JP5646193B2 - Communication terminal and transmission power control method thereof - Google Patents

Description

  The present invention relates to a communication terminal and a transmission power control method thereof.

  In a wireless communication system, generally, an upper limit value of transmission power of a control signal (for example, a synchronization burst) transmitted from a communication terminal to a base station via a control channel is determined. On the other hand, in the communication channel, transmission power control is performed in a closed loop between the base station and the communication terminal, and the transmission power of the radio signal can be increased to the specified maximum transmission power of the communication terminal.

  Reference 1 discloses a transmission power control method for transmitting a radio signal from each base station to a mobile station undergoing handover. Also, cited document 2 discloses a mobile terminal configured to capture the base station having the maximum level among the levels of received signals from a plurality of base stations.

JP 2002-198900 A JP 2009-118197 A

  However, for example, when a communication terminal performs radio communication with a distant base station (for example, when handing over from a nearby base station to a distant base station, when a connection is refused by a nearby base station, In order to increase the transmission power of the radio signal so that the communication terminal reaches a distant base station, the radio signal transmitted from the communication terminal saturates the input level of the nearby base station, May interfere with the communication.

  The present invention has been made in view of the above problems, and a communication terminal capable of reducing the possibility that a radio signal transmitted to a connected base station may interfere with communication of another base station, and the communication terminal An object is to provide a transmission power control method.

  In order to solve the above-described problem, a communication terminal according to the present invention includes a propagation loss estimation unit that estimates a propagation loss of a downlink control signal based on reception power of the downlink control signal transmitted from each of a plurality of base stations. And a base station that has transmitted a downlink control signal whose difference in propagation loss from the minimum value of propagation loss estimated by the propagation loss estimation means is equal to or greater than a predetermined threshold among the plurality of base stations that are connection destination candidates The connection destination candidate selection means for excluding the connection destination candidates, the connection destination determination means for determining any one of the connection destination candidates as a connection destination base station, and the propagation loss estimation means Based on the propagation loss of the downlink control signal transmitted from the connected base station, the transmission power control means for determining the transmission power of the uplink control signal, and the transmission power determined by the transmission power control means, Characterized in that it comprises a transmitting means for transmitting the uplink control signal to continue the previous base station.

  In the present invention, a base station that transmits a downlink control signal whose propagation loss difference with a minimum value of the propagation loss of downlink control signals transmitted from a plurality of base stations to a communication terminal is equal to or greater than a predetermined threshold (usually a remote station) Base station) is excluded from the candidates for the connection destination of the communication terminal. Also, the transmission power of the uplink control signal transmitted from the communication terminal to the connection destination base station (one of the connection destination candidates) is the propagation loss of the downlink control signal transmitted from the connection destination base station to the communication terminal. To be determined.

  For this reason, according to the present invention, the transmission power of the uplink control signal transmitted from the communication terminal to the connected base station is suppressed, and the possibility that the radio signal interferes with the communication of other base stations is reduced. Can do.

  In one aspect of the present invention, the predetermined threshold is an upper limit value for an increase in the transmission power of the uplink control signal, and the transmission power of the uplink control signal is a downlink transmitted from the connection destination base station. It may be the power added to the reference transmission power of the uplink control signal to the propagation loss of the control signal.

  According to this aspect, the transmission power of the uplink control signal transmitted from the communication terminal to the connected base station is the minimum value of the propagation loss of the downlink control signal, and the reference transmission power of the uplink control signal and the transmission power of the uplink control signal It becomes less than the value obtained by adding the upper limit of the increment.

  Also, in one aspect of the present invention, the transmission power control means includes a reference transmission power of the uplink control signal and an increase in transmission power of the uplink control signal to a minimum value of propagation loss estimated by the propagation loss estimation means. A value obtained by adding an upper limit value may be set as the maximum transmission power, and when the transmission unit retransmits the uplink control signal, the transmission power of the uplink control signal may be increased within a range not exceeding the maximum transmission power.

  According to this aspect, the transmission power of the uplink control signal retransmitted from the communication terminal to the connection-destination base station is the minimum transmission loss of the downlink control signal, and the transmission power of the uplink control signal is the reference transmission power of the uplink control signal. It becomes less than the value obtained by adding the upper limit of the increment.

