KR101083081B1 - Transmission time calcuration method and apparatus of frame inserted channel estimation patterns in ofdm system - Google Patents

Abstract

The present invention relates to a method and apparatus for calculating a time taken to transmit a frame in a wireless communication system, and more particularly, to a method and apparatus for calculating a transmission time when inserting a pattern for channel estimation in an orthogonal frequency division system.

According to the present invention, the number of channel estimation patterns inserted into a frame to be transmitted by a mobile station in an OFDM system is determined, and the transmission time of the insertion pattern according to the number of channel estimation patterns is calculated. The transmission time of the frame into which the channel estimation pattern is inserted is calculated in consideration of the transmission time of the insertion pattern.

Thus, in the OFDM system, when the pattern is inserted for channel estimation, the transmission time due to the pattern insertion is prevented by accurately calculating the actual transmission time of the frame.

OFDM, NAV, Frame, Pattern, Channel Estimation

Description

Transmission time calculation method and apparatus therefor for pattern estimation in orthogonal frequency division system {TRANSMISSION TIME CALCURATION METHOD AND APPARATUS OF FRAME INSERTED CHANNEL ESTIMATION PATTERNS IN OFDM SYSTEM}

The present invention relates to a method for calculating a time taken to transmit a frame in a wireless communication system. In particular, the present invention relates to a method for calculating a transmission time when a pattern for channel estimation is inserted between OFDM symbols in an OFDM system. It is about.

The present invention is derived from the research conducted as part of the IT source technology development project of the Ministry of Knowledge Economy and the Ministry of Information and Communication Research and Promotion. [Task management number: 2007-F-039-02, Task name: VMC technology development].

The basic principle of Orthogonal Frequency Division Multiplexing (hereinafter, referred to as OFDM) is to divide a data stream having a high data rate into a large number of data streams having a low data rate and transmit them simultaneously using a plurality of subcarriers. One important reason for using OFDM is that it is robust to frequency selective fading or narrowband interference. In a single carrier system, the entire link can fail due to a single fade or interference, but in a multicarrier system only some subcarriers are affected. Therefore, a few error subcarriers using error correction coding can be corrected. For this reason, OFDM is often used in a wireless transmission system.

In general, an OFDM system uses a carrier sensing medium approach and uses two carrier sensing methods.

The first method is a physical carrier detection method that detects a signal of a wireless channel and determines whether another node is using it. The second method transmits using a value of a network allocation vector (hereinafter, referred to as a NAV). It is a virtual carrier detection method that notifies other nodes of the time and does not try to transmit the time indicated by the NAV value.

The NAV is a field of a frame. The NAV represents a time information in microseconds for a transmission sequence to act as a timer. This value includes not only the transmission time of the frame transmitted by the transmitting node, but also the transmission time of the response frame and the time interval between the two frames when the response frame of the receiving node is required.

A mobile station exchanges frames (eg, Request to Send) and clear to send (RTS) / CTS (Clear to Send) with a service base station to access a wireless medium. The NAV value is included and other nodes (competitive nodes) that have received it defer transmission during the NAV time. That is, the mobile station can transmit traffic without collision by waiting for other nodes accessing the base station via channel reservation by the NAV.

In this case, in order to calculate the NAV value, it is necessary to know a transmission time for transmitting a frame, and a conventional frame transmission time can be calculated through Equation 1 below.

TXTIME = T_PREAMBLE + T_SIGNAL + T_SYM x Ceiling ((16 + 8 x LENGTH + 6) / N_DBPS)

Where TXTIME is the time it takes to transmit the frame, T_PREAMBLE is the preamble transmission time, T_SIGNAL is the signal field transmission time, T_SYM is the time it takes to transmit one OFDM symbol, LENGTH is the byte value of the length of the frame to be transmitted, and N_DBPS Denotes the number of data bits per OFDM symbol, and Ceiling is a function that obtains the smallest integer value equal to or greater than the argument.

On the other hand, in an OFDM system, there is a problem in that a size and a phase distortion occur as a channel changes over time or passes through a channel in which an OFDM symbol changes. A specific pattern for channel estimation may be inserted in the.

