Showing papers on "Spectral efficiency published in 1988"

Comments on "Analysis for spectrum efficiency in single cell trunked and cellular mobile radio

Abstract: Nagata and Akaiwa (see ibid., vol.VT-36, p.100-13, 1987) have committed a principal error in evaluating the area mean power of the local mean power sums with log-normal distribution. This results in overly optimistic estimates of spectrum efficiency for various mobile radio systems. The correct expression for the area mean power is given. An alternative technique for the determination of the area mean power and variance of the joint interference is also reviewed. This is more appropriate for the shadowing phenomena occurring in mobile communications than the (corrected) method proposed by Nagata and Akaiwa. >

Modulation techniques for digital cellular systems

Abstract: A modulation technique is described that uses the properties of linear modulation techniques to achieve high spectral efficiency. When combined with high-quality low-bit-rate speech coding and channel coding, linear modulation provides a substantial increase in system capacity. A QDPSK system provides high-quality speech using a 10-kHz bandwidth, with better S/I protection ratios than the current analog system. A digital cellular system which uses QDPSK is discussed. Bit error rate and spectral efficiency data are presented. >

Spectrum, distance, and receiver complexity of encoded continuous phase modulation

Abstract: A comparison of different classes of encoded continuous phase modulation (CPM) schemes is presented. In terms of joint power-bandwidth performance, it is found that coded eight-level systems are better than coded four-level systems and that partial-response signalling is better than full-response signalling. In general, the price paid for better performance is increased receiver complexity. Heuristic design rules have been used to find good codes for CPM. In most cases the coding gains found are identical to published results that were generated by exhaustive search, indicating that the choice of design rules is quite appropriate. In the present study bandwidth efficiency is considered from both the 99% and 99.9% power-bandwidth points of view. It is found that partial-response signalling is even more jointly power and bandwidth efficient for the latter than for the former bandwidth criterion. >

A handoff control process for microcellular systems

Abstract: A handoff control process, which can handle frequent cell-boundary crossings by mobile radio users in microcellular systems, is presented. Handoff determination criteria are investigated under microcellular propagation models. As a result, it is shown that relative field strength measurement should be applied because of its almost twice higher spectrum efficiency than that of relative distance measurement. In application, measurement frequency greatly increases due to not only cell size reduction but also microcellular propagation characteristics. In order to solve this problem, a mobile-station-originated handoff process is proposed. This process becomes feasible in a TDMA (time-division multiple-access) system because mobile stations can be easily equipped with a measurement function. >

Spectral efficiency of cellular land mobile radio systems

Abstract: A rigorous and comprehensive approach to the definition and evaluation of spectral efficiency of cellular land mobile radio systems is presented. The method accounts for all pertinent system parameters within a cellular land mobile radio network. Subjective tests to evaluate the protection ratio for various systems is thought to be imperative to the evaluation of spectral efficiency. A comparison is made of a number of current and proposed mobile radio schemes based on the spectral efficiency evaluation package developed. >

Spread spectrum multiple access performance of orthogonal codes in fading multipath channels

Abstract: Indoor wireless communications (IWC) is an attractive alternative to wire-based local area networks. However, the indoor environment is characterized by fading multipath channels. Direct-sequence spread-spectrum techniques, with their inherent resistance to multipaths, are promising for IWC. To allow multiple users within a limited bandwidth, code division multiple access (CDMA) is needed. The authors analyze one relevant CDMA technique. A set of M-orthogonal sequences of length N is assigned to each of K users. The sequences consist of phase-modulated signals on the same carrier frequency. The bandwidth efficiency achieved over fading multipath channels is the presence of additive white Gaussian noise and multiple-access interference is determined. >

Trellis-coded MPSK modulation for highly efficient military satellite applications

Abstract: Trellis-coded multiple-phase-shift-keyed (MPSK) modulation is an effective technique for increasing the bandwidth efficiency of an existing channel while maintaining at least a moderate degree of power efficiency through coding. The authors consider the application of this technique to increase markedly the capacity of a 25-kHz military satellite channel. It is shown that with only minor modifications to the QPSK modem to incorporate 8 PSK and 16 PSK modulation and no modification to the rate-1/2 coder used to transmit 16 kb/s over this channel, transmission rates of 32 kb/s and 48 kb/s, can be supported at E/sub b//N/sub 0/ levels only moderately higher than for the lower data rate. In fact, it is demonstrated that 48 Kb/s can be transmitted within exactly the same bandwidth and at the same E/sub b//N/sub 0/ levels as that required to transmit uncoded QPSK at 32 kb/s at bit error rate of 10/sup -5/. >

Comparison of coherent and differential detection of BPSK and QPSK in a quasi-static fading channel

