Rapid converging adaptive interference suppression for direct-sequence code-division multiple-access systems

In most direct sequence code division multiple access (DS-CDMA) systems, the modulation scheme used is a simple one. In this paper, employing a combined modulation scheme in DS-CDMA is proposed. By combining two or more modulation schemes, the resultant symbol energy can be increased, and thus a better symbol error rate performance can be achieved. For the combined modulation scheme, the symbol error rate is determined by the less powerful one of the basic modulation schemes. So a proper selection of modulation combination is essential for power efficiency. In a DS-CDMA system, unlike a narrow-band system, the bandwidth efficiency is closely related to its power efficiency. Thus a combined modulation concept may result in a bandwidth efficient DS-CDMA system. In this paper, we present two DS-CDMA schemes by combining MFSK and coherent MPSK and differential BPSK. These two schemes are respectively denoted as (1) MFSK-MPSK/DS-CDMA, and (2) MFSK-DPSK/DS-CDMA. The proposed schemes have better performance than the conventional CDMA schemes.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A widely linear momentum linearly constrained constant modulus algorithm for the multi-access interferences (MAI) suppression in direct sequence code division multiple access (DS-CDMA) systems is proposed and analyzed in this paper. The widely linear estimation enables constant modulus algorithm (CMA) to produce better output signal to interference plus noise ratio (SINR) and the momentum fastens the convergence. Simulations have confirmed that the proposed algorithm performs better in a DS-CDMA system by employing a BPSK modulation than other algorithms that do not use widely linear processing and momentum.

We propose a multistage joint adaptive array (AA) and spatial interference cancellation (IC) structure for a direct sequence code division multiple access (DS/CDMA) system. The structure utilizes both space and time processing to improve the performance of the base station receiver under the influence of multiple access interference (MAI) and in the absence of power control. The AA comprises a bank of temporal matched filters followed by a beamformer. IC is then used to remove the detected strong user from the received array input. This stage can be repeated for recover and remove more users. Computer simulation shows that, in the absence of power control, the proposed algorithm efficiently detects the weak user information at MAI levels of 30 dB where the conventional space-time structure fails.

Performance analysis of multicell multiuser MIMO MC DS/CDMA system with MMSE user-ordered SIC technique

This paper proposes a new packet rate scheduling scheme for a non-real time data services over the uplink of a burst switching based direct sequence code division multiple access (DS/CDMA) system to support integrated voice/data services. We consider the most general form of optimization problem formulation to determine the optimal number of transmission time groups along with their data rates, which minimizes the average packet transmission delay. An ordered packet length based groupwise transmission (OLGT) scheme is proposed as a simple heuristic solution to this problem, and we present some analytical results for performance comparison with other possible schemes.

This paper proposes a new packet rate scheduling scheme for a non-real time data service over the uplink of a burst switching-based direct sequence code division multiple access (DS/CDMA) system to support the integrated voice/data service. We consider the most general form of optimization problem formulation to determine the optimal number of transmission-time groups along with their data rates, which minimize the average packet transmission delay. An ordered packet length-based group-wise transmission (OLGT) scheme is proposed as a simple heuristic solution approach to this problem and present some analytical results for performance comparison with other possible schemes.

Spatial diversity is an attractive technology for coping with the fading channels encountered in mobile communications. In this paper, the bit error rate (BER) is analyzed theoretically for diversity reception with a RAKE receiver in a Nakagami fading environment using either selection or maximal ratio combining. A coherent binary phase-shift keying (CBPSK) direct sequence code division multiple access (DS/CDMA) system is considered. An arbitrary branch correlation is also considered for any diversity order in the case of identical fading severity on the branches.

ABSTRACTIn this paper, a multi-carrier signaling technique is applied to a direct sequence code division multiple access (DS-CDMA) system. This type of signaling has the desirable properties of lower chip rate, exhibiting a narrow band interference suppression effect, along with robustness to fading, without the need of either an explicit RAKE receiver or an interference suppression filter. Band limited spreading waveforms are used to prevent self-interference. The system performance over a frequency selective Rayleigh channel is evaluated analytically and through computer simulation, in the presence of partial band interference.

This paper introduces an adaptive ( /spl mu/ + /spl lambda/ ) evolutionary algorithm (EA) for multiuser detection (MUD) in direct sequence code division multiple access (DS-CDMA) systems. The EA based multiuser detector takes the output of parallel interference cancellation (PIC) detector as the initial population and adopts maximum likelihood decision rule to detect the user bit sequences. During an EA running, the offspring population size is adaptively adjusted according to the current success probability. The major advantage of the adaptive EA based multiuser detection scheme is that it obtains rather good bit error rate (BER) performance with lower computational complexity. Monte Carlo simulation results show the EA based multiuser detector can always converge to the optimal solution with a small number of generations. Numerical analysis shows its computational time is polynomial complexity and less than other heuristic search algorithms.

