| Future wireless communications networks will be characterized by their broad bandwidth and a wide range of services that they will provide, including multimedia services. In this dissertation, we study various aspects of the air interfaces in cellular radio communications systems and examine the problem of efficient allocation of the available bandwidth to integrate a number of services with different QoS requirements into one system. We present two MAC layer protocols to address this problem in two types of cellular communications systems. One protocol is based on TDMA technology, and the other protocol is based on CDMA technology. We also present in this dissertation, a review of the current cellular radio communications systems, a review of MAC layer schemes proposed in recent academic studies, and a brief description of the simulation tools that we developed for studying the performance of MAC layer protocols in wireless communications systems.; Our simulation tools cover data traffic simulation, radio channel simulation, and air interface simulation. Three typical data traffic models have been implemented in the data traffic simulation part. They are the On-Off traffic model, Discrete Autoregressive Model and Long Range Dependent (self-similar) traffic model. The radio channel simulation part includes Free Space Channel, Slow Fading Channel, Rayleigh Fading Channel, Rician Fading Channel, and Nakagami/Rician Fading Channel. Both TDMA-based and CDMA-based air interfaces (mainly at the MAC layer) are modeled in the air interface simulation component.; The new TDMA-based scheme that we designed is intended for carrying traffic from multiple services in mobile environments, e.g., Personal Communication Systems (PCS). In contrast to other TDMA-based protocols for mobile applications, instead of trying to fit the offered traffic to the slot size, our solution adapts the slot size to the offered traffic. In consequence, as demonstrated by our performance studies, the proposed scheme is more flexible and incurs lower bandwidth overhead than other TDMA-based solutions.; In the CDMA-based scheme, we present a novel radio channel structure based on slotted CDMA technology. The proposed new CDMA-based scheme is intended for carrying traffic with diverse bandwidth/QoS requirements. The essence of our approach is a combination of flexible slotting with allocation of multiple codes to high-bandwidth mobiles. As demonstrated by our performance studies, the proposed scheme efficiently integrates multiple traffic classes into an unified CDMA system. It is highly flexible and incurs low overheads for a wide range of realistic traffic conditions. |
