Resource Allocation For Cellular And D2D Hybrid Networks Using SCMA

Conventional cellular network and orthogonal multiple access technologies can no longer satisfy users' requirements of high transmission rate,massive connections and high capacity in wireless networks.Meanwhile,available spectrum resources that can be used for mobile communications networks are greatly limited.Therefore,research on effective resource allocation schemes has long been a hot topic.Numerous studies have demonstrated that the reuse of spectrum in cellular and device-to-device(D2D)communication hybrid networks is capable of providing significant gains in terms of system sum rate,system capacity and spectral efficiency.In consequence,however,interference between cellular links and D2 D links is generated in the hybrid networks.Besides,multi-dimensional resources based nonorthogonal multiple access technologies are proposed as promising candidates,which can also enhance system sum rate and system capacity because of overloading gain.Nevertheless,multiple access interference(MAI)is generated,which is brought by nonorthogonal data transmission.On this account,we investigate how to allocate resources to cellular users and D2 D users to maximize system sum rate in cellular uplink and D2 D communication hybrid networks,where a typical code-domain based nonorthogonal multiple access technology,namely,sparse code multiple access(SCMA),is utilized.Furthermore,we also analyze the performance of SCMA in hybrid system.In hybrid system,there exist two alternative resource sharing methods between cellular users and D2 D users.In underlaid mode,D2 D users nonorthogonally share the identical SCMA resources with cellular users.In overlaid mode,SCMA resources are partially allocated to cellular users and D2 D users.Considering the two typical resource sharing modes,novel resource allocation schemes are designed to enhance system sum rate in the cellular uplink and D2 D hybrid networks.The contribution of this work can be summarized as follows:1.A greedy resource allocation algorithm is proposed,where SCMA codebooks are preferentially allocated to users inducing less interference to maximize system sum rate.Meanwhile system sum rate gain of SCMA over conventional orthogonal frequency division multiple access(OFDMA)is quantitatively evaluated.In hybrid system,each cellular user is paired with at most one D2 D user and D2 D users reuse SCMA resources with cellular users in underlaid mode.This greedy resource allocation algorithm employs a two-phase method.In the first phase,cellular users with better channel condition are of higher priority to be assigned with SCMA codebooks.In the second phase,the candidate set of cellular users for each D2 D user is identified.Afterward,D2 D users inducing minimum interference are preferentially paired with cellular users in their candidate sets which maximize transmission rate.The results have confirmed that compared to OFDMA based resource allocation algorithm,system sum rate can be improved by 56% and system capacity is enhanced by 60% through SCMA based resource allocation algorithm.2.An interference-aware hypergraph based codebook allocation algorithm is proposed,in which the D2 D user with minimum interference degree is preferentially assigned with SCMA codebook to maximize system sum rate.In hybrid system,each cellular user is paired with multiple D2 D users and D2 D users share SCMA codebooks with cellular users in underlaid mode.In consequence,pairwise interference and aggregate interference between cellular users and D2 D users brought by resources reusing are generated.Since hypergraph can accurately model the aggregate interference,a hypergraph is constructed according to actual system scenario.In the algorithm,the candidate sets of SCMA codebooks for D2 D users are determined.Afterward,D2 D users with minimum interference degree are first matched with cellular users.Simulation results have confirmed that the resource allocation algorithm can significantly increase system sum rate.Meanwhile,the ratio of active D2 D users can be enhanced by 25% using the proposed hypergraph based method,as compared to a graph based method.3.A graph coloring based joint mode selection and resource allocation algorithm is proposed,in which a distance based mode selection criterion is introduced and SCMA codebook is preferentially allocated to D2 D user with minimum relation degree.Furthermore,system sum rate gain from the reuse of OFDMA resource blocks in SCMA structure is explored.In hybrid system,each cellular user is paired with multiple D2 D users and D2 D users can share SCMA resources with cellular users in underlaid mode or overlaid mode.A two-step resource allocation method is designed.In particular,a distance based mode selection criterion is taken into account for users to decide whether to select cellular mode or D2 D mode and SCMA codebooks are assigned to cellular users and D2 D users in overlaid mode in the first step.In the second step,a graph corresponding to network topology is constructed.Moreover,the interference limited area of D2 D users is proposed to identify their candidate sets of SCMA codebooks.Finally,D2 D users with minimum relation degree are of the highest resource allocation priority.We verify via simulation results that the graph coloring based resource allocation method can significantly increase system sum rate.In addition,it is shown that the reuse of OFDMA resource blocks in SCMA structure with more users can increase system sum rate,while larger interference limited area of D2 D users can decrease system sum rate.