KR20060046393A - Method for configuring signals corresponding to adaptive packet format of mimo-wlan system - Google Patents

Abstract

 Disclosed is a signal construction method according to an adaptive packet format in a MIO-WLAN system. In the MIMO-WLAN system for transmitting a data packet as a plurality of signals through a plurality of antennas according to the present invention, a plurality of signal configuration methods include a preamble required for data packet transmission and a data packet transmission in a MIMO-WLAN system. Constructing a data packet so as to include an additional information section required for the service and a service data unit, distributing data of the preamble to at least one of the plurality of signals, and transmitting data of the additional information section to the plurality of signals. And distributing data of the service data unit to at least one of the plurality of signals. Therefore, it is compatible with the existing WLAN technology standard mode and can implement a high data rate.

IEEE802.11a, IEEE802.11N, MIMO, Frame Format, WLAN

Description

Method for configuring signals corresponding to adaptive packet format of MIMO-WLAN system

1 illustrates a frame format of a general WLAN system data packet;

FIG. 2 is a diagram provided for describing bit allocation of the SIGNAL field of FIG. 1;

3 is a diagram illustrating a frame format of a data packet for transmission signal configuration in a MIMO-WLAN system according to an embodiment of the present invention;

4 is a view provided to explain bit allocation of a SIGNAL interval of FIG. 3;

5 is a diagram showing a frame format of a data packet for transmission signal configuration in a MIMO-WLAN system according to another embodiment of the present invention; and

6 is a diagram illustrating a frame format of a data packet for transmission signal configuration in a MIMO-WLAN system according to another embodiment of the present invention.

The present invention relates to a signal configuration method in a wireless LAN (MIMO-WLAN) system to which MIMO (Multiple Inpur Multiple Output) is applied, and maintains compatibility with existing WLAN systems and uses a plurality of antennas. The present invention relates to a method for constructing a signal according to an adaptive packet format to increase data rate.

The existing IEEE 802.11 wireless LAN supports 2 Mbps data rates in the 2.4 GHz Industrial, Scientific and Medical (ISM) band using Direct Sequence Spread Spectrum (DSSS), Frequency Hopping Spread Spectrum (FHSS), and Infrared (IR). . However, these standards cannot meet the increasing demand for high data rates, and in 1999, new physical layer standards of IEEE 802.11a and IEEE 802.11b were finalized.

IEEE 802.11a adopts OFDM modulation scheme to overcome the limitations of DSSS scheme in 5 GHz unlicensed national information infrastructure (U-NII) unlicensed band and obtain higher transmission speed. Convolutional encoders with code rates 1/2, 2/3, and 3/4 are used for error correction, and BPSK, QPSK, 16-QAM, and 64-QAM are used for subcarrier modulation.

Therefore, the combination of the encoder and the modulator in accordance with the channel conditions supports a fast variable rate of 6Mbps to 54Mbps. In addition, since Ethernet-based services are aimed at indoor environments, it has a simple structure of 52 subcarriers. By using the OFDM scheme, short training time and simple equalization are possible, and it is robust to multipath interference.

1 is a diagram showing a frame format of a data packet for wireless LAN data transmission of IEEE802.11a employing the OFDM scheme.

The PHY protocol data units (PPDU) frame of the IEEE802.11a wireless LAN includes an OFDM Physical Layer Convergence Protocol (PLC) preamble (hereinafter referred to as a preamble) section, an OFDM PLCP header, a PHY sublayer service data unit (PSDU), Tail bits and Pad bits.

The preamble section for synchronization consists of a short preamble consisting of 10 short training symbols and a long preamble consisting of two long training symbols, and a PLCP header consists of a SIGNAL field and a SERVICE field. In addition, after the SERVICE field of the PLCP header, that is, the SERVICE field, the PSDU, the tail bits, and the pad bits are defined as DATA sections.

The short preamble, consisting of 10 short training symbols, is used for Auto Gain Control Convergence, timing acquisition and coarse frequency acquisition. A long preamble consisting of two long training symbols is used for channel estimation and fine frequency acquisition and has a guard interval to avoid adjacent symbol interference.

The PSDU including the data to be transmitted is composed of a plurality of symbols together with a 16-bit SERVICE field for scrambler initialization and a 6-bit tail and pad for zeroing the convolutional encoder.

FIG. 2 illustrates bit allocation of the SIGNAL field of FIG. 1. SIGNAL, which represents the data rate and the length of the DATA section, is one OFDM symbol modulated by BPSK after convolutional coding of 1/2 and has a total of 24 bits. As shown in Fig. 2, SIGNAL is allocated with 4 bits of RATE, reserved bits of the fifth bit, 12 bits of LENGTH, and 6 bits of parity and tail for error correction.

