JP2009182801A - Radio transmitter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the power waste of a terminal by avoiding the transmission of excessive reference signals from a radio terminal. <P>SOLUTION: The radio transmitter provided in a radio terminal for communicating with a base station has a reference signal transmitting part 101 for periodically transmitting a reference signal for measuring a channel state between the base station and the radio terminal to the base station at intervals of a first period, a timing control signal detecting part 106 for detecting a timing control signal for controlling transmission timing of the radio terminal, which comes from the base station, at intervals of a second period longer than at least the first period, a transmission data detecting part 107 for detecting the presence of transmission data, and a transmission stopping part 108 for stopping transmitting the reference signal when the timing control signal is detected and the transmission data is not detected. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a radio transmitter provided in a radio terminal that communicates with a base station, and more particularly to a technique for transmitting a reference signal for measuring a channel state between a base station and a radio terminal.

  In general, in a cellular radio communication system, a base station allocates resources (referred to as communication resources) related to radio communication. Communication resources in a cellular radio communication system are resources that can be used for communication between a base station and a radio terminal (hereinafter simply referred to as a terminal), and examples include time resources, frequency resources, and signal power resources.

  These communication resources are generally allocated based on the state of a transmission path (hereinafter referred to as a channel) between the base station and the terminal. Specifically, for allocation of time resources and frequency resources, a resource having a good channel state among resources that can be allocated, that is, a resource that can have a higher signal-to-noise / interference power ratio (SINR) is allocated to each terminal. As a result, the throughput of each terminal can be increased, and as a result, the throughput of the wireless communication system can be improved.

  For signal power resources, appropriate resources are assigned to each terminal to achieve the desired SINR based on the measured channel conditions. Accordingly, each terminal can achieve a desired SINR, and interference given to other terminals can be efficiently reduced.

  Thus, when allocating communication resources, it is necessary to measure the channel state between the base station and the terminal. The measurement of the channel state is generally performed by transmitting and receiving a known signal called a reference signal using a target channel. For example, in a cellular radio communication system employing frequency division duplex (FDD), when measuring an uplink channel state, a terminal transmits a reference signal and a base station receives it. The base station measures the uplink channel state by observing the reference signal thus received.

  The uplink channel state measurement result measured in this way can be used for timing detection, that is, detection of transmission timing error as described below, in addition to communication resource allocation.

  In general, in a cellular radio communication system, a plurality of terminals are connected to one base station. In order to improve the reception performance at the base station, it is desirable that the signals coming from each terminal to the base station have the same timing at the base station end. In a cellular radio communication system, in order to align the timing of incoming signals from each terminal at the base station end, that is, to perform timing synchronization between the base station and the terminal, as a method of adjusting the transmission timing of the terminal, The following processing is known.

  First, the base station issues an instruction to the terminal and causes the terminal to transmit a reference signal. The base station receives the reference signal transmitted from the terminal and analyzes it to measure the uplink channel state, and the transmission timing of the terminal (more specifically, the deviation of the transmission timing from the desired value) Is detected. The base station generates a timing control signal based on the transmission timing thus detected and notifies the terminal. The terminal that has received the timing control signal adjusts the transmission timing of the signal to be transmitted. For example, when the timing control signal instructs to advance the transmission timing by 10 μsec, a process of advancing the transmission timing by 10 μsec is performed. In this way, it is possible to align the timing at the base station end of signals arriving at the base station from a plurality of terminals.

  The deviation of the timing of the incoming signal from the terminal at the base station end is mainly caused by two factors. The first is that the clocks of the base station and the terminal do not completely match, so the timing gradually shifts. The second is that the distance between the terminal and the base station increases or decreases as the terminal moves. The propagation delay amount increases or decreases according to the above. Since both factors change with time, the adjustment of the transmission timing need not be performed only once at the start of communication, but needs to be repeated with the passage of time. Therefore, it is necessary to transmit the timing control signal repeatedly with time. Furthermore, in order to implement this, it is necessary to detect a timing shift using the reference signal, so that the terminal needs to repeatedly transmit the reference signal as time elapses.

  As a specific example of such a method, in Non-Patent Document 1, a wireless terminal continues to transmit a reference signal at a period instructed from a base station, and transmits a timing control signal as necessary at intervals of at least 0.5 sec. It has been shown.

