JP6094995B2 - Cell search device and cell search method - Google Patents

Description

  The present invention relates to a cell search apparatus and a cell search method for searching for neighboring base stations in a terminal or the like in order to select a cell to be connected.

  In cellular systems such as W-CDMA (Wideband Code Division Multiple Access) and LTE (Long Term Evolution), a terminal selects a neighboring base station in order to select a cell to connect to. Perform a cell search to search for.

  For example, a W-CDMA cell search method in which a transmission waveform is defined by Non-Patent Document 1 is conventionally known (see, for example, Patent Document 1). Also, an LTE cell search method in which a transmission waveform is defined by Non-Patent Document 2 has been known (see, for example, Patent Document 2).

  The cell search is performed not only in the terminal but also in measurement equipment such as a femtocell base station and an area analyzer. Femtocell base stations are installed in places where radio waves are difficult to reach, such as indoors, and can supplement the service area. Further, since the femtocell base station has a small cell radius, the communication capacity per area can be expanded as a whole system.

  However, there are a large number of femtocell base stations, and the accurate propagation environment cannot be grasped, for example, the service area is in an individual's home. For this reason, it is difficult in terms of cost to perform prior placement design and adjustment after placement.

  Therefore, the femtocell base station determines the cell ID and the sequence to be used so as not to collide with the surrounding base stations by implementing a cell search function for acquiring information on the surrounding base stations. The transmission power is determined from the surrounding conditions. In addition, even when a measurement device analyzes a downstream signal of W-CDMA or LTE, a cell search is performed in order to extract a signal of a cell to be analyzed.

  When there are a plurality of base stations around, a plurality of base stations are detected also in the cell search. However, since the signals for each base station interfere with each other, the cell search performance deteriorates. In particular, when there is a base station with a high reception level, there is a problem that it is difficult to detect a base station with a low reception level.

  Such inter-cell interference is a problem of cellular systems in general, and an interference canceller is known as a method for reducing the interference (see, for example, Patent Document 3). This Patent Document 3 discloses a base station apparatus that assigns an optimal communication frequency to a communication channel of the base station apparatus of its own station by identifying a communication frequency used in another base station apparatus.

  The interference canceller used in Patent Document 3 calculates a weighting coefficient for suppressing an interference component based on a channel estimation result and a despread processing result, and multiplies the received signal by the calculated weighting coefficient. Then, received data is demodulated from the multiplication result by the interference canceller by the demodulator at the subsequent stage.

JP 2002-77789 A JP 2009-89185 A JP 2002-218528 A

3rd Generation Partnership Project, TS 25.213, V9.3.0 (2010-09) 3rd Generation Partnership Project, TS 36.211, V9.2.0 (2010-09)

However, the prior art has the following problems.
Since the interference canceller described in Patent Document 3 operates at the time of demodulation after cell search, there is a problem that the performance improvement itself of the cell search cannot be performed.

  The present invention has been made to solve the above-described problems, and has an object to obtain a cell search device and a cell search method that reduce interference between base stations and improve cell search performance. To do.

A cell search device according to the present invention is a cell search device including a cell search unit that performs a cell search process based on a received signal and outputs a cell detection result. By applying replica generation processing to generate a replica signal and subtraction processing to subtract the replica signal from the digital baseband signal generated based on the received signal, the digital baseband signal is updated, and interference of the received signal is reduced. An interference removal unit that performs cancellation processing; and a whitening unit that is provided in a preceding stage of the cell search unit and that performs compression processing of interference included in the received signal by performing whitening processing on the signal after subtraction processing by the interference cancellation unit; The digital baseband signal generated based on the received signal is stored as an initial value, and the signal after subtraction processing by the interference removal unit Further comprising a buffer unit for storing the digital baseband signals sequentially updated to, the cell search unit, the cell search process for a signal compression process by the whitening unit is applied to the signal after the removal process by the interference removal unit The cell generation result is sequentially updated by repeating the predetermined number of times , and the interference cancellation unit performs replica generation processing on the cell detection result by the cell search unit and generates a replica signal. And an inverse filter unit that generates a cancel signal by performing a reverse operation of whitening processing by the whitening unit on the replica signal generated by the replica generation unit, and the latest digital baseband stored in the buffer unit The subtraction process is performed by subtracting the cancellation signal generated by the inverse filter unit from the signal, and the result of the subtraction process is added. It is intended to have a subtraction unit for sequentially updating the digital baseband signal stored in the buffer unit Zui.

