KR20080037495A - Method for adjusting rach transmission against frequency offset, method for transmitting rach signal, and method for detecting rach - Google Patents

Abstract

A method for setting the transmission of an RACH(Random Access Channel), a method for transmitting the RACH, and a method for detecting the RACH are provided to reduce the influence due to frequency offset by independently setting an RACH-setting condition for a high-speed terminal and an RACH-setting condition for a low-speed terminal. An RACH-setting condition for a high-speed terminal and an RACH-setting condition for a low-speed terminal are set, respectively. The set RACH-setting conditions are transmitted to a downlink. The RACH-setting conditions include one or more of conditions for RACH structures for the high-speed terminal and the RACH-speed terminal, conditions for preamble structures applied to the high-speed terminal and the low-speed terminal, and conditions for sequence sets for the high-speed terminal and the low-speed terminal.

Description

Method for Adjusting RACH Transmission Against Frequency Offset, Method For Transmitting RACH Signal, And Method For Detecting RACH}

1 is a diagram illustrating a basic structure of a RACH according to whether a cyclic preposition is included.

2 is a diagram for explaining a method of reducing RACH length according to one embodiment of the present invention;

3A and 3B are RACHs having a short length in accordance with one embodiment of the present invention. In the case of using a 0.5 ms RACH, a graph showing detection performance and false alarm rate according to each condition is shown.

4A and 4B are graphs illustrating detection performance and false alarm rates according to respective conditions when using a RACH of 1 ms.

FIG. 5 illustrates the advantages of a scheme for setting a RACH preamble to have a repeating structure in accordance with an embodiment of the present invention. FIG.

6A and 6B are diagrams for explaining the effect of the frequency offset in the frequency domain when the RACH preamble is set to have a repetitive structure according to an embodiment of the present invention.

7A and 7B are graphs illustrating detection performance and false alarm rate when the RACH is designed to have a structure in which the preamble is repeated twice according to an embodiment of the present invention.

8A and 8B are graphs illustrating detection performance and false alarm rate when the RACH is designed to have a structure in which the preamble is repeated three times according to an embodiment of the present invention.

9A through 9C are diagrams for explaining various ways of setting the RACH preamble to have a repetitive structure according to one embodiment of the present invention.

10 is a diagram for explaining a method of setting a high speed terminal RACH and a low speed terminal RACH according to an embodiment of the present invention.

11 is a flowchart illustrating a method of accessing a RACH when a terminal cannot estimate its own speed according to an embodiment of the present invention.

FIG. 12 is a view for explaining an example of using a CAZAC sequence to separately set a fast terminal RACH sequence and a slow terminal RACH sequence according to one embodiment of the present invention; FIG.

FIG. 13 is a diagram for describing a method of performing random access by a terminal predicting a false alarm of a base station according to one embodiment of the present invention; FIG.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to wireless communication technology, and more particularly, to a RACH setting method, a RACH transmission method, a sequence detection method, and a random access method in preparation for frequency offset.

The RACH is a channel used by the terminal to obtain initial uplink synchronization. This is a channel used when the UE first powers on, or when it is in idle mode for a long time and then becomes active again and needs to reconfigure uplink synchronization, and does not synchronize time synchronization or frequency synchronization. Available channel.

The RACH channel basically supports multiple users, and each terminal transmits a specific preamble sequence when accessing the RACH, and when the base station recognizes this and transmits a signal in downlink, the terminal transmits the information. Update his / her time synchronization information. In this case, when the frequency synchronization information is transmitted together, the frequency synchronization information can also be used for the correction of the terminal.

1 is a diagram illustrating a basic structure of a RACH according to whether a cyclic prefix is included.

As shown in FIG. 1, the RACH may be defined in two forms: an RACH 101 using a cyclic prefix (“CP”) and an RACH 102 not using a CP.

When CP is used for RACH like RACH 101, the inter-channel orthogonality is maintained by reducing interference between channels, but the sequence length is slightly shortened, and the correlation length is shortened when the sequence length is shortened. This may worsen the detection performance.

On the other hand, when the RACH does not include a CP, such as the RACH 102, the length of the preamble is long, but when performing the preamble search in the frequency domain, orthogonality between sequences is not maintained and performance is reduced. Can be.

On the other hand, since the RACH preamble is a signal transmitted before a closed loop between the terminal and the base station is generated, the RACH preamble has a feature that is very vulnerable to a frequency offset as the terminal generates and transmits the signal. . Such a frequency offset may cause a problem that the base station receiving the RACH increases a false alarm rate or decreases a detection probability.

Therefore, a study on how to configure the RACH to cope with the effect of this frequency offset in the RACH transmission, and how the UE can transmit the RACH in accordance with the RACH configuration has been discussed.

In order to solve the problems described above, an object of the present invention is to propose how to set the terminal to transmit the RACH to reduce the false alarm rate of the base station due to the frequency offset during RACH transmission, and to increase the probability of detecting the RACH, Accordingly, the present invention proposes how to configure the RACH transmission method according to whether the UE can estimate its own speed.

The RACH transmission setting method according to an embodiment of the present invention for achieving the above object is a method for setting the RACH transmission of the terminal in preparation for the frequency offset, the RACH setting condition for the high speed terminal and the RACH setting condition for the low speed terminal Setting each; And transmitting the set RACH setting condition for the high speed terminal and the RACH setting condition for the low speed terminal in downlink.

In this case, the RACH setting condition for the high speed terminal and the RACH setting condition for the low speed terminal are conditions for the RACH structure itself for each of the high speed terminal and the low speed terminal, each of the high speed terminal and the low speed terminal in a RACH having the same structure. One or more of the conditions for the preamble structure, and conditions for the sequence set for each of the high speed terminal and the low speed terminal to be applied to, specifically, the RACH structure itself for each of the high speed terminal and the low speed terminal In the case of setting a condition for, one of a method of setting the RACH for a high speed terminal to have a shorter length than that of the low speed terminal RACH, and a method of setting the preamble of the RACH for the high speed terminal to have a repetitive structure It can be set by the above method. At this time, the base station may further determine the frequency offset in the cell to set the frequency of the high-speed terminal RACH and the low-speed terminal RACH.

On the other hand, when setting the conditions for the preamble structure applied to each of the high speed terminal and the low speed terminal in the RACH of the same structure, the preamble structure for the high speed terminal is set by a method of repeatedly applying the preamble The preamble structure for the low speed terminal may be configured by applying the preamble without repetition or by applying a long preamble corresponding to a repeated length of the preamble.

