Synchronous CDMA Research Articles

Evaluation of ACF, CCF, RAC, RCC and MF Properties of Different Spreading Sequences Used in DS-CDMA Systems

This paper investigates the different sequences that can be used in direct sequence divisionmultiple access (DS- CDMA) systems. The auto-correlation, cross correlation, the mean square correlationmeasurements ( RAC, RcC ) and merit factor (MF) are used for evaluating the performance of differentspreading sequences. The results obtained small set of Kasami sequences is the most effective of binarysequences families in terms of correlation measure, but this set suffers from the limited number ofsequences. Overall among orthogonal category, Orthogonal Gold sequences and Golay complementarysequences are a better candidate in synchronous CDMA applications.

Low-Complexity Decoder for Overloaded Uniquely Decodable Synchronous CDMA

We consider the problem of designing a low-complexity decoder for antipodal uniquely decodable (UD) /errorless code sets for overloaded synchronous code-division multiple access (CDMA) systems, where the number of signals <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$K_{\mathrm{max}}^{a}$ </tex-math></inline-formula> is the largest known for the given code length <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$L$ </tex-math></inline-formula> . In our complexity analysis, we illustrate that compared to maximum-likelihood (ML) decoder, which has an exponential computational complexity for even moderate code lengths, the proposed decoder has a quasi-quadratic computational complexity. Simulation results in terms of bit-error-rate (BER) demonstrate that the performance of the proposed decoder has only a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1-2$ </tex-math></inline-formula> dB degradation in signal-to-noise ratio (SNR) at a BER of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−3</sup> when compared to ML. Moreover, we derive the proof of the minimum Manhattan distance of such UD codes and we provide the proofs for the propositions; these proofs constitute the foundation of the formal proof for the maximum number users <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$K_{\mathrm{max}}^{a}$ </tex-math></inline-formula> for <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$L=8$ </tex-math></inline-formula> .

Performance analysis of incoherent PPM‐OCDMA networks based on optimised modified prime code for multimedia applications

This study presents the design analysis and correlation properties of a new spreading code for the incoherent synchronous pulse position modulation-optical code division multiple access (PPM-OCDMA) networks. The proposed code called optimised modified prime code (OMPC), which refers to the modified prime codes (MPCs) family. Additionally, this new code designed at a higher code length, optimised code weight and good correlation characteristics to enhance communication security and improve the bit error rate (BER) performance. In this study, the proposed code is used as source code for different kinds of multimedia services such as data, voice, and video. Furthermore, the characteristics and correlation properties of the OMPC in comparison with the other MPCs families that utilised in the PPM-OCDMA networks are presented. Moreover, for the PPM-OCDMA networks, the effect of OMPC auto- and cross-correlation properties on the multiple access interference (MAI) was investigated. Consequently, the MAI is considered in the BER analysis and calculations. Finally, the results show that the proposed OMPC is better than the other existing codes with respect to the channel capacity and system performance.

Performance analysis of optical code division multiple access networks for multimedia applications using multilength weighted modified prime codes

The bit error rate (BER) performance of the incoherent synchronous pulse position modulation optical code division multiple access (PPM-OCDMA) network has been analyzed using a multilength weighted modified prime code (ML-WMPC) for three different multimedia services, such as data, voice, and video. Each service has a different bit rate than the other services and, hence, a different WMPC code length. In the network performance calculations, the multiple access interference (MAI) is included and considered as the only source of noise. In addition, to improve the network performance, the Manchester encoding and the MAI cancellation techniques are used with the WMPC at a higher number of active users. The network performance calculations are introduced in terms of BER for three kinds of PPM-OCDMA receivers, such as a simple receiver, receiver with MAI cancellation (MAIC), and receiver with MAIC and Manchester encoding technique. Finally, the BER calculation has been investigated at different bit rate according to the type of service provided by the network in the presence of the ML-WMPC and the third PPM-OCDMA receiver.

Performance of synchronous CDMA for the PLC-based remote multi-machine control

Performance of synchronous CDMA for the PLC-based remote multi-machine control

Analysis and design of weighted MPC in incoherent synchronous OCDMA network

In this paper, a novel spreading code design in incoherent synchronous Optical Code Division Multiple Access networks is introduced. This new code is designed by remodeling and improvising the existing concept of Modified Prime Code (MPC) sequences. In addition, it has been generated at optimum code weight and sufficient code length with respect to the new MPC, Uniform Cross-Correlation MPC, Double Padded MPC and Enhanced MPC. The proposed new code is named as Weighted MPC (WMPC). The used technique to generate the WMPC sequences is based on XOR operation between code words of MPC and then rearranging between them. Such operation is performed to increase code weight. The proposed coding technique has a capability to provide better correlation results, higher throughput, minimum Multiple User Interference and good network performance. Furthermore, the auto and cross-correlation properties of WMPC sequences were investigated, where the results were compared with the correlation results of other Prime Codes family.

