Telecommunications – Transmitter and receiver at same station – Radiotelephone equipment detail
Reexamination Certificate
1998-12-30
2004-02-24
Trost, William (Department: 2683)
Telecommunications
Transmitter and receiver at same station
Radiotelephone equipment detail
C455S561000, C342S361000
Reexamination Certificate
active
06697641
ABSTRACT:
This application is the national phase under 35 U.S.C. §371 of prior PCT International Application No. PCT/IL98/00104 which has an International filing date of Mar. 3, 1998 which designated the United States of America, the entire contents of which are hereby incorporated by reference.
FIELD OF THE INVENTION
The present invention relates to wireless communication in general and to a method and a transmission system for improving performance, capacity and coverage in particular.
BACKGROUND OF THE INVENTION
Wireless communication is known in the art. A conventional wireless transmitter produces an electromagnetic signal, which is transmitted over a medium. This medium is often non-perfect, being rural or urban, and induces reflections and other disturbances, which cause the signal to fade. This phenomena is called multi-path.
Cellular mobile communication attempts to provide mobility, multi-user capacity (many independent users access the system), coverage (service is offered over a large contiguous area) and grade and quality of service.
Cellular communications are generally limited by local codes to a range of frequencies. A widely used technique of cellular communications employs spatial isolation in order to be able to reuse the same frequencies beyond a given range called a guard zone. The communications of each user is maintained with a base station, whose antenna is elevated above the scenery in order to achieve a well defined and controlled coverage area. Sectorization is achieved by directive antennas that illuminate only one sector, thereby reducing interference, enhancing performance and reducing a pattern of frequency reuse.
The number of concurrent calls communicating with Each sector of cellular communications is limited by the frequency band assigned to the service, by the technology used and by the frequency reuse pattern. The number of calls per unit area, also called area capacity, can be increased by reducing the cell size. Small cells that are positioned below roof tops in urban areas are called microcells. These use lower and smaller antennas. The cell hardware is more compact, and in some cases has less circuits. Another technique for microcells involves the antenna and RF circuitry only, remote from the cell equipment and connected via RF, fiber or microwave link, to the cell. Such an arrangement is especially attractive for operators in possession of RF or fiber trunking, like CATV companies.
Electromagnetic radiation is polarized and allows for two orthogonal polarization states. It will be appreciated by those skilled in the art that an antenna can only transmit in a single polarization state.
The propagation of the signals through an inhomogeneous medium and through scattering may transfer part of the signal to the orthogonal polarization. This is the case for terrestrial communications, for example, and in particular in urban areas, where the signals encounter multipaths from objects on the way.
The transfer of polarization has been found to be typically −10 dB in rural areas, −7.8 dB in urban areas and as high as −4 dB indoors [See for example Jorn Toftgard and Patrick C. F. Eggers: Experimental Characterization of the Polarization State Dynamics of Personal Communication Radio Channels, Proc. IEEE VTC'93, pp.65-69].
The orthogonal polarization components have been found to have an independent fading pattern, with correlation lower than 0.6 and similar fading statistics.
Diversity techniques are used in wireless communications to mitigate the degradation due to signal fading. In space diversity, the antennas for space diversity are spaced apart enough for the fading of the waves arriving to each to be time-independent from those arriving at the other. The spacing required between the antennas is inversely proportional to the angle of intercept of the arriving waves. Accordingly, often the distance between such two antennas is chosen to be considerably large.
A repeater in the cellular system is a device that receives the transmission from the Base Station (the donor side) and retransmits it to the subscribers(the distribution side) with proper amplification. Simultaneously it receives the signals from the subscribers and retransmits it, with proper amplification, to the Base Station. Repeaters are used mainly for the following applications:
Providing RF coverage in areas where the signal received from the Base Station is too week (“Radio Holes”)
Extending the cell coverage, e.g. along highways
Extending the coverage into tunnels, buildings or other structures.
A repeater has to be transparent—the grade of service should not be degraded by the introduction of the repeater in the link. The repeater has to cover the frequency range allocated to the distribution area to be covered. Preferably it is the whole frequency range of the Base Station. The repeater has to have alarms, status reporting and controls, to be controlled from the Base Station, either via land lines or via transmissions. The lack of diversity in the repeaters hampers their performance.
SUMMARY OF THE PRESENT INVENTION
It is an object of the present invention to provide a system for enhancing the coverage of wireless transmission, which overcomes the disadvantages of the prior art.
It is another object of the present invention to provide a novel method for controlling the polarization of a transmitted signal, thereby overcoming the disadvantages of the prior art.
In accordance with a preferred embodiment of the present invention, there is thus provided a modular cellular wireless communication base station, which includes a plurality of active radiator modules located at a desired antenna location, wherein each module includes at least one antenna for transmitting and receiving, a transmitter including a power amplifier, and a receiver.
The base station further includes a beam forming network controlling relative amplitudes and phases of each of the modules, an RF front end transmitting over a low power link with the active radiator modules via the beam forming network and receiving over a lower power link via a low noise amplifier.
The base station further includes a delay diversity module that provides a transmission CDMA delay diversity.
According to one aspect of the invention, the delay diversity module includes a SAW delay line and an amplifier that compensates for a delay line insertion loss.
According to another aspect of the invention, the delay diversity module is connected at a transmission beam forming network input.
According to a further aspect of the invention, the delay diversity module is connected at an active antenna transmission input.
A polarization diversity and matching system for cellular radio, including:
a dual polarized antenna pair at a base station, each antenna including an appropriate receive channel; and
a signal combining and control circuitry that adds polarization diversity to a base station receiver.
Preferably, the circuitry is characterized by two time constants, wherein a fast circuit adapts to fading signals on a received reverse link and changes weights of two antennas, and a slow circuit follows physical movements of a mobile station and averages fading of a received signal.
The slow circuit is driven by information from received signals and matches transmitted signal polarization to that of an incoming signal.
The slow circuit can also detect an average polarization vector direction from received signals and produces an output matched signal from the received signals according to the average polarization vector direction.
Signal portions from two receiving antennas are weighed by weights controlled by the signal combining and control circuitry, the weights being fed into a transform circuit that transforms the weights according to polarizations of the transmitting antennas and differences in gain.
The system can further include a low-pass filter that averages fast control variations and responds only to slow variations resulting from a physical attitude change of the station.
Preferably, a transmit chain is spl
Celletra Ltd.
G.E. Ehrlich (1995) Ltd.
Trost William
Zewdu Meless
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