Investigation On The Techniques Of Layered And Cooperative Transmission In Wireless Multicast Systems

Wireless broadcast and multicast are point-to-multipoint services in which data is transmitted from a single source to multiple destinations. With wide deployment of mobile communication networks, rapid development of mobile communication technologies, and rapid population growth of mobile communcation users, wireless broadcast and multicast communication service has become a hot spot in the development of mobile communication systems. This thesis investigates layered and cooperative transmission technologies in wireless multicast systems, including research on the layered transmission performance, resource allocation and scheduling, and relay forwarding mechanisms for a wireless multicast system which is based on superposition coding (SC), as well as the transmission performance for a wireless cooperative multicast system which is based on network coding.The main contributions of this thesis can be summarized as:1) A mixed multicast and unicast transmission scheme wtih SC is proposed and its performance over Nakagami-m fading channels is analyzed and evaluated, and some distribution functions are derived such as the channel gain distributions for a selected multicast user in the superimposed multicast transmission, and the signal-to-noise ratio (SNR) distributions for a selected unicast user in the superimposed unicast transmission. Numerical results show that when the cell radius is larger than a small size, the SC scheme can outperform the conventional TDM scheme in terms of system capacity.2) Two layered multicast transmission schemes with SC are proposed which are based on two different performance optimization criteria, and the optimal resource allocation for these two schemes are discussed. For a two-layer multicast transmission, i.e., a base layer and an enhancement layer multicast transmssion, an optimization criterion is to maximize the average user capacity for the base layer and the enhancement layer multicast transmission. Under this criterion the optimal power allocation and the optimal user selection ratio are investigated; The other crierion is to balance the tradeoff between the system delay of a base layer multicast and the average throughput of an enhancement layer multicast. Under this criterion the optimal joint rate and power allocation are discussed.3) The performance of a cooperative multicast transmission scheme with network coding is evaluated. To facilitate performance evaluation, three information-theoretic metrics including ergodic capacity, outage probability and diversity gain are studied. Numerical results show that network coding technologies can significantly increase system throughput while maintaining almost the same level robustness for the cooperative multicast system.4) A forwarding scheme with SC for wireless relaying is proposed to reduce redundant forwarding, in which a relay will not forward a message to a destination if the destination has successfully decoded the message. In this scheme, flag signal and data signal are superimposed and transmitted by a source, and according to whether the flag signal has been successfully decoded by the relay, the relay can determine whether to forward the data signal to the destination. Numerical results show that the SC scheme can outperform the conventional decode-and-forward cooperation scheme in terms of spectral efficiency and outage probability.