Enhancing bluetooth tcp throughput via packet type adaptation
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Enhancing Bluetooth TCP Throughput via Packet Type Adaptation. Ling-Jyh Chen, Rohit Kapoor, M. Y. Sanadidi, Mario Gerla Dept. of Computer Science, UCLA. Outline of the Talk. The problem : Wireless interference and bit errors severely affect TCP efficiency.

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Enhancing Bluetooth TCP Throughput via Packet Type Adaptation

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Enhancing Bluetooth TCP Throughput via Packet Type Adaptation

Ling-Jyh Chen, Rohit Kapoor, M. Y. Sanadidi, Mario Gerla

Dept. of Computer Science, UCLA


Outline 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.

ICC 2004


Who still remembers Bluetooth?

Personal Area Network

Designed for “cable” replacement

Application Examples

  • Automatic synchronization of calendars, address books, business cards

  • Proximity operation (camera to cellphone, etc)

ICC 2004


m

s

m

s

s

s

Bluetooth Physical Link

  • Point to point link

    • master - slave relationship

    • radios can function as masters or slaves

  • Piconet

    • Master can connect to 7 slaves

    • Each piconet has max capacity =1 Mbps

    • Frequency hopping pattern is determined by the master

ICC 2004


f1

f5

f3

f4

f2

f6

m

s1

s2

625 µsec

1600 hops/sec

Piconet MAC Protocol : TDM/Polling

ICC 2004


f1

f5

f4

f6

m

s1

s2

625 µsec

Data rate depends on type of packet

Multi Slot Packets

ICC 2004


DM1

DH1

DM3

DH3

DM5

DH5

Data Packet Types

Asymmetric

Symmetric

2/3 FEC

Asymmetric

Symmetric

No FEC

ICC 2004


Bluetooth 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.

ICC 2004


Throughput 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

ICC 2004


PER vs BER

ICC 2004


Bluetooth Throughput

ICC 2004


Proposed 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.

ICC 2004


Simulation 1: Fixed BER

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

ICC 2004


Simulation 2: Varying BER

Time: 600 secondsTCP Packet Size: 500 bytesBuffer Size: 9000 bytesBER: changes between 0.0001 and 0.0005 every 1 second

ICC 2004


Simulation 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

ICC 2004


Simulation 3: measured BER trace

ICC 2004


Conclusions

  • 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

ICC 2004


T h a n k you

ICC 2004


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