Interference Management And Handoff Techniques In Wireless Cellular Networks

With the fast development of mobile internet and the widespread of smart devices, higher requirements for capacity, delay and coverage in wireless cellular communication networks are put forward. Both the academia and the industry are studying many potential techniques in order to improve the performance of current cellular networks. One promising technique is to construct heterogeneous cellular wireless communication networks, where many low power base stations such as picocell base stations, femtocell base stations and relays are added into the conventional macrocell networks. The heterogeneous cellular network has become the leading edge topic in wireless communications. Not only the density of base stations but also the complexity of network structure in heterogeneous netowrks is much larger than that in conventional macrocell networks. Besides, different types of base stations use the same bandwidth due to the limitation of frequency resources. Thus, not only the strength of co-channel interference but also the complexity of interference environment increases significantly. Meanwhile, with the increase of base station density, the number of detected base stations at a mobile device increases. Moreover, the coverage of different base stations are different in size and may overlap with each other, which makes the handoff management more complicated. Therefore, it’s critical to efficiently manage the interference and handoff in improving the performance of heterogeneous cellular wireless communication networks. It’s worth studying the interference management and handoff in heterogeneous networks both from theoretical point of view and from practice. This dissertation studies the interference management and handoff in wireless cellular communication networks, which aims to provide some theoretical and technical insights to the development of future heterogeneous networks. The main content and contributions are as follows. (1) Intra-cell interference management for mobile devices is studied. The limitations of current signal to leakage plus noise ratio (SLNR) based multiuser beamforming scheme for intra-cell interference management and the reasons for the limitations are analyzed. Based on the analysis, an improved scheme is proposed. In the improved scheme, the antenna-receiver structure is incorporated into the optimization process of beamforming, which makes the strength of signal and interference in the optimization process more accurate. Therefore, the co-channel interference among different mobile devices can be better reduced by the optimized beamforming vector. From a theoretical point of view, the improved scheme exhibits a more general expression, which is suitable for multiple recever structures or receive filters. From the system performance point of view, the improved scheme offers about 2 dB effective SIR gains for mobile devices when compared to the original scheme and its variants. In a multi-layer scenario, a new SLNR model, termed layer SLNR, is proposed. The layer SLNR model not only takes care of inter-layer interference from different mobile devices, but also takes into account the inter-layer interference from the same mobile device which is usually assumed to be zero in former studies. Therefore, the signal and interference are modeled more accurately when designing the precoder, which leads to a good balance between signal and interference.(2) The transmission of over-the-air signaling for inter-cell interference management in wireless communication networks is studied. The design requirements, properties and transmissions of conventional over-the-air signaling are analyzed. And detection performance of various over-the-air signaling is compared under multiple scenarios. Since the conventional over-the-air signaling is easy to be interfered in the wireless channel, they are not suitable for the inter-cell over-the-air signaling transmission in heterogeneous networks. The situation is even worse when multiple transmitters exist. This thesis proposes an inter-cell over-the-air signaling (single-tone signaling, STS). The proposed STS scheme has desirable theoretical properties, such as maximum distance separable and multi-signal unambiguous. The detection performance of the STS scheme has been analyzed and simulated under multiple scenarios, and compared with that of conventional over-the-air signaling scheme. Besides, the STS scheme has been shown to have strong resistance of interfence, large coverage and low overhead, which makes it suitable for inter-cell over-the-air signaling transmission. Even when multiple transmitters exist, the STS scheme still has robust and excellent detection performance.(3) Dynamic and distributed inter-cell interference management for heterogeneous networks is studied. Based on STS, this thesis proposes two inter-cell interference management schemes, i.e., ON/OFF power control and inter-cell beam coordination. Both schemes are distributed, negating the need for central controller or coordinator, hence low complexity. The proposed schemes not only reduce the inter-cell interference which improves the performance of the mobile devices in poor channel conditions but also significantly improves the fairness of the mobile devices in the whole system. Particularly, the inter-cell beam coordination scheme not only improves the fairness of the mobile devices but also retains the performance of the mobile devices in good channel conditions. Moreover, the inter-cell beam coordination scheme provides a mechanism for fine-tuning the quality of service for different mobile devices. The performance of proposed schemes is compared with that of the conventional scheme via network level Monte Carlo simulations. The results show the feasibility, effectiveness and superiority of the proposed schemes.(4) The handoff management, particularly the strategy or criterion for handoff, in heterogeneous networks is studied. This thesis analyzes the shortcomings of conventional handoff strategy (the handoff bias can not adapt to the variation of mobile state and the environment of different types of base stations). Based on the analysis, a heuristic handoff strategy is proposed. The proposed scheme incorporates the velocity (including speed and direction) and transmission environment of different types of base stations into the handoff process, which makes the selection of handoff time more accurate. It not only reduces the handoff rate but also reduces the handoff failure rate. Therefore, the system overhead and service outage is reduced. Through Monte Carlo simulations for four typical scenarios in heterogeneous networks, this thesis verifies the effectiveness and superiority of the proposed scheme via comparisons with the conventional scheme.