Self-Organising Load Balancing for OFDMA Cellular Networks
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In this thesis, self-organising load balancing is investigated to deal with the uneven load distribution in OFDMA based cellular networks. In single-hop cellular networks, a self- organising cluster-based cooperative load balancing (CCLB) scheme is proposed to overcome the ‘virtual partner’ and the ‘aggravating load’ problems confronted in the conventional mobility load balancing schemes. Theoretical analysis and simulation results show that the proposed scheme can effectively reduce the call blocking probability, the handover failure rate, and the hot-spot cell’s load. The proposed CCLB scheme consists of two stages: partner cell selection and traffic shifting. In the partner cell selection stage, a user-vote assisted clustering algorithm is proposed, which jointly considers the users’ channel condition and the surrounding cells’ load. This algorithm can select appropriate neighbouring cells as partners to construct the load balancing cluster, and deal with the ‘virtual partner’ problem. In the traffic shifting stage, a relative load response model (RLRM) is designed. RLRM coordinates multiple hot-spot cells’ shifting traffic towards their public partner, thus mitigating the ‘aggravating load’ problem of the public partner. Moreover, a traffic offloading optimisation algorithm is proposed to balance the hot-spot cell’s load within the load balancing cluster and to minimise its partners’ average call blocking probability. The CCLB scheme is modified to apply in multi-hop cellular networks with relays deployed. Both fixed relay and mobile user relay scenarios are considered. For fixed relay cellular networks, a relay-level user shifting algorithm is proposed. This algorithm jointly considers users’ channel condition and spectrum usage of fixed relay, in order to reduce the handover failure rate and deal with the ‘aggravating load’ problem of fixed relay. In the mobile user relay scenario, the user relaying assisted traffic shifting algorithm is proposed to improve the link quality of shifted edge users, which brings about an increase in the achievable rate of shifted edge users and decrease in the handover failure rate.
- Theses