JP6133578B2 - Wireless communication system - Google Patents

Description

  The present invention relates to a wireless communication system that performs coordinated transmission.

  Conventionally, wireless communication systems that perform coordinated transmission in which the same signal is transmitted from a plurality of base stations at the same frequency and the same timing have been proposed. Patent Document 1 describes inter-base station cooperative communication in which a signal is transmitted from a plurality of base stations to the same mobile terminal in a wireless communication system. In Patent Document 1, by determining the optimal frequency and timing based on the frequency quality information and frequency vacancy information, cooperative communication between base stations using the optimal frequency between two geographically distant base stations is possible. It will be. In Patent Document 1, there is no description regarding retransmission.

JP 2011-182063 A

  In the case of performing retransmission in conventional coordinated transmission, the master station first receives a retransmission request and then instructs each slave station through a backhaul (a network network connecting base stations). For this reason, it takes time from the time when the retransmission request is received to the time when retransmission is started, and the response is delayed, which may impair communication efficiency.

  Further, the fact that retransmission is requested means that the quality of the first transmission is low. For this reason, there is a possibility that the retransmitted data cannot be normally received even if cooperative transmission is simply performed with the same configuration. Here, in coordinated transmission, there is a possibility that the overall quality may be deteriorated due to the presence of low communication quality among a plurality of base stations.

  Accordingly, the present invention provides a wireless communication system capable of improving communication quality in retransmission processing without causing a decrease in communication efficiency due to delay when performing retransmission processing in a wireless communication system performing coordinated transmission. The purpose is to do.

  In order to solve the above problems, a representative configuration of a wireless communication system according to the present invention is a wireless communication system that performs coordinated transmission in which the same signal is transmitted from a plurality of base stations at the same frequency and the same timing. The plurality of base stations are composed of one master station and a plurality of slave stations. The master station acquires the wireless communication quality between the terminal and each base station from the terminal, and the master station transmits the slave station to each slave station. A base station that notifies the wireless communication quality with the terminal, and when there is a retransmission request from the terminal, each of the master station and the plurality of slave stations receives the retransmission request, and the wireless communication quality satisfies the first quality threshold. Only perform retransmission by cooperative transmission.

  When there is a retransmission request from the terminal, retransmission is performed by coordinated transmission up to the first retransmission threshold, and after reaching the first retransmission threshold, retransmission is performed from any one of the master station or a plurality of slave stations. Preferably it is done.

  The master station determines the retransmission order based on the radio communication quality of each base station, the master station notifies each slave station of the ordering, and in response to a retransmission request from the terminal, a plurality of retransmissions are received from a single base station. When it is performed once, it is preferable to perform retransmission in the order determined by ranking among the master station or the plurality of slave stations.

  The master station preferably ranks the base stations whose wireless communication quality is equal to or higher than the second quality threshold.

  The master station and the plurality of slave stations preferably stop the retransmission process when the number of retransmissions from a single base station reaches the second retransmission threshold.

  When a master station or a plurality of slave stations communicates with a terminal via a plurality of resource blocks, it is preferable to perform acquisition of wireless communication quality, ranking, and independent retransmission processing for each resource block.

  According to the present invention, when retransmission processing is performed in a wireless communication system that performs coordinated transmission, communication efficiency is not reduced due to delay, and communication quality in the retransmission processing can be improved.

It is a figure explaining the structure of a base station and a terminal. It is a sequence chart explaining operation | movement of a radio | wireless communications system. It is a flowchart explaining operation | movement of a master station. It is a figure explaining an example of the resending operation | movement for every resource block.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The dimensions, materials, and other specific numerical values shown in the embodiments are merely examples for facilitating understanding of the invention, and do not limit the present invention unless otherwise specified. In the present specification and drawings, elements having substantially the same function and configuration are denoted by the same reference numerals, and redundant description is omitted, and elements not directly related to the present invention are not illustrated. To do.

  FIG. 1 is a diagram illustrating the configuration of a base station and a terminal, and FIG. 1 (a) is an overall configuration diagram. A plurality of base stations 100 are installed at predetermined intervals. The range in which the radio waves of each base station 100 can reach (communication range) is called a cell 110. Base stations are connected to each other via a communication network 114 by a backhaul 112, and can appropriately communicate necessary data and control information. In addition, synchronization of clocks and timing phases between base stations is maintained by synchronization processing using a backhaul 112, a GPS device, or the like.

