Keying

About: Keying is a research topic. Over the lifetime, 6598 publications have been published within this topic receiving 82943 citations.

UWB Direct Chaotic Communication Technology for Low-Rate WPAN Applications

Abstract: The goal of this paper is to describe the design of an ultrawideband (UWB) system that is optimized for low-complexity, low-power, low-cost, and low-rate wireless personal area network applications. To this aim, we propose a system based on novel direct chaotic communication (DCC) technology, in which a 2-GHz-wide chaotic signal is directly generated into the lower band of the UWB spectrum. Based on this system, two simple modulation schemes, namely, chaotic on-off keying and differential chaos-shift keying, are studied, and the performance of both noncoherent and differential-coherent transceiver architectures is evaluated. Various system design parameters and tradeoffs are discussed throughout the paper, including frequency band plans, data throughput, and system scalability. In particular, the frequency-division multiplexing technique is proposed as a low-cost alternative to achieving simultaneous operating piconets for short-distance applications. The average power consumption for various operating data rates and the technical feasibility of implementing the DCC system as a low-cost integrated circuit are also addressed. Finally, Monte Carlo simulations are performed based on the IEEE 802.15.4a standard channel models to evaluate the performance of the two modulation schemes. In general, both schemes experience little degradation under multipath environments due to the self-inherent wideband characteristic of the chaotic signal.

A dual-function MIMO radar-communications system using frequency-hopping waveforms

Abstract: The dual use of radio signals for simultaneous operation of radar and communications has recently attracted significant interest. In this paper, we develop a method for information embedding into the emission of multiple-input multiple-output (MIMO) radar using frequency-hopping (FH) waveforms. The set of orthogonal waveforms used to implement the primary MIMO radar operation is generated using FH codes. The secondary communication function is implemented by embedding one phase-shift keying (PSK) communication symbol in each frequency hop, i.e., the number of embedded communication symbols during each radar pulse equals the number of transmit antennas times the length of the FH code. We show that the communication operation is transparent to the MIMO radar function of the dual-function system. Standard ratio testing is used to detect the embedded PSK symbols at the communication receiver. The achievable data rate is proportional to the pulse repetition frequency, the number of transmit elements, the length of the FH code, and the size of the PSK constellation. The performance of the proposed technique is investigated in terms of the symbol error rate.

Uncoded and coded performance of MFSK and DPSK in Nakagami fading channels

Abstract: The author presents uncoded and coded performance results for noncoherent M-ary frequency-shift keying (MFSK) and differentially coherent binary phase-shift keying (DPSK) in a slow nonselective Nakagami-m (1960) fading channel. He gives simple expressions for the asymptotic slopes of probability of bit error for large signal-to-noise ratio and shows that the effective order of diversity compared to an uncoded Rayleigh channel is the product of two parameters, one for the channel and one for the code. He also compares the uncoded Nakagami-m results to those of the Rician channel in order to show performance differences between these two generalized fading channel models. >

Automatic modulation recognition using wavelet transform and neural networks in wireless systems

Abstract: Modulation type is one of the most important characteristics used in signal waveform identification. In this paper, an algorithm for automatic digital modulation recognition is proposed. The proposed algorithm is verified using higher-order statistical moments (HOM) of continuous wavelet transform (CWT) as a features set. A multilayer feed-forward neural network trained with resilient backpropagation learning algorithm is proposed as a classifier. The purpose is to discriminate among different M-ary shift keying modulation schemes and themodulation order without any priori signal information. Pre-processing and features subset selection using principal component analysis is used to reduce the network complexity and to improve the classifier's performance. The proposed algorithm is evaluated through confusion matrix and false recognition probability. The proposed classifier is shown to be capable of recognizing the modulation scheme with high accuracy over wide signal-to-noise ratio (SNR) range over both additive white Gaussian noise (AWGN) and different fading channels.

Performance of a free-space-optical relay-assisted hybrid RF/FSO system in generalized M-distributed channels

Abstract: This paper investigates the average symbol error rate (ASER) performance of a dual-hop hybrid relaying system relying on both radio frequency (RF) and free-space optical (FSO) links. Specifically, an RF link is used for supporting mobile communication, whereas an FSO link is adopted as the backhaul of the cellular infrastructure. Considering nonline-of-sight RF transmissions and a generalized atmospheric turbulence (AT) channel, the associated statistical features constituted of both exact and asymptotic moment-generating functions are derived in the closed form. They are then used for calculating the ASER of M -ary phase-shift keying (PSK), differentially encoded noncoherent PSK (DPSK), and noncoherent frequency-shift keying. A range of additional asymptotic expressions is also derived for all the modulation schemes under high signal-to-noise ratios (SNR). It is observed from the asymptotic analysis that the ASERs of all the modulation schemes are dominated by the average SNR of the RF link in the hybrid relaying system using a fixed relay gain, whereas in the relaying system using a dynamic channel-dependent relay gain, the ASERs of all the modulation schemes depend both on the average SNR and the AT condition of the FSO path. We also find that the fixed-gain relaying strategy achieves twice the diversity order of the channel-dependent relaying strategy, albeit at the cost of requiring a high power amplifier dynamic range at the relay node. Furthermore, by comparing the asymptotic ASERs, we calculate the SNR differences between the different modulation schemes in both the fixed-gain and channel-dependent relaying systems. Finally, simulation results are presented for confirming the accuracy of our expressions and observations