CDMA Scheme Research Articles

FPGA realization of an image encryption system using the DCSK-CDMA technique

This paper describes a four-wing chaotic oscillator-based DCSK-CDMA modulation technique for image encryption and decryption. The system consists of a transmission module for the encrypted and modulated color matrices, and a reception module for the decrypted and demodulated original data. Among our main contributions is the integration for the first time in the state of the art of DCSK chaotic modulation techniques with the CDMA communication scheme, as well as the implementation of our DCSK and CDMA algorithms in VHDL language for Xilinx FPGA cards. The DCSK-CDMA technique enables demodulation and decryption without any loss in the original data. Other contributions arising from this investigation are the encryption process implemented using DCSK-CDMA techniques based on a four-wing chaotic oscillator and the realization on the FPGA of a chaos-based communications system for the secure transmission of images of grayscale and RGB formats using DCSK-CDMA techniques. The system architecture in this work was designed using fixed-point binary arithmetic, with the application of the 4th order Runge–Kutta numerical method for the four-wing chaotic oscillator. The analysis of the correlation coefficients between the original and encrypted information indicates the values of 5.367×10−4 and −2.205×10−7 for grayscale and RGB images, respectively, with a full recovery of the original information. The results of simulations in MATLAB/Simulink coincide with the implementation of the complete system in VHDL on the Xilinx Artix-7 AC701 board.

PERFORMANCE OF MU-MC-DS-CDMA SYSTEM IN RAYLEIGH FADING CHANNEL

The Multi user Multi Carrier Direct sequencing Code Division Multiple Access (MU-MC-DS-CDMA) strategy was developed in response to rising demand for system capacity, higher data rates, and multimedia services. It's essentially a combination of CDMA and OFDM schemes. As a result, MC-CDMA takes the advantages of both CDMA and OFDM technologies. CDMA improves bandwidth consumption performance, whereas OFDM helps to minimize Inter Symbol Interference (ISI) and multipath fading. This dissertation suggests a method for evaluating the performance of multi user MC-DS-CDMA system. BER and PAPR are used to evaluate the results. The Bit Error Rate (BER) output of the proposed method is then examined using MATLAB for various modulation techniques. By using Walsh-Hadamard (W-H) code is used because it eliminates Multiple Access Interference (MAI). In terms of BER, it can be shown that BPSK performs better than QPSK. Key Words: AWGN, BER, ISI, MC-CDMA, Rayleigh Fading Channel, SNR, QPSK, MAI

Complementary Coded CDMA With Multi-Layer Quadrature Modulation

In an orthogonal frequency division multiplexing (OFDM) system, cyclic prefix (CP) has to be added to eliminate multipath-induced inter-symbol interference (ISI) with a severely sacrificed bandwidth efficiency. Peak-to-average ratio (PAPR) may impair its performance further if a large number of carriers are used. On the other hand, traditional multi-carrier modulation suffers a prohibitive complexity, which can not be implemented with colorred current available silicon technologies. This work proposes a cost-effective way to implement multi-carrier modulation, namely multi-layer quadrature (MLQ) modulation, which requires only two oscillators. As an application example, we apply MLQ modulation to a complementary coded code division multiple access (MLQ-CC-CDMA) system, whose multi-carrier transmission is based on MLQ modulation to mitigate ISI and multi-user interference (MUI) with ideal auto- and cross-correlations of complementary codes. Compared to a frequency domain (FD) CC-CDMA system, MLQ-CC-CDMA has a lower RF complexity. Compared to OFDM direct sequence (DS) CDMA and single carrier frequency division multiple access (SC-FDMA) CDMA schemes, MLQ-CC-CDMA achieves a higher spectrum efficiency (SE) and a lower bit error rate with Rake and minimum mean square error (MMSE) detection due to its powerful multipath and multi-carrier diversity gains.

Optical CDMA Scheme Using Generalized Modified Prime Sequence Codes and Extended Bi-Orthogonal Codes

Optical CDMA Scheme Using Generalized Modified Prime Sequence Codes and Extended Bi-Orthogonal Codes

A High Capacity 1D-Chaotic-Collaborative-CDMA Scheme for Shared Band 5G-IoT Operation

This paper presents a chaos based multi-group CDMA (CCCDMA) scheme employing a modified 1D-Bernoulli map for shared band operation of NB-IoT services with the legacy systems (LTE eNodeB’s). The proposed scheme addresses the capacity requirements for NB-IoT for a very low processing gain and compared with current researches on the topic with relevance to the 3GPP technical report (TR 36.752). Computer simulations reveal a maximum of 120 users can be supported by the CCCDMA scheme for a very low processing gain of N = 31 thereby providing an overloading of ≈ 4 at a reference probability of bit error of 10−3 for the IoT scenario. Thus, for a 20 channel system with W = 1 MHz in a 20 MHz band with 4 collaborating user groups, the CCCDMA-IoT scheme provides a Kmax of 2400 IoT UE’s for a 2 dB compromise on SNR.

