Noncoherent Communication Systems Research Articles

Improved Non-coherent Communication Systems Using Noise Reduction Chaotic ON–OFF Keying (NR-COOK) Techniques

The major drawback of the conventional chaotic ON–OFF keying (COOK) scheme is that the transmitted signal energy is not constant due to the non-periodic nature of the chaotic sequences. These chaotic sequences increase the amount of noise present in the received signal and degrade the system performance under multipath fading channel conditions. Moreover, in COOK scheme, the optimum threshold for symbol detection depends on the Signal to Noise Ratio (SNR) available at the detector input. In this paper, a noise reduction COOK scheme is proposed for improved performance. In this scheme, for transmitting binary bit ‘1’ $$\frac{\beta }{R}$$ distinct chaotic samples are generated and each sample is repeated R times to get a required spreading sequence length of β and no signal is being transmitted during binary bit ‘0’. For demodulation of the transmitted data, each of the R identical samples are averaged, correlated with itself and summed over the bit duration $$T_{b}$$ where $$T_{b} = \frac{\beta }{R}T_{c}$$ to recover the transmitted data. The averaging operation over R identical samples reduces the effect of noise present in the received signal and improves the performance of the system over noisy channels. Closed form expression for bit error rate (BER) of the proposed NR-COOK system is derived and analyzed under multipath fading channel and are validated through simulation results to demonstrate performance improvement over conventional non coherent schemes.

Performance analysis of MISO-MU-OHE-DCSK system over Rayleigh fading channels

In this paper, a novel non-coherent communication system, multi-user orthogonal high efficiency differential chaos shift keying (MU-OHE-DCSK) system is presented. In the proposed system, by using an orthogonal chaotic generator (OCG) to generate two orthogonal chaotic signals, therefore the intra-signal interference components in MU-OHE-DCSK are eliminated. As in high efficiency differential chaos shift keying (HE-DCSK), the reference signal is transmitted in the first time slot. The 2N data bits are spread by chaotic sequence and then separated through Walsh codes in the second time slot of the frame. As a result, the superiority of this proposed system is that it can enhance the spectral efficiency when compared with DCSK and HE-DCSK. Furthermore, using multiple antennas at the transmitter end, this system can inhibit the channel fading problem and then obtain more diversity gain. The BER formula of multiple-input single-output MU-OHE-DCSK (MISO-MU-OHE-DCSK) is derived under the assumption of the proposed system over Rayleigh fading channels, respectively. Theoretical analysis is consistent with simulation results and shows that the new system outperforms other DCSK-based systems.

Low-density parity-check codes for noncoherent UWB communication systems

In order to guarantee reliable data transmission, powerful channel coding techniques are usually required in noncoherent ultra- wideband (UWB) communication systems. Accordingly, several forward error correction (FEC) codes, such as Reed-Solomon and convolutional codes have been used in noncoherent UWB systems to improve the bit error rate (BER) performance. In this paper, low-density parity-check (LDPC) codes are further studied as more powerful FEC candidates for noncoherent UWB systems. Two LDPC codes and the corresponding decoding procedures are presented for noncoherent UWB systems. Moreover, performance comparison between the LDPC codes and other FEC codes are provided for three major noncoherent UWB communication systems, namely, noncoherent pulse position modulation (NC-PPM), transmitted reference (TR) and transmitted reference pulse cluster (TRPC). Both theoretical analysis and simulation results show that the two investigated LDPC codes outperform other existing FEC codes with limited penalty in terms of complexity and therefore they are promising FEC candidates for noncoherent UWB systems with low- cost and low-power consumption.

