Showing papers on "Frequency-hopping spread spectrum published in 1987"

A design concept for reliable mobile radio networks with frequency hopping signaling

Abstract: The design of a packet radio network must reflect the operational requirements and environmental constraints to which it is subject. In this paper, we outline those features that distinguish the High Frequency (HF) Intra Task Force (ITF) Network from other packet radio networks, and we present a design concept for this network that encompasses organizational structure, waveform design, and channel access. Network survivability is achieved through the use of distributed network control and frequency hopping spread-spectrum signaling. We demonstrate how the execution of the fully distributed Linked Cluster Algorithm can enable a network to reconfigure itself when it is affected by connectivity changes such as those resulting from jamming. Additional resistance against jamming is provided by frequency hopping, which leads naturally to the use of code division mutiple access (CDMA) techniques that permit the simultaneous successful transmission by several users. Distributed algorithms that exploit CDMA properties have been developed to schedule contention-free transmissions for much of the channel access in this network. Contention-based channel access protocols can also be implemented in conjunction with the Linked Cluster network structure. The design concept presented in this paper provides a high degree of survivability and flexibility, to accommodate changing environmental conditions and user demands.

Throughput Analysis in Multihop CSMA Packet Radio Networks

Abstract: In this paper, we use a Markov model to develop a product form solution to efficiently analyze the throughput of arbitrary topology multihop packet radio networks that employ a carrier sensing multiple access (CSMA) protocol with perfect capture. We consider both exponential and nonexponential packet length distributions. Our method preserves the dependence between nodes, characteristic of CSMA, and determines the joint probability that nodes are transmitting. The product form analysis provides the basis for an automated algorithm that determines the maximum throughput in networks of size up to 100 radio nodes. Numerical examples for several networks are presented. This model has led to many theoretical and practical extensions. These include determination of conditions for product form analysis to hold, extension to other access protocols, and consideration of acknowledgments.

The role of spread spectrum in packet radio networks

Abstract: This paper is devoted to an examination of the key features of spread-spectrum signaling in packet radio networks The multiple-access capability, capture, and anti-multipath capability of spread spectrum are the principal topics, and the basic features of spread spectrum that enable it to provide these capabilities are illustrated The interaction between the spread-spectrum signaling and the network protocols is discussed Methods for performance evaluation are reviewed, and analytical results on the multiple-access capability of spread spectrum are presented

Modeling and performance analysis of multihop packet radio networks

Abstract: The design of packet radio networks involves a large number of issues which interact in a very complex fashion. Many of these pertain to the RF channel and its use, others pertain to the operational protocols. Clearly, no single model can be formulated which incorporates all the necessary parameters and leads to the optimum solution. The one essential element which complicates matters is that, contrary to point-to-point networks in which each channel is utilized by a single pair of nodes, the radio channel in packet radio networks is a multiaccess broadcast resource: i) in a given locality determined by radio connectivity, the channel is shared by many contending users, hence the need for channel access protocols; ii) radio is a broadcast medium and thus the action taken by a node has an effect on the actions taken by neighboring nodes and their outcome. Despite the complexity of the problem, there has been significant progress worth reporting on. The work accomplished so far has been either the analysis of specific examples of networks or an attempt to create models that would be useful in the design of general networks. The purpose of this paper is to survey the various modeling techniques that have been used for the performance analysis of packet radio networks, and to discuss the assumptions underlying these models, their scope of applicability, and some of the results obtained.

Cellular Efficiency with Slow Frequency Hopping: Analysis of the Digital SFH900 Mobile System

Abstract: The new digital cellular SFH900 mobile system, based on "mixed" slow frequency hopping (SFH) combined with time division, is described in detail. The system includes Viterbi quasi-coherent demodulation of GMSK for which performance measurements in multipath conditions are presented. A concatenated coding scheme that takes full benefit of built-in frequency diversity and interference diversity is introduced. A model for SFH cellular performance evaluation is presented and the quality-versus-capacity tradeoff for SFH900 is given for various frequency reuse patterns. With advanced 16 kbit/s speech coding techniques, and including a 25 percent overhead for management and signaling, the spectrum efficiency of a many-celled SFH900 network is around 3.5 users/cell/MHz, a significant increase in comparison to conventional analog systems. SFH provides intrinsic adaptability to varying traffic conditions and enhanced flexibility for multiservice operation. The SFH900 principles, which have been recently validated through field tests, are very promising for second generation cellular systems.

