1,724,351 research outputs found
Two New Coding Techniques for Diversity Communication Systems
No full textIn the classical diversity techniques widely used in combating fading and in spread-spectrum systems, the same information is transmitted over m ≧ 2 channels. The overall error probability is reduced by a suitable combination of the m received signals. This paper presents two new techniques applicable to diversity systems. Using the proposed techniques, the signals transmitted over the m channels corresponding to a given message—albeit different—can be encoded through a suitable error-correcting coding operation, thereby enhancing reductions in the receiver-side bit error probability with respect to classical diversity techniques. Applications to fading-affected communication systems and spread-spectrum systems are discussed. © 1990 IEE
A Selective ARQ Protocol with a Finite-Length Buffer
No full textAutomatic repeat request (ARQ) techniques with error-detecting codes are commonly used in communication systems. Of these, selective protocols, while the most efficient, have the notable drawback of requiring large buffers at the receiver side. A new selective ARQ protocol with a finite-length buffer is described in this paper. If N is the number of codewords transmittable in the round-trip delay, the described protocol requires a buffer having length equal to N + N(a), + N(a) greater-than-or-equal-to 2 being an integer. A lower bound on the throughput of the described ARQ protocol is derived. The proposed protocol achieves higher throughputs than similar schemes, giving comparable results to selective protocols with infinite-length buffers for high error rates in the communication channel
A Go-Back-N Protocol for Mobile Communications
No full textMobile digital communication systems are generally affected by severe noise and disturbances such as multipath fading and Doppler effects that degrade the reliability of the received information. Automatic-repeat-request (ARQ) techniques, which include the go-back-N (GBN) protocol, are widely used to improve the performance of digital communication systems. This paper describes a GBN protocol, with a buffer and memory at the receiver side, which offers low implementation complexity and a structure especially suited to mobile communications. The optimization of the protocol parameters is determined through numerical analysis. Performance is evaluated by computer simulation using a channel model suitable for mobile communications. The results show that the proposed ARQ scheme achieves higher performance than that of other ARQ protocols, and that at high error rates, its efficiency compares favorably with selective repeat protocols having an infinite buffer
Some ARQ Protocols with Finite Receiver Buffer
No full textIn this paper, some new schemes for communication systems using error-detecting codes are described. These schemes employ hybrid strategies for the retransmission of the codewords detected in error, and combine the advantages of the go-back-N and selective protocols. The memory, introduced at the receiver side, enhances their performance with respect to the classical schemes. The results show that the protocols described in this paper permit the achievement of a net improvement with respect to other similar schemes
An ARQ Scheme with Memory and Integrated Modulations
No full textIn this paper, the integration of the modulation operation in an automatic-repeat-request scheme, using error-detecting codes, is analyzed. A new protocol is described, in which the modulation operation facilitates the recovery of the transmitted code word. The results show a net improvement in the throughput of the automatic-repeat-request scheme, particularly for mean and high error-rate conditions. Continuous-phase-frequency shift keying modulations, which present a low bandwidth occupancy, are particularly considered. Copyright 1987 by The Institute of Electrical and Electronics Engineers, Inc
Reliability Improvement for Simplex Communication Systems with Multiple Channels
No full textThe reliability of a communication system can be improved by using channel coding. Complex coding and decoding are often required to achieve high performance. An alternative approach is channel redundancy in which the same information is transmitted over two or more channels at the same time. In this way, the coding complexity required to achieve a given error probability can be appreciably reduced. However, a decoder is required for each channel. This paper describes a method which uses channel redundancy to obtain higher performance compared to similar systems and requires only one channel decoder
New ARQ Protocols Using Concatenated Codes
No full textConcatenated coding techniques present attractive characteristics in many real applications because of their high efficiency. In this paper, two new automatic-repeat-request (ARQ) protocols using a concatenated coding scheme are described. The structure, introduced in a codeword of a concatenated coding scheme, is used to improve the performance of ARQ protocols, especially for high error rates in the communication channel. The performance of the scheme described herein is derived through theoretical analysis. The results show that the proposed schemes outperform other similar ARQ protocols
On a Magical Mystery Tour of Green Insecticide Research: Current Issues and Challenges
Full text linkThe Editorial outlines recent research advances in green insecticide research. Particular attention is devoted to studies shedding light on the modes of action and non-target toxicity of natural substances of plant origin. Research focusing on the development of new formulations (including those relating to nano-objects) to magnify the effectiveness and stability of green insecticides in the field represents key advances. Herein, a carefully reviewed selection of cutting edge articles about green pesticide development recently published in Molecules is presented. The impact of sub-lethal doses of green insecticides on insect behavioral traits is still overlooked, representing a timely challenge for further research
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