Telecommunications – Transmitter and receiver at separate stations – Plural transmitters or receivers
Reexamination Certificate
1999-09-16
2002-01-08
Legree, Tracy (Department: 2681)
Telecommunications
Transmitter and receiver at separate stations
Plural transmitters or receivers
C455S069000, C455S070000, C455S067150, C370S318000, C370S320000, C370S335000
Reexamination Certificate
active
06337989
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention is generally concerned with mobile radiocommunication systems.
The present invention is more particularly concerned with power control techniques used in such systems to improve performances (in terms of quality of service, of capacity, . . . etc.).
The present invention is in particular applicable to mobile radiocommunication systems of CDMA (“Code Division Multiple Access”) type. In particular, the present invention is applicable to UMTS (“Universal Mobile Telecommunication System”).
As is known, CDMA systems use two types of power control techniques, a so-called open-loop power control technique, and a so-called closed loop power control technique (also called hereinafter CLPC). These power control techniques may be recalled for example for the uplink transmission direction, i.e. from MS (“Mobile Station”) to BTS (“Base Transceiver Station”). In the open-loop power control, a MS transmit power is controlled based on the power received by this MS from a BTS. In the CLPC, a MS transmit power is controlled based on the transmission quality of the link between this MS and a BTS, as estimated at this BTS.
The transmission quality of a link between a MS and a BTS depends on the ratio of the received signal power and the interference power, also called SIR (Signal-to-Interference Ratio). When the SIR of a MS is low, or equivalently when the powers of the other MSs are much higher than its power, its performances dramatically decrease. The CLPC algorithm enables to keep the SIR of each user as close as possible to the target SIR.
The principle of the CLPC algorithm is that the BTS periodically estimates the SIR of the received signal from each MS, and compares this estimated SIR to a target SIR (SIR
target
). If the estimated SIR is lower than the target SIR, the BTS sends a power control command to the MS, for the MS to increase its transmit power. Otherwise, the BTS sends a power control command to the MS, for the MS to decrease its transmit power. The target SIR is chosen by the BTS as a function of the required quality of service.
To be efficient and track the variations of the SIR as closely as possible, in particular in fast changing environments, the CLPC needs to be rapid; as all example, in third generation systems like for example UMTS, power control commands are typically sent to a MS every slot in a frame (a slot being an elementary time unit in a data unit, or frame, transmitted in such a system, the frame duration being typically equal to 10 ms, and the slot duration to {fraction (1/15)} of the frame duration).
Now there are some situations in mobile radiocommunication systems, in which transmission of power control commands has to be momentarily interrupted. This will also hereinafter be referred to as transmission interruptions. This is also referred to as “transmission gaps” in UMTS system for example.
As an example, in CDMA systems, downlink transmission from a BTS to a MS may momentarily be interrupted to allow this MS to make measurements on frequencies other than the one used for this downlink transmission (in particular for handover preparation purposes, in particular inter-frequency handovers). Such a transmission mode including transmission interruptions is also referred to as “slotted mode” or “compressed mode” in UMTS system for example. A transmission interruption may last several slots (typically up to 15 slots, i.e. one frame, in downlink compressed mode). During these transmission interruptions, the CLPC is interrupted. Thus, the BTS does not send any more power control commands to the MS, and the uplink signals from this MS are no longer power controlled. Uplink transmission may simultaneously be interrupted, but in either case, as a result, the efficiency of the CLPC is significantly decreased, and the performances of the system may be seriously degraded.
In European patent application no. 99400894.4 filed on Apr. 12, 1999 by Applicant, a solution has been proposed to avoid such degradations of performances, due to such transmission interruptions.
Essentially, according to this prior patent application, when transmission is resumed after a transmission interruption, said power control algorithm is implemented with at least one modified parameter, for a given duration, said at least one modified parameter and said given duration being determined so as to compensate for the effects of said transmission interruption on power control.
According to a first embodiment disclosed in this prior patent application, said given duration has a predetermined value.
According to a second embodiment disclosed in this prior patent application, said given duration is determined to be passed when a given condition is fulfilled, based for example on successive power control results with said at least one modified parameter, for example when two consecutive power control commands obtained with said at least one modified parameter are opposed.
This second embodiment thus has the advantage that this given duration, or “recovery period”, is not fixed and can be adapted to each situation, depending for example on mobile speed, on environment, . . . etc. However, adaptive algorithms are usually very sensitive to errors (which in this context include SIR estimation errors, power control commands errors, . . . ). Thus, with an adaptive compensation length, there is a risk that the recovery period be too short, because of such errors.
On the other hand, a fixed recovery period offers the advantage to be robust to errors, but is not optimal, since it cannot be adapted to each situation.
The present invention enables to take profit of both types of algorithms, i.e. offers the advantage of an adaptive algorithm having a lower sensitivity to errors, or of a fixed algorithm having more flexibility.
SUMMARY OF THE INVENTION
An object of the present invention is therefore a method for improving performances of a mobile radiocommunication system using a power control algorithm and being subject to transmission interruptions, a method wherein a recovery period is provided following a transmission interruption, to compensate for the effects of said transmission interruption on said power control algorithm, and wherein said recovery period includes different parts wherein different types of compensation are successively carried out, said types being determined so as to ensure that a minimum compensation can first be obtained, and that compensation is not higher than necessary thereafter.
According to another object of this invention, said recovery period includes a first part having a length T
MIN
wherein a fixed-length compensation is carried out, followed by a second part having a maximum length T
MAX
−T
MIN
wherein an adaptive-length compensation is carried out, T
MIN
being the minimum compensation length inside said recovery period, and T
MAX
being the maximum compensation length inside said recovery period.
According to another object of the present invention, said first and second parts each have a length equal to half of the length of a transmission interruption period.
According to another object of the present invention, said recovery period includes N segments, each segment “n” including a first part having a length T
min
n
wherein a fixed-length compensation is carried out, followed by a second part having a maximum length T
max
n
−T
min
n
wherein an adaptive-length compensation is carried out, T
min
n
being the minimum compensation length inside segment “n”, and T
max
n
being the maximum compensation length inside segment “n”.
According to another object of this invention, parameters defining said parts of a recovery period and/or said types of compensation may vary from one recovery period to another one.
According to another object of this invention, parameters defining said parts of a segment and/or said types of compensation may vary from one segment to another one.
According to another object of the present invention, said compensation being obtained by modifying at least one parameter of said power con
Alcatel
Legree Tracy
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