KR20060003400A - Improved RF Repeater - Google Patents

Abstract

In the present invention, the downlink path transmitted from the AP to the access terminal (AT) and the uplink signal transmitted from the AT to the AP have the same frequency, and the TDD (Time Division) distinguishes the downlink and uplink signals according to time. In a RF repeater that can be used in a mobile communication network employing a duplex method and an orthogonal frequency division multiple access (OFDMA) multi-user access method, a TDD using a method for generating a switching timing signal for separating downlink and uplink signal paths and associated timing data The present invention also relates to a repeater automatic gain control method that enables the use of a conventional automatic gain control circuit.

The present invention provides a switching timing signal generation method using a TDD scheme and an OFDMA multi-user access scheme and separating downlink and uplink signals from the RF repeater of a mobile communication system including an AP, an AT, and an RF repeater. When the RF signal is transmitted from the AP to the RF repeater, branching a portion of the RF signal to the switching timing signal generation circuit of the RF repeater during internal amplification of the RF repeater; (b) reducing the frequency of the branched RF signal, performing A / D conversion, and then correlating in a correlator to find a start timing (start timing of a downlink signal) included in the signal; (c) detecting, by the correlator, a lower phase switching section (a section between the timing at which the downlink signal end ends and the uplink signal start timing) of a received signal using the detected start timing of the preamble and the AP standard; ; (d) the control unit generates a switching timing using the position data of the frame start timing and the lower phase switching section, and continuously transmits the switching timing of correcting the propagation delay value between the AP and the relay period to the RF switch of the RF repeater. Delivering; (e) the repeater controlling the switch based on the switching timing signal to separately transmit the downlink signal and the uplink signal; (f) correcting a switching timing error accumulated as a frequency precision error of the repeater while the repeater continuously controls the switch to distinguish and transmit the downlink signal and the uplink signal; (g) the lower phase switching interval according to the change of the frame start timing of the AP or the change of the up / down interval ratio of the AP while the repeater continuously controls the switch to distinguish and transmit the downlink signal and the uplink signal; It provides a switching timing signal generation method for separating the up, down signal in the RF repeater of a mobile communication network using a TDD method and OFDMA multi-user access method characterized in that it comprises the step of automatically modifying the switching timing by detecting a position change. .

In addition, the present invention, using the TDD scheme and OFDMA multi-user access scheme, and automatically control the down, upward gain in the RF repeater of a mobile communication system including an access point (AP), AT (Access Terminal) and RF repeater A method of detecting a preamble signal in a downlink signal, the method comprising: (a) detecting a preamble signal level in a downlink signal using frame start timing data calculated by the switching timing signal generation circuit and downlink signal level data received from an AP; (b) Automatically set the gain of the repeater downlink circuit to "(target level of preamble to be output from AT to AT)-(preamble level of AP received at repeater)" and then change the level of newly detected preamble. (C) maintaining the gain of the uplink circuit of the repeater, "(the level of the preamble output from the AP)-(the preamble level of the AP received from the repeater) + (relay reverse noise figure) + Automatically set to " correction value " and maintaining the set gain before the newly detected preamble level is changed; (d) continuously detecting the preamble level of the AP signal and automatically down and up the repeater if the level is changed. Automatically modifying the gain of the path circuit configuration, using the TDD scheme and the OFDMA multiuser access scheme. It provides automatic gain control method in a RF repeater of the same communication network.

According to the present invention, it is possible to effectively relay each signal by dividing the downlink signal and the uplink signal in the RF repeater itself of the mobile communication network using the TDD method and the OFDMA method, and to automate the installation and operation process. This makes it possible to use an RF repeater that has not been possible and significantly reduce the associated costs in use.

Description

Improved RF Repeater {AN IMPROVED RF REPEATER}

1 is a configuration diagram schematically showing the configuration of a conventional RF repeater of the FDD scheme.

2 is a configuration diagram schematically showing a configuration of a duplexer employed in a conventional FDD RF repeater.

3 is a view for explaining a positional relationship between an AP, a repeater, and an AT.

FIG. 4 illustrates a minimum pilot signal for each subchannel (frequency) even when no traffic is transmitted in the section “preamble” which is shown at the beginning of a downlink section and an actual section in the downlink section. FIG. 7 shows that a pilot signal is inserted at some frequencies and times. FIG.

Figure 5 is a schematic diagram showing the configuration of an RF repeater according to a preferred embodiment of the present invention.

6 is a configuration diagram schematically showing a configuration of a preamble used in an OFDM modulation system.

7 is a configuration diagram schematically showing a configuration of a correlation unit according to a preferred embodiment of the present invention.

FIG. 8 is a diagram illustrating an AP transmission section (= downlink signal duration) and an AP reception section (= uplink signal duration) within a frame in order to maintain frame synchronization between APs in a system using a TDD duplex scheme. Is a diagram for explaining that various sets are provided so that the ratio of time) can be changed.

9 illustrates the occurrence of a signal propagation delay between the AP and the repeater according to the present invention, illustrates the reduction phenomenon of the phase changeover section (indicated by TTG in the figure) at the repeater position due to the signal propagation delay, and the repeater. A diagram for explaining a problem that occurs when the reduction of the phase change section is not considered when generating a switching signal.

10 is a view for explaining a compensation method that can be implemented when the signal transmission delay value a between the AP and the repeater is correctly known.

11 is a view for explaining a compensation method that can be implemented even when the signal transmission delay value a between the AP and the repeater is not known according to the present invention.

12 is a view for explaining a compensation method including the switching delay time of the repeater switch in the compensation method that can be implemented even when the signal transmission delay value a between the AP and the repeater is not known.

<Description of main parts of reference numerals>

101: donor antenna 102: service antenna

103: first input stage amplifier 104: first band pass filter

106: first variable attenuator 107: first high output amplifier

108: downconversion section 109: A / D conversion section

110: correlation unit 111: control unit

113: second input stage amplifier 115: second band pass filter                 

121: second variable attenuator 123: second high power amplifier

SW1: first switch SW2: second switch

S1: AP switching period

S2: Repeater received signal when the propagation delay value between AP and AT is a

S3: Repeater switch operation when propagation delay value between AP and AT is a

S4: Repeater received signal when the propagation delay value between AP and AT is z (maximum)

S5: Repeater switch operation when the propagation delay value between AP and AT is z (maximum)

The present invention relates to an improved RF repeater. More particularly, the present invention is applicable to a mobile communication system using a TDD duplex method and an OFDMA multi-user access method in an AP and an AT, thereby enabling coverage to be extended at a low cost. It is about.

Due to the rapid development of mobile communication services, high quality communication services are also required in underground buildings, subways, tunnels, apartment complexes, etc., where mobile communication services were not completely provided to non-demand areas. However, carriers' huge investments in adding APs to these blind spots can deteriorate the operator's financial balance and lead to losses due to huge investment inefficiencies nationally. As a countermeasure, a repeater system that can improve communication quality and service range at low cost is being used, and the use of RF repeater is high among them. The RF repeater is a wireless type repeater that amplifies and transmits a radio signal between the AP and the AT.

1 is a configuration diagram schematically showing a configuration of a conventional frequency division duplexing (FDD) type RF repeater.

Referring to FIG. 1, the RF repeater of the FDD scheme employs two duplexers D1 and D2 to operate the AP downlink in the AT direction and the AT uplink in the AP direction.

That is, the signal having the frequency f1 transmitted from the AP is received through the donor antenna 1 and then transmitted from the first duplexer D1 to the first input stage amplifying unit 5 and then the first variable attenuation unit ( 4), the first level check section 9 detects the level of the signal to determine the forward gain for maintaining the forward signal output level at the predetermined level specified in the specification, and then through the first variable attenuation section 7 Adjust the output signal level. Next, the first high output amplifier 11 and the second duplexer D2 are output to the AT through the service antenna 2.

On the contrary, the signal having the f2 frequency transmitted from the AT is the second duplexer D2, the second input stage amplifier 15, the second attenuator 16, the second output level check unit 17, and the second high output amplification. It is output to the AP through the donor antenna 1 via the unit 18 and the first duplexer D1. In this process, the subsequent output signal level is adjusted through the second variable attenuation unit 17.

As shown in FIG. 2, the duplexers D1 and D2 employed in the FDD-type RF repeater include two ports (first port and second port) capable of passing only one type of frequency signal, and 2 It has a com port through which all kinds of frequencies can pass. In the FDD scheme, the uplink and downlink signals are distinguished from each other by using the duplexer so that the uplink and downlink signals can be accurately input and output through the uplink and downlink paths inside the repeater, respectively.

However, when the TDD (Time Division Duplexing) scheme is used in the AP and the AT, the duplexer can no longer be employed because the uplink and downlink signals are transmitted through the same frequency.

Therefore, instead of the duplexer, the switches SW1 and SW2 are used to output the downlink signal input to the donor antenna 1 to the service antenna 2, and the uplink signal input to the service antenna 2 is outputted. It should be output from the donor antenna 1, and at this time, the switches SW1 and SW2 should be switched to the uplink circuit and the downlink circuit of the repeater at an appropriate timing in accordance with the uplink and downlink signal transmission times.

In this case, the switches should be switched to accurately reflect the transmission time of the uplink signal and the downlink signal used between the AP and the AT, and the propagation delay time between the repeater and the AP. However, since the RF repeater is a wireless device and is not connected to the AP, a switching control signal must be generated by itself from a transmission signal of the AP. At this time, even if there is only one AP transmitting a signal to the RF repeater, a plurality of delayed signal paths are generated by reflection, diffraction, etc. of the signal. In addition, since a plurality of APs are installed and used in a region adjacent to each other in a real environment, a plurality of APs are basically present around the repeater, so that the signals received by the repeater donor antenna 1 are generally plural. (Eg, about 3-10). Therefore, it is very difficult for the repeater to distinguish only one AP signal and generate a switching control signal therefrom.

