Multiple Frequency Shift Keying Research Articles

Evaluation of Polar-Coded Noncoherent Acoustic Underwater Communication

This article investigates several variants of noncoherent multiple-frequency-shift keying (MFSK) that uses Polar coding and evaluates their applicability to robust underwater acoustic underwater communication. A simplified data model is assumed, yielding a low-complexity MFSK symbol estimator, and symbol likelihoods are calculated using sparse pilot symbols. Results presented from field tests in the Stockholm archipelago indicate that a Polar code will decode with a low frame error rate (FER) if not signal-to-noise ratio (SNR) limited and that its performance is superior to convolutional coding. The reliability of short frames, with 0.16–0.5 s transmission time, and long frames, with spectral efficiency up to 0.1 b/s/Hz, are evaluated in the five replay channels of the Watermark benchmark over varying SNR and SNR per bit, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$E_{b}/N_{0}$</tex-math></inline-formula> . Synchronization is solved with a sliding hypothesis approach and the results show a FER <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\lesssim 1 \%$</tex-math></inline-formula> for <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">all</i> Watermark channels, where the robustness is significantly improved by either increasing the frequency separation of tones or lowering the code rate and extending the frame length. The performance compares favorably to methods found in the literature, particularly for the less-benign channels of the benchmark.

Recognition method for the bionic camouflage cetacean whistle modulated by CPMFSK signals

Bionic covert camouflage underwater acoustic communication has drawn great interests in recent years as a promising way for covert underwater acoustic communication. However, there is little relevant literature to research the recognition of bionic camouflage communication signals (BCCS). Concentrating on the countermeasures for the BCCS, this paper proposes a recognition method for a bionic cetacean whistle signal modulated by continuous phase multiple frequency shift keying (CPMFSK) signal. Based on the features that CPMFSK modulated whistle signals carry the information by imitating the tremble phenomenon of the real whistles, a method is designed to extract a tremble signal which vibrates among the time–frequency contour (TFC) of cetacean whistles. As the tremble signal of the real cetacean whistle and bionic whistle has obvious time, and frequency distinction, focusing on these distinctions, characteristics like normalized power spectrum mean, wiener entropy, etc. are extracted as the characteristic vectors for SVM classification to achieve recognition. Simulations demonstrate the accuracy of the recognition method in different conditions, including modulation parameters, SNR, and underwater acoustic channels.

Hadamard–Viterbi Joint Soft Decoding for MFSK Underwater Acoustic Communications

Multiple Frequency-Shift Keying (MFSK) has been used widely for underwater acoustic communications due to its low complexity and channel robustness. However, the traditional MFSK has the limitation of a low bit rate compared with coherent acoustic communication. To increase the bit rate, this study designs a new MFSK with the concept of orthogonal frequency division multiplexing (OFDM). We also adopt a channel-concatenated coding to resist the multipath interference and design the iterative joint decoding. The channel-concatenated coding consists of a Hadamard code and a convolutional code. Correspondingly, the iterative joint decoding uses the Hadamard–Viterbi joint soft decoding framework with a newly designed branch metric, which uses the Hadamard structure. As an important preprocessing link for a received signal, frame synchronization and Doppler compensation are also described in detail in this study. Simulations and experiments are conducted to show the effectiveness of the proposed MFSK underwater acoustic communications.

A Method for Underwater Wireless Data Transmission in a Hydroacoustic Channel under NLOS Conditions

Wireless data transmission in the hydroacoustic channel under non-line-of-sight (NLOS) propagation conditions, for example, during a wreck penetration, is difficult to implement reliably. This is mostly due to the multipath propagation, which causes a reduction in the quality of data reception. Therefore, in this work an attempt has been made to develop a reliable method of wireless underwater communication test it under the NLOS conditions. In our method, we used multiple frequency-shift keying (MFSK) modulation, sending a single bit on two carriers, and diversity combining. The method was tested in laboratory conditions which simulated underwater signal propagation during the penetration of the wreck. The propagation conditions were investigated by determining the impulse responses at selected measurement points using the correlation method. Additionally, for comparison, the data transmission quality was determined by the bit error rate (BER) under the same conditions using direct sequence spread spectrum (DSSS) and binary phase shift keying (BPSK) modulation. The obtained results confirmed the usefulness of the application of the developed method for wireless data transmission in a hydroacoustic channel under NLOS conditions.

