A Distributed Transmission Scheme In Two-way Cooperative Communications With Adaptive Forwarding Factor

In the two-way wireless distributed cooperative communication system, distributed space-time coding scheme and distributed space-frequency coding scheme can overcome the problem of low spectral efficiency in one-way cooperative communication systems which is due to the limitations of half-duplex, and it quickly became a hot topic in recent years. In order to excavate the diversity gain in the two-way distributed cooperative system, designing an effective forwarding mechanism for each relay node has become a valuable research topic. Randomized cyclic delay diversity is an effective-way to get the system spatial diversity, time diversity and frequency diversity at the same time.It makes up for the shortage of the cooperation system with cyclic delay diversity technology that cannot make all occasions access optimal system performance, and it also enhanced system practicality. The adaptive forwarding factor can change the amplitude and phase of amplification factor at each relay node in real-time according to the channel state information, which can improve the system performance. This thesis will study a high-speed two-way distributed transmission scheme by combing with the advantage of aforementioned two technology. The contents of this thesis are organized as follows:(1) The one-way and two-way distributed space-time coding scheme with pre-coding techniques in full-rate transmission model is studied. The internal mechanism of transfer scheme and how to achieve full diversity gain are shown in detail.(2) By introducing the cyclic delay diversity technology, we study the distributed space-frequency coding scheme based on the research of distributed space-time coding. How the randomized cyclic delay diversity technology excavate the system time diversity under the premise of obtaining spatial diversity and frequency diversity is analyzed in detail.(3) The high-speed two-way distributed cooperation scheme with randomized cyclic delay diversity technology is discussed in this thesis. The whole transmission scheme is consist of two time slots. In the first slot, the data to be transmitted is broadcasted simultaneously to all relay nodes at both the two source nodes after quadrature phase shift keying modulated and orthogonal frequency division multiplexing modulated; In the second time slot, each relay node calculate its own unique adaptive forwarding factor according to the channel state information. The superposed signal of the data transmitted from two source nodes is amplified by the respective adaptive forwarding factor. Then the signal is broadcasted to the two source nodes after using randomized cyclic delay. The interaction of information are finished within two time slots, thus achieve a high speed data transmission. Theoretical analysis and MATLAB simulation results show that the introduction of randomized cyclic delay diversity technology can obtain extra time diversity and deduce the system bit error ratio, and the introduction of adaptive forwarding factor can excavate the diversity gain of the system furtherly and improve the system transmission reliability.