If the correct switching control signal is not generated, the service within the repeater coverage may be interrupted, and the repeater itself may fail due to the repeater's over-input, oscillation, etc. It is delivered to the AP receiving end, which can have a big adverse effect on the quality of service. Therefore, there is a need for an RF repeater capable of generating a stable switching control signal even in a situation where a large number of signals cause interference.

On the other hand, since the RF repeater is disposed between the AP and the AT to amplify and transmit the radio signals of the AP and the AT to an appropriate level, the signal level of the AP and the AT received from the repeater and the proper gain setting of the repeater are very important. It is equipment. Since the signal level of the AP and AT received in the repeater depends on the position and propagation environment of the repeater, the repeaters actually used should be used with appropriate gains set according to the situation. However, since the gain cannot be controlled remotely due to the characteristics of the RF repeater operated in a wireless manner, the repeater itself must automatically set the gain.

In order to automate the gain setting of the repeater, a level value at which the AP downlink signal is received by the repeater donor antenna 1 and a path loss value between the AP and the relay period are required. Conventionally, as shown in FIG. 1, the setting of the gain value of the repeater down path circuit (hereinafter, referred to as a down gain value) is performed by the control unit 19 checked by the first level check unit 9. Value ”and“ downlink required output value defined in repeater standard ”, and set the difference as a downlink circuit gain value, and adjust the downlink circuit gain through the first variable attenuator 7 at this time. . At this time, the downlink circuit gain value is corrected by the variable attenuation unit 7 in real time according to the change in the reception level value of the downlink signal.

However, the situation is different for TDD-OFDMA systems. As shown in FIG. 4, the output of the AP is radiated to the maximum value at the time when the preamble signal is transmitted in the downlink signal section. However, the AP output value changes abruptly below the preamble level depending on the presence of traffic in the remaining uplink sections, and the AP does not output at all in the remaining downlink switching section, uplink signal section, and up / down switching section (upward to downward signal section). It is not radiated.

In addition, since the downlink and uplink frequencies are the same, referring to FIG. 3, when an AT directly connected to an AP radiates an output near the repeater donor antenna 1, an abnormally high signal level may be received at the repeater donor antenna even in an uplink region. It may be. Therefore, in the downlink signal level measurement process for setting the repeater gain, it is difficult to set an appropriate repeater downlink gain by the conventional technology without the concept of the measurement time interval.

In addition, in the prior art, the path loss of the AP relay period is used to set the repeater up-gain value, which is calculated by comparing the AP transmit power and the repeater reception level measurement. In this case, the AP output value is assumed to be constant, and a value previously inputted into a repeater memory (not shown) is used. In fact, since the AP output value changes according to the traffic volume, an error occurs in the repeater gain setting by the change amount.

Therefore, the repeater that can be used in the TDD-OFDMA system has the downlink signal level only in the downlink section of the TDD system frame. A new automatic gain control method is required, including the concept of time intervals, that allows accurate gains to be set even when the output changes.

SUMMARY OF THE INVENTION The present invention has been made to solve the aforementioned problems of the prior art, and an object thereof is to provide an RF repeater suitable for operation in a mobile communication network employing a TDD duplex method and an OFDMA multi-user access method.

Another object of the present invention is to provide a method for generating up and down switching control signals at an accurate timing in an RF repeater applicable to a mobile communication network using a TDD duplex method and an OFDMA multi-user access method.

In addition, another object of the present invention is to improve the problem of the automatic gain setting method used in the conventional FDD repeater method can be applied to the RF repeater used in the mobile communication network using the TDD duplex method and OFDMA multi-user access method To present.

Other objects and advantages in addition to the above objects and advantages of the present invention will become apparent from the following detailed description and the accompanying drawings.

According to a first aspect of the present invention, the RF repeater of the present invention uses a TDD duplex method and an OFDMA multi-user access method in which the downlink signal transmitted from the AP to the AT and the uplink signal transmitted from the AT to the AP have the same frequency. Applicable to the system to be used, a first switch connected to the donor antenna (1) for selectively switching the uplink or downlink, and a first switch connected to the service antenna (2) to selectively switch the uplink or downlink 2 a switch, a correlator for detecting a start timing of a frame transmitted from the AP and a position of a lower phase switching section in the frame (meaning a start timing of the lower phase switching section), a frame start timing output from the correlator, and a lower phase Control to generate ON / OFF control signals of the first and second switches based on the switching section position, the frame size of the AP, and the like Contains wealth.

The correlator may include a buffer for temporarily temporarily storing the received AP signal, a correlator for calculating correlation values for AP downlink signal values stored in the buffer, and a correlation value output from the correlator. And a timing detector for detecting frame start timing at the corresponding time.

The correlation unit may further include a power calculator for calculating the power of a received signal received in a buffer, normalizing the correlation value output from the correlator to the power output from the power calculator, and then converting the result into the switching timing detector. It further includes a power normalizer to output.

In addition, the timing detector detects the frame start timing and attempts to detect the position of the lower phase switching section in the frame. After calculating the plurality of phase change interval candidate positions using the detected frame start timing and the frame specification of the AP, the internal signal levels of the phase change interval candidates are detected, and the phase change in which the detected signal level is smaller than a predetermined threshold is performed. Find the section.

In addition, another method of finding the lower phase change section is the autocorrelation method. All other algorithms are identical to the signal level detection method, but instead of detecting the signal level, the autocorrelator is used to calculate the autocorrelation value of the internal signal of the lower phase switching section. Since the correlator calculates a correlation value for white noise within the actual phase change interval, a very low correlation value is detected.

According to the second aspect of the present invention, an improved RF repeater applicable to an OFDM modulation scheme receives a AP signal and a downlink path for amplifying and outputting the signal to the AT side, and an uplink circuit for receiving and amplifying the AT signal and outputting it to the AP side. And a control unit 111 for controlling the overall operation of the RF repeater, a D / C unit 108 and an A / D converter 109 for reducing the frequency of the downlink signal and performing A / D conversion with the frame start timing. And a correlation unit 110 for detecting the position of the lower phase change section.

In the present invention using the concept of a time interval when checking the downlink signal level received from the AP for setting the repeater gain, during the preamble section of the level data of the downlink signal section measured by the correlation unit 110 and transmitted to the control unit The controller separates and extracts only the signal level of the signal and confirms it, and sets the gain of the downlink circuit to "(target level of the preamble to be output from the repeater to the AT)-(preamble level of the AP received by the repeater)", Set the gain of the upstream circuit to "(level of preamble output from AP)-(preamble level of AP received from repeater) + (reverse repeater noise figure) + correction value" before the level of the measured preamble changes. To maintain the AP output in the upward path section and the AP output value changes according to the traffic volume change. Allows you to set stable and accurate repeater gains.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings. 5 is a block diagram schematically illustrating a configuration of an RF repeater applicable to a system using a TDD scheme and an OFDMA multi-user access scheme according to an embodiment of the present invention. Here, the first switch (SW1) and the second switch (SW2) is initially set so that the signal proceeds in the downward path while the power of the RF repeater is turned on.

Ultra short amplification circuits and filters are needed to provide the appropriate downlink signal level for control circuits such as D / C, A / D, and correlation used for switching timing detection and automatic gain control of repeaters. In the present invention, the switch is basically connected to the downlink path when the repeater initial power is applied so that the amplifier and the filter in the first stage of the downlink path circuit can be shared without using an independent amplification circuit and a filter.

Now, referring to FIG. 5, the signal transmitted from the AP is received by the donor antenna 101 and then switched to the downward path side by the first switch SW1 and input to the first input stage amplifier 103. The signal amplified to a predetermined level by the first input stage amplifying unit passes through the first band pass filter 104 and then branches into two paths using a signal divider (not shown).                     

First, in the case of the first path, the branched signal is input to the correlator 110 through a downconversion unit 108 and an A / D converter 109 that lower the frequency of the signal to enable A / D conversion. The correlator 110 detects a start timing of a frame with respect to the received signal, detects a position of a lower phase change section in the frame section, and outputs the detected position to the controller 111. In addition, the correlation unit 110 detects the power level value of the reception preamble calculated by the internal power calculation unit 204 and outputs it to the control unit 111. The control unit 111 controls the overall operation of the RF repeater, as well as the first switch SW1 and the second switch SW2 based on the frame start timing and the position of the phase change section received from the correlator 110. Generate ON / OFF control signal and set uplink circuit gain and downlink circuit gain of repeater based on power level data of preamble.

Next, in the case of the second path, the first variable attenuation unit 106 reduces the passing signal to a predetermined level based on the attenuation value information calculated by the control unit 111. The signal attenuated to a predetermined level by the first variable attenuator 106 is output to the second switch SW2 via the first high power amplifier 107, where it is switched to the service antenna 102 and transmitted to the AT. .

Meanwhile, the signal transmitted from the AT is received by the service antenna 102 and then switched to the uplink side by the second switch SW2 and input to the second input terminal amplifier 113. Here, the signal is amplified to a predetermined level and then transmitted to the second variable attenuation unit 121 via the second band pass filter 115. The second variable attenuation unit 121 reduces the passing signal to a predetermined level by using the attenuation value information calculated by the control unit 111, transfers the signal to the second high output amplifying unit 123, and then returns the second high output amplifying unit ( The signal amplified to a predetermined level at 123 is switched from the first switch SW1 to the donor antenna 101 and transmitted to the AP.

