Showing papers on "Frequency-division multiplexing published in 1971"

Systems Analysis of a TDM-FDM Translator/Digital A-Type Channel Bank

Abstract: In keeping with the trend to greater use of digital circuits for signal processing, a project was undertaken to realize in an exploratory way an important telecommunication function using as great a proportion of digital hardware as possible. The function chosen is that of the A -channel bank; viz., the frequency division multiplexing (FDM) of 12 voiceband signals onto a single wire. Because of the nature of its operation the device to be described can also perform a translation between FDM analog signals and time division multiplexed (TDM) digital signals. This paper describes the overall system design of the device with particular emphasis on a noise analysis. The principal sources of noise are the A/D conversion points and the roundoff points that occur at the outputs of multipliers. Each noise source is examined in turn and its contribution to the total noise assessed. It is concluded that the A/D conversion points are the most important noise sources and the most costly to deal with.

Radio communication transmission system for vehicles

Abstract: A radio communication transmission system for moving vehicles following a track wherein an intermediate frequency communication signal is transmitted on a leaky coaxial cable at a low loss from a ground station. This signal is periodically amplified, if required, to compensate for attenuation, and is also periodically frequency converted into a radio frequency signal which is transmitted along with the aforesaid intermediate frequency signal on the same leaky coaxial cable for uniform leakage therealong for coupling to an antenna on a vehicle traveling adjacent the leaky coaxial cable. A transmitter is provided on the moving vehicle and transmits a second radio frequency signal from the vehicle to couple the signal to the leaky coaxial cable for transmission thereon. This second radio frequency signal is then frequency converted to a second intermediate frequency signal for transmission at a low loss thereafter on the same leaky coaxial cable to a ground station for reception.

SSB/FDM Utilizing TDM Digital Filters

Abstract: Theoretical and practical results in the field of digital filtering encourage the examination of digital filters for use in multiplex communication systems [1]-[3]. Although their economic breaking in will only come in combination with large-scale integration of digital circuits, it appears worthwhile to study their feasibility for various applications [4]-[7], [9]. One application of particular interest is the digital realization of single-sideband frequency-division multiplexing (SSB/FDM), which leads to the study of the digital realization of the SSB-channel bank which is internationally known as the first multiplexed group in the frequency range of 60-108 kHz. This paper describes the conversion of voice-frequency channels into SSB/FDM signals using digital filters. A brief analysis explains the implications of the various steps of signal processing in the time and frequency domains. The digital realization of a channel bank is explained in block diagrams. It is shown that the SSB/FDM signal appears simultaneously as a TDM/SSB signal (TDM/FDM/SSB).

The Effects of Quadratic AM-PM Conversion in Frequency-Division Multiplexed Multiple-Access Communication Satellite Systems

Abstract: A traveling-wave tube amplifier such as those employed in frequency-division multiplexed multiple-access communication-satellite repeaters is considered. The amplifier nonlinearity is assumed to follow an error-function characteristic, and the AM-PM conversion is taken to be a quadratic function of the envelope of the input signal. An exact expression allowing for both arbitrary amounts of amplifier saturation and AM-PM conversion is derived for the autocorrelation function of the amplifier output when the input is a Gaussian bandpass process. Distortion spectra are calculated for the parameters of a typical travelingwave tube transmitter.

Optimal multiplexing of sampled signals on noisy channels

Abstract: This paper deals with the joint optimization of transmitting and receiving filters in multiplex transmission of pulse-amplitude-modulated (PAM) signals. A mean-square-error criterion is used. The signal processes are assumed to be mutually uncorrelated and with equal power spectral densities. Transfer matrix functions for the transmitting and for the receiving filters are used as an expedient tool. It is shown that optimal multiplexing systems can be achieved with a bandwidth of M/T . The transfer matrix functions of optimal transmitters (and corresponding optimal receivers) are defined up to premultiplication by an arbitrary unitary matrix function. This provides for freedom of choice between various multiplexing techniques like frequency-domain multiplexing, time-domain multiplexing, or combinations thereof.

Frequency division multiplex technique

Abstract: A system for monitoring a plurality of condition responsive devices. It consists of a master control station and a remote station. The master control station includes a channel select means, a BCD to binary converter, a parity generator, a storage register, a comparator, a plurality of sources of identifying frequencies, an oscillator driver, and a transmitter. The remote station includes a bank of filters for separating the transmitted signals, a detector, a driver, a parity correlator, a command verification and command reset circuit, a storage register, a random access multiplexer, a plurality of identifying frequency sources, an oscillator driver, and a transmitter. The master control station is capable of transmitting command signals which includes a parity signal to a remote station which transmits the signals back to the command station so that such can be compared with the original signals in order to determine if there are any transmission errors. The system utilizes frequency sources which are 1.21 multiples of each other so that no linear combination of any harmonics will interfere with another frequency.

The early history of amplitude modulation, sidebands and frequency-division-multiplex

Abstract: It is shown that the ideas of f.d.m. originated with Alexander Graham Bell around 1870 and were formulated as an f.d.m. telephone system by Leblanc in 1886. Amplitude modulation of a carrier by speech probably originated also with Leblanc in 1886. The existence of sidebands (or sidetones) was demonstrated experimentally by Mayer in 1875 and theoretically by Rayleigh in 1894, but was not known to the early radio and telephone engineers, being apparently rediscovered in 1915. The main developments up to about 1920 are briefly discussed.

Analysis of multiplex techniques for land mobile radio service

Abstract: Two types of frequency multiplexing are theoretically analyzed for their applicability as a form of modulation in the land mobile radio service (LMRS). Both SSB/FM and FM/FM are analyzed for their signal-to-noise ratio (SNR) versus modulation index. These results are normalized to the signal-to-noise performances of the existing 5-kHz deviation system for comparison purposes. The latter performance is developed using the actual Electronic Industries Association (EIA) response of a LMRS receiver. The spectrum of the multiplex system for the case of equal subchannel signal-to-noise is developed using a computer. The spectrum is used to determine the spectrmm occupancy of multiplex systems. Based on the tradeoffs of transmit power and spectrum occupancy, a discussion of the interference characteristics of the multiplex systems compared to the existing system is presented. Finally, conclusions are drawn on the spectrum efficiency of a multiplex system compared to the present system.

Application of Millimeter Microwaves for the Transmission of a Multiplicity of Television Bandwidth Communication Signals on a Single Carrier

Abstract: A millimeter microwave system has been produced for the American Cable Television (CATV) market which permits the simultaneous transmission of a single carrier of as many as 18, six megahertz wide, television signals in a radio frequency bandwidth of 250 MHz. Any other combination of vestigial sideband, frequency division multiplexed signals which fit the baseband of 5 to 114 MHz, can also be transmitted through the system. The technique utilized, design considerations and the results obtained, are described.

INTELSAT IV Satellite System (Voice) Channel Capacity Versus Earth-Station Performance

Abstract: A comprehensive technical study has been performed to assess the optimum voice-channel capacity of a transponder as a function of the earth-station performance (ratio of receive antenna gain to system noise temperature) for various modulation techniques such as: a) single-carrier per transponder frequencydivision multiplexing frequency modulating (FDM/FM); b) multicarrier per transponder FDM/FM; c) pulse-code modulating, coherent phase-shift keying, time-division multiple access (PCMCPSK-TDMA); and d) SPADE (single-channel per carrier PCMCPSK-FDMA), which will be used in the INTELSAT IV satellite system. This study assumes a homogeneous system, i.e., the transmit and receive earth stations use an appropriately identical antenna performance.