Code Division Multiplexing System Research Articles

Simulation of two dimensional OCDMA-PON system based on FBGs

In order to study the effect of transmission distance on the performance of optical code division multiplexing passive optical network systems based on fiber Bragg Grating (FBG), a two-dimensional OCDMA-PON system based on cascaded FBGs is designed and constructed by using the VPI optical communication software. The spectrum, waveform and eye diagram of the output signal are analyzed by setting different fiber lengths in the system. The experimental results show that different fiber lengths have different effects on the system. Within a certain transmission distance, the longer the fiber length, the smaller the error generated by the output signal and the better the signal quality; beyond this certain distance, the quality of the output signal deteriorates sharply and the error generated becomes larger.

OCDMA System Using Two Code Keying Encryption Introducing a SOA Based CMUX And CDEMUX Over a WDM System

This paper introduces an Optical Code Division multiplexing (OCDMA) system using two code keying encryptions. In this paper proposed OCDMA system is designed using Semiconductor optical amplifiers (SOAs) which has nonlinear character and can implementor different logic functions. SOA based 2 × 1 Codeword Multiplexer (CMUX) is designed to multiplex the user data and a 1 × 2 Codeword DE Multiplexer (CDEMUX) to demodulate the user data. Then a multiple user access is provided using WDM system to design the whole OCDMA system. Transmission distance of 70 km is achieved with acceptable bit error rate and Q factor. Open eye diagram is also verified at the receiving end.

Performance analysis of 2D-OCDMA system in long-reach passive optical network

In this paper, a performance analysis is reported for optical code division multiplexing (OCDM) system for long-reach passive optical network (LR-PON) systems by taking into account multiple access interference (MAI), single-mode fiber (SMF) channel effects and receiver noise. The mathematical model representing the 2-D optical code parameters for different receiver structures used in optical code division multiplexing access (OCDMA) are developed, optimized and implemented using Matlab simulations, where channel imperfections, such as attenuation losses and chromatic dispersion have been considered. In the proposed system configuration, we have investigated the probability of error for Back-to-Back (B2B) with conventional correlation receiver (CCR), SMF with CCR receiver and SMF channel with successive interference cancelation (SIC) receiver. Additionally, SMF channel with SIC receiver system performance has been addressed by taking into account two key metrics, such as BER and Q-factor as function of simultaneous users, and fiber length, respectively. We have managed to substantially improve simultaneous multiuser data transmission over significant fiber lengths without use of amplification, where Q-factor of 6 at fiber length of 190 and 120 km, while a SIC receiver using 5 stages cancelation is employed for 2D prime hop system (2D-PHS) and for 2D hybrid codes (2D-HC), respectively.

Advanced Approximation of Channel Quality in a VLC CDM System

Expanding the functionality of LED indoor lighting with visible light communication (VLC) allows an additional communication channel beside wireless radio in buildings. This service may be based on various channel access methods and modulation types. Code division multiplexing (CDM) is a suitable method to such an application, but it is complicated to measure the signal quality which is essential to compare different codes and settings, and necessary for some applications like position-dependent information services. Computing crest factor is a suitable method to estimate quality, but it may be inaccurate in some cases. This paper presents novel methods to approximate the quality of received CDM signals along with the crest factor, aiding the more accurate investigation of the VLC CDM technique.

A highly sustainable multi-band orthogonal wavelet code division multiplexing UWB communication system for underground mine channel

The underground mine channel is highly hostile for communication. A sustainable communication system is required to be integrated as a multipurpose system capable of transferring all types of information such as data, voice and video on identical infrastructure. With its large bandwidth, the Ultra Wide Band (UWB) provides a promising solution to satisfy these requirements. The Multi-Band Orthogonal Frequency Division Multiplexing (MBOFDM) UWB system provides high resilience to Inter-Symbol Interference (ISI) caused by multipath fading channels. This study compares the performance of various existing multi-band UWB systems in the IEEE UWB channel and underground mine channel: MBOFDM, Multi-Band Orthogonal Frequency Code Division Multiplexing (MBOFCDM) and Multi-Band Orthogonal Wavelet Division Multiplexing (MBOWDM). Further, the application of 2D spreading to the MBOWDM UWB system is attempted, and as a result, the Multi-Band Orthogonal Wavelet Code Division Multiplexing (MBOWCDM) UWB system is proposed. The performance of the MBOWCDM system in the IEEE UWB channel and underground mine channel is investigated. The performance of the MBOWCDM UWB system is observed to be superior to those of other multi-band UWB systems. Moreover, the MBOWCDM UWB system supports a higher data rate with low complexity and lower overheads.