The cell search method according to the present invention includes a cell search unit that performs cell search processing based on a received signal and outputs a cell detection result, an interference cancellation unit that performs processing for removing interference included in the received signal, and a reception A whitening unit that performs compression processing of interference included in the signal, and a buffer unit that stores a digital baseband signal generated based on the received signal as an initial value and stores a digital baseband signal that is sequentially updated. A cell search method applied to a provided cell search device, wherein a interference generation unit generates a replica signal for a cell detection result, and a digital baseband signal generated based on a received signal By applying a subtraction process that subtracts the replica signal from the digital baseband signal, the digital baseband signal is updated to eliminate the interference contained in the received signal. In the interference removal step for performing the processing, and in the whitening unit, white processing for compressing interference included in the received signal by performing whitening processing on the signal after the subtraction processing in the interference removal step as preprocessing of the cell search processing A cell search step for outputting a cell detection result by performing a cell search process on the signal subjected to the compression process by the whitening step on the signal after the removal process by the interference removal step in the cell search unit; interference cancellation step, whitening step, and a series of processing by the cell search step, by repeating the number of times predetermined, and a search result update step of sequentially updating the cell detection result, interference removal step cell search Replica generation processing is performed on the cell detection result in step, and a replica signal is generated. Replica generation step, a reverse filter step for generating a cancel signal by performing a reverse operation of whitening processing by the whitening step on the replica signal generated by the replica generation step, and the latest accumulated in the buffer unit A subtractor step for performing subtraction processing by subtracting the cancellation signal generated in the inverse filter step from the digital baseband signal and sequentially updating the digital baseband signal accumulated in the buffer unit based on the result of the subtraction processing a shall which have a door.

  According to the present invention, in the preceding stage of the cell search process, interference is suppressed by the whitening process, and for the cell search process result, the digital baseband signal is updated by the replica generation process and the subtraction process based on the cell search result. In this way, it is possible to obtain a cell search apparatus and a cell search method that reduce interference between base stations and improve cell search performance by repeatedly performing cell search while removing interference.

It is a block diagram of the cell search apparatus in Embodiment 1 of this invention. It is a block diagram of the cell search apparatus in Embodiment 2 of this invention. It is a block diagram of the cell search apparatus in Embodiment 3 of this invention.

  Hereinafter, preferred embodiments of a cell search apparatus and a cell search method of the present invention will be described with reference to the drawings.

Embodiment 1 FIG.
FIG. 1 is a configuration diagram of a cell search apparatus according to Embodiment 1 of the present invention. The cell search apparatus according to the first embodiment includes antennas 10 and 11, RF (Radio Frequency) units 20, 21, ADCs (AD conversion units) 30, 31, a buffer unit 40, a subtracting unit 50, a whitening unit 60, a cell. A search unit 70, a replica generation unit 80, and an inverse filter unit 90 are provided.

  Next, a series of cell search processes by the cell search apparatus having such a configuration will be described in the order of step 1 to step 7.

Step 1: Reception Processing Respective signals received from the antennas 10 and 11 are converted into baseband signals by the RF units 20 and 21, converted to digital basebands by the ADCs 30 and 31, and stored in the buffer unit 40.

Step 2: Subtraction process (interference removal process)
The subtraction unit 50 reads the digital baseband signal accumulated in the buffer unit 40. Note that, in the first processing step when performing the cell search repetitive processing, the cancel signal (that is, the initial value of the cancel signal) input to the subtraction unit 50 is zero. In this case, the subtraction unit 50 outputs the digital baseband signal read from the buffer unit 40 to the whitening unit 60 as it is.

  On the other hand, the cancel signal calculated by the inverse filter unit 90 is input to the subtracting unit 50 in the second and subsequent processing steps when performing the cell search repetitive processing. In this case, the subtracting unit 50 subtracts the cancel signal from the digital baseband signal read from the buffer unit 40, outputs the subtraction result to the whitening unit 60, and stores the digital signal stored in the buffer unit 40. The baseband signal is updated with this subtraction result.

