KR101587024B1 - Symbol Timing Adjust Method and Recording Medium thereof in OFDM System - Google Patents

Abstract

An embodiment of the present invention relates to a method for adjusting symbol timing in an OFDM system and a recording medium, the method comprising: detecting a plurality of OFDM symbol signals received through a multipath; Calculating a time adjustment value by comparing the selected OFDM symbol signal with a preset time reference value; and transmitting the calculated time adjustment value to a corresponding terminal, The received signal delay of the path may satisfy the CP period of the OFDM system.

OFDM system, OFDM symbol signal, fading, delay, ranging, CP section

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a symbol timing adjustment method and recording medium in an orthogonal frequency division system,

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates generally to an Orthogonal Frequency Division Multiplexing (OFDM) system, and more particularly to a technique for adjusting a timing of a terminal in a ranging process in an OFDM system A method for adjusting symbol timing in an OFDM system, and a recording medium for correcting timing of an uplink timing reference and a terminal in a fading environment.

OFDM technology is a multi-carrier broadband wireless communication technology that has been adopted for many high-speed wireless packet communication methods such as WiMAX, WiBro, LTE, IMT-Advanced and WiFi.

The OFDM technique is advantageous in frequency selective fading compared to the single carrier technique such as CDMA and TDMA, and has higher band efficiency than the conventional FDM scheme. In addition, the channel equalization is simple and the complexity is small.

In OFDM, a plurality of carriers must maintain orthogonality with each other. However, as shown in FIG. 1, when carrier delays occur due to movement and radio environment fading, inter-carrier interference is caused to inter-symbol interference (ISI) and inter carrier interference Interference (ICI) occurs and causes mutual interference.

In order to solve this problem, as shown in FIG. 2, a guard interval is used to remove the ISI, and a cyclic prefix (CP) technique is used to maintain the orthogonal property.

As shown in FIG. 3, the CP technique copies the last part of a symbol and combines it with a guard interval part to maintain the orthogonal property. That is, even if a time delay occurs, it can be demodulated without ISI or ICI if it occurs within the CP section.

Therefore, the OFDM system adjusts the timing of the CP start point of the UE exactly and periodically adjusts the timing so that even if a delay occurs during the symbol transmission, it falls within the CP period. This procedure is called ranging. In addition to timing, the ranging also performs frequency adjustment and terminal transmit power adjustment (Tx Power Adjust).

The OFDM system can demodulate the signal normally when the time delay comes within the CP interval by time adjustment through ranging. However, in a multipath environment in which a base station and a repeater are connected to each other, when signals transmitted from the same terminal are received with different delays through various paths such as a base station main path and a repeater path, And the reference point of the ranging (i.e., the CP start point) is selected based on the symbol signal having the largest intensity. At this time, if the largest symbol signal has a delay larger than the symbol signal of the other path, if a timing adjustment is performed based on this delay, a negative delay occurs in the symbol signal of the other path ahead of the CP section, And the demodulation performance is deteriorated.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems occurring in the prior art, and it is an object of the present invention to provide a method and apparatus for adjusting symbol timing in an OFDM system such that symbol signals of all paths can be received within a CP period.

According to an aspect of the present invention, there is provided a method of adjusting symbol timing in an OFDM system, the method comprising: detecting a plurality of OFDM symbol signals received through a multipath; Calculating a time adjustment value by comparing the selected OFDM symbol signal with a set time reference value; and transmitting the calculated time adjustment value to the corresponding terminal And the signal selecting step may select a first signal having a predetermined reference signal strength or more among the detected OFDM symbol signals and select a signal having the smallest time delay among the first signals.

According to another aspect of the present invention, there is provided a method of adjusting symbol timing in an OFDM system, the method comprising: detecting a plurality of OFDM symbol signals received through a multipath; A signal selection step of selecting a signal having a highest signal intensity; a first calculation step of calculating a first time adjustment value by comparing the selected OFDM symbol signal with a preset time reference value; And a second calculation step of calculating a second time adjustment value by adding the second time adjustment value to the corresponding terminal.

