Transmission power control apparatus and control method thereof

Abstract

When a mobile station controls the transmission power of the uplink using transmission power control information that is sent from a plurality of base stations with which the mobile station is communicating, a radio-state-monitoring unit 681 to 68N monitors the radio states between each base station and the mobile station, then based on the radio state, a power-control-algorithm-instruction unit 69 instructs a transmission power control unit 70 which of a plurality of power-control algorithms should be executed to control the power, and a transmission power control unit stores the plurality of power-control algorithms for control the uplink transmission power using TPC information and controls the uplink transmission power of the mobile station based on the instructed power-control algorithm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a drawing showing the construction of a mobile station.

FIG. 2 is a drawing that shows in detail the overall construction of a baseband processing unit (inverse spreading unit, channel compensation/synchronization detection wave unit, RAKE combining unit, and demodulation unit) that corresponds to one base station.

FIG. 3 is a flowchart for a first transmission power control algorithm.

FIG. 4 is a flowchart for a second transmission power control algorithm.

FIG. 5 is a flowchart for a third transmission power control algorithm.

FIG. 6 is a flowchart for a transmission power control-algorithm-setting process.

FIG. 7 is a drawing for explaining an example of judging TPC information.

FIG. 8 is a drawing that shows the construction of a radio communication system.

FIG. 9 is a drawing for explaining the main radio channels that are used in HSDPA.

FIG. 10 is a drawing for explaining the slot format of a down link DPCH.

FIG. 11 is a drawing for explaining transmission power control of a mobile station.

FIG. 12 is a drawing for explaining the condition when a mobile station performs communication simultaneously with three base stations during handover.

FIG. 13 is a flowchart for a prior transmission power control process during soft handover.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

(A) Construction of a Mobile Station

FIG. 1 is a drawing showing the construction of a mobile station. The mobile station is in a handover state, and is performing communication with a plurality of base stations via radio links.

A radio-receiving unit 51 converts the radio signals that were received from the plurality of base stations to baseband signals using a frequency-down-conversion process, then performs AD conversion and outputs the result.

There are inverse spreading units 61₁ to 61_N, channel compensation synchronization detection wave units 62₁ to 62_N, RAKE-combining units 63₁ to 63_N and demodulation units 64₁ to 64_N that correspond to each of the respective base stations. The inverse spreading units 61₁ to 61_N that correspond to each of the base stations multiply the respective baseband signals by a specified inverse spreading code that was specified from the base station and outputs pilot signals and information signals, then the channel compensation synchronization detection wave units 62₁ to 62_N use the pilot signals to estimate channels, and together with performing channel compensation based on the channel estimation results, returns the information signals to their original phase. The RAKE-combining units 63₁ to 63_N perform RAKE combination of information signals that are output for each path of the multiple paths between the base stations and the mobile station, and the demodulation units 64₁ to 64_N perform demodulation processing on the RAKE-combined signals to demodulate the information (TPC information), then output the results. The demodulation units 64₁ to 64_N will hereafter be called TPC demodulation units. A RAKE-combining unit 65 further combines the RAKE-combined signals that are output from each of the RAKE-combining units 63₁ to 63_N, and a TPC demodulation unit 66 demodulates the TPC information based on that combined signal.

FIG. 2 is a drawing showing in detail the overall construction of a baseband processing unit (inverse spreading unit, channel compensation synchronization detection wave unit, RAKE-combining unit, demodulation unit) that corresponds to one base station. When a direct spread signal that has suffered a multi-path effect is input to a searcher 61a from the radio-receiving unit 51, the searcher 61a uses a matched filter to perform self-correlation computation and detects the multiple paths, and inputs timing data t₁ to t₄ and delay time adjustment data d₁ to d₄ for the start of the inverse spreading for each path to finger units 61b₁ to 61b₄. Each inverse spreading/delay time adjustment unit 61c of the respective finger units 61b₁ to 61b₄ performs inverse spreading processing on the direct wave or delay wave that arrives via the corresponding path at the respective timing t₁ to t₄, and integrates the results, after which it delays the respective integrated signal by a delay time d₁ to d₄ that corresponds to the path and outputs two kinds of signals, a pilot signal and information signal. A phase compensation unit (channel estimation unit) 61d outputs the phase difference θ between the pilot signal that was obtained from inverse spreading and an already known pilot signal, and based on that phase difference θ, a synchronization detection wave unit 61e returns the information signal to its original phase. A RAKE-combining unit 63₁ combines the information signals that were output from each of the finger units 61b₁ to 61b₄, and a TPC demodulation unit 64₁ demodulates the TPC information based on the RAKE-combined signal.

