JP2014068121A - Communication system and communication method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a communication system and a communication method that are able to improve transmission efficiency by making the length of CP of a small cell base station shorter than the length of CP of a macrocell base station.SOLUTION: A communication system comprises: a macrocell base station for forming a macrocell; a small cell base station for forming a small cell designed to overlap with at least one macrocell; and a terminal for connecting with the macrocell base station or the small cell base station. The macrocell base station and the small cell base station transmit a second transmission symbol generated by inserting cyclic prefix into a first transmission symbol, and perform communication by making the length of cyclic prefix inserted by the small cell base station shorter than the length of cyclic prefix inserted by the macrocell base station.

Description

  The present invention relates to a communication system and a communication method.

  3CDMA (Third Generation Partnership Project) WCDMA (Wideband Code Divergent Multiple Access), LTE (Long Term Evolved Electr) and LTE-A (LTE-Advanced Evidence). A communication service area is formed by a cell configuration in which a large number of base stations (transmitting stations, transmitting apparatuses, eNodeBs) are arranged. A cell refers to a range in which a base station can be connected to a terminal (mobile terminal, receiving station, mobile station, receiving apparatus, UE (User Equipment)).

  In a system formed by this cell configuration (hereinafter referred to as a cellular system), traffic distribution is required with an increase in traffic volume due to an increase in large-capacity services. In order to satisfy this requirement, a system is configured in which one cell is a macro cell, and a part or all of the range is overlapped with a range of small cells (pico cells, femto cells) that are different from the macro cell. (It is also called heterogeneous network deployment (HetNet; Heterogeneous Network deployment) (Non-patent Document 1).

  FIG. 22 is an example of HetNet. A cell 2201a in FIG. 22 represents a macro cell, and a cell 2201-1a and a cell 2201-2a represent small cells. The base station 2201 constitutes a macro cell 2201a. Hereinafter, such a base station is referred to as a macro cell base station (main base station). The base station 2201-1 constitutes a small cell 2201-1a. The base station 2201-2 configures a small cell 2201-2a. Hereinafter, such a base station is referred to as a small cell base station (low power base station, LPN: Low Power Node, picocell base station, femtocell base station). The macro cell base station 2201-1 is connected to the small cell base stations 2201-1 and 2201-2 via lines 2201-1b and 2201-2b. The lines 2201-1b and 2201-2b may be optical fibers or other wired lines (eg, X2 interface) or wireless lines. Note that the macro cell base station and the small cell base station may be the same base station.

  For example, traffic distribution is realized by connecting the terminals existing in the small cell 2201-1a to the small cell base station 2201-1 instead of the macro cell base station 2201.

3rd Generation Partnership Project; Technical Specification Group Radio Access Network; http: //www.3rd generationpartnershipp. org / ftp / Specs / html-info / 36814.htm

  However, a small cell generally has a smaller coverage and a different communication environment than a macro cell. Therefore, if the same radio parameters as the macro cell are used, transmission efficiency may be reduced.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a communication system and a communication method capable of improving transmission efficiency by setting small cell radio parameters to be suitable for the small cell. There is to do.

  In order to solve the above-described problems, the configuration of the communication system according to the present invention is as follows.

  (1) A communication system according to the present invention includes a macro cell base station that constitutes a macro cell, a small cell base station that constitutes a small cell designed to overlap with at least one macro cell, and the macro cell base station or the small cell. A terminal connected to a base station, wherein the macro cell base station and the small cell base station transmit a second transmission symbol generated by inserting a cyclic prefix into the first transmission symbol, and the small cell The length of the cyclic prefix inserted by the base station is shorter than the length of the cyclic prefix inserted by the macro cell base station.

  (2) In the communication system described above, the terminal notifies terminal information to the macro cell base station, the macro cell base station determines a small cell to which the terminal is connected based on the terminal information, and the macro cell base The station notifies the small cell information of the small cell to the terminal, and the terminal connects to the small cell based on the received small cell information.

  (3) In the communication system described above, the reception information is a position of the terminal.

  (4) In the above communication system, the reception information is reception power of transmission signals of surrounding small cell base stations measured by the terminal.

  (5) In the communication system described above, the length of the first transmission symbol generated by the macro cell base station is equal to the length of the first transmission symbol generated by the small cell base station.

  (6) In the communication system described above, the length of the first transmission symbol generated by the macro cell base station, the ratio of the length of the cyclic prefix inserted by the macro cell base station, and the small cell base station generate The ratio between the length of the first transmission symbol and the length of the cyclic prefix inserted by the small cell base station is equal.

  (7) In the above-described communication system, the length of the first transmission symbol generated by the macro cell base station is different from the length of the first transmission symbol generated by the small cell base station.

  (8) In the communication system described above, the small cell information includes a length of a cyclic prefix inserted by the small cell base station, and the terminal inserts a cyclic prefix inserted by the small base station based on the small cell information. Determine the length of.

  (9) In the communication system described above, the small cell information includes an ID of the small cell, and the terminal determines a length of a cyclic prefix inserted by the small cell base station based on the ID.

  (10) In the communication system described above, the small cell information includes transmission power of the small cell, and the terminal determines a cyclic prefix length of a signal transmitted by the small cell base station based on the transmission power.

  (11) In the communication system described above, when the terminal detects that the configuration of the reference signal transmitted by the macro cell base station is different from the configuration of the reference signal transmitted by the small cell base station, the small cell The cyclic prefix length of the signal transmitted by the base station is determined.

  (12) In the communication system described above, the small cell information includes a carrier type of the small cell, and the terminal determines a cyclic prefix length of a signal transmitted by the small cell base station based on the carrier type. .

  (13) In the communication system described above, the terminal further determines a length of a first transmission symbol of a signal transmitted by the small cell base station.

  (14) A communication method according to another aspect of the present invention includes a macro cell base station that configures a macro cell, a small cell base station that configures a small cell designed to overlap at least one macro cell, A terminal connected to the macro cell base station or the small cell base station, wherein the macro cell base station and the small cell base station generate a second transmission generated by inserting a cyclic prefix into a first transmission symbol; The length of the cyclic prefix inserted by the small cell base station that transmits a symbol is shorter than the length of the cyclic prefix inserted by the macro cell base station.

  According to the present invention, a communication system includes a macro cell base station constituting a macro cell, a small cell base station constituting a small cell designed to overlap with at least one macro cell, and the macro cell base station or the small cell. A terminal connected to a base station, wherein the macro cell base station and the small cell base station transmit a second transmission symbol generated by inserting a cyclic prefix into the first transmission symbol, and the small cell By performing communication with the length of the cyclic prefix inserted by the base station being shorter than the length of the cyclic prefix inserted by the macro cell base station, it is possible to achieve an excellent effect that transmission efficiency can be improved. .

