Wireless Future - Telenor

throughput bit/s
3
2.5
2
1.5
1
0.5
x 10 7
0
0
1) the gradient of the L UPT is 1 / 10 compared to
the first scenario (5/k and 0.5/n, respectively).
In addition the gradient of L BPT (in the second
scenario) is considerably smaller than the L DPT
in the first scenario. The overall result is that the
throughput for mode 1 decreases more slowly
with the number of connections than with the
number of MTs. For mode 2 and 3 the gradient
of L UPT and L DPT is smaller in the second scenario,
but is offset by a larger increase in the gradient
for the L BPT . The result is that the overall
throughput of the first and second scenario is
similar.
The throughputs of mode 1, 2 and 3 for different
numbers of MTs and active connections are
shown in Figure 9, Figure 10 and Figure 11,
respectively. Mode 1 gives a maximum throughput
of nearly 28 Mbit/s (k = 1, MT = 1), and the
throughput is inverse proportional with the number
of MTs and the number of connections.
From Figure 9 it can be seen that when the number
of MTs exceeds 30 (k > 30) and the number
of connections exceeds 16 (n > 16), the size of
the overhead exceeds or equals the number of
available OFDM symbols, resulting in zero
throughput. For mode 2 (see Figure 10) the
maximum throughput is similar to mode 1
(~28 Mbit/s), but the number of terminals and
connections that can be supported is considerably
smaller than for mode 1. For instance, the
overhead exceeds or equals the number of available
OFDM symbols at k = 40, n = 2 or k = 5, n
Telektronikk 1.2001
10
20
no. of MTs
30
mode 3
40
0
5
10
no. of connections
= 20. For mode 3 (see Figure 11), the region for
zero throughput is similar to mode 2. The maximum
throughput (~4.6 Mbit/s) for mode 3 is
however significantly lower than that of mode 2.
These examples clearly illustrate that N DBPS(FCH) ,
N DBPS(SCH) together with k and n determine the
overhead size (and thereby the number of terminals
and connections that can be supported),
whereas N DBPS(LCH) determines the throughput
for a given overhead size.
Consider an AP serving 10 terminals with two
active connections each. For PHY mode 6 (Figure
9) the MAC throughput will be 26.9 Mbit/s,
or a MAC efficiency of 75 %. In a worst case
scenario, for PHY mode 1 (Figure 11) the MAC
throughput will be 3.2 Mbit/s or a MAC efficiency
of 53 %. This illustrates that the throughput
of the HIPERLAN/2 will be high, even for
poor radio conditions.
In this section the throughput (or the overhead)
of the MAC protocol has been investigated for
a number of settings. It has been shown that the
number of MTs and active connections, as well
as the PHY mode used on the different PDU
trains influence the throughput. Using robust
PHY modes will reduce the throughput but will
be essential for operation in harsh radio conditions.
It has been shown that the PHY modes
used in FSC and SCH determine the number of
terminals and connections that can be supported.
15
20
Figure 11 Throughput for mode 3
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