  Non-Patent Document 2 shows a method of continuously transmitting a reference signal for a period instructed by a base station at a period instructed by the base station. That is, Non-Patent Document 2 discloses a method in which a terminal continues to transmit a reference signal at a constant period when detecting a timing shift for generating a timing control signal as in Non-Patent Document 1.

  Non-Patent Document 3 shows a method in which a terminal continues to transmit a reference signal for a specified period at a certain period when detecting a timing shift for generating a timing control signal as in Non-Patent Document 1.

  The reference signals transmitted by the transmission methods shown in these documents 1 to 3 are used not only for timing detection but also for allocation of communication resources. Thus, it is assumed that the base station instructs the terminal to specify a period of the order of several milliseconds to several hundred milliseconds as the reference signal transmission period. This period can be said to be a suitable value for communication resource allocation.

However, for example, when there is no data to be transmitted to a certain terminal, that is, when it is not necessary to use communication resources in the uplink, the reference signal transmitted from the terminal is not used for allocation of communication resources, and timing It will be used only for detection. This situation is excessive considering that the timing control signal is transmitted only at a minimum interval of 0.5 sec. As a result of excessive transmission of the reference signal, power is wasted at the terminal.
□ MCC Support “Approved Report of 3GPP TSG RAN WG1 # 47bis v2.0.0, (Sorrento, Italy, 15-19 January, 2007), 3GP, [Search January 15, 2008], Internet <URL; http: / /www.3gpp.org/ftp/tsg_ran/WG1_RL1/TSGR1_47bis/Report/R1-071245.zip> Nokia Siemens Networks, Nokia “UL Sounding Arrangement”, [online], 3GPP (publisher), [Search January 15, 2008], Internet <URL; http://www.3gpp.org/ftp/tsg_ran/ WG1_RL1 / TSGR1_50 / Docs / R1-073642.zip> MCC Support “Draft Report of 3GPP TSG RAN WG1 # 50 v0.1.0 (Athens, Greece, 20-24 August, 2007)”, [online], 3GPP (publisher), [Search January 15, 2008], Internet <URL; http: //www.3gpp.org/ftp/tsg_ran/WG1_RL1/TSGR1_50/Report/Draft_ReportWG1%2350_v010.zip (Draft_ReportWG1 # 50_v010.doc)>

  As described above, in the conventional techniques as shown in Non-Patent Documents 1 to 3, even when there is no transmission data in the wireless terminal, the reference signal is transmitted at a very small period compared to the timing control signal interval. Sent to the base station. Therefore, there is a problem in that power is wasted because an excessive reference signal is transmitted in the terminal, and as a result, communication possible time and standby time are shortened.

  An object of the present invention is to suppress the waste of power of a terminal by avoiding transmission of an excessive reference signal from a wireless terminal.

  According to an aspect of the present invention, a wireless transmitter provided in a wireless terminal that communicates with a base station, the reference signal for measuring a channel state between the base station and the wireless terminal is provided. A reference signal transmission unit that periodically transmits to the base station at intervals of a first period, and a transmission timing of the wireless terminal that arrives from the base station with a period longer than a second period longer than the first period. A timing control signal detecting unit for detecting a timing control signal for controlling, a transmission data detecting unit for detecting presence / absence of transmission data to be transmitted from the wireless terminal to the base station, the timing control signal is detected, and There is provided a wireless transmitter including a transmission stop unit that stops transmission of the reference signal when the transmission data is not detected.

  According to the present invention, it is possible to avoid wasting the power of the terminal by not transmitting an excessive reference signal from the wireless terminal, thereby extending the communicable time and standby time of the terminal.

Hereinafter, the present embodiment will be described in detail with reference to the drawings.
(First embodiment)
As shown in FIG. 1, the radio transmitter according to the first embodiment of the present invention includes a reference signal transmission unit 101, a radio transmission unit 102, a transmission antenna 103, a reception antenna 104, a radio reception unit 105, and a timing control signal detection. Unit 106, transmission data detection unit 107, and transmission stop unit 108. The wireless transmitter in FIG. 1 is provided in a wireless terminal (hereinafter simply referred to as a terminal) that communicates with a base station (not shown). FIG. 1 shows only the configuration related to the transmission of the reference signal and the reception of the timing control signal, and the configuration related to the transmission / reception of the data signal is omitted.