Design of a General Hardware in the Loop Underwater Communication Emulation System

Underwater acoustic communication plays an important role in underwater wireless sensor network. Different from terrestrial radio channel, modeling of underwater acoustic channel is very challenging due to its unique and dynamic characteristics. In order to verify the proposed acoustic communication algorithms, a general emulation platform which can reduce the verification cost has a wide application prospect. In this paper, we design a general hardware in the loop underwater communication emulation system based on the LabVIEW and MATLAB software and real acoustic transducer. In the emulation system, LabVIEW calls MATLAB script to achieve algorithm implementation, and then uses DAQmx to send and receive data through the acquisition card. The proposed system supports a variety of modulation and demodulation methods, such as multiple frequency-shift-keying(MFSK), multi-carrier frequency-shift-keying(MCFSK), orthogonal frequency division multiplexing(OFDM), etc. In addition, in order to detect frame efficiently, we propose a light-weight frame synchronous algorithm. To verify the function of the systems, lake test and sea test are conducted for different algorithms.

Tell the Device Password: Smart Device Wi-Fi Connection Based on Audio Waves.

IoT devices are now enriching people’s life. However, the security of IoT devices seldom attracts manufacturers’ attention. There are already some solutions to the problem of connecting a smart device to a user’s wireless network based on the 802.11 transmission such as Smart Config from TI. However, it is insecure in many situations, and it does not have a satisfactory transmission speed, which does not mean that it has a low bit rate. It usually takes a long time for the device to recognize the data it receives and decode them. In this paper, we propose a new Wi-Fi connection method based on audio waves. This method is based on MFSK (Multiple frequency-shift keying) and works well in short distance, which enables the correctness and efficiency. In addition, audio waves can hardly be eavesdropped, which provides higher security than other methods. We also put forward an encryption solution by using jamming signal, which can greatly improve the security of the transmission.

Time reversal MFSK acoustic communication in underwater channel with large multipath spread

It has been recognized that, compared with coherent acoustic communication, Multiple Frequency Shift Keying (MFSK) underwater acoustic communication offers the advantages of low complexity, easy-implementation and channel tolerance, but it is subject to significant performance degradation caused by inter-symbol interference (ISI) when the multipath spread is larger than symbol duration. The time reversal is capable of effectively suppressing the channel multipath by the means of temporal-spatial focusing, which has been widely examined and applied in coherent underwater acoustic communication systems. However, there is a lack of investigations to incorporate the time reversal with MFSK communication. In this paper, we report a multi-channel time reversal MFSK receiver, in which the channel estimate is initially obtained and periodically updated by matched filtering of the sync preamble, meanwhile, down-conversion is adopted to reduce computational complexity. The performance of the proposed receiver is evaluated in a shallow water channel with severe multipath spread, in terms of bit error rate (BER) and robustness upon time variations.

The design and implementation of automotive radar system based on MFSK waveform

As a driving aid system, automotive radar plays a more and more important role in reducing traffic accidents. In this paper, a simple and efficient automotive radar system based on MFSK (Multiple frequency shift keying) is designed, the system structure and implementation algorithm is presented. This system uses FPGA as the signal processing unit to ensure the response speed. In addition, the designed MFSK waveform algorithm achieved high precision and unambiguous measurement. The effectiveness of the system is verified by experiments and field measurements.

Indoor positioning and life detection by using asynchronous multiple frequency shift keying radar

Indoor positioning and life detection using radio frequency has been widely researched; however, to achieve both indoor positioning and life detection has been a very challenging task until now. By careful design of the waveform and a novel detection algorithm, asynchronous multiple frequency shift keying (A-MFSK) is proposed to solve this task for the first time, which can operate between an MFSK mode and a single tone continuous wave mode, providing a possibility of A-MFSK for this task. Detailed explanation about the detection algorithm is given. Simulations and measurements results of both modes demonstrate that A-MFSK has the capability of indoor positioning and life detection.