Returning to FIG. 1, reception SIR measurement units 68₁ to 68_N measure the state of the radio links between the mobile station and the respective corresponding base station, for example, they measure the reception signal quality or the SIR (reception SIR) of the received signals, and input the measurement results to a reliability judgment unit 69.

The reliability judgment unit 69 compares the reception SIR with a first and second threshold value, and based on the comparison results, determines the degree of reliability of the TPC information that is sent from each base station, and based on the judgment results, determines the algorithm to be used for transmission power control. As will be described later, there is (1) a first transmission power control algorithm that is used in a first state in which there is TPC information having high reliability, (2) a second transmission power control algorithm that is used in a second state in which there is no TPC information having high reliability, but there is TPC information having low reliability, and (3) a third transmission power control algorithm that is used in a third state in which none of the TPC information has reliability.

When the reception SIR of the signal received from a base station is greater than a first threshold value A, the reliability judgment unit 69 determines that the reliability of the TPC information is high, and when the reception SIR is greater than a second threshold value B but less than the first threshold value A (B<A), the reliability judgment unit 69 determines that the reliability of the TPC information is low, and when the reception SIR is less then the second threshold value B, the reliability judgment unit determines that the TPC information has no reliability. Also, based on the reliability of TPC information for each base station, the reliability judgment unit 69 determines which of the three states, (the first thru third states), the current state is, and sends an instruction to the transmission power control processing unit 70 to execute transmission power control according to the transmission power control algorithm that corresponds to the current state. The instruction includes algorithm identified data and the reliability judgment results of the TPC information sent from the base stations.

The transmission power control processing unit 70 increases (UP) or decreases (DOWN) the gain of the transmission power amplification unit of a radio-transmission unit 71 according to one of the first to third transmission power control algorithms. The transmission power control processing unit 70 comprises: a TPC information judgment unit 81 that determines whether the transmission power control processing unit 70 specifies that the TPC information is UP, or specifies that the TPC information is DOWN; and a transmission power control unit 82 that increases (UP) or decreases (DOWN) the gain of the transmission power amplification unit of the radio-transmission unit 71 based on the judged TPC information.

The TPC information judgment unit 81 is a microcomputer and stores the first thru third transmission power control algorithms in an internal memory unit 81a, and according to the transmission power control algorithm that is identified by the algorithm identified data sent from the reliability judgment unit 69, determines whether the TPC information specifies to increase the gain (UP) or to decrease the gain (DOWN), and inputs the judged TPC information to the transmission power control unit 82.

(B) Transmission Power Control Algorithm

(a) First Transmission Power Control Algorithm

FIG. 3 is a flowchart for the first transmission power control algorithm, and is used in a first state in which there is TPC information having high reliability.

The TPC information judgment unit 81 checks whether all of the TPC information having high reliability specifies ‘UP’ (step 201), and when all specify ‘UP’ determines that the TPC information is ‘UP’ (step 202) and inputs [TPC information=UP] to the transmission power control unit 82. Based on that TPC information, the transmission power control unit 82 controls the transmission power amplification unit of the radio-transmission unit 71 and increments the transmission power of the uplink DPCH by a specified amount (step 203).

On the other hand, in step 201, when there is even one item of TPC information that specifies ‘DOWN’, the TPC information judgment unit 81 determines that the TPC information is ‘DOWN’, (step 204) and inputs [TPC information=DOWN] to the transmission power control unit 82. Based on that TPC information, the transmission power control unit 82 controls the transmission power amplification unit of the radio-transmission unit 71 and decrements the transmission power of the uplink DPCH by a specified amount (step 203).