  When terminal 200 communicates with base station 100, there is a case where coordinated transmission is performed in which the same signal is transmitted from a plurality of base stations 100 at the same frequency and the same timing. At this time, in the base station 100, the base station to which the terminal 200 is first connected becomes the master station 102, and another base station that performs coordinated transmission becomes the slave station 104.

  FIG. 1B is a diagram illustrating the configuration of the base station 100. The master station 102 and the slave station 104 have the same device configuration. The base station 100 includes a control unit 120 that controls the overall operation, a backhaul communication unit 122 that communicates with the backhaul 112, and a wireless communication unit 124 that communicates with the terminal 200. The base station 100 further includes a quality receiving unit 126 that receives the radio communication quality from the terminal 200, a quality comparison unit 128 that compares the radio communication quality with a predetermined threshold, and a rank determination unit 130 that ranks retransmissions, which will be described later. ing.

  FIG. 1C illustrates the configuration of the terminal 200. The terminal 200 includes a wireless communication unit 202 that communicates with the base station 100, and a quality acquisition unit 204 that acquires wireless communication quality with each base station. The radio communication unit 202 performs communication using radio resources (RB: Resource Block) allocated by the schedule processing of the base station 100.

  The wireless communication unit 202 synthesizes and decodes the data transmitted cooperatively from each base station 100. At this time, it is determined whether or not decoding has been correctly performed, and a delivery signal is transmitted to the base station. The delivery signal is an ACK signal when it is correct data after decoding, and a NACK signal when it is not correct, and is inserted into an upstream signal and transmitted to the base station 100. The base station 100 identifies whether or not the terminal has received correctly, and performs retransmission processing to transmit the same data to the terminal again when a NACK signal is received.

  Here, as a conventional retransmission method in the case of performing coordinated transmission, when the terminal 200 transmits a delivery signal to the master station 102 and the master station 102 determines that retransmission is necessary, each base station performing coordinated transmission A method of instructing the station to perform cooperative retransmission by communication means such as backhaul is conceivable. However, in this configuration, since an instruction is sent to each slave station 104 by means of communication such as backhaul after retransmission processing in the master station 102, there is a problem that the start of retransmission is delayed and efficiency of communication is impaired.

  Therefore, in the present invention, delay is avoided by the following configuration, and communication quality is improved in retransmission processing. The configuration and operation of the wireless communication system according to the present invention will be described below with reference to FIGS. FIG. 2 is a sequence chart for explaining the operation of the wireless communication system, and FIG. 3 is a flowchart for explaining the operation of the master station. 2 and 3, the same operation will be described with the same reference numerals.

(1) Calculation of Quality Average Value As shown in FIG. 2, first, cooperative transmission is started (300). The terminal 200 synthesizes and decodes the received data to determine whether it is correct (302). The terminal 200 returns an ACK signal as a delivery signal when decoding is successful, and returns a NACK signal when it is not correct (304).

  Further, the quality acquisition unit 204 of the terminal 200 measures each wireless communication quality between the terminal 200 and each base station from a reference signal (RS: Reference Signal) from the receivable base station 100. Each base station 100 transmits a reference signal unique to the base station, and these reference signals are orthogonal to each other, and can be detected individually. The wireless communication quality indicates downlink communication quality (CQI information or the like) and is measured by reference signals appropriately arranged in each frequency band. Also, BLER (Block Error Rate) measurement is performed as the quality of the data after decoding. The quality acquisition unit 204 of the terminal 200 transmits the wireless communication quality to the master station 102 via the wireless communication unit 202 (306).

The quality receiving unit 126 of the master station 102 receives the wireless communication quality via the wireless communication unit 124 (308). The quality comparison unit 128 of the master station 102 calculates a quality average value from the received wireless communication quality (310). The calculation formula of the following formula 1 is an example.
Quality average value = (long-time average value × weight value (1) + short-time average value × weight value (2) + current quality value × weight value (3)) / 3 (Expression 1)
Here, for example, the weight (3) may be set so that the current quality value becomes the same weight according to the number of samples of the short time average value and the long time average value (the number of samples of the current quality value is always 1).

  Then, the master station 102 determines a retransmission method (312), and notifies each slave station 104 of the quality average value of each slave station 104 (314). Note that the notification of the quality average value is asynchronous with the notification of the delivery signal from the terminal 200, and the previous value is maintained until it is updated.

  When the master station 102 receives the delivery signal (316) and the delivery signal is an ACK signal, the above procedure is repeated (NO in 318). If the delivery signal is a NACK signal (320), retransmission processing is performed (YES in 318).

