KR20110026150A - Symbol timing adjust method and recording medium thereof in ofdm system - Google Patents

Abstract

PURPOSE: A symbol timing control method and a recording medium in an OFDM(Orthogonal Frequency Division Multiplexing) system are provide to enable a symbol signal of all paths in a CP(Cyclic Prefix) interval. CONSTITUTION: A plurality of OFDM symbol signals received through a multiple path is detected(S801). A signal which has the smallest time delay among the detected OFDM symbols are selected(S803). A time adjustment value is calculated by being compared with a time reference value which the selected OFDM symbols signal is set(S809). The calculated time adjustment value is transmitted to a corresponding terminal(S811). The time adjustment value is transmitted by being including in a RNG-RSP message.

Description

Symbol Timing Adjust Method and Recording Medium in Orthogonal Frequency Division System

An embodiment of the present invention relates to an Orthogonal Frequency Division Multiplexing (OFDM) system, and more particularly, to a technique for synchronizing timing of a terminal in a ranging process in an OFDM system. The present invention relates to a symbol timing adjusting method and a recording medium in an OFDM system for selecting uplink timing criteria and correcting timing of a terminal in a fading environment.

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

OFDM technology has strengths for frequency selective fading compared to single carriers such as CDMA and TDMA, and has higher bandwidth efficiency than conventional FDM. In addition, channel equalization is easy to implement and has a small complexity in implementation.

In OFDM, multiple carriers must maintain orthogonality with each other. However, as shown in FIG. 1, when a carrier delay occurs due to movement and radio environment fading, interference is caused between adjacent carriers, thereby causing inter-symbol interference (ISI) and intercarrier interference. Interference (ICI) occurs, which causes mutual interference.

In order to solve this, as shown in FIG. 2, the Guard Interval is used to remove the ISI, and the Cyclic Prefix (CP) technique is used to maintain orthogonal characteristics.

In the CP technique, as shown in FIG. 3, the last part of the symbol is copied and coupled to the guard interval part to maintain orthogonal characteristics. That is, even if a time delay occurs, it can be demodulated without ISI or ICI if it occurs within a CP section.

Accordingly, the OFDM system accurately adjusts the CP starting point synchronization of the UE, and periodically adjusts timing so as to fall within the CP section even when a delay is issued during symbol transmission. This procedure is called ranging. In addition to timing, ranging also performs frequency adjustment and terminal transmit power adjustment.

When a time delay enters a CP period by time adjustment through ranging, the OFDM system can demodulate a signal normally. However, in a multipath environment in which a base station and a repeater are connected, when a signal transmitted by the same terminal is received with different delays through various paths such as a main path and a repeater path of the base station, generally, The reference point of the ranging (ie, CP start time) is selected based on the symbol signal having the greatest intensity. At this time, if the largest symbol signal has a delay greater than that of the other path, if timing is adjusted based on this, the signal signal of the other path generates a negative delay in front of the CP section, and thus does not enter the CP section. This results in a problem that the demodulation performance is lowered.

SUMMARY OF THE INVENTION An embodiment of the present invention is to solve the above-described conventional problem, and an object thereof is to provide a method and a recording medium for adjusting the timing of an OFDM system in which a symbol signal of all paths can enter a CP section.

According to an aspect of the present invention, there is provided a method of adjusting a timing of a symbol in an OFDM system, the signal detecting step of detecting a plurality of OFDM symbol signals received through multiple paths. A signal selecting step of selecting a signal having the smallest time delay; and 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 a corresponding terminal. The signal selecting step may select a first signal having a predetermined reference signal strength or more among the plurality of 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 symbol timing adjusting method in an OFDM system, including: a signal detecting step of detecting a plurality of OFDM symbol signals received through a multipath; Signal selection step of selecting a signal having the largest level of signal strength First calculation step of calculating the first time adjustment value by comparing the selected OFDM symbol signal with a set time reference value Time offset value set in the first time adjustment value The second calculation step of calculating the second time adjustment value by adding a may include the step of transmitting the calculated second time adjustment value to the corresponding terminal.

