762
21 Wireless Local Area Networks
(PER)
asyn
1
(
P
s
UR
)
N
(
P
s
)
M
(21.7)
21.12.3 Aggregated
Throughput
The aggregated throughput of successfully transmitted
packets in all piconets can
be
expressed as
S
a
(
n
)
nP
s
(
n
,
m
), where
n
is the
number of Bluetooth piconets,
m
is the number of IEEE 802.11 WLANs, and
P
s
(
n,m
)
is the probability that a
Bluetooth packet is free from other piconets and 802.11 network collisions. The
aggregate throughput for different cases are given in Table 21.17.
Example 21.7
Determine the collision probability of 1000 bytes IEEE 802.11
frequency hop-
ping (FH) packet at 2 Mbps and Bluetooth. Assume a dwell period of an 802.11
transmission to be 3 ms. What is the PER with an IEEE 802.11 direct spread (DS)
packet? Duration
of Bluetooth packet
0.625 ms.
Solution
T
w
1000
8
2
10
6
4 ms
\
H
L
]
\
0.625
3
]
1
G
3
4
0.625
1.625 ms
|G|
1.625 ms
(PER)
FH
1
1
1.625
3
78
79
1.625
3
78
79
1
1
0.0195
2%
(PER)
DS
1
1
1.625
3
57
79
1.625
3
57
79
2
0.3873
38.73%
Note the collision probability with 802.11
DS is much higher than with
802.11 FH.
