CDMA

Orthogonal variable spreading factor (OVSF) codes are standard in third generation UMTS cellular systems. The efficient generation of these codes is essential for reducing the area and power of wireless transceivers. In this paper, the basic properties of this family of codes are analyzed from an RTL perspective and two efficient hardware code generators are proposed. Tradeoffs and design solutions as well as low power considerations are discussed. These results represent the first reported implementation of an OVSF code generator. 1 *

An increasing demand to explore the vast ocean floor for various purposes has made it necessary to deploy networks of underwater unmanned vehicles (UUVs) capable of carrying out multiple tasks. For information transfer among these vehicles, it is essential to design efficient communication systems and techniques which reduce the transmission error thereby improving system performance. The network consists of underwater components which perform activities such as communicating with each other using sound waves, gathering information and transmitting this information to the surface buoys which forward the data to a receiver onshore or on board some ship. This report studies the use of Carrier Interferometry (CI) spreading codes in underwater networks which use DS-CDMA technique for transmitting data. A network model has been presented and performance of DS-CDMA/CI has been studied for this model through simulations. The performance of this system has also been compared to those networks using Walsh-Hadamard (WH) codes to prove that DS-CDMA/CI is a better transmission scheme as compared to DS-CDMA/WH. Furthermore, multirate transmission in underwater environment has also been explored with the use of DS-CDMA/CI simulations. The results have shown that DS-CDMA/CI is an excellent candidate for future single rate as well as multirate transmission schemes.

A continuous-time Markov chain model for an asynchronous communication spread spectrum code division multiple access (CDMA) packet radio network is developed. The network is composed of N users, the receiver-based code is considered; a terminal with a packet to send looks up the destination's code and transmits on that code. Each user senses the channel load and refrains from transmission if the channel load exceeds the channel threshold. The model allows us to study the threshold effect of channel load on the performance of the CDMA packet radio network. Improvements in performance of spread spectrum packet radio networks due to channel load sensing are shown. Steady-state results for throughput versus offered traffic and the delay versus throughput are obtained.

Most ad hoc and sensor network research assumes idealised radio propagation models without considering fading and shadowing effects. Experimental results have shown that many well-designed protocols will fail simply because of fading and shadowing experienced in a realistic wireless environment. While fading and shadowing for radio propagation are well understood in the wireless communication community, they are rarely studied in network level research for wireless sensor networks. This paper studies the fading and shadowing effects on the performance of different systems for wireless sensor networks. We show that fading and shadowing can have a significant influence on network performance. We study and compare network performance for three different systems: (1) a multichannel CDMA system; (2) a pure CDMA system; (3) a contention-based system. Through discrete event simulation (using ns-2), we show that the multichannel CDMA system outperforms the pure CDMA system as well as the contention-based system under fading and shadowing environments.

With an increase in the number of end users using internet services, the average data rate of 30 Mbps will not be in a position to accommodate the future mobile technology. So radio and mobile communication specialists started an R&D work on 4G mobile communication systems before even completing IMT-2000 system [2]. 4G is the fourth generation standard for cellular wireless communication. It can offer speed up to 100 Mbps for high mobility communication where else it can deliver up to 1 GB for low mobility communication. The main focus on 4G communication system is to integrate the existing wireless technologies like WCDMA, Wireless LAN, Bluetooth, HSUPA/HSDPA, 1xEVDO [1] . Stability of a system and quality of service will be ensured in 4G communication systems.

    Migrating from an existing system to new systems like 4G has a greater impact on lot of political and technical issues and it has huge challenges to overcome. This project work intends to deal with various factors like fundamental issues within a network technology, effective use of a spectrum, standards, and also about various services of 4G and its impact on future communication system. This project work will also exhibits the development, transition, and the future work with respect to deploying 4G.

