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System capacity and cell radius comparison with several high data rate WLANs. Satoru Hori, Yasuhiko Inoue, Tetsu Sakata, Masahiro Morikura NTT [email protected] Approach to 100 Mbps WLAN. PHY Layer Requirements for Next Generation WLAN - Data rate above 100 Mbps - Enough cell radius

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

Satoru Hori, Yasuhiko Inoue, Tetsu Sakata, Masahiro Morikura

NTT

[email protected]


Approach to 100 Mbps WLAN data rate WLANs

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)


Four candidates extending IEEE 802.11 a data rate WLANs

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.


Parameters of each system data rate WLANs

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)


Cell Radius Calculation data rate WLANs

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%


Cell space data rate WLANs

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%


0 data rate WLANs

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


0 data rate WLANs

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


Performance Comparison data rate WLANs

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


Conclusion data rate WLANs

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.


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