Telecommunication Technique Based on Time Modulation
Development of Receiving and Transmitting Antennas, Tracts and Facilities of Measurement of the Shape of Standard Pulse for Communication Method Based on Time Modulation of the Signals (Time Domain)
Tech Area / Field
- INF-SIG/Sensors and Signal Processing/Information and Communications
- PHY-RAW/Radiofrequency Waves/Physics
3 Approved without Funding
Institute of Measuring Systems, Russia, N. Novgorod reg., N. Novgorod
- Los-Alamos National Laboratory, USA, NM, Los-Alamos\nRheinmetall W&M GmbH, Germany, Unterlöss\nUS Army Space and Missile Defence Command, USA, AL, Huntsville\nTZN Forschungs- und Entwicklungszentrum Unterlüß GmbH, Germany, Unterlöss
Project summaryAs is known, mobile communication systems based on wireless data exchange between a transmitter and a receiver located at short distances from each other, ranging from some decimeters (a personal office based on bluetooth technology) to a few kilometers, have been actively developed since recently.
As for data transmission to long distances, stationary communication channels (optical cables) are usually used instead, and the mobile communication systems cannot compete with the optical cables in this case. However, the mobile systems are competitive with the stationary ones in transmitting not so large data flows and, especially, if the system is required to be capable of changing its architecture. In other words, the end users should not be rigidly linked to definite portals.
However, due to the limitation of the frequency band permitted to be used by the cell systems (frequency bands near 0.9 and 1.8 GHz), the access to Internet via the cell telephones is limited (for example, transmission of a graphics file by using the frequency band about 30 kHz, i.e. the frequency band of a single cell user, requires too long time connection).
Therefore, the problem of developing new methods of wireless data transmission is very relevant. One of such new solutions is a Time Domain (TD) method being mostly developed by the Time Domain Corporation located in Huntsville, Alabama, the USA.
The Time Domain method differs radically from all other methods of the data transmission. In all those methods, the carrier signal is of the sine type, whereas in the TD method there is no carrier signal at all, and the information is transmitted by a sequence of short single pulses, like in old telegraph lines where the current pulses formed the symbols of the Morse code. In the TD method, time modulation of the signal is used instead of phase or frequency modulation; i.e. a bite of information is encoded by the duration between two neighbor pulses. For the standard pulse duration of 1 nsec, the duration between the pulses varies from 25 to 1000 nsec. It is necessary to note that in the TM method, the standard pulse is the single radio pulse, which differs from the pulse in radio location systems, where a video pulse filled by a set of radio pulses plays a role of the standard pulse.
The main advantages of the method are:
1. An ultrawide band of frequencies allow transmission of large data flows.
2. Extremely low spectral density of the signal (10-12 Wt/Hz, as compared to 2.510-6 Wt/Hz for the standard cell telephone signal), i.e. the signal of the TD system does not interfere with the operation of other radio systems. Therefore, the TD communication systems do not require getting a license for using the frequencies.
3. Possibility of the data transmission over the distances of some kilometers by the transmitter with as low as 1 mWt radiation power (which cannot be achieved by any other method). Owing to such a low output power, an amplifier circuit in a transceiver is no longer required, which simplifies the design of the device.
4. High stability against interference and high protection against non-authorized access. Due to the single pulse operation mode, this method is mostly adaptable for computer technologies.
At present, the Time Domain method is at the starting stage of development of this communication technology. Time Domain Corp. has created only a few prototypes for demonstration of this method. From the diagram of the design of the transceiver presented at the web site of Time Domain Corp. (www.time-domain.com), one can see that an electrodynamical part of the device is rather primitive, as the generator of the current pulse is directly connected to the antenna. The device of such a design is sufficient for demonstration, but not for using in a real communication system.
The main problems to be solved are the following:
- it is necessary to develop a technology for coding of not only the time interval between the single pulses but also the amplitude and shape modulation of the single pulses;
- it is necessary to develop a receiver with improved selectivity to separate the signal from signals emitted by other TM transmitters.
Analyzing these tasks, we face the problems which are absent in convenient communication methods. For all those methods, the transmitter and receiver are the devices having similar design because both of them process the sine waves. So, if the first device emits the modulated signal, the second device receives the same signal. It is not the case for the transmission of non-sine-type signals. Both the signal tracts and antennas distort the shape of the pulses and the time intervals between them. It is possible to solve these problems by using faster operation chips, but here we will face physical limitations to the fastness of operation. That is why these problems should be solved by electrodynamical methods, i.e. though improvements of the parameters of the tracts and antennas. Moreover, increasing the distance for transmission of information leads to distortions of the standard pulse becoming too large, so that the only way to solve these problems is to develop the electrodynamical part of the TD devices.
The aim of the Project is to research into processes of propagation of the single current pulse along the transmission line (an analogue of the antenna tract), its radiation and reception. Thus, we intend to solve three major problems:
- to develop the electrodynamical model of propagation of the short current pulse along the transmission line;
- to develop the transmitting and receiving antennas for the short, i.e. wide band, EM pulses;
- to create devices for recognition of the explicit shape of the single pulse in a given frequency band.
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