The first transmission power control algorithm is an algorithm that is used when there is a radio link having a good reception state, and by believing the TPC information from the radio link having high reliability is reliable (steps 201-202), it is possible to increase the probability that the TPC information will be judged correctly, and also by the steps 201 and 204 it is possible to prevent the transmission power of the mobile station from becoming larger than necessary.

(b) Second Transmission Power Control Algorithm

FIG. 4 is a flowchart for the second transmission power control algorithm, and it is used in the second state in which there is no TPC information having high reliability, but there is TPC information having low reliability.

The TPC information judgment unit 81 judges the radio link (base station) having the largest reception SIR (step 301), and checks whether the TPC information received from that base station specifies ‘UP’ (step 302), and when the TPC information specifies ‘UP’, determines the TPC information to be ‘UP’ (step 303) and inputs [TPC information=UP] to the transmission power control unit 82. Based on that TPC information, the transmission power control unit 82 controls the transmission power amplification unit of the radio-transmission unit 71, and increments the transmission power of the uplink DPCH a specified amount (step 304).

However, in step 302, when the TPC information specifies ‘DOWN’, the TPC information judgment unit 81 determines that the TPC information is ‘DOWN’ (step 305), and inputs [TPC information=DOWN] to the transmission power control unit 82. Based on that TPC information, the transmission power control unit 82 controls the transmission power amplification unit of the radio-transmission unit 71, and decrements the transmission power of the uplink DPCH by a specified amount (step 304).

The second transmission power control algorithm is used when there is no radio link having a good reception state, and by believing the radio link selected from among those links having the best reception state, it is possible to prevent the transmission power of the mobile station from dropping too much and the radio link becoming unstable.

(c) Third Transmission Power Control Algorithm

FIG. 5 is a flowchart of the third transmission power control algorithm, and is used in the third state in which none of the TPC information has any reliability.

The combining unit 65 performs RAKE combining of the TPC information signals received from all of the base stations (step 401), and based on the combined signal, the TPC demodulation unit 66 demodulates the TPC information (step 402). The TPC information judgment unit 81 checks whether the TPC information that is demodulated by the TPC demodulation unit 66 specifies ‘UP’ (step 403), and when the information specifies ‘UP’, the TPC information judgment unit 81 determines that the TPC information is ‘UP’ (step 404), and inputs [TPC information=UP] to the transmission power control unit 82. Based on that TPC information, the transmission power control unit 82 controls the transmission power amplification unit of the radio-transmission unit 71, and increments the transmission power of the uplink DPCH by a specified amount.

However, in step 403, when the TPC information specifies ‘DOWN’, the TPC information judgment unit 81 determines that the TPC information is ‘DOWN’ (step 406), and inputs [TPC information=DOWN] to the transmission power control unit 82. Based on that TPC information, the transmission power control unit 82 controls the transmission power amplification unit of the radio-transmission unit 71, and decrements the transmission power of the uplink DPCH by a specified amount (step 405).

The third transmission power control algorithm is used when the reception state is poor, and it performs RAKE combining of the TPC-information signals from all of the radio links, and demodulates the TPC information, and by using that TPC information, has the effect of stabilizing transmission power control.

(C) Transmission Power Control Algorithm Decision Process

The present invention performs reliability judgment of the TPC information received from different base stations for each radio link, and by performing TPC judgment using the reliability judgment results, increases the probability that the TPC information will be judged correctly. Also, by preparing a plurality of transmission power control algorithms and switching the algorithm according to the radio state, it increases the stability of the radio link.

Based on the quality (for example, reception SIR) of the signals received by way of radio links from each base station to the mobile station, the reliability judgment unit 69 performs reliability judgment of the TPC information received from those radio links. Reliability judgment is performed by comparing the reception SIR of each radio link with predetermined first and second threshold values A, B. The radio link, having a reception SIR that is greater than the first threshold value A, is determined to be a radio link having high reliability, and by believing the TPC information from a radio link having high reliability, the probability of judging the TPC information correctly is increased.

