Minimizing correlation effect using zero cross correlation code in spectral amplitude coding optical code division multiple access

The use of minimal multiple access interference (MAI) in code design is investigated. Applying a projection and mapping techniques, a code that has a zero cross correlation (ZCC) between users in optical code division multiple access (OCDMA) is presented in this paper. The system is based on an incoherent light source—LED, spectral amplitude coding (SAC), and direct detection techniques at the receiver. Using power spectral density (PSD) function and Gaussian approximation, we obtain the signal-to-noise ratio (SNR) and the bit-error rate (BER) to measure the code performance. Making a comparison with other existing codes, e.g., Hadamard, MFH and MDW codes, we show that our code performs better at BER 10⁻⁹ in terms of number of simultaneous users. We also demonstrate the comparison between the theoretical and simulation analyses, where the results are close to one another.     

Performance of OCDMA systems with new spectral direct detection (SDD) technique using enhanced double weight (EDW) code

This paper investigates the performance of enhanced double weight (EDW) code for spectral-amplitude-coding OCDMA (SAC-OCDMA) system using a newly proposed spectral direct detection (SDD) technique. EDW is the enhanced version of double weight (DW) code that possesses ideal cross-correlation properties and weight which can be any odd number greater than one. The theoretical and simulation results show that the proposed new spectral direct detection technique improves the performance compared to the conventional complementary subtraction technique.     

Performance analysis of quantum access network using code division multiple access model

A quantum access network has been implemented by frequency division multiple access and time division multiple access, while code division multiple access is limited for its difficulty to realize the orthogonality of the code. Recently,the chaotic phase shifters were proposed to guarantee the orthogonality by different chaotic signals and spread the spectral content of the quantum states. In this letter, we propose to implement the code division multiple access quantum network by using chaotic phase shifters and synchronization. Due to the orthogonality of the different chaotic phase shifter, every pair of users can faithfully transmit quantum information through a common channel and have little crosstalk between different users. Meanwhile, the broadband spectra of chaotic signals efficiently help the quantum states to defend against channel loss and noise.     

Integrated photonic decoder with complementary code processing and balanced detection for two-dimensional optical code division multiple access

We propose a novel integrated photonic decoder for two-dimensional (time spreading, wavelength hopping) optical code division multiple access. The decoder is composed of multiplexers-demultiplexers, variable delay lines, and a coupler, which processes complementary codes and utilizes balanced detection to reduce unwanted cross-correlation interference. We successfully carried out a 10 Gbit/s transmission that demonstrated its effectiveness.     

Cardinality enhancement of spectral/spatial modified double weight code optical code division multi-access system by PIIN suppression

A new two-dimensional (2-D) optical code division multiple access (OCDMA) scheme to increase the achievable system capacity is proposed. The code exhibits good cross-correlation property time and wavelength shift. Performances are analyzed on code size and correlation properties affecting two important system parameters, bit error rate (BER) as a function of cardinality generated and optical power transmission requirement. The proposed system can effectively suppress phase-induced intensity noise (PIIN) and has multi-access interference (MAI) cancellation property. Results in a good agreement indicate that 2-D modified double weight (MDW) offers 163.7% and 336.2% larger cardinality compare to 2-D perfect difference code (PDC) and 2-D modified quadratic congruence (MQC) code. By increasing spatial code (N) and keeps similar code length system performance can be further optimized. 2-D MDW (M = 45, N = 18) accommodates 252.2% and 18.3% cardinality increment and low effective transmitted power (P_sr) at −17.9 dBm, compare to 2-D MDW (M = 247, N = 3) and (M = 84, N = 9) at 10⁻⁹ BER error floor. The architecture of the spectral/spatial MDW OCDMA system with property of MAI cancellation is presented.     

