Code Division Multiplexing Technique Research Articles

Integrated long reach and energy-efficient NGPON-VLC system with OCDM/WDM for smart green buildings

Smart green buildings (SGBs) are composed of numerous services and offer hopeful solutions to the world's continuous and rapid urbanization. Conventional data transmission systems are insufficient to deliver acceptable services because to the sudden surge in high-quality information transmission requirements over long distance for numerous linked residents in SGBs. Consequently, a hybrid next generation passive optical network (NGPON) along with visible light communication (VLC) indoor/outdoor broadcast network is presented in this work to increase the reliability with intelligence, exalted overall efficiency, cost efficiency, and security of SGBs. Bidirectional PON-VLC system incorporates the time and wavelength division multiplexing (TWDM), wavelength division multiplexing (WDM) and optical code division multiplexing (OCDM) techniques. In order to improve system performance, various OCDM codes are used in this work at 10/2.5 Gbps per channel throughput via fiber-VLC channels. According to the simulation results, the modified new zero cross-correlation (MNZCC) code performs better than previous codes and supports 200 active residents at reliable 100 km fiber along with 5 m VLC range. Furthermore, by expanding the received aperture diameter to 25 cm, VLC coverage may be increased till 10 m. Moreover, it provides adequate receiver sensitivities of − 13 to − 12 dB in uplink with − 9.8 to − 6 dBm in downlink for 200 to 600 fields of view angles compared to 00 view angle having sensitivity of − 15 dBm. Additionally, the numerical analysis and comparison performance show that PON-VLC outperforms fiber-VLC link-based scenarios when it comes to noise and channel impairments.

High-security optical transmission system with multi-dimensional multiplexing based on quaternion chaotic encryption.

In this paper, we propose a multi-dimensional multiplexing scheme for space division multiplexing optical transmission systems based on quaternion chaotic encryption. A constellation compression shaping mapping method is designed to replace the traditional 2n mapping scheme, which leads to flexible encoding modulation. In order to achieve orthogonality between data symbols and effectively suppress crosstalk, the spectrally superposed transmission of three-dimensional (3D) constellation data is carried out by code division multiplexing and 4D carrier-less amplitude phase joint modulation techniques based on orthogonal basis. The Chen's chaotic model is utilized to generate the rotation angle of the constellation points, which enables data encryption without changing the transmitted power, enhancing system's security. The feasibility and superiority of the proposed scheme are successfully verified by constructing an experimental platform for a seven-core fiber transmission system.

Complete Separable Reversible Data Hiding for Encrypted Digital Images Using Code Division Multiplexing with Versatile Bit Depth Management

A reversible data hiding in the encrypted domain (RDH-ED) aims to hide data within encrypted images, protecting its content, while allowing additional information to be distributed. This paper presents a complete separable RDH-ED scheme, whose main contribution is allowing the receiver to extract data and restore the image, either from the cryptogram with hidden data or from the directly decrypted version. With versatile bit-depth management, the most significant bits of each pixel are encrypted with AES-CTR cipher algorithm, while the additional data will be inserted inside the least significant bit planes of the encrypted pixels, by means of the code division multiplexing technique. Considering the marked/encrypted images, and encryption/data-hiding keys, a receiver could: (a) directly decrypt the encrypted image and obtain its approximate version, (b) extract the error-free hidden data, and (c) recover the data and original image. Considering an image approximation version and the data hiding key, a receiver could: (d) extract the hidden data from the plaintext domain, and (e) restore the image to its original state, while accessing the hidden data without any loss. Experimental results show the performance of the developed algorithm, evaluating the capacity and imperceptibility of the proposed scheme with respect to current state of the art.

Performance evaluation of a 160-Gbit/s OCDMA-FSO system via Laguerre-Gaussian beams under weather conditions

For capacity enhancement of free space optics (FSO) communication, a new model based on using four Laguerre-Gaussian (LG) beams, each carries four different users use optical code division multiplexing (OCDMA) techniques, is proposed. Additionally, the permutation vector (PV) codes that have zero cross correlation with direct detection (DD) technique are assigned to the OCDMA system. Each user carries 10 Gbps information data, so the overall capacity is 4 LG beams × 4 users (OCDMA) × 10 Gbps = 160 Gbps. Furthermore, the proposed model is simulated under the effects of different attenuations caused by different weather conditions and the performance is studied. The conducted results reveal successful transmission of 13 km under clear air (CA), 1.75 km under heavy haze (HH), 1.1 km under heavy rain (HR), and 0.9 km under heavy fog (HF) with an overall system capacity of 160 Gbps. These results were obtained with an acceptable log bit error rate (BER) less than −9 and quality (Q)-factor nearly 6.

