KR101328939B1 - Method For Allocating Sequence And Method For Setting Circular Shift Sequence Against Frequency Offset - Google Patents

Abstract

The present invention relates to a sequence allocation method for a frequency offset and a cyclic shift sequence setting method. According to the present invention, when a sequence without cyclic shift is assigned to a cell determined to have a frequency offset greater than or equal to a predetermined level, or a sequence applying cyclic shift is assigned, a sequence whose sequence index is within a minimum predetermined range or a last predetermined range is selected. In this case, the cyclic shift application interval may be set in consideration of an alias of the reception sequence.

Frequency Offset, Cyclic Shift, Elias

Description

Method For Allocating Sequence And Method For Setting Circular Shift Sequence Against Frequency Offset}

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a diagram for explaining the influence of frequency offset on pulse shaping in the frequency domain when a sequence is mapped to a subcarrier.

FIG. 2 is a diagram for explaining different frequency offset situations in a plurality of cells. FIG.

3 is a diagram for explaining a sequence allocation method when the sequence used according to one embodiment of the present invention is a CAZAC sequence.

4 is a diagram illustrating a phenomenon in which an alias occurs in a time domain channel response of a reception sequence due to a frequency offset.

FIG. 5 is a diagram for explaining a method of setting a cyclic shift application unit by adding an additional margin to a conventional cyclic shift application unit to reduce the influence of a frequency offset in the RACH according to one embodiment of the present invention; FIG.

6A and 6B are diagrams for explaining a method of setting a cyclic shift sequence using a cyclic shift application unit with an additional margin as shown in FIG. 5 according to one embodiment of the present invention.

FIG. 7 illustrates a method for setting a cyclic shift sequence in consideration of an alias of a reception sequence according to an embodiment of the present invention when the sequence is divided into units of a conventional cyclic shift application interval. FIG.

8A to 8C are diagrams for explaining a method of setting an additional circular shift interval when an interval between a reception sequence and an alias is greater than twice the conventional circular shift application unit according to an embodiment of the present invention.

9 is a view for explaining a method for setting a circular movement applying group and a circular movement applying section in each group according to an embodiment of the present invention.

10A and 10B illustrate a case in which a sequence is divided into units of a conventional cyclic shift application interval, in which a cyclic shift application group and a cyclic shift application interval are set within each group in consideration of an alias of a reception sequence according to an embodiment of the present invention. Drawings for explaining the method.

11 is a view for explaining a method for setting a cyclic shift application interval according to an embodiment of the present invention when the total length of the sum of the channel response of the reception sequence and each alias of the reception sequence is larger than the sequence length.

FIG. 12 is a diagram showing an example of a section to which each embodiment can be applied according to an index of a sequence in the present invention. FIG.

13A and 13B compare the detection error probability and false alarm rate when applying the cyclic shift in the same interval regardless of the index of the conventional CAZAC sequence and the cyclic shift according to each embodiment of the present invention. Each graph shown.

14A and 14B are graphs showing the number of cycles available and the total number of sequences available, respectively, in accordance with an embodiment of the present invention.

The present invention relates to a sequence in a wireless communication system. In particular, a method of assigning a sequence to each cell in consideration of characteristics of a CAZAC sequence for solving a frequency offset problem, and setting a cyclic shift to be applied thereto. It's about how.

There are various sequences used to transmit control information or data including ID and synchronization information for distinguishing types of information in a communication system, but in the case of 3GPP LTE, CAZAC (Constant Amplitude Zero Auto-Correlation) Sequences are the basis. The CAZAC sequence can be used for various IDs and information by using this sequence. These channels include synchronization channels (e.g., primary SCH, secondary SCH, BCH) for downlink synchronization, synchronization channels (e.g., RACH) for uplink synchronization, pilot channels , Data pilot, channel quality pilot). In addition, the above-described CAZAC sequence can also be used for scrambling.

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

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

When a Zadoff-Chu CAZAC sequence given by Equations (1) and (2) and a GCL CAZAC sequence having a conjugate complex number relationship with the Zadoff-Chu CAZAC sequence are expressed by c (k; N, M), they all have the following three characteristics.

In Equation (3), the CAZAC sequence always has a size of 1, and Equation (4) shows that the auto-correlation function of the CAZAC sequence is represented by a delta function. Here, autocorrelation is based on circular correlation. Equation (5) also shows that the cross-correlation function is always constant.

As such, the CAZAC sequence is one of sequences that is actively discussed in 3GPP LTE. There are two methods of using the sequence, namely, a method of changing the sequence of a root index, and a method of circularly shifting a sequence corresponding to one root index.

There are two methods of applying the circular motion to the CAZAC sequence: a method of circularly moving the sequence itself and a method of cyclically moving the time domain or frequency domain sequence by multiplying the exponential function of the other region by the following method.

The method of circularly moving the sequence itself may be expressed as follows.

Here, d represents the amount of circular motion to be applied, and 'mod' represents a modulo operator.

Also, a method of applying a cyclic shift by multiplying a sequence by an exponential function can be expressed as follows.

Such a CAZAC sequence has a small cross-correlation in the case where the root index is different, but there is no restriction on the design of the sequence use. However, the CAZAC sequence to which the cyclic shift is applied has a feature of having a cross correlation value of 0 and is used when a high rejection ratio is required between each other. In particular, the CAZAC sequence with cyclic shift can be used to distinguish different signals / UEs when transmitting data / control signals sharing the same time-frequency resources in the same cell.

However, when a frequency offset may occur with respect to the frequency axis, such as when the CAZAC sequence is transmitted by the OFDM scheme, performance deterioration may occur rapidly.

In the following description, it is assumed that the sequence is transmitted in the frequency domain, and it will be described with an example that assumes the use of OFDM transmission.

FIG. 1 is a diagram for explaining the influence of a frequency offset according to pulse shaping in the frequency domain when a sequence is mapped to a subcarrier.

