Narrow-band Frequency Modulation Research Articles

Simulation and Analysis of Frequency Modulation System in MATLAB as Practical Assessment Method for Communication Engineering Course

COVID-19 pandemic hit has raised new challenges for Outcome-Based Education (OBE) system since the normalization of the online education delivery. Still, this era of endemic imposes challenges in satisfying OBE requirements, especially the students’ practical assessments. As an essential part of Communication Engineering, Frequency Modulation (FM) fundamental can be theoretically and mathematically explained during the online classes. However, its practical assessment needs to be done experimentally. Since buying the real devices and tools needed to create a complete FM system consumes high cost, software simulation is the best solution to accommodate the learning processes for all students. Hence, aided by the MATLAB simulation and analysis approaches, this paper presents the implementation of FM practical assessment at Universiti Teknologi MARA (UiTM) as an institute of higher education. For this task, students have built the FM system by using both mathematical and Simulink model. The model also emphasized students on the association between FM’s important parameters: modulating frequency, modulation index, frequency deviation, and bandwidth, with the type of FM, Narrow Band FM (NBFM) or Wide Band FM (WBFM). Results for all model configurations are recorded and analyzed accordingly. From this practical activity, students have demonstrated a better attainment for this course’s Program Outcome (PO) as compared to the conventional assessment methods.

Accurate optical parameter extraction procedure for broadband near-infrared spectroscopy of brain matter

Modeling behavior of broadband (30 to 1000 MHz) frequency modulated near-infrared (NIR) photons through a phantom is the basis for accurate extraction of optical absorption and scattering parameters of biological turbid media. Photon dynamics in a phantom are predicted using both analytical and numerical simulation and are related to the measured insertion loss (IL) and insertion phase (IP) for a given geometry based on phantom optical parameters. Accuracy of the extracted optical parameters using finite element method (FEM) simulation is compared to baseline analytical calculations from the diffusion equation (DE) for homogenous brain phantoms. NIR spectroscopy is performed using custom-designed, broadband, free-space optical transmitter (Tx) and receiver (Rx) modules that are developed for photon migration at wavelengths of 680, 780, and 820 nm. Differential detection between two optical Rx locations separated by 0.3 cm is employed to eliminate systemic artifacts associated with interfaces of the optical Tx and Rx with the phantoms. Optical parameter extraction is achieved for four solid phantom samples using the least-square-error method in MATLAB (for DE) and COMSOL (for FEM) simulation by fitting data to measured results over broadband and narrowband frequency modulation. Confidence in numerical modeling of the photonic behavior using FEM has been established here by comparing the transmission mode's experimental results with the predictions made by DE and FEM for known commercial solid brain phantoms.

Magnetic force microscopy of alternating magnetic field gradient by frequency modulation of tip oscillation

A new magnetic force microscopy (MFM) technique for measuring alternating magnetic field (ac magnetic field) was proposed by using frequency modulation (FM) phenomenon of tip oscillation. We detected a narrowband FM phenomenon in the tip oscillation of a high-coercivity MFM tip by applying an ac magnetic field to the tip by using a metal-in-gap (MIG) type ring head. In the experiment, the MFM tip was driven at a constant frequency fc near the resonant frequency of the cantilever by a piezoelectric element, and the ac magnetic field with a frequency fm up to 10 kHz was applied to the MFM tip. Two sideband spectra with a frequency of fc±fm were observed by applying ac magnetic field. The intensity of sideband spectra increased linearly with increasing applied current value of the MIG head. It was observed that FM occurred from the analysis of frequency spectra of the MFM signals. This FM phenomenon is caused by the force applied on the cantilever by the field gradient of the head. The FM phenomenon is understood by solving the differential equation for the harmonic oscillator of which the effective spring constant is changed periodically by ac magnetic field. The FM phenomenon can be used for imaging ac magnetic fields.