FIG. 6 is a flowchart for the transmission power control algorithm decision process.

Reception SIR for each radio link is input to the reliability judgment unit 69, and the reliability judgment unit 69 compares each reception SIR with first and second threshold values A, B, then based on the comparison result, determines whether the reliability of the TPC information that is received from each base station is high, low or no reliability (step 501).

Next, the reliability judgment unit 69 checks whether there is a radio link whose reception SIR is greater than the threshold value A, or in other words, whether there is a radio link whose TPC information reliability is high (step 502). When there is a radio link whose reliability is high, the reliability judgment unit 69 sends algorithm identified data and instructs the TPC information judgment unit 81 to perform transmission power control according to the first transmission power control algorithm, as well as notifies it of the radio link (base station) whose reception SIR is greater than threshold value A (step 503). From doing this, the TPC information judgment unit 81 performs transmission power control according to the first transmission power control algorithm. Thereby it is possible to increase the probability that the TPC information will be judged correctly increases, and it is possible to prevent having the transmission power of the mobile station from becoming larger than necessary.

In step 502, when there is no radio link whose reception SIR is greater than threshold value A, the reliability judgment unit 69 checks whether there is a radio link whose reception SIR is greater than threshold value B, or in other words, checks whether there is a radio link whose TPC information reliability is low (step 504). When there is a radio link whose reliability is low, the reliability judgment unit 69 sends algorithm identified data and instructs the TPC information judgment unit 81 to perform transmission power control according to the second transmission power control algorithm, as well as notifies it of the radio link (base station) having the largest reception SIR (step 505). From doing this, the TPC information judgment unit 81 performs transmission power control according to the second transmission power control algorithm. Thereby it is possible to prevent the transmission power of the mobile station dropping too much and the radio link becoming unstable.

In step 504, when there is no radio link whose reception SIR is greater than threshold value B, or in other words, when all of the reception SIR are less than threshold value B, there is no TPC information having any reliability, so the reliability judgment unit 69 instructs the TPC information judgment unit 81 to perform transmission power control according to the third transmission power control algorithm (step 506). From doing this, the TPC information judgment unit 81 performs transmission power control according to the third transmission power control algorithm. The TPC information judgment unit 81 performs RAKE combining of the TPC information signals from all of the radio links and demodulates the TPC information, and by using that TPC information, the probability that power control can be performed correctly increases, and transmission power control is stabilized.

The threshold values A, B, which are the reference criteria for switching the algorithms of this invention, are decided so that communication can be performed stably during HSDPA communication, and so that the transmission power of the mobile station does not become larger than necessary.

When the threshold value is too large, the reliability of a radio link becomes low, and as a result, the probability of performing TPC information judgment using the second and third algorithm becomes high. This means that there is a possibility that the transmission power of the mobile station will become high, that power interfering with other users (mobile stations) will increase, and the radio quality of the overall communication area will become poor. On the other hand, when the threshold value is too small, the reliability of a radio link becomes high, and as a result, the probability of performing TPC information judgment using the first algorithm becomes high. This is the same as the prior TPC information judgment method, and since the probability of determining that the TPC information is ‘DOWN’ becomes high, and the transmission power of the mobile station tends to become lower, the possibility of communication being cut off increases.

(D) Example of TPC Information Judgment

An example of judging TPC information is explained hereinafter.

The reception SIR for each radio link is compared with threshold value A and threshold value B (where, threshold value B<threshold value A), and the comparison results are given in FIG. 7 in which:

◯: Reception SIR>threshold value A (radio link with high reliability).