Optimation of simplified serial concatenated overlapped code division multiplexing system

A simplified serial concatenated overlapped code division multiplexing SC-OVCDM system is proposed in this paper, in this scheme, inner overlapped code division multiplexing OVCDM code matrix is simplified into multiplexing matrix with constraint length 1, which can obtain two benefits. Firstly, system complexity has significant reduction. Moreover, the output constellation diagram distribution is close to the Gaussian distribution and can obtain better BER performance. Secondly, higher spectral efficiency greater than 4 bit/s/Hz can be achieved for its low complexity. Coded simplified SC-OVCDM system is studied at the first time, BCH Bose, Ray-Chaudhuri and Hocquenghem code correcting multiple errors is selected as error correcting code through error histogram analysis, simulations show shorten BCH codes which code rate is close to 1 can effectively eliminate high error floor and reduce loss of spectral efficiency. Proposed system performance needs joint optimisation of encoders, signal sets and multiplexing matrix. Novel multipexing matrices are given for systems that spectral efficiency equals to and greater than 4bit/s/Hz. Simulation results show the effectiveness of the optimal new scheme in AWGN channel.

Fast Code Design for Overloaded Code-Division Multiplexing Systems

We consider the problem of designing binary antipodal code sequences (signatures) for overloaded code-division multiplexing (CDM) systems where the number of concurrent users/signals is greater than the code length. Our goal is to provide an overloaded code that can be constructed and decoded quickly and, more importantly, provide satisfactory recovery performance in conjunction with decoder design specifics. We first introduce a fast and practical method for constructing a code set by operating the Kronecker product with two smaller codes. Under such construction, a fast two-stage maximum-likelihood (ML) detection scheme can dramatically reduce the computational complexity of the ML decoder and make CDM systems practically implementable. To improve the performance in terms of bit error rate, we propose hierarchical criteria for code design, which aims at reducing the cross-correlation of code while maintaining a uniquely decodable (errorless) code property. Simulation studies illustrate that the proposed code design can provide satisfactory performance with low-complexity two-stage ML detection.

Optimation of simplified serial concatenated overlapped code division multiplexing system

Optimation of simplified serial concatenated overlapped code division multiplexing system

Optical Code-Division Multiplexing (OCDM) Networks Adopting Code-Shift Keying/Overlapping PPM Signaling: Proposal and Performance Analysis

Optical code-division multiplexing (OCDM) systems use short pulses compared with bit-duration to achieve high transmission rate. The use of short pulses poses several problems as a result of group velocity dispersion (GVD), intersymbol interference (ISI) (due to avalanche photodiode (APD) buildup time), and receivers limited bandwidth. In this paper, an OCDM system employing code-shift keying (CSK) and overlapping pulse-position modulation (OPPM) signaling is proposed and theoretically investigated. By using CSK while maintaining same data rate, the chip duration can be increased to counteract the GVD effect in 2D OCDM systems. Moreover, by increasing the chip duration, the chip rate is decreased and the stringent requirement on receiver bandwidth is relaxed. In addition, using overlapping property in OPPM allows for further chip duration increase. We consider using correlation receivers with hard-limiters and APDs at the receiver side. The bit error probability (BEP) of the proposed system is derived taking into account the impacts of APD noise, thermal noise, GVD, ISI, and multiple-access interference (MAI). A performance comparison between OOK-, PPM-, OPPM-OCDM and the proposed system is carried out. Our results reveal that the use of CSK/OPPM-OCDM with data rate constraint allows the reduction of MAI, GVD and ISI effects with improved spectral efficiency.

