Frequency Shift Keying System Research Articles

A Human Tracking and Physiological Monitoring FSK Technology for Single Senior at Home Care.

Respiration monitoring for apnea diagnosis and movement tracking for physical activity analysis are essential and valuable indicators of underlying medical conditions in senior health care. Compared with other health sensing technologies, radar has shown its advantages in terms of non-contact implementation, immunity to ambient light and temperature changes, hardware simplicity, and long range coverage. Among various radar types, frequency-shift keying (FSK) radar inherits the ability to measure respiration from Doppler radar, while also having the ability to track the absolute range of a moving target with much less bandwidth requirement than frequency modulated continuous wave (FMCW) radar and ultra-wideband (UWB) radar. Therefore, in this paper, an FSK radar system is employed for both remote respiration monitoring and absolute range tracking. Fundamental theory and operating principle of FSK system are detailed. Respiration monitoring and range tracking experiments of a human subject were performed in an indoor environment. Results are presented to demonstrate the practical feasibility of the FSK sensing technology being applied to single senior home care applications.

The Effects of Multiple Carrier Frequency Offsets on the Performance of Virtual MISO FSK Systems

In this letter, a virtual multiple-input single-output (VMISO) network employing non-coherent frequency shift keying (FSK) is considered. In the VMISO network, spatially separated single-antenna nodes transmit the same information cooperatively to a single receiver where each received signal is affected by an independent carrier frequency offset (CFO). The existing works in this area assume a perfect carrier synchronization between the nodes. However, in this letter, the effects of CFOs on the performance degradation of this network are analyzed. For that purpose, the expression for the probability of symbol error has been derived. The results indicate that the performance is degraded due to CFOs, which is dependent upon the magnitude of CFOs, signal-to-noise ratio (SNR), number of transmitting nodes, and the modulation order of FSK. At high SNR, the CFOs affect the system severely and the performance margin is minimum.

Performance study of fast frequency-hopped/M-ary frequency-shift keying systems with timing and frequency offsets over Rician-fading channels with both multitone jamming and partial-band noise jamming

In this study, the effects of timing and frequency offsets on bit-error rate (BER) performance of fast frequency-hopped M-ary frequency-shift keying communication systems over Rician-fading channels with both multitone jamming (MTJ) and partial-band noise jamming (PBNJ) are investigated. Analytical BER expressions are derived for both linear-combining and product-combining receivers. Numerical results show that under both MTJ and PBNJ conditions, the BER performance falls between the two extreme cases, in which either MTJ or PBNJ presents. It is found that the BER performance is severely degraded as the timing or frequency offset increases. The product-combining receiver is found to be more sensitive to the timing and frequency offsets than the linear-combining receiver. It is also observed that for the linear-combining receiver, the optimum diversity order increases as the timing and frequency offset increases over both Rician-fading and Rayleigh-fading channels; however, the reverse is true for the product-combining receiver.

Study of FSK/IM orthogonal modulation system with optical Manchester-coded payload

We study the performance of an orthogonal modulation system with frequency-shift keying (FSK) label and optical Manchester-coded (MC) payload. Simulation result shows that by introducing an optical MC payload, the available extinction ratio (ER) value of a FSK and intensity modulation (IM) orthogonal modulation system can be improved from 5 to 9 dB for system optimization, exhibiting great advantages over the traditional non-return-to-zero (NRZ) payload. Besides, the bit error rate (BER) characteristics of both label and payload show a more remarkable advantage than that of NRZ coding, verifying itself as a perfect candidate for the payload coding method in orthogonal modulation systems.

Error probability analysis of FFH/MFSK receivers over frequency-selective Rician-fading channels with partial-band-noise jamming

An optimum maximum-likelihood (ML) receiver structure for a fast frequency-hopped M-ary frequency-shift keying system over frequency-selective Rician-fading channels against partial-band-noise jamming and additive white Gaussian noise is proposed. In addition, we propose two suboptimum ML receivers and derive their corresponding analytical bit-error rate expressions.

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.

