Research On Cooperative Transmission Schemes For Relay Channels With Non-ideal Circuit Power

With the growing cost of fossil fuel energy consumpitons,the design of green communications has become an urgent task for both environmental and economical demands and motivations.The energy dissipated on the non-ideal circuits of communication infrastructures takes up a nonnegligible part of the total energy consumption.Therefore,next generation of green communication systems associated with non-ideal circuits needs to be designed both energy and spectrum efficiently.On the other hand,cooperative relaying can mitigate fading and extend coverage in wireless networks,and thus achieves diversity and improves the spectral efficiency of the system,which has been considered as a promising technique in 5G.Energy efficiency maximization problems for relay channel with non-ideal circuits have been extensively studied.However,throughput maximization problems for relay channel with non-ideal circuits under average power constraint were rarely investigated due to the following matters: 1)The average power constraint with non-ideal circuits is non-convex.2)The transmission rate expression of cooperative relaying is complex,which calls for the joint optimization of power allocation for the source and the relay.3)The information causality constraints are non-convex in cooperative buffer-aided relay channels.4)The relationship between the optimal power allocation and non-ideal circuits is more complex in fading relay channels.In this dissertation,the optimal transmission schemes are studied for various relay channels.The transceiver circuitry consumes a constant amount of power in the active mode and negligible power in the sleep mode.The optimal power allocations for the throughput maximization problems are investigated over an infinite time horizon subject to an average power constraint.The main contributions of this dissertation are summarized as follows.First,the optimal transmission scheme for the two hop Gaussian relay channel is studied.By investigating the necessary condition for the throughput maximization problem,the non-convex problem is transformed into a quasiconcave one.The optimal power allocation shows that the source and the relay transmit with certain probability.It also reveals that the optimal transmission scheme consists of two phases: When the average power budget is small,the optimal transmission scheme is to transmit with an on-off structure to maximize the energy efficiency of the considered relay channel;and when the average power budget is large,the optimal transmission scheme is to transmit constantly to maximize the spectral efficiency.Next,the optimal transmission scheme for the cooperative Gaussian relay channel is investigated.For the joint optimization of power allocation for the source and the relay,two suboptimal transmission schemes,i.e.,the direct link transmission(only use the direct link to transmit)and the relay assisted transmission(the source and the relay transmit with equal probability),are firstly studied.The suboptimal power allocations show that the source and the relay transmit with certain probability.Based on the above results,the optimal transmission scheme is derived,which is shown to be either a single type of transmission(direct link transmission or relay assisted transmission)or a time sharing of both transmissions.Then,the optimal transmission scheme for the cooperative buffer-aided Gaussian relay channel is studied.The optimal power allocation under non-convex information causality constraints is obtained by examining two cases on whether the relay can support the source transmissions.Unlike the cases for the two hop Gaussian relay channels and the cooperative Gaussian relay channels,the optimal power allocation for the cooperative buffer-aided Gaussian relay channel is shown to be with different “on-off” structures,i.e.,the source and the relay transmit with certain power values and probabilities,respectively.Next,the dynamics of the stored data at the relay are modelled under the derived optimal power allocation.The minimum buffer size required for data storage is quantified,and the optimal transmission scheme to achieve the mimimum buffer size is specified.Finally,the optimal transmission schemes for the two hop fading relay channel and two hop buffer-aided fading relay channel are investigated.For the two hop fading relay channel,by examining the Karush-Kuhn-Tucker(KKT)conditions,the optimal power allocation is shown to be with a variational water-filling form,which is jointly determined by the instantaneous channel state information(CSI)of both the two links.Moreover,the decision threshold for transmission is derived offline as a function of the non-ideal circuit power,the power budget,and the statistical CSI.For the two hop buffer-aided fading relay channel,by relaxing the binary mode selection indicators into continuous ones(which are later proved that they can only be chosen on the boundaries)and examining the KKT conditions,the optimal power allocation of the source and the relay is obtained,which is determined by the instantaneous CSI of the respective links.Furthermore,the optimal transmission mode selection indicators are obtained by comparing the instantaneous CSI with four decision thresholds,respectively.The decision thresholds are derived as functions of the non-ideal circuit power,the power budget,the instantaneous and statistical CSI.