In a general wireless LAN system according to the IEEE 802.11a standard, a data packet having a frame format as shown in FIG. 1 is transmitted at a transmission rate of up to 54 Mbps through one antenna.

Currently, a method of introducing a multi-input multi-output (MIMO) technology using multiple transmit / receive antennas in the IEEE 802.11a standard has been discussed. MIMO's multiple transmit / receive antenna technology is expected to dramatically improve the frequency efficiency and network link capacity by using multiple antennas at the transmitting and receiving sides, which is the main technology for the system environment requiring high-speed data transmission. I am getting it.

As described above, the maximum data rate that can be realized by the existing wireless LAN standard is 54 Mbps. However, the necessity for implementing a high data rate such as real time transmission of high-definition video is increasing. MIMO technology to increase capacity is considered to be a viable technology to increase the transmission capacity of wireless LAN.

Meanwhile, in order to implement a MIMO-WLAN system, a new frame format for a data packet must be designed to accommodate all the increased transmit antennas. In this case, it is very important to maintain compatibility with a system conforming to the existing WLAN standard. do.

That is, in order to introduce MIMO technology to a wireless LAN according to IEEE 802.11a, signals transmitted and received through multiple antennas must be configured according to a new frame format for transmitting data packets using multiple antennas. In the MIMO-WLAN system according to the data packet and the signal configuration method for transmitting and receiving the packet should be designed to be compatible with the existing IEEE 802.11a system and the method in the transmission and reception.

Accordingly, an object of the present invention is to modify the frame format for data packet transmission in the MIMO-WLAN system to be compatible with the existing wireless LAN system, and to configure a signal transmitted and received through a plurality of antennas according to the modified adaptive frame format By providing a signal configuration method in a MIMO-WLAN system that implements a high transmission rate.

In the multiple input multiple output-wireless LAN (MIMO-WLAN) system for transmitting a data packet according to the present invention to a plurality of signals through a plurality of antennas for achieving the above object, Configuring the data packet such that the packet includes a preamble required for data packet transmission, a SIGNAL, an additional information interval required for data packet transmission in a MIMO-WLAN system, and a service data unit, the preamble and Inserting data of SIGNAL into at least one of the plurality of signals, distributing data of the additional information interval to at least one of the plurality of signals, and data of the service data unit at least of the plurality of signals Dispensing to one.

Preferably, the data of the additional information section includes information on the number of the plurality of signals of the MIMO-WLAN system.

In addition, the data of the additional information section preferably includes a transmission scheme of the MIMO-WLAN system.

In addition, the data of the additional information section preferably includes the data rate of the MIMO-WLAN system.

Preferably, the data of the additional information section includes a training signal for channel estimation of the MIMO-WLAN system.

On the other hand, in the data packet construction step, it is preferable to position the additional information section before the service data unit.

Hereinafter, a signal configuration method in a MIMO-WLAN system according to the present invention will be described with reference to the accompanying drawings.

3 is a diagram illustrating a frame format of a data packet for signal configuration in a MIMO-WLAN system according to an embodiment of the present invention, and FIG. 4 is a diagram provided to explain bit allocation of a SIGNAL section of FIG. 3.

3 illustrates a data packet frame format of a MIMO system transmitted and received through a plurality of antennas. In the MIMO system, a data packet frame is divided into a plurality of signals and transmitted through a plurality of antennas, and a signal transmitted through each antenna is removed. The first transmission signal to the Nth transmission signals TX1 to TXN are called.

The first transmission signal TX1 has a structure similar to a frame format used in a conventional WLAN system, and includes a short preamble, a long preamble 1, a SIGNAL field, and a payload including payload data. Unlike the existing system, a MIMO information field including information about the MIMO system is inserted between the SIGNAL and the payload. The additional information field will be described later in detail.

In addition, the second transmission signal TX2, the third transmission signal TX3 to the Nth transmission signal TXN include a MIMO information field and a payload (Payload2 to Payload N), and the first transmission signal. Unlike the short preamble, long preamble and SIGNAL interval.

The second transmission signal TX2 and the third transmission signal TX3 to the Nth transmission signal TXN have a value of "0" during the short preamble, the long preamble, and the SIGNAL period of the first transmission signal TX1. That is, while transmitting the preamble and SIGNAL in one antenna, the remaining antennas do not transmit a signal, that is, transmit a "zeros" signal, so that a WLAN system conforming to the existing standard can also interpret the signal.

