Fast Frequency Hopping Research Articles

Optical time‐spreading/frequency‐hopping differential OOK–CDMA system

AbstractA new optical time‐spreading/frequency‐hopping differential CDMA (TS/FH CDMA) system is proposed in this paper. It uses new codes called prime/OOC codes as address codes. Fast optical frequency hopping and large capacity can be implemented with the system. By assigning two orthogonal codes for one user, and using these two codes to encode 1 and 0, respectively, the receiver can use differential detection. If they are balanced well between the 1‐branch and 0‐branch, the proposed system can effectively abate multiaccess interference (MAI), background noise, detector noise such as dark current, leakage current, and thermal noise, etc. © 2001 John Wiley & Sons, Inc. Microwave Opt Technol Lett 29: 125–128, 2001.

A periodical frequency synthesizer for a 2.4-GHz fast frequency hopping transceiver

In this paper, a compact architecture of a digital frequency synthesizer for a 2.4-GHz fast frequency hopping radio modem is presented. The synthesizer is designed for generating 12-bit quadrature carrier signals from 50 to 90 MHz in 500 kHz steps. The phase-to-amplitude conversion in the synthesizer is performed with a highly compressed look-up table (LUT). The read-only memory compression is based on the property that only a limited set of discrete frequencies is needed. Simulation and synthesis results for a VHDL-implementation of the architecture are given. In addition, the proposed architecture is compared to a traditional look-up based direct digital frequency synthesizer with similar performance. Layouts were generated for both designs using a 3.3-V 4-metal 0.35-/spl mu/m n-well standard cell CMOS technology. The proposed synthesizer was found to be 59% smaller in area than the reference design.

Blind beamforming/geolocation for wideband-FFHs with unknown hop-sequences

An ESPRIT based adaptive geolocation and blind interference rejection scheme is herein proposed for multiple noncooperative wideband fast frequency-hop (FFH) signals of unknown hop sequences and unknown arrival angles using one electromagnetic vector-sensor. Beamforming weights need no adjustments to accommodate the frequency hops. The sources' polarizational diversity, angular spatial diversity, and temporal characteristics are all exploited. Applications include electronic surveillance and direction finding of noncooperative sources, plus blind cochannel interference rejection in frequency-hop code-division multiple-access (FH-CDMA) wireless communications.

Analytical study of FFH systems with square-law diversity combining in the presence of multitone interference

An analytical study of the performance of fast frequency-hopped (FFH), M-ary orthogonal frequency-shift keyed noncoherent modulation with linear combining of square-law envelopes in the presence of multitone interference is presented. The multiple equal-power interference tones are assumed to correspond to some of the possible FFH/M-ary orthogonal signaling tones. It is also assumed that the channel fading characteristics of the signal and interference tones are independent. We evaluate the effect of the channel fading on the system's performance as a function of various parameters, such as the number of hops per symbol, the signal power to multitone interference power ratio, and the number of interference tones. Our numerical results indicate that by use of square-law time diversity combining, a large number of hops per symbol make the bit-error probability of the system more sensitive to the fading of multitone interference. Finally, the analysis has been proven valid by simulation.

Multiple-dwell and sequential code acquisition with diversity for FFH/MFSK spread-spectrum systems under band multitone jamming

Pseudonoise code acquisition is investigated for constant hopping rate fast frequency-hopped (FFH)/M-ary frequency-shift keying systems under the effects of white Gaussian noise and band multitone jamming. In particular, serial search acquisition systems based on the traditional multiple-dwell test (up to three dwells) and three novel sequential tests are analyzed and compared. Analytical results show the following in a heavily jammed environment: (1) the inherent time diversity in an FFH system can significantly improve the acquisition performance of the multiple-dwell test and (2) the novel sequential tests can significantly outperform the multiple-dwell test. Our analytical results are verified by computer simulations.

Coherent frequency hopping multiple access (CFHMA) with multiuser detection for mobile communication systems

This paper proposes a new multiple-access (MA) scheme, coherent frequency hopping MA (CFHMA) with multiuser detection, which effectively obtains the diversity effect for realizing spectrally efficient mobile communications, CFHMA is fundamentally equivalent to a coherent fast frequency hopping frequency-division MA (FDMA) that incorporates low spreading factor direct-sequence (DS) code-division MA (CDMA). Multiple users occupy the same frequency band, and they are simultaneously detected by multiuser detection. There are several implementations of CFHMA. Two major techniques are introduced: coherent hybrid DS fast FH (FFH) (CHYB-DS-FFH) and interleaved FH (IFH). This paper focuses on IFH and discusses its principle of operation, transmission system configuration, and performance aspects. The results suggest the feasibility of a spectrally efficient mobile radio system.