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

In order to achieve the above object, a computer-readable recording medium having recorded thereon a symbol timing adjusting program in an OFDM system according to another aspect of the present invention is a signal for detecting a plurality of OFDM symbol signals received through multiple paths. Detection function Signal selection function for selecting a signal having the smallest time delay among the plurality of detected OFDM symbol signals A calculation function for comparing the selected OFDM symbol signal with a set time reference value and calculating a time adjustment value and the calculated time adjustment And a transmitting function for transmitting a value to a corresponding terminal, wherein the signal selecting function selects a first signal having a predetermined reference signal strength or more among the detected plurality of OFDM symbol signals, and a time delay among the first signals is best. Small signals can be screened.

In order to achieve the above object, a computer-readable recording medium having recorded thereon a symbol timing adjusting program in an OFDM system according to another aspect of the present invention is a signal for detecting a plurality of OFDM symbol signals received through multiple paths. Detection function A signal selection function for selecting a signal having the largest level of signal strength among the plurality of 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 a time offset value set to the first time adjustment value, and a transmission function for transmitting the calculated second time adjustment value to a corresponding terminal. The time offset value includes a signal having the smallest time delay and a signal having the highest level of signal strength among the OFDM symbol signals. 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 as described above, when the same signal having different delays for each path is received in an OFDM network having a base station and a repeater and having multiple transmit / receive paths, the received signal delays of all paths are determined by the OFDM system. By satisfying the CP interval, the base station demodulation performance is not reduced, thereby reducing the base station reception error rate, eliminating retransmission, and improving the uplink carrier to interference plus noise ratio (CINR), thereby improving the overall base station sector performance. have.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. First of all, in adding reference numerals to the components of each drawing, it should be noted that the same reference numerals are used as much as possible even if displayed on different 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 addition, in describing the component of this invention, terms, such as 1st, 2nd, A, B, (a), (b), can be used. These terms are only for distinguishing the components from other components, and the nature, order or order of the components are not limited by the terms. If a component is described as being "connected", "coupled" or "connected" to another component, that component may be directly connected to or connected to that other component, but there may be another configuration between each component. It is to be understood that the elements may be "connected", "coupled" or "connected".

4 is a flowchart illustrating a ranging procedure in an OFDM system.

First, the ranging code of the OFDM symbol signal transmitted by the terminal is detected by the OFDM system (S410), and the OFDM system receives timing offset, frequency offset, and Tx Power Control information. It determines and transmits to the terminal through a message called RNG-RSP (S420). The terminal retransmits the ranging code of the OFDM symbol signal by reflecting the adjustment information included in the received RNG-RSP (S430), and the OFDM system transmits to the RNG-RSP when the symbol timing, frequency, and the terminal transmission power are within a normal range. Success information is loaded and transmitted to the terminal (S440).

FIG. 5 is a flowchart illustrating an example of a method for adjusting symbol timing in a general OFDM system, and corresponds to the process of step S420 of FIG. 4.

First, a plurality of OFDM symbol signals received through a multi-path is detected (S501), a signal having the highest level of signal strength among the detected plurality of OFDM symbol signals is selected (S503), and the selected OFDM symbol signal The time adjustment value is calculated by comparing with the set time reference value (S505), and the calculated time adjustment value is transmitted to the corresponding terminal (S507).

However, the actual OFDM network is composed of a base station and a plurality of repeaters connected to the base station, the OFDM system has a plurality of receive and transmit paths. Accordingly, the OFDM symbol signal transmitted by the terminal is simultaneously received not only in the main path through the base station but also in the path through the repeater. In this case, although the received multiple path signals are OFDM symbol signals transmitted by the same terminal, delays are different from each other. For example, when received in the order of the base station main path received signal (A), repeater # 1 path received signal (B), and repeater # 2 path received signal, as shown in FIG. 6, the base station of the OFDM system receives the received signal. When timing adjustment is performed based on B, which is the signal having the largest signal intensity level, as shown in FIG. 7, the delay of the signal received through the C path is located within the CP period, but the signal received through the A path indicates a time reference point. As a reference, a negative delay is taken out of the CP section. Therefore, the signal received in the A path acts as an interference and degrades the demodulation performance.

The following example solves the above problem.

