758
21 Wireless Local Area Networks
controlled TDD/TDMA scheme, MAC frame (MF) is allowed to simultaneously
communicate via a number of DLC connections in both downlink and uplink
directions. Each MF allocates time slots for broadcast channel (BCH),
frame
channel, access feedback channel (ACH), random channel (RCH), downlink (DL)
phase, uplink (UL) phase and directlink (DiL) phase. Data is grouped as PDU
trains. There are two kinds of PDU, one is long PDU (LCH PDU) of 54
bytes and
another is short PDU (SCH PDU) of 9 bytes. The PDU error ratio refers to the
error rate of LCH PDU.
21.11.2
Multimedia Access Communication — High Speed Wireless
Access Network
Multimedia access communication (MMAC) — high speed
wireless access network
(HiSWAN) — started in Japan in 1996. It uses two frequency bands: 5 GHz for
HiSWANa and 25 GHz for HiSWANb. The HiSWAN uses the 5 GHz license-free
frequency band and is closely aligned with the HIPERLAN/2. HiSWAN uses the
OFDM physical layer to provide a standard speed of 27 Mbps and 6 to 36 Mbps
by link adaptation. However, MMAC-HiSWANa differs from the HIPERLAN/2
in radio network functions due to the differences in
regional frequency planning
and regulations. Instead of dynamic frequency selection in HIPERLAN/2, carrier
sense functions of access points are mandatory in MMAC-HiSWANa. Also, inter-
access point synchronizations are specifi ed to avoid
interference among access
points and to use four available channels in Japan for wide coverage. Table 21.16
summaries various WLANs.
Example 21.5
Consider the HIPERLAN/2 that uses BPSK and
R
3
/
4
codes for 9 Mbps informa-
tion transmission and 16-QAM with the same coding
for the actual payload data
transmission rate of 36 Mbps. Calculate the coded symbol transmission rate per
subcarrier for each of the two modes. What is the bit transmission rate per subcar-
rier for each of the two modes?
Solution
User data transmission
rate per carrier with
R
3
/
4
convolution encoder
(refer to Table 21.11).
Mode I (9 Mbps)
9
10
6
48
187.5 kbps
Mode II (36 Mbps)
36
10
6
48
750 kbps
Carrier transmission rate with
R
3
/
4
convolutional encoder
Mode I
187.5
(3/4)
250 kbps
•
•
Ch21-P373580.indd 758
5/3/07 10:58:41 PM
Mode II
750
(3/4)
1000 kbps
Carrier
symbol rate
Mode I (BPSK)
250 ksps
Mode II (16-QAM)
1000
4
250 ksps
Example 21.6
What is the user data rate for HIPERLAN/2 with 64-QAM modulation with
R
3
/
4
covolutional coder?
Solution
Carrier symbol rate
250 ksps; bits per symbol for 64-QAM
6
User
data rate
250
3
4
6
48
54 Mbps
