Providing voice and data communications to people away from their wireline telephones has become a major communication frontier. This frontier is being penetrated by evolving approaches to portable communications, e.g., cordless telephones, mobile radiotelephone, and radio paging. However, these approaches have many limitations; none can provide universal portable communications services. This paper discusses limitations of the evolving approaches and considers objectives and approaches for providing more universal digital portable communications as an integrated part of telephone exchange networks. These more universal communications could be accomplished by using demand-assigned radio links for the last thousand feet or so of telephone loops and sharing the remainder of the fixed distribution facilities. Fixed radio ports as integrated parts of telephone distribution networks could be placed throughout service regions. Efficient use of the radio spectrum could be insured by the planned reuse of radio frequencies throughout the regions. The severe multipath radio propagation environment within and around buildings that strongly influences the design of portable communications systems is described in the paper. System configurations and radio link techniques, that can provide reliable communications in the multipath environment, are discussed. Radio system calculations are illustrated for radio ports with 30-ft-high antennas in residential areas. The calculations indicate that radio link availability would be greater than 99 percent for 2000-ft port separations and 5-mW portable transmitters. Reuse of frequencies would require dividing the allocated frequency band into segments for use at adjacent ports. Calculations suggest that link availability in the cochannel interference environment would be greater than 99 percent, if 25 to 35 segments were used in residential areas.

Universal digital portable radio communications

Minimum shift keying with Gaussian shaped transmit pulses is a strong candidate for a modulation technique that satisfies the stringent out-of-band radiated power requirements of the mobil radio application. Numerous studies and field experiments have been conducted by the Japanese on urban and suburban mobile radio channels with systems employing Gaussian minimum-shift keying (GMSK) transmission and differentially coherent reception. A comprehensive analytical treatment is presented of the performance of such systems emphasizing the important trade-offs among the various system design parameters such as transmit and receiver filter bandwidths and detection threshold level. It is shown that two-bit differential detection of GMSK is capable of offering far superior performance to the more conventional one-bit detection method both in the presence of an additive Gaussian noise background and Rician fading.

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Differential detection of Gaussian MSK in a mobile radio environment

Foreword. Preface. Chapter 1: Introduction. Chapter 2: Constant Envelope Modulations. 2.1 The Need for Constant Envelope. 2.2 Quadriphase-Shift-Keying and Offset (Staggered) Quadriphase-Shift-Keying. 2.3 Differentially Encoded QPSK and Offset (Staggered) QPSK. 2.4 /4-QPSK: A Variation of Differentially Encoded QPSK with Instantaneous Amplitude Fluctuation Halfway between That of QPSK and OQPSK. 2.5 Power Spectral Density Considerations. 2.6 Ideal Receiver Performance. 2.7 Performance in the Presence of Nonideal Transmitters. 2.7.1 Modulator Imbalance and Amplifier Nonlinearity. 2.7.2 Data Imbalance. 2.8 Continuous Phase Modulation. 2.8.1 Full Response-MSK and SFSK. 2.8.2 Partial Response-Gaussian MSK. 2.9 Simulation Performance. References. Chapter 3: Quasi-Constant Envelope Modulations. 3.1 Brief Review of IJF-QPSK and SQORC and their Relation to FQPSK. 3.2 A Symbol-by-Symbol Cross-Correlator Mapping for FQPSK. 3.3 Enhanced FQPSK. 3.4 Interpretation of FQPSK as a Trellis-Coded Modulation. 3.5 Optimum Detection. 3.6 Suboptimum Detection. 3.6.1 Symbol-by-Symbol Detection. 3.6.2 Average Bit-Error Probability Performance. 3.6.3 Further Receiver Simplifications and FQPSK-B Performance. 3.7 Cross-Correlated Trellis-Coded Quadrature Modulation. 3.7.1 Description of the Transmitter. 3.7.2 Specific Embodiments. 3.8 Other Techniques. 3.8.1 Shaped Offset QPSK. References. Chapter 4: Bandwidth-Efficient Modulations with More Envelope Fluctuation. 4.1 Bandwidth-Efficient TCM with Prescribed Decoding Delay-Equal Signal Energie. 4.1.1 ISI-Based Transmitter Implementation. 4.1.2 Evaluation of the Power Spectral Density. 4.1.3 Optimizing the Bandwidth Efficiency. 4.2 Bandwidth-Efficient TCM with Prescribed Decoding Delay-Unequal Signal Energies. References. Chapter 5: Strictly Bandlimited Modulations with Large Envelope Fluctuation (Nyquist Signaling). 5.1 Binary Nyquist Signaling. 5.2 Multilevel and Quadrature Nyquist Signaling. References. Chapter 6: Summary. 6.1 Throughput Performance Comparisons. References.

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Bandwidth-Efficient Digital Modulation with Application to Deep Space Communications

The error probability performance of differential detection of narrow-band FM is determined and compared with the analogous results for limiter-discriminator detection of the same modulation. It is shown that over a large class of benign and hostile environments, e.g., Gaussian IF filter, 1 \leq BT \leq 3, h \leq 1 , AWGN, partial-band noise jamming, the differential detector offers no theoretical performance advantage over the limiter-discriminator receiver with integrate-and-dump postdetection filtering.

Differential Versus Limiter--Discriminator Detection of Narrow-Band FM

The maximum likelihood sequence estimator for the reception of coded digital phase modulated signals with single or multiamplitude constellations, transmitted over a multiplicative, frequency-nonselective (i.e., flat) correlated fast fading Rayleigh or Rician channel and corrupted by additive white Gaussian noise (AWGN), is derived. Due to this correlation, the errors caused by fading tend to occur in bursts. In the analysis, no assumption simplifying the problem is made. For fast fading the authors consider the most general case where both phase and amplitude distortion resulting from the fading process could change significantly and thus cannot be assumed to be constant over a number of transmitted symbols. It is shown that the estimator's hardware structure consists of a combination of envelope, multiple differential and coherent detectors. With multiple differential detectors they define a receiver structure consisting of a combination of more than one distinct differential detectors each of them employing a progressively increasing (by the symbol duration) time-delay element. The outputs of these detectors are jointly processed by means of an algorithm which is presented in a recursive form. The derivation of this new receiver is general enough to accommodate trellis coded phase shift keying (PSK) and quadrature amplitude modulated (QAM) systems. Differentially encoded signals, such as the /spl pi//4-shift differential quadrature phase shift keying (DQPSK) scheme can also be incorporated. In order to reduce the overall receiver implementation complexity, several reduced complexity, near-optimal versions of the algorithm are presented. These reduced complexity receivers are based on the use of only a few multiple differential detectors. Performance evaluation results for reduced complexity trellis coded /spl pi//4-shift DQPSK, /spl pi//4-shift 8-DQAM (differential quadrature amplitude modulation) and 8-DPSK (differential phase shift keying) systems have demonstrated that the proposed receivers significantly reduce the error floors caused by fading. >

Optimal decoding of coded PSK and QAM signals in correlated fast fading channels and AWGN: a combined envelope, multiple differential and coherent detection approach

A proposed scheme for differential detection of MSK with nonredundant error correction utilizes the output detected from the difference in phase between alternate signaling intervals, along with the output of the conventional differential detector, in accordance with the concept of a convolutional error correcting code. Theoretical analysis and experimental results show that the degradation from coherent detection is about 0.1 dB at a 10 dB signal-to-noise ratio.

H. Fuketa

Papers

Differential Detection of MSK with Nonredundant Error Correction