JP4144618B2 - Cellular system transmission power control method - Google Patents

Description

  The present invention relates to a transmission power control method for comparing a reception signal SIR (signal-to-interference power ratio) on a reception side with a target SIR and controlling transmission power on the transmission side according to the difference and magnitude relationship in a cellular system.

  Conventionally, a radio link is bidirectionally connected between a mobile station and a base station in a cellular system. In a CDMA cellular system using a CDMA (Code Division Multiple Access) system, which is a radio link between a mobile station and a base station, in general, all mobile stations transmit signals (uplink signals) at the same frequency. ). All base stations transmit signals (downlink signals) at the same frequency. However, the frequency of the upstream signal is different from the frequency of the downstream signal, that is, an FDD (Frequency Division Duplex) system is used.

  Since the same frequency is used for each of the uplink and the downlink, a signal transmitted from a certain mobile station (or base station) becomes interference for other signals. As the transmission power increases, the interference increases, so in a CDMA cellular system, both the mobile station and base station perform transmission power control to minimize the transmission power and reduce the interference (mobile The transmission power control of the station is referred to as uplink transmission power control, and the transmission power control of the base station is referred to as downlink transmission power control).

  When performing transmission power control of a mobile station, a base station measures a reception SIR of a signal from the mobile station, and if the value is larger than a target SIR (hereinafter referred to as “target SIR”), the base station Is instructed to reduce the transmission power. Conversely, when the received SIR is smaller than the target SIR, the base station instructs the mobile station to increase the transmission power.

  When performing the transmission power control of the base station, the same control as the transmission power control of the mobile station is performed only by switching the roles of the mobile station and the base station.

  The transmission power control as described above has a function of making the reception SIR substantially constant, but the communication quality such as the frame error rate or the bit error rate is not necessarily constant even if the reception SIR is constant. Therefore, in order to make the frame error rate or the bit error rate substantially constant, a control called outer loop control is used. In the outer loop control, if the detected communication quality is worse than the target quality based on the communication quality (frame error rate or bit error rate) detected on the receiving side, the target SIR is increased. When the detected communication quality is better than the target quality, control is performed to reduce the target SIR.

  Conventional outer loop control methods are described in, for example, the document “Effects of Outer Loop Transmission Power Control in W-CDMA Mobile Communication Systems” (Usuda et al., 1998 IEICE General Conference, B-5-114, 1998 3). Month). According to this method, the frame error rate (FER) is measured by exponential weighting, and this is compared with the target FER (target FER) for every fixed number of frames, and the target SIR (target Eb in the literature is determined by the magnitude relationship). (Equivalent to / Io) is increased / decreased by a fixed value (the same value for both). As a modified method of this method, the paper “Transmission experiment characteristics of adaptive transmit power control using outer loop in W-CDMA” (Higuchi et al., 1998 IEICE General Conference, B-5-92, As shown in (March 1998), there is also a method in which the frame error rate is measured by counting the number of frame errors per fixed number of frames.

  However, there may be a lower limit in transmission power due to functional restrictions of the device. At this time, for example, although the transmission power on the transmission side is the lower limit, the reception SIR on the reception side may exceed the target SIR and no frame error occurs, and the above outer loop control is performed. And the target SIR will endlessly decrease. After that, when the situation changes and a frame error occurs, the target SIR is lower than the original required SIR. Therefore, the target SIR is set again to the required value by the outer loop control. Until the recovery, frame errors occur with a higher probability than the target FER.

  Accordingly, an object of the present invention is to provide a cellular system transmission power control method that can cope with the above-described problems.

  The cellular system transmission power control method according to the present invention disables the control to change the target SIR when the transmission side detects that the transmission power on the transmission side is the minimum level within the range allowed in advance. It is a method to do.

  According to another embodiment of the present invention, when the transmission power on the transmission side is a minimum level within a range allowed in advance, information indicating the minimum level is notified from the transmission side to the reception side. It is also preferable to detect the minimum level by receiving the information on the receiving side.

  According to another embodiment of the present invention, it is also preferable to perform the minimum level detection by detecting that the state where the reception SIR is higher than the target SIR continues for a certain time or longer on the reception side.

  According to the present invention, it is possible to prevent the target SIR from being lowered more than necessary when the transmission power is at the minimum level.

  Hereinafter, embodiments of a cellular system transmission power control method according to the present invention will be described in detail with reference to the drawings. Here, the transmission side / reception side means a base station or a mobile station in a cellular system. When the transmission side is a base station, the reception side is a mobile station. Conversely, when the transmitting side is a mobile station, the receiving side is a base station.

  FIG. 1 is a block diagram showing a cellular system transmission power control method according to the present invention.

  According to FIG. 1, it comprises a transmission unit 1 on the transmission side and a reception unit 2 on the reception side.

  The transmission unit 1 includes a signal transmission unit 10 and a transmission power increase / decrease control unit 11. On the other hand, the reception unit 2 has a transmission power control unit 29 for the transmission unit 1 so that the SIR of the reception signal of the reception unit 2 is equal to the value of the target SIR given from the outside of the transmission power control unit 29. In addition, the transmission power on the transmission side is controlled. The transmission power control unit 29 includes a detection unit 291, a reception SIR measurement unit 292, an SIR comparison unit 293, and a transmission power increase / decrease amount determination unit 294.

  A transmission signal from the signal transmission unit 10 of the transmission unit 1 is received by the detection unit 291 of the reception unit 2. The received signal is output from the detection unit 291 to the outside of the transmission power control unit 29 and also input to the reception SIR measurement unit 292. Reception SIR measurement section 292 measures the SIR of the reception signal. The SIR comparison unit 293 compares the measured reception SIR with the target SIR input from the outside of the transmission power control unit 29. The comparison result is notified to the transmission power increase / decrease amount determination unit 294. The transmission power increase / decrease amount determination unit 294 determines the increase / decrease amount of the transmission power on the transmission side based on the SIR comparison result (magnitude relationship, difference, etc.). Information on the transmission power increase / decrease amount is transmitted to the transmission unit 1.