MAI statistics estimation and analysis in a DS-CDMA system

A primary limitation of Direct Sequence Code Division Multiple Access DS-CDMA link performance and system capacity is multiple access interference (MAI). To examine the performance of CDMA systems in the presence of MAI, i.e., in a multiuser environment, several works assumed that the interference can be approximated by a Gaussian random variable. In this paper, we first develop a new and simple approach to characterize the MAI in a multiuser system. In addition to statistically quantifying the MAI power, the paper also proposes a statistical model for both variance and mean of the MAI for synchronous and asynchronous CDMA transmission. We show that the MAI probability density function (PDF) is Gaussian for the equal-received-energy case and validate it by computer simulations.

Approximate equiangular tight frames for compressed sensing and CDMA applications

Performance guarantees for recovery algorithms employed in sparse representations, and compressed sensing highlights the importance of incoherence. Optimal bounds of incoherence are attained by equiangular unit norm tight frames (ETFs). Although ETFs are important in many applications, they do not exist for all dimensions, while their construction has been proven extremely difficult. In this paper, we construct frames that are close to ETFs. According to results from frame and graph theory, the existence of an ETF depends on the existence of its signature matrix, that is, a symmetric matrix with certain structure and spectrum consisting of two distinct eigenvalues. We view the construction of a signature matrix as an inverse eigenvalue problem and propose a method that produces frames of any dimensions that are close to ETFs. Due to the achieved equiangularity property, the so obtained frames can be employed as spreading sequences in synchronous code-division multiple access (s-CDMA) systems, besides compressed sensing.

Method for Minimizing Total Generalized Squared Correlation of Synchronous DS-CDMA Signature Sequence Sets in Multipath Channels

We characterize the Total Generalized Squared Correlation (TGSC) for a given signature sequence set used in uplink synchronous code division multiple access (S-CDMA) when channel state information is known perfectly at bothtransmitter and receiver. We give a definition of the TGSC based on the eigenvalues of Gram matrix associated to signature sequences set for multipath channels in the presence of the colored noise. Total Squared Correlation (TSC) and Total Weighted Squared Correlation (TWSC) measures are particular cases of TGSC. We present a method for minimizing TGSC (TSC, TWSC) in multipath channels and in the presence of the colored noise. Numerical results for overloaded synchronous CDMA systems are presented in order to support our analysis.

Cooperative MIMO relay beamforming in overloaded DS/CDMA multicast networks

A new beamforming scheme is proposed for multi-input multi-output (MIMO) non-regenerative relays in an overloaded synchronous direct sequence code division multiple access (DS-CDMA) network in which the number of users is larger than the processing gain. In this scheme, several transmitters multicast their data to their groups of receivers through MIMO relays and DS-CDMA technique is utilised to decrease the level of multiple access interference (MAI) at the relays and the receivers. At the relays, the data of transmitters are despread, beamformed and re-spread. The aim of the beamformer is to minimise the total relays transmission power subject to the signal to interference and noise ratio (SINR) constraints at the receivers. This optimisation problem is an indefinite quadratic (non-convex) programming. Semi-definite programming (SDP) and second-order cone programming (SOCP) are two existing methods to solve the problem. However, they, respectively, suffer from high computational complexity and performance degradation when the number of antennas or users increase. To effectively mitigate these deficiencies, we propose a novel DC (difference of two convex functions) programming method. Our simulation results demonstrate the computational advantage of the proposed DC programming over SDP, while a better performance over SOCP is achieved. Moreover, the superiority of the proposed MIMO-CDMA scheme over other multiplexing schemes is shown by several scenarios.

Two dimension MDW OCDMA code cross-correlation for reduction of phase induced intensity noise

In this paper, we first review 2-D MDW code cross correlation equations and table to be improved significantly by using code correlation properties. These codes can be used in the synchronous optical CDMA systems for multi access interference cancellation and maximum suppress the phase induced intensity noise. Low Psr is due to the reduction of interference noise that is induced by the 2-D MDW code PIIN suppression. High data rate causes increases in BER, requires high effective power and severely deteriorates the system performance. The 2-D W/T MDW code has an excellent system performance where the value of PIIN is suppressed as low as possible at the optimum Psr with high data bit rate. The 2-D MDW code shows better tolerance to PIIN in comparison to others with enhanced system performance. We prove by numerical analysis that the PIIN maximally suppressed by MDW code through the minimizing property of cross correlation in comparison to 2-D PDC and 2-D MQC OCDMA code.scheme systems.