The development of technological capability (TC) is critical for manufacturing firms in high-tech industries. Stages of development of industrial technology in a developing country: a model. Research Policy 9, 254-277] model of acquisition, assimilation, and improvement is widely accepted to explain TC development in developing economies. However, some R&D practices we observed in Chinese manufacturing companies appear to be in disagreement with Kim's model. Based on four in-depth cases studies set in China's mobile phone industry, we hypothesize (a) a complementary stage in Kim's model, and (b) those stages can be traversed concurrently. r

Spread spectrum code-division multiple-access (CDMA) systems are currently considered as very attractive alternatives to the more familiar FDMA and TDMA systems, especially in the presence of multipath fading and external interference. The problem of code selection in a CDMA system with a finite number of users is addressed in this paper. A simple and efficient method for the selection of finite code sets with relatively high processing gain from Gold and Kasami code families of relatively large sizes is described in detail. Selected code sets of period 63 are presented along with their overall average performance parameters for different number of users.

Code Division Multiple Access (CDMA) is technology for digital transmission of radio signal in telecommunication systems. In this technology, multiple users can transmit the data simultaneously in a channel using same frequency. Each user is assigned a distinguished code for transmission.
There are different codes are used for this purpose. Here, Pseudo-Noise (PN) sequence, Gold sequence and Walsh code are generated using MATLAB programming. Using Walsh code, the data is transmitted to receiver in Additive white Gaussian noise (AWGN) and Rayleigh Fading channels.
In this project, transmitted data is generated randomly using MATLAB function.  During  transmission, Signal to Noise Ratio (SNR) values of signal changes to calculate Bit Error Rate (BER) value to plot BER vs. SNR graph for two users in AWGN and Rayleigh Fading channels.

Multi Carrier Code Division Multiple Access (MC-CDMA) is an attractive choice for high speed wireless communication as it avoids the problem of Inter Symbol Interference (ISI) and also exploits frequency diversity. In order to support multiple users with high speed data communications, the MC-CDMA technique is used to address these challenges. MC-CDMA experiences severe multipath fading which badly affects its performance. When transmission over fading channel multi-cell interference occurs and this degrades the performance of the system. This paper specially analyzes the BER performance under Rayleigh fading channel conditions of MC-CDMA in presence of AWGN (Additive White Gaussian Noise) using BPSK modulation for different number of subcarrier, different number of users using MATLAB program, and finally the paper also presents a comparison between simulated results, which shows the reduction in BER performance.

In modern communication systems, spread spectrum is playing an increasingly important role day by day due to its inherent advantages like noise immunity and also due its practical applications like mobile communications in CDMA. Our project is in accordance with this increasingly important communication technology. This project aims to Generate Gold Code sequence and modulate a message signal to produce a corresponding spreaded baseband modulated signal which is actually used in much higher proportions for transmission of voice and data signals in technologies like CDMA. The project also incorporates a receiver unit which demodulates the entire received signal with the assistance of the same gold code to generate the original message signal. An addition to this primary aim of our project is to study the cross correlation of two Gold Codes sequences and two Pseudo Noise sequences to ascertain which is a better tool for modulating the given message signal in terms of better noise immunity and security with the help of graphs using the MATLAB programming language.

Wavelets have been favorably applied in almost all aspects of digital wireless communication systems including data compression, source and channel coding, signal denoising, channel modeling and design of transceivers. The main property of wavelets in these applications is in their flexibility and ability to characterize signals accurately. In this paper recent trends and developments in the use of wavelets in wireless communications are reviewed. Major applications of wavelets in wireless channel modeling, interference mitigation, denoising, OFDM modulation, multiple access, Ultra Wideband communications, cognitive radio and wireless networks are surveyed. The confluence of information and communication technologies and the possibility of ubiquitous connectivity have posed a challenge to developing technologies and architectures capable of handling large volumes of data under severe resource constraints such as power and bandwidth. Wavelets are uniquely qualified to address this challenge. The flexibility and adaptation provided by wavelets have made wavelet technology a strong candidate for future wireless communication.