Δ: Threshold value A>reception SIR>threshold value B (radio link with low reliability)

X: Threshold value B>reception SIR (radio link with no reliability)

(a) JUDGMENT EXAMPLE 1

As shown in (A) FIG. 7, when the reliability of all of the radio links RL1 to RL6 is high, then all radio links have reliability. Therefore, the first transmission power control algorithm is used, and when the TPC information of all of the radio links RL1 to RL6 indicate ‘UP’, the TPC information is determined to be ‘UP’, however, when even one of the TPC information is ‘DOWN’, the TPC information is determined to be ‘DOWN’.

(b) JUDGMENT EXAMPLE 2

In the case of the reliability judgment results for radio links RL1 to RL6 shown in (B) of FIG. 7, the first transmission power control algorithm is used for radio links RL1, RL2 whose reception SIR values are greater than threshold value A. When the TPC information for both radio links RL1, RL2 indicate ‘UP’, the TPC information is determined to be ‘UP’, however, when either TPC information indicates ‘DOWN’, the TPC information is determined to be ‘DOWN’.

(c) JUDGMENT EXAMPLE 3

In the case of the reliability judgment results for radio links RL1 to RL6 shown in (C) of FIG. 7, the second transmission power control algorithm is performed for radio links RL1, RL2 and RL3 whose reception SIR values are greater than threshold value B. The TPC information is judged according to the TPC information of the radio link having the largest reception SIR value among the radio links RL1, RL2 and RL3. When the reception SIR values are RL1>RL2>RL3, and when the TPC information of radio link RL1 indicates ‘UP’, the TPC information is determined to be ‘UP’, when the TPC information of radio link RL1 indicates ‘DOWN’, the TPC information is determined to be ‘DOWN’.

(d) JUDGMENT EXAMPLE 4

In the case of the reliability judgment results for radio links RL1 to RL6 shown in (D) of FIG. 7, the third transmission power control algorithm is used since there no radio links having any reliability. RAKE combining (soft decision combining) is performed for the TPC information of all of the radio links RL1 to RL6, and when the result (hard decision output) indicates ‘UP’, the TPC information is determined to be ‘UP’, and when the result indicates ‘DOWN’, the TPC information is determined to be ‘DOWN’.

According to the invention described above, it is possible to perform transmission power control stably even when the radio links have no reliability, which makes it possible to stabilize the communication quality. More specifically speaking, according to the present invention, by using the second or third algorithm when the reliability of the radio links is low, or when there is no reliability, the TPC information of a plurality of radio links are processed fairly, so it is possible to increase the transmission power of the mobile station, and thus lower the possibility that communication will be cut off.

As many apparently widely different embodiments of the present invention can be made without departing from the spirit and scope thereof, it is to be understood that the invention is not limited to the specific embodiments thereof except as defined in the appended claims.

Claims

1. A transmission power control method for a mobile station that controls the transmission power of the uplink using transmission power control information that is sent from a plurality of base stations with which the mobile station is communicating, comprising: a first step of storing a plurality of power-control algorithms for controlling the uplink transmission power using said transmission power control information;a second step of monitoring radio state between each base station and the mobile station; anda third step of controlling the uplink transmission power of the mobile station based on one of said plurality of power-control algorithms according to the radio state.

2. The transmission power control method of claim 1, wherein in said first step, said power-control algorithms are created and saved so that they correspond to a first state in which there is transmission power control information having high reliability; a second state in which there is no transmission power control information having high reliability, but there is transmission power control information having low reliability; and a third state in which there is no transmission power control information having any reliability, respectively;in said second step,the degree of reliability of the transmission power control information is checked for each base station based on said radio state, and the current state is set to one of said first thru third states based on the reliability of the transmission power control information for each base station; andin said third step,the uplink transmission power of the mobile station is controlled using a power-control algorithm according to said set state.

3. The transmission power control method of claim 2, wherein said second step comprises:a step of measuring reception SIR of a base station using a signal received from that base station;a step of determining that reliability of the transmission power control information is high when the reception SIR is greater than a first threshold value, determining that reliability of the transmission power control information is low when the reception SIR is greater than a second threshold value but less than the first threshold value, and determining that the transmission power control information has no reliability when the reception SIR is less than the second threshold value; anda step of setting the current state to one of said first thru third states based on the reliability of the transmission power control information for each base station.

