Abstract:
A mobile communication system in which a working frequency band is divided into a plurality of predetermined frequency bands, and time division multiplexing is performed, the mobile communication system includes a base station to insert a known pilot symbol into the plurality of predetermined frequency bands at a predetermined reference interval, and to insert to arrange the known pilot symbol into at least one of the plurality of predetermined bands at a smaller interval than the predetermined reference interval, wherein a frequency band in which the known pilot symbol is inserted at a smaller interval than the predetermined reference interval is to be set cyclically in time; and a mobile terminal to receive the known pilot symbol transmitted from the base station.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 12/688,319, filed on Jan. 15, 2010, now pending, which is a continuation of international application PCT/JP2007/000831, filed on Aug. 2, 2007, the contents of each are herein wholly incorporated by reference. This application also relates to U.S. Pat. No. 8,503,284, which issued Aug. 6, 2013. 
    
    
     FIELD 
     The present invention relates to a pilot arrangement method in a mobile radio communication system and a transmitter/receiver adopting the same. 
     BACKGROUND 
     On the subject of next generation radio access systems for the third generation mobile communication of mobile radio communication systems, discussions on LTE (Long Term Evolution) is in progress at 3GPP (3rd Generation Partnership Project). 
     In LTE, it is a precondition that frequency and time scheduling are performed in resource block (RB) or resource unit (RU) units. 
       FIG. 1  is a diagram depicting this frequency and time scheduling. The working band is divided into resource blocks, and the frequency is allocated to a plurality of user terminals, that is mobile terminals (UE: User Equipment). 
     The working band is also time-divided into sub-frames in the time axis direction, and frequency in resource block units is switched and allocated to a plurality of mobile terminals (UE). 
     This scheduling of allocation in sub-frame units in the frequency axis and time axis directions is performed by the base station. 
     Scheduling is normally performed based on channel quality information (CQI) in resource block (RB) or resource unit (RU) units. 
     CQI corresponds to signal-to-interference ratio (SIR), and SIR at the mobile terminal side is normally measured by monitoring the level of a common pilot, which is common to users, from the base station. 
     In the above mentioned LTE, common pilot channels are arranged in the frequency direction with intervals downlink (Non-patent Document 1). 
       FIG. 2  is a diagram depicting the example of arranging common pilot channels (PC) in the frequency direction with intervals, which is described in Non-patent Document 1. 
     Patent Document 1 proposes a structure of attaching common pilot symbols and a known series in each slot in order to enhance the SIR measurement accuracy, and a communication device at the reception side estimates the SIR using common pilot symbols and a known series in the received slot. 
     In the above mentioned mode shown in LTE, the pilot arrangement interval increases if the insertion interval of the pilot channels is very large, if the number of transmission antennas is high, or if the number of multiplexed users is high. Because of this, the number of common pilots to be arranged in a resource block and resource unit in specific units decreases. 
     Measurement of I (interference power) to measure SIR is normally expressed by Expression 1, and  FIG. 3  shows a conceptual diagram of the measurement. Expression 1 determines the difference between the average value of the pilot levels before and after and the position of the pilot channel as the interference power. 
     
       
         
           
             
               
                 
                   
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     DISCLOSURE OF THE INVENTION 
     Problems to be Solved by the Invention 
     In the above Expression 1, Pj is a pilot after cancelling a pilot pattern based on the j-th subcarrier, as shown in  FIG. 3 . Non-patent Document 1: 3GPP TR 25.814 v7.0.0 (7.1.1.2.2) Patent Document 1: Japanese Laid-Open Patent Publication No. 2003-348046 
     If the arrangement interval of the pilot channels is large, that is if the pilot frequency interval to be used for measurement increases, an estimated value of I (interference power) increases because of the frequency selectivity between subcarriers, especially in an environment where delay dispersion is large. 
     Because of this, the accuracy of SIR estimation in a resource block RB or resource unit RU units deteriorates. 
     Therefore if the interval of the pilot channels is large, scheduling may be affected and throughput may drop, because accuracy of SIR estimation deteriorates and the CQI accuracy also deteriorates since the CQI corresponds to SIR in scheduling. 
     The above mentioned Patent Document 1 describes improving SIR estimation accuracy using pilots and known series, but does not mention the interval of pilot channels. 
     With the foregoing in view, it is an object of the present invention to provide a pilot arrangement method in a mobile radio communication system that solves the problem that occurs when the interval of pilot channels is large, and a transmitter/receiver adopting the same. 
