| Two distinct features characterize the modern wireless mobilecommunication systems, which are broadband high-speed transmission andinter-communication in mobility. Those two features pose several challengesfor system designs, such as inter-cell interference mitigation, reliableconnection during movement, distributed/centralized signal processing and soon. Cooperative communication is regarded as one of the most effectivetechnologies to meet the challenges. In particular, it has been shown thatcooperative communication is the core technology to improve the spectrumutilization, cell-edge throughput as well as the overall throughput. MultipleInput Multiple Output (MIMO) technology is widely used in the cooperativecommunication systems and if channel state information (CSI) is available atthe transmitter, advanced MIMO transmit signal processing technologies suchas precoding can be applied to further improve system performance. However,in practice only imperfect channel state information can be obtained. InFrequency-Division Duplex (FDD) systems, the receiver first quantizes CSIand then feeds back the quantized CSI to the transmitter, but since quantizationor feedback bits are limited, quantization errors always exit. Hence, extensiveresearch in both precoding and feedback techniques are of critical importancein the development of wireless communication, which are also the hot points inboth academic and industry.The cooperative communication technologies are usually divided into twocategories, relay cooperative communication technology and multi-pointcooperative (CoMP) communication technology. Based on this, this papermainly focuses on the following three techniques, precoding technology in two-way relay system, precoding technology in multi-user two-way relay systemwith limited feedback, and feedback technology in CoMP systems.In the research of precoding technology in two-way relay system, wejointly design the source non-linear precoder, relay linear precoder and minimum-mean-squared-error (MMSE) receiver based on the MMSE criterion.Compared with traditional precoding schemes which apply linear precoder atsource node, our scheme can obtain better bit error rate (BER) performance. Itis due to the fact that non-linear precoder can eliminate the interference fromdifferent user streams. Since the original problem is a complex non-convexproblem, we decompose it into three more tractable sub-problems. An iterativealgorithm is proposed to jointly optimize the source and relay precoder.Simulation results show that the proposed scheme achieves better BERperformance than the traditional precoding schemes which apply linearprecoder at source node.In the research of precoding technology in multi-user two-way relay systemwith limited feedback, we consider that only quantized channel directioninformation (CDI) is available at relay, and design the relay precoder tominimize the sum mean squared errors conditioned on quantized CDI.Simulation results show that the proposed robust scheme achieves better BERperformance than the non-robust scheme that does not take CDI quantizationerrors into account.In the research of feedback technology in CoMP systems, we mainly focuson the total system performance and the edge user performance when feedbackextra aggregate CQI information and phase information between base stationsunder Joint transmission (JT) mode. System level simulation results show thatwhen feedbacks the aggregate CQI information, the edge user can get27.27%throughput gain. While when feedbacks the phase information between basestations, the edge user can get24.73%throughput gain.The cooperative communications can have different modes. In this paper,we only consider the precoding and limited feedback technologies under relaycooperative communication mode and CoMP JT mode. It is also worthstudying the precoding and limited feedback technologies under othercooperative communications modes, like cooperative scheduler and cooperativebeamforming, etc. |
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