Development And Implementation of a Novel Code Family for Optical Code Division Multiple Access Systems

Future telecommunication systems and networks are expected to provide a variety of integrated broadband services to the customers. There has been a tremendous interest in applying Code Division Multiple Access (CDMA) techniques to fiber optic communication systems. This technique is one of the multiple access schemes that is becoming popular because of the flexibility in the allocation of channels, ability to operate asynchronously, enhanced privacy and increased capacity in bursty networks. The performance of any Optical CDMA (OCDMA) system strongly depends on the codes properties. In this study we introduce a new code for Optical CDMA namely Double Weight Code family (DW). Double Weight Code (DW) has a basic fixed weight of 2 and exists for every natural number. The DW codes possess ideal cross correlation properties, which have important characteristics in OCDMA systems since these can eliminate multiple access interference (MAI) and reduce noise. Also proposed in this study, a Modified Double-Weight (MDW) code, which is a variation of DW code family that can have a variable weight greater than two. The MDW code possesses ideal crosscorrelation properties and exists for every natural number too. It is shown through simulations, theoretical analysis and partially by the experiments that the transmission performance of DW code family is significantly better than that of existing codes such as Modified Frequency Hopping code (MFH) and Hadarnard code. The performance of DW code family, MFH and Hadamard codes were simulated using commercial simulation software, OptiSystem Version 3.0. The performance of the systems was characterized by referring to the bit error rate (BER) and the eye patterns. DW code family has shown superior performance compared to other OCDMA codes. The simulated eye pattern of one of the four MDW coded carriers running at lOGbps over a cornrnunication-standard fiber shows a good quality transmission at the BER of 10 -12 as opposed to only 1o ' ~an d 1o 4 for Hadamard and MFH codes. In optical CDMA systems, the detection process affects the design of transmitters and receivers. Cross-correlation functions are generated which creates Multiple Access Interference (MAI) and this will degrade the system performance. MA1 can be reduced by using subtraction techniques. The most common subtraction technique is the complementary subtraction technique and also known as balanced detection technique. In this thesis, we also introduce a new approach called AND subtraction technique. This method rejects unwanted signals that interfere with the original signals. Furthermore, the purpose of this new subtraction technique is to reduce the receiver complexity and increase system performance. It has been shown through theoretical analysis, simulation and experimental work, the performance of the system with AND subtraction technique can be improved significantly. Based on the theoretical analysis, BER as good as 10-l2is achieved at the bit rate of 622 Mbps over 70 km distance

Design configuration of encoder and decoder modules for modified double weight (MDW) code spectral amplitude coding (SAC) optical code division multiple access (OCDMA) based on fiber Bragg gratings

In this work, we are proposing the serial and parallel configurations of encoder and decoder modules to encode and decode a new developed spectral amplitude coding (SAC) known as modified double weight (MDW) code for optical code division multiple access (OCDMA) system. This coding scheme is designed in a way to decrease the number of FBGs used in the encoder and decoder modules and to maintain the cross-correlation parameter to 1

A new code for optical code division multiple access systems

A new code structure based on Double-Weight (DW) code families is proposed for Spectral-Amplitude-Coding Optical Code Division Multiple Access (OCDMA) system. The constraint of a constant weight of 2 for the DW code can be relaxed using a mapping technique. By using this technique, codes that have a larger number of weight can be developed. Modified Double-Weight (MDW) Code is another variation of a DW code family that can has a variable weight greater than two. The MDW code possesses ideal cross-correlation properties and exists for every natural number n. A much better performance can be provided by using the MDW code compared to the existing codes such as Hadamard and Modified Frequency-Hopping (MFH) codes. This has been demonstrated from the theoretical analysis and simulation

Comparative performance of hybrid SCM SAC-OCDMA system using complementary and AND subtraction detection techniques

This paper presents the comparative performance of two detection schemes based on subtraction detection technique for a hybrid scheme of subcarrier multiplexed spectral-amplitude-coding optical code division multiple access (SCM SAC-OCDMA) system. SAC-OCDMA systems are receiving more attention because of their ability to completely eliminate multi access interference by using code sequences with fixed in-phase cross correlation. On the other hand, the SCM scheme is capable of improving the channel data rate of OCDMA systems. This hybrid scheme is proposed for the benefit of combining the advantages of both schemes. Consequently, the hybrid system is robust against interference and is much more spectrally efficient. Double weight code family is a new code structure used for SAC-OCDMA system. The experimental simulation results show that the proposed new AND subtraction detection technique improve the system performance significantly