Design Concepts and Performance Analysis of Multicarrier CDMA for Indoor Visible Light Communications

In this paper, we present a design methodology with implementational insight and evaluate the performance of a multicarrier code-division multiple access (MC-CDMA) system using intensity modulation/direct detection scheme suitable for an indoor visible light communication (VLC) environment. The proposed system is a CDMA system based on an orthogonal frequency division multiplexing (OFDM) platform. To overcome the light-dimming issue, we use a newly proposed methodology, namely, polarity reversed optical OFDM (PRO-OFDM). A unipolar signal is either added to the minimum current or subtracted from the maximum current in the LED linear current range to provide various amounts of dimming. The CDMA part employs Hadamard sequences to provide synchronous resource sharing. Combining the robustness of orthogonal modulation with the flexibility of CDMA schemes makes the proposed system a viable candidate for future indoor wireless communications such as VLC. The performance of the proposed MC-CDMA is evaluated, and mathematical formulations for the proposed system are derived. For example, closed-form equations for the signal-to-interference-plus-noise ratio and bit error rate (BER) performance are obtained. Furthermore, the analytical formulations are used in numerical analysis to verify the BER performance achieved in simulation results.

Performance Evaluation of Rotational Interleaver for IDMA Scheme in Acoustic Environment

The whole globe is covered universally by water with a majority space. In view of extraction of minerals as well as national security reasons, underwater communication has become quite important for all the mankind. Researchers, around the world are working for optimizing the multiple scheme in acoustic channel. Recently, the researchers have reported valuable employability of IDMA scheme in acoustic communication. In IDMA Scheme, the users are distinguished with user-specific interleaving sequences based on chip-level interleaving mechanism instead of user-specific signature sequences as engaged in CDMA scheme. However the role regarding formation of interleavers plays vital notch for performance of IDMA scheme in underwater communication. In this paper, the performance of user-specific rotational interleaver has been observed in acoustic environment for BPSK signaling scheme on MATLAB platform. Simulation results demonstrate that the rotational interleaver performs better in terms of bit error rate (BER) for underwater channel employing iterative IDMA system.

Multi-carrier coded division multiple access multiplexing against multi-path fading

In recent years, multi-carrier techniques such as multi-carrier code division multiple access CDMA schemes have become popular in wireless communications over multipath fading channels. The MCCDMA used to improve security, data transmission rate and to minimise inter symbol interference ISI. CDMA was suffering from multipath fading which affects its performance. In this research, the performance of multi-carrier code division multiple access MC-CDMA system is studied and evaluated, virtual frequency and phase synchronisation algorithm for the sub-carrier is proposed to reduce the BER of MC-CDMA. The simulation have been done using MATLAB programme, the results indicate that significant improvement in the system achieved under AWGN and Rayleigh fading channels using BPSK modulation. Increasing digital modulation orders and power have led to reduction in the BER for the system.

Paper] A Novel Multicarrier CDMA Scheme With Interference Free Performance in Very Large Delay Spread

Paper] A Novel Multicarrier CDMA Scheme With Interference Free Performance in Very Large Delay Spread

3D Packaging- Synthetic Quartz Substrate and Interposer for High Frequency Applications

Glass for use as an Interposers with through vias (TGV) are emerging as the next generation substrates for die level and wafer level packaging substrates. This need is being driven increasing number of interconnects, desire to have a KGD (known good die) at the wafer level package (WLP), high electrical/thermal conductivity vias, and hermeticity between the PWB and the die, while being cost competitive with a TSV passive interposer. These TGV characteristics translate to longer battery life, higher yield at the end user applications, and an optimized WLP solution that not require silicon processing foundries to fabricate a passive interposer. The next generation of communication devices will operate at much higher frequencies to allow video on demand and video vis a vis communication. Coupled with multiple frequencies, to facilitate a phone to work with GSM, CDMA and other communication schemes require multiple filter and low noise amplifiers. This paper will describe work done with Alkali free, copper filled (not plated) hermetic vias that are both low cost and provide engineering design flexibility for the more advance low cost personal handheld devices.

