摘要:

A series of field trials has been conducted in which a 900 MHz CW signal was transmitted from a vehicle moving along a test route some 1·3 km from a base station. The recorded envelopes of the signals received on two vertically-separated antennas at the base station have been used in a computer simulation of two-branch predetection diversity reception. Several different systems have been simulated and the computed results show that the theoretical diversity advantages can still be obtained for an envelope cross-correlation (ρenv) of less than 0·7 for all strategies except switching. For a 1·3 km radius cell, a ρenvless than 0·7 can be obtained using antennas with a vertical separation of about 12λ. It has been found that the cumulative distribution and level-crossing rates of the signal are substantially improved and the average fade duration is approximately halved.

DOI:10.1049/jiere.1987.0112

出版商:IERE    

年代:1987

数据来源: IET

摘要:

After a brief description of the use of mobile radio in the fuel and power industries, the development of mobile networks over the period 1956–1979 is examined. This examination is concluded by describing a processor-based management system which was introduced to improve channel efficiency. Changes to the International Frequency Allocation Table require the Fuel and Power Industries to move mobile services to a new frequency band and the design requirements for a regular frequency re-use strategy are discussed. Methods of dealing with the traffic densities found in the major urban areas are considered, together with the development of a computer aid for network planning.

DOI:10.1049/jiere.1987.0111

出版商:IERE    

年代:1987

数据来源: IET

摘要:

A reliable model for UHF radiowave signal propagation into and variability within buildings is required to aid in the planning of cellular mobile radio systems serving portable transceivers. However, no such model has been presented in the literature to date and, with the imminent introduction of cellular mobile radio into New Zealand, a study of this problem has been undertaken with the aim of developing a model suitable for New Zealand buildings and situations. Two initial phases of this study have been completed in which suitable equipment and data collection and analysis procedures were established by conducting measurements at 927 and 851 MHz in a single building and at 851 MHz in another, dissimilar building where there was a line-of-sight path to all but one floor in both buildings. A preliminary model investigation using the data from unobstructed floors has shown that the measured cumulative probability density function of the received signal on a floor is best modelled by the Suzuki (Rayleigh plus log-normal) distribution and that the median signal level is not overly dependent on floor height.

DOI:10.1049/jiere.1987.0110

出版商:IERE    

年代:1987

数据来源: IET

摘要:

Growing interest in the potential of satellite mobile services in offering facilities complementary to those provided by the pan-European cellular radio network has stimulated a number of in-depth studies into possible system architectures. These activities are now coming together in a co-ordinated European programme and this paper summarizes the service opportunities which are emerging and some of the major technical issues which must be addressed in preparation for viable commercial operations.

DOI:10.1049/jiere.1987.0109

出版商:IERE    

年代:1987

数据来源: IET

摘要:

Digital transmission of speech over highway microcellular channels is investigated and theoretical results of bit error rate (BER) as a function of channel SNR and co-channel interference are presented. MSK modulation is used and the co-channel interferer has both a carrier phase difference and data stream time offset from the wanted signal.Transmissions over Rayleigh fading and AWGN channels are studied, and the theoretical and simulation results are in close agreement. Simulations were also performed using log-PCM, ADPCM and SBC speech. It was found that for toll quality speech it was necessary to operate with a channel SNR and co-channel SIR that both exceeded 30 dB for a BER of 5×10−4. No channel coding or equalization was used. For free flowing vehicular traffic conditions where the average vehicular speed was 112 km/h, a three-cell cluster yielded a cell length of 2·13 km, assuming an allotted duplex bandwidth of 10 MHz, a channel spacing of 25 kHz and 133 mobile users per microcell. The spectral efficiency for 2% and 10% blocking was found to be 36·1 and 42·1 erlang/MHz/base station, while the corresponding erlang/MHz/km2for a cell length of 2·13 km was 807·1 and 941·2.

DOI:10.1049/jiere.1987.0108

出版商:IERE    

年代:1987

数据来源: IET

摘要:

Propagation measurements are provided for highway and city centre microcells. Measurements along various motorways were taken with base station (BS) antennas at 10 m elevations. Pseudo-random binary sequences (PRBS) were transmitted via non-coherent FSK at 905 MHz. Low radiated power (16 mW into an 18-element Yagi) was used, and the signal level and bit error ratio (BER) were recorded by a mobile station (MS). The microcell length was found to be a function of the received field strength and, therefore, the BER. It was found that the cell lengths varied between 1 to 2 km for a BER of 10−3or better. Although the PDF of the received signal was Rician the microcell length was determined using the more pessimistic Rayleigh PDF. Two and three microcell clusters were considered. An inverse fourth power law was observed, and the received signal power in the microcell varied linearly with radiated power. For power levels of only 1 μW, error free transmission was found to occur over a cell length of 400 m.Detailed measurements in the Harley Street area in Central London enabled us to study how signals propagate in a nearly rectilinear grid pattern of roads. A theoretical model was established that provided signal levels that were close to those measured. Experiments were performed with the base station at junctions, roundabouts and at major city arteries. The inverse fourth power loss characteristics occurred, and the radiation distribution was found to be relatively insensitive to antenna type as the street pattern was the dominant factor.