Further, when setting conditions for the sequence set for each of the high speed terminal and the low speed terminal, the sequence set for each of the high speed terminal and the low speed terminal is set to a CAZAC sequence set, and the sequence set for the high speed terminal is CAZAC An index may be set to a sequence set consisting of ZCZ sequences within the first predetermined range or the last predetermined range, wherein the sequence set for the fast terminal is a sequence set that can be commonly used for all cells. The sequence number of the sequence set for a user may be set to be less than the number determined to maintain a predetermined sequence reuse rate. Alternatively, the sequence number of the sequence set for the high speed terminal is set to be greater than or equal to the number determined to maintain a predetermined sequence reuse rate. Each cell through cell planning It may be allocated.

Meanwhile, as another case of setting a condition for a sequence set for each of the high speed terminal and the low speed terminal, a sequence set for each of the high speed terminal and the low speed terminal is set as a CAZAC sequence set, and the sequence for the high speed terminal is set. The set may be set not to include a ZCZ sequence. In the above-described cases, the sequence set for the low speed terminal is preferably a sequence set excluding the sequence set for the high speed terminal among the entire RACH sequence sets.

On the other hand, the RACH setting method according to another embodiment of the present invention, the step of setting the RACH length to a predetermined length or less determined according to the frequency offset level; And transmitting the set RACH length information on the downlink.

In addition, the RACH configuration method according to another embodiment of the present invention, the step of setting the RACH preamble having a repetitive structure; And transmitting the configured RACH preamble repetition structure information on a downlink.

In this case, the setting of the RACH preamble to have a repetitive structure may include a method in which the entire RACH structure includes one repetitive preamble but only the preamble repetitive structure, and does not include the recursive preamble. It is possible to set the preamble of the RACH to have a repeating structure by any one of a method having only a repeating structure and a method in which the cyclic prefix unit and the preamble have the same number of repeating structures.

On the other hand, the RACH transmission method according to another embodiment of the present invention, obtaining information on whether the terminal itself is a high speed terminal or a low speed terminal in the initial cell search step; Acquiring uplink information including each of a fast UE RACH setting condition and a fast UE RACH setting condition; Selecting and setting a RACH connection condition according to the RACH setting condition for the high speed terminal or the RACH setting condition for the low speed terminal according to the information on whether the high speed terminal or the low speed terminal; And transmitting a RACH signal according to the set RACH connection condition.

In addition, the RACH transmission method according to another embodiment of the present invention, the method comprising the steps of: obtaining uplink information including each of the RACH configuration conditions for the fast terminal and the RACH configuration conditions for the low speed terminal; Selecting one RACH setting condition with a first selection probability for the RACH setting condition for the high speed terminal and a second selection probability with respect to the RACH setting condition for the low speed terminal; First transmitting a RACH signal according to the selected RACH setting condition; And repeating the RACH setting condition selection step when the first transmission fails, transmitting the RACH signal a second time, and when the failure is due to no response, the first transmission in the second transmission step. The selection probability and the second selection probability are different from the first selection probability and the second selection probability in the first transmission step.

In this case, when the failure is due to the reception of the NACK signal, the first selection probability and the second selection probability in the second transmission step are the first selection probability and the second selection probability in the first transmission step. It may be equal to the selection probability.

The first selection probability and the second selection probability in the first transmission step may be the same as each other, or a method of setting the first selection probability lower than the second selection probability. And the first selection probability in the second transmission step is set higher than the first selection probability in the first transmission step, and the second selection probability in the second transmission step. May be set lower than the second selection probability in the first transmission step. More specifically, the first selection probability may be set in proportion to the number of failures due to no response.

In addition, the RACH detection method according to another embodiment of the present invention, the step of receiving a RACH signal inserted with the RACH preamble sequence for each subcarrier index of a predetermined interval; And detecting the RACH preamble sequence at a detection index including the subcarrier indexes of the predetermined intervals and the index shifted by left and right subcarrier indexes of the subcarrier indexes of the predetermined intervals.

Finally, the random access method according to another embodiment of the present invention, obtaining information on the frequency offset and the sequence detection algorithm information of the base station in the initial cell search step; Receiving a response signal for the RACH signal transmission; And interpreting the response signal in consideration of the frequency offset.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. The detailed description, which will be given below with reference to the accompanying drawings, is intended to explain exemplary embodiments of the present invention and is not intended to represent the only embodiments in which the present invention may be practiced. The following detailed description includes specific details in order to provide a thorough understanding of the present invention. However, one of ordinary skill in the art appreciates that the present invention may be practiced without these specific details. In some instances, well-known structures and devices are omitted or shown in block diagram form, centering on the core functions of each structure and device, in order to avoid obscuring the concepts of the present invention. In addition, the same components will be described with the same reference numerals throughout the present specification.

The frequency offset affects the detection performance of the receiver and, in particular, in the frequency domain detector, the degradation of the detection performance is greater. For example, when using a frequency domain detector, for a 1 ms RACH with a preamble length of 0.8 ms, when the frequency offset reaches 625 Hz, it is difficult to distinguish between ZCZ sequences. Although the oscillator accuracy is correctly set to the target subcarrier frequency, the doppler frequency can cause significant performance degradation in the frequency domain detector.

However, the frequency domain detector has a significantly lower detection complexity than the time domain detector, and it is preferable to use the aforementioned frequency domain detector to reduce the RACH detection complexity.

Accordingly, an embodiment of the present invention proposes a solution to a situation in which the preamble transmitted to the RACH cannot be properly detected due to the frequency offset when the frequency domain detector is used as described above. When the initial terminal approaches the RACH, since the signal is transmitted without any time / frequency synchronization for the uplink, the base station receiving the RACH preamble inevitably suffers from degradation in detection performance due to frequency offset.

Considerable methods to improve this include relatively high frequencies, such as 1) adjusting the length of the RACH, 2) adjusting the available sequence, and 3) setting the preamble to include a repetitive structure. There are a method for setting conditions for the entire RACH for the fast terminal having an offset, and a method for setting different RACH transmission conditions for each of the fast terminal and the slow terminal.

Among these, a method of setting different RACH transmission conditions for each of the high speed terminal and the low speed terminal is configured to set specific conditions in preparation for performance degradation due to frequency offset for the high speed terminal instead of setting the same RACH transmission condition to all terminals. Specifically, 1) a method of differently setting the RACH structure for each of the high speed terminal and the low speed terminal, 2) differently setting a preamble structure applied to each of the high speed terminal and the low speed terminal in the RACH of the same structure 3) a method for defining and allocating sequence sets for the high speed terminal and the low speed terminal, respectively.

According to a method of setting different RACH transmission conditions for each of the high speed terminal and the low speed terminal among each of these configuration methods, the method of accessing the RACH may vary depending on whether the UE can estimate its own speed. have.

