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Introduction to Digital Cellular Radio

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... Orthogonal spreading sequences are used in direct sequence code division multiple access (DS CDMA) systems for channel separation and to provide a spreading gain, e.g. [1]. The most popular class of such spreading sequences are the sets of Walsh-Hadamard sequences [2], which are easy to generate. ...
... Orthogonal spreading sequences are used in direct sequence code division multiple access (DS CDMA) systems for channel separation and to provide a spreading gain, e.g. [1]. The most popular class of such spreading sequences are the sets of Walsh- Hadamard sequences [2], which are easy to generate. ...
Chapter
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Golay complementary sequences, often referred to as Golay pairs, are characterized by the property that the sum of their aperiodic autocorrelation functions equals to zero, except for the zero shift. Because of this property, Golay complementary sequences can be utilized to construct Hadamard matrices defining sets of orthogonal spreading sequences for DS CDMA systems of the lengths not necessary being a power of 2. In the paper, we present an evaluation, from the viewpoint of asynchronous DS CDMA applications, of some sets of spreading sequences derived from Golay complementary sequences. We then modify those sets of sequences to enhance their correlation properties for asynchronous operation and simulate a multiuser DS CDMA system utilizing the modified sequences.
... Orthogonal sequences are of a great practical interest for the current and future direct sequence(DS) code-division multiple-access(CDMA) systems where the orthogonality principle can be used for channels separation, e.g. [1]. However, most of the known sets of orthogonal spreading sequences possess very poor aperiodic cross-correlation characteristics, i.e. when there is any misalignment between the sequences corresponding to different users, the cross-correlation between such misaligned sequences is usually quite high, resulting in significant multi-access interference(MAI) problems where it is impossible to guarantee sequence alignment due, for example to different propagation delays. ...
... Let Ai be a complex sequence. Let VfAiAi denote the aperiodic autocorrelation function of the sequence Ai and VAiAi (k) be the kth element in the sequence V'AiAi Sequences (Ai, 1 The matrix AB32x32 defines the set of 32-chip spreading sequences which are characterized by the following correlation parameters: Cmax = 0.9325, Amax = 0.5590, RCC = 0.7269, RAC = 2.0938. The above parameters, used for measuring "good" signatures for CDMA systems, were introduced by Oppermann and Vucetic in [4]. ...
Conference Paper
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This paper presents a new family of complex spreading sequences designed using mutually orthogonal(MO) complementary sets. Based on the technique described in this paper, the correlation properties of sets of sequences are compared to well-known Walsh-Hadamard sequence sets. Further improvement of correlation qualities can be achieved by employing a diagonal modification method. We also present simulation results of an asynchronous multiuser CDMA system using the modified sequences.
... The network planning process requires an adequate representation of the territory. In past years, the standard approach was to subdivide the territory into equally sized hexagons (see [27]) and basic propagation laws were implemented in order to calculate field strengths. By straightforward analytical computations these simplified models could provide the (theoretical) position of the antennas and their transmission frequencies. ...
Article
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We describe a Mixed Integer Linear Programming formula-tion to optimize base stations location and configuration of a wireless network implementing the IEEE standard 802.16 (WiMAX). The system elements relevant to the optimiza-tion model are discussed in detail.
... Orthogonal bipolar sequences are of a great practical interest for the current and future direct sequence (DS) code-division multiple-access (CDMA) systems where the orthogonality principle can be used for channels separation, e.g. [1]. The most commonly used sets of bipolar sequences are Walsh-Hadamard sequences [2], as they are easy to generate and simple to implement. ...
Article
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In the paper, we present a new class of orthogonal bipolar spreading sequences designed based on Goethals-Seidel construction with nega-cyclic matrices. The sequences can be designed for any length equal to 4 (mod 8), and possess good correlation properties. In particular, their aperiodic autocorrelation characteristics are very good. That can be traded off for improvement in the cross-correlation performance using a diagonal modification method, as shown in the example.
... Walsh-Hadamard bipolar spreading sequences are generally used for channel separation in direct sequence code division multiple access (DS CDMA) systems, e.g. [1]. They are easy to generate, and orthogonal [2] in the case of perfect synchronization. ...
Article
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In this paper, we propose a simple method for modifying Walsh-Hadamard spreading sequences to improve their correlation properties for asynchronous DS CDMA applications, while maintaining their orthogonality for perfect synchronization. Simulation results for the DS CDMA systems utilizing 32-chip modified Walsh-Hadamard sequences and are presented and compared to those achieved in the case of system utilizing pure 32-chip Walsh-Hadamard sequences.
