Performance of first order pseudonoise code tracking loop using smart antenna under multi-path fading environment

A modified pseudonoise (PN) code tracking loop is proposed for direct-sequence spread-spectrum communications in the fast fading channel and strong interference environment. First, to formulate the problem we analyze PN code autocorrelation character in the fast fading channel and strong interference. Then the modified PN code tracking model using limited-length curve fitting algorithm is developed to improve the tracking performance. Analytical expressions of the curve fitting algorithm are derived and then confirmed by means of extensive computer simulation results. In addition, utilizing a DS/BPSK experimental system, several simulation results for PN code tracking performance are also presented in this paper. Very attractive behaviors obtained using the proposed technique are verified.

Pseudonoise (PN) code tracking loops in direct-sequence spread-spectrum systems are often implemented using digital hardware. Performance degradation due to quantization and sampling effects is not adequately characterized by the traditional analog system feedback loop analysis. A low-complexity digital PN code tracking loop with one-bit non-commensurate sampling is analyzed, and the steady-state delay error variance is derived. The results are compared with that of an equivalent analog loop.

In an effort to transmit information over communication channels that contain both Gaussian and non-Gaussian noise components, military and commercial applications frequently rely upon the use of direct sequence spread spectrum (DSSS) techniques. Whilst DSSS is an interference tolerant modulation scheme, situations may be encountered when the processing gain offered by the pseudonoise (PN) spreading code is inadequate. Enhancements to the interference immunity of a DSSS system can be accomplished through the use of signal processing techniques that suppress unwanted interference prior to despreading. To date, the majority of interference suppression techniques developed for DSSS applications, have concentrated on improving detector performance exclusively, and perfect synchronisation between transmitter and receiver is assumed. However, the process of PN code acquisition and tracking within a DSSS receiver is arguably one of the most critical functions within the receiver structure since, if it fails to operate correctly, the wanted signal will not be successfully recovered. An evaluation of the benefits of any interference suppression technique within a DSSS receiver would not be complete without considering at least one level within the synchronisation hierarchy. We examine the improvements in receiver performance, when the process of PN code tracking and detection employs a novel wavelet packet denoising (WPD) procedure for a variety of non-Gaussian channel scenarios.

This paper presents a code synchronization scheme-the time-window control loop (TWCL)-for postdetection RAKE receiver systems that offers the path-diversity effect. Laboratory test results from a postdetection RAKE receiver system with TWCL under a frequency-selective fading environment are introduced. RAKE combining methods, a simple integral demodulation method within a time window, and a recursive least squares (RLS) demodulation method within the time window that uses the RLS algorithm to realize maximal ratio combining, are investigated. It is found that TWCL performance with delay paths (double-spike frequency-selective Rayleigh-fading model) surpasses the performance of both acquisition and tracking without delay paths (nonfrequency-selective Rayleigh-fading model) because of the path-diversity effect. The laboratory results show that TWCL provides good acquisition and tracking performance under the fading conditions experienced with maximum Doppler frequencies of 5 or 80 Hz. It is also shown that the signal energy per bit to noise-power spectral-density ratio (E/sub b//N/sub 0/) required to achieve the bit error rate (BER) of 10/sup -3/ under the double-spike frequency-selective Rayleigh-fading model is reduced by 10 dB compared to the nonfrequency-selective Rayleigh-fading model. The difference in path-diversity effect between the two RAKE combining methods is only 1 dB. From a structural viewpoint, the simple integral demodulation method supports miniaturization and high-speed data-transmission.

This paper presents laboratory test measurement results from a post-detection RAKE receiver system with a time-window control loop (TWCL) as the code synchronization scheme under a frequency-selective fading environment. RAKE combining methods, a simple integral demodulation method within a time-window and a recursive least squares (RLS) demodulation method within the time-window that uses the RLS algorithm to realize maximal ratio combining, are investigated. The result shows that the TWCL provides good acquisition and tracking performance under the fading conditions experienced with maximum Doppler frequencies from 5 to 80 Hz. It is also shown that the required E/sub b//N/sub 0/ when the bit-error rate must be 10/sup -3/ under the double-spike frequency-selective Rayleigh-fading model is reduced by 10 dB compared to the non-selective Rayleigh-fading model. The difference of the path-diversity effect between the two RAKE combining methods is only 1 dB.

