Communication system, primary station and method of transmit power control
A transmit power control scheme for use in point-to-multipoint communication uses a random access channel for power control signals transmitted by the receiving stations ( 200 ).
1. A method of transmit power control in a communication system comprising a primary station and a plurality of secondary stations, the method comprising the steps of:
at each secondary station:
receiving a first signal transmitted by the primary station;
measuring a parameter of the received first signal;
deriving a second signal from the measured parameter;
transmitting the second signal; and
at the primary station:
transmitting the first signal;
receiving the second signals;
deriving a power control signal from the received second signals;
controlling the transmit power of the first signal in accordance with the power control signal;
wherein the transmitting of the second signal takes place with a sub-unity probability such that there is a functional relationship between the sub-unity probability and the measured parameter of the first received signal and wherein parameters determining said functional relationship are signaled to a secondary station of the plurality of secondary stations
wherein at each secondary station transmitting second signal comprises selecting a combination of spreading code, time period and frequency allocation from a plurality of combinations, the selection being dependent on a value of the measured parameter.
2. A method as claimed in claim 1 , wherein the plurality of combinations comprises different codes for transmission in a common time period.
3. A method as claimed in claim 1 , wherein the plurality of combinations comprises a common code for transmission in different time periods.
4. A method as claimed in claim 1 , wherein the plurality of combinations comprises a common code for transmission in a common time period using different frequency allocations.
5. A method as claimed in claim 1 , wherein the probability is dependent on the value of the measured parameter of the received first signal.
6. A method as claimed in claim 1 , wherein each second signal comprises at least one of:
an indication to increase the transmit power;
an indication to decrease the transmit power;
an indication that the first signal was decoded successfully;
an indication that the first signal contained unrecoverable errors;
an indication that an error rate of the first signal exceeds a threshold value; or
an indication of a quality level of the first signal.
7. A method as claimed in claim 6 , wherein the indication of a quality level comprises at least one of:
an indication of an error rate;
an indication of a signal-to-interference ratio;
an indication of a signal-to-noise ratio;
an indication of a signal level.
8. The method as claimed in claim 1 , comprising the steps of:
at each secondary station, increasing transmit power during the second signal;
at the primary station, in response to receiving a portion of the second signal, transmitting a third signal; and
at each secondary station, in response to receiving the third signal, ceasing the power increase.
9. The method as claimed in claim 8 , wherein ceasing the power increase comprises ceasing transmission of the second signal.
10. A communication system comprising a primary station and a plurality of secondary stations, each secondary station comprising:
a receiver configured to receive a first signal transmitted by the primary station;
a processor adapted to measure a parameter of the received first signal;
the processor being further adapted to derive a second signal from the measured parameter;
a transmitter configured to transmit the second signal; and
the primary station comprising:
a transmitter configured to transmit the first signal;
a receiver configured to receive the second signals;
a processor adapted to derive a power control signal from the received second signals;
the processor being further adapted to control the transmit power of the first signal in accordance with the power control signal;
wherein the transmitting of the second signal takes place with a sub-unity probability such that there is a functional relationship between the sub-unity probability and the measured parameter of the first received signal and wherein parameters determining said functional relationship are signaled to a secondary station of the plurality of secondary stations
wherein the processor is further adapted to select a combination of spreading code, time period and frequency allocation from a plurality of combinations, the selection being dependent on a value of the measured parameter.
11. The communication system as claimed in claim 10 , wherein the plurality of combinations comprises different codes for transmission in a common time period.
12. The communication system as claimed in claim 10 , wherein the plurality of combinations comprises a common code for transmission in different time periods.
13. The communication system as claimed in claim 10 , wherein the plurality of combinations comprises a common code for transmission in a common time period using different frequency allocations.
14. A communication system as claimed in claim 10 , wherein the probability is dependent on the value of the measured parameter of the received first signal.
15. A communication system as claimed in claim 10 , wherein each second signal comprises at least one of:
an indication to increase the transmit power;
an indication to decrease the transmit power;
an indication that the first signal was decoded successfully;
an indication that the first signal contained unrecoverable errors;
an indication that an error rate of the first signal exceeds a threshold value; or
an indication of a quality level of the first signal.
16. The communication system as claimed in claim 15 , wherein the indication of a quality level comprises at least one of:
an indication of an error rate;
an indication of a signal-to-interference ratio;
an indication of a signal-to-noise ratio; or
an indication of a signal level.
17. A communication system as claimed in claim 10 , wherein:
the secondary station means for transmitting is adapted to increase its transmit power during the second signal;
the primary station comprises means, responsive to receiving a portion of the second signal, for transmitting a third signal; and
the secondary station means for transmitting is further adapted to, responsive to receiving the third signal, cease the power increase.
18. A primary station for use in a communication system comprising a plurality of secondary stations, the primary station comprising:
a transmitter configured to transmit a first signal;
a receiver configured to receive from secondary stations second signals;
a processor adapted to derive a power control signal from the received second signals;
the processor being further adapted to control the transmit power of the first signal in accordance with the power control signal;
wherein the transmitting of the second signal takes place with a sub-unity probability such that there is a functional relationship between the sub-unity probability and the measured parameter of the first received signal and wherein parameters determining said functional relationship are signaled to a secondary station of the plurality of secondary stations, and
wherein the second signals received from the secondary stations are transmitted by selecting a combination of spreading code, time period and frequency allocation from a plurality of combinations, the selection being dependent on a value of the measured parameter.