WiMAX Possible ResearchAxis in Radio ResourceManagement … Research Axis... · Possible...

WiMAXPossible Research Axis in Radio Resource Management

Loutfi Nuaymi TELECOM Bretagne, Rennes (ex: ENST Bretagne)

Lisbon, Feb 19, 2008

L. Nuaymi (c), Telecom Bretagne, NSM (RSM) Dept - v2.1 - 2008 2

Presentation Plan

• WiMAX Framework

• Possible research in radio resource management

• Conclusions and Future works

• Discussion


1- The context:

� WiMAX technology, based on IEEE 802.16 standard ([802.16-2004] and [802.16e]), has a very rich set of features.

A technical introduction to WiMAX is proposed in �

[802.16-2004] IEEE 802.16-2004, IEEE Standard for local and metropolitan area networks, Air Interface for Fixed Broadband Wireless Access Systems, Oct 2004.

[802.16e]IEEE 802.16e, IEEE Standard for local and metropolitan area networks, Air Interface for Fixed Broadband WirelessAccess Systems, Amendment 2: Physical and Medium Access Control Layers for Combined Fixed and Mobile Operation inLicensed Bands and Corrigendum 1, Feb 2006 (Approved: 7dec 2005).


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, …


1- The context:… and mobility was added

Initially ‘wireless DSL’,

… 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


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 802.16 standard.

� 2004: IEEE 802.16-2004 : revises and consolidates previous 802.16 Standards � Fixed WiMAX

� dec 2005: approval of IEEE 802.16e amendment which (mainly) adds mobility � Mobile WiMAX

� Other 802.16 standards : 802.16f (MIB, SNMP), 802.16g (QoSmanagement, radio resource management procedures, MIH), 802.16h (License-Exempt Operation), 802.16j (Mesh networks)and … mainly: 802.16m: Higher data rates (> 100 Mb/s) for mobiles users (approval expected by 2009). Other (possible) names : WiMAX2 , WiMagic , …?


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 2005.

Commercial offers (Mobile WiMAX) since june 2006.


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 2006-2012", Maravedis Report, Sept 2006


1- The context:

United States:The US operator Sprint-Nextel announced (august 2006) a wide scaledeployment of Mobile WiMAX.

First commercial services expected before end 2007.

Update � Joint network between Sprint and Clearwire announced in July 07.

Abandoned since! Delays expected: 2009?

… many other expected Mobile WiMAX deployments


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.


2- WiMAX Standard basics:

Two topologies (modes) can be used:PMP andMesh

�PMP (Infrastrucure)Point-to-MultiPoint

wireless terminal

PMP topology: the BScovers its SSs. All

transmissions end orstart at the BS

PDA

OtherWiMAX SS


(Mesh) optional mode� Traffic can be routed through other SSs until the BS. Also can take place only between SSs.


Base station (BS)

SS3

SS1

SS2



PossiblePHYsical layers

of WiMAX

Service-SpecificConvergenceSublayer (CS)

MAC CommonPart Sublayer

(CPS)

Security Sublayer

OFDM PHY Layer

[Section 8.3 ofthe standard]

OFDMA PHY Layer

[Section 8.4 ofthe standard]

WiMAX(common)MAC Layer


The Service-Specific Convergence Sublayer(CS) is in charge ofmapping of data coming from an external network: IPv4, IPv6, Ethernet, ATM,... Received at the CS service access point (SAP)

CS sublayer tasks include:- classificationof SDUs;- association of each SDUsto the appropriate MAC SFID (service flow identifier) and CID(connection identifier);- (optional) PHS, Payload Header Suppression: suppression of repetitive header parts.

2- WiMAX Standard basics:Convergence Sublayer (CS)


CS SAP

MAC SAP


(CPS)

External Network.Example: IP ou ATM

MSDU


2- WiMAX Standard basics:Convergence Sublayer (CS)

(Packet) CS Classification � MAC SDU are mapped on convenient CIDs … beforetransmission between corresponding MAC entities. Figure: downlink

Figure source: standard

Upper Layer Entity (e.g., bridge, router, host)

SDU

SAP

Classifier

CID #1

CID #2

CID #...

CID #n {SDU, CID …}

802.16 MAC CPS

SAP

{SDU, CID …}

SAP

Reconstitution (e.g., undo PHS)

SDU

Upper Layer Entity (e.g., bridge, router, host)

802.16 MAC CPS

SAP


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, QoSClass (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 11.13 of the standard.


2- WiMAXStandard basics:

ARQ

All flavors of ARQ included.

