Coherent Frequency Shift Keying Research Articles

Experimental demonstration of the near-quantum optimal receiver.

We implement the cyclic quantum receiver based on the theoretical proposal of Roy Bondurant and demonstrate experimentally below the shot-noise limit (SNL) discrimination of quadrature phase-shift keying signals (PSK). We also experimentally test the receiver generalized for longer communication alphabet lengths and coherent frequency shift keying (CFSK) encoding. Using off-the-shelf components, we obtain state discrimination error rates that are 3 dB and 4.6 dB below the SNLs of ideal classical receivers for quadrature PSK and CFSK encodings, respectively. The receiver unconditionally surpasses the SNL for M=8 PSK and CFSK. This receiver can be used for the simple and robust practical implementation of quantum-enhanced optical communication.

A New CPFSK Demodulation Approach for Software Defined Radio

This paper proposes a new coherent Frequency-Shift Keying (FSK) demodulation technique for software defined radio platform, based on a new Digital Phase Locked Loop (DPLL) architecture. The proposed DPLL addresses the frequency dependence on classic DPLL architectures found in the literature. In classical approaches, the loop filter constants are dependent on the frequency level of the FSK transmitted symbols. The proposed approach applies a simpler feedback loop, with a single integrator and a phase detector architecture based on the small-angle approximation [Formula: see text], which resulted in a DPLL totally independent of frequency. The proposed demodulator has been implemented in Very High Speed Integrated Circuits (VHSIC) Hardware Description Language (VHDL) and evaluated for continuous-phase frequency shift keying (CPFSK) and Gaussian minimum shift keying (GMSK) signals. For CPFSK signals, the demodulator has been evaluated for 2, 4 and 8 frequency levels, with modulation indexes [Formula: see text], [Formula: see text] and [Formula: see text], respectively. For evaluation of GMSK signals, several Gaussian filter bandwidths were considered. In addition, a brief analysis for 2-CPFSK and GMSK is presented over multipath and carrier frequency offset. Results show that the proposed method presents a significantly reduced bit error rate when compared to other coherent methods presented in the literature.

Multiple access interference cancelation technique in optical CDMA systems

This paper presents a simple and efficient multiple access interference (MAI) cancelation technique in optical code division multiple access (OCDMA) system. The proposed technique is based on hybrid frequency shift keying (FSK) with an enhanced modified prime code as a signature sequence for coding techniques. Coherent FSK modulation along with incoherent demodulation using Arrayed-Waveguide Grating has been examined in the transceiver structure. In the proposed technique, a reference signal is constructed by using one of the addressed spreading sequences, and MAI cancelation is performed by subtracting the reference signal from the received signal of the desired user. The performance of the proposed FSK-OCDMA system is compared with the performance of the existing pulse position modulation (PPM)---OCDMA system. The simulation results reveal that the bit-error rate performance of the proposed technique is superior to the performance of the pulse position modulation (PPM) technique. Also, the results indicate that the proposed technique is very power efficient, and when the bit rate is constant, the network capacity can be expanded to accommodate a large number of simultaneous active users with low error rate. Moreover, the proposed technique simplifies the hardware of the receiver design.

Error probabilities of noncoherent and coherent FSK in the presence of frequency and phase offsets for two-hop relay networks

We analyze the error performance of two-hop relay networks adopting frequency shift keying (FSK) over frequency flat Rayleigh fading channels. It is assumed that relay networks consist of a source, a relay, and a destination without a direct path signal from the source to the destination and the relay adopts the amplify-and-forward protocol with a fixed gain. Firstly, considering imperfect frequency and phase synchronization, we obtain the exact error probability expressions for noncoherent and coherent binary FSK (BFSK). Secondly, assuming perfect frequency and phase synchronization, we derive a closed-form error probability approximation for coherent M-ary FSK (MFSK). The proposed methods can also be used for the error performance analysis of classical one-hop FSK systems with perfect/imperfect frequency and phase synchronization. The obtained error probability expressions will help the design of two-hop relay networks adopting FSK in determining the system parameters such as the transmission power at the source, the amplifying coefficient at the relay, and the maximum affordable frequency and phase offsets to satisfy the required error performance.