Uniquely Factorable Hexagonal Constellation Designs for Noncoherent SIMO Systems

In this paper, we propose the design of a uniquely factorable hexagonal constellation for a noncoherent wireless communication system with a single transmitter antenna and multiple receiver antennas [single-input multiple-output (SIMO)]. The hexagonal constellation has a densely packed 2-D “honeycomb” structure and is more energy efficient than the commonly used cross quadrature amplitude modulation (QAM) constellations. By using the hexagonal lattice formed from the Eisenstein integers and the recently developed concept of the uniquely factorable constellation (UFC) for the QAM constellation, an algorithm is developed to effectively and efficiently construct constant norm hexagonal UFCs of various sizes. In addition, an optimal energy scale is found to maximize the coding gain for the constant norm training hexagonal UFC schemes subject to a transmission bit rate constraint. Computer simulations show that the hexagonal unitary UFC proposed in this paper has the best error performance in comparison to the current literature results for the noncoherent SIMO system.

Very high efficiency differential chaos shift keying system

In this study, a new non-coherent communication system, i.e. very high efficiency differential chaos shift keying system, is proposed. This system is a generalised form of the high efficiency differential chaos shift keying (HE-DCSK) system, with an arbitrary number (N) of transmitted bits per frame. The major advantage of this new proposition is its ability to significantly improve the spectral efficiency compared with DCSK and HE-DCSK. The theoretical bit error rate of this system is found using the Gaussian approximation method under different communication channels: additive white Gaussian noise and two-ray Rayleigh fading channels. Simulations in both environments show a perfect match with the analytical expressions for large spreading factors. Simulation results for the two-ray Rayleigh fading channel show clearly the diversity gain compared with the single-ray Rayleigh channel.

주파수 종속 다중경로 페이딩이 비코히어런트 수중통신시스템에 미치는 영향

주파수 종속 다중경로 페이딩이 비코히어런트 수중통신시스템에 미치는 영향

Generation of spectral-encoded signals in noncoherent optical communication systems based on acousto-optic multiwavelength filters

New acousto-optical (AO) methods and devices necessary for the creation of noncoherent optical code division multiple access (O-CDMA) systems are considered. Based on an AO multiwavelength filter, an original device generating spectral-encoded signals for O-CDMA systems with optimum WDM has been created and studied. It is shown that modern AO technology is capable of surmounting difficulties that previously hindered the transition of optical communication systems to CDMA data transmission.

On the Accuracy of the High-SNR Approximation of the Differential Entropy of Signals in Additive Gaussian Noise: Real and Complex Cases

One approach to the analysis of the high signal-to-noise ratio (SNR) capacity of noncoherent wireless communication systems is to ignore the noise component of the received signal in the computation of its differential entropy. In this paper, we consider the error incurred by this approximation when the transmitter and the receiver have one antenna each and when the noise has a Gaussian distribution. We consider the complex and real cases, and we show that when the probability density function (pdf) of the signal component of the received signal is piecewise differentiable, the approximation error decays as 1/SNR, which tightens the available result that the error decays as $o(\mbox{1})$ . In addition, we consider the special instance in which the signal component of the received signal corresponds to a signal transmitted over a channel with a Gaussian fading coefficient. For that case, we provide explicit expressions for the first nonconstant term of the Taylor expansion of the differential entropy, and we invoke Schwartz's inequality to obtain an efficiently computable bound on it. Our results are supported by numerical examples.

Performance Evaluation of Non-redundant Error Correcting Scheme Using Logistic Chaotic Map

In this paper an efficient error-correcting scheme based on logistic chaotic map for non-coherent chaos communication system without redundancy is presented and its performance is evaluated. The scheme uses one chaotic generator to generate two sequences one for each data bit value in a way that the end of the current chaotic sequence sets the initial value of the next sequence of the same symbol. With this arrangement, successive chaotic sequences having the same chaotic dynamics are created for the purpose of error correction. A suboptimal detection algorithm based on shortest distance calculation between the received sequence and the chaotic trajectories over nth-dimension is used for detecting the transmitted symbol and performing the errors-correction. The simulation results show that the scheme offers improvement in Eb/N0 over the method before the error-correcting scheme and this improvement is increased as the trajectory dimension is increased. At bit-error probability of 10?3, a gain of 0.5 dB is obtained in Eb/No over the method before the error-correcting scheme when the dimension is 4. The power point in the scheme is that error correction is based on chaotic dynamics and no redundant bits are needed. This would make the scheme a good candidate for applications that require high data transmission rates.

