doc.: ieee 802.11-02/180r0 submission march 2002 monisha ghosh, et al., philips slide 1 on the use...
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March 2002
Monisha Ghosh, et al., PhilipsSlide 1
doc.: IEEE 802.11-02/180r0
Submission
On The Use Of Multiple Antennae On The Use Of Multiple Antennae For 802.11For 802.11
Monisha Ghosh, Xuemei Ouyang, Guido Dolmans
Philips Research.
March 2002
Monisha Ghosh, et al., PhilipsSlide 2
doc.: IEEE 802.11-02/180r0
Submission
Goal Of Next Generation WLANS?Goal Of Next Generation WLANS?
• Increased robustness. (-> fewer errors -> less retransmission -> higher throughput)
• Increased data rate in terms of raw Mbps.
• Backward compatibility through headers.
March 2002
Monisha Ghosh, et al., PhilipsSlide 3
doc.: IEEE 802.11-02/180r0
Submission
Exploiting Channel DiversityExploiting Channel Diversity
• Frequency diversity: Bit interleaved coded modulation.
• Space diversity: Multiple antennae.• Question: In an indoor situation, is there
sufficient diversity among closely spaced antennae?
• Answer: Preliminary measurements in 5 gHz indicate that there is.
March 2002
Monisha Ghosh, et al., PhilipsSlide 4
doc.: IEEE 802.11-02/180r0
Submission
Channel Measurements At 5gHzChannel Measurements At 5gHz
March 2002
Monisha Ghosh, et al., PhilipsSlide 5
doc.: IEEE 802.11-02/180r0
Submission
Multiple AntennaeMultiple Antennae• Well studied topic for the last few years.• OFDM is very well suited for use with
multiple antennae. (802.16 has an optional mode using multiple antennae.)
• Many (all?) 802.11 receivers already have 2 antennae, using switched diversity.
• Additional component required for exploiting full diversity is an additional RF front-end.
• Recent advances in RF technology will make this cost effective in the near future.
March 2002
Monisha Ghosh, et al., PhilipsSlide 6
doc.: IEEE 802.11-02/180r0
Submission
Higher (> 100 Mbps) Data Rate Higher (> 100 Mbps) Data Rate Options For 802.11Options For 802.11
• Larger Constellation: 54Mbps already uses 64 QAM. Can a wireless system support a larger constellation?
• Turbo-coding: Requires at least 3 or 4 iterations for good performance.
• Double bandwidth: Inefficient use of bandwidth.
• Multiple antenna: Cost is in the additional antenna and RF front end, the DSP does not add much complexity to existing receivers.
March 2002
Monisha Ghosh, et al., PhilipsSlide 7
doc.: IEEE 802.11-02/180r0
Submission
Possible Configurations For 2x2 systemPossible Configurations For 2x2 system
• 1 Tx/2 Rx: same data rate, increased robustness, backward compatible.
• 2 Tx/1 Rx, space-time coded (e.g. Alamouti): same data rate, increased robustness, backward compatiblity through header.
• 2 Tx/2Rx, space-time coded: same data rate, increased robustness, backward compatibility through header.
• 2 Tx/2 Rx, MIMO: Increased data rate and robustness.
March 2002
Monisha Ghosh, et al., PhilipsSlide 8
doc.: IEEE 802.11-02/180r0
Submission
1 Tx, 2 Rx System Performance1 Tx, 2 Rx System Performance
March 2002
Monisha Ghosh, et al., PhilipsSlide 9
doc.: IEEE 802.11-02/180r0
Submission
2 Tx, 1 Rx System Performance2 Tx, 1 Rx System Performance
March 2002
Monisha Ghosh, et al., PhilipsSlide 10
doc.: IEEE 802.11-02/180r0
Submission
2 Antennae At AP 2 Antennae At AP
March 2002
Monisha Ghosh, et al., PhilipsSlide 11
doc.: IEEE 802.11-02/180r0
Submission
2 Tx/2 Rx MIMO Performance2 Tx/2 Rx MIMO Performance
March 2002
Monisha Ghosh, et al., PhilipsSlide 12
doc.: IEEE 802.11-02/180r0
Submission
2 Antennae At AP, 1 Antenna At 2 Antennae At AP, 1 Antenna At MobileMobile
•Use transmit diversity from AP to mobile: would require a change to allow for Alamouti encoding. Gives 2 to 4 dB gain over 1 Tx/1 Rx.
•Use receive diversity for mobile to AP. Gives 4 to 6 dB over 1 Tx/1 Rx.
•Simple way to increase robustness for all mobiles by the addition of a single extra antenna and RF unit at the AP.
March 2002
Monisha Ghosh, et al., PhilipsSlide 13
doc.: IEEE 802.11-02/180r0
Submission
ConclusionsConclusions
• A simple 2 x 2 antennae system can improve both robustness and bit-rate.
• Various options possible, depending on level of complexity desired.
• Backward compatibility easily maintained through header.