Downlink Space–Time Spreading Using Interference Rejection Codes

In this paper, the authors will investigate the performance of a loosely synchronized (LS) code-based space–time spreading (STS) scheme in comparison to that of classic Walsh code and pseudonoise code-based STS when communicating over dispersive Nakagami-m multipath channels. Closed-form formulas are derived for characterizing the bit-error-rate performance as a function of the number of resolvable paths L and the number of users K. Our numerical results suggest that the employment of LS code-based STS scheme is beneficial in a low-user-load and low-dispersion channel scenario, where a near-single-user performance can be achieved without a multiuser detector. Index Terms—Code-division multiple access (CDMA), Gaussian approximation, interference-free window (IFW), large area synchronized (LAS) codes, loosely synchronized (LS) codes, Nakagami-m fading

COSSAP simulation model of DS-CDMA indoor microwave ATM LAN

This thesis presents an original work in the area of designing and implementing a simulation testbed for modelling a high speed spread spectrum Asynchronous Transfer Mode (ATM) Local Area Network (LAN). The spread spectrum technique used in this LAN model is Direct Sequence Code Division Multiple Access (DS-CDMA). The simulation model includes at least a physical layer of such a LAN, embedded into the COSSAP1 simulation environment, and has been fully tested. All the newly developed building blocks are comprised of standard blocks from the COSSAP libraries or compatible user-built primitive blocks (only where it is absolutely necessary), and are flexible enough to allow the modification of simulation or model parameters; such as the number of signal channels, modulation method used, different spreading code sequences and so on. All these changes can be made with minimal effort. Another significant contribution made in this thesis is the extended research into evaluating the Bit Error Rate (BER) performance of different spread spectrum COMA coding schemes for an indoor microwave A1M LAN [8]. Different spread spectrum CDMA coding schemes are compared for their transmission error rate in Additive White Gaussian Noise (AWGN) channel with varying transmitted signal power and at different channel Signal to Noise Ratio (SNR) levels. Since a wireless microwave channel is very prone to transmission errors, a major contribution of the simulation testbed developed in this thesis is its use in the finding of an optimal physical layer transmission scheme with the best Bit Error Rate (BER) performance in an indoor environment

COMPLEX PULSE FORMING TEACHNIQUE USING AM DETECTOR TYPE CIRCUITRY AND THE APPLICATION OF CDMA TO RFID FOR THE SIMULTANEOUS READING OF MULTIPLE TAGS

A novel complex ultra wideband RF pulse forming technique has been implemented in this research, using the coefficients derived from discrete Fourier transform of a virtual pulse train. Incorporated in this technique is a multiple frequency communication systems designed such that transmitter receiver proximity and the fading effect of the individual frequencies make part of a corresponding modulation technique. A code division multiple access (CDMA) application to RFID to greatly reduce read time, while at the same time eliminating inter tag interference, has been investigated with the analysis of a typical cart aisle scenario. With the current rate of growth of inventory world wide there is a tremendous need for more efficient method of data gathering, data storage, and data retrieval. In this dissertation, the application of the CDMA RFID technology has been analyzed to demonstrate the potentials of integrating the RFID technology to the EPC global numbering system

Investigation of Generalized DSSS Under Multiple Access and Multipath

In this thesis we investigate and compare the average performances of ordinary and generalized direct sequence spread spectrum (DSSS) systems under multi-path fading and multiple-access interference. As part of multiple access performance, we also consider generation of orthogonal and semi-orthogonal codes using various algorithms, and compare cross correlation properties of codes formed by 2-level and 3-level signature sequences. In order to simulate ordinary and generalized DSSS performance under various scenarios, we develop a complete Java library with classes that are well encapsulated with regard to communication modules and loosely coupled so that we can reuse them to create any type of DSSS communication model. We verify the library under Gaussian noise before performing simulations under multi-path fading and multiple-access interference. We find with regards to multi-path fading that generalized DSSS does not perform any better than ordinary DSSS, regardless of how the signature sequences are generated. For multiple access, when using perfectly orthogonal signature sequences, we observe that ordinary and generalized DSSS perform exactly the same. We investigate semi-orthogonal sequences in great detail, and observe that generalized DSSS can accommodate more users than ordinary DSSS for the same performanc