Performance of a fast frequency-hopped noncoherent MFSK receiver with nonideal adaptive gain control

An error probability analysis is performed for an orthogonal noncoherent M-ary frequency-shift keying (MFSK) communication system employing fast frequency-hopped (FFH) spread spectrum with diversity. The signal is assumed to be transmitted through a frequency-nonselective slowly fading channel with partial-band noise interference. The partial-band interference is modeled as a Gaussian process. Both the information signal and the partial-band noise interference signal are assumed to be affected by channel fading; it is assumed that the two fading processes are independent and that channel fading need not necessarily affect the information signal and the interference signal in the same way. Each diversity reception is assumed to fade independently according to a Rician process. Adaptive gain control is employed to minimize partial-band interference effects, and the effect of inaccurate noise measurement on the ability of the adaptive gain control receiver to reject partial-band interference is examined. The effect of thermal noise is included in the analysis.

Partial-band jamming rejection of FFH/BFSK with product combining receiver over a Rayleigh-fading channel

An exact closed-form expression of the characteristic function is derived for a fast frequency-hopping (FFH) binary orthogonal frequency-shift-keying (FSK) spread-spectrum (SS) communication system. The FFH system employs a product combining receiver over a Rayleigh-fading channel with partial-band jamming and additive white Gaussian noise (AWGN). The derived characteristic function is then used to obtain a compact bit error rate (BER) expression for different diversity levels. Our study shows that there exists an optimum diversity level under certain channel conditions.

Capacity of synchronous coded DS SFH and FFH spread-spectrum multiple-access for wireless local communications

The performance of synchronous spread-spectrum multiple-access (SSMA) communications based on direct-sequence (DS), slow frequency-hopped (SFH), and fast frequency-hopped (FFH) systems for wireless local communications of micro-cellular personal communications is analyzed. Using an indoor multipath fading channel model with clusters of arriving rays, we investigate multiuser DS systems with RAKE and diversity reception by selection combining (SC), multiuser SFH systems with equal-gain (EG) diversity reception, and multiuser FFH systems with correlated EG and self-normalization (SN) combining techniques. Reed-Solomon codes are considered to further improve the system performance. Given a fixed available bandwidth with narrow band interference (NBI), capacities and packet error rates are determined under various system configurations. Total capacities of hybrid frequency-division multiple-access (FDMA)/SSMA (DS and SFH) systems are compared with those of wide-band SSMA systems. For high data rate communications, wide-band DS-SSMA systems have larger capacities than hybrid FDMA/DS-SSMA systems. For low data rate communications, a capacity comparison between wide-band DS-SSMA and hybrid FDMA/DS-SSMA systems depends on fading statistics. Hybrid FDMA/SFH-SSMA systems have larger capacities than wide-band DS-SSMA systems, FFH-SSMA systems could not provide satisfactory performance due to correlation among hopping bands.

Digital frequency synthesizer/modulator for continuous-phase modulations with slow frequency hopping

This paper gives a description of a modulator for burst-by-burst carrier frequency hopping in time-division multiple-access (TDMA) systems. The architecture consists of a digital frequency synthesizer/modulator for continuous-phase modulations (CPMs) and a fast frequency settling RF synthesizer consisting of one phase-locked loop (PLL). The performance of the digital frequency synthesizer/CPM modulator has been analyzed theoretically and simulated by a computer program. The analyses show that the proposed digital frequency synthesizer/CPM modulator achieves 2.5-W lower power consumption and 18-dB lower spurious levels than the fast frequency hopping systems synthesizing digitally a full frequency band. In the computer simulations the effect of the digital frequency synthesizer/CPM modulator parameters on the power spectrum and the phase error is investigated.

