JP6099459B2 - Communication system, base station, terminal, and base station power saving control method - Google Patents

Description

  The present invention relates to a communication system.

Conventionally, in wireless communication, a multi-base station cooperative transmission technique has been studied in order to improve user throughput, particularly cell edge user throughput. When two base stations transmit the same signal to one terminal, the received signal level of the terminal is higher than when receiving from one base station, and throughput may be improved. Such techniques, in standardization group ^{3GPP (3 rd Generation Partnership Project)} , CoMP (Coordinated Multi-Point Operation for LTE) considered is advanced as is standardized (see Non-Patent Document 1). CoMP has been studied based on LTE (Long Term Evolution) already standardized by 3GPP.

  In recent years, not only terminals but also power savings of base stations have been studied. In the following Patent Document 1, the base station periodically searches for whether or not a terminal exists in the own station, and continuously transmits a pilot signal when the terminal exists, and transmits a pilot signal when the terminal does not exist. A technique for intermittent transmission is disclosed. In the base station, when the terminal is not present, the pilot signal is intermittently transmitted, so that it is possible to save power consumption necessary for transmission. The intermittent period when the base station intermittently transmits a pilot is generally determined by the time it takes for a terminal that has not been able to search for a base station to search for a base station and obtain frequency and time synchronization. is there.

International Publication No. 2009/154038

3GPP TR36.819 V11.1.0 (2011-12)

  However, according to the conventional technique, the longer the intermittent period, the higher the power saving effect of the base station. However, if the intermittent period is too long, the time until the terminal synchronizes with the base station becomes longer, and the service quality To affect. For example, the time from when the terminal is turned on until the communication becomes possible becomes longer, the handover time when the terminal switches the communication base station becomes longer, the time until the terminal returns to a communicable state, etc. is there. Therefore, the pilot intermittent transmission cycle of the base station depends on the base station search / synchronization performance of the terminal, and there is a problem that a sufficient intermittent transmission cycle cannot be obtained.

  The present invention has been made in view of the above, and an object of the present invention is to obtain a communication system capable of saving power of a base station while ensuring service quality for a terminal.

  In order to solve the above-described problems and achieve the object, the present invention provides a communication system including a terminal and a plurality of base stations that perform CoMP communication with the terminal, wherein the plurality of base stations Then, each base station determines a pilot signal transmission sequence pattern and a pilot signal transmission timing in cooperation with other base stations, and a base station having a predetermined pilot signal transmission timing transmits a pilot signal to the terminal. At the pilot signal transmission timing, another base station transmits a pilot signal to the terminal and intermittently transmits the pilot signal. The terminal transmits a pilot signal from a base station different from the base station that transmitted the previously received pilot signal. The signal is received at the next reception timing.

  According to the present invention, there is an effect that the base station can save power while ensuring the service quality for the terminal.

FIG. 1 is a diagram illustrating a configuration example of a communication system. FIG. 2 is a diagram illustrating a state where the base station transmits a pilot signal at the intermittent transmission period T and the terminal receives the pilot signal. FIG. 3 is a diagram illustrating a configuration example of a base station. FIG. 4 is a diagram illustrating a configuration example of a terminal. FIG. 5 is a diagram illustrating the transmission timing of the pilot signal on the base station side and the reception timing of the pilot signal on the terminal side. FIG. 6 is a diagram illustrating the transmission timing of the pilot signal on the base station side and the reception timing of the pilot signal on the terminal side when there are three base stations. FIG. 7 is a diagram illustrating the transmission timing of the pilot signal on the base station side and the reception timing of the pilot signal on the terminal side when there are four base stations. FIG. 8 is a diagram illustrating frequency bands in which the base station intermittently transmits pilot signals. FIG. 9 is a diagram showing a flowchart showing operations in the base station and the terminals constituting the communication system. FIG. 10 is a diagram illustrating an example of a transmission signal of the base station when the base station is communicating with a terminal using CoMP. FIG. 11 is a diagram illustrating an example of a transmission signal of the base station when the base station is communicating with a terminal using CoMP.

