20 ms in addition for OFDMA: 2 ms For FDD, the frame duration is the same in uplink and downlink. L. Nuaymi (c), Telecom Bretagne, NSM (RSM) Dept - v

36 3- Multiple Access and Scheduling The BS decides for resource allocation Source Fig:Nair et al., Intel Journal Aug 2004 L. Nuaymi (c), Telecom Bretagne, NSM (RSM) Dept - v

37 3- Multiple Access and Scheduling The frame structure is transmitted by the BS to the SSs for both ways: - downlink: through DL-MAP MAC Management message; for the current frame; - uplink: through UL-MAP MAC Management message ; for the current frame or the following one (cf figure). Fig. from the standard Frame n-1 Frame n Frame n+1 Frame n+2 Frame control DL-MAP n-1 UL-MAP n DL-MAP n UL-MAP n+1 DL-MAP n+1 DL-MAP n+2 UL-MAP n+2 UL-MAP n+3 Downlink subframe Uplink subframe L. Nuaymi (c), Telecom Bretagne, NSM (RSM) Dept - v

38 3- Multiple Access and Scheduling Downlink The scheduler determines the appropriate burst profile for the communication with each SS. Burst profile: modulation and coding scheme and OFDM parameters (see below) The scheduler determines the bandwidth requirements of each SS based on: - connexions service class; - the observation of queues and required traffic. L. Nuaymi (c), Telecom Bretagne, NSM (RSM) Dept - v

39 3- Multiple Access and Scheduling Uplink bandwidth reservation Uplink access and bandwidth allocation are realized using one of the following methods: - unsolicited bandwidth grants; - piggyback bandwidth request; - unicast polling, sometimes simply referred to as polling; - contention-based procedures, including broadcast or multicast polling; contention-based bandwidth request procedures have variants depending of the PHYsical layer used: OFDM (Focused Contention) or OFDMA (CDMA-Request). L. Nuaymi (c), Telecom Bretagne, NSM (RSM) Dept - v

40 3- Multiple Access and Scheduling Uplink: Contention-based group polling The three SSs shown are group (multicast or broadcast) polled. They all have bandwidth request. SS #1 SS #2 Request for Bandwidth from SS #2 BS allocate Bandwidth for the SS that wins the contention e.g. SS #2 Request for Bandwidth from SS #1 BS SS #3 Request for Bandwidth from SS #3 L. Nuaymi (c), Telecom Bretagne, NSM (RSM) Dept - v

41 3- Multiple Access and Scheduling Downlink frame structure (same for TDD and FDD) (OFDM PHY) Downlink multiple access DL frame (or subframe) duration DL PHY PDU (DL Subframe) One or more bursts is (are) transmitted in a DL PHY PDU. Each burst has its modulation and coding scheme. The bursts are sorted in decreasing robustness order. TDM Preamble FCH DL burst #1 DL burst #2 DL burst #m Figure From the standard DLFP Broadcast Messages Regular MAC PDUs Padding Regular MAC PDUs Padding Length(es) and profile(s) of the first burst(s) (Possibly)DL- MAP, UL-MAP, DCD, UCD,... MAC Header MAC Payload CRC (Optional) L. Nuaymi (c), Telecom Bretagne, NSM (RSM) Dept - v

42 3- Multiple Access and Scheduling Uplink frame structure UL subframe duration Contention Slot for Initial Ranging Contention Slot for BandWidth (BW) Requests UL PHY PDU coming from SS#i UL PHY PDU coming from SS#j Uplink : TDMA multiple access Each uplink PHY PDU has its burst profile. It is then transmitted with a modulation and coding scheme specific to a given SS at a given instant Preamble UL burst Figure from the standard MAC Msg 1 (MAC PDU 1) MAC Msg n (MAC PDU n) Padding MAC Header (6 Bytes) MAC Payload (Optionnel) CRC (Optionnel) L. Nuaymi (c), Telecom Bretagne, NSM (RSM) Dept - v

