Research On Key Technologies Of SCMA-OFDM/OQAM Based ROF System

5G will be commercially available around 2020.Its network rate will reach 10 Gbps,its spectrum efficiency will be 10 times higher than that of 4G,and it will be able to support massive users.To achieve this goal,the introduction of new multiple access technology,network architecture and modulation technology is imperative.Orthogonal frequency division multiple access(OFDMA)is the core technology of 4G network,and the number of users is limited by schedulable time-frequency resources,which cannot meet the needs of 5G.To solve this problem,sparse code multiple access(SCMA)is proposed.It can achieve user overload by non-orthogonal superposition of codewords,thus increasing the number of users.On the other hand,OFDM with offset quadrature amplitude modulation(OFDM/OQAM)has become a popular 5G modulation waveform due to its low out-of-band leakage and high spectral efficiency.In addition,radio over fiber(ROF)has become a feasible scheme for 5G fronthaul network due to its advantages of low loss,low cost and high speed.In this paper,a ROF system based on SCMA-OFDM/OQAM is proposed,which effectively improves the system capacity and the number of access users.The main work of this paper is as follows:(1)Firstly,the demand of 5G is analyzed,and some new technologies,such as SCMA,OFDM/OQAM and ROF,are introduced.Then,the basic principles of each technology are elaborated,and the algorithm is written and simulated.(2)A bidirectional ROF system based on SCMA-OFDM/OQAM is proposed.Experimental results show that 1.932 Gb/s SCMA-OFDM/OQAM signal can be transmitted over 24.5 km single mode fiber and 0.3 m wireless distance,and the number of accessed users is increased by 50%.(3)A 4×4 MIMO-ROF system based on SCMA-OFDM/OQAM technology is demonstrated by combining multi-input and multi-output(MIMO)technology and multi-core optical fibers.The hybrid transmission of 11.04 Gb/s SCMA-OFDM/OQAM signals in 20 km multi-core optical fibers and 0.4 m wireless link is realized.Compared with OFDM,the system capacity of SCMA-OFDM/OQAM is increased by 65.2%.(4)Three codebooks with higher overload rate are designed,and a ROF experimental system is demonstrated based on these three SCMA codebooks and filter orthogonal frequency division multiplexing technology.With the increase of overload rate,the number of users and system capacity will increase,but the BER performance will decrease.Therefore,the appropriate codebook can be chosen according to the actual situation.