Heuristic based data scheduling algorithm for OFDMA wireless network

A system model based on joint layer mechanism is formulated for optimal data scheduling over fixed point-to-point links in OFDMA ad-hoc wireless networks. A distributed scheduling algorithm （DSA） for system model optimization is proposed that combines the randomly chosen subcarrier according to the channel condition of local subcarriers with link power control to limit interference caused by the reuse of subcarrier among links. For the global fairness improvement of algorithms, a global power control scheduling algorithm （GPCSA） based on the proposed DSA is presented and dynamically allocates global power according to difference between average carrier-noise-ratio of selected local links and system link protection ratio. Simulation results demonstrate that the proposed algorithms achieve better efficiency and fairness compared with other existing algorithms.

Interference-Cancellation-Based Carrier Frequency Offset Estimation for OFDMA Uplink Transmissions

A carrier frequency offset （CFO） estimator was developed based on an interference cancellation scheme for an orthogonal frequency division multiplex access uplink. An initial CFO estimate was first ob- tained based on the received training signals at each user＇s prescribed subcarder positions. Then, the re- ceived training signals were compensated by using the initial CFO estimates in the frequency domain and the multi-user interferences were estimated. Finally, the interference-cancelled training signals were used to reliably estimate each user＇s CFO. The CFO estimator performance was evaluated by the bit error rate per- formances of the CFO compensation-based receivers at the base station. Simulations show that with this optima CFO compensation receiver, the performance gain with the esti- mated CFO values is approximately 3 dB better at the 0.1% bit error rate than the initial CFO estimates.

Resource allocation algorithm with limited feedback for multicast single frequency networks

The single frequency network (SFN) can provide a multimedia broadcast multicast service over a large coverage area. However, the application of SFN is still restricted by a large amount of feedback. Therefore, we propose a multicast resource allocation scheme based on limited feedback to maximize the total rate while guaranteeing the quality of service (QoS) requirement of real-time services. In this scheme, we design a user feedback control algorithm to effectively reduce feedback load. The algorithm determines to which base stations the users should report channel state information. We then formulate a joint subcarrier and power allocation issue and find that it has high complexity. Hence, we first distribute subcarriers under the assumption of equal power and develop a proportional allocation strategy to achieve a tradeoff between fairness and QoS. Next, an iterative water-filling power allocation is proposed to fully utilize the limited power. To further decrease complexity, a power iterative scheme is introduced. Simulation results show that the proposed scheme significantly improves system performance while reducing 68% of the feedback overhead. In addition, the power iterative strategy is suitable in practice due to low complexity.

Carrier Frequency Offset Compensation for an Interleaved OFDMA Uplink

This paper reports an investigation of the carrier frequency offset （CFO） compensation in the uplink of the orthogonal frequency division multiple access （OFDMA） system with interleaved subcarrier assignment. The presence of CFOs between the transmitters and the uplink receiver will destroy the orthogonality among the different subcarriers, resulting in inter-carrier interference and multiuser interference. This paper proposes a pseudoinverse CFO compensation method based on the signal structure. The proposed method can compensate the CFOs of all users simultaneously and isolate the signals from all users at the same time. Compared with the existing CFO compensation methods, the new method provides a considerable signal-to-noise ratio gain on the bit error rate performance and has a relatively low implementation complexity.

Improving coarse frame synchronization by UE-UE interference for OFDMA-TDD systems

This article studies the coarse flame synchronization of orthogonal frequency division multiplexing access-time division duplex （OFDMA-TDD） systems and proposes a new method to improve coarse frame synchronization performance. The new method utilizes the user equipment to user equipment （UE-UE） interference, which is usually considered as a specific challenge for time division duplex （TDD） and also as implicit frame boundary information to enhance coarse frame synchronization performance. Numerical results show the synchronization performance is imoroved bv the new method.