This paper proposes a spectral efficient multiuser scheme for single-carrier transmission. In the proposed scheme, a combination (hybrid) of localized and distributed subcarrier mapping types is employed, where the signals of users with different subcarrier mapping types are superimposed on a common set of subcarriers. We first present mathematical formulations of multiuser detection and derive the equalization coefficients for the hybrid type. In fading environments, the proposed scheme allows users to employ any subcarrier mapping types (localized, distributed, hybrid types), which can support low and high speed users. To estimate the performance of the proposed scheme, we develop a density evolution technique and show that the predicted performances are consistent with simulated performances. Further, based on the performance estimation of the proposed scheme, we discuss channel-dependent resource allocation algorithms: opportunistic scheduling and adaptive modulation and coding (AMC) schemes. These resource allocation algorithms increase the spectral efficiency of the proposed scheme with guaranteed quality-of-service (QoS). Simulation results show that the proposed multiuser scheme achieves both multiuser and frequency diversity gains in fading environments.

This paper proposes a space-time block coded (STBC) transmission with phase feedback for two-user multi-input multi-output multiple access channels (MIMO-MAC). In the proposed system, the phase feedback is transmitted to only one user, which reduces the overhead of the reverse link. We derive a closed-form solution for the proposed phase feedback, in order to maximize the overall received signal-to-interference-plus-noise power ratio (SINR). This allows the receiver to separate the two users with a linear detection. We also propose an efficient search method for the phase feedback, which reduces the complexity of computation. For practical applications, the quantized feedback of the proposed system is designed. Simulation results show that the proposed system with only 1-bit feedback considerably improves the performance of the MIMO-MAC system.

This paper proposes a bit-interleaved coded multilevel modulation for non-orthogonal cooperative transmissions. The proposed system encodes and interleaves multiple layers together, using one encoder and one interleaver, in order to average the performance of multiple layers with unequal error probabilities. The multiple layers are mapped by hierarchical symbol mapping. To improve the performance of the proposed system, the relay transmits the layers with a different hierarchical mapping pattern from the source, which is optimally derived for minimizing mean square error. To mitigate error propagation from the relay, we propose a power scaling scheme based on the error performance of the layers. The detected signals at the relay are scaled before being transmitted to the destination. A corresponding destination structure is also presented, where multiple layers can be decoupled by an iterative equalization with improved soft information. To estimate the performance of the proposed system, we develop a density evolution technique, and show that the predicted performances are consistent with simulated performances. Simulation results indicate that by using the optimal mapping pattern, power scaling, and iterative equalization with improved soft information, the proposed technique achieves both cooperative diversity and coding gains, and thus outperforms conventional cooperative schemes.

This paper proposes a spectral efficient cooperative diversity technique with multi-layered modulation for high data rate transmissions. The proposed system transmits with different cyclic delay and phase rotation patterns, in order to achieve cooperative diversity gain for all transmit signals from the source. Since these patterns increase the interference between the layers, we derive optimal cyclic delay and phase rotation patterns to minimize mean square error. With the optimal patterns, the proposed system still suffers from inter-layer interference, especially in high-order modulations. To overcome this problem, multiple layers are separately interleaved by layer-specific interleavers and are mapped by hierarchical symbol mapping for the high data rate transmission with cooperative diversity. A destination structure with iterative equalization is also presented to separate each layer and extract diversity gain for high data rate transmissions. The proposed system can use reliable feedback from the layers and effectively remove the inter-layer interference. To estimate the performance of the proposed system, we develop a density evolution technique. It is shown that the predicted performances agree with simulated performances. Simulation results indicate that the proposed system achieves cooperative diversity and has better performance than conventional cooperative systems.

This paper proposes a bit-interleaved coded transmission with multilevel modulation for multiple-input multiple-output orthogonal frequency-division multiplexing (MIMO-OFDM) systems. In the proposed system, multiple layers are encoded and interleaved together, using one encoder and one interleaver, and then mapped by hierarchical symbol mapping. A corresponding receiver structure is presented, where multiple layers can be decoupled by iterative MIMO detection and equalization with ordered successive interference cancellation (SIC) and full log-likelihood ratio (LLR). Full LLR provides reliable estimates of transmit signals, and significantly improves the performance of proposed multilevel modulation. Simulation results show that the proposed system has better performance than conventional modulation schemes such as bit-interleaved coded modulation (BICM) and multilevel BICM (MLBICM).

This paper proposes a full-rate cooperative communication technique with spatial diversity for single-carrier transmissions. In order to achieve both the spatial diversity and the full-rate, data streams are simultaneously transmitted through all direct and relay channels with different phase rotation and cyclic delay patterns. The phase rotation and cyclic delay patterns are derived in the sense of minimizing interlayer interference and a corresponding destination structure is presented for decoupling each layer at the destination. Simulation results show that the proposed technique achieves spatial diversity without sacrificing spectral efficiency and outperforms conventional full-rate cooperative communication techniques.

In this letter, we propose a new multiuser detection scheme for a space-frequency block code (SFBC) single-carrier modulation with frequency-domain equalization (SC-FDE). The iterative multiuser detection method used for the single transmit antenna system cannot be directly applied to SFBC SC-FDE, because there exists the off-diagonal components of channel matrices corresponding to multiuser interferences after maximal ratio combining. The output equations of SFBC combiner are reformulated, and the equalizer coefficients are derived for the SFBC SC-FDE system. Simulation results show that the proposed SFBC IMD-FDE efficiently provides the diversity gain, in the presence of multiuser interferences.