摘要:

The paper investigates the application of neural networks to adaptive congestion control in broadband ATM networks. A neural control scheme is proposed which is a direct application of the backpropagation neural networks with those modifications required to pose the problem in the framework of a general quality-of-service control. The learning algorithms regulating traffic loads to meet performance requirements are described and validated. To illustrate the present scheme's ability to control, three examples of networks consisting of simple dynamic queuing models are studied through simulations.

DOI:10.1049/ip-i-2.1992.0033

出版商:IEE    

年代:1992

数据来源: IET

摘要:

Pulse-position modulation (PPM) is presented within the context of a local-area network (LAN) application. A simplified analysis is used to calculate the advantage of converting from pulse-code modulation (PCM) to PPM signalling in a LAN, assuming in each case the same fibre network and the same optical transmitting device. Although PPM exploits its wide bandwidth to give greater sensitivity in noise, the true system advantage is obtainable only by using a large peak-to-mean-power ratio in the transmitter. It is shown that this performance is possible for both a laser diode and for an edge-emitting LED. An experimental system is reported, operating at a data rate of 4 Mbit/s, and good correspondence with theory is obtained. Design procedures are given for broad classes of situation.

DOI:10.1049/ip-i-2.1992.0034

出版商:IEE    

年代:1992

数据来源: IET

摘要:

This paper deals with the throughput efficiency and queueing analysis of efficient stopand-wait ARQ protocols suitable to control errors in data communication systems. Some novel stopand-wait ARQ schemes are also proposed. These stop-and wait ARQ schemes involve simple modifications of the classical scheme to provide an higher system reliability. The performance of the stop-and-wait techniques studied in the paper are analytically derived to compare their effectiveness in control errors in data communication systems with previous proposed efficient stop-and-wait ARQ schemes, in particular under high error rate conditions.

DOI:10.1049/ip-i-2.1992.0035

出版商:IEE    

年代:1992

数据来源: IET

摘要:

The average error probabilityPein many digital communications systems can be expressed as the statistical expectation of a known functionf(·) of some random interference variable (or vector)X. This paper presents a unified theory to evaluatePebased on moment error bounds or approximations, when the moments ofXare available. The theory can also be extended to random variables with inaccurately known moments. The relevant numerical question of accuracy and roundoff errors due to averaging with the aid of high-precision rules is addressed. Examples of application to spread-spectrum multiple-access systems, optical fibre systems and microwave digital radio-relay links are presented to show the applicability of the proposed methods to different environments.

DOI:10.1049/ip-i-2.1992.0036

出版商:IEE    

年代:1992

数据来源: IET

摘要:

An analytical approach is presented for the jitter performance of a timing recovery circuit consisting of a hard-limiter, an exclusive-or gate, followed by a second-order phase-locked loop. Exact expressions for the autocorrelation function and the power spectral density of the zerocrossing jitter in the data signal are derived, and then the phase jitter variance of the timing wave, generated at the output of the timing circuit, is obtained analytically as a function of various system parameters. Finally, numerical results and a comparative performance analysis show that considerable improvement can be achieved in jitter performance in addition to having the advantage of low cost and simple hardware implementation.

DOI:10.1049/ip-i-2.1992.0037

出版商:IEE    

年代:1992

数据来源: IET

摘要:

With the development of hand-free radio communications there is great interest in noise cancelling or speech enhancement in a car. We assume that M observations are available; each one is composed of signal and noise(si+bi), and s1is the signal to be estimated. Whatever the distance between microphones is, the signals are strongly correlated, while the correlation between noises becomes rather weak for a sufficiently great distance. The coherence function is then a pertinent criterion to know whether a speech signal exists or not. The three methods presented use the coherence function to filter the observations so giving an estimate of the signals1. The procedures presented are first shown forM= 2. Then, a generalisation of these procedures is offered. The performances of the three methods have been evaluated on real noisy speech signals by objective tests (gain on the signal-to-noise ratio, distance measures) and informal listening tests.

DOI:10.1049/ip-i-2.1992.0038

出版商:IEE    

年代:1992

数据来源: IET

摘要:

Digital generation methods of FMCW signals include frequency synthesis and direct waveform synthesis. The signal can be either generated directly at IF or from its baseband components which are combined by a SSB modulator. The IF signal is subsequently upconverted to RF. In this paper the different generation methods at IF, and a number of upconversion methods are described. A simplified digital technique for combining the baseband components to produce a signal at IF is presented. Application to wideband characterisation of the mobile radio channel is illustrated by a simulation example. Finally, a comparison with PRBS sounders demonstrates the advantages of FMCW sounders which employ heterodyne detection.

DOI:10.1049/ip-i-2.1992.0039

出版商:IEE    

年代:1992

数据来源: IET

摘要:

In using a CSMA (Carrier-Sense Multi-Access) protocol in a packet radio network, we cannot ignore the probability that the environment is so noisy that the channel state is misdetected. Similarly, with a BTMA (Busy-Tone Multi-Access) protocol, we must take into account the probability of misdetecting the busy or idle state of the channel. The paper focuses on these problems and tries to evaluate the throughput performance inppersistent access schemes, using an iterative approximation method. Furthermore, new protocol is suggested, which can effectively cope with the imperfect sensing property to achieve an improved throughput by sensing the channel in several consecutive slots.

DOI:10.1049/ip-i-2.1992.0040

出版商:IEE    

年代:1992

数据来源: IET

摘要:

The throughput of packet radio channels is analysed using the interference model in Rician fading environment and capture effect. Three types of packet protocols are considered, namely: (i) slotted ALOHA; (ii) unslotted nonpersistent inhibit sense multiple access (np-ISMA); and (iii) slotted nonpersistent ISMA. The test signal is always considered as Rician distributed and the interfering signal is modelled by either uncorrelated Rician or uncorrelated Rayleigh distributed. Numerical results are presented, indicating the effect of propagation impairments on channel capacity (i.e. maximum throughput). The results are of importance for mobile data networks, wireless office communications and other packet systems with contention-limited performance.

DOI:10.1049/ip-i-2.1992.0041

出版商:IEE    

年代:1992

数据来源: IET

摘要:

Time-of-arrival-based retransmission scheduling algorithms for unslotted ALOHA-type random access channels with high propagation delay are introduced and analysed in this paper. The techniques described are motivated by the fact that collision bursts on asynchronous channels can be analysed to create a partial time-ofarrival based ordering between the conflicting packets. Packets successfully ordered by collision burst analysis are then retransmitted in a locally synchronous, scheduled manner, thus eliminating potential further conflict between a large fraction of retransmitted messages. Collision resolution algorithms appropriate for channels with continuous signal detection, signal and collision detection, or signal and modified collision detection are described and evaluated in terms of throughput using a simple Poisson traffic model. The maximum throughput is shown to be 0.41, 0.47 and 0.509 for the three cases, thus demonstrating that the proposed time-of-arrival algorithms are competitive with the best slotted collision resolution algorithms. The practicality of the techniques described is also established by showing that maximum throughput is relatively insensitive to inaccuracies in channel feedback for a typical implementation of modified collision detection on a radio frequency channel.

DOI:10.1049/ip-i-2.1992.0042

出版商:IEE    

年代:1992

数据来源: IET