In addition, in an embodiment of the present invention, as described above, various RACH setting conditions are considered in advance, and only RACHs according to any one of these conditions are set or RACHs according to some or all of them are set, and this is transmitted to each terminal. Suggest ways to inform via BCH.

Hereinafter, each of these methods will be described in detail.

First, a method of adjusting the length of the RACH will be described.

The main reason that frequency offset is a big problem in the RACH is that the length of the RACH is too long. In other words, if the unit is very small, such as the length of the OFDM symbol, the frequency offset due to transmission and reception is not a big problem. However, in the case of RACH, since the length is relatively long compared to the OFDM symbol in time, it is very sensitive to a slight frequency offset. Respond. Currently, the length of the RACH under discussion in 3GPP LTE is 1 ms.

2 is a view for explaining a method of reducing the RACH length according to an embodiment of the present invention.

The frequency offset that the preamble of the conventional RACH 201 of FIG. 2 can tolerate is much smaller than 1 / T _{P, which} is the inverse of the RACH preamble length. Therefore, a countermeasure according to an embodiment of the present invention is to reduce the length of the RACH accordingly.

FIG. 2 shows setting the length T _R of the RACH 201 to _{R R} ′ to be set together with the RACH 202. When the RACH length is reduced and set as in the RACH 202 of FIG. 2, since the frequency offset that the preamble can withstand becomes large (for example, 1 / T _P to 1 / T _P ', except that T _P '< T _P ), the probability that a detection error occurs at the base station is also reduced. In this case, the reduced RACH length may be set to maintain the detection probability required by the system in consideration of the influence of the frequency offset. Meanwhile, in 3GPP LTE, it is currently discussed to use a RACH having a length of 0.5 ms when the influence of the frequency offset is severe. As described above, when a 0.5 ms long RACH is used, a problem of deterioration of detection performance due to a frequency offset can be solved and up to 500 Km / h of the terminal can be supported.

Specifically, when a 0.5 ms long RACH is used, the length of the preamble is 0.4 ms, the CP length, and the guard time is 50 us. As such, when the preamble length is 0.4 ms, the half of subcarrier space becomes 1250 Hz, assuming a base station oscillator deviation of 0.05 ppm and a terminal oscillator deviation of 0.1 ppm. It can support the terminal speed of Km / h. Assuming that the maximum performance degradation occurs in the above-described half subcarrier interval, it can be seen that when using the RACH of 0.5 ms as described above, sufficient performance is shown.

On the other hand, if the performance of the oscillator is poor, performance degradation due to frequency offset may be more severe.

3A and 3B are RACHs having a short length in accordance with one embodiment of the present invention. In the case of using a 0.5 ms RACH, it is a graph showing detection performance and false alarm rate according to each condition.

 Specifically, FIGS. 3A and 3B show a CAZAC sequence as a sequence, and when using a frequency domain detector in a TU channel having a pilot signal-to-noise ratio (Ep / No) of 18 dB, the frequency offsets are 0 Hz and 300, respectively. The detection performance at left (left) and false alarm rate (right) are shown. In addition, one axis in the planar direction in each graph represents the index of the CAZAC sequence, and the other axis represents the speed of the terminal.

3A, it can be seen that when 0.5 ms RACH is used, detection performance is degraded for a fast UE in some CAZAC indexes. In addition, even if this detection performance deterioration is not large, it can be seen that the false alarm rate is relatively large, which may waste processing time and resources of the base station.

On the other hand, Figure 3b shows the detection performance and false alarm rate in the presence of a frequency offset of 300Hz, it can be seen that there is no significant performance difference compared to Figure 3a.

4A and 4B are graphs illustrating detection performance and false alarm rates according to respective conditions when 1 ms RACH is used.

Specifically, FIGS. 4A and 4B use a CAZAC sequence as a sequence similar to FIGS. 3A and 3B, and use a frequency domain detector in a TU (Typical Urban) channel having a pilot signal-to-noise ratio (Ep / No) of 18 dB. The detection performance (left) and false alarm rate (right) when the frequency offsets are 0 Hz and 300 Hz, respectively, are shown. 3A and 3B and the setting of each axis are also the same.

When comparing the results shown in FIGS. 4A and 4B with the results shown in FIGS. 3A and 3B, when using 1 ms RACH, significant performance deterioration in detection performance and false alarm rate compared with 0.5 ms RACH is used. It can be seen that there is a.

It can be seen from the detection performance and false alarm rate graphs shown in FIGS. 4A and 4B that performance degradation in some CAZAC sequences is measured relatively small compared to other CAZAC sequences. Such a method through CAZAC index selection will be described later.

3A to 4B, when the length of the RACH is set to be small, it can be seen that it can be more robust to the frequency offset.

However, if the length of the RACH is simply reduced as shown in FIG. 2, the number of usable sequences may be reduced, and the spreading gain may be reduced.

Accordingly, another embodiment of the present invention proposes a method of setting the RACH preamble to include a repetitive structure when the RACH is designed and allocated.

FIG. 5 is a diagram for explaining an advantage of a method of setting a RACH preamble to have a repetitive structure according to one embodiment of the present invention.

When the RACH length is simply reduced to increase the frequency offset level that the RACH preamble can endure, such as the RACH 301 illustrated in FIG. 5, the length of the sequence to be applied to the preamble is reduced as described above. The disadvantage is that the number of possible sequences is reduced. Specifically, the RACH 301 is a case where the total RACH length T _R is 0.5 ms, for example, and has a CP of 0.1 ms (T _CP = 0.1 ms) and 0.1 ms to have a coverage of about 15 Km. It includes the Guard Time (T _G = 0.1 ms).

On the other hand, in the case of the RACH 302 according to another embodiment of the present invention, the preamble includes a repeating structure while maintaining the length T _R of the RACH at 1 ms. In this case, when considering the same coverage as the RACH 301, including a CP of 0.1 ms and a guard time of 0.1 ms (T _CP = T _G = 0.1 ms), the basic unit length of a preamble having a repeating structure is It can be seen that it includes 0.4 ms long compared to the preamble of the RACH 301 (T _P = 0.4 ms). In this case, the RACH 302 may use more sequences than the RACH 301.

In addition, in the case of the RACH 303, a RACH structure having a structure in which the preamble is repeated three times in order to have a structure more robust to the frequency offset is shown. If it is necessary to design a RACH to support a large cell or to have a larger sequence reuse rate, the RACH length T _R can be set longer than 1 TTI, and the RACH 303 sets the total RACH length to 2. The RACH is designed with ms, CP length T _CP of 405 us or less, protection time length T _G of 395 us, and preamble length T _P of 0.4 ms.