Diversity Combining for Channels with Fading and Partial-Band Interference

Abstract: Diversity combining techniques that employ a ratiothreshold test (RTT) are suggested for communications with fading and partial-band interference. We consider a system with binary orthogonal signaling and noncoherent demodulation. The fading channel is modeled as a group of independent narrow-band channels, each with nonselective Rician fading. We assume that the partial-band interference is Gaussian, and we include additive white Gaussian quiescent noise in the analysis to account for wide-band noise sources. The performance measures we use to evaluate the diversity combining schemes are the narrow-band interference rejection capability and the signal-to-noise ratio requirement over the entire range of partial-band interference duty factors. The performances of the RTT with square-law combining and the RTT with majority logic decoding are compared to each other and to the performance of the optimum diversity combining technique.

Frequency Compensation in an Adaptive Antenna System for Frequency-Hopping Communications

Abstract: For the full exploitation of an adaptive antenna system forwideband frequency-hopping communications, some form offrequency compensation is necessary. Parameter-dependent,spectral, and anticipative processing are the three methods offrequency compensation that are examined; their strengths,limitations, and variations are discussed. The underlying adaptivealgorithm is the Maximin algorithm, which has major advantagescompared with other algorithms.

Code Acquisition for a Frequency-Hopping System

Abstract: Code acquisition for a frequency-hopping code-division multiple-access system using Reed-Solomon coding is investigated. The one-coincidence codes which minimize the user interference are shown to be well suited for initial synchronization but are less appropriate for regaining synchronism during transmission. A modified code construction is proposed, which has good capability of both startup and resynchronization.

Adaptive Receiver for Digital Communication Over HF Channels

Abstract: The fading characteristics of the HF channel make communication over this channel difficult, even at moderate data rates. In this correspondence, a practical communication system is presented which has a near-optimal receiver for data detection and adaptive optimization of the receiver to channel parameters. The channel tracking is performed during the training sequence as well as during the detected data sequence. The receiver is fast converging, therefore suitable for frequency hopping. The correspondence presents the performance obtained on fading HF channels and the computational complexity via comparisons to previously published results. The performance is shown to be superior at comparable computational complexity.

Apparatus and method for processing of frequency hopping communications

Abstract: The present invention relates to signal processors and processing, and more particularly to apparatus and method for sensing, detection and/or demodulation of frequency hopping signals.

Frequency hopping patterns for simultaneous multiple-beam sonar imaging

Abstract: This paper describes the design of frequency-hopped signals for a multi-beam imaging system. A frequency hopping pattern is a frequency-coded uniform pulse train. The signal is divided into M time intervals, with each interval assigned a different frequency chosen from a set of N frequencies. A set of N patterns composed of N-1 frequencies can be generated using first-order Reed-Solomon codewords. These patterns exhibit very good correlation properties. In a frequency-hopped multi-beam imaging system, each beam is associated with a pattern and transmits a coded waveform. All N beams can be transmitted simultaneously resulting in a high scan-rate, high resolution imaging device. Furthermore, in the presence of noise and medium spreading effects, a frequency-hopped imaging device performs better than conventional systems by showing better noise rejection and less sensitivity to spreading effects.

A Generalized Analysis for a Dual Threshold Sequential Detection PN Acquisition Receiver

Abstract: Spread spectrum techniques have become very useful in modern communications. A common spread spectrum technique is to directly modulate a pseudorandom noise (PN) code onto the carrier. Systems employing this technique are called direct sequence (DS) systems. A primary concern with direct sequence systems involves PN code synchronization (acquisition) of the incoming and local signals to within at least one PN symbol followed by a fine alignment (tracking) which must be maintained throughout transmission. This paper is concerned with the PN acquisition aspect of code synchronization. Specifically, a dual threshold sequential detection receiver is analyzed and a general expression is derived which addresses the probability that the sequential detection procedure ceases after an arbitrary number of samples. This expression is needed in order to support a characteristic function approach in deriving acquisition Probability as a function of time which will be the topic of a subsequent paper.

