1. Field of the Invention
The present invention relates to the field of communications, and more particularly, the present invention relates to an ultrawide-band impulse communication transceiver system and method employing a full duplex mode wherein information is sent and received essentially simultaneously.
2. Related Art
Conventional transceivers operating with narrow band signals typically use the same antenna to transmit and receive signals. The transmit and receive signals are usually the same or very close in frequency. Switching between the transmit and receive mode can be done at very high rates, depending on the density of each packet of data.
Full duplex operation has traditionally been accomplished by either frequency domain or a time domain multiple access (FDMA or TDMA). In order to isolate the transmitter and receiver, FDMA uses frequency filters and hybrids, while TDMA uses a duty cycle scheme in which the transmitter and receiver alternate operation.
An example of an FDMA full duplex voice communication system is an amateur radio transceiver that operates with different transmit and receive frequencies. For example, the separated frequencies could be 144 Mhz and 436 Mhz. In such a system, the antennas are usually different, and filters must be used in the receiver to eliminate transmitter noise from the adjacent transmit antenna. Otherwise, the receiver could easily be overloaded by its own transmitter.
Impulse radio technology, on the other hand, is ultrawide-band by definition. The original descriptions of impulse radio may be found in a number of United States Patents by the present inventor. Three of these are U.S. Pat. No. 4,641,317 (issued Feb. 3, 1987), U.S. Pat. No. 4,813,057 (issued Mar. 14, 1989) and U.S. Pat. No. 4,979,186 (issued Dec. 18, 1990). Because of the ultrawide-band characteristics of impulse radio, it is difficult to modify impulse radio systems to use conventional duplex schemes.
In order to achieve full duplex in impulse radio technology, separate transmit and receive antennas are required for hand-held transceiver applications. This is because the receiver can not be disconnected from the antenna fast enough to permit transmission using the same antenna. Therefore, the size of the impulse radio antennas must be relatively small.
An impulse radio system with many users communicating with one another requires that they all have the same size antennas. In addition, for impulse radio communications in the same bandwidth, it is assumed that the transmit and receive antennas are the same size as well. These constraints complicate the implementation of full duplex in impulse radio technology, because both the transmitter and receiver must be operated in the same ultrawide frequency bandwidth.
Impulse radio technology permits operation at rates so high that there is no time for the signal to reach the intended receiver before the next pulse is transmitted. This situation causes several pulses to be present in the space between the two transceiver units. When there is motion between them such as in mobile communications, there occurs the unavoidable condition wherein the transmitter and receiver must operate simultaneously.
In order to operate in full duplex mode in a mobile environment, the transmitter and receiver would be required to operate simultaneously whenever the distance separating them increases or decreases by a multiple of C/R, where C is the speed of light and R is the repetition rate. For example, if R=1 million pulses per second, these zones would be about 300 meters, and so on. Although full duplex mode of operation is very desirable, this effect makes it unpractical to do so.
The problem is quite clear: How can an impulse radio receiver distinguish the signals transmitted by other impulse radio transmitters in the presence of more powerful impulse radio signals transmitted by its own adjacent transmit antenna? What is needed as a solution is a technique, applicable to impulse radio technology, that avoids interference between transmit and receive signals.
The present invention is directed to an impulse radio transceiver for full duplex ultrawide-band communications. The transceiver comprises an impulse radio transmitter to transmit impulse radio signal pulses, an impulse radio receiver to receive impulse radio signal pulses. Either or both of the impulse radio transmitter and the impulse radio receiver is configured for synchronizing the transmission and the reception of the impulse radio signal pulses for pulse interleaved communications. Pulse interleaving avoids self-interference between the transmitted impulse radio signal pulses and the received impulse radio signal pulses. In addition to pulse interleaved communications, bursts of pulses can be transmitted between two transceivers in an interleaved fashion.
Alternatively, The present invention avoids simultaneous operation by transmitting and receiving at different repetition rates, which forces the overlap condition to occur at a constant rate independent of spatial distribution. In order to overcome the overlap condition, the impulse radio receiver employs logic which prevents it from operating during the few overlapping pulses which occur per second.
Thus, the present invention is directed to a system and method whereby it is possible to send and receive information at the same time using the same antenna in an impulse radio.
One embodiment of the present invention allows the distance between two transceiver units in communication to be continuously varied, without it becoming necessary for either unit to transmit a monocycle and then operate its correlation receiver within a time period which would cause undesirable cross-talk. This is accomplished by the use of a slightly different repetition rate for each of the transmit and receive directions, and by turning off the transmitter for the period of time during which the beat period between the two repetition rates would otherwise require the transmission soon before or simultaneously with the reception of an impulse signal containing information.