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

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

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

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


Bluetooth physical link

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


Piconet mac protocol tdm polling

f1

f5

f3

f4

f2

f6

m

s1

s2

625 µsec

1600 hops/sec

Piconet MAC Protocol : TDM/Polling

ICC 2004


Multi slot packets

f1

f5

f4

f6

m

s1

s2

625 µsec

Data rate depends on type of packet

Multi Slot Packets

ICC 2004


Data packet types

DM1

DH1

DM3

DH3

DM5

DH5

Data Packet Types

Asymmetric

Symmetric

2/3 FEC

Asymmetric

Symmetric

No FEC

ICC 2004


Bluetooth packet types

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

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

PER vs BER

ICC 2004


Bluetooth throughput

Bluetooth Throughput

ICC 2004


Proposed approach

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

Simulation 1: Fixed BER

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

ICC 2004


Simulation 2 varying ber

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

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

Simulation 3: measured BER trace

ICC 2004


Conclusions

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

T h a n k you

ICC 2004


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