In a cellular system, many Mobile stations communicate with the Base Station simultaneously. Resources such as frequency and time have to be shared among them so that each one gets a chance to communicate. Optimum and effective utilization of these resources is a challenging task. Hence the need of multiple access techniques arises. Multiple access schemes are used to allow many users simultaneously to communicate to a single transreceiver. To do this, the users share the same spectrum. Many might get confused with terms Multiple Access techniques and Multiplexing. The explanation is given after the first type of access technique is discussed. Depending on the methodology used to share the spectrum, multiple access techniques are classified as follows:

• Frequency Division Multiple Access (FDMA)
• Time Division Multiple Access (TDMA)
• Code Division Multiple Access (CDMA)
• Space Division Multiple Access (SDMA)
• Orthogonal Frequency Division Multiple Access ( OFDMA)