77 GHz waveform generator with multiple frequency shift keying modulation for multi‐target detection automotive radar applications

A waveform generator for a 77 GHz automotive radar that uses multiple frequency shift keying (MFSK) modulation is presented. The use of this modulation can improve the detection ability of radar applications in multi-target situations. The proposed generator consists of a conventional 77 GHz Σ-Δ fractional-N synthesiser and MFSK modulation control logic (MMCL). The key innovation is the introduction of the MMCL, which has the ability to track the linear frequency increase while generating the frequency shift keying in each time step. Prior to realising the hardware implementation, a behavioural simulation was evaluated. In addition, a 77 GHz generator module was designed using 130 nm CMOS technology. In a chirp time of 6 ms, there were a total of 128 modulation steps. The bandwidth and frequency step of the chirp were 100 MHz and 300 kHz, respectively.

In brief

PAGE 644 Researchers in Hong Kong have created flexible pentacene organic thin-film transistors (OTFTs) with HfYO gate dielectric at room temperature on adhesive vacuum tape. Their results suggest that this method, and the combination of materials, are promising for high-performance flexible pentacene OTFTs. Such TFTs could be used in adhesive RFID devices and flexible bending and strain sensors. PAGE 642 An in-situ calibration method for dual-mask spatial light modulators (SLMs) is presented in work from Germany. Using an evolutionary algorithm to determine phase-voltage relationships of the SLM liquid-crystal masks, it avoids the ambiguity of manual methods and the separate setups required by interferometry approaches. The proposed method simplifies calibration of SLM pulse shapers for applications including ultra-short pulse shaping, particularly using external-cavity semiconductor lasers with intra-cavity pulse-shaping. Flexible and adhesive pentacene OTFTs made at room temperature with vacuum tape and HfYO PAGE 595 A waveform generator for a 77-GHz automotive radar using multiple frequency shift keying (MFSK) modulation is demonstrated in research from Korea. MFSK modulation can improve detection in multi-target applications such as adaptive cruise control. The key innovation in this generator is the use of MFSK modulation control logic (MMCL), which has the ability to track the linear frequency increase while generating the FSK in each time step. The method provides accurate in-situ calibration of SLMs for applications such as high-resolution femtosecond pulse shaping PAGE 601 Researchers in China present a high-power cavity-backed helical antenna with unit ceramic radome. Using a unit ceramic radome in a thin-wall structure, a vacuum seal for a single element is achieved and using a backed cavity, mutual coupling among elements is significantly reduced. S-band prototypes applied in 16- and 256-element array antennas demonstrate circularly polarised radiation in the axial direction at 2.7-3.0 GHz and single element average power-handing capacity of at least 4.7 MW. The waveform generator uses MMCL to improve multi-target detection for automotive applications like adaptive cruise control PAGE 640 The first results of using SiGe microwave phototransistors in radio-over-fibre applications is presented by researchers in France. They show error-free transmission of a 3.08 Gbps IEEE 802.15.3c HSI signal at 5 GHz, after cycle redundancy check correction, demonstrating the potential of these devices for radio-over-fibre links. Individually vacuum sealed and backed for reduced coupling, each unit has an average power-handling capacity of at least 4.7 MW The results are the first reported that concentrate on the devices in a radio-over-fibre application context

New chirp sequence radar waveform

The general requirement in the automotive radar application is to measure the target range R and radial velocity v <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> simultaneously and unambiguously with high accuracy and resolution even in multitarget situations, which is a matter of the appropriate waveform design. Based on a single continuous wave chirp transmit signal, target range R and radial velocity v <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> cannot be measured in an unambiguous way. Therefore a so-called multiple frequency shift keying (MFSK) transmit signal was developed, which is applied to measure target range and radial velocity separately and simultaneously. In this case the radar measurement is based on a frequency and additionally on a phase measurement, which suffers from a lower estimation accuracy compared with a pure frequency measurement. This MFSK waveform can therefore be improved and outperformed by a chirp sequences waveform. Each chirp signal has in this case very short time duration T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">chirp</sub> . Therefore the measured beat frequency f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</sub> is dominated by target range R and is less influenced by the radial velocity v <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> . The range and radial velocity estimation is based on two separate frequency measurements with high accuracy in both cases. Classical chirp sequence waveforms suffer from possible ambiguities in the velocity measurement. It is the objective of this paper to modify the classical chirp sequence to get an unambiguous velocity measurement even in multitarget situations.

