Performance Analysis and Evaluation of WiMedia UWB

MAC protocols

Masters Thesis Proposal

Rukhsana Ruby

University of Victoria

History of IPTV

• IP/TV – First Internet Video product, 1995• An IPTV over DSL broadband by Kingston

Communications, 1999• IPTV service by AT&T, 2006 – 300 channels in

11 cities• Nowadays Broadband connections are

widespread Served more than 200 million households, 2005Will grow to 400 million by 2010

IPTV in-home distribution

• Ethernet solution – Rewiring is expensive and awkward

• No new-wires solution – availability and achievable performance is uncertain

• Wireless solution

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Outline• Existing WLAN/WPAN Technologies

• UWB Overview

• Summary of UWB Experimentation

• Methodology

• Performance Results

• Discussion of limitations of current work

• Future Research

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Existing WLAN Technologies

• Support low data rate (11 to 54 Mbps) 802.11b and 802.11a/g (Achieve less than 50% of actual data rate)

• Work in 2.4 and 5 Ghz frequency band. avg throughput of 802.11g 10 Mbps

• Contention – based MAC• 802.15 family supports maximum 55 Mbps data

rate in very short range (10 metre)

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UWB Overview• UWB is a radio technology• UWB is regarded as the best technology

for the high-speed wireless PAN. Why?High speed at short range

o Up to 480Mb/s currently. Ultimately support the speed at Gbit/s.

o In the range of 10 meters.

Radio spectrum: 3.1 to 10.6 GHz (very large).Low energy consumption level

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UWB MAC• Time is divided into super frames.

256 MAS (Each MAS is 256us)

• Beacon Period (First 32 MAS)Contract and Expand able

• Data PeriodDRP and PCA (Like 802.11e)

• Acknowledgement PolicyNo, Block and Immediate Acknowledgement

Overview of EDCAF

• User traffic is differentiated Minimum contention window size Retry limit Arbitration inter-frame space TXOP limit

• Backoff counter is decremented ahead of slot time no matter slot is busy or idle

• User traffic is denoted by ACi {i = 1, 2, 3,4}

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Discussion (UWB Experimentation)

• Tradeoff between TxRate and Retry Limit• Throughput, Latency tradeoff between clustered

and scattered reservation.

Fig. Goodput vs. TxRate and Retry Limit Fig. Throughput vs. Reservation Pattern

Renewal Reward Theorem

Other station’s transmission Tagged station’s

transmission

EDCAF Analysis

Fig: Illustration of renewal cycle

C C S

Frame service time = (E[R] + E[B])*generic slot

EDCAF Analysis(Cont.)

Expected number of backoff slots

Expected number of retransmissions

Transmission probability

Collision probability of AC2 station

Collision probability of AC1 station

EDCAF Analysis(Cont.)

Generic slot calculation

Frame service time for AC1 station

EDCA Analysis (Cont.)

• Frame service time for low priority station are two parts Number of generic slots in zone 2 Pre-backoff waiting period

First part of frame service time for AC2 station

Each pre-backoff waiting period length

Total pre-backoff waiting period

Frame service time for AC2 station

EDCAF Analysis (With DRP)

No. of DRP faced by AC1 station

Frame service time for AC1 station

Frame service time for AC2 station

TQ is the summation of DATA tx time, ACK tx time, SIFS and

guard time

Simulation Methodology

• Simulator – ns-2

• Modified TKN implementation of 802.11e 802.11 physical layer to UWB Incorporate super frame structureInsert some hard drp in super frame

Simulation Scenario

AC2 station

AC1 station

Base station

Radius of circle: 20 metre

Tx range: 250 metre

Freespace propagation model

Data rate: 480 Mbps

MAC layer Packet size with all overhead: 1500 bytes

Min contention window for AC1: 7

Min contention window for AC2: 15

Retry limit: 7

AIFS1: 2 slots

AIFS2: 4 slots

Saturated Simulation and Analysis Results (Without and with DRP)

Fig. Frame service time without DRP Fig. Frame service time with DRP

Beacon period: 1-32

DRP: 100-132, 200-232

Unsaturated Analysis

Pre-backoff waiting period per backoff segment for AC2

Prob of no AC1 station transmits in zone 1

Collision Prob of AC2 station

Collision Prob of AC1 station

Unsaturated Simulation and Analysis Results (Without DRP)

Fig. Frame service time without DRP Fig. Frame service time without DRP

Number of stations: 10 Offered Load: 0.00086 frames/slot

Discussion

• Difficult to get the exact pre-backoff waiting period for AC2 station.

• Due to propagation delay perfect simulation result is not possible.

• Frame service time in the presence of DRP is also approximation.

Future Research

• Extend the model to allow heterogeneous traffic.

• Send video over UWB, find performance metrics and improvement scope.

• Distributed algorithm for DRP allocation

Thank You!

Questions?