  Further, in one aspect of the present invention, the transmission power control means may control transmission power of an uplink communication signal transmitted immediately after establishing a wireless connection with the connection destination base station so as not to exceed the maximum transmission power. The transmission means may transmit the uplink communication signal to the connection destination base station with the transmission power determined by the transmission power control means.

  According to this aspect, the transmission power of the uplink communication signal transmitted from the communication terminal to the connection destination base station immediately after establishment of the wireless connection (before the transmission power control by the closed loop is started) is also propagated in the downlink control signal. It becomes less than the value obtained by adding the reference transmission power of the uplink control signal and the upper limit value of the increase of the transmission power of the uplink control signal to the minimum value of the loss.

  In the aspect of the invention, the transmission power control unit may update the maximum transmission power at a timing when a minimum value of the propagation loss estimated by the propagation loss estimation unit changes.

  In the aspect of the invention, the connection destination candidate selection unit may update the connection destination candidate at a timing when the minimum value of the propagation loss estimated by the propagation loss estimation unit changes.

  The transmission power control method for a communication terminal according to the present invention includes a step of estimating a propagation loss of a downlink control signal based on reception power of the downlink control signal transmitted from each of a plurality of base stations, and a connection destination Among the plurality of base stations that are candidates for transmission, a base station that has transmitted a downlink control signal whose propagation loss difference from the estimated minimum value of propagation loss is equal to or greater than a predetermined threshold is excluded from the connection destination candidates A step of determining one of the connection destination candidates as a connection destination base station, and uplink control based on a propagation loss of a downlink control signal transmitted from the estimated connection destination base station. A step of determining a transmission power of the signal, and a step of transmitting the uplink control signal to the connection destination base station with the determined transmission power.

It is a figure which shows the structure of the radio | wireless communications system which concerns on embodiment of this invention. It is a figure which shows the radio channel structure in the radio | wireless communications system which concerns on this embodiment. It is a functional block diagram of the communication terminal which concerns on this embodiment. It is a figure which shows an example of the base station search process which concerns on this embodiment. It is a figure which shows an example of the synchronous burst process which concerns on this embodiment. It is a figure which shows an example of the synchronous burst process which concerns on this embodiment.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a diagram showing a configuration of a wireless communication system 10 according to an embodiment of the present invention. As shown in FIG. 1, the wireless communication system 10 includes a communication terminal 12 and a plurality of base stations 14 (only the base stations 14-1 to 14-3 are shown here) located around the communication terminal 12. Consists of including.

  Each base station 14 uses the TDMA / TDD (Time Division Multiple Access / Time Division Duplex) method and the FDMA (Frequency Division Multiple Access) method in its own cell. Wireless communication with the communication terminal 12 located in The communication terminal 12 corresponds to a mobile phone, a communication card, a portable information terminal with a built-in communication function, and the like.

  FIG. 2 is a diagram showing a radio channel configuration in the radio communication system 10 (horizontal axis: time, vertical axis: frequency). As shown in FIG. 2, in the wireless communication system 10, a TDMA frame having a predetermined period (here, 5 ms) is divided into an uplink (uplink) subframe, a downlink (downlink) subframe, and a guard time. The subframes are asymmetrically divided, and each subframe is equally divided into a plurality of time slots (here, Slot 1 to Slot 3). Further, eight carriers (here, f1 to f8) are predetermined in a predetermined frequency band (here, system bandwidth 5 MHz). That is, in the radio communication system 10, 24 radio channels are defined for each of the uplink and the downlink.

  Among these, one specific channel (here, a radio channel belonging to f1 and slot 1) is used as a control channel (Control Channel: CCH) for transmitting a control signal, and the remaining 23 channels transmit communication signals. It is used as a communication channel (Traffic Channel: TCH). Since the control channel is shared by a plurality of base stations 14, the control signal transmitted via the control channel can be identified as a base station ID (base station identification information) so that the base station 14 that is the transmission source or the transmission destination can be identified. A predetermined encoding process is performed using the above. On the other hand, at least one communication channel is assigned to each communication terminal 12, and different communication channels are assigned to the communication terminals 12 located in the same cell.