In the example as shown in FIG. 1, sequence samples are mapped to subcarriers, respectively. If a frequency offset is present and a signal is sampled at the receiving end as a red position, one sample is located in an adjacent subcarrier. The signals are mixed together. That is, assuming that the pulse shaping function is p (x), the response in any subcarrier is given as follows.

Here, r (k, f _off ) represents a reception frequency response at the kth subcarrier position when the frequency offset is _off , c (n) represents a CAZAC sequence mapped to subcarriers at the UE side, and p ) Denotes a pulse shaping function in the frequency domain, and w _o denotes a subcarrier interval.

이면, 위의 식에서 값은 보통 c(k)값만 나오게 된다. 하지만

이면, 인접 서브 캐리어의 신호가 들어올 수 있게 되고, 그로 인해서 성능 열화가 생기게 된다. 이와 같은 주파수 옵셋으로 인한 성능 열화로는 주로 수신단의 검출 오류 확률이 증가하고, 수신단이 잘못된 알람 비율(false alarm rate)이 증가하는 것을 들 수 있다.if,

, Then the value in the above equation is usually only c (k). However

, Signals of adjacent subcarriers can be received, thereby deteriorating performance. Such performance deterioration due to the frequency offset mainly includes an increase in the detection error probability of the receiving end and an increase in the false alarm rate of the receiving end.

In particular, when the cyclic shift is applied in the time domain and the CAZAC sequence is sent in the frequency domain, it may occur that the sequence cannot be distinguished. The same phenomenon occurs when a CAZAC sequence is applied in the time domain and a cyclic shift is performed in the frequency domain due to a timing offset. In other words, when a frequency offset or a timing offset occurs, methods using cyclic shift may suffer from performance degradation.

In such a situation where a frequency offset occurs, a technique for preventing performance degradation of a sequence, particularly a CAZAC sequence, is required. In particular, when cyclic shift is applied to the CAZAC sequence, the degree of frequency offset or timing offset is severe, for example, when it is more than half of one subcarrier interval, it is necessary to solve the problem of difficulty in distinguishing a sequence.

In order to solve the above problems, an object of the present invention is to assign a sequence in consideration of the characteristics of the CAZAC sequence according to the degree of frequency offset in the cell, and confusion due to frequency offset when cyclic shift is applied to the sequence. It provides a method for setting a circular movement sequence to prevent the.

A sequence allocation method according to an embodiment of the present invention for achieving the above object is a method for allocating a sequence in a cellular mobile communication system including a plurality of cells, the method comprising obtaining cell information determined that the frequency offset is a predetermined level or more Making; And allocating a sequence not to apply cyclic shift to the cell determined that the frequency offset is equal to or greater than a predetermined level.

In addition, a sequence allocation method according to another embodiment of the present invention includes a method for allocating a sequence in a cellular mobile communication system including a plurality of cells, the method comprising: obtaining cell information determined that a frequency offset is equal to or greater than a predetermined level; And allocating a sequence for applying cyclic shift to a cell determined that the frequency offset is greater than or equal to a predetermined level, allocating a sequence whose sequence index is within a minimum predetermined range or last within the predetermined range.

In addition, the sequence allocation method according to another embodiment of the present invention, a method for allocating a sequence in a cellular mobile communication system including a plurality of cells, the method comprising: obtaining cell information determined that the frequency offset is a predetermined level or more; And when a sequence for applying cyclic shift is allocated to a cell determined that the frequency offset is greater than or equal to a predetermined level, setting a cyclic shift applying interval in consideration of positions of one or more aliases of a reception sequence generated due to the frequency offset. Steps.

In this case, the setting of the cyclic shift application interval may include: checking a channel response position of the reception sequence and the alias; And setting a cyclic shift applicable section so that the reception sequence and the channel response positions of the aliases do not overlap even by a shift due to at least one of a round trip delay and a channel delay spread.

Further comprising: obtaining cell information determined in the embodiments that a frequency offset is less than the predetermined level; And allocating an unassigned sequence to a cell determined that the frequency offset is greater than or equal to a predetermined level to a cell determined that the frequency offset is less than or equal to a predetermined level.

In addition, in the above embodiments, the cell determined that the frequency offset is greater than or equal to a predetermined level may be a cell having a probability that a fast mobile user equipment (UE) exists or more than a predetermined threshold.

On the other hand, the method of setting a cyclic shift sequence according to another embodiment of the present invention is a method of setting a cyclic shift sequence using a first cyclic shift application unit preset in consideration of a round trip delay time and a channel delay spread, Identifying channel response locations of one or more aliases of the received sequence resulting from sequence and frequency offsets; And setting a cyclic shift application interval such that the reception sequence and the channel response positions of the aliases do not overlap by a shift due to at least one of the round trip delay and the channel delay spread.

In this case, the step of applying the cyclic shift section, the second cyclic shift by adding a margin proportional to the interval between the channel response position of the reception sequence and the channel response position of the Elias to the first cyclic shift application unit. Setting an application unit; And setting the circular movement applying section as the second circular movement applying unit.

In addition, the step of setting a circular movement applying interval may include forming a circular movement applying group within the entire length of the received sequence for each second circular movement applying unit; And setting an additional cycle movement application section in the cycle movement application group when the interval between the channel response position of the reception sequence and the channel response position of the alias is greater than two times the first cycle movement application unit. It may also include.

In addition, the step of setting the cyclic shift applying section, the step of dividing the entire interval of the received sequence into a candidate section having a length of the first cyclic shift application unit; Grouping the candidate sections into groups including as many candidate sections as the number of channel responses of the entire received signal including the received sequence and the alias; And selecting the grouped candidate sections as a circular movement applying section.

Here, in the grouping step, it may be preferable to group the candidate sections so that they are not included in two or more groups.