     Means for Solving the Problem 
     In order to solve the above problem, the present invention provides a pilot arrangement method in a mobile communication system by which a working frequency band is divided into a plurality of predetermined bands, and time division multiplexing is performed, characterized in that a known pilot symbol is inserted into the plurality of predetermined frequency bands at a predetermined reference interval, and the known pilot symbol is inserted and arranged into at least one of the plurality of predetermined frequency bands at a smaller interval than the predetermined reference interval. 
     Moreover, the pilot symbols can be inserted and arranged at a smaller interval than the predetermined reference interval into at least one frequency band out of the plurality of predetermined frequency bands, based on the signal-to-interference ratio measurement information at the reception side. 
     Because of this characteristic, opportunities to measure SIR using known pilots increase, and the frequency interval decreases, therefore I (interference power) estimation accuracy improves, and as a result the problem of performing scheduling based on CQI corresponding to SIR at the transmission side, and poor CQI accuracy which affects and deteriorates throughput, can be prevented. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram depicting frequency and time scheduling; 
         FIG. 2  depicts an example of arranging common pilot channels with an interval in the frequency direction, which is described in Non-patent Document 1; 
         FIG. 3  is a conceptual diagram depicting measurement of I (interval power) when SIR, generally given by Expression 1, is measured; 
         FIG. 4  depicts a first arrangement example of pilot channels according to the present invention; 
         FIG. 5  is a diagram depicting a configuration of a transmitter of a base station, which is a transmission side device corresponding to the embodiment in  FIG. 4 ; 
         FIG. 6  is a diagram depicting a configuration example of a transmitter/receiver at a mobile terminal side corresponding to the transmitter in  FIG. 5 ; 
         FIG. 7  is a diagram depicting a pilot channel arrangement according to a second embodiment; 
         FIG. 8  is a diagram depicting a configuration of a transmitter at a transmission side corresponding to the embodiment in  FIG. 7 ; 
         FIG. 9  is a diagram depicting a configuration of a transmitter/receiver at the pilot channel reception side, that is the mobile terminal side, corresponding to  FIG. 7 ; 
         FIG. 10  is a diagram depicting a configuration of a transmitter at the transmission side according to the third embodiment of the present invention; 
         FIG. 11  is a diagram depicting a configuration of a transmitter/receiver at the reception side corresponding to the transmitter at the transmission side in  FIG. 10 ; 
         FIG. 12  is a diagram depicting a configuration of a transmitter at the transmission side according to the fourth embodiment of the present invention; 
         FIG. 13  is a diagram depicting a configuration of a transmitter/receiver at the reception side corresponding to the transmitter at the transmission side in  FIG. 12 ; 
         FIG. 14  is a diagram depicting a pilot channel arrangement according to the fifth embodiment of the present invention; 
         FIG. 15  is a diagram depicting a configuration example for limiting the number of common pilot channels to densely insert depending on the information volume to be transmitted by such as a control channel (communication rate); 
         FIG. 16  is a diagram depicting an example of limiting the number of common pilot channels to be densely inserted depending on the information volume to be transmitted by such as a control channel (communication rate); 
         FIG. 17  is a diagram depicting an example of controlling the arrangement of common pilot channels according to the state of delay dispersion; and 
         FIG. 18  is a graph depicting the effect of the present invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Embodiments of the present invention will now be described with reference to the drawings. 
       FIG. 4  is a first arrangement example of a pilot channel according to the present invention. 
     When pilot channels (PC) are arranged with a predetermined reference interval, such as an interval of six subcarriers (SC) (six frequency bands of a plurality of predetermined bands generated by dividing a working frequency) according to a standard, the pilot channels are densely arranged (e.g. continuously arranged) in a predetermined frequency area at a smaller interval than the normal arrangement interval, according to the present invention, as depicted in  FIG. 2 . 
     In other words, according to the first embodiment depicted in  FIG. 4 , pilot channels are arranged continuously after the first resource block RB of each sub-frame. 
       FIG. 5  depicts a configuration example of a transmitter of a base station, which is a transmission side communication device corresponding to the embodiment in  FIG. 4 , and  FIG. 6  depicts a configuration example of a transmitter/receiver of a mobile terminal, which is a corresponding reception side communication device. 
     In the transmission side depicted in  FIG. 5 , a pilot signal from a pilot channel generator  2 , and data and a control signal from a data and control signal generator  4  are channel-multiplexed by a multiplexing circuit  3 , and modulated, amplified and transmitted via a transmission antenna  6  by a transmission unit  5 . 
