The paper presents a performance analysis of direct-sequence ultra-wideband (DS-UWB) timing synchronization by means of a delay-locked loop (DLL) systems. The tracking metrics including residual timing error jitter and mean-time-to-loose lock (MTTL) are derived and shown to depend on the UWB waveforms and DLL S-curve characteristics. DLL branch offset tuning in conjunction with signal waveform selection is emphasized. Numerical results are obtained with UWB pulses based on Gaussian monocycle derivatives and modified Hermite polynomials, and the tradeoff between the tracking jitter and MTTL is analyzed. Novel hybrid pulses are introduced and optimized to select proper designs that can achieve a good balance between the different UWB signal timing synchronization figures of merit, with multi-user interference effects taken into account.

The paper presents a comparative analysis of tracking synchronization performance for different ultra-wideband (UWB) signaling waveforms employing a delay-locked loop (DLL) system. Relevant measures, such as residual timing error variance and mean-time-to-loose lock (MTTL), are obtained and shown to be strongly dependent upon the signal waveforms and their spectra. Numerical results are presented to show that the DLL tracking jitter and MTTL are affected by proper signal waveform selection and early-late DLL branch spacing. Illustrative comparisons are given based on representative examples of UWB pulses obtained from Gaussian monocycle derivatives and modified Hermite polynomials. The results can be used as guidelines for proper selection of early-late DLL spacing for each specific signal waveform in order to optimize overall system performance.

The paper addresses the modeling and performance analysis of non-coherent delay-locked loop (NC-DLL) code synchronization for quadrature-spread direct-sequence spread-spectrum (DS-SS) signals in fading channels. A discrete-time stochastic difference equation is presented to model the DLL tracking error dynamics as a first-order Markovian process. The stationary probability density function (PDF) of the tracking error is derived iteratively by solving a Kolmogorov-Chapman integral equation. Numerical examples with different network loading assumptions show that the proposed technique, while having some computational complexity, produces more accurate results when compared to simplified Gaussian approximations. Numerical results are given to illustrate the analysis methodology, where DLL tracking error PDFs are obtained for different signal-to-noise ratios and fading conditions based on Rayleigh, Rician and Nakagami-m models.

The paper investigates the optimum pairing of attribute weighting techniques used with Distance to Ideal Alternative (DIA) selection in Multi-Attribute Decision Making (MADM) applied to wireless network vertical handover. The performance of the DIA algorithm is investigated with Analytical Hierarchy Process (AHP), Fuzzy AHP, Analytic Network Process (ANP), Random Weighting (RW) and Least Squared weighting (LSW) techniques for different user service classes including background, conversational, interactive, streaming traffic. It is found that the use of different weighting techniques for every traffic class results in widely varying performance figures. Comparative numerical results are given to quantify the system performance in terms of best network selection and ranking abnormalities. The paper findings provide guidelines for selecting weighting techniques for each traffic class in order to achieve ideal network selection with minimal ranking abnormality.

Coordinated Multi-Point (CoMP) Multiple Input Multiple Output (MIMO) transmission improves user's coverage and data throughput particularly on the cell edges. To make full advantage of CoMP, radio planning tools need very accurate models that fully capture the MIMO channels characteristics. This paper presents detailed modeling and analysis of an uplink CoMP system using Ray-Tracing (RT)-based channel modeling. The contribution of this paper is to show how close RT simulations can predict end-to-end system performance compared to the real-world measured performance. Thorough drive test measurements and RT simulations were performed. CoMP and Conventional MIMO systems performances are evaluated and compared for measured and RT-simulated channels. The results of several scenarios show that the RT matches the measurements in terms of rates and geometrical properties. The CoMP gain resulting from the measurements is almost double the gain of RT simulations. The differences come from the hardware and the RT 3D models impairments.

Ultra-Wideband (UWB) signaling is finding many applications in through-wall imaging, target positioning, and indoor communications. In this context, signal propagation through walls has to be modeled accurately since the different building materials have varying attenuation and dispersion properties that impact UWB signal propagation. One of the interesting properties of a UWB signal is its ability to penetrate walls and obstacles which comes from the lower frequency components of the signal. However, as the signal propagates through these obstacles, it gets attenuated, slows down, and gets dispersed. In this paper, we present experimental results on the frequency-domain measurements of UWB signal transmission and reflection over a frequency range of 1-18 GHz. The results presented give a thorough characterization of UWB wave propagation through walls made of common building materials (including glass, wood and gypsum). This is done by measuring the insertion transfer function given as the ratio of two signals measured in presence and absence of walls. The materials' dielectric constant and propagation loss are extracted from the measured insertion transfer function. Double layer walls and three layer walls are also investigated. Results from transmission and reflection measurements give good agreement with each other and with other related work in the literature.

This paper presents a novel mobile localization algorithm under non-line-of-sight (NLoS) conditions in a Gaussian scattering channel model involving two base stations (BS) at most. By using such a small number of BSs, the proposed technique avoids problems relative to weak mobile hearability, network overload and linear BSs layout. Based on the known scattering distribution, the Gaussian NLoS hybrid approximate maximum likelihood (G-NLoS HAML) approach presented herein estimates the distances between the mobile station (MS) and the scatterers through the measured hybrid time-of-arrival/angle-of-arrival (ToA/AoA) statistics. Then, it matches the calculated distances to the Gaussian scatterers' distribution in a maximum likelihood (ML) sense. Numerical results prove that the proposed algorithm gives better performance compared to previous approaches.