At this time, the attenuation values of the uplink and downlink circuits of the repeater are controlled using the power level data of the downlink preamble transmitted by the correlator 110 to the control unit 111 and the preamble output value data of the AP stored in the repeater memory (not shown). The value calculated in (111) is for setting an appropriate uplink and downlink circuit gain of the repeater.

Now, a method of generating switching control signals of the first switch SW1 and the second switch SW2 in the above configuration will be described in more detail. In a mobile communication system using a TDD-OFDMA scheme, one frame has a constant length as shown in Fig. 6, and the start and end timing of the frame is kept the same at all APs to avoid interference. Remain the same within the margin of error within CP).

However, since it is a TDD system, the ratio of downlink and uplink sections can be changed within a frame, and several ratio sets are defined in the standard (see the example illustrated in FIG. 8). However, the downlink and uplink ratios are used by all APs equally for frame synchronization between several APs and ATs, and all APs simultaneously change even when the APs are changed.

In the present invention, first, the frame start timing (= start interval of the downlink section) of the signal transmitted from the AP is detected, and then the position of the downlink switching section, i.e., the downlink switching section, is detected within the frame. This operation is performed in the correlator 110.

FIG. 6 schematically illustrates the structure of an OFDM preamble and a frame, and FIG. 7 schematically illustrates a configuration of a correlation unit according to a preferred embodiment of the present invention.

First, referring to FIG. 6, a cyclic prefix (CP) that prefixes the rear end is disposed at the front end of the preamble to overcome the influence of the in-symbol interference (ISI). As shown, in a system using an OFDM modulation scheme, the preamble includes data in a predetermined form so that the AT receives the preamble and finds frame synchronization. In most OFDM modulation systems, the preamble is referred to the intermediate point. Often have repeatability. The present invention provides a method for finding a frame start timing that can be applied even when a frame does not have a repetitive structure. However, the present invention focuses on a method for more stably detecting a starting point of a frame when the frame has a repetitive structure. Suggests.

If the preamble is a system having a repetitive structure, the technique of the present invention can stably detect the start timing of a more accurate frame despite deterioration of signal characteristics due to signal interference, diffraction, reflection, etc. between preambles of multiple APs. . In particular, even in the case of a technique in which preamble data differs for each AP, which is currently employed by most OFDM mobile communication technologies, the start timing of a frame can be stably detected.

Referring to FIG. 7, the correlator 110 includes a shift buffer 200, a correlator 202, a power calculator 204, a power normalizer 206, and a timing detector 208.

First, the basic method of finding the frame start timing by using the preamble is to store the preamble data of the AP, which transmits the downlink signal to the repeater, in the memory of the repeater in advance, and obtain a correlation value between the data and the received signal.

First, assuming that the preamble has a repetitive structure based on the intermediate point, and the related details are described, a part of the AP downlink signal received by the repeater is transmitted to the first path of the downlink circuit and then the frequency downconversion unit. After changing to a low frequency (D / C 108), the A / D converter 109 is converted into digital data and input to the correlation unit 110. There is a shift buffer 200 at the first stage inside the correlation part, and this data is stored in the shift buffer 200 up to NFFT / 2 (that is, dk (i), i = 0,1, ... NFFT / 2-1). It is entered and stored in the order of reception. The correlator 202 calculates a correlation value between the data stored in the shift buffer and the preamble data p (i) previously stored in the repeater's memory (not shown). At this time, the correlation is shown in Equation 1 below.

Here, Xk is a correlation value and dk (i) is a received signal stored in a buffer. I represents the sample data index of the data string stored in the shift buffer, and k represents the index of the correlation result value. The power calculator 204 calculates the power of the received signal through Equation 2 below.                     

The power normalizer 206 then normalizes the calculated correlation value to the power of the received signal. At this time, the calculation is as shown in Equation 3 below.

here,

At this time, the Ck value also has a value between 0 and 1.

The Ck data is transmitted to the timing detector 208. The timing detector 208 checks whether the Ck is greater than a predetermined threshold.

On the other hand, since the above procedure is performed on the received signals of NFFT / 2 (dk (i), i = 0,1, ..., NFFT / 2-1), the remaining NFFT / 2 (dk (i ), i = NFFT / 2, ... NFFT-1)). Accordingly, the timing detector may check whether Ck is greater than a predetermined threshold value twice in one preamble period.

Therefore, in the case of the preamble having repeatability, if the second maximum Ck occurs while the Ck is greater than the predetermined threshold value twice in one preamble period, the second maximum Ck becomes the end position of the preamble. Through this, the start point of the preamble, that is, the start timing of the frame can be determined.

This method uses the preamble data that is accurately known in advance in the repeater, so it detects relatively accurate frame start timing even when the signal-to-noise ratio (S / N) of the AP downlink signal received by the repeater is small. There is an advantage to this. This method is also applicable to the case where the preamble does not have repeatability. Of course, in this case, whether Ck is larger than a predetermined threshold value needs only be determined once.

 However, this method has many problems in practical application. In urban areas where RF repeaters are mainly used, the AP radius is very small (200 ~ 500m), so the overlapping phenomenon between multiple AP signals appears in most areas, especially at the boundary area between APs, at least three to as many as 15 The above-mentioned AP downlink signal is received, a sudden relative level change between signals and a change in propagation delay value frequently occur. Therefore, since the quality of the preamble signal received by the repeater is severely degraded in the boundary area between APs, it is difficult to detect the frame start timing by storing the preamble data in the repeater and correlating the received signal with the preamble. However, since the AP signal level received by the AT in the region is low, the probability that the repeater is used causes a problem.

In particular, recently, in the OFDMA system, a preamble having a different data value for each AP is used for the purpose of improving handoff performance. In this case, since the preamble signals of the respective APs act as interference sources to each other, the signal-to-interference ratio (C / I) of the preamble signal received by the repeater is deteriorated, so that it is very difficult for the repeater to detect the frame start timing. For example, if 10 AP signals are received at the repeater donor antenna (1) at a level of -80 dBm / 10 MHz, the total reception level is -70 dBm, so the S / N value is very good at over 35 dB compared to the thermal noise level. Since the C / I value is greatly deteriorated to -10dB, it is difficult to calculate accurate frame start timing at the repeater's correlator.

In addition, even in actual use, the preamble data stored in the repeater should be sorted and inputted as the AP that the repeater will receive the down signal, and eventually, the customized unit needs to be produced, resulting in higher production costs, and for the operator to improve wireless network quality. When the AP is relocated, newly established, or the antenna is changed, the preamble received by the repeater is changed, so the preamble data of the repeater must also be changed. However, dozens of RF repeaters are used in one AP coverage, and there are many movements and new APs in actual mobile communication networks, and change of AP antenna direction is very frequent, which increases cost and time. In addition, due to the characteristics of the wireless network, it is difficult to determine the limit of clear coverage serviced by one AP, so it is practically difficult to determine the appropriate preamble data for the repeaters in the boundary area between the APs. In addition, in the coverage overlap area between APs, the relative power level between mixed AP signals is frequently changed according to time, so that the signal of the AP having the highest reception level at the time of repeater installation is changed It may be lower than the reception level, in which case the repeater cannot find the starting point of the frame.                     

Therefore, the following autocorrelation method is required. In detail, when the preamble has repeatability with respect to the intermediate point thereof, the signal input from the first band pass filter 104 is transmitted to the D / C 108 and the A /. Via the D conversion unit 109, the digital data is converted into digital data and input to the correlation unit 110 as described above. The signals input to the correlator 110 are sequentially stored in the shift buffer 200 having a size of NFFT, and the signals stored in the shift buffer 200 are input to the correlator 202 and the power calculator 204.

The correlator 202 calculates a correlation value between i = 0 to NFFT / 2-1 th signals and i = NFFT / 2 to NFFT-1 th signals among the received signals stored in the shift buffer 200. In this case, the correlation is shown in Equation 4 below.

Here, Xk is a correlation value and dk (i) is a received signal stored in a buffer. I represents the sample data index of the data string stored in the shift buffer, and k represents the index of the correlation result value.

Next, the power calculator 204 calculates the power of the received signal through Equation 5 below.

Nk is the power (= power value) of the received signal.

As described above, the correlation value calculated by the correlator 202 and the power calculator 204 and the power value of the received signal are transmitted to the power normalizer 206, where the correlation value is received through Equation 6 below. Normalize at power.

Here, Ck becomes a power normalized value, and thus Ck has a value between 0 and 1 independently of the received signal power.

Next, the power normalized data is input to the timing detector 208. The timing detector 208 obtains the sum D of Ncp + 1 CK values through Equation 7 below.

Next, the sum D is compared with a predetermined threshold. Since the sum D is greater than a predetermined threshold and the maximum becomes the end position of the preamble, the start point of the preamble, that is, the start timing of the frame, can be determined. Of course, even when the Ck value is maximum, the start timing of the frame can be determined, but it is more reliable to determine the start timing of the frame by the D value.                     

According to this method, even if a multipath is generated by diffraction, reflection, etc. in the AP downlink signal received at the repeater, and the transmitted signals output from multiple APs are mixed, the repeater can stably detect the starting point of the frame. do. In particular, since the data of the preamble is different for each AP, even when the carrier-to-interference (C / I) of the signal received by the repeater is extremely poor, it is possible to accurately find the frame start timing. The reason is that many multipath signals are generated and received at the repeater, and even though data is received at the repeater by mixing a plurality of different AP signals, each preamble signal has repeatability, so that the final signal formed by overlapping multiple signals is also included. This is because the first half and the second half of the preamble still have the same shape, and a high correlation between the first half and the second half is maintained, so the correlation value between the first half and the second half is very large.

