Showing papers on "Frequency-division multiplexing published in 1972"

Multiplexing and concentration

Abstract: Obtaining a cost-effective teleprocessing network is postulated on efficient utilization of the communication links and processing equipment. A variety of line-sharing devices and procedures are commonly used for this purpose. The functional, economic, and application aspects of frequency-division multiplexing (FDM), synchronous time-division multiplexing (STDM), asynchronous time-division multiplexing (ATDM), message switching concentration (MSC), and line (or circuit) switching techniques are discussed. The motivations for line sharing stem from economies of scale in the cost of bandwidth and from the traffic smoothing effect which such devices produce when serving a large terminal population characterized by unscheduled requests for service. The discussion of these techniques includes a detailed contrast between multiplexing and concentration, two terms which are often (and unfortunately) used synonymously. It is shown that FDM and STDM are examples of conventional multiplexing, whereas message switching and line switching usually illustrate concentration. ATDM is shown to be a hybrid line-sharing scheme embodying certain features of both concepts. Thus it is often referred to as statistical multiplexing. The first part of the paper is devoted to a functional explanation of the various concepts referenced above. The balance of the paper is concerned with applications and systems-design considerations involving multiplexing and concentration techniques. The application section focuses on important economic factors pertaining to the selection and use of the various methods. The role of line-sharing devices in contemporary common-carrier and end-user networks is also considered. The economic and technical aspects of these contrasting application environments are emphasized and illustrate the multiplicity of uses for line-sharing devices. The concluding portion of the paper includes a discussion of system-design considerations. This section illustrates precisely how the decision to use multiplexers or concentrators in a typical computer-communication network is implemented. Various techniques for geographically positioning multiplexers and concentrators to minimize total costs are presented. The use of one of these procedures is demonstrated using a typical design problem as a case study.

Communication system utilizing frequency division multiplexing to link a plurality of stations each containing a switchable synthesizer

Abstract: A switchable communications system utilizing frequency division multiplexing is shown for providing communication between a plurality of stations, each including a synthesizer and each operated from a single reference frequency. Each station is assigned a fixed home frequency at which it transmits information. When calling, the synthesizer within the calling station adjusts the transmit frequency of that station to correspond to the receive frequency of the called station, which automatically adjusts the receive frequency of the calling station to correspond to the transmit frequency of the called station. Full duplex transmission is thus permitted between any and all stations within the communications system through the utilization of a wide range acquisition synthesizer within each station.

Equivalance of Time-Multiplexed and Frequency-Multiplexed Signals in Digital Communications

Abstract: In comparing different techniques for multiplexing N binary data signals into a single channel, time-division multiplexing (TDM) is known to have a theoretic efficiency of 100 percent (neglecting sync power) and thus seems to outperform frequencydivision multiplexing systems (FDM). By considering more general FDM systems, we will show that both TDM and FDM are equivalent and have an efficiency of 100 percent. The difference between the systems is in the multiplexing and demultiplexing subsystems, but not in the performance or in the generated waveforms.

Head end interconnection system for cable tv systems

Abstract: This relates to an arrangement for interconnecting head ends of two or more conventional cable TV systems over the distribution cable or trunk employed for the TV signal distribution in a cable TV system The technique employed is frequency division multiplexing a digitally encoded TV signal or signals capable of being received at one head end but not at the other head end of the two cable TV systems on the distribution cables of the two cable TV systems employed for conventional TV signal distribution under conditions avoiding mutual interference between the frequency division multiplexed digitally encoded TV signal or signals and the conventional analog TV signal or signals being distributed

Method and apparatus for frequency-division multiplex communications by digital phase shift of carrier

Abstract: A system is disclosed for subcarrier frequency multiplexing to separate independent pulse-code-modulated data streams on a common carrier by modulating the carrier in a digital-to-phase shift converter by codes produced in an encoder as Boolean functions of the data, subcarriers, and mode control signals treated as binary variables. The mode control variable is included to program ratios between modulated subcarriers. Alternatively, 2n registers can be provided to store m-bit words representing different carrier phases, where n is the number of squarewave subcarriers. The codes are then selected as functions of the subcarriers and data. The contents of the registers can be changed at will under control of a computer or data processing system.

Frequency and time in communications

Abstract: Modern communications systems make use of sophisticated multiplexing techniques in order to achieve efficient spectrum utilization and thereby realize the maximum number of message channels through a particular transmission medium. Synchronization of transmit/receive carrier (or clock) generators is essential in such systems to avoid distortion; also, close tolerances on the accuracy of carrier and pilot frequencies must be imposed to maintain transmission through minimal bandwidth channel selection filters. Typical requirements on both synchronization and accuracy for several categories of commercial communications systems range from several parts in 106to a few parts in 1010.

Communication system utilizing frequency division multiplexing and a frequency plan therefor

Abstract: A communications system utilizing frequency division multiplexing is shown for providing switchable communication between any two stations through a frequency plan which uses a single reference frequency throughout the system. Each station is assigned a fixed home frequency at which it receives information and a second fixed home frequency at which it transmits information. When calling, the calling station adjusts its transmit and receive frequencies to correspond to the receive and transmit frequencies of the called station, respectively. Full duplex transmission is thus permitted between any and all stations over a single coaxial cable utilizing a fixed-adjustable paired frequency plan.

Microwave and Millimeter-Wave Communications in Japan

Abstract: This paper reviews the status of research and development in both microwave radio-relay systems and millimeter-wave transmission systems as well as the technical features in these fields, mainly developed under the auspices of Nippon Telegraph and Telephone Public Corporation (NTT). Recent activities have been the development of new solid-state devices and high-capacity systems. The application of solid-state techniques is being extended to systems of both analog and digital transmission, such as the 2700 multichannel telephone transmission system in frequency division multiplexing (FDM)-FM radio-relay system, an experimental 20-GHz PCM radio-relay system capable of 400 Mbits/s pulse transmission, and a guided millimeter-wave system of 800-Mbit/s transmission at 40-80 GHz. The microwave integrated circuit (MIC) is also becoming very important in utilizing these high-frequency regions, which should be a valuable resource in the future when a vast information transmission capability will be required.

The A6 Channel Bank

Abstract: The A6 channel bank is the latest of a series of Bell System frequency division multiplex terminal equipments used to provide the first step of modulation and the final step of demodulation in carrier telephony Cost and size reduction are the primary objectives of the development and are realized through the use of monolithic quartz crystal filters and hybrid monolithic silicontantalum thin film integrated circuits This paper includes a general description of system organization, a discussion of system features, and gives objective performance values of the significant transmission parameters Of special interest are the channel filter discrimination characteristic and the hybrid integrated circuit functions Designed to meet stringent inter-toll performance criteria, the A6 channel bank is intended to become the standard for new installations in the Bell System