Subcarrier Allocation In OFDMA Systems Research Articles

Balanced Frequency Reuse with Ordering and Directional Subcarrier Allocation in OFDMA Systems

In multi-cell OFDMA-based networks, co-channel interference (CCI) is inevitable when the frequency reuse scheme is used. The CCI affects the performance of users, especially that of cell edge users. Several frequency reuse schemes and subcarrier allocation algorithms have been proposed to solve the CCI problem. Nevertheless, it is difficult to improve both the cell capacity and the performance of cell edge users since they have a trade-off. In this paper, we propose a new balanced frequency reuse (BFR) as a new frequency partitioning scheme that gives more power to the users in the outer region and allocates more subcarriers to the users in the inner region. In addition, we propose ordering and directional subcarrier allocation (ODSA) for our frequency partitioning proposal to mitigate the CCI effectively when cells have heterogeneous traffic loads. The performance of the proposed BFR with the ODSA algorithm is investigated via analyses and simulations. Performance evaluation shows that the proposed BFR with the ODSA algorithm can increase both the spectral efficiency and the performance of cell edge users if the transmission power is appropriately handled.

Max-matching diversity in OFDMA systems

This paper considers the problem of optimal subcarrier allocation in OFDMA systems to achieve the minimum outage probability while guaranteeing fairness. The optimal subcarrier allocation algorithm and the maximum frequency diversity gain are both analyzed through the maximum matching method based on the random bipartite graph theory. Accordingly, a surprising result is found, which shows that the maximum frequency diversity gain in subcarrier-sharing OFDMA systems is the same as that in point-to-point OFDM systems that serve only one user by using N subcarriers. It is then demonstrated that this maximum frequency diversity gain can be achieved by a proposed Random Vertex Rotation based Hopcroft-Karp (RVRHK) algorithm with the time complexity of O(N <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2.5</sup> ), where N is the number of subcarriers. Because the theoretical analysis and the RVRHK algorithm are both based on the maximum matching method, the maximum frequency diversity in OFDMA systems is referred to as the max-matching diversity in this paper.

A probabilistic model for sub-carrier allocation in OFDMA systems

Orthogonal frequency division multiple-access technique showed a successful utilization of channel features. It implements an orthogonal sub-carrier space to be shared among different users. The management of these sub-carriers in both power and frequency allocation is reflected on the systems performance as better utilization of bandwidth, and hence, better capacity is obtained. Sub-carrier allocation is used to avoid deep fading that might occur at some user’s locations but not at other user’s locations. In this paper, we devise an algorithm based on probabilistic model for sub-carrier allocation to avoid deep fading in some user’s signals. By controlling the sub-carrier allocation for each user, we can create a full rank channel for each user and hence, provide maximum capacity for the system. Simulation results showed that using the devised algorithm will avoid deep fading and utilize the bandwidth up to 40% more than localized allocation strategies.