The setting of the cyclic shift application section may include: dividing the entire reception sequence into candidate sections of the first cyclic shift application unit; And when the channel response of the reception sequence is positioned in each of the candidate sections, selecting a candidate section in which the reception sequence and the at least one alias do not overlap as the cyclic shift application section.

Lastly, a sequence allocation method according to another embodiment of the present invention is a method for allocating a sequence in a cellular mobile communication system, wherein one or more aliases of one or more aliases of the received sequence are generated due to a received sequence and a frequency offset. Identifying a channel response location; Setting a cycle movement application interval such that the reception sequence and the channel response positions of the aliases do not overlap even by a shift due to at least one of a round trip delay and a channel delay spread; And allocating a sequence applying the set cycle movement interval.

Hereinafter, preferred embodiments according to the present invention will be described in detail with reference to the accompanying drawings. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following detailed description, together with the accompanying drawings, is intended to illustrate exemplary embodiments of the invention and is not intended to represent the only embodiments in which the invention may be practiced.

The following detailed description includes specific details in order to provide a thorough understanding of the present invention. However, those skilled in the art will appreciate 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 around the core functions of each structure and device in order to avoid obscuring the concepts of the present invention. In the following description, the same components are denoted by the same reference numerals throughout the specification.

In a cellular mobile communication system, the degree of frequency offset may be different for each cell. In addition, the sequence, in particular the CAZAC sequence includes a sequence having a strong characteristic to the frequency offset and a sequence having a characteristic weak to the frequency offset.

Accordingly, one embodiment of the present invention proposes a method of allocating different sequences according to the frequency offset degree of each cell as described above.

2 is a diagram for explaining different frequency offset situations in a plurality of cells.

In a cellular mobile communication system including a plurality of cells, for example, a cell with many UEs moving at high speed may be regarded as having a high degree of frequency offset in the cell, and a cell including a residential complex is located in the cell. Since the UE is generally a low speed UE, it can be considered that the degree of intra-cell frequency offset is not large.

Specifically, FIG. 2 shows, for example, cells A, B adjacent to a high speed train and a cell C away from such high speed means of movement. In the case of cells A and B adjacent to the high-speed train, since there is a high probability of including a large number of high-speed UEs among UEs in the cell, it is advantageous to allocate a strong sequence to the frequency offset in sequence allocation. In addition, in the case of a cell C far away from a high-speed train, for example, adjacent to a residential complex, it is not particularly likely to include a fast UE in the cell, and thus it is not necessary to assign only a strong sequence to the frequency offset.

Meanwhile, in the case of a CAZAC sequence among available sequences, frequency offset characteristics of sequences according to a root index of each sequence and sequences in which a cyclic shift is applied to a sequence according to each root index may be different from each other.

3 is a diagram for explaining a sequence allocation method when a sequence used according to one embodiment of the present invention is a CAZAC sequence.

The CAZAC sequence may include a root sequence according to each root CAZAC index and a ZCZ (Zero Correlation Zone) sequence in which different cyclic shifts (ie, "CS") are applied to each root sequence. Specifically, FIG. 3 shows that a root sequence according to each of the Nt root indices and a ZCZ sequence set to which L different cyclic shifts are applied to each root sequence are defined. In this case, ZCZ means a cyclic shift application section in which CS can be applied so that the RACH signal can be distinguished from the base station.

On the other hand, when the CAZAC sequence is used in the presence of the frequency offset, it is difficult to distinguish between the ZCZ sequences due to the frequency offset. Accordingly, one embodiment of the present invention proposes not to use a ZCZ sequence as a sequence used in a cell that is determined to have a frequency offset equal to or greater than a predetermined level. As such, the threshold used to determine the degree of frequency offset of each cell may be appropriately determined according to the number of available sequences of the corresponding system and the degree of frequency offset of each cell. In addition, a cell determined to have a frequency offset greater than or equal to a predetermined level may be set to a cell having a high probability that a fast UE exists, for example, cells A and B in FIG. 2.

However, when the ZCZ sequence is set not to be used in a cell in which the frequency offset is determined to be greater than or equal to a predetermined level, as shown in FIG. 3, only Nt indexes according to the CAZAC indexes can be used, so that the number of available sequences is small. There is a problem. Accordingly, when the sequence reuse factor becomes small, it is inevitable to allocate the sequence through the cell plan. This may increase complexity in assigning a sequence to each cell, so if the number of available sequences is problematic, another solution may be needed.

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

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

As can be seen from Equation 9, if the CAZAC index M has a very small value or has the largest value among all Nt sequence indexes, the influence of the exponential function item due to the frequency offset is reduced. It can be seen that the effect of the frequency offset on the received signal is reduced.

Therefore, in a more specific embodiment of the present invention, when a CAZAC sequence is allocated to a cell determined to have a frequency offset greater than or equal to a predetermined level, when only the root sequence is allocated or the number of sequences is insufficient because only the root sequence is used, the ZCZ CAZAC sequence is used. 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 depending on the detection performance of the system.

As described above, according to the above-described embodiment of the present invention, the number of sequences that can be used is increased compared to the method of not using the ZCZ sequence in a cell having a high frequency offset, so that almost no cell planning is required.

Specifically, when the entire CAZAC index exists up to Nt as shown in FIG. 3, it is possible to use CAZAC indexes 0, 1, 2 and Nt-2, Nt-1, and Nt as a sequence to be used in a cell having a high frequency offset. .

Meanwhile, in the case of a CAZAC sequence for a cell having a frequency offset less than a predetermined level, it is not necessary to use only an index except for indexes having the CAZAC indexes of 0, 1, 2, and Nt-2, Nt-1, and Nt. Can be selected and used. However, in order to reduce interference with a sequence used in a cell having a high frequency offset, it may be more efficient not to use a sequence index used in a cell having a high frequency offset.