Like the RACH 302 and the RACH 303 described above, if the preamble is set to be repeated in the RACH slot, the base station has a method of determining a frequency offset from the received preamble signal. That is, if the frequency offset is estimated based on the repetition pattern, the frequency offset can be removed from the received signal, and the performance of the preamble detection need not be reduced.

In detail, when the preamble includes a repetitive structure in the time domain, an interval between subcarriers carrying a sequence in the frequency domain is changed. This is because N repetitions from the time domain to the time axis correspond to the insertion of sequences in N subcarrier intervals in the frequency domain.

Therefore, when the RACH preamble is not repeated, the sequence signal is carried on all adjacent curve carriers. When the preamble is repeated twice, such as the RACH 302, the sequence is carried by two spaces. In the case of three iterations, such as the RACH 303, three spaces are carried.

In this situation, if a frequency offset occurs, the wider the interval between sequences, the less interference and the lower the detection performance or the frequency of false alarms.

6A and 6B are diagrams for explaining the effect of the frequency offset in the frequency domain when the RACH preamble is set to have a repetitive structure according to an embodiment of the present invention.

FIG. 6A illustrates a case in which a preamble sequence is transmitted for every subcarrier since the RACH preamble does not include a repetitive structure in the time domain, and FIG. 6B illustrates a time when the RACH preamble is timed according to an embodiment of the present invention. The case where the sequence is delivered at two subcarrier intervals by including two repeating structures in the region is shown.

As shown in FIG. 6A, when there is a frequency offset, it can be seen that the interference from immediately adjacent subcarriers is very large, whereas in FIG. 6B, since an interference signal is not transmitted to a immediately adjacent subcarrier, FIG. It can be seen that it is relatively small compared to 6a.

Thus, if the preamble is repeated in one RACH, even if there is a frequency offset, the false alarm rate of the base station can be lowered.

As described above, the detection performance and the false alarm rate when the preamble is configured to have a repetitive structure in the RACH structure will be described in detail.

7A and 7B are graphs illustrating detection performance and false alarm rates when the RACH is designed to have a structure in which the preamble is repeated twice according to an embodiment of the present invention.

Specifically, FIGS. 7A and 7B use a CAZAC sequence as a sequence similarly to FIGS. 3A through 4B, and when a frequency domain detector is used in a TU (Typical Urban) channel having a pilot signal-to-noise ratio (Ep / No) of 18 dB, The detection performance (left) and false alarm rate (right) when the frequency offset is 0 Hz and 300 Hz, respectively, are shown. In addition, the setting of each axis is also the same as FIG. 3A-4B.

7A and 7B, when compared with the case of FIGS. 4A and 4B, it can be seen, among other things, that the false alarm ratio shown on the right side of each graph is reduced to an acceptable range. On the other hand, in the detection performance shown on the left side, it is difficult to find a large performance improvement as in the wrong alarm ratio, but it can be seen that the detection performance is uniform in the case of FIGS. 7A and 7B. That is, in the case of FIGS. 3A to 4B, the detection performance does not change according to the speed of the UE in a specific CAZAC index, and always shows poor performance. In the case of FIGS. 7A and 7B, the detection performance is shown in the entire sequence index. It can be seen that according to the speed of the reduction sequentially.

Overall, it can be seen that the detection performance and false alarm rate shown in FIGS. 7A and 7B show better performance than the case of FIGS. 4A and 4B.

8A and 8B are graphs illustrating detection performance and false alarm rates when the RACH is designed to have a structure in which the preamble is repeated three times according to an embodiment of the present invention.

Specifically, FIGS. 8A and 8B also use the CAZAC sequence as the sequence similar to FIGS. 3A to 4B, and when a frequency domain detector is used in a TU (Typical Urban) channel having a pilot signal-to-noise ratio (Ep / No) of 18 dB, The detection performance (left) and false alarm rate (right) when the frequency offset is 0 Hz and 300 Hz, respectively, are shown. In addition, the setting of each axis is also the same as FIG. 3A-4B.

When the detection performance and false alarm ratios shown in FIGS. 8A and 8B are compared with those of FIGS. 7A and 7B, it can be seen that the false alarm ratios are not significantly improved. This ensures sufficient subcarrier spacing even when the preamble has two repetition structures, as in the case of FIGS. 7A and 7B, and thus the performance improvement of securing the subcarrier spacing additionally is great because the preamble has three repetition structures. It may mean that it may not.

On the other hand, when the RACH preamble is set to include a repetitive structure as described above, and the terminal transmits the RACH signal accordingly, the method for detecting the RACH signal is as follows.

When a frequency offset corresponding to a half-subcarrier space of a transmitted RACH signal occurs when receiving a RACH signal having a sequence inserted for each subcarrier of a predetermined interval according to an embodiment of the present invention Since the size of the peak becomes very small, it is preferable to perform the sequence detection even at a position where the sequence is not loaded at the time of preamble detection.

That is, when a sequence is transmitted to subcarrier Nos. 1, 3, 5, 7, 9, as shown in FIG. 6B, the subcarrier indexes 2, 4, 6, and 8 are detected at the time of preamble detection. 10. The sequence includes the same subcarrier index.

In this case, it may be desirable to detect both cases under the assumption that the frequency offset is positive and negative. (I.e., it can be detected assuming that the sequence is shifted one shift to the right or one shift to the left)

Meanwhile, according to an embodiment of the present invention, there may be various methods for setting the RACH preamble to include a repetitive structure, and include the following cases.

9A to 9C are diagrams for describing various methods of setting the RACH preamble to have a repetitive structure according to one embodiment of the present invention.

The number of repetitions of the preamble may be two, three, or any number of times as necessary. The RACH 501, RACH 503, and RACH 505 of FIGS. 9A to 9C may have two repetition structures. Including RACH 502, RACH 504, and RACH 506 are shown to include a three times repetition structure. Accordingly, a sequence is inserted every two subcarriers on the frequency axis of the RACH 501, the RACH 503, and the RACH 505, and the RACH 501, the RACH 503, and the RACH 505 sequence every three subcarriers. Will be inserted.

Meanwhile, FIG. 9A illustrates a case where a CP is inserted into the RACH, and FIG. 9B illustrates a case where the CP is not inserted into the RACH. FIG. 9C illustrates a RACH including a CP and a repeated structure includes the CP. It is shown as a whole and includes a predetermined gap between both structures.

9A and 9B, in the case of FIG. 9B, the orthogonality is disadvantageous as described above with respect to the related art, but the length of the preamble can be increased by a length corresponding to the CP length. There is an advantage. In addition, the spacing between each subcarrier in the frequency axis depends on the inverse of the preamble length of the RACH, and when the RACH preamble is transmitted with the N subcarrier spacing including N repeating structures, the RACH as shown in FIG. 9A. If the preamble length is too short, there is a fear that the spacing between subcarriers into which a sequence is inserted in the frequency domain becomes too wide. Accordingly, in one embodiment of the present invention, as shown in FIGS. 9A and 9B, the length of the preamble can be adjusted according to whether the CP is inserted or not, thereby adjusting the interval between subcarriers in the frequency domain.