Development of OCDMA system based on Flexible Cross Correlation (FCC) code with OFDM modulation

The performance of the OCDMA systems is governed by numerous quantitative parameters such as the data rate, simultaneous number of users, the powers of transmitter and receiver, and the type of codes. This paper analyzes the performance of the OCDMA system using OFDM technique to enhance the channel data rate, to save power and increase the number of user of OSCDMA systems compared with previous hybrid subcarrier multiplexing/optical spectrum code division multiplexing (SCM/OSCDM) system. The average received signal to noise ratio (SNR) with the nonlinearity of subcarriers is derived. The theoretical results have been evaluated based on BER and number of users as well as amount of power saved. The proposed system gave better performance and save around −6dBm of the power as well as increase the number of users twice compare to SCM/OCDMA system. In addition it is robust against interference and much more spectrally efficient than SCM/OCDMA system. The system was designed based on Flexible Cross Correlation (FCC) code which is easier construction, less complexity of encoder/decoder design and flexible in-phase cross-correlation for uncomplicated to implement using Fiber Bragg Gratings (FBGs) for the OCDMA systems for any number of users and weights. The OCDMA–FCC_OFDM improves the number of users (cardinality) 108% compare to SCM/ODCMA–FCC system.

A Novel Wireless Statistical Division Multiplexing Communication System and Performance Analysis

This paper proposes a new wireless statistical division multiplexing (SDM) communication system, which is based on the two-input and two-output wireless communication experimental platform constructed and presented in our previous work. This novel system aims to transmit source signals simultaneously in the same frequency band over wireless channel and recovers the source signals at the receiver by utilizing the statistical characteristics of source signals and broadcasting characteristics of wireless channel. Therefore, the spectrum efficiency of SDM system is high compared to those of time division multiplexing (TDM), frequency division multiplexing (FDM), and code division multiplexing (CDM) systems, in which TDM, FDM and CDM signals are limited in time interval, frequency band and code. Taking advantage of the statistical properties of transmitted source signals, the SDM system can easily recover or retrieve them through the blind source separation (BSS) techniques at the receiver. This paper first introduces the system model of SDM briefly, but the main purpose is to analyze the performance of it including the relationship between the separation quality and the characteristics of source signals, the power of transmitters and separation algorithms. The performance validity and corresponding analysis are confirmed and performed through realistic experiments.

CDM-Based <inline-formula> <tex-math notation="TeX">\(\lambda \) </tex-math></inline-formula>-OTDR for Rapid TDM- and WDM-PON Monitoring

A novel OTDR-system is introduced, which enables a significant reduction of measurement times in TDM- and WDM-PON measurements compared to a conventional \(\lambda \) -OTDR. It has the ability to measure multiple wavelengths simultaneously with just one receiver photodiode. The working principle is similar to a code division multiplexing transmission system. Furthermore, the measurement time is not only reduced by the simultaneous measurements on different wavelengths but also by means of coding gain, which reduces the OTDR averaging time. The coding gain has its origin in the correlation of signals based on complete complementary codes. In an experiment, measurements were performed, which provided results 15 times faster than with a conventional \(\lambda \) -OTDR. Further improvements are possible with different measurement parameters.

Performance of OCDM/WDM Optical Packet Switches with DPSK-OCDM modulation system

The performance of a Differential-Phase-Shift-Keying Optical Code-Division Multiplexing (DPSK-OCDM) system with balanced detection is investigated in the case in which Gold codes are used. Allowing more optical codes to be supported, the performance in Packet Loss Probability of a DPSK-OCDM Optical Packet Switch, using both code and wavelength domains to solve output packet contentions, may be increased. In the proposed case study the increase is of three orders of magnitude when the offered traffic is 0.7.

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.

