Power control in telecommunications networks

This application is a continuation of U.S. application Ser. No. 10/528,639, filed 2005Sep. 28, now pending, which was the National Stage of International Application No. PCT/EP03/10588 filed Sep. 23, 2003, which claims benefit of U.S. Provisional Application 60/500,427 filed Sep. 5, 2003 and U.S. Provisional Application 60/422,939 filed Oct. 31, 2002. This application incorporates by reference the entire disclosure of U.S. Provisional Application 60/500,427 and 60/422,939.

Not Applicable

Not Applicable

The present invention relates to power control in telecommunications networks, and, in particular, in RF mobile telephone networks and systems.

Power control is important in mobile telephone networks, for example, because it is important to obtain desirably high capacity and efficiency, particularly in COMA systems. The variable that is controlled is called quality. Quality of the communication is controlled with reference to a quality measure such as BER (Bit Error Rate), FER (Frame Erasure Rate, BLER (Block Error Rate), number of iterations of a turbo decoder, or the average reliability of decision statistics. Below, for the sake of brevity, the quality measurement will be referred to as BLER. It will, however, be readily appreciated that BER or FER, or other quality measurement could be used. Usually an integrating controller is provided to achieve a steady state performance with zero control error. The control scheme used is cascade control, see for example FIG. 1 of the accompanying drawings. The idea with cascade control is to make an inner control loop (2) much faster than an outer control loop (4). For transmission power control (TPC) the inner loop controls another quality measure such as for example the signal to interference ratio (SIR). The outer loop sets the SIR reference value SIRr for the inner loop. The goal of the outer loop is to control the SIR reference value to achieve a BLER that is equal to the BLER reference BLERr. To get a control system that in steady state achieves a BLER that is equal to the BLER reference, an integrating controller (9), which can be, for example, a PI controller, a PID controller, or a pure integrating controller, can be used. The cascade controller illustrated in FIG. 1 comprises an inner control loop (2) and an outer control loop (4). Both control loops have an input of a received signal (y(k)). In the outer control loop 4, the BLER is estimated in a BLER estimation unit (5) and compared with a BLER reference signal. A subtractor (7) calculates the difference between the reference signal and the BLER estimate to supply an input signal to an integrating controller (9). The integrating controller (9) produces a SIR reference signal. The SIR reference signal is compared with an SIR estimate from an SIR estimation unit (3) in the inner control loop (2). The difference between the SIR reference and the SIR estimate is supplied to a function, for example a step function (11) for determining a command u(k) that sets transmission power. More generally, the SIR estimate and the SIR reference value could both be supplied to a function that determines a command u(k) for setting the transmission power.

A known problem with an integrating controller (such as a PI, PID, or pure integrating controller) is that it becomes unstable if the control signal saturates. This problem is often referred to as the windup problem. Transmission power control (TPC) saturation of the control signal corresponds to situations when the maximum (or minimum) transmitter power is used. The windup problem in the power control algorithms for third generation mobile telephony systems is well known. The specific problem of windup protection in WCDMA makes several additions to anti-windup schemes used in other areas necessary. As is well known, integrating controllers have the nice property of being able to achieve zero control error in steady state. As an example of an integrating controller, a continuous time PI-controller is shown in FIG. 2: Discrete time controllers have similar behaviour; see for example, Karl Johan Astrom and Tore Hagglund, “PID Controllers: Theory, Design and Tuning”, Instrument Society of America, Research Triangle Park, NC, second edition, 1995. A known problem with integrating controllers is that the integrator part turns unstable when the control signal saturates. This instability occurs because feedback from the process is needed to stabilize the controller, which is not open loop stable. In the case of transmission power control, saturation can occur when maximum (or minimum) transmission power is used. In this situation the transmission power can only be decreased (or increased in the case of a minimum), which can be seen as open loop operation of the integrator. As the controller is not open loop stable the controller state (the integrator, I-part) can start to build up a large state. This usually results in that it takes a long time for the control loop to start functioning again after the saturation state is left. This problem is usually referred to as the windup problem.

According to one aspect of the present invention there is provided a method for controlling a radio frequency (RF) transmitter, the method having an integrating controller to produce a reference value of a first quality measure from a first error signal; producing an estimated value of the first quality measure relating to an actual value of the first quality measure; and supplying a tracking signal related to the estimated value of the first quality measure and the reference value of a first quality measure to the reference integrating controller.

According to another aspect of the present invention, there is provided a controller for controlling a radio frequency (RF) transmitter, the method having an integrating controller operable to produce a reference value of a first quality measure from a first error signal; an estimator operable to produce an estimated value of the first quality measure relating to an actual value of the first quality measure; and a tracking unit operable to supply a tracking signal related to the estimated value of the first quality measure and the reference value of a first quality measure to the reference integrating controller.

It is emphasized that the term “comprises” or “comprising” is used in this specification to specify the presence of stated features, integers, steps or components, but does not preclude the addition of one or more further features, integers, steps or components, or groups thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a controller for a third generation mobile system;

FIG. 2 illustrates an integrating controller;

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