In addition, when the entire RACH structure including the CP is repeated as shown in FIG. 9C, and a predetermined interval is set between each RACH structure, sequences independent of each other are inserted into each RACH preamble, and the RACH signal is distinguished through a combination thereof. This has the advantage of increasing the number of available sequences.

As described above, there are various ways of setting the RACH preamble to include a repeating structure according to an embodiment of the present invention, and the present invention need not be limited to any one way.

Meanwhile, a method of setting different RACH transmission conditions for the high speed terminal and the low speed terminal will be described below.

FIG. 10 is a diagram for describing a method of setting a high speed terminal RACH and a low speed terminal RACH according to an embodiment of the present invention.

If the RACH is not necessarily allocated and used only in one form, it is possible to make a structure that can be used differently according to the terminal speed. For example, if all preambles need to be cut in half for high speed users, the number of available sequences is reduced to one quarter. This has the effect of reducing the sequence reuse factor to 1/4, which has the disadvantage of causing cell-planning problems.

Therefore, in one embodiment of the present invention, if a high speed terminal is to be supported, the RACH structure for a high speed terminal and the RACH structure for a general low speed terminal are not a problem when the high speed terminal is used rather than setting the entire RACH structure to the high speed terminal. Each suggestion is made so that the UE uses the corresponding RACH structure.

In this case, the UE accesses the RACH in the case of estimating its speed in an initial cell search step (ie, in case of estimating whether it is high speed or low speed in comparison to a predetermined threshold speed even if it is not accurate speed). This may be defined differently if it is not possible to estimate its own speed.

FIG. 10 illustrates an example of additionally defining and setting not only a low speed terminal RACH (RACH Type 1) but also a high speed terminal RACH (RACH Type 2) as described above.

Here, as long as the RACH (Type 2) for the high speed terminal takes a form in which the high speed terminal has no problem accessing the base station through the RACH, the specific method may be based on a method of setting and reducing the RACH length as shown in FIG. As shown in FIG. 5, the RACH preamble may be configured to include a repetitive structure. As described below, the RACH preamble may be configured to use only a specific sequence, and need not be limited to any one method.

In this way, the method for defining the low speed terminal RACH (Type 1) and the high speed terminal RACH (Type 2) can be collectively shown as the following example.

In Table 1, * denotes a case of designing a RACH to support a large cell, TR denotes the total length of the RACH, TP denotes the preamble length, and TG denotes the length of the guard time. In addition, 'RPF' indicates 'Repetition Factor', that is, the repetition coefficient of the preamble.

Specifically, the first column of Table 1 is a RACH (RACH Type 1) for a low speed terminal, and sets a RACH having a length of 1 ms without preamble repetition as in the RACH 201 of FIG. FIG. 5 shows a case in which the RACH has a structure in which a preamble is repeated twice as in the RACH 302 of FIG. 5 and a length of 1 ms in total is set. In addition, the second column of Table 1 sets the RACH 302 of FIG. 5 as a RACH type 1 (RACH Type 1) for a low speed terminal and the RACH 303 of FIG. 5 as a RACH type 2 (RACH Type 2) for a high speed terminal. In this case, this corresponds to a structure for supporting a large cell.

In addition, the last column of Table 1 sets the RACH 201 of FIG. 2 as a low speed terminal RACH (RACH Type 1), and sets the RACH 303 of FIG. 5 as a high speed terminal RACH (RACH Type 2). The case is shown.

As such, in one embodiment of the present invention as shown in FIG. 10, the RACH (Type 2) for a high speed terminal may be set to have a short length as long as the high speed user is defined in a form that is not a problem for accessing the base station. Although the length of the preamble may be set to have a repeating structure, the preamble may not be limited to any one form.

In addition, according to an embodiment of the present invention, as described above, the RACH (Type 2) for a high speed terminal is defined as a form that is not a problem for a high speed user to access a base station. The RACH structure to be used in the environment with the frequency offset and the RACH structure to be used in the environment without the frequency offset can be selected according to the presence or the like. That is, two RACH structures may exist in one base station at the same time, or only one of them may be provided by the base station.

That is, the allocation frequency of each RACH structure may be determined and set by the base station at a predetermined ratio according to the frequency offset situation in the cell. Accordingly, when the number of high speed terminals is small, as shown in FIG. 10, the set frequency of the high speed terminal RACH may be low. Specifically, FIG. 10 shows that the RACH for Type 2 (Type 2) is arranged in a long period of "RACH Type 2 Period", and the RACH for Type Low Speed (Type 1) is arranged in a short period of "RACH Type 1 Period". have.

Meanwhile, the low speed terminal may use both types of RACH shown in FIG. 10, while the high speed terminal should use only RACH (Type 2) for the high speed terminal among the two types of RACHs, which will be used as described below. The sequence is also limited.

In consideration of this, in consideration of the fact that most terminals are low speed in one embodiment of the present invention, a high speed terminal can be supported without reducing the number of sequences to be used by the low speed terminal. In addition, it is possible to avoid the problem that the RACH length can be lengthened by avoiding preamble repetition for the low speed terminal. In other words, the overhead of the RACH can be reduced.

Meanwhile, in the case of defining a fast terminal RACH (Type 2) and a low speed terminal RACH (Type 1) as shown in FIG. 10 according to an embodiment of the present invention, the terminal may determine its speed in an initial cell search step or the like. Depending on whether it can be estimated, the RACH access method may be different as follows.

When the terminal can determine whether the terminal is a high speed terminal or a low speed terminal in an initial cell search step or the like, the terminal receives setting condition information on the high speed terminal RACH and the low speed terminal RACH from the downlink and corresponds to its own speed. Access to the RACH.

However, in some cases, the terminal may not know its speed. In this case, in one embodiment of the present invention, a method of changing the selection probability for the RACH setting condition when retrying according to the initial RACH connection and connection failure (specifically, connection failure due to the influence of the frequency offset) of the UE is provided. Suggest.

11 is a flowchart illustrating a method of accessing a RACH when a terminal cannot estimate its own speed according to an embodiment of the present invention.

