Showing papers on "Spectral efficiency published in 1980"

Optimization of the Processing Gain of an FSK-FH System

Abstract: It is desired to determine the performance of a noncoherent FSK frequency-hopped spread spectrum communication system using MARK and SPACE tones which are not necessarily orthogonal, and in addition using an error-correction code to reduce the susceptibility of the system to jammer-induced errors. The overall bandwidth of the system (i.e., the spread bandwidth) will be held constant so that the processing gain of the system will always be adjusted to maintain this constant bandwidth as other factors (e.g., the bandwidth expansion due to the error correction coding) change the underlying baseband bandwidth.

The Effects of Filtering and Limiting on the Performance of QPSK, Offset QPSK, and MSK Systems

Abstract: The effects on spectral densities, symbol waveshapes and P e versus S/N performances, resulting from the addition of filtering followed by hard limiting on raised cosine filtered QPSK, offset QPSK, and MSK point-to-point radio systems are studied. A mathematical model and physical insight are presented into the crosstalk phenomenon between quadrature channels, created in the systems by the effect of limiting on filtered signals. This crosstalk is shown to result whether the filtering is ideal or otherwise. Computergenerated and measured eye diagrams showing crosstalk as predicted on a filtered, then limited, offset QPSK signal are given. Measured and computed spectral density results are given which are in close agreement with each other, indicating that the computer model provides a good representation of the real system. In addition, an explanation of the shape of the power spectra associated with filtered, then limited, modulated signals is provided by studying the symbol waveshapes of these signals. Using the spectral density results and the P_{e} (S/N) performance findings, it is shown that for a microwave system which: 1) incorporates an amplitude limiting amplifying device in the transmitter, 2) must operate within the FCC limits for radiated spectrum, and 3) must operate at a spectral efficiency greater than 1 bit/s/Hz, offset QPSK modulation is the best choice of the three modulation methods studied.

On efficient spectrum utilization from the standpoint of communication theory

Abstract: This paper reviews the concepts of spectrum efficiency, the parameters for assessing system performance, and the techniques for improving spectrum utilization. The rationale of possible bandwidth reduction and power savings by combined modulation techniques is discussed and special attention is given to combined amplitude and phase modulation (APSK) systems. It is believed, based on the available results of several analyses over additive Gaussian noise channels, that certain combined modulation systems can have significant power savings over single-parameter modulation systems when the number of bits per symbol of the signal is large and can achieve more efficient use of the spectrum for signal-to-noise ratios greater than certain levels.

Error Probability and Bandwidth of Digital Modulation

Abstract: The bandwidth in which 99 percent of the power is contained is presented for ASK, QASK, OQASK, PSK, FSK, and MSK. An example is given in which the bandwidth of FSK is one eighth the bandwidth of ASK and of the modulating signal. Error probability is presented for the various types of modulation with various detectors, detector filters and Butterworth receiver filters of order N = 4 or \infty . Comparisons are made between the performance and bandwidth efficiency of the various systems.

Second year technical report on-board processing for future satellite communications systems

Abstract: Advanced baseband and microwave switching techniques for large domestic communications satellites operating in the 30/20 GHz frequency bands are discussed The nominal baseband processor throughput is one million packets per second (16 Gb/s) from one thousand T1 carrier rate customer premises terminals A frequency reuse factor of sixteen is assumed by using 16 spot antenna beams with the same 100 MHz bandwidth per beam and a modulation with a one b/s per Hz bandwidth efficiency Eight of the beams are fixed on major metropolitan areas and eight are scanning beams which periodically cover the remainder of the US under dynamic control User signals are regenerated (demodulated/remodulated) and message packages are reformatted on board Frequency division multiple access and time division multiplex are employed on the uplinks and downlinks, respectively, for terminals within the coverage area and dwell interval of a scanning beam Link establishment and packet routing protocols are defined Also described is a detailed design of a separate 100 x 100 microwave switch capable of handling nonregenerated signals occupying the remaining 24 GHz bandwidth with 60 dB of isolation, at an estimated weight and power consumption of approximately 400 kg and 100 W, respectively