DPSK Modulation Research Articles

Using Semiconductor-Optical Amplifiers With Constant Envelope WDM Signals

Semiconductor-optical amplifiers (SOAs) could be used in wavelength-division multiplexing (WDM) systems with constant envelope modulation formats. However if chromatic dispersion affects their constant envelope, WDM signals can interact via the SOA carrier density fluctuations, resulting into relevant penalty. We experimentally and theoretically investigate the operating conditions for SOA-based amplification with DPSK and POLSK modulation formats and clarify the role of input power, residual dispersion and modulation format. We also determine that, for a given format, the various detection schemes can result into very different impairments. These results can be used as guidelines for the system design.

Corrections to “Joint Effect of MLSE and Receiver Filters Optimization on Dispersion Robustness of IMDD, DPSK, DQPSK, and Duobinary Modulation” [15 Dec 07 2003-2005

In the above titled paper (ibid., vol. 19, no. 24, pp. 2003-2005, 15 Dec 07), the value of bit rate reported in the second line of Section II (10.7 Gb/s) is not correct. The correct value of the bit rate used in the simulation is 10 Gb/s.

40 Gbit/s DPSK modulation using an InGaAlAs-InAlAs MQW n-i-n Mach-Zehnder modulator

Phase modulation characteristics are investigated using an InGaAlAs-InAlAs MQW n-i-n Mach-Zehnder modulator. A 40 Gbit/s DPSK modulation is successfully demonstrated at a driving voltage of only 3 Vpp in a push-pull configuration.

Model for Optical DPSK Systems including Practical Rx Implementation Specifics

A rigorous time-domain based ASK transmission system model is extended to account for DPSK modulation. This is done in a system regime where the signal interaction with amplified spontaneous emission (ASE) noise during fiber transmission is not significant. The special structure of the covariance matrix for the DPSK case is identified. The model represents a new, unique, rigorous and complete tool for design of practical high capacity DPSK transmission systems.

Joint Effect of MLSE and Receiver Filters Optimization on Dispersion Robustness of IMDD, DPSK, DQPSK, and Duobinary Modulation

We analyze the effectiveness of a 32-state maximum-likelihood sequence-estimation (MLSE) receiver on chromatic dispersion robustness of optical transmission based on several binary modulation formats: intensity modulation direct detection, differential phase-shift keying, and duobinary line coding. Multilevel differential quadrature phase-shift keying modulation is also analyzed using a four-state 2-bit/symbol joint MLSE processor. For all modulation formats, receiver filters are optimized together with the use of the MLSE technique.

Adaptive DS/CDMA Packet Radio Communications over Indoor Multipath Fading Channels

In this paper, we propose an adaptive data transmission scheme for DS/CDMA packet radio communication systems in bandlimited indoor multipath fading channels. We first analyze the relationship between the code rate and the processing gain (defined as the number of chips per coded bit) in maximizing the normalized throughput in connection with the channel state of the indoor multipath fading channels. One observation made is that the maximum throughput with BPSK modulation is attained when the code rate is chosen as low as possible irrespective of the channel state, and the processing gain is increased (decreased) as the channel becomes worse (better). The other observation made is that when DPSK modulation is employed, there exists an optimal combination of the code rate and the processing gain in maximizing the normalized throughput for each channel state. Based on these observations, we propose to adapt the processing gain and/or code rate according to the fading conditions in order to maximize the normalized throughput. We analyze the performance of the proposed scheme and compare it with the non-adaptive data transmission scheme. Our results show that the adaptive transmission scheme yields a significant performance improvement over the nonadaptive scheme, and increasing the adaptation level is more effective as the channel gets worse, but the 3-state adaptation seems to be practically optimum.

Transmission performance of 20×10Gb/s WDM signals using cascaded optimized SOAs with OOK and DPSK modulation formats

Abstract We investigated 20 channels at 10 Gb/s wavelength division multiplexing (WDM) transmission over 1190 km single mode fiber and dispersion compensating fiber using cascaded inline semiconductor optical amplifier at a span of 70 km for RZ-DPSK (return zero differential phase-shift keying) modulation format by using same channel spacing, i.e. 100 GHz. We show for RZ-OOK (return zero on–off keying) format a transmission distance of up to 1050 km with Q factor more than 15 dB, without any power drops. We developed the SOA model for inline amplifier having minimum cross-talks and ASE (amplified spontaneous emission) noise power with sufficient gain. At optimal bias current of 400 mA, a high constant gain of 36.5 dB is obtained up to a saturation power of 21.36 mW. So reduction of cross-talk and distortion is possible by decreasing the bias current at appropriate amplification factor. The DPSK modulation format has less cross-talk as compared to OOK format for nonlinearities and saturation case. The impact of optical power received and Q factor at different distance for both RZ-OOK and RZ-DPSK modulation format has been illustrated. We have shown the optical spectrum and clear Eye diagram at the transmission distance of 1190 km in RZ-DPSK system and 1050 km in RZ-OOK systems. The bit error rate (BER) for all channels observed is less than 10 −10 up to gain saturation for both DPSK and OOK systems. Finally, we investigated that the transmission distance decreases with a decrease in channel spacing of up to 20 GHz.

