JP2004364338A - Method of controlling transmission power enabling selection of base station, base station equipment, and mobile station - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of updating conditions of the main base station that ensures stable operations, even if there is loss in base station selection signals, thus enabling the reception point of a mobile station to be synchronized, at the updating of the main base station. <P>SOLUTION: According to the method, each base station inspects the amount of loss in the base station selection signals, and if the loss amount turns is a predetermined value (H-001) or larger, each station, including a base station intrinsically assumed to be a non-main base station, is made so as not to control transmission power. Each of the base stations, which may be handed over to in a soft hand-over set, always updates the conditions of the main base station at a predetermined timing so that the update timing of the main base station in the mobile station is synchronized. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a transmission power control method and a base station device in a cellular system, and more particularly to a base station selection type transmission power control method and a base station device for updating a main base station state.

  In a cellular system in which a plurality of base stations are arranged on a service area and a mobile station connects to and communicates with a nearest base station, when the mobile station moves, the connected base station is switched (handover). . In a cellular system or the like to which code division multiple access is applied, a handover control method capable of eliminating line breaks due to base station connection switching is applied. This method, called soft handover, establishes a connection with the switching destination base station while maintaining the connection with the switching source base station, and performs simultaneous communication with multiple base stations and the mobile station, thereby causing instantaneous line disconnection. Avoid occurrence. One mobile station transmits and receives the same information to and from a plurality of base stations, so that the effect of site diversity is obtained, and a good call is achieved.

  However, when soft handover is applied to the downlink, a large number of base stations transmit signals to the mobile station at the same time, which causes a great deal of interference to neighboring cells. As a technique for suppressing an increase in interference during such a downlink soft handover, a downlink transmission power control method (method A) described in Non-Patent Document 1 is known. Hereinafter, the outline of the method A will be described with reference to FIGS. 4 to 10, only components necessary for the method A are extracted and described.

  FIG. 4 is a diagram showing a configuration of a mobile station to which scheme A is applied. Downlink signals received from antenna ANT are converted to baseband signals in downconverter A-002 via coupler A-001. A pilot signal included in the baseband signal from each base station during soft handover is received by pilot receiver A-003, and its reception strength or reception quality is measured. This measurement result is input to the main base station determiner A-004, and the base station having the maximum reception strength or the maximum reception quality is selected, and this is set as the main base station. The determination result of the main base station is input to the base station selection signal generator A-005, and generates a base station selection signal corresponding to the base station number assigned to the main base station. The base station selection signal is input to a control signal generator A-006, and is input to a combiner A-007 together with another control signal such as a transmission power control signal. The uplink information signal generated by the uplink information signal generator A-008 is also input to the combiner A-007. After the control signal and the uplink information signal are combined in the combiner A-007, the output signal is input to the upconverter A-009, and further passes through the amplifier A-010 to the combiner A-001 and the antenna ANT. Transmitted to the connected base station via

  FIG. 5 shows a frame configuration assumed in the present invention. The frame D-001 includes Fn slots D-002, and each slot in the frame is assigned a serial number as shown in FIG.

  The transmission of the base station selection signal will be schematically described with reference to FIG. Each base station during soft handover is assigned a base station selection codeword consisting of a plurality of bit strings for identifying each base station. By constructing the base station selection codeword with a plurality of bit strings, the signal is made redundant, and transmission errors due to noise, fading, etc. are reduced. E-002 shows an example of the base station selection codeword. A dedicated field E-001 for transmitting a part of the base station selection codeword is provided in the uplink slot E-003, and each part of the base station selection codeword consisting of a plurality of bit strings is shown in FIG. And transmitted via dedicated field E-001. As described above, the base station selection control cycle E-004 extends over a plurality of slots in order to transmit the base station selection codeword composed of a plurality of bit strings. Note that the dedicated field E-001 can accommodate a plurality of bits, and the base station selection control cycle E-004 can be shortened as the number of bits that can be accommodated increases.

