On the performance of multicarrier CDMA using multiple transmitters (original) (raw)
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Design and performance of multicarrier CDMA system in frequency-selective Rayleigh fading channels
Vehicular Technology, IEEE Transactions …, 1999
This paper presents the advantages and disadvantages of a multicarrier code-division multiple-access (MC-CDMA) system. The transmitter/receiver structure and the bandwidth of transmitted signal spectrum are compared with those of a conventional direct-sequence (DS) CDMA system, and an MC-CDMA design method, how to determine the number of subcarriers and the length of guard interval is discussed. The bit error rate (BER) lower bounds for DS-CDMA and MA-CDMA systems are derived and their equivalence is theoretically demonstrated. Finally, the BER performance in downlink and uplink channels with frequency-selective Rayleigh fading is shown by computer simulation.
Multi-code multicarrier CDMA: performance analysis
2004 IEEE International Conference on Communications (IEEE Cat. No.04CH37577), 2004
A novel multi-code multicarrier code division multiple access (MC-MC-CDMA) system is proposed and analyzed in a frequency selective fading channel. By allowing each user to transmit multiple orthogonal codes, the proposed MC-MC-CDMA system can support various data rates, as required by next generation standards, and achieve spreading gain in the time domain. Multicarrier CDMA provides robustness to multipath and spreading in the frequency domain. The bit error rate of the system is analytically derived in frequency selective fading, with Gaussian noise and multiple access interference. The results show that the proposed MC-MC-CDMA system clearly outperforms both single-code multicarrier CDMA (MC-CDMA) and singlecarrier multi-code CDMA in a fixed bandwidth allocation. This indicates that MC-MC-CDMA should be seriously considered for next generation cellular systems.
Diversity performance of multi-code multi-carrier CDMA communications systems
2005
In this paper, multi-code spread spectrum CDMA system is analyzed. The transmitter and receiver needed for this system are described and its performance is evaluated for different parameters and different diversity techniques. The channel is assumed to be a multipath slowly fading Nakagami channel. The performance of the system is evaluated in terms of its average bit error rate and is compared to that of the conventional single-code spread spectrum CDMA system. The performance of the system is obtained for three diversity schemes namely, selection diversity, equal gain combining and maximal ratio combining. The effect of changing the number of substreams, users, diversity branches, power level and Nakagami parameter are also investigated.
ANALYSIS THE PERFORMANCE OF MULTI-CARRIER CDMA SYSTEM WITH FADING AND INTERFERENCE
Users moving at vehicular speed communicate over a wireless channel that exhibits time-variant frequency-selective characteristics due to multipath propagation and doppler effects. Multi Carrier Code Division Multiple Access (MC-CDMA) is a relatively new concept to improve the performance over multipath links. MC-CDMA is a modulation method that uses multi carrier transmission of DS-CDMA type signals and an MC-CDMA transmitter spreads the original data stream in the frequency domain over different sub carriers using a given spreading code. The MC-CDMA offers better frequency diversity to combat frequency selective fading. In this paper we evaluate the performance results of MC-CDMA in terms of bit error rate, power, length, code length and no. of subscriber.
Performance of orthogonal multicarrier CDMA in a multipath …
A new multicarrier direct sequence code-division multiple-access (DS-CDMA) system is proposed. Transmitted data bits are serial to parallel converted to a number of parallel branches. On each branch each bit is direct-sequence spread spectrum (DS-SS) modulated and transmitted using orthogonal carriers. This procedure provides the following advantages: the transmission bandwidth is more efficiently utilized, the effect of frequency selective mUltipath interference can be mitigated, and frequency/time diversity is acbieved. The system is analyzed with both a conventional matched-filter (MF) receiver and a RAKE receiver for each carrier. The performance is compared to that of the conventional single carrier system with RAKE receiver. It is shown that the multicarrier system is able to out-perform the RAKE receiver when the system parameters are selected properly. I. INTRODUCTION T HERE has been increasing interest recently in using direct sequence spread spectrum CDS-SS) code division multiple access (CDMA) for commercial applications. DS-CDMA is proposed [or cellular [12], microcellular [14], indoor [15], and satellite [13] communications. CDMA is also a candidate for high data rate applications, such as wireless local area networks LI81 and video phones [19]. Also, DS-CDMA is proposed for consumer communications [16] and communi cations through the power lines [17]. The SS modulation is used to mitigate the different problems encountered in different communication media. Therefore, it is advantageous to design this signal in a fl exible way to be adaptable to various communication channel conditions. The multicanier (MC) system proposed here is one way of achieving this goal. DS-SS CDMA signals have a wide bandwidth (BW) and may be subject to frequency selective multipath fading. It is known that without coding or diversity, the performance of DS-CDMA degrades rapidly when the number of users increases [7], A RAKE receiver [1], [11] can be utilized to achieve path diversity. It must, however, continuously estimate the relative delay of eaeh path and, if maximal-ratio combining is utilized, the gain of each path must also be estimated. A signifi cant signal processing is needed, especially with the existence of other users' multi path interference.