Effects of fading and partial-band noise jamming on a fast FH/BFSK acquisition receiver with noise-normalization combination

We present the performance analysis of a fast frequency-hopped (FH) binary orthogonal frequency-shift keying acquisition receiver for communication against adverse environments. The receiver employs noncoherent, noise-normalized, matched-filtered (MF) correlation detection for rapid acquisition in the search mode. Our analysis includes four types of communication environments, namely additive white Gaussian noise (AWGN) channel, AWGN channel with partial-band noise jamming, fading channels, and fading channels with partial-band noise jamming. The considered fading channels include Nakagami-m, Rician, and Rayleigh amplitude models. Based on Beaulieu's (see ibid., vol.38, no.9, p.1463, 1990) convergent series approach, efficient analytical formulas are developed for performance evaluation. Example performance results for various environments are presented in terms of two acquisition probabilities, namely the detection probability and the false alarm probability of the noise-normalized MF detector. It is analytically shown that with a short MF correlation length and with a sufficiently large ratio of signal power to noise power the fast FH diversity combining yields noticeable performance improvement for environments with strong fading. When the MF correlation is lengthened, this improvement tends to fade away and the diversity combining results in performance loss.

Fast frequency hopping transmitter and receiver based on digital signal processing and its performance

AbstractFrequency hopping is an effective technique in which error correction is performed by randomizing the bust error due to fading. In this paper, frequency translation based on digital signal processing is applied and the structure of fast frequency hopping transmitter and receiver is proposed. the principles of frequency hopping modulator and frequency translating filter for hopped‐signal reception are first described. Then an experimental 1.5 GHz transmitter and receiver (128 kbps, differentially encoded /4‐shifted quadriphase‐shift keyed (QPSK), differential detection) that can hop among 96 frequencies (12.288 MHz bandwidth) are developed. It is confirmed that a frequency switching time of 2(32) s is realized at the transmitter (receiver) and that the receiver successfully frequency translates and demodulates the hopped signal within approximately 75 s. Finally, the combined effect of frequency hopping in a fading environment and with forward error correction is experimentally evaluated. the proposed structure replaces the conventional frequency synthesizers consisting of frequency divider and phase‐locked loop by fixed frequency oscillators so that fast frequency switching can be realized. Moreover, the proposed system uses very little power and is small, making it suitable for miniaturization of LSI.

A coherent demodulator for fast frequency‐hopping spread‐spectrum signal employing an adaptive algorithm

AbstractIt has been considered impossible to demodulate a fast frequency‐hopping (FFH) spread‐spectrum signal coherently in a frequency selective fading channel as a result of difficulties with making the receiver local oscillator track the phase of a received signal that lacks phase continuity. This paper proposes a coherent demodulator for both FFH‐PSK (phase‐shift keying) and FFH‐FSK (frequency‐shift keying) signal employing a method in which the received signal is noncoherently down‐converted and phase‐adjusted by an adaptive algorithm.Computer‐simulations show that performance is better than in the case of noncoherent demodulators and that the interference‐rejection effect of the adaptive algorithm produces strong protection against interferences from other CDMA users.

The performance of diversity combining for fast frequency hopped NCMFSK in rayleigh fading

AbstractFrequency hopping (FH) spread spectrum is a well known technique used in communications systems to provide protection against interference such as jamming. With fast FH (FFH) (one or more hops per transmitted data symbol), powerful and robust methods for diversity combining have been developed as an additional jamming countermeasure. These same techniques can be applied to reduce the effects of multiple access interference, and so can be considered for civilian CDMA applications. Although the performance of a FFH communications system can be degraded considerably by fading, few results exist which show the effects of fading on the diversity combining process. In this paper, both analytic and simulation results are presented for several diversity combining methods in a Rayleigh fading channel, which is often considered to be the worst case. The performance of these combining methods in fading is compared with that in AWGN and multitone interference to determine which methods are effective against these degradations.

