enhancing bluetooth tcp throughput via packet type adaptation
DESCRIPTION
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. - PowerPoint PPT PresentationTRANSCRIPT
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
ICC 2004 2
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.
ICC 2004 3
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
ICC 2004 4
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
ICC 2004 6
Piconet MAC Protocol : TDM/PollingPiconet MAC Protocol : TDM/Polling
m
s1
s2
625 µsec
f1 f2 f3 f4
1600 hops/sec
f5 f6
ICC 2004 7
Multi Slot PacketsMulti Slot Packets
m
s1
s2
625 µsec
f1 f4 f5 f6
Data rate depends on type of packet
ICC 2004 8
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
ICC 2004 10
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.
ICC 2004 11
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
'
ICC 2004 12
PER vs BERPER vs BER
ICC 2004 13
Mode BER range
DH5 <0.0001529
DM5 >0.0001529, and <0.0060795
DM3 >0.0060695, and <0.0157813
DM1 >0.0157813
Bluetooth ThroughputBluetooth Throughput
ICC 2004 14
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.
ICC 2004 15
Simulation 1: Fixed BERSimulation 1: Fixed BER
Time: 600 secondsTCP Packet Size: 500 bytesBuffer Size: 9000 bytes
ICC 2004 16
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
ICC 2004 17
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
ICC 2004 18
Simulation 3: measured BER traceSimulation 3: measured BER trace
ICC 2004 19
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
ICC 2004 20
T h a n k youT h a n k you