WIMAX Radio Resource Management (RRM)

Efficient utilization of radio resources within an access network is performed by the radio resource management entity. The mobile WiMAX RRM is based on a generic architecture. The RRM defines mechanisms and procedures to share radio resource related information between BS and ASN-GW. The RRM procedures allow different BSs to communicate with each other or with a centralized RRM entity residing in the same or a different ASN to exchange information related to measurement and management of radio resources. Each BS performs radio resource measurement locally based on a distributed RRM mechanism. It is also possible to deploy RRM in an ASN using base stations with RRM function, as well as a centralized RRM entity that does not reside in the BS and collects and updates radio resource indicators such as choice of target BS, admission or rejection of service flows, etc., from several BSs. The RRM procedures facilitate the following WiMAX network functions: 

• MS admission control and connection admission control, i.e., whether the required radio resources are available at a candidate target BS prior to handover; 

• Service flow admission control, i.e., creation or modification of existing/additional service flows for an existing MS in the network, selection of values for admitted and active QoS parameter sets for service flows; 

• Load balancing by managing and monitoring system load and use of counter-measures to enable the system back to normal loading condition; 

• Handover preparation and control for improvement/maintenance of overall performance indicators (for example, the RRM may assist in system load balancing by facilitating selection of the most suitable BS during a handover).  

The RRM is composed of two functional entities, i.e., radio resource agent (RRA) and radio resource control (RRC). The radio resource agent is a functional entity that resides in the BS. Each BS includes a radio resource agent. It maintains a database of collected radio resource indicators. An RRA entity is responsible for assisting local radio resource management, as well as communicating to the RRC to collect and measure radio resource indicators from the BS and from a plurality of mobile terminals served by the BS using MAC management procedures as specified by the IEEE 802.16 specifications. It also communicates RRM control information over the air interface to the MS, as defined by the IEEE 802.16 specifications. An example of such RRM control information is a list of neighbor BSs and their parameters. It further performs signaling with RRC for radio resource management functions, as well as controlling the radio resources of the serving BS, based on the local measurements and reports received by the BS and information received from the RRC functional entity. 

The local resource control includes power control, monitoring the MAC and PHY functions, modifying the contents of the neighbor advertisement message, assisting the local service flow management function and policy management for service flow admission control, making determinations and conducting actions based on radio resource policy, assisting the local handover functions. 

The radio resource control functional entity may reside in BS, in ASN-GW, or as a standalone server in an ASN, and is responsible for collection of radio resource indicators from associated RRAs. The RRC can be collocated with RRA in the BS. The RRC functional entity may communicate with other RRCs in neighboring BSs which may be in the same or different ASN. The RRC may also reside in the ASN-GW and communicate to other RRAs across R6 reference point. When the RRC is located in the ASN, each RRA is associated with exactly one RRC. The RRC relay functional entity may reside in ASN-GW for the purpose of relaying RRM messages. The RRC relay cannot terminate RRM messages, but only relays them to the final destination RRC. Standard RRM procedures are required between RRA and RRC, and between RRCs across network interfaces to ensure interoperability. These procedures are classified into two types: information reporting procedures for delivery of BS radio resource indicators from RRA to RRC; and between RRCs and decision support procedures from RRC to RRA for communicating recommendations on aggregated RRM status (e.g., in neighboring BSs) for various purposes. 

The RRM primitives can be used either to report radio resource indicators (i.e., from RRA to RRC or between RRCs) or to communicate decisions from RRC to RRA. The former type of primitive is called information reporting primitive and the latter is called decision support primitive. The available radio resource information provided by the RRAs to RRC is used by RRC for load balancing. The RRC may interact with the handover controller to ensure load balance.