摘要:

The paper investigates the problem of information storage in a defective medium where real-time noisy information is available on the defects at both the encoder and the decoder. The problem is modelled as communication over a finite state channel with noisy state information available at both sides, It is shown that this problem can be transformed into Shannon's channel with side information problem. An optimal coding strategy is described and the capacity is derived. In general the capacity is given in terms of strategies. It is further shown that in some cases of interest the capacity can be described without employing Shannon strategies.

DOI:10.1049/ip-i-2.1992.0016

出版商:IEE    

年代:1992

数据来源: IET

摘要:

Line spectrum pairs (LSP) is one interesting way of representing the filter parameters of a linear production model. In particular, LSPs have been used for quantisation, i.e. for the spectral coding problem of speech coding. The concept of close-to-optimal search strategies, as well as optimal quantiser design, is discussed for the case of LSP-based quantisation. Previous scalar approaches are generalised to a vectorial treatment by carefully selecting a VQ technique that can provide robust results with low complexity. Simulation results are presented both for the scalar and for the vectorial case, showing that a two-dimensional VQ approach can provide substantial bit savings in realistic cases.

DOI:10.1049/ip-i-2.1992.0017

出版商:IEE    

年代:1992

数据来源: IET

摘要:

The paper presents evidence to support its claim that the space of trajectories of speech exists and may be approximated by a fourdimensional manifold which is nonlinearly embedded in both a space of LPC coefficients and also in a filter bank space. It also investigates the possibility that there are different dimensions for different phonetic categories, but finds no evidence to support this hypothesis. The dimension is of interest since it is the smallest number of independent parameters needed to specify speech.

DOI:10.1049/ip-i-2.1992.0018

出版商:IEE    

年代:1992

数据来源: IET

摘要:

The error-control performance of a set of recently introduced combined error-control line codes (ECLCs) is assessed. A comparison is made with the conventional arrangement of a cascade connection of error-control and line-code systems, based on three familiar, illustrative line codes. The results obtained by theoretical analysis are backed up by software simulation and experimental performance measurements.

DOI:10.1049/ip-i-2.1992.0019

出版商:IEE    

年代:1992

数据来源: IET

摘要:

The discrete cosine theorem (DCT)- based real-valued linear code is derived for the first time in the literature. A BCH-like subclass of DCT linear codes is also developed, for which fast decoding algorithms exist. It is shown that the DCT-based error control codes proposed in the paper can be viewed as a bridge to link the fields of source coding and channel coding.

DOI:10.1049/ip-i-2.1992.0020

出版商:IEE    

年代:1992

数据来源: IET

摘要:

Digital pulse-position modulation (PPM) is a scheme whereby the abundance of bandwidth available in monomode fibres may be exchanged for improved receiver sensitivity. As this format relies on the position of the pulse to convey information, it is subject to a positional error as well as to the familiar false-alarm and erasure errors. A performance and optimisation analysis for both uncoded homodyne digital PPM and digital PPM employing Reed-Solomon errorcorrection codes is presented. System performance for a range of fibre bandwidths and PPM symbol sizes is analysed, and it is shown how the predetection filter may be configured in order to minimise the three error sources and achieve maximum transmission efficiency (nats/photon). Results are presented at a bit rate of 565 Mbit/s and a wavelength of 1.5 μm, comparing both uncoded and coded homodyne digital PPM with shot-noise-limited coherent PCM. It is shown that there are optimum PPM symbol sizes, fibre bandwidths and Reed-Solomon code rates at which to operate. The conclusion is that uncoded digital PPM offers an improvement of 5 dB over homodyne PSK PCM, and that the Reed-Solomon error-correction coded system offers a 4 dB improvement over uncoded PPM, when operating at the optimum 3/4 code rate.

DOI:10.1049/ip-i-2.1992.0021

出版商:IEE    

年代:1992

数据来源: IET

摘要:

The object of the paper is to compare the performance of coherent and noncoherent modulation schemes in the presence of phase noise, and to determine whether the noncoherent schemes might be more robust than the coherent schemes more usually employed. The paper considers the effect of phase noise on two types of noncoherent modulation schemes: wide-shift FSK and differential PSK, and compares the performance with coherently demodulated PSK. Analytical models are derived for the performance of the three schemes, and numerical results are calculated for a system using a typical oscillator subject to phase noise. The results show that noncoherent schemes are indeed more robust than coherent ones, and that wideshift FSK is more robust than differential PSK. Thus the noncoherent schemes will operate successfully at much lower data rates than the coherent. These results are backed up by computer simulations of the three schemes, which show the same increase in susceptibility from FSK to DPSK to coherent PSK.

DOI:10.1049/ip-i-2.1992.0022

出版商:IEE    

年代:1992

数据来源: IET

摘要:

The paper presents the results of a software study of multiple cochannel interferers in a digital system, employing Gaussian minimum shift keying (GMSK) modulation with a bandwidth data rate productBbT= 0.3. The bit-error rate (BER) performance was determined in a Rayleigh and log-normal fading environment typically encountered in mobile radio systems. It has been shown that the error rate is independent of the number of interferers present when the total S/I ratio of up to 6 interferers are considered. Additional performance measures were investigated such as block-error rates, the probability,P(m,n)of havingmerrors in a block of lengthn, burst and gap-length distributions. These measures have shown that the interference causes errors to occur in a more bursty manner than Gaussian noise.

DOI:10.1049/ip-i-2.1992.0023

出版商:IEE    

年代:1992

数据来源: IET

摘要:

Increasing user demands to access resources, such as databases and application programmes, beyond those available in a single network has resulted in the introduction of teleprocessing systems and communication services between networks supported by different organisations. Consequently, the sharing of network resources introduces security threats such as unauthorised reading, modifying, adding or deleting of the contents of resources. It is therefore necessary to implement certain access control mechanisms to protect these resources from unauthorised access. In the paper, an internet access control scheme which operates at the network level (or the packet level) is presented. This scheme allows controlled access to the internal resources of a network, and only trusted systems can gain access to external networks. In this scheme, a secure communication link is established between a requesting machine and the requested remote resource at the initiation of an external session. All the entities, the network gateways and the machines at the end points, along this communication path are authenticated during the initiation process. Any subsequent packets transmitted along this path are also authenticated throughout the session to ensure that they originated from the machine initiating the session. The scheme uses the RSA and the DES security algorithms to implement session initiation and packet origin authentication, respectively. A major issue in internet access control is the distribution of packet keys (which are used for packet authentication purposes) to network entities for each communication session. This problem has been overcome in the scheme by deriving the packet authentication key from the RSA private key of each network entity, using a reference key number concept, and allowing a different packet authentication key for each external session between communicating entities. This eliminates the need to distribute the packet authentication keys, which otherwise could be a major threat to the integrity of an access control scheme. The overheads incurred due to the extra access control procedures have been quantified and are presented in the paper. It was found that the overheads of this scheme are smaller in comparison with the visa scheme [1].

DOI:10.1049/ip-i-2.1992.0025

出版商:IEE    

年代:1992

数据来源: IET

摘要:

Effects of multipath propagation on a digital radio hop employing a plane reflector as a passive repeater were analysed by using a ray tracing method. The calculations of raypath parameters on the hop show that a large-aperture plane reflector increases attenuation fading due to the main ray's angle-of-arrival variation by its sharp radiation pattern, and it can reduce dispersive fading. A digital transmission experiment on a reflector-equipped hop showed that plane reflectors could be used for small-capacity digital microwave systems.

DOI:10.1049/ip-i-2.1992.0026

出版商:IEE    

年代:1992

数据来源: IET