1.3.4 Multiplexing And Multiple Access

When a communications channel has sufficient capacity to carry more than one signal, multiplexing techniques may be used to combine multiple information streams into a single composite signal. Multiplexing improves utilization of the physical medium and allows expensive communications infrastructure to be shared efficiently among many services.

For example, a single optical fiber may simultaneously carry thousands of telephone calls, television programs, and Internet connections. Similarly, communication satellites routinely relay traffic from many independent users through a single spacecraft. Without multiplexing, separate communication links would be required for each service, making large-scale communications prohibitively expensive.

Closely related are multiple-access techniques, which allow multiple independent users—often geographically separated—to share a common communications channel. Whereas multiplexing typically combines signals generated at a common point before transmission, multiple access addresses the problem of coordinating transmissions from many separate users who wish to access the same shared resource.

The choice of multiplexing and multiple-access methods strongly influences system capacity, latency, complexity, and cost. These techniques have become increasingly important as the demand for communications continues to grow, allowing millions of users to share limited spectrum and transmission infrastructure efficiently.