Orthogonal Variable Spreading Factor Code Research Articles

Design of a networking bolted joints monitoring method based on PZT

As the failure of bolt connections by corrosion can result in major disasters and cause casualties and property damage, monitoring bolted joints is of great importance. However, current researches on lamb wave based bolted joint monitoring mainly focused on single-input-single-output (SISO) systems, which require a long diagnosis time and numerous transducers. To reduce the number of transducers on monitoring, the multiple-input systems, i.e. multiple-input-multiple-output (MIMO) system and multiple-input-single-output (MISO) system, can be adopted. However, both multiple-input systems are prone to failure due to the interference among the excited waves generated from multiple simultaneously-operated actuators. To remove such interference, an orthogonal variable spreading factor (OVSF) code based bolted joint monitoring method is proposed here. Firstly, instead of using the same detection signal, multiple detection signals generated using OVSF codes are emitted from different input ports. Then, for each considered input port, the corrosion information carrying waveforms are recovered from the acquired signals via timing acquisition and demodulation and utilized to reveal the status of the bolted joints via wavelet packet based analysis. To validate the proposed method, experiments with a MIMO system (i.e. three-input-two-output system) and a MISO system (i.e. six-input-single-output system) were conducted to simultaneously reveal six given bolted joint corrosion status in this research. Since the proposed method effectively suppresses the interference, the MIMO/MISO bolted joint monitoring system can present a performance similar to that of the SISO monitoring system but require fewer transducers.

UAV-Aided Transceiver Design for Secure Downlink OW-DFTs-OFDM System: A Multi-User mmWave Application

Unmanned aerial vehicle (UAV)-based communication system design has already attracted substantial interest due to UAV flexibility in deployment, cost effectiveness, and in-built line-of-sight air-to-ground channels. However, there is a persistent issue of security threats associated with the broadcast nature of UAV: physical layer security (PLS) can be introduced to enhance the secrecy performance in that regard. In the system proposed here, the combined effect of 3D fractional-order Liu chaotic system and 3D fractional-order Li chaotic system is introduced to enhance the PLS of the UAV-to-ground communication network. In addition, to reduce multi-user interference (MUI), efficient orthogonal variable spreading factor (OVSF) codes are integrated with a zero forcing (ZF) scheme. Moreover, to improve bit error rate (BER), a combined MUI signal discrimination and ZF signal detection scheme is introduced, strengthened by various channel coding techniques with multi-user beamforming weighting. The numerical outcomes establish the efficacy of the proposed system in terms of PLS and improvement of data rate with signal-to-interference-plus-noise ratio. This approach achieved an out-of-band emission reduction of 119 dB. Furthermore, an improved BER of <inline-formula> <tex-math notation="LaTeX">$1 \times 10^{-4}$ </tex-math></inline-formula> is achieved in 16-QAM for a signal-to-noise ratio of 6 dB.

Design of Orthogonal Variable Spreading Factor (OVSF) Performance Simulation Program in Multipath Fading Channels

The characteristics of wireless channel are determined by multipath propagation. The transmitted signal will be scattered so that it produces fading. Fading influenced by multipath component will cause delay spread which damages the signal. Thus, spread spectrum technology is used by using a bandwidth that is greater than the original signal. The objective of this study was to determine the effect of the number of multipath components on orthogonal variable spreading factor (OVSF) codes on multipath fading channels viewed from values and Bit Error Rate (BER) graphs versus Energy Bits per Noise (Eb/No). This study would compare the performance of OVSF code communication system on multipath channels by varying multipath components of 4, 8, 12, 16 and the length of OVSF codes used of 16, 8 and 4. The simulation results showed an increase in BER values when the number of multipath components was added. The more the number of multipath components used, the more the number of reflected signals that will interfere with the desired signal in the receiver. The length of the OVSF code influences the performance of the OVSF code on the multipath fading channel, because each code has a different processing gain value that is affected by the length of the code used

A power waveform design based on OVSF-PPM for stress wave based wireless power transfer

