Total Data Rate Research Articles

A discrete multitone transceiver system for HDSL applications

A discrete multitone (DMT) transceiver design for high bit rate digital subscriber line (HDSL) access is presented and analyzed. The DMT transmitter and receiver structure and algorithms are detailed, and the computational requirements of DMT for HDSL are estimated. At a sampling rate of 640 kHz, using an appropriate combination of a short finite-impulse-response (FIR) equalizer and a length-512 DMT system, 1.6 Mb/s data transmission is possible within the carrier serving area (CSA) at an error rate of 10/sup -7/ on a single twisted pair. A significant performance margin can be achieved when two coordinated twisted pairs are used to deliver a total data rate of 1.6 Mb/s. In terms of a performance-per-computation figure of merit, the DMT system is an excellent candidate for HDSL implementation.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

An Accurate Fast Response Temperature System Using Thermocouples

Abstract An accurate and fuss response thermocouple-based temperature system has been developed for use in the atmospheric surface layer. The absolute accuracy is better than ±0.01°C and the relative accuracy between thermocouples is ±0.01°C. A number of special features were incorporated into the system to achieve the required performance. These include front-end multiplexing to allow one amplifier to process all channels; microprocessor-based control; handling of large, fast-changing temperature variations with no degradation in performance; and sophisticated noise removal and error reduction techniques. The system can accommodate up to 22 thermocouples with a total data rate of 180 s−1. Humidity is measured by converting standard thermocouples to wet bulbs through the use of wetted wicks.

Waveform Peak Detector Reduces Data Rate to Microcomputer Speeds

A commercially available detector array outputs data hundreds of times faster than the input READ rate of a microcomputer (/g=m/C). This waveform analyzer sifts out uninteresting signals and permits the /g=m/C to read all useful data. A 1024-bin detector array can output 16 parallel channels of analog information every 15 /g=m/s. This total data rate is 68.3 MHz, but a Motorola-68000-based VERSAbus-compatible /g=m/C (VM01) reads data at about 100 kHz. In order for the /g=m/C to keep up, the data rate must be reduced by a factor of 684 (or more). A solution is possible because, at any given time, only a few bins of the detector array contain useful information. This waveform peak detector finds the few interesting signals and reports the peak magnitude, location, and time of arrival to the /g=m/C. Several algorithms were designed to handle a wide dynamic range of input waveforms.

Surface-acoustic-wave multiplexing techniques

Two approaches to frequency division multiplexing using SAW devices are described. The first one uses a 9-channel filter array, where the signal combining and splitting is performed using wide-band power splitters. Two of these filter arrays were used in a data link, with data rates up to 7.5 Mbit/s for a total data rate of 67.5 Mbit/s. The second approach uses offset multistrip couplers to channel a wide-band signal into various narrow-band outputs according to frequency. Consequently, this approach exhibits lower insertion loss and is especially suitable for a large number of channels. An 8-channel MSC multiplexer has been constructed with less than 10-dB insertion loss.

Time-frequency (RADA) signaling with a random number of active subscribers

The probability of word error is determined for a RADA (random-access discrete address) system in which m-ary transmission is employed by a random number of active subscribers. It is shown that the ratio of total system data rate to system bandwidth becomes relatively high when the average number of active subscribers is large.

Optimal Design of One-Way and Two-Way Coherent Communication Links

This paper is concerned with the optimal design of one-way and two-way communication systems which are of greatest interest in space applications. A two-way communication system is defined to be one composed of two radio links or channels, viz., an up-link channel and a down-link channel. The down-link RF carrier is derived from the carrier tracking loop located in the uplink receiver. Transmission of information which does not make use of the carrier derived in the up-link receiver is referred to as oneway communications. In particular, a design technique is presented in the form of a universal set of design curves which enable the communications engineer to make a "best" choice of parameters when faced with a given set of design constraints. This means that, given a certain desired error probability, a total transmitter power limitation, data rate, and carrier tracking loop bandwidth, the modulation index, i.e., the square root of the ratio of the power in the carrier to the total transmitted power, may be chosen so as to minimize the probability of error. As an alternate technique, and one which is not as difficult to carry out, the design may be predicted on the basis of selecting that value of modulation index which maximizes the signal-to-noise ratio at the output of the data demodulator. Design curves are given which allow one to employ this alternate criterion. Further, these results should prove useful when attempting to check experimentally a design based upon the criterion of minimum error probability.

A Comparison of Frequency-Shift Anti-Multipath Signaling Techniques for Digital Communication Systems

An important result of multipath propagation is the lengthening of the received signal due to a single transmitted pulse. The received pulse duration may be increased by the difference in propagation times between the longest and shortest of the active paths. This time difference represents the minimum pulse repetition period which can be used if errors due to inter-symbol interference are to be avoided. This minimum pulse repetition period places a limit on the available data rate per channel. The total data rate can be increased by frequency division multiplexing. Several recent papers have described a technique for synchronous frequency-division multiplexing for use under the multipath conditions described above. This synchronous system is analyzed to show its bandwidth, data rate, and signal-to-noise properties, and these parameters are compared with those of a conventional FSK system. A second refinement of conventional FSK is the use of more than two possible frequencies for each pulse. The bandwidth, data rate, and signal-to-noise properties of multilevel synchronous FSK are presented, and some circumstances under which it may be used to advantage are described.