A NOVEL CONSTRUCTION OF VECTOR COMBINATORIAL (VC) CODE FAMILIES AND DETECTION SCHEME FOR SAC OCDMA SYSTEMS

There has been growing interests in using optical code division multiple access (OCDMA) systems for the next generation high-speed optical fiber networks. The advantage of spectral amplitude coding (SAC-OCDMA) over conventional OCDMA systems is that, when using appropriate detection technique, the multiple access interference (MAI) can totally be canceled. The motivation of this research is to develop new code families to enhance the overall performance of optical OCDMA systems. Four aspects are tackled in this research. Firstly, a comprehensive discussion takes place on all important aspects of existing codes from advantages and disadvantages point of view. Two algorithms are proposed to construct several code families namely Vector Combinatorial (VC). Secondly, a new detection technique based on exclusive-OR (XOR) logic is developed and compared to the reported detection techniques. Thirdly, a software simulation for SAC OCDMA system with the VC families using a commercial optical system, Virtual Photonic Instrument, “VPITM TransmissionMaker 7.1” is conducted. Finally, an extensive investigation to study and characterize the VC-OCDMA in local area network (LAN) is conducted. For the performance analysis, the effects of phase-induced intensity noise (PIIN), shot noise, and thermal noise are considered simultaneously. The performances of the system compared to reported systems were characterized by referring to the signal to noise ratio (SNR), the bit error rate (BER) and the effective power (Psr). Numerical results show that, an acceptable BER of 10−9 was achieved by the VC codes with 120 active users while a much better performance can be achieved when the effective received power Psr > -26 dBm. In particular, the BER can be significantly improved when the VC optimal channel spacing width is carefully selected; best performance occurs at a spacing bandwidth between 0.8 and 1 nm. The simulation results indicate that VC code has a superior performance compared to other reported codes for the same transmission quality. It is also found that for a transmitted power at 0 dBm, the BER specified by eye diagrams patterns are 10-14 and 10-5 for VC and Modified Quadratic Congruence (MQC) codes respectively

Minimizing information asymmetry interference using optimal channel assignment strategy in wireless mesh networks

Multi-radio multi-channel wireless mesh networks (MRMC-WMNs) in recent years are considered as the prioritized choice for users due to its low cost and reliability. MRMCWMNs is recently been deployed widely across the world but still these kinds of networks face interference problems among WMN links. One of the well-known interference issue is information asymmetry (IA). In case of information asymmetry interference the source mesh nodes of different mesh links cannot sense each other before transmitting data on the same frequency channel. This non-coordination leads to data collision and packet loss of data flow and hence degrades the network capacity. To maximize the MRMC-WMN capacity and minimize IA interference, various schemes for optimal channel assignment have been proposed already. In this research a novel and near-optimal channel assignment model called Information Asymmetry Minimization (IAM) model is proposed based on integer linear programming. The proposed IAM model optimally assigns orthogonal or non-overlapping channels from IEEE 802.11b technology to various MRMC-WMN links. Through extensive simulations we show that our proposed model gives 28.31% network aggregate network capacity improvement over the existing channel assignment model

A NOVEL CONSTRUCTION OF VECTOR COMBINATORIAL (VC) CODE FAMILIES AND DETECTION SCHEME FOR SAC OCDMA SYSTEMS

There has been growing interests in using optical code division multiple access (OCDMA) systems for the next generation high-speed optical fiber networks. The advantage of spectral amplitude coding (SAC-OCDMA) over conventional OCDMA systems is that, when using appropriate detection technique, the multiple access interference (MAI) can totally be canceled. The motivation of this research is to develop new code families to enhance the overall performance of optical OCDMA systems. Four aspects are tackled in this research. Firstly, a comprehensive discussion takes place on all important aspects of existing codes from advantages and disadvantages point of view. Two algorithms are proposed to construct several code families namely Vector Combinatorial (VC). Secondly, a new detection technique based on exclusive-OR (XOR) logic is developed and compared to the reported detection techniques. Thirdly, a software simulation for SAC OCDMA system with the VC families using a commercial optical system, Virtual Photonic Instrument, “VPITM TransmissionMaker 7.1” is conducted. Finally, an extensive investigation to study and characterize the VC-OCDMA in local area network (LAN) is conducted. For the performance analysis, the effects of phase-induced intensity noise (PIIN), shot noise, and thermal noise are considered simultaneously. The performances of the system compared to reported systems were characterized by referring to the signal to noise ratio (SNR), the bit error rate (BER) and the effective power (Psr). Numerical results show that, an acceptable BER of 10−9 was achieved by the VC codes with 120 active users while a much better performance can be achieved when the effective received power Psr > -26 dBm. In particular, the BER can be significantly improved when the VC optimal channel spacing width is carefully selected; best performance occurs at a spacing bandwidth between 0.8 and 1 nm. The simulation results indicate that VC code has a superior performance compared to other reported codes for the same transmission quality. It is also found that for a transmitted power at 0 dBm, the BER specified by eye diagrams patterns are 10-14 and 10-5 for VC and Modified Quadratic Congruence (MQC) codes respectively