According to an embodiment of the present invention as shown in FIG. 11, when the UE cannot estimate its own speed, first, in step S701, the UE includes a RACH setting condition for a fast terminal and a RACH setting condition for a low speed terminal. Acquire uplink information. Then, in step S702, when the initial RACH is transmitted, the initial RACH transmission (hereinafter referred to as "first transmission") is performed by arbitrarily selecting the RACH for the fast terminal and the RACH for the slow terminal with any probability. That is, in step S702, 1) two RACH types of the high speed terminal RACH and the low speed terminal RACH are selected with the same probability, or 2) in the case of the RACH connection through the first transmission, the collision probability with the terminal through retransmission is determined. In order to reduce, the selection probability of the RACH structure for the high speed terminal is reduced or 3) the first transmission is performed by setting only the RACH structure for the low speed terminal.

Accordingly, it is determined whether the RACH connection is successful in step S703. If the RACH connection is successful due to the receipt of the Aquisition Indicator (AI) from the base station, then a communication procedure according to the RACH connection purpose is performed.

On the other hand, if the RACH connection fails, in step S704 it is determined whether the RACH connection failure is due to NACK reception from the base station, and if not due to NACK reception, i.e., no response from the base station, the process proceeds to step S706. RACH retransmission is performed by selecting a RACH structure for retransmission. In this case, a method of selecting the RACH structure may include 1) selecting both the RACH for the high speed terminal and the RACH for the low speed terminal with the same probability, and 2) increasing the probability of selecting the RACH structure for the high speed terminal. If the RACH connection fails due to no response, it is highly likely that the case is due to a frequency offset. Therefore, the selection of the RACH structure upon retransmission, as shown in 2), preferably increases the probability of selecting the RACH structure for the fast terminal.

In addition, when the RACH connection failure is due to the NACK reception from the base station as a result of the determination in step S704, it is difficult to assume that the RACH connection failure is due to the frequency offset, and thus through the operation such as power boosting again in step S705. In operation S702, the RACH structure may be selected and transmitted with the same probability as that of the first transmission.

Meanwhile, in another embodiment of the present invention, among the methods for setting the RACH condition for the high speed terminal and the RACH condition for the low speed terminal differently, a sequence in which the high speed terminal has no problem connecting to the RACH and a sequence available to the general low speed terminal are adjusted. It proposes a setting method by, and will be described in detail below.

Depending on the type of sequence used for the RACH preamble, different results may be obtained for the RACH connection under the same environment. That is, while there is a robust sequence for frequency offset, there is a very weak sequence.

FIG. 12 is a diagram for explaining an example of using a CAZAC sequence to separately set a high speed terminal RACH sequence and a low speed terminal RACH sequence according to an embodiment of the present invention.

Two types of CAZAC sequences are GCL CAZAC and Zadoff-Chu CAZAC. They are conjugated to each other and GCL CAZAC can be obtained by taking the conjugated complex number of Zadoff-Chu. Zadoff-Chu CAZAC is given by

Here, k denotes a frequency axis index of the sequence, N denotes a length of a CAZAC sequence to be generated, and M denotes a CAZAC index.

In addition, as shown in FIG. 12, the sequence according to each of the Nt CAZAC indexes includes L Zero Correlation Zone (ZCZ) sequences to which different cyclic shifts (“CS”) are applied, where ZCZ is a base station. In this case, it means a section in which CS can be applied so that the RACH signal can be distinguished.

When CAZAC is used as the RACH preamble sequence in a situation where there is a frequency offset, there is a problem in that the ZCZ sequence cannot be distinguished by the frequency offset. Therefore, one embodiment of the present invention proposes not to use a ZCZ sequence as a RACH sequence for a high speed terminal.

However, when the high speed terminal is configured not to use the ZCZ sequence, as shown in FIG. 12, only Nt indexes according to the CAZAC indexes may be used, thereby reducing the number of available sequences. As a result, when the sequence reuse coefficient decreases, it is inevitable to allocate a sequence through cell planning.

In addition, as described above, the problem of not distinguishing between ZCZ sequences due to frequency offset becomes serious when the CAZAC index is not very large or very small. Specifically, if k is a frequency axis index, N is a CAZAC sequence, M is a CAZAC index, and a transmission signal is assumed to be c (k, N, M), the received signal R (k, N , M) can be expressed as

Here, d represents the frequency axis delay amount due to the frequency offset.

As can be seen from Equation 3, if the CAZAC index M has a very small value or has the largest value among all Nt sequence indexes, it can be seen that the effect of the frequency offset on the received signal is reduced. have.

Such results can be confirmed through the fact that the detection performance is very high when the CAZAC index is very large or very small in FIG. 3A to FIG. 4B as described above, and the false alarm rate is very low.

Therefore, according to another embodiment of the present invention, when using a ZCZ CAZAC sequence as a preamble sequence for a fast terminal, it is proposed to use a sequence in which the CAZAC index is within the first predetermined range or the last predetermined range of all the indexes. The predetermined range here may be set differently according to the detection performance of the system.

As described above, according to the above-described embodiment of the present invention, compared to the method of not using the ZCZ sequence for the high speed terminal, the type of the sequence that can be used is increased, so that almost no cell planning is required.

Specifically, when the entire CAZAC index exists up to Nt as shown in FIG. 12 as a sequence for a fast terminal, it is possible to use CAZAC indexes 0, 1, 2 and Nt-2, Nt-1, and Nt. In addition, since the CAZAC index with less influence of the frequency offset is common to all cells, the CAZAC index for the fast terminal can be set to be used by the fast user in common to all the cells. In this case, interference may occur between neighboring cells. However, since the terminal receives only a response from a cell to which it is involved, there is no problem in operation.

Meanwhile, in the case of a CAZAC sequence for a low speed terminal, an arbitrary index may be selected and used regardless of the index size. However, in order to reduce the collision probability with the high speed terminal, it is more efficient not to use the sequence index allocated for the high speed terminal.

In addition, instead of using the CAZAC index common to all cells for the fast terminal, it is also possible to perform cell planning only for the CAZAC of the index available for high speed. In this case, however, the sequence reuse coefficient may be in conflict with the intention to avoid cell planning. Accordingly, in one embodiment of the present invention, in order to minimize such sequence reuse coefficient and cell plan, it can be set as follows.

That is, according to an embodiment of the present invention, in allocating sequences for high speed terminals and low speed terminals, in consideration of the sequence reuse factor, the distribution ratio of the high speed user sequences is limited to a part of the total number of sequences supported by the base station. can do. That is, for example, the total number of sequences supported by the base station is 64, and the combination of the sequences is represented as (a sequence sensitive to frequency offset (sequence for low speed terminal), a sequence robust to frequency offset (sequence for high speed terminal)). In this case, it may be set as (60, 4), (56, 8), (48, 16), (32, 32), or the like. This is because when the robust sequence for frequency offset uses the ZCZ sequence, the number available is small, so only a small number is allocated to avoid cell planning. However, if you want to make a large number available, use a combination like (32, 32), but do cell planning within the total number of sequences that are robust to frequency offset.