8 is a method of adjusting the timing of a symbol in an OFDM system according to an embodiment of the present invention, based on a received signal of a path having the earliest timing among path signals that are levels at which a reception level can be detected by a base station of the OFDM system; This is a method of ranging to fit the reference point.

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

It is determined whether the strength of the selected OFDM symbol signal is greater than or equal to the set reference signal (S805). If not, the corresponding OFDM symbol signal is excluded from the plurality of detected OFDM symbol signals (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 OFDM symbol signals having a signal strength equal to or greater than a reference signal.

Subsequently, a time adjustment value is calculated by comparing the selected OFDM symbol signal with a set time reference value (S809), and the calculated time adjustment value is loaded into an RNG-RSP message and transmitted to the corresponding terminal (S811).

As shown in FIG. 9, when timing adjustment is performed based on a signal having a smallest time delay, that is, an A path signal, among OFDM symbol signals having a signal strength greater than or equal to the reference signal according to the method of FIG. Normal demodulation is possible because it enters the CP section. In the case of a multipath signal, timing adjustment is generally performed 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 symbol timing adjustment method in an OFDM system according to another embodiment of the present invention, in which a positive delay is added at a time reference point when a time adjustment value is calculated by a base station of an OFDM system and transmitted to the RNG-RSP. This is a method of reflecting and sending.

First, a plurality of OFDM symbol signals received through multiple paths are detected (S1001), and among the detected plurality of OFDM symbol signals, a signal having the largest level of signal strength is selected (S1003).

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

The time offset value in step S1007 may be set according to the characteristics of the OFDM network. For example, as shown in FIG. 11, the signal A having the smallest time delay among the plurality of OFDM symbol signals and the signal strength are shown. It can be set based on the reception time difference between the signals B with the largest level. In addition, the time offset value is a CP period of a time reference value (or referred to as a reference point) in which a signal C having the largest time delay among the plurality of OFDM symbol signals after the time adjustment by the second time adjustment value is set in an OFDM system. Set to a value that does not exceed.

As shown in FIG. 11, the timing is adjusted according to the time reference point (ie, according to the first time adjustment value) based on the path signal B having a large reception level according to the method of FIG. 10, and the second time adjustment is performed. If the value is set as 'the first time adjustment value + time offset value t' and is transmitted, the terminal performs OFDM based on t having a delay time offset value t from the time reference point according to the second time adjustment value. The symbol timing is adjusted so that the signals A, B, and C of all paths enter the CP section as a whole.

According to the present embodiment, it is very simple to implement because it is not necessary to modify the entire algorithm for ranging but only add the offset value set to the RNG-RSP transmission value (that is, the time adjustment value).

The symbol timing adjustment method in the OFDM system according to the 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-implemented operations. have. The computer readable recording medium may include program instructions, local data files, local data structures, etc. alone or in combination. The recording medium may be those specially designed and constructed for the embodiments of the present invention, or may be known and available to those skilled in computer software. Examples of computer-readable recording media include magnetic media such as hard disks, floppy disks, and magnetic tape, optical recording media such as CD-ROMs, DVDs, magnetic-optical media such as floppy disks, and ROM, RAM, flash memory, and the like. Hardware devices specifically configured to store and execute the same program instructions are included. The recording medium may be a transmission medium such as an optical or metal wire, a waveguide, or the like including a carrier wave for transmitting a signal specifying a program command, a local data structure, or the like. Examples of program instructions may include high-level language code that can be executed by a computer using an interpreter as well as machine code such as produced by a compiler.

In the above description, all elements constituting the embodiments of the present invention are described as being combined or operating in combination, but the present invention is not necessarily limited to the embodiments. In other words, within the scope of the present invention, all of the components may be selectively operated in combination with one or more. In addition, although all of the components may be implemented in one independent hardware, each or all of the components may be selectively combined to perform some or all functions combined in one or a plurality of hardware. It may be implemented as a computer program having a. Codes and code segments constituting the computer program may be easily inferred by those skilled in the art. Such a computer program is stored in a computer readable storage medium, which is read and executed by a computer, thereby implementing embodiments of the present invention. The storage medium of the computer program may include a magnetic recording medium, an optical recording medium, a carrier wave medium, and the like.