In addition, there is no need to use different preamble data for each repeater, which makes mass production of the repeater easier, resulting in lower unit costs. Do.

Next, after the start timing of the frame is detected by the correlator 110, the position of the lower phase switching section in the frame should be detected. Due to the characteristics of the TDD system, as shown in FIG. 8, since a ratio of an uplink section and a downlink section may be variable in a frame having a constant overall length, the position of a lower phase switching section in a signal received at a repeater is determined by the AP. It is determined by which of the ratios specified in the standard is applied to the actual signal. Therefore, only the frame start timing detection cannot completely control the switches SW1 and SW2 of the repeater.

At this time, the signal level measuring method and the autocorrelation method can be used as the lower phase switching section detection method. First, the signal level measuring method will be described.

First, the timing detector 208 can easily calculate the positions of the candidates for the lower phase switching section by using the start timing of the frame and the ratio specifications of the downward and upward intervals. After the timing detector 208 calculates the candidate positions of the phase change section, the timing detector 208 uses the data received from the power calculator 204 to advance the received power of the candidate phase change sections on the time axis. Review them in order.

In this case, referring to FIG. 4, the candidate phase change section that is temporally ahead of the actual phase change section is located in a section in which traffic inside the downward section is transmitted, and the candidate phase change section that is later than the actual phase change section is upward. It is located inside the section. Referring back to FIG. 4, in the OFDMA system, for the purpose of channel estimation and AT frequency synchronization correction, some frequencies are allocated for pilot purposes regardless of the presence or absence of traffic even after the preamble part in the downlink section, and the signals are continuously transmitted. send. Therefore, in the candidate phase change section that is temporally ahead of the actual phase change section, although the level is several to tens of decibels lower than the preamble portion, the signal is detected. This becomes the candidate lower phase change section later. The timing detector 208 examines the signal level data input from the power calculator 204 to determine a section in which the signal level falls below a predetermined level among the plurality of time interval candidates as an actual lower phase switching section, and controls related time position information. Output to (111).

However, if there is a candidate lower phase switching section that is later than the actual lower phase switching section and thus no signal level is detected in the plurality of lower phase switching section candidates, the faster one is selected as the true value. This is because there is no downlink signal transmitted from the AP during the downlink to uplink, that is, no signal is input to the downlink path of the repeater. Of course, when the AT of another user directly accessing the AP near the repeater donor antenna 101 transmits an uplink signal, the corresponding signal may be received at the repeater, but in this case, the reception level is not detected among the candidates of the lower phase switching section. There is no problem because a plurality of sections do not appear.

At this time, there is a matter to be careful in the process of detecting the signal level inside the lower phase switching section. As the repeater installation position moves away from the AP, the size of the section for switching the downlink signal from the downlink signal, i.e., the lower phase switching section, is reduced. The reduction of the phase change section occurs due to the path delay value for propagation between the AP and the repeater. As the path delay value increases, the degree of reduction increases.

In more detail, as shown in S2 of FIG. 9, the AP downlink signal is delayed by a because of propagation delay, and thus the repeater arrives at the repeater. Therefore, the repeater indicates delayed frame start timing (indicated by FS in FIG. 9) in the delayed signal. After the search, the frame structure specification of the FS and the AP is used to detect the position of the lower phase switching section (starting point of the lower phase switching section, indicated by FE in FIG. 9). In this case, the repeater can calculate a plurality of FE candidate positions from the frame structure specification of the AP, and the calculated FE candidate positions are also calculated with a predetermined time delay compared to the FE candidates in the AP. If one of the candidates is FE indicated in S2 of FIG. 9, if the repeater does not consider the reduction phenomenon of the lower phase switching section, the repeater may have a section width between T in the FE shown in S2 of FIG. It is checked whether the downlink signal level of the AP exists for a time interval equal to the width of the switching section (denoted by TTG in S1 in FIG. 9). However, as shown in S2 of FIG. 9, the uplink signal of the AT reaching the repeater arrives at the repeater (preferably through the repeater and reaches the donor antenna of the repeater) as much as a rather than the uplink start timing of the AP.

This is because the uplink signal of the AT should be able to reach the AP receiver at the start timing of the upstream of the AP. Specifically, the propagation delay value of the AP and the relay period is a so that when the AT signal starts from the repeater to the AP, It is necessary to start as early as the uplink start timing of to reach the AP in the uplink start timing of the AP.

As a result, the length of the phase change section in the repeater is reduced by a total of "2 x a" by a before and after the length of the phase change section in the AP. In this case, the magnitude of a is proportional to the distance between the AP and the relay period, so that the shorter the phase change interval is, the larger the repeater is installed from the AP. However, S4 and S5 of FIG. 9 have a delay value of z having a larger delay than a. Explaining.

When the signal level is detected without reflecting the reduced portion of the lower phase switching section, as described above, the section width between FE and T shown in S2 of FIG. 9, that is, the width of the lower phase switching section in the AP (S1 in FIG. 9). The TTG checks whether there is a downlink signal level of the AP for the same time interval as the TTG. The upstream signal of the ST as shown in S2 of FIG. The level can be detected, resulting in an error in the determination of the actual phase change section.

Therefore, the propagation delay value for each repeater installation location should be checked, and the width of time for detecting the downlink signal level should be different in consideration of the reduction in size of the lower phase switching section. However, this method is impossible to realize a realistic propagation delay because it is difficult for the repeater to reliably grasp the exact propagation delay value in a mobile communication environment where multiple AP signals are simultaneously received and multipath delay is frequently generated.

Of course, the delay time is calculated by embedding a GPS clock in the repeater and storing the frame start timing time data when the downlink signal is transmitted for the first time after the base station is installed in the repeater memory (not shown) and comparing the frame start timing detected by the repeater. There is a method, but if the repeater unit price increases and the frame start timing of the base station is changed in a specific situation, the repeater cannot measure the normal propagation delay value.

The present invention proposes a method for confirming the actual position of the phase change section (start timing of the phase change section) irrespective of the phenomenon of reducing the phase change section by the propagation delay value of the AP and the relay period. Now, it is assumed that the propagation delay value is z at the AP having the largest radius among APs constructing the entire wireless network (assume that the time required for the downlink signal of the AP to propagate to the end of coverage of the AP is z). Assuming that the repeater is installed at the end of coverage, the size reduction of the riverbed switching section appearing in the repeater is larger than that of the repeater installed at any other position in the wireless network. This is because the path delay value z of the corresponding AP is the largest in the wireless network, and the extent of the switching interval is reduced is proportional to the size of the path delay value. At this time, referring to S4 of Fig. 9, the length of the lower phase switching section at the repeater position is “TTG-2 xz of the AP.” Therefore, even if the repeater is installed at any position inside the wireless network, The interval where the start timing is FE and the width of "AP TTG-2 xz" is always empty without signal. Therefore, in the algorithm for finding the actual phase change section, the signal level detection for the candidate phase change sections should be performed for [sections having a starting timing of candidate FE and a width of "APTTG-2 xz". FE candidates can be easily calculated using the downlink width data of the AP specified in the AP frame specification when the frame start point FS is detected as described above.

In this case, however, the switching switching time of the repeater switch is assumed to be "zero". If the switching time of the actual switch is ST, the signal level detection for the candidate lower phase switching sections is performed by the ST before and after the signal detection section. It is necessary to reduce the width (the section in which the starting timing is "candidate FE + ST" and the width is "TTG-2 xz-ST" of the AP) and is indicated by the section "s" in S5 of FIG.

In addition, in the above, the signal transmission delay value in the repeater, the propagation delay value in the repeater coverage, and the time delay value for the AT signal processing are ignored. If these values are not "zero", the starting timing is "candidate FE. + ST "and the width" TTG-2 xz-ST "of AP] is [sum of signal propagation delay value in repeater and propagation delay value in repeater coverage and time delay value for AT signal processing] Therefore, when designing a wireless network, it is necessary to consider the hardware delay of the repeater and AT together with the propagation delay in repeater coverage when determining the maximum radius of the AP, that is, the z value.

In general, however, this is very unlikely to be a problem. In the mobile communication system using the TDD duplex method, in order to maximize the AP service radius, the AP radius allowed by the maximum path delay is larger than the AP radius allowed by the maximum path loss. In addition, since the AP radius is determined so that the coverage overlaps substantially between the APs for smooth handoff support when constructing a wireless network, the radius of the largest AP is smaller than the maximum allowable path loss. Therefore, the AP radius allowed by the maximum path delay in the AP standard is significantly larger than the radius of the AP having the maximum radius among APs constructing a wireless network (usually 2 to 5 times or more). Therefore, the "Length of transition phase defined by the AP specification-2 x z" value is always considerably greater than the "Hardware delay value of repeater and AT + sum of bidirectional propagation delay value in repeater coverage".

Next, when the correlation method is used to detect the lower phase switching section position, the timing detector 208 receives the autocorrelation value of the signal received from the correlator 202. In this case, the autocorrelation value is a magnitude of a correlation value calculated for a received signal in a switching time interval from downward to upward using an autocorrelator used to find frame synchronization. However, the correlator in this case is not a correlator which compares the received signal with the preamble data embedded in the repeater, and compares the first half and the second half of the received signal preamble using the repeatability of the preamble. Correlator. Since the magnitude of the phase changeover section is much larger than the size of the correlator, the correlation value output at this time becomes the correlation value between white noise in the actual phase changeover section. Since the autocorrelation value between these white noises is markedly low (approximately 'zero'), this characteristic can be used to find the actual phase change section. Except for the portion that uses the correlation value instead of the signal level check, the above-described reception signal level check method is completely identical to the remaining parts.