Nonbinary convolutional codes and modified M-FSK detectors for power-line communications channel

The Viterbi decoding algorithm, which provides maximum ¿ likelihood decoding, is currently considered the most widely used technique for the decoding of codes having a state description, including the class of linear error-correcting convolutional codes. Two classes of nonbinary convolutional codes are presented. Distance preserving mapping convolutional codes and M-ary convolutional codes are designed, respectively, from the distance-preserving mappings technique and the implementation of the conventional convolutional codes in Galois fields of order higher than two. We also investigated the performance of these codes when combined with a multiple frequency-shift keying (M-FSK) modulation scheme to correct narrowband interference (NBI) in powerline communications channel. The modification of certain detectors of the M-FSK demodulator to refine the selection and the detection at the decoder is also presented. M-FSK detectors used in our simulations are discussed, and their chosen values are justified. Interesting and promising obtained results have shown a very strong link between the designed codes and the selected detector for M-FSK modulation. An important improvement in gain for certain values of the modified detectors was also observed. The paper also shows that the newly designed codes outperform the conventional convolutional codes in a NBI environment.

Underwater Acoustic Communication of FH-MFSK Method with Multiple Orthogonal Properties

본 논문에서는 다중 직교 특성을 갖는 FH-MFSK(Frequency-Hopped Multiple Frequency Shift Keying) 방식의 수중음향통신을 제안한다. 일반적으로 FSK(Frequency Shift Keying) 방식은 처리 과정이 단순하지만 다중 경로 전달로 인해 발생하는 인접 심볼간 간섭에 취약하다. 본 논문에서는 전송하고자 하는 심볼 수와 동일한 서로 직교 성질을 갖는 코드들을 생성한다. 이 코드 값들은 각각 다수의 주파수들에 대응된다. 이러한 다중 직교 코드를 생성하기 위해 m-sequence를 이용하였다. 실험을 통해 제안된 방법의 성능을 기존의 MFSK 방식과 비교하였다. 100 bps 전송율에서 제안한 방법은 기존의 방법보다 오차율이 6 ~ 10 % 낮게 나타났다. In this paper, we propose an underwater acoustic communication of FH-MFSK(Frequency-Hopped Multiple Frequency Shift Keying) system with multiple orthogonal property. Generally, the processing of FSK(Frequency Shift Keying) method is simple, but it is vulnerable to ISI (Inter-Symbol Interference) caused by multipath transmission. In this paper, the orthogonal codes are generated with the same number of transmitting symbols, and these codes are corresponding to multiple frequencies. We used m-sequence to generate multiple orthogonal codes. We compared the performance of proposed method with conventional MFSK method via the experiment. As a result, we confirmed that the proposed method shows 6~10 % lower error rate at 100 bps than conventional method.

Robust Iterative Noncoherent Reception of Coded FSK over Block Fading Channels

An iterative noncoherent receiver is developed for bit-interleaved coded orthogonal multiple frequency-shift keying (FSK) over block fading channels. The receiver uses the Expectation Maximization (EM) algorithm to jointly estimate the received amplitude and noise spectral density of each block. The received symbols and their corresponding channel estimates are passed through a soft-output demapper, deinterleaved, and decoded. Soft-outputs from the decoder are passed back to the channel estimator and demapper to refine estimates of the channel and bit likelihoods, respectively. Several techniques for reducing the estimator's complexity are discussed, and the performance is assessed through simulation.

