Power-efficient transmission design for MISO broadcast systems with QoS constraints

This paper considers a novel transmitter optimization problem for MISO broadcast systems, where a multi-antenna base station (BS) serves a set of single-antenna mobile stations (MSs) with Quality of Service (QoS) targets formulated in terms of Symbol Error Probability (SEP): data inputs are drawn from a discrete alphabet, precoding is performed by the BS to generate appropriate signals transmitted over the channel, symbol-by-symbol detection is performed at each MS, and a minimum SEP target is imposed at each MS as the QoS target. Starting with the system adopting standard constellations and with focus on 16-QAM, the SEP constraints are formulated and characterized by a set of convex relaxations on the received signals. The resulting problem is convex, and can be efficiently solved by the primal-dual interior point method. Numerical results demonstrate that the proposed precoder provides significant transmission power reduction compared with the linear zero-forcing (ZF) precoder under the same SEP targets. Turning to the system with Tomlinson-Harashima type constellations, a similar convex relaxation approach is applied and the corresponding convex optimization problem is presented. The proposed precoding scheme is shown to outperform both the previous scheme (based on regular constellations with convex relaxation) and the standard Tomlinson-Harashima precoding using zero forcing.7 page(s

Energy-Efficient System Design for Future Wireless Communications

The exponential growth of wireless data traffic has caused a significant increase in the power consumption of wireless communications systems due to the higher complexity of the transceiver structures required to establish the communication links. For this reason, in this Thesis we propose and characterize technologies for improving the energy efficiency of multiple-antenna wireless communications. This Thesis firstly focuses on energy-efficient transmission schemes and commences by introducing a scheme for alleviating the power loss experienced by the Tomlinson-Harashima precoder, by aligning the interference of a number of users with the symbols to transmit. Subsequently, a strategy for improving the performance of space shift keying transmission via symbol pre-scaling is presented. This scheme re-formulates complex optimization problems via semidefinite relaxation to yield problem formulations that can be efficiently solved. In a similar line, this Thesis designs a signal detection scheme based on compressive sensing to improve the energy efficiency of spatial modulation systems in multiple access channels. The proposed technique relies on exploiting the particular structure and sparsity that spatial modulation systems inherently possess to enhance performance. This Thesis also presents research carried out with the aim of reducing the hardware complexity and associated power consumption of large scale multiple-antenna base stations. In this context, the employment of incomplete channel state information is proposed to achieve the above-mentioned objective in correlated communication channels. The candidate’s work developed in Bell Labs is also presented, where the feasibility of simplified hardware architectures for massive antenna systems is assessed with real channel measurements. Moreover, a strategy for reducing the hardware complexity of antenna selection schemes by simplifying the design of the switching procedure is also analyzed. Overall, extensive theoretical and simulation results support the improved energy efficiency and complexity of the proposed schemes, towards green wireless communications systems