However, in this case, due to the transmission time of the inserted pattern, there is a problem that the exact transmission time cannot be calculated by the above Equation 1. That is, since the value calculated by Equation 1 is smaller than the value when the pattern is inserted, the time to be transmitted cannot be accurately calculated. At this time, if the time to insert the inserted pattern is not accurately calculated, the NAV is calculated. Since the channel reserved time is shorter than the actual transmission time, there is a problem in that the probability of transmission collision occurs.

Accordingly, the present invention is to solve the above problems, by inserting a pattern to be inserted for channel estimation in an OFDM system in a predetermined pattern and interval, and by considering the transmission time of the inserted pattern, the frame accurate regardless of the insertion reference value and the insertion interval It is to provide a method for calculating the transmission time.

In order to solve the above technical problem, the mobile station of the wireless communication system according to an embodiment of the present invention to calculate the transmission time of the frame,

a) identifying the number of channel estimation patterns inserted in a frame to be transmitted; b) calculating a transmission time of an insertion pattern according to the number of patterns for channel estimation; And c) calculating a transmission time of a frame into which the channel estimation pattern is inserted in consideration of the transmission time of the insertion pattern.

And calculating the length of the frame as a bit value before step a); And inserting the channel estimation pattern when the calculated frame length is larger than a reference value of the preset channel estimation insertion pattern.

On the other hand, in the wireless communication system according to an embodiment of the present invention, a mobile station for calculating a transmission time when inserting a pattern for channel estimation,

A transmission frame inspecting unit determining whether a length of a frame to be transmitted is greater than a reference value of a preset channel estimation insertion pattern; A pattern insertion unit for inserting a channel estimation pattern into the frame when it is determined that the length of the frame is large; And a transmission time calculator configured to calculate an insertion pattern transmission time according to the number of inserted channel estimation patterns, and calculate a transmission time of a frame into which the channel estimation pattern is inserted in consideration of the transmission time of the insertion pattern. .

The apparatus may further include a controller for generating a network allocation vector based on a transmission time of a frame into which the channel estimation pattern is inserted and requesting a medium access to a base station.

The transmission time calculating unit may calculate the number of the channel estimation patterns using at least one of the length of the frame, the reference value of the channel estimation pattern, the insertion period of the channel estimation pattern, and the ceiling. do.

According to the above configuration, the actual transmission time of the frame can be accurately calculated by calculating the transmission time in consideration of the transmission time of the inserted pattern when inserting the pattern for channel estimation in the OFDM system. By synchronizing, the effect of preventing transmission collision can be expected.

In addition, even if the interval of the inserted pattern and the insertion start reference value change for channel estimation, an accurate frame transmission time can be calculated by the same method.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the present invention. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention. In the drawings, parts irrelevant to the description are omitted in order to clearly describe the present invention, and like reference numerals designate like parts throughout the specification.

Throughout the specification, when a part is said to "include" a certain component, it means that it can further include other components, without excluding other components unless specifically stated otherwise. In addition, the terms “… unit”, “… unit”, “module”, etc. described in the specification mean a unit that processes at least one function or operation, which may be implemented by hardware or software or a combination of hardware and software. have.

Now, a method of calculating a transmission time when inserting a pattern for channel estimation in an OFDM system according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

1 illustrates a network configuration for channel reservation in an OFDM system according to an embodiment of the present invention.

Referring to FIG. 1, an OFDM system according to an embodiment of the present invention is a base station 200, a mobile station 100 that performs channel reservation for medium transmission to a base station 200, and a mobile station for medium access. And a contention node 300 that competes with 100.

The mobile station 100 generates a NAV by calculating a transmission time of a frame considering a transmission time of an inserted pattern for channel estimation, and includes a NAV in a message requesting access to a medium to transmit to the base station 200 to reserve a channel. Do this.

In this specification, the mobile station 100 (Mobile Station, MS) is a terminal (Mobile Terminal, Mobile Terminal (MT)), Subscriber Station (SS), Portable Subscriber Station (PSS), User equipment May refer to a user equipment (UE), an access terminal (AT), and the like, and may include all or some functions of a mobile terminal, a subscriber station, a portable subscriber station, a user device, and the like.

The base station 200 receives a message requesting access to the medium from the mobile station, and reserves a channel with the mobile station 100 when the contention node 300 does not exist or takes precedence over the contention node 300 after a predetermined time (DIFS). Accept.

