KR101295159B1 - Method of timing offset detection for initial ranging process of fixed wireless communication system and apparatus for performing the same - Google Patents

Abstract

PURPOSE: A detection method and device of a time offset for the initial ranging of a fixed-type wireless communications system are provided to improve performance degradation caused by code errors. CONSTITUTION: A detection device (1300) of a time offset for the initial ranging of a fixed-type wireless communications system includes an interval dividing part (1310), an error generation determining part (1330), and an error correcting part (1350). The interval dividing part divides a symbol into a confidence interval and a distrust interval, designates an interval containing a code transition point as the distrust interval, and designates an interval not containing the code transition point as the confidence interval. If a time offset value, which is estimated through a differential operation between sub-carriers separated by d numbers, is included in the distrust interval, the error generation determining part determines whether a code error is generated. If a code error is generated according to the determination result, the error correcting part corrects the code error. [Reference numerals] (1310) Interval dividing part; (1330) Error generation determining part; (1350) Error correcting part; (1370) Aggravated equalization part

Description

METHOD OF TIMING OFFSET DETECTION FOR INITIAL RANGING PROCESS OF FIXED WIRELESS COMMUNICATION SYSTEM AND APPARATUS FOR PERFORMING THE SAME}

The present invention relates to a method and apparatus for detecting an offset for initial ranging in a wireless communication system, and more particularly, to a method and apparatus for detecting offset based on a cumulative differential operation.

In an OFDMA system, all terminal signals must be synchronized to a base station in order to maintain orthogonality between subcarriers in uplink. This is done through an initial uplink synchronization process called initial ranging, and the system uses this initial ranging process to achieve near / waves caused by different transmission delay times (TTDs) and received power. far) compensation for problems is possible.

In a fixed wireless communication environment having a wide coherence bandwidth, a cumulative differential detection technique may be applied as a time offset detection technique for initial ranging. It is a method of estimating the time offset value by increasing the interval between two subcarriers performing the differential operation, accumulating it and detecting the final time offset value, and improving the detection performance through the noise suppression effect. However, a sign error of an estimated time offset value caused by a difference in channel frequency response (CFR) characteristics between noise and subcarriers causes deterioration of detection performance.

Korean Patent No. 10-0682162 ("Symbol Timing Offset and Carrier Frequency Error Recovery Systems and Methods and Diversity Systems and Methods", IBQ Digital Corporation, Dec. 7, 2001)

As described above, when applying a cumulative differential calculation based time offset detection technique for initial ranging of a wireless communication system considering fixed operation, a sign error of an estimated time offset value occurs due to a difference in noise and CFR characteristics. What is needed is a way to overcome the estimated performance degradation.

An object of the present invention is to provide a time offset estimation method with improved performance by correcting a sign error occurring when applying a cumulative differential operation based time offset detection technique and using a cumulative effect that is obtained through weighted averaging.

In addition, another object of the present invention is to provide a time offset estimation apparatus having improved performance by correcting a sign error that occurs when applying a time offset detection technique based on a cumulative differential operation and using a cumulative effect that occurs through a weighted averaging process. will be.

In order to achieve the above object of the present invention, a time offset detection method for initial ranging in a fixed wireless communication system according to an embodiment of the present invention includes a symbol confidence interval (CI) and a distrust interval (Distrust Interval). , DI); determining whether a sign error occurs when a time offset value estimated through a differential operation between d interval subcarriers is included in the untrusted interval; And correcting a sign error when a sign error occurs as a result of the determination. Here, in the step of dividing the symbol into a confidence interval and an untrusted interval, an interval including a code transition point may be designated as an untrusted interval, and an interval not including a code transition point may be designated as a confidence interval. The code transition point may be ± 0 or ± NFFT / 2 sample points. The step of dividing the symbol into a confidence interval and an untrusted interval divides the symbol into five intervals, but the symbol transition point. The point shifted by one-eighth of the NFFT (FFT Fourier Transform Size) to the left or the right of the edge may be the boundary of each section. The determining of whether a sign error occurs may include searching for an initial time offset value included in a confidence interval among time offset values estimated through subcarrier differential operations of the d integer multiple number intervals; The first time offset value included in the confidence interval is different from the time offset value estimated through the differential operation between the d interval subcarriers and the time offset value estimated through the differential operation between the subcarriers of the d integer multiple number interval. In this case, the method may include determining that a sign error has occurred. The determining of whether a sign error occurs may include searching for an initial time offset value included in a confidence interval among time offset values estimated through subcarrier differential operations of the d integer multiples; And the following equation

는 d개 간격 부반송파 간 차동 연산을 통해 추정된 시간 오프셋 값,

는 상기 d개의 정수배 개수 간격의 부반송파 간 차동 연산을 통해 추정된 시간 오프셋 값, N_FFT는 FFT 크기를 나타냄 - 을 만족하지 못하면 부호 오류가 발생한 것으로 판정하는 단계를 포함할 수 있다. 여기서, 상기 부호 오류를 정정하는 단계는 상기 d개 간격 부반송파 간 차동 연산을 통해 추정된 시간 오프셋 값의 부호를 역전시킬 수 있다. 여기서, d개 간격 부반송파 간 주파수 영역 채널 상관도, 차동 연산의 누적 횟수 및 정규화 과정의 잡음 분산 감소 효과를 기반으로 상기 추정된 시간 오프셋 값을 가중 평균화하여 누적하는 단계를 더 포함하는 것을 특징으로 할 수 있다. 또한, 상기 누적하는 단계는 하기의 수학식Where sgn is a sine function,