Expanded Trellis Designs for Noncoherent Communications with Frequency Offset

In this letter, we propose a noncoherent communication system that can be used in the communication environment in which the frequency estimation is only roughly obtained and the phase synchronization is not employed. The transmitter side has the serial turbo coding structure composed of a convolutional encoder followed by an interleaver, an MPSK signal mapper and a differential modulator. At the receiver side an expanded trellis is employed to represent not only the possible paths of the differentially encoded MPSK but also the paths resultant from the possible phase variations due to the frequency offset and the phase noise.

Non-coherent MIMO Communication Systems Employing per Transmit Antenna Differential Mapping (PADM)

Non-coherent MIMO Communication Systems Employing per Transmit Antenna Differential Mapping (PADM)

New super-orthogonal space-time trellis codes using differential M-PSK for noncoherent mobile communication systems with two transmit antennas

In this paper, we develop super-orthogonal space-time trellis codes (SOSTTCs) using differential binary phase-shift keying, quadriphase-shift keying and eight-phase shift keying for noncoherent communication systems with two transmit antennas without channel state information at the receiver. Based on a differential encoding scheme proposed by Tarokh and Jafarkhani, we propose a new decoding algorithm with reduced decoding complexity. To evaluate the performance of the SOSTTCs by way of computer simulations, a geometric two-ring channel model is employed throughout. The simulation results show that the new decoding algorithm has the same decoding performance compared with the traditional decoding strategy, while it reduces significantly the overall computing complexity. As expected the system performance depends greatly on the antenna spacing and on the angular spread of the incoming waves. For fair comparison, we also design SOSTTCs for coherent detection of the same complexity as those demonstrated for the noncoherent case. As in the case of classical single antenna transmission systems, the coherent scheme outperforms the differential one by approximately 3 dB for SOSTTCs as well.

A Polarization-Stabilized Fiber-Optical Output Infrared Laser Source

In this paper, we successfully invented a polarization controlled light source for coherent or noncoherent fiber communication systems. The structure of our experiment includes 89C51 control board and feedback circuit which can stabilize states of polarization (SOPs) of output light. From the SOP modulation results, the given degree of polarization can be effectively controlled and the polarization state can be arbitrarily changed.

A General Method for Calculating Error Probabilities Over Fading Channels

Signal fading is a ubiquitous problem in mobile and wireless communications. In digital systems, fading results in bit errors, and evaluating the average error rate under fairly general fading models and multichannel reception is often required. Predominantly to date, most researchers perform the averaging using the probability density function method or the moment generating function (MGF) method. This paper presents a third method, called the characteristic function (CHF) method, for calculating the average error rates and outage performance of a broad class of coherent, differentially coherent, and noncoherent communication systems, with or without diversity reception, in a myriad of fading environments. Unlike the MGF technique, the proposed CHF method (based on Parseval's theorem) enables us to unify the average error-rate analysis of different modulation formats and all commonly used predetection diversity techniques (i.e., maximal-ratio combining, equal-gain combining, selection diversity, and switched diversity) within a single common framework. The CHF method also lends itself to the averaging of the conditional error probability involving the complementary incomplete Gamma function and the confluent hypergeometric function over fading amplitudes, which heretofore resisted to a simple form. As an aside, we show some previous results as special cases of our unified framework.

A new twist on the Marcum Q-function and its application

A new form of the Marcum (1950) Q-function is presented that has both computational and analytical advantages. The new form is particularly useful in simplifying and rendering more accurate the analysis of the error probability performance of uncoded and coded partially coherent, differentially coherent, and noncoherent communication systems in the presence of fading. It also enables simple upper and lower bounds to be found analogous to the Chernoff bound on the Gaussian Q-function.