The time offset value may be set based on a reception time difference between a signal having the smallest time delay and a signal having the highest signal strength among the plurality of OFDM symbol signals, The signal having the largest time delay among the plurality of OFDM symbol signals may be set not to deviate from the CP interval of the set time reference value.

According to another aspect of the present invention, there is provided a computer-readable recording medium on which a symbol timing adjustment program is recorded. The computer-readable recording medium includes a signal for detecting a plurality of OFDM symbol signals received through a multipath, A signal selection function for selecting a signal having the smallest time delay among the detected OFDM symbol signals; a calculation function for calculating a time adjustment value by comparing the selected OFDM symbol signal with a set time reference value; And a signal transmission function for transmitting a value of the first signal to a corresponding terminal, wherein the signal selection function selects a first signal equal to or greater than a preset reference signal strength among the detected OFDM symbol signals, Small signals can be selected.

According to another aspect of the present invention, there is provided a computer-readable recording medium on which a symbol timing adjustment program is recorded. The computer-readable recording medium includes a signal for detecting a plurality of OFDM symbol signals received through a multipath, A signal selecting function for selecting a signal having a highest level of signal intensity among the detected OFDM symbol signals; a first calculation function for calculating a first time adjustment value by comparing the selected OFDM symbol signal with a set time reference value; A second calculation function for calculating a second time adjustment value by adding the time offset value set to the first time adjustment value, and a transmission function for transmitting the calculated second time adjustment value to the corresponding terminal, The time offset value is a signal having the smallest time delay among the plurality of OFDM symbol signals and a signal having the highest signal intensity level But in the set based on the reception time difference, the first time can be set so that after the adjustment by the second control time value deviating from the CP interval of the plurality of OFDM symbol time reference signal time delay is set, the largest of the signal.

According to various aspects of the present invention, when an identical signal having different delays is received for each path in an OFDM network having a base station and a repeater, and having multiple transmission / reception paths, CP section is satisfied so that the demodulation performance of the base station is prevented from being lowered, thereby reducing the base station reception error rate and eliminating the retransmission and improving the uplink CINR (carrier to interference plus noise ratio) have.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the drawings, the same reference numerals are used to designate the same or similar components throughout the drawings. In the following description 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 invention rather unclear.

In describing the components of the present invention, terms such as first, second, A, B, (a), and (b) may be used. These terms are intended to distinguish the constituent elements from other constituent elements, and the terms do not limit the nature, order or order of the constituent elements. When a component is described as being "connected", "coupled", or "connected" to another component, the component may be directly connected to or connected to the other component, It should be understood that an element may be "connected," "coupled," or "connected."

4 is a flowchart showing a ranging procedure in the OFDM system.

The ranging code of the OFDM symbol signal transmitted from the UE is detected in the OFDM system in step S410 and the OFDM system receives the timing offset, frequency offset, and Tx power control information And transmits the determined RNG-RSP message to the mobile station (S420). The MS retransmits the ranging code of the OFDM symbol signal by reflecting the adjustment information included in the received RNG-RSP (S430). When the symbol timing, the frequency, and the terminal transmission power are within the normal range, the MS retransmits the RNG- Success information is transmitted to the terminal (S440).

5 is a flowchart for explaining an example of a symbol timing adjustment method in a general OFDM system, and corresponds to the process of step S420 of FIG.

First, a plurality of OFDM symbol signals received through the multipath are detected (S501), and a signal having the highest signal intensity level is selected among the detected OFDM symbol signals (S503), and the selected OFDM symbol signal (S505), and transmits the calculated time adjustment value to the corresponding terminal (S507).

However, an actual OFDM network is composed of a base station and a plurality of repeaters connected to the base station, and the OFDM system has a plurality of reception and transmission paths. Therefore, the OFDM symbol signal transmitted by the terminal is simultaneously received through the path through the repeater as well as the main path through the base station. At this time, although the received multipath signals are OFDM symbol signals transmitted from the same terminal, delays are different from each other. For example, when the base station main path receiving signal A, the repeater # 1 path receiving signal B, and the repeater # 2 path receiving signal are received in this order as shown in FIG. 6, 7, the delay of the signal received through the C path is located within the CP interval, while the signal received through the A path is the time reference point As a result, it has a negative delay and is out of CP range. Therefore, the signal received through the A path acts as an interference and degrades demodulation performance.

