Comparison of hybrid FDMA/CDMA systems in frequency selective Rayleigh fading (original) (raw)

MFSK-based modulations for hybrid DS/FH-CDMA systems operating in slowly Rayleigh fading channels

IEEE Transactions on Vehicular Technology, 1997

ABSTRACT This paper presents an analytical evaluation of a direct-sequence/frequency-hopped code-division multiple-access (DS/FH-CDMA) system in a Rayleigh fading environment. The modulations under consideration are noncoherent M-ary-frequency-shift keying (MFSK) and an MFSK-based joint-frequency phase modulation utilizing differential binary phase-shift keying (PSK). Multiple-access interference has been taken into account, and the spectral efficiency for uncoded as well as convolutionally coded systems has been calculated

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.

Spectral efficiency for a hybrid DS/FH code-division multiple-access system in cellular mobile radio

IEEE Transactions on Vehicular Technology, 2001

The spectral efficiency of a hybrid cellular direct-sequence/frequency hopping code-division multiple-access (DS/FH-CDMA) system operating in a Rayleigh-fading environment is examined. In this work, spectral efficiency is evaluated in terms of the theoretically achievable channel capacity (in the Shannon sense) per user, on the condition that this is estimated in an average sense. The analysis covers the downlink assuming a static model of operation and a direct-sequence/slow-frequency hopping (DS/SFH) as well as a direct-sequence/fast-frequency hopping (DS/FFH) scheme. As it is shown, the spectral efficiency of cellular DS/FFH-CDMA operating in a Rayleigh-fading environment is greater than that of broad-band DS-and DS/SFH-CDMA systems operating under normalized conditions. This is justified by the combination of path-diversity reception as achieved by conventional coherent RAKE receivers and the frequency diversity that is inherently present in FFH transmission.

Analysis of extended ofdm-cdma system

2001

This paper proposes a hybrid extended OFDM-CDMA modulation technique which can be used principally in mobile communication. It supports the advantages of both of the OFDM and the CDMA systems. The detailed specification is set down. The examination is partitioned into two divisions that are the transmitter and the receiver. The channel which has been used by the simulation is set to linear time-varying filter channel. The performance of these system has been tested by extensive simulations and compared with the OFDM and the CDMA. In very noisy multipath channel the proposed hybrid scheme works efficiently and gives good Bit Error Rate value.

Broadband MC DS-CDMA using space-time and frequency-domain spreading

Proceedings IEEE 56th Vehicular Technology Conference, 2002

In this contribution multicarrier direct-sequence codedivision multiple-access (MC DS-CDMA) using space-time spreading (STS) assisted transmit diversity and frequency-domain (F-domain) spreading is investigated in the context of broadband communications over frequency-selective Rayleigh fading channels. We consider the attainable capacity extension of broadband MC DS-CDMA with the advent of using Time-Frequency-domain (TF-domain) spreading. The BER performance of STS assisted broadband MC DS-CDMA using Binary Phase Shit Keying (BPSK) modulation and TF-domain spreading is investigated by simulation for a range of parameter values. Both the correlation based singleuser detector and the decorrelating multiuser detector are considered. Our study shows that the number of users supported by the broadband MC DS-CDMA system is determined by the product of the T-domain spreading factor and the F-domain spreading factor, while it is independent of the frequency diversity order. Furthermore, when multiuser detection assisted F-domain spreading is considered, the broadband MC DS-CDMA system is capable of supporting a substantially increased number of users, while maintaining a similar bit error ratio (BER) performance to that of the broadband MC DS-CDMA system using no F-domain spreading.

IJERT-Performance Analysis of Multiuser DS-CDMA System

International Journal of Engineering Research and Technology (IJERT), 2021

https://www.ijert.org/performance-analysis-of-multiuser-ds-cdma-system https://www.ijert.org/research/performance-analysis-of-multiuser-ds-cdma-system-IJERTCONV9IS05052.pdf This paper examines the Bit Error Rate (BER) performance of Multiuser Direct Sequence Code Division Multiple Access (DS-CDMA) using spreading codes in fading channels. Code Division Multiple Access (CDMA) system operating over frequency selective, slowly fading channels is considered and its performance is studied analytically and by computer simulations. We consider the downlink of a cellular radio system where for each user a BPSK modulation is used. The spreading codes are arranged in a way that reduces the effect of the multipath fading channel and restores some of the orthogonality losses between users. The obtained results show considerable performance improvement compared to conventional OFDM and to CDMA that uses single spreading codes. Moreover, the spreading codes chosen by the method are in a consistent sequence. Using this code selection method, the system capacity of MU-CDMA can be effectively increased without increasing too much system complexity. Simulation results show that the presented method can work well for fading channels.