Optimal Frequency Hopping Sequences: A Combinatorial Approach

Frequency hopping multiple access (FHMA) spread-spectrum communication systems employing multiple frequency-shift keying (MFSK) as data modulation technique are investigated from a combinatorial approach. A correspondence between optimal frequency hopping (FH) sequences and partition-type difference packings is first established. By virtue of this correspondence, FHMA systems with a single optimal FH sequence each are constructed from various combinatorial structures such as affine geometries, cyclic designs, and difference families. Combinatorial recursive constructions are also presented. Many new infinite series of optimal FH sequences are thus obtained. These new FH sequences are also useful in ultra wideband (UWB) communication systems.

Performance of MFSK Signals With Postdetection Square-Law Diversity Combining in Arbitrarily Correlated Nakagami-&amp;lt;tex&amp;gt;$m$&amp;lt;/tex&amp;gt;Fading Channels

This letter presents an analysis of the error probability for noncoherent orthogonal multiple frequency-shift keying (MFSK) signals with postdetection square-law combining (SLC) when the signals transmitted over additive white Gaussian noise (AWGN) and slow frequency-nonselective arbitrarily correlated Nakagami-m fading channels. New exact expressions in a onefold integral for the probability of error of MFSK signals with postdetection square-law diversity combining operating in AWGN channel as well as in arbitrarily correlated Nakagami-m fading channels are derived. The effects of arbitrarily values of fading severity parameter m and the arbitrarily correlation between the L diversity channels are considered. The derived expressions can be easily computed, and hence, can be usefully exploited in the performance evaluation of digital mobile radio systems.

DEVELOPMENT OF A CLASSIFIER FOR MFSK SIGNALS OVER TIME VARYING CORRELATED FADING CHANNELS UNDER CLASS- A IMPULSIVE NOISE

In a recent work [1], we developed and analyzed a classifier for multiple M-ary Frequency Shift Keying (MFSK) signals that traveled over a static frequency non-selective Rayleigh fading channel and are contaminated with additive white Gaussian noise. In this paper, we extend the classifier to the case in which the MFSK signals traveled over a time varying flat correlated fading channel and contaminated with impulsive noise. Specifically, the considered impulsive noise is the Middelton's class A noise model. The classifier is based on approximating the likelihood function (LF) of the received signal. We use complex envelope representation of the signals and noise to derive the likelihood function. The Karhunen-Loeve expansion is used to have a more precise description of the fading process. Simulation experiments are illustrated to evaluate the performance of the classifier and to validate the theoretical developments.

Advanced frequency hopping modulation for spread spectrum WLAN

A wireless LAN standard developed by IEEE committee P802.11 operates in the unlicensed 2.4 GHz ISM band. This band is a very hostile environment due to many unpredictable interference sources, such as microwave ovens, utilizing the same frequency bands. At the same time the allowed signal power density that can be used is limited in order to minimize the interference to other users in the same band. In order to avoid these interference and keep a low signal power density the standard supports both direct sequence (DS) and frequency hopping (FH) modulation for these applications. The new test beds for multimedia wireless (WLANs) also use FH modulation. We analyze the performance of a modification of the FH multiple frequency shift keying (MFSK) system that includes a multitone multiamplitude MFSK signal, designated as amMFSK modulation. In this case, in order to meet the transmitted power density limits imposed in the ISM band, the signal energy is split into m separate tones. This makes the system more vulnerable to noise and fading, but still the overall flow of useful information will be increased. The results demonstrate that under the large range of the signal, channel and interference parameters this system offers better performance.

Performance of asynchronous slow frequency-hop multiple-access networks with MFSK modulation

The performance of asynchronous slow frequency-hop spread-spectrum multiple-access networks where each user transmits L, M-ary symbols per hop using M-ary frequency-shift keying (FSK) modulation with noncoherent demodulation is investigated. Expressions for the decision variables are derived for a given multiple FSK (MFSK) symbol within a hop hit by K' interfering users under additive white Gaussian noise and Rayleigh fading channel models. For the special case when M=2, an accurate analytic approximation for the average error probability is derived as a function of L and K' and semianalytic Monte Carlo simulations are performed to estimate the probability of error for M larger than 2. The results are used to investigate the dependence of the average symbol error probability on L and M. Finally, the effect of enforcing phase transition between the MFSK symbols within a hop is investigated.