Telecommunications – Transmitter and receiver at separate stations – Plural transmitters or receivers
Reexamination Certificate
1998-09-16
2001-05-01
Urban, Edward F. (Department: 2683)
Telecommunications
Transmitter and receiver at separate stations
Plural transmitters or receivers
C455S069000, C455S504000
Reexamination Certificate
active
06226525
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to Local Multipoint Delivery/Communication Systems (LMDS/LMCS) operating at millimeter wave frequencies (above 20 GHz) and more particularly to systems and methods for controlling base station transmission power to compensate for time varying attenuation in the wireless link between the base station and network interface units (NIUs) at customer sites.
BACKGROUND
LMDS/LMCS typically utilizes cellular topologies to achieve coverage of a given service area. The cell topology is frequently depicted as a circular area with a centrally deposed base station. Typically the cells are 1-5 km in diameter. Customer sites, having terminals to interface with the base station over a wireless link, are located within the circular area. In a large metropolitan area several similar cells are arranged in a fixed pattern to provide wide area coverage.
As will be discussed later a cellular area may be divided into sectors with the base station employing a sectored antenna to provide separate coverage to each sector. The bandwidth, licensed to the service provider operating the system, is divided into radio frequency (RF) carriers to provide better utilization of the available bandwidth. Generally, network interface units (NIUs) at customer sites are in fixed locations within a cell or sector and communicate with the base station in a point to point protocol utilizing highly directional antennas.
Wireless transmission of millimeter wave frequencies travels over a line of sight (LOS) path and any obstacles within the path will influence communication between the base station and network interface units at the customer site. Similarly, any time-dependent attenuation of radio signals within the path will result in service degradation. Time dependent path attenuation is caused principally by rain within a cell or sector although other weather related conditions can have similar influences. Such other conditions include snow, sleet or hail, and wind blown materials such as dust, sand etc. In the following discussion, time dependent path attenuation is referred to as rain fade but this term is intended to include the other sources of attenuation.
In view of the variable nature of rain fade, both in terms of duration and intensity, it is desirable to provide some type of controllable power compensation to the radio signal. In conventional cellular and Personal Communications Services (PCS) systems base station power control is used to overcome Rayleigh fading and inter-cell interference. In those systems the typical power step is 3 dB and makes no consideration of the mobile terminal's dynamic power control mechanism.
SUMMARY OF THE INVENTION
The present invention addresses the problem of rain fade by way of methods and systems for dynamically adjusting the base station transmission power to compensate for variations in path attenuation.
In one aspect of the invention base station power control is applied to respective radio frequency (RF) carriers of a multi carrier transmission implementation.
Therefore in accordance with a first aspect of the present invention there is provided in a broadband wireless system having a base station for communicating with a network interface unit (NIU) over a wireless link a system for compensating for time variable path attenuation of the link comprising: polling means at the base station to periodically obtain status from the NIU and control means at the base station to adjust transmission power in accordance with the status information.
In a preferred embodiment of this aspect of the invention several NIUs are located within a cellular area and the base station polls status information from a designated reference NIU.
In this aspect of the invention base station power control is based on the nominal power level of the RF signal received at the designated reference NIU.
In accordance with a further aspect of the invention the power level of the RF signal transmitted from the NIU to the base station (uplink) is based on the power level of the signal received by the NIU. In this aspect the nominal uplink power is established in accordance with a long loop power control and a short loop power control adjusts the NIU transmit power level in response to instantaneous changes in receive power.
In accordance with a further aspect of the invention there is provided a method of controlling the power level of the transmission from a base station to a network interface unit over a wireless link in a cellular, broadband wireless communication system in order to compensate for time dependent path attenuation, the method comprising: periodically polling the network interface unit for status information and adjusting transmission power at the base station in accordance with the status information.
In accordance with a preferred embodiment of this aspect of the invention the status information used by the base station to adjust transmission power is the power level of the RF signal received at a designated network interface unit.
In accordance with another aspect of the invention a closed loop downlink (base station to NIU) power control scheme is used in conjunction with uplink (NIU to base station) power control. The uplink power control at the NIU preferably includes a first receive power level sampling interval (long loop) for establishing a nominal power level and a second sampling interval (short loop) for controlling uplink transmit power based on dynamic receive power levels. The first sampling interval is longer than the second to ensure system stability.
REFERENCES:
patent: 5809431 (1998-09-01), Bustamante et al.
patent: 5862171 (1999-01-01), Mahany
patent: 5886989 (1999-03-01), Evans et al.
Boch Eric H.
Ployer John Scott
Yee Jung F.
Alcatel Networks Corporation
Larson & Taylor PLC
Tran Congvan
Urban Edward F.
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