Energy consumption is one of the important challenges in WSNs deployment and applications. This is because power of WSNs is limited by battery which is difficult if not impossible to replace or recharge in some manner in the sensor nodes. Power consumption can be controlled in WSNs in more than one layer. In this thesis, power efficiency problems and techniques of enlarging battery life using WSNs physical layer are investigated in the second layer MAC sub-layer. The latter has been achieved using the multiple access techniques, TDMA and CDMA.
Initially, the research attempt to divide the WSN nodes into clusters such that at any time only one specific cluster will operate and the remaining cluster sill be switched off to reduce the power consumption. Each cluster consists of several nodes and one sub-station (SS), the total number of nodes equal to 128 nodes at each case of cluster, all the nodes in one cluster send its data to this (SS) and this (SS) forwards this data to main station (MS). Furthermore, the link between nodes, SS, and MS is controlled and scheduled such that cluster and node switched to active or sleep. Four systems with multi-types of multiple access are proposed and tested with each case of clustering have been adopted. These systems are classified according to the way multiple access provided in the link: TDMA-TDMA-OFDM system, CDMA-CDMA system, CDMA-TDMA-OFDM system, and TDMA-OFDM-TDMA-OFDM system. These systems have been simulated and investigated. By comparing the results of each system with different case of cluster, it has been found that the less consumed powers achieved with 8 clusters of 16 nodes/cluster case. The results also show that the best performance is achieved with CDMA-CDMA system with 8 clusters of 16 nodes/cluster case.
Extra power consumption reduction has been achieved in this research via the application of convolutional coding and interleaving with four proposed systems. It has been found that convolutional code makes better performances and less error rates with different ratio in the proposed system. Furthermore, more enhancement has been achieved by using convolutional code with interleaving to all system except CDMA-CDMA system which gives results similar to the results of convolutional code only. By comparing the results of the proposed system with each other after enhancement, the results show that the CDMA-CDMA system is still has the less error bit ratio and the best performance and achieves the most power consumption reduction.

A design of the code-division multiple access (CDMA) cellular system architecture is presented. The base station architecture is based on a universal platform that can support CDMA and other cellular standards such as AMPS and TDMA in the same base station. The mobile switching center (MSC) architecture is enhanced to support the various CDMA system features such as soft handoff and variable bit rate vocoding. In particular, the digital cellular switch (DCS) at the MSC provides a frame relay packet switching interface to the base station. It is shown that such a packet switching interface can support more voice channels that the conventional DS0/DS1 circuit switching interface and is an essential element in achieving the soft handoff capability

ABSTRAK ANALISIS STRATEGI PENETAPAN HARGA JASA LAYANAN KOMUNIKASI ESIA SEBAGAI TITIK BALIK FAKTOR PENGUBAH PERILAKU PASAR. Telekomunikasi sebagai faktor penting dalam era globalisasi membuat jasa layanan komunikasi semakin berkembang pesat. Perkembangan jasa layanan komunikasi yang demikian pesat tidak lepas dari perilaku pasar yang responsif. Pembentukan perilaku pasar ini, tidak lepas dari kemunculan produk Esia yang membuat harga layanan jasa menjadi semakin murah seiring dengan kemunculan. Penentapan dan strategi harga Esia dalam bersaing dengan produk sejenis di pasar telekomunikasi seyogyanya mampu menurunkan harga jasa layanan telekomunikasi secara nasional. Esia sebagai jasa layanan komunikasi dalam perkembangan telah berhasil menjadi salah satu faktor titik balik pengubah perilaku pasar dari inelastis menjadi elastis

This paper describes how CDMA (Code Division Multiple Access) technique in CDMA communication system is used. Walsh Hadamard orthogonal codes are used as orthogonal code words. DSK(Dsp Starter Kit -TMS320C6713) along with CCStudio V3.1 is used to simulate the whole process.Voice input (or Digital Data) is taken as information, which is broken as packets and transmitted using CDMA technique, the recieved data is Decoded and played back.