  Next, the configuration of a base station to which scheme A is applied will be described using FIG. The uplink signal received from the antenna ANT is input to the down-converter B-002 via the coupler B-001. The uplink reception signal converted into a baseband signal by downconverter B-002 is input to transmission power control signal demodulator B-003 and base station selection signal demodulator B-004, respectively. Transmission power control signal demodulator B-003 demodulates the transmission power control signal included in the uplink reception signal, and the demodulated transmission power signal is input to transmission power control section B-005. The transmission power control unit B-005 updates the internal transmission power value P1 based on the demodulated transmission power control signal, and P1 is input to the main base station state updating unit B-006. On the other hand, the base station selection signal demodulator B-004 demodulates the base station selection codeword included in the baseband signal, and inputs the demodulated base station selection codeword to the main base station state update unit B-006. Is done. The main base station state updating unit B-006 updates the actual transmission power value P2 based on the internal transmission power value P1 and the base station selection signal, and P2 is input to the output controller B-008. The downlink signal generated by the downlink transmission signal generator B-007 is input to the output controller B-008, and output control is performed so that the output of the downlink signal becomes the actual transmission power value P2. The downlink transmission signal output-controlled by the output controller B-008 is frequency-converted by the up-converter B-009, and then transmitted to the mobile station via the amplifier B-010, the coupler B-001, and the antenna ANT. .

  The operation of the main base station status update unit B-006 in FIG. 7 will be described in more detail with reference to FIG. Based on the base station selection codeword demodulated by the base station selection signal demodulator B-004, the base station identification number is determined in C-001. In C-002, it is determined whether or not the determination result of the base station identification number is equal to the identification number of the own base station, and if so, the state of the own base station is set to the main base station state in C-003, and the actual transmission is performed. Power value P2 is set equal to internal transmission power value P1. On the other hand, when it is determined in C-002 that the determination result of the base station identification number is not the identification number of the own base station, the state of the own base station is set to the non-main base station in C-004, and the actual transmission power value Set P2 to the minimum transmission power value Pmin. Here, Pmin may be 0.

  As described above, in the method A, the transmission output is turned on / off at each base station based on the base station selection signal transmitted from the mobile station. This prevents a plurality of base stations from emitting the same signal to one mobile station at the same time, that is, suppresses interference to neighboring cells. As a result, a high line capacity can be achieved.

Furukawa, IEICE Technical Report, RCS97-218, February 1998, pp. 40, Chapter 2

  In each base station and each mobile station of the cellular system, measurement of pilot signals and interference signals from neighboring cells is periodically performed for the purpose of handover control and call admission control. When the measurement is performed at the base station, a method of performing more accurate measurement by temporarily stopping transmission from a mobile station connected to the base station is adopted. Further, in the case of packet transmission or for the purpose of suppressing uplink interference during silence, transmission of a mobile station may be temporarily stopped during a call.

  FIG. 9 is a diagram illustrating a state of an uplink reception signal when transmission of a part of the uplink transmission signal is stopped. F-003 represents a slot, and F-004 represents a dedicated field for transmitting a base station selection codeword. When transmission is stopped during the period of F-001, the base station selection codeword included in the uplink received signal is lost as in F-002. When transmission from a mobile station during a call is suspended in this way, part or all of the base station selection signal required in scheme A is lost, and the reliability of base station selection is impaired. Was.

  During soft handover, a plurality of base stations transmit the same signal to one mobile station. At this time, the transmission timing of the signal transmitted by each base station is adjusted and transmitted so that the reception timing received by the mobile station falls within a certain allowable range. Since the propagation distance between each of the base stations and the mobile station is different, the transmission timing has a different value for each base station. On the other hand, the uplink signals received by the base stations from the mobile station are received at different reception timings also due to the difference in propagation distance.

  In the method A, each base station in the same soft handover group judges whether or not the own station can output by referring to the base station selection information transmitted from the mobile station. As described above, since the reception timing of the uplink signal received by each base station is different, the timing of receiving the same base station selection information differs for each base station. Further, since the transmission timing of the downlink signal transmitted by each base station is also different as described above, as a result of the above, the timing at which each base station actually determines whether to output from the reception of the base station selection signal and then updates the output In some cases, synchronization may not be achieved with the update timing of the main base station at the reception point of the mobile station.

