edVirtus Reference

What Is Demand-Assigned Multiple Access?

What Is DAMA?

Demand-Assigned Multiple Access (DAMA) is a multiple-access technique in which communication resources are allocated dynamically only when a user requests them. Rather than permanently assigning frequencies, time slots, or channels to individual users, a central controller allocates available resources on demand and releases them when the communication session ends. This greatly improves the efficiency of communication systems in which user activity is intermittent.

The basic principle is straightforward. When a user wishes to communicate, a request is sent to a network controller over a signalling or control channel. If sufficient resources are available, the controller assigns a frequency channel, time slot, or other communication resource to the user. Once the transmission is complete, the assigned resource is returned to the common pool, making it immediately available for other users.

A useful analogy is a library study room. Rather than assigning every student a permanently reserved room, the library allocates rooms only when they are requested. When a student finishes, the room becomes available for someone else. DAMA applies the same principle to communication resources, ensuring that they are used only when required.

The principal advantage of DAMA is its high spectrum efficiency. Because communication resources are shared dynamically, a relatively small number of channels can support a much larger number of users than would be possible with Fixed Assigned Multiple Access (FAMA). This is particularly effective for voice and data traffic, where individual users are active only a small proportion of the time.

DAMA has been widely used in satellite communication networks, military communication systems, and private communication networks. In satellite systems, where transponder bandwidth is both limited and expensive, dynamic channel assignment allows many geographically separated Earth stations to share the available satellite capacity efficiently. This significantly reduces operating costs while increasing overall network utilization.

Several forms of DAMA exist. Some systems allocate complete frequency channels on demand, while others assign time slots, codes, or packet resources depending on the underlying multiple-access technique. Modern cellular networks extend the same concept by dynamically allocating radio resources every few milliseconds according to user demand, although they generally do not use the term DAMA explicitly.

The principal disadvantage of DAMA is its greater complexity. A signalling mechanism and network controller are required to process requests, allocate resources, and manage the shared communication pool. During periods of heavy demand, users may experience brief delays while waiting for resources to become available.

It is important to distinguish Demand-Assigned Multiple Access (DAMA) from Fixed Assigned Multiple Access (FAMA). In FAMA, communication resources are permanently assigned regardless of whether they are being used. In DAMA, resources are assigned only for the duration of the communication and are then released for use by others. As a result, DAMA generally achieves much higher resource utilization, particularly in networks where traffic is bursty or unpredictable.

Today, the principles of demand-assigned multiple access are used throughout modern communications. Satellite networks, cellular systems, broadband wireless networks, and packet-switched communication systems all allocate resources dynamically in response to user demand. Although the specific implementation varies between technologies, the underlying concept of assigning communication resources only when they are needed remains one of the key techniques for maximizing network capacity and spectrum efficiency.