Performance analyses of selection combining diversity receiver over –μ fading channels in the presence of co-channel interference

An approach to the performance analyses of dual selection combining (SC) diversity receiver over correlated alpha - mu fading channels with the arbitrary parameters is presented. Fading between the diversity branches and interferers is correlated and distributed with alpha - mu distribution. Infinite series expressions are obtained for the output SIR's probability density function (PDF), cumulative distribution function (CDF) and an important measure of the system's performances, the outage probability (OP). An average error probability is efficiently evaluated for coherent and non-coherent modulation schemes such as coherent frequency-shift keying (CFSK), coherent phase-shift keying (CPSK), binary frequency-shift keying (BFSK) and binary differentially phase-shift keying (BDPSK). Numerical results are presented to show the effects of various parameters such as fading severity, input SIR unbalance and the level of correlation between received desired signals and interferences on system's performances.

Modulation and Detection for Simple Receivers in Rapidly Time-Varying Channels

We investigate the performance degradation of basic modulation schemes in a rapidly time-varying channel using a first-order autoregressive channel model. Various performance metrics are used to indicate the relative advantages of each modulation scheme. We find that noncoherent frequency-shift keying (FSK) is suitable for operating at very high mobility and high signal-to-noise ratio, ideal for some military applications. We then propose a partially coherent detector for FSK and differential phase-shift keying that exploits partial channel knowledge to enable the receiver to operate effectively in both fast and slow fading. The maximum-likelihood rule obtained for the partially coherent FSK turns out to be a linear combination of coherent and noncoherent detection rules. Results demonstrate that significant performance improvement can be achieved over the best of coherent and noncoherent FSK detection. The detector is robust to estimation errors present in the channel statistics. We also propose a few adaptive schemes that employ various combinations of modulation schemes to increase the robustness of the system in fast fading

New results on selection diversity

The performances of selection diversity receiver structures in a slow flat Rayleigh-fading environment are assessed. A number of new and interesting results are obtained. Binary digital signaling using noncoherent frequency-shift keying (NCFSK), differential phase-shift keying (DPSK), coherent phase-shift keying (CPSK), and coherent frequency-shift keying (CFSK) is considered. The traditional analysis (the traditional selection diversity model) of a selection diversity system is based on choosing the branch with the largest signal-to-noise (SNR) power ratio while assuming that the noise power is constant across all branches. However, many practical selection systems choose the branch based on a largest signal-plus-noise (S+N selection) sample of a filter output. This paper comprises accurate analyses of such S+N selection systems. Results show that S+N selection systems perform better than predicted by the traditional selection diversity model. This is because the former includes the statistical nature of the noise, whereas the latter does not. The performance difference between the two models increases as the number of diversity branches increases. For each of DPSK and CPSK, the dual diversity equal gain (EG) combining and S+N selection systems perform identically. For each of NCFSK and CFSK, receiver structures which are equivalent when there is no diversity perform differently in a diversity environment. Certain dual diversity S+N selection systems give the same performances as EG combining or square law combining. The results are contingent upon perfect cophasing for the EG combining. In systems where estimates of the combining carrier phases contain noise, S+N selection outperforms EG combining for dual diversity.

Improved receivers for coherent FSK systems

There has been considerable interest over the last decade in the detection of digital coherent lightwave signals corrupted by phase noise. However, the majority of the work has been in the performance analysis of various modulation schemes. In addition, the receivers studied have, in general, been zero-phase noise optimal or ad hoc modifications of these. In this paper, we consider the design problem of constructing optimal receivers for systems using frequency shift keying (FSK). Using the innovations approach, we show the format of the optimal receiver and use a small phase noise approximation to derive suboptimal receivers. Also, receivers based on optimum linear filters are also derived. Both receivers are analyzed by simulation and performance improvements over the standard receivers are shown. Furthermore, the receivers developed can equally well be used to further improve the performance of other detection schemes such as postdetection filtering and time diversity. The methodology is also used to derive equivalent receivers for systems using on-off keying (OOK).

