Time Hopping

Spread-spectrum modulation techniques have been adopted for many current and future military communication systems to accommodate high data rates with high link integrity, even in the presence of significant multipath effects and interfering signals. A more recent synergistic combination is a direct-sequence spread-spectrum (DSSS) signaling with the use of integrally coordinated frequency hopping (FH) and/or time-hopping (TH) modulation, generically dubbed hybrid spread-spectrum (HSS). A highly useful form of this transmission scheme for many types of command, control, and sensing applications is the specific code-related combination of standard DSSS modulation with "fast" frequency hopping (FFH), wherein multiple frequency hops occur within a single data-bit time. In this paper, detailed error-probability analyses are performed for a hybrid DS/FFH system over standard Gaussian and fading-type channels, progressively including the effects from wide-band, partial-band, and follow-on jamming, multi-user interference and/or varying degrees of Rayleigh and Rician fading. In addition, a simulation-based study of the DS/FFH performance is performed and compared to several forms of existing standard DSSS and FHSS wireless networks. The parameter space of HSS is also explored to further demonstrate the adaptability of the waveform for varied harsh RF signal environments.

This paper presents a novel authentication and encryption method for an RFID system. In this paper, DES (Data Encryption Standard), algorithm will be used to encrypt and verify accuracy data within an RFID tag. The new DES algorithm use permutation box with assigned a permutation pattern keeps changing in time. The proposed technique increase the difficulties for any hackers behave. The proposed algorithm measured and evaluated the time to read/write encrypted data and compared that with the time to read/write unencrypted data. Also, this study measured and analyzed the effect of encryption, on the accuracy of the read/write function in an RFID infrastructure. Experimental results show that proposed method has more efficient performance with the encryption data group, since the encryption time is less than 1 ms, it is negligible compared to the transmission time. KEYWORDS

We present an efficient, low-cost implementation of time-ho pping impulse radio that fulfills the spectral mask mandated by the FCC and is suitable for high-data-rate, short-range communications. Key features are: (i) all- baseband implementation that obviates the need for passband components, (ii) symbol-rate (not chip rate) sampling, A/D conversion, and digital signal processing, (iii) fast a cquisition due to novel

Recently, pulse position amplitude modulation (PPAM) has been proposed for ultra-wideband (UWB) communication systems. PPAM combines pulse position modulation (PPM) and pulse amplitude modulation (PAM) to provide better performance and higher system capacity with low computational complexity. A rake receiver can make use of the rich multipath of UWB systems to improve system performance and capacity. In this paper we present the performance of a rake receiver employing maximal ratio combining (MRC) in a time hopping (TH) UWB system with PPAM modulation. Performance in a practical multipath fading channel is considered. The error probability and a union bound on performance are derived for a block fading environment Numerical results are given to illustrate the system performance.

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Ultra-wideband (UWB) communication has been the subject of extensive research due to its unique capabilities and potential applications. Some see UWB as an enabling technology for new wireless applications that span from high-data-rate transmission of raw multimedia video to new location-aware, low-data-rate, and low-power communication of sensor and actuator data. Underground mines, which are characterized by their tough working conditions and hazardous environments, require foolproof mine-wide communication systems for smooth functioning of mine workings and ensuring better safety. During the last years, a number of Canadian mining companies have started to deploy modern communications systems in order to automate processes, reduce operational costs and with the objective of increasing safety and productivity. However, many important aspects of UWB communication systems have not yet been thoroughly investigated in this kind of environments. In this paper we give an overview on UWB...

In this paper a joint symbol, frame and chip synchronization method for an ultra-wideband (UWB) system is presented. We assume that the channel is estimated using pilot wave- form assisted modulation (PWAM), and that synchronization is achieved by maximizing the energy of the estimated mul- tipath channel. In order to improve the time and accuracy capabilities, importance sampling was applied for designing a time-hopping system simulator. While keeping complexity low enough for real time implementation, simulation shows the good performance of this method in terms of bit error rate (BER) versus signal to noise ratio (SNR). It is also shown that this synchronization system helps to mitigate the negative effects of timing offset. The performance degrada- tion of the downlink system at a BER=10 -2 is only 4 dB compared to the case of perfect timing, and 5 dB in the up- link employing single user detection 1 .