A new family of optical code sequences for spectral-amplitude-coding optical CDMA systems

A new code structure for spectral-amplitude-coding optical code-division multiple-access system based on double-weight (DW) code families is proposed. The DW code has a fixed weight of two. By using a mapping technique, codes that have a larger number of weights can be developed. Modified double-weight (MDW) code is a DW code family variation that has variable weights of greater than two. The newly proposed code possesses ideal cross-correlation properties and exists for every natural number n. Based on theoretical analysis and simulation, MDW code is shown here to provide a much better performance compared to Hadamard and modified frequency-hopping codes

Development of modified double-weight code and its implementation in multi-rate transmissions

This paper presents a new code structure and its ability in supporting multiple transmission rates in point to point Spectral Amplitude Coding- Optical Code Division Multiple Access (SAC-OCDMA) links. The Double-Weight (DW) code family that has a basic fixed weight of 2 was proposed. Modified Double Weight (MDW) Code is a DW code family variation that has variable weight of greater than two. The ability of MDW codes to support simultaneous transmissions at different bit rates is shown through simulated results of the bit error rate (BER) and the eye patterns. Four MDW encoded channels were used at the bit rates of 2.5Gbps and 10Gbps. MDW code shown here significantly performs better than Hadamard and Modified Frequency Hopping (MFH) codes

Multiband slot-loaded dipole antenna for WLAN and LTE-A applications

A multiband printed dipole antenna for wireless local area network (WLAN) and long-term evolution-advanced (LTEA) applications is investigated here. Its multiband characteristic is enabled by the Y-slot present in the upper arm of the dipole, while the antenna\u27s dimensions are 0.08λo × 0.384λo at the lowest operating frequency. It features bandwidth of 14.6% centred at 2.4 GHz, and ∼30.5% centred at 5.5 GHz for WLAN operation. An additional bandwidth of 6.9% centred at 3.5 GHz supporting LTE-A applications is also featured. Besides being compact, the proposed antenna radiates omnidirectionally with a gain of up to 4.09 dBi. Simulations and measurements are in good agreement

Effects of the power differences in the AND-subtraction detection technique in SAC-OCDMA system performance

This project concentrates on the effects detection technique to the system performance of spectral amplitude coding optical code division multiple access (SAC-OCDMA). The system employed the encoder and decoder modules based on the fiber Bragg gratings (FBGs) to generate the unique code sequences for the users. These modules are basically designed for the modified double weight (MDW) code which allows higher code weight w in the even number which is greater than two. The study is mainly focusing on the effects of the power differences between the upper and lower branches of the AND-subtraction technique used as the detection technique to the system performance. The results show that the system will achieve the best system performance when the power difference between the upper and lower branches is approximately 5dB

Wavelength shifting in the Fiber Bragg Grating (FBG) based encoder and decoder modules for SAC-OCDMA system

This project concentrates on the design of Fiber Bragg Grating (FBG) based encoder and decoder modules for Spectral Amplitude Coding of Optical Code Division Multiple Access (SAC-OCDMA) system. In SAC-OCDMA system, the unique code sequence is formed by using spectral components which are inherently arranged. This is done by multiplexing the Bragg wavelengths from an array of FBGs. However, the Bragg wavelength is largely depends on the strain and temperature experienced by the gratings. This paper presents the effects of the Bragg wavelength shifting of the uniform FBG used in the encoder and decoder modules for an SAC-OCDMA code to the system performance. The results show a sharp increase of bit error rate (BER) from 10-12 and 10 -14 to 10-4 and 10-5 for Channel 1 and Channel 2 respectively at 0.01 nm Bragg wavelength left and right shifts. It shows that the system performance is significantly affected by the shifting of the Bragg wavelength

Hybrid WDM/OCDMA system to support differentiated services in access network

This paper presents a new scheme of WDM/OCDMA system that capable of providing differentiated services in access network. We implement the proposed double-weight (DW) code in this system. The double-weight (DW) code has a fixed weight of 2 and exists for every natural number, n. In spectral-amplitude-coding optical code division multiple access (CDMA) systems, DW code has an ideal cross correlation to eliminate multiuser interference and suppress the noise. We analyze the performance of the system by evaluating the bit error rate (BER) of different services