Two Dimensional Tunable Optical-CDMA System

&lt;p&gt;In this work an experimental demonstration is proposed to implement the synchronous optical code division multiple access system using two dimensional wavelength hopping and time spreading optical prime code is presented. An optical CDMA system is configured on latest version of optisystem by optiwave for the 20 users (Prime Number = 5) connected in a network operating at a bit rate 10 Gbps each. Tunability is achieved by using a MATLAB based delay selector which serves as the source of control signal for optical delay lines. The encoded optical signal of each user has been assigned a particular mode. The resulting optical signal is then transmitted over parabolic index multimode optical fiber. The received signal can successfully be retrieved at the decoder, when the encoder and decoder are configured for the same user. The performance of Optical CDMA system is evaluated in terms of the autocorrelation and cross correlation function, BER, Q factor, eye diagram and compared with 1D code for a given prime number. &lt;/p&gt;

Set of uniquely decodable codes for overloaded synchronous CDMA

In this study, the authors consider the designing of a new set of uniquely decodable codes for uncoded synchronous overloaded code division multiple access for the number of codes exceeding the assigned code length. For the construction, the proposed recursive method at iteration-k generates a matrix that can be classified into k orthogonal subsets of different dimensions. Out of them, all besides the largest (binary Hadamard) one are ternary in nature. There resides an inbuilt twin tree structured cross-correlation hierarchy that facilitates an advantageous balance between the auto and intergroup cross-correlation for the signatures in a subset. This opportunity is further leveraged by the proposed multi-stage detector to maintain the uniquely decodable (errorless) nature of the matrices for noiseless transmission. The simple logic of matched filtering serving as the basic designing block of the decoder provides an enormous saving over the complexity of optimum maximum likelihood decoder. For the noisy channel, the authors derive the theoretical expression of the average bit error rate for the individual subset. Moreover, the authors explain the role of the two factors (cardinality of the subset, and net level of interference) in being responsible for the non-uniformity in the order of their error performance.

Embedded Spectrum Sensor Network Architecture and Transmission Medium Test Based on TCP/IP

Electromagnetic spectrum monitoring that fully covers spectrum resources guarantees the orderly use of key technologies. However, existing monitoring equipment and methods cannot satisfy the increasing demand. A feasible solution for this problem is a wireless sensor network that is developed using a wireless self-organized network technology for a new type of distributed information system. For the wireless spectrum-monitoring network used by software, this study analyzes the operating system and hardware platform and then tests the physical transport layer under different transmission rates. Factors that may affect transmission performance are also investigated. A two-layer network model is eventually used based on the network to adapt to the requirements and the minimum transmission rate. The first layer uses cable, wideband code-division multiple access (CDMA), and time-division synchronous CDMA; the second layer network uses Wi-Fi/cable. This two-layer network model combines two heterogeneous networks, thereby enabling perception among nodes and gateway nodes. The management center can smooth the data transmission process. To perform several tasks simultaneously, we design our own two layers at the application layer protocol, namely, transmission protocol and data. The two-stage ad-hoc network process, the working principle, and the implementation method of each network application layer module are analyzed. The new spectrum sensor network structure exhibits low power consumption, low cost, as well as distributed and self-organization characteristics. It can guarantee the safety of data transmission with a good transmission rate.

Design of variable–weight quadratic congruence code for optical CDMA

A variable–weight code family referred to as variable–weight quadratic congruence code (VWQCC) is constructed by algebraic transformation for incoherent synchronous optical code division multiple access (OCDMA) systems. Compared with quadratic congruence code (QCC), VWQCC doubles the code cardinality and provides the multiple code-sets with variable code–weight. Moreover, the bit-error rate (BER) performance of VWQCC is superior to those of conventional variable–weight codes by removing or padding pulses under the same chip power assumption. The experiment results show that VWQCC can be well applied to the OCDMA with quality of service (QoS) requirements.

Globalisation, indigenous innovation and national strategy: comparing China and India's wireless standardisation

ABSTRACTThis comparative case study investigates the contrasting approaches to telecommunications standard-setting adopted by two developing countries, China and India, using the 3G standard as a case study. Despite facing comparable opportunities in the form of fast-growing markets, and comparable challenges in terms of meeting consumer demand and fostering industrial development, the two countries adopted sharply different standards strategies, with China investing heavily in its home-grown Time Division Synchronous Code Division Multiple Access standard, and India allowing operators to choose any international standard. In this paper, we trace the antecedents of this divergence to the different policy approaches that the two countries adopted to their respective electronics industries in the early to mid-1990s.

