Frequency Hopping Communication System Research Articles

Study of LDPC Coded SFH System with Partial-Band Interference

The application of Low Density Parity Check (LDPC) code in the anti-interference systems has drawn an increasing attention, due to its admiring performance which is very close to the theory limit. This paper focuses on a LDPC encoded slow frequency hopping (SFH) communication system with partial-band interference. Firstly, a modified soft- decision algorithm based on the utilization of interference information is proposed, and its performance is compared with some other soft-decision methods. Secondly, with numerical simulation, the influence of code rate, code length and the number of symbols per hops on the performance of the system with partial band noise interference is illustrated and examined in detail. Considering the great influence of hops per symbol on the performance, interleaver should be used and its influence on the performance is further examined by simulation. Finally, some constructive advises for the design of LDPC coded SFH system are given. Simulation results show that, with a reasonable design, the SFH system with LDPC code could achieve a desirable performance.

Impact of RF interference between a passive RFID system and a frequency hopping communications system in the 900 MHz ISM band

We present experimental measurements and analysis of RF interference between a passive RFID system and a generic frequency hopping communications system in the 902 MHz to 928 MHz ISM radio band. Interference in both directions is considered, RFID to communications and vice-versa, and interference mitigation strategies are assessed. Variables of interest include transmission power, antenna locations and polarization, and frequency hopping channel bandwidth and dwell time. Among the findings are the susceptibility of the RFID backscatter link to sources operating within regulatory limits, characterization of the performance asymmetry between the systems, and the constructive effect of interference to RFID at low powers.

Maximum-Likelihood FFH/MFSK Receiver over Rayleigh-Fading Channels with Composite Effects of MTJ and PBNJ

A maximum-likelihood (ML) receiver structure is proposed for fast frequency-hopped M-ary frequency-shift keying communication systems over Rayleigh-fading channels with the composite effects of multitone jamming (MTJ) and partial-band noise jamming (PBNJ). The corresponding semi-analytical bit-error rate (BER) expressions of the proposed ML receiver are also presented and validated by simulation results. Numerical results show that the BER performance with both MTJ and PBNJ is bounded by the two extreme cases, where only MTJ or PBNJ is present. It is also found that the proposed ML receiver can better counteract MTJ than PBNJ.

A New Blind Beamforming and Hop-Timing Detection for FH Communications

Hop-timing detection is of extreme importance for the reception of frequency hopping (FH) signals. Any error in the hop-timing detection has a deleterious effect on the performance of the receiver in frequency hopping (FH) communication systems. However, it is not easy to detect the hop-timing under low signal to noise power ratio (SNR) environments. Adaptive array antennas (AAA) have been expected to improve the performance of FH communication systems by beamforming for the direction of arrival of the desired signal. Since the conventional AAA exploits at least the coarse synchronization for dehopping of FH signals before achieving the beamforming, any fault in the hop-timing detection causes the deterioration of the performance of AAA. Using AAA based on the constant modulus algorithm (CMA), this paper proposes a new method for blind beamforming and hop-timing detection for FH signals. The proposed method exploits both the spatial and temporal characteristics of the received signal to accomplish the beamforming and detect the hop-timing without knowing any a priori information such as fine/coarse time synchronization and training signal. The performance verifications of the proposed method based on pertinent simulations are presented.

Novel frequency hopping sequences generator based on AES algorithm

A novel frequency hopping (FH) sequences generator based on advanced encryption standard (AES) iterated block cipher is proposed for FH communication systems. The analysis shows that the FH sequences based on AES algorithm have good performance in uniformity, correlation, complexity and security. A high-speed, low-power and low-cost ASIC of FH sequences generator is implemented by optimizing the structure of S-Box and MixColumns of AES algorithm, proposing a hierarchical power management strategy, and applying the dynamic clock gating technology based on finite state machine and clock gating. SMIC 0.18 μm standard CMOS technology shows that the scale of ASIC is only about 10.68 kgate, power consumption is 33.8 μW/MHz, and the maximum hop-rate is 1 098 901 hop/s. This design is suitable for portable FH communication system for its advantages in high-security and hop-rate, low-power and low-cost. The proposed FH sequences generator has been employed in Bluetooth SoC design.

Intermodulation distortion in narrowband amplifier circuits

The contribution of bandpass filter memory to intermodulation distortion in narrowband amplifier circuits is examined. A method for generating multisines from filtered switched tones is presented, and techniques for measuring an amplifier's IP3 and extracting a filter's passband using these multisines are developed. It is shown that amplified filtered pulses produce intermodulation distortion in frequency-hopping communication systems. In the experimental study, 465 and 900-MHz Chebyshev bandpass filters are considered.

