Char-Dir Chung

Bio: Char-Dir Chung is an academic researcher. The author has contributed to research in topics: Diversity combining & Additive white Gaussian noise. The author has an hindex of 1, co-authored 1 publications receiving 5 citations.

ading and Partial-Band Noise Jamming a Fast FH/BFSK Acquisition Receiver Noise-Normalization Combination

Abstract: 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 chamei with pdd- band noise jamming, fading channels, and fading channels with partial-band noise jamming. The considered fading channels include Nakagami-m, Rician, and Rayleigh amplitude mcdels. Based on Beaulieu's convergent series approach (l), eEcient 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.

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

Abstract: 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.

Packet acquisition for low-complexity frequency-hop receivers

Abstract: The diversity provided by frequency-hop (FH) signaling can protect against jamming and multiple access interference (MAI). A FH transmission consists of two parts - an acquisition preamble and a data payload. The acquisition preamble allows the receiver to detect and synchronize with an incoming packet. Acquisition must be at least as robust as demodulation and decoding. If acquisition fails, the receiver is unable to process the payload. Once acquisition has occurred, a receiver can simply tune a narrowband demodulator to the current hopping channel. However, during the acquisition stage, the lack of timing information makes it impossible to know what the current channel is. Instead, the optimal receiver must make an acquisition decision by simultaneously processing all channels over which the preamble is spread. If the preamble uses M channels, the receiver must have resources to tune to all M. Thus, it is desirable that M be small to keep the receiverpsilas complexity low. However, if M is small, the preamble lacks frequency diversity and may be vulnerable to jamming and MAI. We consider FH acquisition for cases where the preamble has limited frequency diversity and explore the trade-offs that must be made for robust performance in the presence of interference.

Wideband energy detection for partial-band interference in FFH systems

Abstract: A fast frequency hopped spread spectrum system is described which employs a wideband receiver to detect partial-band jamming. We assume that the interference is locally statistically stationary over numbers of hop intervals. The signal energy of each channel is first calculated and then compared with a threshold to determine whether the channel is jammed. Different threshold configuration method is discussed. It is shown that the interference can be detected in very low jamming to signal plus noise ratio.

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

Abstract: 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.

Adaptive jamming suppression in coherent FFH system using weighted equal gain combining receiver over fading channels with imperfect CSI

Abstract: Fast frequency hopping (FFH) is commonly used as an antijamming communication method. In this paper, we propose efficient adaptive jamming suppression schemes for binary phase shift keying (BPSK) based coherent FFH system, namely, weighted equal gain combining (W-EGC) with the optimum and suboptimum weighting coefficient. We analyze the bit error ratio (BER) of EGC and W-EGC receivers with partial band noise jamming (PBNJ), frequency selective Rayleigh fading, and channel estimation errors. Particularly, closed-form BER expressions are presented with diversity order two. Our analysis is verified by simulations. It is shown that W-EGC receivers significantly outperform EGC. As compared to the maximum likelihood (ML) receiver in conventional noncoherent frequency shift keying (FSK) based FFH, coherent FFH/BPSK W-EGC receivers also show significant advantages in terms of BER. Moreover, W-EGC receivers greatly reduce the hostile jammers' jamming efficiency.