Smart Antennas

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Smart Antennas

  1. 1. doc.: IEEE 802.11-00/269 Submissio n Performance of Smart AntennasPerformance of Smart Antennas and PCFand PCF Vinayak NandikalVinayak Nandikal Courtesy: Nokia Research CenterCourtesy: Nokia Research Center
  2. 2. March 31, 2015 Vinayak NandikalSlid doc.: IEEE 802.11-00/269 Submissio n Introduction • IEEE802.11 will be an important method for providing high rate low mobility data services • While existing capacity may seem high, particularly for IEEE802.11a, the enterprise environment may experience capacity limits • Antenna technologies offer a means to boast IEEE802.11 capacity without changing the existing PHYs
  3. 3. March 31, 2015 Vinayak NandikalSlid doc.: IEEE 802.11-00/269 Submissio n What is a SMART Antenna? AP G S WG S W P D E G S WG S W G S WG S W G S WG S W D X 2 0 0 STA STA Antenna that adjusts its beam pattern based upon the channel and interference between AP and STA
  4. 4. March 31, 2015 Vinayak NandikalSlid doc.: IEEE 802.11-00/269 Submissio n Approach to Model Performance • Measure channel using a channel sounder to determine – Multipath power profile as a function of time – Signal-to-interference ratio • Simulate PHY to obtain PER information as a function of channel measurements and the number of packets delivered as a function of time • Use PER, number of packets delivered by the PHY as a function of time and models of real-time traffic to examine delay and throughput using a PHY with and without smart antennas • PCF is used for delivery of audio and video packets
  5. 5. March 31, 2015 Vinayak NandikalSlid doc.: IEEE 802.11-00/269 Submissio n PHY Simulation Parameters DOCUMENTTYPE 1 (1) TypeUnitOrDepartmentHere TypeYourNameHere TypeDateHere Parameter Value Data Rate 12 Mbps/channel Packet LossRate 10-2 Channel Model experimental Number of Antenna Elements 4 Adjacent BSSInterference Level varying Center Frequency 5.3 GHz
  6. 6. March 31, 2015 Vinayak NandikalSlid doc.: IEEE 802.11-00/269 Submissio n PHY Channel Sounder Approach • 127 chip pn sequence is transmitted at 5.3 GHz with a bandpass bandwidth of 30 MHz • A 32 element array with 0.5 wavelength space is used to downconvert the transmitted pn sequence • Snap shots of the delay spread are written to memory and stored on a hard disk For further information see: Jarmo Kivinen, Timo O. Korhonen, Pauli Aikio, Ralf Gruber, Pertti Vainikainen, and Sven-Gustav Häggman, IEEE Transactions on Instrumentation and Measurement, vol. 48, no. 1, pp. 39-44, 1999.
  7. 7. March 31, 2015 Vinayak NandikalSlid doc.: IEEE 802.11-00/269 Submissio n Smart Antenna Operation (5GHz) RF A/D FFT RF A/D FFT RF A/D FFT AntennaCombining Weight Calculation [ ] [ ] [ ]pkxkwpky n N n n ,, 1 * ∑= = Decoding [ ]pkx ,1 [ ]pkx ,2 [ ]pkxN , [ ]kw STA [ ]kH1 [ ]kH2 [ ]kHN [ ]kc STA [ ]kH1 [ ]kH2 [ ]kHN OFDM Symbol IndexSubcarrier D/A RF D/A RF D/A RF IFFT IFFT IFFT AntennaWeighting Coding & Modulation [ ]kH1 [ ]kH2 [ ]kHN STA STA Uplink Operation Downlink Operation
  8. 8. March 31, 2015 Vinayak NandikalSlid doc.: IEEE 802.11-00/269 Submissio n Channel Correlation • The figure to the right shows the correlation coefficient for different measurement environments • For smart antenna operation, the AP needs the ability to probe the channel between any STA and AP 0 50 100 150 200 250 300 350 400 450 0.93 0.94 0.95 0.96 0.97 0.98 0.99 1 time [ms] amplitudecorrelationcoefficient average over TX positions Ruoholahti Heikkilä ntie Airport Airport 2 Note: Ruholahti and Heikkiläntie are Nokia office buildings
  9. 9. March 31, 2015 Vinayak NandikalSlid doc.: IEEE 802.11-00/269 Submissio n MAC Simulation Parameters DOCUMENTTYPE 1 (1) TypeUnitOrDepartmentHere TypeYourNameHere TypeDateHere Parameter Value Speech Packet Size 640 bits Video Packet Size 3.8 kb CFP 1.5 ms Packet Buffer Lifetime Audio: 5 ms Video: 100 ms CFPRepetition Interval 3 ms Average # of Speech STAs 10/30 users Average# of Video STAs 10/30 users