43 3- Multiple Access and Scheduling Fig. from the standard Full structure of a TDD MAC frame (OFDM PHY) L. Nuaymi (c), Telecom Bretagne, NSM (RSM) Dept - v

44 3- Multiple Access and Scheduling Full structure of a TDD MAC frame (OFDMA PHY) Fig. from the standard L. Nuaymi (c), Telecom Bretagne, NSM (RSM) Dept - v

45 3- Multiple Access and Scheduling Scheduling The scheduling algorithm is not given by the standard. Only the scheduling framework is defined. The MAC layer differentiates the QoS depending on the application type. Main QoS parameter QoS handling mechanism: the QoS class. Also called (in the stadard): Scheduling service or Service flow scheduling type L. Nuaymi (c), Telecom Bretagne, NSM (RSM) Dept - v

46 3- Multiple Access and Scheduling Four QoS defined in Four Classes of QoS (Scheduling Services) were defined in : UGS rtps nrtps BE Unsolicited Grant Services. Designed to support real-time data streams. Fixed-size data packets are issued at periodic Intervals Real-Time Polling Services. designed to support real-time data streams consisting of variable-sized data packets that are issued at periodic intervals. Non-Real-Time Polling Services. In the nrtps Scheduling Service, the BS provides unicast uplink request polls on a regular basis, which guarantees that the service flow receives request opportunities even during network congestion. Best Effort. No minimum service guarantees are required. L. Nuaymi (c), Telecom Bretagne, NSM (RSM) Dept - v

47 3- Multiple Access and Scheduling 16e update: a fifth QoS class e added a fifth scheduling service: ertps, Extended real-time Polling Service. ertps is suitable for variable rate real-time applications that have data rate and delay requirements. Builds on the efficiency of both UGS and rtps. Example: Voice over IP with silence suppression. L. Nuaymi (c), Telecom Bretagne, NSM (RSM) Dept - v

48 3- Multiple Access and Scheduling rtps Scheduling Service uplink grants allocation and request mechanism The rtps is designed to support real-time data streams consisting of variable-sized data packets that are issued at periodic intervals. Ex: MPEG (moving pictures experts group) video transmission. In this service, the BS provides periodic unicast (uplink) request opportunities, which meet the flow s real-time needs and allow the SS to specify the size of the desired grant. Transmitted packets Periodic uplink request opportunities Variable packet size Time Constant (Periodic) Time Intervals L. Nuaymi (c), Telecom Bretagne, NSM (RSM) Dept - v

49 4- The physical layer OFDM PHY Transmission Chain The Transmission chain of OFDMA is very close PHYsical PDU to be transmitted Randomization FEC encoder (CC, Turbo Code or other) Interleaving Modulation To OFDM Part: IFFT, CP, etc Randomization introduces protection through information-theoretic uncertainty, avoiding long sequences of consecutive ones or consecutive zeros. Interleaving is used to protect the transmission against long sequences of consecutive errors, which are very difficult to correct. Channel Coding, Modulation and Cyclic Prefix L. Nuaymi (c), Telecom Bretagne, NSM (RSM) Dept - v

50 4- The physical layer Channel Coding For WiMAX FEC, the following coding rate are defined : 1/2, 2/3, 3/4 et 5/6. Puncturing patterns defined in the standard can be used to realize the following different code rates: 2/3, 3/4 and 5/6. L. Nuaymi (c), Telecom Bretagne, NSM (RSM) Dept - v

51 4- The physical layer The digital modulation used Four modulations are supported by the IEEE standard: BPSK (mainly for signalling messages) QPSK 16-QAM : 16 states (= 4bits/symbole) 64-QAM (= 6 bits/symbol). Optional in some cases. Many modulations Link Adaptation The link adaptation algorithm is not defined in the standard Figure source: WirelessMAN.org L. Nuaymi (c), Telecom Bretagne, NSM (RSM) Dept - v