... Walsh-Hadamard bipolar spreading sequences are generally used for channel separation in direct sequence code division multiple access systems, e.g. [1]. They are easy to generate, and orthogonal [2] in the case of perfect synchronization . ...
Article
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In this paper, we propose a simple but efficient method for improving correlation properties of polyphase spreading sequences for asynchronous direct sequence code division multiple access (DS CDMA) applications. The pro-posed method can be used to reduce the mean square value of aperiodic crosscorrelation or the mean square value of aperi-odic autocorrelation, the maximum value of aperiodic cross-correlation functions, merit factor or other properties of the sequence set. The important feature of the method is that while it modifies correlation properties of the sequence set, it preserves sequence orthogonality for perfect synchronization, if this is the property of the original sequence set.
... Walsh-Hadamard bipolar spreading sequences can be used for channel separation in direct sequence code division multiple access (DS CDMA) systems, e.g. [1]. They are easy to generate, and orthogonal [2] in the case of perfect synchronization. ...
Article
We propose a simple but efficient method for modifying Walsh–Hadamard sequences to achieve correlation properties suited for asynchronous DS CDMA applications. The proposed method can be used to minimize the mean square value of aperiodic cross-correlation or the mean square value of aperiodic autocorrelation, the maximum value of aperiodic cross-correlation functions, merit factor or other properties of the sequence set. The important feature of the method is that it modifies correlation properties of the sequence set, while preserving their orthogonality for the perfect synchronization. The proposed method can be applied to obtain bipolar, quadri-phase, or general polyphase sequences. Copyright © 2002 John Wiley & Sons, Ltd.
... Orthogonal bipolar sequences are of a great practical interest for the current and future direct sequence (DS) code division multiple access (CDMA) systems where the orthogonality principle can be used for channels separation, e.g. Reference [1]. The most commonly used sets of bipolar sequences are Walsh–Hadamard sequences [2], as they are easy to generate and simple to implement. ...
Article
Summary Orthogonal bipolar spreading sequences are used in direct sequence code division multiple access (DS-CDMA) systems for both spectrum spreading and channel separation. The most commonly used sequences are Walsh- Hadamard sequences of lengths being an integer power of 2. A construction based on Williamson's arrays leading to sequences of lengths N:4 (mod 8) is presented in the paper. Aperiodic correlation characteristics, for example sequence sets of lengths 12-252 are presented. The correlation properties of the sequence sets are later improved using a diagonal modification technique. Copyright # 2003 John Wiley & Sons, Ltd.
... Bipolar spreading sequences derived from Sylvester-Hadamard matrices by simply considering each row of the matrix as a spreading sequence can be used for channel separation in direct sequence code division multiple access (DS CDMA) systems, e.g. Steele (1999). Because of the connection between Sylvester-Hadamard matrices and the Walsh functions described in the previous section, these sequences are often referred to as Walsh-Hadamard sequences in literature dealing with communication systems. ...
Article
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Modern communications systems are heavily reliant on statistical techniques to recover information in the presence of noise and interference. One of the mathematical structures used to achieve this goal is Hadamard matrices. They are used in many different ways and some examples are given. This paper concentrates on code division multiple access systems where Hadamard matrices are used for user separation. Two older techniques from design and analysis of experiments which rely on similar processes are also included. We give a short bibliography (from the thousands produced by a google search) of applications of Hadamard matrices appearing since the paper of Hedayat and Wallis in 1978 and some applications in telecommunications.
Chapter
The personal radio communication industry has spawned much research into propagation phenomena in the 1 to 3 GHz frequency spectrum, and has provided technological advances that create opportunities to capitalize on the use of these higher frequencies for military tactical communications and civilian wireless uses. However, the interests of the personal communication industry has focused upon propagation path configurations that can be considered “high-low,” that is, paths in which one end is close to the ground (an individual user) and the other end is at a higher elevation and utilizes an antenna support structure such as a tower or a building, aircraft or orbiting satellite. Tactical military communication and other emerging wireless applications, on the other hand, usually employ “low-low” path configurations—paths between individual users where the antenna heights at both ends of each link will be 1.5 meters above the ground or less. The difference in geometry of a “high-low” and a “low-low” path is rather obvious, but what is not so obvious is the difference in propagation phenomena, especially fading characteristics, of the two types of paths. A “high-low” path in an urban area is usually characterized by Rayleigh propagation in which no direct line-of-sight propagation path exists and all of the energy from radio transmitter to receiver is by forward scatter and reflections. A “low-low” path between two users is usually via a direct line-of-sight propagation path, but with insufficient terrain clearance to support Gaussian propagation; therefore, the path is characterized as Rician. This paper reviews the Rayleigh, Gaussian and Rician propagation phenomena; describes the different factors that are associated with each of these three types of propagation; and discusses research and experimental work to enable more accurate prediction of Rician propagation loss, expected fading and bit-error rates under different environmental (terrain, foliage, weather, etc.) conditions.