Inter-subcarrier interference compensation in the frequency-hopped single-carrier frequency division multiple access communication system

Single-carrier frequency division multiple access (SC-FDMA) system having very good characteristic on peak-to-average power ratio is promising in communication area. But the performance of SC-FDMA system is very sensitive to inter-subcarrier interference (ICI), and existing phase noise suppression algorithm has reduced just phase noise only. Therefore the authors propose effective method, phase noise and frequency offset suppression (PNFS) algorithm, using comb-type pilot. PNFS algorithm can suppress phase noise, carrier frequency offset and even Doppler effect simultaneously in frequency domain. Through PNFS algorithm, SC-FDMA system has robust characteristic against ICI of performance degradation. Moreover, in these days, most electronic communication systems are weak to jamming. So, frequency-hopped (FH) scheme, which is one kind of spread spectrum techniques as a means of making performance better to supplement a disadvantage of SC-FDMA system on jamming attack, is considered. The authors would like to analyse ICI and jamming in SC-FDMA system and employ FH technique in SC-FDMA system because existing studies have not considered the situation regarding ICI and jamming exist simultaneously in mobile channel. So, the authors analyse degradation factors in FH-SC-FDMA system about ICI and jamming signal categorised as partial band jamming and multi-tone jamming. Then, the proposed FH-SC-FDMA system using PNFS algorithm has strong performances about ICI and jamming.

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.

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.

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.

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.

Bayesian generation of dependent erasures for frequency-hop communications and fading channels

The use of block coding and errors-and-erasures decoding can enhance performance in frequency-hop (FH) communication systems, provided that a good scheme is employed to determine which symbols to erase. The problem of making erasure decisions from collections of receiver outputs is investigated in this paper. Methods to determine which received symbols to erase are derived from Bayesian decision theory. Decision rules are developed for a system with M-ary orthogonal signaling, noncoherent demodulation, and frequency-selective fading. One result is a class of Bayesian schemes in which erasure decisions are made independently from symbol to symbol. Within this class is a rule that uses signal amplitude estimates for improved performance. A second result is a Bayesian technique in which erasure decisions are mutually dependent and are made collectively for each codeword. These techniques are analyzed and compared with the performance of receivers that use erasure techniques that require multiple applications of bounded distance decoding. The performance of the Bayesian techniques for dependent erasures are also compared with the performance of receivers that do not permit erasures. It is found that each of the Bayesian techniques offers substantial performance gains over errors-only decoding, and the dependent erasure scheme provides the best performance among the techniques of lower complexity.

The performance of trellis-coded nonorthogonal noncoherent FSK in noise and jamming

The performance of trellis-coded FSK modulation with noncoherent detection is presented, as applicable to a frequency-hopped spread spectrum communication system or a conventional FSK system. Nonorthogonal tone spacing is considered as a parameter to control bandwidth occupancy of the hopped signal and to allow an increased number of users. Soft decision decoding with a maximum metric decoder is employed. The metrics considered are the energy metric with and without perfect jammer state information as well as a practical self-normalized metric that compensates for jamming or interference. Performance analyses for full and partial band, and both noise and multitone jammings are presented. For nonorthogonal tone spacing, the signals are correlated, and so Chernoff bounds on the pairwise error probability for energy detectors with correlated signals are presented and evaluated. These bounds supplement earlier performance estimates for trellis coded FSK. To assess the tightness of the bounds, simulations have been carried out, with results that come within 1 to 3 dB of the bounds. System performance is evaluated for 2, 4 and 8-state trellis codes with tone spacings of 1/3T, 1/2T, 2/3T and 1/T Hz. >

Bayesian methods for erasure insertion in frequency-hop communication systems with partial-band interference

The erasure of unreliable symbols improves the performance of most types of error-control coding if a good method is used to decide which symbols should be erased. Bayesian decision theory is employed to obtain such a method for use in frequency-hop communications with Reed-Solomon coding and errors-and-erasures decoding. The performance of frequency-hop communications with Bayesian erasure insertion is analyzed for channels with both partial-band and wideband Gaussian noise. The Bayesian technique is compared with Viterbi's ratio-threshold test, and these are compared to receivers that do not erase and use errors-only decoding. Comparisons are also made with receivers that erase all the symbols that are affected by the partial-band interference. When interference is strong, large coding gains result from the Bayesian method, and error probabilities are reduced by several orders of magnitude.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A spread spectrum communication system for load management and distribution automation

Based on a discussion of channel characteristics and the design objective of a high overall link availability, it is shown that a frequency-hopping communication system using phase-shift-keying modulation can overcome the problems of the more traditional narrowband communication systems. The design parameters of such a system are then discussed. The performance is evaluated, and results of measurements in testbeds and on the power mains are presented.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>