Doc.: IEEE 802.11-04/0991r0 Submission September 2004 Rui Zhao, ComNets, RWTH Aachen UniversitySlide...

September 2004

Rui Zhao, ComNets, RWTH Aachen University

Slide 1

doc.: IEEE 802.11-04/0991r0

Submission

W-CHAMBWireless CHannel Oriented Ad-hoc Multi-hop Broadband

A new MAC for better support of Mesh networks with QoS

Rui Zhao, Bernhard Walke, Guido R. HiertzComNets

Chair of Communication NetworksRWTH Aachen University

AachenGermany

September 2004


Slide 2

doc.: IEEE 802.11-04/0991r0

Submission

Outline

• Overview of W-CHAMB

• Better Multi-hop Support

• QoS Support of W-CHAMB

• Synchronization of W-CHAMB

• Summary

• Simulation Result

September 2004


Slide 3

doc.: IEEE 802.11-04/0991r0

Submission

Overview of W-CHAMB• TDMA based• Channel-oriented• Fully distributed MAC

protocol • Possible PHY

– IEEE 802.11a/g– OFDMA– MC-CDMA

• Full scale QoS guarantee– Prioritized access

(DiffServ)

• Multi-hop operation

• Energy (E) signals– Access-E-Signal

• Prioritized access to wireless medium

– Busy-E-Signal• Calm down hidden stations• Control transmission direction

• Adaptive multi-slot option– Control of capacity of Traffic

Channel (TCH)– Increase of channel utilization

• Large-scale ad-hoc Mesh networks

September 2004


Slide 4

doc.: IEEE 802.11-04/0991r0

Submission

W-CHAMB Protocol Stack• Radio Resource Control (RRC)

– Call Admission Control (CAC)– Dynamic Frequency Selection (DFS)– Power Control (PC)– Link Adaptation (LA)

• Media Access Control (MAC)– Multiple access to wireless medium– TDMA channels with dynamic TDD

mode– Hidden station elimination (busy

tone)– TDMA Traffic Channel (TCH) to

connect neighbored Mesh points– Priority handling of packet data

flows per Mesh point– Multiplex packets to TCHs under

DiffServ

• Radio Link Control (RLC)– Un-/acknowledged data

IEEE802.11 PHYor other

W-CHAMB MAC

W-CHAMB RLC

W-CHAMB RRC(CAC,DFS,PC,LA)

IP

TCP/UDP

APPLICATION

IEEE802.11 PHYor other

W-CHAMB MAC

W-CHAMB RLC

W-CHAMB RRC(CAC,DFS,PC,LA)

IP

TCP/UDP

APPLICATION

Layer 1

Layer 2

Layer 3

Layer 4

Layer 5

Layer 6

September 2004


Slide 5

doc.: IEEE 802.11-04/0991r0

Submission

Important Notice!

• All PHY parameters are examples only

• All durations are example values

• No assumption on PHY to be used is made

• Here: “.11a” OFDM like realistic PHY assumed

September 2004


Slide 6

doc.: IEEE 802.11-04/0991r0

Submission

MAC Frame and Energy Signals

• Access Channel (ACH)• Traffic Channel (TCH) • Energy signal Channel (ECH)

• Single Value Busy-E-Signal (SVB)– Signal “TCH occupied” to hidden

stations• Double Value Busy-E-Signal (DVB)

– Signal “TCH occupied & Reverse (TDD) transmission requested”

ACH TCH1 … TCHn …

ACH1-n45us x n

ECH 1-n 6us x n

6us x (n +m) + 28us

Priori-tization Phase

Contention Phase

Transmission Phase

n m 28us

Access-E-signal

1us

2us 2us

1us

6us

TxOff

TxOn

GuardSignal

1us 1us 2us 2us

6us

TxOff

TxOn

GuardSignal

1us

2us 2us

1us

6us

TxOff

TxOn

GuardSignal

Single Value Busy-E-Signal (SVB)

Double Value Busy-E-Signal (DVB)

September 2004


Slide 7

doc.: IEEE 802.11-04/0991r0

Submission

Access Channel (ACH)

• ACH-Prioritization Phase– QoS-related contention– n binary Access-E-signals

• ACH-Contention Phase– Contention with m binary

Access-E-signals– Higher success probability

of an access packet– m depends on network size

• ACH-Transmission Phase– Transmission of request-

packet– Network control data

6us x (n +m) + 28us

Prioritization Phase

Contention Phase

Transmission Phase

n m 28us

September 2004


Slide 8

doc.: IEEE 802.11-04/0991r0

Submission

Req-Packet0 0 11

0 1 11

0 0 11

0 0 11 0 0 11

0 1 110 1 11

0 0 11 0 0 11

1 0 1 1 1 0 0 1

0 1 1 0 0 1 1 1

1 0 1 1 1 0 0 11 0 1 1 1 0 0 1

0 1 1 0 0 1 1 10 1 1 0 0 1 1 1

Sends E-signal

listens

Send E-signal

listen

Access Method(similar to HiperLAN/1)