In this way, when the "start timing of the frame" and the "position of the lower phase switching section" is determined, the correlation unit 110 transmits this data to the control unit 111. The control unit 111 generates the ON / OFF control signals for the first switch SW1 and the second switch SW2 in the repeater by using the data to control each switch.

There are additional considerations for this. As described above, because the width of the lower phase switching section decreases in proportion to the propagation delay value between the AP and the repeater at the repeater installation position, only the start timing of the frame and the lower phase switching section position data are generated when generating the switch control signal inside the repeater. The control signal cannot be generated. In order for the repeater to generate its own ON / OFF control signals for the first switch SW1 and the second switch SW2, the start timing of the downlink section, that is, the start timing of the frame and the upstream section, Data on the timing at which the switching section ends is required. Given these two timing data, the remaining timings can be easily calculated using data such as frame length, downward section length and upward section length in AP specification data.

However, although the data transmitted from the correlation unit 110 to the control unit has the start position of the frame (FS in FIG. 9), there is no data of the start timing of the uplink section, that is, the timing at which the lower phase switching section ends. Only the position of the phase change section, that is, the timing of the start of the phase change section (FE in FIG. 9) is transmitted, and the timing data at which the phase change section ends is provided only in exceptional cases and when the width of the phase change section is the smallest. It will be. However, since the phase change section is reduced in the repeater in proportion to the propagation delay value between the AP and the repeater, it is necessary to know the exact propagation delay value of the AP and the repeater period so that the exact reduction degree of the phase change section can be known. Therefore, the exact contraction degree must be calculated to know the timing at which the lower phase change section ends, that is, the start timing of the upward section. At this time, since it is impossible to calculate the propagation delay value of the AP and the relay period as described above, another alternative is needed.

  Now, a description will be given of how to operate the switches SW1 and SW2 of the repeater without problems in any environment using only the start timing FS of the frame and the start timing data FE of the lower phase switching section. In FIG. 9, the lower phase switching section means a time required to switch from the downlink signal section to the uplink signal section as described above, and the width of the lower phase switching section in the AP is TTG as shown in S1 of FIG. 9. The interval means the time required to switch from the uplink signal interval to the downlink signal interval, and the width of the up-and-down switching interval in the AP is defined as RTG as shown in S1 of FIG. 9. In addition, referring to the switching operation of the AP final RF stage as shown in S1 of FIG. 9, the AP output signal is radiated in the downlink signal interval from the AP and the AT output signal is received by the AP in the uplink signal interval. S2 of FIG. 9 is a diagram for explaining a signal propagation delay value between the AP and the repeater, and the AP downlink signal is received by the repeater donor antenna 101 with a delay value a depending on the propagation path length of the AP and the repeater period. .

The repeater analyzes the AP downlink signal received by the donor antenna 101, finds the start timing of the downlink signal section, and then checks the AP frame specification (downlink uplink ratio, downlink switching section length, downlink switching section length, and overall frame length). The start timing of the lower phase switching section is found by using the reception level (or correlation value) of the and downlink signals. The expected switching schedule of the repeater prepared by the found timing data and the AP frame standard may be written as S3 of FIG. 9.

However, if the propagation delay value a between the AP and the repeater is not taken into consideration, as in S3 of FIG. 9, as described above, a part of the uplink signal emitted from the ST is called out. In detail, the upstream output signals of all ATs operating within the AP coverage must be able to reach the AP at the start timing of the uplink section of the AP. In particular, in the system using the OFDMA multi-user access method, different ATs are used at the AP receiving end. In order to maintain orthogonality between the signals, all AT signals must be able to reach the AP receiver at the same time as the start timing of the upstream signal of the AP. Therefore, if the propagation delay value of the AP and the relay period is a, the AT signal passing through the repeater At (exactly at the repeater donor antenna), the AP should be radiated to the AP by a time faster than the start timing of the uplink section of the AP (see S2 in FIG. 9).

For example, in a system of 100 상 in the bottom switching interval specification of an AP, if two ATs exist at 10 10 and 30 으로부터 from the AP, the AT at 10 있는 is 80 80 after receiving the AP downlink signal. Wait for and transmit AT signal to AP. AT at 30 ㎲ point waits 40 후 after receiving AP down signal and transmits AT signal to AP. Therefore, all AT transmission signals reach the receiver at the same time 100 kHz after the end of the AP downlink signal. Therefore, if the repeater is located between the AP and the AT to relay the signal, the uplink signal of the AT, which is amplified by the repeater and radiated from the donor antenna to the AP, is timed at a time as fast as the signal transmission delay between the AP and the repeater Radiated from the donor antenna to the AP.

However, when the system divides the downlink and uplink sections into multiple time intervals by using the TDMA concept and allocates them to a plurality of ATs, some AT signals allocated later in the uplink section are transmitted to the AP at the start timing of the uplink section. This AT may not need to be reached, but in other circumstances this AT may be allocated the earliest time interval of the uplink and the AT in the repeater's service area may be allocated the earliest time interval of the upstream, so basically all The upstream signal of the AT should be able to reach the AP at the start point of the upstream region of the AP.

However, as shown in S3 of FIG. 9, in the relay predicted switch operation S3 made of only the frame start timing and the phase change section start timing detected by the repeater and the AP frame specification without considering the AP and the relay period propagation delay value a, the frame Since the start timing is delayed, the uplink signal start timing of the repeater is also delayed by a rather than the uplink signal start timing of the AP. Therefore, as shown in S2 of FIG. 9, the signal during the period [2 × a] of the AT signal which reaches the repeater by [2 × a] faster than the start timing of the repeater uplink section does not pass through the repeater. (Refer to the signal disappearance of S3 in Fig. 9) In the above description, it is assumed that the signal propagation delay value is "zero" in the internal hardware of the repeater. If the repeater hardware delay value is not "zero," the hardware signal of the repeater is lost. The signal is further lost by the propagation delay. However, the front part of the AT uplink signal contains important control signals that inform the AP about the details of the data part following the back part, so if this part is lost, data uplink is impossible.

In order to solve this problem, a method of compensating a signal transmission delay value between the AP and the repeater can be considered as shown in S3 'of FIG. That is, the start timing of the uplink signal section in the relay switching signal is shifted by a forward of the uplink signal start timing of the AP. In this case, the widths of the downlink and uplink sections in the repeater are the same as the widths of the downlink and uplink sections in the AP. The size of the downlink switching section, which is the time to switch from the downlink signal section to the uplink signal section, is reduced to [TTG width of AP-2 × a]. It is increased by [RTG width of AP + 2 x a] (see S3 'in FIG. 10).

As a result, the switching operation inside the repeater shown in S3 'of FIG. 10 is arranged as follows. First, the start timing of the downlink signal section of the repeater itself is delayed by a time than the AP, and the width of the downlink signal section is kept the same as the downlink signal section width of the AP. After that, the uplink signal section is started through the switching time of [AP TTG width-2 × a], and the uplink signal section is kept equal to the uplink signal section width of the AP. In addition, the downlink signal period starts again after the switching time of [RTG width of AP + 2 × a].

However, this method has the following disadvantages. Since the propagation delay value a is different depending on the installation position of the repeater, the individual repeater must determine the exact value of a and set the uplink signal position of the repeater itself on the time axis. However, as described above, it is difficult for the repeater to accurately grasp the propagation delay value a.

Of course, as described above, the GPS clock is embedded in the repeater, and the frame start timing data when the first downlink signal is transmitted after the base station is installed is stored in the repeater memory (not shown) and compared with the frame start timing detected by the repeater. There is a method of calculating a value, but there is a disadvantage that the repeater cannot generate a normal switching signal when the repeater unit price increases and the frame start timing of the base station is changed in a specific situation.

Therefore, the present invention proposes a method for generating a switching signal of a repeater without a problem even when the path delay value a is not known.

In general, it is assumed that one of the main parameters determined when designing a wireless network is the maximum service radius of the AP, and the propagation delay value of the AP having the maximum service radius among APs forming a wireless network is z. This is the case where the bed changing section is the smallest, and as shown in S5 of FIG. 9, the bed changing section in the repeater is reduced to "TTG-2 x z" of the AP.

Referring to FIG. 9, the data clearly recognized by the repeater includes two types of timing data of the FS and FE detected by the repeater, the overall frame length provided by the AP standard, the uplink section width in the AP, and the downlink section width in the AP. It is a total of six data, including three data and the TTG-2 xz value of the AP, which is the smallest riverbed section width calculated by the maximum path delay value z in the wireless network.

By using the six data sets the switching timing of the repeater as shown in S5 '' of FIG. 11 can be a problem in the signal relay no matter where the repeater is installed. In the repeater switching schedule, the downward section is known as the section where the FS and FE are known data detected by the repeater, and the start timing is FS and the ending timing is FE.

In the uplink, when the general path delay value a occurs, the start timing and the end timing are changed by the signal propagation delay value a between the AP and the relay period, so that an accurate timing cannot be determined. However, in the case of the AP having the largest signal propagation delay value z because the radius is the largest in the wireless network, the repeater present at the outermost point is the TTG-2 xz of the known value of the lower phase switching section. Is a timing at which the start timing of the uplink section has elapsed by the lower phase switching section width of the repeater (TTG-2xz of AP) at the end timing (FE) of the repeater downlink section, " FE + (TTG-2xz of AP) " The start timing of the uplink section of the repeater can be determined.

