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In this paper, we propose and analyze a multiuser receiver using a decorrelating filter and Viterbi decoders for trellis coded DS/CDMA systems with biorthgonal signal constellation in asynchronous channels. The biorthogonality is implemented by user signature waveforms and the decorrelating filter. The performance of the proposed system is investigated: it is shown that the proposed system can provide...
In this paper we study the use of projection pursuit[12] and independent component analysis[2] in blind demodulation of CDMA signals in the presence of high multiple access interference. The blind single-user receiver is assumed to be unaware of the signals transmitted by co-channel users. Conventionally, linear MMSE receivers have been applied to solve the problem[10]. However, it is well known that...
This paper proposes a new adaptive blind equalization scheme for asynchronous direct-sequence code-division multiple-access (DS-CDMA) systems based on recursive least squares (RLS). Linear equalizer based blind direct symbol estimation is considered, which is related to sub-space based blind direct symbol estimation. Compared with the subspace based algorithm, the proposed algorithm has increased...
This paper addresses the problem of blind Multiple Access Interference (MAI) suppression in Direct Sequence (DS) Code Division Multiple Access (CDMA) systems. The Constant Modulus (CM) criterion is used to devise a blind adaptive DS CDMA receiver that achieves the same performance as the Minimum Mean Square Error (MMSE) receiver for high values of the Signal to Noise Ratio (SNR). The main limitation...
In multi-path environments, Spread Spectrum multiple access techniques offer attractive properties of rejection of undesired signals and an high spectral efficiency. In this paper is presented a design method for spreading codes which employs Perfect Sequences, a class of complex sequences with singular correlation properties. The main advantage from the use of Perfect Sequences is the oppportunity...
The desired performance of a wireless system depends on the interaction of the number of users carried by the system, hence, influencing the choice of the multiple access scheme (e.g., FDMA vs. TDMA vs. CDMA). This choice has a major impact on the selection of the power control techniques and on the physical layout of the entire system. It is the intention of this paper to provide a fast converging...
In search of acceptable cost versus performance trade-off points for DS-CDMA receivers linear tap-weight filters are considered. Based on stochastic approximation concepts a recursive algorithm is developed for the adaptive optimization of linear filters in the minimum Bit Error Rate (BER) sense. The recursive form is decision driven and distribution free. For AWGN channels, theoretical analysis of...
This paper presents a novel technique to globally estimate and track the direction of arrival (DOA) of different users in an asynchronous CDMA system. The estimates are obtained exploiting the temporal structure of CDMA signals. No training signal nor a priori spatial information is required. The necessary information is extracted directly from the received signals. The proper combining of the overall...
While wireless systems with multiple transmit and receive antennas have been thoroughly investigated over the past ten years, experimental work to corroborate theoretical results is lagging behind. A major reason for this situation is given by the fact that strong theoretical researchers often have no expertise in implementation issues. Also, building an experimental system is very time-consuming...
Kudekar et al. proved that the belief-propagation (BP) performance for low-density parity check codes can be boosted up to the maximum a posteriori (MAP) performance by spatial coupling. In this paper, spatial coupling is applied to sparsely spread code-division multiple-access systems to improve the performance of iterative multiuser detection based on BP. Two iterative receivers based on BP are...
The radio covering area in band shape could be produced by dual antennas system for directional transmitting (DASDT), which transmits radio signals in the same phase by two antennas. DASDT is a kind of transmitter that is compatible with the radio coveringchannelin band shape, and it could be applied in the environment of common radio coveringchannel in band shape, such as corridors, highways and...
Multiuser communication creates some practical difficulties at the receiver for signal detection. When the number of users are more compared to the number of receiver elements of base station, many of the existing detection techniques degrades their performance. For ML (maximum likelihood) MUD (Multiuser detection) an exhaustive search is needed which will increase the system complexity and computating...
This paper deals with a cancellation multiuser detector for CDMA communication systems. Proposed receiver is supposed to be used at the end of up-link channel, leading to consider multipath fading phenomena. Proposed receiver approach consists in performing a weighted selective cancellation of the co-channel interfering signals, divided in two different groups according to the received power level:...
This paper deals with narrowband interference suppression in direct-sequence code-division multiple-access (CDMA) systems. In order to take advantage of the cyclostationary nature of the interfering signal, we propose here to adopt a linear conjugate-linear (LCL) polyperiodically time-varying (PTV) filter in the suppression stage, whose adaptive implementation is based on the RLS algorithm. Unlike...
A modified implementation of the MMSE receiver to be used in a UTRA TDD environment is presented. Simulations are carried out in a multipath fading environment and BER values are obtained, demonstrating that this structure reduces the MAI that appears due to the loss of orthogonality between orthogonal codes in multipath channels. The performance of the proposed structure is compared with that of...
Linearly constrained optimization techniques based on the minimization of the output energy have been proposed for the design of single rate DS-CDMA detectors. The goal of this paper is to apply this approach to dual rate systems where low rate users have symbol periods which are multiples of those of high rate users. It is observed that a high rate (HR) user experiences the same frequency selective...
In this paper, a blind subspace-type single-user array direct-sequence code division multiple access (DS-CDMA) receiver is proposed based on a new joint space-time channel estimation technique for frequency-selective channels. In the proposed approach, the spatio-temporal multipath channel parameters associated with the desired user are jointly estimated with the number of identifiable paths not limited...
This paper deals with an adaptive multiuser detector for DS-CDMA (Direct Sequence Code Division Multiple Access) wireless communication systems, whose main features are low complexity and joint utilization of the time diversity and blind adaptive processing techniques. The proposed multiuser detector, defined as Pre-combining Advanced Blind Adaptive Multiuser Detector (PABA-MUD), a window reprocessing...
This paper compares the performance of several multiuser detection (MUD) algorithms for TD-CDMA (time division CDMA) uplink. The performance study includes the zero-forcing detector, the LMMSE (linear miminum mean squared error) detector and hard-decision parallel interference cancellation (HD-PIC) detector. Overview of the UTRA TDD mode based on TD-CDMA is also given.
Code division multiple access (CDMA) is the multiple access scheme retained for the third generation wireless communication systems, that must support high data rate transmissions, and operate over jammed Rayleigh fading channels. In the current work, we propose and analyze multi-antenna spatio-temporal adaptive receiving structures of detection at the base station, able to cope with degradations...
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