Step 3: Whitening processing (interference compression processing)
The whitening unit 60 performs processing for suppressing interference on the subtraction result read from the subtraction unit 50. Specifically, the whitening unit 60 has three whitening processing functions: whitening on the time axis, whitening on the frequency axis, and whitening between antennas.

  Here, the whitening unit 60 performs the same processing as AGC (Auto Gain control) as the whitening processing on the time axis, and multiplies the reciprocal of the square root of the power of the input signal for each antenna, thereby Generates a signal with reduced temporal fluctuation and compresses interference.

  In addition, the whitening unit 60 performs frequency transform whitening processing by performing Fourier transform on the signal for each antenna, multiplying by the inverse of the square root of the power spectrum, and performing inverse Fourier transform so that the spectrum becomes constant. Signal is generated and interference is compressed.

  The whitening unit 60 compresses interference by obtaining a covariance matrix between antennas and multiplying by an inverse matrix of a Cholesky decomposition result corresponding to the route for whitening between antennas.

  Note that the whitening unit 60 may use any one of three whitening processes including a time axis whitening process, a frequency axis whitening process, and a whitening process between antennas. May be used. Then, the whitening unit 60 outputs the whitened signal to the cell search unit 70.

Step 4: Cell Search Process The cell search unit 70 performs a cell search process similar to that of the prior art and outputs a cell detection result. Here, the cell detection result includes code information, timing, reception level, transmission path information, broadcast channel demodulation result, and the like of the base station detected based on the received signal.

  The cell search unit 70 performs W-CDMA cell search processing or LTE cell search processing. In addition, when a plurality of systems are operated at the same frequency, the cell search unit 70 performs a cell search process for each system.

The cell search unit 70 performs the following series of processes as the W-CDMA cell search process.
-PSC (primary synchronization code) is detected.
Next, SSC (secondary synchronization codes) is detected, and frame timing and scrambling code candidates are obtained.
Next, a scrambling code is identified from CPICH (Common Pilot Channel).

Thereafter, transmission path estimation is performed from CPICH, and PCCPCH (Primary Common Control Physical Channel) in which broadcast information is transmitted is demodulated.
Since PCCPCH is encoded with a convolutional code, it is decoded by Viterbi decoding to obtain broadcast information.

The cell search unit 70 performs the following series of processes as the LTE cell search process.
Detect PSS (Primary synchronization signal).
Next, SSS (Secondary synchronization signal) is detected to obtain frame timing and PCI (Physical Cell ID).

Thereafter, transmission path estimation is performed from RS (Reference signal), and PBCH (Physical broadcast channel) is demodulated.
Since PBCH is encoded with a convolutional code, it is decoded with Viterbi decoding to obtain broadcast information (MIB (Master Information Block)).

Further, PCFICH (Physical control format channel), PDCCH (Physical downlink control channel), and PDSCH (Physical downlink shared channel) are sequentially demodulated.

Since PDSCH is turbo-encoded, broadcast information (SIB (System Information Block)) is obtained by turbo-decoding the demodulation result of PDSCH.

Step 5: Replica Generation Processing The replica generation unit 80 inputs the cell detection result by the cell search unit 70. Then, the replica generation unit 80 generates a transmission signal of the base station from the cell detection result, multiplies the transmission path information, generates a replica signal, and outputs the replica signal to the inverse filter unit 90.

  Specifically, the replica generation unit 80 generates a W-CDMA replica signal for the W-CDMA cell search result, and generates an LTE replica signal for the LTE cell search result. .

  Here, the replica generation unit 80 obtains a W-CDMA replica signal by multiplying a signal obtained by multiplexing CPICH, PCCPCH, PSS, and SSS with a channel estimation value. On the other hand, the replica generation unit 80 obtains an LTE replica signal by multiplying a signal obtained by multiplexing RS, PSS, SSS, PBCH, PCFICH, PDCCH, and PDSCH with a channel estimation value.

Step 6: Inverse Filter Processing The inverse filter unit 90 is an inverse filter of the whitening unit 60, and outputs the output to the subtraction unit 50 as a cancel signal. Specifically, the inverse filter unit 90 only needs to perform the inverse operation of the whitening unit 60, and multiplies the replica signal generated by the replica generation unit 80 by the inverse of the value multiplied by the whitening unit 60.