Performance evaluation of space-time-frequency spreading for MIMO OFDM-CDMA systems

In this article, we propose a multiple-input-multiple-output, orthogonal frequency division multiplexing, code-division multiple-access (MIMO OFDM-CDMA) scheme. The main objective is to provide extra flexibility in user multiplexing and data rate adaptation, that offer higher system throughput and better diversity gains. This is done by spreading on all the signal domains; i.e, space-time frequency spreading is employed to transmit users' signals. The flexibility to spread on all three domains allows us to independently spread users' data, to maintain increased system throughput and to have higher diversity gains. We derive new accurate approximations for the probability of symbol error and signal-to-interference noise ratio (SINR) for zero forcing (ZF) receiver. This study and simulation results show that MIMO OFDM-CDMA is capable of achieving diversity gains significantly larger than that of the conventional 2-D CDMA OFDM and MIMO MC CDMA schemes.

A Learning Automata-Based Cognitive Radio for Clustered Wireless Ad-Hoc Networks

In current wireless networks, the radio systems are regulated by a fixed spectrum assignment strategy. This policy partitions the whole radio spectrum into a fixed number of radio ranges, each exclusively assigned to a specific user. Such a spectrum assignment strategy leads to an undesirable condition under which some systems only use a small portion of the allocated spectrum while the others have very serious spectrum insufficiency. The learning automata-based cognitive radio which is proposed in this paper is a highly potential technology to address the spectrum scarcity challenges in wireless ad hoc networks. This paper proposes a learning automata-based dynamic frame length TDMA scheme for slot assignment in clustered wireless ad-hoc networks with unknown traffic parameters, where the intra-cluster communications are scheduled by a TDMA scheme, and a CDMA scheme is overlaid on the TDMA to handle an interference-free inter-cluster communication. In this method, each cluster-head is responsible for a collision-free slot assignment within the cluster and determines the input traffic parameters of its own cluster members. It then takes these traffic parameters into consideration for an optimal channel access scheduling in the cluster. The medium access control layer in each cluster is based on a time division multiple access (TDMA) scheme, in which each host is assigned a fraction of the TDMA frame proportional to its traffic load. The simulation experiments show the superiority of our proposed slot assignment algorithm over the existing methods in terms of the channel utilization, control overhead, and throughput, specifically, under bursty traffic conditions.

Performance Analysis of Optimum Interleaver based on Prime Numbers for Multiuser Iterative IDMA Systems

In recently proposed multiple access techniques like IDMA and OFDM-IDMA, the user separation is done by user specific interleavers in contrast to the conventional CDMA scheme, where user separation is assured with user-specific signature sequences. The user specific interleavers must demonstrate minimum probability of collision amongst each other in addition to other merits, including minimal consumption of bandwidth, least hardware for their generation, and least memory requirement. In this paper, the authors propose an interleaver based on prime numbers for the generation of user specific interleavers to remove the problem of high consumption of bandwidth. The simulation results demonstrate the optimal performance of prime interleaver (PI), which is based on prime numbers, apart from other merits in comparison to random and other interleavers.

An efficient cluster-based CDMA/TDMA scheme for wireless mobile ad-hoc networks: A learning automata approach

In this paper, we design a dynamic frame length CDMA/TDMA scheme for clustered wireless ad hoc networks with unknown traffic parameters. In this scheme, the collision-free intra-cluster communications are organized by the cluster-heads using a TDMA scheme, and a CDMA scheme is overlaid on the TDMA to organize the interference-free inter-cluster communications. Therefore, to design such a scheme, we encounter three important problems, namely cluster formation, code assignment, and slot assignment. In this paper, we propose three algorithms to solve the addressed problems based on learning automata. In our scheme, by the proposed clustering algorithm, the wireless hosts are grouped into non-overlapping clusters. Then, by the proposed code assignment algorithm (considering the concept of code spatial reuse), an interference-free code is assigned to each cluster. Finally, by the slot assignment algorithm, each cluster member is assigned a fraction of TDMA frame proportional to its traffic load. The simulation results show that the proposed CDMA/TDMA scheme outperforms the existing methods in terms of almost all metrics of interest, specifically, under bursty traffic conditions.

Collaborative spreading for the downlink of overloaded CDMA

AbstractA new scheme called ‘Collaborative Spreading’ is proposed for the downlink of CDMA to allow the sharing of the same spreading sequence by more than one user. In particular, it addresses the problem of user overloading and maintain the use of the same set of available orthogonal sequences and simple receiver structure. In this scheme, a total of K users are divided into G groups each containing T users which are collaboratively coded to form uniquely decodable composite codewords. These codewords are spread using a single sequence to perform the CDMA function between the groups. At the receiver, a low complexity maximum likelihood (ML) joint detection and decoding is carried out over a small set of allowed composite codewords to recover the desired user's data. Theoretical and simulation performance analysis of the bit error rate (BER) and user capacity are presented in different channel conditions. It is shown that the proposed collaborative spreading is a simple and very effective means for extending the user capacity at the cost of a modest degradation in BER performance compared with non‐overloaded fully orthogonal CDMA. It can achieve higher signal‐to‐interference plus noise ratio (SINR) and higher overloading ratio compared with Orthogonal CDMA/Orthogonal CDMA schemes and other group orthogonal CDMA schemes. Copyright © 2009 John Wiley & Sons, Ltd.