  The reference signal transmission unit 101 periodically transmits a reference signal for measuring a channel state between the base station and the terminal at intervals of the first period. That is, the reference signal transmission unit 101 generates a reference signal to be transmitted, and transmits the reference signal from the transmission antenna 103 to the base station via the wireless transmission unit 102. The wireless transmission unit 102 includes, for example, a digital-analog converter (DAC) that converts a digital signal that is a reference signal into an analog signal, a frequency converter that up-converts the reference signal, a power amplifier, and the like. Frequency) signal and supplied to the transmitting antenna 103.

  On the other hand, a timing control signal for controlling the transmission timing of the wireless terminal that arrives at the terminal with at least a second period from the base station (in other words, a timing control signal for timing synchronization between the base station and the terminal) ) Is detected by the timing control signal detection unit 106 via the reception antenna 104 and the wireless reception unit 105. The detection result of the timing control signal detection unit 106 is given to the transmission stop unit 108.

  The wireless reception unit 105 includes, for example, a low noise amplifier (LNA) that amplifies an RF reception signal including a timing control signal from the reception antenna 104, a frequency converter that downconverts the amplified RF reception signal, and a downconverted reception signal. And an analog-digital converter (ADC) for converting an analog signal into a digital signal.

  The transmission data detection unit 107 detects the presence / absence of data to be transmitted from the terminal to the base station (hereinafter referred to as transmission data). The detection result of the transmission data detection unit 107 is given to the transmission stop unit 108.

  When the timing control signal detector 106 detects the timing control signal and the transmission data detector 107 detects that there is no transmission data, the transmission stop unit 108 transmits the reference signal by the reference signal transmitter 101. Is configured to stop.

  In this way, when there is no transmission data, it is possible to stop transmission of the reference signal transmitted after the timing control signal is detected. That is, it is possible to avoid waste of power in the terminal by not transmitting an excessive reference signal. As a result, the communicable time and standby time of the terminal can be extended.

  Next, the first embodiment will be described in more detail with reference to FIGS. 2 to 4 show the exchange of signals between the base station and the terminal, and the meanings of the three types of arrows are as shown in the figure.

  For example, the reference signal transmission unit 101 periodically transmits a reference signal in a period instructed by the base station at an interval of a first period instructed by a base station (not shown). As an example, in the case of LTE (Long Term Evolution), which is considered as one of high-speed data communication specifications in 3GPP (Third Generation Partnership Project), the reference signal is SRS ( Sounding Reference Signal). SRS is a known signal used for channel estimation in LTE.

  On the other hand, a base station (not shown) detects a timing shift using the reference signal transmitted from the terminal, and transmits a timing control signal to the terminal with an interval of at least a second period based on the detection result. For example, as shown in FIG. 2, the timing control signal 201 and the timing control signal 202 are transmitted with an interval equal to or longer than the second period, and the timing control signal 202 and the timing control signal 203 are also transmitted in the second period. It is transmitted with the above interval. Here, the second period is set longer than the first period.

  When transmission of a reference signal is assigned as shown in FIG. 2, timing detection for generating the timing control signal 201 in the base station is performed using one or a plurality of reference signals sent before that. . Similarly, timing detection for generating the timing control signal 202 is performed using one or more reference signals sent before that. That is, in the example shown in FIG. 2, it can be seen that the reference signal transmitted in the section 204 is not used for timing detection.

  When there is transmission data (data to be transmitted) in the terminal, the reference signal transmitted in the section 204 is used to allocate communication resources for communication with the base station to the terminal. However, even when there is no transmission data in the terminal, it is not necessary to allocate communication resources to the terminal, so that the transmission of the reference signal in the section 204 is wasted. However, the transmission data here means a signal that is not known between the terminal and the base station, and includes, for example, a control signal.

  As described above, the reference signal transmitted in the section 204 in FIG. 2 is not used for timing detection or communication resource allocation when there is no transmission data in the terminal. Therefore, in the present embodiment, when the timing control signal is detected by the timing control signal detection unit 106, the presence or absence of transmission data is detected by the transmission data detection unit 107, the timing control signal is detected, and the transmission data is not detected. Stops the operation of the reference signal transmission unit 101, that is, stops the transmission of the reference signal.

  For example, when the transmission data is not detected when the timing control signal 201 is received in the example of FIG. 2, the operation of the reference signal transmission unit 101 is stopped, and the reference signal in the section 301 as shown in FIG. Stop sending. After that, even when periodic transmission is started again from the reference signal 205 according to an instruction from the base station, if transmission data is not detected when the timing control signal 202 is received, the reference signal transmission unit 101 is stopped, and the reference signal in the section 303 is stopped as shown in FIG.

