FR2859347A1 - Signal transmission power control optimizing method for e.g. UMTS cellular network, involves reducing value of signal to interference ratio when threshold of convergence of measured quality of service towards target is reached - Google Patents

Abstract

The method involves defining a threshold for convergence of a measured quality of service towards a target quality of service. Value of signal to interference ratio is reduced by reducing values of respective increment and decrement constants, when the convergence threshold is reached. The quality of service is measured by block error rate or by binary error rate on exchanged signals. Independent claims are also included for the following: (a) a mobile terminal; and (b) a base station.

Description

POWER CONTROL OPTIMIZATION METHOD

  EMISSION IN A TELECOMMUNICATION NETWORK

CELLULAR

DESCRIPTION TECHNICAL FIELD

  The invention is in the field of telecommunications and relates more specifically to a method of optimizing the control of the transmission power in a cellular telecommunication network.

  The invention more specifically relates to a method for optimizing the control of the transmission power of the signals exchanged between a mobile terminal and a base station in a cellular telecommunication network, said method comprising two simultaneous processing phases: a first phase during which a target quality of service is defined, a target interference signal ratio (SIRe) is defined according to said target quality of service, the quality of service of each received signal is measured and incremented (respectively decremented ) the signal-to-target interference ratio (SIRe) of a PAS step inc (or PASdec step, respectively) to achieve an optimum signal to interference ratio (SIRCO) for which said target quality of service is achieved; a second phase during which the current signal-to-interference ratio (SIR) of a received signal is estimated and the power S is adjusted The invention also relates to a mobile terminal and a base station comprising means for measuring the quality of service of the signals exchanged in a transmission network. cellular telecommunication.

STATE OF THE PRIOR ART

  The transmission power of a mobile terminal or of a base station in a cellular telecommunication network is systematically controlled so as, on the one hand, to provide the terminal with the same quality of service regardless of its position in the network and, on the other hand, to increase the battery life while avoiding unnecessarily increasing the level of interference in a cell. This control can be performed on both the uplink and the downlink.

  In the uplink, the base station (node B) measures the signal-to-interference ratio (SIR) on the received signal and transmits to the terminal a command so that the latter adjusts its transmission power. In the downstream path, the mobile terminal performs similar operations and transmits to the base station the value of the SIR which in turn it measures. This power control mechanism where the terminal and the base station mutually adjusts their transmit powers is known in CDMA as closed-loop power control or closed-loop power control in English.

  The commands exchanged between the base station and the terminal in order to adjust their transmission power SP 22940 HM are based on a quality threshold established by a radio network controller (RNC) for managing radio resources. in the cells he controls.

  The power control process described above can be represented by two loops, schematically illustrated in FIG. 1, in which quality of service measurements and power matching commands are performed simultaneously.

  The first processing loop, called the internal loop, performs a fast processing to adjust the power of the signal received by the terminal or the base station to maintain the signal-to-interference ratio (SIR) equal to a predetermined target value SIR. by the second loop.

  The second loop, called an external loop, has the function of defining the signal-to-interference ratio SIRc so as to maintain the bit error rate (BER) or the block error rate measured on the blocks of transport of the received signal (BLER for Block Error Rate in English) to a target value BER, (respectively BLERC) ensuring for the inner loop the quality of service to the required level.

  As illustrated by FIG. 1, the internal loop comprises a matched filter 2, a RAKE receiver 4, a SIR interference signal ratio calculation module 6 and a control bit generation module 8 (TPC) for Transmit Power. Control).

  SP 22940 HM The external loop comprises a channel decoder 10, an error block detector module 12 and a module 14 for updating the SIRC.

  The module 6 calculates the current SIR relative to a received signal and transmits the calculated SIR to the module 8 which generates a bit 0 If the calculated SIR is greater than the target value SIRC, or a bit 1 If the calculated SIR is less than SIRC.

  The SIRC estimate is based on a measurement of link quality in BER terms or in terms of BLER. The optimal value of the SIRC shall be such that the desired quality in the link is achieved with the minimum transmit power of the base station or mobile terminal. If the estimated quality is better than the target quality, the value of the SIRC is decreased, and if not, this value is increased.

  Once the mobile terminal has established communication with the base station, the closed loop power control is activated. In the uplink, the base station permanently measures the signal quality in terms of signal-to-interference ratio (SIR) and sends the terminal a command on the downstream channel to ask it to either increase the transmission power if the measured SIR is below the SIRC, which is to decrease the transmission power if the measured SIR is above the SIRC.

