OFDM Baseband Receiver Design for Wireless Communications

3

Multiple Access and Error-Correcting Codes

Multiple access schemes enable resource sharing of a communication link among many users. Error correction codes apply some redundant information in the transmitted signal so that errors/erasures incurred during transmission can be identified and even corrected. Both of them are essential for the success and widespread acceptance of digital communication systems.

3.1 Multiple Access

In a wireless communication system, the number of users is usually large, and their demands must be met through careful distribution of resources. The mechanism of how the communication needs of these users are fulfilled is called multiple access. The purpose of multiple access is to allow a number of users to transmit and receive the information that they need through the wireless communication system. There are several possible techniques that can achieve this goal.

3.1.1 Frequency-Division Multiple Access (FDMA)

Frequency-division multiple access (FDMA) divides the whole spectrum of the wireless communication system into several frequency bands, and allots each band to a user or a group of users. Due to the potential frequency-domain spreading of the transmitted signal through the amplifier and the wireless channel, the signal inside a frequency band may spread to adjacent bands. To remedy this situation, a guard band is introduced between two adjacent frequency bands in the FDMA system. As shown in Figure 3.1, such an arrangement can mitigate interference ...