Limiter discriminator-detected GMSK with FM and GMSK interference in a land mobile channel

This paper addresses Gaussian minimum-shift keyed (GMSK) receiver performance analysis for limiter discriminator detection with cochannel interference resulting from a combined cellular voice and packet radio network. A specific example is cellular digital packet data (CDPD), which shares spectrum with cellular voice users; thus, the CDPD receiver will see both narrow-band frequency modulation (NBFM) voice and GMSK data interference. Previous studies investigated the performance of a GMSK receiver with a single GMSK interferer and multipath delay. In this paper, we extend earlier work to multiple Rayleigh fading (Doppler spread) interferers having NBFM (f/sub dm/=12 kHz) analog modulation and/or GMSK modulation. Probability of bit-error expressions are derived for the frequency modulation (FM) and GMSK interferer cases assuming medium-to-high signal-to-noise ratio regions. For scenarios of from one to six NBFM interferers, having the same total power, a corresponding Gaussian approximation is within 1.5 dB. Simulation results are also presented for various combinations of FM and GMSK interference. FM interference is only slightly worse than GMSK interference. Delay spread representing an urban scenario resulted in only a slight increase in the error floor.

A narrow-band CMOS FM receiver based on single-sideband modulation IF filtering

A narrowband frequency-modulation (FM) receiver with high selectivity is implemented using a switched-capacitor baseband intermediate-frequency (IF) filter. Measured adjacent channel selectivity was more than 46 dB, and input sensitivity with -30-dB quieting level was 5 mV without considering a front-end radio-frequency amplifier stage. A fully integrated experimental receiver needs no adjustment or trimming, relying instead on a single reference clock. The prototype chip occupies 12 mm/SUP 2/ and dissipates 20 mW with a 5-V supply.

Arbitrary spectral separation of upper and lower sidebands in linear modulation

A technique to spectrally separate the sidebands in amplitude and narrow-band frequency modulation is presented. With this technique, the upper and lower sidebands can be right and left shifted respectively by an arbitrary amount and thus either sideband can be selected by a bandpass filter.

Helium-cadmium laser with intracavity phase modulation

A study was made of the spectral and time characteristics of a helium-cadmium laser operated under phase-locked and frequency-modulated conditions. Narrow-band frequency modulation should be useful in various physics experiments and in laser communication and radar systems. Stable stimulated emission of a single pulse train was possible in the phase-locked modulation range.

Letter: Masking with narrow-band FM noise.

Masked thresholds were measured for signal frequencies below, within, and above two 190-Hz noise bands centered arithmetically at 1125 Hz. One noise band was computer synthesized and had amplitude fluctuations characteristic of analog noise bands typically used in masking experiments. The other noise band, matched in spectrum and level to the synthesized noise band, was generated by a frequency modulation (FM) process. The resulting waveform was free of envelope fluctuations. Masked thresholds in the FM noise were 5–10 dB lower than in the synthetic noise in the flat portions of the spectra. Synthesized noise resulted in trapezoidal appearing audiograms. The FM noise audiogram tended to be unimodal. Results are discussed with reference to envelope detection hypotheses.

Intelligibility Improvement of Analog Communication Systems Using an Amplitude Control Technique

Mobile satellite relay voice communications systems must provide high quality and reliable voice communications using relatively simple and inexpensive mobile equipment and easily achievable effective isotropic radiated power. High noise level reception will occur with analog voice communication systems operating over a power-limited link. At high noise levels, the low-level speech phonemes become masked by noise, which results in reduced speech intelligibility. In addition, a listener subjected over an extended period of time to this high noise level can become discomforted to the extent that his ability to understand what is being communicated is significantly reduced. An amplitude control technique has been employed for use with analog voice communication systems, which improves low-level phoneme reception and eliminates the received noise between words and syllables. Tests were conducted at the NASA Goddard Space Flight Center on a narrow-band frequency-modulation simplex voice communication channel employing the amplitude control technique. Presented for both the modified rhyme word tests and the phonetically balanced word tests are a series of graphical plots of the tests' score distribution, mean, and standard deviation as a function of received carrier-to-noise power density ratio. At low received carrier-to-noise power density ratios, a significant improvement in the intelligibility was obtained. A voice intelligibility improvement of more than 2 dB was obtained for the modified rhyme test words, and a voice intelligibility improvement in excess of 4 dB was obtained for the phonetically balanced word tests.