  Embodiments of a communication system according to the present invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.

Embodiment 1 FIG.
FIG. 1 is a diagram illustrating a configuration example of a communication system according to the present embodiment. The communication system includes a base station 100, a base station 101, and a terminal 200. This is an overview of CoMP. Base stations 100 and 101 transmit the same signal to terminal 200 by CoMP. Since the same signal is transmitted from two base stations, the received signal level of terminal 200 is higher than when receiving from one base station, and throughput may be improved.

  Here, conventional control in which a base station intermittently transmits a pilot signal will be described. FIG. 2 is a diagram illustrating a state where the base station transmits a pilot signal at the intermittent transmission period T and the terminal receives the pilot signal. As shown in the above-mentioned Patent Document 1, the conventional base station continuously transmits a pilot signal when a terminal exists in the own station, and intermittently transmits a pilot signal when the terminal does not exist in the own station. As a result, the power is saved in the section where the pilot signal is not transmitted. In this case, the conventional terminal has received the pilot signal at the period T. However, if the intermittent period for transmitting the pilot signal is too long on the base station side, the time until the terminal synchronizes with the base station becomes long, which affects service quality.

  Therefore, in this embodiment, a base station that performs CoMP communication intermittently transmits pilot signals at different timings.

  FIG. 3 is a diagram illustrating a configuration example of the base station according to the present embodiment. Base stations 100 and 101 include a control unit 111, a data encoding / decoding unit 112, a transmission / reception unit 113, a pilot signal generation unit 114, and an inter-base station cooperation unit 115.

  The control unit 111 manages the connection sequence with the terminal 200 and the arrival of communication data from the communication network, and instructs the data encoding / decoding unit 112 to encode / decode communication data or control data.

  The data encoding / decoding unit 112 performs encoding of data instructed from the control unit 111 or decoding of a signal received by the transmission / reception unit 113.

  The transmission / reception unit 113 combines the encoded data obtained from the data encoding / decoding unit 112 and the pilot signal obtained from the pilot signal generation unit 114, performs modulation and conversion into a high frequency signal, and transmits the radio signal. Do. In addition, the transmission / reception unit 113 receives a signal from the terminal 200, performs conversion to a low-frequency signal and demodulation, and then passes the received data to the data encoding / decoding unit 112.

  Pilot signal generation section 114 generates a pilot signal in accordance with a pilot signal sequence pattern instruction and pilot signal transmission timing instruction from control section 111.

  The inter-base station cooperation unit 115 contacts and cooperates with another base station that performs CoMP, and determines a pilot signal sequence pattern and a pilot signal transmission timing.

  Here, the pilot signal sequence pattern is a 1/0 array of pilot signals transmitted by each base station. This array includes not only real numbers but also imaginary numbers. The pilot signal transmission timing is information indicating a timing (timing offset) at which a pilot signal is transmitted in relation to another base station that is linked.

  FIG. 4 is a diagram illustrating a configuration example of a terminal according to the present embodiment. The terminal 200 includes a control unit 211, a user interface unit 212, a data encoding / decoding unit 213, a transmission / reception unit 214, a pilot signal detection unit 215, and a signal level measurement unit 216.

  The control unit 211 manages the connection sequence with the base stations 100 and 101, the arrival of communication data from the user interface unit 212, and instructs the data encoding / decoding unit 213 to encode / decode communication data or control data. To do. The connection sequence includes searching for the base stations 100 and 101 and frequency / time synchronization with the base stations 100 and 101.

  The user interface unit 212 notifies a control (button operation) by the user to the control unit 211, sends communication data, outputs voice received from the control unit 211, displays a data screen, and the like.

  The data encoding / decoding unit 213 performs encoding of data instructed by the control unit 211 or decoding of a signal received from the transmission / reception unit 214. Further, the data encoding / decoding unit 213 uses the pilot signal sequence pattern detection information, predicts the radio quality from the detection state of the pilot signal, and performs decoding of the data unit.

