Research Of Selecting SUB-Carrier Modulation Technology

Selecting Sub-carrier Modulation (SScM) is a scheme that based on Orthogonal Frequency Division Multiplexing (OFDM) system. In this scheme, sub-carriers are divided into groups, each group contains activated sub-carriers and mute sub-carriers. Information bits are used for both modulation and activated sub-carrier selection. On one hand, a part of bits are transmitted explicitly without energy consuming. On the other hand, the mute sub-carriers save energy.Firstly, the essay analyzes the energy efficiency (EE) and spectral efficiency (SE) of SScM, revealing the relationship between EE, SE and the parameters of SScM. The optimal activated sub-carrier number is derived to reach the optimal SE. The closed-forms and the asymptotic values of the optimal SE ratio, as well as the corresponding EE ratio are derived. Simulation results show that SScM can improve EE and SE simultaneously. Besides, peak to average power ratio (PAPR) is discussed which is proved to be another advantage of SScM.Secondly, three detection methods are proposed, including enhanced energy detection (ED), enchanced log-likelihood ratio (LLR) algorithm and soft demodulation algorithm. After comparing the simulation results of five detection methods, we can conclude that maximum likelihood detection (MLD) performs best at the cost of high complexity, while ED and LLR perform poor. Enhanced ED could promote the performance of ED about3dB, and enhanced LLR performance1.5dB better than LLR. When the convolution channel code is used, the performance of soft demodulation will have4dB gain.Finally, the demodulation performance of cell edge is concerned. MLD and LLR in this scenario are proposed. Simulation results show that SScM can get8dB and3dB gain without or with the convolution channel code, respectively. Compared with MLD, due to the lower complexity, LLR is not as good as MLD. However, it still performs better than traditional OFDM system.