(2) Retransmission processing by coordinated transmission In this embodiment, all base stations 100 (master station 102 and each slave station 104) performing coordinated transmission directly receive a delivery signal transmitted by terminal 200. In this embodiment, as described below, first, retransmission processing by cooperative transmission is performed, and then retransmission processing by single transmission is performed.

  When the master station 102 and the slave station 104 receive a NACK signal that is a retransmission request from the terminal as a delivery signal (320), the count of the number of retransmissions is started or incremented (322), and the first retransmission threshold is not reached. After coordinated transmission (NO in 324) and reaching the first retransmission threshold, retransmission is performed from a single base station (YES in 324) as described later.

When coordinated transmission is performed (NO in 324), the quality average value is compared with a predetermined first quality threshold as shown in Equation 2 (326).
Quality average value ≧ first quality threshold (Formula 2)
The first quality threshold is a threshold for determining whether or not the base station 100 performs retransmission. If the quality average value is higher than the first quality threshold, retransmission by cooperative transmission is performed (328), and if it is lower, Not performed. That is, only a base station with a good quality average value performs retransmission by cooperative transmission. The first quality threshold value can be set in the base station 100 in advance.

  When terminal 200 receives the retransmission data, terminal 200 determines the received data as usual (302), and returns a delivery signal. When the delivery signal is an ACK signal (304), the retransmission process is stopped and the normal cooperative transmission is returned (NO in 318). When the delivery signal is a NACK signal (YES in 318), the number of retransmissions is incremented (322), and further retransmission processing is performed.

  Here, the reason why the base station 100 is selected based on the first quality threshold is that, if reception signals from base stations with poor communication quality are mixed, the combining effect in the terminal 200 may be reduced. By excluding the base station 100 having a poor quality average value as described above, it is possible to prevent deterioration of wireless communication quality and improve communication quality in retransmission processing.

(3) Processing when the delivery signal NACK (retransmission request) reaches the first retransmission threshold or when the delivery signal cannot be received by the specified time In the retransmission processing by the above coordinated transmission, the number of retransmissions is set to the first retransmission threshold. If it has been reached (YES in 324), the retransmission method is changed to single transmission. If the number of retransmissions reaches the first retransmission threshold, there is a possibility that there is no effect of coordinated transmission, or any base station does not satisfy the threshold, and any base station does not retransmit. For this reason, single transmission is performed from a base station in the best possible state.

(4) Retransmission processing by a single base station When the number of retransmissions reaches the first retransmission threshold (YES in 324), the master station 102 determines the quality within the local station and the slave station 104 as shown in Equation 3 Ranking is performed among those whose average value satisfies the predetermined second quality threshold (330).
Quality average value ≧ second quality threshold (Formula 3)
When there are two or more base stations 100 satisfying Equation 3, only the satisfied base station 100 is set as a retransmission base station, and the base stations having a good quality average value are ranked in order. Here, when the quality average value is the same, the one having the better current quality value may be ranked higher, and the order may be determined based on the priority of the short time average value and the long time average value. When the number of base stations 100 satisfying Equation 3 is one or less, retransmission is performed only by the base station 100 having the best quality average value. The ranking determined in this way is notified to each slave station 104 (332).

  The master station 102 and the slave station 104 start or increment the count of the number of retransmissions (334). Then, the master station 102 and the slave station 104 independently perform retransmission according to the above ranking. The ranking maintains information until it is newly notified.

  The above ranking and retransmission are performed for each resource block when there are a plurality of resource blocks. FIG. 4 is a diagram for explaining an example of a retransmission operation for each resource block. In the example of FIG. 4, BS1, BS2, and BS3 indicate three base stations. RB1 and RB2 indicate that two resource blocks are used. In the quality average value, the parentheses indicate the rank. In the above state, retransmission (first time) is transmitted from RB1 of BS2 for data D1 and from RB2 of BS3 for data D2. If a NACK signal is still received, data D1 is transmitted from RB1 of BS3 and data D2 is transmitted from RB2 of BS1. Further, when a NACK signal is received, data D1 is transmitted from RB1 of BS1, and data D2 is transmitted from RB2 of BS2.

