Optimal Noncoherent Detection Research Articles

Optimal Post-Detection Integration Techniques for the Reacquisition of Weak GNSS Signals

This paper tackles the problem of finding the optimal non-coherent detector for the reacquisition of weak Global Navigation Satellite System (GNSS) signals in the presence of bits and phase uncertainty. Two solutions are derived based on using two detection frameworks: the Bayesian approach and the generalized likelihood ratio test (GLRT). We also derive approximate detectors of reduced computation complexity and without noticeable performance degradation. Simulation results reveal a clear improvement of the detection probability for the proposed techniques with respect to the conventional detectors implemented in high sensitivity GNSS (HS-GNSS) receivers to acquire weak GNSS signals. Finally, we draw conclusions on which is the best technique to reacquire weak GNSS signals in practice considering a trade-off between performance and complexity.

Non-Coherent MIMO Scheme Based on OFDM-MFSK

We propose a non-coherent transmission system based on orthogonal frequency division multiplexing (OFDM) for use in low-power applications. The proposed system uses ${M}$ -ary frequency shift keying (MFSK) and employs two transmitting and two receiving antennas, with encoding performed across the space, frequency and time domains. For the resulting scheme, we develop a novel optimal non-coherent detector that produces soft bit information for a state-of-the-art error correction decoder. The proposed solution eliminates the need for channel knowledge and enables a simple receiver structure. Simulation results demonstrate up to 8 dB of coding gain for the proposed scheme compared to single-antenna OFDM-MFSK. When compared with coherent systems based on OFDM and binary phase shift keying, the designed scheme offers a receiver sensitivity gain of 9 dB and beyond.

Log-Linear-Complexity GLRT-Optimal Noncoherent Sequence Detection for Orthogonal and RFID-Oriented Modulations

Orthogonal modulation, for example, frequency-shift keying (FSK) or pulse-position modulation (PPM), is primarily used in relatively-low-rate communication systems that operate in the power-limited regime. Optimal noncoherent detection of orthogonally modulated signals takes the form of sequence detection and has exponential (in the sequence length) complexity when implemented through an exhaustive search among all possible sequences. In this work, for the first time in the literature, we present an algorithm that performs generalized-likelihood-ratio-test (GLRT) optimal noncoherent sequence detection of orthogonally modulated signals in flat fading with log-linear (in the sequence length) complexity. Moreover, for Rayleigh fading channels, the proposed algorithm is equivalent to the maximum-likelihood (ML) noncoherent sequence detector. Simulation studies indicate that the optimal noncoherent FSK detector attains coherent-detection performance when the sequence length is on the order of 100, offering a 3–5 dB gain over the typical energy (single-symbol) detector. While the conventional exhaustive-search approach becomes infeasible for such sequence lengths, the proposed implementation requires a log-linear only number of operations, opening new avenues for practical deployments. Finally, we show that our algorithm also solves efficiently the optimal noncoherent sequence detection problem in contemporary radio frequency identification (RFID) systems.

Scaling Laws for Noncoherent Energy-Based Communications in the SIMO MAC

We consider a one-shot communication setting in which several single antenna transmitters communicate with a receiver with a large number of antennas, i.e., the receiver decodes transmitted information at the end of every symbol time. Motivated by the optimal noncoherent detector in a Rayleigh fading channel, we consider a noncoherent energy-based communication scheme that does not require any knowledge of instantaneous channel state information at either the transmitter or the receiver; it uses only the statistics of the channel and noise. We show that, for general channel fading statistics, the performance of the considered one-shot multiuser noncoherent scheme is the same, in a scaling law sense, as that of the optimal coherent scheme exploiting perfect channel knowledge and coding across time. Furthermore, we present a numerical evaluation of the performance of this scheme in representative fading and noise statistics.

