International Journal of Advanced Network, Monitoring and Controls Volume 03, No.03, 2018 Multi Antenna Precoding Algorithm Based on M Spread Spectrum Sun Ruihua Bai Junying College of Information Engineering College of Information Engineering North China University of Science and Technology North China University of Science and Technology Tangshan, Hebei, China Tangshan, Hebei, China e-mail: [email protected] e-mail: [email protected] An Yongli* College of Information Engineering, North China University of Science and Technology Tangshan, Hebei, 063009, China *Corresponding Author [email protected] Abstract—MIMO multi antenna technology can increase the signals. In order to achieve the purpose of simplifying the capacity and channel utilization of the communication system receiving device. without increasing the bandwidth, and become the key technology in the new generation of mobile communication II. MULTI ANTENNA MIMO SYSTEM system. However, each channel has its own channel parameters, so in the process of signal transmission, the influence of A. Multi Antenna MIMO System Model channel parameters should be considered. When the signal is MIMO multi antenna technology is a major breakthrough received, it needs to be restored, which leads to the complexity in antenna technology in the field of wireless mobile of the receiving signal. Therefore, this paper proposes a multi communication. In theory, it can improve the system antenna precoding algorithm based on M spread spectrum, capacity and frequency efficiency without increasing the precoding before sending signal spread spectrum to simplify time and frequency. Its concept is very simple. It needs a the signal receiving equipment, and verify the feasibility of the transmitter and a receiver that have multiple antennas to algorithm through system error rate. carry out signal transmission simultaneously, so that a wireless MIMO system can be formed. Figure 1 is a Keywords-MIMO; Multi Antenna Technology; Mobile schematic block diagram of the MIMO system: Communication; Spread Spectrum; Precoding I. INTRODUCTION With the rapid popularization of the practical application of wireless communication system, the number of wireless communication users and user service demand have increased exponentially, but the radio spectrum resources which can be used in wireless communication services are extremely limited. The contradiction between the increasing demand of wireless service and the limited radio spectrum resources is becoming more and more prominent. MIMO multi antenna technology is a new type of wireless Figure 1. MIMO system schematic diagram communication technology developed under this background. Multi antenna [1] can effectively improve the channel The transmitter mapped the data signal sent by the space- capacity and is widely used. Multi antenna technology can time map to multiple antennas and sent them out. The make full use of space resources to achieve multiple and receiver sent the signals received by all the antennas to the multi harvest. Without increasing the spectrum resources and space-time decoding to restore the data signals sent by the transmitting power of the antenna, it can increase the transmitting terminal. According to the difference of space- capacity of the system channel, and has obvious advantages time mapping, MIMO technology can be roughly divided in many technologies. It is regarded as the core technology into two categories: spatial diversity and spatial multiplexing. of the next generation mobile communication. Spatial diversity refers to the use of multiple transmission However, the influence of channel parameters on antennas to send signals with the same information through receiver terminals can not be ignored in signal transmission. different paths, and at the same time, multiple independent Therefore, a precoding algorithm based on M spread fading signals of the same data symbol are obtained at the spectrum is proposed, which is pre processed before sending receiver end, thus obtaining the reliability of the diversity DOI: 10.21307/ijanmc-2019-007 61 International Journal of Advanced Network, Monitoring and Controls Volume 03, No.03, 2018 enhancement. For example, in the slow Rayleigh fading If we transmit different information streams on these channel, using a transmitting antenna, the N root receiving parallel sub channels, we can provide transmission data rate, antenna sends signals through N different paths. If the fading which is called spatial multiplexing. According to the between antennas is independent, the maximum diversity correspondence between sub data stream and antenna, the gain can be N. For transmitter diversity technology, the gain spatial multiplexing system can be roughly divided into three of multiple paths is also used to improve the reliability of the modes: D-BLAST, V-BLAST and T-BLAST. system. In a system with the N root receiving antenna with the M root transmitting antenna, the maximum diversity gain B. Main Teachnolody of M*N can be obtained if the path gain between the antenna There are three main technologies in MIMO system: pairs is an independent uniform distribution of Rayleigh space multiplexing, transmission diversity and beamforming. fading. At present, the commonly used spatial diversity 1) Space reuse: techniques in MIMO systems are Space Time Block Code The system divides the data into multiple parts, and the (STBC) and beamforming technology. STBC is an important system is transmitted on the multiple antennas at the coding form based on transmit diversity, the most basic of transmitter. After receiving the mixed signals of multiple which is the Alamouti design for two antennas. data, the parallel data streams are distinguished by the independent fading characteristics between different space The signal model of MIMO multi antenna system: channels. It achieves the purpose of obtaining higher data rate in the same frequency resource. 2) Transmission diversity technology: r1 h11 h12 h1Nt x1 n1 Taking the space time coding as the representative, the r2 h21 h22 h2Nt x2 n2 data stream is jointly encoded at the transmitter side to reduce the symbol error rate due to channel fading and noise. r Nr hNr1 hNr2 hNrNt xNt nNt Space time coding increases the redundancy of the signal at the transmitter, so that the diversity gain is obtained at the The matrix is r Hx n , r is the received signal, H is receiver. the channel matrix, x is the transmit signal, and n is the At present, the commonly used spatial diversity noise signal. techniques in MIMO systems are Space Time Block Code The transmitter mapped the data signal sent by the space- (STBC) and beamforming technology. STBC is an important time map to multiple antennas and sent them out. The coding form based on transmit diversity, the most basic of receiver sent the signals received by all the antennas to the which is the Alamouti design for two antennas. space-time decoding to restore the data signals sent by the 3) Beamforming: transmitting terminal. According to the difference of space- The system generates a directivity beam through multiple time mapping, MIMO technology can be roughly divided antennas, concentrating the signal energy in the direction of into two categories: spatial diversity and spatial multiplexing. the desired transmission, thus improving the quality of the Spatial diversity refers to the use of multiple transmission signal and reducing the interference to other users. antennas to send signals with the same information through Space reuse can maximize the average transmission rate different paths, and at the same time, multiple independent of MIMO system, but only a limited diversity gain can be fading signals of the same data symbol are obtained at the obtained. It may not be used in high order modulation, such receiver end, thus obtaining the reliability of the diversity as 16QAM, in the use of SNR. enhancement. Spatial multiplexing technology uses multiple Wireless signals will be reflected frequently in dense antennas to transmit independent data at the same time, thus urban areas, indoor coverage and other environments, increasing the data capacity of the system. making the fading characteristics of multiple spatial channels For example, in the slow Rayleigh fading channel, using more independent, thus making the effect of space a transmitting antenna, N root receiving antennas sends multiplexing more obvious. Wireless signals are less in the signals through N different paths. If the fading between suburbs and in rural areas, and the correlation between antennas is independent, the maximum diversity gain can be different spatial channels is larger, so space reuse is therefore N. For transmitter diversity technology, the gain of multiple reused. Which effect is much worse. The extra diversity gain paths is also used to improve the reliability of the system. In and coding gain can be obtained by space-time coding of the a system with the N root receiving antennas and with the M transmitted signal, so the high order modulation can be used root transmitting antennas, the maximum diversity gain of in the wireless environment with relatively small SNR, but M*N can be obtained if the paths gain between the antenna the rate bonus of the space parallel channel can not be pairs is an independent uniform distribution of Rayleigh obtained. Space coding technology also performs well in fading. situations where wireless correlation is large. The diversity technique is mainly used