  On the other hand, when transmission data is detected when the timing control signal 201 is received, the reference signal transmission unit 101 is not stopped. Accordingly, the reference signal in the section 401 is transmitted as shown in FIG.

  As described above, according to the first embodiment, it is possible to stop the transmission of the surplus reference signal as in the section 204 in FIG. 2 as shown in FIG. 3, thereby avoiding the waste of power at the terminal. Can do. As a result, the communicable time and standby time of the terminal can be extended.

(Second Embodiment)
Next, a second embodiment of the present invention will be described. FIG. 5 shows a wireless transmitter according to the second embodiment, and a transmission resuming unit 109 is added to the wireless transmitter according to the first embodiment shown in FIG. The transmission resuming unit 109 is configured to resume the operation of the reference signal transmitting unit 101 after a lapse of a third period after the operation of the reference signal transmitting unit 101 is stopped by the transmission stopping unit 108.

  As described above, in the second embodiment, the transmission restarting unit 109 is further provided, so that after the operation of the reference signal transmitting unit 101 is stopped after receiving a certain timing control signal, the reference signal is transmitted before the next timing control signal. Transmission can be resumed. Thereby, it is possible to reliably transmit a reference signal necessary for timing detection in the base station, and to obtain an effect that timing detection can be performed with high accuracy.

  Next, the second embodiment will be described in more detail with reference to FIGS. 6 to 9 show exchange of signals between the base station and the terminal, and the meanings of the three types of arrows are as shown in the figure.

  In the second embodiment, operations other than the transmission resuming unit 109 are basically the same as those in the first embodiment. Here, consider a case where the reference signal repetitive transmission period is longer than the second period as shown in FIG. If transmission data is not detected when the terminal receives the timing control signal 601, it is desirable to stop the subsequent reference signal from the viewpoint of avoiding power consumption of the terminal. On the other hand, after the second period has elapsed from the timing control signal 601, the next timing control signal may arrive.

  In order to generate a timing control signal in the base station, it is necessary to detect timing, that is, to detect a timing shift. Therefore, the terminal needs to transmit a reference signal before the base station performs timing detection. As described above, the timing shift changes with time. Therefore, it is easier to improve the accuracy of timing detection at the base station by using a reference signal transmitted as recently as possible. For this reason, if the terminal stops transmitting the reference signal for the second period or more after detecting the timing control signal 601, the base station transmits the reference signal transmitted before transmitting the timing control signal 601. It is necessary to detect a timing shift by using it, and the detection accuracy may deteriorate. In order to avoid this, it can be said that the period during which the transmission of the reference signal is stopped is preferably shorter than the second period.

  Therefore, a third period shorter than the second period is set as shown in FIG. 7, and the operation of the reference signal transmission unit 101 is resumed after the third period has elapsed. More precisely, the third period is set to be equal to or less than the value obtained by subtracting the first period from the second period. For example, when the third period is set as shown in FIG. 7, the reference signal can be transmitted once at the end of the second period. Therefore, when the base station generates a timing control signal immediately after the second period elapses, at least one of the timings can be detected using the latest reference signal.

  According to the example of FIG. 7, the base station uses the two most recent reference signals when generating the timing control signal 702, and the three most recent reference signals when generating the timing control signal 703. Timing deviation can be detected.

  As described above, according to the second embodiment, it is possible to improve the accuracy of the timing shift detection performed in the base station by resuming the transmission of the reference signal before the second interval elapses. It is done.

  Further, as shown in FIG. 8, when the third period 801 shorter than the third period 704 shown in FIG. 7 is used, the number of reference signals transmitted until the second period elapses is increased. As a result, it is possible to further improve the accuracy of timing shift detection performed in the base station. However, in this case, since the number of reference signals transmitted increases, the effect of extending the communication possible time and standby time of the terminal decreases. Accordingly, the third period may be set shorter if the timing shift detection accuracy is important, and the third period may be set longer than the second period if the terminal communicable time and standby time are important.

  As is clear, for example, when there is transmission data when the timing control signal 601 is received, the reference signal transmission unit 101 is not stopped. Therefore, the reference signal in the second period 901 is transmitted as shown in FIG.

