System capacity and cell radius comparison with several high data rate WLANs

1. System capacity and cell radius comparison with several high data rate WLANs Satoru Hori, Yasuhiko Inoue, Tetsu Sakata, Masahiro Morikura NTT hori@ansl.ntt.co.jp

2. Approach to 100 Mbps WLAN PHY Layer Requirements for Next Generation WLAN - Data rate above 100 Mbps - Enough cell radius - Large system capacity Comparison between several candidates - Extension of IEEE 802.11a - Data rate of 108 Mbit/s (twice as 54 Mbit/s in IEEE 802.11a)

3. Four candidates extending IEEE 802.11 a A: double clock rate clock rate of the system is twice as fast as that of IEEE 802.11 a e.g. clock rate: 20 MHz 40 MHz B: double sub-carrier numbers number of sub-carriers is twice as many as that of IEEE 802.11 a e.g. 52 sub-carriers 104 sub-carriers C: 4096 QAM-OFDM increasing the number of bits in M-ary QAM on each sub-carrier e.g. 64 QAM 4096 QAM D: OFDM/SDM (multi-carrier MIMO) system using multiple transmit and receive antennas each antenna transmit different data to increase transmit data rate e.g. 2 transmit antennas and 2 receive antennas Reference A. van Zelst, R. van Nee, and G. A. Awater, “Space Division Multiplexing (SDM) for OFDM systems,” Proc. IEEE VTC2000-spring, vol. 2, pp.1070-1074, May 2000. P.Vandenameele, L. V. D.Perre, M. G. E.engels, B. Gyselinckx, and H. J. D. Man, “A Combined OFDM/SDMA Approach,” IEEE J. Sel. Areas in Commun., vol. 18, no. 11, Nov. 2000.

4. Parameters of each system A: double clock rate B: double sub-carriers C: 4096 QAM- OFDM D: OFDM/ SDM Data rate 108 Mbit/s 108 Mbit/s 108 Mbit/s 108 Mbit/s Band width 33.1 MHz 33.1 MHz 16.6 MHz 16.6 MHz 6 channels (USA) 6 channels (USA) 12 channels (USA) 12 channels (USA) Number of channels 52 104 52 52 Number of sub-carriers 2 ms symbol length 4 ms 4 ms 4 ms GI length 400 ns 800 ns 800 ns 800 ns Mod. scheme 64 QAM 64 QAM 4096 QAM 64 QAM receiver : 2 (diversity) receiver : 2 (diversity) transmitter : 2 receiver : 2 Number of antennas receiver : 2 (diversity)

5. Cell Radius Calculation d = (l / 4p) 10(Lp /10 a) [m] Lp = Pt + Gt + Gr - Pr [dB] Pr = Np + Cr + Df [dBm] Np = Nf + 10log10(kBwT) + 30 [dBm] d : cell radius l : wave length ( = c/f = 0.0576923 [m] for 5.2GHz ) a : propagation loss coefficient Lp : allowed propagation loss Pt , Pr : transmit power and required received power, respectively Gt, Gr : the gain of transmit antenna and receive antenna, respectively (was assumed to be 0 dBi) Np : noise power Nf : noise figure of the receiver (was assumed to be 7 dB) Df : degradation due to various factors (was assumed to be 6 dB) Bw : bandwidth of signals T : temperature (was assumed to be 300 K) k : Boltzman coefficient (= 1.38 * 10-23 [J/K] ) Cr : required CNR to realize PER of 1%

6. Cell space Interference area System Capacity Calculation Th=(R * h * Nch)/C=3sqrt(3) * Nch * R * h/(2p * 102CIR/10a) Th : Maximum throughput R : data rate of PHY layer ( = 108 Mbit/s) h : MAC efficiency for throughput (was assumed to be 1.0) Nch : Number of channels ( = 12 for 20MHz band width and 6 for 40MHz band width ) (Lower, Middle and Upper UNII bands) C : Cluster size ( = Interference area / Cell space ) CIR : Required CIR to achieve PER of 1%

7. 0 10 B:double sub-carriers C: 4096 QAM-OFDM -1 10 D: OFDM/SDM PER -2 10 A:double clock rate -3 10 15 20 25 30 35 40 CNR [dB] Required CNR Data rate 108 Mbit/s Packet size 64 byte Exponentially decaying Rayleigh fading (delay spread 100 ns) No space correlation Ideal synchronization Ideal channel estimation FEC coding rate = 3/4 constraint length = 7 5 bit soft-decision diversity (A, B, C) Maximum ratio combining

8. 0 10 A:double clock rate C: 4096 QAM-OFDM -1 10 PER -2 10 D: OFDM/SDM B:double sub-carriers -3 10 15 20 25 30 35 40 CIR [dB] Required CIR Data rate 108 Mbit/s Packet size 64 byte Exponentially decaying Rayleigh fading (delay spread 100 ns) No space correlation Ideal synchronization Ideal channel estimation FEC coding rate = 3/4 constraint length = 7 5 bit soft-decision diversity (A, B, C) Maximum ratio combining

9. Performance Comparison A: double clock rate B: double sub-carriers C: 4096 QAM- OFDM D: OFDM / SDM Required CNR 19.5 dB 18.8 dB 36.1 dB 29.2 dB Transmit power 13 dBm 13 dBm 13 dBm 13 dBm Propagation loss coefficient a 3.1 3.1 3.1 3.1 11.4 m 12.0 m 4.1 m 6.9 m Cell radius Required CIR 20.3 dB 20.0 dB 37.2 dB 29.8 dB Cluster size 24.7 23.6 303.7 101.2 System capacity 26.4 Mbit/s 27.6 Mbit/s 4.2 Mbit/s 12.9 Mbit/s

10. Conclusion Systems with 40 MHz band width (A and B) - CNR and CIR are pragmatic. - Total number of channels is one half of that of IEEE 802.11 a. e.g. 6 channels in USA, only 2 channels in Japan Systems with 20 MHz band width (C and D) - Total number of channels is same as that of IEEE 802.11 a. - CNR and CIR must be improved significantly.