Meanwhile, according to the signal configuration method in the MIMO-WLAN system according to an exemplary embodiment of the present invention, the MIMO expansion is instructed using the reserved bits of the SIGNAL field of the first transmission signal TX1. An embodiment of the present invention proposes a configuration of a MIMO-WLAN (Multi Input Multi Output-Wireless LAN) frame format compatible with 802.11a by carrying MIMO information on the reserved bits.

Referring to FIG. 4, the fifth spare bit of the SIGNAL field of the first transmission signal TX1 is allocated as a bit for MIMO mode determination according to an embodiment of the present invention. A signal having a frame format, when "1", indicates that a signal of a new MIMO-WLAN frame format is transmitted. The MINO information configuration method presented in this embodiment is merely an example, and various methods may be considered.

In this case, when the MIMO extension indication bit is set, an interval for transmitting additional information necessary for the extended MIMO-WLAN system is provided between SIGNAL and DATA. The additional information section may include the number of transmit antennas, for example, a transmission scheme such as a modulation scheme and a coding rate in channel coding, MIMI-WLAN system information such as data rate, a training signal for MIMO channel estimation, and the like. Therefore, the receiving side of the MIMO-WLAN system can obtain necessary information.

When the MIMO extension bit is not set, that is, when the fifth reserved bit of the SIGNAL of the first transmission signal TX1 is "0", the first transmission signal TX1 having a preamble and SIGNAL having the same format as the existing WLAN system. ) Is transmitted through one transmit antenna and the other antenna does not transmit a signal, that is, transmits a zero signal.

Therefore, the existing WLAN system understands the data transmitted from the MIMO-WLAN system in the same way as the transmission data of the existing WLAN system, so that the MIMO-WLAN system using multiple transmit / receive antennas is compatible with the WLAN system conforming to the existing standard. Can have

In addition, as the additional data section is inserted and the data rate is increased due to the expansion of the MIMO, the LENGTH included in the SIGNAL is changed to LENGTH_N so that the WLAN system conforming to the existing standard can estimate the duration of the MIMO-WLAN frame. Maintains system compatibility

Meanwhile, in a WLAN system using CSMA / CA as a multiple access method, it is necessary to estimate a section in which a surrounding WLAN system transmits data, and the MIMO-WLAN system according to the present invention is compatible with an existing WLAN system. In order to estimate the signal duration of the existing WLAN system through the transmission signal.

Therefore, the LENGTH information included in the SIGNAL of the MIMO-WLAN system frame format should be appropriately changed and transmitted according to the actual data rate. For example, if the data rate used in the MIMO-WLAN system is "T" times the rate of the existing WLAN system indicated in the RATE, the actual data transmission time will be "1 / T" times. In addition, since additional information used in the MIMO-WLAN system is further inserted, time information about the additional information section should also be included. Accordingly, the changed LENGTH_N may be represented by Equation 1 below.

Here, "M" represents the additional information interval as the number of OFDM symbols, and N _DBPS represents the number of bits per OFDM symbol corresponding to the RATE, as defined in the existing WLAN standard.

5 is a diagram illustrating a frame format of a MIMO-WLAN data packet according to another embodiment of the present invention. In another embodiment of the present invention, each antenna transmits a long preamble in a time division manner in an additional information interval to enable channel estimation of a signal transmitted in a MIMO-WLAN system. That is, when one antenna transmits a long preamble in an additional information interval, the other antenna does not transmit a signal.

Referring to FIG. 5, the first transmission signal TX1 includes a short preamble, a long preamble 1, a SIGNAL field, a SERVICE field, a PSDU1, a tail, and a pad.

As described above with reference to FIG. 4, in another embodiment of the present invention, when the fifth reserved bit of the SIGNAL field of the first transmission signal TX1 is assigned as a bit for MIMO mode determination, the IEEE is IEEE when it is “0”. In 802.11a mode, when it is "1", it operates in MIMO mode.

In addition, in FIG. 5, the second transmission signal TX2 to the Nth transmission signal TXN include a long preamble 2 to a long preamble N, a SERVICE field, a PSDU2, a tail, and a pad. Otherwise it does not include the short preamble and SIGNAL fields. Instead, the second transmission signal TX2 to the Nth transmission signal TXN have a value of "0" during the short preamble, the long preamble, and the SIGNAL period of the first transmission signal TX1. That is, while transmitting a preamble and a SIGNAL in one antenna, the remaining antennas are configured not to transmit a signal, that is, to transmit a "zeros" signal, so that a WLAN system conforming to the existing standard can also interpret the signal.