  The transmission / reception unit 214 transmits the data received from the data encoding / decoding unit 213 or receives signals from the base stations 100 and 101.

  The pilot signal detection unit 215 receives a signal from the transmission / reception unit 214 and detects the pilot signal sequence pattern received from the control unit 211. Also, the result is notified to the data encoding / decoding unit 213.

  The signal level measurement unit 216 measures the signal level of the signal received from the transmission / reception unit 214 and reports the result to the control unit 211.

  Next, a specific pilot signal transmission method in the two base stations 100 and 101 that perform communication by CoMP will be described.

  FIG. 5 is a diagram illustrating the transmission timing of the pilot signal on the base station side and the reception timing of the pilot signal on the terminal side. Two base stations 100 and 101 that perform communication by CoMP each transmit a pilot signal at an intermittent transmission period 2T, and the terminal 200 receives a pilot signal at a period T. Base stations 100 and 101 transmit pilot signals with a timing offset of time T from each other. Also, the pilot signal sequence patterns transmitted by the two base stations 100 and 101 are the same. Since terminal 200 receives pilots from two base stations 100 and 101, terminal 200 can detect a pilot signal at period T (see FIG. 2) that is not different from the conventional one.

  Regarding the determination of the pilot signal sequence pattern and the pilot signal transmission timing, the relationship between the master and the slave is determined between the base stations 100 and 101 that perform communication by CoMP, and the pilot signal sequence pattern and the pilot signal are transmitted from the master to the slave. Specify the timing. As the pilot signal transmission timing, the absolute timing of the slave may be notified, or an offset value from the reference timing of the master may be notified.

  As another method of determining the pilot signal sequence pattern, one pattern may be determined in advance for the entire communication system without performing exchange in the inter-base station cooperation unit 115. Further, in the base station group that performs CoMP communication, the pattern may be different for each group, and the pattern may be determined from the group ID.

  Note that the number of base stations that perform CoMP communication is not limited to two, and may be three or more.

  FIG. 6 is a diagram illustrating the transmission timing of the pilot signal on the base station side and the reception timing of the pilot signal on the terminal side when there are three base stations. The state of the pilot signal intermittent transmission in the case of three base stations performing communication by CoMP is shown. The base stations 100 and 101 are the same as those in FIG. The third base station 102 transmits at the same pilot signal transmission timing as the base station 100. Since signals of the same pilot signal sequence pattern are received, terminal 200 increases signal reception power and improves pilot signal detection accuracy.

  FIG. 7 is a diagram illustrating the transmission timing of the pilot signal on the base station side and the reception timing of the pilot signal on the terminal side when there are four base stations. The state of the pilot signal intermittent transmission in the case of four base stations performing communication by CoMP is shown. Compared to FIG. 6, a fourth base station 103 is added, and the base station 103 transmits at the same pilot signal transmission timing as the base station 101. As described above, when the number of CoMP base stations increases, pilot signal transmission is performed at the same pilot signal transmission timing as one of the first and second base stations (here, base stations 100 and 101). To implement. The same operation is performed with five or more units.

  When there are three or more base stations, the intermittent transmission period of the pilot signal on the base station side may be 3T or more. For example, three base stations transmit pilot signals with a pilot signal intermittent transmission period of 3T and each base station with timing offsets of T and 2T. In the case of four base stations, pilot signals are transmitted with an intermittent transmission period of pilot signals of 4T and timing offsets of T, 2T, and 3T at each base station. As a result, terminal 200 can detect a pilot signal at period T that is not different from the conventional one, and the base station can further save power.