Figure: Cumulative ARQ process (use of a sliding window)

Transmitter Receiver

Frame #1

Cumulative ACK

Frame #2

Cumulative NACK

....

Frame #k

Acknowledgment for the previous block frames

Frame #k+1

....

Frame #k+k

No Acknowledgment for the previous block frames

Frame #k+1

....

Frame #k+k

Cumulative ACK

Acknowledgment for the previous block frames

Sliding Window = K


2- WiMAX Standard basics:HARQ

HARQ (Hybrid ARQ): can be used only with OFDMA PHYsicalLayer

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).


2- WiMAX Standard basics:(OFDMA) Channel Quality Information CHannel

For OFDMA PHY, the SS may send CINR (Carrier-to-Interference-and-Noise Ratio) reports using one of these methods:

- REP-RSPMAC Management message (Type = 37);

- the fast-feedback channel (CQICH ), see OFDMA f rame.

- MAC Header (MAC header format without payload), see below.


2- WiMAX Standard basics:AAS, beamforming and smart antenna

Smart antennas guarantee better performances: capacity(throughput) and range.

Figure Source : Schwarz, John,

WiMAX Summit 06

user

omni/sectorreference

co-channel user

coherent gain

passive mitigation

active mitigation


2- WiMAX Standard basics:MIMO

MIMO: Multiple Input, Multiple Output

The MIMO technique expected to be used in WiMAX isSTC, 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


2- WiMAX Standard basics: MIMO

MIMO-STC performance

- 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


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 space-time precoding theory);

• SM not included in present versions of WIMAX

Figure: J. Andrews, Univ. of Texas at Austin


2- WiMAX Standard basics:Architecture

IEEE 802.16 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 theNWG (Network Group) of the WiMAX Forum.

� Network Reference Model

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

NAP

R1 R3 R5

SS/MS

R2

ASN CSN CSN

ASP Network ORInternet

ASP Network ORInternet

R4

Another ASN

R2Visited NSP Home NSP


2- WiMAX Standard basics:Handover

In 802.16e, 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


2- WiMAX Standard basics:Power-Save Modes

Active Mode : the normal mode that exists in 802.16-2004.

IEEE 802.16e defines two new modes: Sleep Modeand Idle Modein order to have:- power-efficient MS operation,- a more efficient handover.


2- WiMAX Standard basics:Ranging

The ranging process is defined in 802.16 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


2- WiMAX Standard basics:Mobile WiMAX (System) Profiles

• Release 1of 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- 2.3 GHz

Wave 2: MIMO, AAS, MBS (Broadcast Service)

• (expected) Release 2: bandwidthes of 15 and 20 MHz. More ambitiousservices.


2- WiMAX Standard basics:Mobile WiMAX (System) Profiles!! Delays !! Update!!

Source: WiMAX forum, white paper, Jan 07


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 andmore 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


2- WiMAX Standard basics:Frequency reuse

Example :� Cluster Size: 1 ou 3 � Tri-sectorisation

Fig Source : Dean Chung, Aperto Networks, WIMAX Summit, Feb 06


3- Multiple Access and SchedulingScheduling and link adaptation

Objectives of schedulingand link adaptation :

The purpose of scheduling is to allow every user, if possible, to havethe (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 differentapplications and a good optimization of using the radio resources (= frequency bandwidth), realizing the QoS required for thetransmission of the data stream.


The MSDUs (MAC SDU) are:

- received by theMAC CPS;

- placed in MPDU(s);

- transmitted on theradio interface.

3- Multiple Access and SchedulingTransmission of MAC PDU (MPDU)

OSI Layer 1:PHYsical layer

MAClayer


CS SAP

MAC SAP


(CPS)

Security Sublayer

PHY SAP

PHYsical Layer

IEEE802.16

Standardscope

External Network.Example: IP or ATM

MSDU

MPDU(s)

OSI Layer 2:data link

layer


3- Multiple Access and SchedulingGeneral 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.


3- Multiple Access and SchedulingTDD and Frame durations

Figure from the standard (16-2004)

� 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.


3- Multiple Accessand SchedulingThe BS decides for resource allocation

Source Fig:Nair et al., Intel Journal Aug 2004


3- Multiple Access and Scheduling

� The frame structure is transmitted by the BS to the SSs for both ways:- downlink: throughDL-MAP MAC Management message; for the currentframe;

- uplink: throughUL-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

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

Frame control

Downlink subframe

Uplink subframe


3- Multiple Access and SchedulingDownlink

The scheduler determines theappropriate burst profile for thecommunication 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.


3- Multiple Access and SchedulingUplink 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).


3- Multiple Access and SchedulingUplink: Contention-based group polling

The three SSsshown are group (multicast or broadcast) polled.

