Research On Technologies Of Increasing Capacity Based On Offloading In Cellular Networks

With the rapid development of mobile Internet, users require increasingly high transmission rates. Increasing the network capacity is one of the most important researches for the cellular communication networks. In the study of the fifth-generation communication technology for cellular networks, the offloading technology has been widely concerned.The core idea of the offload technology is dispersing the transmission load of networks by utilizing some additional resources, which can increase network transmission rates.This paper studies the three offloading methods and the corresponding techniques: The technique of small cells, which offloads traffics to small cell basestations. The technique of unlicensed spectrum access, which offloads traffics to unlicensed spectrum. The technique of device-to-device(D2D), which offloads traffics to user equipments.For the technique of small cells, this thesis studies the offload algorithms in dynamically switching on/off small cell basestations. This thesis proposes a Stackelberg-gamebased dynamic small cell on/off switching algorithm. Compared to a conventional centralized algorithm, the algorithm decreases the computational complexity and the amount of information exchange, and increases the frequency of small cell on/off switching. Compared to the existing baseline algorithms, the algorithm can effectively improve the transmission rate and reduce energy consumption. Based on the above Stackelberg-game-based algorithm, this thesis also proposes a fully distributed dynamic small cell on/off switching algorithm. Compared to the above Stackelberg-game-based algorithm, the algorithm further reduces the computational complexity and the amount of information exchange.For the technique of unlicensed spectrum access, this thesis studies the offload algorithms in dynamically switching on/off unlicensed carriers. This thesis proposes a carrier on/off switching algorithm for accessing unlicensed spectrum using learning-based prediction. The algorithm utilizes Lyapunov technique to optimize energy consumption and transmission rate. By applying Vapnik-Chervonenkis theory, this thesis shows that the algorithm approaches the optimal algorithm in time-varying systems. the algorithm can significantly reduce energy consumption, compared to the all-carrier-on algorithm, and it can also significantly enhance transmission rate, compared to the random-carrier-on algorithm.For the technique of D2 D, this thesis studies the offload algorithms with the mobility information of user equipments. Using Lagrange duality, this thesis gives the impact of mobility features on network capacity. This thesis proposes a throughput-optimal user equipment selecting and scheduling algorithm using mobility information. By the Lyapunov analysis and the first hitting time analysis, the delay performance of the algorithm is given. The algorithm can improve throughput and reduce delay, compared to the existing heuristic algorithms.For the technique of D2 D, this thesis also studies the offload algorithms without the mobility information of user equipments. This thesis proposes a user equipment selecting and scheduling algorithm based on random linear coding(RLC). By the regularized incomplete beta function and first hitting time analysis, the theoretical performance of the algorithm is obtained. The algorithm can significantly decrease the delay caused by D2 D technology, compared to the existing baseline algorithms.For the technique of D2 D, this thesis studies the offload algorithms in the coordination between user equipments and basestations. This thesis proposes a RLC-based distributed user equipment selecting and scheduling algorithm, which can achieve the asymptotically optimal throughput-delay trade-off. The algorithm can improve the throughputdelay trade-off, compared to the conventional algorithms. Furthermore, by reversible Markov chains, the closed-form expressions of the asymptotically optimal throughputdelay trade-off are obtained under the coordination between user equipments and basestations.The end of this thesis summarizes the main contents and the corresponding innovations and prospects, and further points out the future work on the offloading technology for increasing capacity in cellular networks.