Fiber communications using convolutional coding and bandwidth-efficient modulation

In this paper we evaluate numerically the advantage of combining convolutional coding and bandwidth-efficient modulation. We compare different multilevel modulation formats, line codes, and hard/soft decision decoding. Compared with DPSK modulation (with the same bandwidth and information transmission rate), an improvement of almost 5 dB is observed for bit error rates around 10-8. We also study the robustness to intersymbol interference in the form of chromatic dispersion, and find that the improvement of the coded transmission lines improves over the uncoded even in presence of chromatic dispersion.

Bidirectional DPSK transmission of 16 × 10-Gb/s DWDM channels over 80-km SMF-28 using semiconductor optical amplifiers

A constant-intensity modulation format such as differential phase-shift-keying is in principle immune to XGM-induced crosstalk in SOAs. We report the reduction of crosstalk in a bidirectional system and successfully realize 16 × 10-Gb/s DWDM signals transmission over 80-km SMF-28 using a DPSK modulation format for the first time. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 46: 525–527, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21036

Nonlinear tolerance benefit of modified-CSRZ DPSK modulation format

An experimental study of a modified-CSRZ DPSK modulation format (MCSRZ-DPSK) is reported. Superior single-channel transmission performance and nonlinear tolerance were demonstrated for MCSRZ-DPSK at 10 Gbit/s, in comparison with other DPSK formats including CSRZ-DPSK, RZ-DPSK and NRZ-DPSK.

Comparison of DPSK and OOK modulation format in 160 Gbit∕s transmission system

Single-polarisation 160 Gbit/s OTDM transmission over 3×80 km dispersion-managed SLA fibre using DPSK and OOK modulation is reported. The influence of the fibre input power is experimentally and theoretically investigated. A significant advantage for DPSK is revealed.

DPSK 32 x 10 Gb/s transmission modeling on 5 x 90 km terrestrial system

Reduction of DWDM nonlinear fiber penalties by the use of DPSK modulation and an optically preamplified self-homodyning receiver is discussed. Maintaining a constant instantaneous channel power by phase shift keying, we can anticipate reduction of cross-phase modulation penalties. Our modeling results show 0.9-dB benefit in Q performance for 50-GHz spaced, 32/spl times/10 Gb/s transmissions with nonzero dispersion shifted fiber.

Multiservice/multirate pure CDMA for mobile communications

Future mobile communication systems should be able to support a wide range of services with different bit rates. Spread-spectrum code-division multiple-access (CDMA) techniques have attracted much attention to be employed in such a system. Different techniques of CDMA could be used to map low-, medium-, and high-bit rates data into the same allocated bandwidth, including pure or wide-band CDMA, FDM/FH/CDMA, TDM/TH/CDMA, or a hybrid of these techniques. This paper investigates multirate pure CDMA using multiuser interference statistics derived for both Gaussian and Rayleigh fading channels. Approximation of multiuser/multipath interference, in general, helps in the theoretical approach to error performance evaluation and, in particular, is quite useful for simulation approach in a fading channel. Some results of a multirate pure CDMA system with two services (low- and high-bit rates), for both BPSK and DPSK modulation schemes, are presented and compared.

Differential phase shift keying direct sequence spread spectrum single SAW based correlator receiver

This paper presents the design and measurement of a SAW device to be used in a correlator receiver for a differential phase shift keying direct sequence spread spectrum (DPSK/DSSS) system. The DPSK modulation format allows noncoherent data demodulation while the SAW device correlator acts as the despreading operator. In a conventional DPSK receiver, the received signal is normally split into a lower and upper path. One of the paths contains a correlator, and the other path contains a one data bit delay element and another correlator. The outputs of both paths are then fed to a noncoherent data demodulator. The device presented in this paper combines both the delay element and the two correlators in a single SAW device; therefore, a better temperature tracking mechanism, simplicity, as well as the elimination of the broadband SAW delay line are achieved. The SAW structure contains a broadband SAW transducer, and two serially coded pseudo noise (PN) DPSK filters. The SAW based correlator was built on lithium tantalate. The center frequency was set to 150 MHz, with a 63 chip PN spreading code and a data rate of 300 Kbps. Experimental measurements of the SAW device autocorrelation results are presented.