Is a time offset value estimated by a differential operation between d interval subcarriers,

The method may include determining that a code error has occurred if the time offset value estimated through the differential operation between subcarriers of the integer multiple number interval, N _FFT indicates the FFT size, is not satisfied. The correcting of the sign error may reverse the sign of the time offset value estimated through the differential operation between the d interval subcarriers. The method may further include weighting and averaging the estimated time offset values based on a frequency domain channel correlation between d interval subcarriers, a cumulative number of differential operations, and a noise variance reduction effect of a normalization process. Can be. In addition, the accumulating step is the following equation

는 누적 차동 연산 기반의 시간 오프셋 값, N_range는 최대 부반송파 간 간격, (N_code-d)는 차동 연산의 누적 횟수, R_f(d)는 d개 간격 부반송파 간 주파수 영역 채널 상관도,

는 d개 간격 부반송파 간 차동 연산을 통해 추정된 시간 오프셋 값을 정규화한 값의 크기를 나타냄 - 을 기반으로 상기 추정된 시간 오프셋 값을 누적하는 것을 특징으로 할 수 있다. -Where,

Is the time offset value based on the cumulative differential operation, N _range is the maximum interval between subcarriers, (N _code -d) is the cumulative number of differential operations, R _f (d) is the frequency domain channel correlation between d interval subcarriers,

The estimated time offset value may be accumulated based on a value obtained by normalizing a time offset value estimated through a differential operation between d interval subcarriers.

An apparatus for detecting time offset for initial ranging of a fixed wireless communication system according to an embodiment of the present invention for achieving another object of the present invention described above may include a symbol between a confidence interval (CI) and an untrusted interval (Distrust). An interval division unit for dividing into Interval, DI); an error occurrence determining unit determining whether a sign error occurs when a time offset value estimated through a differential operation between d interval subcarriers is included in the untrusted interval; And an error correction unit that corrects a sign error when a sign error occurs as a result of the determination. Here, the interval dividing unit may designate a section including a code transition point as an untrusted section, and designate a section not including a code transition point as a confidence section. The code transition point may be ± 0 or ± NFFT / 2 sample points. Here, the interval dividing unit divides the symbol into five intervals, and may make the boundary of each interval a point shifted by one-eighth of the NFFT (FFT Fourier Transform Size) to the left or right of the code transition point. have. The error occurrence determining unit may include: a confidence offset search unit searching for an initial time offset value included in a confidence interval among time offset values estimated through subcarriers differential operations of the d integer multiples; The first time offset value included in the confidence interval is different from the time offset value estimated through the differential operation between the d interval subcarriers and the time offset value estimated through the differential operation between the subcarriers of the d integer multiple number interval. In this case, it may include a sign comparison unit that determines that a sign error has occurred. The error occurrence determining unit may include: a confidence offset search unit searching for an initial time offset value included in a confidence interval among time offset values estimated through subcarriers differential operations of the d integer multiples; And the following equation

는 d개 간격 부반송파 간 차동 연산을 통해 추정된 시간 오프셋 값,

는 상기 d개의 정수배 개수 간격의 부반송파 간 차동 연산을 통해 추정된 시간 오프셋 값, N_FFT는 FFT 크기를 나타냄 - 을 만족하지 못하면 부호 오류가 발생한 것으로 판정하는 부호 비교부를 포함할 수 있다. 여기서, 상기 오류 정정부는 상기 d개 간격 부반송파 간 차동 연산을 통해 추정된 시간 오프셋 값의 부호를 역전시킬 수 있다. 또한, d개 간격 부반송파 간 주파수 영역 채널 상관도, 차동 연산의 누적 횟수 및 정규화 과정의 잡음 분산 감소 효과를 기반으로 상기 추정된 시간 오프셋 값을 가중 평균화하여 누적하는 가중 평균화부를 더 포함할 수 있다. 여기서, 상기 가중 평균화부는 하기의 수학식Where sgn is a sine function,

Is a time offset value estimated by a differential operation between d interval subcarriers,

May include a code comparison unit that determines that a code error has occurred if the time offset value estimated through the differential operation between subcarriers of the number of integer multiples, N _FFT indicates the FFT size, is not satisfied. Here, the error correction unit may reverse the sign of the time offset value estimated through the differential operation between the d interval subcarriers. The apparatus may further include a weighted averaging unit that weights and averages the estimated time offset values based on the frequency domain channel correlation between the d interval subcarriers, the cumulative number of differential operations, and the noise variance reduction effect of the normalization process. Here, the weighted averaging unit is the following equation

는 누적 차동 연산 기반의 시간 오프셋 값, N_range는 최대 부반송파 간 간격, (N_code-d)는 차동 연산의 누적 횟수, R_f(d)는 d개 간격 부반송파 간 주파수 영역 채널 상관도,

는 d개 간격 부반송파 간 차동 연산을 통해 추정된 시간 오프셋 값을 정규화한 값의 크기를 나타냄 - 을 기반으로 상기 추정된 시간 오프셋 값을 누적하는 것을 특징으로 할 수 있다.
-Where,

Is the time offset value based on the cumulative differential operation, N _range is the maximum interval between subcarriers, (N _code -d) is the cumulative number of differential operations, R _f (d) is the frequency domain channel correlation between d interval subcarriers,

The estimated time offset value may be accumulated based on a value obtained by normalizing a time offset value estimated through a differential operation between d interval subcarriers.

