a smart switched sector array for wideband interference
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1726+,%$�5HVHDUFK�(XURSH�/LPLWHG ConfidentialConfidential
3rd IEEE Workshop on WLAN, 27 Sept 2001, Newton MA
A Smart Switched Sector Array for A Smart Switched Sector Array for Wideband Interference Mitigation in an Wideband Interference Mitigation in an
OFDMOFDM--based WLANbased WLAN
Hidehiro Matsuoka, Yong Sun, Steve Parker and Chris Simmonds
Toshiba Research Europe Limited, UK
2726+,%$�5HVHDUFK�(XURSH�/LPLWHG ConfidentialConfidential
3rd IEEE Workshop on WLAN, 27 Sept 2001, Newton MA
OutlineOutline
• Introduction• Simulation environment• BER performance with or without interference• Switching success probability• Capacity improvement• Conclusions
3726+,%$�5HVHDUFK�(XURSH�/LPLWHG ConfidentialConfidential
3rd IEEE Workshop on WLAN, 27 Sept 2001, Newton MA
IntroductionIntroduction
• 2.4GHz and 5GHz WLAN system will provide high-rate data services
• WLAN service area can cover office, home, conference hall, station, airport, etc.
• OFDM-based wireless LAN provides robustness to multipath
IP Network RT
Service Area
MT
MT
AP
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3rd IEEE Workshop on WLAN, 27 Sept 2001, Newton MA
Future problem and solutionFuture problem and solution
In the Near Future• Due to the limited spectrum allocation and predicted uptake of
WLANs, co-channel interference will become an issue
Solution• Antenna technology for interference reduction
– Switched sector array (simple structure solution)
– Beam- and null-forming (good performance)
Competing MT
AP
5726+,%$�5HVHDUFK�(XURSH�/LPLWHG ConfidentialConfidential
3rd IEEE Workshop on WLAN, 27 Sept 2001, Newton MA
Antenna pattern and Rx structureAntenna pattern and Rx structure
0.2
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1
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180 0
0.2
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180 0
RSSI measurementFor each sector
SectorSwitch
Dem
SWcontrol
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3rd IEEE Workshop on WLAN, 27 Sept 2001, Newton MA
Spatial channel modelSpatial channel model
8 SectorSwitch
-30.0
-25.0
-20.0
-15.0
-10.0
-5.0
0.0
0 30 60 90 120
150
180
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510
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Delay ns
Pow
erdB
ETSI-B channel model(each path varies basedon Rayleigh fading)
18 paths are spatially distributed at random over time (frame by frame)
RSSI measurementRSSI measurement
RSSI measurementRSSI measurement
RSSI measurementRSSI measurement
RSSI measurementRSSI measurement
7726+,%$�5HVHDUFK�(XURSH�/LPLWHG ConfidentialConfidential
3rd IEEE Workshop on WLAN, 27 Sept 2001, Newton MA
Simulation ParametersSimulation Parameters
The same channel property as required signalsInterference
8 element circular sector array (90o cosine beam)Antenna array
Largest measured RSSI selectionSector switching method
At random on a frame by frame basisSpatial signal distribution
ETSI-B (Excess Delay: 720nsec, Delay Spread: 100nsec)Channel model
312.5kHzSubcarrier spacing
Preamble(4symbols) + payload(180symbols)Frame structure
4usec (0.8usec cyclic prefix)Symbol interval
52 … 48 (data subcarriers) [No DC component]
… 4 (pilot at positions 7, -7, 21, -21)
Number of subcarrier
OFDM (Uncoded QPSK and 16QAM for each subcarrier)
Modulation scheme
ValueParameters
8726+,%$�5HVHDUFK�(XURSH�/LPLWHG ConfidentialConfidential
3rd IEEE Workshop on WLAN, 27 Sept 2001, Newton MA
BER performance (ETSIBER performance (ETSI--B channel)B channel)
0 5 10 15 20 25 3010
-6
10-5
10-4
10-3
10-2
10-1
100
Eb/No [dB]
Unc
oded
Bit
Err
or R
ate
(BE
R)
QPSK(omni)16QAM(omni)QPSK(sector)16QAM(sector)10dB SNR
improvement compared to single omni-directional system 10dB
9726+,%$�5HVHDUFK�(XURSH�/LPLWHG ConfidentialConfidential
3rd IEEE Workshop on WLAN, 27 Sept 2001, Newton MA
BER performance with multipath BER performance with multipath interference (ETSIinterference (ETSI--B channel)B channel)
0 5 10 15 20 25 3010
-6
10-5
10-4
10-3
10-2
10-1
100
Eb/No (dB)
Unc
oded
Bit
Err
or R
ate
(BE
R)
SIR = 0 dBSIR = 3 dBSIR = 10 dBSIR = 20 dB
Interference will deteriorate the BER performance even using switched sector array
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3rd IEEE Workshop on WLAN, 27 Sept 2001, Newton MA
