Wireless communication systems are a key means to meet the increasing demands for greater capacity and increased quality-of-service. MIMO systems have the potential to reduce the operational power consumption and enable the use of low complexity schemes for suppressing MU interference (MUI).
One of the cellular communication technologies is CDMA. The combine of MIMO and CDMA is most able technique beyond 4G technologies.
The DS-CDMA system is widely known for removing the effects of Multiple Access Interference (MAI) which degrades the performance of the system.
The addition of interference cancellation which is a sub-optimal procedure of multiuser detector (MUD) in a DS-CDMA-MIMO system can greatly enhance its performance relative to that of conventional CDMA receiver and this can be verified with the help of MATLAB.
MIMO is the key technology in advanced wireless systems. It offers significant benefits over classical systems [1-2]. By using several antennas at both sides, improves the receiving of better signal that solves the major wireless communication system problem. CDMA is the most enabling technology, most suitable for cellular systems . CDMA is used in 2G, 3G and in 4G, 5G along with multiple carrier technologies [4-5]. It is the technique ideally suitable for mobile communications. The CDMA technology combined with MIMO is prominent method for wireless systems.
Multiple access interference is the major challenge in multi access systems. As the users are sharing the resources that causes interference among them.
In order to solve these issues there are several design methods were introduced. They are matched filters, linear optimum filters, sub optimum filters, interference cancellation receiving systems. Among those techniques, interference suppression techniques are most popular and efficient methods. As the techniques used optimization process in order to reduce the error. In the proposed system, non coherent adaptive interference cancellation receiver developed for MIMO-CDMA system. The adaptive system is worked with MMSE scheme.
In Section II, proposed system model discussed. In section III, receiver methods are discussed. Section IV is about simulation results finally the paper is concluded in section V.
II. SYSTEM MODEL
The Figure 1, shows various operations of proposed system. The data which is to be transmitted is mapped in to parallel according to the number of antennas present in the system and then spread with signature codes, then it is modulated with Binary PSK modulation.
Then it is transmitted through MIMO antennas. In the proposed system MIMO antennas configured with spatial multiplexing method. Where the data before sending grouped first and the passed through several blocks and transmitted.
At the receiver side the data received and passed through adaptive filter to solve the wireless issue and then demodulated then despread with the spreading codes and converted back to serial data.
The CDMA system performance depends on the attributes of spreading codes. There are several robust code tracking algorithms available in literature . The combination of MIMO and CDMA is the key method for advanced wireless systems, also the basis for next generation wireless systems.
IV. NUMERICAL RESULTS
The proposed system is simulated with MATLAB. Walsh Hadamard codes are used for spreading . Rayleigh channel used for simulation. BPSK scheme used for modulating the data. Number of antennas are 2X2. The input data is 10k.
Figure 4, represents the BER vs SNR performance of both receivers. Non coherent receiver providing better performance than coherent receiver.
Similarly the figure 5, shown the throughput performance plot. In this graph also non coherent receiver providing better performance.
In the proposed technique the Non coherent receiver for MIMO-CDMA system is designed. And the proposed method providing better performance compared to coherent receiver. It significantly improves the bit error rate and thus capacity of the system. Since, the proposed receiver is applicable for Multimedia messages, video, high-speed Internet access, digital camera and also used in 3G, 4G, Mobile Internet, Mobile phone and next generation wireless systems. The proposed receiver design is very flexible and one can very easily make the necessary modification to investigate the Non-Coherent receivers performance under practical conditions.
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