Joint admission/congestion control for wireless CDMA systems supporting integrated services

A new data traffic control scheme is developed for maintaining the packet error rate (PER) of real-time voice traffic while allowing nonreal-time data traffic to utilize the residual channel capacity of the multi-access link in an integrated service wireless CDMA network. Due to the delay constraint of the voice service, voice users transmit their packets without incurring further delay once they are admitted to the system according to the admission control policy. Data traffic, however, is regulated at both the call level (i.e., admission control) and at the burst level (i.e., congestion control). The admission control rejects the data calls that will otherwise experience unduly long delay, whereas the congestion control ensures the PER of voice traffic being lower than a specified quality of service (QoS) requirement (e.g., 10/sup -2/). System performance such as voice PER, voice-blocking probability, data throughput, delay, and blocking probability is evaluated by a Markovian model. Numerical results for a system with a Rician fading channel and DPSK modulation are presented to show the interplay between admission and congestion control, as well as how one can engineer the control parameters. The tradeoff of using multiple CDMA codes to reduce the transmission time of data messages is also investigated.

Performance analysis of a hybrid DS/SFH CDMA system using analytical and measured pico cellular channels

This paper presents the throughput and delay analysis of a packet-switched code division multiple access (CDMA) network based on the hybrid direct sequence (DS)/slow frequency hopping (SFH) spread-spectrum multiple access (SS MA) technique with Q-, B-, and D-PSK modulation using analytical and measured pico cellular channels. The performance of the hybrid DS/SFH, DS, and SFH multiple access techniques have been compared in a pico cellular personal communications network (PCN) environment. Multipath and multiple access interference are considered. The performance is evaluated for a given delay spread and a fixed bandwidth. The effects of forward error correction (FEC) coding and diversity techniques, such as selection diversity and maximal ratio combining on the performance, are also investigated.

Error performance of DPSK mobile communication systems over non-Rayleigh fading channels

In this paper, the problem of detecting binary data transmitted using DPSK modulation over channels with non-Rayleigh fading statistics is considered. The results are obtained by employing a quasimoment expansion technique. The method is tested by carrying out a numerical evaluation of the performance of the DPSK system for two non-Rayleigh fading channels. A two-term approximation is shown to provide good agreement with the exact computation that requires, in general, a complete statistical description of the channel. Moreover, new expressions for the probability of error are obtained for the case of asymmetrical in-phase and quadrature components.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Decision feedback differential phase detection of M-ary DPSK signals

Multiple-symbol differential phase detection (DFDPD) based on decision feedback of past detected symbols is presented for M-ary DPSK modulation. Adopting a Gaussian phase noise assumption, we obtain the a posteriori joint probability density function (PDF) of the outputs of L DPD defectors of orders of 1 to L symbols and derive a DF-DPD algorithm which is based on feeding back the L-1 past detected symbols and minimizing the sum of phase errors of L DPD detectors. A practical implementation of the DF-DPD receiver is presented that uses a single conventional (one-symbol) DPD detector. The bit error rate (BER) performance in an additive white Gaussian noise (AWGN) channel is analyzed taking into account decision error propagation. Performance improvements are evaluated by computer simulations in AWGN and Rayleigh fading channels.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Dispersion effects in optical millimeter-wave systems using self-heterodyne method for transport and generation

This paper describes the detrimental effects of chromatic and polarization mode dispersion (PMD) on systems using single-laser-based optical self-heterodyning for generation and transport of millimeter (mm)-wave signals. The decrease of the generated mm-wave power due to chromatic dispersion in conjunction with nonnegligible laser phase noise is calculated and experimentally verified. Considering statistical properties of the PMD an analytical expression for the cumulative probability distribution of the power penalty is found and used to determine the required system margin for a given system outage rate. Furthermore, two system experiments using ASK and DPSK modulation scheme, respectively, are presented showing no limitation due to the dispersion effects.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Asynchronous polarization diversity receivers for coherent optical communications: A performance review

AbstractThe performance of coherent receivers in optical communication systems is impaired by polarization mismatchings between the received optical signal and the local laser field. One of the most effective techniques to cope with such a phenomenon is the use of polarization‐diversity receivers which, at the cost of a higher complexity in the optical front‐end and a small performance degradation, guarantee insensitivity to changes in the state of polarization of the received signal. The goal of this paper is twofold: firstly, we present here an exact theoretical analysis of balanced polarization‐diversity receivers for ASK, FSK or DPSK modulation schemes in the shot‐noise‐limited regime, deriving closed‐form expressions for the receiver Bit Error Rate (BER) of each of the cited modulations. Secondly, we assess the sensitivity of the same receivers to a slowly‐varying frequency detuning of the heterodyne laser, in order to allow for a well‐aimed design of the Automatic Frequency Control (AFC) circuit of the local laser. This work was performed in the Framework of the “Telecommunications” project funded by the Italian National Research Council (CNR).