Multi-tone Code Division Multiple Access Research Articles

Multi-tone CDMA design for arbitrary frequency offsets using orthogonal code multiplexing at the transmitter and a tunable receiver

The authors propose a new multi-tone (MT) code division multiple access (CDMA) design which has a superior bit error rate (BER) performance than conventional MT CDMA in the presence of frequency offset. The design involves multiplexing of Walsh codes onto the sub-carriers in conjunction with double differential modulation. To exploit the full potential of the design a partial correlation receiver has been proposed. Depending on the signal-to-noise ratio (SNR) and frequency offset it is possible to tune this receiver for the best possible performance. The simulated BER performance of the proposed system has been found to be better than MT CDMA for small as well as large frequency offsets for both single and multi-user systems in additive white Gaussian noise (AWGN) and Rayleigh fading channels.

Performance analysis of uplink spatial multiplexing MIMO MT‐CDMA over multipath fading channels

In this paper, we consider multiple‐input multiple‐output (MIMO) multi‐tone code division multiple access (MT‐CDMA) uplink transmission over multipath fading channels. The zero‐forcing vertical Bell Laboratories layered space‐time architecture (ZF V‐BLAST) algorithm and maximum ratio combining scheme are applied at the receiver. The average bit error rate (BER) expression is derived provided that the number of receive antennas is not less than that of transmit antennas. The BER expression is verified by simulations. Numerical results show that the numbers of transmit and receive antennas have significant effects on the BER performance of the considered system. Spatial and path diversity show different capabilities to improve the BER performance. The MIMO MT‐CDMA system based on the ZF V‐BLAST algorithm is capable of achieving a better BER performance and a higher capacity than the conventional MT‐CDMA system. Copyright © 2011 John Wiley & Sons, Ltd.

A 0.5 V 4.85 Mbps Dual-Mode Baseband Transceiver With Extended Frequency Calibration for Biotelemetry Applications

This work provides a dual-mode baseband transceiver chipset for wireless body area network (WBAN) system. The modulation schemes include multi-tone code division multiple access (MT-CDMA) and orthogonal frequency division multiplexing (OFDM) to meet multi-user coexistence (up to 8) and high data rate purposes. Based on the analysis of the WBAN operation behavior, several methods including higher data rate, optimal storage determination, and low power implementation techniques are proposed to reduce the transmission energy. To achieve tiny area integration, an embedded phase frequency tunable clock generator and frequency error pre-calibration scheme are provided to extend the frequency mismatch tolerance to 100 ppm (2.5 x of state-of-the-art systems). This chipset is manufactured in 90 nm standard CMOS process. Working at supply voltage of 0.5 V, this chipset is able to provide maximum date rate of 4.85 Mbps with modulator power consumption of 5.52 muW.

A novel bandwidth efficient channel coding scheme using super orthogonal code-based turbo code for S/P-Replica MT-CDMA system

In this paper, we analyze the bit error rate (BER) performance of a new modified structure of multitone code-division-multiple-access (MT-CDMA) system that is serial-to-parallel (S/P)-Replica MT-CDMA. It is shown that with the same bandwidth, the S/P-Replica MT-CDMA system outperforms the conventional system that we name it S/P MT-CDMA. We also propose a novel bandwidth-efficient-channel-coding-scheme (BECCS) based on super-orthogonal-code (SOC)-assisted serially concatenated turbo code (SCSOC) for S/P-Replica MT-CDMA system so that by using it, the coded system without extra bandwidth, significantly improves the performance of an uncoded system over fading channel.

The performance of MT-CDMA system in the presence of carrier frequency offset

In this letter, the sensitivity of an uplink Multi-Tone Code-Division Multiple Access (MT-CDMA) system to the Carrier Frequency Offset (CFO) is investigated. The analytical expression for the Bit Error Rate (BER) of uplink MT-CDMA in the presence of CFO is derived in a multipath Rayleigh fading channel which is verified through simulations. Both Maximal Ratio Combining (MRC) and Equal Gain Combining (EGC) are considered in combining multipath signals in the analysis. It is found that the BER performance can be improved with the number of multipath increasing in the presence of CFO.

Performance Analysis of MT-CDMA System with Antenna Array in a Multipath Fading Channel

In this paper, we propose a multitone code-division multiple-access (MT-CDMA) system employing antenna array at base station with quaternary phase shift keying modulation (QPSK) modulation. Based on the detailed analysis of interference characteristics the BER performance of the proposed MT-CDMA system is provided. With regard to spatial domain combining, the optimum and suboptimum combining weight is derived while the suboptimum set of weights is simplified on sense of that only the knowledge of array vector of desired user alone is sufficient for the optimum combining. Simulation results verify the analysis and show that better performance is achieved for the proposed antenna array system than single antenna MT-CDMA approach.

