Performance Analysis of Duty-Cycle Division Multiplexing for Optical Fiber Communication Systems

The ever increasing demand for network capacity motivates the explorations for new modulation formats and multiplexing techniques. Wavelength division multiplexing (WDM) channel capacity can be improved by using time division multiplexing (TDM). However, TDM requires precise bit and symbol synchronization and limited from the operating speed of electronic components. The introduction of return-tozero (RZ) line coding facilitates TDM synchronization in high speed transmission systems. Alternatively WDM channel capacity can be doubled by using polarization division multiplexing (PDM) or differential quadrature phase-shift-keying (DQPSK) modulation format. Duty-cycle division multiplexing (DCDM) is another multiplexing technique that can support multiple users per WDM channel. Previously, initial version of DCDM (IVDCDM) is proposed for optical fiber communications. DCDM takes advantage of RZ and offers even better synchronization at the lower clock frequency with smaller spectral width. However, IV-DCDM is badly affected from the fiber chromatic dispersion (CD). In addition, it requires high optical signal-to-noise ratio (OSNR) and less tolerance to self-phase modulation (SPM). For implementation, the IV-DCDM architecture required n modulators for n channels at the multiplexer and n + 1 sampling circuits at the receiver, which is not economically efficient. In this study, the design of DCDM multiplexer and demultiplexer is improved. A new set of algorithm are developed for data recovery in the receiver. At the same time, a model for BER estimation based on the decision algorithms is established. Performance of the proposed demultiplexer with the new decision algorithm is evaluated using the same multiplexer design used in IV-DCDM. Since in the improve setup the multiplexer operates in optical domain this system is referred to as O-DCDM. Using the O-DCDM, performance of IV-DCDM is improved significantly by around 40 times in terms of CD tolerance, 6.5 dB better OSNR and around 3 dB higher SPM threshold. The number of sampling circuits is also reduced by one count in the proposed demultiplexer, which leads towards design simplification. Performance of the proposed multiplexer architecture is evaluated together with the proposed demultiplexer. Since the proposed multiplexer operates in electrical domain this system is referred to as E-DCDM. Using the E-DCDM, the numbers of required modulators are reduced to only one regardless of the number of user. Using EDCDM, performance of IV-DCDM is improved by around 48 times in terms of CD tolerance, 1.6 dB better OSNR and around 4.5 dB higher SPM threshold. Performance of E-DCDM is improved further by using amplitude distribution controller (ADC). Using E-DCDM with ADC, referring to IV-DCDM, performance is improved by around 46 times in CD tolerance, 7.5 dB better OSNR and 3.5 dB more SPM threshold. Based on these developments, performance of DCDM is comparable against the available multiplexing and modulation techniques with an advantage, which is simpler transmitter and receiver. DCDM can support multiple users per WDM channel without the needs of increasing the clock rate at the receiver. Using this technique, 7 × 10 Gb/s is transmitted over 139 km and recovered by using 10 GHz clock

Effect of optical filtering on the performance of 40 Gbps DCDM systems

The effect of optical filtering on 40 Gbps on-off keying over 2 x 20, 3 x 13.33, 4 x 10, and 7 x 5.714 Gbps duty-cycle division multiplexing (DCDM) is investigated. The system can tolerate down to 30 GHz optical filter bandwidth for 2 users, and 47.5 GHz for 7 users. At this bandwidth, 40 Gbps was successfully transmitted over 464 km and 193 km SSMF using 2 and 7 users, respectively

Duty-cycle division multiplexing (DCDM): a novel and economical optical multiplexing and electrical demultiplexing technique for high speed fiber optics networks

A new multiplexing and demultiplexing technique based on duty cycle division is proposed, thus the name duty cycle division multiplexing (DCDM). DCDM can be applied in both electrical and optical domains. The new technique allows for more efficient use of time slots as well as the spectrum, taking advantage of both the conventional TDM and FDM. In this paper, three channels operating at the same speed of 10 Gbps are multiplexed in the optical domain and demultiplexed in the electrical domain. The performance comparison is made against 30 Gbps TDM, and the experimental simulation results show that the minimum sensitivity achieved is -26 dBm and -25.5 dBm for the two systems respectively, thus a 0.5 dB improvement

