Access priority schemes in UMTS MAC

UMTS is a third generation radio access network which supports multimedia-capable mobile communication such as packet data and Internet access. In order to provide end-to-end quality of service (QoS) in the UMTS network, certain features need to be incorporated into the MAC design. One possible way of providing different QoS is via providing priority mechanisms. The priority mechanism can be implemented in terms of access priority, service priority and/or buffer management schemes. In this paper, we three access priority schemes based on the random access channel structure. The three schemes are: random chip delay access (RCDAP), random backoff based access (RBBAP), and variable logical channel based access priority (VLCAP). We discuss scenarios where such access priority schemes may be useful. Via simulations, we evaluated and compared these three access priority schemes, Our results indicate that all three schemes provide delay differentiation. However, only the RBBAP scheme provides delay differentiation among different priority classes over a wide range of access request rates without impacting the throughput of the access requests. The other two schemes may cause the throughput of access requests from the lower priority classes to drop apart from forcing them to have a higher access delay