Convolutional Codes over GF(q) with Applications to Frequency-Hopping Channels

Abstract: We discuss the design and performance of convolutional codes over non-binary fields, with an eye toward use of orthogonal signaling and noncoherent detection as might be imposed by a frequency-hopping scenario. Orthogonal signaling combined with low-rate coding (convolutional or otherwise) has been shown to afford efficient transmission on AWGN, Rayleigh fading, and partial-band noise channels.

Coding for spread-spectrum communications networks

Abstract: : The multiple-access capability of a frequency-hop packet radio network is investigated from a coding point of view. The achievable region of code rate and channel traffic and the normalized throughput are considered as performance measures. We model the communication system from the modulator input to the demodulator output as an I-user interference channel, and evaluate the asymptotic performance fo various coding schemes for channels with perfect side information, no side information, and imperfect side information. The coding schemes being considered are Reed-Solomon codes, concatenated codes, and parallel decoding schemes. We derive the optimal code rate and the optimal channel traffic at which the normalized throughput is maximized, and from these optimum values the asymptotic maximum normalized throughput is derived. The results are then compared with channel capacities.

An Anticipative Adaptive Array for Frequency-Hopping Communications

Abstract: Adaptive antenna array processing and wideband frequency hopping are two of the most powerful methods for providing interference rejection in military communication systems. However, for the full exploitation of the theoretical processing gain achievable when these two methods are combined, frequency compensation is required. This paper examines an anticipative adaptive filter that adapts the complex weights at each antenna element to the appropriate values for a carrier frequency before that frequency is transmitted. The underlying adaptive alogrithm is the Maximin algorithm which has major advantages compared with other algorithms. Computer simulation results are used to compare different versions of anticipative processing. These results show that an appropriate version can ensure the rapid convergence of weights to values that provide wideband nulling of the interference and noise.

Performance of Adaptive Transmission for FH/MFSK Signaling Over Jammed Fading Channels

Abstract: This paper gives an evaluation of the performance of adaptive signaling techniques for jammed fading channels. These techniques perform remarkably well for fading channels with AWGN. The performance of both uncoded and coded systems is examined in the presence of jamming. Adaptive signaling schemes are shown to offer little improvement for uncoded antijam systems. However, for coded antijam systems, they provide improvements in the performance and, in some cases, simplify the receiver implementation.

Anti-Jam Performance of Fast Frequency Hopped MFSK with Coding against Worst-Case Multitone Jamming

Abstract: Fast frequency hopped (FFH) MFSK with coding can significantly improve anti-jam (AJ) performance against partial band jamming. Multitone (MT) jamming has been shown to be the most effective partial band jamming technique, particularly against higher order M-ary FSK modulation. The results of many jamming analyses performed on FFH MFSK against worst-case MT jamming differ due to simplifying assumptions and to the use of different analytical techniques. To resolve discrepancies in the analytic results, a digital simulation of a demodulator and a Viterbi decoder was developed, yielding a more accurate characterization of the nonlinearities in the demodulator, the soft decision decoding metrics, and the jammer tone configuration. Results for a specific 8-ary FSK with a rate ? and k = 7 convolutional code implementation are presented.

Throughput Analysis of a Random Access Tree Protocol for Frequency-Hopped Spread-Spectrum Packet Radio Networks

Abstract: Work on the two methods of multiple access code division [using spread-spectrum (SSMA)] and collision resolution, has proceeded more or less separately. In this paper, a more combined approach is taken to the multiple access problem, by integrating the interference reduction properties of the spreading code (frequency-hopping pattern) with an algorithm for collision resolution (CRA). An approach is proposed which makes specific use of the properties of frequency-hopped (FH) signaling to aid in making the CRA efficient. A throughput analysis is performed, and a tight lower bound to the maximum stable throughput is derived. An approach is presented for evaluating an important quantity that arises in FH/SSMA systems, namely the probability of exactly m users suffering packet error given that k users transmit simultaneously. Finally, a procedure is proposed for estimating the level of channel traffic, by making use of the nature of the signaling involved.