Algebraic cancellation of inter-channel cross talk in multiplexed heterodyne interferometry.

We demonstrate the algebraic cancellation of residual phase cross talk in digitally enhanced heterodyne interferometry (DEHeI), a code division multiplexing technique for interferometric sensing. By using linear combinations of parallel decoding operations at multiple delays, we synthesize a zero correlation for spurious signals and remove phase cross talk: a method we call offset decoding. We experimentally demonstrate 70 dB of signal isolation and over 40 dB greater isolation than the equivalent standard implementation of DEHeI.

TECHNOLOGICAL APPROACH TO SOLVING THE PROBLEM OF MINIMIZING THE INFLUENCE OF DESTABILIZING FACTORS ON THE WORK OF DISTRIBUTED STRUCTURES OF THE GROUND-ROCKOTECHNICAL COMPLEX IN AN INTEGRAL PROJECT «OBJECT-SYSTEM»

Mobile structures of the ground-based robotic complex (RTC) are investigated as an active component formation of an integrated project “object-system”, which is operated in a destabilizing environment. The relevant problem of minimizing the influence of external destabilizing factors on the operation of mobile spatially-distributed structures of the ground-based RTC is stated in the descriptions of the conceptual apparatus of complex, poorly formalized multicomponent technical systems. Following the logic of this approach, the basic principles of distributed control are determined and their applications are implemented in the mobile structures of the ground-based RTC with elements of subsidiarity. The quintessence of the latter is represented by the technology of multi-antenna MIMO systems, which made it possible to determine the trade-offs of using classical transmission methods and strategies for receiving and processing MIMO signals in the multi-sensory channels of the information-control system (ICS) and radio communication with the data transmission system and commands. Given the complexity of performing the stated tasks, a set of technological functions of reducing the influence of destabilizing factors and their practical variations in the algorithms for obtaining the target result are proposed. A situational model of reducing (minimizing) information losses at the output of the information-control system of the ground-based robotic complex under destabilization has been built. Options have been proposed to achieve the target result: integration of structural and parametric adaptation methods, MIMO technologies, code division multiplexing techniques with CDMA channels, taking into account the heterogeneity factor of information exchange channels and the artificial redundancy of the system itself with respect to the number of external interference sources.

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.

Optimization of the Microwave Properties of the Kinetic-Inductance Bolometer (KIBO)

Silicon nitride membrane based cryogenic bolometers exhibit high sensitivity and enable ultra-sensitive detector applications. Multi-pixel instruments were already introduced as devices for submillimeter-wave imaging. Nevertheless, the numbers of pixels are limited by the readout process which is typically a time-division multiplexing or code-division multiplexing technique. To overcome this challenge, a replacement of the transition-edge sensor as thermometer by a lumped-element resonance circuit seems to be a promising solution. Therefore, one can benefit from the intrinsic capability of frequency-division multiplexing that allows the readout of large detector arrays simultaneously and in real-time. The number of pixels is then limited by the available readout bandwidth and the quality factors of each individual resonance circuit. We successfully demonstrated, based on our feasibility study, the principal operation of such a device, what we call kinetic-inductance bolometer (KIBO). But the overall performance of the achievable noise-equivalent power (NEP) was limited by implementation and operation temperature of KIBO. Therefore, improved KIBO designs were developed and fabricated with niobium thin-film technology. In this paper, we describe the improvement procedure and estimate the expected NEP value.

Code Optimization for a Code-Modulated RF Front End

Recently, a novel class of on-site coding receivers was proposed. The architecture is suitable for digital beamforming in addition to offering multiple-input multiple-output capabilities. Essential to its realization is a code division multiplexing technique aggregating multiple signal paths at the analog front end into a single analog-to-digital converter. As a result, a significant hardware reduction and a higher power efficiency are achieved when compared with the conventional digital beamforming techniques. In this paper, we examine the system's performance with different types of spreading codes, both orthogonal and nonorthogonal, namely Walsh-Hadamard and Gold codes. Bit error rate calculations show that Walsh-Hadamard codes outperform Gold codes in achieving higher dynamic range with less signal-to-noise ratio degradation, assuming a perfectly synchronous system.