In the present specification, the base station 200 (Base Station, BS) is an access point (Access Point, AP), a radio access station (Radio Access Station, RAS), Node B (Node B), base transceiver station (Base Transceiver Station, BTS) It may also refer to MMR (Mobile Multihop Relay) -BS and the like, and may include all or part of functions such as an access point, a radio access station, a Node B, a base transceiver station, and an MMR-BS.

The contention node 300 is a node competing for the channel reservation with the mobile station 100 in the service base station 200 area, and when the channel reservation between the mobile station 100 and the base station 200 is performed, the mobile station 100 reserves the reservation. Delay medium access to the base station 200 for a fixed time according to the NAV value.

In this specification, the contention node 300 is merely named the contention node 300 to distinguish it from the mobile station 100, and may be a terminal having a function similar to that of the mobile station 100.

Meanwhile, a channel reservation method using NAV in an OFDM system according to an embodiment of the present invention will be described with reference to FIG. 2.

2 is a flowchart illustrating a channel reservation method using NAV in an OFDM system according to an embodiment of the present invention.

Hereinafter, in the embodiment of the present invention, for convenience of description, it is assumed, but not limited, to channel reservation through RTS / CTS exchange between the mobile station 100 and the base station 200.

Referring to FIG. 2, in the OFDM system according to an embodiment of the present invention, the mobile station 100 transmits a medium access request message (RTS) for channel reservation with the base station 200 to the base station 200 (S201). ). In this case, the header of the medium access request message preferably includes a NAV value whose transmission time is calculated in consideration of the inserted pattern for channel estimation.

When the base station 200 receives the medium access request message from the mobile station 100, the base station 200 checks the NAV and responds to the message (CTS) allowing the channel reservation for the transmission time included in the NAV after the short interframe space (SIFS) (S202). ).

Here, SIFS is a waiting time after transmitting and receiving a frame and an RTS / CTS at a defined short frame interval, and the CTS transmitted from the base station 200 is compared to the RTS as indicated by a bar on the time axis at the bottom of FIG. 2. Short NAV values are included. In addition, the RTS / CTS is delivered to the contention node 300, thereby deferring the contention node 300's medium access for the transmission time reserved according to the NAV.

When the mobile station 100 receives the CTS from the base station 200, the mobile station 100 transmits a data frame after SIFS (S203). When the transmission of the data frame is completed, the base station 200 notifies the mobile station 100 of the ACK of the data frame after SIFS. At this time, the preset channel reservation is terminated at the same time as the ACK is transmitted (NAV = 0). (S204). After that, the contention window starts after the DIFS (DCF Interframe Space).

As described above, the mobile station 100 calculates a transmission time in consideration of a pattern inserted for channel estimation in a data frame when calculating a transmission time for data frame transmission, and performs channel reservation based on the NAV. To perform. Then, transmission of the data frame is completed within the channel reserved NAV time (NAV = 0).

However, conventionally, the NAV time is shorter than the actual data frame transmission time by calculating the transmission time without considering the inserted pattern for channel estimation, and the channel reservation is terminated when the data frame transmission is not completed (NAV = 0). There has been a problem causing transmission conflicts.

Meanwhile, a configuration in which a transmission time is calculated in consideration of an inserted pattern for channel estimation of the mobile station 100 according to an embodiment of the present invention will be described with reference to FIG. 3.

3 is a block diagram schematically illustrating a configuration of a mobile station according to an exemplary embodiment of the present invention.

Referring to FIG. 3, the mobile station 100 according to an embodiment of the present invention includes a transmission frame inspecting unit 110, a pattern inserting unit 120, a transmission time calculating unit 130, a control unit 140, and a communication unit ( 150).

The transmission frame inspecting unit 110 calculates a length of a frame to be transmitted as a bit value. The length of the frame is compared with a preset reference value of the channel estimation insertion pattern to determine whether the length of the frame is larger than the reference value.

The pattern inserting unit 120 inserts at least one channel estimation pattern for a frame larger than a predetermined reference value determined by the transmission frame inspecting unit 110. Here, the channel estimation pattern refers to a channel estimation value for compensating for distortion of magnitude and phase occurring while passing through a channel environment and a channel rapidly changing with frequency and time.

For example, the estimated value may be a channel estimated value using a pilot symbol assisted modulation (PSAM), a training symbol, a blind, and the like, and may be inserted in a predetermined pattern (format) and interval.