Two enhancements are proposed to the application and theory of support vector machines. The first is a method of multicategory classification based on the binary classification version of the support vector machine (SVM). The method, which is called the -ary SVM, represents each category in binary format, and to each bit of that representation is assigned a conventional SVM. This approach requires only log 2 ( ) SVMs, where is the number of classes. We give an example of classification on an octaphase-shift-keying (8-PSK) pattern space to illustrate main concepts.

We present a game-theoretic treatment of distributed power control in CDMA wireless systems. We make use of the conceptual framework of noncooperative game theory to obtain a distributed and market-based control mechanism. Thus, we address not only the power control problem, but also pricing and allocation of a single resource among several users. A cost function is introduced as the difference between the pricing and utility functions, and the existence of a unique Nash equilibrium is established. In addition, two update algorithms, namely, parallel update and random update, are shown to be globally stable under specific conditions. Convergence properties and robustness of each algorithm are also studied through extensive simulations.

In this paper, we study the effect of the assigned Walsh function to each user in a synchronous CDMA system on the power spectral density (PSD) of the transmitted CDMA signal. We show that the PSD of the CDMA signal depends primarily on the PSD of the assigned Walsh functions. Also, based on the Walsh code properties, an algorithm for Walsh code assignment in CDMA systems is introduced. The algorithm achieves lower spectral regrowth in terms of adjacent channel power ratio (ACPR) at all values of input back off (IBO). Performance measurements show that using such an algorithm for 17 active channels, a reduction of about 6 dB and 5 dB in the ACPR is achieved at IBO = 1 dB and 2 dB, respectively. This reduction in the spectral regrowth implies that using this algorithm, the high power amplifier (HPA) can operate at high values of input power approaching the saturation level with minimal spectral regrowth, and in turn the HPA efficiency is improved.

This article presents a survey on medium access control protocols for wireless multimedia networks. A basic overview of MAC protocol concepts is presented, and a framework is developed for comparisons. The MAC protocols covered in this article include Random Access protocols, Contention less protocols, TDMA CDMA, third-generation WCDMA schemes and Hybrid protocols proposed for wireless Multimedia Networks. The operation of each protocol is explained, and its advantages and disadvantages are presented. Finally, a qualitative comparative outline of the discussed protocols is provided.

Wireless Sensor Network (WSN) is an attractive choice for a variety of applications as no wired infrastructure is needed. Other wireless networks are not as energy constrained as WSNs, because they may be plugged into the mains supply or equipped with batteries that are rechargeable and replaceable. Among others, one of the main sources of energy depletion in WSN is communications controlled by the Medium Access Control (MAC) protocols. An extensive survey of energy efficient MAC protocols is presented in this article. We categorise WSN MAC protocols in the following categories: controlled access (CA), random access (RA), slotted protocols (SP) and hybrid protocols (HP). We further discuss how energy efficient MAC protocols have developed from fixed sleep/wake cycles through adaptive to dynamic cycles, thus becoming more responsive to traffic load variations. Finally we present open research questions on MAC layer design for WSNs in terms of energy efficiency.

Mobile communication has been readily available for several years, and is major business today. It provides a valuable service to its users who are willing to pay a considerable premium over a fixed line phone, to be able to walk and talk freely. Because of its usefulness and the money involved in the business, it is subject to fraud. Unfortunately, the advance of security standards has not kept pace with the dissemination of mobile communication.
Some of the features of mobile communication make it an alluring target for criminals. It is a relatively new invention, so not all people are quite familiar with its possibilities, in good or in bad. Its newness also means intense competition among mobile phone service providers as they are attracting customers. The major threat to mobile phone is from cloning.

