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

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 a
- Data rate of 108 Mbit/s (twice as 54 Mbit/s in IEEE a)

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 a
e.g. clock rate: 20 MHz MHz
B: double sub-carrier numbers
number of sub-carriers is twice as many as that of IEEE a
e.g. 52 sub-carriers sub-carriers
C: 4096 QAM-OFDM
increasing the number of bits in M-ary QAM on each sub-carrier
e.g. 64 QAM 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 , 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

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
Number of
channels
6 channels
(USA)
6 channels
(USA)
12 channels
(USA)
12 channels
(USA)
Number of
sub-carriers 52
104 52 52
symbol length
2 ms
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
Number of
antennas
receiver : 2
(diversity)
receiver : 2
(diversity)
receiver : 2
(diversity)
transmitter : 2
receiver : 2

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) [dBm]
d : cell radius
l : wave length ( = c/f = [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 * [J/K] )
Cr : required CNR to realize PER of 1%

6. 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%
Cell space
Interference area

7. Required CNR PER CNR [dB] A:double clock rate B:double sub-carriers10 -3 -2 -1 15 20 25 30 35 40
CNR [dB]
PER
A:double clock rate
B:double sub-carriers
C: 4096 QAM-OFDM
D: OFDM/SDM
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. Required CIR PER CIR [dB] A:double clock rate C: 4096 QAM-OFDM10 -3 -2 -1 15 20 25 30 35 40
A:double clock rate
B:double sub-carriers
C: 4096 QAM-OFDM
D: OFDM/SDM
CIR [dB]
PER
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 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 a.
- CNR and CIR must be improved significantly.