They all have bandwidth request.

SS #1

BS SS #2

SS #3

Request for Bandwidth from SS #1

Request for Bandwidth from SS #2

Request for Bandwidth from

SS #3

BS allocate Bandwidth for the SS that wins

the contention e.g. SS #2


3- Multiple Access and SchedulingDownlink frame structure (same for TDD and FDD)

(OFDM PHY)Downlink

multiple

access

TDM

Figure

From the

standard

Length(es) andprofile(s) of the first

burst(s)

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. Thebursts are sorted in decreasing robustness order.

DL frame (or subframe) duration

DL burst #mDL burst #2DL burst #1Preamble FCH

DLFPRegular MAC

PDUsBroadcastMessages

PaddingRegular MAC

PDUsPadding

MACPayload

MACHeader

CRC(Optional)

(Possibly)DL-MAP, UL-MAP,DCD, UCD, ...


3- Multiple Access and SchedulingUplink frame structure

Uplink :

TDMAmultiple

access

Figure

from

the standard

UL PHY PDUcoming from SS#j

UL subframe duration

Preamble UL burst

Each uplink PHY PDU has its burstprofile. It is then transmitted with amodulation and coding schemespecific to a given SS at a giveninstant

Padding

MAC Payload(Optionnel)

MACHeader (6

Bytes)

CRC(Optionnel)

UL PHY PDUcoming from SS#i

Contention Slot forInitial Ranging

Contention Slot forBandWidth (BW)

Requests

MAC Msg 1(MAC PDU 1)

MAC Msg n(MAC PDU n)


3- Multiple Access and SchedulingFig. from the standard

Full

structure

of a TDD

MAC

frame

(OFDM

PHY)



Fig. from the standard

Full structure of a TDD MAC frame (OFDMA PHY )


3- Multiple Access and SchedulingScheduling

� 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


3- Multiple Access and SchedulingFour QoS defined in 802.16-2004

Four Classes of QoS (Scheduling Services) were defined in 802.16-2004 :

UGS Unsolicited Grant Services.Designed to support real-time data streams. Fixed-size data packets are issued at periodic Intervals

rtPS Real-Time Polling Services.designed to support real-time data streams consisting of variable-sized data packets that are issued at periodic intervals.

nrtPS 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 duringnetwork congestion.

BE Best Effort. No minimum service guarantees are required.


3- Multiple Access and Scheduling16e update: a fifth QoS class

• 802.16e added a fifth scheduling service:ertPS, Extended real-time Polling Service.

• ertPS is suitable for variable rate real-time applications that have data rateand delay requirements. Builds on the efficiency of both UGS and rtPS.Example: Voice over IP with silence suppression.



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.

Constant (Periodic) Time Intervals

Variable packet size

Transmitted packets

Time

Periodic uplink request opportunities


4- The physical layerOFDM PHY Transmission Chain

� The Transmission chain of OFDMA is very close

� 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

PHYsical PDU to be transmitted

Rando-mization

FEC

encoder (CC, Turbo

Code or other)

Interleaving

Modulation

To OFDM Part: IFFT, CP, etc


4- The physical layerChannel 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 torealize the following different code rates: 2/3, 3/4 and 5/6.


4- The physical layerThe digital modulation used

� Four modulations are supported by the IEEE 802.16 standard:

BPSK (mainly for signalling messages)

QPSK16-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


4- The physicallayer

Adaptive PHY

Each burst profile has two definedthresholds:

- mandatory exitthreshold

- minimum entry threshold

These thresholds are indicated in the DCD and UCD messages

Figure source : 802.16-2004

BS SS

DL Data at DIUC n

C/(N+I) too low

for DIUC n

Yes

Continue monitoring DL data through

DIUC n

Send DL data at DIUC k

RNG_REQ or DBPC_REQ Change to DIUC k

DL Data at DIUC k

RNG_RSP or DBPC_RSP

Monitor DL only data through DIUC k

DL Data at DIUC k

NO


4- The physical layerOFDM 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


4- The physical layerModulation 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:

Table (Columns 1, 2 and 3) from [802.16].

