Novel feedback and signalling mechanisms for interference management and efficient modulation

摘要

In order to meet the ever-growing demand for mobile data, a number of different technologiesudhave been adopted by the fourth generation standardization bodies. These include multiple accessudschemes such as spatial division multiple access (SDMA), and efficient modulation techniquesudsuch as orthogonal frequency division multiplexing (OFDM)-based modulation. Theudspecific objectives of this theses are to develop an effective feedback method for interferenceudmanagement in smart antenna SDMA systems and to design an efficient OFDM-based modulationudtechnique, where an additional dimension is added to the conventional two-dimensionaludmodulation techniques such as quadrature amplitude modulation (QAM).udIn SDMA time division duplex (TDD) systems, where channel reciprocity is maintained, uplinkud(UL) channel sounding method is considered as one of the most promising feedback methodsuddue to its bandwidth and delay efficiency. Conventional channel sounding (CCS) only conveysudthe channel state information (CSI) of each active user to the base station (BS). Due toudthe limitation in system performance because of co-channel interference (CCI) from adjacentudcells in interference-limited scenarios, CSI is only a suboptimal metric for multiuser spatialudmultiplexing optimization. The first major contribution of this theses is a novel interferenceudfeedback method proposed to provide the BS with implicit knowledge about the interferenceudlevel received by each mobile station (MS). More specifically, it is proposed to weight theudconventional channel sounding pilots by the level of the experienced interference at the user’sudside. Interference-weighted channel sounding (IWCS) acts as a spectrally efficient feedbackudtechnique that provides the BS with implicit knowledge about CCI experienced by each MS,udand significantly improves the downlink (DL) sum capacity for both greedy and fair schedulingudpolicies. For the sake of completeness, a novel procedure is developed to make the IWCS pilotsudusable for UL optimization. It is proposed to divide the optimization metric obtained from theudIWCS pilots by the interference experienced at the BS’s antennas. The resultant new metric, theudchannel gain divided by the multiplication of DL and UL interference, provides link-protectionudawareness and is used to optimize both UL and DL. Using maximum capacity scheduling criterion,udthe link-protection aware metric results in a gain in the median system sum capacity ofud26.7% and 12.5% in DL and UL respectively compared to the case when conventional channeludsounding techniques are used. Moreover, heuristic algorithm has been proposed in order toudfacilitate a practical optimization and to reduce the computational complexity.udThe second major contribution of this theses is an innovative transmission approach, referredudto as subcarrier-index modulation (SIM), which is proposed to be integrated with OFDM. Theudkey idea of SIM is to employ the subcarrier-index to convey information to the receiver. Furthermore,uda closed-form analytical bit error ratio (BER) of SIM OFDM in Rayleigh channeludis derived. Simulation results show BER performance gain of 4 dB over 4-QAM OFDM forudboth coded and uncoded data without power saving policy. Alternatively, power saving policyudmaintains an average gain of 1 dB while only using half OFDM symbol transmit power.