  When the base station 14 further adopts an SDMA (Space Division Multiple Access) system in addition to the FDMA system and the TDMA / TDD system, the number of radio channels increases in accordance with the number of spatial multiplexing. For example, if the number of spatial multiplexing is 3, the number of control channels is 3 (3 times 1) and the number of communication channels is 69 (3 times 23).

  When the communication terminal 12 performs wireless communication with the base station 14, the communication terminal 12 receives the downlink synchronization burst (one of the downlink control signals) transmitted from the base station 14 via the control channel, and receives the frequency and timing. Adjustment is performed to synchronize the downlink with the base station 14. Further, the communication terminal 12 transmits an uplink synchronization burst (one of the uplink control signals) to the base station 14 via the control channel, and receives a response (synchronization confirmation burst) from the base station 14, whereby the base station 14 is synchronized with the uplink.

  At this time, the communication terminal 12 must transmit the uplink synchronization burst with transmission power that can reach the connection destination base station 14. Therefore, the transmission power of the uplink synchronization burst transmitted to the base station 14 is determined based on the propagation loss of the broadcast channel (one of the downlink control signals) transmitted from the connection destination base station 14 to the communication terminal 12. .

  For example, when the communication terminal 12 performs radio communication with a distant base station 14, the broadcast channel transmitted from the distant base station 14 is greatly attenuated during propagation, so that the communication terminal 12 is transmitted to the base station 14. It is necessary to increase the transmission power of the uplink synchronous burst. In this case, the uplink synchronization burst transmitted from the communication terminal 12 may saturate the input level of the nearby base station 14 and interfere with the communication.

  Therefore, in this embodiment, the communication terminal 12 acquires the minimum value of the propagation loss of the broadcast channel transmitted from each of the plurality of base stations 14 located in the vicinity thereof, and the propagation loss difference from the minimum value is a predetermined value. A base station 14 (usually a distant base station 14) that has transmitted a broadcast channel that is equal to or greater than the threshold is excluded from connection destination candidates. For this reason, the transmission power of the uplink synchronization burst transmitted from the communication terminal 12 to the connected base station 14 is suppressed, and the uplink synchronization burst can interfere with communication of other base stations 14 (especially communication in the control channel). Can be reduced.

  Below, the structure with which the communication terminal 12 is provided in order to implement | achieve the said process is demonstrated concretely.

  FIG. 3 is a functional block diagram of the communication terminal 12. As shown in the figure, the communication terminal 12 includes an antenna 20, a radio unit 22, a baseband control unit 24, a control unit 26 (propagation loss estimation unit 28, connection destination candidate selection unit 30, connection destination determination unit 32, synchronization management. Unit 34, communication channel management unit 36, transmission power control unit 38), and storage unit 40.

  The antenna 20 receives a radio signal transmitted from the base station 14 and outputs the received radio signal to the radio unit 22. Further, the antenna 20 transmits a radio signal supplied from the radio unit 22 to the base station 14. Radio signal reception and transmission are switched in a time-sharing manner so as to correspond to the uplink subframe and the downlink subframe shown in FIG.

  The radio unit 22 includes a low noise amplifier, a power amplifier, a frequency converter, a band pass filter, an A / D converter, and a D / A converter. The radio unit 22 amplifies the radio signal input from the antenna 20 with a low noise amplifier, then down-converts the radio signal into an intermediate frequency signal, converts the signal to a digital signal, and outputs the digital signal to the baseband control unit 24. The radio unit 22 converts the digital signal input from the baseband control unit 24 into an analog signal, then up-converts the digital signal to a radio signal, amplifies it to a transmission output level with a power amplifier, and then supplies it to the antenna 20 To do.

  The baseband control unit 24 includes a radio control unit that controls the radio unit 22, a modulation / demodulation unit that performs signal modulation / demodulation, a frequency setting unit that sets a reception frequency and a transmission frequency, and the like.