Orthogonal variable spreading factor (OVSF) codes are standard in third generation UMTS cellular systems. The efficient generation of these codes is essential for reducing the area and power of wireless transceivers. In this paper, the basic properties of this family of codes are analyzed from an RTL perspective and two efficient hardware code generators are proposed. Tradeoffs and design solutions as well as low power considerations are discussed. These results represent the first reported implementation of an OVSF code generator. 1 *

In the design of mobile ad hoc networks, a challenging problem is how to route information reliably and efficiently from one node to another in moderate to high level of mobility. Due to mobility, limited residual energy of the node, selection of stable and durable path for the communication is the challenge. Also remaining queuing capacity is also affected on the packet loss. Many proposals have been addressed to this problem; however, few papers consider a proactive protocol like Optimized Link State Routing Protocol (OLSR) to better manage the energy consumption and link stability in routing path selection algorithms. In this paper, we explored modification to MPR selection and integrating appropriate routing metrics in the routing decision scheme to lessen effects of reason that lead to more packet loss. Our power-aware version of OLSR is proven by simulations in NS3 under a range of different mobile scenarios and network density. Significant performance gains are obtained in terms of packet loss ratio and MPR count for our modified OLSR version.

The research conducted in this paper is aimed at developing a CDMA shared bus as the efficient communication architecture for SOC. The main benefits of using this technique relate to reduction of the number of wires on system bus which varies from 25% up to 81%, while the main disadvantage is increase of the latency of processor read and write operations. The structure of a CDMA wrapper as an interface logic between the shared bus and IP connecting to it is described. VHDL models of two wrapper types (master and slave) are developed and verified. Four different implementations of the CDMA coding technique are presented and realized in FPGA and ASIC technologies.

This paper reviews the state of the art and current trends towards 3G and 3G+ mobile satellite systems that are being planned in parallel or within the International Mobile Telecommunications (IMT-2000) framework. The subject is firstly approached by introducing the key and enabling technologies both for satellites and high altitude platform stations. After having introduced an overall picture, another review is presented on physical layer research activities including propagation and channel modeling. Finally, the use of the reviewed channel models for Code Division Multiple Access system level analysis is introduced and some current efforts towards system design are presented. Copyright © 2002 John Wiley & Sons, Ltd.

In this paper, we investigate and revisit the structure and performance of a Multiple Input/Multiple Output (MIMO) Decision Feedback Equalizer (DFE) for a Minimum Mean Square Error (MMSE) criterion. The output model dealt with is very general, and applies to filterbank based multi-carrier transmission, CDMA , TDMA, FDMA systems, systems with Transmitter Induced Cyclostationarity and so on. Moreover, the transmission model and the associated receiver account for excess bandwidth and multi-sensors configurations. The purpose of the paper is to derive MIMO MMSE DFE in a concise manner by means of fractionally spaced devices. From the receiver derived here it clearly appears that the first operation to be performed is matched filtering. Besides, it is also demonstrated why the geometrical MSE is the criterion to be used. As an illustrative example, an OFDM transmission scheme is considered.

In this paper, the multipath decorrelating (MD) detector which is used in code division multiple access (CDMA) systems to eliminate multiple access interference (MAI) is considered. The MD detector requires the inversion of a signature sequence correlation matrix. This process is computationally expensive and it also enhances the channel noise. Recently, an adaptive path selective decorrelating (APSD) detector has been proposed to reduce both the computational complexity and noise enhancement at a marginal increase in residual MAI due to unselected paths. The APSD detector requires the channel knowledge. In practice, the channel coefficients are not known and must be estimated. Although several channel estimation methods exist for CDMA systems, a maximum-likelihood approach using short preamble sequences is adopted in this paper. The estimation process has an impact on the overall system performance by introducing estimation errors in actual channel coefficients. Therefore, this paper proposes a semi-analytic method to analyze the performance of the APSD detector in the presence of those channel estimation errors. Extensive simulations are carried out and reported to show tradeoffs for different system parameter settings.

This paper gives an overview on communications system based and global navigation satellite system (GNSS) based navigation. Starting from the physical layer model of a mobile communications or navigation receiver, we highlight similarities and differences between the two receivers. We explain navigation principles for timing measurements and present the possible navigation accuracies of different communications systems and GNSSs. Finally, we examine synergies of combined receivers and systems.

The architecture and dynamics of a code-vision multiaccess (CDMA) cellular radio network are discussed. The network's layout, power control equation, cell coverage, signal quality, cell radio design, and heterogeneous cell clustering are described. It is shown that ...