Adaptive Binary Spreading Sequence Assignment Using Semidefinite Relaxation

We consider the problem of designing binary spreading sequences in code-division multiplexing (CDM) systems. Our objective is to find the binary spreading sequence that maximizes the pre-detection signal-to-interference-plus-noise (SINR) at the output of maximum-SINR (MSINR) linear filter. However, the maximization problem over the binary field is NP-hard with complexity exponential in the sequence length. In this paper, we present a semidefinite-relaxation-based algorithm with a polynomial computational complexity that outputs the desirable binary solution with the deterministic SINR performance guarantee. Simulation studies demonstrate performance improvement over other known binary sequence assignment algorithms.

Code-division multiplexing for x-ray microcalorimeters

We demonstrate the code-division multiplexing (CDM) readout of eight transition-edge sensor microcalorimeters. The energy resolution is 3.0 eV (full width at half-maximum) or better at 5.9 keV, with a best resolution of 2.3 eV and a mean of 2.6 eV over the seven modulated detectors. The flux-summing CDM system is described and compared with similar time-division multiplexing (TDM) readout. We show that the Npixels multiplexing disadvantage associated with TDM is not present in CDM. This demonstration establishes CDM as both a simple route to higher performance in existing TDM microcalorimetric experiments and a long-term approach to reaching higher multiplexing factors.

Optimization and Analysis of Code-Division Multiplexed TES Microcalorimeters

We are developing code-division multiplexing (CDM) systems for TES arrays with the goal of reaching multiplexing factors in the hundreds. We report on x-ray measurements made with a four-channel prototype CDM system that employs a flux-summing architecture, emphasizing data-analysis issues. We describe an empirical method to determine the demodulation matrix that minimizes cross-talk. This CDM system achieves energy resolutions of between 2.3 eV and 3.0 eV FWHM at 5.9 keV.

4096-Ary OCDM/OCDMA System Using Multidimensional PSK Codes Generated by a Single Multiport En/Decoder

We experimentally demonstrate a record 4096 (=16 × 16 × 16)-ary optical code division multiplexing (OCDM) system at 2.5 Gbps using multidimensional phase shift keying (PSK) codes generated/processed by a single multiport optical encoder/decoder (E/D). To analyze the system performance, we evaluate the power margin and the data confidentiality. For application to access networks, we propose and numerically evaluate the performance of 10 Gbps, 4096-ary optical code division multiple access (OCDMA)-based passive optical network (PON).

Evaluation of Optimum Threshold in OCDM/WDM Optical Packet Switches

In this paper we illustrate a procedure to evaluate the optimum receiver threshold in Optical Code Division Multiplexing (OCDM) systems using Gold Codes. The use of the optimum threshold allows for a higher number of optical codes carried on each wavelength. The increase in OCDM/WDM Optical Packet Switch performance is also evaluated when the threshold optimization is performed. We show that when the offered traffic is equal to p=0,7, the packet loss probability of the OCDM/WDM switch in saturation conditions, equals 1,28*10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-6</sup> in the case in which the optimal receiver threshold is used. On the contrary the performance reaches only 3,91*10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-4</sup> if a traditional threshold is chosen.

Performance of multiple-input and multiple-output orthogonal frequency and code division multiplexing systems in fading channels

In broadband downlink transmission, orthogonal frequency-division multiplexing (OFDM) combined with code-division multiple access (CDMA) is a prospective technique for high-data rate transmission in future wireless communication systems. By adding spatial diversity, multiple-input and multiple-output orthogonal frequency and code division multiplexing (MIMO-OFCDM) offers superior performance relative to both traditional OFDM systems and single-input and single-output OFCDM (SISO-OFCDM) systems. In this study, the authors present an analytical study and investigation of a MIMO-OFCDM downlink system that hires orthogonal variable spreading factor codes to spread each transmitted symbol in both time and frequency domains. Different gain combining schemes are employed in the frequency domain to recover the data symbols of the desired code channels, and space–time block coding is used to achieve spatial diversity. The more general Ricean fading channel is used to model the MIMO channel. The OFCDM system employs Alamouti transmit diversity scheme with multiple receive antennas. For systems without multi-code interference (MCI), analytical bit-error rate results are obtained and compared with simulation results. The authors also investigate the effect of correlation in frequency domain, where we verify that minimum mean-square error frequency combining is more robust to MCI than equal-gain combining.