Analysis: Wireless Communication and associated network coding technology

Network encoding is based on the storage and forwarding of network information flows at network relay nodes to improve network throughput and save network bandwidth.

In wireless communication networks, network coding, as one of the key technologies, can reduce network resource consumption to a certain extent, improve spectrum resource utilization, and transmit as much data as possible in limited spectrum resources, increase the channel transmission capacity.

At the same time, the wireless network itself is different from the transmission characteristics of the wired network, it also brings new benefits to network coding, it can improve network performance, structure and protocol.

Currently, most solutions are based on random linear Network encoding. How can we design network encoding solutions under the disadvantage of multi-path fading, making it equally effective in wireless networks is a challenging problem.

Many domestic and foreign scholars and scientific research institutions are committed to the study of network coding, from the initial network information flow to the current combination of cooperative diversity technology and MIMO technology.

This article analyzes network coding in wireless networks and other application technologies from the perspective of physical layer, such as combining them with MIMO, making full use of redundancy and improving system throughput, based on the complex environment of the network in the future, this paper describes its further research direction.

1. Associated Network encoding

With the in-depth research, many advantages of Network encoding are gradually reflected, such as good network throughput, balanced network load, and improved bandwidth utilization. At the same time, the application of network encoding in wireless networks also faces many problems. If Network encoding is combined with other application technologies, the performance of the application system will be greatly improved.

1.1 combination of Network encoding and channel compilation Codes

The core idea of the combination of network coding and channel compilation and code technology is to use redundant information of network coding to assist channel coding, so as to achieve good anti-noise performance and achieve the maximum channel capacity;

Diversity increase is achieved through redundancy of relay transmission. The combined Encoding Based on Turbo code and low-income ratio code has been widely studied and compared with the traditional network encoding scheme in multi-access Relay channels and time-division multiplexing bidirectional relay channels [and BSC, this fully demonstrates the advantages of combined encoding in terms of energy consumption, channel capacity, and bit error rate, effectively reducing coding complexity and distortion caused by channel noise.

1.2 combination of network coding and cooperative diversity technology

Collaborative diversity technology, that is, in a multi-user environment, each antenna user sends information to their partners when sending their own information. through collaboration between nodes, a virtual antenna system is formed, to obtain a large diversity gain and overcome the fading of wireless channels.

In addition, network Encoding Based on cooperative diversity can simultaneously obtain the diversity gain and Network encoding gain. In the cooperative transmission process, the data transmission rate can be further improved by placing relay on the source and terminal nodes, improving the fading performance of the wireless communication system, and improving the resource efficiency and system capacity.

Collaborative network coding is currently one of the hot topics in wireless mobile communication systems, especially the wireless collaborative communication system based on the physical layer network coding. for dual-source and dual-sink wireless communication systems, it is assumed that both the SI and S of the source broadcast their respective information to the two chinanetcenter dl and.

Due to the limited transmit power, d will exceed the transmission range of S (). S and S will expand the transmission range through shared relay. In traditional cooperative relay systems, to ensure that signals can be transmitted over orthogonal channels, four time slots are required to complete the process, and only two time slots are required after wireless network coding. They are:

(1) broadcast signals to and while broadcasting their signals to R and;

(2) R performs physical layer network coding for the overlapping signals, and broadcasts the encoded signals to dl and d. Because d has received the information broadcast by St (S) in 1st time slots, at the end of 2nd time slots, d, information that can be extracted from the encoded signal. This scheme makes full use of network resources and diversity technology to obtain relatively low error probability, interruption probability, and high encoding gain.

Therefore, a cooperative relay system using physical layer Network encoding can reduce transmission time loss and make data better transmitted in fading channels.

1.3 combination of network coding and MIMO technology

MIMO technology uses multi-antenna and multi-channel at the transmitting end and the receiving end to obtain high diversity gain to improve the channel's multi-path fading characteristics, as well as improve the system capacity, spectrum utilization and data transmission rate; generally, multi-path fading causes packet loss. For MIMO systems, the multi-input and multi-output technology uses spatial diversity to solve this problem.