Noncoherent coded modulation

Trellis coded modulation with two or multidimensional signal constellations, together with coherent maximum-likelihood detection, is considered an attractive solution for communications over the additive white Gaussian noise (AWGN) channel. In this paper a new noncoherent communication system is introduced called noncoherent coded modulation (NCM) as an alternative to coherent coded modulation. NCM achieves almost the same power efficiency, without bandwidth expansion or an extensive increase in complexity. As a noncoherent system, the method does not need carrier phase estimation. Nonetheless, differential encoding is not required. High performance noncoherent detection is achieved by using multiple symbol observations. Unlike previous approaches, a sliding window for the observations is used, with each observation covering several branches of the trellis, such that the observations are time-overlapped. We define a new type of noncoherent maximum-likelihood sequence estimator (MLSE), and analyze its performance over the AWGN channel by numerical calculation of the union bound. We perform a computerized search and present new codes for noncoherent detection with their performance. The new codes cover many useful rates and complexities and achieve higher performance than existing codes for noncoherent detection. The method can also be used for multiple symbol demodulation of MDPSK with better results than existing methods.

Error floors in the satellite and land mobile channels

In a satellite mobile channel (SMC) and land mobile channel (LMC) because of fading and nonlinear power amplifiers, constant envelope modulation and noncoherent detection methods may outperform other schemes. It is shown how to compute the error floor for four noncoherent digital communication systems in satellite and land mobile channels. Differential phase shift keying (DPSK) with differential phase detection (DPD) or frequency shift keying (FSK) with DPD, limiter discriminator integrator detection. (LDID), or limiter discriminator detection (LDD) are studied. The error floor is the residual error probability when SNR is infinity, i.e. the error probability in the system is limited by the error floor. The error floor is computed as a function of Doppler frequency, modulation index, and ratio of powers in the specular and diffuse signal components for DPSK-DPD, FSK-DPD, FSK-LDID and FSD-LDD systems. >

Analysis of non-coherent receivers for bandpass data transmission

The effect of restricted bandwidth (BW) on the performance of non-coherent digital communication systems is investigated. It is assumed that the signal is corrupted by both gaussian noise and Inter Symbol Interference (ISI). Under this assumption the probability density function of the received signal, given that a ‘’ or a ‘’transmitted is obtained. Bit error probabilities are calculated as a function of both SNR and available bandwidth. It is found that there is rapid degradation of system performance at low values of BW, caused primarily by ISI.

Digital Communication Systems in Impulsive Atmospheric Radio Noise

Analyses are presented of the performance of binary and M-ary coherent and noncoherent communication systems operating in the impulsive atmospheric radio noise environment. The receiver is usually a maximum likelihood detector for white Gaussian interference and therefore has the form of a parallel bank of matched filters followed by decision circuitry. By employing a Poisson or generalized Shot noise model for the impulsive noise with a suitable probability density function (pdf), closed-form expressions and bounds of error probabilities for M-ary noncoherent and coherent amplitude-shift keying (ASK), phase-shift keying (PSK), and frequency-shift keying (FSK) systems are obtained and the results discussed.

Design Criteria for Noncoherent Gaussian Channels with MFSK Signaling and Coding

This paper presents data and criteria to assess and guide the design of modems for coded noncoherent communication systems subject to practical system constraints of power <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S</tex> , bandwidth <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">W</tex> , noise spectral density N <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</inf> , coherence time T <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> , and number of orthogonal signals <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</tex> . Three basic receiver types are analyzed for the noncoherent multifrequency-shift keying (MFSK) additive white Gaussian noise channel: hard decision, unquantized (optimum), and quantized (soft decision). Channel capacity and computational cutoff rate R <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">comp</inf> are computed for each type and presented as functions of the predetection signal-to-noise ratio <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ST/N_{0}</tex> and the number of orthogonal signals <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M = 2TW</tex> . This relates the channel constraints of power, bandwidth, coherence time, and noise power to the optimum choice of signal duration <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T \leq T_{c}</tex> and signal number <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</tex> .