Improvement of three-level code division multiplexing via dispersion mapping

A new dispersion map is designed for three-level code division multiplexing (3LCDM) of a 40 Gb/s (2 x 20 Gb/s) over 500 km (5 x 100km) standard single mode fiber. The results show that an 87.5 % dispersion compensation ratio was the optimum map for the 3LCDM system. The system performance is improved by 6 dB in optical signal-to-noise ratio, 6 dB in receiver sensitivity and 3 dB in self-phase modulation threshold. Based on these improvements, the 3LCDM performance is comparable to the available multiplexing and modulation techniques while offering simpler transmitter and receiver architecture

Absolute polar duty cycle division multiplexing (APDCDM); technique for wireless communications

A new multiplexing and demultiplexing technique for wireless communications which is called Absolute Polar Duty Cycle Division Multiplexing (APDCDM) is presented in this paper. APDCDM can become an alternative multiplexing technique in wireless communications. The new technique allows for better error detection, correction, clock recovery and more efficient use of time slots as well as spectrum. The principle of the APDCDM technique has been discussed in this paper based on theoretical analysis as well as simulation studies. The performance comparison is made against time division multiplexing technique (TDM). The simulation has been set for wireless transmission, based on free space propagation model with adaptive white Gaussian noise (AWGN); QAM is used as modulation scheme to evaluate this technique against data rate and number of users. The simulation result correspond with the theoretical study show that APDCDM has better performance than TDM for supporting higher number of multiplexing users and bit rate

A novel economical duty cycle division multiplexing with electrical multiplexer and demultiplexer for optical communication systems

Duty cycle division multiplexing (DCDM) is proposed as an alternative multiplexing technique. In this technique, the channel multiplexing and demultiplexing are performed electrically. This technique allows aggregate bit rate to be recovered at the single channel bit rate, which is very economic. In this paper, we examine three channels system where each channel operates at 10 Gb/s over a single optical carrier. Performance of the system is evaluated based on back-to-back receiver sensitivity, optical signal-to-noise ratio (OSNR) and chromatic dispersion tolerance. The performance comparison is made against return-to-zero (RZ) format. The results show that, DCDM can support higher amount of chromatic dispersion than that RZ. At 3 × 40 Gb/s, a receiver sensitivity and OSNR of −16.8 dBm and 34.6 dB is respectively required for the worst DCDM channel

Improving the performance of three level code division multiplexing using the optimization of signal level spacing

In order to optimize the performance of three level code division multiplexing (3LCDM) at 2×20 Gb/s data rate, signal level spacing technique is investigated in this paper. The 3LCDM performance is improved considerably using both electrical and optical level spacing optimization configurations. The results demonstrate that by optimization, in conditions of the optical signal-to-noise ratio, an improvement of around 4.5 dB can be achieved in both approaches as well as 3.3 dB in the electrical configuration and 3.5 dB in the optical configuration can be accomplished for the 3LCDM in terms of the receiver sensitivity

Duty Cycle Division Multiplexing (DCDM): a new electrical multiplexing technique for high speed optical communication systems

A new multiplexing technique based on duty cycle division is proposed, thus the name duty cycle division multiplexing (DCDM). DCDM can be applied in both electrical and optical domains, for wired and wireless systems. The new technique allows for more efficient use of time slots as well as the spectrum, taking advantage of both the conventional TDM and FDM. In this paper, three channels operating at the same speed of 10 Gbps per channel are multiplexed in the electrical domain. The performance comparison is made against 3times10 Gbps TDM, and the experimental simulation results show that the DCDM system can support higher bit rate than TDM and also, it is less sensitive to the chromatic dispersion effect

Effect of guard band on the performance of AP-DCDM technique in 40 Gb/s optical fiber communication system

The effect of guard band (GB) on the performance of 40 Gb/s Absolute Polar Duty Cycle Division Multiplexing (AP-DCDM) is investigated and reported. It is demonstrated that the spectral width occupied by 40 Gb/s AP-DCDM with GB is 100 GHz (with minimum spectral efficiency of 0.4 b/s/Hz) whereas, this value can be reduced to around 80 GHz for AP-DCDM without GB (with minimum spectral efficiency of 0.5 b/s/Hz). In addition to better spectral efficiency, this amount of saving in the spectral width leads to ~ 60 ps/nm improvement in chromatic dispersion tolerance