Telecommunications – Transmitter and receiver at separate stations – Plural transmitters or receivers
Reexamination Certificate
2001-09-14
2004-11-16
Ramakrishnaiah, Melur (Department: 2643)
Telecommunications
Transmitter and receiver at separate stations
Plural transmitters or receivers
C455S069000, C455S561000
Reexamination Certificate
active
06819936
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to gain control in communications systems, and specifically to gain control of repeaters within communications systems.
BACKGROUND OF THE INVENTION
A cellular communications network which operates in regions closed off from electromagnetic radiation, such as within buildings or inside tunnels, typically achieves coverage within the closed-off regions by using a repeater system. The repeater system comprises a first repeater outside the region communicating directly with a base-station transceiver system (BTS), a second repeater inside the region communicating directly with mobile units within the closed-off region, and cabling connecting the two repeaters. It is known in the art that varying signal levels at the BTS or at the mobile units adversely affect operation of the network, by effectively increasing the noise in the network, thus decreasing signal
oise levels. The effect is overcome by constantly monitoring signal levels at the BTS and at the mobile units, and most preferably adjusting gains of the mobile units to maintain the signal levels as constant as possible. With the interposition of a repeater system between the BTS and the mobile units, it is important that signal level changes caused by changes of gain within the repeater system are minimized, and that they are made slowly, to ensure that the repeater system remains substantially transparent to the network.
U.S. Pat. No. 5,799,005 to Soliman, whose disclosure is incorporated herein by reference, describes a system and method for estimating the quality and path loss associated with a communications channel. The estimate is made by measuring the power of a pilot signal received by a communications receiver. The communications receiver measures a received signal power, and also makes a relative pilot strength measurement of the received pilot signal. The power of the pilot signal is then computed using the received signal power and the relative pilot strength measurement. A base station also transmits an indication of the power at which the pilot signal was transmitted. An estimate of the path loss is then made by determining the difference between the indicated power of the transmitted pilot signal and the received pilot signal power.
U.S. Pat. No. 5,991,284 to Willenegger, et al., whose disclosure is incorporated herein by reference, describes a method for controlling the transmitted power of each subchannel generated by a station transmitting a channel. The station generates a channel made up of a sum of subchannels so that each subchannel or group of subchannels is amplified with a unique gain value that is varied in accordance with subchannel power control messages from a receiving station. The receiving station generates each subchannel power control message after monitoring and calculating metrics based on that received subchannel.
SUMMARY OF THE INVENTION
It is an object of some aspects of the present invention to provide a method and apparatus for controlling a gain between repeaters in a cellular communications network.
It is a further object of some aspects of the present invention to provide a method and apparatus for setting gains in an automatic calibration process for a cellular communications network.
In preferred embodiments of the present invention, a base-station transceiver system (BTS) communicates with a master repeater unit within a cellular communications network. The master unit communicates via cables with remote units, which remote units in turn communicate with mobile transceivers which are cut-off from direct communication with the BTS, inside a building, for example. The communication comprises a forward transmission path from the master unit to the remote units, and a reverse transmission path from the remote units to the master unit. The communication between the master unit and remote units enables the mobile transceivers to function within the network.
During an initialization phase, a forward gain and a reverse gain of each of the remote units are set separately, preferably in a substantially automatic manner. The forward gains are set so as to generate default power outputs, preferably substantially equal, at each remote unit. Alternatively, the power outputs of each remote unit are set according to settings transmitted thereto from the master unit. The reverse gain of each remote unit is adjusted in response to forward parameters, such as cable insertion loss, measured during the installation phase, and known differences of these parameters for the reverse transmission path.
In order to set the forward gain, a pilot reference frequency is injected after an input stage of the master unit, most preferably at a level substantially equal to the level generated by the input stage when the latter is operational. The input stage is de-activated during the initialization phase, so that only the pilot signal is transmitted in the system during initialization. The pilot reference signal is most preferably a narrow-band signal at a frequency within a band used for communication within the network. The pilot signal is detected by a respective first detector comprised in each remote unit. Using the known input level and the level read by the first detector a forward gain of the remote unit is then set so as to generate the required power output for the specific unit. Also, a cable forward insertion loss between the master and specific remote unit is calculated from the two levels.
Reverse gain levels for each remote unit are evaluated by extrapolating the forward insertion loss measurements found during the initialization phase, to find a reverse insertion loss. The extrapolation takes account of differences between the forward and reverse paths. The differences comprise cable loss differences caused by differences in transmission frequencies between the forward and reverse paths, as well as different insertion losses of elements in the two paths. Most preferably, the reverse gain set for each remote unit is generally greater than the cable reverse insertion loss by a predetermined value, such as 5 dB.
Each remote unit comprises an output stage which is de-activated during a period when the specific remote unit is being initialized. The first detector of the remote unit is positioned before the output stage. The de-activated master unit input stage and remote unit output stages act as isolators. Thus, forward and reverse gain adjustments may be implemented for each remote unit without the pilot signal generating any external interference, and without external signals causing interference with the adjustments.
In an operational phase the pilot is de-activated, and the master unit input stage and the output stage of each remote unit are activated. A forward gain of the master unit input stage is set to generate a substantially fixed nominal output level. (Most preferably, the level at which the pilot is injected in the initialization phase substantially equals this output level.) Most preferably, a master unit reverse gain is set so that a system reverse gain is substantially equal to a system forward gain. Alternatively, the reverse gain is set to be different from the forward gain by a predetermined value.
Each remote unit comprises a second detector which is used to monitor power output from the output stage of the respective remote unit. Forward and reverse gains of the master unit and each of the remote units are maintained as constant as possible in order to maintain system gain settings substantially unchanged from their installation settings, which in turn maintains signal
oise ratios in the forward and reverse transmission paths. During operation of the system, forward and reverse gains and power outputs of each of the remote units are monitored and adjusted when necessary, for example when system parameters change, so as to maintain the forward and reverse gains substantially unchanged, according to the site design. The input master unit stage and/or one or more of the remote unit output stages may be temporarily de-
Brown Charles D.
Kordich Donald
Qualcomm Incorporation
Ramakrishnaiah Melur
Wadsworth Philip
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