Research On Relay Mapping Scheme Of Physical-Layer Network Coding Based On Modulation Technology

With the rapid development of communication technology, People’s requirements on the speed and reliability of wireless networks are also getting higher. But the openness of the wireless environment brings a great challenge to the reliable transmission of communication. Therefore, relay coordination is needed to complete the data interaction in many cases. In 2000, Dr. R.Alshwede proposed the concept of Network Coding (NC for short):The relay node encodes the data received and then transmits, which effectively improves the throughput of the communication system. S.Zhang applied the ideology of Network Coding to the wireless environment, and introduced the concept of Physical-layout Network Coding (PNC for short) in 2006. PNC uses broadcast features of wireless systems and the superposition of electromagnetic waves to further reduce the communication time slots and improve the system throughput.This paper takes the Wireless Two-way Relay Channel (WTRC for short) as the basic model, emulates and analyses the performances of various modulation strategies in PNC, and go a step further, designs a scheme of combining PNC with channel coding in the case of higher order modulation.This paper firstly introduces the domestic and foreign research status of physical layer network coding. Starting with three relay modes of wireless two-way relay communication systems, the paper introduced the basic theory of network coding and three models of information transmission in WTRC. After that it introduced the applications of NC in wireless communication, i.e. physical layer network coding, besides, the paper introduced the mapping rules of PNC modulation and demodulation with BPSK modulation.In the wireless two-way relay channel with Additive Gauss White Noise (AWGN for short), based on the maximum a posteriori, simulates and analyses the relay mapping and BER performances of various lower order modulation strategies of the physical layer network coding such as PSK, DPSK, FSK etc. analyses and compares BER performances of relay nodes under various modulations. It figures out that the performance of lower order PSK is better than that of FSK in PNC, and with the increase of the modulation order, the PSK’s anti-noise performance in PNC decreases, and the FSK’s anti-noise performance gets better. However, higher order FSK modulation has higher demanding on the equipment. At last, the paper summarizes and compares the PNC application scenarios under various modulations.With the increase of the modulation order, the performance of QAM is better than that of PSK. This paper analyzes the problems existing in the traditional 16QAM modulation relay mapping, and strives to improve the relay-mapping scheme. According to the fact that the decrease in Euclidean distance of constellation points may bring about increase in BER performance, introduced the linear block code with low complexity, and designed a scheme of combining physical layer network coding with linear block code under the condition of higher order modulation. Simulated and analyzed the performances of relay nodes in the scheme, which shows that the scheme proposed in this paper can not only decrease the communication time slots and improve the transmission efficiency, but also can improve the system’s reliability without increasing the system’s complexity.