The Research And Implementation Of Relaying Systems Based On Physical Network Coding

The paper has analyzed the influence of Physical-layer Network Coding (PNC) in improving the capacity of a relaying system. Then, a simple demodulation scheme for superposed signals in PNC-based systems has been proposed Furthermore, an implementation model of a two-way relaying system has been designed and turned into reality with the Software Define Radio (SDR) technology.Firstly, with the assumption that transmitting power, occupied bandwidth and timeslots in the two relaying systems are equal, transmission capacities of traditional time-division one-way relaying systems and two-way relaying systems based on PNC have been analyzed referring to the Shannon theorem. In the analysis, the channel fading is different in transmission links between different sources and the relay. Referring to the analyzing results,a conclusion has been drawn that the capacity performance of the two-way relaying system based on PNC is not always better than that of the traditional time-division one-way relaying system, especially when the channel fading of different transmission links differs much. In addition, make use of the numerical calculation and the drawing principle of contour maps, a unique map (named pH map) has been conceived out, which shows the average maximum transmission rates in each transmission timeslot in all communication conditions and the corresponding optimal transmitting power distribution factors between different sources. Observing the pH map, we know PNC’s ability to enhance the transmission rate of relaying systems is from exploiting the transmission capacity of relaying systems when the systems are working in balancing communication scenarios.Secondly, statistic characteristics of superposed signals have been analyzed in two-way relaying systems where the channel noise is the Gaussian white noise and the channel fading is known. Based on the statistic characteristics, a novel demodulation algorithm for superposed signals is proposed by applying the Maximum APosteriori (MAP) principle to demodulations of two orthogonal signal domains. The computation complexity of the proposed demodulation algorithm is much less than that of the existing minimum Euclidean distance algorithm; and simulation results show that the proposed algorithm has the similar performance with the optimal minimum Euclidean distance algorithm when the difference between two phase offsets caused by two different transmission links is multiples of π/2. At last, an implementation model of a two-way relaying system based on the Demodulation-and-Forward (DmF) PNC is proposed. In the system Orthogonal Frequency Division Multiplexing (OFDM) are adopted; two sources and a relaywork in the same frequency and using the transmission sources with the time-division multiple access technique. In addition, the system has been realized on the SDR platform consisting of the Universal Software Radio Peripheral (USRP) and LabVIEW.