Frequency Hopping Communication Research Articles

Modeling differential frequency hopping communication in the underwater acoustic channel.

Differential frequency hopping (DFH) is a fast frequency hopping digital modulation scheme with proven multiple‐access and jamming robustness properties in typical wireless channels. Characterizing the capabilities of DFH modulation in the more challenging underwater acoustic channel requires careful analyses that rely on both computer simulations and data collected at sea. The Sonar Simulation Toolkit (SST) is used to model challenging underwater environments and simulate the propagation of DFH waveforms in the corresponding underwater acoustic channels. Our simulations provide baseline performance results that can be used to assess the capabilities of DFH modulation and guide future algorithmic improvements to the receiver. In particular, our simulations show that incorporating equalization techniques into the DFH baseline receiver leads to improved decoding performance in challenging environments characterized by long channel impulse responses, which are known to cause inter‐symbol interference in the received acoustic bit stream. To ensure their relevance to practical applications, our computer‐based SST models are calibrated to the environmental parameters measured during recent at‐sea experiments, including the Rescheduled Acoustic Communications Experiment (RACE08), and the corresponding performance is analyzed.

Response of RF Networks to Transient Waveforms: Interference in Frequency-Hopped Communications

The long-tail transient responses of a bandpass network to pulsed and switched-tone stimuli are examined and a time-domain closed-form expression of the envelope response is developed. It is shown that the long-tail response leads to interference in frequency-hopping communication systems. Interference, and in particular co-site interference, can result in any radar, communication, or RF sensor system becoming exposed to unintentional pulsed RF signals. In the experimental study, 900-MHz Chebyshev bandpass filters are considered.

BER analysis of a GMSK system using decision feedback

There are considerable literatures on the Bit Error Rate (BER) evaluation of Differential Detection of Gaussian Minimum Shift Keying (DDGMSK) system using Decision Feedback (DF), but most of them give the performance based on the Monte Carlo Error Counting (MCEC) technique. From the probability distribution of the phase angle between two vectors perturbed by Gaussian noises, the formulae of BER are derived for the performance analysis of DDGMSK system with DF in this letter. Considering the m-bit dock-tailed sequence, the new formulae of Gaussian Minimum Shift Keying (GMSK) modulated phase and the Time-Varying Signal to Noise Ratio (TVSNR) of the demodulated signal are presented, and it is proved that the relationship between the TVSNR of the demodulated signal and the size of eye opening is not inevitable. Simulation results show that the theoretical investigation gives analogous results with the MCEC technique. The formulae presented are useful for the performance analysis of systems using GMSK as modulating and demodulating method, for instance, the analysis of synchronous performance of frequency-hopping communication system.

Research progress in SAW filter banks

SAW (Surface Acoustic Wave) filter bank is a single input, single or multi-output device consisting of multi-SAW-filters with input interconnection network or switch circuits, and can be divided into two categories: channelizer (multi-output) and switchable (programmable, single output). The former is mainly used in military channelized receiver for spectrum analysis; the latter has wide application in frequency synthesizer and frequency-hopping radar and communication system receiver as anti-jamming filter, and has been widely used in various military electronic equipments ever since the 1970s. Research abroad was done mainly by Americans, few documents on related work done by Japan and Russia are available. Domestic research started in the 1980s, mainly by No. 26 Research Institute, China Electronics Technology Group Co., Institute of Acoustics, Chinese Academy of Sciences, No. 23 and No. 25 Research Institute, China Spaceflight Tech. Group Co. This paper first briefly introduces Chinese and foreign research on SAW filter banks; then discusses research progress in device design, the input interconnection network or switch circuit and miniaturization; and ends in a brief perspective of developing trends in future.

Iterative demodulation and decoding of frequency-hopped PSK in partial-band jamming

This paper considers the problem of developing and utilizing side information in a frequency-hopped communication system using phase-shift keying (PSK) and operating in an environment with partial-band jamming. Two aspects of side information are studied. The first deals with estimating the unknown random carrier phase that varies from hop to hop. The second aspect is the detection of jamming signals. We use a serially concatenated convolutional code structure with differential M-ary PSK as the inner code. The iterative receiver uses an expanded trellis in the inner decoder to resolve the phase ambiguity and is augmented by a ratio-threshold test for detecting jammer energy. Performance is compared for different dwell interval lengths and both log-APP and max-log-APP decoding algorithms. This paper also considers the effect of different thresholds on the false alarm and detection probabilities of the ratio-threshold test.