A unified approach to the analysis of multicarrier DS-CDMA over Nakagami-m fading channels
2001
A class of unified multicarrier DS-CDMA (MC DS-CDMA) schemes is defined and its performance is considered over multipath Nakagamim fading channels. The spacing between two adjacent subcarriers of the unified MC DS-CDMA scheme is a variable, allowing us to gain insight into the effects of the spacing on the bit error rate (BER) performance of MC DS-CDMA systems. This unified MC DS-CDMA scheme includes the subclasses of multitone DS-CDMA and orthogonal MC DS-CDMA as special cases. The optimum spacing of the MC DS-CDMA system required for achieving the minimum BER is investigated and the BER performance of the system having optimum spacing is evaluated. The resultant BER is compared with that of both multitone DS-CDMA and orthogonal MC DS-CDMA.
EURASIP Journal on Wireless Communications and Networking, 2016
Multicarrier complementary-coded code division Multiple Access (MC CC-CDMA) is becoming an attractive multiple access technique for high data rate transmission in future wireless communication systems. MC CC-CDMA systems transmitting over frequency-selective channels suffer from multiple access interference (MAI) owing to non-ideal correlation properties of complementary codes (CC). MC CC-CDMA with equalization has recently gained much attention for its ability to offer an excellent performance than traditional systems in frequency-selective fading channels. In this paper, the authors present an analytical study and investigation of MC CC-CDMA downlink system using different combining schemes. The use of parallel interference cancellation (PIC) under frequency-selective Nakagami-m fading channels is also analyzed. A comparison among different combining schemes is provided to show the impact of PIC with minimum mean square error combining (MMSEC) and maximal ratio combining (MRC) on the performance of MC CC-CDMA system. The analytical and simulation results show that the combination of general combining schemes with PIC provides an efficient solution to suppress MAI in downlink MC CC-CDMA system than conventional MC-CDMA systems using Walsh codes under frequency-selective channels.
IEEE Transactions on Communications, 2006
The carrier-frequency offset effect on the performance of asynchronous multicarrier direct-sequence code-division multiple-access (MC-DS-CDMA) systems with aperiodic random spreading and correlated Rayleigh fading is studied in this paper. We obtain the optimum combining filter that maximizes the signal-to-interference-plus-noise ratio (SINR) of the combined statistics and exploits correlated information among subchannels. A closed-form expression for the unconditional covariance matrix of the interference-plus-noise vector, which forms the basis of our theoretical analysis of the maximum SINR and the average bit error probability formula, is derived by averaging several random parameters including asynchronous delays, correlated Rayleigh fading, and signature sequences. The analytic results obtained are applicable to MC-CDMA with appropriate modifications. Furthermore, we show that the MC-CDMA system with a common random signature sequence over all subcarriers for a given user outperforms that with distinct sequences over different subcarriers. Finally, the performance of MC-CDMA systems using the optimum combining technique is compared with that of different combining filters in the simulation.
MC-CDMA with quadrature spreading over frequency selective fading channels
1997
Abstract Multicarrier CDMA (MC-CDMA) schemes resolve the frequency selectivity in multipath fading channels and have good spectral properties. Spreading the information over many subcarriers adds flexibility to the system and a redundancy between subcarriers that can be combined with the derived frequency diversity from the fading channel. The performance of an MC-CDMA scheme over frequency selective, slowly fading channels is studied analytically and by computer simulations.