In the case of assigning a sequence not using a ZCZ sequence as a sequence robust to a frequency offset, that is, a sequence for a fast terminal, it should be determined in consideration of the overall sequence reuse coefficient. That is, in the above example, if too many sequences are assigned to the second item, the overall sequence reuse coefficient may be reduced, which may cause problems.

Thus, even if a high-speed user allocates a sequence divided into using and not using a ZCZ sequence, the separation between them is practically meaningless at the base station. That is, the base station only determines whether a specific sequence has been detected and responds accordingly.

On the other hand, when the high-speed terminal sequence and the low-speed terminal sequence, respectively, as described above, a method for connecting the terminal to the RACH will be described as follows.

If the UE can estimate its speed through an initial cell search process, the RACH access can be performed through the RACH sequence corresponding to its speed. However, there is a case in which the terminal does not have information about its own speed. In this case, even if the sequence is allocated as described above, there is a possibility that the terminal may not be used properly. Accordingly, in a method of differently configuring the RACH structure for the high speed terminal and the RACH structure for the low speed terminal, the terminal may access the RACH through a process similar to that described with reference to FIG. 11.

Specifically, first, the UE performs downlink synchronization and collects uplink information including RACH sequence allocation information. Thereafter, in the initial connection, the terminal may select a sequence for the fast terminal and a sequence for the slow terminal with a random probability and apply it to the preamble. That is, 1) a method for selecting all the available sequences with the same probability, and 2) in order to reduce the probability of impulse with the reconnected terminal thereafter and also to use the ZCZ sequence as the sequence for the fast terminal as described above. In order to reduce the inter-cell interference because the user sequence is commonly used in all cells, a method of setting a higher probability of selecting a sequence for a low speed terminal than a probability of selecting a sequence for a high speed terminal, and 3) the above reason. In the initial connection, a method of establishing a connection to the RACH through a low speed terminal sequence may be used.

When receiving an AI from the base station for this initial access, the following communication procedure may be performed according to the reason for accessing the RACH. However, if NACK is received from the base station or if there is no response from the base station, reconnection is performed as follows.

If reconnection is performed because there is no response from the base station, a sequence set for reconnection is selected. In this case, it is preferable to increase the selection probability of the high speed terminal sequence set differently from the selection probability of the high speed terminal sequence set and the low speed terminal sequence set in the initial connection. That is, when reconnection is performed, the sequence set selection probability for the fast terminal and the sequence set selection probability for the slow terminal are both 1) selected by the same selection probability, and 2) the sequence set selection probability for the fast terminal is set to the slow terminal. And a method of increasing the selection of the sequence set selection probability and selecting the sequence set for the fast terminal. However, in the case of 1), even when there is no response from the base station and reconnection of the RACH is performed, it is preferable to perform this connection failure if it is not caused by the frequency offset.

On the other hand, when receiving the NACK signal from the base station and the RACH connection is failed, the selection probability of the high speed terminal sequence set and the low speed terminal sequence set at the time of reconnection can be set to be transmitted in the same manner as in the initial connection.

In this case, as the number of times that cannot be detected due to no response at the base station increases, the selection probability for the sequence set allocated for the high speed terminal is preferably increased.

As described above, when there is no response from the base station (RACH preamble is not detected) by changing the type of sequence that the UE selects during the RACH reconnection process, even if the UE does not have a measurement for the speed, By increasing the probability of selection of a sequence that is easy to detect, the degradation caused by the frequency offset by the speed can be reduced. As described above, the method of changing the probability is ON / OFF as described above, and is not used initially but must be selected when retrying. It can be implemented in a soft way that gradually changes the probability each time.

Next, in another embodiment of the present invention, among the methods for setting the RACH condition for the fast terminal and the RACH condition for the slow terminal differently, conditions for a preamble structure applied to each of the fast terminal and the slow terminal in the RACH having the same structure It proposes a different way to set, and will be described in detail below.

The embodiments described above with respect to the present invention are for the case where only one sequence that can be used for one RACH structure is defined and indicated. However, various preamble patterns may be defined in one RACH structure without sticking to this. For example, a preamble including a repeating structure and a preamble that does not repeat may be defined at the same time. If the preamble structure is repeated, the short preamble is repeated (for example, repeated twice). If the preamble structure is not repeated, the short preamble is used as it is. Alternatively, a long preamble may be defined and used as long as the length of the preamble in which the short preamble is repeated.

Various combinations are possible, but the description will be made based on the case where the short preamble is repeated twice and the long preamble is not repeated. The preamble repeated twice shows good performance even when there is a frequency offset, but has a small number of sequences that can be actually used. In the case of the long preamble, the number of sequences increases, but the weak preamble has a disadvantage.

Therefore, when the UE knows its own speed, the short preamble or the long preamble can be appropriately selected and transmitted according to the situation. However, in general, there may be a situation in which the terminal does not know its speed. In this case, since there is no answer to which preamble to select, an arbitrary preamble may be selected during initial RACH transmission or selected according to its current CQ information, and the short preamble side may be selected when there is no response from the base station. You can choose to make a trend or choose a long preamble. In this case, the selection criterion is that when the long preamble repeats the short preamble, the selection at the time of retransmission toward the short preamble corresponds to a case where the CQ of the UE is good or slow, and the CQ when the long preamble is selected. Is bad or fast. On the other hand, if the long preamble is generated using a single long sequence rather than a repetition of the short preamble, it is appropriate to select the opposite. Of course, the selection probability between the short preamble and the long preamble is set as in the process described above with reference to FIG. 7, and initially transmitted in a uniform or long preamble preference form, and if the base station does not detect the selection probability of the short preamble, It is apparent to those skilled in the art through the above description that a heightening scheme is also possible.

On the other hand, another embodiment of the present invention proposes a method for the terminal to predict in advance that the base station makes a false alarm due to the frequency offset to interpret the AI value received from the base station, which will be described in detail below.

FIG. 13 is a diagram for describing a method in which a terminal performs random access by predicting a false alarm of a base station according to one embodiment of the present invention.

If the UE knows its speed and the accuracy of the OSC to some extent, it is possible to predict the error occurring for the RACH preamble transmitted by the UE itself. That is, as shown in FIG. 13, the UE may transmit a specific sequence K, and it may be predicted that this is likely to be detected in another sequence P by the base station under the influence of the frequency offset. have. Then, without special modification to the RACH, the base station processes the detected sequence in the same manner as before, but the terminal knows in advance that the sequence transmitted by itself is not detected properly but is detected as another sequence. Treat it as your own.