Revisiting Non-Coherent Detection in Doubly Selective Multipath

We revisit the problem of non-coherent signal detection in multipath scattering by exploring the effect of bandwidth and signaling duration on detection performance in doubly selective rich and sparse multipath. We begin with a general sampled representation of multipath channels that allows us to quantify the independent degrees of freedom (DoF) in non-uniform and sparse channels as a function of the physical propagation environment and the signaling parameters. We then develop the optimal non-coherent detector for such channels. Based on analytical and numerical results, we conjecture that detection performance is optimized in any multipath environment, rich or sparse, if two conditions are met: C1) the number of independent DoF induced by the transmit signal on the channel is approximately SNR/3, a condition empirically observed in earlier work, and C2) the variance of the channel coefficients (each corresponding to a DoF) is identical. We then show how to achieve these conditions given statistical characterization of the channel. In the most general setting of non-uniform power distribution across both delay and Doppler, it may not be possible to meet the two conditions above.

Non-Coherent Detection for Two-Way AF Cooperative Communications in Fast Rayleigh Fading Channels

Two-way cooperative communications are considered to improve the throughput of conventional one-way cooperative communications. For fast Rayleigh fading channels, we propose optimal and suboptimal non-coherent detectors for on-off keying (OOK) and frequency-shift keying (FSK) modulated two-way amplify-and-forward (AF) cooperative communications in this paper. In the proposed system, the relaying node combines the received signals from two nodes, amplifies them and retransmits the conjugate of the combined and amplified signals to the above-mentioned nodes. At the receivers of above-mentioned nodes, the optimal non-coherent detection is employed which is based on maximum likelihood rule. Since it involves integration operation, the optimal detector is simplified to a suboptimal detector which omits the real component of the relayed signal over the frequency which includes interference. The simulation results have shown that compared with the optimal detector, the proposed suboptimal detector reduces the receiver complexity at the expense of acceptable performance degradation. Furthermore, we have analytically studied the bit-error-rate performance upper and lower bounds of proposed non-coherent FSK modulated two-way AF cooperative communications.

Tight lower bound of optimal non-coherent detection for FSK modulated AF cooperative communications in Rayleigh fading channels

When wireless channels undergo fast fading, non-coherent frequency shift keying (FSK) (de)modulation schemes may be considered for amplify-and-forward (AF) cooperative communications. In this paper, we derive the bit-error-rate performance of partial non-coherent receiver as a lower bound of the optimal non-coherent receiver for FSK modulated AF cooperative communications. From the simulation and analytical results, it is found that the derived lower bound is very closed to simulation results. This result shows that knowing partial channel state information may not improve system performance significantly. On the other hand, conventional optimal non-coherent receiver involves complicated integration operation. To address the above complexity issue, we also propose a near optimal non-coherent receiver which does not involve integration operation. Simulation results have shown that the performance gap between the proposed near optimal receiver and the optimal receiver is small.

Non-coherent detectors for quadrature-multiplexed continuous phase modulation signals

Here, non-coherent detectors for quadrature-multiplexed continuous phase modulation (QM-CPM) signals are developed (Fonseka et al. , 2008). QM-CPM signals are more spectrally efficient than CPM signals, and multiamplitude QM-CPM signals can be constructed that outperform QAM. The non-coherent detectors view a QM-CPM signal as having composite states that represent the information modulated both onto the in-phase and quadrature-phase carriers. Viterbi decoding is used to jointly detect the quadrature-multiplexed signal components. Optimal sequence-based quadrature-matched filter (QMF) detectors are presented for use with QM-CPM detection and a QM-MSK detector is developed in detail. Differential phase and envelope (DPE) detectors are also presented which require less computation and are able to outperform the QMF-type detectors when the unknown carrier phase varies (phase jitter, phase hits etc.) within the sequence length used in the sequence-based QMF detectors. In the absence of these phase fluctuation effects, as the sequence length used in the QMF detectors increases, the performance of the QMF detectors approaches the performance of optimal non-coherent detection. The DPE-type detectors perform within about 2.5 dB of optimal coherent detection.