  For example, the baseband control unit 24 performs time division separation processing, demodulation (symbol demapping), decoding, error detection, error correction, and the like on the digital signal input from the radio unit 22, and obtains control information and reception Data is output to the control unit 26. In addition, the baseband control unit 24 performs error detection code addition, encoding, modulation (symbol mapping), time division multiplexing processing, and the like on the control information and transmission data addressed to the base station 14 input from the control unit 26. Then, the obtained digital signal is output to the wireless unit 22.

  In addition, the baseband control unit 24 sets the reception frequency and transmission frequency of the communication terminal 12 so that radio signals are transmitted and received via the control channel and the communication channel assigned to the communication terminal 12.

  In addition, the baseband control unit 24 transmits the uplink synchronization burst and the uplink communication signal to the connection destination base station 14 with the transmission power determined by the transmission power control unit 38 (described later) of the control unit 26. 22 is controlled.

  Further, the baseband control unit 24 performs base station search (reception of broadcast channels transmitted from each of the plurality of base stations 14 located in the vicinity of the communication terminal 12) according to the instruction of the control unit 26, The DSSI (Desired Signal Strength Indicator) of the broadcast channel received via the control channel is detected. Further, the baseband control unit 24 detects DSSI of a radio signal received from a base station 14 via a communication channel during communication with a certain base station 14. Note that the DSSI of a radio signal is obtained by subtracting a noise component from the RSSI (Received Signal Strength Indicator) of the radio signal.

  The control unit 26 includes, for example, a CPU and a program that controls the operation of the CPU, and controls each unit of the communication terminal 12. In particular, the control unit 26 functionally includes a propagation loss estimation unit 28, a connection destination candidate selection unit 30, a connection destination determination unit 32, a synchronization management unit 34, a communication channel management unit 36, and a transmission power control unit 38. The connection destination of the terminal 12 is determined and the transmission power of the communication terminal 12 is controlled.

  The storage unit 40 is composed of, for example, a semiconductor memory element, and stores programs, data, tables, and the like necessary for the operation of the communication terminal 12.

  Here, the functional configuration of the control unit 26 will be described in more detail.

  The propagation loss estimation unit 28 estimates the propagation loss of the broadcast channel based on the received power of the broadcast channel transmitted from each of the plurality of base stations 14 located around the communication terminal 12 during the base station search. . Specifically, the propagation loss estimation unit 28 uses the difference between the broadcast channel DSSI detected by the baseband control unit 24 and the broadcast channel transmission power included in the broadcast channel as the propagation loss of the broadcast channel. presume.

  The broadcast channel DSSI detected by the baseband control unit 24 and the broadcast channel propagation loss estimated by the propagation loss estimation unit 28 are stored in association with the base station ID of the base station 14 that transmitted the broadcast channel, for example. Stored in the unit 40.

  The connection destination candidate selection unit 30 selects connection destination candidates based on the propagation loss of the broadcast channel received by the communication terminal 12. First, the connection destination candidate selection unit 30 sets a plurality of base stations 14 that transmitted the broadcast channel received by the communication terminal 12 as connection destination candidates. Next, the connection destination candidate selection unit 30 acquires a minimum value (hereinafter referred to as “minimum propagation loss”) from the propagation losses estimated by the propagation loss estimation unit 28. Then, the connection destination candidate selection unit 30 excludes, from the connection destination candidates, the base station 14 that has transmitted the broadcast channel whose propagation loss difference from the minimum propagation loss is equal to or greater than a predetermined threshold. However, when the communication terminal 12 receives only the broadcast channel transmitted from one base station 14, the connection destination candidate selection unit 30 sets the one base station 14 as a connection destination candidate.

  In the present embodiment, as the predetermined threshold for selecting connection destination candidates, an upper limit value of an increase in transmission power of the uplink control signal defined by the wireless communication system 10 (for example, modulation applied to the uplink control signal). It is assumed that the upper limit of the increase in transmission power corresponding to the method is used.

  Note that the connection destination candidate selection unit 30 desirably updates (reselects) the connection destination candidates at the timing when the minimum propagation loss, which is a reference parameter for selecting connection destination candidates, has changed.

  The connection destination determination unit 32 determines any one of the connection destination candidates selected by the connection destination candidate selection unit 30 as the connection destination base station 14. For example, the connection destination determination unit 32 may determine, as the connection destination, the base station 14 that has transmitted the broadcast channel with the maximum DSSI in the communication terminal 12 among the connection destination candidates.