In this case, the base station corresponds to a false alarm, but the terminal is not a false alarm, so proper operation is possible. However, for this purpose, the terminal should be able to know in advance that the base station will be detected in a different sequence with respect to the sequence transmitted by the terminal. For this purpose, the base station should inform the terminal in a downlink about its detection algorithm. FIG. 13 illustrates a situation in which the terminal has prediction values for sequences K, P, and Q that can be transmitted.

The detailed description of the preferred embodiments of the invention disclosed as described above is provided to enable any person skilled in the art to make and practice the invention. Although the above has been described with reference to the preferred embodiments of the present invention, those skilled in the art will variously modify and change the present invention without departing from the spirit and scope of the invention as set forth in the claims below. I can understand that you can. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

According to the RACH configuration method according to an embodiment of the present invention as described above, even when there is a frequency offset, the RACH preamble length is reduced, the RACH preamble is set to include a repetitive structure, or the frequency offset is less affected. By using a specific sequence, it is easy to detect the RACH preamble of the base station, and when setting different conditions for the high speed terminal and the low speed terminal, the system overhead is reduced compared to setting the entire RACH condition for the high speed terminal You can.

In addition, by specifically defining the RACH access method according to whether the UE can estimate its own speed with respect to the RACH configuration described above, even if the UE does not know its own speed, the influence of the frequency offset is reduced. RACH can be sent to make it.

Claims (20)

In the method for setting the RACH transmission of the terminal in preparation for the frequency offset, Setting a RACH setting condition for a high speed terminal and a RACH setting condition for a low speed terminal, respectively; And And transmitting the configured RACH setting condition for the high speed terminal and the RACH setting condition for the low speed terminal in downlink. The method of claim 1, The RACH setting condition for the high speed terminal and the RACH setting condition for the low speed terminal, Conditions for the RACH structure for each of the high speed terminal and the low speed terminal, Conditions for a preamble structure applied to each of the high speed terminal and the low speed terminal in the same structure RACH, and for each of the high speed terminal and the low speed terminal And one or more of the conditions for the sequence set. The method of claim 2, When setting the conditions for the RACH structure for each of the high speed terminal and the low speed terminal, A RACH set by at least one of a method of setting the RACH for the high speed terminal to have a shorter length than the RACH for the low speed terminal, and a method of setting the preamble of the high speed terminal RACH to have a repetitive structure How to set up transmission. The method of claim 3, wherein And determining, by a base station, an intra-cell frequency offset situation and setting frequency counts of the RACH for the high speed terminal and the RACH for the low speed terminal. The method of claim 2, When setting the conditions for the preamble structure applied to each of the high speed terminal and the low speed terminal in the RACH of the same structure, The preamble structure for the fast terminal is set by a method of repeatedly applying the preamble, The preamble structure for the low speed terminal is set by a method of applying the preamble without repetition or a method of applying a long preamble corresponding to a repeated length of the preamble. The method of claim 2, When setting the conditions for the sequence set for each of the high speed terminal and the low speed terminal, Setting a sequence set for each of the high speed terminal and the low speed terminal to a CAZAC sequence set, And the sequence set for the fast terminal is set to a sequence set consisting of a ZCZ sequence whose CAZAC index is within the first predetermined range or last within the predetermined range. The method of claim 6, The sequence set for the fast terminal is a sequence set that can be commonly used for all cells, and the sequence number of the sequence set for the fast terminal is set to be less than the number determined to maintain a predetermined sequence reuse rate. The method of claim 6, The sequence set for the high speed terminal is a sequence set that can be commonly used for all cells. When the number of sequences of the sequence set for the high speed terminal is set to be greater than or equal to a number determined to maintain a predetermined sequence reuse rate, the cell planning is performed. Assigned to each cell via a RACH transmission setup method. The method of claim 2, When setting the conditions for the sequence set for each of the high speed terminal and the low speed terminal, Setting a sequence set for each of the high speed terminal and the low speed terminal to a CAZAC sequence set, And the sequence set for the fast terminal does not include a ZCZ sequence. The method according to any one of claims 6 to 9, And the sequence set for the low speed terminal is a sequence set excluding the sequence set for the high speed terminal among all RACH sequence sets. Setting the RACH length to less than or equal to a predetermined length determined according to the frequency offset level; And Transmitting the set RACH length information on the downlink. Setting the RACH preamble to have a repeating structure; And Transmitting the configured RACH preamble repetition structure information on a downlink. The method of claim 12, The setting of the RACH preamble to have a repetitive structure may include: Including a single cyclic prefix, but having a repeating structure of only the preamble, a scheme of having a repeating structure of only the preamble without the cyclic prefix, and the repeating structure and the preamble has a repeating structure of the same number of times And setting the preamble of the RACH to have a repetitive structure by any one of schemes. Acquiring information about whether the terminal is a high speed terminal or a low speed terminal in an initial cell search step; Acquiring uplink information including each of a fast UE RACH setting condition and a fast UE RACH setting condition; Selecting and setting a RACH connection condition according to the RACH setting condition for the high speed terminal or the RACH setting condition for the low speed terminal according to the information on whether the high speed terminal or the low speed terminal; And Transmitting a RACH signal in accordance with the established RACH connection condition. Acquiring uplink information including each of a fast UE RACH setting condition and a fast UE RACH setting condition; Selecting one RACH setting condition with a first selection probability for the RACH setting condition for the high speed terminal and a second selection probability with respect to the RACH setting condition for the low speed terminal; First transmitting a RACH signal according to the selected RACH setting condition; And If the first transmission fails, repeating the RACH setting condition selection step to transmit a second RACH signal, If the failure is due to no response, the first selection probability and the second selection probability in the second transmission step are different from the first selection probability and the second selection probability in the first transmission step. RACH transmission method. The method of claim 15, If the failure is due to receiving a NACK signal, the first selection probability and the second selection probability in the second transmission step are equal to the first selection probability and the second selection probability in the first transmission step. RACH transmission method. The method of claim 15, The first selection probability and the second selection probability in the first transmission step may be equal to each other, or a method of setting the first selection probability lower than the second selection probability. RACH transmission method to set. The method according to any one of claims 15 to 17, The first selection probability in the second transmission step is set higher than the first selection probability in the first transmission step, And the second selection probability in the second transmission step is set lower than the second selection probability in the first transmission step. The method of claim 18, The first selection probability is set to be high in proportion to the number of failures due to no response. Receiving a RACH signal in which a RACH preamble sequence is inserted for each subcarrier index at predetermined intervals; And And detecting the RACH preamble sequence at a detection index including the subcarrier indexes of the predetermined intervals and the index shifted by left and right subcarrier indexes of the subcarrier indexes of the predetermined intervals.

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