Meanwhile, in another embodiment of the present invention, when the ZCZ sequence is used to secure the number of sequences that can be used in a cell having a high frequency offset as described above, the cyclic shift application section in consideration of an alias due to the frequency offset By setting, it is possible to prevent performance degradation due to frequency offset, which will be described in detail below.

If there is a frequency offset, the frequency response of the received signal can be expressed as shown in Equation 8.

On the other hand, Equation (8) indicates that the signal values in all adjacent subcarriers are overturned due to the frequency offset, but the components that have a relatively large influence on the channel response of the received signal are substantially adjacent to both sides of the corresponding subcarriers. Carrier's signal will be over. Therefore, when only such a first component is considered (first order case), Equation 8 may be represented by three terms as follows.

,

,

와 같은 상수로 나타내었다.On the other hand, on the receiving side, the conjugate complex number of the sequence c (n) is applied to the received signal, and can be expressed as follows. Here, the pulse shaping function of Equation 10 may be simply expressed by a raised cosine or a sinc function, respectively, for convenience of explanation.

,

,

As shown in Fig.

In Equation 11, it can be seen that the channel response of the received signal appears in three positions of the target position t, the left position tM and the right position t + M in the time domain. It can be seen that the channel response appearing at the shifted position by M corresponds to the alias of the received signal.

As such, the shape in which aliases occur in the channel response due to the frequency offset is illustrated in FIG. 4.

4 is a diagram illustrating a phenomenon in which an alias occurs in a time domain channel response of a reception sequence due to a frequency offset.

When cyclic shift is applied to a sequence used in a cell having a frequency offset greater than or equal to a predetermined level, two aliases as well as the target position may additionally occur in the reception channel response of the sequence as shown in FIG. 4. Therefore, when the period for applying the cyclic shift is set without considering the position of the target and the position of the alias, overlapping occurs between the channel response and the alliance of the reception sequence itself due to channel delay spread and propagation delay, A confusion between the target position and the position of the eliance may occur between the sequences to which the movement is applied.

Therefore, in one embodiment of the present invention, when setting the interval to apply the cyclic shift to the CAZAC sequence, in the interval where the position between the channel response of the reception sequence and the alias thereof does not overlap in consideration of the aliases generated in the channel response as described above It is proposed to set the cycle movement interval.

As such, a method of setting a circular movement applying section in consideration of Elias includes 1) a method of setting an additional margin in an existing circular movement applying unit (ie, ZCZ) (hereinafter, referred to as “first approach (approach) for convenience of description). 1) ", 2) when the interval between the channel response and the alias for the reception sequence itself is larger than the existing cyclic shift unit, a method for setting an additional cyclic shift interval between them (hereinafter, referred to as" second Method (approach 2) ", 3) when the total signal length of the channel response of the received sequence itself and its aliases is larger than the total length of the sequence, the entire sequence is divided into existing circular shift intervals, and each candidate The number of pulses that appear in the channel response due to the frequency offset (for example, to select a period that does not overlap between the channel response location of the receive sequence and its alias location) Air, neunghada the like 3) for selecting a candidate by determining the grouping by area (hereinafter referred to as "the third method (third approach)" term).

In addition, in each of the first to third methods, a method of dividing and accessing a sequence into units suitable for each method and a method of classifying and accessing an entire sequence into units of a conventional cyclic shift application may be possible. A detailed description of each of the schemes described above is as follows.

First, a method of setting an additional margin to an existing circular movement applying unit (ie, ZCZ) will be described as follows.

In general, in determining the cyclic shift application unit (ie, ZCZ) of the CAZAC sequence, different units may be used according to the applied system. For example, in the case of a synchronized channel, there is no propagation delay in sequence use and only a channel delay spread. Therefore, in such a synchronized system, a unit of application of cyclic shift is simply defined. It can be determined considering only the delay spread of the channel. That is, if the application unit of the cyclic shift is T ₀ , T ₀ can be simply processed in the synchronized channel as follows.

는 채널의 지연 확산을 나타낸다. here,

Represents the delay spread of the channel.

However, when the ZCZ sequence to which the cyclic shift is applied is used for the asynchronous channel, propagation delay must be additionally considered, and thus the unit of applying the cyclic shift becomes large as follows.

는 UE와 기지국 사이의 물리적 거리를 전파가 진행하는 시간을 나타낸다.here,

Denotes the time for propagation of the physical distance between the UE and the base station.

A representative example of such an asynchronous channel is a random access channel (RACH). The RACH is a channel used when the UE obtains information of the base station in downlink and transmits a signal without synchronization in uplink. Since there is no synchronization information between the base station and the UE in this channel, there is an ambiguity in the positional accuracy of the signal by twice the propagation delay.

Hereinafter, based on the asynchronous channel such as the above-described RACH, it will be described based on the basic unit (T ₀ ) of the cyclic shift that is set in consideration of the propagation delay and the channel delay spread in this channel.

FIG. 5 is a diagram for describing a method of setting a cyclic shift application unit by adding an additional margin to a conventional cyclic shift application unit to reduce the influence of a frequency offset in the RACH according to an embodiment of the present invention.

In FIG. 5, a unit for applying a cyclic shift in consideration of a propagation delay and channel delay spread in an asynchronous channel such as a RACH is T ₀ , and a new cyclic shift with an additional margin according to a frequency offset according to an embodiment of the present invention. The application unit is shown as T _O '.

When cyclic shift is applied to a CAZAC sequence based on a cyclic shift application unit (T ₀ ) determined in consideration of the conventional propagation delay and channel delay spread, each ZCZ sequence has a different ZCZ by eliminating aliases of a reception sequence in their channel response. Confusion with sequences can be difficult to distinguish. Therefore, as described above, the additional margin set in consideration of the frequency offset should be set so that the position between the target position of the reception sequence and the alias of the reception sequence does not overlap in consideration of the alias of the received signal. Here's how to set the extra margin length:

6A and 6B are diagrams for describing a method of setting a cyclic shift sequence using a cyclic shift application unit to which additional margin is added as shown in FIG. 5 according to an embodiment of the present invention.