PERFORMANCE ANALYSIS OF OPTICAL CDMA SYSTEM USING VC CODE FAMILY UNDER VARIOUS OPTICAL PARAMETERS

The intent of this paper is to study the performance of spectral-amplitude coding optical code-division multiple-access (OCDMA) systems using Vector Combinatorial (VC) code under various optical parameters. This code can be constructed by an algebraic way based on Euclidian vectors for any positive integer number. One of the important properties of this code is that the maximum cross-correlation is always one which means that multi-user interference (MUI) and phase induced intensity noise are reduced. Transmitter and receiver structures based on unchirped fiber Bragg grating (FBGs) using VC code and taking into account effects of the intensity, shot and thermal noise sources is demonstrated. The impact of the fiber distance effects on bit error rate (BER) is reported using a commercial optical systems simulator, virtual photonic instrument, VPITM. The VC code is compared mathematically with reported codes which use similar techniques. We analyzed and characterized the fiber link, received power, BER and channel spacing. The performance and optimization of VC code in SAC-OCDMA system is reported. By comparing the theoretical and simulation results taken from VPITM, we have demonstrated that, for a high number of users, even if data rate is higher, the effective power source is adequate when the VC is used. Also it is found that as the channel spacing width goes from very narrow to wider, the BER decreases, best performance occurs at a spacing bandwidth between 0.8 and 1 nm. We have shown that the SAC system utilizing VC code significantly improves the performance compared with the reported codes

Two-dimensional permutation vectors’ (PV) code for optical code division multiple access systems

In this paper, we present a new algorithm to generate two-dimensional (2D) permutation vectors’ (PV) code for incoherent optical code division multiple access (OCDMA) system to suppress multiple access interference (MAI) and system complexity. The proposed code design approach is based on wavelength-hopping time-spreading (WHTS) technique for code generation. All possible combinations of PV code sets were attained by employing all permutations of the vectors with repetition of each vector weight (W) times. Further, 2D-PV code set was constructed by combining two code sequences of the 1D-PV code. The transmitter-receiver architecture of 2D-PV code-based WHTS OCDMA system is presented. Results indicated that the 2D-PV code provides increased cardinality by eliminating phase-induced intensity noise (PIIN) effects and multiple user data can be transmitted with minimum likelihood of interference. Simulation results validated the proposed system for an agreeable bit error rate (BER) of 10−9

The application of SOA for dispersion management of 2D-WH/TS codesin incoherent OCDMA system