In this paper, the performance of uncoded uplink transmissions in a broadband code division multiple access (CDMA) system using tapped delay line (TDL) antenna array under multipath conditions is investigated. An expression for broadband CDMA system is derived to calculate the optimal weights of TDL antenna array. Using the derived broadband expression, the performance of TDL antenna array is investigated and compared with that of the already existing narrowband systems. Simulation results show that TDL antenna array can reduce multipath fading and multiple access interference (MAI). It is shown that if the signal-tonoise ratio (SNR) level is maintained at 20 dB and two-ray channel model is used, two antennas with four taps each can support 30 users with a BER of 10 3 . If three-ray channel model is used, the same antenna arrangement is not enough to support 30 users. To support these 30 users with BER of 10 3 , the number of taps needs to be increased to eight. Finally, the number of taps needs to be further increased to 16 if four-ray channel model is used. Not only that, the SNR should also be increased to 25 dB to achieve the same BER. DS-CDMA system, several receiver structures, such as the decorrelator, the minimum mean square error (MMSE) receiver, the multistage parallel interference cancelation receiver, the successive interference cancelation receiver, and the decorrelating decision feedback receiver, have been investigated in DS-CDMA system in literatures . In DS-CDMA system using parallel interference canceler (PIC) receiver with four stages, the signal-to-noise ratio (SNR) required to achieve a BER performance of 10 3 is 8 dB, whereas the single-stage PIC receiver with feedback approach requires only 2 dB to achieve the same BER . The effect of using PIC in multiuser detection (MUD) scheme is also investigated in where the authors show its superiority in satellite systems using either CDMA or a combination of time division multiple access and CDMA techniques. Using combination of soft and hard PIC detectors, the authors provide a comparative study of improving system performance using more stages of PIC in MUD schemes. In , blind user identification detection (UID) scheme based on linear prediction algorithm for asynchronous DS-CDMA systems over multipath fading channels is investigated and compared with the existing subspace-based UID algorithms; the authors concluded the paper showing the superiority of their proposed scheme in asynchronous CDMA systems.

Uluru is a software platform that provides a number of enabling services to mobile multimedia applications including content-personalisation and charging. This paper describes the design of such an enabling platform and explores its applicability from a business perspective. We describe the platform's functionalities and overall architecture, and discuss Callsong, an application that makes extensive use of Uluru's personalization and charging services.

Constant modulus transforms like discrete Fourier transform (DFT), Walsh transform, and Gold codes have been successfully used over several decades in several engineering applications, including discrete multi-tone (DMT), orthogonal frequency division multiplexing (OFDM) and code division multiple access (CDMA) communications systems. In this paper, we present a generalized framework for DFT called Generalized DFT (GDFT) with nonlinear phase by exploiting the phase space. We show that GDFT offers sizable correlation improvements over DFT, Walsh, Oppermann and Gold codes, leading to better performance in all multi-carrier communications scenarios investigated. We also highlight how known constant modulus orthogonal transforms are special solutions of the proposed GDFT framework. Moreover, we introduce practical design methods offering computationally efficient implementations of GDFT as enhancements to DFT. We conclude the paper with examples of communications applications where GDFT is shown to outperform DFT and other known constant modulus bases.

We consider joint beamforming (BF) and power control to minimize cochannel interference in a CDMA wireless uplink, where an antenna array of different geometries receives from single-antenna wireless users. The problem is to find the optimum beamforming weight vector and the minimum transmission power of each terminal such that the quality of service (QoS) requirements of the users are fulfilled and the so-called near-far effect is alleviated. This will increase the channel capacity and further prolongs the battery lives of the mobile terminals. The particle swarm optimization method is used to determine the optimum beamforming weight vector and the minimum transmission power of each terminal. Uniform linear and circular array geometries are considered, with and without correlated shadow fading. Simulation results illustrate the advantage of using BF jointly with power control and the robustness of the optimization technique used.

