In the uplink of orthogonal frequency division multiple access (OFDMA) systems, rate adaptation may not be exploitable mainly because of severe inter-carrier interference (ICI). In this study, the authors propose a novel hybrid link adaptation that simultaneously uses power adaptation for ICI adjustment and rate adaptation for capacity improvement in the uplink of OFDMA systems. The proposed hybrid link adaptation determines a maximum allowable transmission power according to the channel gain and velocity of each user, enabling all users to have a guaranteed loss of carrier to interference ratio (CIR). Moreover, the proposed hybrid link adaptation adjusts the transmission rate according to CIR of each user, while keeping the maximum allowable transmission power unchanged. The performance of the proposed hybrid link adaptation is analysed in OFDMA cellular uplink systems. Finally, the analytic results are verified by computer simulation.

This paper considers cooperative eigen beamforming with the use of partial channel information (e.g., transmit correlation) to maximize achievable sum-rate of multi-user dual-hop multiple-input single-output relay channels. By exploiting the transmit correlation in a cooperative manner, the proposed scheme selects a pair of users whose transmit correlation have the largest phase difference of the desired and interference channel from the relay. It is analytically shown that the achievable sum-rate of selected two-users is maximized when the principal eigenvectors of the transmit correlation matrix of the desired and interference channel from the relay are orthogonal to each other. By generating an eigen-beam by the principal eigenvector of the transmit correlation matrix of own desired channel, the proposed scheme can provide the achievable sum-rate comparable to the full channel information-based minimum mean square error beamforming scheme in correlated channel environments. Finally, the proposed scheme is verified by computer simulation.

We consider a power allocation strategy to maximize the end-to-end capacity of a regenerative dual-hop multiple-input single-output (MISO) relay channel with the use of transmit beamforming. In a dual-hop MISO relay channel, the optimum power allocation can be determined by means of a max-min technique with sum power constraints. The proposed scheme adaptively allocates the transmit power of the source and relay according to the achievable beamforming gain as well as the average channel gain to balance the capacity between the dual- hop MISO relay channels. Simulation results show that the proposed scheme can provide noticeable performance improvement over the average signal-to-noise ratio (SNR)-based power allocation scheme in a dual-hop MISO relay channel with the use of the transmit beamforming.

This letter investigates the effect of the transmit correlation on the sum-rate capacity of a two-user broadcast channel (BC) with the use of equal-power allocation in high signal-to-noise ratio (SNR) environments. It is shown using an upper-bound analysis that the sum-rate capacity of a correlated two-user BC at high SNR highly depends on the phase difference between the transmit correlation coefficients of two users as well as the magnitude of the transmit correlation coefficients, and it is maximized (or minimized) when the principal eigenvectors of the transmit correlation matrix of two users are orthogonal (or parallel) to each other. The analytic results are verified by computer simulation.

In this paper, we propose a user scheduling scheme to maximize the ergodic capacity of multi-user MIMO uplink systems. The proposed scheduling scheme only considers the use of the receive correlation matrix of users, not the instantaneous channel state information of users. The proposed user scheduling scheme is applied to collaborative spatial multiplexing systems specified in the IEEE 802.16e, where the base station receives two user signals at each time slot using two receive antennas. Analytic and numerical results show that the proposed user scheduling scheme outperforms conventional random user scheduling scheme in terms of the ergodic capacity without loss of opportunity fairness.

In orthogonal frequency division multiple access \n(OFDMA)-based uplink systems, it may not be feasible \nto exploit the rate adaptation due to severe intercarrier \ninterference (ICI). In this paper, we propose a \nnovel hybrid link adaptation scheme that employs \npower adaptation for ICI adjustment and rate \nadaptation for capacity improvement in OFDMAbased \nuplink systems. The proposed scheme determines \nthe maximum allowable transmit power in response to \nthe channel gain and mobility of the user, \nguaranteeing the carrier to interference power ratio \n(CIR) loss of all users.

Orthogonal frequency division multiplexing (OFDM) is considered as one of the most promising techniques for next generation mobile systems. When the OFDM is applied to cellular environments, it may suffer from so-called other-cell interference (OCI). In this paper, we propose a novel resource allocation scheme in OFDM-based asynchronous cellular systems. It can reduce the OCI by exploiting the repetitive property of a cyclic prefix (CP) of OFDM symbols. The proposed scheme can be applied to OFDM-frequency division multiple access (FDMA) and OFDM-code division multiple access (CDMA) systems. Computer simulation results show that the proposed scheme can reduce the OCI by nearly up to 1 dB in a typical cellular OFDM environment, compared to the conventional scheme.