     In the transmission device shown in  FIG. 5 , the pilot channel generator  2  acquires position information for arranging the pilot channels from a pilot channel arrangement information generation unit  1 , and outputs a common pilot signal to the multiplexing circuit  3  at a timing of a corresponding position. 
       FIG. 6  is a block diagram depicting a configuration of a transmitter/receiver at a pilot reception side, that is a mobile terminal side, corresponding to  FIG. 5 . 
     The pilot signal and the signal in which data and control signal are multiplexed are received by an antenna  10 . The reception signal is demodulated by the reception unit  11 , branched by a demultiplexing circuit  12 , and input to a data and control signal demodulation/decoding circuit  13  and pilot channel extraction unit  14 . 
     The pilot channel extraction unit  14  controls pilot detection timing in the pilot channel extraction unit  14  based on common pilot channel arrangement information  15 , which is notified by the transmission side in advance or which is known. 
     Information on the common pilot channel arrangement information  15  from the transmission side is either already known or can be notified by a control signal before changing scheduling or by any arbitrary method. 
     The pilot channel extraction portion  14  detects a common pilot symbol at a pilot detection timing to be controlled, and outputs the level to an SIR measurement unit  16 . 
     The pilot channel extraction unit  14  notifies a pilot detection timing to a data and control signal demodulation/decoding circuit  13  so as to provide reference of data and control signal reception timing in the control signal demodulation/decoding circuit  13 . 
     The SIR measurement unit  16  measures SIR, which is a signal-to-interference ratio, based on the level for each receive pilot symbol notified from the pilot channel extraction unit  14 . 
     The measured SIR is sent to a CQI information generation unit  20 . Other information  21  related to the line state is also sent to the CQI information generation unit  20  if necessary. 
     The CQI information generation unit  20  creates CQI information corresponding to the SIR value by a conventional processing method based on the measured SIR sent from the SIR measurement unit  16 , and other information  21  related to the line state. 
     The multiplexing circuit  23  multiplexes the CQI information created like this and a data and control signal from a data/control signal generation unit  22 , and transmits it to a transmission unit  24 . 
     The transmission unit  24  modulates and amplifies the multiplexed signal and transmits it from an antenna  25  to the base station side. 
     The base station side estimates SIR based on the CQI information that is sent from the transmitter/receiver at the mobile terminal side. And based on the estimated SIR, the pilot channel arrangement information generation unit  1  generates position information for arranging the pilot channels using a conventional method. 
     The new common pilot channel arrangement information that is generated like this is set based on the reception state of the reception side, so the SIR estimation accuracy which is based on the common pilot channel can be enhanced. 
       FIG. 7  is a diagram depicting a pilot channel arrangement according to a second embodiment. In the first embodiment in  FIG. 4 , a position from which the pilots are continuously arranged is the first position of each sub-frame. On the other hand, in the configuration of the example depicted in  FIG. 7 , the position from which pilots are continuously arranged at a predetermined time interval is changed. 
     For this, a transmitter at the transmission side shown in  FIG. 8 , which corresponds to the embodiment in  FIG. 7 , has a function to set a time cycle for the pilot arrangement information generation unit  1  using a time cycle setting unit  7 . Therefore a pilot arrangement generation unit  1  changes the pilot channel arrangement at the time cycle which is set, and so as to control the pilot generation timing of the pilot channel generator  2 . 
     The other configuration functions of the transmitter at the transmission side is the same as the configuration in  FIG. 5  described above. 
       FIG. 9  depicts the configuration of a transmitter/receiver at the pilot reception side, that is at the mobile terminal side, corresponding to  FIG. 7 . 
     The transmitter/receiver at the reception side shown in  FIG. 9  also has a time cycle setting unit  26 . This time cycle is already known or has been notified from the transmission side in advance, just like the previous embodiment. Therefore a pilot channel arrangement information generation unit  15  of the reception side can create pilot channel arrangement information synchronizing with the transmission side. 
     The pilot channel extraction timing in the pilot channel extraction unit  14  is controlled at the pilot channel positions created by the pilot channel arrangement information generation unit  15 . The other configuration and operations are the same as those described with reference to  FIG. 6 . 
       FIG. 10  is a diagram depicting a configuration of a transmitter at the transmission side according to the third embodiment of the present invention, and  FIG. 11  is a diagram depicting a configuration of a transmitter/receiver at the reception side corresponding to the transmitter of  FIG. 10 . 
     In the transmitter at the transmission side in  FIG. 10 , a fixed pattern generation unit  70  is disposed at the transmission side so that a fixed timing is sent to a pilot channel information generation unit  1  to control the pilot channel arrangement positions. 