Abstract: The advantage of coherent detection over differential detection for both BPSK (binary phase-shift keying), and QPSK (quaternary phase-shift keying) in a multipath radio channel with either frequency-flat or frequency-selective fading is evaluated. The difference in receiver sensitivity is compared on the basis of three criteria: (1) bit-error rate (VER) averaged over fading samples, (2) BER distribution, and (3) distribution of block error rate. For a quasistatic fading channel, (2) and (3) provide a more meaningful comparison. Both analytical expressions and simulation are used in the comparison. The difference between differential detection of 2- and 4-level PSK is taken into consideration, as is the difference between pure coherent detection and coherent detection that uses differential encoding to resolve phase ambiguity. Both selection diversity and channel coding are considered as techniques for mitigating fading effects. It is found that coherent detection is superior to differential detection by at least 2.4 dB, which converts to about 30% improvement of spectral efficiency in a two-dimensional frequency reuse system with a fourth-power propagation exponent. >

Spectrum efficiency and digital cellular

Abstract: A spectrum-efficiency formula for cellular systems has been derived and used to compare digital and analog systems. Since the digital system is always less susceptible to interference, the tolerable interference level can be higher; in other words, the cochannel reuse distance can be less. This reuses distance proves that digital cellular is a spectrum-efficient system. In order to take advantage of digital nature and implement digital systems in cellular structures, several schemes can be introduced to further increase the spectrum efficiency. A theoretical analysis is carried out to indicate the advantages of developing digital cellular systems. >

Digital implementation of a coherent CPM system for mobile radio

Abstract: The authors describe the digital implementation of a continuous-phase-modulation (CPM) signaling scheme for land mobile radio applications. The transmitted signal is optimized in terms of bandwidth efficiency by nonlinear filtering. In the coherent receiver, synchronization and detection are performed separately to reduce complexity and improve acquisition performance. The authors explain the principles of transmitter and receiver and give details on the implementation. It is noted that the demonstration system will be capable of transmitting data at 16 kb/s over the narrowband mobile radio channel with channel spacing of 20 kHz. >

Class-IV PRS above the Nyquist rate

Abstract: An improved efficiency technique for class-IV (modified duobinary) partial-response signalling (PRS) above the Nyquist rate transmission is described. Computer simulations and hardware measurements for a base-band seven-level class-IV PRS system using this technique are shown in good agreement. It is then demonstrated by computer simulations that, with the use of this technique for class-IV 225-QPRS (quadrature PRS), an increase of 4% or more above the Nyquist rate, i.e., a spectral efficiency of 6.24 b/s/Hz or higher, can be achieved by simple symbol-by-symbol detection with a small degradation. It is further shown that the advantages of combining this technique with class-IV PRS are that a small band-width around DC can be carved out for the use of a service channel and that an even higher increase in spectral efficiency can be obtained in an FDM SSB system.

Direct RF modulation 256QAM microwave system

Abstract: A 2 GHz common carrier system utilizing 256-QAM for high spectrum efficiency is described A simplification in system design is accomplished by the use of direct RF modulation and demodulation rather than a more traditional IF (intermediate frequency) heterodyne approach Technical considerations for this direct approach are discussed The use of automatic power control results in reduced battery requirements, improved reliability, and easier frequency coordination With inclusive M12 muldems, extensive error correction, and time domain equalization techniques, the radio system provides 12 DS1 (19 MBS) in a 35 MHz bandwidth >

Channel assignments in mobile radio systems using channel interleaving

Abstract: Channel assignments in mobile radio systems which are constrained not only by cochannel interference but also by adjacent channel interference are examined, and the relationship between the minimal adjacent channel user distance and the increase in available channels by means of channel interleaving is clarified. The method described to obtain effective channel assignments deals with arbitrary interference conditions and clarifies the performance under various conditions, including cases in which the zone structure and antenna pattern are not homogeneous. This method is readily applicable to actual system planning, and should provide not only labor-saving for system design but also spectrum efficiency. >

ENCAP-4: an OQPSK-type modulation technique for digital radio

Abstract: A class of OQPSK-type signals (offset quadrature phase shift keyed) is defined which generalises several well known modulation formats. These signals are generated by means of a set of encoding rules which introduce a controlled amount of correlation between the in-phase (I) andquadrature (Q) components and between signal elements in each component. These encoding rulesimply the specification of four generating functions directly related to the eye diagram of the I and Q baseband signals. It is shown that the proposed signal representation provides an efficient means of design and performance evaluation. Advantageous trade-offs between spectral efficiency and power efficiency can be achieved with some of the proposed signals, making them suitable for digital radio applications.

