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26
4.1.2 Margin Adaptive Approach
As mentioned before, MA usually focuses on minimizing the total transmission power while
requiring a minimum user data rate [28]. In general terms, MA minimizes the total transmit
power while maintaining a minimum quality of service (QoS) for each user. The QoS
requirements can be data rate, bit error rate, jitter and delay. In this subsection, I first define the
MA approach using the simple case of a single user. Next, I define the MA approach for the
multiuser system described in section 4.1.1. After that, I will survey some algorithms that use
this approach. Finally, I will simulate a few MA algorithms in MATLAB and verify the results.
To understand MA better, consider the simple case of a singleuser system. The OFDMA system
has
N
subcarriers and a total bandwidth of
B
Hz. The goal of MA is to assign the minimum
possible power
p
n
(where
n
is an integer ranging from 1 to N) to each subcarrier
n
such that the
number of bits transmitted in (1/
T
s
) OFDM symbols (OFDM symbol time is
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 Spring '09
 Prof

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