  The synchronization management unit 34 adjusts the reception frequency and reception timing in the radio unit 22 based on the downlink synchronization burst transmitted from the connection-destination base station 14 via the control channel. Synchronize the line. Also, the baseband control unit 24 performs uplink synchronization burst to the connected base station 14 and receives a response (synchronization confirmation burst) from the base station 14 to synchronize uplink with the base station 14. Take.

  The communication channel management unit 36 performs management of the communication channel assigned from the connected base station 14, control of transmission / reception of communication signals through the communication channel, and the like.

  Based on the propagation loss of the broadcast channel (propagation loss estimated by the propagation loss estimation unit 28) transmitted from the connection destination base station 14 determined by the connection destination determination unit 32, the transmission power control unit 38 The transmission power of the uplink control signal transmitted to the station 14 is determined.

  In this embodiment, the transmission power control unit 38 uses the uplink control signal standard defined in the radio communication system 10 as the propagation loss of the broadcast channel (one of the downlink control signals) transmitted from the connected base station 14. The power added to the transmission power (for example, the transmission power corresponding to the modulation scheme applied to the uplink control signal) is set as the transmission power of the uplink synchronization burst (one of the uplink control signals). In this way, the transmission power of the uplink synchronization burst transmitted from the communication terminal 12 to the connected base station 14 has the minimum transmission loss, the reference transmission power of the uplink control signal, and the upper limit of the increase in the transmission power of the uplink control signal. Therefore, the possibility that the uplink synchronization burst interferes with communication of other base stations 14 can be reduced.

  However, when the connected base station 14 cannot normally receive the uplink synchronization burst, the communication terminal 12 retransmits the uplink synchronization burst. In this case, the transmission power control unit 38 sets a value obtained by adding the reference transmission power of the uplink control signal and the upper limit of the increase in transmission power to the minimum propagation loss as “CCH maximum transmission power”, and sets the transmission power of the uplink synchronization burst to Increase within a range not exceeding the CCH maximum transmission power. This CCH maximum transmission power is the transmission power of the uplink control signal transmitted from the communication terminal 12 to the base station 14 (usually the base station 14 closest to the communication terminal 12) that has transmitted the broadcast channel with the smallest propagation loss. This is the upper limit.

  When the communication terminal 12 establishes a wireless connection with the base station 14 to which the communication terminal 12 is connected, the transmission power control unit 38 transmits via the communication channel immediately after that (before the transmission power control by the closed loop is started). The transmission power of the transmitted uplink communication signal is also determined so as not to exceed the CCH maximum transmission power. In this way, it is possible to reduce the possibility that the uplink communication signal transmitted from the communication terminal 12 to the connected base station 14 will interfere with the communication of other base stations 14.

  On the other hand, when transmission power control by closed loop is started between the base station 14 and the communication terminal 12, the transmission power control unit 38 does not exceed the maximum transmission power of the communication terminal 12 defined in the wireless communication system 10. In the range, the transmission power of the uplink communication signal is determined according to the instruction of the base station 14.

  Note that it is desirable that the transmission power control unit 38 updates (re-determines) the CCH maximum transmission power at the timing when the minimum propagation loss, which is a reference parameter for determining the CCH maximum transmission power, changes.

  Next, the operation of the communication terminal 12 will be described with reference to FIGS. 4, 5A and 5B.

  FIG. 4 is a diagram illustrating an example of base station search processing in the communication terminal 12. As shown in FIG. 4, first, the communication terminal 12 searches for a frequency synchronization burst and performs frequency synchronization (S100). The communication terminal 12 receives the timing synchronization burst and synchronizes the frame timing (S102). Here, the communication terminal 12 can obtain a timing difference with each of the base stations 14 located around the communication terminal 12 by searching for the timing synchronization burst at the current frame timing of the communication terminal 12. The distance to each base station 14 can be calculated. The timing synchronization burst includes base station information such as the base station ID of the receivable base station 14.