Performance of single- and double-ring resonators using 3*3 optical-fiber coupler

This paper investigates theoretically the transmission characteristics of single- and double-ring resonators using 3*3 optical-fiber couplers. Two configurations of a 3*3 coupler are considered: configuration A, with the three fibers centered at the vertices of an equilateral triangle, and configuration B, with their centers aligned in a straight line. It is found that a ring resonator using configuration A does not show any performance improvement over ring resonators using 2*2 couplers. On the other hand, a single-ring resonator using configuration B has a performance close to resonators using 2*2 couplers. It is also shown that a double-ring resonator using a 3*3 coupler exhibits resonance with a double peak, which may find application in the filtering of coherent frequency-shift keying (FSK) signals after optical amplification in an optical-fiber line repeater. >

Analytical analysis of IF-penalties for different FSK and CPFSK detection schemes

Due to the nonnegligible laser linewidth in coherent optical systems, IF bandwidths larger than the Nyquist signaling rate are required. This causes additional sensitivity penalties, which are evaluated for three types of coherent optical FSK (frequency-shift-keying) detection; two-filter-, delay-line discriminator-, and phase-diversity detection. Sensitivity as a function of the relative IF-bandwidth is given in a fully analytical form and confirmed by experimental measurements.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Analytical and practical evaluation of diversity penalties in multi-bit-rate coherent FSK systems

Fully analytical expressions are presented for calculating the bit-error-rate (BER) and sensitivity penalties in frequency-shift-keying (FSK) receivers with noncoherent square-law IF detection. With these results one can directly compute the sensitivity and diversity penalties as a function of the IF filter bandwidth. Postdetection filtering is included in the analysis. The BER of such receivers can be expressed in terms of a sum of generalized Laguerre polynomials, which can easily be evaluated. This yields relations between the IF bandwidth expansion factor and the sensitivity that can be applied directly for practical system analysis. This is illustrated using the results from a coherent multi-bit-rate, multichannel FSK receiver, which was used at bit rates of 140 and 560 Mb/s. The discrepancy between theory and practice is less than 0.15 dB for diversity penalties and 0.4 dB for the bit rate penalty. >

A novel analysis technique for coherent FSK lightwave systems

The authors present a simple approximate analysis of frequency-shift keying (FSK) coherent optical communications systems and obtain a closed-form estimate of the bit error rate. The inaccuracy of the approximate analysis is about 1 dB. The sensitivity penalty prediction of the approximate analysis is also within 1 dB of the accurate analysis for linewidths up to 100%.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

20 channel coherent FSK system using subcarrier multiplexing

A 20-channel multioctave coherent frequency shift keying (FSK) system using subcarrier multiplexing techniques is described. The microwave subcarriers range from 2.1 to 5.9 GHz with a 200-MHz channel spacing. The receiver consists of a p-i-n photodiode, electrical isolator, low-noise amplifier, and bandpass filter to provide channel selection. The channels are modulated at 100 Mb/s, corresponding to one digitized video channel. Results for the optimal phase modulation index and degradation due to second- and third-order intermodulation distortion are discussed. For the worst-case channel, a receiver sensitivity of -27 dBm was achieved.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The Distribution of Error Probability for Rayleigh Fading and Gaussian Noise

The distribution function of the probability of error in the presence of Rayleigh fading and Gaussian noise is determined for the basic binary modulation schemes of coherent frequencyshift keying (CFSK), noncoherent frequency-shift keying (NCFSK), differential phase-shift keying (DPSK), and coherent phase-shift keying (CPSK). General expressions for the distribution function of error probability are also derived when linear maximal-ratio diversity combining is employed. Results are given for various values of average error probability and various orders of diversity.

Combined Frequency and Time-Shift Keyed Transmission Systems

Consideration is given to a transmission technique which is based on the combination of frequency-shift keying (FSK) and time-shift keying (TSK). In the resulting frequency and timeshift keyed (FTSK) transmission, the two possible states of a binary waveform are represented by the order of two pulses which occur on different frequencies, for instance, f <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</inf> and f <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> . For example, if the ordered pair <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">(f_{1}, f_{2})</tex> represents a Mark, then <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">(f_{2}, f_{1})</tex> represents a Space. The power spectrum, as well as the performance of both coherent and noncoherent systems in an interference environment, is investigated. The following cases are considered: 1) white noise interference, with and without fading and 2) CW interference. It is shown that with white noise interference and no fading, the performance of a coherent FTSK system is identical to that of coherent FSK and TSK systems operating at the same data rate. Under similar conditions, the performance of a noncoherent FTSK system would be slightly degraded (less than 1 db for digit error probabilities less than 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> ) compared to that of noncoherent FSK and TSK systems. FTSK's dual frequency diversity is shown to provide a substantial antifading capability to both coherent and noncoherent transmissions. Furthermore, it is observed that FTSK offers the potential for: 1) complete rejection of CW and other forms of narrow-band interference, 2) simplified postdetection signal coupling circuits, 3) enhanced performance of digit synchronization circuits and 4) error detection and correction.