52 4- The physical layer Adaptive PHY BS DL Data at DIUC n SS Each burst profile has two defined thresholds: - mandatory exit threshold - minimum entry threshold Send DL data at DIUC k RNG_REQ or DBPC_REQ Change to DIUC k DL Data at DIUC k C/(N+I) too low for DIUC n Yes Continue monitoring DL data through DIUC n NO These thresholds are indicated in the DCD and UCD messages RNG_RSP or DBPC_RSP Monitor DL only data through DIUC k Figure source : DL Data at DIUC k L. Nuaymi (c), Telecom Bretagne, NSM (RSM) Dept - v

53 4- The physical layer OFDM transmission technique : OFDM is a very powerful transmission technique. It is based on the principle of transmitting simultaneously many narrow-band orthogonal frequencies, often also called OFDM subcarriers or also subcarriers. source: WiMAX forum, white paper L. Nuaymi (c), Telecom Bretagne, NSM (RSM) Dept - v

54 4- The physical layer Modulation and coding schemes of WiMAX What is there in an OFDM Symbol? Four digital modulations and many channel coding possibilities (2 coding rates) are provided in WiMAX which gives way for many Modulation and Coding Schemes (MCS), shown in this table: Modulation BPSK QPSK QPSK 16-QAM 16-QAM 64-QAM 64-QAM Coding rate 1/2 1/2 3/4 1/2 3/4 2/3 3/4 Receiver SNR (db) Number of Useful Bits per OFDM Symbol 192 x 1 x 1/ x 2 x 1/ x 2 x 3/ x 4 x 1/ x 4 x 3/ x 6 x 2/ x 6 x 3/4 864 Table (Columns 1, 2 and 3) from [802.16]. L. Nuaymi (c), Telecom Bretagne, NSM (RSM) Dept - v

55 4- The physical layer Data rates PHY data rate in for different MCS (Modulation and coding scheme) Channel bandwidth: 7 MHz; OFDM PHY Interface Sampling factor n=8/7; G Ratio BPSK 1/2 QPSK 1/2 QPSK 3/4 16-QAM 1/2 16-QAM 3/4 64-QAM 2/3 64-QAM 3/4 1/ / / / L. Nuaymi (c), Telecom Bretagne, NSM (RSM) Dept - v

56 4- The physical layer Scalable OFDMA, SOFDMA Scalable OFDMA (SOFDMA): the scalability is due to the possibility of changing the FFT size and then the number of subcarriers. Supported FFT sizes (IFFT orders) are : 128, 512, 1024 and 2048 Note: Only 1024 and 512 are (presently) mandatory for Mobile WiMAX Profiles. L. Nuaymi (c), Telecom Bretagne, NSM (RSM) Dept - v

57 4- The physical layer Different types of subcarriers (or tones) All the subcarriers of an OFDM symbol do not carry useful data. There are four subcarrier types: -Data subcarriers: useful data transmission; -Pilot subcarriers: mainly for channel estimation and synchronisation; For OFDM PHY, there are 8 pilot subcarriers. -Null subcarriers : no transmission; these are frequency guard bands. -Another Null subcarrier is the DC (Direct Current) subcarrier. Fig Source : [WiMAX Forum White Paper, 2006] L. Nuaymi (c), Telecom Bretagne, NSM (RSM) Dept - v

58 4- The physical layer Subcarrier permutations For both uplink and downlink, the pilot subcarriers and data subcarriers are allocated according to one or another of the defined OFDMA permutation modes. A slot in the OFDMA PHY has both a time and subchannel dimension. A slot is the minimum possible data allocation unit in standard. Fig Source: L. Nuaymi (c), Telecom Bretagne, NSM (RSM) Dept - v

59 4- The physical layer Subcarrier permutations Two families of distribution modes can be distinguished : Diversity (or distributed) permutations: the subcarriers are distributed pseudo-randomly. This family includes: - FUSC (downlink only) - PUSC Main advantages (of distributed permutations): frequency diversity and intercell interference averaging Contiguous (or adjacent) permutations: considers a group of adjacent subcarriers. This family includes : - AMC (also called Band AMC) Choice of the best-conditions part of the bandwidth. Channel estimation is easier as the subcarriers are adjacent. L. Nuaymi (c), Telecom Bretagne, NSM (RSM) Dept - v