A new class of modulation schemes with variable envelope

Abstract: A novel class of linear modulation schemes is proposed. Excellent spectral efficiency is achieved only at the expense of a small envelope fluctuation in the transmitted signal. Extensive computer simulations have been carried out which show that for noncoherent limited-discriminator (LD) detection the three-phase scheme presented performs better than MSK (minimum-shift keying). A Viterbi detector for coherent detection of the three-phase scheme is described which provides an improvement of 1-2 dB over LD detection and so could be used in low signal level areas. Good performance for both noncoherent and coherent detectors is therefore possible, while also fitting the signal into a channel spacing of 1.5* the bit rate with minimal levels of adjacent channel interference. The results presented suggest that nonconstant envelope schemes should be considered very seriously for future communications systems. >

Modification of a radio link system from analog to digital

Abstract: The authors describe the modifications in converting an analog radio-link system for use in digital communication. The existing analog system uses frequency modulation at the 6-GHz band to transmit 1860 frequency-division-multiplexed (FDM) voice channels. The baseband units of this system are replaced by digital circuits without any changes in radio-frequency sections. The system can transmit and receive 34 Mb/s (480 channels) standard third-level PCM (pulse code modulated) data in HDB3 or NRZ format. Although the modification reduces the bandwidth efficiency, it is an attractive choice for converting the analog communication network to digital in rural areas. >

Bandwidth-efficient high-speed coded trellis modulation

Abstract: A burst-mode coded trellis modulation system is discussed which is capable of 200-Mbit/s information rate transmission over nonlinear satellite transponders whose center frequencies are separated by 100 MHz. An overall real bandwidth efficiency of 2 bit/s per Hz of the allocated spectrum is projected. Convolutional codec and 8-PSK modulation subsystems together maximize the minimum Euclidean distance between the modulated codeword sequences in the overall coded trellis, resulting in a 4.3-dB asymptotic coding advantage over an uncoded 8-PSK system signalling at the same information rate over the same channel. The system performance has been evaluated by computer simulation.

Software simulation for MSK and RC modulation schemes in time- and frequency-selective mobile radio channels

Abstract: The class of minimum shift keyed (MSK) and RC modulation schemes provides several properties useful in mobile radio, e.g. spectral efficiency, constant envelope, and moderate complexity. In order to profit from multipath reception, a data rate of 525 kHz, resulting in moderate bandwidth, is chosen. For the mobile radio channels, appropriate Gaussian wide sense stationary uncorrelated scattering (GWSSUS) models are assumed and a software simulator for those channels is described. An improved method for calculating the channel parameters is proposed. Based on the GWSSUS model, bit error rates (BERs) of MSK and RC modulation schemes in time- and frequency-selective mobile radio channels are measured and compared with computed data. >

Spectral efficiency improvement techniques for nonlinearly amplified mobile radio systems

Abstract: A study is reported of 'double-jump' Nyquist channel filters which lead to reduced spectral spreading and an important bit error rate (BER) performance in nonlinearly amplified (NLA) mobile radio systems. In linearly amplified systems the filter retains the intersymbol-interference free properties of Nyquist filters and has the advantage of lower overshoot than the conventional raised cosine (RCS) filters. This reduced overshoot power (ROP) filter leads to a 1 dB system gain over conventional RCS filtered 16-QAM systems in NLA channels. >

Spectrum efficiency potential of 25 kHz offset channel assignments in the 821-824/866-869 MHz public safety bands

Abstract: The US Federal Communications Commission (FCC) recently allocated the paired bands of 821-824 MHz and 866-869 MHz to the Public Safety Radio Services and solicited comment on service rules and technical standards (Docket 87-112). The author examines the spectrum efficiency attainable through the use of 25-kHz offset channel assignments and contrasts it with that attainable via 12.5-kHz split channel assignments. It is concluded that due to the limited and well-defined coverage requirements typical of public safety applications, the offset approach can offer nearly as much spectrum efficiency as the split channel approach, while avoiding problems with timeliness of application, expansion of existing systems, high-speed data and encrypted voice needs, and mutual aid communication. >

Bandwidth and power efficient satellite TDMA demodulator and decoder

Abstract: A proof-of-concept demodulator for TDMA applications requiring high total data rates composed of many low data rate users is proposed. High-spectrum efficiency is obtained via a bandwidth efficient combined modulation and coding system, and low TDMA overhead is obtained via a fast acquiring digital phase lock loop. The system employs a data rate of 200 Mb/s with a bit error rate of better than 5 x 10 to the -7th in the presence of adjacent channel interference 20 dB above the weakest user. The 8-PSK modulation combined with the rate 5/6 forward error correction coding results in a bandwidth efficiency of better than 2 bits/second per Hz.