A novel single base station based localization technique is proposed. Starting from the probability density function of the scatterers' distribution around the mobile station, we apply the maximum likelihood estimator. The mobile location estimate is then approximated iteratively starting from a set of nonlinear equations. Simulation results show that the technique herein can enhance mobile positioning accuracy by as much as 40% (for certain scattering environments). In addition, the performance of the proposed approximate maximum likelihood technique can be further improved when accurate angle-of-arrival (AOA) data is used.

The paper presents a novel approach to increase the performance and/or throughput of iterative belief propagation (BP) decoding of low density parity check (LDPC) codes. The proposed approach is based on utilizing the decoder idle time by introducing two queue s: one at the decoder input and the other at the decoder output. At the presence of an input queue, the decoder runs extra iterations beyond the maximum allowable iterations as long as the input queue is not full. The function of the output queue is to preserve decoder timing, guaranteeing frames to be decoded within a fixed time similar to a conventional LDPC decoder, making it practical for real time applications. Simulation results for a rate ½ (1024,512) progressive edge-growth (PEG) LDPC code show that the proposed approach can increase the decoder performance up to 69% keeping the same throughput, or doubling the throughput while keeping performance almost the same.

Powerful rate-compatible codes are essential for achieving high throughput in hybrid automatic repeat request (ARQ) systems for networks utilising packet data transmission. The paper focuses on the construction of efficient rate-compatible low-density parity-check (RC-LDPC) codes over a wide range of rates. Two LDPC code families are considered; namely, regular LDPC codes which are known for good performance and low error floor, and semi-random LDPC codes which offer performance similar to regular LDPC codes with the additional property of linear-time encoding. An algorithm for the design of punctured regular RC-LDPC codes that have low error floor is presented. Furthermore, systematic algorithms for the construction of semi-random RC-LDPC codes are proposed based on puncturing and extending. The performance of a type-II hybrid ARQ system employing the proposed RC-LDPC codes is investigated. Compared with existing hybrid ARQ systems based on regular LDPC codes, the proposed ARQ system based on semi-random LDPC codes offers the advantages of linear-time encoding and higher throughput.

This paper addresses timing acquisition aspects in direct-sequence code division multiple access (DS-CDMA) systems. Various chip waveform shaping schemes are considered, including both one-chip long full-response pulses, and partial-response ones occupying several chip periods. Different figures of merits are considered in a comparative analysis that seeks to establish performance limits in terms of correct timing detection capability, false alarm rate, bandwidth occupancy, multiple-access interference (MAI), and inter-chip interference (ICI). A waveform design algorithm is formulated to optimize system performance in terms of signal-to-interference-ratio (SIR) subject to other signalling constraints, and a solution based on the use of prolate spheroidal wave functions (PSWF) is derived. Numerous waveform design examples are then constructed to illustrate acquisition detection capability versus system load for both faded and unfaded cases. A comparative assessment of the performance of conventional signalling waveforms against the optimized ones is also presented. In particular, the numerical results show that the half-sine pulse used in minimum shift keying (MSK) is quasi-optimal within the full-response category, while root-raised cosine (RRC) Nyquist filtering with 22% rolloff (used in third generation CDMA standards) is also close to optimal when considering many-chip-long pulses.

This paper considers the bit error probability analysis of direct-sequence code-division multiple access with offset quadrature phase-shift keying (OQPSK) modulation and random signature sequences. A statistical characterization of the decision variable at the output of the correlation receiver is obtained, and several techniques for evaluating the error performance, previously derived for binary phase-shift keying (BPSK)-modulated systems, are then extended to the case of OQPSK. This includes exact bit error evaluation, as well as various approximation methods based on Gaussian modeling of the multiple-access interference terms. These techniques, known as the standard and improved Gaussian approximations, have increasing complexity depending on the level of accuracy required. For BPSK, the standard approximation is typically found to be inaccurate, unless the number of users becomes large, and only the improved approximation yields sufficient accuracy in general. But for the case of OQPSK, the relative performance comparison developed in this paper shows that, for all practical purposes, the simple standard approximation is surprisingly very accurate even with a small number of users.

This paper investigates the effect of chip waveform shaping on the error performance, bandwidth confinement, phase continuity, and envelope uniformity in direct-sequence code-division multiple-access communication systems employing offset quadrature modulation formats. An optimal design methodology is developed for the problem of minimizing the multiple-access interference power under various desirable signal constraints, including limited 99% and 99.9% power bandwidth occupancies, continuous signal phase, and near-constant envelope. The methodology is based on the use of prolate spheroidal wave functions to obtain a reduced-dimension discrete constrained optimization problem formulation. Numerous design examples are discussed to compare the performance achieved by the optimally-designed chip waveforms with other conventional schemes, such as offset quadrature phase-shift keying, minimum-shift keying (MSK), sinusoidal frequency-shift keying (SFSK), and time-domain raised-cosine pulses. In general, it is found that while the optimized chip pulses achieved substantial gains when no envelope constraints were imposed, these gains vanish when a low envelope fluctuation constraint was introduced. In particular, it is also shown that MSK is quasi-optimal with regard to the 99% bandwidth measure, while the raised-cosine pulse is equally good with both the 99% and 99.9% measures, but at the expense of some envelope variation. On the other hand, SFSK is quasi-optimal with regard to the 99.9% bandwidth occupancy, among the class of constant-to-low envelope variation pulses.

The effect of chip waveform shaping on the power efficiency and spectral occupancy of DS-CDMA communication systems is investigated assuming random sequences and coherent reception. A method for designing optimum chip waveforms that minimise the average power of the multiple access interference at a given bandwidth occupancy is derived. The performance improvements of the optimally designed chip waveforms are illustrated by comparing the achieved SIR gain and capacity increase with the figures of some known examples of modulation schemes (such as OQPSK and MSK) that employ conventional chip shaping pulses.