  The transmission unit 1 receives the transmission power increase / decrease information transmitted from the reception unit 2 by the transmission power increase / decrease control unit 11. The transmission power of the signal transmission unit 10 is increased or decreased according to the transmission power increase / decrease amount.

  With such an operation, the transmission power of the transmission unit 1 is controlled so that the SIR of the reception signal from the transmission unit 1 becomes equal to the value of the target SIR given from the outside of the transmission power control unit 29. In particular, the present invention is configured to provide an appropriate target SIR for such a transmission power control unit 29.

  In addition to the transmission power control unit 29, the reception unit 2 includes a frame error detection unit 21, a frame error count unit 22, a threshold determination unit 23, a target SIR increase / decrease amount determination unit 24, and a target SIR determination unit 26. And a transmission level minimum detection unit 28.

  The frame error detection unit 1 detects a frame error for each frame in the reception signal output from the transmission power control unit 29. Information about the presence or absence of a frame error is input to the frame error count unit 21 for each frame.

  The frame error count unit 22 always counts the number of frame errors in the immediately preceding N frame based on the information input for each frame, and outputs the value for each M frame (N and M are both 1 or more) Integer).

  The threshold determination unit 23 compares the number of input frame errors (assumed to n) with preset thresholds t1, t2 (t1 ≧ t2), and whether or not n ≧ t1 as a comparison result. In addition, the target SIR increase / decrease determination unit 24 is notified of whether or not n ≦ t2.

  The target SIR increase / decrease determining unit 24 determines that the target SIR increase / decrease is + S1 when n ≧ t1 is reported. If n ≦ t2 is reported, the target SIR increase / decrease amount is determined to be −S2. When it is notified that neither n ≧ t1 nor n ≦ t2, it is determined that the target SIR increase / decrease amount is zero. The target SIR increase / decrease amount determined in this way is notified to the target SIR determination unit 26.

  The target SIR determination unit 26 holds the value of the target SIR and always outputs it. The target SIR determination unit 26 increases or decreases the target SIR held when the target SIR increase / decrease amount is notified from the target SIR increase / decrease determination unit 24 by the target SIR increase / decrease amount, and then holds the target SIR after the increase / decrease is performed. Always output. The target SIR value output from the target SIR determination unit 6 is input to the transmission power control unit 29 and used as the target value of the reception SIR as described above.

  The transmission level minimum detection unit 8 detects whether or not the transmission power on the transmission side is the minimum level within a range allowed in advance. When the minimum level is detected, the target SIR determination unit 6 is instructed not to increase or decrease the target SIR. When the target SIR determination unit 6 receives an instruction not to increase or decrease the target SIR from the transmission level minimum detection unit 8, the target SIR determination unit 6 does not change the held target SIR value even if the target SIR increase / decrease amount is input.

  As a method of detecting whether or not the transmission power on the transmission side is the minimum level within the range allowed in advance in the transmission level minimum detection unit 8, for example, when the transmission power is minimum, this is indicated. It is possible to detect that the transmission power on the transmission side is minimum by including the information in the signal to be transmitted and detecting the information in the transmission level minimum detection unit 8. As another method, the SIR of the received signal can be monitored, and it can be determined that the transmission power on the transmission side is the minimum when a state in which the received SIR is higher than the target SIR continues for a certain period of time.

  The parameters N, M, t1, and t2 can be set to arbitrary values, and in some cases, the values can be changed during operation.

  By such a method, it is possible to prevent the target SIR from being lowered more than necessary when the transmission power is at the minimum level.

  In the above description, the transmission power control unit 29 controls the received SIR to be equal to the target SIR, but the signal power (S) of the received signal is equal to the target signal power value (target S). The present invention can also be applied to such control. In that case, in the above description, the present invention achieves the contents obtained by replacing SIR with S.

  As described above, the embodiments described in detail have been described by taking the CDMA cellular system as an example. However, in application (including partial application) to a cellular system using a radio system other than CDMA, the technical idea and scope of the present invention Various changes, modifications, and omissions can be easily made by those skilled in the art. Therefore, the above-described embodiment is merely an example, and is not intended to be limited in any way. The invention is limited only as defined in the following claims and the equivalents thereto.

It is a block diagram showing the cellular system transmission power control method in this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Transmission part 10 Signal control part 11 Transmission power increase / decrease control part 2 Reception part 21 Frame error detection part 22 Frame error count part 23 Threshold determination part 24 Target SIR increase / decrease amount determination part 26 Target SIR determination part 28 Transmission level minimum detection part 29 Transmission power control unit 291 Detection unit 292 Reception SIR measurement unit 293 SIR comparison unit 294 Transmission power increase / decrease determination unit

Claims (3)

In the cellular system that compares the reception signal SIR on the reception side with the target SIR and controls the transmission power on the transmission side according to the difference or magnitude relationship,
Cellular system transmission power, wherein control for changing the target SIR is invalidated when the reception side detects that the transmission power on the transmission side is a minimum level within a range allowed in advance. Control method. When the transmission power of the transmission side is the minimum level within a range allowed in advance, information indicating the minimum level is notified from the transmission side to the reception side,
The cellular system transmission power control method according to claim 1, wherein the minimum level detection is performed by receiving the information on the receiving side.   The cellular system transmission power control method according to claim 1, wherein the minimum level detection is performed by detecting that a state in which the reception SIR is higher than the target SIR has continued for a predetermined time or longer on the reception side.

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