(Third embodiment)
Next, a third embodiment of the present invention will be described. The wireless transmitter according to the third embodiment basically has the configuration shown in FIG. 5 as in the second embodiment, but the operation of the transmission resuming unit 109 is different from that in the second embodiment. That is, in the third embodiment, after the operation of the reference signal transmission unit 101 is stopped by the transmission stop unit 108, after a value obtained by subtracting the fourth period from the second period has elapsed, the transmission resumption unit 109 transmits the reference signal. The operation of the unit 101 is resumed.

  As described above, the third embodiment is different from the second embodiment in the method of setting the period from when the transmission of the reference signal from the reference signal transmission unit 101 is stopped to when the transmission is resumed by the transmission resuming unit 109. In other words, in the second embodiment, the period from the stop of transmission of the reference signal to the restart is represented as the third period, whereas in the third embodiment, the period obtained by subtracting the fourth period from the second period. The period is from the stop of transmission of the reference signal to the restart.

  According to the third embodiment, the same effect as the second embodiment can be obtained. That is, after the operation of the reference signal transmission unit 101 is stopped after receiving a certain timing control signal, the reference signal can be restarted before the next timing control signal. This will be described with reference to FIGS.

  For example, when the third period 704 is set as shown in FIG. 7, the fourth period 1101 is set as shown in FIG. 12 as a value obtained by subtracting the third period 704 from the second period. Similarly, in the case of FIG. 12 and FIG. 12, one reference signal can be transmitted before the second period elapses. Further, for example, when the third period 801 is set as shown in FIG. 8, the fourth period 1201 is set as a value obtained by subtracting the third period 801 from the second period as shown in FIG. Similarly, in the case of FIG. 8 and FIG. 12, two reference signals can be transmitted before the second period elapses. In addition, as is apparent from FIG. 6 and FIG. 9, if there is transmission data when the timing control signal 1001 of FIG. 10 is received, the second period as shown in FIG. A reference signal 1302 is transmitted.

  As described above, in the third embodiment, similarly to the second embodiment, it is possible to reliably transmit the reference signal necessary for timing detection at the base station, and to obtain the effect that the timing detection can be performed with high accuracy. It is done. Further, according to the third embodiment, in addition to this, there is an effect that the setting of the period can be further simplified.

Next, effects unique to the third embodiment will be described with reference to FIGS. 7 and 12.
As described with reference to FIG. 7, in the second embodiment, the reference signal can be transmitted before the second period elapses by restarting the transmission of the reference signal after the third period elapses. At this time, the number of reference signals that can be transmitted is proportional to the value obtained by subtracting the third period from the second period. In the present embodiment, as shown in FIG. 12, the period expressed as a value obtained by subtracting the third period from the second period in FIG. 7 is expressed as the fourth period. In other words, it can be said that the fourth period is substantially equivalent to a value obtained by subtracting the third period from the second period.

  When the number of reference signals to be transmitted is given before the second period elapses, when the transmission resuming unit 109 is operated by setting the third period, the third period is set in accordance with the value of the second period. It is necessary to increase or decrease the value of, but there is an effect that the fourth period does not need to be changed even if the value of the second period changes. In addition, when the second period is very long compared to the first period, the value of the fourth period is much smaller than the value of the third period, so that the control used to set the period is used. There is also an effect that the number of bits of information can be reduced.

(Fourth embodiment)
Next, a fourth embodiment of the present invention will be described. FIG. 14 shows a wireless transmitter according to the fourth embodiment, and the connection from the transmission data detection unit 107 to the transmission start unit 109 with respect to the wireless transmitter according to the second embodiment shown in FIG. Has been added. In the fourth embodiment, the operation of the transmission resuming unit 109 is different from that of the second embodiment, and the transmission starting unit 109 has passed the third period after the transmission of the reference signal is stopped by the transmission stopping unit 108. Alternatively, the operation of the reference signal transmission unit 101 is resumed when the transmission data detection unit 107 detects that there is transmission data.

  That is, in the transmission resuming unit 109 in the fourth embodiment, a condition that transmission data is detected by the transmission data detecting unit 107 is added as a transmission resuming condition. Thereby, when data is to be transmitted before the third period elapses, the transmission of the reference signal can be resumed along with this.

  The base station can allocate communication resources more accurately by performing communication resource allocation using the reference signal whose transmission has been resumed. As a result, it is possible to improve the throughput of communication from the terminal to the base station.

Hereinafter, the fourth embodiment will be described in more detail with reference to FIGS. 9 and 15.
As described with reference to FIG. 9, in the second embodiment, when transmission data is not detected when the timing control signal 903 is received, the reference signal is not transmitted during the third period 901. Further, when transmission data is not detected when the timing control signal 904 is received, the reference signal is not transmitted during the third period 905.

