8.2 DETERMINISTIC MULTIPLE ACCESS TECHNIQUES

Deterministic multiple access techniques allocate channel resources in a predefined and controlled manner so that users do not interfere with one another under normal operating conditions. Unlike contention-based methods, which rely on probabilistic access and retransmission after collisions, deterministic techniques partition one or more fundamental dimensions of the communication channel in advance.

As discussed in Section 8.1, electromagnetic communication offers several independent degrees of freedom. Deterministic multiple access exploits these degrees of freedom to separate users in one or more domains:

Frequency: users occupy distinct portions of the available spectrum.
Time: users transmit in non-overlapping intervals.
Code: users share the same time and frequency resources but are distinguished through orthogonal or pseudo-random spreading sequences.
Space: users are separated by antenna directivity, beamforming, sectoring, or spatial multiplexing.

In the first two cases, separation is achieved by preventing overlap in the physical channel. In the latter two, signals may overlap in time and frequency but remain separable at the receiver through correlation or spatial processing.

Deterministic techniques are widely used in terrestrial, satellite, broadcast, and mobile systems because they provide predictable capacity, controlled interference, and support for quality-of-service guarantees. They do, however, require coordination, synchronization, or centralized management to maintain orthogonality among users.

We now examine each of these deterministic techniques in turn, beginning with separation in the frequency domain.