However, the method of determining the start timing of the uplink section may be applied to other situations other than the situation of the repeater, that is, the repeater is present in the region having the maximum signal propagation delay value z. In other words, it is also applicable when the repeater is present at a position with a delay value less than z. To explain the reason, referring to S2 " and S4 " of FIG. 11, where the signal propagation delay values are " a " and &quot; z &quot;, respectively, the actual uplink of S2 &quot; The starting timing is later in time by "TTG-2 xa" of AP. However, in the FE of S2 ", it is later in time by" TTG-2 xz "of AP and the timing is always S2 because z is greater than a. It is temporally ahead of the actual upstream start timing of '' (see S2 '' and S3 '' in FIG. 11). Therefore, in all cases where the path loss between the AP and the repeater period is less than z, the start point of the upstream segment in the repeater switching time schedule is the timing that has elapsed by the end timing (FE) of that repeater downstream segment (TTG-2 xz of the AP). By specifying "FE + (AP TTG-2 xz of the repeater)", the AT uplink signal can be relayed without loss in any case.

Now, it is necessary to determine the end timing of the upstream section in the relay switching time schedule. Generally, if the AP and the relay signaling delay value are not known, the end timing of the upstream section is not known because the repeater does not know the end timing of the upstream section. The timing FS2 is determined. The start timing FS2 of the next frame can be calculated using the FS and the frame length, and can also be detected by the correlation unit (110 of FIG. 5). As shown in S2 &quot; and S4 &quot; of FIG. 11, in the repeater having any signal propagation delay value, the end timing of the AT uplink signal is always present in time before the start timing FS2 of the next frame. The reason is that the downlink start timing FS2 of the next frame is present after the uplink section ends and the up / down transition section ends according to the frame specification.

Therefore, in order to arrange the switching time schedule in the repeater, the down section is [the start timing is FS and the ending timing is the FE section], and the up section is the [start timing is “FE + of the repeater (TTG-2 xz of AP)”. And end timing is “FS2 which is the start timing of the next frame”]. Also, the phase changeover section becomes [“Start timing is FE and duration width (AP TTG-2 xz)”]. The up-and-down switching interval becomes [FS2 having a width of “zero.” S2 " to S5 &quot; of Fig. 11 show that this repeater switching time schedule is a general value a smaller than z to z where the path delay value is maximum. It also shows that it can be applied without difficulty.

However, since the switching points are the result of assuming that the switch of the repeater has a switching transition delay time of "zero", some modifications are necessary when considering the reality that the switch has a switching transition time. First, there is no problem in the case of phase change in the switching time schedule. This is because there is a phase changeover section “TTG-2 × z” corresponding to the switching switching delay time, as shown in S5 ″ of Fig. 11. In general, the “TTG-2 xz” time means that the switch of the repeater switches the state. The reason is that the time width must be greater than the sum of hardware propagation delay and propagation delay in repeater coverage and signal processing delay value of ST which occur when the signal passes through the repeater. It is not a problem at all because it is larger than the switch delay value. The problem is that the width of the up-and-down switching section is “zero”, so that the switch switching delay time required to switch the circuit connection in the downlink path while the internal switch of the repeater is connected in the uplink path is not obtained.

Referring now to S2 ″ and S4 ″ of FIG. 11, the upstream signal of the AT passing through the repeater does not actually pass through the repeater later than the end point of the uplink segment of the AP shown in S1 ″. Because the AT signal that has passed through the repeater later than the end of the uplink segment of the AP can be received by the AP because the uplink section of the AP is already over when the AP is reached, even if the propagation delay value between the APs is close to “zero” in the repeater. Because there is not. That is, the uplink signal of the AT in all the repeaters completes the relay pass before the end timing of the AP uplink, regardless of the AP and the signal propagation delay value of the relay period. Therefore, it is most appropriate to set the end point of the upstream section of the repeater as the end point of the downlink section of AP, but it is not possible to know the end point of the AP upstream section because the signal propagation delay value a of the AP and the relay section is not known for each repeater. For this reason, the end point of the upstream section of the repeater is FS2, and it is clearly seen in S3 '' and S5 '' of FIG. 11 that the end timing of the upstream section of all repeaters is independent of the signal propagation delay value of the AP and the repeater period. After that, the timing at which the "AP RTG interval width of AP + AP and relay signal delay time" elapses becomes FS2, which is the start timing of the next frame. Therefore, the timing that is temporally ahead of FS2 by "RTG interval width of AP". In addition, regardless of the signal propagation delay value, it is later than the end timing of the upstream section of the AP, thus excluding the time corresponding to the RTG section width of the AP from the back section of the repeater up section (after the time axis). However, the end timing of the AP uplink section is always included in the uplink section of the repeater, and as shown in S3 '' 'and S5' '' of FIG. It can be reduced as much as the width of the RTG section of the AP, and the RTG of the AP can be used as a value known by the repeater because it is a value determined by the AP standard. It is common to have enough time for the switch of the AP to switch, so there is no problem with the switching of the repeater.                     

As a result, referring to S3 '' 'and S5' '' of FIG. 12, the downlink section in the repeater switching schedule is a section in which [start timing is FS and ending timing is FE], and the uplink section is [start timing is US (FE). Is the time when the time elapses by the AP's TTG-2 xz "and the ending timing is the UE (the timing that is ahead of the AP's RTG in time than the FS2)]. FE, the end timing is US], and the up-and-down switching section is a section in which [start timing is UE and end timing is FS2] (S3 '' 'and S5' '' in FIG. 12).

 S2 '' 'to S5' '' of FIG. 12 shows that such a relay switching time schedule can be applied to all cases where the path delay value is smaller than z.

As a result, the switching schedule of the repeater is as shown in S3 '' 'or S5' '' of FIG. 12. In general, the switching delay time of the switch according to the development of the technology is the phase changeover shown in S3 '' 'or S5' '' of 12. Since it may be much shorter than the section or the up-and-down switching section, the width of the up-and-down switching section of S3 '' 'and S5' '' proposed in FIG. 12 may be reduced to the switching delay time of the switch. At this time, the lower phase switching section or the upper and lower switching section shortened to the switching delay time duration of the switch may be in the lower phase switching section or the upper and lower switching section shown in S3 '' 'and S5' '' of FIG. That is, the rule for setting the start and end timings of the lower and upper switching sections proposed in FIG. 12 defines the maximum range in which each section can exist on the time axis, and the maximum section width is defined between the starting and ending timings proposed in FIG. 12. All of the sections are used as the switching section, and the minimum section width is used as the switching section as much as the switching delay time width of the switch used in the repeater. Therefore, the embodiment of the present invention is located between the start and end timing of the lower and lower section of the upper and lower switching section illustrated in S3 '' 'and S5' '' of Figure 12, the section width The maximum values S3 '' 'and S5' '' may be applied to all embodiments reduced to the switching delay time width of the switch used in the minimum repeater.

Now, when the repeater detects the operation timing of the switches SW1 and SW2 at the initial stage of installation, it changes the downward / upward ratio inside the frame in the AP during the operation of the repeater, or the frequency precision error of the internal parts of the repeater, and other unexpected An algorithm for coping with problems caused by radio interference will be described.

When the repeater starts the operation of the internal switches SW1 and SW2 by finding the frame start timing and the lower phase switching section position, the correlator 110 then returns to the original frame start timing detection mode for a predetermined time, and then operates again for a predetermined time. It operates in position detection mode of lower phase change section. The predetermined time may be appropriately determined in units of seconds.

First, if the down: up ratio is changed in the AP, the repeater finds a problem in the down-changing section detection mode within the predetermined time. For example, if the length of the downward section becomes shorter, it is found that there is no AP downlink signal level in the lower phase switching section candidate which is located in a position temporally ahead of the current lower phase switching section position. The repeater can detect the downlink signal level in the current phase change phase. At this time, the repeater checks whether the same situation is detected more than a predetermined number of times (for example, 30 times), and if the same situation is repeated, the repeater performs a new operation for finding the position of the lower section switching section and switches the position of the newly detected lower section switching section. This is reflected in the operation of SW1 and SW2.

However, if the signal level is detected in all the phase change sections, the repeater regards the cause as the interference or the occurrence of ambient noise and continues switching using the existing phase change section positions.

 Next, the frequency precision error of the repeater internal standard oscillator (existing in the control unit, not shown) used to switch SW1 and SW2 may accumulate in the switching timing over time, and may eventually cause a problem in the accuracy of the switching timing. have. Therefore, the controller 111 averages the frame start timing data transmitted from the correlator 110 for a predetermined number of times (for example, 20000 times), and updates the switching timings of the switches SW1 and SW2 based on the average value. The average number of times is determined by the error standard of the standard oscillator used in the repeater. The larger the error, the smaller the number of average frames.

 In addition, when the repeater cannot find the frame start timing due to other unexpected interference, the repeater responds as follows. First of all, in the case of a frame start timing detection error that occurs due to a short period of time (e.g., less than 1 second) propagation disturbance, since the appearing phenomenon will not be detected or will be detected at a very different position from the existing value, In the process of calculating the average value created by the controller for updating the frame start timing, the controller differs by a certain level or more from the previous average value. If data appear only for a period of time (for example, less than one second), the solution can be solved by creating an average, excluding the data for that period of time. If the frame start timing cannot be found due to jamming for more than a certain time, the repeater displays a frame timing detection error alarm and continues operation using existing switching timing data. If a certain frame start timing data is continuously detected again after the elapse of time, the repeater also redetects the position of the lower phase switching section, updates the time schedule for operating the repeater switch with the corresponding data, and operates the repeater.

