Multiple Access

Multiple access in satellite communications refers to the techniques that allow multiple users or nodes to share a common transmission medium, such as a satellite transponder, in an orderly and efficient manner. Multiple-access schemes define how available radio-frequency resources are divided so that many terminals can transmit and receive signals without unacceptable mutual interference.

Common multiple-access techniques used in satellite communications include frequency-division multiple access (FDMA), time-division multiple access (TDMA), code-division multiple access (CDMA), and hybrid schemes such as FDMA/TDMA and FDMA/CDMA. Each technique differs in how spectrum, time, or coding resources are allocated among users.

Multiple-access schemes may be implemented using either fixed or dynamic resource allocation. In fixed-assigned multiple access (also known as pre-assigned multiple access), capacity is permanently allocated to specific users or terminals. In demand-assigned multiple access (DAMA), capacity is assigned dynamically based on user demand, allowing more efficient utilization of satellite resources when traffic is variable.