It is a schematic block diagram which shows the structure of macrocell base station a1 which concerns on the 1st Embodiment of this invention. It is a figure which shows an example which produces | generates a 2nd transmission symbol. It is a schematic block diagram which shows the structure of the small cell base station b1 which concerns on the 1st Embodiment of this invention. It is a figure which shows an example of the length of CP (cyclic prefix; Cyclic Prefix) which macrocell base station a1 inserts, and the length of CP which small cell base station b1 inserts. It is a flowchart which shows operation | movement of the small cell base station b1. It is a schematic block diagram which shows the structure of the small cell base station b2 which concerns on the 2nd Embodiment of this invention. It is a figure which shows an example of the length of the 2nd transmission symbol which macrocell base station a1 transmits, and the length of the transmission symbol which small cell base station b2 transmits. It is a flowchart which shows operation | movement of the small cell base station b2. It is a schematic block diagram which shows the structure of the small cell base station b3 which concerns on the 3rd Embodiment of this invention. It is a figure which shows an example of the length of CP and 1st transmission symbol which macrocell base station a1 transmits, and the length of CP and 1st transmission symbol which small cell base station b3 transmits. It is a flowchart which shows operation | movement of the small cell base station b3. It is a sequence diagram which shows the process between macrocell base station a1, small cell base station b1, and terminal c4 of the communication system which concerns on the 4th Embodiment of this invention. It is a schematic block diagram which shows the structure of the terminal c4 which concerns on the 4th Embodiment of this invention. It is a flowchart which shows the operation | movement of the downlink of the terminal c4. It is a flowchart which shows the operation | movement of the uplink of the terminal c4. It is a schematic block diagram which shows the structure of the terminal c5 which concerns on the 5th Embodiment of this invention. It is a flowchart which shows the operation | movement of the downlink of the terminal c5. It is a flowchart which shows the operation | movement of the uplink of the terminal c5. It is a schematic block diagram which shows the structure of the terminal c6 which concerns on the 6th Embodiment of this invention. It is a flowchart which shows the operation | movement of the downlink of the terminal c6. It is a flowchart which shows the operation | movement of the uplink of the terminal c6. It is a figure which shows an example of the macro cell and small cell which concern on this invention.

(First embodiment)
Hereinafter, a first embodiment of the present invention will be described. The communication system in the present embodiment includes a macro cell base station a1 and a small cell base station b1. The small cell base station b1 communicates with a terminal arranged in the small cell, and the macro cell base station a1 communicates with a terminal inside the macro cell and outside the small cell.

  FIG. 1 is a schematic block diagram showing the configuration of the macrocell base station a1. The macro cell base station a1 includes an upper layer a101, a first transmission symbol generation unit a102, a CP insertion unit a103, a transmission unit a104, and a transmission antenna a105.

  Upper layer a101 generates data addressed to all terminals communicating with macrocell base station a1 and outputs the data to first transmission symbol generation unit a102.

  The first symbol generation unit a102 modulates the data input from the upper layer a101, and performs OFDM (Orthogonal Frequency Division Multiplexing) and MC-CDMA (Multicarrier Code-Division Multiple Access). The first transmission symbol is generated using modulation or single carrier modulation such as SC-FDMA (Single Carrier-Frequency Division Multiplexing Access). The first transmission symbol generation unit a102 outputs the generated first transmission symbol to the CP insertion unit a103. When OFDM is used, the processing performed by the first transmission symbol generation unit a102 is IFFT (Inverse Fast Fourier Transform). Hereinafter, the number of points for performing IFFT is referred to as the number of FFT points. Unless otherwise noted, this also applies to the following embodiments.

  CP insertion section a103 inserts a CP into the first transmission symbol input from transmission signal generation section a102. A signal in which a CP is inserted into the first transmission symbol is referred to as a second transmission symbol.

  The transmission unit a104 performs digital / analog conversion on the second transmission symbol input from the CP insertion unit a103, and shapes the waveform of the converted analog signal. The transmission unit a104 up-converts the waveform-shaped signal from the baseband band to the radio frequency band, and transmits the signal from the transmission antenna a105 to the terminal connected to the macrocell base station a1.

  FIG. 2 is a schematic diagram illustrating a second transmission symbol. The second transmission symbol is created by inserting CPs 201a, 202a, 203a into the first transmission symbols 201, 202, 203. CP is a partial copy behind the first transmission symbol. For example, CP 201 a is a copy of the rear part 201 b of the first transmission symbol 201.

  Note that a part of the front copy may be inserted immediately after the first transmission symbol. Further, instead of copying, a known transmission sequence may be used as the CP. The CP has a trade-off that, when the length is increased, the resistance to multipath interference is improved, but the transmission efficiency is lowered.

  FIG. 3 is a schematic block diagram showing the configuration of the small cell base station b1. The small cell base station b1 includes an upper layer b101, a first transmission symbol generation unit b102, a CP insertion unit b103, a transmission unit b104, and a transmission antenna b105.

  The upper layer b101 generates data addressed to all terminals communicating with the small cell base station b1, and outputs the data to the first transmission symbol generation unit b102.

  The first transmission symbol generation unit b102 modulates data input from the upper layer b101, and performs first transmission using multicarrier modulation such as OFDM or MC-CDMA, or single carrier modulation such as SC-FDMA. Generate a symbol. In the first embodiment, the length of the first transmission symbol output from the first transmission symbol generation unit b102 (FIG. 3) of the small cell base station b1 and the first transmission symbol generation unit a102 of the macrocell base station a1. The lengths of the first transmission symbols output by (FIG. 1) are equal. The first transmission symbol generation unit b102 outputs the generated first transmission symbol to the CP insertion unit b103.

  CP inserting section b103 inserts a CP into the first transmission symbol input from transmission signal generating section b102. Here, the length of the CP inserted by the CP insertion part b103 in FIG. 3 is set shorter than the length of the CP inserted by the CP insertion part a103 in FIG. By doing in this way, the transmission efficiency of communication in a small cell can be improved.

  The transmission unit b104 performs digital / analog conversion on the second transmission symbol input from the CP insertion unit b103, and shapes the waveform of the converted analog signal. The transmission unit b104 up-converts the waveform-shaped signal from the baseband band to the radio frequency band, and transmits the signal from the transmission antenna b105 to all terminals connected to the small cell base station b1.

FIG. 4 is a schematic diagram illustrating transmission symbols transmitted by the macro base station and the small base station.
The upper part of FIG. 4 is a second transmission symbol output from the CP insertion unit a103 of the macro base station a1. The second transmission symbol in the upper part of FIG. 4 includes first transmission symbols 201, 202, and 203 and CPs 201a, 202a, and 203a.

  The lower part of FIG. 4 is a second transmission symbol output from the CP insertion unit b103 of the small base station b1. In the second transmission symbol in the lower part of FIG. 4, CPs 401 a, 402 a, and 403 a are inserted into the first transmission symbols 401, 402, and 403. The lengths of the transmission symbols 201, 202, and 203 are equal to the lengths of the transmission symbols 401, 402, and 403.