The following problems are solved through the following embodiments.

FIG. 8 is a diagram illustrating a method for adjusting symbol timing in an OFDM system according to an embodiment of the present invention. Referring to FIG. 8, And the ranging process is performed so as to meet the reference point.

First, a plurality of OFDM symbol signals received through the multipath are detected (S801), and a signal having the smallest time delay among the detected OFDM symbol signals is selected (S803).

If it is determined in step S805 that the strength of the selected OFDM symbol signal is equal to or greater than the preset reference signal strength, the selected OFDM symbol signal is removed from the detected plurality of OFDM symbol signals in step S807. Again, select the signal with the smallest time delay. That is, steps S803 to S807 are performed to select a signal having the smallest time delay among the OFDM symbol signals having the signal strength of the reference signal or more.

Then, the selected OFDM symbol signal is compared with a preset time reference value to calculate a time adjustment value (S809), and the calculated time adjustment value is transmitted to the corresponding terminal in an RNG-RSP message (S811).

As shown in FIG. 9, if the timing adjustment is performed based on a signal having the smallest time delay, that is, the A path signal, among the OFDM symbol signals having the signal strength of the reference signal or more according to the method of FIG. 8, It is possible to demodulate normally. In the case of a multi-path signal, it is general to perform timing adjustment based on a signal having the highest reception level. However, in this embodiment, timing adjustment is performed based on a signal having the smallest delay in order to eliminate adverse effects of negative delay.

FIG. 10 is a method for adjusting symbol timing in an OFDM system according to another embodiment of the present invention. When a base station of an OFDM system calculates a time adjustment value and transmits the time adjustment value to the RNG-RSP, a positive delay is added at a time reference point And then transmitting it.

First, a plurality of OFDM symbol signals received through the multipath are detected (S1001), and a signal having the highest signal intensity level is selected among the detected OFDM symbol signals (S1003).

Then, the selected time alignment value is calculated by comparing the selected OFDM symbol signal with a preset time reference value (S1005), and the second time adjustment value is calculated by adding the time offset value set in the first time adjustment value (S1007), transmits the calculated second time adjustment value to the RNG-RPS message, and transmits the RNG-RPS message to the corresponding terminal (S1009).

The time offset value in step S1007 is set according to the characteristics of the OFDM network. For example, as shown in FIG. 11, among the plurality of OFDM symbol signals, And the reception time difference between the signal B having the highest level. In addition, the time offset value may be set such that a signal (C) having the largest time delay among the plurality of OFDM symbol signals after time adjustment based on the second time adjustment value is divided into a CP section (referred to as a reference point) Is set to a value that does not deviate.

As shown in FIG. 11, according to the method of FIG. 10, timing adjustment is performed according to a time reference point (i.e., according to the first time adjustment value) on the basis of a path signal B having a high reception level, (T) with a time offset value (t) from the time reference point according to the second time adjustment value, the terminal generates a first time adjustment value + time offset value (t) The symbol timing is adjusted so that the signals A, B and C of all the paths as a whole enter the CP section.

According to this embodiment, not only the entire algorithm for ranging but also the offset value set in the RNG-RSP transmission value (i.e., time adjustment value) is added, so that it can be implemented very simply.

The method of adjusting symbol timing in an OFDM system according to an embodiment of the present invention described with reference to FIGS. 8 to 11 may be implemented as a computer-readable recording medium including program instructions for performing various computer- have. The computer-readable recording medium may include a program command, a local data file, a local data structure, or the like, alone or in combination. The recording medium may be those specially designed and constructed for the embodiments of the present invention or may be those known to those skilled in the computer software. Examples of computer-readable media include magnetic media such as hard disks, floppy disks and magnetic tape, optical recording media such as CD-ROMs and DVDs, magneto-optical media such as floppy disks, and ROMs, And hardware devices specifically configured to store and execute the same program instructions. The recording medium may be a transmission medium such as an optical or metal line, a wave guide, or the like, including a carrier wave for transmitting a signal designating a program command, a local data structure, or the like. Examples of program instructions may include machine language code such as those generated by a compiler, as well as high-level language code that may be executed by a computer using an interpreter or the like.

