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Performance Evaluation of WiMAX/IEEE 802.16 OFDM Physical Layer - page 35 / 107

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Multipath components

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Figure 3.4: Cyclic Prefix in OFDM

3.3.4 OFDM SYSTEM DESIGN CONSIDERATIONS

OFDM system design issues aim to decrease the data rate at the subcarriers, hence, the symbol duration increases and as a result, the multipath effects are reduced effectively. The insertion of higher valued CP will bring good results against combating mautipath effects but at the same time it will increase loss of energy. Thus, a tradeoff between these two parameters must be done to obtain a reasonable system design.

3.3.4.1 SYSTEM DESIGN REQUIREMENTS: OFDM system depends on the following four requirements: [23]

Available bandwidth: The bandwidth limit will play a significant role in the selection of number of sub­carriers. Large amount of bandwidth will allow obtaining a large number of subcariers with reasonable CP length. Required bit rate: The system should be able to provide the data rate required for the speci ic purpose. Tolerable delay spread: An user environment specific maximum tolerable delay spread should be known beforehand in determining the CP length.

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