  On the other hand, in the fourth embodiment, when it is detected that there is transmission data even within the third period, the transmission of the reference signal is resumed. For example, as shown in FIG. 15, when it is detected that there is transmission data at timing 1501, transmission of the reference signal is resumed even within the third period. By doing in this way, the measurement precision of the channel state used when a base station allocates the communication resource for transmitting transmission data to this terminal can be improved, and a communication resource can be allocated more accurately. As a result, it is possible to improve the throughput of communication from the terminal to the base station.

(Fifth embodiment)
Next, a fifth embodiment of the present invention will be described. The wireless transmitter according to the fifth embodiment basically has the configuration shown in FIG. 14 as in the fourth embodiment, and the operation of the transmission resuming unit 109 is different from that of the third embodiment. That is, in the fifth embodiment, after the operation of the reference signal transmission unit 101 is stopped by the transmission stop unit 108, a value obtained by subtracting the fourth period from the second period has elapsed, or the transmission data detection unit 107 When transmission data is detected by, the transmission resuming unit 109 resumes the operation of the reference signal transmission unit 101.

  As described above, in the fifth embodiment, the operation of the transmission resuming unit 109 is different from that in the third embodiment. That is, in the transmission resuming unit 109 in the fifth embodiment, a condition is added as a condition for resuming transmission when the data detection unit detects that there is transmission data. The difference in operation between the fifth embodiment and the third embodiment is basically the same as the difference in operation between the fourth embodiment and the second embodiment. Furthermore, the specific effect obtained by the fifth embodiment as compared with the third embodiment is basically the same as the specific effect obtained by the fourth embodiment compared with the second embodiment. is there.

  As described above, in the transmission resuming unit 109 in the fifth embodiment, the condition that the transmission data is detected by the data detecting unit 107 is added as the transmission resuming condition. When data is to be transmitted before the period of the value obtained by subtracting four periods elapses, the transmission of the reference signal can be resumed together with this. In the base station, communication resources can be allocated with higher accuracy by performing communication resource allocation using the reference signal whose transmission has been resumed in this way. As a result, it is possible to improve the throughput of communication from the terminal to the base station.

Next, the fifth embodiment will be described in more detail with reference to FIGS.
As described with reference to FIG. 12, in the second embodiment, when transmission data is not detected when the timing control signal 1202 is received, a period of a value obtained by subtracting the fourth period 1201 from the second period. The reference signal is not transmitted. If transmission data is not detected when the timing control signal 1203 is received, the reference signal is not transmitted during a period obtained by subtracting the fourth period 1204 from the second period.

  On the other hand, in the fifth embodiment, transmission of the reference signal is resumed when it is detected that there is transmission data even within the period of the value obtained by subtracting the fourth period from the second period. For example, as shown in FIG. 16, when it is detected that there is transmission data at the timing 1601, the transmission of the reference signal is resumed even within the period of the value obtained by subtracting the fourth period from the second period.

  As described above, according to the fifth embodiment, it is possible to improve the measurement accuracy of the channel state used when the base station allocates the communication resource for transmitting the transmission data to the terminal, and the communication resource can be improved more accurately. Can be assigned. As a result, it is possible to improve the throughput of communication from the terminal to the base station.

(Calculation method for the 4th period)
As described in the third embodiment, when the transmission of the reference signal is resumed only before the fourth period elapses before the second period elapses, the base station can transmit the reference signal necessary for timing detection, The effect that the timing detection can be performed with high accuracy is obtained.

  At this time, as the fourth period is set longer, the accuracy of timing detection is improved, but the power consumption of the terminal is increased. For this reason, it is desirable to set the fourth period to a minimum length necessary for obtaining desired timing detection accuracy.

  In general, in order to detect a timing shift with an accuracy of ΔT seconds, a signal having a bandwidth of 1 / ΔT [Hz], which is the inverse of ΔT, is required. For example, in order to detect a timing shift with an accuracy of 1 [μsec], a signal having a bandwidth of 1 [MHz] is required. For example, when the signal band for one reference signal is only 500 [kHz], if two reference signals are transmitted at different transmission frequencies, the signal becomes 1000 [kHz] = 1 [MHz] in total. By using these to detect a timing shift, it is possible to achieve an accuracy of 1 [μsec].