Performance of switched selection transmission diversity in FDD/DS-CDMA system

2008 National Radio Science Conference, 2008

In this paper, the performance of Switched Selection Transmission Diversity in FDD/DS-CDMA system will be investigated. This performance will be evaluated by considering the effect of space distance between the diversity antennas and the maximum Doppler frequency (f d) on bit error rate (BER) performance under optimum conditions. This performance is not clarified until now. Moreover, the effect of error on Feedback Antenna Selection bit on uplink will be studied. Rayleigh fading will be assumed. The proposed scheme significantly decreases the average transmit power at the Base Station or the Mobile Station and shows robustness against the BER performance degradation compared with the conventional scheme.

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.

IJERT-A Bi-Level FH-CDMA Scheme For Wireless Communication Over Fading Channels

International Journal of Engineering Research and Technology (IJERT), 2013

https://www.ijert.org/a-bi-level-fh-cdma-scheme-for-wireless-communication-over-fading-channels https://www.ijert.org/research/a-bi-level-fh-cdma-scheme-for-wireless-communication-over-fading-channels-IJERTV2IS90482.pdf In this project, we propose a "Bi-level" frequency hopping code-division multiple-access (FH-CDMA) scheme for wireless communication systems. The new scheme provides flexibility in the selection of modulation codes and FH patterns. By partitioning the modulation codes, our Bi-level scheme can be modified to support more possible users without increasing the number of FH patterns. The performance and spectral efficiency (SE) of the scheme are analyzed. Our results show that the partitioned Bi-level FH-CDMA scheme supports higher data rate and greater SE than Goodman's frequency-shift-keying FHCDMA scheme under some conditions. 1.Introduction FREQUENCY-HOPPING code-division multiple access (FH-CDMA) provides frequency diversity and helps mitigate multi path fading and diversify interference. Major advantages of FH-CDMA over direct-sequence CDMA include better resistance to multiple access interference (MAI), less stringent power control, and reduced near-far problem and multi path interference. By assigning a unique FH pattern to each user, a FH-CDMA system allows multiple users to share the same transmission channel simultaneously. MAI occurs when more than one simultaneous users utilize the same carrier frequency in the same time slot. "One-hit" FH patterns have been designed in order to minimize MAI. In addition, good man, proposed to add Marry frequency shift keying(MFSK) atop FH-CDMA in order to increase data rate by transmitting symbols, instead of data bits. we propose a partitioning method on the modulation codes, such that modulation codes with lower cross-correlation values are grouped together. Using different groups of modulation codes as an additional level of address signature, the partitioned Bi-level FH-CDMA scheme allows the assignment of the same FH pattern to multiple users, thus increasing the number of possible users. The performance of our Bi-level FH-CDMA scheme over additive white Gaussian noise (AWGN), and Rayleigh and Rician fading channels are analyzed algebraically. 2. ORTHOGONAL MC-CDMA  MC-CDMA is a form of CDMA or spread spectrum, but we apply the spreading in the frequency domain (rather than in the time domain as in Direct Sequence CDMA).  MC-CDMA is a form of Direct Sequence CDMA, but after spreading, a Fourier Transform (FFT) is performed.  MC-CDMA is a form of Orthogonal Frequency Division Multiplexing (OFDM), but we first apply an orthogonal matrix operation to the user bits. Therefore, MC-CDMA is sometimes also called "CDMA-OFDM".  MC-CDMA is a form of Direct Sequence CDMA, but our code sequence is the Fourier Transform of a Walsh Hadamard sequence.  MC-CDMA is a form of frequency diversity. Each bit is transmitted simultaneously (in parallel) on many different sub carriers. Each subcarrier has a (constant) phase offset. The set of frequency offsets form a code to distinguish different users. The MC-CDMA method described here is NOT the same as DS-CDMA using multiple carriers. In the latter system the spread factor per sub carrier can be smaller than with conventional DS-CDMA. Such a scheme is sometimes called MC-DS-CDMA. This does not use the special OFDM-like waveforms to ensure dense spacing of overlapping, yet orthogonal sub carriers. MC-DS-CDMA has advantages over DS-CDMA as it is easier to synchronize to this type of signals.