Signal Energy Distribution Based Resource Sharing Between Cellular And D2D Users

As the number of mobile users and video traffics grow explosively,the cellular network gradually shows its potential drawbacks.In contrast,the short-range characteristics of D2 D communications can make up the disadvantages of the cellular centralized control mode,and provide more advantages.For example,D2 D communications could decrease the transmission power,save energy,and shorten the transmission delay.Particularly,the spatial reuse feature of D2 D communications allows the D2 D users share the same resources with cellular users by means of spatial reuse and proper resource allocation,which increases the network capacity and unit power capacity.However,when the nonorthogonal resource sharing mode is adopted,new interferences between cellular users and D2 D users are produced,which will affect the communication quality of both cellular and D2 D links.Therefore,the induced interferences are needed to be suppressed.Conventional resource sharing methods are mainly based on resource allocation,distance limitation and power control,and try to maximize the sum rate of D2 D users while meeting the minimum rate demands of the cellular users.However,the above-mentioned three techniques are all on the basis that cellular links and D2 D links communicate on the totally overlapped resources.Under this condition,if the interferences are suppressed by increasing the reuse distance between the D2 D user and the cellular user,the number of permitted reuse users will be decreased;if the interferences to the D2 D users are mitigated by reducing the transmission power of the cellular user,the SINR(Signal to Interference and Noise Ratio)of the cellular link itself will decline,and vice versa.The purpose of this doctoral thesis is to analyze the spectrums and time-varying spectrums of cellular and D2 D signals,and allocate resources for cellular and D2 D users according to their energy distributions in the frequency domain and time-frequency domain.Then the SINRs of both cellular and D2 D users could be increased by proper filters with unchanged reuse distances and transmission powers.According to the energy characteristics of the single-carrier pulse shaping FDMA(Frequency Division Multiple Access)signals in the frequency domain,this thesis proposes a guard-band based uplink resource sharing method,and analyzes its advantages theoretically.The proposed method locates the center frequencies of cellular users and D2 D users at each other's low energy areas in the frequency domain,and then the mutual interferences could be suppressed by bandpass filters at the receivers.The outage probabilities of D2 D users in both flat fading channel and frequency-selective channel are derived and simulated.In the flat fading channel,the results show that the proposed method outperforms the conventional one in terms of the D2 D outage probability;while in the frequency-selective channel,a conclusion is drawn that the performance improvement by the proposed method is not so obvious with too little or too much noise.The pulse shaping procedures and resource allocation methods of the single-carrier system and the multi-carrier system are different.According to the low energy characteristics of OFDM pulse shaping signals in the guard band,this thesis proposes a downlink resource sharing method in the multi-carrier system.The proposed method first allocates the available resource blocks in the guard band to the D2 D users,and then reuses the resource blocks with cellular users.By utilizing resource blocks in the guard band,the interference between D2 D users and cellular users can be reduced.In the flat fading channel,the proposed resource sharing method optimizes the D2 D sum rate on the guard band resources and sharing resources separately,and the advantage of the proposed method is verified in terms of D2 D sum rate and spectral efficiency.In the frequency selective channel,the resource allocation is optimized according to the frequency response of each sub-channel,which is also named water filling theorem,and the sum rate of the D2 D users is analyzed in the frequency domain.Simulation results show that the proposed method can improve D2 D users' sum rate while keeping the cellular communication data rate demands in the frequency selective channel.Finally,according to the time-varying energy distributions of the I/Q separated4 QAM pulse shaping signals,this thesis proposes a resource sharing method based on the time-frequency analysis and the time-varying filter.The author analyzes the timefrequency distributions of 4QAM modulated signals,discusses the effect of the analyzing window length on the time-frequency resolution,exploits the equivalence between the time frequency analysis at the baseband and at the radio front end,and finally reveals the advantages of the proposed method.According to the time-varying energy characteristics of the I/Q separated pulse shaping 4QAM signals,the author designs the pass region for the linear time varying filter,where the optimum masking threshold is obtained by the optimum-BER criterion,and then a masking threshold constrained time-varying filter is proposed.The proposed resource sharing method is evaluated in aspects of SINR and BER,and simulation results show that the proposed method outperforms existing methods with low-pass or band-pass filters.