<Operation of Small Cell Base Station b1>
FIG. 5 is a flowchart showing the operation of the small cell base station b1 according to the present embodiment. The operation shown in this figure is processing after the upper layer b101 in FIG. 3 outputs data to the first transmission symbol generation unit b102.

(Step S501) The first transmission symbol generation unit b102 generates a first transmission symbol. Thereafter, the process proceeds to step S502.

(Step S502) The CP insertion unit b103 inserts a CP into the first transmission symbol obtained in Step S501, and generates a second transmission symbol. This CP is shorter than that used in the macrocell base station a1. Thereafter, the process proceeds to step S503.

(Step S503) The transmission unit b104 performs digital / analog conversion, waveform shaping, and up-conversion on the second transmission symbol obtained in step S502, and transmits the result via the transmission antenna b105. Thereafter, the small cell base station b1 ends the operation.

  Thus, according to the present embodiment, the length of the CP in the second transmission symbol transmitted by the small cell base station b1 is greater than the length of the CP in the second transmission symbol transmitted by the macrocell base station a1. Since it is small, the redundancy of the second transmission symbol transmitted by the small cell base station b1 is reduced, and the transmission efficiency is improved. Thereby, the transmission efficiency of the whole system can be improved.

(Second Embodiment)
Hereinafter, a second embodiment of the present invention will be described in detail with reference to the drawings. In the first embodiment, a case has been described in which the macro cell base station a1 and the small cell base station b1 perform communication by inserting CPs having different lengths to improve transmission efficiency. In the present embodiment, a case will be described in which the small cell reduces the length of the second transmission symbol without changing the ratio of the length of the CP and the length of the first transmission symbol in the second transmission symbol. .

  Since the macrocell base station according to the present embodiment is the same as the macrocell base station a1 according to the first embodiment, the description thereof is omitted.

  FIG. 6 is a schematic block diagram showing the configuration of the small cell base station b2 according to this embodiment. In this figure, the small cell base station b2 includes an upper layer b201, a first transmission symbol generation unit b202, a CP insertion unit b203, a transmission unit b204, and a transmission antenna b205.

  The upper layer b201 generates data addressed to all terminals communicating with the small cell base station b2, and outputs the data to the first transmission symbol generation unit b202.

The first transmission symbol generation unit b202 modulates data input from an upper layer, and uses the first carrier symbol using multicarrier modulation such as OFDM or MC-CDMA or single carrier modulation such as SC-FDMA. Is generated. The first transmission symbol generation unit b202 outputs the generated first transmission symbol to the CP insertion unit b203.

  The CP insertion unit b203 inserts a CP into the first transmission symbol input from the first transmission symbol generation unit b202.

  The transmission unit b204 performs digital / analog conversion on the second transmission symbol input from the CP insertion unit b203, and shapes the waveform of the converted analog signal. The transmitter b204 up-converts the waveform-shaped signal from the baseband band to the radio frequency band, and transmits the signal from the transmission antenna b205 to all terminals connected to the small cell base station b2.

  FIG. 7 shows an example of the state of the second transmission symbol output by the CP insertion unit b203. FIG. 7 also shows the first transmission symbols 201, 202, 203 and CPs 201a, 202a, 203a of FIG. 701, 702, and 703 are the first transmission symbols output from the first transmission symbol generator b202, and 701a, 702a, and 703a are CPs inserted into them. In this embodiment, the length of the CP and the length of the first transmission symbol are reduced on the assumption that the ratio of the first transmission symbol and the CP is not changed from that of the macro cell base station a1. That is, the CP lengths of the macro cell base station a1 and the small cell base station b2 may be the same number of sample points. FIG. 7 shows an example in which each length is halved. By shortening the lengths of the CP and the first transmission symbol in this way, communication can be performed with high accuracy even when the terminal is moving at high speed, and transmission efficiency can be improved.

  When OFDM is used, shortening the length of the first transmission symbol corresponds to increasing the subcarrier interval. As the subcarrier interval increases, the number of FFT points may be changed. Alternatively, the sampling frequency for performing FFT may be changed without changing the number of FFT points.

<Operation of Small Cell Base Station b2>
FIG. 8 is a flowchart showing the operation of the small cell base station b2 according to this embodiment. The operation shown in this figure is processing after the upper layer b201 in FIG. 6 outputs data to the first transmission symbol generation unit b202.

(Step S801) The first transmission symbol generation unit b202 generates a first transmission symbol. The length is shorter than the length of the first transmission symbol output from the first transmission symbol generation unit a102 (FIG. 3) of the macrocell base station a1. Thereafter, the process proceeds to step S802.

(Step S802) The CP insertion unit b203 inserts a CP into the first transmission symbol obtained in Step S801, and generates a second transmission symbol. This CP is smaller in length than that used in the macrocell base station a1 by the proportion of the first transmission symbol shortened in step S801. Thereafter, the process proceeds to step S803.

(Step S803) The transmission unit b204 performs digital / analog conversion, waveform shaping, and up-conversion on the second transmission symbol obtained in step S802, and transmits the result via the transmission antenna b205. Thereafter, the small cell base station b2 ends the operation.

  Thus, according to this embodiment, since the length of the 2nd transmission symbol which small cell base station b2 transmits is shorter than the length of the 2nd transmission symbol which macrocell base station a1 transmits, the terminal which receives The signal can be detected with high accuracy even when the is moving at high speed, and the transmission efficiency is improved. Thereby, the transmission efficiency of the whole system can be improved.

(Third embodiment)
Hereinafter, the third embodiment of the present invention will be described in detail with reference to the drawings. In the second embodiment, the case where the macro cell base station a1 and the small cell base station b2 perform communication using the second transmission symbols having different lengths to improve the transmission efficiency has been described. The ratio of the first transmission symbol and CP included in the same as that of the macro cell. In the present embodiment, a case will be described in which the length of the CP used by the small cell is made shorter than the length of the CP used by the macro cell without fixing this ratio.

  Since the macrocell base station according to the present embodiment is the same as the macrocell base station a1 according to the first embodiment, the description thereof is omitted.

  FIG. 9 is a schematic block diagram showing the configuration of the small cell base station b3 according to this embodiment. In this figure, the small cell base station b3 includes an upper layer b301, a first transmission symbol generation unit b302, a CP insertion unit b303, a transmission unit b304, and a transmission antenna b305.

  The upper layer b301 generates data addressed to all terminals communicating with the small cell base station b3 and outputs the data to the first transmission symbol generation unit b302.

  The first transmission symbol generation unit b302 modulates data input from the upper layer b301, and performs first transmission using multicarrier modulation such as OFDM or MC-CDMA, or single carrier modulation such as SC-FDMA. Generate a symbol. The first transmission symbol generation unit b302 outputs the generated first transmission symbol to the CP insertion unit b303.