Performance of fast FH/MFSK signals in jammed binary channels

Soft-decision decoded performance of fast frequency-hopped (FH) M-ary FSK signals over partial band noise jammed binary channels is studied. The effects of metrics conversion, quantization, and the presence of regenerative nodes on the system's cutoff rate performance are investigated. It is found that the conversion from an M-ary metric to a binary one suffers only negligible degradations. For communication links without regenerative nodes, as expected, the infinite-bit soft-decision is the optimal metric, followed by finite-bit soft decision and then hard-decision. For those with regenerative nodes, however, the infinite-bit soft-decision is outperformed by the hard-decision, but the finite-bit soft-decision decoder still keeps its edge over the latter. The issue concerning the order of metric conversion and diversity combining is also analyzed. Numerical results indicate that the conclusion obtained by an earlier simulation report addressing a similar design alternative in fading channels is valid for jammed binary channels, as well. That is, the precombining metric conversion technique gives up only minor performance degradations when compared to the more sophisticated postcombining metric conversion technique. >

Path diversity for FFH/PSK spread-spectrum communication systems

A fast frequency hopping (FFH) method which uses path-diversity combining is proposed. Diversity techniques are realized when a signal is received from diverse independent paths, each of which carries identical information but suffers from independent fading variations. The improvement of communication performance of FFH systems is possible as the delayed paths are used and path-diversity combination is realized. The advantages of this method, operating in Rayleigh fading channels are confirmed by theoretical analyses. The improvement is in order of 2/spl sim/3 dB at bit error rate (BER) of 10/sup -3/. This method can be also effective against interferences from other users in a code division multiple access (CDMA) environment. The performance of this system in a CDMA environment is evaluated by theoretical analyses and is shown to be superior to non-combining method. At BER of 10/sup -3/ the required E/sub b//N/sub 0/ of the proposed system is 5 dB lower. If E/sub b//N/sub o/ is fixed, a greater number of users can be accommodated using the proposed system. >

Design and analysis of a fast frequency-hopped DBPSK communication system. I. System description and hop timing tracking loop analysis

Design and performance analyses of a fast frequency-hopped (FFH) spread spectrum communication system employing differential binary phase shift keying (DBPSK) modulation and differentially coherent demodulation are presented. The receiver utilizes a hop timing tracking loop to lock the hop clock. Through this tracking loop, the differentially coherent demodulation of an FFH signal is made possible. The authors present the system model of an FFH/DBPSK system. A digital, full-time early-late gate timing error estimator is investigated. The tracking loop is shown to be a Markov chain, and various performance characteristics of the tracking loop are studied.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Design and analysis of a fast frequency-hopped DBPSK communication system. I. Error performance in AWGN plus partial-band noise jamming

The purpose of the paper is to present the design and performance analysis of a fast frequency-hopped (FFH) spread spectrum communication system employing differential binary phase-shifted-keying (DBPSK) modulation and differentially coherent demodulation. The receiver utilizes a hop time tracking loop to lock the hop clock. The authors present an analysis of the average bit error probability of the overall system when it is operating in additive white Gaussian noise plus partial-band noise jamming. The effect of channel phase distortion is also studied. >

Performance of fast frequency-hopped MFSK receivers with linear and self-normalization combining in a Rician fading channel with partial-band interference

An error probability analysis is performed for both self-normalized and conventional M-ary orthogonal frequency-shift-keying (MFSK) noncoherent receivers using fast frequency-hopped (FFH) spread-spectrum waveforms transmitted over a Rician fading channel with partial-band interference. The self-normalization receiver uses a nonlinear combination procedure to minimize performance degradation due to partial-band interference. The performance of the conventional receiver is significantly degraded by worst-case partial-band interference regardless of the modulation order or number of hops per data symbol used, while the self-normalization receiver can provide a significant immunity to worst-case partial-band interference for many channel conditions when diversity is used, provided the signal-to-thermal-noise ratio is large enough to minimize degradation due to nonlinear combining losses. The improvement afforded by higher modulation orders is dependent on channel conditions. >

Error probabilities of fast frequency-hopped FSK with self-normalization combining in a fading channel with partial-band interference

Error probability analysis is performed for a binary orthogonal frequency-shift-keying (FSK) receiver using fast frequency-hopped (FFH) spread-spectrum waveforms transmitted over a frequency-nonselective slowly fading channel with partial-band interference. Diversity is performed using multiple hops per data, bit. A nonlinear combination procedure referred to as self-normalization combining is used by the receiver to minimize partial-band interference effects. Diversity is found to completely negate degradation of the self-normalized receiver caused by partial-band interference and offers definite receiver performance improvement when the direct signal component is weak. The self-normalized receiver is sensitive to fading channels. For severe channel fading, the performance of a conventional noncoherent binary FSK receiver is generally either equivalent or superior to that of the self-normalized receiver.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>