The lifetime of wireless sensors and devices is restricted by their limited battery capacities, since it is quite time-consuming and costly to replace batteries. Wireless power transfer is recognized as a feasible solution to charge wireless sensors and portable devices, since it can provide energy continuously for wireless electronic devices. This paper explores a waveform design for stress wave power transfer. In the proposed method, pulse position modulation (PPM) signals are firstly designed based on orthogonal variable spreading factor (OVSF) code. Then, power transfer waveforms for multiple receivers are created via analyzing the correlation among the PPM signals. When applied in stress wave power transfer, the proposed waveform is demonstrated to effectively improve power transfer performance at the intended receiver. We investigate three different transmission schemes, namely the pulse waveform, the time reversal waveform, and the proposed power transfer waveform, by comparing and analyzing their performances in experiments when one energy transmitter and one energy transfer array are respectively used. Due to multiple stress wave modes, rich dispersion and mutual interference among energy transfer signals, energy transfer efficiencies (ETE) and peak to average power ratios (PAPR) tend to be low by using pulse waveforms or traditional time reversal waveforms to transfer stress wave energy. On the contrary, by implementing the proposed waveform in stress wave power transfer, the ETE and the PAPR are effectively improved. In the experiment, three piezoceramic transducers mounted on a pipeline are used for stress wave power transfer. The experimental results demonstrate that the proposed waveform significantly improves the ETE and the PAPR, as compared with the other two waveforms.

Spreading-Based Voice Encryption by Means of OVSF Codes

This paper presents a new methodology to encrypt voice signals, in such a way that they simulate being a noise signal. The objective is to obtain a signal that does not generate suspicions about its content, while protecting the message. The process is based on the spread and scrambling of the signal through the use of OVSF (orthogonal variable spreading factor) codes. The security of the method is based mainly on the input value used for the randomization phase. From a computational cost point of view, the use of fixed-length codes allows for a shorter retrieval time compared to a similar method based on variable-length codes. Regarding the encrypted signal, its main characteristic is its high entropy (very close to the ideal value). Finally, in the recovery process, a signal identical to the original is obtained.

Service Time-Based Region Division in OVSF-Based Wireless Networks with Adaptive LTE-M Network for Machine to Machine Communications

The 3GPP standards have presented the LTE-M as one of the main technologies to provide services to Internet of Things (IoT). The IoT applications are usually short-lived applications like smart sensing, surveillance systems for home or businesses, and data uploading applications like metering. In this paper, the proposed architecture of the base station has a LTE interface which assigns resource blocks (RBs) and another 3G interface which is equipped with orthogonal variable spreading factor (OVSF) codes. The IoT devices deployed ubiquitously leads to massive machine type communication, which leads to burst traffic on current cellular services. The IoT devices when assigned large resources will reduce the radio efficiency. The work in this paper assigns OVSF codes available on 3G interface to the IoT devices. The LTE resources are used for IoT devices in case of emergency or when resources of 3G interface are 100% utilized. This will solve the problem of both small data transfer and connectivity requirement of IoT devices. The IoT applications are event-driven and time-bound also, and the resources are also reserved for these applications in the proposed work. The simulations and results show that proposed work increases both network efficiency and capacity.

Accuracy of Bit Error Probability for W-CDMA System Using Code Tree

W-CDMA is radio access utilized for 3G cell frameworks. A code tree allocation scheme is one of the most explored channelization techniques, used to improve system performance and capacity through adjustable data rates. This work investigates the accuracy of bit error probability for W-CDMA system using code tree orthogonal variable spreading factor (OVSF) codes, compared to pseudo-noise (PN) codes under various noise conditions, such as additive white Gaussian Noise (AWGN) and Random Noise (RN). Results are carried out theoretically and by computer simulation. The simulation includes the scenario of simple model representation for W-CDMA system. It was concluded that, the system has better performance using OVSF compared with PN code under different noisy channels.

Authenticity verification of audio signals based on fragile watermarking for audio forensics

Abstract This paper presents a new fragile watermarking method for digital audio authenticity for audio forensics purposes. The aim is to verify if an audio proof has been tampered and to locate the segments where the signal was modified. Our proposal is based on an embedding process of a text that is encoded through OVSF (Orthogonal Variable Spreading Factor) codes and spread into the entire signal using automatic adjustment. Several tests were performed in order to quantify the accuracy and the reliability of the tampering detection against four classical attacks (cropping, replacement, additive noise and amplitude reduction) by using kappa index, sensitivity and specificity. It was demonstrated that even if a small number of samples is modified, the system correctly labels the audio proof as manipulated, and locates both the start and end of the manipulation; the kappa index (reliability) is around 0.96, sensitivity is always 1, and specificity is around 0.995. The proposed algorithm could be used as a decision support tool for audio forensics verification purposes, that allows to identify if an audio proof has been modified, and the time segments in which it has been modified.

