KR20130058166A - Method and apparatus for prach detection in lte system - Google Patents

Abstract

PURPOSE: A physical random access channel detecting method in an LTE(Long Term Evolution) system and a device thereof are provided to calculate a peak value by adding up a plurality of sequences. CONSTITUTION: A sequence reception unit receives two or more sequences from a plurality of Zadoff-Chu sequences. An adder(502) adds up the sequences received from the sequence reception unit. A calculator(506) calculates a random access pre-amble received from a user terminal and a signal outputted from the adding unit. An IFFT(Inverse Fast Fourier Transform) unit(508) executes the IFFT of a signal outputted from the calculator. A peak value detector(510) detects a peak value of a signal outputted from the IFFT unit. [Reference numerals] (504) Multiplexer; (506) Calculator(A·B*); (510) Peak value detector

Description

Method and apparatus for detecting physical random access channel in LTE system {Method and apparatus for PRACH detection in LTE system}

The present invention relates to a PRACH detection method in an LTE system, and more particularly, to a method for detecting a root Zadoff-Chu sequence used by a user terminal among a plurality of Root Zadoff-Chu sequences.

The PRACH of LTE refers to a physical channel for transmission of a random access (RA) preamble corresponding to the first step of a random access process in which a UE requests to establish a connection with a network. That is, the time-frequency resource on which the RA preamble is transmitted is called PRACH. The network broadcasts to all terminals through system information (SIB-2) indicating which time-frequency resource can be used for RA preamble transmission.

The RA preamble means RA request information of a UE transmitted to a network through a PRACH. There are a total of 64 available RA preambles in one network, and how these 64 preambles can be generated is broadcast through the system information of the network.

1 illustrates an RA preamble. As shown in FIG. 1, the RA preamble includes a preamble sequence and a Cyclic Prefix (CP), and is classified into five types according to the length of the sequence and the CP.

2 illustrates preamble type-specific parameters. As shown in FIG. 2, the length of the preamble may be slightly shorter than 1 Sub-frame (1 ms) and slightly shorter than (Format 0), 2 Sub-frame (Format 1,2) or 3 Sub-frame (Format 3). It can also be a length. Therefore, in the case of a preamble using format 0, the preamble transmission time can be every sub-frame, and formats 1 and 2 are transmitted at least two sub-frame intervals, and format 3 is transmitted at least three sub-frame intervals. It is possible. The transmission possible time of the preamble is also known to the terminal by the system information of the network.

The preamble format used in the network is determined by the cell radius. That is, in case of a large radius cell, the RA preamble can be detected without a loss of data even if there is a large propagation delay by using a preamble format that supports a long CP. The preamble is generated based on Zadoff-Chu and Cyclic Shift Value. Zadoff-Chu sequences have the property of ensuring orthogonality to cyclic shifts. That is, even if all the sequences with different Cyclic Shift Values derived from one root Zadoff-Chu sequence are summed, each Zadoff-Chu sequence component is generated through correlation with the root Zadoff-Chu sequence. It can be detected without loss. This makes it possible to detect all RA preambles at once even if several UEs transmit RA preambles at the same time.

The RA preamble that can be used in the network can be determined by a combination of the root index, the cyclic shift index, and the unit cyclic shift value of the Zadoff-Chu sequence. . The root index is an index that determines the root Zadoff-Chu sequence, a single cyclic shift value is a basic unit of the cyclic shift value, and a cyclic shift index is used to perform a cyclic shift by applying a single cyclic shift value several times. Index to determine whether or not. Among them, information known to the terminal through system information of the network is a root index and a single cyclic shift value, and the cyclic shift index is arbitrarily determined by the terminal within a range of 64.

Basically, the terminal selects an arbitrary cyclic shift index to the root Zadoff-Chu sequence informed by the network to configure the RA preamble sequence. In some cases, 64 RA preambles may not be generated by cyclic shifts from one root Zadoff-Chu sequence alone. In this case, RAs may be generated from a root Zadoff-Chu sequence at another root index to support 64 RA preambles. You will create a preamble.