  Next, the communication terminal 12 receives the broadcast channel transmitted from each of the neighboring base stations 14 based on the base station information acquired in S102 (S104). Then, for each of the received broadcast channels (for each base station 14 that has transmitted the broadcast channel to the communication terminal 12), the communication terminal 12 determines the DSSI of the broadcast channel and the broadcast channel transmission power included in the broadcast channel. The difference is estimated as the propagation loss of the broadcast channel (S106).

  Subsequently, for each base station 14 that has transmitted the broadcast channel, the communication terminal 12 sets a value obtained by adding the reference transmission power of the uplink control signal to the propagation loss estimated in S106, according to the “CCH minimum transmission” Calculated as “power” (S108). The CCH minimum transmission power related to a certain base station 14 is the transmission power of the uplink synchronization burst that the communication terminal 12 first transmits to the base station 14 (the transmission power increases during retransmission of the uplink synchronization burst).

  Further, the communication terminal 12 obtains a value obtained by adding the reference transmission power of the uplink control signal and the upper limit value of the increase in the transmission power of the uplink control signal to the minimum value of propagation loss estimated in S106 (minimum propagation loss). The maximum transmission power "is calculated (S110). This CCH maximum transmission power is the transmission power of the uplink synchronization burst transmitted by the communication terminal 12 to the base station 14 (usually the base station 14 closest to the communication terminal 12) that has transmitted the broadcast channel with the smallest propagation loss. This is the upper limit. Then, the communication terminal 12 selects, from the connection destination candidates, the base station 14 whose CCH minimum transmission power is equal to or higher than the CCH maximum transmission power among the base stations 14 (connection destination candidates) that transmitted the broadcast channel to the communication terminal 12. Exclude (S112). That is, the communication terminal 12 excludes the base station 14 that has transmitted the broadcast channel whose propagation loss difference from the minimum propagation loss is equal to or greater than the upper limit of the increase in transmission power of the uplink control signal from the connection destination candidates.

  Thereafter, the communication terminal 12 creates a base station list in which base station IDs are arranged in order of the received signal strength (for example, DSSI) of the broadcast channel (S114). Thereby, normally, the base station ID of the base station 14 closest to the communication terminal 12 is arranged at the head of the base station list. And the communication terminal 12 performs the synchronous burst process demonstrated below based on the base station list created here (S116).

  5A and 5B are diagrams illustrating an example of the synchronous burst process in the communication terminal 12. FIG. When the synchronization burst processing is started, the communication terminal 12 connects the base station 14 indicated by the base station ID arranged at the head of the base station list created in S114 to the connection destination base station 14 as shown in FIG. 5A. (S200). Next, the communication terminal 12 corrects the frame timing of the communication terminal 12 based on the information included in the downlink synchronization burst transmitted from the connected base station 14, and synchronizes the base station 14 with the downlink ( S202).

  Subsequently, the communication terminal 12 sets the ramp-up component, which is an increase component of transmission power when retransmitting the uplink synchronization burst, to 0 (S204), and sets the transmission power of the uplink synchronization burst transmitted to the connected base station 14 to 0. Calculate (S206). Specifically, the sum of the CCH minimum transmission power and the ramp-up component related to the connection destination base station calculated in S108 becomes the transmission power of the uplink synchronization burst. Here, if the transmission power calculated in S206 is equal to or greater than the CCH maximum transmission power calculated in S110 (S208: Y), the communication terminal 12 limits the transmission power of the uplink synchronization burst to the CCH maximum transmission power ( S210). In addition to the processing of S208 and S210, the transmission power of the uplink synchronization burst may be limited to the maximum transmission power of the communication terminal 12 defined by the wireless communication system 10.

  Then, the communication terminal 12 transmits an uplink synchronization burst to the connection destination base station 14 with the transmission power determined in S206 to S210 (S212), and subsequently performs a synchronization confirmation burst reception process (S214).

  As shown in FIG. 5B, when a synchronization confirmation burst is received from the connected base station 14 in S214 (S216: Y), the communication terminal 12 uses the timing information included in the burst to determine the frame timing of the communication terminal 12. And the base station 14 and the uplink are synchronized (successful synchronization).