  In addition, as a case where the base stations 100 and 101 intermittently transmit pilot signals, it is conceivable to apply only to a partial frequency band instead of all frequency bands available for communication. FIG. 8 is a diagram illustrating frequency bands in which the base station intermittently transmits pilot signals. Both base stations 100 and 101 perform intermittent pilot signal transmission only in the frequency band f2, and perform normal pilot signal continuous transmission in the frequency band f1. In the frequency band f2, the base stations 100 and 101 perform pilot transmission with a timing offset of time T.

  In such a case, although there is a terminal 200 that performs communication, since communication is performed at a low transmission rate, the frequency band f1 is used for the communication, and the remaining frequency band f2 is used for data communication for power saving. For example, intermittent transmission of pilot signals is also possible. In such a state, when the terminal 200 that performs communication in the frequency band f1 measures the communication quality in the frequency band f2, or as a preparation for a new terminal to perform communication using the frequency band f2, the communication quality When the base stations 100 and 101 have an offset of timing T and transmit the same pilot signal sequence pattern, the communication quality measurement on the terminal side can be performed in a short time. .

  Operations of base stations 100 and 101 and terminal 200 so far will be described based on flowcharts. FIG. 9 is a flowchart showing operations in the base station and the terminals that constitute the communication system. First, in the base stations 100 and 101, the inter-base station cooperation unit 115 determines the pilot signal sequence pattern and the pilot signal transmission timing in cooperation between the base stations (step S1). Here, the pilot signal sequence pattern is the same, and the pilot signal transmission timing has a timing offset of time T as shown in FIG.

  Next, base stations 100 and 101 transmit pilot signals to terminal 200 with the determined pilot signal sequence pattern and pilot signal transmission timing (step S2). In base stations 100 and 101, control unit 111 instructs pilot signal generation unit 114 on the pilot signal sequence pattern and pilot signal transmission timing determined by inter-base station cooperation unit 115, and pilot signal generation unit 114 A pilot signal is generated in accordance with an instruction from 111, and transmitted from transmission / reception section 113 together with data from data encoding / decoding section 112. As shown in FIG. 5, pilot signals (including signals) are transmitted from any of the base stations at intervals of the transmission period T.

  Terminal 200 receives pilot signals (including signals) at intervals of reception period T (step S3). In terminal 200, when a signal from the base station is received by transmission / reception section 214, pilot signal detection section 215 detects the pilot signal, and control section 211 searches for a base station (step S4).

  As described above, according to the present embodiment, a base station that performs CoMP communication determines a pilot signal sequence pattern and a pilot signal transmission timing in cooperation with other base stations, and alternately pilots. By transmitting a signal, when the base station searches for the base station and measures the communication quality while the base station is transmitting the pilot signal intermittently, the base station may lengthen the intermittent transmission period compared to the conventional case. it can. As a result, since the terminal receives the pilot signal at the same intermittent reception cycle as in the prior art, the base station can ensure the quality of service by obtaining the same base station search time and quality measurement accuracy as in the past, while the base station can improve the pilot quality compared to the prior art. Since the signal transmission cycle can be lengthened, a power saving effect can be obtained.

  In addition, when there are three or more base stations, the third and subsequent base stations transmit pilot signals at the same timing as the first and second base stations, which increases the signal reception power at the terminal. The base station search time shorter than before and high quality measurement accuracy can be obtained.

Embodiment 2. FIG.
In this embodiment, a method for determining the transmission power of pilot signals between base stations 100 and 101 that perform CoMP communication will be described. As one method, there is a method of fixedly determining pilot transmission power at the time of intermittent transmission of a pilot signal on the base station side. As another method, the terminal 200 that has received the pilot signal in the past measures the pilot signal reception level and reports it to the base station side, and the base station side uses the reported pilot signal reception level result. There is a method of adjusting transmission power at the next intermittent transmission of pilot signals.

  FIG. 10 is a diagram illustrating an example of a transmission signal of the base station when the base station is communicating with a terminal using CoMP. For CoMP, in addition to the mode in which two or more base stations simultaneously transmit the exact same data signal, a base station with good radio conditions and good quality communication is selected, and only one base station communicates. There is a mode (sends data signals). FIG. 10 assumes this mode.

