Ary Frequency Shift Keying Research Articles

On the Use of FFH-MFSK for Ultra-Low Power Communications in a Jamming Environment

We are interested in a communication system that operates in the presence of an intelligent jammer, under stringent power constraints, but with flexible bandwidth constraints.We optimize some of the key elements in the transceiver design for low power consumption, and thus high complexity components of the system, such as matched filters (MF), forward error correction (FEC) that employs iterative decoders, coherent demodulators, and bandwidth-efficient modulation formats, are not feasible for this research. Rather, our system is designed using <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</i> -ary frequency shift keying (MFSK) with non-coherent detection and fast frequency hopping (FFH), optimized two-pole bandpass filters (BPF), and Reed-Solomon (RS) codes with hard-decision decoding. Among other things, we show that by properly optimizing the key parameters of the BPFs and RS codes, we can design the system to be significantly less complex than the MF system with a performance loss of less than 1.4 dB for most scenarios that we considered. Further, the 2-pole BPF system can actually outperform the corresponding MF system by up to 2.4 dB in the presence of multi-tone jamming.

A Novel Weighted LLR Algorithm for Non-Coherent OFDM-MFSK System in Ionospheric Scatter Channel

A novel weighted log likelihood ratio (LLR) algorithm is proposed for the non-coherent orthogonal frequency division multiplexing with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${M}$ </tex-math></inline-formula> -ary frequency shift keying (OFDM-MFSK) system in an ionospheric scatter channel (ISC) with serious frequency-selective fading. In the algorithm, the bit LLR is derived according to the probability distribution of non-coherent received signals in the MFSK symbol and is approximately simplified to a concise expression, which reveals that LLRs cannot indicate the effect of the frequency-selective fading channel on different MFSK symbols. The proposed weighted LLR algorithm maximizes the signal-to-noise ratio (SNR) of the metric combined with LLRs in channel decoding. The weighted factors were estimated blindly from the received MFSK signals. Simulation results show that the bit error rate (BER) of OFDM-MFSK systems with the proposed LLR-weighted algorithm is superior than that of conventional LLR algorithms, and has approximately 1.6 dB SNR gain when BER is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${10^{-4}}$ </tex-math></inline-formula> .

Bit Error Rate and Channel Capacity Performance of Telemetry Modulation Methods Under Typical Reentry Plasma Sheath Channel

Due to the severe impact of plasma turbulence on electromagnetic waves, the dynamic plasma sheath can degrade communication quality, even resulting in communication blackouts. This article studies the effect of different frequency bands and two typical telemetry modulation methods on communication signals under a time-varying plasma sheath channel. First, considering plasma dynamics on different scales, a typical reentry plasma sheath channel response is simulated and analyzed. Then, the average bit error rate (BER) and channel capacity of $M$ -ary phase-shift keying (MPSK) and $M$ -ary frequency-shift keying (MFSK) evaluating the telemetry communication performance are derived theoretically and simulated numerically based on the typical reentry plasma sheath channel response. The simulation results show that BPSK and noncoherent-MFSK (NC-MFSK) in the Ka -band and above bands have a preferable communication performance; when bit-to-noise ratio > 10 dB, BER $ and channel capacity loss $ for both BPSK and NC-MFSK ( $M\ge 8$ ) modulations in the especial reentry plasma condition (ERPC). Comparing BPSK and NC-MFSK in the Ka -band and above bands, the performances of BER and channel capacity follow the order: NC-MFSK ( $M \ge 8$ ) > BPSK > NC-4FSK > NC-2FSK. In particular, results indicate that under the dynamic plasma channel, terahertz communication can effectively improve communication performance and alleviate communication blackout.

Convolutionally Coded Hopping Pattern for MFSK Modulation in Underwater Acoustic Communication

A convolutionally coded $M$ -ary frequency shift keying (MFSK) modulation scheme for underwater acoustic communication is introduced. It uses a rate $1/\log _{2}{M}$ inner convolutional code, whose coded symbols are used as transmission symbols. An interleaver in the frequency domain is applied to improve the average channel clearing time. It thereby achieves almost the same data rate as a comparable uncoded frequency hopped frequency shift keying (FH-FSK) modulation scheme, but obtains the error correcting properties of the convolutional code. Bit and packet error rates are evaluated on the additive white Gaussian noise (AWGN) channel and the so-called Watermark channel model, which is a benchmark for underwater acoustic modulation schemes based on sea trial measurements. The JANUS standard which uses convolutionally coded FH-FSK is used for comparison. On the AWGN channel, the proposed scheme achieves a gain of 4 dB with respect to the required $E_{b}/N_{0}$ for a given packet error rate (PER) compared with JANUS. In the Watermark scenarios, the best proposed-scheme achieves a PER $10^{-3}$ at more than 10 dB lower $E_{b}/N_{0}$ than the JANUS implementation.