As described above, according to the method and apparatus for detecting a time offset for initial ranging in a fixed wireless communication system according to an embodiment of the present invention, a sign error is applied by applying a sign error correction technique by comparing a sign with an integer estimated time offset value. The performance deterioration due to the error can be improved, and weighted averaging based on channel correlation and noise variance can give high reliability to each estimated time offset value. Therefore, accurate time offset detection performance can be obtained as compared with the conventional technique.

1 is a conceptual diagram illustrating a frequency domain ranging channel structure in a WiBro system.
2 is a conceptual diagram illustrating a time domain ranging channel structure in a WiBro system.
3 is a conceptual diagram illustrating two code parts and a sign transition point of an estimated time offset value.
4 is a conceptual diagram illustrating a conventional cumulative differential operation based time offset detection technique.
5 is a conceptual diagram illustrating an example of two types of sign error.
6 is a conceptual diagram illustrating a method of correcting a code error by setting five code parts in consideration of a code transition point and comparing a sign with an integer estimated time offset value according to an embodiment of the present invention.
7 is a graph comparing the time offset estimation performance of the offset estimation method and the conventional method according to an embodiment of the present invention in a TTD 300 sample, 7km SUI-1 channel model.
8 is a graph comparing the time offset estimation performance of the offset estimation method and the conventional method according to an embodiment of the present invention in a TTD 300 sample, 7km SUI-2 channel model.
9 is a graph comparing the time offset estimation performance of the offset estimation method and the conventional method according to an embodiment of the present invention in a TTD 500 sample, 7km SUI-1 channel model.
FIG. 10 is a graph comparing time offset estimation performance of an offset estimation method and a conventional method in a TTD 500 sample, 7 km SUI-2 channel model.
11 is a flowchart of a time offset detection method according to an embodiment of the present invention.
12 is a detailed flowchart of a step of determining whether a sign error occurs in FIG. 12.
13 is a block diagram illustrating a configuration of an apparatus for detecting time offsets according to an embodiment of the present invention.
14 is a detailed block diagram of the error occurrence determining unit of FIG. 13.

While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail.

It should be understood, however, that the invention is not intended to be limited to the particular embodiments, but includes all modifications, equivalents, and alternatives falling within the spirit and scope of the invention.

In the following description of the embodiments of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present disclosure rather unclear.

The terms first, second, etc. may be used to describe various components, but the components should not be limited by the terms. The terms are used only for the purpose of distinguishing one component from another. For example, without departing from the scope of the present invention, the first component may be referred to as a second component, and similarly, the second component may also be referred to as a first component. And / or < / RTI > includes any combination of a plurality of related listed items or any of a plurality of related listed items.

When a component is referred to as being "connected" or "connected" to another component, it may be directly connected to or connected to that other component, but it may be understood that other components may be present in between. Should be. On the other hand, when an element is referred to as being "directly connected" or "directly connected" to another element, it should be understood that there are no other elements in between.

The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting of the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In this application, the terms "comprise" or "having" are intended to indicate that there is a feature, number, step, operation, component, part, or combination thereof described in the specification, and one or more other features. It is to be understood that the present invention does not exclude the possibility of the presence or the addition of numbers, steps, operations, components, components, or a combination thereof.

In addition, the components shown in the embodiments of the present invention are shown independently to represent different characteristic functions, which does not mean that each component is composed of separate hardware or software constituent units. That is, each constituent unit is included in each constituent unit for convenience of explanation, and at least two constituent units of the constituent units may be combined to form one constituent unit, or one constituent unit may be divided into a plurality of constituent units to perform a function. The integrated embodiments and separate embodiments of the components are also included within the scope of the present invention, unless they depart from the essence of the present invention.

Unless defined otherwise, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art. Terms such as those defined in commonly used dictionaries should be interpreted as having a meaning consistent with the meaning in the context of the relevant art and are to be interpreted in an ideal or overly formal sense unless explicitly defined in the present application Do not.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In order to facilitate the understanding of the present invention, the same reference numerals are used for the same constituent elements in the drawings and redundant explanations for the same constituent elements are omitted.

The terminal may be a mobile station (MS), a user equipment (UE), a user terminal (UT), a wireless terminal, an access terminal (AT), a terminal, a subscriber unit, a subscriber station (SS) ), A wireless device, a wireless communication device, a Wireless Transmit / Receive Unit (WTRU), mobile node, mobile or other terms. Various embodiments of the terminal may be used in various applications such as cellular telephones, smart phones with wireless communication capabilities, personal digital assistants (PDAs) with wireless communication capabilities, wireless modems, portable computers with wireless communication capabilities, Devices, gaming devices with wireless communication capabilities, music storage and playback appliances with wireless communication capabilities, Internet appliances capable of wireless Internet access and browsing, as well as portable units or terminals incorporating combinations of such functions However, the present invention is not limited thereto.