Adaptation of the Code Rate and Transmitter Power in Frequency-Hop Communications

An adaptive transmission technique for frequency-hop packet transmission is described and its performance is evaluated for certain channels with unknown or time-varying parameters. The power in the transmitted signal and the rate of the error-control code are adapted in a way that provides energy-efficient communications. The slow-frequency-hop packet transmissions have several bits per hop and several hops per packet. Feedback is limited to a few bits in each acknowledgment packet, and the feedback for our adaptive transmission consists of only the counts of errors and erasures from the previous packet transmission. The performance of the adaptive transmission system is evaluated for channels with unknown but fixed partial-band interference and propagation loss and for certain channels with time-varying partial-band interference and propagation loss.

Interference rejection for frequency-hopping communication systems using a constant power algorithm

Partial-band interferences are known to have a deleterious effect on the receiver performance in frequency-hopping communication systems. We consider the rejection of such interferences using an array of sensors. A simple yet effective method is proposed based on a constant power algorithm. The principle behind this method is that partial-band interferences contribute to power variations in the received signal, hence, the idea to constrain the output power of the array to be constant in order to reject interferences. It is shown that the algorithm converges in a reasonably low number of hops. Additionally, it achieves a nearly optimal signal-to-interference-plus-noise ratio without requiring any information about the location of the desired user. Finally, its robustness to synchronization errors is illustrated via numerical simulations.

Staggered interleaving and iterative errors-and-erasures decoding for frequency-hop packet radio

Information about the reliabilities; of the received symbols is very beneficial in frequency-hop communication systems. This information, known as side information, can be used to erase unreliable symbols at the input to an errors-and-erasures decoder. For slow-frequency-hop systems it is common that special redundant symbols, referred to as side-information symbols, are included in each dwell interval, and the demodulation of these symbols provides the side information. The corresponding decrease in the number of message symbols that can be sent in each dwell interval makes it desirable to develop alternative methods that do not require side-information symbols. In this paper, one such alternative is proposed, and its performance is evaluated for channels with partial-band interference. It is shown that staggered interleaving of Reed-Solomon code words and iterative errors-and-erasures decoding facilitates the erasure of unreliable symbols without the need for side-information symbols. The performance of this method is compared with the performance of systems that employ standard block interleaving and errors-only decoding or errors-and-erasures decoding with side information obtained from test symbols.

An adaptive-transmission protocol for frequency-hop wireless communication networks

An energy-efficient adaptive-transmission protocol for mobile frequency-hop spread-spectrum wireless communication networks is described and evaluated. The purpose of the protocol is to permit each...

Adaptive Equalization and Reed-Solomon Coding in High-Data-Rate Frequency-Hop Spread-Spectrum Communications

There is an increasing need for mobile packet radio networks that support link data rates of hundreds of kilobits per second to several megabits per second. If a radio network employing slow-frequency-hop (SFH) spread-spectrum modulation operates at these high data rates, however, the channel is likely to exhibit frequency-selective fading within each frequency slot of the SFH system. The frequency selectivity manifests itself as intersymbol interference at the receiver, and adaptive equalization must be employed in the receiver for each dwell interval in order to compensate for the intersymbol interference. In this paper, we examine the performance of a SFH spread-spectrum system with Reed–Solomon coding in a channel that exhibits time-selective and frequency-selective fading within each frequency slot. The performance is evaluated for systems in which the receiver employs maximum-likelihood sequence estimation in an equalizer that is retrained on a hop-by-hop basis. The performance of a receiver that uses errors-only decoding of Reed–Solomon codewords is considered. The use of the parity-bit method for erasure insertion and errors-and-erasures decoding is also investigated. The performance of a receiver that employs erasures of individual symbols only is compared with the performance of a receiver that also employs threshold-based erasures of entire dwell intervals. The effect of the system bandwidth and the Doppler spread on the comparison is also examined.