Two-Stage Maximum Likelihood Estimation (TSMLE) for MT-CDMA Signals in the Indoor Environment

This paper proposes a two-stage maximum likelihood estimation (TSMLE) technique suited for multitone code division multiple access (MT-CDMA) system. Here, an analytical framework is presented in the indoor environment for determining the average bit error rate (BER) of the system, over Rayleigh and Ricean fading channels. The analytical model is derived for quadrature phase shift keying (QPSK) modulation technique by taking into account the number of tones, signal bandwidth (BW), bit rate, and transmission power. Numerical results are presented to validate the analysis, and to justify the approximations made therein. Moreover, these results are shown to agree completely with those obtained by simulation.

Noncoherent MT-CDMA system with post-detection diversity combining

This paper presents a theoretical analysis of a noncoherent multitone code division multiple access (MT-CDMA) system with diversity combining in terms of average bit error rate performance. The study is carried out for both slow Rayleigh and Ricean fading frequency-selective channels with differential binary phase-shift keying (DBPSK) modulation in the indoor environment. The investigation considers post-detection diversity with maximal ratio combining. Assuming a fixed bandwidth, bit rate and transmitter power, the effect of diversity order and number of tones on the systems performance is studied. Numerical results are presented to validate the analysis and to justify the approximations made.

Effect of fading, diversity and interference on the performance of multitone CDMA systems

AbstractThe performance of a multitone Code Division Multiple Access (CDMA) system is investigated in this paper by considering the effect of multipath fading, diversity and narrowband interference. The performance is evaluated in terms of the average bit error rate when both multiple access and partial band interference are present. Results are obtained by deriving the statistics of the receiver output parameters and then tested by numerical evaluation. The bit error rate performance is analyzed as a function of bit rate, bandwidth, delay range and different diversity techniques, while considering issues relevant to system implementation. Comparisons were made between conventional single‐tone CDMA systems and multitone CDMA systems. The effectiveness of multitone CDMA in suppressing interference compared to conventional CDMA system is analyzed. Results reveal considerable performance improvement of multitone CDMA system over conventional CDMA system. Copyright © 2002 John Wiley & Sons, Ltd.

Fractionally spaced decision feedback joint detection for multitone CDMA systems

We consider a fractionally spaced decision feedback joint detector (FS-DFJD) for multitone code division multiple access (CDMA) systems. We first derive the structure of the receiver for an minimum mean-squared error (MMSE) criterion. Then we investigate the bit-error rate (BER) performance achieved by this detector for binary phase-shift keying (BPSK) modulation in steady-state conditions. We consider an asynchronous scenario where the signal of each user propagates over a two-path channel. The resistance of the detector against timing errors is studied, and the resistance against a near-far scenario is also demonstrated.

Fractionally spaced linear joint detection for multitone CDMA systems

We consider a fractionally spaced linear joint detector (FS-LIJD) for multitone code-division multiple-access (CDMA) systems. We first derive the structure of the receiver for a minimum mean-squared error (MMSE) criterion. Then, we exactly evaluate the bit-error rate (BER) achieved by this detector for binary phase-shift keying (BPSK) modulation in steady-state conditions. We consider an asynchronous scenario, where the signal of each user propagates over a two-path channel. The resistance of the detector against timing errors is studied, and the resistance against a near-far scenario is also demonstrated.

Performance analysis of linear joint equalization and multiple access interference cancellation for multitone CDMA

In [18] the combination of multitone modulation with direct sequence spectrum spreading has been introduced. The performance of a correlation receiver with diversity has been evaluated for a multipath channel in the presence of a multiple access interference (MAI) using the Gaussian assumption. In the present paper we analyze the problem of joint equalization and cancellation of the multipath and multiple access interferences for these multitone CDMA (Code Division Multiple Access) systems. A linear structure is first investigated for a mean square error (MSE) criterion. In order to understand the potential of the system we study the steady-state behavior of the joint equalizer-canceler. The investigation is carried out for a joint device following a bank of matched filters and assuming perfect carrier phase and timing recovery. An exact expression for the bit error probability of BPSK symbols before and after cancellation, is obtained in the form of an integral The performance of the joint device is investigated for different types of channels. The resistance to the near-far effect is also demonstrated. Then adaptive structures are derived from a least square approach. Their performance is demonstrated by means of computer simulations.