Evaluation of optimal bandwidth in optical FSK system influenced by laser phase noise

In this paper, an optical frequency shift keying (FSK) system with TFS (two-filter structure), also known as dual-filter FSK, is observed in the presence of laser phase noise. Sensitivity of the receiver is shown as a function of intermediate frequency (IF) bandwidth and a bandwidth of the low-pass postdetection filter. It is shown that there is an optimal pair of bandwidths which minimizes required sensitivity; a few figures for different amounts of phase noise are given. The results in this paper are based on truncated Taylor expansion method and a method based on complex analysis is used to evaluate the integrals involved.

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 linecoded optical heterodyne FSK systems with nonuniform laser FM response

A simple theoretical analysis for evaluating the performance of linecoded optical frequency shift keying (FSK) systems is presented. It accounts for the combined effects of laser phase noise, receiver noise, and nonuniform BM response of distributed feedback lasers. A close form expression for the random frequency noise due to the combined effect of laser nonuniform FM response and phase noise is developed. The analysis is carried out for three different linecoding schemes, i.e., alternate mark inversion, Miller code or delay modulation, and Manchester coding, to investigate the efficacy of the line coding schemes in counteracting the effect of nonflat FM response. Theoretical and simulation results show that the sensitivities of linecoded FSK systems are within 0.7 and 0.4 dB for single-branch and dual-branch detection, respectively, at a bit error probability of 10/sup -9/ relative to the random non-return to zero FSK with flat FM response.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A Performance Comparison of Optical Heterodyne OOK and FSK Communications Systems

An error probability analysis is performed for two types of optical communications systems employing spread-spectrum code-division multiple-access (CDMA) techniques. Spread-spectrum is specifically employed to overcome additive noise and increase system user capacity. The two types of systems considered are a coherent optical heterodyne on-off keying (OOK) system using optical orthogonal spreading code sequences (OOCs), and a coherent optical heterodyne frequency shift keying (FSK) system using randon spreading codes. The OOK system spreads the signal optically, and the FSK system spreads the signal electromagnetically before converting it to an optical signal for transmission. System performance is degraded by laser phase noise, additive Gaussian multiuser interference, and additive Gaussian receiver noise. Single user OOK system performance for different linewidth-to-bit rate ratios is analyzed over a range of both signal-to-noise-ratios (SNR) and normalized decision thresholds. This analysis is used to determine which noise source dominates system performance and the maximum acceptable linewidth-to-bit rate ratio. The limiting linewidth-to-bit rate ratio is then used in previously derived equations to obtain the performance of the coherent optical heterodyne OOK-CDMA system for various spreading code length and numbers of users. An error probability analysis is then performed for the coherent optical heterodyne FSK-CDMA system for various spreading code length and numbers of users. Finally, the performance of the two systems is compared, and it is shown that optical FSK-CDMA systems perform better than optical OOK-CDMA systems

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. >

Penalty free biphase linecoding for pattern independent FSK coherent transmission systems

Biphase coding is used to eliminate the unwanted influence of nonuniform laser characteristics in frequency-shift-keying (FSK) transmission systems. Compared to other (ternary) linecoding schemes, biphase has the advantage that it does not give a 3-dB sensitivity penalty when properly decoded in the receiver. This has been demonstrated in a 140-Mb/s 280-Mbaud transmission experiment. The receiver features a new type of reliable unambiguous clock extraction. Due to the compact IF spectrum, as compared with ternary linecoding schemes, biphase equipped FSK systems are especially suited for efficiently spaced coherent multichannel (CMC) systems. FSK heterodyne transmission experiments show a sensitivity eta P of -56.7 dBm for 2/sup 10/-1 pseudorandom patterns, only 4.8 dB from the shot-noise limit.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Highly reproducible ridge waveguide multielectrode DFB lasers for optical communication systems

Highly reproducible 1.5μm multielectrode DFB lasers have been fabricated for use as transmitters in frequency shift keying (FSK) transmission systems. These devices were grown using atmospheric pressure metal-organic vapour phase epitaxy and are based on the ridge waveguide structure with a 900μm long cavity. In a 2.4Gbit/s FSK system, sensitivities of −27dBm were obtained for devices from different wafers under identical biasing conditions. This is the first time that mulltielectrode DFB lasers have demonstrated the degree of reproducibility required for practical systems.