One of the underlying difficulties with the application of a prediction pathloss model for any environment is that no two areas are identical in the composition of the buildings and terrain. A pathloss model developed by Walfisch-Bertoni considers the impact of rooftops and building heights by using diffraction to predict average signal strength loss at street level. However, the error between the average path loss predicted by the model and that observed in practice will be smallest when the propagation environment conforms closely with the models assumptions (i.e. those urban environments exhibiting minimal variation in the height and separation of buildings). In particular, any building height variations can be expected to cause a significant error in the model predictions. Firstly, in this paper, we demonstrate the sensitivity impact of varying certain parameters on the performance W/B model in the study environments. The goal is to give the user an idea of the value associated with altering parameters that are in fact adjustable and showing the significance of the unchangeable parameters in the loss calculations. Secondly, a new statistical tuning method is proposed by extending the technique of Walfisch-Bertoni model which is now valid for generalized conditions in the CDMA2000 signal propagation environments. The results showed that tuned pathloss data agree strongly with measured data in the different study locations.

In direct-sequence code-division multiple-access (DS-CDMA) communication systems, the partial cancellation weight (PCW) in the partial parallel interference cancellation (PPIC) multiuser detection scheme does not give us any idea about the correctness of the bit-decision in the previous stage. Therefore, in this study, we investigate the statistical behavior of the adaptation PCW based on the least mean square (LMS) algorithm in which the adaptation PCW of the last chip in a symbol period reveals the information of the correctness of the bit-decision. Then, an adaptive decision-threshold obtained by maximum a posteriori probability (MAP) detection criterion is proposed to judge the correctness of the bit-decision in the previous stage and the bit-inversion (BI) procedure is proposed to invert the incorrect bit-decision. Furthermore, after BI procedure, a full PIC is performed to cancel the multiple access interference (MAI). Simulation results show that the proposed three-stage BI-based full PIC (BI-FPIC) multiuser detector can reach the performance of single-user-bound over flat fading channels under perfect channel estimation.

A sensor may be deployed in an open space; on a battle field in front of, or beyond, enemy lines; in the interior of industrial machinery; at the bottom of water Body; in a biologically and chemically contaminated field; in a commercial building; in a home; or in on a human body. It is not possible to recharge the batteries in all environments and hence lifetime of a sensor is very crucial. So to increase the lifetime, the sensors are grouped into clusters and information is exchanged with base station via cluster head. An energy efficient cluster head selection technique is required to increase the lifetime of WSN. The traditional LEACH protocol selects the cluster head by random time which may select low energy sensors as cluster head. In this paper, the cluster head selection is based on energy variable and mean distance of neighboring nodes. This methodology is implemented using both CDMA and TDMA approaches and results show that using the CDMA approach reduces the energy consumption and improves the network lifetime compared to TDMA approach.

One of the critical and costly components in digital cellular communication systems is the RF power amplifier. Theoretically, one of the main concerns in an RF power amplifier design is the nonlinear effect of the amplifier. Quantitatively, no explicit relationship or expression currently exists between the out-of-band emission level and the nonlinearity description related to the third-order intercept point (IP3). Further, in experiments and analysis, it was discovered that, in some situations, using IP3 only is not accurate enough to describe the spectrum regrowth, especially when the fifth-order intercept point (IP5) is relatively high compared to the third-order intermodulation. In this article, we analyze the nonlinear effect of an RF power amplifier in CDMA (IS-95 Standard), TDMA (IS-54 Standard) and MIRS M-16-QAM (Motorola MIRS standard) system, give expressions of the estimation of the out-of-band emission levels for each system expressed by power spectrum respectively, in t...

