Ken Murray, Dirk Pesch

State of the Art: Admission Control and Mobility Management in Heterogeneous Wireless Networks

Future mobile networks will not consist simply of one radio access technology such as WCDMA (wideband code division multiple access) or EDGE (enhanced data rate for GSM evolution), but will contain many different technologies. Seamless intersystem roaming across heterogeneous networks, as depicted in Figure 1, will be one of the main features in future generation mobile networks such as those envisaged in an integrated smart space environment. The motivation for heterogeneous networks arises from the fact that no one technology or service can provide ubiquitous coverage and continuous high QoS (quality of service) levels across multiple smart spaces. It will therefore be necessary for a mobile terminal to employ various points of attachment to maintain connectivity to a corresponding node at all times. Many wide area wireless network technologies are emerging. WCDMA is designed to meet the future requirements of third generation wireless communication services with data rates up to 2Mbps. UMTS (Universal Mobile Telecommunications System) will be based on this radio access technology. Both packet and circuit switched services can be freely mixed, with variable bandwidth and delivered simultaneously to the same user with specific quality levels. GPRS (General Packet Radio System) is a packet data service within GSM allowing bit rates from 9 to more than 150kbps. The user will be charged for the amount of data that is transferred and not for the connection time. Satellite networks promise global coverage and total ubiquitous computing but with lower QoS constraints than its cellular counterparts, while WLAN provides high-speed data service (up to 11Mb/s with 802.11b and 54Mb/s with 802.11a/g) over a geographically small area. All these network technologies differ in bandwidth, latency, power consumption and cost. Mobile terminals in a smart space environment will seamlessly roam between these access networks so as to maintain minimum QoS contracts for different applications and support user preferences. Supporting this seamless mobility is seen as one of the key issues in resource management for heterogeneous wireless networks (Shiao-Li Tsao, 2002). With intersystem mobility, users will benefit from the different coverage and capacity characteristics of each network throughout the interconnected smart spaces. Low tier WLAN offers high bandwidth but with less mobility than a UMTS network which offers medium bandwidth but with greater mobility. Services carried by future generation mobile networks will demand varying QoS for both real-time and non real-time applications. It is only with efficient mobility management and sophisticated admission control algorithms that these QoS constraints can be met and maintained (Nokia CRRM, White Paper, 2001). In a network with a mixture of resources (a heterogeneous network) offering a mixture of different services, it will be vital to provide the optimum radio bearer for each service.

This paper presents a state of the art survey in resource management in heterogeneous networks, in particular, emphasis is given to admission control and mobility management between different access schemes both of which are critical in a heterogeneous network environment as they balance the load across networks while maintaining sufficient QoS for varying traffic types.