In high data rate optical fibre communication networks, dispersion phenomenon plays a pivotal role. It is important to investigate the dispersion effects in a multi-wavelength picosecond optical code division multiple access (OCDMA) system. This research is focused on the analysis of the effects of fibre dispersion on the OCDMA autocorrelation; and how these effects can be resolved in a tuneable way so that the originally recovered OCDMA autocorrelation function at the decoder receiver can be revived without further manual adjustment of fibre (SMF-28) cable lengths.;The environmental effects and the subsequent mitigation process are also investigated further in this research. The chirp in OCDMA is examined experimentally and analytically in an initiative to find the more in-depth understanding of finely tuneable chromatic dispersion (CD) compensation technique in a coarsely compensated link by using semiconductor optical amplifier (SOA). A practical investigation was carried over a partially CD compensated 17 km bidirectional testbed between the University of Strathclyde and the University of Glasgow to perform the fine-tuning of CD adjustment using SOA.;A 19.5 km SMF-28 fibre spool was also used in an environmental chamber to investigate the temperature induced dispersion effects and subsequent mitigation. The tuneable dispersion compensation measures are vital to ensure the high data rate optical communication using an all-optical approach in future data network end-points where the advantages of ultra-high speed optical communication bandwidth are at present disrupted due to opto-electronic conversions commonly known as 'electronic bottlenecks'.In high data rate optical fibre communication networks, dispersion phenomenon plays a pivotal role. It is important to investigate the dispersion effects in a multi-wavelength picosecond optical code division multiple access (OCDMA) system. This research is focused on the analysis of the effects of fibre dispersion on the OCDMA autocorrelation; and how these effects can be resolved in a tuneable way so that the originally recovered OCDMA autocorrelation function at the decoder receiver can be revived without further manual adjustment of fibre (SMF-28) cable lengths.;The environmental effects and the subsequent mitigation process are also investigated further in this research. The chirp in OCDMA is examined experimentally and analytically in an initiative to find the more in-depth understanding of finely tuneable chromatic dispersion (CD) compensation technique in a coarsely compensated link by using semiconductor optical amplifier (SOA). A practical investigation was carried over a partially CD compensated 17 km bidirectional testbed between the University of Strathclyde and the University of Glasgow to perform the fine-tuning of CD adjustment using SOA.;A 19.5 km SMF-28 fibre spool was also used in an environmental chamber to investigate the temperature induced dispersion effects and subsequent mitigation. The tuneable dispersion compensation measures are vital to ensure the high data rate optical communication using an all-optical approach in future data network end-points where the advantages of ultra-high speed optical communication bandwidth are at present disrupted due to opto-electronic conversions commonly known as 'electronic bottlenecks'

Optical code division multiple access systems in AlGaInAs/InP

The rise of photonic integration makes optical code division multiple access (OCDMA) worth revisiting due to its promising role in future all-optical networks. OCDMA has the potential to exploit the surplus bandwidth of optical fibres and to carry over to the optical domain the benefits seen CDMA radio communication systems, such as the effective sharing of the spectrum for multiple network subscribers, and resistance to jamming and eavesdropping. One of the major requirements for the deployment of OCDMA in networks is integration. This thesis presents a research study of integrated OCDMA systems using the AlGaInAs/InP semiconductor material system. This material is considered due to its useful intrinsic properties such as thermal stability, strong electron confinement, and low threshold, making it suitable for fabricating optoelectronic devices. Two bespoke OCDMA systems are considered for integration: coherent temporal phase coding (TPC), and incoherent wavelength-hopping time-spreading (WHTS) OCDMA systems. TPC systems are excellent for high speed communications due to their static en/decoding enabling features. In this research, a 2×2 asymmetric Mach Zehnder interferometer (AMZI) is used to generate a 2-bit phase code, allowing multiplexing for up to four users. A semiconductor mode-locked ring laser is also embedded in the circuit, and using a synchronous mode-locking method, adequate signal en/decoding is achieved. WHTS systems on the other hand fully exploit the spectral and temporal space available in networks by assigning each user with a unique wavelength-time hop sequence for en/decoding data signals. Here, a mode-locked laser array is used with intracavity distributed Bragg reflectors (DBRs) for spectrally tuning each laser, and a 4:1 multimode interference coupler is used to combine the laser signals into a single channel for amplification, modulation and transmission. The integrated system is fully characterised and synchronisation experiments are performed to show the potential for its use in high speed multi-user networks. Mode-locked lasers play an important role in many OCDMA implementations due to their wide spectrum and discrete temporal properties, which can be easily exploited during data en/decoding. Various mode-locked laser devices have been studied during this research with additional embedded components such as intracavity DBRs and phase controllers for precise tuning of the wavelength and pulse repetition frequency. However, the noisy nature of passively operating mode-locked lasers make them prone to high jitter, which can result in high bit error rates. Synchronisation schemes are thereby explored in order to temporally stabilise the pulse oscillations to make them suitable for use in long haul transmission systems. This includes synchronous and hybrid mode-locking, as well as a passive technique using an optical fibre loop to provide phase feedback, which is shown to promote ultralow RF linewidths in mode-locked lasers