DOI:10.1049/jiere.1987.0107

出版商:IERE    

年代:1987

数据来源: IET

摘要:

This paper describes a novel synchronization technique for wide-band TDMA systems. The technique employs a complex matrix operation to detect the start of the sounding or synchronizing signal. The matrix operation can be used for both channel estimation and synchronization. The matrix technique not only enables a substantial reduction in computational processes to be achieved relative to that of the correlation method, but also improves the SNR in channel estimation.

DOI:10.1049/jiere.1987.0106

出版商:IERE    

年代:1987

数据来源: IET

摘要:

The theory for a new class of Analysis by Synthesis LPC coding algorithms, called Backward Excitation Recovery (BER) LPC, is presented in this paper for the general case where an ARMA type filter is employed in the speech synthesis process. These coders differ from conventional Analysis by Synthesis LPC systems in that their excitation signal is defined from past information which is available at both the transmitter and the receiver. As a result only the filter parameters are required at the receiver for the recovery of the speech signal.A plethora of sequential filter optimization algorithms are proposed for both Single-input and Multi-input Synthesis filters. Two excitation adaptation algorithms are also proposed. The excitation signal is updated by using either ‘Past Decoded Speech’ (PDS) samples or ‘Past Excitation Samples’ (PES). The PES sequence is the signal which drives the all-pole part of the ARMA synthesis filter. It is shown that a specific BER-LPC codec, which employs one of the proposed PES algorithms, is equivalent to the recently proposed 4·8 kbit/s Self-Excited LPC system (SE-LPC).Computer simulation results highlight the SNR performance of BER-LPC codecs employing the proposed filter optimization and excitation adaptation algorithms, and demonstrate the superiority of several BER-LPC codecs over the SE-LPC system. Furthermore, it is shown that BER-LPC codecs which use the PDS excitation adaptation approach can operate successfully with a very low encoding delay. This property is valuable to low bit rate speech codecs operating in applications such as digital mobile radio.

DOI:10.1049/jiere.1987.0105

出版商:IERE    

年代:1987

数据来源: IET

摘要:

The design, simulation, and implementation of a modem specifically for use on mobile radio channels at frequencies allocated to the existing UK cellular system is described. In particular a novel technique for transmitting two phase-modulated digital signals from two mobile vehicles on nominally the same carrier frequency, and performing detection and separation of them at the receiver is covered.The potential application of this system in cellular mobile radio is discussed, together with an assessment of typical improvements in system capacity that might be achieved.

DOI:10.1049/jiere.1987.0104

出版商:IERE    

年代:1987

数据来源: IET

摘要:

The modems operate in the 900 MHz band and with a channel spacing of 25 kHz. Each transmitted signal from a mobile is a four-level QAM signal, with an element rate of 12,000 bauds and a total bandwidth of 24 kHz. 20% redundancy is allowed for retraining and synchronization purposes, giving a useful transmission rate of 19,200 bit/s for each QAM signal. Coherent demodulation together with a new technique of combined signal-detection and channel-estimation are used at the receiver, for more accurate tracking of the rapidly fading signal. Two four-level QAM signals can be transmitted simultaneously over each separate frequency band, giving a resultant bandwidth efficiency of just over 1·5 bit/s per Hz for useful data. The independent fading of the two signals, together with the particular detection and estimation processes employed at the receiver, prevent any undue interference between the two signals.The signals fed from the base station to the mobiles are 16-level QAM signals, that are frequency division multiplexed, with a channel spacing of 25 kHz. Each signal has an element rate of 12,000 bauds and a total bandwidth of 24 kHz. Two mobiles are fed from any one 16-level QAM signal, and the bandwidth efficiency for useful data is again just over 1·5 bit/s per Hz.The base station/mobile receiver uses two antennas, in an arrangement of space diversity, together with the maximum-likelihood combining of the two signals. The channel estimator is regularly retrained, so that it is not subject to catastrophic failure, and the detector achieves near-maximum-likelihood detection of the received data signal.

DOI:10.1049/jiere.1987.0103

出版商:IERE    

年代:1987

数据来源: IET