TABLE OF CONTENTS Efficient allocation of signaling dimensions between users is a key design aspect of both uplink and downlink channels, since bandwidth is usually scarce and/or very expensive. When dedicated channels are allocated to users it is often called multiple access. [4] Applications with continuous transmission and delay constraints, such as voice or video, typically require dedicated channels for good performance to ensure their transmission is not interrupted. Dedicated channels are obtained from the system signal space using a channelization method such as time division, frequency division, code division, or some combination of these techniques. Allocation of signaling dimensions for users with bursty transmissions generally use some form of random channel allocation that does not guarantee channel access. Bandwidth sharing using random channel allocation is called random multiple access or simply random access, which will be described in Section 14.3. In general, the choice of whether to use multiple access or random access and which specific multiple or random access technique to apply will depend on the system applications, the traffic characteristics of the users in the system, the performance requirements, and the characteristics of the channel and other interfering systems operating in the same bandwidth.
Multiple access techniques divide up the total signaling dimensions into channels and then assign these channels to different users. The most common methods to divide up the signal space are along the time, frequency, and/or code axes. The different user channels are then created by an orthogonal or nonorthogonal...