  Using this property, the signal bandwidth W [Hz] of the reference signal, the first period T1 [sec] that is the reference signal transmission cycle, and the transmission timing control accuracy ΔT [sec] by the timing control signal are used. Thus, the minimum value of the fourth period necessary for obtaining the detection accuracy of ΔT is larger as T1 [sec] is larger, and is smaller as W [Hz] and ΔT [sec] is larger as follows. Is calculated as follows.

First, the signal bandwidth necessary to obtain the detection accuracy ΔT is expressed as 1 / ΔT. On the other hand, since the bandwidth per reference signal is W, the number of reference signals necessary to obtain a bandwidth of 1 / ΔT is
(1 / ΔT) / W = (1 / (ΔT × W)) (1)
It can be expressed.

However, the value of Formula (1) may be a decimal number. To express the number of reference signals necessary to obtain a bandwidth of 1 / ΔT as an integer, use ceil (·), which is a function that returns the smallest integer that does not exceed the value of the argument.
ceil (1 / (ΔT × W)) (2)
And it is sufficient.

Since the period required to send one reference signal is T1, the fourth period is used in order to transmit the number of reference signals represented by Equation (2).
T1 × ceil (1 / (ΔT × W)) (3)
Should be set.

  Next, the calculation method for the fourth period will be described using a specific example with reference to FIGS. 17 to 20 show the signal exchange between the base station and the terminal on the upper side of the figure, and the lower side shows how the center frequency of the reference signal changes with time. Three types of arrows and the reference signal are shown. The meaning of the square representing is as shown in the figure. Here, the control accuracy required by the timing control signal will be described as an example where ΔT = 0.52 [μsec]. In this case, a signal bandwidth of about 1.92 [MHz] is required for the reference signal in order to detect a timing shift with a desired accuracy. For example, when the bandwidth of the reference signal is 1.44 [MHz], the fourth period is as follows.

T1 × ceil (1 / (0.52 × 10 ⁻⁶ × 1.44 × 10 ⁶ ))
= T1 * ceil (1.33 ...)
= T1x2 (4)
When the fourth period calculated by Equation (4) is used, two reference signals are transmitted within the fourth period as shown in FIG. 17, and when these are combined, a desired signal bandwidth can be achieved. it can.

Further, when the bandwidth of the reference signal is, for example, 0.72 [MHz], the fourth period is as follows.
T1 × ceil (1 / (0.52 × 10 ⁻⁶ × 0.72 × 10 ⁶ ))
= T1 x ceil (2.67 ...)
= T1x3 (5)
When the fourth period calculated by Equation (5) is used, as shown in FIG. 18, three reference signals are transmitted within the fourth period, and when these three reference signals are combined, a desired signal bandwidth is obtained. Can be achieved.

  17 and 18 show an example in which the center frequency of the reference signal shifts in one direction with time. On the other hand, when the center frequency of the reference signal changes irregularly with time as shown in FIG. 19, the calculation method for the fourth period is the same. However, when the center frequency of the reference signal changes irregularly as shown in FIG. 19, the bands of several reference signals that are temporally continuous may overlap.

  For example, since the reference signal 2001 and the reference signal 2002 shown in FIG. 20 have the same center frequency, even if these reference signals 2001 and 2002 are combined, the signal bandwidth is only one. In such a case, a value obtained by adding a margin to the value calculated by the above method may be used as the fourth period. In the example of FIG. 20, an example in which T1 is added as a margin is shown. By doing so, it is possible to obtain a reference signal having a desired bandwidth even in the fourth period 2003 including the reference signals 2001 and 2002 in FIG.

(Expansion to the third period)
As is apparent from the description of the third embodiment, the third period is basically equivalent to the value obtained by subtracting the fourth period from the second period. Therefore, if the value calculated by subtracting the value calculated by the above calculation method from the second period is used as the third period, the same effect can be obtained.

(Method for setting the third and fourth periods)
(1) How the base station determines
The values instructed from the base station may be used for the third period and the fourth period described so far. In this way, the period can be controlled by the base station. In instructing the third period and the fourth period, for example, the values of the third period and the fourth period may be transmitted to the terminal and notified using a dedicated control signal. Also, for example, as shown in FIGS. 21 and 22, information (third period information and fourth period information) representing values of the third period and the fourth period may be transmitted to the terminal as part of the timing control signal. Good. In the examples of FIGS. 21 and 22, the main component of the timing control signal is the timing error information, and the third period information and the fourth period information are added after the timing error information.