  FIG. 10 is used to explain in more detail the situation where the update timing of the main base station cannot be synchronized at the reception point of the mobile station. G-001 represents a slot, and the number shown in each slot represents the serial number of the slot. G-002 and G-003 indicate downlink transmission signals transmitted from a group of base stations during soft handover, respectively. G-002 indicates a downlink transmission signal transmitted from the base station 1, and G-003 indicates a downlink transmission signal transmitted from the base station 2. Each of the transmission signals is received by the mobile station like G-004 and G-005. The downlink transmission signals G-002 and G-003 are transmitted with their transmission timings adjusted so that the reception timings at the mobile station are aligned. As a result, as in G-004 and G-005, the reception timings of the downlink reception signals from the respective base stations received by the mobile station become uniform. The transmission timing of the downlink transmission signals G-002 and G-003 varies depending on the length of the propagation delay G-012. The uplink transmission signal G-006 transmitted from the mobile station is transmitted after being delayed by the transmission / reception timing offset G-013 from the reception timing of the downlink reception signals G-004 and G-005. The uplink transmission signal G-006 is received by the base stations at different reception timings, such as G-007 and G-008, due to the propagation delay G-014. In each slot of the uplink reception signals G-007 and G-008, one part of the base station selection code word is transmitted on the dedicated fields G-020 and G-021. Now, assuming that transmission of one base station selection codeword is completed at G-020, G-021, that is, the serial number 14 of the slot, each base station receives this from the received base station selection codeword. The state of the main base station described with reference to 8 is updated. At this time, the update timing is updated in the slot G-016 in the base station 1 and in the slot G-017 in the base station 2. Since the serial numbers of the respective slots for updating the status of the main base station are G-016 and G-017, respectively, 2 and 1, as a result, the update timing of the status of the main base station observed by the mobile station is G-016. A shift occurs as in 018 and G-019.

  As described above, if the update timing of the main base station is shifted at the reception point of the mobile station, the base station selection cycle is constant, so that a downlink received signal may be lost, or the update timing of the mobile station may be changed. However, there is a problem that an additional circuit is needed to keep track of the data.

  A first object of the present invention is to provide a main base station state updating method for guaranteeing stable operation even when a base station selection signal is lost.

  A second object of the present invention is to provide a main base station state updating method that synchronizes the update timing of the main base station at the receiving point of the mobile station.

  Each base station checks the amount of missing base station selection signals, and if the missing amount is equal to or greater than a certain value, the transmission power is not suppressed even for a non-main base station.

  Each base station in the soft handover group always updates the state of the main base station at a predetermined timing so that the update timing of the main base station in the mobile station is synchronized.

  By not suppressing the transmission power if the missing amount of the base station selection signal is a certain value or more, it is possible to avoid a base station selection error by demodulating a base station selection signal with poor reliability, In addition, it is possible to avoid a disadvantage that a base station that should be a primary base station erroneously suppresses output as a non-primary base station.

  By constantly updating the state of the base station at a predetermined timing at each base station in the soft handover group, the update timing of the main base station at the time of mobile station reception is synchronized, and the downlink reception signal at the mobile station is obtained. Is avoided. Further, an additional circuit for monitoring the update timing at any time in the mobile station becomes unnecessary.

  According to the embodiment shown in FIG. 1, when a base station selection codeword received by a base station is dropped beyond a certain amount due to a pause of an uplink transmission signal, the base station selection signal actually transmitted is Regardless, by always setting the base station in the main base station state, it is possible to reduce erroneous determination to the non-main base station due to a reception error of the base station selection signal and maintain stable downlink reception quality. Become.

  According to the embodiment shown in FIG. 2, the update of the state of the main base station is performed in synchronization with the downlink signal received by the mobile station, so that the loss of the downlink received signal due to the synchronization deviation is avoided. Further, an additional circuit for monitoring the update timing at any time in the mobile station becomes unnecessary.

  FIG. 1 is a configuration diagram illustrating an embodiment of the present invention, and particularly illustrates a configuration for avoiding a problem caused by a missing base station selection signal. This configuration diagram corresponds to the main base station status update unit shown in FIG. The base station checks the amount of the base station selection signal missing, and does not stop or suppress the transmission power if the missing amount exceeds a threshold value. Hereinafter, a more specific configuration will be described.

