Overview of Research Topics/Projects in Mobile Communications Research Group at UoP

Mobility Management		Future-generation wireless systems are expected to provide multimedia mobile communications anytime and anywhere. Advanced mobility management is thus the key enabler to fulfil such an attractive vision by supporting all kinds of mobility types of different levels. This work contributes to this interesting while challenging topic. Approaches are taken from the perspectives of the host protocol stack and network architecture to facilitate advanced handoff and location management for various mobility scenarios. Especially, the interactions and joint optimisation of the Session Initiation Protocol (SIP) and the Mobile IP protocol (MIP) are focused on. Simulations are partially based on the OPNET software under the University Programmes.
MC-CDMA Systems		The work deals with the receiver structure of the multi-carrier CDMA (MC-CDMA) system. The receiver requires an appropriate synchronisation technique and an optimum detection strategy. In multicarrier modulation, the synchronisation process includes symbol timing and carrier frequency offset. The process must be performed very accurately; otherwise there will be loss of orthogonality between subcarriers. This synchronisation will be performed on a system that undergoes frequency selective fading and therefore low E_b/N₀.
OFDM Systems		The project analyses, simulates and evaluates the performance of cellular erasure-coded OFDM wireless communications in mobile environment. The wireless network consists of a cluster of cells; each cell contains a randomly distributed group of roaming active users send/receiving packets of content-rich sessions through the network. To achieve this goal, instead of using the conventional enhancing techniques of channel coding and adaptive transmission to combat deep fading, the project uses efficient erasure codes in a digital fountain solution to reconstruct the lost packets when sufficient correctly detected packets are acquired. Packets received in error will be detected, erased and reconstructed in a similar method to packets that are lost. The performance measures include access interference, BER, reception efficiency, and system capacity.
WCDMA Systems		Work is carried out on low cross-correlation codes for "channelisation" which include a large number of nearly orthogonal codes (for example polyphase codes) that have low MAI. The research of Multi-User (joint) Detection (MUD) and Interference Cancellation System (ICS) aim at building a new algorithm of ICS to combat MAI and ICI in conjunction with MUD. Work on Adaptive Rate Allocation (ARA) and Dynamic Capacity Assignment (DCA) investigates the concept and procedure of ARA and DCA algorithms. The cellular radio access networks evolve first to GPRS and then to EDGE. The high-speed W-CDMA will co-exist with GPRS enhanced GSM networks as proposed by 3GPP release 2000. Thus, further work includes radio interface of the two protocols, and DSP compatibility such as modulation and coding, compression algorithms, and protocol convergence.
QoS Adaptation		QoS (Quality of Service) adaptation to mobility is an important aspect in advanced mobility support. In a wireless network, QoS can hardly be guaranteed and mobility further complicates this matter. Thus, adaptive QoS would be more cost-effective and practical in such a context. Since QoS requirements are distributed among all the protocol layers, QoS adaptation may well entail a cross-layer design approach.
AAA, CAC and Context Transfer Schemes		The Authentication, Authorisation and Accounting (AAA) schemes are required for a secure and successful mobile business. AAA servers authenticate a mobile user in a foreign domain, and grant for the roaming behaviours of the user and for paying for the services he/she receives. Call Admission Control (CAC), together with Capacity Control, is related to both QoS and mobility. For QoS, CAC is one of the QoS management functions, e.g., in UMTS. For mobility, CAC brings about additional handoff metrics such as handoff call dropping rate. Another mobility-generated issue is context transfer. It is mainly concerned on how the ‘context’ associated with a live session is transferred between terminals / base stations / networks / systems. Examples of the context include QoS settings, AAA profiles and other control information needs to be transferred during a handoff.
Robust Underwater Communications		Sound over electromagnetic waves is a preferred candidate for underwater communications. However, underwater sound propagation is highly affected by environmental and natural factors such as heterogeneities of the water column, variations of sound velocity versus depth, temperature and salinity, multiple and random sea reflections and significant scattering by fish, bubble clouds and plankton. The underwater background noise level is determined by shipping density, sea state, and interference by marine mammals and manmade underwater equipment such as sonar devices, or acoustic positioning and navigation devices. Less predictable sources of noise are rain and even underwater seismic waves. Therefore, this environment, harsh for acoustic signals, poses great challenges to robust underwater communications. Several projects in this group are underway to contribute to this topic.
		More individual projects are outlined with Researchers.