Research On Adaptive Bit Allocation Algorithm In OFDM System For 5G Cellular Networks

In recent years, with the rapid growth of demand for information rate for wireless communication, the fifth generation mobile communication system becomes a hot research topic in mobile communication realm at home and abroad. OFDM will also be one of the key technologies for 5G. It has strong capacity of combating with multipath interference. Simultaneously, OFDM can do adaptive bit allocation according to sub-channel’s fading and multipath delay characteristics to optimize the whole system performance. But the complexity of adaptive bit allocation algorithm will grow exponentially while the bandwidth of 5G becomes larger, and the sub-carriers are more and more. And it becomes a big obstacle for the practical use of OFDM system in 5G cellular networks. This paper does a series of research on the adaptive bit allocation algorithm in OFDM system for 5G cellular networks, and improves the traditional bit allocation algorithm, and put forward the improved sub-carrier bit allocation algorithm.At first, this paper analyses the characteristics of wireless access channels and channel model and centers on the research of multipath fading channels. Then analyses the basic principle of OFDM and key technology. Then select the arguments of OFDM system for 5G based on analyzing the characteristic and demand of 5G. Then compare some traditional bit allocation algorithms especially Chow algorithms and Fischer algorithm based on introducing the principles of adaptive bit allocation technology. Simulate the two algorithms and compare the characteristics of them. Then design the system based on rule of maximum transmission rate according to characteristic of 5G. Although traditional algorithm can achieve the goal of bit allocation, it cannot be used in practical system because of the high complexity and long time consuming. This paper improves Fischer algorithm to reduce algorithm complexity for the problem. The simulation reveals that the improved Fischer algorithm can speed up computations and decrease the delay while having the comparable performance. Then this paper has the research of Simple Block Loading Algorithm. Also improves Simple Block Loading Algorithm and does the simulation. The simulation reveals that the improved Simple Block Loading Algorithm has a similar performance than traditional bit allocation algorithm, and has a very low complexity. It can achieve the goal to improve computing speed greatly and decrease the delay while having a similar performance.