Saleh Seyedzadeh

Performance comparison of OCDMA codes for quasi-distributed fiber vibration sensing

The performance of Khazani Syed (KS) code based fiber vibration measurement for distributed sensing has been investigated. The setup was aimed at implementing quasi distributed vibration sensing with less complexity and optimum performance against Multiple Access Interference. The three sensor points system were compared with existing Optical Orthogonal Code (OOC) and Modified Congruence Code (MQC) in terms of level of power received, supported fiber length and complexity in implementation. Slightly better received power and longer fiber length were demonstrated by the system employing MQC code but a wide gap to OOC code. However, since KS code is implemented with less number of components which tends to reduce the cost and complexity of the system which becomes obvious as the sensor points grow, KS code is recommended for the quasi distributed vibration sensing.

Simultaneous vibration and humidity measurement using a hybrid WDM/OCDMA sensor network

In this paper a hybrid Wavelength Division Multiplexing (WDM) and Optical Code Division Multiple Access (OCDMA) sensor network is proposed to detect vibration and humidity simultaneously. Evaluation of the results for the proposed system is demonstrated using simulation setup. OCDMA is used for detection of vibration levels while WDM is for sensing humidity changes. Fiber Bragg gratings (FBGs) is used in both systems. In OCDMA FBGs were used as filter to form the OCDMA code and sensors to senses the vibration. In WDM FBGs were used as sensor alone to sense the humidity.

New dynamic technique for SAC-OCDMA system

In this paper a family of novel spreading sequences, called a Multi-Service (MS) code have been proposed for SAC-OCDMA system. The performance of the proposed code is demonstrated using mathematical analysis. Reference to the Bit Error Rate (BER) of 10-9 MS code supports up to 90 users simultaneously, choosing code weight of 5 when the bit-rate is 622 Mbps. Thus, from the results it indicates that MS code does not only preserve the capability of suppressing Multiple Access Interference (MAI), but also improves BER performance due to low cross-correlation (λc) between code sequences. (i. e. 0 ≤ λc ≤ 1). Furthermore, the results showed that with lower value of basic users can support larger number of subscribers as well as better performance in terms of acceptable BER.

A new signal combination for 3-channel duty-cycle division multiplexing technique

Duty-cycle division multiplexing (DCDM) technique allows the transmission of multiple users transmission over single wavelength. In this technique return-to-zero (RZ) signals with different duty-cycles are used to electrically combine users signals. In this paper a new signal combination method for 3-channel DCDM is proposed. The modified system which uses dual drive Mach Zehnder Modulator (DD-MZM) is simulated and the DDMZM bias voltages and splitting ratio is optimized for proposed system. The performance of system is demonstrated as BER of users. Results show that the proposed system at BER of 10-9 has 1 dB advantage over normal DCDM. Performance of system over 8 channels WDM network is also investigated. It is shown that the performance gap between proposed system and normal DCDM increases by decreasing the channel spacing.

Variable weight Khazani-Syed code using hybrid fixed-dynamic technique for optical code division multiple access system

Abstract. Future Internet consists of a wide spectrum of applications with different bit rates and quality of service (QoS) requirements. Prioritizing the services is essential to ensure that the delivery of information is at its best. Existing technologies have demonstrated how service differentiation techniques can be implemented in optical networks using data link and network layer operations. However, a physical layer approach can further improve system performance at a prescribed received signal quality by applying control at the bit level. This paper proposes a coding algorithm to support optical domain service differentiation using spectral amplitude coding techniques within an optical code division multiple access (OCDMA) scenario. A particular user or service has a varying weight applied to obtain the desired signal quality. The properties of the new code are compared with other OCDMA codes proposed for service differentiation. In addition, a mathematical model is developed for performance evaluation of the proposed code using two different detection techniques, namely direct decoding and complementary subtraction.

A novel asynchronous hybrid duty-cycle division multiplexing/optical code division multiple access system

The growing demand for larger optical bandwidth and new services rises the need for efficient multiplexing techniques. Recently, hybrid optical code division multiple access (OCDMA) systems have been developed in order to expand the capacity of optical networks. In this paper a new asynchronous hybrid duty-cycle division multiplexing (DCDM) spectral amplitude coding (SAC) OCDMA system is proposed. In the proposed system, each code-word of SAC-OCDMA carries 2-channel DCDM where each user is operating at data rate of 622 Mb/s which forms 3 × 2 × 0.622 Gb/s optical system. In hybrid DCDM/OCDMA system, users are first electrically multiplexed using different duty-cycles and then optically coded using multiple wavelengths. The performance of users with different duty-cycles are optimized by controlling the electrical amplitude levels. Results show that the bit error rate of 10-9 for worst user is achieved at received power per chip of -22.5 dBm. Performance of proposed DCDM/OCDMA system operating at high speed data rate (i.e. 40 Gb/s per OCDMA channel) is also demonstrated.

Proposal of multi-service (MS) code to differentiate quality of services for OCDMA systems

The emergence of a broad range of network-driven applications (e.g. multimedia, online gaming) rises the demand for network environments with ability to provide multiservice capabilities with diverse Quality of Service (QoS) requirements. In this paper, a new code family of novel spreading sequences, called Multi-Service (MS) code has been constructed in order to support multiple services in OCDMA system. The performance of the proposed code is demonstrated using mathematical analysis. Different numbers of basic users are used to support triple-play services (audio, data and video) with different QoS requirements. Results indicate that the technique can clearly provide a relative QoS differentiation. Lower value of basic users can support larger number of subscribers as well as delivering better performance in terms of acceptable BER of 10-9 at fixed code weight.

Performance Analysis of Duty-Cycle Division Multiplexing over Wavelength Division Multiplexing System

Abstract Performance optimization of a duty-cycle division multiplexing system over 8- and 40-channel wavelength division multiplexing networks is reported in this article. The modified duty-cycle division multiplexing system with optical domain multiplexing using a dual-drive Mach–Zehnder modulator is simulated with two and three users per wavelength. Using conventional dispersion compensation, the 40 × 40-Gbps system with two and three users per channel can support 240 and 160 km of transmission distance, respectively. The dispersion management technique based on a chirped fiber Bragg grating is proposed for a 40 × 3 × 13.33-Gbps duty-cycle division multiplexing/wavelength division multiplexing system that allows double the transmission distance compared to conventional technique.

Performance of multi-wavelength erbium doped fiber laser on free space optical medium

The rocketing grow of demand for communication capacity in fiber back hauls led researchers to a new wireless carrier medium. Laying down optical fibers and maintaining them has proven to be enormously costly and time taking therefore, free space optical (FSO) communication has been introduced to provide fiber like transmission capacity to short reach users. One of the main features of a FSO system is the laser that is used for transmission. In this paper a new multiwavelength erbium doped fiber laser (EDFL) is introduced and its effectiveness in FSO communication is investigated. In our proposed setup 8 channels are extracted from EDFL with each channel transmitting 1.25 Gbps then sent through a single FSO channel. Each channel has a corresponding wavelength which lies on C-band of optical spectrum. Wavelength division multiplexing (WDM) is used to combine 8 signals on transmitter and demultiplexer is used to split signals on receiver. We consider a point to point FSO system with intensity modulation and direct detection (IM/DD). Results of simulation of This single input single output (SISO) FSO system show bit error rate (BER) of (10-9) is achieved at link range of 1.4 km. Reliability of signal is investigated and proved to be efficient by optical signal to noise ratio (OSNR) analysis.