On Optimal Detection of Noncoherent Chaos-Shift-Keying Signals in a Noisy Environment

Recently, an optimal noncoherent detection technique for chaos-shift-keying digital communication system has been proposed. It has been stated that computational intensity showed increases that were exponential with the spreading factor. In this Letter, we show that the implementation of the optimal detector can be made independent of the chaotic maps used, and that the computational intensity will increase almost linearly with the spreading factor. In particular, we use a tent map as an example to illustrate the decoding algorithm. The bit error performance of the system is then evaluated by computer simulations for a range of spreading factors. Further, we extend the optimal decoding algorithm for maps of higher dimension. The bit error performance for the case of simple 2-D maps are compared with that obtained using the tent map. Finally, the effect of increasing spreading factor on the bit error performance is studied for the case of 2-D maps.

APPROXIMATE-OPTIMAL DETECTOR FOR CHAOS COMMUNICATION SYSTEMS

Recently, an optimal noncoherent detection technique for chaos-shift-keying digital communication system has been proposed. The computational intensity required, however, increases exponentially with the spreading factor. In this Letter, we propose an approximate-optimal detection technique, whose computational effort increases only linearly with the spreading factor. In particular, we use the chaotic sequences generated by a skew tent map as an example to illustrate the approximate-optimal detection method. The bit error performance of the proposed detector is evaluated by computer simulations and the results are compared with those obtained using the optimal detector.

Optimal noncoherent detection of FSK signals transmitted over linearly time-selective Rayleigh fading channels

Linearly time-varying fading models are used to investigate noncoherent detection of frequency shift keying (FSK) signals transmitted over frequency-flat fading channels. The structure of the optimal noncoherent FSK detector is derived and a novel analytical technique is proposed to compute the error performance of noncoherent FSK detectors in fast fading. Error performance results obtained by computer simulation are in excellent agreement with the analytical predictions.

Performance analysis of asymptotically optimal noncoherent detection of trellis-coded multi-amplitude/-phase modulation signals in Gaussian noise and ISI channels

Performance upper bounds for noncoherent receivers employed in conjunction with single and multi-amplitude/-phase signals, transmitted over time dispersive and Gaussian noise channels are derived. Based upon a metric which has been previously derived by the authors, we present analytical expressions and computer generated results for the performance of asymptotically optimal noncoherent detection over such channels. As a typical application of the developed theoretical analysis, we consider wideband telecommunication systems. Where time dispersion resulting in intersymbol interference (ISI) is one of the significant sources of system performance degradation. Numerical evaluation of the optimal noncoherent decoding algorithms, shows the proposed bounds to be an effective and efficient means of evaluating the performance of the noncoherent receivers under investigation. Using the derived bounds, performance evaluation results for modulation schemes such as /spl pi//4-shift DQPSK (differential quadrature phase shift keying), 8- and 16-DQAM (differential quadrature amplitude modulation), at very low bit-error rates (BER), which would otherwise pose impractically high computational loads when using Monte-Carlo error counting techniques, are readily obtained. At BER>10/sup -4/ evaluation results generated via computer simulation have verified the tightness of the bounds. >

Noncoherent Detection of Tamed Frequency Modulation

Continuous-phase, constant-envelope digital modulation schemes are useful in various applications where a high spectrum utilization as well as immunity to nonlinear distortion is required. From this point of view, typical efficient schemes are digital partialresponse frequency modulation methods. The aim of this work is to investigate noncoherent detection in order to avoid the RF carrier recovery problem. In this paper we select for analysis tamed frequency modulation (TFM) as a particularly representative member of this class, but a similar analysis could be carried out for other partialresponse digital FM systems. After an evaluation of the optimal noncoherent detection and of differential phase detection of TFM, we propose a demodulation method based on a simple and efficient baseband processing of the output of a frequency demodulator. It turns out that the power loss with respect to coherent or optimal demodulation of TFM is on the order of 2 dB. The baseband processing here proposed is in some way equivalent to a partial recovery of the carrier phase and could be improved by using a more complex baseband processing such as a decoding scheme based on the Viterbi algorithm.