Investigation of Generalized DSSS Under Multiple Access and Multipath

In this thesis we investigate and compare the average performances of ordinary and generalized direct sequence spread spectrum (DSSS) systems under multi-path fading and multiple-access interference. As part of multiple access performance, we also consider generation of orthogonal and semi-orthogonal codes using various algorithms, and compare cross correlation properties of codes formed by 2-level and 3-level signature sequences. In order to simulate ordinary and generalized DSSS performance under various scenarios, we develop a complete Java library with classes that are well encapsulated with regard to communication modules and loosely coupled so that we can reuse them to create any type of DSSS communication model. We verify the library under Gaussian noise before performing simulations under multi-path fading and multiple-access interference. We find with regards to multi-path fading that generalized DSSS does not perform any better than ordinary DSSS, regardless of how the signature sequences are generated. For multiple access, when using perfectly orthogonal signature sequences, we observe that ordinary and generalized DSSS perform exactly the same. We investigate semi-orthogonal sequences in great detail, and observe that generalized DSSS can accommodate more users than ordinary DSSS for the same performanc

Multi-carrier CDMA using convolutional coding and interference cancellation

SIGLEAvailable from British Library Document Supply Centre-DSC:DXN016251 / BLDSC - British Library Document Supply CentreGBUnited Kingdo

Intelligent Processing in Wireless Communications Using Particle Swarm Based Methods

There are a lot of optimization needs in the research and design of wireless communica- tion systems. Many of these optimization problems are Nondeterministic Polynomial (NP) hard problems and could not be solved well. Many of other non-NP-hard optimization problems are combinatorial and do not have satisfying solutions either. This dissertation presents a series of Particle Swarm Optimization (PSO) based search and optimization algorithms that solve open research and design problems in wireless communications. These problems are either avoided or solved approximately before. PSO is a bottom-up approach for optimization problems. It imposes no conditions on the underlying problem. Its simple formulation makes it easy to implement, apply, extend and hybridize. The algorithm uses simple operators like adders, and multipliers to travel through the search space and the process requires just five simple steps. PSO is also easy to control because it has limited number of parameters and is less sensitive to parameters than other swarm intelligence algorithms. It is not dependent on initial points and converges very fast. Four types of PSO based approaches are proposed targeting four different kinds of problems in wireless communications. First, we use binary PSO and continuous PSO together to find optimal compositions of Gaussian derivative pulses to form several UWB pulses that not only comply with the FCC spectrum mask, but also best exploit the avail- able spectrum and power. Second, three different PSO based algorithms are developed to solve the NLOS/LOS channel differentiation, NLOS range error mitigation and multilateration problems respectively. Third, a PSO based search method is proposed to find optimal orthogonal code sets to reduce the inter carrier interference effects in an frequency redundant OFDM system. Fourth, a PSO based phase optimization technique is proposed in reducing the PAPR of an frequency redundant OFDM system. The PSO based approaches are compared with other canonical solutions for these communication problems and showed superior performance in many aspects. which are confirmed by analysis and simulation results provided respectively. Open questions and future Open questions and future works for the dissertation are proposed to serve as a guide for the future research efforts

Design And Simulation For Encoded Pn-ofc Saw Sensor Systems

Surface acoustic wave (SAW) sensors provide versatility in that they can offer wireless, passive operation in numerous environments. Various SAW device embodiments may also be employed for retrieval of the sensed data. Single sensor systems typically use a single carrier frequency and a simple device embodiment since tagging is not required. However, it is necessary in a multi-sensor environment to both identify the sensor and retrieve the information. Overlapping sensor data signals in time and frequency present problems when attempting to collect the sensed data at the receiver. This dissertation defines a system simulation environment exclusive to SAW sensors. The major parameters associated with a multi-device system include the transmitter, the channel, and the receiver characteristics. These characteristics are studied for implementation into the simulation environment. A coupling of modes (COM) model for SAW devices is utilized as an accurate software representation of the various SAW devices. Measured device results are presented and compared with COM model predictions to verify performance of devices and system. Several coding techniques to alleviate code collisions and detection errors were investigated and evaluated. These specialized techniques apply the use of time, frequency, and spatial diversity to the devices. Utilizing these multiple-access techniques a multi-device system is realized. An optimal system based on coding technique, frequency of operation, range, and related parameters is presented. Funding for much of this work was provided through STTR contracts from NASA Kennedy Space Center