Performance of directly modulated DFB lasers in 10-Gb/s ASK, FSK, and DPSK lightwave systems

A comparison is presented of the performance of amplitude-shift-keying (ASK), frequency-shift keying (FSK), and differential-phase-shift-keying (DPSK) lightwave systems which operate at 10 Gb/s with directly modulated 1550-nm distributed feedback (DFB) laser transmitters and conventional 1310-nm dispersion-optimized fiber. Computer modeling techniques were used to accurately simulate the amplitude modulation response and the frequency modulation response of DBF lasers. The system performance is evaluated from simulated eye patterns for both direct and heterodyne detection. With the narrow-optical spectral widths of these signal formats, fiber chromatic dispersion limits up to 70 km were obtained for transmission at 1550-nm using conventional 1310-nm optimized fiber.< <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>

Adjacent channel and cochannel interferences in CPFSK systems with nonlinear transmitters and limiter-discriminator detection

The performance of continuous-phase FSK (frequency-shift keying) systems with rectangular modulation pulse shaping and limiter-discriminator detection is analytically evaluated in the presence of transmission nonlinearities as well as adjacent channel and cochannel interference. Consideration of modulation pulses with length tau , shorter than symbol time, T, is investigated. The algorithm developed to evaluate bit-error probability shows that the choice tau /T=1, and even more so in the presence of adjacent channel interference. Moreover, for tau /T=0.5, numerical results are reported that describe system performance under different working conditions and can be used to develop design criteria. >

Error-correcting codes and nonlinear diversity combining against worst case partial-band noise jamming of frequency-hopping MFSK systems

Error probability analyses are performed for a coded M-ary frequency-shift keying system (MFSK) using L hops per M-ary word frequency-hopping spread-spectrum waveforms transmitted over a partial-band Gaussian noise jamming channel. The bit error probabilities are obtained for a square-law adaptive gain control receiver with forward-error-control coding under conditions of worst-case partial-band noise jamming. Both thermal noise and jamming noise are included in the analyses. Performance curves are obtained for both block codes and convolutional codes with both binary and M-ary channel modulations. The results show that thermal noise cannot be neglected in the analysis if correct determinations of the optimum order of diversity and the worst-case jamming fraction are to be obtained. It is shown that the combination of nonlinear combining, M-ary modulation, and forward-error-control coding is effective against worst-case partial-band noise jamming.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Sensitivity penalty in multichannel coherent optical communications

The error rates and sensitivity penalties for multichannel coherent optical communications systems are evaluated for amplitude-shift keying (ASK), phase-shift keying (PSK), and frequency-shift keying (FSK) modulation, taking into account adjacent channel interference. Both time-domain and frequency-domain analysis are used, the latter being based on a Gaussian approximation. Both techniques yield similar results for sensitivity penalties below 1 dB. For FSK systems, larger values of the modulation index Delta do not necessarily lead to larger channel spacings. ASK and PSK systems both require larger channel spacings than FSK systems with Delta =1. The study was conducted for sources with linewidths narrow enough so that phase noise does not degrade the performance of receivers with matched filter demodulators. >

The effect of spurious intensity modulation in semiconductor diode lasers on the performance of optical heterodyne frequency shift-keyed communications systems

Analytical expressions are derived for the bit-error rate (BER) of an <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</tex> -ary frequency shift-keyed (FSK), heterodyne, optical communication system with noncoherent demodulation in the presence of spurious intensity modulation (SIM) and frequency noise. The SIM degradation of an FSK system, implemented with semiconductor diode lasers, is estimated for lasers with zero and nonzero linewidths and will be discussed for a distributed feedback laser operating at 1.5μm and a channeled substrate planer laser operating at 0.83 μm. The SIM power penalty is typically less than 1 dB, but can exceed 1 dB for 2-, 4-, and 8-ary FSK at data rates above 1 Gbit/s.

Periodic switching diversity effect on co-channel interference performance of a digital FM land mobile radio

The effect of periodic switching diversity on the bit error rate (BER) performance of a binary frequency-shift keying (FSK) system in the presence of co-channel interference is described. The distribution of the signal-to-interference energy ratio per bit presented to the FM detector is found and the diversity effect on the BER performance in a Rayleigh fading environment is analyzed. The diversity effect on the BER performance in a Manchester-coded FSK system with limiter-discriminator detection is verified by laboratory simulation tests using a Rayleigh fading simulator.