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为了实现高能效绿色通信同时满足高速增长的业务量需求,未来网络将引入超蜂窝架构,通过控制与业务覆盖分离的方式实现柔性覆盖.在超蜂窝架构里,当用户有业务需求时,将免授权地随机接入控制信道发送请求信令.作为目前较为理想的随机接入方案,稀疏码多址接入(sparse code multiple access,SCMA),通过为用户分配不同码本实现非正交多址接入,从而在资源数一定的情况下提升系统的容量,允许大量用户同时接入,进而可以作为控制信道中的随机接入方式.然而,在随机接入的过程中,可能会出现采用相同码本的用户同时接入的情况,称之为码本碰撞,这会导致接收性能的恶化,并且解码算法的运算量随着码本碰撞的用户数成指数增长,严重增加了最坏情况延时.为此,本文提出一个基于时变码本的跳码方案.仿真结果表明这一新方案提升了解码准确性,进一步通过在发生严重码本碰撞时有选择地抛弃SCMA子块,可以在较低的误码率代价下大大降低整体的解码延时,从而满足控制信令高可靠、低延时的传输需求.
In order to achieve energy-efficient green communications while meeting the rapidly growing traffic demand, the future network will introduce a super-cellular architecture to achieve flexible coverage by separating control and service coverage. In a super-cellular architecture, when users have business needs, Authorized random access control channel to send the request signaling.As the current more ideal random access scheme, sparse code multiple access (Sparse code multiple access, SCMA), by allocating different codebooks for users to achieve non-orthogonal multiple access Access, so as to increase the capacity of the system with a certain number of resources and allow a large number of users to simultaneously access, which can be used as a random access control channel .However, in the random access process, may appear to adopt The simultaneous access of users of the same codebook is called a codebook collision, which leads to a deterioration of reception performance and an exponential increase in the computation amount of the decoding algorithm exponentially with the number of users colliding with the codebook, which seriously increases the worst case Delay.Therefore, this paper presents a code hopping scheme based on time-varying code.The simulation results show that this new scheme enhances the decoding accuracy, further through the strict SCMA selectively discard sub-blocks, decoding can greatly reduce the overall delay in the cost of a lower bit error rate, control signaling to meet high reliability, low latency transmission requirements of the present time code collision.