| Frequency Division Multiplexing (OFDM) is an effective multi-carrier solution for broadband wireless communications In the OFDM system, the data stream with high rate is transformed into a number of lower rate components. Then, the lower rate components are mapped onto different subcarriers which are orthogonal in frequency domain. Since the bandwidth of each subcarrier in OFDM is narrower than the coherent bandwidth of the propagation channel, the frequency-selective fading is transformed to flat fading. Orthogonal Frequency Division Multiplexing Address (OFDMA), which is the multi-user vision of OFDM, prevails in the proposed future wireless network standards like 4G cellular networks. In OFDMA networks, the interference between different cells, which is called inter-cell interference (ICI), cause performance degradation. In order to solve this problem, this paper research on the OFDMA resource allocation related technology.This article first gives an overview over resource allocation problem in OFDMA systems. On this basis, the author summarizes the perspectives and progresses of the current resource allotion algorithms in OFDMA systems. Resource allocation algorithm for OFDMA system acquires the channel state information, the access rate requirements and the minimal tolerable delay for all users who desire to access the network. Besides, the algorithm needs the information about the resources provided by the system (including time slots, sub-carrier, power, modulation choices and available airspace). With all these prerequisites, resource allocation algorithm means to allocate each of the resource blocks to appropriate user and to satisfy the users'the expectation with minimal resource expenses. On this basis, for resource allocation algorithms in OFDMA systems, there are many key aspects to consider, which include channel effects, imperfect channel feedback effects, inter-cell interference, relay network model effects, multiple input multiple output model effects and so on.Within the existing resource allocation schemes for OFDMA systems, there is a class of integer programming based modeling and resource allocation algorithms. The author takes an indepth study over integer programming based OFDMA resource allocation modeling schemes, proposes integer programming based algorithms which highlights the thoughts of branch-and-bound algorithm and hidden variable algorithm respectively to achieve the optimal solution with a lower complexity. In addition, the author also proposes an algorithm which combines hidden variable algorithm with pre-assignment and reassignment algorithm to supply a suboptimal solution with even lower complexity. Furthermore, the author proposes the best user selection scheme and the user selection with the lowest complexity scheme. And after applying the user selection schemes in branch-and-bound algorithm based resource allocaiton, the algorithm can achieve large complexity reduction without palpable thoughput loss.Subsequently, the author focuses on inter-cell co-channel interference problem, takes multiple data services into account, deeply considers the influence introduced by the bit loading of the cell over the bit loading of its neighboring cell, and finally gives the problem a model. And after that, research proves that the problem is convex under a given limitation of the number of the loaded bits. On this basis, hybrid subcarrier exclusivity and sharing (HSEnS) scheme with optimized bit loading in uplink multicell OFDMA system is proposed in this article. The HSEnS scheme is proposed for making tradeoff between throughput performance and algorithm failure rate when interference is strong, moderate or weak. Simulations support our proposals and HSEnS with optimized bit loading outperforms other schemes.Afterwards, two Inter-cell Interference (ICI) management algorithms, Primary Interference Balancing (PIB) algorithm and Interfering Bits Loading Avoidance (IBLA) algorithm, are proposed for canceling the ICI effects which the existing efficient radio resource allocation algorithms do not consider. The efficient radio resource allocation algorithm, Pre-assignment and Reassignment (PR) algorithm, has the lowest complexity and meanwhile achieves good throughput performance in single cell OFDMA system. However, in multi-cell multi-sector OFDMA networks, PR algorithm is not applicable because it does not take ICI into consideration. On the basis of this, PIB algorithm balances the number of the bits loading for the desired User Equipment (UE) and the major interfering UE, which optimizes the SINR performance, and IBLA avoids loading certain number of interfering bits which would make SINR unqualified. Simulations confirm the ICI management effectiveness and feasibility of both the proposals.Finally, the author considers a resource allocation diffusion algorithm, which is designed to keep the resource allocation in pace with resource allocated for its neighbouring cells and meanwhile posseses a quite low complexity. At the end, the author gives some prospects over the resource allocation within OFDMA systems. |