For example, if the root index is 0, the single cyclic shift value is 15, and the length of the RA preamble sequence is 839 Sample, only 839/15 = 55 RA preambles can be generated from the length 839 to the single cyclic shift value 15. . In this case, nine additional RA preambles having a single cyclic shift value 15 are supported from the next root index root index 1 so that the total number of RA preambles available in the network can be 64. Therefore, when the UE selects 60 as the cyclic shift index, the RA preamble sequence generated by the UE applies a cyclic shift index of 60-55-1 = 4 to the root Zadoff-Chu sequence of the root index 1 and thus total 4 *. The sequence is applied with a cyclic shift of 15 = 60 samples.

The RA preamble generated by the UE-selected cyclic shift index is modulated by SC-FDMA like other uplink channels of LTE. At this time, unlike general channels supporting 15 kHz subcarrier spacing, 1.25 kHz or 7.5 kHz (preamble format) By applying Subcarrier Spacing of 4 Only), the preamble is transmitted in a narrow area of about 1.4MHz relative to the system bandwidth.

An object of the present invention is to propose a method for reducing the complexity of detecting a PRACH in a base station.

To this end, in the LTE system of the present invention, an apparatus for detecting a physical random access channel includes a sequence receiving unit which receives at least two sequences of a plurality of Zadoff-Chu sequences; An adder configured to add a sequence received by the sequence receiver; A calculator for calculating a signal output from the adder and a random access preamble received from a user terminal; An IFFT unit for IFFT converting the signal output from the operation unit; And a peak detector for detecting a peak value of the signal output from the IFFT unit.

To this end, in the LTE system of the present invention, a method for detecting a physical random access channel includes receiving at least two sequences of a plurality of Zadoff-Chu sequences at each of a plurality of sequence receiving units; Adding the sequences received for each sequence receiver; Outputting the added sequences sequentially one by one for each sequence receiving unit; Calculating the output sequence and the random access preamble received from the user terminal; IFFT transforming the computed signal; Detecting a peak value of the IFFT-converted signal, wherein the calculating step multiplies the random signal preamble by conjugating the output signal.

When the PRACH is detected using the PRACH detection algorithm in the base station according to the present invention, the complexity of the base station can be reduced. That is, although the peak value is calculated for each of the existing 64 sequences, the present invention has the effect of significantly reducing the complexity at the base station by calculating the peak value by summing the plurality of sequences.

1 illustrates an RA preamble.
2 illustrates preamble type-specific parameters.
3 illustrates an example of a PRACH received by a base station according to an embodiment of the present invention.
4 illustrates a structure of a PRACH detection algorithm in a base station according to an embodiment of the present invention.
5 illustrates a correlation and peak detector according to an embodiment of the present invention.

The foregoing and further aspects of the present invention will become more apparent through the preferred embodiments described with reference to the accompanying drawings. Hereinafter will be described in detail to enable those skilled in the art to easily understand and reproduce through this embodiment of the present invention.

When the UE accesses the network through the PRACH, the RA preamble sequence is generated by selecting one of the 64 preamble IDs (identifiers) supported by the network at the PRACH transmission time indicated by the system information, and then transmitting the preamble on the PRACH resource. Done. In fact, the system information defines two subsets for the 64 preamble IDs, and the UE randomly selects the preamble IDs from one subset of the two subsets. In this case, since the UE already knows the synchronization of the network through the DL synchronization channel, the UE can know the time resource capable of PRACH transmission. Signals are timed by propagation delay to the network.

From the network's point of view, a preamble sent by several terminals may be received. The received preambles may have different IDs or may have the same IDs. If different terminals transmit preambles having the same ID, the base station transmits only one DL response message (RAR) for the overlapping preamble ID. In this case, several terminals respond to one response and a collision occurs. Resolving such collisions is the responsibility of the Random Access procedure after the RA preamble transmission. If different UEs transmit different preambles with different IDs, the network can detect the preambles sent by each UE, so that different DL response messages for each RA attempt are transmitted to the UEs, thus ensuring a reliable DL without conflict. Signaling becomes possible.