A base station generally refers to a fixed point for communicating with a terminal, and includes a base station, a Node-B, an eNode-B, a base transceiver system (BTS), and an access point. access point).

The sign error correction and weighted averaging process of the present invention is designed based on a cumulative differential operation based time offset detection method that increases and spaces between subcarriers performing differential operations and obtains and accumulates estimated time offset values.

1 is a conceptual diagram illustrating a frequency domain ranging channel structure in a WiBro system, and FIG. 2 is a conceptual diagram illustrating a time domain ranging channel structure in a WiBro system.

The present invention considers the same ranging channel structure as the initial ranging channel structure of the WiBro system. As shown in FIG. 1, the initial ranging channel structure in the frequency domain is composed of six sub-channels of 144 subcarriers. In addition, each subcarrier is a form of BPSK modulation of a PN (Pseudo Noise) sequence. As shown in FIG. 2, the ranging code in the time domain transmits two consecutive OFDMA symbols, that is, a first ranging symbol and a second ranging symbol, to maintain phase continuity. To prevent orthogonal destruction between subcarriers, the signal of the last section of the effective symbol section is copied and inserted in the front (Cyclic Prefix, CP) or the signal of the first section is copied and inserted in the rear (Cyclic Suffix, CS). Therefore, when the size of the TTD is within N _FFT (Fast Fourier Transform Size, FTT size), orthogonality is maintained in at least the second ranging symbol.

The base station generally estimates the TTD of the uplink signal through a differential operation based detection scheme in the frequency domain. After performing a Fast Fourier Transform (FFT) operation on the second symbol interval of the ranging signal as shown in Equation 1 below, the received ranging signal is divided into an arbitrary ranging code as shown in Equation 2 below.

Where n is a time domain sample index, k is a frequency domain subcarrier index, and i is an arbitrary ranging code index. In addition, τ represents a TTD value and N _FFT represents an FFT size. X _i (k) represents the transmitted ranging code, H (k) represents the Channel Frequency Response (CFR), and y [n] and Y (k) represents the received ranging signal in the time domain, respectively Receive ranging signals in the frequency domain. The TTD generates linear phase rotation in the frequency domain, and in order to obtain a constant phase offset value and remove the influence of the CFR, the base station performs a differential operation between two adjacent subcarriers as shown in Equation 3 below.

Where (·) * means conjugate complex product operation. Equation 3 requires the assumption that the CFR characteristics between two adjacent subcarriers have exactly the same value. Thereafter, the base station estimates τ through an arc-tan operation as shown in Equation 4 below.

값의 부호는

의 크기가 FFT 크기의 절반보다 작은지, 또는 큰지에 따라 결정된다.
Where N _code represents the length of the ranging code. Estimated time offset by arc-tan operation characteristic in Equation 4

The sign of the value is

It depends on whether the size of is less than or equal to half the size of the FFT.

의 크기가 N_FFT/2보다 작은 경우에는 음의 부호를 나타내며, 반대로 N_FFT/2보다 큰 경우에는 양의 부호를 갖는다. 또한,

의 부호는 N_FFT/2 지점에서 부호 천이를 나타내게 된다.
3 is a conceptual diagram illustrating two code parts and a sign transition point of an estimated time offset value.

If the size is smaller than N _FFT / 2 is represents the negative sign or, conversely, it has a positive sign if greater than N _FFT / 2. Also,

The sign of denotes a sign transition at the N _FFT / 2 point.

을 추정한다.In a wireless communication environment considering fixed operation, the coherence bandwidth of the channel is very large because there is a Loss of Signal (LOS) component that reduces the frequency selectivity of the channel. In consideration of these characteristics, a cumulative differential detection technique can be applied to time offset detection in a fixed wireless communication system. This technique estimates TTD by performing differential operation between subcarriers with multiple tone intervals. It is possible to improve detection performance by accumulating multiple estimated time offset values by increasing the tone interval between subcarriers. As shown in Equation 5 below, a differential operation between subcarriers having d subcarrier spacings is performed, and a phase rotation value of d times as shown in Equation 6 below.

.

Here, N _range means the interval between the maximum subcarriers when performing the cumulative differential operation.

의 크기는 d에 비례하여 증가한다. 또한,

의 크기가 N_FFT/2 보다 클 경우, arc-tan 연산 특성에 의하여

의 부호가 반전된다. 따라서, 추정 시간 오프셋 값은 부반송파 간 간격 d와 부호 천이 경계를 고려하여 하기의 수학식 7과 같은 정규화 과정이 요구된다.4 is a conceptual diagram illustrating a conventional cumulative differential operation based time offset detection technique. As shown in FIG. 4, a time offset value in a time domain estimated through a differential operation between d interval subcarriers

The size of increases in proportion to d. Also,

If the size of is greater than N _FFT / 2,

The sign of is reversed. Therefore, the estimated time offset value requires a normalization process as shown in Equation 7 below in consideration of the interval d between subcarriers and a code transition boundary.