Finally, the controller 117 not only controls the overall operation of the repeater, but also uses the frame start timing data and the downlink reception level data obtained in the process of acquiring the switching timing of the RF repeater, and the downlink circuit gain and the uplink path of the repeater. Set the circuit gain by itself. Since the RF repeater is a device that amplifies and transmits the signals of the AP and AT in a wireless manner, since the reception level of the AP downlink signal is different according to the installation position of the repeater, the gain setting value must also be different for each repeater. In particular, as the downlink signal reception level of the relay changes from time to time due to the AP's movement, new construction, or antenna changeover, the automatic gain setting function is essential. Its utility increases.

However, as described above, the automatic gain control technique of the conventional FDD repeater (repeater used in FDD CDMA mobile telephone system) has no concept of time in repeater gain control. It is difficult to apply to the classification TDD system. In the FDD type repeater, as shown in FIG. 1, the uplink circuit and the downlink circuit gain are set in real time according to the downlevel data of the currently received AP. However, this method is not applicable to the TDD-OFDMA system. First, since the downlink signal of the AP is not radiated during the uplink section of the frame in the TDD system, the repeater cannot use the downlink signal level to set the gain. Therefore, TDD repeater should introduce the concept of time interval when measuring downlink signal level of AP for automatic gain setting operation.

For example, the AP downlink signal level is measured during the downlink signal period of the frame, and the average value is stored. Using this data, the repeater gain is set and maintained, and the AP downlink signal level is changed to the next downlink signal level. A way of changing the repeater gains may be proposed. However, in this method, it is difficult to adequately respond to fluctuations in AP downlink output according to traffic volume. For example, fluctuations in the downlink output of the AP cause errors in the path loss calculation of the repeater, which causes problems in the uplink circuit gain setting, and at high instantaneous traffic, the downlink received signal is 4-6 decibels higher than the measured average. As a result, the possibility of overload in the repeater downlink circuit is very high.

Therefore, in the present invention, the conventional gain automation scheme is difficult to apply in the TDD system that separates the up and down paths with time, and in particular, the error in the gain setting caused by the traffic volume is improved to improve the repeater service quality. Suggest ways to improve.

As described above, referring to the first aspect of the present invention, it can be seen that frame start timing data and downlink reception level data are obtained while the repeater detects the operation timing of the switches SW1 and SW2. Therefore, using these two data and frame specification data, it is possible to calculate the level of the preamble signal portion in the downlink signal section. However, unlike the traffic signal, this preamble signal is always present at a predetermined time, and the output level is kept constant. Therefore, it is possible to set repeater gain more accurately than setting repeater gain by using the reception level of the entire downlink section whose output value varies depending on the traffic volume or frame down: uplink ratio.

First, in the method using the preamble of the present invention, once the gain of the repeater downlink circuit is determined based on the preamble level, the AP gain is maintained in all sections within the frame regardless of whether there is traffic in the downlink signal in the same frame. The downlink signal level is not amplified and is normally amplified and transmitted to the AT. Since there is no situation in which the repeater reception level is higher than that of the preamble, failure of the repeater downlink circuit due to over input is prevented. That is, in the downlink signal received from the AP, the level difference between the non-traffic section and the existing section is transmitted without being distorted.

Next, a part of the present invention that is more effective is the gain path setting portion of the uplink circuit of the repeater. By storing the level of the preamble output from the AP in the repeater's memory (not shown) and detecting and comparing the level of the preamble received from the repeater, it is possible to obtain a very accurate AP and repeater path loss value. The path loss obtained at this time is an accurate value that is not affected at all by the traffic volume of the AP.                     

The automatic gain control method of detecting the AP signal level only while the AP preamble signal is present and setting the repeater gain will be described in detail. Since the start time data of the frame and the downlink signal reception level data output from the correlator 110 of the repeater can be used to know the existence time of the preamble and the reception power level (ie, Nk) of the preamble, the repeater receives the reception power of the preamble. The level is used to set the gain of the repeater as follows and maintain the same gain for the duration of the frame. If the reception power level of the preamble is changed in the next frame, the gain of the repeater is modified using the changed preamble level value and maintained for the corresponding frame.

Iii) Downlink circuit gain (GF) = RPTX-RPRX

Ii) Uplink Circuit Gain (GB) = BPTX-RPRX-(Repeat Reverse Noise Figure) + Correction Value (α)

However, BPTX: level of preamble output from AP

 RPTX: Target level of preamble output from AT to AT side

 RPRX: level of preamble received from the AP to the repeater

Here, the BPTX and RPTX is a value determined by the AP standard, and is a value previously stored in the repeater itself, and the repeater reverse noise figure is a value determined by the repeater standard.

The RF repeater according to the present invention can effectively cope with a mobile communication system employing a TDD scheme and an OFDMA scheme. In particular, since the duplexer cannot be used in the TDD system, the up and down paths must be separated using a switch, but the RF repeater, which plays a very important role in the mobile communication system, cannot transmit the timing of the switch operation to the wireless RF repeater. There was no technical alternative to develop and apply, but the RF repeater itself can generate accurate and stable switching control signal, so that the RF repeater can be used in the TDD system as well as improve the reliability of the repeater and provide mobile communication services. We also suggested a way to improve quality.

In addition, according to the present invention, since the stable gain setting of the repeater itself can be performed even in the TDD system, the quality of service can be improved in a mobile communication network employing the TDD system.

While the present invention has been described with reference to the preferred embodiments, those skilled in the art will understand that the present invention may be modified without departing from the spirit and scope of the invention. In other words, the invention is not to be considered as being limited to the above-described exemplary embodiments as they may be modified within the scope of the appended claims.

Claims (38)