  In the illustrated time range, the first half transmits a data signal from the base station 100, and the second half transmits a data signal from the base station 101. The pilot signal is transmitted by both base stations regardless of data transmission. Here, base station 100 and base station 101 have the same pilot signal sequence pattern. In this case, since terminal 200 recognizes which base station is transmitting the data signal, the reception level of the pilot signal received when base station 100 is transmitting data is from base station 100. Therefore, it can be determined that the reception level of the pilot signal received when the base station 101 is transmitting data is from the base station 101. In terminal 200, signal level measurement section 216 measures the signal reception level. The terminal 200 periodically reports both the base station (base stations 100 and 101) that has performed the measurement and the signal reception level information to both the base stations 100 and 101.

  The base stations 100 and 101 store the reported information and adjust the transmission power at the next intermittent pilot signal transmission. For example, when the base station 100 and 101 are both transmitting pilot signals with a transmission power of “PT”, the report result from the terminal 200 is the pilot signal reception level “Pr” of the base station 100 and the pilot of the base station 101. If the signal reception level is “Pr + X”, the base station 100 performs intermittent transmission with transmission power of “PT” and the base station 101 performs transmission power of “PT-X” at the next intermittent pilot signal transmission. Here, with reference to the pilot signal reception level at terminal 200 on base station 100 side, adjustment is performed on base station 101 side so that the pilot signal reception level at terminal 200 is equivalent to that on base station 100 side.

  In addition, although the terminal 200 is transmitting the base station (base station 100,101) which performed the measurement, and the information of a signal reception level to each base station (base station 100,101), it does not limit to this. Absent. For example, the terminal 200 transmits information on the measured base station (base stations 100 and 101) and signal reception level to a base station that adjusts transmission power and transmits a pilot signal, and receives a pilot signal as a reference. You may make it not transmit to the base station (base station which does not adjust the transmission power of a pilot signal) of the transmission source of a pilot signal of a level. In addition, terminal 200 may transmit only the information on the signal reception level of the base station serving as a reference to the base station that adjusts the transmission power and transmits the pilot signal. This can reduce the amount of communication between the terminal 200 and the base station, and is particularly effective when there are many base stations.

  FIG. 11 is a diagram illustrating an example of a transmission signal of the base station when the base station is communicating with a terminal using CoMP. An example in which different pilot signal sequence patterns are transmitted between the base station 100 and the base station 101 is shown. In this case, since the sequence patterns are different, the terminal 200 can be separated even if it simultaneously receives the pilot signal 1 from the base station 100 and the pilot signal 2 from the base station 101, and measures the reception level of each pilot signal. Can do. The processing after the measurement is the same as in the case of FIG.

  Further, when the base stations 100 and 101 communicate with the terminal 200 using the partial frequency band f1 of the usable frequency bands as described in FIG. 8, the received signal level of the pilot signal during the communication. Can be immediately reflected in the adjustment of the pilot transmission power in the frequency band f2.

  As described above, according to the present embodiment, the pilot signal transmission power is adjusted between the base stations so that the signal reception levels of the pilot signals are equalized at the terminals. As a result, the terminal can perform more accurate search and measurement.

  As described above, the communication system according to the present invention is useful for wireless communication, and is particularly suitable for a system including a plurality of base stations.

  100, 101 base station, 111 control unit, 112 data encoding / decoding unit, 113 transmission / reception unit, 114 pilot signal generation unit, 115 inter-base station cooperation unit, 200 terminals, 211 control unit, 212 user interface unit, 213 data Encoding / decoding unit, 214 transmitting / receiving unit, 215 pilot signal detecting unit, 216 signal level measuring unit.