Control packet signaling mechanism using electronic code division multiple access for packet-based networks

We propose and experimentally demonstrate the feasibility of a control packet signaling technique using electronic code division multiple access for a wavelength division multiplexing packet-based network, whereby each wavelength channel is assigned a unique electronic code based label on a radio frequency subcarrier. Such a technique allows each wavelength channel to be electronically identified without requiring the use of a WDM demultiplexer. We experimentally demonstrate this technique with two wavelength channels each with 1.25 Gb/s baseband payload data and 10 Mb/s header coded onto an electronic code at 160 Mb/s. A performance study of the electronic code division multiple access based control signaling scheme in a wavelength division multiplexed packet-based access network is also performed in terms of the required power budget to monitor the electronic code division multiple access control signals in the presence of several sources of noise for error-free transmission of both payload data and electronic code division multiple access based control signals. It is shown that the modulation depth of each signal impacts the amount of required optical tap power. As the modulation depth of the electronic code division multiple access based control signal is increased, the required optical tap power is reduced. However, this increases the bit-error-rate for the payload data. Therefore, there lies a maximum and a minimum of the required tap optical power for the successful recovery of both signals. The lower bound of this range is usually determined by the successful recovery of electronic code division multiple access based control signal while the upper bound is determined by the successful recovery of payload data. The required optical tap power is analyzed for different transmission bit rates of the payload data for various receiver architecture scenarios without an optical amplifier at the receiver. The scalability analyses were repeated with an optical amplifier placed in the receiver terminal of the network. The resulting optical tap power that is required for the successful monitoring of the electronic code division multiple access based control signals are compared with that of the case without the amplifier.     

Performance analysis of electronic code division multiple access based virtual private networks over passive optical networks

A solution for implementing multiple secure virtual private networks over a passive optical network using electronic code division multiple access is proposed and experimentally demonstrated. The multiple virtual private networking capability is experimentally demonstrated with 40 Mb/s data multiplexed with a 640 Mb/s electronic code that is unique to each of the virtual private networks in the passive optical network, and the transmission of the electronically coded data is carried out using Fabry-Perot laser diodes. A theoretical scalability analysis for electronic code division multiple access based virtual private networks over a passive optical network is also carried out to identify the performance limits of the scheme. Several sources of noise such as optical beat interference and multiple access interference that are present in the receiver are considered with different operating system parameters such as transmitted optical power, spectral width of the broadband optical source, and processing gain to study the scalability of the network.     

10 Gb/s two-dimensional free-space optical code division multiple access wiretap channel with spatial diversity

We experimentally demonstrate a 10 Gb/s free-space optical wiretap channel based on a spatial-diversity scheme and optical code division multiple access. In weak and middle turbulence cases, the bit error rate of a legitimate user can be decreased, and physical layer security can be simultaneously enhanced.     

基于重构等效啁啾制作光纤光栅编解码器的光码分多址系统实现

在光码分多址(OCDMA)系统中，光纤布拉格光栅(FBG)编解码器是极具竞争力的核心器件，满足光接入网低成本、高性能的要求. 将重构等效啁啾 (REC) 技术制作的FBG作为编解码器运用于OCDMA系统. 实验采用一对511个码片、编码速率为6.4×10⁹/s的FBG编解码器，在编码匹配的情况下能恢复出输入信号，与编码非匹配的情况相比获得了8 dB的功率增益.这为REC技术制作的编解码光栅在OCDMA系统中的应用提供了实验依据. 关键词： 光纤布拉格光栅 光码分多址 重构等效啁啾 编解码器     

Performance improvement of direct detection systems using local and/or long-distance pumped fiber amplifiers

Erbium-doped fiber amplifiers (EDFAs) in eight different system configurations are investigated, using a full-scale model, and the midline placement of the amplifier is shown to be optimal. A distributed amplifier compared to the remote pumping scheme shows no system improvement. Use of a booster (next to the transmitter), a midline remote-pumped amplifier, and a preamplifier (next to the receiver) allows up to 180 km of extra transmission fiber to be added.     

Performance analysis of spectral-amplitude-coding optical CDMA systems with new subtract exclusive OR detection (SED) using vectors combinatorial (VC) code

This paper investigates the performance of vector combinatorial (VC) code for spectral amplitude coding optical code-division multiple-access (SAC-OCDMA) system using a newly proposed subtract exclusive OR detection (SED) technique. VC code is constructed using Euclidean vector and algebraic ways. One of the important properties of this code is that the maximum cross correlation is one, which means that multi-user interference (MUI) and phase induced intensity noise (PIIN) are reduced. The weight for the VC code can be any positive integer number. The system performance was evaluated by comparing the theoretical studies using related equations and simulation results taken from the commercial optical systems, “VPI? TransmissionMaker 7.1”. Significant improvement in system performances has been observed when the proposed SED technique employing VC code was applied compared to other codes that utilize conventional balance detection techniques for spectral amplitude coding.     