부터

까지 추정된 시간 오프셋 값들이 음의 부호에서 양의 부호로 변화하는 횟수를 의미한다. 이후, 하기의 수학식 8과 같이 정규화된 시간 오프셋 값들을 누적한다.Where y _sign is

from

The number of times the estimated time offset values change from a negative sign to a positive sign. Then, the normalized time offset values are accumulated as shown in Equation 8 below.

Cumulative differential detection can improve performance through accumulation, but there is a problem in that time offset detection performance is greatly degraded when the codes of estimated time offset values are reversed due to the difference in CFR characteristics between noise and subcarriers.

가 부호 천이 경계인 0 또는 N_FFT/2 샘플 지점에 근접할 경우 추정 시간 오프셋 값의 부호가 역전되어 정규화 과정에서 잘못된 TTD 값을 추정하게 될 가능성이 높다. 따라서, 기존의 누적 차동 검출 기법에 의해 추정된 시간 오프셋 값들을 누적하기 위해서는 도 5에 도시된 바와 같은 부호 오류 문제를 해결해야 한다.
5 is a conceptual diagram illustrating an example of two types of sign error. In particular, even if the effect of the difference between the noise and the CFR characteristics is not significant,

Is close to 0 or N _FFT / 2 sample point, which is the sign transition boundary, it is likely that the sign of the estimated time offset value will be reversed, leading to the estimation of an incorrect TTD value during normalization. Therefore, in order to accumulate time offset values estimated by the existing cumulative differential detection technique, a sign error problem as illustrated in FIG. 5 must be solved.

Sign error correction

6 is a conceptual diagram illustrating a method of correcting a code error by setting five code parts in consideration of a code transition point and comparing a sign with an integer estimated time offset value according to an embodiment of the present invention.

As shown in FIG. 6, one symbol is first divided into five TTD estimation intervals. Three intervals 611, 613, and 615 proximate to the code transition boundary are defined as a Distrust Interval (DI), and the remaining two intervals 612 and 614 are defined as a Confidence Interval (CI). The noise margin of the estimated time offset values present in CI is large enough so that the sign is always correct. On the other hand, since the estimated time offset values located in DI have a small noise margin, it is determined that a sign error may occur. Therefore, if the estimated time offset value is within DI, it must be checked whether a sign error occurs.

를 탐색한다.

는 CI 내에 위치하므로 부호가 옳다고 가정하며,

와

간 부호 비교를 통하여

의 부호가 옳은지, 또는 역전되었는지 확인이 가능하다. 부호 오류가 발생하지 않았다면,

와

는 하기의 수학식 9와 같은 간단한 조건을 만족하게 된다.In order to determine whether a sign error occurs, a differential operation between n · d subcarriers corresponding to n times the d subcarrier intervals is sequentially performed, and the first one located in the CI is performed.

.

Assumes the sign is correct because it is located within the CI,

Wow

By comparing the sign between

It is possible to check whether the sign of is correct or reversed. If no sign error occurred,

Wow

Is satisfied with a simple condition as shown in Equation 9 below.

는 d개 간격 부반송파 간 차동 연산을 통해 추정된 시간 오프셋 값,

는 상기 d개의 정수배 개수 간격의 부반송파 간 차동 연산을 통해 추정된 시간 오프셋 값, N_FFT는 FFT 크기를 나타낸다. Where sgn is the sine function,

Is a time offset value estimated by a differential operation between d interval subcarriers,

Denotes a time offset value estimated through differential operations between subcarriers of the d integer multiples, and N _FFT denotes an FFT size.

와

의 관계가 상기 수학식 9의 조건을 만족하지 않는다면,

에 부호 오류가 발생했음을 의미하며,

의 부호를 역전시키는 간단한 과정을 통해 부호 오류 정정이 가능하다.
But,

Wow

If the relationship does not satisfy the condition of Equation 9,

Means a sign error occurred in,

Code error correction is possible through a simple process of reversing the sign of.

Weighted averaging technique

By applying a weighted averaging technique that assigns weights based on the reliability, the time offset estimation performance can be further improved.

의 신뢰도는 하기의 수학식 10과 같은 d개 간격 부반송파 간 주파수 영역 채널 상관도에 비례한다.first

The reliability of is proportional to the frequency domain channel correlation between d interval subcarriers as shown in Equation 10 below.

Where L is the number of multipaths, σ _i ² is the power of the i-th path, and τ _i is the sample delay of the i-th path.

의 신뢰도는 각 차동 연산의 누적 횟수 (N_code-d)에 비례한다. 잡음 억제 효과로 인하여, 누적 횟수가 증가할수록 해당하는 추정 값은 더 높은 신뢰도를 가지게 된다. Secondly,

The reliability of is proportional to the cumulative number of each differential operation (N _code -d). Due to the noise suppression effect, as the cumulative number increases, the corresponding estimated value has higher reliability.

는 상기 수학식 7에 따라 정규화 과정을 수행해야 하는데, 이 과정에서 잡음 분산이 1/d²만큼 감소하는 효과가 나타난다. Finally,

Should perform a normalization process according to Equation 7, in which the noise variance is reduced by 1 / d ² .