The transmission time calculating unit 130 calculates a transmission time of a frame into which at least one channel estimation pattern is inserted for channel estimation, which will be described sequentially through the following equation.

First, the transmission time calculating unit 130 calculates the number of patterns to be inserted into the frame. When the pattern is inserted into the frame at predetermined intervals, a larger number of patterns may be inserted as the length of the frame is longer.

At this time, the transmission time calculation unit 130 calculates the number of patterns to be inserted into the frame through the following equation (2).

N_MID = Ceiling ((LENGTH_BIT-MID_TH) / MID_CYC)

Where N_MID is the number of insertion patterns, LENGTH_BIT is the bit value of the frame length, MID_TH is the reference value of the insertion pattern, MID_CYC is the insertion period of the insertion pattern, and Ceiling is a function, the smallest integer value equal to or greater than the argument. Means a function to find.

Next, the transmission time calculating unit 130 calculates the number of patterns to be inserted and then calculates the time taken to transmit the pattern inserted into the frame through Equation 3 below.

T_MID_TOTAL = T_MID x N_MID

Here, T_MID_TOTAL is a time taken to transmit a pattern inserted into a frame, T_MID is a time taken to transmit one insertion pattern, and N_MID refers to the number of inserted patterns.

Next, the transmission time calculating unit 130 calculates a time taken to transmit the frame inserted with at least one pattern for channel estimation through Equation 4 below.

TXTIME = T_PREAMBLE + T_SIGNAL + T_SYM x Ceiling ((16 + 8 x LENGTH + 6) / N_DBPS) + T_MID_TOTAL

Where TXTIME is the time it takes to transmit the frame, T_PREAMBLE is the preamble transmission time, T_SIGNAL is the signal field transmission time, T_SYM is the time it takes to transmit one OFDM symbol, LENGTH is the byte value of the length of the frame to be transmitted, and N_DBPS Denotes the number of data bits per OFDM symbol, and Ceiling denotes a function that obtains the smallest integer value equal to or greater than the argument. T_MID_TOTAL means a time taken to transmit a pattern inserted into a frame.

The controller 140 controls the overall operation for calculating the pattern insertion and the frame transmission time according to the channel estimation of the mobile station 100.

In particular, the controller 140 generates a NAV based on the frame transmission time calculated by the transmission time calculator 130, and inputs the generated NAV on a media access request message (RTS) for channel reservation.

At this time, the NAV (RTS) is required to transmit and receive various frames with the base station 200 as well as the time for transmitting the data frame (including the time required to transmit the inserted pattern) in the mobile station 100 as shown in FIG. All time intervals (SIFS) are included.

The communicator 150 transmits a media access request message (RTS) for channel reservation generated by the controller 140 to the base station 200.

Meanwhile, a method in which the mobile station 100 calculates a frame transmission time and sets an NAV according to the embodiment of the present invention will be described with reference to FIG. 4.

4 is a flowchart illustrating a method in which a mobile station calculates a frame transmission time and sets an NAV according to the present invention.

Referring to FIG. 4, the mobile station 100 according to an embodiment of the present invention calculates a length of a frame to be transmitted as a bit value (S401). Then, the frame is compared with a reference of a preset channel estimation insertion pattern (S402), and it is determined whether the length of the frame is larger than the reference value (S403). That is, it is determined whether the channel estimation pattern is inserted by checking whether the frame length is larger than the reference value.

If it is determined in step S402 that the size of the frame is larger (S402, YES), the mobile station 100 inserts N channel estimation patterns for the frame (S404). In this case, as the length of the frame is longer, a larger number of patterns may be intermittently inserted, and the pattern size may also have a preset size.

The mobile station 100 calculates the number of channel estimation patterns (Equation 2) inserted into the frame (S405). Subsequently, a transmission time (Equation 3) is obtained according to the number of inserted patterns, and the frame transmission time (Equation 4) is calculated in consideration of this (S406).

Then, the mobile station 100 generates a NAV according to the calculated frame transmission time, and inputs the generated NAV on a medium access request message (RTS) for channel reservation (S408).

On the other hand, if it is determined in step S402 that the size of the frame is smaller (S402, NO), the mobile station 100 calculates the transmission time of the frame through Equation 1 (S407), and performs step S408. To perform.

