Enhancing Bluetooth TCP Throughput via Packet Type Adaptation

1
Enhancing Bluetooth TCP Throughput via Packet
Type Adaptation

• Ling-Jyh Chen, Rohit Kapoor, M. Y. Sanadidi,
  Mario Gerla
• Dept. of Computer Science, UCLA

2
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.

3
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)

4
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

5
Piconet Topology

• Page - scan protocol
• Polling

6
Piconet MAC Protocol TDM/Polling
7
Multi Slot Packets
8
Data Packet Types
Asymmetric
Symmetric
108.8 108.8 108.8
258.1 387.2 54.4
286.7 477.8 36.3
2/3 FEC
Symmetric
Asymmetric
No FEC
172.8 172.8 172.8
390.4 585.6 86.4
433.9 723.2 57.6
9
Scatternet
10
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.

11
Throughput Analysis

• DH mode (ARQ)PER1 hop Throughput2 hop
  Throughput
• DM mode (ARQFEC)PER1 hop Throughput2 hop
  Throughput
• P Packet Error Rate, B Bit Error Rate, S
  Packet Size, T Max Throughput

12
PER vs BER
13
Bluetooth Throughput
Mode BER range
DH5 lt0.0001529
DM5 gt0.0001529, and lt0.0060795
DM3 gt0.0060695, and lt0.0157813
DM1 gt0.0157813
14
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.

15
Simulation 1 Fixed BER
Time 600 secondsTCP Packet Size 500
bytesBuffer Size 9000 bytes
16
Simulation 2 Varying BER
Time 600 secondsTCP Packet Size 500
bytesBuffer Size 9000 bytesBER changes
between 0.0001 and 0.0005 every 1 second
17
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 lt 40/40000, LQ 255 BER 40000.
• If 40/40000 lt BER lt 4000/40000, LQ 215 ((BER
  / 32) 40000).
• If 4000/40000 lt BER lt 40000/40000, LQ 105
  ((BER / 256) 40000).
• Simulation
• Time 600 seconds TCP Packet Size 500
  bytesBuffer Size 9000 bytesBER using the BER
  trace

18
Simulation 3 measured BER trace
19
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

20
T h a n k you