Therefore, as shown in Equation 11 below, an optimal cumulative effect may be obtained by applying the above three reliability weights to each estimated time offset value and accumulating and averaging them.

는 누적 차동 연산 기반의 시간 오프셋 값, N_range는 최대 부반송파 간 간격, (N_code-d)는 차동 연산의 누적 횟수, R_f(d)는 d개 간격 부반송파 간 주파수 영역 채널 상관도,

는 d개 간격 부반송파 간 차동 연산을 통해 추정된 시간 오프셋 값을 정규화한 값의 크기를 나타낸다.
Where,

Is the time offset value based on the cumulative differential operation, N _range is the maximum interval between subcarriers, (N _code -d) is the cumulative number of differential operations, R _f (d) is the frequency domain channel correlation between d interval subcarriers,

Denotes the magnitude of a value obtained by normalizing a time offset value estimated through a differential operation between d interval subcarriers.

Early days of fixed wireless communication systems Ranging  Time offset detection method

11 is a flowchart of a time offset detection method according to an embodiment of the present invention, and FIG. 12 is a detailed flowchart of a step of determining whether a sign error occurs in FIG. 11.

As shown in FIGS. 11 to 12, a method for detecting a time offset for initial ranging in a fixed wireless communication system according to an embodiment of the present invention first includes a symbol confidence interval (CI) and an untrust interval (Distrust). Interval, DI) (S110). For offset values, the sign transition point can be ± 0 or ± NFFT / 2 sample points. Here, a section including a sign transition point may be designated as an untrusted section, and a section not including a sign transition point may be designated as a confidence section.

Referring to FIG. 6 again, in dividing the symbol, the symbol is divided into five intervals, and the left or right side of the code transition point is shifted by one eighth of the N _FFT (FFT Fourier Transform Size). It may be characterized in that as a boundary of each section. That is, as shown in FIG. 6, three intervals close to the code transition boundary may be designated as an untrusted interval DI, and the remaining two intervals may be designated as a confidence interval CI. The boundary between the confidence interval and the untrusted interval may be -N _FFT / 8, -3N _FFT / 8, ± N _FFT / 2, + 3N _FFT / 8, and + N _FFT / 8, as shown in FIG. .

When the interval division of the symbol is completed, it is determined whether a code error occurs when the time offset value estimated through the differential operation between d interval subcarriers is included in the untrusted interval (S130). It is assumed that the sign is always correct because the noise margin of the estimated time offset values present in the CI is large enough, and since the estimated time offset values located in the DI have a small noise margin, it is determined that a sign error may occur, Determine whether or not.

In the determining of whether a sign error occurs (S130), searching for a first time offset value included in a confidence interval among time offset values estimated through subcarrier differential operations of the d integer multiple number intervals ( S131) and a sign of the first time offset value included in the confidence interval among time offset values estimated through the differential operation between the d interval subcarriers and time offset values estimated through the differential operation between the subcarriers of the d integer multiple number interval. If is different may include the step (S132) to determine that a sign error has occurred. Since the sign is assumed to be correct for the time offset value included in the confidence interval, the sign of the time offset value estimated by the differential operation between the d interval subcarriers is the difference between the subcarriers of the first d integer number intervals included in the confidence interval. It is assumed that the sign is equal to the time offset value estimated through the operation.

Here, the step (S132) of determining that the sign error occurs may be characterized as determining that a sign error occurs if the following equation is not satisfied.

는 d개 간격 부반송파 간 차동 연산을 통해 추정된 시간 오프셋 값,

는 상기 d개의 정수배 개수 간격의 부반송파 간 차동 연산을 통해 추정된 시간 오프셋 값, N_FFT는 FFT 크기를 나타낸다. Where sgn is the sine function,

Is a time offset value estimated by a differential operation between d interval subcarriers,

Denotes a time offset value estimated through differential operations between subcarriers of the d integer multiples, and N _FFT denotes an FFT size.

If a sign error occurs as a result of the determination, the sign error is corrected (S150). The correction of the sign error may be characterized by reversing the sign of the time offset value estimated through the differential operation between the d interval subcarriers.

The time offset detection method for the initial ranging of the fixed wireless communication system includes the estimated time offset value based on the frequency domain channel correlation between d interval subcarriers, the cumulative number of differential operations, and the noise variance reduction effect of the normalization process. The method may further include accumulating by weighted averaging (S170). The accumulating step S170 is based on the weighted averaging technique described above.

Early days of fixed wireless communication systems Ranging  Time offset detection device for

FIG. 13 is a block diagram illustrating a configuration of an apparatus for detecting time offsets according to an embodiment of the present invention, and FIG. 14 is a detailed block diagram of an error occurrence determining unit of FIG. 13.

