Study Of Network Capacity In SCMA Enabled Wireless Networks

Network capacity of wireless networks can be defined as the maximum number of connections that can be simultaneously supported or the sum of data networks can convey.According to statistics,the global mobile data traffic will increase 20 thousand folds by 2030,compared to that in 2010.To satisfy the requirement brought by the explosion of global mobile data traffic,increasing the network capacity is the most direct approach.It has been proved by industry and academia that network densification and high-efficiency novel multiple access technologies are among the most effectively methods to enhance the network capacity in wireless networks.Therefore,it is of most significance to explore the fundamental limits of network densification and multiple access technologies in improving network capacity.Nevertheless,future wireless networks are bound to be heterogeneous networks of high degree of integration,the form of which will be greatly complicated.Meanwhile,the design and analysis of multiple access have transited from orthogonal multiple access to nonorthogonal multiple access,which basically considers the joint design of multi-dimensional resources.In consequence,it is of great difficulty to evaluate the performance of novel multiple access techniques in large-scale networks.Worsestill,as network densification significantly reduces transmission distance and enables proximity communications,the signal propagation may transit from far-to near-field propagation.The near-field propagation of signals brings about intrinsic changes to the interference statistics as well.The above factors lead to great difficulty in the capacity analysis of densely deployed wireless networks.Hence,how to provide valid analysis on network capacity considering the near-field signal propagation features? How does network densification impact the network performance?The above questions are to be answered and fully explored.According to the above discussion,we investigate the performance of a novel nonorthogonal multiple access method,i.e.,sparse code multiple access(SCMA),from the perspective of spatial throughput in the cellular and device-to-device(D2D)communications hybrid networks.Note that spatial throughput has been widely used to accurately characterize network capacity in cellular networks.Meanwhile,we study the benefits of network densification as well.The target of this work is to explore the capacity enhancement achieved by different techniques.The contribution of this work can be listed as follows:1.This article has proposed a capacity analysis method in SCMA enabled cellular networks,based on which the capacity gain brought by SCMA has been quantitatively evaluated.With the aid of stochastic geometry,we model the multiple access interference in SCMA networks,and accordingly,the relationship between interference statistics and spatial throughput is formulated and closed-form expression of spatial throughput is obtained.Specifically,the expression can capture the impact of important parameters on the performance of the hybrid network,including base station(BS)density,user density,user transmit power,large-scale fading,small scale fading,codeword sparsity and SCMA overloading gain,etc.Compared to conventional code division multiple access(CDMA)and orthogonal frequency division multiple access(OFDMA),the results reveal that the spatial throughput can be improved by more than 2 folds using SCMA.The results have confirmed the high efficiency of SCMA in exploiting code and time-frequency resources.2.This article has investigated the impact of D2 D communications mode on the network capacity of cellular networks and proposed efficient interference avoidance and resource allocation methods in SCMA enabled cellular and D2 D hybrid network.In the hybrid system,this article quantified the capacity enhancement brought by introducing D2 D communications mode.In particular,it is shown that D2 D communications could increase the network capacity by 1 fold under typical settings.Meanwhile,in the underlaid mode,where cellular users and D2 D users simultaneously transmit data over the same resources(e.g.,spectrum resources),this article has proposed a simple interference management technique to combat the cross-tier interference.Specifically,we enable D2 D transmitters to use an activated probability to control the generated cross-tier interference to cellular users.The optimal activated probability is obtained such that proportional fairness utility function is maximized.In the overlaid mode,where SCMA codebooks are partially allocated to cellular users and D2 D users,we study SCMA codebook allocation for cellular network and D2 D network.Specifically,we find out the optimal codebook allocation rule when cellular users are densely deployed,in order to maximize the proportional fairness utility function.The results can serve as a guideline for the efficient design of SCMA mechanisms and resource allocation in the D2 D and cellular hybrid network.3.This article has explored the interference characteristics in ultra-dense cellular networks,analyzed the scaling law of network spatial throughput and quantified the critical density.A bounded pathloss model(BPM)has been applied to characterize the near-field propagation feature in ultra-dense scenarios.On this basis,we derive the interference distribution when BSs are densely deployed in uplink cellular networks and reveal that spatial throughput first increases and then decreases with the BS density.In other words,network densification indeed degrades network capacity when the BS density is sufficiently large.Finally,we study the capacity enhancement caused by network densification.Particularly,spatial throughput is shown to be increased 1000 folds by network densification,compared to the BS deployment density in the 4th generation(4G)mobile communications system.The results are useful for the BS deployment and network design.