60 Possible research in radio resource management: (Global questions) Performance evaluation: simulation, queuing theory, experiments Proposals in the standard framework: scheduling algorithms, admission control, size of contention windows, header suppression mechanisms and much others are needed. Also needed: algorithms related to algorithms of WiMAX: pricing, vertical handover, network consideration, Beat the standard! Propose a polling scheme, subchannel allocation, ranging that do better than the ones proposed in the standard but first: define your WiMAX system model = may be some restrictions will have to be considered L. Nuaymi (c), Telecom Bretagne, NSM (RSM) Dept - v

61 5- Link adaptation, power control Power control algorithm is mandatory for the uplink channel. Power control must include: - initial calibration (or ranging) initial transmitted power choice; - periodic adjustment procedure Backup: ( ) FPC: the BS may adjust the power levels of multiple subscribers simultaneously with the Fast Power Control (FPC) MAC Management message. The decision of the change of the power control mode (open loop or closed loop) is done at BS. The decision is indicated by the PMC_RSP MAC message. PMC_REQ can be used to request to change the power control mode. L. Nuaymi (c), Telecom Bretagne, NSM (RSM) Dept - v

62 5- Link adaptation, power control Possible question: power control or rate control? (example) Economic consideration: increase power? You have to pay more! L. Nuaymi (c), Telecom Bretagne, NSM (RSM) Dept - v

63 Link adaptation is the possibility to change modulation and coding scheme according to the radio link quality in order to have a high global efficiency. This procedure is not limited to WiMAX. For example, it is included in GSM/EDGE, WiFi, Throughput of a 3.5 MHz WiMAX Channel 5- Link adaptation, power control Link adaptation Figure form Ball, VTC2005Spring L. Nuaymi (c), Telecom Bretagne, NSM (RSM) Dept - v

64 5a- DFS: Dynamic Frequency Selection DFS: Dynamic Frequency Selection. Mandatory Procedure in ETSI zone when unlicensed frequencies are used. The IEEE standard requires DFS to facilitate the detection and avoidance of interference and the prevention of harmful interference into other users, including specific spectrum users identified by regulations* as priority users. Other advantage: interference decrease. * Recommendation ITU-R M.1652, Dynamic frequency selection (DFS) in wireless access systems including radio local area networks for the purpose of protecting the radio determination service in the 5 GHz band, L. Nuaymi (c), Telecom Bretagne, NSM (RSM) Dept - v

65 6- Bit loading, subchannel allocation OFDMA subchannels allocation and MCS (Modulation and Coding Scheme) Choice is another interesting optimization problem. Example of research result: (From: Lengoumbi et al., Subchannelization Performance for the Downlink of a Multi-Cell OFDMA System, WiMob 2007) bda: Basic Dynamic Assignment RPO: Rate Profit Optimization Alg ASS: Adjacent subcarriers subchannelization L. Nuaymi (c), Telecom Bretagne, NSM (RSM) Dept - v

66 7- Network deployment Now-well (relatively) known design principles inherited from GSM/EDGE/UMTS have to be redefined for WiMAX: - OFDM or OFDMA - Higher frequencies - Specific WiMAX MAC considerations - Service-oriented? in order to compute: BS positions, reuse factors and many other radio parameters The goal is still: push always higher the b/s/hz number L. Nuaymi (c), Telecom Bretagne, NSM (RSM) Dept - v

67 Results Example: 7- Network deployment (From: K. Ntagkounakis, Cost-efficient WiMAX network deployment: the hybrid outdoor/indoor dual-layer coverage approach,, PIMRC 2007 ) L. Nuaymi (c), Telecom Bretagne, NSM (RSM) Dept - v

68 8- Multihop and mesh Mesh for WiMAX is still rather unclear: j amendment should eliminate some of the confusion. The first draft, D1, dates from Aug Proposals must be (are) done for multi-hop routing and (WiMAX mesh specific-) scheduling Energy and cost considerations (see ad hoc networks research) L. Nuaymi (c), Telecom Bretagne, NSM (RSM) Dept - v

