Showing papers on "Bandwidth expansion published in 1980"
TL;DR: 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.
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.
39 citations
TL;DR: In this article, the power spectral density of the output symbol sequence of a convolutional encoder is computed for two different input symbol stream source models, namely, an NRZ signaling format and a first-order Markov source.
Abstract: The power spectral density of the output symbol sequence of a convolutional encoder is computed for two different input symbol stream source models, namely, an NRZ signaling format and a first-order Markov source. In the former, the two signaling states of the binary waveform are not necessarily assumed to occur with equal probability. The effects of alternate symbol inversion on this spectrum are also considered. The mathematical results are illustrated with many examples corresponding to optimal performance codes. It is demonstrated that only for the case of a purely random input source (e.g., NRZ data with equiprobable symbols) and a particular class of codes is the output spectrum identical to the input spectrum except for a frequency scaling (expansion) by the reciprocal of the code rate. In all other cases, the output spectrum is sufficiently changed relative to the input spectrum that the commonly quoted statement "a convolutional encoder produces a bandwidth expansion by a factor equal to the reciprocal of the code rate" must be exercised with care.
17 citations
TL;DR: In this paper, a method for transforming audio input signals with variable amplitude and narrow bandwidth into outputs with relatively fixed amplitude and variable bandwidth responsive to input signal amplitude is presented, by the steps of dividing the range of amplitude into an odd number of equal intervals, detecting the interval of amplitude instantaneously occupied by said signal, shifting said instantaneous signal to the central interval and smoothing the resulting discontinuous signal with a continuous and bilaterally tapered transfer function.
Abstract: A method and apparatus for transforming audio input signals with variable amplitude and narrow bandwidth into outputs with relatively fixed amplitude and variable bandwidth responsive to input signal amplitude, by the steps of dividing the range of amplitude into an odd number of equal intervals, detecting the interval of amplitude instantaneously occupied by said signal, shifting said instantaneous signal to the central interval, and smoothing the resulting discontinuous signal with a continuous and bilaterally tapered transfer function. This method permits bandwidth expansion and control of the output bandwidth of musical tones produced in electronic musical instruments in response to control of the input amplitude of the tones.
1 citations
01 Jan 1980
TL;DR: This chapter shall study another coding scheme, convolutional coding, and generalize the notion of channel capacity, which has so far been defined only for gaussian channels.
Abstract: We saw in the last chapter how Shannon’s limit may be approached for the infinite-bandwidth white gaussian channel by the use of orthogonal or biorthogonal codes of ever-increasing bandwidth. In this chapter we shall study another coding scheme, convolutional coding. Convolutional codes give good performance at a moderate bandwidth expansion. They are now nearly universally used as the general-purpose coding technique for communication from distant planetary spacecraft to earth We will also generalize the notion of channel capacity, which we have so far defined only for gaussian channels. We will see what the loss in capacity is when we make a gaussian channel into a digital channel. We also will study the capacity of systems that use photon counters, and compare the results with those of Chapters 2 and 11 for ideal amplification.