(2) Method to determine in advance
A value determined in advance may be used for the third period and the fourth period. For example, the values of the third period and the fourth period may be determined and set in advance as the specifications of the wireless communication system. By doing in this way, the process which notifies separately the information which shows a 3rd period and a 4th period, the process which calculates | requires a 3rd period and a 4th period by calculation, etc. can be eliminated, and a 3rd period and a 4th period Is easier to set.

  Note that the present invention is not limited to the above-described embodiments as they are, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. Moreover, various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the above embodiments. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over a plurality of different embodiments may be appropriately combined.

Block diagram showing the transmitter of the first embodiment The figure which shows exchange of the signal between the base station and terminal in 1st Embodiment The figure which shows exchange of the signal between the base station and terminal in 1st Embodiment The figure which shows exchange of the signal between the base station and terminal in 1st Embodiment Block diagram showing transmitters according to second and third embodiments The figure which shows exchange of the signal between the base station and terminal in 2nd Embodiment The figure which shows exchange of the signal between the base station and terminal in 2nd Embodiment The figure which shows exchange of the signal between the base station and terminal in 2nd Embodiment The figure which shows exchange of the signal between the base station and terminal in 2nd Embodiment The figure which shows the exchange of the signal between the base station and terminal in 3rd Embodiment. The figure which shows the exchange of the signal between the base station and terminal in 3rd Embodiment. The figure which shows the exchange of the signal between the base station and terminal in 3rd Embodiment. The figure which shows the exchange of the signal between the base station and terminal in 3rd Embodiment. Block diagram showing transmitters according to fourth and fifth embodiments The figure which shows the exchange of the signal between the base station and terminal in 4th Embodiment The figure which shows the exchange of the signal between the base station and terminal in 5th Embodiment The figure explaining the calculation method of the 4th period The figure explaining the calculation method of the 4th period The figure explaining the calculation method of the 4th period The figure explaining the calculation method of the 4th period The figure which shows the example of the timing control signal The figure which shows the example of the timing control signal

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 ... Reference signal transmission part 102 ... Radio transmission part 103 ... Transmission antenna 104 ... Reception antenna 105 ... Radio reception part 106 ... Timing control signal detection part 107 ... Transmission data detection Unit 108 ... transmission stop unit 109 ... transmission resumption unit

Claims (9)

In a wireless transmitter provided in a wireless terminal that communicates with a base station,
A reference signal transmission unit that periodically transmits a reference signal for measuring a channel state between the base station and the wireless terminal to the base station at an interval of a first period;
A timing control signal detector for detecting a timing control signal for controlling the transmission timing of the wireless terminal, which arrives from the base station after a period longer than a second period longer than the first period;
A transmission data detection unit for detecting presence or absence of transmission data to be transmitted from the wireless terminal to the base station;
A wireless transmitter comprising: a transmission stop unit that stops transmission of the reference signal when the timing control signal is detected and the transmission data is not detected.   The wireless transmission according to claim 1, further comprising a transmission resuming unit that resumes the transmission of the reference signal after a third period has elapsed after the transmission of the reference signal is stopped by the transmission stopping unit. Machine.   The third period is a value obtained by subtracting a fourth period from the second period, and further includes a transmission resuming unit that resumes the transmission of the reference signal after the third period has elapsed. Item 2. The wireless transmitter according to Item 1.   The transmission restarting unit restarts transmission of the reference signal by the reference signal transmitting unit even when the transmission data is detected by the transmission data detecting unit. The wireless transmitter according to item.   The fourth period is calculated so as to increase as the first period increases, and to decrease as the signal bandwidth of the reference signal and the control accuracy of the transmission timing by the timing control signal increase. The wireless transmitter according to claim 3. In the fourth period, the first period is T1, the signal bandwidth of the reference signal is W, and the transmission timing control accuracy ΔT by the timing control signal is used to calculate T1 × ceil (1 / (ΔT × W ))
Where ceil (•) represents a function that returns the smallest integer that does not exceed the value of the argument,
The wireless transmitter according to claim 3, wherein the wireless transmitter is calculated according to:   4. The radio transmitter according to claim 2, wherein a value instructed by the base station is used for the third period or the fourth period. 5.   The radio transmitter according to claim 7, wherein the third period or the fourth period is indicated as a part of the timing control signal.   4. The wireless transmitter according to claim 2, wherein a value determined in advance is used for the third period or the fourth period. 5.

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