SIR robustness over omniSIR robustness over omni--directional directional systemsystem
0 2 4 6 8 10 12 14 16
10-4
10-3
10-2
10-1
100
SIR [dB]
Irre
duci
ble
BE
R
SW (multipath Interference)Omni (multipath Interference)
10-5
Switched sector array based on RSSI (SW) can improve SIR robustness by 2-3dB compared to single omni-directional system
Irreducible BER:is the value of BERfloor at Eb/No = ∞
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3rd IEEE Workshop on WLAN, 27 Sept 2001, Newton MA
Switching success probability in ETSISwitching success probability in ETSI--B B channel with interferencechannel with interference
0 5 10 15 20 25 300
0.1
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0.3
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0.5
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0.9
1
Eb/No (dB)
Pro
babi
lity
SIR = 0 dBSIR = 3 dBSIR = 10 dBSIR = 20 dBSuccessful
switching probability depends on SIR and SNR
12726+,%$�5HVHDUFK�(XURSH�/LPLWHG ConfidentialConfidential
3rd IEEE Workshop on WLAN, 27 Sept 2001, Newton MA
Switching method comparisonSwitching method comparison
0 5 10 15 20 25 3010
-6
10-5
10-4
10-3
10-2
10-1
100
Eb/No (dB)
Unc
oded
Bit
Err
or R
ate
(BE
R)
Omni antennaSWOptimal switchingWorst switching
OptimalSwitching:
WorstSwitching:
selects the sectorthat providesthe best BER
selects the sectorthat providesthe worst BER Signal Channel: ETSI-B
Interference Channel: ETSI-BSIR = 10dB
13726+,%$�5HVHDUFK�(XURSH�/LPLWHG ConfidentialConfidential
3rd IEEE Workshop on WLAN, 27 Sept 2001, Newton MA
Capacity improvementCapacity improvement
10 12 14 16 18 20 22 24 26 28 3010
-4
10-3
10-2
Eb/No (dB)
Unc
oded
Bit
Err
or R
ate
(BE
R)
BPSK (Omni antenna)BPSK (SW on RSSI)16QAM (optimal SW)64QAM (optimal SW)
Signal Channel: ETSI-BInterference Channel: ETSI-BSIR = 10dB
Approximately five-fold data rate improvement can be expected using optimum switchingCompared to single omni-directional system
14726+,%$�5HVHDUFK�(XURSH�/LPLWHG ConfidentialConfidential
3rd IEEE Workshop on WLAN, 27 Sept 2001, Newton MA
Approach to optimum switchingApproach to optimum switching
• Successful switching probability based on RSSI measurement is strongly dependent on SIR rather than SNR
• Interference detection is useful for switching criteria in the presence of strong interference
15726+,%$�5HVHDUFK�(XURSH�/LPLWHG ConfidentialConfidential
3rd IEEE Workshop on WLAN, 27 Sept 2001, Newton MA
0 5 10 15 20 25 300
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Eb/No (dB)
Pro
bab
ility
of
succ
ess
swit
chin
g
Interference detection
RSSI-based SW
S: 2path channelI: 2path channel
Successful switching probability is improved at low SIR
Switching success probability using Switching success probability using interference detectioninterference detection--based switchingbased switching
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3rd IEEE Workshop on WLAN, 27 Sept 2001, Newton MA
BER performance comparisonBER performance comparison
0 5 10 15 20 25 3010
-5
10-4
10-3
10-2
10-1
100
Eb/No (dB)
Un
cod
ed B
it E
rro
r R
ate
SIR = 15dB
SIR = 3dB
S: 2path channelI: 2path channel
Switching method based on interference detection can approach the optimum sector switching
17726+,%$�5HVHDUFK�(XURSH�/LPLWHG ConfidentialConfidential
3rd IEEE Workshop on WLAN, 27 Sept 2001, Newton MA
ConclusionsConclusions
• Performance of switched sector array for OFDM system in the environment with multipath interference was shown:
– 10dB SNR improvement over an omni-directional system– Two-fold SIR improvement over an omni-directional system– Successful RSSI-based switching depends on the prevailing
SIR.– Five-fold increase in data rate using the optimum sector
selection– Switching method based on interference detection can
approach the optimum sector switching at low SIR conditions
18726+,%$�5HVHDUFK�(XURSH�/LPLWHG ConfidentialConfidential
3rd IEEE Workshop on WLAN, 27 Sept 2001, Newton MA
Switching success probability using Switching success probability using interference detectioninterference detection--based switchingbased switching
- Successful switching probability is improved at low SINR- Correct switching depends on multipath
Eb/No (dB)
Pro
bab
ility
Eb/No (dB)
Pro
bab
ility
S: 2path channelI: 2path channel
S: ETSI-B channelI: ETSI-B channel
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