Eradication of pilot contamination and zero forcing precoding in the multi‐cell TDD massive MIMO systems

In massive multiple-input multiple-output (M-MIMO) systems, the base station (BS) estimates the downlink and uplink channels using the uplink pilot training in conjunction with channel reciprocity property of time division duplex (TDD) operation. However, this channel estimation is contaminated due to the use of non-orthogonal pilot sequences for the uplink training in neighbouring cells that results in inter-cell interference. This study proposes an effective pilot contamination elimination scheme along with zero forcing precoding for multi-cell TDD M-MIMO systems. In the proposed scheme, each BS is assigned with a specific orthogonal variable spreading factor (OVSF) code row and a set of Zadoff–Chu (ZC) sequences are used for uplink pilot training. Then, the set of ZC sequences is multiplied element-wise at each BS with its OVSF code row to generate the orthogonality among the pilot sequences across the neighbouring cells. The proposed method can promise uncontaminated channel estimation and interference free downlink transmission without requiring the knowledge of the channels’ second-order statistics and without increasing the training overhead by a factor equal to the number of interfering cells. The simulation results authenticate the effectiveness and superiority of the proposed scheme over other schemes.

Pilot Decontamination in TDD Multicell Massive MIMO Systems With Infinite Number of BS Antennas

The performance of time division duplex (TDD) multiple-input multiple-output (M-MIMO) systems is mainly limited by the pilot contamination, which is a negative effect of reusing uplink pilot sequences in the neighboring cells. A pilot decontamination scheme for TDD multicell M-MIMO systems with an infinite number of base station (BS) antennas is proposed in this paper. The proposed scheme uses Zadoff-Chu (ZC) sequences as uplink pilot sequences and implements distinct orthogonal variable spreading factor (OVSF) code rows at each BS. The set of uplink pilot sequences at each BS is multiplied element-wise with the BS-specific OVSF code row to make uplink pilot sequences orthogonal across the network. Then, a mobile station randomly selects one of these multiplied ZCs from a given set and transmits it on the random access channel at the commencement of coherence interval. The performance of the uplink and downlink rates of the proposed scheme is compared with those of the time-shifted pilot scheme for an infinite number of BS antennas. The simulation results authenticate the validity of the proposed scheme.

An Efficient Multicode Design for Real Time QoS Support in OVSF Based CDMA Networks

Orthogonal variable spreading factor (OVSF) codes are used for CDMA based networks to handle multimedia rates. While waiting time (or call establishment delay) is a significant QoS parameter for real time calls, its impact on non-real time calls is negligible. Traditionally, the call handling in OVSF based CDMA system has been accomplished with multi code approach, where the arriving call is divided into many quantized fractions and each fraction is handled by different code. These designs are very efficient for non-real time calls, but the code search corresponding to each fraction needs significant time that makes existing multi code approaches unsuitable for real time calls. This paper describes a novel multi code design, in which the waiting time for real time call is zero. The design initially assigns the incoming call to the vacant code with the capacity equal to call capacity, and subsequently looks for the vacant codes for each quantized fraction after code assignment. Once the vacant codes with capacities equal to the capacity of all rate fractions are available, the call is shifted to these codes. The information of this code assignment for every fraction needs to be sent to the receiver like existing schemes. Therefore, there is no additional hardware requirement for the proposed design. Simulation results show significant dominance of our scheme as compared to the existing multi code schemes.

OVSF Dynamic Code Allocation Quality based Glowworm Swarm Optimization Approach in WCDM

OVSF codes are used as channelization codes to support applications with different bandwidth requirements for the downlink of 3G mobile communication systems. The code assignment and reassignment problem focuses on the subject of minimizing the number of code relocations. OVSF (Orthogonal Variable Spreading Factor) code assignment method considering traffic characteristics in the WCDMA systems. The previously proposed Dynamic Code Assignment (DCA) scheme allows code reassignments to improve code utilization, but induces some service delay time to on-going calls, unlikely assumptions, including fixed service data rates and code-limited system capacities. Thus, OVSF code tree has insufficient number of available codes. Method/Statistical Analysis: In order to solve these problems and efficiently utilized OVSF codes, in this paper presents novel Glow warm Swarm Intelligence (GSO) based approach for active OVSF code assignment in WCDMA based networks. GSO algorithm is completely dependent on the behavioral pattern of glowworm (fireflies). The optimization algorithm requires an understanding of this behavioral pattern. The intensity of the emission of Lucifer in can be changed by glow worms which glow at different intensities. In order to improve the ability of the GSO it employs various phases until code allocation is completed. Results: By permitting only codes in the data branch to be reassigned the quality of service guarantee for real time traffic is possible. The simulation results shows that proposed GSO schemes not only guarantees the QoS but also gives high code utilization which is comparable with other existing techniques. Conclusion/ Application: Performances of these methods are evaluated in terms of blocking probability, spectral efficiency, delay and throughput. In addition to this different GSO operator are tested under varying traffic loads to increase the overall system performance.

