Showing papers on "Spectral efficiency published in 1983"
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TL;DR: The research results in spread spectrum mobile radio are summarized, and the areas requiring further investigation before a commercial system can be implemented are identified.
Abstract: In 1977, Cooper and Nettleton proposed a spread spectrum mobile radio system using frequency-hopping multiple access, Hadamard coding for error correction, and differential phase shift keyed (DPSK) modulation, and they claimed higher spectral efficiency than frequency-division (FD) FM systems. Subsequent analyses showed that the DPSK system has a spectral efficiency of 8.4 percent as compared to the efficiency of unity for a FD-FM system with 30-kHz channel spacings. Goodman et al. suggested an alternative modulation scheme in 1980, using multilevel frequency shift keying (MFSK), and a 30 percent efficiency was obtained. The research results in spread spectrum mobile radio are summarized, and the areas requiring further investigation before a commercial system can be implemented are identified.
42 citations
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TL;DR: This work has investigated the performance of an adjustable source/channel codec in a cellular mobile-radio environment and found that this approach offers an improved grade of service.
Abstract: The performance of an adjustable source/channel codec in a cellular mobile-radio environment is investigated. The speech transmission rate and the amount of forward error correction change in response to changing channel conditions. The channel rate is constant at 32 kb/s, and when the channel is good all of these bits are used for speech transmission. In intermediate and poor channels the speech rate is 24 or 16 kb/s, and the remaining channel symbols are used for forward error correction. Relative to conventional transmission this approach offers an improved grade of service. For example, the outage rate (the proportion of "poor or worse" communications) goes from nine percent with fixed-rate to three percent with variable-rate transmission. Alternatively, this improved grade of service can be exchanged for higher bandwidth efficiency. The fixed-rate system (with nine percent outage) has 23 users per cell. With 52 users per cell the outage of the variable-rate system is only six percent.
31 citations
01 Sep 1983
TL;DR: Four-D modulations based upon subsets of lattice-packings in four-D, which afford simplification of encoding and decoding are described, providing a (Nyquist) spectral efficiency of up to 10 bps/Hz.
Abstract: Four dimensional modulation as a means of improving communication efficiency on the band-limited Gaussian channel, with the four dimensions of signal space constituted by phase orthogonal carriers (cos omega sub c t and sin omega sub c t) simultaneously on space orthogonal electromagnetic waves are discussed. "Frequency reuse' techniques use such polarization orthogonality to reuse the same frequency slot, but the modulation is not treated as four dimensional, rather a product of two-d modulations, e.g., QPSK. It is well known that, higher dimensionality signalling affords possible improvements in the power bandwidth sense. Four-D modulations based upon subsets of lattice-packings in four-D, which afford simplification of encoding and decoding are described. Sets of up to 1024 signals are constructed in four-D, providing a (Nyquist) spectral efficiency of up to 10 bps/Hz. Energy gains over the reuse technique are in the one to three dB range t equal bandwidth.
22 citations
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TL;DR: This paper specifies and analyze the Viterbi receiver for MSK modulation with correlative encoded symbols, using first- and second-order encoding polynomials, and the transfer function bound technique is utilized.
Abstract: It has previously been shown that MSK modulation with correlative encoded symbols, using first- and second-order encoding polynomials, can give rise to signals with excellent bandwidth efficiency. In this paper we specify and analyze the Viterbi receiver for such signals. The receivers are not very complex as they either require four or eight states to be stored and processed during each symbol interval. Our analysis concerns the bit error rate and the transfer function bound technique is utilized. Perfect coherent operation of the receiver is assumed in the error analysis.
20 citations
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TL;DR: Analytic techniques have been developed which predict probabilistically (without dependence on simulation) the power spectral density that results from pulse modification combined with hard limiting where necessary to achieve constant envelope.
Abstract: Considerable recent attention has been given to the use of pulse modification to reduce spectral sidelobes in constant envelope data transmission within the "offset" modulation format that includes offset QPSK and MSK. Analytic techniques have been developed which predict probabilistically (without dependence on simulation) the power spectral density that results from pulse modification combined with hard limiting where necessary to achieve constant envelope. Here the computational results are compared with experimental results. Agreement between theory and experiment is seen to be good. The implications for bandwidth efficiency and communication efficiency are discussed.
14 citations
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TL;DR: It is expected that the IJF-OQPSK scheme will have applications in low-cost power and bandwidth efficient earth-stations and terrestrial radio systems with transmit high-power amplifiers operating in saturation.