As shown in FIG. 4 and Equation 11, the interval between the channel response of the reception sequence itself and the alias thereof is equal to 'M' which is an index of the CAZAC sequence. As such, the interval between the channel response of the received sequence and the aliases depends on the index of the CAZAC sequence. Accordingly, according to one embodiment of the present invention, the cyclic shift application unit (T _O ′) including additional margin due to frequency offset is also CAZAC. It can be expressed as a function of index M of a sequence as follows.

Here, T _margin (M) is a margin additionally given in consideration of the frequency offset, T (M) is a cyclic shift application unit including an additional margin to the conventional cyclic shift application unit (T _O ) according to an embodiment of the present invention Indicates.

6A and 6B, it can be seen that the total length of the signal including the channel response of the reception sequence itself and the two aliases corresponds to 'T ₀ + 2M', and the cyclic shift is applied to the entire signal as a unit. In this case, both the channel response of the reception sequence itself and its aliases may not overlap each other even if the shift occurs by 'T _O ' due to a propagation delay and a channel delay spread.

Therefore, in one embodiment of the present invention, it is proposed to set the length of the additional margin due to the frequency offset to '2M', and to set the total cyclic shift application unit (T ₀ ') to' T ₀ + 2M '.

Specifically, FIG. 6A is an index of a CAZAC sequence and 'M' corresponding to an interval between a channel response of the sequence itself and an alias thereof in the present invention is smaller than 'T ₀ ', and FIG. 6B illustrates that 'M' is 'T' _{The case} is greater than ₀ 'but smaller than' 2T ₀ '.

In addition, in another embodiment of the present invention, as described above, an additional margin is added in consideration of the position of Elias according to the index of the CAZAC sequence, and the newly set cyclic shift application unit is set to '3M' instead of 'T ₀ + 2M'. Suggest setting. As described above, when the unit for applying the circular movement is set to '3M', the number of applicable circular movements may be reduced compared to when setting the 'T ₀ + 2M'. Have In addition, this may be more advantageous as a cyclic shift application group when applying additional cyclic shifts between the receiving sequence and the alias as described below.

When setting the cyclic shift application unit as in each embodiment of the present invention according to the first scheme, the entire signal including the channel response of the reception sequence itself and its aliases is circulated like the shaded area in FIGS. 6A and 6B. The movement can be applied and can be distinguished from other ZCZ sequences, even though each of them is shifted by T _O. Such a situation may be maintained when 'M <2T ₀ ', and within this range, an additional cyclic shift application section may not be defined between the channel response and the alias, as described below.

Meanwhile, another embodiment of the present invention uses the first method as described above, but uses a method of dividing the circular movement applying section based on the conventional circular movement applying unit T ₀ based on the approach, and will be described. Is as follows.

FIG. 7 is a diagram for describing a method for setting a cyclic shift sequence in consideration of an alias of a reception sequence according to an embodiment of the present invention, when a sequence is divided into units of a conventional cyclic shift application interval.

According to an embodiment of the present invention, it is proposed to set the cyclic shift application unit in units of candidate region groups including the entire signal including the channel response of the reception sequence itself and its aliases.

According to such an embodiment of the present invention, when using the candidate region divided by the conventional cyclic shift application unit (T ₀ ), that is, ZCZ, as shown in FIG. The location of the aliases may exist within each candidate region, but may be located at the boundary between each candidate region as shown in FIG. 7.

If the aliases are located in the candidate region immediately adjacent to the candidate region in which the channel response region of the reception sequence itself is present, such three candidate regions may be set as a cyclic shift application unit, as shown in FIG. 7. If they are located at the boundary of the candidate region, it is inevitable to set the cyclic shift application unit by including both candidate regions having the boundary. That is, in FIG. 7, cyclic shift is applied in units of five candidate regions.

In this case, the number of available sequences may be reduced by not flexibly adjusting the cyclic shift application unit according to the position of Elias. However, there is an advantage of reducing the inconvenience of newly setting the cyclic shift application unit.

Meanwhile, in the embodiment of the present invention, a second method of the above-described methods for setting a cycle movement application interval will be described.

According to the first method described above, when the unit for applying the cyclic shift is set to T ₀ 'by adding an additional margin considering the frequency offset to the conventional T ₀ , the additional margin T _margin (M) is 2M, and the cyclic shift set by adding it It can be seen that the application unit can be expressed as 'T ₀ + 2M'.

In this way, by simply applying additional margins for all indices, it is possible to define robust cyclic shifts for frequency offsets and / or timing offsets. However, as the sequence index M increases, the T _margin M increases, and eventually, the applicable circular movement can be reduced to one.

Accordingly, the second scheme according to an embodiment of the present invention closely examines when the CAZAC index has grown to cope with the reduction in the number of applicable cyclic shifts, and thus provides a method of additionally applying cyclic shifts.

8A to 8C are diagrams for describing a method of setting an additional circular shift application interval when an interval between a reception sequence and an alias is greater than twice the conventional circular shift application unit according to an embodiment of the present invention.

Specifically, FIG. 8A illustrates a case where the index M of the CAZAC sequence is 2T ₀ to 3T ₀ , FIG. 8B illustrates a case where M is 3T ₀ to 4T ₀ , and FIG. 8C illustrates M as a PT ₀ to (P +1) T ₀ The case is illustrated.

If the index of the CAZAC sequence as shown in Figure 8a is greater than 2T _0, a distance between a channel response position of the received sequence itself and the alias of the T ₀ range that can cause confusion by the typical propagation delay and channel delay spread Since it is larger than twice, additional circular movements can be applied to the spaces in between. That is, even when the cyclic shift is applied such that the reception sequence and each alias are shifted as shown by hatched portions in FIG. 8A, confusion may not occur between the reception sequence and each alias due to the propagation delay and the channel delay spread.

