Overlapped OFDMA——新颖的多载波频谱共享传输机制

Overlapped OFDMA:a novel spectrum sharing scheme

针对现有非连续正交频分复用(DOFDM)等系统通常只允许认知用户利用授权用户未使用的频带进行共享传输的问题,提出一种新颖的频谱共享传输机制,即混叠正交频分复用多址接入(Overlapped OFDMA),能够在一定条件下实现认知用户与授权用户的混叠频谱共享.通过对一般OFDM系统的信号结构进行研究发现,当认知用户的子载波带宽采用授权用户子载波带宽的一半进行传输、其频谱和授权用户频谱存在一定混叠时,只要认知用户保持和授权用户时域信号准同步且其子载波分配方案满足一定的限制条件,授权用户将不受干扰.由于各载波上的干扰都包含有其它载波的信息,因此认知用户可以通过适当的恢复算法将信息完整地恢复.仿真和分析结果表明,尽管Overlapped OFDMA会带来一定的复杂度,但授权用户的性能和DOFDM系统相比几乎相同,而认知用户却获得了更加优异的吞吐量性能.该机制为频谱共享传输体制的设计提供了新的可能性.

In order to further improve the spectrum efficiency in cognitive radio systems such as discontiguous orthogonal frequency division multiplexing （DOFDM） where the secondary user can only utilize the subcarriers unused by the primary user, a novel spectrum sharing transmission scheme, namely Overlapped OFDMA, was proposed in this paper. By investigating the conventional OFDM signal architecture, it was found that, the secondary user and the primary user will not interfere with each other even if their subcarriers are partly overlapped, as long as the secondary user adopts a subcarrier space half of that of the primary user and their subcarriers are properly allocated and quasi-synchronized. The information carried by different subcarriers can be jointly recovered due to that its interference in fact contains information from the other subcarriers. Both the analysis and simulation results show that, the proposed Overlapped OFDMA scheme can achieve similar performance as DOFDM for the primary user, and much better throughput for the secondary user, at a price of increased system complexity. It thus provides a new choice for the design of future spectrum sharing communication systems.