摘要:

The paper describes a simple technique for achieving bit synchronisation with transparent tone-in-band (TTIB) systems. The composite system operates such that carrier and bit sychnronisation with narrow-band data communications are attained simultaneously in fading and nonfading environments. Consequently, the technique has wide application including line, satellite and mobile communications.

DOI:10.1049/ip-f-1.1985.0012

出版商:IEE    

年代:1985

数据来源: IET

摘要:

The paper describes the behaviour of narrowband phase-locked loops in the mobile multipath environment. It is shown that the loop will often track individual frequency components of the pilot's spectrum and that the loop can give rise to frequency-tracking errors of upto ±ωdrad/s in estimating the nominal frequency of the received pilot.

DOI:10.1049/ip-f-1.1985.0013

出版商:IEE    

年代:1985

数据来源: IET

摘要:

In the paper, a new error-trellis syndrome decoding technique for convolutional codes is developed. This algorithm is specialised then to the entire class of systematic convolutional codes. Finally, this algorithm is applied to the high-rate Wyner-Ash convolutional codes. A special example of the one-error-correcting Wyner-Ash code, a 3/4 rate code, is treated in the paper. The error-trellis syndrome decoding method applied to this example shows in detail how much more efficient syndrome decoding is than, say, Viterbi decoding would be if applied to the same problem. For standard Viterbi decoding, 64 states would be required, whereas in the example only seven states are needed. Also, within the seven states required for decoding, many less transitions are needed between the states.

DOI:10.1049/ip-f-1.1985.0014

出版商:IEE    

年代:1985

数据来源: IET

摘要:

The parity check matrix of an (n, k, t) linear error-correcting code provides a unique mapping between binary vectors of lengthn, whose Hamming weight does not exceedt, and binary vectors of length (n–k), which are the syndrome obtained by multiplying the vector of lengthnby the parity check matrix. This enables the ‘compression’ of binary vectors having a limited Hamming weight. It is shown in the paper how this principle can be applied in ARQ schemes, where, upon detection of an error in a received message, further retransmitted messages can be made shorter from one retransmission to the next.

DOI:10.1049/ip-f-1.1985.0015

出版商:IEE    

年代:1985

数据来源: IET

DOI:10.1049/ip-f-1.1985.0016

出版商:IEE    

年代:1985

数据来源: IET

摘要:

The case of a direction-finding antenna (or an antenna array) with a beam shape which can be approximated by a cosine or a sine function is considered, and a probability function is found for the direction indications when two co-channel signals are present under Rayleigh fading conditions. Simulated case studies are described and compared with the analytical results.

DOI:10.1049/ip-f-1.1985.0017

出版商:IEE    

年代:1985

数据来源: IET

摘要:

The threshold effect is a phenomenon experienced in the reception of frequency modulated (FM) signals. It is found to be particularly troublesome in FM quasisynchronous (QS) mobile radio schemes, in the parts of the coverage area where carrier cancellation occurs due to carrier components interaction. This results in sharp noise bursts punctuating the receiver output and a consequent degradation in the speech quality. The paper describes a technique which was implemented as a receiver modification in the form of an add-on unit for the purpose of minimising the threshold noise effects with satisfactory results. Measurements conducted on a commercial receiver incorporating this modification revealed that an improvement of 12 dB in the output S/N was achieved.

DOI:10.1049/ip-f-1.1985.0018

出版商:IEE    

年代:1985

数据来源: IET

摘要:

A large number of small-area statistical channel descriptors in the form of average-power/time-delay profiles have been obtained in urban and suburban areas. The average excess delay and the delay spread are meaningful parameters which adequately describe the dispersiveness of the channel, and the variability of these parameters over a large area has been used as part of a two-stage model for characterisation of a UHF mobile radio channel. Suburban and urban areas exhibit quite different characteristics, reflecting the different nature of the environment. The variability of the statistical parameters is also a useful estimator of the performance bounds of radio systems. Using the measured data, together with relationships available in the literature for the performance of a given system in the presence of multipath, consideration is given to several system, such as DPSK data, SSB with pilot, FM voice and a phase ranging automatic vehicle location system. It is concluded that system techniques such as diversity reception can often lead to useful improvements in performance.

DOI:10.1049/ip-f-1.1985.0020

出版商:IEE    

年代:1985

数据来源: IET

摘要:

It is well known that the transform operation results in a large expansion of the numerical range of values encountered when input data is subjected to a one- or more dimensional transformation. It is usually assumed that the dynamic range expansion factor isNc, whereNis the transform order andcits dimension, but it is demonstrated here that this result is only true under very restricted conditions, and that, in general, coefficient dynamic range expansion is not only transform dependent, but is often significantly greater than the above value. It is suggested that this effect may influence the transform processing operation in feature extraction and coding applications to a greater degree than has previously been realised.

DOI:10.1049/ip-f-1.1985.0021

出版商:IEE    

年代:1985

数据来源: IET

摘要:

A general expression is developed for the basic circuit reliability when any number of different propagation modes may be present. This is used to formulate a full method of evaluation for two propagation modes, assuming that daily values of mode basic MUF and signal/noise ratio each follow a normal distribution. Approximations to the full method lead to the generation of a new simplified method, suitable for routine prediction application, which takes account of the correlation between mode basic MUFs. Results are presented of sample comparisons between values of reliability given by the full method, the simplified method and other existing approximate methods.

DOI:10.1049/ip-f-1.1985.0023

出版商:IEE    

年代:1985

数据来源: IET