  In the base station selection codeword output from the base station selection signal demodulator B-004, it is determined in the H-001 whether the amount of signal loss exceeds a threshold. Here, the signal missing amount is given by the number of bits, the ratio of the number of missing bits to the total number of bits included in the base station selection codeword, and the like. Further, the threshold value may be varied according to the length of the base station codeword. If the amount of signal loss exceeds the threshold, it is determined that the reliability of the demodulated base station selection codeword is poor, and therefore, in H-005, regardless of whether it is originally the main base station or not, The state is set to the main base station state, and the transmission power is not suppressed. When setting as the main base station in H-005, the value of the actual transmission power value P2 is set to the internal transmission power value P1. On the other hand, if the signal loss amount is less than or equal to the threshold value in H-001, the base station identification number is determined from the base station selection codeword in H-003, and the base station identification number is further determined in H-002. It is determined whether the number matches the identification number of the base station. If the base station identification number matches the identification number of the own base station, the state of the own base station is set to the main base station state in H-005. On the other hand, when the base station identification number does not match the identification number of the own base station, the state of the own base station is set to the non-main base station state in H-004, and the actual transmission power value P2 is set to the minimum transmission power value Pmin. Set. Here, the minimum transmission power value Pmin can be zero. In the determination of the non-main base station, the reception quality of the base station selection codeword is observed, and if the reception quality is less than the desired value, the reliability of the base station selection codeword is also regarded as low. In some cases, the state of the own base station may be determined as the main base station.

  According to the embodiment of the main base station state update unit shown in FIG. 1, when the amount of loss of the base station selection signal received by the base station exceeds the threshold value, that is, when the demodulated base station selection codeword When the reliability is deemed to be poor, the state of the own base station is always set to the state of the main base station, regardless of whether it is originally the main base station, and the operation is performed so as not to suppress the transmission power.

  FIG. 2 is a configuration diagram showing an embodiment of the present invention, similarly to FIG. 1, and particularly shows a configuration for avoiding a problem due to a shift in the update timing of the state of the main base station. This configuration diagram also corresponds to the main base station status update unit shown in FIG. 8, as in FIG. In all base stations, the output state is updated from the downlink slot having the same serial number. Hereinafter, the operation will be described more specifically.

  In I-001, the base station identification number is determined from the base station selection codeword output from the base station selection signal demodulator B-004. After setting the slot number at which the last part of the base station selection codeword is transmitted to j in I-002, the apparatus waits until the current slot number satisfies the following equation (1).

  Formula (1) (j + Tos) mod Fn Here, Tos represents a state update waiting time, and Fn represents the number of slots included in one frame. X mod Y is an operator that gives the remainder when X is divided by Y. After waiting at I-003, it is determined at I-004 whether the base station identification number matches the identification number of the own base station, and if they match, the state of the own base station is mainly determined at I-005. The base station state is set, and the actual transmission power value P2 is set to the internal transmission power value P1. If they do not match, the state of the own base station is set to the non-main base station state in I-006, and the actual transmission power value P2 is set to the minimum transmission power value Pmin. Here, Pmin can be 0. When setting the state of the own base station as a non-main base station in I-006, refer to the reception quality of the base station selection codeword, and set only when good reception quality is obtained. It is possible. If good reception quality is not achieved, it is considered that the reliability of the base station codeword is poor. In that case, the base station is always in the main base station state, whether or not it is originally the main base station.

  The operation of the main base station status update unit shown in FIG. 2 will be described in detail with reference to FIG. FIG. 3 is a diagram schematically showing the update timing of the main base station state in the base station, and is a diagram corresponding to FIG. 10 described in the related art. J-001 represents a slot, and the number shown in each slot represents the serial number of the slot. J-002 and J-003 indicate downlink transmission signals transmitted from the base station group during soft handover, respectively. J-002 indicates a downlink transmission signal transmitted from the base station 1, and J-003 indicates a downlink transmission signal transmitted from the base station 2. Each of the transmission signals is received by the mobile station like J-004 and J-005. The downlink transmission signals J-002 and J-003 are transmitted with their transmission timings adjusted so that the reception timings at the mobile station are aligned. As a result, as in J-004 and J-005, the reception timing of the downlink reception signal from each base station received by the mobile station becomes uniform. The transmission timing of the downlink transmission signals J-002 and J-003 varies depending on the length of the propagation delay J-012. The uplink transmission signal J-006 transmitted from the mobile station is transmitted after being delayed by the transmission / reception timing offset J-013 from the reception timing of the downlink reception signals J-004 and J-005. The uplink transmission signal J-006 is received by the base stations at different reception timings such as J-007 and J-008, respectively, due to the propagation delay J-014. In each slot of the uplink reception signals J-007 and J-008, one part of the base station selection code word is transmitted on the dedicated fields J-020 and J-021. Now, assuming that transmission of one base station selection codeword is completed at J-020, J-021, that is, at slot serial number 14, each base station receives the base station selection codeword from the received base station selection codeword. The state of the main base station described with reference to 2 is updated. When the state update waiting time Tos is set to 3, since the slot serial number j of the last part of the base station selection codeword is 14 and the number of slots Fn included in the frame is 15, as shown in FIG. Is the slot of slot serial number 2. Therefore, the update of the state of the main base station is updated in the slot of J-016 in the base station 1 and in the slot of J-017 in the base station 2. As a result, the update timing of the state of the main base station observed by the mobile station is synchronized as in J-018 and J-019, and no deviation occurs.