A systematic approximation for the mean time to lose lock (MTLL) of a coherent third-order PN-code tracking loop has been derived. Such loops are essential in various spread spectrum systems (Global Positioning System, for example). The computation of the MTLL is based on the singular perturbation method. The application of this method to the coherent delay-locked loop (DLL) yields an approximate expression for the MTLL. Therefore, with the proposed loop model the authors are able to analyze this third-order system at a level that gives a well understanding of the nonlinear loop behavior and the exit phenomenon. The influence of a loop offset due to an acceleration rate (jerk) between transmitter and receiver on the optimal filter parameters is described by comparing MTLL and tracking error performance. As intuitively might be expected it turns out that acceleration rate and code rate are exchangeable in the sense that a lower code rate allows a higher acceleration rate (and vice versa) for the same signal-to-noise ratio in order to maintain the same performance. In a case study, GPS code tracking for objects with high jerk is briefly discussed. >

In this article, a computationally-efficient approach is presented for Bit Error Rate (BER) calculations in multi-user Multiple Input Multiple Output (MIMO) frequency selective fading environments, operating in spatial multiplexing transmission mode. To this end, theoretical expressions for the equivalent Signal to Interference plus Noise Ratio (SINR) per active user and transmission mode, as well as mean BER, are derived. The key idea is that all parameters related to BER calculations can be expressed as sums of identically distributed random variables (RVs). Hence, computational burden can be reduced, since summation formulas take into account the parameters of a standalone RV along with the correlation of an arbitrary pair of RVs. As results indicate, the proposed approach can accurately estimate mean BER in multiuser MIMO orientations with increased reception diversity order, for arbitrary number of transmit/receive antennas, a modulation scheme, and a number of resolvable multi-path components.

The use of smart or adaptive array antennas has attracted considerable interest in the mobile communications community. We investigate the combined use of an adaptive/smart array antenna and Rake receiver (space-time processing) to jointly mitigate the effect of multiple access interference (MAI) and multipath fading in a CDMA system, while taking angle spread into account. We provide simulation results concerning mean bit error rate (BER) performance of such a system for different numbers of antenna elements, numbers of users and angle spreads. The obtained results show that the investigated smart antenna system can effectively combat adverse MAI and fading effects and improve the CDMA system performance.

The landscape of Global Navigation Satellite Systems (GNSS) signals is undergoing significant change. The parallel development of new, more robust and versatile signals along with two new GNSS systems with global reach is having a dramatic impact on the development of GNSS receivers. Receiver manufacturers are continually developing and implementing unique signal acquisition and tracking algorithms, advanced integrity monitoring algorithms, advanced multipath mitigation algorithms and a host of other enhancements in an effort to improve the performance of GNSS receivers and make their products stand out in a crowded field. The objective of this research is to develop a methodology for comparing the pseudorandom noise (PRN) code tracking performance of various receivers. While the overall performance of a receiver depends on many more factors, effective PRN code tracking is fundamental to the operation of a GNSS receiver. The methodology developed in this research requires three fundamental measurements from the receiver under test – code pseudorange, carrier pseudorange and carrier-to-noise-density ratio (C/No). These measurements are generated by all GNSS receivers but may not always be available to the user. Therefore, this methodology can only be performed on receivers that output these values. This methodology might be useful as a tool to evaluate the suitability of various receivers in certain environments or applications (e.g., weak signal environments, high dynamic environments, unfriendly radio frequency (RF) interference environments, etc.) and also as a means of comparing the relative performance of receivers in those environments or applications. Expectations for the research were that the data collection and analysis techniques would generate code loop tracking jitter plots that closely tracked with theoretical curves. In addition, it was expected that different receivers would yield slightly different jitter plots giving them a unique “signature.” Finally, it was expected that some receivers might incorporate scalar code tracking loops and others might incorporate vector tracking loops. The methodology was developed and refined using three receivers from three popular manufacturers, each with a unique set of capabilities. Raw data was collected from each receiver and processed using purpose built algorithms to estimate the code loop tracking jitter for each signal for each receiver. The code loop tracking observations for each of the three receivers tested were compared with theoretical curves generated using closed form equations published in previous papers. In most cases, the data compared favorably. However, there were some significant outliers that are worthy of additional research and analysis. In addition, the jitter plots for one receiver tested indicated that it used scalar code tracking loops and the jitter plots for the other two receivers indicated that they use vector tracking loops. It appears to be possible to determine if a receiver uses scalar tracking loops or vector tracking loops based on the jitter estimates generated in this research. This research indicated that the methodology might be a useful tool for 2 characterizing GNSS receivers and, eventually evaluating their performance in various environments. However, more data collection and analysis is required to further validate and refine the methodology. Also, more analysis of the signals that yielded “non-conforming” jitter plots should be examined in more detail.

Recently, space-time block coded OFDM (ST-OFDM), that applies space-time block codes (STBC) to OFDM, has been proposed. Space-frequency block coded OFDM (SF-OFDM) has also been proposed, where the block codes are formed over the space and frequency domain. ST-OFDM and SF-OFDM achieve good performance over multipath fading environments and fast fading environments, respectively. For systems with two transmit antennas, orthogonal conditions are required to separate the received signals: in ST-OFDM, the frequency responses of two consecutive OFDM symbols are almost identical; in SF-OFDM, the frequency responses of two adjacent subcarriers are almost identical. In practical fading environments, however, these orthogonality conditions sometimes cannot be satisfied. In those environments, the received signals cannot be well separated and the performances are degraded. Recently, a new zero-forcing (ZF) diagonalized maximum likelihood decoder (DMLD) was proposed for the space-time block coded single carrier QPSK system to maintain the orthogonality of STBC under fast fading environments and flat fading environments; the channel separation in DMLD is performed by the ZF algorithm using two receive signals at time index 2n, 2n+1 (STC) or two subcarriers (SFC). The matrix generated after the channel separation is not an identity matrix, but a matrix proportional to an identity matrix. We show that ST/SF-OFDM with DMLD outperform ST/SF-OFDM in terms of bit error rate (BER).

