Conventional near field inductive wireless power transfer theory shows that systems suffer from splitting frequency behaviors when strong coupling condition exists between the transmitter and the receiver. However, this characteristic has not been explored for communication. Our analysis demonstrates that the splitting behaviour of frequency creates multiple frequencies that support inductive communication in MIMO configuration. As a result, we implement a binary chirp modulation on an FPGA and validate two channel communication using splitting. This paper introduces the use of chirp signals to spread data and excite inductive MIMO systems. The simulation and experiment show that the splitting frequency depends on a quality factor and the flux coupling condition between the data source and receiver. In other words, the degree of mutual coupling defines the splitting mode. This paper proves that multi-channel communication using splitting can be used for data transmission. The results show that data rates of 50 Mbps or 69 Kbps can be achieved for each channel between the transmitters and receivers when the transmitter and receiver operate at the original resonant frequency of 13.56 MHz or 28 KHz, respectively and the distance between them varies from about 1 cm to 10 cm.

FPGA-Based Implementation of Multiple Modes in Near Field Inductive Communication Using Frequency Splitting and MIMO Configuration

Reactive jamming is not only cost effective, but also hard to track and remove due to its intermittent jamming behaviors. Frequency Hopping Spread Spectrum (FHSS) and Direct Sequence Spread Spectrum (DSSS) have been widely used to defend against jamming attacks. However, both will fail if the jammer jams all frequency channels or has high transmit power. In this paper, we propose BitTrickle, an anti-jamming wireless communication scheme that allows communication in the presence of a broadband and high power reactive jammer by exploiting the reaction time of the jammer. We develop a prototype of BitTrickle using the USRP platform running GNURadio. Our evaluation shows that when under powerful reactive jamming, BitTrickle still maintains communication, whereas other schemes such as 802.11 DSSS fail completely.

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BitTrickle: Defending against broadband and high-power reactive jamming attacks

In underwater acoustic communications (UAC), signal synchronization plays a key role in the performance. It is usually performed using a known preamble transmitted prior to the data. However, the underwater acoustic (UWA) channel is characterized as time-varying and frequency-varying, which makes the preamble fluctuated as well as the transmitted data. Thus, it contains uncertainty to set a constant threshold for synchronization by using information (e.g., Doppler shift) extracted from the preamble. In this paper, we propose an adaptive scheme for UAC synchronization. The scheme uses the symmetrical triangular linear frequency modulation (STLFM) signal to design a fractional Fourier transform (FrFT)-based detection algorithm. It establishes the frame synchronization by detecting the deviation of the two energy peaks which usually emerge in their “optimal” FrFT domain in pairs. Instead of detecting the absolute peaks, the proposed method performs an initial synchronization and a precise correction based on the relative positional relationship and amplitude attenuation of the two peaks, which makes full use of the two peaks of the STLFM signal in the FRFT domain. The effectiveness of the scheme has been verified by simulations and field works. The results suggest that it is able to peak the time-varying signal amplitude for each frame in UWA channels. Besides, the proposed scheme performs better accuracy and stability in the frame synchronization compared to the traditional LFM method, which is shown as three times less detection error and five-to-ten times dropping of mean square error.

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STLFM signal based adaptive synchronization for underwater acoustic communications

M-ary chirp modulated signals are described and illustrated as a function of modulation parameters-h, the peak-to-peak frequency deviation divided by the symbol rate; and w, the frequency sweep width divided by the symbol rate. The detection of these signals in AWGN channel is addressed and optimum receiver structures for both coherent and non-coherent cases are derived. Closed-form expressions for symbol error probabilities for these receivers have been obtained. Optimum 2-, 4-, and 8-ary coherent chirp systems that minimize symbol error rate have been determined. The performances of both coherent and non-coherent M-ary chirp systems are compared with respective conventional M-ary digital modulations.

M-ary chirp modulation for coherent and non-coherent data transmission

A class of chirp signals for M-ary data transmission, referred to as M-ary chirp modulation (MCM), is considered. The performance analysis of this MCM over frequency-selective and -nonselective fading channels is carried out and closed-form error probability results that are easy for numerical computation are derived. The parameters that affect error performance are identified and illustrated. These analytical results are then compared using extensive Monte Carlo simulations. Specifically, the results are presented over Rayleigh and Nakagami-m flat fading and over Nakagami-m frequency-selective channels. It is shown that analytical results compare well with simulations.

Closed-form error probability for M-ary chirp modulation in frequency-selective and -nonselective fading channels

This paper analyzes the structure and modem scheme of chirp-BOK system. In additive white Gaussian noise channel, an approach of studying the performance of chirp-BOK is presented and the BER-SNR result is evidently improved compared with traditional BOK. Furthermore, the BER of multi-user chirp-BOK system is discussed.

Performance of chirp spread spectrum in wireless communication systems

In this paper the performance improvement of wireless networks caused by chirp spread spectrum (CSS) as PHY is addressed. Firstly, the bit error rate function is firstly derived theoretically. Then an OPNET modulation curve is created through EMA (external model access) programming using the BER result. By doing this, CSS is introduced into OPNET as an alternate modulation method. Furthermore, simulations are designed and carried out in OPNET, taking advantage of the new modulation curve. Simulation results show that networks using CSS have lower delay owing to the feature of CSS. This advantage becomes more evident when traffic increases under real-time circumstances.

Xin Li

Papers

Performance of chirp spread spectrum in wireless communication systems

Performance evaluation of wireless networks based on chirp spread spectrum