An Autonomous Satellite Time Synchronization System Using Remotely Disciplined VC-OCXOs

An autonomous remote clock control system is proposed to provide time synchronization and frequency syntonization for satellite to satellite or ground to satellite time transfer, with the system comprising on-board voltage controlled oven controlled crystal oscillators (VC-OCXOs) that are disciplined to a remote master atomic clock or oscillator. The synchronization loop aims to provide autonomous operation over extended periods, be widely applicable to a variety of scenarios and robust. A new architecture comprising the use of frequency division duplex (FDD), synchronous time division (STDD) duplex and code division multiple access (CDMA) with a centralized topology is employed. This new design utilizes dual one-way ranging methods to precisely measure the clock error, adopts least square (LS) methods to predict the clock error and employs a third-order phase lock loop (PLL) to generate the voltage control signal. A general functional model for this system is proposed and the error sources and delays that affect the time synchronization are discussed. Related algorithms for estimating and correcting these errors are also proposed. The performance of the proposed system is simulated and guidance for selecting the clock is provided.

Innovation in China’s information and communications technology industry

Purpose – This paper aims to identify the sources of innovation in the current business environment of China. With the set target of transforming China into an innovative society by 2020, the Chinese government has taken dramatic measures to foster the nation’s innovation capability. Whether this Chinese model of promoting innovation has been successful and can be sustainable are controversial issues which need to be analyzed from an academic perspective. In recent years, there have been successful cases of innovation driven by grassroots entrepreneurs, especially in the information and communications technology (ICT) industry. Therefore, it is time to analyze their success factors from the perspectives of both corporate strategy and government policy. Design/methodology/approach – The methodology used in this research is a comparative case analysis, and several high-profile cases in China’s ICT industry have been selected for this comparative study. Information used in the analysis comes from publicly available sources such as business school case studies and industry and news media reports. The authors have been following the evolution of China’s ICT industry for more than a decade; insights from their prior research and knowledge gained through industry contacts are also used in the analysis. Findings – Generally speaking, the types of innovation in China’s ICT industry can be categorized into a top-down or a bottom-up approach. For the top-down approach of innovation driven by the government, the authors analyzed the case of the Chinese government’s effort to build an industry value chain through fostering the Chinese indigenous third-generation mobile communications standard time division–synchronous code division multiple access. In comparison, the authors use several success cases, including the ecosystem built around the highly successful XiaoMi mobile phone and Tencent’s mobile portal WeChat, as it showcases of the bottom-up approach of innovation driven by grassroots entrepreneurship. The comparison of these two approaches suggests that massive government-sponsored projects are unlikely to generate genuine innovation in the highly competitive and dynamic ICT sector. The government’s role should be to foster entrepreneurship and to create a fair business environment. Originality/value – This research uses the method of comparative case studies to identify the source of innovation in a highly dynamic and uncertain business environment. Findings of this study shed light on the government policy toward innovation in the ICT industry and on the business firms’ strategy on innovation.

Interference Free Window (IFW) in Las Cdma System and Comparison with Traditional CDMA

Large area synchronous code-division multiple access (LAS-CDMA) is a proposed fourth generation cellular standard. The feature that distinguishes LAS-CDMA from traditional CDMA is the new set of codes used to separate users. LAS code has zero cross-correlation in the Zero Interference Window and has only an impulse auto- correlation in the Zero Interference Window. These excellent features of the technique help to eliminate

An Improved Channel Estimation in a TD-SCDMA System Based on the Threshold of Detect Energy and its Performance Analysis

B. Steiner estimator used in the time-division synchronous code-division multiple access (TD-SCDMA) system is a low cost estimator. The precision of the estimated channel impulse responses (CIRs) is affected by noises in the channel, which result in worse performance of the estimation. For the reason that there are many threshold processing algorithms based on Steiner algorithm, the optimal threshold value becomes a crucial factor. In this paper, based on statistical information of channel in the data field, an improved channel estimation algorithm is proposed by detecting energy of CIR's tap in time-domain, and the amplitude of estimated channel impulse response is adjusted by a gain coefficient. Simulation results prove the validity of the proposed technique for channel estimation good performance. Additionally, it is shown that the improved estimators outperform traditional channel estimators.