Packet error probabilities in frequency hopped spread spectrum packet radio networks-Memoryless frequency hopping patterns considered

Abstract: In this paper we compute the packet error probability induced in a frequency hopped spread spectrum packet radio network. The frequency spectrum is divided into q frequency bins and the packets are divided into M bytes each. Every user in the network sends each of the M bytes of his packet at a frequency chosen among the q frequencies with equal probability, and independently of the frequencies chosen for other bytes (i.e. memoryless frequency-hopping patterns). Furthermore, statistically independent frequency hopping patterns correspond to different users in the network. We show that, although memoryless frequency hopping patterns are utilized, the byte errors at the receiver are not statistically independent" instead they exhibit a Markovian structure. We also compute the packet error probability induced when Reed-Solomon codes are used for the encoding of the packets.

Transmission and reception equipment

Abstract: PURPOSE:To simplify constitution and to reduce the synchronizing time by using a spread code generating circuit for frequency hopping (FH) and direct spread (DS) and synchronize the phase of a FH pattern with that of a DS code in a transmission/reception device of the spread spectrum communication system. CONSTITUTION:The spread code generating circuit 8 is used for the FH and DS. In case of the transmission, the information input is coded and a spread modulation circuit 2 multiplies the code with a PN code (pseudo random number code) of the circuit 8. The direct spread signal is subject to radio modulation by a modulation circuit 3 and mixed with an output of a frequency synthesizer circuit 9 by a mixer 4. The output frequency of the circuit 9 is changed according to the series generated by the circuit 8. An FH pattern and the DS code are synchronized in phase at the transmission wave as shown in figure so that direct spread of one period (8-bit in figure) at one hop of the frequency is applied. Then the uncertainty of the phase of a high speed code series of the DS code is changed from 8-bit into 2-bit by the synchronization of the FH pattern.

Impedance matching arrangement for an antenna

Abstract: An impedance matching arrangement is suitable for use with a frequency hopping radio communications system which is operable over a wide frequency band, so as to match the operating impedance of the antenna 5 at each of the frequencies used. As the frequency of the radio system hops from one frequency to another, a note of any impedance mismatch is noted and data derived therefrom is stored at 7 for future use when that frequency is next selected so as to reduce any impedance mismatch. To preserve impedance matching values over long periods when the system is not used or when another antenna is used they are periodically entered into a memory 8 and can be down loaded back into memory 7 when required.

Optimal Performance of Coded Interleaved PSK Modulation in Slowly Varying Rician Fading

Abstract: It is shown that in direct line-of-sight communications multiple reflections which give rise to Rician amplitude fading statistics need not degrade performance (compared to the case of specular component only), provided the fading is slow compared to several bit times and sufficient interleaving with powerful low rate coding is employed. Theoretical bounds as well as simulation results with practical codes are presented to support this conclusion.

Comparison of Parametric and Nonparametric Nonlinear Diversity Combining Schemes for Frequency-Hopping FSK Systems in Partial-Band Noise Jamming

Abstract: Direct comparison is made of error probabilities achieved by several nonlinear diversity combining schemes for L-hop/bit FH/BFSK in worst-case partial-band noise jamming The schemes studied for combining the L square-law envelope detector samples include adaptive gain control, majority logic combining of perhop hard decisions, a self-normalizing technique, and a method in which the samples are normalized by their maximum on each hop The first method mentioned is "parametric", while the others are not Both conventional and random hopping are considered, and thermal noise is included in the analysis The results show that diversity improvement is realized for all the receiver combining schemes, provided that the thermal noise is relatively weak, not giving rise to substantial noncoherent combining losses The hard decision scheme is shown to be most vulnerable to such losses