Performance enhancement using the bipolar capacity of bipolar coded fiber Bragg gratings and balanced detection in the spectral encoded code-division-multiple-access systems

This paper proposes a performance-enhanced code-division-multiple-access (CDMA) system using modified pseudorandom noise (PN) coded fiber Bragg gratings (FBGs) with a bipolar optical CDMA encoder/decoder. The data were encoded either by a unipolar signature sequence of modified PN code or by its complement, depending on whether the data bit was ‘1’ or ‘0’. Numerical simulation confirmed that bit error rate (BER) performance largely improved due to the increased decision margin at the receiver. Furthermore, at the BER of 10⁻⁹, the tolerance of spectral power distortion in the optical source appeared to be nearly twice that of conventional optical CDMA systems.     

Performance characteristics and weight distribution analysis of turbo product code with Reed-Muller component codes

In this paper, we present simulation results for Reed-Muller (RM) turbo codes over AWGN and Rayleigh fading channels. We also compare the simulation results of turbo product codes and block turbo codes with RM component codes over an AWGN channel. We show that minimum distance is not important as far as the BER performance of long codes is concerned. The weight distribution of RM codes of different lengths and turbo product codes with first-order RM component codes are obtained and analyzed for their good performance. We show that the weight distribution asymptotically approaches that of random coding as the code length increases.     

Performance improvement of AlGaN-based deep ultraviolet light-emitting diodes with double electron blocking layers

The AlGaN-based deep ultraviolet light-emitting diodes(LED) with double electron blocking layers(d-EBLs) on both sides of the active region are investigated theoretically. They possess many excellent performances compared with the conventional structure with only a single electron blocking layer, such as a higher recombination rate, improved light output power and internal quantum efficiency(IQE). The reasons can be concluded as follows. On the one hand, the weakened electrostatic field within the quantum wells(QWs) enhances the electron–hole spatial overlap in QWs, and therefore increases the probability of radioactive recombination. On the other hand, the added n-AlGaN layer can not only prevent holes from overflowing into the n-side region but also act as another electron source, providing more electrons.     

Performance analysis of dense wavelength division multiplexing secure communications with multiple chaotic optical channels

The performance of dense wavelength division multiplexing secure communications with multiple chaotic optical channels is numerically analyzed in this paper. Taking the multiplexing of three chaotic optical channels as an example, we investigate the effects of second-order dispersion coefficient and nonlinear coefficient of fiber, channel spacing, message amplitude and bit rates on chaotic synchronization and multiplexing communications. Chaotic synchronization quality and Q-factor of the recovered message decrease with the increasing fiber length. A 1.25 Gbits/s non-return-to-zero (NRZ) sequence can be securely transmitted up to 60 km under the influence of the other two chaotic optical channels. Compared with the fiber dispersion, the cross-phase modulation is the primary factor which deteriorates the quality of communications. The results also show that the quality of communications is unlimited to the channel spacing as long as chaotic synchronization can be maintained. In addition, the effect of the amplitude of encrypted message on Q-factor and the confidentiality is demonstrated.     

Error probability of the data transmission in mimo systems with space-division multiple access in Rayleigh fading environments

We consider multiple-input multiple-output (MIMO) communication systems with adaptive antenna arrays at both ends of the link in which the data transmission is performed via parallel eigenchannels matched to the random spatial channel. The effectiveness of the projection method of space-division multiple access is studied. The method does not require estimation of the arrival directions of signals and is based on orthogonalization of all eigenchannels. Exact analytical expressions are obtained for the bit-error probability during the data transmission via the channel with uncorrelated Rayleigh fading of signals in an MIMO system with an arbitrary number of users and antennas. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 49, No. 9, pp. 816–828, September 2006.     

Performance limits of pico-cell systems using radio-over-fiber techniques with an electroabsorption modulator

We investigate the performance limits of a pico-cell system using the radio- over-fiber technique with an electroabsorption modulator (EAM) in a 2.4 GHz wireless local area network (WLAN) environment. To understand the performance limits of the system using an EAM as the optical transceiver, we vary the optical modulation index (OMI) of the transmitter for different bias voltages to the EAM. Power margins in the links are found to estimate a possible service range, and packet loss rates (PLRs) in the pico-cell system are measured to evaluate the transmission performance. The total service range can be extended up to 3 m by adjusting the OMI of the transmitter for different applied bias voltages to the EAM.