  CP insertion section b303 inserts the CP into the first transmission symbol input from first transmission symbol generation section b302.

  The transmission unit b304 performs digital / analog conversion on the second transmission symbol input from the CP insertion unit b303, and shapes the waveform of the converted analog signal. The transmission unit b304 up-converts the waveform-shaped signal from the baseband band to the radio frequency band, and transmits the signal from the transmission antenna b305 to all terminals connected to the small cell base station b3.

  FIG. 10 shows an example of the state of the second transmission symbol output from the CP insertion unit b303. FIG. 10 also shows the first transmission symbols 201, 202, 203 and CPs 201a, 202a, 203a of FIG. Reference numerals 1001, 1002, and 1003 denote first transmission symbols output from the first transmission symbol generation unit b302, and reference numerals 1001a, 1002a, and 1003a denote CPs inserted therein. In the present embodiment, the length of the CP is reduced on the assumption that the ratio of the first transmission symbol and the CP does not have to be the same as that of the macro cell base station a1. FIG. 10 shows an example in which the CP length is ３ and the first transmission symbol length is halved. Note that the length of the first transmission symbol may be increased.

<Operation of Small Cell Base Station b3>
FIG. 11 is a flowchart showing the operation of the small cell base station b3 according to this embodiment. The operation shown in this figure is processing after the upper layer b301 in FIG. 9 outputs data to the first transmission symbol generation unit b302.

(Step S1101) The first transmission symbol generation unit b302 generates a first transmission symbol. Then, it progresses to step S1102.

(Step S1102) The CP insertion unit b303 inserts a CP into the first transmission symbol obtained in Step S1101, and generates a second transmission symbol. This CP is smaller in length than that used in the macrocell base station a1. Thereafter, the process proceeds to step S1103.

(Step S1103) The transmission unit b304 performs digital / analog conversion, waveform shaping, and up-conversion on the second transmission symbol obtained in step S1102, and transmits the result via the transmission antenna b305. Thereafter, the small cell base station b3 ends the operation.

  Thus, according to the present embodiment, the CP length included in the second transmission symbol transmitted by the small cell base station b3 is smaller than that transmitted by the macrocell base station a1, and the redundancy is reduced and the transmission efficiency is improved. improves. Also, the length of the first transmission symbol in the second transmission symbol transmitted by the small cell base station b3 may be variable from that transmitted by the macrocell base station a1, and the extension from the existing system becomes easy. . Thereby, the transmission efficiency of the whole system can be improved.

(Fourth embodiment)
A fourth embodiment will be described. In the first, second, and third embodiments, the case has been described in which the lengths of the CP and the first transmission symbol transmitted by the macro cell base station and the small cell base station are changed. In the fourth embodiment, an example of communication performed between a macro cell base station, a small cell base station, and a terminal will be specifically described. The communication system according to the fourth embodiment includes a macro cell base station a1, a small cell base station b1, and a terminal c4.

  FIG. 12 is a sequence diagram illustrating an example of processing until the terminal c4 connects to the small cell base station b1 and data communication is started. The terminal c4 performs a cell search for detecting a connection destination from a plurality of macro cell base stations (s1201). It is assumed that the macro cell base station a1 is selected as the connection destination. The terminal c4 makes a connection request to the macro cell base station a1 (s1202). When receiving the connection request from the terminal c4, the macro cell base station a1 transmits a terminal information request to the terminal c4 (s1203). Here, the terminal information is information for determining whether the terminal c4 is connected to a small cell around the terminal c4 or a macro cell. For example, the terminal information is the position of the terminal c4, and the macro cell base station a1 may determine the connection destination of the terminal c4 based on the distance between the terminal c4 and the surrounding small cell base stations. For example, the terminal information is the power of the surrounding small cells measured by the terminal c4, and the macro cell base station a1 may determine the connection destination of the terminal c4 based on the power. When the terminal c4 receives the terminal information request, the terminal c4 reports the terminal information to the macro cell base station a1 (s1204). The macro cell base station a1 determines the connection destination of the terminal c4 based on the received terminal information. Here, a case where the macro cell base station a1 instructs the terminal c4 to connect to the small cell base station b1 will be described. The macro cell base station a1 transmits a terminal connection request to the small cell base station b1 (s1205). The small cell base station b1 notifies the macro cell base station a1 of resources for the terminal c4 to connect to the small cell base station b1 (s1206). The macro cell base station a1 notifies the terminal c4 of the small cell information including the resource (s1207). The terminal c4 synchronizes with the small cell base station b1 based on the notified small cell information (s1208). The terminal c4 reports the channel information to the small cell base station b1 (s1209). Here, the channel information is a channel estimation value, a MIMO channel rank, and the like, and the small cell base station b1 performs data communication with the terminal c4 based on the notified channel information (s1210).

  FIG. 13 is a schematic block diagram showing the configuration of the terminal c4. In this figure, a terminal c4 includes a reception antenna c401, a reception unit c402, a CP length determination unit c403, a CP removal unit c404, a signal detection unit c405, an upper layer c406, a first transmission symbol generation unit c407, a CP insertion unit c408, A transmission unit c409 and a transmission antenna c410 are included.

  First, the downlink will be described. The receiving unit c402 performs frequency conversion and analog-digital conversion on the received signal received via the receiving antenna c401. The receiving unit c402 outputs the converted received signal to the CP removing unit c404.

  The CP length determination unit c403 determines the length of the CP to be removed based on whether the other party currently communicating is the macro cell base station a1 or the small cell base station b1, and determines the CP length as CP. It outputs to the removal part c404. Note that the information of the other party that is communicating is input from the upper layer c406.

  The macro cell base station a1 may notify the terminal c4 of the CP length as small cell information, so that the terminal may determine the CP length.

  Note that the small cell information transmitted by the macro cell base station a1 may include the ID of the small cell base station b1, and the terminal c4 may determine the length of the CP based on the ID.

  Note that the small cell information transmitted by the macrocell base station a1 may include the transmission power of the small cell base station b1, and the terminal c4 may determine the length of the CP based on the transmission power. Note that the transmission power notification may be sent from the small cell base station b1 to the terminal c4.

  Note that the terminal c4 may determine the length of the CP based on the difference between the RS (Reference Signal) configuration transmitted by the macrocell base station a1 and the RS configuration transmitted by the small cell base station b1. . For example, in LTE or LTE-A format, CRS (Cell-Specific Reference Signal) is always transmitted, but it is proposed to formulate a new format (hereinafter referred to as a new carrier type) that does not transmit CRS. In the new carrier type, it is assumed that a CP having a shorter length than the normal CP and extended CP defined in LTE or LTE-A is used. For example, when the macro cell base station a1 communicates in the LTE or LTE-A format and the small cell base station b1 communicates in the new carrier type format, the terminal c4 receives the signal from the small cell base station b1. The length of the CP may be determined based on whether or not CRS is included. For example, the terminal c4 can calculate the correlation between the received signal and the time waveform of the CRS, and determine whether or not the CRS is included based on whether or not a peak appears in the correlation.

