Volume 60, Nº 8 (2017)

In this paper a novel channel shortening equalizer (CSE) for time hopping ultra wideband (TH-UWB) multiple access system with pulse position modulation (PPM) is presented. As UWB channels have very long impulse responses as compared to the narrow pulse width, CSE can reduce the number of correlators. In UWB systems, due to the received pulse that is very similar to the channel impulse response (CIR), the proposed algorithm maximizes the shortening signal to inter-symbol and multiuser interferences ratio (SSINR), defined as the ratio of the received signal energy inside the desired window to the energy in the wall and multiuser interference. The existence of the proposed CSE before correlation receiver decreases the complexity of the receiver architecture by significantly reducing the number of effective channel taps. Further we extend our method to derive general expression for the bit error rate (BER) performance in the presence of inter-symbol and multiuser interferences. Computer simulation results are provided to compare the performance of the proposed method with a MSSNR CSE, lower bound, also known as All-Rake, Partial-Rake, and Selective-Rake in terms of Rake operational temporal windows and BER.

Quasi-likelihood and maximum likelihood algorithms of duration estimation for ultra-wideband quasi-radio signal of arbitrary shape with unknown amplitude and initial phase, influenced by additive Gaussian white noise, are synthesized. It was considered that conditions of relatively narrow band of received signal are not satisfied and its duration can constitute only several periods or a fraction of period of harmonic oscillation. It is shown that the structure of the algorithm for duration estimation of ultra-wideband quasi-radio signal is significantly different from the structure of duration estimation algorithm for narrowband radio signal. Relative bias and variance are determined as the statistical characteristics of synthesized duration estimates. The influence of unknown amplitude and initial phase on the accuracy of duration estimation is investigated. Quantitative limits for relation of signal bandwidth to its center frequency are formulated, such that the classical solution of the problem of duration estimation for narrowband radio signal possesses the required accuracy.

The results of computer simulation of 8-mm band high-power avalanche-oscillator diodes (AOD) based on abrupt reverse biased p–n junctions with constant voltage have been presented. It is shown that AOD synchronously generate two oscillations in p- and n-regions of p–n junction, respectively. A technique is proposed for determining the parameters that ensure the diode operation in the mode of coherent oscillations. It is shown that the diode output power in this operation mode increases at the expense of summing-up the electron and hole components. The dynamic range of output power and the electronic efficiency are also determined.