A Frequency Control Strategy Using Power Line Communication in a Smart Microgrid

This paper presents an application of power-line communication (PLC) as a viable solution for frequency regulation in a smart microgrid. The microgrid under consideration comprises a diesel generator with a frequency controller and another synchronous generator operating in the constant power mode. Frequency regulation is achieved in the microgrid by communicating the frequency deviation (information) from the control center to the diesel generator using PLC. The information received at the other end is used for frequency regulation. A simple yet effective M -ary amplitude-shift keying (ASK) modulation-based PLC system is proposed for information transmission. A comparative analysis of M -ary ASK and M -ary frequency-shift keying (FSK)-based PLC systems is also presented. Approximate closed-form expressions for the average symbol error rate and the average achievable rate are derived for both the PLC systems, assuming that the PLC channel coefficients and the additive impulsive noise samples are derived from a log-normal distribution and a Bernoulli-Gaussian process, respectively. The results show that M -ary ASK is a better choice for PLC than M -ary FSK. Furthermore, the delay introduced in the control loop while using the proposed PLC system is negligible, and therefore, the stability of the microgrid is also ensured.

Equal Gain Combining-Based Maximum Likelihood Detector for FFH/MFSK Systems

In this letter, a new multi-user detector based on equal gain combining (EGC) and maximum likelihood (ML) principle is proposed, which is referred to as an EGC-aided ML (EGC-ML) detector. The detection performance of fast frequency-hopping $M$ -ary frequency-shift keying (FFH/MFSK) systems with a novel EGC-ML receiver is investigated in the presence of multi-user interference and additive white Gaussian noise over Rayleigh fading channels. After envelop detection and frequency de-hopping operations, the proposed algorithm picks up several most possible estimations based on the EGC principle and then make final decision via an ML detector within the possible searching range. Our simulation results show that this novel EGC-ML detector may noticeably reduce the complexity of the ML detector with an acceptable bit error rate performance decrement, when a reasonable searching range is chosen by the EGC principle.

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.

A Coherent Multi-User Frequency Shift Keying Receiver for Wireless Sensor Networks Based on Clustering Algorithms

We explore the use of ${M}$ -ary frequency shift keying (FSK) as an integrated modulation/random access scheme for wireless sensor networks whereby multiple sensor nodes may transmit data simultaneously to a master node. Specifically, we propose exploiting the presence of multiple signal dimensions and using a clustering algorithm to estimate blindly the channel gains required for coherent multi-user detection. To demonstrate the feasibility of this concept, we simulate the bit error rates (BER) of 4FSK and 8FSK systems with three and four simultaneously transmitting sensor nodes, respectively. It was found that the BER of the proposed blind multi-user detector is very close to that achieved under perfect channel state information. This suggests that the proposed integrated modulation/random-access approach can significantly improve spectral efficiency and mitigate multi-user interference. Compared to no multi-user detection, less energy is wasted on the retranmissions caused by packet collisions and this helps to extend the lifetime of the sensor nodes.

Frequency-Hopping Based Communication Network With Multi-Level QoSs in Smart Grid: Code Design and Performance Analysis

Smart grid is a modern infrastructure for improving the efficiency and reliability of power grid by integrating automated control, sensing and metering technologies, modern communication infrastructure and modern energy management techniques. Security and quality-of-service (QoS) are two most critical requirements for the communications network in smart grid. Frequency hopping (FH) technology, due to its inherent security, is a promising candidate technology in the physical layer of smart gird communication infrastructure. Unfortunately, all the existing FH systems can support only a single level of QoS due to the fact that traditional FH sequence sets can provide the same level of Hamming cross-correlation. In this paper, an FH-based communication network is developed for smart grid, particularly the advanced smart metering (AMI), to address the above two key challenges. A novel type of FH sequence set which meets the multi-level QoS requirement is designed. Then, the data traffic in AMI is investigated and modeled as a general Poisson process which is validated by real measurements of power consumptions. With the proposed sequence set and data model, the analytic performance in terms of error probabilities for the proposed FH communication with <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$M$</tex></formula> -ary frequency-shift keying (FSK) modulation is derived for a slow Rayleigh fading channel. The analytic results are validated by numerical simulation results.