In addition, in FIG. 8B, the interval between the reception sequence and each alias is wider than that in FIG. 8A, and the number of available sequences can be extended three times by entering up to two cyclic shift applicable sections therebetween. 8C shows that when the interval between them is larger than PT ₀ , the P-1 interval can be added as the applicable cyclic shift application interval, so that the number of available sequences can be expanded by P times. Able to know.

FIG. 9 is a diagram for explaining a method for setting a circular movement applying group and a circular movement applying section in each group according to an embodiment of the present invention.

That is, according to an embodiment of the present invention, as shown in Figure 9, the interval corresponding to three times the interval between each of the aliases due to the reception sequence and the frequency offset (that is, 3M) is defined as a cyclic shift application group In addition, in each group, as described above with reference to FIGS. 8A to 8C, the cyclic shift sequence may be set in consideration of the cyclic shift application interval set in addition to the interval between the reception sequence and the alias.

FIG. 9 illustrates the number of cyclic shift application groups set in consideration of an alias according to a frequency offset in the entire sequence. In addition, when the number of intervals to which cyclic shift can be additionally applied in each group is P, in one embodiment of the present invention, ZCZ capable of applying cyclic shift so as not to be affected by the frequency offset for each route sequence It can be seen that the number of sequence sets is P * G.

On the other hand, in the above-described scheme, the case where the cyclic shift application group is not exactly a divisor of the entire length of the sequence, that is, the cyclic shift application group may be set in the sequence, and some empty space may be left. In a preferred embodiment of the present invention, as a countermeasure in this case, 1) the remaining space is left unused, and 2) the remaining space is larger than 2M + T ₀ to define and add one or more cyclic shift sets. , And 3) proposes a method of using the remaining space as a guard interval between the groups. In addition, these methods can be applied to all cases in which the total sequence length is not an exact integer multiple of the cyclic shift application group length.

On the other hand, even in the second method as described above, the entire sequence can be accessed using the candidate interval divided by T ₀ unit, the method according to this will be described as follows.

10A and 10B illustrate a cycle movement applying group and a cycle movement applying interval within each group in consideration of an alias of a reception sequence according to an embodiment of the present invention, when the sequence is divided into units of a conventional cycle movement applying interval. It is a figure for demonstrating the method.

Specifically, when dividing the entire sequence interval into candidate regions divided by T ₀ units, FIG. 10A illustrates a case where a reception sequence and its aliases are positioned at two candidate interval intervals. In this case, the size T ₀ ′ of the cyclic shift application group may be set to 5T ₀ and define two sets of ZCZ sequences in each group.

10B illustrates a case where the reception sequence and its aliases are positioned at three candidate intervals. In this case, the size T ₀ ′ of the cyclic shift application group may be set to 7T ₀ and define three ZCZ sequence sets within each group.

Accordingly, in the method for setting a cyclic shift sequence according to an embodiment of the present invention, when the entire sequence is divided into candidate intervals having a length of T ₀ , the cyclic shift application group is set to the number of candidate intervals including a reception sequence and an alias thereof, A method for setting a cyclic shift applicable section as many as the number of candidate sections corresponding to the interval between the reception sequence and the alias in each group is proposed.

On the other hand, if the index M of the CAZAC sequence is increased, and if the second method as described above is maintained until the length of the entire signal including the channel response of the received sequence itself and the aliases thereof is larger than the total length of the sequence, between the cyclic shift applying groups Duplicates can occur. That is, when 3M is larger than the total length N of the sequence, the above-described second scheme cannot be maintained, and accordingly, an embodiment of the present invention proposes the following third scheme when M> N / 3. The explanation is as follows.

FIG. 11 is a diagram for describing a method of setting a cyclic shift application interval according to an embodiment of the present invention when the total length of the sum of the channel response of the reception sequence and each alias of the reception sequence is greater than the total length of the sequence.

When the CAZAC index is increased, and there is only one cyclic shift group, it can be seen that duplication occurs between the region in which the reception sequence is shifted by M to the right and the region shifted by M to the left. For example, FIG. 11 illustrates a length M section shifted to the left based on the length M section on the left (hence the length M section shown on the right in FIG. 11) and the length M on the left when M> N / 3. It can be seen that overlap occurs between sections having a length M to the right of the section, and accordingly, the third scheme follows the following approach.

First, as shown in FIG. 11, candidate regions having a length of T ₀ are divided into regions having a length M. FIG. Thereafter, an applicable cyclic shift section may be selected by grouping the candidate sections with three candidate sections separated by M to the left and right. Of course, it will be apparent to those skilled in the art that the section separated by M to the left and right is a distance in consideration of the cyclic characteristics of the sequence. In the example of FIG. 11, an example of selecting a usable circular movement section through the operation of grouping three candidate sections spaced by M to the left and right, respectively, based on the candidate sections within the M length section on the left side. Here, the three candidate sections painted with the same color may correspond to the channel response position of the reception sequence itself and the position of the alias thereof when the same cyclic shift is applied.

When the candidate sections are bundled in this way, each candidate section may not be used more than two times, and if there are candidate sections used two or more times, the cyclic shift may not be distinguished due to the frequency offset.

The index (Shift ID) of the cyclic shift applicable candidate section selected according to the embodiment of the present invention as described above may be selected as follows according to the size of 'N-2M' shown in FIG. 11.

Here, [x, y] represents all integers including x to y, and X (M), Q (M), and R (M) may be represented as follows.

In Equation 18, O (M) may be expressed as follows.

That is, from the above equations, X (M) represents the number of candidate intervals of size T _{0 in the} interval 'N-2M' in FIG. 11, or 1 when 'N-2M' is smaller than T ₀ , which is shown in FIG. 11. It can be seen that the unit is a division unit of the cyclic shift applicable interval range according to an embodiment of the present invention. Further, it can be seen that Q (M) represents a variable for determining the number of such cycle-moveable unit sections, and R (M) represents the size of the remaining sections in the final cycle-moveable section.