As described above, according to the present invention, the actual transmission time of the frame can be accurately calculated by calculating the transmission time in consideration of the transmission time of the inserted pattern when inserting the pattern for channel estimation in the OFDM system. By synchronizing with the channel reservation time, the effect of preventing transmission collision can be expected.

In addition, even if the interval of the inserted pattern and the insertion start reference value change for channel estimation, the accurate frame transmission time can be calculated by the same method.

Therefore, even when the reference value and the insertion period are not constant values when the pattern is inserted for channel estimation, the accurate time required to transmit the frame can be calculated by identifying the number of inserted patterns.

The embodiments of the present invention are not limited to the above-described apparatuses and / or methods, but may be implemented through a program for realizing functions corresponding to the configuration of the embodiment of the present invention, a recording medium on which the program is recorded And such an embodiment can be easily implemented by those skilled in the art from the description of the embodiments described above.

Although the embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements of those skilled in the art using the basic concepts of the present invention defined in the following claims are also provided. It belongs to the scope of rights.

1 illustrates a network configuration for channel reservation in an OFDM system according to an embodiment of the present invention.

2 is a flowchart illustrating a channel reservation method using NAV in an OFDM system according to an embodiment of the present invention.

3 is a block diagram schematically illustrating a configuration of a mobile station according to an exemplary embodiment of the present invention.

4 is a flowchart illustrating a method in which a mobile station calculates a frame transmission time and sets an NAV according to the present invention.

Claims (12)

A method for a mobile station of a wireless communication system to calculate a transmission time of a frame, a) channel estimation pattern inserted in a frame to be transmitted; the channel estimation pattern is a channel estimation value for compensating for the size and phase distortion of the frame generated when passing through a channel or a channel environment that varies with frequency and time; Determining the number of means; b) calculating a transmission time of an insertion pattern according to the number of patterns for channel estimation; And c) calculating the transmission time of the frame into which the channel estimation pattern is inserted in consideration of the transmission time of the insertion pattern; Transmission time calculation method comprising a. The method of claim 1, Before step a), Calculating the length of the frame as a bit value; And Inserting the channel estimation pattern when the calculated frame length is larger than a reference value of the preset channel estimation insertion pattern. Transmission time calculation method further comprising. The method according to claim 1 or 2, The channel estimation pattern is And a predetermined reference value and a period (interval) inserted between the frames. The method of claim 3, wherein The number of patterns for channel estimation in step a) is And calculating at least one of a length of the frame, a reference value of the channel estimation pattern, an insertion period of the channel estimation pattern, and a ceiling. The method of claim 4, wherein B), And calculating the transmission time of one of the channel estimation patterns by multiplying the number of the channel estimation patterns. The method of claim 5, C), And calculating the sum of the transmission time of the insertion pattern and the transmission time according to the length of the frame. The method of claim 1, After step c), And generating a network allocation vector including a transmission time of a frame into which the channel estimation pattern is inserted and requesting a medium access to a base station. An apparatus for calculating a transmission time when inserting a pattern for channel estimation in a wireless communication system, A transmission frame inspecting unit determining whether a length of a frame to be transmitted is greater than a reference value of a preset channel estimation insertion pattern; When the length of the frame is determined to be large, the channel estimation pattern in the frame--the channel estimation pattern compensates for the size and phase distortion of the frame generated when passing through a channel environment or channel that varies with frequency and time. A channel inserter for inserting a channel estimate value; And A transmission time calculation unit for calculating an insertion pattern transmission time according to the number of inserted channel estimation patterns and calculating a transmission time of a frame into which the channel estimation pattern is inserted in consideration of the transmission time of the insertion pattern Transmission time calculation device comprising a. The method of claim 8, The transmission time calculation unit, And calculating the number of the channel estimation patterns using at least one of the length of the frame, the reference value of the channel estimation pattern, the insertion period of the channel estimation pattern, and the ceiling. delete The method of claim 8, And a controller for generating a network allocation vector based on a transmission time of a frame into which the channel estimation pattern is inserted and requesting media access to a base station. The method of claim 11, The network allocation vector, And a transmission time of a frame into which the channel estimation pattern is inserted and a time interval (SIFS) required for transmitting and receiving a message with the base station.

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