May 2002
doc.: IEEE 802.11-02/320r0
¼ Giga-Bit/s WLAN
Gerhard Fettweis
Gunnar Nitsche
Systemonic AG
Submission
Slide 1
Gerhard Fettweis, Systemonic AG
May 2002
doc.: IEEE 802.11-02/320r0
Historically Based Projection
802.11new: ¼ Gb/s
5x
802.11a: 54Mb/s
100Mb/s
5x
802.11b: 11Mb/s
5x
802.11: 2Mb/s
Submission
Slide 2
Gerhard Fettweis, Systemonic AG
May 2002
doc.: IEEE 802.11-02/320r0
Increasing Data Rate by Doubling the
Bandwidth
D0 D4 D5 D17 D18 D23 D24 D29 D30 D42 D43 D47
P0
P1
DC
P2
P3
-26 -21
-7
0
7
21
D0 D4 D5 D17 D18 D23 D24 D29 D30 D42 D43 D47
26
P0
P1
DC
P2
P3
-26 -21
-7
0
7
21
D107
D0
P0
-58
26
P1
P2
P3
DC
P4
P5
P6
P7
0
58
• By doubling bandwidth data rate can be increased by a
factor 108/48=2.25
Submission
Slide 3
Gerhard Fettweis, Systemonic AG
May 2002
doc.: IEEE 802.11-02/320r0
MIMO Systems
Vector system
Traditional scalar
system
P watts
Tx Data
Total transmit power P
Estimate
and
decode
Tx Data
Rx Data
Each Rx SNR= S
a1
a2
P/2 watts
Estimate
and
decode
Rx Data
P/2 watts
Total transmit power P
Each Rx SNR= S/2
Bandwidth = 1/T=W
(All transmitters operate co-channel)
Cscalar  W log 2  2S 
 W log 2 S  W log 2 2
Scalar system capacity: Ignore
fading statistics, account only for
antenna gain
Submission
Vector
encode:
DEMUX
data into
QAM
symbols
Cvector  2W log 2 (S )
Idealized vector case: Assume
signals from each transmitter
can be separately detected
without penalty
Slide 4
Gerhard Fettweis, Systemonic AG
May 2002
doc.: IEEE 802.11-02/320r0
Use of Higher Order Modulations
• To attain bandwidth efficiencies it is
necessary to couple coding with
symbols from higher order
modulation
• If higher modulation orders are used
the phase difference between the
constellation points gets smaller
• Phase noise introduced would cause
an error in interpreting the
constellation point
• Degradation in the signal to noise
ratio occurs
• By allowing the use of 256 QAM
data rate is increased by a factor 8/6
Submission
Slide 5
Gerhard Fettweis, Systemonic AG
May 2002
doc.: IEEE 802.11-02/320r0
Using Transmit Diversity to Increase
Diversity
• Employ coding techniques appropriate to multiple transmit
antennas
• Space Time Codes introduce temporal and spatial correlation into
signals transmitted from different antennas
• They provide diversity at the receiver and coding gain over an
uncoded system without sacrificing bandwidth
• Obtained diversity can compensate for the loss caused by phase
noise
Submission
Slide 6
Gerhard Fettweis, Systemonic AG
May 2002
doc.: IEEE 802.11-02/320r0
Increasing Capacity Using Multiple Antennas
and STC (Space Time Coding)
c1
a1
Encoder
&
Input data DEMUX
a2
Space
Time
Coding
c2
Increase Increase Diversity
data rate
using STC
#layers
P/2 watt
P/2 watt
Estimate
&
Decode Rx Data
Each Rx SNR=S/2
Clayered  2W log 2 ( S )  2Csingle antenna
• The effective transmission rate is increased roughly in proportion to a
number of min(#Tx antennas, #Rx antennas)
Submission
Slide 7
Gerhard Fettweis, Systemonic AG
May 2002
doc.: IEEE 802.11-02/320r0
Resulting Data Rate
• Increased bandwidth factor: 2.25
• Vector (layered) system factor: <2 (take  1.5)
• Higher order modulation factor: 8/6 (by using 256-QAM)
Using these parameters ¼ Gb/s rate is achievable
Submission
Slide 8
Gerhard Fettweis, Systemonic AG