When each terminal transmits a preamble having a different ID, each preamble reaching the base station is received with a different propagation delay according to the position of the terminal. For example, assuming that three terminals simultaneously transmit preambles having different IDs, and the positions of each terminal are very close to the base station, the midpoint of the cell, and the edge of the cell, each preamble received by the base station is as follows. It can be expressed as

3 illustrates an example of a PRACH received by a base station according to an embodiment of the present invention. 3 will be described in detail with respect to the PRACH received by the base station according to an embodiment of the present invention.

Referring to FIG. 3, when the RA preamble is received by the base station, the base station extracts data after the CP length according to the preamble format set in the base station based on the system synchronization managed by the base station by the preamble sequence length ( T _SEQ ) and preambles it. Used for detection. If the RA preamble transmitted from a specific terminal reaches the base station through a propagation delay longer than the CP length ( T _CP ), the preamble sequence extracted by the base station cannot be accurately performed because the data is lost by a specific length. Do. Thus, the cell radius is limited by the CP length.

The base station performs a detection operation on the transmission preamble based on the extracted received data. At this time, by using the characteristics of the Zadoff-Chu sequence, it is possible to detect the preambles of several terminals at once. As described above, the preamble sequence derived from one root Zadoff-Chu sequence is guaranteed orthogonality according to Cyclic Shift. Through the correlation operation of the cyclic shift value of each preamble sequence can be estimated. If there is a propagation delay in each preamble sequence, the cyclic shift value estimated by the base station is a value obtained by adding the propagation delay to the original preamble sequence cyclic shift value. The PRACH detection method will be described later.

4 illustrates a structure of a PRACH detection algorithm in a base station according to an embodiment of the present invention. Hereinafter, the structure of the PRACH detection algorithm in the base station according to an embodiment of the present invention will be described in detail with reference to FIG. 4.

4, the detection algorithm structure includes an ADC, a frequency shift compensator, a BPF, an integer generator, a down sampling unit, an FFT, a root Zadoff-Chu sequence generator, a correlation and a peak detector. Of course, it is obvious that other configurations may be included in the detection algorithm structure in addition to the above-described configuration.

The ADC 400 converts the received analog signal into a digital signal.

The frequency shift compensator 402 shifts the signal to the baseband frequency band by compensating the 7.5 kHz frequency shift applied during the preamble modulation process.

The BPF 404 performs band pass filtering to leave only signals in the PRACH frequency band in order to prevent aliasing that may occur during downsampling.

The integer generator 406 stores the filter constants of the BPF in the form of a table and transfers them to the BPF during filtering.

The down sampling unit 408 down-samples 24576 samples at 30.72MHz sampling rate 12 times to perform 248-point FFT to reduce the amount of computation.

The FFT unit 410 performs an FFT to convert the time domain signal into a frequency domain signal.

The Zadoff-Chu sequence generation unit 412 reduces the amount of calculation by storing the root Zadoff-Chu sequence to be a reference in advance by performing a DFT.

The correlation and peak detector 414 sequentially estimates the preamble ID and delay time by sequentially correlating a signal output from the FFT and a sequence generated by the root Zadoff-Chu sequence generator to search for a sequence having the highest peak value.

5 illustrates a correlation and peak detector according to an embodiment of the present invention. Hereinafter, FIG. 5 will be described in detail with reference to the correlation and peak detector according to an embodiment of the present invention.

Referring to FIG. 5, the correlation and peak detector includes a plurality of sequence receivers, an adder, a multiplexer, a calculator, an IFFT unit, and a peak detector. Of course, it is obvious that other configurations may be included in the correlation and peak detection units in addition to the above configurations.

The sequence receiver 500 receives a root zadoff-chu sequence generated by the sequence generator. As described above, 64 sequences are generated by the sequence generator, and the generated sequences are provided to one of the plurality of sequence receivers.