Claims (10)

A communication system including a terminal and a plurality of base stations that perform CoMP communication with the terminal,
In the plurality of base stations, each base station determines a pilot signal transmission sequence pattern and a pilot signal transmission timing in cooperation with other base stations, and a base station having a predetermined pilot signal transmission timing sends a pilot signal to the terminal. And, at the next pilot signal transmission timing, another base station transmits a pilot signal to the terminal, intermittently transmits the pilot signal, and as the plurality of base stations, the pilot signal increases as the number of linked base stations increases. The pilot signal is intermittently transmitted to the terminal with a transmission period of
The terminal receives a pilot signal from a base station different from the base station from which the pilot signal was received last time at the next reception timing, and intermittently receives pilot signals from the plurality of base stations,
A communication system characterized by the above. The plurality of base stations transmit pilot signals using the same pilot signal transmission sequence pattern;
The communication system according to claim 1. The plurality of base stations transmit pilot signals at the pilot signal transmission sequence pattern and the pilot signal transmission timing in a part of the frequency bands available for communication.
The communication system according to claim 1 or 2 . A base station in a communication system including a terminal and a plurality of base stations that perform CoMP communication with the terminal;
In the plurality of base stations, each base station determines a pilot signal transmission sequence pattern and a pilot signal transmission timing in cooperation with other base stations, and a base station having a predetermined pilot signal transmission timing sends a pilot signal to the terminal. And, at the next pilot signal transmission timing, another base station transmits a pilot signal to the terminal, intermittently transmits the pilot signal, and as the plurality of base stations, the pilot signal increases as the number of linked base stations increases. The transmission cycle of is extended and a pilot signal is intermittently transmitted to the terminal.
A base station characterized by that. The plurality of base stations transmit pilot signals using the same pilot signal transmission sequence pattern;
The base station according to claim 4 . The plurality of base stations transmit pilot signals at the pilot signal transmission sequence pattern and the pilot signal transmission timing in a part of the frequency bands available for communication.
The base station according to claim 4 or 5 , wherein A terminal in a communication system including a terminal and a plurality of base stations that perform CoMP communication with the terminal;
In the plurality of base stations, each base station determines a pilot signal transmission sequence pattern and a pilot signal transmission timing in cooperation with other base stations, and a base station having a predetermined pilot signal transmission timing sends a pilot signal to the terminal. And, at the next pilot signal transmission timing, another base station transmits a pilot signal to the terminal, intermittently transmits the pilot signal, and as the plurality of base stations, the pilot signal increases as the number of linked base stations increases. When a pilot signal is intermittently transmitted to the terminal with a longer transmission cycle ,
Receiving a pilot signal from a base station different from the base station that transmitted the pilot signal received last time at the next reception timing, and intermittently receiving pilot signals from the plurality of base stations,
A terminal characterized by that. A base station power saving control method in a communication system comprising a terminal and a plurality of base stations that perform CoMP communication with the terminal,
In the plurality of base stations, each base station cooperates with other base stations to determine a pilot signal transmission sequence pattern and pilot signal transmission timing, and a base station cooperation step;
In the plurality of base stations, a base station at a predetermined pilot signal transmission timing transmits a pilot signal to the terminal, and at a next pilot signal transmission timing, another base station transmits a pilot signal to the terminal, A pilot signal transmission step of intermittently transmitting a signal, and as the plurality of base stations, the pilot signal is intermittently transmitted to the terminal by increasing the transmission period of the pilot signal as the number of linked base stations increases .
The terminal receives a pilot signal from a base station different from the base station that transmitted the pilot signal received last time at the next reception timing, and receives a pilot signal from the plurality of base stations intermittently. Receiving step;
A base station power saving control method comprising: In the base station cooperation step, the plurality of base stations determine to transmit pilot signals using the same pilot signal transmission sequence pattern.
The base station power saving control method according to claim 8 . In the base station cooperation step, the plurality of base stations transmit pilot signals with the pilot signal transmission sequence pattern and the pilot signal transmission timing in a part of the frequency bands available for communication. decide,
The base station power saving control method according to claim 8 or 9 , wherein

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