While the present invention has been described in connection with what is presently considered to be the most practical and preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. That is, within the scope of the present invention, all of the components may be selectively coupled to one or more of them. In addition, although all of the components may be implemented as one independent hardware, some or all of the components may be selectively combined to perform a part or all of the functions in one or a plurality of hardware. As shown in FIG. The codes and code segments constituting the computer program may be easily deduced by those skilled in the art. Such a computer program may be stored in a computer-readable storage medium, readable and executed by a computer, thereby implementing embodiments of the present invention. As the storage medium of the computer program, a magnetic recording medium, an optical recording medium, a carrier wave medium, or the like may be included.

It is also to be understood that the terms such as " comprises, "" comprising," or "having ", as used herein, mean that a component can be implanted unless specifically stated to the contrary. But should be construed as including other elements. All terms, including technical and scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs, unless otherwise defined. Commonly used terms, such as predefined terms, should be interpreted to be consistent with the contextual meanings of the related art, and are not to be construed as ideal or overly formal, unless expressly defined to the contrary.

The foregoing description is merely illustrative of the technical idea of the present invention, and various changes and modifications may be made by those skilled in the art without departing from the essential characteristics of the present invention. Therefore, the embodiments disclosed in the present invention are intended to illustrate rather than limit the scope of the present invention, and the scope of the technical idea of the present invention is not limited by these embodiments. The scope of protection of the present invention should be construed according to the following claims, and all technical ideas within the scope of equivalents should be construed as falling within the scope of the present invention.

As described above, the embodiment of the present invention is applied to the ranging process in the OFDM system, so that the received signal delay of all paths satisfies the CP section of the OFDM system, so that the demodulation performance of the base station is not degraded, This is a very useful invention that provides an effect of improving base station sector performance by eliminating retransmission by reducing the base station reception error rate and improving the uplink CINR.

1 to 3 are views for explaining a problem in a conventional OFDM system,

4 is a flowchart showing a ranging procedure in an OFDM system,

5 to 7 are diagrams for explaining an example of a symbol timing adjustment method in a general OFDM system,

8 to 9 are diagrams illustrating a method of adjusting a symbol timing in an OFDM system according to an embodiment of the present invention,

10 to 11 are diagrams illustrating a method of adjusting symbol timing in an OFDM system according to another embodiment of the present invention.

Claims (9)

delete delete delete A signal detecting step of detecting a plurality of OFDM symbol signals received through the multipath; A signal selecting step of selecting a signal having the highest level of signal strength among the detected OFDM symbol signals; A first calculation step of calculating a first time adjustment value by comparing the selected OFDM symbol signal with a set time reference value; A second calculation step of calculating a second time adjustment value by adding the time offset value set in the first time adjustment value; Transmitting the calculated second time adjustment value to a corresponding terminal; And adjusting the symbol timing in the OFDM system. 5. The method of claim 4, Wherein the time offset value is set based on a reception time difference between a signal having the smallest time delay and a signal having the highest signal strength among the plurality of OFDM symbol signals. 6. The method of claim 5, Wherein the time offset value is set so that a signal having the largest time delay among the plurality of OFDM symbol signals after the time adjustment based on the second time adjustment value does not deviate from a CP interval of the set time reference value. How to adjust symbol timing. 5. The method of claim 4, Wherein the transmitting step includes transmitting the second time adjustment value in an RNG-RSP message. delete A signal detection function for detecting a plurality of OFDM symbol signals received through the multipath; A signal selecting function for selecting a signal having a highest signal intensity level among the detected OFDM symbol signals; A first calculation function for calculating a first time adjustment value by comparing the selected OFDM symbol signal with a set time reference value; A second calculation function for calculating a second time adjustment value by adding the time offset value set in the first time adjustment value; And a transmission function for transmitting the calculated second time adjustment value to a corresponding terminal, Wherein the time offset value is set based on a reception time difference between a signal having the smallest time delay and a signal having the highest signal strength among the plurality of OFDM symbol signals, The OFDM symbol signal having the largest time delay is set not to deviate from the CP section of the set time reference value Wherein the symbol timing adjustment program in the OFDM system is characterized in that:

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