Step 7: Iterative Processing of Steps 2 to 6 In the cell search processing in the first embodiment, interference is suppressed by the whitening processing at Step 3, and interference is performed by the replica generation processing at Step 5 and the subtraction processing at Step 2 and Step 6. The cell search process of step 4 is repeatedly executed while removing.

  Here, the number of repetitions is set in advance. However, when the desired number of base stations is detected, the process is repeated at that point, and the series of cell search processes is terminated.

  As described above, according to the first embodiment, interference suppression is performed by the whitening process before the cell search process. Furthermore, the cell search processing result is repeatedly subjected to cell search while removing interference by performing replica generation processing and subtraction processing to update the digital baseband signal based on the cell detection result. Yes. As a result, it is possible to obtain a cell search apparatus and a cell search method that reduce interference between base stations and improve cell search performance.

Embodiment 2. FIG.
In the second embodiment, a cell search device and a cell search method that can obtain the same effect with a configuration different from that of the first embodiment will be described.

  FIG. 2 is a configuration diagram of the cell search apparatus according to Embodiment 2 of the present invention. The cell search apparatus according to the second embodiment includes antennas 10 and 11, RF units 20 and 21, ADCs 30 and 31, buffer unit 40, subtraction unit 50, whitening unit 60, cell search unit 70, and replica generation unit 80. It is prepared for.

Compared with the configuration of FIG. 1 in the first embodiment, the configuration of FIG. 2 in the second embodiment is different in the following two points.
(Difference 1) In the first embodiment, the digital baseband signal accumulated in the buffer unit 40 is updated by the subtraction result (that is, the signal before whitening processing) by the subtraction unit 50. On the other hand, in the second embodiment, the digital baseband signal accumulated in the buffer unit 40 is updated by the signal after the whitening process by the whitening unit 60.
(Difference 2) Along with the difference 1, the inverse filter unit 90 is unnecessary.

  As described above, according to the second embodiment, similarly to the first embodiment, the interference suppression is performed by the whitening process before the cell search process. Further, as in the first embodiment, the cell detection processing result is repeatedly subjected to cell search while performing interference generation by performing replica generation processing and subtraction processing. As a result, an effect similar to that of the first embodiment can be obtained. Furthermore, an additional effect of reducing the amount of calculation can be obtained by adopting a configuration in which the subtracting process is performed between the signals after the whitening process, thereby eliminating the need for the inverse filter unit.

Embodiment 3 FIG.
In the third embodiment, a cell search apparatus and a cell search method that can obtain the same effect with a configuration different from those of the first and second embodiments will be described.

  FIG. 3 is a configuration diagram of the cell search apparatus according to Embodiment 3 of the present invention. The cell search apparatus according to the third embodiment includes antennas 10 and 11, RF units 20 and 21, ADCs 30 and 31, buffer unit 40, subtraction unit 50, whitening unit 60, cell search unit 70, and replica generation unit 80. It is prepared for.

Compared with the configuration of FIG. 2 in the second embodiment, the configuration of FIG. 3 in the third embodiment is different in the following one point.
(Difference 1) In the second embodiment, processing is performed in the order of the buffer unit 40, the subtracting unit 50, and the whitening unit 60, whereas in the third embodiment, the subtracting unit 50, white color is processed. Processing is performed in the order of the conversion unit 60 and the buffer unit 40.

  As described above, according to the third embodiment, similarly to the second embodiment, the interference suppression is performed by the whitening process before the cell search process. Further, the cell search processing result is repeatedly performed while removing the interference by applying the replica generation processing and the subtraction processing to the cell detection processing result as in the second embodiment. As a result, the same effect as in the second embodiment can be obtained. Furthermore, by arranging the buffer unit immediately before the cell search unit, an additional effect of facilitating the interface to the cell search unit can be obtained.

  10, 11 Antenna, 20, 21 RF unit, 30, 31 ADC, 40 buffer unit, 50 subtraction unit, 60 whitening unit, 70 cell search unit, 80 replica generation unit, 90 inverse filter unit.