Article
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We present an evaluation, from the viewpoint of DS CDMA applications, of the sets of 12-chip spreading sequences based on Paley's matrix, and sequences of length 20 based on Golay complementary sequences of length 10.
Article
Modern communications systems are heavily reliant on statistical techniques to recover information in the presence of noise and interference. One of the mathematical structures used to achieve this goal is Hadamard matrices. They are used in many different ways and some examples are given. This paper concentrates on code division multiple access systems where Hadamard matrices are used for user separation. Two older techniques from design and analysis of experiments which rely on similar processes are also included. We give a short bibliography (from the thousands produced by a google search) of applications of Hadamard matrices appearing since the paper of Hedayat and Wallis in 1978 and some applications in telecommunications.
Conference Paper
Full-text available
The paper deals with the novel technique of designing complex spreading sequences with only four phases (0.257π, 0.75π, 1.25π, 1.75π). The interesting feature of those new sequences is the fact that not only the complex sequences are orthogonal but the real parts and imaginary parts are independently orthogonal. This can be utilized for spreading of complex constellation signals where the independent spreading using bipolar sequences (real part for in-phase component and imaginary part for quadrature component) can be applied. The paper introduces the theoretical background, and some example constructions of the amicable Hadamard matrices and the corresponding complex spreading sequences. The sequences are later modified using a diagonal method to achieve better correlation properties.
Conference Paper
Most of the recent propagation research that has been sponsored in the 1 to 3 GHz frequency spectrum has centered on propagation phenomena in urban settings to support military operations in urban terrain (MOUT) and the development of personal communication systems. There is a dearth of empirical propagation data in this region of the frequency spectrum that is applicable to tactical military operations. The difference in geometry of a “high-low” and a “low-low” path is rather obvious, but what is not so obvious is the difference in propagation phenomena, especially fading characteristics, of the two types of paths. A “high-low” path in an urban area is usually characterized by what is called “Rayleigh” propagation in which there is no direct line-of-sight (LOS). A “low-low” path between two soldiers is usually via a direct LOS propagation path, but with insufficient terrain clearance to support what is called “Gaussian” propagation. This path is called “Rician.” This paper reviews Rayleigh, Gaussian, and Rician propagation phenomena; describes the different factors that are associated with each of these three types of propagation; and discusses the research and experimental work that is needed to enable more accurate prediction of Rician propagation loss and expected fading under different environmental (terrain, foliage, weather, etc.) conditions
Article
Ray-tracing techniques have proven to be very useful for the analysis and design of wireless systems both in urban microcells and in indoor picocells. At present, the optimization of these techniques enables not only the signal mean level but also the local statistics to be estimated accurately, which is of great practical importance. A wide range of comparisons between measurements and simulations confirming this have been carried out by the authors, and some examples are presented. The most interesting contribution of this paper is that starting from the signal information at one single point, obtained using ray-tracing techniques, it is possible to estimate the signal statistics in a local area of that point. This possibility substantially reduces the local statistics calculation time, confirming the idea that an efficient site specific channel model might be feasible. Finally, it is also shown that ray-tracing techniques are able to accurately estimate the first- and second-order statistics in those environments where the Clarke (1968) or isotropic scattering model is not applicable
Article
Contents Chapter 1 Introduction 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.1 Problem statement 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.1.1 Optimum receivers for fading channels 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.1.2 Synchronisation in conventional receivers 7 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.2 Motivation: digital mobile and portable radio 14 . . . . . . . . . . . . . . . . . . . . . 1.3 Chapter overview and original contribution 20 . . . . . . . . . . . . . . . . . . . . . . Chapter 2 Fading channel models 23 . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1 Statistical characterisation of fading channels 23 . . . . . . . . . . . . . . . . . . . . . 2.1.1 Short term fading 24 . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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