Frequency-hopped multiple-access communications with multicarrier on-off keying in Rayleigh fading channels

We propose the multicarrier on-off keying (MC-OOK) as a bandwidth-efficient modulation method for frequency-hopped multiple-access (FHMA) communications. The motivation for using MC-OOK is that a more bandwidth-efficient modulation scheme allows a larger number of frequency slots, and thus provides a higher immunity against multiple-access interference in FHMA systems. We analyze the average bit-error probability in slow frequency-nonselective Rayleigh fading channels with background noise. We find that the capacity gain that MC-OOK/FHMA system provides over the MFSK/FHMA system in an interference-limited region is more than 2.5 when the modulation alphabet size M is 8, and even a higher capacity gain can be obtained with a larger M.

Bayesian approach for erasure insertion in frequency-hop multiple-access communications with selective fading

We propose a decision rule for symbol erasure insertion in a dispersive propagation environment based on Bayesian decision theory. The method is applied to frequency-hop communications with Reed-Solomon coding and error-and-erasures decoding. The proposed algorithm is based on decision feedback to eliminate statistical dependence among the envelope detectors' outputs of an M-ary frequency-shift keying noncoherent demodulator. The performance is analyzed for fading channels with different levels of frequency selectivity and synchronous multiple-access interference. It is shown that the use of memoryless decision rules results in complete inefficiency in such channel conditions, whereas the proposed rule provides large coding gains even for severe selectivity. The performance sensitivity with respect to the estimation of the power delay profile denotes high robustness of the proposed approach, provided that the selectivity is somewhat overestimated. Sensitivity results for error propagation due to decision feedback are also given.

Modulation and coding for the Gaussian collision channel

We study signal-space coding for coherent slow frequency-hopped communications over a Gaussian multiple-access collision channel (G-MACC). We define signal sets and interleavers having maximum collision resistance. The packet-error probability and the spectral efficiency obtained by these signal sets concatenated with outer block coding and hard (error-only) decoding is evaluated without assuming perfect interleaving. Closed-form expressions are provided and computer simulations show perfect agreement with analysis. The structure of good interleavers is also discussed. More generally, we present expressions for the information outage probability and for the achievable (ergodic) rate of the G-MACC at hand, under various assumptions on user coding and decoding strategies. The outage probability yields the limiting packet-error probability with finite interleaving depth (delay-limited systems). The achievable rate yields the limiting system spectral efficiency for large interleaving depth (delay-unconstrained systems). Comparisons with other classical multiple-access schemes are provided.

Adaptive-rate coding for frequency-hop communications over Rayleigh fading channels

Because of the variability of the channels in frequency-hop wireless systems and networks, the performance of error-control coding can be improved by adapting the rate of the code to the channel conditions. In this paper, adaptive-rate error-control coding is investigated for slow frequency-hop communications with Reed-Solomon coding. Two methods are investigated that use decoder side information as a means for selecting the code rate. These methods are based on counts of errors and erasures, which are provided by the demodulator and the decoder. The performance of the adaptive-rate coding system is evaluated for channels with Rayleigh fading, partial-band interference, and thermal noise.

Routing for multimedia traffic in wireless frequency-hop communication networks

A new method is described for routing multimedia traffic in a frequency-hop (FH) store-and-forward packet radio network. The method is illustrated for traffic of two types, each type having its own throughput, delay, and error-rate requirements. A typical application is the routing of voice and data packets in a distributed multiple-hop network. In such an application, voice packets cannot tolerate much delay, but they are allowed to contain a small number of frame erasures while data packets must be delivered error-free even if a moderate delay is required to do so. The fully distributed routing protocol presented in the paper takes into account the type of service required for each type of traffic, and it adapts to the interference as seen by the FH radio receivers in the network. Our approach to multimedia routing is based on least-resistance routing with different link and path resistance metrics for different message types. Each of the resistance metrics for a link reflects the ability of the link to provide the service required by the one of the message types. This includes, but is not limited to, a measure of the likelihood of successful reception by the FH radio receiver for that link. The route selection for a particular type of packet depends on the resistances of the links along the routes from that packet's source to its destination. In general, different routes may be selected for different types of packets. The primary conclusion of this paper is that the quality of service increases for each of the two types of multimedia traffic if the routing protocol accounts for the type of message that is being relayed.

