Enhancing Bluetooth TCP Throughput Enhancing Bluetooth TCP Throughput

via Packet Type Adaptationvia Packet Type Adaptation

Ling-Jyh Chen, Rohit Kapoor, M. Y. Sanadidi, Mario GerlaLing-Jyh Chen, Rohit Kapoor, M. Y. Sanadidi, Mario GerlaDept. of Computer Science, UCLADept. of Computer Science, UCLA

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Outline of the TalkOutline of the Talk The problem: Wireless interference and bit errors

severely affect TCP efficiency.

The opportunity: Bluetooth offers multiple packet type options with different FEC and packet lengths. Moreover, the link layer API provides link error quality information. Opportunity for cross-layer adaptation.

Key idea: dynamically select packet type based on measured link quality.

The results: we show that the “Adaptive Packet Type” approach in Bluetooth can effectively enhance TCP performance.

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Who still remembers Bluetooth?Who still remembers Bluetooth?

Application Examples Automatic synchronization of calendars, address

books, business cards Proximity operation (camera to cellphone, etc)

Personal Area NetworkPersonal Area Network

Designed for “cable” Designed for “cable” replacementreplacement

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Bluetooth Physical LinkBluetooth Physical Link Point to point link

master - slave relationship radios can function as masters or slaves

m s

ss

m

s

Piconet Master can connect to 7 slaves Each piconet has max capacity =1 Mbps Frequency hopping pattern is

determined by the master

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Piconet MAC Protocol : TDM/PollingPiconet MAC Protocol : TDM/Polling

m

s1

s2

625 µsec

f1 f2 f3 f4

1600 hops/sec

f5 f6

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Multi Slot PacketsMulti Slot Packets

m

s1

s2

625 µsec

f1 f4 f5 f6

Data rate depends on type of packet

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Data Packet TypesData Packet Types

DM1

DM3

DM5

DH1

DH3

DH5

2/3 FEC

No FEC

Symmetric Asymmetric

108.8 108.8 108.8

258.1 387.2 54.4

286.7 477.8 36.3

Symmetric Asymmetric

172.8 172.8 172.8

390.4 585.6 86.4

433.9 723.2 57.6

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Bluetooth packet typesBluetooth packet types DH: Stop and Wait ARQ

DM: ARQ as well as 2/3 FEC codes to correct single bit errors

FEC coding scheme: (15, 10) Hamming code, each block of 10 information bits is encoded into a 15 bit codeword can correcting a single bit error in each block.

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Throughput AnalysisThroughput Analysis DH mode: (ARQ)

PER:1 hop Throughput:2 hop Throughput:

DM mode: (ARQ+FEC)PER:1 hop Throughput:2 hop Throughput:

P: Packet Error Rate, B: Bit Error Rate, S: Packet Size, T: Max Throughput

SB)(P 11

15/1415 )1(15)1(1S

BBBP

kbpsB)(TPTT S 1 )1('

kbpsBBBTTS 15/1415 )1(15)1('

kbpsB)(TP

TT S

12

2

1'

kbpsBBBT

T 1415 )1(15)1(2

'

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PER vs BERPER vs BER

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Mode BER range

DH5 <0.0001529

DM5 >0.0001529, and <0.0060795

DM3 >0.0060695, and <0.0157813

DM1 >0.0157813

Bluetooth ThroughputBluetooth Throughput

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Proposed ApproachProposed Approach Adaptive Packet Type (APT):

In BT specs, the function call, Get_Link_Quality, returns the Quality of the specified Link.

We read the returned link Quality Value, and adapt packet type so as to optimize throughput.

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Simulation 1: Fixed BERSimulation 1: Fixed BER

Time: 600 secondsTCP Packet Size: 500 bytesBuffer Size: 9000 bytes

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Simulation 2: Varying BERSimulation 2: Varying BERTime: 600 secondsTCP Packet Size: 500 bytesBuffer Size: 9000 bytesBER: changes between 0.0001 and 0.0005 every 1 second

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Simulation 3: Measured BER TracesSimulation 3: Measured BER Traces 802.11 interference experiments using CSR chipset CSR provides LQ vs BER conversion tables:

If BER (Bit Error Rate) = 0, LQ (Link Quality) = 255; perfect channel.

If BER <= 40/40000, LQ = 255 – BER * 40000.

If 40/40000 < BER <= 4000/40000, LQ = 215 – ((BER / 32) * 40000).

If 4000/40000 < BER <= 40000/40000, LQ = 105 – ((BER / 256) * 40000).

Simulation:Time: 600 seconds TCP Packet Size: 500 bytesBuffer Size: 9000 bytesBER: using the BER trace

0

50

100

150

200

250

300

0

0.01

0.02

0.02

0.03

0.04

0.05

0.06

0.06

0.07

0.08

0.09 0.1

Bit Error Rate

Lin

k Q

ual

ity

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Simulation 3: measured BER traceSimulation 3: measured BER trace

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ConclusionsConclusions

In Bluetooth, TCP throughput collapses with BER above 0.03% (eg, BER caused by near 802.11 interference)

APT (Adaptive Packet Type) approach can restore TCP throughput to acceptable values for much higher BER (we tested up to .3%)

APT technique can be applied to any wireless link with packet length and FEC options, and with link quality (ie BER) feedback.

Further work on BT crosslayer optimization will include: Adaptive optimization of number of retransmissions (for a mix of TCP

and real time traffic) Interleaved FEC over multiple frames

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T h a n k youT h a n k you