In the RF repeater applicable to the TDD scheme in which the downlink signal transmitted from the AP to the AT direction and the uplink signal transmitted from the AT to the AP have the same frequency, A first switch connected to the donor antenna 101 to selectively switch an uplink path or a downlink path; A second switch connected to the service antenna 102 for selectively switching an uplink path or a downlink path; A correlator for detecting a start timing of a frame transmitted from the AP and a start timing of a lower phase change section in the frame; A controller configured to generate ON / OFF control signals of the first and second switches based on a frame start timing and a start timing of a lower phase change section output from the correlator; Improved RF repeater comprising a. The method of claim 1, wherein the correlation unit A buffer for temporarily temporarily storing the received AP signal; A correlator for calculating a correlation value for AP downlink signal values stored in the buffer; A power calculator for calculating the power of the received signal stored in the buffer; A power normalizing unit for normalizing the correlation value output from the correlator to the power output from the power calculating unit; A timing detector for determining whether a normalized correlation value output from the power normalizing unit exceeds a predetermined threshold value and detecting a frame start timing at a corresponding time; Improved RF repeater comprising a. The method of claim 2, wherein the timing detector And using the detected frame start timing data and a plurality of frames in the downlink: uplink ratio data defined in the AP specification, automatically calculating starting positions of candidates for a lower downlink section in a frame section. The method of claim 1, The control unit does not directly control the switches SW1 and SW2 in the repeater using the detected frame start timing data and the lower phase switching section start position data, and uses the detected timing data and AP frame specification data in the repeater. An improved RF repeater that creates and uses its own switching control signals to compensate for instantaneous timing detection errors and to maintain operation when no timing is detected for a certain period of time, enabling more stable repeater switching operations. The method of claim 4, wherein The control unit uses the detected frame start timing and lower phase switching section position data, and the downlink section is a section in which [start timing is FS and the ending timing is FE], and the uplink section is “FE + ( AP's TTG-2 xz) ”, and the end timing is“ FS2, the start timing of the next frame ”], and the phase changeover section is [“ start timing is FE and duration duration is (TTG-2 xz of AP). RF repeater comprising a time schedule for controlling the repeater switches SW1 and SW2 so that the section becomes []], and the up-and-down switching section is the [FS2 timing of width “zero”]. The method of claim 4, wherein The control unit uses the detected frame start timing and lower phase switching section position data in order to secure the width of the up / down switching section in the relay switching schedule, and the downlink section is a section in which [start timing is FS and ending timing is FE]. The upstream section is a section in which [start timing is US (time elapsed by “AP TTG-2 xz” in FE) and end timing is UE (timing ahead of FS2 by AP RTG width)], The time schedule for controlling the relay switches SW1 and SW2 is set so that the lower phase switching section is the section in which the start timing is FE and the end timing is US, and the upper and lower switching section is the section in which the starting timing is UE and the ending timing is FS2. RF repeater, characterized in that. The method of claim 6, In the relay switching schedule prepared by the controller, the minimum phase change section width is greater than the switching delay time of the switch used in the repeater, and the position of the phase change section is located between the start and end timings of the phase change section. RF repeater. The method of claim 6, In the repeater switching schedule prepared by the control unit, the minimum upper and lower switching section width is greater than the switching delay time of the switch used in the repeater, the position of the upper and lower switching section is located between the start and end timing of the upper and lower switching section RF repeater. After the timing detector of the repeater finds the frame start timing and the lower phase switching section position, and the controller starts the operation of the internal switches SW1 and SW2 using the timing data, the correlator 110 detects the frame start timing detection mode for a predetermined time. The RF repeater is characterized in that for operating the position detection mode in the lower phase switching section again for a predetermined time to correct the timing errors occurring in the repeater operation process. The method of claim 9, By changing the Downward: Upward ratio at the AP during the repeater operation, if the repeater repeatedly detects the signal level in the current phase change section, or repeatedly finds a new phase change section at an earlier time than the current, An RF repeater which automatically searches for a section and reflects the detected position of the lower phase change section in the operation of the repeater switches SW1 and SW2. The method of claim 10, When the signal level is detected in all the phase switching sections due to radio interference around the repeater, switching using the existing phase switching section position is continued until a signal is detected that the phase switching section falls below a certain level. RF repeater. The method of claim 9, In order to prevent the frequency precision error of the repeater internal standard oscillator accumulating at the switching timing of the switches SW1 and SW2 over time, increasing the timing error, the control unit 111 starts the frame received from the correlator 110. And averaging the timing data for a plurality of times, and updating the switching timings of the switches SW1 and SW2 at regular intervals according to the average value to compensate for the frequency precision error of the internal standard oscillator. The method of claim 12, When the average value of the frame start timing is detected for a short time due to external factors including ambient noise due to an external factor including the ambient noise, the average value is excluded except the corresponding frame start data. RF repeater, characterized in that calculated. The method of claim 9, If the start timing of the frame is not found for a predetermined time due to external noise or external factors such as interruption of signal transmission from the AP, the repeater displays a frame timing detection error alarm and continues operation using existing switching timing data. If a certain frame start timing data is continuously detected after the time elapses, the repeater re-detects the position of the lower phase switching section, updates the time schedule for operating the repeater switch with the corresponding data, and then operates the repeater. . The method of claim 3, wherein When the AP and the relay period signal transmission delay value are known, the timing detection unit may correct the phenomenon in which the phase change section is reduced according to the AP and the relay signal delay value, and the duration widths of the candidates of the phase change interval candidates are reduced. RF repeater, which is calculated by calibrating [TTG-2 xa of AP] (a is AP and relay signal transmission delay value) The method of claim 3, wherein the timing detection unit If the AP and the relay period signal transmission delay value are unknown, the timing detector may adjust the duration width of the candidates for the phase change interval section to correct the phenomenon in which the phase change section is reduced according to the AP relay signal delay value. TTG-2 xz] of the AP, the improved RF repeater (z is the AP and relay period signal transmission delay value of the AP with the largest radius in the wireless network) The method of claim 3, wherein The timing detector checks the reception level of the AP signal input to the reception buffer of the correlator in the calculated start timing and duration period of the calculated phase change interval candidates, and determines a section in which the level falls below a predetermined level as the actual phase change interval. RF repeater, characterized in that. The method of claim 3, wherein The timing detection unit determines an interval falling below a predetermined value as an actual lower phase switching interval by checking an autocorrelation value of an AP signal input to the reception buffer of the correlation part within the calculated starting timing and duration period of the lower phase switching interval candidates. RF repeater, characterized in that. The method of claim 16, The timing detection unit takes into account the switching delay time of the repeater switch, and the start timing is "candidate FE + ST" and the width "AP TTG-2 xz-" And the section where the reception level of the AP signal falls below a certain level with respect to the &quot; ST &quot; section &quot;. The method of claim 16, The timing detection unit takes into account the switching delay time of the repeater switch and includes a starting point of "candidate FE + ST" and a width of "AP TTG-2 xz-ST, which is a section excluding the switching delay time before and after the lower phase switching section. And a section in which the autocorrelation value of the AP signal falls below a predetermined value with respect to the &quot; in section &quot; The method of claim 19, The RF repeater characterized in that if the signal level is detected in a plurality of lower phase change section candidates below a certain level, the faster time is determined as the actual lower phase change section. The method of claim 20, An RF repeater comprising an algorithm for determining a faster time as a lower phase switching section when the autocorrelation value is detected below a predetermined value in a plurality of phase changing section candidates. Calculating the delay value by storing the frame start timing time data when the downlink signal is first transmitted after the base station is installed in the repeater is stored in the repeater memory (not shown) and compared with the frame start timing detected by the repeater. RF repeater characterized by. The method of claim 1, In order to process the digital signal of the correlator, a part of the signal received in the downlink circuit of the repeater is extracted and the frequency is reduced, the A / D converter for analog-to-digital conversion and the digitally received signal are converted to the correlator. An RF repeater characterized by a circuit configuration to input. The method of claim 1, When measuring the level of the signal received by the RF repeater, the concept of time interval is introduced to measure the downlink signal reception level only within the downlink signal section, and the repeater gain is automatically set using the measured data, and the measured data does not change. RF repeater, characterized in that the measured data is continuously used for gain setting and the set gain is maintained in the remaining section, and the repeater gain is automatically reset to the corresponding data when the downlink reception level measurement data of the next frame is changed. The method of claim 25, When measuring the level of the signal received by the RF repeater, the downlink signal level during the preamble period is measured using the frame start timing detected by the repeater, and it is used to automatically set the repeater gain, and the rest of the measurement data is not changed. The RF repeater, characterized in that the measured data is continuously used for gain setting and maintains the set gain, and automatically resets the repeater gain with the corresponding data when the measured data of the preamble level of the next frame is changed. The method of claim 26, The control unit separates and extracts only the signal level during the preamble section from the level data of the downlink signal section measured by the correlator 110 and transmitted to the controller, and checks the gain of the downlink circuit from “(relay to AT). Target level of the preamble to be output)-(preamble level of the AP received at the repeater) ", and the gain of the uplink circuit is set to" (level of the preamble output from the AP)-(preamble level of the AP received at the repeater). ) + (Repeater reverse noise figure) + correction value ". The method of claim 27, The RF repeater calculates an accurate path loss between the AP and the relay period by storing the AP preamble signal output value in the repeater's memory (not shown) and comparing the AP with a preamble signal level value received at the repeater. The method of claim 27, And setting the gain of the uplink circuit of the repeater using the calculated AP and the path loss value of the relay period, and maintaining the set gain until the path loss value is changed. The method of claim 27, Compare the preamble signal level value of the received AP with the preamble target output level value of the repeater downlink circuit required by the repeater standard, set the difference to the repeater downlink gain, and before changing the preamble signal level value of the received AP. The RF repeater, by maintaining a set gain value, it is possible to maintain a constant repeater downlink circuit gain even if the AP output by the traffic volume changes in the data transmission section of the downlink signal section. The method of claim 1, Independent amplification circuit and filter to provide appropriate downlink signal level to control circuits such as D / C, A / D, and correlation used for switching timing detection and automatic gain control of repeaters and to remove out-of-band signals An improved RF repeater that allows the switch to be connected to the down path by default when the repeater initial power is applied so that it can share the amplifier and filter at the first stage of the repeater down path circuit without using The method of claim 2, An RF repeater for detecting a frame start timing from a preamble by using a system using an OFDM modulation scheme by always placing and using a preamble signal at the beginning of a frame. 33. The method of claim 32, After receiving the downlink signal from the AP, it is stored in the shift buffer at the beginning of the correlator. The stored NFFT signals (ie, dk (i), i = 0,1, ... NFFT-1) and repeater memory (not shown) NFFT (i.e., P1 * (i), i = 0,1, ... NFFT-1) stored in the time frame of the AP preamble data is calculated to detect the timing exceeding the threshold by detecting the timing exceeding the threshold. RF repeater, characterized in that looking for. 33. The method of claim 32, When the preamble is an OFDM preamble and has a repeatability with respect to its midpoint (NFFT / 2) and the same data is repeated twice, NFFT / 2 received from the AP and stored in the shift buffer at the first stage of the correlation part. (I.e., dk (i), i = 0,1, ... NFFT / 2-1) AP down signals and NFFT / 2 (i.e. P1 * (i) stored in repeater memory (not shown) , i = 0,1, ... NFFT / 2-1) The correlation between AP preamble data is calculated twice in one frame to confirm that the timing exceeding the threshold appears two times. RF repeater, characterized in that looking for. 33. The method of claim 32, When the preamble is an OFDM preamble and has a repeatability with respect to its midpoint (NFFT / 2) and the same data is repeated twice, the AP downlink stored in the shift buffer 200 at the first stage of the correlation part The first signal group [dk (i)] from i = 0 to NFFT / 2-1 th signal and the second signal group [dk (i + NFFT / 2) from i = NFFT / 2 to NFFT-1 th signal RF repeater which finds the start timing of a frame by calculating the autocorrelation value with]] and confirming the timing which the correlation value exceeding a threshold value appears. 36. The method of claim 35 wherein When the preamble is an OFDM preamble and has a repeatability with respect to its midpoint (NFFT / 2) and the same data is repeated twice, the AP downlink stored in the shift buffer 200 at the first stage of the correlation part The first signal group [dk (i)] from i = 0 to NFFT / 2-1 th signal and the second signal group [dk (i + NFFT / 2) from i = NFFT / 2 to NFFT-1 th signal RF repeater which finds the start timing of the frame by calculating the autocorrelation value with)] and calculating the sum D of NCP + 1 (CP: Cyclic Prefix) and checking the timing at which the value of D exceeds the threshold. . The method of claim 1, wherein the correlation unit A power calculator for calculating the power of the received signal output from the buffer; Normalizes the correlation value output from the correlator to the power output from the power calculator, so that the correlation value is between 0 and 1 regardless of the downlink signal reception level, and outputs the result to the switching timing detector. An improved RF repeater, further comprising a normalizer. The method of claim 27, And wherein (the level of the preamble output from the repeater) and (the level of the preamble output from the AP) are values determined by the standard.

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