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.

RSFQ electronics for controlling superconducting polarity switches

Superconducting radiation sensors are of particular interest for imaging applications in the sub-mm wavelength band because of their extraordinary sensitivity. The rising number of sensors integrated in one array entails the requirement of multiplexing techniques in order to reduce the number of wires leading into the cryogenic stage and thus reduce the thermal losses. One kind of promising code division multiplexing technique is based on a current steering switch (CSS), which is composed of two identical superconducting quantum interference devices (SQUIDs) in parallel current paths. One of them is switched from the superconducting into the normal state controlled by the applied magnetic flux. In this way the signal path can be altered and they can act as a polarity switch for analogue signals. We pursue this concept to use rapid single flux quantum (RSFQ) electronics for controlling these switches. As a first step, the SQUIDs of the CSS are inductively coupled to the storing loops of two delay flip flops (DFFs). Thus, one is able to toggle the polarity of the analogue switch by controlling the state of the DFF by RSFQ control signals. The results of simulations and measurements and also margin analyses are discussed.

A novel architecture of optical code label processing in parallel designed for all optical routing system

A novel architecture of optical code label routing is designed based on optical code division multiplexing techniques, which performs the data packet forwarding and processing in parallel with a way of making the label and payload encoded and decoded separately. It uses optical polarity characteristics to realize the separation of the label and payload, employs fiber Bragg grating to encode/decode the label and payload so as to process them in parallel, and makes the forwarding and routing process realized in the optical domain. In the core router, the separation of the label and payload guarantees that the switch processing only includes the short label code recognition, without processing the payload. The payload recognition is carried out in the edge router. Thus, the router can simplify the processing of encoding and decoding in the core router, accelerating the switching, and increase the throughput greatly. Moreover, the novel routing scheme not only supports the varying of data packets, transparent transmission, fine granularity switching, and so on, but also is suitable for the aggregation of data service. It is attractive for the future development of all optical routing.

Proposal of Spectrum-Interleaved Duplex WDM-PON Using Spectrum-Sliced Broadband Incoherent Light with Reflection Remover

A Wavelength division multiplexing passive optical network (WDM-PON) system that uses spectrum-sliced broadband incoherent light is attractive because it avoids the cost of operating/administering wavelengths in optical network units (ONU) at customer premises. However, it is difficult to enhance the spectrum efficiency to ensure a sufficient signal to noise ratio because it would demand broad channel width. To overcome this problem, we proposed a spectrum-interleaved duplex technique. It enables upstream and downstream communications to share one channel by using a cyclic filter. This sharing of one channel eliminates the need for a guard interval between signal lights duplexed in the channel. One residual issue regarding single band transmission is its robustness to reflection in the transmission medium. To increase the reflection robustness of the spectrum-interleaved duplex scheme, we propose a reflection remover based on an optical code division multiplexing technique. We also evaluate the extent to which capacity of the spectrum efficiency of the spectrum-interleaved duplex WDM-PON system that uses spectrum-sliced broadband incoherent light can be increased.

Combining cryptographic and steganographic security with self-wrapped optical code division multiplexing techniques

Experimental results for a novel transmission system using self-wrapped optical code division multiplexed signals to achieve enhanced data security at the physical layer of the optical network are presented. Key distribution is performed by encoding and time-spreading, thus allowing for both cryptographic and steganographic security in the public network.

Joint transform correlator with spatial code division multiplexing

A joint transform correlator may suffer from overlapping of the zero diffraction order of the output, which does not contain relevant information, and the correlation peaks that appear in the first diffraction orders if objects are not sufficiently separated. Such overlapping significantly reduces the signal-to-noise ratio of the identification process. We propose a novel approach based on code division multiplexing technique in which the contrast of the identification peaks is significantly enhanced. The approach does not include placing the two objects side by side but rather includes code multiplexing them. Moreover, the code division multiplexing technique allows the space-bandwidth product to be improved. Optical implementation results are given.