  Note that the small cell information transmitted by the macro cell base station a1 may include the carrier type of the small cell base station b1, and the terminal c4 may determine the CP length based on the carrier type.

  The CP removal unit c404 removes the CP from the reception signal input from the reception unit c402 based on the CP length input from the CP length determination unit c403. The CP removal unit c404 outputs a signal from which the CP has been removed to the signal detection unit c405.

  The signal detection unit c405 detects data destined for the terminal c4 from the signal from which the CP is input from the CP removal unit c404. The signal detection unit c405 outputs the detected data to the upper layer c406.

  Next, the uplink will be described. The upper layer c406 outputs data to the small cell base station b1 to the first transmission symbol generation unit c407.

  The first transmission symbol generation unit c407 generates a first transmission symbol by using multicarrier modulation such as OFDM or MC-CDMA or single carrier modulation such as SC-FDMA for the data input from the upper layer c406. . The first transmission symbol generation unit c407 outputs the generated first transmission symbol to the CP insertion unit c408.

  The CP insertion unit c408 inserts the CP into the first transmission symbol input from the first transmission symbol generation unit c407 based on the CP length input from the CP length determination unit c403, and performs the second transmission. Generate a symbol. The CP insertion unit c408 outputs the generated second transmission symbol to the transmission unit c409.

  The transmission unit c409 performs digital / analog conversion on the second transmission symbol input from the CP insertion unit c408, and shapes the converted analog signal. The transmission unit c409 up-converts the waveform-shaped signal from the baseband to the radio frequency band, and transmits the signal from the transmission antenna b410 to the small cell base station b1.

<About operation of terminal b4>
FIG. 14 is a flowchart showing a downlink operation of the terminal c4 according to the present embodiment. The operation shown in this figure is an operation after the reception unit c402 in FIG. 13 outputs a reception signal to the CP removal unit c404.

  (Step S1401) The CP length determination unit c403 determines the length of the CP. Thereafter, the process proceeds to step S1402.

  (Step S1402) The CP removing unit c404 removes the CP from the received signal based on the CP length obtained in Step S1401. Thereafter, the process proceeds to step S1403.

  (Step S1403) The signal detection unit c405 detects the data transmitted to the terminal c4 from the reception signal from which the CP obtained in step S1402 is removed. The detected data is output to the upper layer c406. Thereafter, the terminal c4 ends the downlink operation.

  FIG. 15 is a flowchart showing an uplink operation of the terminal c4 according to the present embodiment. The operation shown in this figure is an operation after the upper layer c406 in FIG. 13 outputs data to the first transmission symbol generation unit c407.

  (Step S1501) The first transmission symbol generation unit c407 generates a first transmission symbol based on the data from the upper layer c406. Thereafter, the process proceeds to step S1502.

  (Step S1502) The CP length determination unit c403 determines the length of the CP. Thereafter, the process proceeds to step S1503.

  (Step S1503) CP insertion section c408 inserts a CP into the first transmission symbol obtained in step S1501 based on the CP length obtained in step S1502, and generates a second transmission symbol. Thereafter, the process proceeds to step S1504.

  (Step S1504) The transmission unit c409 transmits the second transmission symbol obtained in step S1503 via the transmission antenna c410. Thereafter, the terminal c4 ends the uplink operation.

  Thus, according to the present embodiment, the length of the CP in the second transmission symbol transmitted by the small cell base station b1 is greater than the length of the CP in the second transmission symbol transmitted by the macrocell base station a1. Since the redundancy of the second transmission symbol transmitted by the small cell base station b1 is short, the transmission efficiency is improved when the terminal c4 communicates with the small cell base station b1. Further, the macro cell base station a1 notifies the small cell information, so that the terminal c4 can easily know the length of the CP. Thereby, the transmission efficiency of the whole system can be improved.

  In the present LTE and LTE-A, the normal CP and the extended CP are defined in the macro base station. For example, when the extended CP is used in the macro base station, such as MBMS (Multimedia Broadcast and Multicast Service), the small CP is used. The case where the cell base station uses the normal CP is also included in the present invention.

(Fifth embodiment)
A fifth embodiment will be described. In 4th Embodiment, the case where b1 was used as a small cell base station was demonstrated. In the fifth embodiment, a case where b2 is used as a small cell base station will be described. The communication system according to the fifth embodiment includes a macro cell base station a1, a small cell base station b2, and a terminal c5.

  In the communication system according to the present embodiment, the processing until the terminal c5 connects to the small cell base station b2 and the data communication starts is only to change the small cell base station b1 to b2 in the sequence diagram of FIG. Since the operation is the same, the description is omitted.

  FIG. 16 is a schematic block diagram showing the configuration of the terminal c5 according to this embodiment. In this figure, a terminal c5 includes a reception antenna c501, a reception unit c502, a second transmission symbol length determination unit c503, a CP removal unit c504, a signal detection unit c505, an upper layer c506, a first transmission symbol generation unit c507, a CP. An insertion unit c508, a transmission unit c509, and a transmission antenna c510 are included.

  First, the downlink will be described. The receiving unit c502 performs frequency conversion and analog-digital conversion on the received signal received via the receiving antenna c501. The receiving unit c502 outputs the converted received signal to the CP removing unit c504.

  The second transmission symbol length determination unit c503 determines the length of the second transmission symbol based on whether the other party currently communicating is the macro cell base station a1 or the small cell base station b2, and The length is output to CP removing section c504, signal detecting section c505, first transmission symbol generating section c507, and CP inserting section c508. Note that information on the other party that is communicating is input from the upper layer c 506.

  Note that the macro cell base station a1 may notify the terminal c5 of the length of the second transmission symbol as small cell information, so that the terminal may determine the length of the second transmission symbol.

  Note that the small cell information transmitted by the macro cell base station a1 may include the ID of the small cell base station b2, and the terminal c5 may determine the length of the second transmission symbol based on the ID.

  Note that the small cell information transmitted by the macro cell base station a1 may include the transmission power of the small cell base station b2, and the terminal c5 may determine the length of the second transmission symbol based on the transmission power. Note that the transmission power notification may be sent from the small cell base station b2 to the terminal c5.

  Note that the terminal c5 may determine the length of the second transmission symbol based on the difference between the RS configuration transmitted by the macrocell base station a1 and the RS configuration transmitted by the small cell base station b2. . For example, a CRS is always transmitted in the LTE or LTE-A format, but a new carrier type that does not transmit a CRS can be assumed. In the new carrier type, it is assumed that the second transmission symbol having a length shorter than the length of the second transmission symbol defined in LTE or LTE-A is used. For example, when the macro cell base station a1 communicates in the LTE or LTE-A format and the small cell base station b2 communicates in the new carrier type format, the terminal c5 receives the signal from the small cell base station b2. The length of the second transmission symbol may be determined based on whether or not CRS is included.