24.4

22.7

18.2

16.4

11.2

9.4

6.4

Receiver SNR (dB)

192 x 6 x 3/4� 864

192 x 6 x 2/3� 768

192 x 4 x 3/4 � 576

192 x 4 x 1/2 � 384

192 x 2 x 3/4 � 288

192 x 2 x 1/2 � 192

192 x 1 x 1/2 � 96

Number of Useful Bits per OFDM Symbol

3/464-QAM

2/364-QAM

3/416-QAM

1/216-QAM

3/4QPSK

1/2QPSK

1/2BPSK

Coding rateModulation


4- The physical layerData rates

PHY data rate in for different MCS (Modulation and coding scheme)

Channel bandwidth: 7 MHz; OFDM PHY Interface

Sampling factorn=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

1/32 2.92 5.82 8.73 11.64 17.45 23.27 26.18

1/16 2.82 5.65 8.47 11.29 16.94 22.59 25.41

1/8 2.67 5.33 8.00 10.67 16.00 21.33 24.00 1/4 2.40 4.80 7.20 9.60 14.40 19.20 21.60


4- The physical layerScalable 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.


4- The physical layerDifferent 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]


4- The physical layerSubcarrier permutations

� For both uplink and downlink, the pilot subcarriersand 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 slotis the minimum possible data allocation unit in 802.16 standard.

Fig Source: 802.16-2004


4- The physical layerSubcarrier 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.


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


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:� (802.16-2004) 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.


5- Link adaptation, power control

� Possible question: power control or rate control?

(example) Economic consideration: increase power? You have to pay more!


5- Link adaptation, power control Link adaptation

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

Figure form Ball, VTC2005Spring


5a- DFS: Dynamic Frequency Selection

DFS: Dynamic Frequency Selection. Mandatory Procedure in ETSI zone when unlicensed frequencies are used.

The IEEE 802.16 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, 2003.


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., “Subchan-nelization Performance for the Downlink of a Multi-CellOFDMA System,” WiMob 2007)

• bDA: Basic Dynamic Assignment• RPO: Rate Profit Optimization Alg • ASS: Adjacent subcarriers subchannelization


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


7- Network deployment

Results Example:

(From: K. Ntagkounakis, “Cost-efficient WiMAX network deployment: the hybrid outdoor/indoor dual-layer coverage approach,”, PIMRC 2007 )


8- Multihop and mesh

• Mesh for WiMAX is still rather unclear: 802.16j amendment should eliminate some of the confusion. The first draft, D1, dates from Aug 2007.

• Proposals must be (are) done for multi-hop routing and (WiMAX mesh specific-) scheduling

• Energy and cost considerations (see ad hoc networks research)


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.


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 ?


10- SchedulingScheduling algorithms: well-known algorithms used for WiMAX

(example)

• Deficit Round Robin (DRR):

Q1=350

Q2=300

Q3=250

a1 200

a2 750

a3 280

b1 500

b2 300

b3 280

c1 100

c2 900

c3 300

Increment the deficit counter (Di) by the fixedquantum (Qi)

D1= 150

D3= 150

D1= 350

D2= 300

D3= 250

Compare between Qi and the length of the packet (Li)

a1 200

c1 100

If Di > Li � send pkt + decrement Di by Li


10- SchedulingOther 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 802.16 Networks”

• [6] K. Vinay, N. Sreenivasulu, D. Jayaram, D. Das, “PerformanceEvaluation of

End-to-end Delay by Hybrid Scheduling Algorithm for QoS in IEEE 802.16

Network”

• [7] S. A. Xergias, N. Passas, L. Marekos, “Flexible Resource Allocation inIEEE

802.16 Wireless Metropolitan Area Networks”

• ….


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).

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.

Payload header

Payload

Payload

PHSI

Useful portion

Useful portion

…

…

…

…

PHSF


11- Header suppression

802.16e 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


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


11- Header suppressionComputation 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 802.16 standard.

• The same type fo computation is done for uplink taking into account the initial ranging contention slot and BW request contention slots


11- Header suppressionHeader 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

Voice Payload

Application Layer



• 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.



• 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)



• Suppressed fields: IPv6, UDP and RTP headers (gray fields)

Version (v6), 4 bits

Traffic Class (8 bits)

Flow Label (20 bits)

Payload Length (16 bits)Next Header (8

bits)Hop Limit (8

bits)

Source Address (128 bits)

Destination Address (128 bits)

Version Pad Ext.Contributing Source Count

MarkPayload

Type

Sequence Number

Time Stamp

Synchronization Source (SSRC) Identifier

(Optional) Contributing Source (CSRC) Identifiers

bits 0 - 15 bits 16 - 31

UDP Source Port UDP Destination Port

UDP Message Length Checksum



• 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


11- Header suppressionProposed 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.


11- Header suppressionHeader compression for VoIP over WiMAX

• We also compute the application layer data rates for ROHC


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 802.16g


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.


Final Words

• WiMAX research and UMTS/LTE research: many common points but also … some new questions

WiMAX Possible ResearchAxis in Radio ResourceManagement … Research Axis... · Possible...

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