Claims (6)

A cell search device including a cell search unit that performs a cell search process based on a received signal and outputs a cell detection result,
By performing a replica generation process for generating a replica signal and a subtraction process for subtracting the replica signal from a digital baseband signal generated based on the received signal, with respect to the cell detection result by the cell search unit, An interference removal unit that updates the digital baseband signal and performs a removal process of interference included in the received signal;
A whitening unit that is provided in a preceding stage of the cell search unit and performs a compression process of interference included in the received signal by performing a whitening process on the signal after the subtraction process by the interference removal unit ;
A buffer unit that accumulates a digital baseband signal generated based on the received signal as an initial value, and that sequentially updates and accumulates the digital baseband signal with the signal after the subtraction processing by the interference removal unit; Prepared,
The cell search unit repeats the cell search process on the signal subjected to the compression process by the whitening unit with respect to the signal after the cancellation process by the interference cancellation unit a predetermined number of times. To update the cell detection results sequentially ,
The interference removing unit
A replica generation unit that performs the replica generation process on the cell detection result by the cell search unit and generates the replica signal;
An inverse filter unit that generates a cancel signal by performing a reverse operation of whitening processing by the whitening unit on the replica signal generated by the replica generation unit;
The subtraction process is performed by subtracting the cancellation signal generated by the inverse filter unit from the latest digital baseband signal stored in the buffer unit, and the buffer unit stores the subtraction process based on the result of the subtraction process. A subtractor for sequentially updating the digital baseband signals received;
A cell search device having: A cell search device including a cell search unit that performs a cell search process based on a received signal and outputs a cell detection result,
By performing a replica generation process for generating a replica signal and a subtraction process for subtracting the replica signal from a digital baseband signal generated based on the received signal, with respect to the cell detection result by the cell search unit, An interference removal unit that updates the digital baseband signal and performs a removal process of interference included in the received signal;
A whitening unit that is provided in a preceding stage of the cell search unit and performs a compression process of interference included in the received signal by performing a whitening process on the signal after the subtraction process by the interference removal unit ;
A buffer unit that accumulates the digital baseband signal generated based on the received signal as an initial value, and that sequentially updates and accumulates the digital baseband signal by the signal after the whitening processing by the whitening unit; In addition,
The cell search unit repeats the cell search process on the signal subjected to the compression process by the whitening unit with respect to the signal after the cancellation process by the interference cancellation unit a predetermined number of times. To update the cell detection results sequentially ,
The interference removing unit
A replica generation unit that performs the replica generation process on the cell detection result by the cell search unit and generates the replica signal;
A subtracting unit that performs the subtraction process by subtracting the replica signal generated by the replica generating unit from the latest digital baseband signal stored in the buffer unit;
Have
The cell search device , wherein the whitening unit sequentially updates the digital baseband signal stored in the buffer unit based on the result of the whitening process . A cell search device including a cell search unit that performs a cell search process based on a received signal and outputs a cell detection result,
By performing a replica generation process for generating a replica signal and a subtraction process for subtracting the replica signal from a digital baseband signal generated based on the received signal, with respect to the cell detection result by the cell search unit, An interference removal unit that updates the digital baseband signal and performs a removal process of interference included in the received signal;
A whitening unit that is provided in a preceding stage of the cell search unit and performs a compression process of interference included in the received signal by performing a whitening process on the signal after the subtraction process by the interference removal unit ;
A buffer unit for sequentially storing digital baseband signals after the whitening processing by the whitening unit ;
The cell search unit repeats the cell search process on the signal subjected to the compression process by the whitening unit with respect to the signal after the cancellation process by the interference cancellation unit a predetermined number of times. To update the cell detection results sequentially ,
The interference removing unit
A replica generation unit that performs the replica generation process on the cell detection result by the cell search unit and generates the replica signal;
The replica signal generated by the replica generation unit from a signal that is sequentially updated by the latest digital baseband signal stored in the buffer unit, with a digital baseband signal generated based on the received signal as an initial value. Subtracting unit for performing the subtraction process by subtracting
Have
The cell search unit performs the cell search process on the latest digital baseband signal stored in the buffer unit after the whitening process by the whitening unit by repeating a predetermined number of times. A cell search device for sequentially updating the cell detection results . A cell search unit that performs a cell search process based on a received signal and outputs a cell detection result;
An interference removal unit that performs a process of removing interference included in the received signal;
A whitening unit for compressing interference included in the received signal ;
A cell search method applied to a cell search apparatus including a buffer unit that stores a digital baseband signal generated based on the received signal as an initial value and stores the digital baseband signal updated sequentially. There,