  In the present embodiment, the ratio of the length of the first transmission symbol and the CP in the second transmission symbol transmitted by the macrocell base station a1, and the second transmission symbol transmitted by the small cell base station b2. Since the ratio of the length of the first transmission symbol and CP is equal, the length of the second transmission symbol can be determined from the length of CP. Therefore, the second transmission symbol length determination unit c503 may first determine the length of the CP, and may determine the length of the second transmission symbol based on the CP length. Similarly, second transmission symbol length determination section c503 first determines the length of the first transmission symbol, and determines the length of the second transmission symbol based on the length of the first transmission symbol. May be.

  Note that the small cell information transmitted by the macro cell base station a1 may include the carrier type of the small cell base station b2, and the terminal c5 may determine the length of the second transmission symbol based on the carrier type.

  CP removing section c504 removes the CP from the received signal input from receiving section c502 based on the length of the second transmitting symbol input from second transmitting symbol length determining section c503. Since the ratio of the length of the CP in the second transmission symbol transmitted by the small cell base station b2 and the length of the first transmission symbol is the same as that transmitted by the macrocell base station a1, the second transmission symbol The length of the CP can be determined from the length. The CP removal unit c504 outputs a signal from which the CP has been removed to the signal detection unit c505.

  The signal detection unit c505 detects data addressed to the terminal c5 from the signal from which the CP is input, which is input from the CP removal unit c504. At this time, the signal detection unit c505 determines the length of the first transmission symbol from the length of the second transmission symbol input from the second transmission symbol length determination unit c503, and determines the length of the first transmission symbol. Signal detection is performed based on the length. The signal detection unit c505 outputs the detected data to the upper layer c506.

  Next, the uplink will be described. The upper layer c506 outputs the data for the small cell base station b2 to the first transmission symbol generation unit c507.

  The first transmission symbol generation unit c507 generates a first transmission symbol by using multicarrier modulation such as OFDM or MC-CDMA or single carrier modulation such as SC-FDMA for the data input from the upper layer c506. . At this time, the first transmission symbol generation unit c507 determines the length of the first transmission symbol from the length of the second transmission symbol input from the second transmission symbol length determination unit c503, and first The first transmission symbol is generated based on the length of the transmission symbol. The first transmission symbol generation unit c507 outputs the generated first transmission symbol to the CP insertion unit c508.

  CP insertion section c508 determines the length of the CP from the length of the second transmission symbol input from second transmission symbol length determination section c503, and based on the length of the CP, the first transmission symbol A second transmission symbol is generated by inserting a CP into the first transmission symbol input from the generation unit c507. The CP insertion unit c508 outputs the generated second transmission symbol to the transmission unit c509.

  The transmission unit c509 performs digital / analog conversion on the second transmission symbol input from the CP insertion unit c508, and shapes the waveform of the converted analog signal. The transmission unit c509 up-converts the waveform-shaped signal from the baseband to the radio frequency band, and transmits the signal from the transmission antenna b510 to the small cell base station b2.

<About operation of terminal b5>
FIG. 17 is a flowchart showing a downlink operation of the terminal c5 according to the present embodiment. The operation shown in this figure is an operation after the reception unit c502 in FIG. 16 outputs a reception signal to the CP removal unit c504.

  (Step S1701) Second transmission symbol length determination section c503 determines the length of the second transmission symbol. Thereafter, the process proceeds to step S1702.

  (Step S1702) CP removing section c504 obtains the CP length from the length of the second transmission symbol obtained in step S1701, and removes the CP from the received signal based on the CP length. Then, it progresses to step S1703.

  (Step S1703) The signal detection unit c505 detects data transmitted to the terminal c5 from the reception signal from which the CP obtained in step S1702 is removed. At this time, the length of the first transmission symbol is obtained from the length of the second transmission symbol obtained in step S1702, and signal detection is performed based on the length of the first transmission symbol. The detected data is output to the upper layer c506. Thereafter, the terminal c5 ends the downlink operation.

  FIG. 18 is a flowchart showing an uplink operation of the terminal c5 according to this embodiment. The operation illustrated in this figure is an operation after the upper layer c506 in FIG. 16 outputs data to the first transmission symbol generation unit c507.

  (Step S1801) Second transmission symbol length determination section c503 determines the length of the second transmission symbol. Thereafter, the process proceeds to step S1802.

  (Step S1802) The first transmission symbol generation unit c507 generates a first transmission symbol based on the data from the upper layer c506. At this time, the length of the first transmission symbol is obtained from the length of the second transmission symbol obtained in step S1801, and the first transmission symbol is generated based on the length of the first transmission symbol. Thereafter, the process proceeds to step S1803.

  (Step S1803) CP insertion section c508 determines the CP length from the second transmission symbol length obtained in step S1802, and based on the CP length, CP insertion section c508 adds the CP to the first transmission symbol obtained in step S1802. To generate a second transmission symbol. Thereafter, the process proceeds to step S1804.

  (Step S1804) The transmission unit c509 transmits the second transmission symbol obtained in step S1803 via the transmission antenna c510. Thereafter, the terminal c5 finishes the uplink operation.

  Thus, according to this embodiment, the length of the second transmission symbol transmitted by the small cell base station b2 is shorter than the length of the second transmission symbol transmitted by the macrocell base station a1, and the receiving terminal Since signal detection can be performed with high accuracy even when moving at high speed, transmission efficiency is improved when the terminal c5 communicates with the small cell base station b2. Further, the macro cell base station a1 notifies the small cell information, so that the terminal c5 can easily know the length of the second transmission symbol. Thereby, the transmission efficiency of the whole system can be improved.

(Sixth embodiment)
A sixth embodiment will be described. In the fifth embodiment, the case where b2 is used as the small cell base station has been described. In the sixth embodiment, a case where b3 is used as a small cell base station will be described. The communication system according to the sixth embodiment includes a macro cell base station a1, a small cell base station b3, and a terminal c6.

  In the communication system according to the present embodiment, the processing until the terminal c6 connects to the small cell base station b3 and the data communication starts is only to change the small cell base station b1 to b3 in the sequence diagram of FIG. Since the operation is the same, the description is omitted.

  FIG. 19 is a schematic block diagram showing the configuration of the terminal c6 according to this embodiment. In this figure, a terminal c6 includes a reception antenna c601, a reception unit c602, a CP length determination unit c603, a CP removal unit c604, a signal detection unit c605, an upper layer c606, a first transmission symbol generation unit c607, a CP insertion unit c608, A transmission unit c609, a transmission antenna c610, and a first transmission symbol length determination unit c611 are configured.

  First, the downlink will be described. The receiving unit c602 performs frequency conversion and analog-digital conversion on the received signal received via the receiving antenna c601. The receiving unit c602 outputs the converted received signal to the CP removing unit c604.

