Telecommunications – Transmitter and receiver at separate stations – Plural transmitters or receivers
Reexamination Certificate
1998-05-15
2001-10-23
Maung, Nay (Department: 2681)
Telecommunications
Transmitter and receiver at separate stations
Plural transmitters or receivers
C455S069000, C455S127500, C455S561000
Reexamination Certificate
active
06308080
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
This invention relates to point-to-multipoint systems and more particularly to downstream and or upstream power control of these systems.
BACKGROUND OF THE INVENTION
Point-to-multipoint communication systems provide service to a large number of subscribers or remote stations from a central base station (or central base station) at each node. To maximize the number of subscribers serviced by the base station, the node may be sectorized into several sectors with a separate transceiver (transmitter and receiver) and antenna system for each sector. This provides for 100% frequency reuse on each sector. The polarization of transmitted and received signal may alternate about the node as disclosed in J. Leland Langston application Ser. No. 08/345,183, filed Nov. 28, 1994 entitled “Low Power, Short Range Point-to-Multipoint Communications System” incorporated herein by reference. This provides for 100% frequency reuse but creates sector to sector interference possibilities.
Previous 2-way point-to-multipoint systems include cellular telephony systems, wireless local loop systems, and satellite communication systems. Cellular telephone systems and wireless local loop systems incorporate a method of power control to minimize subscriber transmitted power. The power control system maintains each subscriber at threshold. In addition, both cellular telephone systems and wireless local loop systems do not re-use the same frequency at a base station. This does not eliminate the interference problems associated with systems like that in the Langston application that reuse frequencies at a base station to maximize capacity.
Other fixed wireless systems are known to use a measurement of signal to noise ratio to perform power control. The disadvantage of using signal to noise as a criteria for power control is that the power setting at the subscriber is performed on system interference as well as receiver noise. This is because the signal to noise measurement includes interference and actually measures signal to noise plus interference ratio. If subscriber power is increased when high interference is measured, the result is a further increase in interference.
The interference increase caused by increasing subscriber power may occur elsewhere in the system on a common frequency channel (frequency reuse between sectors and between nodes) and would be difficult to detect. It could further cause an increase in subscriber power elsewhere in the system resulting in or snowball effect, or system instability.
SUMMARY OF THE INVENTION
This invention overcomes the problem of sensing interference by sensing this signal power received.
Point-to-multipoint communications systems provide service to a large number of subscribers from a central base station location. To maximize the number of subscribers serviced by a base station, the base station may be sectorized into several sectors or sub-sectors. This provides for 100% frequency reuse on each sector but creates sector to sector interference issues that must be addressed.
A solution to address the sector to sector interference issues according to one embodiment is to incorporate a system wide power control system that controls transmitter power at both the base station and the subscriber. Both downstream and upstream paths require different methods of power control .
Downstream power according to another embodiment is required to be controlled and therefore a need to maintain output power levels of the transmitters. The base station transmitter must provide for adequate power levels to provide services to all subscribers in its servicing area over environmental conditions but the transmitter must operate in a linear region to control side lobe distortion.
Upstream communications from all subscribers to the base station is accomplished with a base station receiver. In the case where the base station receiver is shared with multiple subscribers, some method must be employed to control the upstream power levels of the multiple carriers to prevent destructive interference of the upstream carriers.
In accordance with another embodiment of the present invention both downstream and upstream power control for a point-to-multipoint communication system is provided. In accordance with one embodiment a method of controlling downstream power is provided. In accordance with other embodiments two methods for upstream power control is described. A first method in accordance with another embodiment enables the subscriber unit to obtain levels for transmitted power by performing measurements on received signals from the base station. A second method in accordance with another embodiment incorporates a closed loop approach that is unique because it applies power control from the subscriber to the base station back to a central office. One embodiment incorporates a unique injection tone in the base station receiver used for power control reference and receiver calibration. Two methods are presented for receiver calibration in accordance with other embodiments. Both methods are unique in that they offer a continuous calibrations scheme maximizing power control accuracy.
The invention maximizes the subscribers that have service by minimizing the chance for interference between cells and subscribers. The invention is ideal for use local multipoint distribution service (LMDS) systems.
Another reason to minimize transmitted power is to mitigate potential interference with other services that may share the same frequency band. For example, a local multipoint distribution system will share spectrum with satellite services in some portion of the bands. Total interference to other services is a function of all the local multipoint distribution system transmitters in aggregate. By controlling individual transmitter power to a minimum and then raising power to overcome impairment such a rain, the aggregate power remains almost at the minimum.
These and other features of the invention that will be apparent to those skilled in the art from the following detailed description of the invention, taken together with the accompanying drawings.
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Burt Donald G.
Darbe Kevin B.
Langston J. Leland
Marin James Scott
Myers William K.
Maung Nay
Telecky , Jr. Frederick J.
Texas Instruments Incorporated
Troike Robert L.
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