A unified analysis of hybrid ARQ protocol in frequency-hop spread-spectrum systems subject to frequency-selective fading and interference

This paper presents an exact analysis of the type-I hybrid automatic repeat request (ARQ) protocol for a frequency-hop (FH) communication system that uses symbol interleaving, multiple codewords per packet, and multiple symbols per dwell interval. The analysis relies on exact formulas for the probabilities of decoder error and failure with an arbitrary number of different conditional symbol error and erasure probabilities. We specialize our analysis to two channel models. The first channel exhibits frequency-selective fading, and the second exhibits frequency-selective interference. The results show that the interrelationships between system and channel parameters are complex and not always intuitive. Numerical results show that: (1) depending on the channel parameters, frequency-selective channel phenomena can result in either an improvement or degradation in system performance compared with an equivalent nonselective channel and (2) in a fading channel, increasing the number of symbols per dwell interval can result in a significant improvement in reliability at only a modest reduction in throughput.

One-hot residue coding for low delay-power product CMOS design

CMOS implementations of arithmetic circuits for One-Hot Residue (OHR) encoded operands are presented. They are shown to possess SPICE-simulated delay-power (DP) products that are significantly reduced below those of their binary number system counterparts (ripple-carry adder and Wallace tree multiplier). The reduction is attributable to the one-hot representation, which decreases the number of critical path transistors and signal activity factors. An OHR-based direct digital frequency synthesizer for frequency-hopped communication systems is presented, and analytical estimates of its DP-product are derived. The design exhibits a DP-product reduction in excess of 90% below that of a binary-encoded residue synthesizer.

Frequency-hopped multiple-access communication with nonorthogonal BFSK in Rayleigh fading channels

Nonorthogonal binary frequency-shift keying is considered in frequency-hopped multiple-access communication systems with Reed-Solomon coding. The effect of tone spacing on the average number of successfully transmitted information bits per unit time per unit bandwidth (called normalized throughput) is examined in Rayleigh fading channels. The tradeoff among tone spacing, code rate, and number of frequency slots in maximizing the normalized throughput is examined, keeping the total bandwidth fixed. The optimal tone spacing, code rate, and number of frequency slots in terms of the number of users and E~/sub b//N/sub 0/ is also discussed. The throughput gain attained by using the optimal tone spacing becomes more significant as the number of users is increased.

Spectral-estimation-based acquisition for frequency-hopping spread-spectrum communications in a nonfading or Rayleigh-fading channel

Acquisition of frequency-hopping spread-spectrum (FH/SS) signals based on autoregressive spectral estimation is addressed for nonfading and Rayleigh-fading channels. The hopped frequency is synthesized using a linear feedback shift register (LFSR). The most significant bit (MSB) of the frequency estimate is loaded into the LFSR. A new acquisition logic is devised for the acquisition scheme that employs the autoregressive spectral-estimation acquisition technique (ASEAT). To characterize the statistical distributions of the frequency estimation error, the truncated Gaussian and uniform distributions are considered. The probability of the MSB error and the mean acquisition time of the acquisition logic are derived. For the ASEAT with the acquisition logic, the acquisition scheme that uses multiple antennas is also addressed. Numerical results for the probability of the MSB error and the corresponding mean acquisition time are illustrated for the performance evaluation of both cases.

Erasure insertion in frequency-hop communications with fading and partial-band interference

The use of block coding and errors-and-erasures decoding can enhance performance substantially in frequency-hop communication systems, provided that a good scheme is employed to determine which symbols to erase. In this paper, methods for determining erasures derived from Bayesian decision theory are applied to the mitigation of fading and partial-band interference. The performance of receivers using the Bayesian technique is compared with that of receivers that make erasure decisions using Viterbi's (1982) ratio-threshold test. The performance of hard-decision demodulation and the theoretical performance of receivers with access to perfect side information are also compared. It is found that the Bayesian receiver provides the best performance, and that error probabilities for the Bayesian receiver are lower than those for hard-decision demodulation by as much as six orders of magnitude.