Same rate and pattern recognition search of orthogonal variable spreading factor code tree for wideband code division multiple access networks

Orthogonal variable spreading factor-based code division multiple access systems allocate vacant codes when new call(s) arrive. This study proposes a same rate assignment scheme which allocates a new call to most favourable code in the region crowded by same rate calls. This does not add to blocked codes because of previous calls but utilise the unused scattered capacity created by previous calls. A vacant code whose parent code is handling maximum number of ongoing calls of same rate is the most favourable code for new call assignment under that sub tree. This reduces higher rate blocking because of scattering of lower rate calls due to the fact that same rate calls will be assigned in the same portion of code tree. If a tie occurs for two parent codes it is resolved using pattern recognition of codes. In the proposed scheme, the most favourable search starts from higher layers that reduce number of code searches before assignment significantly. The proposed single code and multi code schemes are compared with other schemes based on code blocking probability, throughput and number of code searches required before assignment. Simulation results indicate that the proposed scheme outperforms other schemes for various traffic distributions.

Fixed capacity and variable member grouping assignment of orthogonal variable spreading factor code tree for code division multiple access networks

Orthogonal variable spreading factor codes are used in the downlink to maintain the orthogonality between different channels and are used to handle new calls arriving in the system. A period of operation leads to fragmentation of vacant codes. This leads to code blocking problem. The assignment scheme proposed in this paper is not affected by fragmentation, as the fragmentation is generated by the scheme itself. In this scheme, the code tree is divided into groups whose capacity is fixed and numbers of members (codes) are variable. A group with maximum number of busy members is used for assignment, this leads to fragmentation of busy groups around code tree and compactness within group. The proposed scheme is well evaluated and compared with other schemes using parameters like code blocking probability and call establishment delay. Through simulations it has been demonstrated that the proposed scheme not only adequately reduces code blocking probability, but also requires significantly less time before assignment to locate a vacant code for assignment, which makes it suitable for the real-time calls.

An Efficient Dynamic Orthogonal Variable Spreading Factor Code Allocation Approach in WCDMA through Modified Adaptive Genetic Algorithm

Orthogonal Variable Spreading Factor (OVSF) codes would give variable data rate transmissions for different bandwidth supplies in Wideband CDMA (WCDMA) networks. These OVSF codes are used for the channelization of codes in WCDMA. In WCDMA, effective utilization of OVSF codes has become an active area of research as the number of codes is very limited. It is a fact that the successor and predecessor codes of OVSF cannot be used simultaneously when a specific code is used in OVSF as their encoded sequences become indistinguishable. Consequently, OVSF code tree has inadequate number of available codes. Thus, this research study uses Adaptive Genetic Algorithm (AGA) based approach for dynamic OVSF code assignment in WCDMA networks. Different from existing Conventional Code Assignment (CCA) and dynamic code assignment schemes, population is adaptively constructed according to existing traffic density in the OVSF code-tree. In existing technique in order to improve the ability of the GA, ＂dominance and diploidy＂ structure is employed to adapt to changing traffic conditions. Because in SGA algorithm cannot convergence if the new user is included into the existing OVSF code tree while SGA is running to find optimum OVSF code tree, SGA cannot adapt its structure to this unexpected variation. This problem can be overcome by the Modified Adaptive Genetic Algorithm (MAGA). Performance of the proposed MAGA approach is evaluated in terms of blocking probability and spectral efficiency and is compared with SGA, D&D GA.

Modelling and Simulation of Interference Cancellation Receiver for MIMO Multicarrier CDMA based Cognitive Radio

In this paper, modeling and simulation of a receiver with interference cancellation technique for the downlink transmission of multiple input multiple output (MIMO) multicarrier code-division multiple access (MC-CDMA) based cognitive radio is investigated. Synchronous transmission of multiple users’ signals over frequency selective Rayleigh channel is considered. Linear MMSE frequency domain equalization is utilized to overcome channel effect. Orthogonal Variable Spreading Factor (OVSF) codes are used to support users of different data bit rates. An adaptive subcarrier deactivation method is proposed for deactivating a set of subcarriers used for downlink transmission by the cognitive radio base station that overlap with primary user’s transmission in order to avoid causing interference to the primary user. Orthogonality between the spreading codes is lost due to subcarrier deactivation which causes interference among secondary cognitive radio users. In this paper a modified Group-wise Successive Interference Cancellation (m-GSIC) technique is proposed to suppress the interference caused due to subcarrier deactivation. The simulation results show that the proposed interference cancellation technique results in better BER performance over conventional interference cancellation techniques