Highly Spectral-Efficient Optical Code-Division Multiplexing Transmission System

A highly spectral-efficient transmission system based on optical code-division multiplexing (OCDM) technique is investigated. To meet the rapid increase in the demand of data bandwidth, spectral efficiency is becoming a key factor in optical transport systems. Several modulation formats along with the optical receiver design have been proposed to upgrade the spectral efficiency. OCDM is one of the promising techniques for this purpose. OCDM is the other class of multiplexing technique than optical time-division multiplexing and wavelength-division multiplexing (WDM). OCDM provides unique features such as asynchronous transmission, secure communication, soft capacity on demand, and high degree of scalability. In this paper, we apply OCDM technique to the highly spectral-efficient transmission system by quaternary phase-shift keying optical encoding/decoding along with ultrafast optical time-gating and optical hard thresholding. As a result, a transmission of 6.4 Tbit/s OCDM/WDM (4 OCDM/spl times/40 WDM/spl times/40 Gbit/s) using only C-band wavelength region is experimentally demonstrated with 1.6-bit/s/Hz spectral efficiency.

Applications of multirate optical fibre code-division-multiplexing systems to high-speed data communications for air traffic control

AbstractFuture air traffic control will be based on the distributed processing environment. This leads to the use of high-speed optical fibre networks and systems to connect many processors (for both general and specific purposes) and workstations in the air traffic control centres. To efficiently support such applications, communication systems should be capable of multirate operations. To achieve this aim, we propose an efficient optical fibre code-division multiplexing (OF-CDM) technique that can support multirate data communications without any increase of system complexity when compared with the equal-rate operation case. Unlike conventional optical orthogonal codes (OOCs), the use of our proposed unequal-length OOCs can eliminate any possible violation of the minimum cross-and auto-correlation constraint (i.e. ‘1’) in multirate OF-CDM systems. Thus, using unequal-length OOCs can achieve a better bandwidth efficiency and a lower bit error rate for multirate transmissions than employing conventional OOCs. Moreover, we present the design of cost-effective OF-CDM transmitters for multirate data transmissions. The proposed systems can be also employed to support future airborne real-time data distributions and computer interconnects.

Design of integrated services digital broadcasting systems using multirate optical fiber code-division multiplexing

This paper presents the design of a new type of integrated services digital broadcasting (ISDB) systems which use a multirate optical fiber code-division multiplexing (OF-CDM) technique. The proposed system can efficiently multiplex various kinds of digital signals with multiple bit rates. This is feasibly achieved by using strict optical orthogonal codes of both auto- and cross-correlation constraints being 1 in multirate OF-CDM systems. Moreover, the low-cost design of OF-CDM transmitters is presented, and experimental demonstrations are also carried out. The measured results show that a transmission distance up to 13 km can be feasibly accomplished by using the proposed transmitter design and the external optical injection-locking scheme. It is expected that the proposed ISDB systems can be employed to cost-effectively transmit fast ethernet (125 Mbit/s), FDDI (125 Mbit/s), ATM (155 Mbit/s), and ESCON (200 Mbit/s) protocol data. Their potential applications include Internet services and multimedia broadcasting, such as videoconferencing, video on demand, HDTV, distance learning, and World Wide Web.

Study of a code division multiplexing technique with short orthogonal coding sequences and application to an indoor diffused IR network

Abstract The dominant view that code division multiplexing (CDM) is always wasteful of bandwidth, when compared to alternative multiplexing schemes is disputed. The authors show that a synchronous CDM technique with short orthogonal coding sequences can be employed in a network with inherent bandwidth restrictions, such as an indoor-diffused-infrared (IR) wireless link, offering a higher 'simultaneously active user's capacity’ than conventional CDM (PN codes) and time division multiplexing (TDM) schemes. A set of equations for predicting the network's performance and user's capacity for different CDM schemes is derived, the results are verified by computer simulation and laboratory prototype implementation.

Code-division multiplex technique using bridge functions

A code-division multiplexing technique using a set of orthogonal functions known as bridge functions as carrier codes has been investigated. These functions are three-valued functions which take the values +1, 0 and −1. The results of a computer simulation on the performance of the system in additive white Gausian noise are presented, and the system is compared with conventional time-division multiplexing.