     As  FIG. 11  depicts, the reception side has a corresponding fixed pattern generation unit  27  to control the pilot channel arrangement information generation unit  15 . 
     At least for the fixed pattern, a fixed pattern to densely arrange pilots from the reference pilot channel arrangement position, that is specified by a standard, is set. 
       FIG. 12  is a diagram depicting a configuration of a transmitter at the transmission side according to the fourth embodiment of the present invention, and  FIG. 13  is a diagram depicting a configuration of a transmitter/receiver at the reception side corresponding to the transmitter of  FIG. 12 . 
     In the configuration of the fourth embodiment, information on the pilot arrangement positions generated by a pilot channel arrangement information generation unit  1  is embedded in a control signal channel and transmitted to the reception side. 
     Therefore as  FIG. 13  depicts, the reception side device extracts the pilot channel arrangement information inserted in the control channel, that is demodulated/decoded by a data and control signal demodulation/decoding circuit  13 , using a pilot channel arrangement information generation unit  15 . 
     The extraction timing in a pilot channel extraction unit  14  is generated based on the extracted pilot channel arrangement information, which is the same as the previous embodiment. 
     According to the fourth embodiment, it is unnecessary to notify the pilot arrangement information to the reception side in advance. 
       FIG. 14  is a diagram depicting a pilot channel arrangement according to the fifth embodiment of the present invention. 
     In the configuration example of this embodiment, a continuous pilot channel arrangement is disposed adaptively in a plurality of locations. 
       FIG. 15 ,  FIG. 16  and  FIG. 17  are possible configuration examples to be a reference to dispose continuous pilot channel arrangement adaptively in a plurality of locations. 
     In other words,  FIG. 15  is a configuration example for limiting the number of pilots to be densely inserted depending on the information volume to be transmitted of such as a data channel (communication rate) in a transmitter at the transmission side. 
     If priority is assigned to the transmission of the data channel, the state of the data signal which is transmitted by a data and control signal generator  4  is notified to a pilot channel arrangement information generation unit  1 . Because of this, the pilot channel arrangement information generation unit  1  judges the communication rate, and generates arrangement information with which pilot signals can be densely (continuously) inserted. A pilot channel generation unit  2  transmits a pilot to a multiplexing circuit  3  at a pilot insertion timing based on the pilot arrangement information. 
     Subsequent processing in  FIG. 15  is the same as the previous embodiment. 
       FIG. 16  is a diagram depicting an example of limiting the number of pilots to be densely inserted depending on the information volume to be transmitted by such as a data channel (communication rate) in the transmitter at the transmission side. 
     This is an example of controlling the pilot arrangement depending on the state of throughput. In other words, in the transmission side device, cell and sector throughputs are monitored using a device, which is not illustrated. During this monitoring, if the corresponding throughput deteriorates and becomes smaller than a threshold, the pilot channel arrangement information generation unit  1  is controlled to make the pilot arrangement dense. The pilot channel arrangement information generation unit  1  inserts the pilot channel arrangement information in which the pilot arrangement is made to be dense, into the control channel, and transmits it to the reception side, just like the embodiment depicted in  FIG. 12 . Thereby the continuous pilot channel arrangement can be adaptively changed. 
       FIG. 17  is an example of controlling pilot signal arrangement according to the state of delay dispersion. In other words, in the transmission side device, delay dispersion is monitored using a device, which is not illustrated. During this monitoring, if delay dispersion exceeds a threshold, estimation accuracy for the pilot arrangement positions deteriorates, so the pilot channel arrangement information generation unit  1  is controlled to make the pilot arrangement dense. The pilot channel arrangement information generation unit  1  also inserts the pilot channel arrangement information in which the pilot arrangement is made dense, into the control channel, and transmits it to the reception side, just like the embodiment shown in  FIG. 16 . 
       FIG. 18  is a graph depicting the effect of the present invention. By the present invention, the pilot channels are inserted continuously into the reference insertion positions (reference positions determined by a standard) so that arrangement of the pilot channels become dense. Thereby as  FIG. 18  depicts, deterioration of estimated SIR decreases as the pilot insertion interval decreases (that is, as the pilot insertion becomes more dense), even if deterioration of SIR increases. 
     In  FIG. 18 , I is the case when the insertion interval is 1, II is the case when the insertion interval is 3, and III is the case when the insertion interval is 6, so deterioration of the estimated SIR increases as the insertion interval increases. In other words, according to the present invention, the drop in accuracy of interference power can be suppressed even more as the pilot signal insertion interval decreases.