OFDMA_Part4 - than the delay spread of the wireless...

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4 Figure 1. Illustration of Multiple User Access in OFDMA This report first discusses the theory of OFDM to prepare all readers of this report for the subsequent sections. Next, basics of radio resource allocation are presented followed by a detailed discussion of resource allocation in OFDMA systems. Finally, the conclusions are described followed by the references. 2.0 THEORY OF OFDM As the world of wireless communication grows, people are finding newer things to do on their wireless devices. Today, one can even watch live television on one’s smartphone. To make such heavy applications possible, the data rate must be increased and hence the symbol time must reduced. However, wireless channels suffer from multipath fading and hence have a delay spread. To mitigate the effect of Inter-Symbol-Interference (ISI), the symbol time must be larger
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Unformatted text preview: than the delay spread of the wireless channel. The data rate is limited by this restriction for single-carrier Time-Division Multiple Access (TDMA) systems. In [1] Claude Shannon suggested that the highest data rate can be achieved for frequency selective channels by using a multicarrier system with an infinitely dense set of subcarriers and adapting transmission powers and data rates according to the signal-to-noise ration (SNR) at different subcarriers. In general, multicarrier modulation schemes divide the available bandwidth into many subcarriers and transmit multiple data streams in parallel over them. Orthogonal Frequency Division Multiplexing (OFDM) is a type of multicarrier transmission that divides the entire channel into many narrow band subcarriers. These subcarriers are transmitted in parallel...
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