On the other hand, when the index of the CAZAC sequence is half of the total sequence length N, duplication occurs between the aliases shifted by M to the left and the aliases sequenced by M to the right. Therefore, in this case, the number of usable cyclic shifts is N / 2, and the index (Shift ID) of the candidate section to which cyclic shifts are applicable is [1, M].

As described above, the method for setting the cyclic shift sequence according to each embodiment of the present invention has been described until the CAZAC index M is 0 to N / 2. However, when the CAZAC index is larger than N / 2, it can be seen that the same applies to the case of 0 to N / 2 due to the symmetry of the CAZAC sequence. However, in the above description, the length based on 'M' is different only in that the length based on 'N-M' is applied due to symmetry.

Based on this, a section for applying the first to third methods as described above according to the index of the CAZAC sequence may be summarized as follows.

12 is a diagram showing an example of a section to which each embodiment can be applied according to the index of a sequence in the present invention.

보다 작은 구간 및 M이

보다 크고 'N-2T₀'보다 작은 구간에서는 상술한 본 발명에 따른 방식 중 제 2 방식을 이용할 수 있다. 아울러, M이

보다 크고

보다 작은 구간에서는 상술한 본 발명에 따른 방식 중 제 3 방식을 이용할 수 있다.As shown in FIG. 12, the CAZAC sequence index M is used in a section smaller than 2T _{0 and} greater than N-2T _{0, which} is twice the T cyclic unit T ₀ , and the first method according to the present invention described above may be used. Can be. Also, M is _greater than 2T ₀

Less than interval and M

In the section larger and smaller than 'N-2T ₀ ', the second method of the aforementioned method according to the present invention may be used. In addition, M

Greater than

In a smaller section, the third method among the methods according to the present invention described above may be used.

13A and 13B compare the detection error probability and false alarm rate when applying the cyclic shift in the same interval regardless of the index of the conventional CAZAC sequence and the cyclic shift according to each embodiment of the present invention. Each is a graph.

According to each embodiment of the present invention through FIG. 13A, it can be seen that the detection probability is greatly improved in a situation where the frequency offset is higher than that of the conventional method, and according to each embodiment of the present invention, FIG. It can be seen that if higher, the false alarm rate does not increase significantly.

The conditional parameters which performed the simulation shown in FIG. 13A and 13B can be summarized as follows.

In addition, another point to look at for each embodiment of the present invention as described above is the number of cycle movement opportunities available. In the short preamble structure, all cyclic shifts are available, while in the long preamble structure, the number of cyclic shifts is 1 to avoid ambiguity due to frequency offset.

14A and 14B show some examples of the number of cyclic shifts available based on the sequence index and the minimum cyclic shift unit T ₀ .

14A and 14B are graphs showing the number of cycles available and the total number of sequences available, respectively, according to an embodiment of the invention.

14A illustrates the number of cyclic shifts available according to the sequence index when setting the cyclic shift length according to the sequence index in accordance with some embodiments of the present invention. 14B illustrates a case in which only a root sequence is used without using a cyclic shift in a situation such as a cell having a frequency offset of a predetermined level or more according to an embodiment of the present invention, when cyclic shift is applied regardless of a conventional sequence index. According to one embodiment of the present invention, for each case of setting a cyclic shift according to a sequence index and using a short preamble (specifically, 1/3 of a general preamble length) in preparation for a high frequency offset. It is shown against the total number of sequences available.

As can be seen from FIG. 14A, when the length of a cyclic shift is set differently according to an index according to an embodiment of the present invention, the number of available cyclic shifts may vary according to each sequence index. When allocating a sequence, it may be desirable to allocate it in consideration of such a point. In addition, as can be seen from FIG. 14B, when there are enough available root sequences, it may be convenient to allocate only the sequence using the root index to a cell having a frequency offset level equal to or greater than a predetermined level. If it is a problem to reduce the number of sequences according to another embodiment of the present invention can solve the problem caused by the frequency offset by setting the ZCZ sequence according to the method of setting the cyclic shift differently according to the sequence index.

Until now, the method for setting the cyclic shift according to an embodiment of the present invention assumes only the case where the pulse shaping function p (x) is assumed to be negligible in the portion over one subcarrier (first order case). to be. If more contiguous subcarriers are considered, the area bounded by the cyclic shift group from above may be increased in the same manner by increasing the second order case (5M), the third order case (7M), and the like.

In addition, although the above description of the present invention has been described in terms of frequency offset, it can be seen that the principle applied here can be applied to the case where the effect of the timing offset is reduced as it is.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The foregoing description of the preferred embodiments of the present invention has been presented for those skilled in the art to make and use 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. Accordingly, 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 one embodiment of the present invention as described above, by allocating a sequence that does not apply the cyclic shift to a cell having a frequency offset of more than a predetermined level, it is possible to greatly increase the detection error or false alarm rate due to the frequency offset.

Also, in order to secure the number of available sequences, when a cyclic shift is applied to a CAZAC sequence to a cell having a high frequency offset, a sequence having an index within a first predetermined range or a final predetermined range is allocated. This can reduce the effects of frequency offset.

In addition, when assigning a sequence for applying a cyclic shift to a cell having a frequency offset equal to or more than a predetermined level, considering the channel response of the received sequence and the position of the alias of the received sequence, these received signals are caused by the channel delay spread and the propagation delay. It is possible to greatly reduce the detection error and false alarm rate due to the frequency offset by setting the cyclic shift application section in a position not overlapping each other even if shifted.