• Mesh Points generatenumber ∈ [0;2n-1]– According to QoS requirement

• Check number bit by bit– If 1, send E-signal– If 0, listen– If Mesh point hears E-signal, it

defers from contention• Winners of prioritization

phase contend again– Draw random number

from [0;2m-1]• Winner sends request packet

(or other) via ACH

Prioritized Access Method

September 2004


Slide 9

doc.: IEEE 802.11-04/0991r0

Submission

Contention Sub-phase in ACH• Guarantee single winner

– In almost every contention– Even in high density mesh

• Failed Mesh Points– Initiate new contention in

next frame– Use bigger contention

number• Increase chance to win

• Achieve fairness among Mesh points– With control algorithms of

TCH

• Support bottle-neck Mesh Points (Mesh AP, portal)– Get bigger contention

number• Win more access trials• More transmission chances

6us x (n +m) + 28us

Prioritization Phase

Contention Phase

Transmission Phase

n m 28us

September 2004


Slide 10

doc.: IEEE 802.11-04/0991r0

Submission

TransmissionSender Receiver

Forward Transmission

Send packet data via the reserved TCH(s). (Data might be station`s own or relay data)

Signal SVB on the corresponding ECH(s)

Send packet data via the reserved TCH(s)

Signal DVB on the ECHs to request reverse TDD transmissionSend packet data via the reserved TCH(s) in alternate direction

Signal SVB(DVB) on the corresponding ECH(s)

Reverse Transmission

(On Demand TDD)

Check available channelsSend a request packet on ACH containing proposed TCHs and QoS description

Accept the request by signaling SVB on ECH(s) corresponding to the selected TCH(s)

Connection Setup

Check available channels

A TCH is defined on a per hop basis only.

September 2004


Slide 11

doc.: IEEE 802.11-04/0991r0

Submission

• Busy-E-Signal (6μs)– Does not contain

user related information

– Preamble notneeded

• TCHs definedon disjointtime slots

Busy-E-Signal to Calm DownHidden Stations

STA1

STA8

STA4

STA2

STA3

STA5

STA6

STA7

TCH3

ECH3

TCH4

ECH4

September 2004


Slide 12

doc.: IEEE 802.11-04/0991r0

Submission

Capacity Increase: Release of a TCH After Specified Hang-on Time

• TCH freed by a Mesh Point– No packet in TCH buffer– Hang-on time expired

• Dependent on type of service

• Higher service level = longer hang-on time

• Longer value → lower transmission delay

– Packet-oriented behavior

Example for hang-on time equal to 2 MAC frames

4 3 2 1

Arrival of packets

Req

ACH ECHsTCHs

time

1

2

Req

Hang-on

3

4

Hangon

Released

September 2004


Slide 13

doc.: IEEE 802.11-04/0991r0

Submission

Req

ACH ECHTCH

Req

14 3 2 1

Packets in buffer

2 3

time

5

4 3 25

4 56 5 4

6

7

6

78

88

910

11

12

13

14

15

910

Req

910

11

11

12

11

12

13

14

15

16

17

18

13

14

15

16

14

15

16

17

18

17

18

17

18

Dynamic Adjustment of Number of TCH for a Connection

• Mesh points contend for more TCHs if QoS cannot be satisfied

• Release TCH after hang-on time– Service specific

• Here– Hang-on time = 1 MAC

frame– Max TCHs = 3 TCHs

Efficient resource use even for rt-VBR

September 2004


Slide 14

doc.: IEEE 802.11-04/0991r0

Submission

PDU Trains for better Efficiency

• PDU trains – Achieve higher

efficiency– >2 adjacent TCHs used

from source to same destination

ACH

ECHsTCH

ACH ECHs

TCHs

ACH ECHsTCHs

PDU

4.7µs

45µs

Tx power

on

AGC

SYN

36µs 4.3µs

Tx poweroff

PDU

4.7µs

90µs

Tx power

on

AGC

SYN

81µs4.3µs

Tx poweroff

PDU PDU

27µs

PDU

4.7µs

Tx power

on

AGC

SYN

126µs 4.3µs

Tx poweroff

PDUPDU

135µs

PDU

31.5µs

September 2004


Slide 15

doc.: IEEE 802.11-04/0991r0

Submission

Medium Access Fully Decentralized • No central control

• Mesh Points connect to neighbor pico-nets

• Any Mesh point is centre of a pico-net

• Power control/save mode depend on Mesh point

• Routing modes:– Bridge/router

based

– MANET

• Mesh points care for TCHs to neighbors

September 2004


Slide 16

doc.: IEEE 802.11-04/0991r0

Submission

Traffic Schemes for Bottle-necks

• Bottle-necks (BNs), Mesh APs or portals– More in & out traffic than average– Powerful computational ability & plenty

power supply & large memory– In “right” location

• Schemes for transmission between BNs– Several continuous TCHs reserved

• According to load• Longer hang-on time values

– Multiplexing of different traffic streams into reserved TCHs• Expedited forwarding (EF) PHB (Per-Hop

Behaviors) (DiffServ) [6]

ACH ECHsTCHs

Hang-on times(unit:

MAC frames)10 8 4

Prrmium

Silver

Bronze

GoldTCHs

BN

STA

September 2004


Slide 17

doc.: IEEE 802.11-04/0991r0

Submission

Better Multi-hop Support

Transmission range

Interference rangeSensing range

CTS

1 2 3 4 5RTS

IEEE802.11

ACH-Req

has knowledge about existing transmission

1 2 3 4 5W-CHAMBTCHs

ECHs

TCHsTransmitting in

parallel in different TCHs

• Ongoing transmission between Mesh point 4 & 5• Mesh point 1 attempts to initiate a transmission to 2 (Instability, see [4])

September 2004


Slide 18

doc.: IEEE 802.11-04/0991r0

Submission

QoS Support

• Efficient prioritized access– Up to 16 levels

• TCH Valid transmission time (VTT)– Associated with QoS type– Higher Qos level=higher

value– Statistical interruption of

lower level transmission• TCH Hangon time

– Depends on priority– Controls traffic performance

(longer value → lower transmission delay)

• Multi-slots capability for higher throughput

• QoS guarantee under heavy load– Due to channel-oriented

structure• No probing packets for CAC

(Call Admission Control)– Observe TCHs & ECHs

September 2004


Slide 19

doc.: IEEE 802.11-04/0991r0

Submission

Beacon

Every Mesh Pointcan send Beacon

Higher priority in Beacongeneration to bottle necks

Synchronization of W-CHAMB [5]

• Periodic Beacons– Every Mesh Point participates in generation– Analysis by recipients– In full ad-hoc operations mode – Able to support large scale networks– Support multi-hop operation– Support Mesh Point mobility

• Clock shift compensation algorithm– Combat clock

drifts– Accuracy for

one-hopnetwork = 0.4±0.1 µs

September 2004


Slide 20

doc.: IEEE 802.11-04/0991r0

Submission

W-CHAMB Summary

• Channel-Oriented

• On top of any existent or future PHY layer

• Decentral Control Scheme

• Flexible Multi-Hop (Mesh) Support

• Perfect Ad-Hoc Mesh Networking

• Sophisticated QoS Guarantee

• Support of large number of Mesh points in ad-hoc Mesh

September 2004


Slide 21

doc.: IEEE 802.11-04/0991r0

Submission

References

• [1]. B. Xu, B. Walke, W-CHAMB: A Wireless Channel-oriented Ad-hoc Multihop Broadband Network – Comparison with IEEE 802.11. In Proc. European Wireless’99, Munich, Germany, October 1999. pp. 79-84

• [2]. B. Xu, B. Walke, Protocols and Algorithms supporting QoS in an Ad-hoc Wireless ATM Multihop Network, in Proc. EPMCC’99, pp. 79-84, Paris, France, Mar. 1999.

• [3]. M. Lott and B. Walke, Performance of theWireless Ad hoc Network W-CHAMB, in Proc. European Wireless (EW’99), (Munich, Germany), Oct. 1999.

• [4]. S. Xu and T. Saadawi – “Does the IEEE 802.11 MAC Protocol Work Well in Multihop Wireless Ad Hoc Networks?” IEEE Communications Magazine, June 2001, pp 130-137.

• [5]. R. Zhao, and B. Walke: A Synchronization Scheme for the Wireless Channel-oriented Ad-hoc Multi-hop Broadband System (W-CHAMB). In Wireless World Research Forum, Zurich, Switzerland, July 2003

• [6]. RFC 2598, An Expedited Forwarding PHB, June 1999

September 2004


Slide 22

doc.: IEEE 802.11-04/0991r0

Submission

Simulation

MAP

MAP1 MAP2

MAP5 MAP4

MAP6 MAP3

STA1 STA2

STA3

STA4STA5

STA6

1 hop

2 hop2

A two hop scenario

MAP: Mesh AP

STA: Station

• Comparing maximum through-put, 802.11 & W-CHAMB– PHY: 802.11a (OFDM)– Packet size = 9 symbols

• W-CHAMB– 81B @ QPSK¾,

162B @ 16QAM¾,243B @ 64QAM¾

• 802.11– 115B @ QPSK¾ ,

192B @ 16QAM¾,277B @ 64QAM¾

• W-CHAMB MAC– Number of TCH & ECH

• 16– TCH

• 45µs– Energy signal

• 6µs– ACH

• (6*4+8*4+28)µs = 100µs

September 2004


Slide 23

doc.: IEEE 802.11-04/0991r0

Submission

Maximum Throughput

1 2 3 4 5 6 7 8 90

5

10

15

20

25

Number of MAP/STA

Maxim

um

Thro

ughput

(Mbps)

IEEE 802.11a 18MbpsIEEE 802.11a 36MbpsIEEE 802.11a 54MbpsW-CHAMB 18 MbpsW-CHAMB 36 MbpsW-CHAMB 54 Mbps

September 2004


Slide 24

doc.: IEEE 802.11-04/0991r0

Submission

Thanks for your attention

[email protected]@ieee.org

[email protected]://www.comnets.rwth-aachen.de

Doc.: IEEE 802.11-04/0991r0 Submission September 2004 Rui Zhao, ComNets, RWTH Aachen UniversitySlide...

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