  In order to achieve high-speed state switching, the state update standby time Tos is preferably short. Since the transmission path delay and the processing delay of the base station apparatus can change, Tos can be varied during a call. In addition, Tos may be varied according to the value of the reception slot serial number j of the last part of the base station selection codeword. By varying Tos by j, it becomes possible to control the main base station state update timing in the mobile station to a desired timing.

  The configuration shown in FIG. 1 may be combined with the configuration of the main base station status update unit shown in FIG. 2 and operated simultaneously. In this configuration, in the comparison between the receiving base station identification number in I-004 and the identification number of the own base station, a condition that the amount of codeword missing is equal to or less than the threshold is added, and the receiving base station identification number is And the process proceeds to I-005 only when the codeword missing amount is equal to or less than the threshold value. Further, as described above, a condition that the reception quality of the codeword satisfies the desired quality may be added.

FIG. 4 is a diagram showing a configuration for avoiding a problem related to a main base station state update of the present invention, particularly a lack of a base station selection codeword. The figure which shows the structure for avoiding the problem regarding the synchronization deviation of the main base station state update of this invention, especially the main base station state update. The figure which shows the mode of the update of the main base station state of this invention. FIG. 2 is a diagram showing an embodiment of a mobile station to which a base station selection method is applied. Diagram showing frame configuration Diagram showing transmission of base station selection signal The figure which shows embodiment of the base station to which the base station selection system is applied. Diagram showing a conventional base station selection state updating method The figure which shows a mode of an uplink reception signal when an uplink transmission signal is stopped. Diagram showing the state of conventional main base station status update

Explanation of reference numerals

ANT: Antenna
Fn: Number of slots included in one frame
P1: Internal transmission power value
P2: Actual transmission power value
Pmin: minimum transmission power value j: slot number in which the last part of the base station selection codeword was transmitted
Tos: Main base station status update standby time (number of slots)

Claims (3)

  The mobile station selects one or a plurality of main base stations from a plurality of base stations in a soft handover state with the mobile station to generate a base station selection signal, and the mobile station changes the base station selection signal to a soft handover state. Transmitted to the base station group located in the base station, the base station performs normal downlink signal transmission if the received base station selection signal indicates its own station, if it does not indicate its own station, the downlink signal transmission is stopped or A base station selection type transmission power control method for suppressing, wherein, when the main base station is changed, the main base station change of the downlink signal received by the mobile station is synchronized with each other between the main base stations before and after the change. A base station selection type transmission power control method, wherein the main base station state update timing is set in the base station.   The mobile station selects one or a plurality of main base stations from a plurality of base stations in a soft handover state with the mobile station, generates a base station selection signal, and transmits the base station selection signal to a base station group in the soft handover state. A base station device receives a base station selection signal, performs normal downlink signal transmission if the received base station selection signal indicates the own station, and stops or suppresses downlink signal transmission if the received base station selection signal does not indicate the own station. When the main base station is changed, the main base station change of the downlink signal received by the mobile station is performed in synchronization with each other between the main base stations before and after the change. A base station apparatus for setting an update timing of a main base station state.   A base station selection signal is generated by selecting one or a plurality of main base stations from a plurality of base stations in a soft handover state with the own mobile station, and the base station selection signal is transmitted to a base station group in a soft handover state. If the base station selection signal received by each base station indicates its own station, the base station performs normal downlink signal transmission, and if it does not indicate its own station, the mobile station stops or suppresses downlink signal transmission. In the base station, when the main base station is changed, the main base station change of the downlink signal received by the mobile station is performed in synchronization with each other between the main base stations before and after the change. A mobile station, wherein an update timing of a main base station state in the base station is set, and the downlink signal is received at the set update timing.

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