In the interference removal unit, the cell detection result is subjected to replica generation processing for generating a replica signal and subtraction processing for subtracting the replica signal from a digital baseband signal generated based on the received signal. An interference removal step of updating the digital baseband signal and performing a removal process of interference included in the received signal;
In the whitening unit, as a pre-process of the cell search process, a whitening step of performing a compression process of interference included in the received signal by performing a whitening process on the signal after the subtraction process in the interference removal step; ,
In the cell search unit, a cell that outputs the cell detection result by performing the cell search process on the signal subjected to the compression process in the whitening step with respect to the signal after the removal process in the interference removal step A search step;
A search result update step of sequentially updating the cell detection result by repeating a series of processes by the interference removal step, the whitening step, and the cell search step a predetermined number of times , and
The interference cancellation step includes
Performing the replica generation process on the cell detection result by the cell search step, and generating the replica signal;
An inverse filter step of generating a cancel signal by performing a reverse operation of the whitening process by the whitening step on the replica signal generated by the replica generation step;
The subtraction process is performed by subtracting the cancel signal generated in the inverse filter step from the latest digital baseband signal stored in the buffer unit, and the subtraction process is performed based on the result of the subtraction process. Subtracting step for sequentially updating the digital baseband signal
A cell search method comprising: A cell search unit that performs a cell search process based on a received signal and outputs a cell detection result;
An interference removal unit that performs a process of removing interference included in the received signal;
A whitening unit for compressing interference included in the received signal ;
A cell search method applied to a cell search apparatus including a buffer unit that stores a digital baseband signal generated based on the received signal as an initial value and stores the digital baseband signal updated sequentially. There,
In the interference removal unit, the cell detection result is subjected to replica generation processing for generating a replica signal and subtraction processing for subtracting the replica signal from a digital baseband signal generated based on the received signal. An interference removal step of updating the digital baseband signal and performing a removal process of interference included in the received signal;
In the whitening unit, as a pre-process of the cell search process, a whitening step of performing a compression process of interference included in the received signal by performing a whitening process on the signal after the subtraction process in the interference removal step; ,
In the cell search unit, a cell that outputs the cell detection result by performing the cell search process on the signal subjected to the compression process in the whitening step with respect to the signal after the removal process in the interference removal step A search step;
A search result update step of sequentially updating the cell detection result by repeating a series of processes by the interference removal step, the whitening step, and the cell search step a predetermined number of times , and
The interference cancellation step includes
Performing the replica generation process on the cell detection result by the cell search step, and generating the replica signal;
A subtraction step for performing the subtraction process by subtracting the replica signal generated by the replica generation step from the latest digital baseband signal stored in the buffer unit;
Have
The cell search method in which the whitening step sequentially updates the digital baseband signal stored in the buffer unit based on the result of the whitening process. A cell search unit that performs a cell search process based on a received signal and outputs a cell detection result;
An interference removal unit that performs a process of removing interference included in the received signal;
A whitening unit for compressing interference included in the received signal ;
A cell search method applied to a cell search device comprising a buffer unit that sequentially stores digital baseband signals after processing by the whitening unit ,
In the interference removal unit, the cell detection result is subjected to replica generation processing for generating a replica signal and subtraction processing for subtracting the replica signal from a digital baseband signal generated based on the received signal. An interference removal step of updating the digital baseband signal and performing a removal process of interference included in the received signal;
In the whitening unit, as a pre-process of the cell search process, a whitening step of performing a compression process of interference included in the received signal by performing a whitening process on the signal after the subtraction process in the interference removal step; ,
In the cell search unit, a cell that outputs the cell detection result by performing the cell search process on the signal subjected to the compression process in the whitening step with respect to the signal after the removal process in the interference removal step A search step;
A search result update step of sequentially updating the cell detection result by repeating a series of processes by the interference removal step, the whitening step, and the cell search step a predetermined number of times , and
The interference cancellation step includes
Performing the replica generation process on the cell detection result by the cell search step, and generating the replica signal;
The replica signal generated by the replica generation step from a signal that is sequentially updated by the latest digital baseband signal stored in the buffer unit, with the digital baseband signal generated based on the received signal as an initial value Subtracting step for applying the subtraction process by subtracting
Have
In the cell search step, the cell search process is repeated for a predetermined number of times on the latest digital baseband signal accumulated in the buffer unit after the whitening process in the whitening step. A cell search method for sequentially updating the cell detection results .

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