A. A. Sudakov

The article describes possibility of ultra-wideband (UWB) communication. It describes structure and principle of operation of developed UWB system as well as sensitivity calculation results. Experiments with video date transfer and electromagnetic compatibility (EMC) with narrowband systems were performed. Ultra-wideband systems have lot of advantages for using in modern digital communication systems. Prototype of UWB system, which was developed, has many of advantages like high communication data rate, simultaneous operation in the same frequency band with narrow band systems, low emitted power, low power consumption etc. Ultra-wideband system consists of transmitter with on-off keying modulation, horn antenna and two-channels receiver. Transmitter produces short radio pulses with 2.5 ns duration and 1.25 MHz central frequency. Second receiver channel in-tends for estimation of external noises and noises due to multipass propagation. Time gating is used during receiving of UWB signal. Time gating interval is 3 ns that allow to reduce protection from miltipass interferences. Ultra-wideband system has several operation modes like calibration, operation etc. Microcontroller (MCU) changes operation mode accordance to criteria processing signals from two receiver channels and different influences. Receiver of the system consists signal detector, which has big influence to communication range and data rate of the system. Signal detector compares two voltages - reference voltage and instantaneous voltage of UWB signal after receiving. If UWB signal-s voltage is bigger than reference voltage so detector produce high-level digital signal at its output. In case when UWB signal-s voltage is lower than reference voltage so detector produce low-level digital signal. Detector operates only at time gating interval. UWB receiving signal, which goes to detector, does not any additional processing like envelope detection. It is true radiofrequency (RF) signal. Instantaneous RF signal detection possible when tunnel diode is used in signal detector. Tunnel diode intends for operation in centimeter and millimeter wavelength bands so at 1.25 GHz central frequency it can freely detect instantaneous RF voltage. Detector sensitivity accordance to calculation is -78.4 dBm. MCU changes reference voltage, which goes to two-channel detectors accordance to detection criteria. MCU also controls synchronization unit. Synchronization unit of the UWB receiver is digital and operate as phase lock loop (PLL). PLL operate under harmonics of receiving signal. Synchronization unit consists PLL, delay block and other blocks of receiver. Apparatus of synchronization unit allow to automatically starting synchronization process during start of communication process and during signal loss. Synchronization unit operates only when RF pulses are received. When RF pulses are absent so no any tuning of PLL generator is produced. If tuning is absent, so frequency of PLL generator is changed. In this case, it is necessary to limit number of zero in receiving signal. Range of developed UWB system is 187 m. Checking was produced accordance to special algorithm with test signal at 0.625-10 Mb/s data rates. Video data follows with 10 Mb/s rate and number of zeros in transmitted pulse sequence was not more than seven. At theses conditions no any data error at receiver side was fixed. It was found influence of time gating at transferred data quality. Bit error rate (BER) graph analysis shows that reducing duration of time-gating interval increases communication quality. At very small durations of time-gating interval communication quality is decreased. This caused by spurious capacitance present at detector circuit. Analysis of EMC shows that no any influence to cellular systems operation. At the same time it is impossible to have full intercept communication especially at small distances (3 meters) if scanning receiver has bandwidth similar or more than signal bandwidth (500 MHz).