An approximate analytical formulation of the resource allocation problem for handling video services with scene changes in a cellular multirate direct sequence code division multiple access (DS-CDMA) system is presented. The video traffic accounts for slow and fast motions. The novelty in this paper is that all grade of service (GoS) or quality of service (QoS) requirements at the connection level, packet level and link layer are satisfied simultaneously, instead of being satisfied at the connection level or at the link layer only. The analytical formulation shows how the GoS/QoSs in the different layers are intertwined across the layers. A complete sharing (CS) scheme with guard capacity is used for the resource sharing policy at the connection level based on the mean rates of the connections. The CS model is solved using a K-dimensional Markov chain. Numerical results illustrate that significant gain in system utilization is achieved through the joint coupling of connection/packet levels and link layer.

The reverse link performance of direct sequence code division multiple access (DS-CDMA) system in wireless communication over a frequency selective multipath fading channel has been investigated in this paper. The channel has been modeled as Nakagami-m distributed frequency selective multipath fading channel. A conventional correlator type receiver has been considered for the analysis. Noise is taken as additive white Gaussian noise (AWGN) with two sided power spectral density N/sub 0//2 . To model multiple access interference (MAI), standard Gaussian approximation (SGA) has been considered in this paper. To mitigate the near-far problem, a power control scheme, but imperfect has been assumed in this paper. The bit error rate (BER) expression for the system has been derived and simulated by varying number of users, number of fading path, processing gain, fading parameter, SNR per bit E/sub b//N/sub 0/ and variation in the amplitude of the received signal. The analysis shows that as the number of simultaneous active user, the number of fading path and the variation in the power of the received signal increases, the BER of the system increases indicating the performance degradation. As the value of the processing gain, the ratio E/sub b//N/sub 0/ and the fading parameter increases, the BER performance of the system improves.

The capacity and error probability of space-time block codes (STBC) are considered for a DS-CDMA system with PAM/PSK/QAM modulation in fading channels. The approach is based on an equivalent scalar A WON (additive white Gaussian noise) channel with a channel gain proportional to the Frobenius norm of the matrix channel for the STBC. Using this effective channel, capacity and probability of error expressions are derived for PSK/PAM/QAM modulation with STBC. Rayleigh, Ricean and Nakagami fading channels are considered. These results are extended to obtain the capacity and probability of error for a multiuser direct sequence code division multiple access (DS-CDMA) system employing STBC.

Criteria for selecting spreading codes for a downlink transmission in a direct sequence code division multiple access (DS-CDMA) system are reviewed. For the most general case of a non-code inversion keying system (CIK) it turns out that the codes must have good partial aperiodic cross and autocorrelation properties as far as the optimisation of the RAKE receiver performance is concerned. Codes generally used such as the Gold or Kasami codes have good cross and auto correlation properties on their whole period but do not have any particular partial correlation properties. In order to solve this limitation, the author proposes a method for building a set of so-called extended structured codes. Each long code is obtained by concatenation of cyclically different short codes of period the processing gain, the short codes of the initial set presenting good correlation properties. This construction is an extension of the structured codes proposed by T. O'Farrell (1991) that overcomes some of their drawbacks such as a short period and a small number of long codes in the constructed set. Simulation results show that the 'extended structured codes' bring a large improvement with respect to Gold and m-sequences.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The multiuser detection (MUD) performance analysis in a synchronous direct sequence code division multiple access (DS-CDMA) system using decorrelating and decision feedback (DFB) receivers, including single path Nakagami fading channel is presented. The lower bounds of the receivers bit error probability (BER) are derived. The analytical and numerical results show that the DFB receiver performs better in the presence of the high Nakagami fading channels.

This paper presents a study on the performance of a wideband direct sequence code division multiple access (DS-CDMA) system for use in wireless local loop (WLL). The WLL environment allows the use of directional subscriber antennas and reverse link time-alignment, reducing both intercell and intracell interference that dictate system capacity. By simulating the intercell interference with directional subscriber antennas and the bit error rate performance in a slowly fading Rician channel, the capacity of both forward and reverse link are calculated. It is demonstrated that convolutional coding alone is not effective in the WLL channel, but, when combined with dynamic power control, gives E/sub b//N/sub 0/ that is within 1 dB of that in a Gaussian channel for moderate Rician K factors.