Approximate interference of a microcellular spreadspectrum system

In this paper adaptive algorithms that may be used for spatial filtering or spatio-temporal filtering in a direct sequence code division multiple access (DS-CDMA) communication system are compared on the basis of signal-io-interference-and-noise-raiio (SINE,) improvements, algorithm convergence rates, capacity enhancement, and computational complexity. Algorithms that have already been proposed as well as some new algorithms are presented for this application. These algorithms fall into two categories: (1) conventional algorithms and (2) channel estimation algorithms. The conventional algorithms use knowledge of a desired reference signal and measurements of the received signal to adapt the antenna weights. In contrast, the channel estimation algorithms use properties of the underlying code structure of DS-CDMA systems to estimate the array response vectors. The estimated array response vectors are then used to determine appropriate antenna weights, either directly or via Capon beamforming.

A new RLS adaptive algorithm with variable forgetting factor for direct sequence code division multiple access (DS-CDMA) communication system is presented. Intersymbol interference (ISI) arises due to multipath propagation, which destroys the code orthogonality, gives rise to multiple access interference(MAI). Therefore, the objective of this paper is to minimize the effect of ISI with a long impulse response environment based on the proposed receiver. We consider an adaptive Laguerre lattice equalizer which applies an optimal method based on the variable step-size least mean square (VSLMS) algorithm for adaptable forgetting factor RLS algorithm to improve bit error rate (BER) performance of the receiver.

The performance of a multi-user chaos-based direct sequence code division multiple access (DS-CDMA) communication system with a sequence synchronisation unit incorporated is examined. Synchronisation is achieved through code acquisition and maintained through the code tracking phase. The performance of the proposed system is evaluated in a Rayleigh fading channel with additive white Gaussian noise and interuser interference. Results are compared to a fade-free channel. It is shown that, although the system is robust to the influence of noise and interuser interferences, it fails to satisfy the maximum allowable bit error rate limit of 10−3 in the Rayleigh fading channel.

In this paper, we consider direct sequence code division multiple access (DS-CDMA) communications, (wireless LAN in the ISM band), where the undesired DS-CDMA signals have different PN sequence lengths compared with the desired DS-CDMA signal. In this situation the conventional orthogonal matched filter (OMF) receiver's performance is poor, and so we propose a new OMF receiver to take into account these undesired signals. We show, through computer simulations, that our proposed OMF receiver will outperform the conventional OMF receiver.

A DS/CDMA (direct-sequence code division multiple access) system using BPSK (binary phase shift keying) modulation is simulated to determine the bit error probabilities for various numbers of users with a processing gain close to that of a cellular network. The results are compared to results obtained using the Gaussian approximation equations. The results obtained are to the feasibility of a DS/CDMA cellular network. It is concluded that DS/CDMA cellular networks appear to offer higher subscriber capacities than existing analog or TDMA (time division multiple access) formats. In addition, DS/CDMA offers additional advantages such as inherent privacy through the use of spreading codes and the ability to combat problems such as multipath fading and narrowband noise. >

Due to the complexity and variability of the underwater acoustic channel, the communication signal is affected by multi-path, time delay, and Doppler frequency shift. Based on the advantageous characteristics of fractional Fourier transform on chirp signal processing, a fractional Fourier transform–based algorithm using combined linear frequency–modulated signal is proposed, which can estimate parameters of underwater acoustic channel and has a better performance than the existing methods. To distinguish multi-user in underwater acoustic communication system, a single-carrier direct sequence code division multiple access communication system combined with the fractional Fourier transform–based algorithm is proposed. Thus, a preliminary study on underwater multi-target identification is carried out. The simulation and experimental results show that the fractional Fourier transform–based algorithm is simple and effective, and the energy can be focused at the “best” fractional order, which can directly determine the multi-path number and complete the channel estimation. The proposed single-carrier direct sequence code division multiple access communication system has good performance on bit error rate when we use corresponding spreading code to distinguish multi-user.

This paper considers the application of I-Q trellis coded modulation (TCM) techniques to synchronous direct sequence code division multiple access (S-DS/CDMA) communication over frequency-selective fading mobile radio channels. The effect of the optimum adaptive coherent RAKE receiver structure with selection of the largest outputs is studied and an exact analytical expression for the pairwise error probability is obtained. This expression is used to evaluate the average BER upper bound through the transfer function bounding technique. The influence over the average BER of various system parameters like the number of active users, the number of selected outputs or sequence length are considered.

The probability of error (Pe) performance of asynchronous direct sequence code division multiple access (DS-CDMA) signals over multi-path Rayleigh fading channels for general (i.e. time-limited and band-limited) chip waveforms is investigated. The numerical values of the Pe are calculated for DS-CDMA signals using conventional time-limited chip waveforms and a band-limited square root raised cosine (SRRC) chip waveform. Analytical calculations are verified by conducting simulations. In terms of the Pe, the SRRC-based system results in a worse performance value than those of the time-limited chip waveform-based systems. However, due to its compact bandwidth, the SRRC-based system provides the highest capacity defined as the number of users per Hertz for a same Pe performance level.