As shown in FIG. 13 to FIG. 14, the apparatus 1300 for time offset detection for initial ranging of a fixed wireless communication system according to an embodiment of the present invention may include a symbol as a confidence interval (CI) and an untrusted symbol. Interval segmentation unit 1310 that divides the interval (Distrust Interval, DI), when the time offset value estimated by the differential operation between the d interval subcarrier is included in the untrusted interval, an error that determines whether a code error occurs The determination unit 1330 may include an error correction unit 1350 that corrects a sign error when a sign error occurs. The apparatus further includes a weighted averaging unit 1370 that weights and averages the estimated time offset values based on the frequency domain channel correlation between d interval subcarriers, the cumulative number of differential operations, and the noise variance reduction effect of the normalization process. can do.

Here, the interval dividing unit 1310 may designate a section including a code transition point as an untrusted section, and designate a section not including a code transition point as a confidence section. Further, the sign transition point may be ± 0 or ± NFFT / 2 sample points. The interval dividing unit 1310 divides the symbol into five intervals, and the boundary of each interval is a point shifted by one eighth of the N _FFT (FFT size, Fast Fourier Transform Size) to the left or right of the code transition point. You can do

The error occurrence determination unit 1330 is a confidence offset search unit 1331 for searching for an initial time offset value included in a confidence interval among time offset values estimated through subcarrier differential operations of the d integer multiples. If the sign of the time offset value estimated through the differential operation between the d interval subcarriers and the time offset value estimated through the differential operation between the subcarriers of the d integer number intervals is different, the sign of the first time offset value included in the confidence interval is different. And a code comparison unit 1333 for determining that an error has occurred.

In addition, the error occurrence determining unit 1330 searches for the first time offset value included in the confidence interval among time offset values estimated through the subcarrier differential operation of the d integer multiples. And a code comparison unit 1333 for determining that a code error has occurred if the following equation is not satisfied.

는 d개 간격 부반송파 간 차동 연산을 통해 추정된 시간 오프셋 값,

는 상기 d개의 정수배 개수 간격의 부반송파 간 차동 연산을 통해 추정된 시간 오프셋 값, N_FFT는 FFT 크기를 나타낸다. Where sgn is the sine function,

Is a time offset value estimated by a differential operation between d interval subcarriers,

Denotes a time offset value estimated through differential operations between subcarriers of the d integer multiples, and N _FFT denotes an FFT size.

The error correction unit 1350 may reverse the sign of the time offset value estimated through the differential operation between the d interval subcarriers.

In addition, the weighted averaging unit 1370 is based on the weighted averaging technique described above.

Experimental Example

7 to 10 compare time offset estimation root mean square error (RMS) performance in a Stanford University Interim (SUI) channel environment.

7 is a graph comparing time offset estimation performance of an offset estimation method and a conventional method according to an embodiment of the present invention in a TTD 300 sample, 7 km SUI-1 channel model, and FIG. 8 is a TTD 300 sample, 7 km SUI-2. In the channel model, it is a graph comparing the time offset estimation performance of the offset estimation method and the conventional method according to an embodiment of the present invention. As shown in FIG. 7 and FIG. 8, the conventional cumulative differential detection technique improves detection performance as the N _range increases, and the proposed technique can obtain a larger performance gain than the conventional technique.

9 is a graph comparing time offset estimation performance of an offset estimation method and a conventional method according to an embodiment of the present invention in a TTD 500 sample, 7 km SUI-1 channel model, and FIG. 10 is a TTD 500 sample, 7 km SUI-2. In the channel model, it is a graph comparing the time offset estimation performance of the offset estimation method and the conventional method according to an embodiment of the present invention. If the TTD is 500 samples, it is very likely that a sign error occurs because the TTD is close to the sign transition boundary. Therefore, due to the sign error, the conventional technique can confirm that performance deteriorates by increasing the estimated time offset accumulation count with an incorrect sign as the N _range increases. On the other hand, the method according to an embodiment of the present invention can be seen that there is still a performance gain as the N _range increases. This shows that the method according to an embodiment of the present invention can correct all sign errors according to the magnitude of the estimated time offset value with high accuracy.

What has been described above has described one embodiment according to the present invention, and the present invention is not limited to the above-described embodiments, and as claimed in the following claims, without departing from the gist of the present invention, the field to which the present invention belongs. It will be within the scope of the present invention to the extent that a person skilled in the art can change.

1300: time offset detection device for initial ranging
1310: section divider
1330: error occurrence determination unit
1331: confidence offset search unit
1333: code comparison unit
1350: error correction unit
1370: weighted average

Claims (18)

A time offset detection method for initial ranging of a fixed wireless communication system,
Dividing the symbol into a confidence interval (CI) and a distrust interval (DI);
determining whether a sign error occurs when a time offset value estimated through a differential operation between d subcarriers is included in the untrusted interval; And
And correcting a sign error when a sign error occurs as a result of the determination.
The method of claim 1, wherein dividing the symbol into a confidence interval and an untrusted interval
A time offset detection method for initial ranging in a fixed wireless communication system, characterized in that a section including a code transition point is designated as an untrusted section, and a section without a code transition point is designated as a trusted section.
The method of claim 2, wherein the sign transition point is
A time offset detection method for initial ranging in a fixed wireless communication system, characterized in that it is ± 0 or ± N _FFT / 2 sample points.
The method of claim 2, wherein dividing the symbol into a confidence interval and an untrusted interval
The wireless _signal is divided into five sections, and the fixed wireless point is characterized in that the boundary of each section is a point shifted by one-eighth of the NFTFT (FFT Fourier Transform Size) to the left or right of the code transition point. A time offset detection method for initial ranging of a communication system.
The method of claim 1, wherein determining whether the sign error occurs
Searching for a first time offset value included in a confidence interval among time offset values estimated through the differential operation between subcarriers of the d integer multiple number intervals; And
The sign of the first time offset value included in the confidence interval is different from the time offset value estimated through the differential operation between the subcarriers of the d intervals and the time offset value estimated through the differential operation between the subcarriers of the d integer multiples. And determining that a code error has occurred in the case of initial ranging of the fixed wireless communication system.
The method of claim 1, wherein determining whether the sign error occurs
Searching for a first time offset value included in a confidence interval among time offset values estimated through the differential operation between subcarriers of the d integer multiple number intervals; And
Equation

