Multiple Access Techniques for Next Generation Wireless: Recent Advances and Future Perspectives

The advances in multiple access techniques has been one of the key drivers in moving from one cellular generation to another. Starting from the first generation, several multiple access techniques have been explored in different generations and various emerging multiplexing/multiple access techniques are being investigated for the next generation of cellular networks. In this context, this paper first provides a detailed review on the existing Space Division Multiple Access (SDMA) related works. Subsequently, it highlights the main features and the drawbacks of various existing and emerging multiplexing/multiple access techniques. Finally, we propose a novel concept of clustered orthogonal signature division multiple access for the next generation of cellular networks. The proposed concept envisions to employ joint antenna coding in order to enhance the orthogonality of SDMA beams with the objective of enhancing the spectral efficiency of future cellular networks

Opportunistic Downlink Sum-Rate with Multiple Feedback Thresholds

The achievable sum-rate capacity in multiuser systems grows as an increasing function of the number of users when opportunistic scheduling is employed. The scheduling requires the knowledge of channel state information (CSI) which is generated and sent from the users. It has been verified that the sum-rate capacity of a multiuser system with one-bit CSI feedback scheme by which each user whose channel quality is above an optimally selected threshold sends one-bit feedback has the same growth rate as that with the full CSI. However, the one-bit feedback scheme introduces non-negligible capacity loss to the achievable sum-rate. In this paper, a feedback reduction technique with multiple feedback thresholds is presented and analysed. The analysis yields closed-form expressions of the achievable sum-rate and its lower bound. The numerical results show that approximately 84% of the capacity loss can be eliminated in the system employing three optimally selected feedback thresholds. The lower-bound of the achievable sum-rate approaches the full-CSI sum-rate as the number of thresholds increases

Multiple Access Techniques for Next Generation Wireless: Recent Advances and Future Perspectives

The advances in multiple access techniques has been one of the key drivers in moving from one cellular generation to another. Starting from the first generation, several multiple access techniques have been explored in different generations and various emerging multiplexing/multiple access techniques are being investigated for the next generation of cellular networks. In this context, this paper first provides a detailed review on the existing Space Division Multiple Access (SDMA) related works. Subsequently, it highlights the main features and the drawbacks of various existing and emerging multiplexing/multiple access techniques. Finally, we propose a novel concept of clustered orthogonal signature division multiple access for the next generation of cellular networks. The proposed concept envisions to employ joint antenna coding in order to enhance the orthogonality of SDMA beams with the objective of enhancing the spectral efficiency of future cellular networks

Reduced Feedback Designs for SDMA-OFDMA Systems

IEEE International Conference on Communications, ICC 2009; Dresden; Germany; 14 June 2009 through 18 June 2009In SDMA-OFDMA wireless communication systems, the feedback load increases with the number of users, subcarriers and antennas in the cell. In this paper, we propose two efficient reduced feedback algorithms by selecting the clusters at the user side. For each cluster, we select the users according to their norm and their orthogonality. We evaluate the performance of the user selection algorithms considering the quantization effect. We also design a specific codebook design to quantize CSI for the proposed criterion

Opportunistic Feedback Assisted Scheduling and Resource Allocation in OFDMA Systems

Abstract-This paper proposes an efficient channel information feedback method to minimize feedback overhead without performance loss for orthogonal frequency division multiple access (OFDMA) frequency division duplexing (FDD) systems in time-varying channel. The proposed best M users' best L subbands feedback method can significantly reduce the feedback overhead. The proposed scheme utilizes the property of the proposed fair (PF) scheduler that most of the subbands are assigned to the users with high average SNR by time selectivity of channel and some high SNR subbands are assigned to the users by frequency selectivity. For adaptive implementation, the threshold assisted feedback method is proposed. In the numerical results, it is showed that the feedback overhead of the proposed scheme is about 12% of the full CSI feedback method with little throughput loss when the number of users is 50