OFDMA_Part38 - n (E28) where p n P max n (E29) and p n 0, n...

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38 4.1.3 Rate Adaptive Approach As mentioned before, the Rate Adaptive (RA) approach focuses on maximizing the sum of user data rates while using a fixed amount of power [26]. In this sub-section, I first define the RA approach using the simple case of a single user. Next, I define the RA approach for the multi- user system described in section 4.1.1. After that, I will survey some algorithms that use this approach. Finally, I will simulate select RA algorithms in MATLAB and verify the results. To understand RA better, consider the simple case of a single-user system. The OFDMA system has N subcarriers and a total bandwidth of B Hz. The goal of RA is to assign power p n to each subcarrier n such that the number of bits transmitted in (1/ T s ) OFDM symbols (the OFDM symbol time is T s and hence 1/ T s OFDM symbols are transmitted per second) is maximized. In other words, we need to solve the following equations [26]: max p n B N log 2 1 + p n h n 2 Γ σ 2
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Unformatted text preview: n (E28) where p n P max n (E29) and p n 0, n (E30) In the above equations, the noise power per subcarrier is given by 2 and h n is the channel gain seen by the user for subcarrier n . is defined as the SNR gap, i.e. the difference between the SNR needed to obtain a certain data rate and the SNR needed to reach the theoretical limit. P max is the maximum power that can be transmitted. Now consider the multi-user cellular system of section 4.1.1 that uses OFDMA for the downlink. For the purpose of this sub-section, the system of Figure 11 employs some RA resource allocation algorithm/approach that will maximize the total data rate while using a fixed amount of power. The employed RA algorithm will also allocate a non-negative power p n for each subcarrier n such that the total power is less than P max [26]: p n 0, n and p n P max n (E31)...
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This note was uploaded on 09/27/2009 for the course ECE 399 taught by Professor Prof during the Spring '09 term at University of Texas at Austin.

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