It is widely believed that cooperative relay technologies can improve the throughput of multicasting in mobile cellular networks significantly, however, the mobility of the relay terrninals may cause frequent relay link outage. This paper proposes a stream layered cooperative relay scheme to deal with this problem. In order to study the characteristics of layered relay channels in the scheme, the capacity region is determined based on a single and a multi relay abstract model with streams layering. Besides, to satisfy the cellular network scenario, the results are extended to a wireless Gaussian channel model. The analysis and simulation results show that the scheme guarantees the continuity of the multicast streams, and maintains the high bandwidth of relay channel, with a slight loss on system capacity.
In Cognitive Radio(CR) networks,cooperative communication has been recently regarded as a key technology for improving the spectral utilization efficiency and ensuring the Quality of Service(QoS) for Primary Users(PUs).In this paper,we propose a distributed joint relay selection and power allocation scheme for cooperative secondary transmission,taking both Instantaneous Channel State Information(I-CSI) and residual energy into consideration,where secondary source and destination may have different available spectrum.Specifically,we formulate the cognitive relay network as a restless bandit system,where the channel and energy state transition is characterized by the finite-state Markov chain.The proposed policy has indexability property that dramatically reduces the computation and implementation complexity.Analytical and simulation results demonstrate that our proposed scheme can efficiently enhance overall system reward,while guaranteeing a good tradeoff between achievable date rate and average network lifetime.
Cooperative transmission is a promising way to improve system performance in orthogonal frequency division multiple access (OFDMA) based cellular networks.This paper proposes two heuristic cooperation schemes including relay selection and resource allocation using hierarchical modulation (HM) to fully exploit the radio resources in cellular networks where user equipments (UEs) relay for each other.The relay selection procedure considers both the channel conditions and the energies left in relays to make the cooperative communications behave better.To mitigate the spectrum efficiency loss due to the half-duplex mode,the bits of relayaided UE and its relay (which is also a UE) are transmitted simultaneously in one sub-channel using HM to improve the utilization efficiency of sub-channels.Besides,time resources are used effectively with the adaptively changed proportion of the two sub-frames divided for relay transmission.Simulation results show that the proposed schemes can improve the spectrum efficiency compared with the traditional schemes.