Synchronous CDMA based on the cyclical translations of a CAZAC sequence

A new scheme of synchronous CDMA is introduced in the paper. The new scheme is based on a code made by all the cyclical translations of a basic sequence having constant amplitude and white discrete spectrum. Such a code is proposed here for the first time as a code for CDMA. According to the proposed scheme, a cyclic prefix is appended to the multiplexed signal. The proposed scheme has a property that none of the known CDMA schemes has: in a multipath environment, it allows multiuser interference to become cyclic intersymbol interference. Noticeably, the memory of the finite state machine that describes the ISI model is equal to memory of the multipath channel. The main advantage of our proposed scheme is that optimal and suboptimal detectors can be obtained from detectors proposed in the past for the ISI channel, which are much easier to implement than conventional multiuser detectors of classical CDMA schemes. Another advantage of our scheme is that it leads naturally to a signal processing architecture similar to that of OFDM systems, hence based on the efficient FFT/IFFT algorithm.

A chaos-based CDMA scheme with a chaos-based encryption algorithm

An encryption algorithm based on a discretized chaotic map controlled by a Δ-modulated feedback is applied to a direct sequence code-division-multiple-access (DS-CDMA) scheme, which improves security at the cost of lowering the performance of bit error rate (BER). However, numerical simulations show that the DS-CDMA scheme still has a satisfactory performance by means of the spreading sequences generated by a continuous chaotic system. These spreading sequences are chosen from the local maximums of the output of the continuous chaotic system. This scheme is also robust against the channel noise.

Space-Code CS-CDMA Systems over MISO Frequency-Selective Rayleigh Fading Channels

We propose a transmit diversity CDMA scheme which is a combination of convolutional spreading (CS) and space-time spreading (STS) over multiple-input single-output (MISO) multipath Rayleigh fading channels. With our scheme, multiuser detection over an MISO multipath channel is transformed to single-user detection over a single-input single-output (SISO) multipath channel as the scheme by Petre et al. Because of its simple configuration, it is immediate to see that our scheme realizes full transmit- and path-diversity for two transmit antennas. We extend the system to four transmit antennas employing quasi-orthogonal construction and show a necessary and sufficient condition for full transmit- and path-diversity to be realized. The proposed scheme requires less hardware complexity and less latency than the one by Petre et al.

Genetic algorithm optimization of a hybrid analog/digital predistorter for RF power amplifiers

This study presents a genetic algorithm optimization of a hybrid analog/digital predistorter, in order to reduce the intermodulation distortion (IMD) caused by the nonlinear properties of the radio frequency (RF) power amplifier (PA). Designed predistorter based on polynomial work function and the coefficient of the polynomial is optimized in order to reduce IMD by spectrum monitoring. The design procedure and validation of predistorter have been carried out by Agilent-ADS2005A. In order to validate the predistorter two different modulation schemes as CDMA and 16-QAM have been used. Also in order to verifying the linearization a test power amplifier circuit has been examined including Motorola MOSFET MRF9742 showing the nonlinear characteristics with memory. Simulations have been shown that adjacent channel power ratio (ACPR) improvements were acceptable for both CDMA and 16-QAM modulation schemes.

CS-CDMA/CP with ZCZ Codes from an M-Sequence and Its Performance for Downlink Transmission over a Multipath Fading Channel

Convolutional spreading CDMA with cyclic prefix (CS-CDMA/CP) is a multiuser interference-free (MUI-free) CDMA scheme proposed for multipath channels based on the convolution between user data and zero correlation zone (ZCZ) code, and its characteristics depend on the employed ZCZ codes. Although ternary ZCZ codes have more sequences than binary ZCZ codes in general, transmitted signal with ternary ZCZ codes give a slightly higher peak-to-average power ratio (PAPR). In this paper we propose the use of periodic ZCZ codes generated from an M-sequence which not only provides the same user capacity as ternary ZCZ codes but allows more design flexibility. Simulation results show that the new ZCZ code shows stronger robustness against an imperfect transmitter with clipping and enjoys better BER performances when used in CS-CDMA/CP compared to the conventional DS-CDMA with MRC-RAKE.