69 9- Admission Control Only the admission control framework and tools are defined in the standard. Admission control decision algorithms are left to the manufacturers. Admission Control could be studied along with the pricing strategy (see below) Also: scheduling considerations must be taken account at least for capacity expected values. L. Nuaymi (c), Telecom Bretagne, NSM (RSM) Dept - v

70 10- Scheduling (OFDM PHY) Number of useful bits / OFDM symbol for each MCS (OFDMA PHY) Number of useful bits / OFDMA subchannel for each MCS Bandwidth requests Network occupation or congestion QoS classes Scheduling algorithm? L. Nuaymi (c), Telecom Bretagne, NSM (RSM) Dept - v

71 10- Scheduling Scheduling algorithms: well-known algorithms used for WiMAX (example) Deficit Round Robin (DRR): Increment the deficit counter (Di) by the fixed quantum (Qi) D1= a3 280 a2 750 a1 200 Q1=350 Compare between Qi and the length of the packet (Li) If Di > Li send pkt + decrement Di by Li D2= 300 b3 280 b2 300 b1 500 Q2=300 c1 100 a1 200 D3= Q3=250 c3 c2 c L. Nuaymi (c), Telecom Bretagne, NSM (RSM) Dept - v

72 10- Scheduling Other Scheduling algorithms proposed for WiMAX [4] Q. Liu, X. Wang, G. B. Giannakis, A Cross-Layer Scheduling Algorithm With QoS Support in Wireless Networks [5] T. Tsai, C. Jiang, C. Wang, CAC and Packet scheduling Using Token Bucket for IEEE Networks [6] K. Vinay, N. Sreenivasulu, D. Jayaram, D. Das, PerformanceEvaluation of End-to-end Delay by Hybrid Scheduling Algorithm for QoS in IEEE Network [7] S. A. Xergias, N. Passas, L. Marekos, Flexible Resource Allocation inieee Wireless Metropolitan Area Networks. L. Nuaymi (c), Telecom Bretagne, NSM (RSM) Dept - v

73 11- Header suppression PHS, Payload Header Suppression If PHS is enabled at MAC connection, each MAC SDU is prefixed with a PHSI (Payload Header Suppression Index), which references the PHSF (Payload Header Suppression Field). Payload header Useful portion PHSF Payload PHSI Useful portion Payload The classifier (located at the sending entity) uniquely maps packets to its associated PHS Rule. The receiving entity uses the CID and the PHSI to restore the PHSF. L. Nuaymi (c), Telecom Bretagne, NSM (RSM) Dept - v

74 11- Header suppression e amendment added these two Header Compression algorithms: - ROHC, RObust Header Compression, RFC 3095; Note: ROHC is mandatory in WiMAX Mobile profiles. - ECRTP, Enhanced Compressed RTP, RFC 3545 L. Nuaymi (c), Telecom Bretagne, NSM (RSM) Dept - v

75 11- Header suppression (research example) Our WiMAX hypothesis:* OFDM PHY Layer; PMP topology; no MPDU packing or fragmentation; frame duration values considered: 5 ms and 10 ms; bandwidth: 3.5 MHz and 7 MHz. * Nuaymi et al., Headers Overhead Estimation, Header Suppression and Header Compression in WiMAX, WiMOB 07 L. Nuaymi (c), Telecom Bretagne, NSM (RSM) Dept - v

76 11- Header suppression Computation of MAC and PHY overhead Using the two previous relations, we can compute the downlink MAC and PHY headers overhead. Downlink figures for some frame durations defined in the IEEE standard. The same type fo computation is done for uplink taking into account the initial ranging contention slot and BW request contention slots L. Nuaymi (c), Telecom Bretagne, NSM (RSM) Dept - v

