Utilizing the channel correlation for MAI reduction in downlink multi-carrier CDMA systems
نویسندگان
چکیده
An OFDM-CDMA system that utilizes the channelcorrelation in both time and frequency to reduce multiple access interference is proposed. Orthogonal Walsh-Hadamard codes are used for spreading and in order for the codewords to stay orthogonal at the receiver, the channel response must be flat in both time and frequency. A frequency selective fading channel will, however, distort the codewords and thus introduce correlation. The proposed system, named Time-Frequency Localized CDMA (TFLCDMA), places the codeword-chips in rectangular blocks on the time-frequency-grid in a such a way that the difference in scaling of the codeword chips is reduced. The proposed system is found to outperform competing schemes, such as Multi-Carrier (MC) and Multi-Carrier Direct-Sequence CDMA (MC-DS), in terms of bit error rate. The MCand MC-DS-CDMA systems are special cases of the proposed scheme.
منابع مشابه
Performance Analysis of ZF Pre-Coder and Extended Joint Channel Estimation Method in Downlink CDMA with HPA
In the down link scenario of code division multiple access (CDMA) systems, multi user detectors (MUDs) such as linear de-correlating detector (LDDs) provide satisfactory symbol error rates (SERs) at the expense of much increased complexity, they require all active users’ spreading sequences, which is impractical from privacy point of view. To overcome this impracticality, a simple matched filte...
متن کاملBit Error Performance for Asynchronous Ds Cdma Systems Over Multipath Rayleigh Fading Channels (RESEARCH NOTE)
In recent years, there has been considerable interest in the use of CDMA in mobile communications. Bit error rate is one of the most important parameters in the evaluation of CDMA systems. In this paper, we develop a technique to find an accurate approximation to the probability of bit error for asynchronous direct–sequence code division multiple–access (DS/CDMA) systems by modeling the multipl...
متن کاملPower-Controlled Multicarrier and Multiuser Detection Techniques in Wireless CDMA Systems
This paper describes power-controlled multi carrier and multiuser detection techniques for Code Division Multiple Access (CDMA) systems. In conventional CDMA systems, a RAKE receiver is employed to overcome wireless channel effect due to frequency selective characteristics of wireless CDMA systems. Alternatively, multi carrier technique can also be used to overcome the effect of frequency selec...
متن کاملTime-frequency Localized Cdma for Downlink Multi-carrier Systems
An OFDM-CDMA system that utilizes the channel-correlation in both time and frequency to reduce multiple access interference is proposed. Orthogonal Walsh-Hadamard codes are used for spreading and in order for the codewords to stay orthogonal at the receiver, the channel response must be flat in both time and frequency. A frequency selective fading channel will, however, distort the codewords an...
متن کاملFrequency-Domain Pre-Equalization Transmit Diversity for MC-CDMA Uplink Transmission
Recently, multi-carrier code division multiple access (MC-CDMA) has been attracting much attention for the broadband wireless access in the next generation mobile communications systems. In the case of uplink transmissions, the orthogonality among users’ signals is lost since each user’s signal goes through different fading channel and hence, multi-access interference (MAI) is produced, thereby...
متن کامل