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OFDMA_Part25 - different users based on the channel gains...

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25 the multi-user system shown in Figure 11. The wireless system shown in Figure 11 is a cellular system that uses OFDMA for the downlink and consists of one base-station and K users. This system employs either an MA or an RA resource allocation algorithm that will optimize the relevant system metric. Furthermore, this system uses B Hz of bandwidth, N subcarriers and possibly different modulation schemes for each subcarrier. Figure 11. Single-Cell Multi-User Cellular System With OFDMA Downlink In a wireless communication channel, each user experiences different channel gains on different subcarriers. At any given time, let h k,n denote the channel gain as perceived by user k on subcarrier n . The resource allocation algorithm employed will assign the available subcarriers to
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Unformatted text preview: different users based on the channel gains they perceive at any given time. Let c k,n represent the corresponding element of a K by N matrix of indicator variables. c k,n is 1 if subcarrier n is assigned to user k and 0 otherwise. [26] proved that the total data rate of the multi-user OFDMA system is maximized when a subcarrier is allocated to exactly one user during a given OFDM symbol period. To ensure that each subcarrier is allocated to exactly one user at a given time, c k,n is subject to the following constraints: c m , n = 1, ∀ n ∀ m ∑ and c m , n = N ∀ n ∑ ∀ m ∑ …(E15) Now that I have described the setup for the multi-user scenario, let us move onto the detailed discussion of MA and RA approaches....
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