4. The transmission power control method of claim 2, wherein the power-control algorithm that corresponds to said first state comprises: a step of checking whether all of the transmission power control information having high reliability specifies ‘power UP’; anda step of increasing the transmission power by a specified amount when all of the transmission power control information specifies ‘power UP’, and decreasing the transmission power by a specified amount even when only one item of the transmission power control information specifies ‘power DOWN’;the power-control algorithm that corresponds to said second state comprises:a step of determining the base station having the largest reception SIR; anda step of increasing the transmission power by a specified amount when the transmission power control information that is sent from that base station specifies ‘power UP’, and decreasing the transmission power by a specified amount when that transmission power control information specifies ‘power DOWN’; andthe power-control algorithm that corresponds to said third statecomprises:a step of performing RAKE combining of signals received from all base stations, and demodulating the transmission power control information based on the RAKE combination result; anda step of increasing the transmission power by a specified amount when that demodulated transmission power control information specifies ‘power UP’, and decreasing the transmission power by a specified amount when that transmission power control information specifies ‘power DOWN’.

5. A transmission power control apparatus for a mobile station that controls the transmission power of the uplink using transmission power control information that is sent from a plurality of base stations with which the mobile station is communicating, comprising: a radio-state-monitoring unit that monitors the radio states between each base station and the mobile station;a transmission power control unit that stores a plurality of power-control algorithms for controlling uplink transmission power using said transmission power control information, and controls the uplink transmission power of the mobile station based on one of said plurality of power-control algorithms; anda power-control-algorithm-instruction unit that, based on said radio state, instructs said transmission power control unit which power-control algorithm should be used to execute transmission power control.

6. The transmission power control apparatus of claim 5, wherein said transmission power control unit stores power-control algorithms that correspond to a first state in which there is transmission power control information having high reliability; a second state in which there is no transmission power control information having high reliability, but there is transmission power control information having low reliability; and a third state in which there is no transmission power control information having any reliability, respectively; andsaid power-control-algorithm-instruction unit checks the degree of reliability of the transmission power control information for each basestation based on said radio state, sets which state of said first thru third states to the current state based on the reliability of the transmission power control information for each base station, and instructs said transmission power control unit to execute transmission power control according to the power-control algorithm that corresponds to the current state.

7. The transmission power control apparatus of claim 6, wherein said radio-state-monitoring unit measures reception SIR of a base station using a signal received from that base station; andsaid power-control-algorithm-instruction unit determines that reliability of the transmission power control information is high when the reception SIR is greater than a first threshold value, determines that reliability of the transmission power control information is low when the reception SIR is greater than a second threshold value but less than the first threshold value, determines that the transmission power control information has no reliability when the reception SIR is less than the second threshold value, and sets the current state to one of said first thru third states based on the judgment result.

8. The transmission power control apparatus of claim 6, further comprising: a RAKE-combining unit that performs RAKE combining of signals received via multi paths for each base station;a demodulation unit that demodulates the transmission power control information based on the combined signal that is output from each RAKE-combining unit;a combining unit that combines the RAKE-combination results for all base stations; anda demodulation unit that demodulates the transmission power control information based on the combined signal that is output from the combining unit; whereinsaid transmission power control unitin said first state, increases the transmission power by a specifiedamount when all of the transmission power control information having high reliability specifies ‘power UP’, and decrease the transmission power by a specified amount when even one item of transmission power control information having high reliability specifies ‘power DOWN’;in said second state, increases the transmission power by a specified amount when the transmission power control information that is send from the base station having the largest reception SIR specifies ‘power UP’, and decreases the transmission power by a specified amount when that transmission power control information specifies ‘power DOWN’; andin said third state, performs RAKE combining of signals received from each base station, and increases the transmission power by a specified amount when the transmission power control information that is demodulated based on the RAKE combination result specifies ‘power UP’, and decreases the transmission power by a specified amount when that transmission power control information specifies ‘power DOWN’.