RAC (radio admission control)

Radio Admission Control (RAC) is a crucial component in wireless communication systems, particularly in cellular networks, that manages the admission of new users or connections into the network. It is responsible for allocating and controlling the available radio resources to ensure efficient and reliable communication while maintaining quality of service (QoS) requirements.

The primary objective of RAC is to make efficient use of the limited radio spectrum and network resources by determining whether a new connection request can be accepted or denied based on various factors. These factors include available network capacity, signal quality, system load, user priority, and QoS requirements.

The RAC process typically involves the following steps:

1. Connection Request: When a new user or device wants to establish a connection with the cellular network, it sends a connection request to the base station (eNodeB in LTE or gNB in 5G) or the access point. The connection request includes information such as user identity, requested QoS parameters, and other relevant data.
2. Resource Assessment: Upon receiving the connection request, the RAC algorithm assesses the availability of radio resources needed to accommodate the new connection. It checks factors like channel availability, bandwidth, power, modulation schemes, and other resource-related constraints.
3. QoS Evaluation: The RAC evaluates the requested QoS parameters against the network's capability and available resources. This evaluation ensures that the network can meet the minimum requirements for the requested service, such as latency, throughput, reliability, and priority.
4. Admission Decision: Based on the resource assessment and QoS evaluation, the RAC makes a decision to either accept or reject the connection request. If the network has sufficient resources and can meet the requested QoS, the connection is accepted. Otherwise, the request is rejected, and the user/device may need to retry later or choose alternative options.
5. Resource Allocation: If the connection request is accepted, the RAC allocates the necessary radio resources to establish the connection. This involves assigning frequency channels, time slots, transmit power levels, and other relevant parameters required for the communication session.
6. Ongoing Resource Management: Once the connection is established, the RAC continues to monitor the resource usage and QoS parameters. It may dynamically adjust resource allocation based on changing network conditions, user mobility, traffic patterns, or other factors to optimize resource utilization and maintain QoS.

The RAC mechanism aims to strike a balance between maximizing the network capacity and providing a satisfactory user experience. By intelligently managing resource allocation and controlling admission, RAC helps prevent overloading of the network, mitigates congestion, and ensures fair distribution of resources among users, thus improving overall network performance.