  The CP length determination unit c603 determines the length of the CP to be removed based on whether the other party currently communicating is the macro cell base station a1 or the small cell base station b1, and determines the CP length as CP. It outputs to the removal part c604. In addition, information of the other party who is communicating is input from the upper layer c606. The CP length determination unit c603 may know the length of the CP by the same method as the CP length determination unit (FIG. 13) of the terminal c4 according to the fourth embodiment.

  The CP removal unit c604 removes the CP from the reception signal input from the reception unit c602 based on the CP length input from the CP length determination unit c603. The CP removal unit c604 outputs a signal from which the CP has been removed to the signal detection unit c605.

  The signal detection unit c605 detects data addressed to the terminal c6 from the signal from which the CP is input, which is input from the CP removal unit c604. At this time, the signal detection unit c605 performs signal detection based on the length of the first transmission symbol input from the first transmission symbol length determination unit c611 described later. The signal detection unit c605 outputs the detected data to the upper layer c606.

  Next, the uplink will be described. Upper layer c606 outputs the data for small cell base station b3 to first transmission symbol generation section c607.

  The first transmission symbol generation unit c607 generates a first transmission symbol by using multicarrier modulation such as OFDM or MC-CDMA or single carrier modulation such as SC-FDMA for the data input from the upper layer c606. . At this time, the first transmission symbol generation unit c607 generates a first transmission symbol based on the length of the first transmission symbol input from a first transmission symbol length determination unit c611 described later. The first transmission symbol generation unit c607 outputs the generated first transmission symbol to the CP insertion unit c608.

  When OFDM is used, the number of FFT points may be changed to change the length of the first transmission symbol. Alternatively, the FFT sampling frequency may be changed, and the number of FFT points may be unchanged.

  The CP insertion unit c608 inserts the CP into the first transmission symbol input from the first transmission symbol generation unit c607 based on the CP length input from the CP length determination unit c603, and performs the second transmission. Generate a symbol. The CP insertion unit c608 outputs the generated second transmission symbol to the transmission unit c609.

  The transmission unit c609 performs digital / analog conversion on the second transmission symbol input from the CP insertion unit c608 and shapes the waveform of the converted analog signal. The transmission unit c609 up-converts the waveform-shaped signal from the baseband to the radio frequency band, and transmits the signal from the transmission antenna b610 to the small cell base station b3.

  The first transmission symbol length determination unit c611 determines the length of the first transmission symbol based on whether the other party currently communicating is the macro cell base station a1 or the small cell base station b3. The length of the signal detection unit c605 and the first transmission symbol generation unit c607. In addition, information of the other party who is communicating is input from the upper layer c606.

  Note that the macro cell base station a1 may notify the terminal c6 of the length of the first transmission symbol as small cell information, so that the terminal may determine the length of the first transmission symbol.

  Note that the small cell information transmitted by the macro cell base station a1 may include the ID of the small cell base station b3, and the terminal c6 may determine the length of the first transmission symbol based on the ID.

  Note that the small cell information transmitted by the macro cell base station a1 may include the transmission power of the small cell base station b3, and the terminal c6 may determine the length of the first transmission symbol based on the transmission power. Note that the transmission power notification may be sent from the small cell base station b3 to the terminal c6.

  Note that the terminal c6 may determine the length of the first transmission symbol based on the difference between the configuration of the RS transmitted by the macrocell base station a1 and the configuration of the RS transmitted by the small cell base station b3. . For example, a CRS is always transmitted in the LTE or LTE-A format, but a new carrier type that does not transmit a CRS can be assumed. In the new carrier type, it is assumed that the second transmission symbol having a length shorter than the length of the first transmission symbol defined in LTE or LTE-A is used (the first transmission of the new carrier type). The length of the symbol may be longer than the length of the first transmission symbol of LTE or LTE-A). For example, when the macro cell base station a1 communicates in the LTE or LTE-A format and the small cell base station b3 communicates in the new carrier type format, the terminal c6 receives the signal from the small cell base station b3. The length of the first transmission symbol may be determined based on whether or not CRS is included.

  Note that the small cell information transmitted by the macro cell base station a1 may include the carrier type of the small cell base station b3, and the terminal c6 may determine the length of the first transmission symbol based on the carrier type.

<About operation of terminal b6>
FIG. 20 is a flowchart showing a downlink operation of the terminal c6 according to this embodiment. The operation shown in this figure is an operation after the reception unit c602 in FIG. 19 outputs a reception signal to the CP removal unit c604.

  (Step S2001) The CP length determination unit c603 determines the length of the CP. Thereafter, the process proceeds to step S2002.

  (Step S2002) The CP removing unit c604 removes the CP from the received signal based on the CP length obtained in Step S2001. Thereafter, the process proceeds to step S2003.

  (Step S2003) The first transmission symbol length determination unit c611 determines the length of the first transmission symbol. Thereafter, the process proceeds to step S2004.

  (Step S2004) The signal detection unit c605 detects data transmitted to the terminal c6 from the reception signal from which the CP obtained in step S2002 is removed. At this time, signal detection is performed based on the length of the first transmission symbol obtained in step S2003. The detected data is output to the upper layer c606. Thereafter, the terminal c6 ends the downlink operation.

  FIG. 21 is a flowchart showing an uplink operation of the terminal c6 according to this embodiment. The operation shown in this figure is an operation after the upper layer c606 in FIG. 19 outputs data to the first transmission symbol generation unit c607.

  (Step S2101) The first transmission symbol length determination unit c611 determines the length of the first transmission symbol. Then, it progresses to step S2102.

  (Step S2102) The first transmission symbol generation unit c607 generates a first transmission symbol based on the data from the upper layer c606. At this time, a first transmission symbol is generated based on the length of the first transmission symbol obtained in step S2101. Thereafter, the process proceeds to step S2103.

  (Step S2103) The CP length determination unit c603 determines the length of the CP. Thereafter, the process proceeds to step S2104.

  (Step S2104) CP insertion section c608 inserts the CP into the first transmission symbol obtained at step S2102 based on the CP length obtained at step S2103, and generates a second transmission symbol. Thereafter, the process proceeds to step S2105.

  (Step S2105) The transmission unit c609 transmits the second transmission symbol obtained in step S2104 via the transmission antenna c610. Thereafter, the terminal c6 ends the uplink operation.

  Thus, according to the present embodiment, since the CP length included in the second transmission symbol transmitted by the small cell base station b3 is shorter than that transmitted by the macrocell base station a1 and the redundancy decreases, the terminal c6 Increases the transmission efficiency when communicating with the small cell base station b3. Also, the length of the first transmission symbol in the second transmission symbol transmitted by the small cell base station b3 may be variable from that transmitted by the macrocell base station a1, and the extension from the existing system becomes easy. . Further, the macro cell base station a1 notifies the small cell information, so that the terminal c6 can easily know the length of the CP and the length of the first transmission symbol. Thereby, the transmission efficiency of the whole system can be improved.