  A disadvantage of the method of the prior art described above stems from the appearance of instability of the value of the SIRC when the value is adjusted to converge the quality of service measured on a received signal to the quality of service. SP 22940 HM service required, previously defined by the external loop.

  This instability results from the fact that the programs implemented in the external loop are designed to update the value of the SIRC as quickly as possible to obtain a BLER (respectively a BER) greater than or equal to the target BLERC (respectively at the target BERc). .

  FIG. 2 schematically illustrates the evolution of the SIRC during the convergence phase of the BLER measured on a received signal towards a predefined BLERC target value. During this phase, it appears that the interference generated in the cell is not minimized optimally because the value of the SIRC reached illustrated by the curve I is significantly greater than the optimal value.

  The aim of the invention is to reduce the instabilities of the SIRC in the convergence phase towards the target quality of service so as to converge the value of the SIRC illustrated by the curve I towards that illustrated by the curve II.

  DISCLOSURE OF THE INVENTION The invention recommends a method of optimizing the control of the transmission power of the signals exchanged between a mobile terminal and a base station in a cellular telecommunication network, said method comprising two simultaneous processing phases: a first phase during which a target service quality and a target interference signal ratio (SIRC) are defined according to SP 22940 HM, said quality of service target, the quality of service of each received signal is measured and increments (respectively decrements) the value of the target signal-to-interference ratio (SIRe) of a PAS_inc step (respectively of a PAS_dec step) to reach an optimal value of (SIR, o) for which said target quality of service is reached a second phase during which the current signal-to-interference ratio (SIR) of a received signal is estimated and the transmission power is controlled to reach According to the invention, said first phase comprises the following steps: defining a convergence threshold CONVdB of the quality of service measured towards the target quality of service, - reducing the values of the target signal over optimal interference (SIR, o). respective steps PAS inc and PAS dec when said convergence threshold is reached.

  Preferably, said quality of service is measured by the block error rate (BLER) or the bit error rate (BER) on the signals exchanged.

  In a particular implementation of the method according to the invention, said first phase comprises the following steps: - define a target error rate (BLERc) (respectively (BER,)), SP 22940 HM - define a signal-to-interference ratio target (SIRe) to ensure said target value (BLERc) (respectively (BER,)), measure the error rate on a received signal, - when the convergence threshold is reached, divide the step of incrementation PAS inc (respectively of decrementation PASdec) by a coefficient KI (respectively Kd) greater than 1.

  The mobile terminal according to the invention and the base station implementing the method according to the invention each comprise means for defining a convergence threshold CONVdB of the quality of service measured towards a predefined target quality of service, and means for reduce the value of the target quality of service when said convergence threshold CONVdB is reached.

BRIEF DESCRIPTION OF THE DRAWINGS

  Other characteristics and advantages of the invention will emerge from the description which follows, taken by way of non-limiting example, with reference to the appended figures in which: FIG. 1, previously described, schematically illustrates two control loops of power of the prior art, - Figure 2, described above, represents a first curve I illustrating the SIRE convergence phase and a second curve II illustrating the SIR, convergence phase.

  SP 22940 HM - Figure 3 is a flowchart schematically illustrating a preferred embodiment of the method according to the invention.

  DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS The following description relates to an implementation of the method in a UMTS cellular network in which a mobile terminal exchanges data and / or services with a base station (node B).

  Figure 3 shows a power control algorithm in the uplink or downlink.

  When the terminal transmits a signal to the base station, the latter measure (step 20) the quality of the link in BER terms or in terms of BLER and compares this quality to a target value BLERc.

  Simultaneously the base station permanently measures the signal-to-interference ratio (SIR) and compares the measured value with a target value (SIRe) defined so that the desired quality in the link is reached with the minimum transmit power. mobile terminal.

  Group 3 GPP (Third Generation Partnerschip Group) technical specifications define the power control adjustment procedure. The latter is performed step by step by 1 dB, 2 dB or 3 dB (case of transmission in compressed mode) for the terminal and 0.5 dB (optional) or 1 dB (required) for node B. In the conventional power control method, if the measured quality is less than the quality required for the exchanged service, the target SP 22940 HM (SIRC) value is increased. At a given instant, the signal-to-target interference ratio is given by the expression SIRC (t + 1) = SIRC (t) + PAS inc where - SIRC (t) represents the target value (SIRC) at time t, and SIRC (t + 1) represents the target value (SIRC) at the next instant.

  - PAS inc represents the incrementation step of the SIRC.