In the design of mobile ad hoc networks, a challenging problem is how to route information reliably and efficiently from one node to another in moderate to high level of mobility. Due to mobility, limited residual energy of the node, selection of stable and durable path for the communication is the challenge. Also remaining queuing capacity is also affected on the packet loss. Many proposals have been addressed to this problem; however, few papers consider a proactive protocol like Optimized Link State Routing Protocol (OLSR) to better manage the energy consumption and link stability in routing path selection algorithms. In this paper, we explored modification to MPR selection and integrating appropriate routing metrics in the routing decision scheme to lessen effects of reason that lead to more packet loss. Our power-aware version of OLSR is proven by simulations in NS3 under a range of different mobile scenarios and network density. Significant performance gains are obtained in terms of packet loss ratio and MPR count for our modified OLSR version.

Hierarchical Genetic Algorithms (HGA) as a tool for search and optimizing methodology have now reached a mature stage. The minimum resource facility to carry user traffic, termed a channel unit (CU), is composed of a one time-slot and one code in the TD-CDMA/TDD system. The control of the number of CUs depends on the traffic load solves varied and asymmetrical traffic problems in the 3G system. In a cellular network, the call arrival rate, call duration and the communication overhead between the base stations and the control center are vague and uncertain, regardless of whether the criteria of concern are nonlinear, constrained, discrete or NP hard. In this paper, the HGA is used to tackle the neural network (NN) topology as well as the fuzzy logic controller for the dynamic CU allocation scheme in wireless cellular networks. Therefore, we propose a new efficient HGA CUs Allocation (HGACA) in cellular networks. It aims to efficiently satisfy the diverse quality-of-service (QoS) requirements of multimedia traffic. The results show our algorithm has a lower blocking rate, lower dropping rate, less update overhead, and shorter channel-acquisition delay than previous methods.

Novel objectives such as very low outage, high capacity, and high throughput are major challenging problems in radio resource management of mobile communication systems. More specifically, in radio resource scheduling (RRS), the aim is how to optimize available resources such as transmission power and data rate to achieve certain targeted objectives. Conventional RRS algorithms are based on optimizing one objective while keeping others as constraints. This paper proposes a novel distributed RRS algorithm based on analytic multi-objective optimization. The proposed algorithm relaxes the constraints and jointly optimizes all the required objectives. Infinity set of optimal solutions, called Pareto optimal, is obtained. Each solution in the set is optimal in a specific sense. The decision maker selects the required solution that fulfills the network requirements and conditions. Some of the conventional RRS algorithms are special cases of our multi-objective based algorithm. Detailed mathematical analysis of the proposed algorithm is given. Simulation results show the behavior of the proposed algorithm as well as its advantages over conventional algorithms.

An efficient method for equalization of downlink CDMA channels is presented. By describing the observed signal in terms of a state-space model, the method employs the Kalman filter (KF) to achieve an unbiased signal estimate satisfying the linear minimum mean-squared error (LMMSE) criterion. The state-space model is realized at the symbol and chip levels. With the symbollevel model, the KF is used to estimate the transmitted chips that correspond to each symbol interval; whereas at the chip level, the transmitted chips are estimated individually. The symbol-level KF has a built-in tracking capability that takes advantage of the a priori known scrambling sequence, which renders the transmitted signal nonstationary. The chip-level KF reduces the complexity of the symbol-level KF significantly by ignoring the nonstationarity introduced by scrambling. A simple method for further reducing the KF complexity is also presented. The computational complexity of the proposed technique is analyzed and compared with that of several linear approaches based on finite-impulse response (FIR) filtering. Simulations under realistic channel conditions are carried out which indicate that the KF-based approach is superior to FIR equalizers by 1-2 dBs in error-rate performance.

In this paper, we derive the error probability
of multi-hop networks employing code-division multiple
access transmission in amultiuser environment. The standard
Gaussian approximation is used tomodel themultiple access
interference in the network.We consider multi-hop networks
employing serial, parallel, and selection relaying using the
decode-and-forward technique. For the selection relaying,
we consider two schemes; namely, the threshold-based relay
selection and the maximum relay selection. In addition, we
investigate the effect of different system parameters on the
error performance of the system, such as the spreading gain,
the number of interfering users, and the path loss exponent.
Results show that as the number of users increases,
the improvement coming from the relaying decreases.