Highly Efficient Voice Modulation For Low C/N0Communications Channels with Hard Limiting Repeaters

A highly efficient subcarrier modulation technique, suppressed clock pulse duration modulation (SCPDM) has been developed that outperforms narrow-band frequency modulation in very noisy channels. Developed primarily for hard limiting satellite repeaters, the technique utilizes a phase-shift key (PSK) carrier and phase-lock demodulators. The SCPDM technique is shown to be extremely useful and cost effective where the overall objective is to obtain maximum traffic rather than toll quality voice communication. Design considerations are discussed and test data from a typical hardware implementation are presented.

Optimum filters for narrow-band frequency modulation

A computer search was made for the optimum second- and third-order bandpass filters for use in narrow-band FM and PM systems. The optimum filter for minimum distortion was found to be near the Bessel filter. The results were fairly independent of modulation index and bandwidth.

Carrier Transmission of Binary Data in a Restricted Band

The spectra of digital frequency modulation (FM) signals have been observed to be narrow compared with the spectra of digital baseband signals or the corresponding amplitude modulation (AM) and phase modulation (PM) signals. This suggests a high efficiency of transmission in terms of occupied bandwidth for binary FM. Here the desirability of digital FM systems is investigated further with an examination of the probability of bit error. The FM receiver considered consists of a predetection filter, a limiter-discriminator, and a postdetection filter. New results are presented on the effect of predetection bandwidth restriction on the error performance of binary FM systems for various frequency deviations. Theoretical results have been obtained by a Fourier analysis of the distorted FM signals and by Rice's click analysis of FM noise. The data presented permits an optimum selection of system parameters such as frequency deviation ratio and predetection filter bandwidth. It is found that in narrow-band operation a peak-to-peak frequency deviation of about 0.7 times the bit rate and a bandpass filter bandwidth of about 1.0 times the bit rate yield a minimum probability of error. Experimental measurements have been made and there is, in general, good agreement with the theory. A comparison of the error performance of noncoherent binary FM, coherent AM, and coherent PM in a restricted band is made. Narrow-band noncoherent FM proves superior to AM in any bandwidth. In narrow-band operation, the noncoherent FM gives a somewhat better error performance than the coherent PM. For example, for an error rate of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-4</sup> and a bandpass filter bandwidth of one times the bit rate, the performance of a noncoherent FM system is 0.7 dB better than that of a coherent PM system.

Effect of multipath propagation on performance of narrowband frequency-modulation radiotelegraph systems

An explanation is given of the high error rate and poor diversity action experienced with narrowband frequency-modulation radiotelegraph systems with fading multipath signals, even in the absence of noise. The mechanism of occurrence of these residual errors is examined in detail, and they are shown to be due to a combined effect of the frequency modulation and spurious amplitude modulation of the signal, which together cause severe phase aberrations during the signal transitions at troughs in the fading. The spurious amplitude modulation is due to the removal of the higher-order frequency-modulation sidebands by the normal channel filters, and it is shown that a useful reduction in the residual-error rate and improved diversity operation may be achieved if the second-order sidebands reach the output of the channel-receiving filter at their correct level. A method of establishing this condition in a multichannel system with practical filters is described, but it is concluded that some increase in channel spacing in relation to modulation rate would be necessary to restrict interchannel interference.