77 11- Header suppression Header Suppression for VoIP over WiMAX We now consider the specific case of the transmission of Voice over IP (VoIP) over WiMAX. The protocols used in addition to WiMAX are RTP, UDP and IPv6 Application Layer Voice Payload L. Nuaymi (c), Telecom Bretagne, NSM (RSM) Dept - v

78 11- Header suppression Header Suppression for VoIP over WiMAX Header sizes of each of these layers: between 12 and 72 bytes for RTP; 8 bytes for UDP; 40 bytes for IP (IPv6 is used). the total length of RTP/UDP/IPv6 header is between 60 and 120 bytes. PHS suppresses repetitive (redundant) parts due to the higher layers in the payload header of the MAC SDU. The receiving entity restores the suppressed parts. It is the responsibility of the higher-layer service entity to generate a PHS Rule that uniquely identifies the (repetitive) suppressed header within the service flow. L. Nuaymi (c), Telecom Bretagne, NSM (RSM) Dept - v

79 11- Header suppression Header Suppression for VoIP over WiMAX A Payload Header Suppression Index (PHSI), an 8-bit field which references the Payload Header Suppression Field (PHSF) that has been used for header suppression. The PHS rule has also a Payload Header Suppression Mask (PHSM) option to allow the choice of bytes of PHSF that cannot be suppressed. Packet Transmission Packet Header Reconstruction (using PHSI and CID) L. Nuaymi (c), Telecom Bretagne, NSM (RSM) Dept - v

80 11- Header suppression Header Suppression for VoIP over WiMAX Suppressed fields: IPv6, UDP and RTP headers (gray fields) bits 0-15 bits UDP Source Port UDP Destination Port Version Pad Ext. Contributing Source Count Mark Payload Type UDP Message Length Checksum Sequence Number Time Stamp Version (v6), 4 bits Traffic Class (8 bits) Flow Label (20 bits) Synchronization Source (SSRC) Identifier Payload Length (16 bits) Next Header (8 bits) Hop Limit (8 bits) (Optional) Contributing Source (CSRC) Identifiers Source Address (128 bits) Destination Address (128 bits) L. Nuaymi (c), Telecom Bretagne, NSM (RSM) Dept - v

81 11- Header suppression Header Suppression for VoIP over WiMAX Number of suppressed bytes per header: IPv6: 37 bytes UDP: 4 bytes RTP: 4 bytes The RTP/UDP/IPv6 Header drops from 60 bytes to 15 bytes (45 Header bytes are suppressed). We also make the computations for an average PHS that reduces the RTP/UDP/IPv6 header from 60 bytes to 30 bytes L. Nuaymi (c), Telecom Bretagne, NSM (RSM) Dept - v

82 11- Header suppression Proposed Header Suppression for VoIP over WiMAX application layer data rates : PHS has an important effect on data rates. The same physical data rate provides a very different data rate for the voice (source) coder of VoIP. L. Nuaymi (c), Telecom Bretagne, NSM (RSM) Dept - v

83 11- Header suppression Header compression for VoIP over WiMAX We also compute the application layer data rates for ROHC L. Nuaymi (c), Telecom Bretagne, NSM (RSM) Dept - v

84 12- Vertical Handover WiMAX has a very open architecture, different ASNs (access networks) radio coexistence problems Optimization of vertical handover Media Independent Handover is treated in g L. Nuaymi (c), Telecom Bretagne, NSM (RSM) Dept - v

85 13- Pricing policies Until now, the economic implications of the introduction of WiMAX technology have received little attention. Pricing mechanisms (main) constraints: - handle the network congestion - manage the QoS of the different services - maximize the operator revenue Pricing cannot (should not?) be separated from Radio Resource Management Specific WiMAX model and pricing parameters (utility functions and other) have to be defined. (As expected) pricing proposals for WiMAX including game theory are (and will be) proposed. L. Nuaymi (c), Telecom Bretagne, NSM (RSM) Dept - v

86 Final Words WiMAX research and UMTS/LTE research: many common points but also some new questions L. Nuaymi (c), Telecom Bretagne, NSM (RSM) Dept - v