Because multi-person multi-channel multi-path wireless channel is used, when the transmitted information flow passes through the blank time encoding, M Information substreams are formed, and filM antennas are sent out, received by N receiving antennas after the spatial channel. The receiver uses empty-time Encoding to process the received symbol vectors through Detection Decoding and decodes the data.

The ultimate goal of these two technologies is to restore the original information from the received symbol vector, in order to fully utilize the diversity characteristics of MIMO technology and redundant information not used in traditional network coding, network coding and MIMO technology are combined (MIMO-NC ).

Transmit the received information to the decoder to the maximum extent, reduce the packet loss rate, complete the Detection Decoding process, and obtain a high signal-to-noise ratio gain. The coding process of the MIMO-NC scheme: the information sent by the source is output by the channel encoding, and the information units generated by each node are stored in the cache, and then Network encoding is carried out, generate the encoding package and use Gabis ~ Signal, and then the corresponding waveform is transmitted through the wireless channel through the conversion modulation.

Decoding process: Evaluate the channel of the received packets at the receiving end and extract the Network encoding coefficient from the header. If the header is damaged, the packets are discarded. Otherwise, all packets are stored in the cache, and update the network estimation matrix.

In order to correctly obtain the sending information of the source at the receiving end, the node memory must have at least the same number of independent original data packets to solve the encoding equation D: GX. If the number is less than the required number, the probability that the terminal correctly restores the original information is very low. Therefore, when decoding is enabled, the node starts to detect the number of packets received, determine the number of relay nodes, and finally recover the original information through soft decoding: case.

Similarly, in order to obtain high diversity gain, two network encoders can be used at the sending end in the encoding phase. In this way, there are two Network encoding matrices G1 and G2, And the header stores the encoding coefficient, and encode the same information.

At this time, the encoding gain will be significantly improved, but at the cost of reduced transmission rate, and in the decoding process using self-adaptive MIMO-NC technology, is to improve the transmission rate, reduce the error probability, however, the complexity is also increased. Specific code compilation process: x... It refers to the channel-encoded information unit, which is the encoding coefficient contained in the header of each encoding package. {bn. B coconut} refers to Galois ~ The modulated vector s corresponding to the number .... Y indicates the encoding package received by the receiver from different sources at different times.

In the traditional network encoding, the demodulation process of each data packet and the process of extracting the NC coefficient are separated. In the decoding phase, each data packet is used only to successfully receive data packets, therefore, the advantage of receiving the same information from different nodes is limited. MIMO_NC uses the damaged CP to transmit all received information to the decoder, making full use of redundant information to improve its performance.

2. Further research

At present, the research on Network encoding has become diversified and practical. Multi-path fading is restrained by MIMO diversity technology in LTE-A; Channel characteristics are improved and system performance is improved.

The network architecture of the next generation wireless communication network is complex and changeable. It is not only reflected in the network layer and basic architecture, it is also reflected in complex wireless scenarios, communication environments, and hybrid wireless community structures. How to further meet the requirements of improving system throughput, channel capacity, and reducing bit error rate in such an environment is currently a hot topic. Therefore, we can consider the following aspects in the future study:

(1) network coding is a cooperative communication mode port. It can be combined with other technologies to optimize network performance. In various wireless communication environments, it fully integrates the multi-input, multi-output antenna technology, study the impact of data stream transmission on the network. This paper studies the joint design scheme of physical layer network coding and channel coding based on cooperative diversity technology, as well as data transmission based on network coding, and studies network coding algorithms with low complexity and low latency.

(2) In actual wireless communication networks, channels are often frequency-selective fading. In this environment, the performance analysis of MIMO Network encoding is also worth studying. In addition to the theoretical study of MIMO Network encoding technology, we also need to consider actual scenarios to solve various problems encountered in the application process, such as the impact of compilation Code complexity and latency on system performance, improve system efficiency, coding efficiency and robustness.

3. Conclusion

Network coding technology plays an important role in wireless networks and has broad application prospects. Due to the inherent characteristics of the channel in the wireless communication network, network coding is performed on the physical layer and combined with some related detection technology, error correction coding technology, and MIMO technology. Compared with the traditional network coding method, to achieve better system performance. This paper mainly introduces the scheme and research progress of the combination of Network encoding and cooperative diversity and MIMO technology, and puts forward the direction to be further studied.