Innovations of modern digital radio technology has enabled many large mobile and distributed information systems, such as inventory tracking systems, to provide readily accessible voice and data services to end users despite mobility of data servers. These systems often contain components that are equipped with radio frequency identification (RFID) tags and interrogators for wireless connectivity. However, there are usually large number of these tagged items in these systems that are highly mobile. The wireless connections among them are also prone to failure. In this paper, we evaluate and compare the performance of two RF tag data access protocols in a single channel per cell implementation: slotted ALOHA Time Division Multiple Access (slotted ALOHA/TDMA) and Direct Sequence Code Division Multiple Access (DS/CDMA).We use a discrete event simulation model to study the impact of these protocols on data service under a diversity of highly mobile operating conditions. Mobile conditions are captured separately by various levels of burst error, uplink and downlink disconnections, and tag population. The results show that performance of DS/CDMA dominates in all mobile conditions. In the most general cases, DS/CDMA outperforms slotted ALOHA/TDMA by 1.5 times faster message time. DS/CDMA is particularly superior in the case of pure uplink disconnections. For burst error and pure downlink disconnections, DS/CDMA renders as much as 2.0 times and 4.5 times faster message time respectively.

In this paper a variable step-size algorithm for adaptive decision feedback equalizer (DFE) for turbo coded direct-sequence code division multiple access (DS/CDMA) communication systems is presented. The proposed adaptive equalizer is using a performance of the system or bit error rate to control the adaptation process of the DFE. By this technique, the performances of the proposed adaptive equalizer cooperate with the attractive soft output Viterbi algorithm (SOVA) of turbo decoder for the DS/CDMA system provides a good statistical in non-stationary channel condition scenario. The simulation results confirm that the performance of the proposed system in terms of bit error rate has been improved over the finite impulse response (FIR) equalizer.

The evaluation of a hybrid acquisition performance has been considered for the pilot signal in the direct sequence code division multiple access (DS/CDMA) forward link. The hybrid acquisition is introduced by the combination of two schemes, parallel and serial acquisitions. The mean acquisition time of the proposed scheme is derived by considering both case 1 (the correct code-phase offsets are included in one subset) and case 2 (the correct code-phase offsets exist at the boundary of two subsets), which are caused by the distribution of correct code-phase offsets in the subset. Detection, false alarm, and miss probabilities are derived for the cases of multiple correct code-phase offsets and multipath Rayleigh fading channel. Results are provided for the acquisition performance with respect to design parameters such as postdetection integration length in search and verification modes, subset size, and number of I/Q noncoherent correlators. Also, comparison between the hybrid acquisition and the fully parallel acquisition is provided in terms of the minimum mean acquisition time.

This paper proposes a packetized direct sequence code division multiple access (DS-CDMA) multimedia wireless communication system that allows for seamless interfacing to asynchronous transfer mode (ATM) broadband networks. The issue of reverse link power control is examined in the context of an indoor environment characterized by a slowly Rayleigh fading channel. Three algorithms are discussed: open loop, channel estimation, and closed loop power control. It is shown that closed loop power control with channel estimation achieves the best performance. The system capacity with perfect power control is calculated. The effect of power control imperfection on the capacity and received signal statistics is studied based on computer simulation. It is shown that actual cell capacity using a two-bit power control command is approximately 40% greater than that using a one-bit power control command at the expense of twice the feedback overhead.

The future wireless mobile communication systems will be required to support high-speed transmission rate and high quality of service. Direct sequence code division multiple access (DS-CDMA) is an important scheme for high-rate wireless communication. The capacity of DS-CDMA can be impaired by two problems; near-far effect and multiple-access interference (MAI). The use of conventional-matched filter detector for multiple users in DS-CDMA fails to combat any of these problems. The performance degradation caused by MAI can be overcome using multiuser detection (MUD). The use of maximum likelihood (ML) sequence estimation detector provides excellent results, but involves high computational complexity. In this paper, we propose a new meta-heuristic approach for MUD using honeybees mating optimization (HBMO) algorithm to detect the user bits based on the ML decision rule for DS-CDMA systems in additive white-Gaussian noise and flat Rayleigh fading channels. In order to improve the solutions generated by the HBMO, a second meta-heuristic method simulated annealing is used. By computer simulations, the bit error rate performance and the complexity curves show that the proposed HBMO-SA MUD is capable of outperforming the other conventional detectors and genetic algorithm detector.

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>

We introduce a novel merger of direct sequence code division multiple access (DS-CDMA) and smart antenna arrays. With regard to the DS-CDMA scheme, we employ carrier interferometry DS-CDMA (CI/DS-CDMA), a novel implementation of DS-CDMA where chips are decomposable into N narrowband frequency components. With regard to the antenna array, we deploy the oscillating-beam smart array. Here, applying proper time-varying phases to the array elements, we create small movement (oscillation) in the antenna array's pattern, while steering the antenna pattern main lobe to the position of the intended user. The oscillating antenna pattern creates a time-varying channel with a controllable coherence time. This, in turn, provides transmit diversity in the form of a time diversity gain at the mobile receiver side. At the receiver, three stages of combining are available: combining time components of the received signal within symbol duration Ts (each experiencing a different fade) to enhance performance via time diversity; combining frequency components which make up the CI/DS-CDMA chip to enhance the performance via frequency diversity; and combining across chips to eliminate the interfering users on the system. Merging CI/DS-CDMA with the oscillating-beam smart antenna at the base station, we achieve very high capacity via the merger of SDMA (available through directionality of the antenna array) and code division multiple access (inherent in CI/DS-CDMA), and very high performance via the construction of receivers that exploit both transmit diversity and frequency diversity. We present the performance gains of the proposed merger.