The present invention proposes 8 sequence receivers, and each sequence receiver receives 8 of 64 sequences sequentially. Of course, the number of sequence receivers may vary, and in this case, the number of sequences provided to each sequence receiver also varies. That is, when the number of sequence receivers is 16, each sequence receiver receives four sequences. In addition, when the number of sequence receivers is four, each sequence receiver receives 16 sequences.

Of course, in addition to the above-described manner may proceed in other ways. That is, eight sequences are provided to each sequence receiver having four sequence receivers to perform a series of operations. When the series ends, the sequence receiving unit sequentially receives 8 sequences that have not performed the sequence and performs a series of operations. When the number of such sequence receivers is small, a series of processes proposed by the present invention may be performed through the above-described process.

The sequence receiver includes an adder 502 therein. Of course, the sequence receiver and adder may be configured separately. The adder 502 adds the sequence received by the sequence receiver 500 and provides it to the multiplexer 504.

The multiplexer 504 provides any one of sequence addition values provided from the plurality of adders to the correlation unit. That is, the multiplexer 504 provides the received sequence additions to the calculator 506 one by one in a set time unit.

The calculation unit 508 calculates the preamble signal provided from the received FFT unit and the sequence addition value provided from the multiplexer 504. That is, the calculating unit 506 multiplies one of the preamble signal provided from the FFT unit 508 and the sequence addition value provided from the multiplexing unit and then multiplies the complex conjugate.

The IFFT unit 510 performs IFFT conversion on the signal output from the calculator. The signal output from the IFFT unit 510 is peak data that can be distinguished according to the root Zadoff-Chu sequence and the Cyclic Shift Value of each preamble.

The peak detector 512 extracts the peak value of the received signal. The peak detector stores the received signal and the extracted peak value, and searches for a signal having the maximum peak value. The above process is repeated with respect to the maximum peak signal. That is, one of the sequences included in the signal having the maximum peak value is a sequence included in the preamble transmitted by the terminal.

Therefore, the above-described process is repeated with respect to the sequence included in the signal having the maximum value to finally retrieve the sequence having the maximum value. It is possible to estimate the ID and propagation delay of the preamble using the retrieved sequence.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the scope of the present invention .

400: ADC 402: frequency shift compensation unit
404: BPF 406: integer generation unit
408: down sampling unit 410: FFT
412: Root Zadoff-Chu sequence generation unit
414: correlation and peak detector

Claims (7)

A sequence receiver configured to receive at least two sequences of a plurality of Zadoff-Chu sequences;
An adder configured to add a sequence received by the sequence receiver;
A calculator for calculating a signal output from the adder and a random access preamble received from a user terminal;
An IFFT unit for IFFT converting the signal output from the operation unit;
And a peak detector for detecting a peak value of the signal output from the IFFT unit.
The method of claim 1, wherein the operation unit,
The apparatus for detecting a physical random access channel in an LTE system, characterized in that after multiplying the signal output from the adder and multiplied by the random access preamble.
The method of claim 2,
And a multiplexer for transmitting one of the signals received from a plurality of sequence receivers to the calculator.
4. The apparatus of claim 3, wherein the number of Zadoff-Chu sequences input to each sequence receiving unit is the same.
5. The method of claim 4,
An ADC for converting an input analog signal into a digital signal;
A frequency shift compensator for compensating the 7.5 kHz frequency shift to shift the signal to the baseband frequency band;
A BPF that performs band pass filtering;
A down sampling unit performing down sampling;
And an FFT unit for converting the time domain signal into a frequency domain signal.
And a random access preamble, which is a signal output from the FFT unit, to the operation unit.
The apparatus of claim 5, further comprising: an integer generator configured to transfer the filter constant of the BPF to the BPF.
Receiving at least two sequences of a plurality of Zadoff-Chu sequences at each of the plurality of sequence receiving units;
Adding the sequences received for each sequence receiver;
Outputting the added sequences sequentially one by one for each sequence receiving unit;
Calculating the output sequence and the random access preamble received from the user terminal;
IFFT transforming the computed signal;
Detecting a peak value of the signal after IFFT conversion;
Wherein the calculating comprises:
And conjugating the output signal and multiplying the random access preamble by the random access preamble.

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