scispace - formally typeset
Search or ask a question

Showing papers on "Frequency-division multiplexing published in 1970"


Journal ArticleDOI
O.E. DeLange1
01 Oct 1970
TL;DR: Calculations are made to determine the approximate information capacity and other characteristics of several 4000-mile repeaterad systems.
Abstract: Frequency-division multiplexing techniques offer means for circumventing the bandwidth limitations of optical modulators and detector. Practical broad-band long-distance optical communication system of this type appear feasible and some possible embodiments are described. Calculations are made to determine the approximate information capacity and other characteristics of several 4000-mile repeaterad systems.

84 citations


Patent
09 Jun 1970
TL;DR: In this article, a circuit for AGC amplification of signals in different acoustic frequency bands was proposed, where the signals in all frequency bands were normalized to the signal in one particular band by using a single logarithmic detector responsive to signals in the band to which the other bands are normalized.
Abstract: A circuit for AGC amplification of signals in different acoustic frequency bands so that the signals in all frequency bands are normalized to the signal in one particular band by using a single logarithmic detector responsive to signals in the band to which the other bands are normalized

7 citations


Patent
13 Nov 1970
TL;DR: In this article, a system 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.
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.

7 citations


Journal ArticleDOI
01 Jan 1970
TL;DR: Two low complexity adaptive step-size mechanisms based on the normalised orthogonal gradient algorithm for frequency-domain equalisation in orthogonal frequency division multiplexing (OFDM) systems can achieve good performance for an OFDM receiver.
Abstract: We propose two low complexity adaptive step-size mechanisms based on the normalised orthogonal gradient algorithm for frequency-domain equalisation in orthogonal frequency division multiplexing (OFDM) systems. These algorithms are derived from employing a mixed-subcarrier exponentially weighted least squares criterion. Two low complexity adaptive stepsize approaches are investigated by exploiting an estimate of autocorrelation between previous and present weight-estimated mixed-subcarrier errors. We compare our approaches with a previously fixed stepsize normalised orthogonal gradient adaptive algorithm and other existing algorithm for implementation. Simulation results demonstrate that the proposed algorithms can achieve good performance for involving an OFDM receiver.

6 citations


Journal ArticleDOI
01 Jan 1970
TL;DR: Simulation results are presented to demonstrate the effectiveness of proposed iterative based time domain equalization (TDE) method with the CIR estimation method for the TS inserted DFTS-OFDM signal as comparing with the conventional One-Tap MMSE-FDE method.
Abstract: Under highly mobile environments, signal quality of discrete Fourier transform spreading-orthogonal frequency division multiplexing (DFTS-OFDM) with a frequency domain equalization method would be degraded relatively due to the occurrence of interchannel interference (ICI). To solve this problem, this paper proposes an iterative based time domain equalization (TDE) method with a time domain channel impulse response (CIR) estimation method for DFTS-OFDM signal. The salient features of proposed method are to employ a time domain training sequence (TS) in the estimation of CIR instead of using the conventional pilot subcarriers and to employ the TDE method with a maximum likelihood (ML) estimation method instead of using the conventional one-tap minimum mean square error frequency domain equalization (One-Tap MMSE-FDE) method. This paper also proposes a low-complexity iterative based TDE method by using a good property of symmetric banded CIR transfer matrix for solving the simultaneous equations instead of using a direct calculation of inverse matrix. This paper presents various simulation results under highly mobile environments to demonstrate the effectiveness of proposed iterative based TDE with the CIR estimation method for the TS inserted DFTS-OFDM signal as comparing with the conventional One-Tap MMSE-FDE method.

1 citations


Journal ArticleDOI
01 Jun 1970
TL;DR: A unified theory from which the design of a large class of coherent digital communication systems can be optimally carried out is presented and it is pointed out that there is significant parametric dependence of the optimal choice of system parameters on the carrier loop signal-to-noise ratio and the data rate.
Abstract: A unified theory from which the design of a large class of coherent digital communication systems can be optimally carried out is presented. In the design of digital communication systems, the error rate is the criterion which is invariably emphasized. In many digital systems, however, there is relative motion between transmitter and receiver which must be estimated by making use of Doppler frequency information. A new analysis of a general class of coherent digital systems is herein developed, in which the tradeoffs that exist between Doppler measurement capability and bit demodulation error rate are quantitatively presented. The theoretically unrecoverable power loss which exists when employing frequency division multiplexing subcarriers as compared to time division multiplexing is described. The results point out that there is significant parametric dependence of the optimal choice of system parameters on the carrier loop signal-to-noise ratio and the data rate.

1 citations


Proceedings ArticleDOI
01 Dec 1970
TL;DR: A travelling wave tube amplifier such as those employed in FDM multiple access communication satellite repeaters is considered in this paper.
Abstract: A travelling wave tube amplifier such as those employed in FDM multiple access communication satellite repeaters is considered in this paper. 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. A closed form 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 band-pass process.

1 citations



Journal ArticleDOI
TL;DR: It was found that both theoretically and experimentally FDM/FM troposcatter systems can support data transmission of various rates from 2.4 to 40.8 kbit/s for path lengths from 86.7 to 381.5 statute miles in smooth earth geometry with diversity reception, if proper path and equipment parameters are chosen.
Abstract: There are more than one hundred troposcatter systems of various sizes in existence all over the world [1]. As the transmission of computer data becomes more and more common and in popular demand, such systems are certain to be involved in these services. Two methods are generally used for transmitting data over troposcatter channels: direct transmission and the frequency division multiplex/frequency modulation (FDM/FM) technique. In the latter, the individual data channels are combined into an FDM baseband to frequency or phase modulate a common radio carrierthe same technique used conventionally for the carrier transmission of multiplex telephone channels. In a study program, under a contract [2]-[4] to the U. S. Air Force Rome Air Development Center, both the direct transmission by time-division multiplex/frequency-shift keying (TDMF/SK) and the FDM/FM techniques are investigated. This paper, however, concerns the FDM/FM techniques only. It was found that both theoretically and experimentally FDM/FM troposcatter systems can support data transmission of various rates from 2.4 to 40.8 kbit/s for path lengths from 86.7 to 381.5 statute miles in smooth earth geometry with diversity reception, if proper path and equipment parameters are chosen.