In addition, the terms "comprise", "comprise" or "having" described above mean that the corresponding component may be included, unless otherwise stated, and thus excludes other components. It should be construed that it may further include other components instead. All terms, including technical and scientific terms, have the same meanings as commonly understood by one of ordinary skill in the art unless otherwise defined. Terms commonly used, such as terms defined in a dictionary, should be interpreted to coincide with the contextual meaning of the related art, and shall not be construed in an ideal or excessively formal sense unless explicitly defined in the present invention.

The above description is merely illustrative of the technical idea of the present invention, and those skilled in the art to which the present invention pertains may make various modifications and changes without departing from the essential characteristics of the present invention. Therefore, the embodiments disclosed in the present invention are not intended to limit the technical idea of the present invention but to describe the present invention, and the scope of the technical idea of the present invention is not limited by these embodiments. The protection scope of the present invention should be interpreted by the following claims, and all technical ideas within the equivalent scope should be interpreted as being included in the scope of the present invention.

As described above, the embodiment of the present invention is applied to a ranging process in an OFDM system so that the received signal delays of all paths satisfy the CP interval of the OFDM system, so that the base station demodulation performance is not degraded. This reduces the base station reception error rate, eliminates retransmissions, and improves uplink CINR, thus providing an effect of improving the base station sector performance as a whole.

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

4 is a flowchart illustrating a ranging procedure in an OFDM system;

5 to 7 illustrate an example of a symbol timing adjusting method in a general OFDM system;

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

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

Claims (9)

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 smallest time delay among the plurality of detected OFDM symbol signals; Calculating a time adjustment value by comparing the selected OFDM symbol signal with a set time reference value; And A transmitting step of transmitting the calculated time adjustment value to a corresponding terminal; Symbol timing control method in an OFDM system comprising a. The method of claim 1, The signal selecting step may include selecting a first signal having a predetermined reference signal strength or more among the plurality of detected OFDM symbol signals, and selecting a signal having a smallest time delay among the first signals. How to adjust the timing. The method of claim 1, The transmitting step, symbol timing control method in the OFDM system, characterized in that for transmitting the time adjustment value in the RNG-RSP message. 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 largest level of signal strength among the plurality of 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 a time offset value set to the first time adjustment value; A transmitting step of transmitting the calculated second time adjustment value to a corresponding terminal; Symbol timing control method in an OFDM system comprising a. The method of claim 4, wherein And 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 level of signal strength among the plurality of OFDM symbol signals. The method of claim 5, In the OFDM system, the time offset value is set such that a signal having the largest time delay among the plurality of OFDM symbol signals does not deviate from the CP interval of the set time reference value after the time adjustment by the second time adjustment value. How to adjust symbol timing. The method of claim 4, wherein The transmitting step, symbol timing control method in the OFDM system, characterized in that for transmitting the second time adjustment value in the RNG-RSP message. A signal detection function for detecting a plurality of OFDM symbol signals received via the multipath; A signal selection function for selecting a signal having the smallest time delay among the plurality of detected OFDM symbol signals; Calculating a time adjustment value by comparing the selected OFDM symbol signal with a set time reference value; And A transmission function for transmitting the calculated time adjustment value to a corresponding terminal; The signal selection function is to select a first signal of a predetermined reference signal strength or more among the plurality of detected OFDM symbol signals, and to select a signal having the smallest time delay among the first signals. A computer-readable recording medium having recorded thereon a symbol timing adjusting program in an OFDM system. A signal detection function for detecting a plurality of OFDM symbol signals received via the multipath; A signal selection function for selecting a signal having the largest level of signal strength among the plurality of 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 of calculating a second time adjustment value by adding a time offset value set to the first time adjustment value; A transmission function for transmitting the calculated second time adjustment value to a corresponding terminal; The time offset value may be set based on a difference in a reception time between a signal having the smallest time delay and a signal having the highest level of signal strength among the plurality of OFDM symbol signals, and after the time adjustment is performed by the second time adjustment value. Is such that the signal having the largest time delay among OFDM symbol signals does not deviate from the CP section of the set time reference value. A computer-readable recording medium having recorded thereon a symbol timing adjusting program in an OFDM system.

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