  As described above, each base station 100 determines whether or not the base station 100 is a retransmission target (336). If the base station 100 is a retransmission target, the base station 100 performs the retransmission alone (338). Do not retransmit (NO in 336). Then, a delivery signal is received from terminal 200 (340), and when the delivery signal is an ACK signal (346), the retransmission process is terminated (NO in 342). If the delivery signal is a NACK signal (340), retransmission processing is repeated independently from different base stations 100 according to the ranking (YES in 342). When the number of retransmission requests by the delivery signal NACK reaches a predetermined second retransmission threshold (YES in 344), the retransmission process is stopped. In the example of FIG. 2, it is determined that the received data is correct at the third retransmission, and the retransmission process is completed.

  According to the above configuration, each base station can start the retransmission process independently without waiting for an instruction from the master station 102, so that a reduction in communication efficiency due to delay can be avoided. In addition, when there is no effect in the retransmission processing by cooperative transmission, by performing the retransmission processing one by one from the base station with good communication quality, it is possible to eliminate the influence from the base station with poor communication quality, Communication quality can be improved. Furthermore, when it is determined whether or not to retransmit simply by threshold determination, all base stations may not perform retransmission processing. As a countermeasure, the number of retransmission processing by threshold determination is set in advance (first retransmission threshold), and the number of times If it exceeds the value, it is possible to eliminate the case where no retransmission is performed at all by retransmitting from a single base station.

  In the present embodiment, the base station that communicates with the terminal before starting the coordinated transmission is the master station 102 and the instruction is sent to the other slave stations 104. However, necessary information may be provided to the center station that supervises the base station via the communicating base station (master station), and the center station may perform control instead of the master station 102.

  As mentioned above, although preferred embodiment of this invention was described referring an accompanying drawing, it cannot be overemphasized that this invention is not limited to the example which concerns. It will be apparent to those skilled in the art that various changes and modifications can be made within the scope of the claims, and these are naturally within the technical scope of the present invention. Understood.

  The present invention can be used as a wireless communication system that performs coordinated transmission.

DESCRIPTION OF SYMBOLS 100 ... Base station, 102 ... Master station, 104 ... Slave station, 110 ... Cell, 112 ... Backhaul, 114 ... Communication network, 120 ... Control part, 122 ... Backhaul communication part, 124 ... Wireless communication part, 126 ... Quality Receiving unit, 128 ... quality comparison unit, 130 ... ranking determination unit, 200 ... terminal, 202 ... wireless communication unit, 204 ... quality acquisition unit

Claims (5)

In a wireless communication system that performs coordinated transmission in which the same signal is transmitted from a plurality of base stations to a terminal at the same frequency and the same timing,
The plurality of base stations comprises one master station and a plurality of slave stations,
When there is a retransmission request from the terminal, each of said master station and said slave station receives the retransmission request, the master station and the slave station, in accordance with the number of retransmissions from a single base station, coordinated transmission Or a wireless communication system that performs retransmission from a single base station of the master station or the slave station,
The master station determines retransmission ranking based on wireless communication quality between the master station and the slave station and the terminal,
The master station notifies the ranking to the slave station,
Radio communication , wherein retransmission is performed in the order determined by the ranking among the master stations or slave stations when retransmission is performed a plurality of times from a single base station in response to a retransmission request from the terminal system.   The wireless communication system according to claim 1, wherein the master station ranks base stations whose wireless communication quality is equal to or higher than a second quality threshold.   When the master station or a plurality of slave stations communicates with the terminal via a plurality of resource blocks, the acquisition, ranking, and single retransmission processing of the wireless communication quality are performed for each resource block The wireless communication system according to claim 1, wherein the wireless communication system is a wireless communication system. In the base station of the master station that performs coordinated transmission to transmit the same signal to the terminal as one or more slave stations at the same frequency and the same timing,
A base station of a master station that receives a retransmission request transmitted from the terminal and performs retransmission by coordinated transmission according to the number of retransmissions or performs retransmission from a single base station ,
Determine the retransmission ranking based on the wireless communication quality of the master station and the slave station,
Notifying the slave station of the ranking,
A base station that performs retransmission in the order determined by the ranking when retransmission is performed a plurality of times from a single base station in response to a retransmission request from the terminal . In the base station of the slave station that performs coordinated transmission that transmits the same signal as the base station of the master station to the terminal at the same frequency and the same timing,
The base station of the slave station that receives the retransmission request transmitted from the terminal and performs retransmission by cooperative transmission according to the number of retransmissions or performs retransmission from a single base station,
When the master station determines the retransmission ranking based on the wireless communication quality of the master station and the slave station, and notifies the slave station of the ranking,
A base station that performs retransmission in the order determined by the ranking when retransmission is performed a plurality of times from a single base station in response to a retransmission request from the terminal.

Images