  On the other hand, if the synchronization confirmation burst is not received from the connected base station 14 in S214 (S216: N), the communication terminal 12 updates the ramp-up component (S218). Specifically, a specified value is added to the ramp-up component. Here, if the number of repeated transmissions of the uplink synchronization burst does not exceed the specified number (S220: N), the communication terminal 12 re-executes the processing from S206 shown in FIG. 5A to retransmit the uplink synchronization burst. On the other hand, if the number of repeated transmissions of the uplink synchronization burst exceeds the specified number (S220: Y), the communication terminal 12 checks whether there is a next candidate in the base station list (S222). Here, if there is no next candidate in the base station list, synchronization fails (S222: N), but if there is a next candidate in the base station list (S222: Y), the communication terminal 12 newly sets the next candidate. Is selected as the connection-destination base station 14 (S224), and the processes in and after S202 shown in FIG. 5A are re-executed.

  The communication terminal 12 described above acquires the minimum value of the propagation loss of the broadcast channel transmitted from each of the plurality of base stations 14 located in the vicinity thereof, and the propagation loss difference from the minimum value is a predetermined threshold (here, A base station 14 (usually a distant base station 14) that has transmitted a broadcast channel equal to or greater than the upper limit of an increase in transmission power of the uplink control signal is excluded from connection destination candidates. For this reason, the transmission power of the uplink synchronization burst transmitted from the communication terminal 12 to the connected base station 14 is suppressed, and the uplink synchronization burst can interfere with communication of other base stations 14 (especially communication in the control channel). Can be reduced.

  The present invention is not limited to the above embodiment.

  For example, in the above embodiment, the broadcast channel is shown as the downlink control signal and the uplink synchronization burst is shown as the uplink control signal, but these are only examples of control signals transmitted and received between the communication terminal and the base station. 2 is merely an example, and the configuration of the radio channel used for communication between the communication terminal according to the present invention and the base station is not limited to this.

10 wireless communication systems, 12 communication terminals, 14 base stations, 20 antennas, 22 wireless units, 24 baseband control units, 26 control units, 28 propagation loss estimation units, 30 connection destination candidate selection units, 32 connection destination determination units, 34 Synchronization management unit, 36 communication channel management unit, 38 transmission power control unit, 40 storage unit.

Claims (2)

Propagation loss estimation means for estimating the propagation loss of the downlink control signal based on the received power of the downlink control signal transmitted from each of the plurality of base stations;
Among the plurality of base stations that are connection destination candidates, a base station that has transmitted a downlink control signal whose propagation loss difference with a minimum value of propagation loss estimated by the propagation loss estimation means is equal to or greater than a predetermined threshold, Connection destination candidate selection means to be excluded from the connection destination candidates;
Connection destination determination means for determining any of the connection destination candidates as a connection destination base station;
Transmission power control means for determining the transmission power of the uplink control signal based on the propagation loss of the downlink control signal transmitted from the connected base station estimated by the propagation loss estimation means;
Transmitting means for transmitting the uplink control signal to the connection destination base station with transmission power determined by the transmission power control means;
Only including,
The predetermined threshold is an upper limit for an increase in the transmission power of the uplink control signal, and the transmission power of the uplink control signal is the propagation loss of the downlink control signal transmitted from the connected base station. The transmission power is the sum of the reference transmission power of the control signal.
Communication terminal, wherein a call. Estimating the propagation loss of the downlink control signal based on the received power of the downlink control signal transmitted from each of the plurality of base stations;
Among the plurality of base stations that are connection destination candidates, a base station that has transmitted a downlink control signal whose propagation loss difference from the estimated minimum propagation loss value is equal to or greater than a predetermined threshold is selected as the connection destination candidate. Steps to exclude from,
Determining any of the connection destination candidates as a connection destination base station;
Determining the transmission power of the uplink control signal based on the propagation loss of the downlink control signal transmitted from the estimated base station of the connection;
Transmitting the uplink control signal to the connected base station with the determined transmission power; and
Only including,
The predetermined threshold is an upper limit for an increase in the transmission power of the uplink control signal, and the transmission power of the uplink control signal is the propagation loss of the downlink control signal transmitted from the connected base station. The transmission power is the sum of the reference transmission power of the control signal.
Transmission power control method of the communication terminal characterized by and this.

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