Claims (28)

In the method for transmitting a random access preamble to a base station, Generating the random access preamble from a Zadoff-Chu (ZC) sequence having a length N; And Transmitting the random access preamble to the base station; The random access preamble is generated in consideration of the cyclic shift of the ZC sequence, The cyclic shift is given by using a variable M corresponding to the Doppler shift of one subcarrier interval, The related parameters for defining the cyclic shift are defined differently depending on whether the variable M is less than one third of the length N. The method of claim 1, Wherein the parameters include a number G of one or more groups defined from the ZC sequence, a length S of each of the one or more groups, and a number of one or more applicable cyclic shift opportunities for each of the one or more groups. Preamble transmission method. 3. The method of claim 2, The number G, the length S and the number P are applicable when the variable M is smaller than N / 3. The method of claim 3, If the remaining space of the ZC sequence is greater than 2M + T, the number of one or more additional cyclic shift opportunities is defined, The T indicates a length in cyclic shift units, random access preamble transmission method. The method of claim 3, If (N-G * P) is not less than (2M + T), the total number of applicable cyclic shift opportunities is greater than the product of the number G and the number P, The T indicates a length in cyclic shift units, random access preamble transmission method. The method of claim 3, The number G of the one or more groups is

Lt; / RTI &gt; The number P of the one or more applicable opportunities is less than or equal to M / T, The length S is defined as S = 2M + P * T, The T indicates a length in cyclic shift units, random access preamble transmission method. 3. The method of claim 2, If the variable M is not less than N / 3, the number G is 1, random access preamble transmission method. In the method for receiving a random access preamble at the base station, Receiving the random access preamble from a terminal, The random access preamble is generated from a Zadoff-Chu (ZC) sequence having a length N in consideration of the cyclic shift of the ZC sequence, The cyclic shift is given by using a variable M corresponding to the Doppler shift of one subcarrier interval, The related parameters for defining the cyclic shift are defined differently depending on whether the variable M is less than 1/3 of the length N. 9. The method of claim 8, Wherein the parameters include a number G of one or more groups defined from the ZC sequence, a length S of each of the one or more groups, and a number of one or more applicable cyclic shift opportunities for each of the one or more groups. Preamble Receiving Method. 10. The method of claim 9, The number G, the length S and the number P are applicable when the variable M is smaller than N / 3. The method of claim 10, If the remaining space of the ZC sequence is greater than 2M + T, the number of one or more additional cyclic shift opportunities is defined, The T indicates a length in cyclic shift units, random access preamble receiving method. The method of claim 10, If (N-G * P) is not less than (2M + T), the total number of applicable cyclic shift opportunities is greater than the product of the number G and the number P, The T indicates a length in cyclic shift units, random access preamble receiving method. The method of claim 10, The number G of the one or more groups is

Lt; / RTI &gt; The number P of the one or more applicable opportunities is less than or equal to M / T, The length S is defined as S = 2M + P * T, The T indicates a length in cyclic shift units, random access preamble receiving method. 10. The method of claim 9, If the variable M is not less than N / 3, the number G is 1, random access preamble receiving method. A terminal for transmitting a random access preamble to a base station, The terminal is: Generate the random access preamble from a Zadoff-Chu (ZC) sequence having a length N, and transmit the random access preamble to the base station, The random access preamble is generated in consideration of the cyclic shift of the ZC sequence, The cyclic shift is given by using a variable M corresponding to the Doppler shift of one subcarrier interval, Associated parameters for defining the cyclic shift are defined differently depending on whether the variable M is less than 1/3 of the length N. 16. The method of claim 15, Wherein the parameters comprise a number G of one or more groups defined from the ZC sequence, a length S of each of the one or more groups, and a number of one or more applicable cyclic shift opportunities for each of the one or more groups. 17. The method of claim 16, The number G, the length S and the number P are applicable when the variable M is smaller than N / 3. 18. The method of claim 17, If the remaining space of the ZC sequence is greater than 2M + T, the number of one or more additional cyclic shift opportunities is defined, The T represents the length of the cyclic shift unit. 18. The method of claim 17, If (N-G * P) is not less than (2M + T), the total number of applicable cyclic shift opportunities is greater than the product of the number G and the number P, The T represents the length of the cyclic shift unit. 18. The method of claim 17, The number G of the one or more groups is

Lt; / RTI &gt; The number P of the one or more applicable opportunities is less than or equal to M / T, The length S is defined as S = 2M + P * T, The T represents the length of the cyclic shift unit. 17. The method of claim 16, If the variable M is not less than N / 3, the number G is 1, the terminal. In the base station receiving the random access preamble, The base station is configured to receive a random access preamble from the terminal, The random access preamble is generated from a Zadoff-Chu (ZC) sequence having a length N in consideration of the cyclic shift of the ZC sequence, The cyclic shift is given by using a variable M corresponding to the Doppler shift of one subcarrier interval, Associated parameters for defining the cyclic shift are defined differently depending on whether the variable M is less than one third of the length N. 23. The method of claim 22, Wherein the parameters comprise a number G of one or more groups defined from the ZC sequence, a length S of each of the one or more groups, and a number of one or more applicable cyclic shift opportunities for each of the one or more groups. 24. The method of claim 23, And the number G, the length S and the number P are applicable when the variable M is smaller than N / 3. 25. The method of claim 24, If the remaining space of the ZC sequence is greater than 2M + T, the number of one or more additional cyclic shift opportunities is defined, Wherein T represents a length in cyclic shift units. 25. The method of claim 24, If (N-G * P) is not less than (2M + T), the total number of applicable cyclic shift opportunities is greater than the product of the number G and the number P, Wherein T represents a length in cyclic shift units. 25. The method of claim 24, The number G of the one or more groups is

Lt; / RTI &gt; The number P of the one or more applicable opportunities is less than or equal to M / T, The length S is defined as S = 2M + P * T, Wherein T represents a length in cyclic shift units. 24. The method of claim 23, And the number G is 1 if the variable M is not less than N / 3.

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