Two‐dimensional spreading scheme employing 2D orthogonal variable spreading factor codes for orthogonal frequency and code division multiplexing systems

Future 4G systems require transmission of richer multimedia services which inevitably implies an increase in data rate. Orthogonal frequency and code division multiplexing (OFCDM) technique has shown promising results in achieving a high data rate while simultaneously combating multipath fading. OFCDM is an amalgamation of orthogonal frequency division multiplexing and two-dimensional (2D) spreading. 2D spreading helps to achieve diversity gains in both time and frequency domains. The present OFCDM systems employ 1D orthogonal variable spreading factor (OVSF) codes to achieve the required 2D spreading in code multiplexed channels. However, 2D OVSF codes have better correlation properties in comparison to 1D OVSF codes. Motivated by this principle, the authors propose a spreading scheme for OFCDM systems using 2D OVSF codes. The spreading scheme is designed to increase the system throughput and reduce multi-code interference. Here, the authors study the OFCDM system performance using the proposed spreading scheme in a multipath fast fading channel with varying spreading factors in both time and frequency domains. The results are compared with the existing OFCDM systems using 1D OVSF codes.

Reduction in code blocking using scattered vacant codes for orthogonal variable spreading factor‐based wideband code division multiple access networks

3G and beyond wideband code division multiple access networks use orthogonal variable spreading factor (OVSF) codes to handle multimedia traffic. OVSF codes suffer from the limitation of code blocking, which leads to new call blocking. Scattered vacant codes in the OVSF code tree are the main cause of code blocking. This study proposes compact single code and multicode assignment schemes to reduce code blocking. The vacant codes used for incoming calls are the ones surrounded by a minimum number of consecutive vacant codes. Furthermore, finding consecutive vacant codes at the leaves of the tree is sufficient to find the consecutive vacant codes for all other layers. Handling non-quantised rates with a single code assignment produces wastage of code capacity, which is avoided with the use of a multicode assignment. Multicode usage facility along with the use of vacant codes from the minimum consecutive vacant code groups results in minimum code blocking. Two categories of the multicode assignment schemes are considered: the first one uses the least number of codes and is suitable for rake limited OVSF system, and the second scheme uses maximum number of codes to reduce code blocking significantly.

Fair Single Code and Multi Code Designs for 3G and Beyond CDMA Systems

Multimedia rates are handled in 3G and beyond CDMA networks using orthogonal variable spreading factor (OVSF) codes. Multimedia rates can have non uniform distribution of real time and non real time users. The paper describes fair single code and multi code designs to handle these rates. The single code design is for quantized rates and divides the OVSF code tree capacity according to the arrival distribution. The change in the distribution is dynamically reflected in the division of the code tree capacity for different rates. The multi code design is preferred for the system dominated by non quantized rates. Simulation results are presented to show the superiority of the proposed designs with its existing counterparts.

(1+ε)-competitive algorithm for online OVSF code assignment with resource augmentation

This paper studies the online Orthogonal Variable Spreading Factor (OVSF) code assignment problem with resource augmentation introduced by Erlebach et al. (in STACS 2004. LNCS, vol. 2996, pp. 270---281, 2004). We propose a (1+1/?)-competitive algorithm with help of (1+???)lg? h trees for the height h of the OVSF code tree and any ??1. In other words, it is a (1+?)-competitive algorithm with help of (1+?1/??)lg? h trees for any constant 0<?≤1. In the case of ?=1 (or ?=1), we obtain a 2-competitive algorithm with 2lg? h trees, which substantially improves the previous resource of 3h/8+2 trees shown by Chan et al. (COCOON 2009. LNCS, vol. 5609, pp. 358---367, 2009). In another aspect, if it is not necessary to bound the incurred cost for individual requests to a constant, an amortized (4/3+?)-competitive algorithm with (11/4+4/(3?)) trees for any 0<?≤4/3 is also designed in Chan et al. (COCOON 2009. LNCS, vol. 5609, pp. 358---367, 2009). The algorithm in this paper gives us a new trade-off between the competitive ratio and the resource augmentation when ??3 (or ?≤1/3), although the incurred cost for individual requests is bounded to a constant.