MISO CDMA transmission with simplified receiver for wireless communication handsets

Wideband code-division multiple-access (CDMA) will be utilized in the third generation or 3G wireless communication systems because of its high frequency utilization efficiency and suitability for handling multimedia and multi-rate services. In this paper, we present a system with a simplified receiver structure for DS/CDMA wireless communication handsets, in which improved performance is demonstrated when compared to a conventional DS/CDMA system with a RAKE receiver at the mobile station. The proposed system is obtained by finding the optimal solution to a general multiple-input single-output (MISO) DS/CDMA smart antenna system. It is shown that this solution reduces to a pre-RAKE with space transmit diversity system under the assumption that a simplified receiver structure is invoked. Numerical results show that significant system performance and capacity improvements are possible. They also reveal that the proposed system is not too sensitive to channel estimation errors.

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. >

A CDMA scheme based on perfect Gaussian integer sequences

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.

As Electronic Warfare (EW) relevant technologies develops, more complex and solid defense algorithm is required to keep the military secrets and message in safe. In the wireless communication system, Low Probability of Interception (LPI) communication algorithms, based on Code Division Multiple Access (CDMA), had been introduced to keep the message safe. Frequency Hopping CDMA (FH-CDMA) and Direct Sequence CDMA (DS-CDMA) are the representative methods of the LPI communication algorithm. FH-CDMA is widely used; however, the system has an expensive hardware configuration requirement due to the implementation complexity. In addition, several studies presented improved LPI communication algorithms with a physical-layer level processing; however, they have limitations of unable to well-hide the original signal. To address these problems, we propose an algorithm, called noise communication, which generates Gaussian distributed random numbers that added to In-phase and Quadrature (I/Q) input data independently to hide the original signal. Through Matlab simulation, we compare the conventional DS-CDMA and the proposed algorithm applied DS-CDMA and evaluate the effect of the algorithm with different configurations of PN sequence length and the effective level of the algorithm. Through the evaluations, we observe the algorithm can provide Signal-to-Noise Ratio (SNR) gain than the conventional DS-CDMA and SNR gain has an inverse relationship with system stability. Moreover, we exploit a Software Defined Radios (SDR) hardware to implement the algorithm for the demonstration of a noise-shaped Radio Frequency (RF) signal.

This paper presents an open and flexible radio interface architecture based on Code Division Multiple Access (CDMA) which is particularly tailored to the requirements of third-generation mobile communication systems (FPLMTS/UMTS). The proposed multi-rate radio interface is based on direct sequence CDMA with variable spreading factors, multiple chip rates and multiple RF bandwidths. The basic concept of the multi-rate radio interface is elucidated and some indicative figures as to key parameters of the radio interface are given.

The effect of signal quantisation on noncoherent matched filter code acquisition in a direct-sequence code division multiple access (CDMA) system is considered. The signal structure is applicable to a wideband CDMA system. The effect of quantisation is derived mathematically and verified using computer simulations with several users. The results indicate that the effect of quantisation is not significant, i.e. from the point of view of acquisition, only a few bits are needed. The effect of signal quantisation can be modelled as a noise increase.

Wideband code division multiple access (WCDMA), a widely accepted 3G interface, is based on direct sequence (DS) CDMA technology. In this paper, a simulator implemented in Ptolemy software according to the physical layer specification of the WCDMA system is described. This paper is concerned with providing an analysis and simulation scheme to calculate the error probabilities of WCDMA system in additive white Gaussian noise (AWGN) and multipath Rayleigh fading channels when a simple Rake receiver is employed at the receiver side. The bit error rate (BER) at the uplink (from mobile station to base station) for different channel environments using simulation and then compared with the analysis results are investigated.

Chaotic sequences have good correlation properties and they can be used as address sequences in Spread Spectrum Communication. Chaotic functions are highly sensitive to initial condition and exhibit non-linear behavior. In Chaotic spread spectrum communication systems, different user may be assigned different sequences generated with different initial conditions. Set of binary sequences with good pair wise cross- correlation property finds applications in Direct Sequence- Code Division Multiple Access (DS-CDMA) systems. Security in Direct Sequence-Code Division Multiple Access systems is relatively limited. To enhance security in Direct Sequence- Code Division Multiple Access systems, chaotic sequences are generated. In this paper we analyze the generation of chaotic binary sequences and study of auto correlation and cross correlation properties.

In code division multiple access (CDMA) mobile communication systems with time-varying multipath channels, both intersymbol interference (ISI) and multiple-access interference (MAI) must be considered. The multipath effect usually change the characteristics of the spreading codes. Modification of the conventional receiver structure is needed to account for the interference of the multipath fading. This paper proposes an adaptive receiver for such multiuser direct sequence (DS) CDMA systems in multipath fading. We also analyze the mean square error (MSE) performances of the proposed receiver and the conventional receiver. Both the MSE analysis and simulation results show that the performance of the proposed receiver are better than that of the conventional receiver.

Code division multiple access (CDMA) systems are actively being considered for use in mobile environments. In this paper, new analytical expressions for the bit error rate (BER) of an asynchronous direct sequence (DS) CDMA system employing noncoherent binary demodulation in a Nakagami multipath fading channel are derived. Two binary demodulation schemes are considered, namely, the differential phase shift keying (DPSK) and the square-law demodulation with orthogonal spreading sequences. In each case, the analysis assumes that an arbitrary number of independent but nonidentical resolvable paths are combined by a RAKE receiver.

We consider a combined space-time (ST) block coding and direct-sequence code division multiple access (DS/CDMA) scheme for downlink transmissions over multipath fading channels, in which ST block coding is performed at the chip level, i.e. after code spreading. For this scheme, we develop low complexity and low decoding delay linear ST single-user detection algorithms. In addition, we demonstrate that by exploiting the signal structure imposed by the chip-level ST block coding, blind channel multipath estimation (with only a scalar ambiguity) is feasible, even with the assignment of a single code vector to each user.

A direct sequence optical code division multiple access technique is investigated. This paper introduces, first, the principles definitions of Code Division Multiple Access in radio communications. After that, the performances of Optical Code Division Multiple Access are evaluated in association with a realistic amplified optical channel model.

Blind detection of a desired user's signal in a code-hopping (CH) direct sequence code-division multiple access (CDMA) system is considered. In CH CDMA systems each user switches between a predetermined set of short-code sequences. A user signal in such systems may be treated as the superposition of several virtual short-code signals. A code-constrained inverse filter criterion (IFC)-based blind detector for short-code CDMA signals in asynchronous multipath channels to detect a desired user's signal was recently presented by Tugnait and Li (2001). A novel approach combining the code-constrained IFC and a penalty function is proposed to simultaneously extract all virtual users associated with a given CH user. Global minima of the proposed cost function are analyzed. An extension of an existing subspace-based approach is also investigated. An illustrative simulation example is provided where the proposed algorithm is compared with a clairvoyant matched filter receiver, two linear minimum mean-square error (MMSE) receivers with channels known, and the subspace-based approach.

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.