This paper presents a new study in an attempt to apply Fast Euclidean Direction Search (FEDS) algorithm on adaptive smart antennas. The novelty in this work is the use of FEDS algorithm in a smart antenna system for mobile communications because up to our knowledge this algorithm is not applied on smart antenna so far. In order to properly evaluate the performance of smart antenna for mobile communication systems, an Additive White Gaussian Noise (AWGN) channel model is required that each received signal at each element in the array includes only an additive, zero mean, Gaussian noise . The ability of the FEDS algorithm to operate in a fast changing signal environment is examined by subjecting the input signal to Rayleigh fading with a Jakes power spectral density which is a popular choice for land mobile communications systems. Through simulation results of smart antennas for AWGN channel, the RLS and FEDS start to converge from the initial iteration and 10 respectively, whereas, the LMS and NLMS start to converge after 50 and 10 iterations respectively. In the presence of the Rayleigh fading channel, the LMS, and NLMS algorithms converge after 60 and 25 iterations respectively, while the RLS convergence from the initial iteration and FEDS converge from the iteration number 25. On the other hands, the FEDS algorithm shows better tracking and estimation of the desired input signal compared with both LMS and NLMS algorithms and comparable with RLS algorithm. The comparison of linear plot of array factor using FEDS and RLS , both algorithms generates the same deeper null for undesired signals of about í30 dB towards the interferer using an AWGN channel, while it generates deeper null of about -23 dB and -30 dB respectively using the Rayleigh fading channel.

Most proposed space-time codec schemes focus on the single-user scenario, which cannot be applied directly in mobile communication systems. Hence, the paper focuses on a multiuser system with multi-transmit-multi-receive antennas in the frequency-selective fading environment. A vertical Bell Labs layered space-time (V-BLAST) coded direct-sequence code-division multiple-access (DS-CDMA) scheme and its blind channel identification algorithm are proposed. By exploiting an ESPRIT-like method and singular value decomposition, the channels between every transmit antenna of every user and every receive antenna of the base station can be estimated with a closed-form solution. The channel identification algorithm includes two steps and reduces the computational complexity dramatically.

In order to fulfil the increasing demands on capacity and coverage of mobile communication systems smart or intelligent antennas have been suggested. These antennas increase the spectral efficiency of a wireless system by using arrays of antenna elements to shape RF signals in particular directions. Generally, smart antennas can be divided into two approaches: switched multi-beam and adaptive. Adaptive antennas utilize sophisticated signal processing algorithms to continuously distinguish between the desired signal, multipath and interfering signal as well as to calculate their direction of arrival (DOA). This makes it possible to smoothly track users with main lobes and interferers with nulls and thereby constantly maximizing the SINR (signal-to-interference and noise ratio). The DOA is one of the most important parameter for an adaptive antenna system to estimate. It is also the main subject of this paper. We establish whether or not it is plausible to assume the array to be ideal (which is often assumed in array signal processing theory) when the received signals are actually collected with a physical array consisting of standard folded dipoles. In doing so we first measured the element patterns (or steering vectors) of a twelve element antenna array. The results were then used in array signal processing simulations. The performance of two DOA estimation algorithms, MUSIC and ESPRIT, are studied and compared.

The demand for mobile communication systems has dramatically increased in recent years. New concepts and methods, which can optimally exploit the limited resources, are necessary which required the need for new Technologies to satisfy that demand. Smart antenna system is one of those, which combats the co-channel interference and maximizes the user capacity of mobile communication system By shaping and locating the beam of the antenna on the mobile or the target thus decreasing interference to other users. It is now recognized by its higher user capacity in 4G wireless networks by efficiently reducing multipath fading. This paper presents a tool for the modelling, analysis and simulation of Smart Antenna System direction-of-arrival (DOA) estimation and adaptive beamforming needed in the design of smart antenna arrays for wireless mobile communications. The performance of smart antenna system had been studied for some linear and planar array antennas with different numbers of elements. Starting by transmitting the signal through smart antenna system, receiving it and calculating its BER under some 3G Network parameters environment.

Smart antennas have become a promising technology for future mobile communication systems. They can effectively improve the performance of mobile communication systems. With smart antennas, channel modeling is an important issue for the design and performance analysis. In this article, we review some fundamental channel models that combine the time and spatial properties of mobile channels. Although channel models in which the parameters are based on measurement might be more closed to the real channel, we only discuss those models that completely or partially employ theoretical analyses. This is because the data obtained form measurement should only be applied to the associated environments and cannot be generalized.