  The program operating in the macro cell base station a1, the small cell base stations b1, b2, and b3 and the terminals c1, c2, c3, c4, c5, and c6 related to the present invention realizes the functions of the above embodiments related to the present invention. As described above, it is a program for controlling a CPU or the like (a program for causing a computer to function). Information handled by these devices is temporarily stored in the RAM at the time of processing, then stored in various ROMs and HDDs, read out by the CPU, and corrected and written as necessary. As a recording medium for storing the program, a semiconductor medium (for example, ROM, nonvolatile memory card, etc.), an optical recording medium (for example, DVD, MO, MD, CD, BD, etc.), a magnetic recording medium (for example, magnetic tape, Any of a flexible disk etc. may be sufficient. In addition, by executing the loaded program, not only the functions of the above-described embodiment are realized, but also based on the instructions of the program, the processing is performed in cooperation with the operating system or other application programs. The functions of the invention may be realized.

  In the case of distribution in the market, the program can be stored and distributed in a portable recording medium, or transferred to a server computer connected via a network such as the Internet. In this case, the storage device of the server computer is also included in the present invention. In the embodiment described above, a part or all of the macro cell base station a1, the small cell base stations b1, b2, b3 and the terminals c1, c2, c3, c4, c5, c6 described with reference to the drawings are typical. Specifically, it may be realized as an LSI which is an integrated circuit. Each functional block of the macro cell base station a1, the small cell base stations b1, b2, b3 and the terminals c1, c2, c3, c4, c5, c6 may be individually chipped, or a part or all of them may be integrated. It may be chipped. Further, the method of circuit integration is not limited to LSI, and may be realized by a dedicated circuit or a general-purpose processor. In addition, when an integrated circuit technology that replaces LSI appears due to progress in semiconductor technology, an integrated circuit based on the technology can also be used.

  The embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration is not limited to this embodiment, and includes design changes and the like without departing from the gist of the present invention. The present invention can be modified in various ways within the scope of the claims, and embodiments obtained by appropriately combining technical means disclosed in different embodiments are also included in the technical scope of the present invention. It is. Moreover, it is the element described in each said embodiment, and the structure which substituted the element which has the same effect is also contained.

  In addition, this invention is not limited to the above-mentioned embodiment. The terminal device of the present invention is not limited to application to a mobile station device, but is a stationary or non-movable electronic device installed indoors or outdoors, such as AV equipment, kitchen equipment, cleaning / washing equipment Needless to say, it can be applied to air conditioning equipment, office equipment, vending machines, and other daily life equipment.

  The present invention is suitable for use in a radio base station apparatus, a radio terminal apparatus, a radio communication system, and a radio communication method.

a1 Macrocell base stations b1, b2, b3 Small cell base stations c4, c5, c6 Terminals a101, b101, c406 Upper layers a102, b102, b202, b302, c407, c507, c607 First transmission symbol generators a103, b103, b203, b303, c408, c508 CP insertion part a104, b104, c409 Transmission part a105, b105, c410 Transmission antenna c401 Reception antenna c402 Reception part c403 CP length judgment part c404, c504 CP removal part c405, c505, c605 Signal detection part c503 Second transmission symbol length determination unit c611 First transmission symbol length determination unit 201, 202, 203, 401, 402, 403, 701, 702, 703, 1001, 1002, 1003 First transmission symbol 20 1a, 202a, 203a, 401a, 402a, 403a, 701a, 702a, 703a, 1001a, 1002a, 1003a CP
201b, 202b, 203b Part behind the first transmission symbol

Claims (14)

A macro cell base station constituting a macro cell, a small cell base station constituting a small cell designed to overlap with at least one macro cell, and a terminal connected to the macro cell base station or the small cell base station,
The macro cell base station and the small cell base station transmit a second transmission symbol generated by inserting a cyclic prefix into a first transmission symbol obtained by modulating data,
A communication system in which a length of a cyclic prefix inserted by the small cell base station is shorter than a length of a cyclic prefix inserted by the macro cell base station. The terminal notifies the macro cell base station of terminal information,
The macro cell base station determines a small cell to which the terminal is connected based on the terminal information,
The macro cell base station notifies the terminal of small cell information of the small cell,
The communication system according to claim 1, wherein the terminal is connected to the small cell based on the received small cell information. The communication system according to claim 2, wherein the terminal information is a position of the terminal. The communication system according to claim 2, wherein the terminal information is reception power of a transmission signal of a surrounding small cell base station measured by the terminal. The length of the first transmission symbol generated by the macro cell base station is:
The communication system according to any one of claims 1 to 4, wherein a length of a first transmission symbol generated by the small cell base station is equal. A ratio of a length of a first transmission symbol generated by the macro cell base station and a length of a cyclic prefix inserted by the macro cell base station;
The communication system according to any one of claims 1 to 4, wherein a ratio of a length of the first transmission symbol generated by the small cell base station and a length of a cyclic prefix inserted by the small cell base station is equal. . A length of a first transmission symbol generated by the macrocell base station;
The communication system according to any one of claims 1 to 4, wherein lengths of first transmission symbols generated by the small cell base station are different. The small cell information includes a length of a cyclic prefix inserted by the small cell base station,
The communication system according to any one of claims 5 to 7, wherein the terminal determines a length of a cyclic prefix inserted by a small base station based on the small cell information. The small cell information includes an ID of the small cell,
The communication system according to any one of claims 5 to 7, wherein the terminal determines a length of a cyclic prefix inserted by the small cell base station based on the ID. The small cell information includes transmission power of the small cell,
The communication system according to any one of claims 5 to 7, wherein the terminal determines a cyclic prefix length of a signal transmitted by the small cell base station based on the transmission power. When the terminal detects that the configuration of the reference signal transmitted by the macro cell base station is different from the configuration of the reference signal transmitted by the small cell base station, the terminal cyclically transmits a signal transmitted by the small cell base station. The communication system according to any one of claims 5 to 7, wherein a prefix length is determined. The small cell information includes a carrier type of the small cell,
The communication system according to any one of claims 5 to 7, wherein the terminal determines a cyclic prefix length of a signal transmitted by the small cell base station based on the carrier type. The communication system according to any one of claims 8 to 12, wherein the terminal further determines a length of a first transmission symbol of a signal transmitted by the small cell base station. A macro cell base station constituting a macro cell, a small cell base station constituting a small cell designed to overlap with at least one macro cell, and a terminal connected to the macro cell base station or the small cell base station,
The macro cell base station and the small cell base station transmit a second transmission symbol generated by inserting a cyclic prefix into the first transmission symbol,
A communication method in which a length of a cyclic prefix inserted by the small cell base station is shorter than a length of the cyclic prefix inserted by the macro cell base station.