Least squares symbol detection for two-antenna frequency hopping/ M -ary frequency shift keying systems in the presence of follower jamming

The jamming robustness of frequency hopping systems with M -ary frequency shift keying (MFSK) modulation may be potentially neutralised by a follower partial-band jammer. To remove these harmful effects, a novel detection scheme for slow frequency hopping/MFSK systems, which use two receive antennas in a quasi-static flat fading channel, is proposed. The relative complex gain factor between the two jamming components is derived and is used to aid the symbol detection process. The improved performance of the new scheme is verified by using simulated bit error rate results.

Exact Performance Analysis of Synchronous FH-MFSK Wireless Networks

In this paper, a new approach is presented to derive the exact bit-error-rate (BER) performance of frequency-hopping spread-spectrum (FHSS) wireless networks with noncoherent <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</i> -ary frequency-shift keying (MFSK) in additive white Gaussian noise (AWGN) and Rayleigh fading channels. The new approach has enabled an exact evaluation of the BER, regardless of the modulation order <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</i> or the number of interferers. Theoretical results validated by simulations have shown that system performance is dominated by the first two hits, which lead to an accurate and computationally efficient approximation for the AWGN channel case. The exact and approximated results are compared with the simulation and semianalytic results presented in the literature.

Average BER Analysis for $M$-ary FSK Signals in Nakagami-$q$ (Hoyt) Fading With Noncoherent Diversity Combining

This paper analyzes the average bit error rate (BER) of noncoherent M-ary frequency-shift keying (FSK) signals over multichannel nonidentically distributed Nakagami-q (Hoyt) fading employing diversity combining. The first part of the paper considers the conventional postdetection noncoherent equal-gain combiner (NC-EGC), in which a Fourier series inversion formula is employed to derive a simple and rapidly converging series-based expression for the system average BER. This expression is valid for arbitrary values of received average signal-to-noise ratios (SNRs) and fading parameters. The derived expression is then compared with some existing ones in the literature, and the results show a large reduction in computational complexity, particularly when M and/or the diversity order increases. In the second part, a new noncoherent combiner is proposed to achieve improvements over the conventional NC-EGC. It is also shown that this new combiner results in a simple closed-form expression for the system average BER that is given in terms of elementary functions; hence, it can be easily numerically evaluated with noticeable computation efficiency.

M-ary FSK Performance for Coherent Optical Communication Systems Using Semiconductor Lasers

This paper describes the design and performance of an M ary frequency shift keyed (FSK) signaling and demodulation scheme for an optical communication system using semiconductor lasers and heterodyne detection. Frequency or phase noise in semiconductor lasers causes spectral spreading, producing a nonzero linewidth laser signal. This degrades communication performance when compared to a system using an ideal laser with zero linewidth. We present estimates of the bit error rate (BER) performance of M -ary frequency shift keying (FSK) with noncoherent demodulation in the presence of white Gaussian frequency noise and additive channel noise. This is typical of an optical system using semiconductor lasers and heterodyne detection. Estimates use the union-Chernoff bound with a simplified channel model to predict the effects of frequency noise. Two effects of frequency noise are identified: signal attenuation or suppression, and crosstalk. These cause an offset in the BER curve from the BER in the absence of frequency noise, and an error rate floor, respectively. The error rate floor is lower than previously predicted. When performance is not crosstalk limited, M -ary FSK is found to perform better than binary FSK with the same system bandwidth constraints, as would be predicted if ideal lasers are used. Theoretical results are compared with Monte Carlo simulations of the system.

On Nonuniform Windowing M-ary FSK Data in a DFT-Based Detector

Nonuniform amplitude windowing <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</tex> -ary frequency shiftkeying (FSK) data prior to demodulation reduces the crosstalk normally caused by Doppler and oscillator drift. A major disadvantage of such nonuniform windowing is the loss in signal detectability as a result of the mismatch between the nonuniform windowed signal and the uniform windowed detectors. This paper is concerned with the tradeoff of nonuniform windowing to combat frequency offset degradation and signal detectability losses caused by the use of such windows in a DFT (discrete Fourier transform)-based detector of noncoherent <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</tex> -ary FSK. What is shown here is that if a frequency control system can maintain frequency to within a certain deviation (which depends on error rate and nonuniform window), nonuniform windowing is not warranted; on the other hand, if the frequency deviation becomes too large, nonuniform windowing is advised. A technique is developed that will determine this crossover deviation.

The Design of a Low Data Rate MFSK Communication System

Low data rate communications are of considerable interest for applications in which the received signal-to-noise ratio is very low. At data rates below the neighborhood of 5 bit/s, coherent communication techniques become inefficient, and noncoherent techniques such as <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</tex> -ary frequency shift keying (MFSK) become attractive. In this paper, the design of an MFSK low data rate communication system is discussed. The problems of synchronization in time and frequency are analyzed, and experimental results of successful laboratory tests of the system are presented.