Where sgn is a sine function,

Is a time offset value estimated by a differential operation between d interval subcarriers,

The fixed wireless communication comprising the step of determining that a code error occurs if the time offset value estimated by the differential operation between the sub-carrier interval of the integer multiple times, N _FFT indicates the FFT size-is not satisfied A method for detecting time offsets for initial ranging of a system.
The method of claim 1, wherein correcting the sign error
And reversing a sign of a time offset value estimated through the differential operation between the d interval subcarriers.
The method of claim 1,
and weighting averaging the estimated time offset values based on the frequency domain channel correlation between the d interval subcarriers, the cumulative number of differential operations, and the noise variance reduction effect of the normalization process. A time offset detection method for initial ranging of a communication system.
The method of claim 8, wherein the accumulating step
Equation

-Where,

Is the time offset value based on the cumulative differential operation, N _range is the maximum interval between subcarriers, (N _code -d) is the cumulative number of differential operations, R _f (d) is the frequency domain channel correlation between d interval subcarriers,

Denotes the magnitude of a value obtained by normalizing an estimated time offset value through a differential operation between d interval subcarriers, and accumulates the estimated time offset value on the basis of an initial ranging of the fixed wireless communication system. Time offset detection method.
An apparatus for detecting time offset for initial ranging in a fixed wireless communication system,
An interval dividing unit for dividing the symbol into a confidence interval (CI) and an untrust interval (DI);
an error occurrence determining unit that determines whether a sign error occurs when a time offset value estimated through a differential operation between d interval subcarriers is included in the untrusted interval; And
And an error correction unit for correcting a sign error when a sign error occurs as a result of the determination.
The method of claim 10, wherein the section divider
And a section including a code transition point as an untrusted section, and a section without a code transition point as a trusted section.
12. The method of claim 11, wherein the sign transition point is
A time offset detection device for initial ranging in a fixed wireless communication system, characterized in that it is ± 0 or ± N _FFT / 2 sample points.
The method of claim 11, wherein the section divider
The wireless _signal is divided into five sections, and the fixed wireless point is characterized in that the boundary of each section is a point shifted by one-eighth of the NFTFT (FFT Fourier Transform Size) to the left or right of the code transition point. An apparatus for detecting time offsets for initial ranging of a communication system.
The method of claim 10, wherein the error occurrence determination unit
A confidence offset search unit searching for a first time offset value included in a confidence interval among time offset values estimated through the differential operation between subcarriers of the d integer multiples; And
When the time offset value estimated through the differential operation between the d interval subcarriers and the first time offset value included in the confidence interval among the time offset values estimated through the differential operation between the subcarriers of the d integer number interval are different, And a code comparator for determining that a code error has occurred.
The method of claim 10, wherein the error occurrence determination unit
A confidence offset search unit searching for a first time offset value included in a confidence interval among time offset values estimated through the differential operation between subcarriers of the d integer multiples; And
Equation

Where sgn is a sine function,

Is a time offset value estimated by a differential operation between d interval subcarriers,

The fixed radio includes a code comparison unit for determining that a code error has occurred if the time offset value estimated by the differential operation between the sub-carriers of the interval of d integer multiples, N _FFT indicates the FFT size-is not satisfied. An apparatus for detecting time offsets for initial ranging of a communication system.
The method of claim 10, wherein the error correction unit
And a time offset detection device for initial ranging in the fixed wireless communication system, wherein the sign of the time offset value estimated through the differential operation between the d interval subcarriers is reversed.
The method of claim 10,
and a weighted averaging unit that weights and averages the estimated time offset values based on the frequency domain channel correlation between the d interval subcarriers, the cumulative number of differential operations, and the noise variance reduction effect of the normalization process. An apparatus for detecting time offsets for initial ranging of a wireless communication system.
18. The method of claim 17, wherein the weighted averaging unit
Equation

-Where,

Is the time offset value based on the cumulative differential operation, N _range is the maximum interval between subcarriers, (N _code -d) is the cumulative number of differential operations, R _f (d) is the frequency domain channel correlation between d interval subcarriers,

Denotes the magnitude of a value obtained by normalizing an estimated time offset value through a differential operation between d interval subcarriers, and accumulates the estimated time offset value on the basis of an initial ranging of the fixed wireless communication system. Time offset detection device.

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