  And if the measured quality is greater than the quality required for the exchanged service, the target value (SIRC) is decreased. And at a given moment, the signal to target interference ratio is given by the expression SIRC (t + 1) = SIRC (t) - PAS dec - PAS dec representing the step of decrementation of the SIRC Whether it is in the rising channel or in the downlink, if the measured SIR is below the SIRC, the base station sends the terminal a Transmit Power Control (TPC) on the downstream channel to ask it to increase the transmit power.

  And if the measured SIR is above the SIRC the base station sends the terminal a TPC command to decrease the transmit power.

  Recall that in a UMTS network, the value of the estimated interference signal (SIR e) is expressed in relation to the power of the Dedicated Physical Control Channel (DPCCH) representing SP 22940 HM the dedicated control physical channel used in the upstream channel and in the downstream path for carrying the control information generated by the physical layer.

  Step 22 compares the difference between the estimated block error rate (BLERe) at step 20 and the predetermined target value BLERC at a convergence coefficient CONVdB expressed in dB which depends on the service exchanged between the terminal and the base station.

  The convergence criterion CONVdB thus defines a mode, referred to as the convergence mode in the following description, in which IBLER is BLER CONVdB.

  Thus, when one is in the convergence mode, that is to say when IBLERest-BLERcI S CONVdB, the steps of incrementation PAS inc and decrementation PAS dec of the SIR, are divided respectively by a coefficient KI and Kd greater than 1 (step 24). Otherwise, said divisor coefficients are maintained at 1 (step 26).

  In step 28, the outer loop checks whether the current SIRE target interference signal ratio is to be increased or decreased from the estimate of the quality of service at step 20.

  If the quality of service measured in step 20 is greater than the target quality of service, illustrated by the BLERO rate, then the SIR, is decremented in step 30 according to the following expression: SIR, (t + 1) = SIR, (t) PAS dec / Kd where Ki is a coefficient greater than 1.

  SP 22940 HM On the other hand, if the quality of service measured in step 20 is lower than the target quality of service, illustrated by the rate BLER then the SIR, is incremented in step 32 according to the following expression.

  SIR, (t + 1) = SIR, (t) + PAS dec / Ki where KI is a coefficient greater than 1.

  The invention thus makes it possible to reduce the average value of the SIR while guaranteeing the quality of service required. This results in a reduction of the interference generated by the base station in the downstream channel and those generated by the terminal in the uplink. This results in an improvement of the capacity of the network.

SP 22940 HM

Claims (5)

  A method for optimizing the control of the transmission power of the signals exchanged between a mobile terminal and a base station in a cellular telecommunication network, said method comprising two simultaneous processing phases: a first phase during which a target service quality is defined, a target interference signal ratio (SIRe) is defined according to said target quality of service, the quality of service of each received signal is measured, and the value of the report is incremented (respectively decremented). target interference signal (SIR0) of a step PAS inc (or a step PAS dec) respectively to reach an optimal value of (SIRCO) for which said target quality of service is reached, - a second phase during which one estimates the signal-to-interference ratio (SIR) of a received signal and adjusts the transmit power to achieve the optimal target signal to interference ratio (SIR, o ), characterized in that said first phase comprises the following steps: - defining a convergence threshold CONVdB of the quality of service measured towards the target quality of service, - reducing the respective values of the steps PAS inc and PAS dec when said threshold convergence is achieved.   SP 22940 HM 2. Method according to claim 1, characterized in that said quality of service is measured by the block error rate (BLER) or the bit error rate (BER) on the exchanged signals.   3. Method according to claim 2, characterized in that said first phase comprises the following steps.   - define a target error rate (BLERc) 10 (respectively BERC), define a target interference signal ratio (SIRe) to ensure said target value (BLERd (respectively (BER,)), - measure the error rate on a received signal, - when the convergence threshold is reached, divide the incrementation step PAS inc (respectively decrementation PAS_dec) by a coefficient KI (respectively Kd) greater than 1.   8. Method according to claim 2, characterized in that the cellular network is a CDMA type network.   9. Mobile terminal comprising means for measuring the quality of service of the signals exchanged with a base station in a cellular telecommunications network, characterized in that it further comprises.   SP 22940 HM - means for defining a convergence threshold CONVdB of the measured quality of service towards a predefined target quality of service, means for reducing the value of the target quality of service when said convergence threshold CONVdB is reached.   6. Base station of a cellular telecommunication network comprising means for measuring the quality of service of the signals exchanged with a mobile terminal, characterized in that it further comprises.   means for defining a convergence threshold CONVdB of the measured quality of service towards a predefined target quality of service; means for reducing the value of the target quality of service when said convergence threshold CONVdB is reached.   means for reducing the respective values of the PAS steps inc and PAS_dec when said convergence threshold is reached. SP 22940 HM