摘要:

Two suboptimum detection procedures, one based on the binary matched filtering and the other based on the weighting of partial decisions, were introduced earlier into the literature as very suitable for the cost-effective microprocessor-based implementation of the medium-speed voice-band data modems. Previous analysis of these two detection procedures was limited to the case when only Gaussian noise is present in the communications system. Here, both procedures are treated comparatively under conditions typical of realistic applications. These conditions refer to the cases when Gaussian noise is combined with intersymbol interference or timing jitter. To provide a reference against which the new detection procedures can be evaluated, results known from the literature for the optimal detector are here utilised and are comparatively presented.

DOI:10.1049/ip-f-1.1984.0052

出版商:IEE    

年代:1984

数据来源: IET

摘要:

For each of four separate conditions placed on a waveform (amplitudes at certain epochs and slopes at those epochs), constraints on the corresponding spectra are obtained for a system of any bandwidth. Waveforms which satisfy certain combinations of amplitude and slope constraints, within a minimum bandwidth, are shown to have unique spectra. The method confirms that Nyquist's first and second conditions are satisfied by the raised-cosine frequency spectrum, and spectra are obtained for other waveform conditions. The results are of interest in practical systems where constraints are placed on intersymbol interference and telegraph distortion, or as design targets in theoretical systems.

DOI:10.1049/ip-f-1.1984.0053

出版商:IEE    

年代:1984

数据来源: IET

摘要:

A method of generating sinusoidal frequency-modulated pulses using a 1 bit digital technique is developed. The method utilises the information in the zero crossings of the signal, rather than sampling and voltage quantisation, to reconstruct the signal. An intuitive view of the spectrum of a frequency-modulated square wave (FMSW) is derived, and confirmed by mathematical analysis. The spectrum consists of a series of harmonics of the form associated with the modulation law used. The bandwidth andTBproduct of the harmonics increase in direct proportion to the order of the harmonic. The effect of the time quantisation of the zero crossings necessary to generate a FMSW using digital logic is analysed. The relationship between the time quantisation, signal bandwidth and clock frequency is discussed. The generation of nonlinear FM pulses is illustrated using a truncated Gaussian 15 dB spectrum, and the effect of the time quantisation on the compressed pulse sidelobe levels is computed. The effect of Doppler shift on the sidelobe levels is also illustrated. Hardware for generating FMSWs is described, and the effect of the logic risetime on the spectrum is analysed. The concept of the FMSW is verified using a simple TTL circuit to generate a LFM pulse.

DOI:10.1049/ip-f-1.1984.0054

出版商:IEE    

年代:1984

数据来源: IET

摘要:

In this paper a cellular land-mobile radio system with combined mobile telephone and dispatch services is considered. A hybrid scheme for channel assignment is considered. Two flow control levels for dispatch users are introduced to preserve the quality of mobile telephone service. Results are obtained by computer simulation of the system.

DOI:10.1049/ip-f-1.1984.0055

出版商:IEE    

年代:1984

数据来源: IET

摘要:

A combination of transparent tone-in-band (TTIB) and feedforward signal regeneration (FFSR) audio signal-processing techniques enable the efficient transmission of speech and data communications over mobile radio links, and amplitude companded pilot tone single sideband (SSB) in particular. The contribution is concerned primarily with data communications, coherent and noncoherent, over such networks in the presence of multipath induced amplitude and phase distortion. A detailed consideration of the properties of the combined TTIB/FFSR system show it to have several significant advantages over data-derived reference schemes.

DOI:10.1049/ip-f-1.1984.0056

出版商:IEE    

年代:1984

数据来源: IET

摘要:

The paper considers the receiver of a digital data-transmission system which is fed from a number of different transmitters in an arrangement where separate short messages are transmitted, in turn, from the different transmitters, with arbitrary time gaps between adjacent messages when no signal is transmitted. The signals received from the different transmitters may be subjected to widely different levels of amplitude and phase distortions, so that a training or synchronising signal must be transmitted at the start of each message, during which the receiver must obtain a reasonably accurate estimate of the sampled impulse response of the channel. The latter may then be used for the initial adjustment of an adaptive equaliser, but this or any other application of the channel estimate is not studied here. Since a satisfactory estimate of the sampled impulse response of the channel is needed in the shortest possible time, in order to maximise the transmission rate of useful data over the duration of the message, an optimum, estimation process must be used together with the training signal that enables the best estimate of the channel response to be obtained. The paper derives the maximum-likelihood estimation process for the sampled impulse response of the channel, which, under the assumed conditions, gives the unbiased estimate with the minimum mean-square error. The paper then determines the conditions that must be satisfied by the training signal to minimise the mean-square error in the channel estimate, and lists a number of such optimised training signals using two-, three-and four-level symbols. Finally, the new systems are compared with the more promising of the techniques previously described.

DOI:10.1049/ip-f-1.1984.0057

出版商:IEE    

年代:1984

数据来源: IET

摘要:

Polarisation filtering is applied in radar systems to improve target detection in adverse environments. Fluctuations of the polarisation states of unwanted incident signals dictate the need for filters that suppress such signals in the polarisation domain and cover a controllable area of polarisation space. This has led to the concept of the multinotch logic-product (MLP)polarisation filter which attempts to meet the above need. The paper describes the parameters that affect the general characteristics of the MLP filter, gives a typical design example and uses a representative set of experimentally derived rain clutter data to evaluate the performance of this MLP filter.

DOI:10.1049/ip-f-1.1984.0059

出版商:IEE    

年代:1984

数据来源: IET

摘要:

A locally optimum receiver structure is derived for the coherent detection of continuous phase frequency shift keying in non-Gaussian noise. Performance of the receiver, which consists of a zero-memory nonlinearity followed by a correlator, is evaluated for a number of important noise models. The effects of varying the observation interval and modulation index on receiver error probability are determined.

DOI:10.1049/ip-f-1.1984.0060

出版商:IEE    

年代:1984

数据来源: IET

摘要:

This paper considers the problem of evaluating the performance of a 16-ary quadrature amplitude modulation (QAM) signal transmitted through a bandpass nonlinearity (BPNL), exhibiting AM-AM and AM-PM conversions, and in the presence of additive gaussian noise (AGN) both preceding and following the nonlinearity. An expression for the error probability is derived and computed. Also, the effect of TWT back-off from saturation on 16-ary QAM system performance is studied. Finally, as an example, a comparative study of 16-ary CPSK and 16-ary QAM transmissions is undertaken with the BPNL operated at various levels of back-off from saturation.

DOI:10.1049/ip-f-1.1984.0061

出版商:IEE    

年代:1984

数据来源: IET

摘要:

This paper proposes a new 16-ary quadrature amplitude modulation (QAM) direct regenerator to be used in digital communications systems. Theoretical analysis follows to evaluate the performance of a two-link system in additive Gaussian noise (AGN) incorporating a practical 16-ary QAM direct regenerator and an ideal coherent receiver. In addition to nonlinearities and circuit limitations in the regenerator, optimum detection in the receiver is also taken into account.

DOI:10.1049/ip-f-1.1984.0062

出版商:IEE    

年代:1984

数据来源: IET