The application of Reed-Solomon codes in slow frequency-hopped systems has been extensively studied. Earlier investigations assumed an infinite interleaving length and considered partial-band noise jammers only. This paper extends previous efforts by analyzing the effect of finite interleaving length and the impact of band multitone jammers. We also explain why two-threshold (2T) erasure-insertion methods (EIM) are needed and examine their performance. Numerical results are presented to compare the effectiveness of EIM's and jammer types and to study the relationships among the hop rate, the interleaver size, and the code rate. The use of 2T EIM's necessitates the estimation of several additional channel and signal parameters. Simple and effective estimation algorithms are provided as well. Index Terms-Errors-and-erasures decoding, frequency-hop, jamming, RS code. I. INTRODUCTION A FAST frequency-hopped (FFH) system employs both frequency and time diversity and enjoys the advantage of having a "coding gain." On the other hand, to acquire a satisfactory antijam (AJ) capability, a slow frequency-hopped (SFH) system usually has to add an extra mechanism of protection-that is where forward error-control (FEC) coding comes into play. Stark [1] compared the performance among repetition codes, convolutional codes, and Reed-Solomon (RS) codes for SFH systems.-ary frequency-shift keying (MFSK) or differential phase-shift keying (DPSK) are two practical modulation schemes that most frequently go with RS-coded FH signals. An excellent review of the application of RS codes to SFH/MFSK systems can be found in [10]. Side information, which offers the information about the received symbol's reliability, can help increase the error-correcting capability of a given code. Stark [1] showed that the use of binary side information about the presence of a jammer to determine whether a received symbol should be erased can enhance the error-control capability of RS codes. Hagenauer and Lutz [4] used channel state and erasure information derived from received waveform's amplitude to improve the performance of a mobile satellite system. In [6], test symbols were utilized as a reference of symbol reliability in various
The performance of low-density parity-check (LDPC) codes is investigated for fast frequency hopping / binary frequency shift keying (FFH/BFSK) in partial-band noise jamming channels. We employ different diversity combining schemes to compute the codeword bit decision reliability. In this paper, we consider the maximum-likelihood (ML) diversity combining scheme and two low-complexity suboptimal diversity combining schemes: square-law with adaptive gain control (AGC) combining and square-law with equal gain combining. Simulation results show that, by combining both of the diversity and coding gain, our proposed system can provide excellent performance against partial-band noise jamming.
Manufacturing systems are hardly modelled and analysed in detail due to the complex and interactive behaviours of the production, movement, maintenance and dispatch on the shopfloor. In this paper, an agent-based modelling methodology is proposed to model the manufacturing systems using the separation model design approach. The agent models are constructed using the distributed agent-oriented Petri net (DAOPN). The DAOPN is a high-level Petri net (PN) and is designed based upon the coloured time Petri net (CTPN). The new designed DAOPN is especially desired to model the manufacturing systems in the separation and decomposition manners to reduce the modelling efforts and increase the modelling extensibility. The proposed DAOPN components include the immediate, pitch-type, catch-type, status-source and status-duplication places; immediate, timed, decision and database-accessing transitions; and directed, inhibitor and interrupt arcs. In addition to the separation characteristics, the DAOPN can also model manufacturing systems with flexible routes of products, flexible automation of equipment, product model mixes, and huge production information intercommunication. Especially, the separation design is advantageous to the manufacturing model reconstruction and maintenance. Finally, the DAOPN is defined in this paper, and several typical applications including the production, movement, equipment failure and preventive maintenance are all discussed and evaluated.
Frequency-hopping spread-spectrum (FH-SS) is an efficient technique to combat jamming. Previous works in jamming channels pay more attention to partial band noise jamming (PBNJ). In this paper, Low-Density Parity-Check (LDPC) coded fast frequency hopping binary frequency shift keying (FFH/BFSK) spread-spectrum (SS) systems are investigated under band multitone noise jamming (BMTJ). We take the advantage of both diversity gain and coding gain for enhancing the system performance. We consider maximumlikelihood (ML) diversity combing and square-law with equal gain combing schemes which are used to compute the codeword bit decision reliability. The sum-product algorithm (SPA) based on belief propagation is exploited for iterative decoding. Simulation results reveal that our proposed system provides excellent performance against band multitone noise jamming.
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