  10. 10. March 31, 2015 Vinayak NandikalSlid doc.: IEEE 802.11-00/269 Submissio n Traffic Model: • All traffic measured in data-units/slot-time – 1 data-unit takes 1 slot-time for transmission – Max traffic in network = 1.0 • Audio and video traffic originates from “calls” made by the user • Calls are Poisson distributed; once placed, each call generates periodic packet traffic • Mean inter-call-arrival-time controls load on the network
  11. 11. March 31, 2015 Vinayak NandikalSlid doc.: IEEE 802.11-00/269 Submissio n Traffic Model (cont.): • Real-time traffic load =       + + + vcallsacalls vcalls x timearvlvpkt szvpkt vcallsacalls acalls x timearvlapkt szapkt X timearvlcall durncall ___ _ ___ _ ___ _ intint int apkt_sz: audio packet size vpkt_sz: video packet size int_call_arvl_time: mean intercall arrival time (8:1 ratio between audio and video calls) int_apkt_arvl_time, int_vpkt_arvl_time: arrival time between audio packets and video packets respectively acalls, vcalls: number of audio anc video calls respectively
  12. 12. March 31, 2015 Vinayak NandikalSlid doc.: IEEE 802.11-00/269 Submissio n Throughput & Latency Curves: Audio Packets Packets/Seconds Packets/Second NormalizedThrougput PCFLatencies 0 0.5 1 1.5 2 2.5 x 10 4 10 -4 10 -3 10 -2 10 -1 No SDMA 3-channel SDMA DCF:PCF = 1:1 Audio Packets 0 0.5 1 1.5 2 2.5 x 10 4 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 No SDMA 3-channel SDMA DCF:PCF = 1:1 Audio Packets
  13. 13. March 31, 2015 Vinayak NandikalSlid doc.: IEEE 802.11-00/269 Submissio n Throughput & Latency Curves: Audio Packets Packets/Seconds Packets/Second NormalizedThroughput PCFLatencies 0 1 2 3 4 x 10 4 10 -4 10 -3 10 -2 10 -1 No SDMA 3-channel SDMA DCF:PCF = 1:3 Audio Packets 0 0.5 1 1.5 2 2.5 3 3.5 4 x 10 4 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 No SDMA 3-channel SDMA DCF:PCF = 1:3 Aduio Packets
  14. 14. March 31, 2015 Vinayak NandikalSlid doc.: IEEE 802.11-00/269 Submissio n Throughput & Latency Curves: Video Packets Packets/Seconds Packets/Second NormalizedThroughput PCFLatencies 0 100 200 300 400 500 10 -4 10 -3 10 -2 10 -1 No SDMA 3-channel SDMA DCF:PCF = 1:1 Video Packets 0 100 200 300 400 500 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 No SDMA 3-channel SDMA DCF:PCF = 1:1 Video Packets
  15. 15. March 31, 2015 Vinayak NandikalSlid doc.: IEEE 802.11-00/269 Submissio n Throughput & Latency Curves: Video Packets Packets/Seconds Packets/Second NormalizedThroughput PCFLatencies 0 200 400 600 800 10 -4 10 -3 10 -2 10 -1 No SDMA 3-channel SDMA DCF:PCF = 1:3 Video Packets 0 100 200 300 400 500 600 700 800 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 No SDMA 3-channel SDMA DCF:PCF = 1:3 Video Packets
  16. 16. March 31, 2015 Vinayak NandikalSlid doc.: IEEE 802.11-00/269 Submissio n New Control Frame Subtypes for Smart Antennas • AP to STA – A message requesting the STA to transmit a preamble (null frame) for channel estimation – Channel Id Request • STA to AP – A response to the above request – Channel Id Response Duration RA TA FCS Message Fields Frame Control
  17. 17. March 31, 2015 Vinayak NandikalSlid doc.: IEEE 802.11-00/269 Submissio n Remove Polling Dependence • The existing standards reads, "During each CFP, the PC shall issue polls to a subset of the STAs on the polling list in order by ascending AID value".
  18. 18. March 31, 2015 Vinayak NandikalSlid doc.: IEEE 802.11-00/269 Submissio n Conclusions • Particularly in a large enterprise environment, smart antennas can help boast capacity – Wireless office replacement for "wired" Ethernet – Public service networks such as airports • Changes to the existing MAC are minor to enable antenna technologies in IEEE802.11a networks • SDMA is not for all WLANS – Multiple antennas cost additional money for the AP that may not be required in homes and small businesses

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