Developments in long-distance H.F. point-to-point communications

The paper surveys technical developments in the point-to-point h.f. communication system of the British Post Office. In the first part, the development of radio-telegraph systems is discussed, and it is shown that these are tending to standardize on multichannel voice-frequency systems, using 2-tone for normally difficult routes (e.g. long routes subject to severe multipath effects) and narrow-band frequency modulation on the easier routes. Similarly, the development of radio-telephone systems is considered, and it is shown how the efficiency of these can be improved by the use of 4-wire privacy, with consequent simplification. The successful application in radio-telephony systems of a syllabic constant-volume amplifier, in conjunction with a complementary device at the receiving end regulated by a separate control channel, should-further increase their efficiency and may enable the radio terminals to be regarded as simple repeater stations. The second part describes modern systems which are to be provided at the rebuilt Leafield transmitting and Bearley receiving stations of the Post Office. The Leafield station will have two groups of six 30kW linear self-tuning transmitters, remotely controlled to radiate any of 25 synthesized frequencies and to have access to 10 aerial systems, each comprising two or three rhombic aerials. The Bearley station will have capacity for a large number of remotely controlled receivers with synthesized frequency control. New receivers will be of transistorized design, and the closer frequency tolerance provided by synthesized frequencies should, eventually, enable automatic frequency correction (a.f.c.) to be eliminated. It is planned to extend the control of the stations to the traffic terminals in due course, and this, together with the increased reliability of equipment which the fullest use of semiconductor devices is expected to bring, could lead to substantial economy in staffing.

Factors Affecting Modulation Techniques for VHF Scatter Systems

An experimental program at approximately 50 mc has been carried out over a 1295-km east-west ionospheric-scatter path to determine the comminucation capacity of the propagation medium using ordinary modulation techniques. Binary error-rate studies using dual-narrow-band frequency-shift-keyed terminal equipment were made to observe the dependence of error rate in scatter propagation on signal-to-noise ratio, multipath factors, and Doppler shifts. With respect to multipath limitation, using antennas of 6° beamwidth, error rate is found to be independent of transmission speed to 500 binary digits per second. Tests were made using dual-diversity narrow-beam rhombic antennas, and dual- and quadruple-diversity broad-beam Yagi antennas. The use of four Yagi antennas gave very promising results as compared to use of two narrow-beam antennas. Frequency shifts of 2, 4, and 6 kc were used to determine the effect of meteor Doppler components in the received signal, leading to recommendations for minimum frequency shift. Though actual modulation tests have so far been made at a frequency of 49.6 mc only, systematic observations of longdelay signals of the order of 10 to 80 msec were made at 30 and 40 mc, using pulse techniques. These delayed signals arrived at the receiver via the F <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> backscatter mode, and were occasionally of sufficient strength to cause binary errors for circuits operating in these frequency ranges. Studies of intelligibility for voice transmission were made using narrow-band frequency modulation and single-sideband modulation. Using 20-kw power, the frequencymodulation tests with dual-diversity receivers and narrow-beam rhombic antennas gave good results at levels of signal-to-noise ratio exceeded for 90 per cent of the year at 50 mc.

A 150-Kc Carrier System for Radio Relay Applications

The carrier system described was developed by the Western Union Telegraph Company for use with microwave radio relay circuits. Thirty-two voice-band communication channels, each 3,000 cycles wide, are derived in the frequency range 4 to 147 kc. Tandem stages of group modulators maintain a high degree of spectrum efficiency and eliminate the necessity for crystal filters. A crystal-controlled harmonic carrier supply insures the frequency stability required by narrow-band frequency-modulation telegraph circuits.

A Stabilized Narrow-Band Frequency-Modulation System for Duplex Working

A system is described whereby the two terminals of a duplex radiotelephone channel are stabilized against each other by the use of standard automatic-frequency-control circuits and the common use of an oscillator for both transmitting oscillator and superheterodyne high-frequency oscillator. The send and receive frequencies are separated from each other by an interval which is the frequency of the intermediate-frequency channel. The system can be designed to give adequate frequency stability for most applications without the use of crystal control.