Abstract: The error probability (P e ) performance of intersymbolinterference and jitter-free offset-QPSK (IJF-OQPSK) modems in a cochannel and adjacent-channel interference environment is evaluated using a computer simulation technique. Hardware design and experiments have been completed to verify the simulation results. The results indicate that a spectral efficiency of 1.5 bits/s/Hz can be obtained with hard-limited IJF-OQPSK channels. This is a significant improvement compared to hard-limited QPSK, OQPSK, and MSK systems. It is expected that the IJF-OQPSK scheme will have applications in low-cost power and bandwidth efficient earth-stations and terrestrial radio systems with transmit high-power amplifiers operating in saturation.
13 citations
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25 May 1983TL;DR: The performance of an adjustable source/channel codec in a cellular mobile-radio environment is investigated and it is found that this approach offers an improved grade of service.
Abstract: We have investigated the performance of an adjustable source/channel codec in a cellular mobile-radio environment. The speech transmission rate and the amount of forward error correction change in response to changing channel conditions. The channel rate is constant at 32 kb/s and when the channel is good all of these bits are used for speech transmission. In intermediate and poor channels the speech rate is 24 or 16 kb/s and the remaining channel symbols are used for forward error correction. Relative to conventional transmission this approach offers an improved grade of service. For example, the outage rate (the proportion of "poor or worse" communications) goes from 9% with fixed-rate to 3% with variable-rate transmission. Alternatively, this improved grade of service can be exchanged for higher bandwidth efficiency. The fixed-rate system (with 9% outage) has 23 users per cell. With 52 users per cell the outage of the variable-rate system is only 6%.
4 citations
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01 Sep 1983TL;DR: A 16 QAM-modem for 140 Mb/s radio systems is described, with which a spectral efficiency of 3.5 bit/s/Hz is achieved and the incorporation of an adaptive baseband equalizer employing a complex transversal filter is discussed.
Abstract: A 16 QAM-modem for 140 Mb/s radio systems is described, with which a spectral efficiency of 3.5 bit/s/Hz is achieved. In the digital signal processing parts extensive use is made of ECL gate arrays. Spectrum shaping according to Nyquist's criterion is performed in the IF with the aid of SAW-bandpass filters (? = 0.5). Experimental results obtained with this modem are reported. The incorporation of an adaptive baseband equalizer employing a complex transversal filter is discussed.
2 citations
01 Jan 1983
TL;DR: In this article, the performance of the IJF-OQPSK modulation schemes in the presence of adjacent-channel and cochannel interference (AC1,CCI) and additive white Gaussian noise (AWGN) is investigated and presented.
Abstract: achieve high power and spectral efficiency in digital communi- cation systems. The spectral properties and probability of error (P,) performance of IJF-OQPSK modems in linear and nonlinear channels were reported in our previous publications. It was shown that the IJF-OQPSK schemes have significant spectral advantages over QPSK, offset-QPSK, and MSK, and a better performance in saturated channels. As an extension of our previous work, the P, performance of the IJF-OQPSK modulation schemes in the presence of adjacent-channel and cochannel interference (AC1,CCI) and additive white Gaussian noise (AWGN) is investigated and presented in this paper. Section I1 presents a computer simulation technique used to evaluate the performance of IJF-OQPSK schemes in both linear and hard-limited multichannel systems. This technique makes use of a computation of all the conditional error pro- babilities followed by an average over the conditioning random variables. Illustrative Pe performance results of an IJF-OQPSK modem in the presence of ACI, CCI, and AWGN are reported in Section 111. The results indicate that the receive raised- cosine-type filter having a rolloff factor CY = 0.4 provides the best performance for narrow channel spacings. The effects of ACI on the performance of the IJF-OQPSK scheme are also experimentally investigated. The experimental IJF-OQPSK modem has a bit rate of 64 kbits/s, an intermed- iate carrier frequency of 512 kHz, and a sixth-order elliptic equalized receive bandpass filter. The experimental results, re- ported in Section IV, are in agreement with the simulation results.
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25 May 1983TL;DR: It is shown that the CDMA (spread spectrum) bounds are uniformly higher than the channel reuse bounds, and that the potential improvement using spread spectrum is much greater than that of the channel-reuse scheme.
Abstract: The problem of spectrally efficient communication in a cellular mobile radio system is discussed. Information-theoretical bounds are derived for the spectral efficiency of cellular systems using the channel-reuse method, where each user has a distinct channel that is also reused elsewhere in the system; and for the code-division multiple-access system, where all users use the same spectrum simultaneously and signature sequences are used to distinguish them. It is shown that the CDMA (spread spectrum) bounds are uniformly higher than the channel reuse bounds. Results for practical signalling techniques are compared with the bounds, showing that a real potential for improvement exists using either scheme, but that the potential improvement using spread spectrum is much greater.