Meanwhile, during the long preamble period of the second transmission signal TX2 to the Nth transmission signal TXN, the first transmission signal TX1 transmits a "0" signal. The long preamble field is for knowing channel information of each signal transmitted to a plurality of antennas, and in order to prevent mixing of each long preamble signal, the second transmission signal TX1 to the Nth transmission signal TXN and the other transmission signal are also transmitted. During the long preamble interval of to have a value of "0". Therefore, each of the first transmission signal TX1 to the Nth transmission signal TXN has a signal value of "0" in the long preamble section of the other transmission signal.

As described above with reference to FIG. 4, since the long preamble is inserted into the second transmission signal TX2 to the Nth transmission signal TXN to increase the DATA length LENGTH of the entire transmission signal, the LENGTH of the SIGNAL field is IEEE 802.11. The length of the long preamble of the second transmission signal TX2 to the Nth transmission signal TXN is converted to "LENGTH_N" by adding the DATA length of the transmission signal according to a.

Meanwhile, according to IEEE 802.11a, the long preamble has 32 guard intervals before two symbols, but since SIGNAL processes 16 guard intervals per symbol, the second transmission signal TX2 transmitted after the SIGNAL field is processed. In the long preamble of the N th transmission signal TXN, it is preferable to have 16 guard intervals for each training symbol to facilitate compatibility with IEEE 802.11a.

Estimation of the MIMO channel is essential for the MIMO-WLAN system to work. In the conventional WLAN system, the channel is estimated using the long preamble, but in the MIMO-WLAN system, since the number of transmit antennas increases, channel estimation for each transmit antenna is necessary.

Therefore, in another embodiment according to the present invention, each transmit antenna transmits the same long preamble as that used in the existing WLAN system in a time division manner in the additional information interval. That is, when one antenna transmits a long preamble, the other antenna transmits a "zeros" signal, so that the receiver sequentially performs channel estimation for each transmitting antenna in the same manner as channel estimation in the existing WLAN system. can do.

6 is a diagram illustrating a frame format of a data packet of a MIMO-WLAN system according to another embodiment of the present invention.

For the automatic gain control, each transmitting antenna transmits a short preamble so that the size of a received signal can be effectively estimated in the MIMO-WLAN system's MIMO extended environment.

In this case, each short preamble uses the same or cyclic shifted signal as the short preamble defined in the existing WLAN standard, so that a WLAN system conforming to the existing standard may recognize the short preamble of the MIMO-WLAN system. To help.

In general, in a conventional WLAN system, a receiver performs automatic gain control using a short preamble. In a MIMO-WLAN system, a receiver should perform auto gain control on the sum of signals transmitted from all transmit antennas.

When automatic gain control is performed using the short preamble transmitted from one transmitting antenna, there may be a case in which all transmitting antennas do not properly reflect the signal magnitude generated in the DATA section in which the signal is transmitted. Accordingly, in another embodiment according to the present invention, the signals transmitted through the respective transmit antennas are configured to include the short preamble, so that the receiver performs automatic gain control on the sum of the signals received from all the receive antennas.

The short preambles transmitted by the respective transmit antennas may use the same signal or different cyclic shifted signals. In this case, since signal repeatability is maintained, the existing WLAN system can still recognize the short preamble.

On the other hand, the short preamble in the first transmission signal (TX1) to N-th transmission signal (TXN) is preferably transmitted at a power lower than the power of the transmission signal according to IEEE 802.11a for the convenience of automatic gain control. For example, when the first transmission signal and the second transmission signal are transmitted by two antennas, the short preamble is transmitted at half the power of the transmission power according to IEEE 802.11a using two antennas.

Therefore, in the above example, since one signal is transmitted through two antennas, the maximum transmission rate may be 108 Mbps, which is twice the maximum transmission rate of 54 Mbps of IEEE 802.11a.

In addition, according to the method of allocating MIMO information to the SIGNAL field, it is easy to switch to the MIMO mode or the IEEE 802.11a mode.

That is, in the above scheme, when the MIMO bit is "0", the MIMO bit is operated in the same manner as IEEE 802.11a, and when "1", the MIMO bit is operated in the MIMO mode. Since the short preamble transmitted first in the MIMO mode has half the power of the two transmission signals TX1 and TX2 in the above example, the combined power value of the two signals at the receiving side has the same value as that of IEEE 802.11a.

In addition, in the MIMO mode, the signal transmitted through the antenna passes through different paths. In the example, the first transmission signal TX1 and the second transmission signal TX2 transmit long preambles at different times, Channel estimation of each path is performed by using each received long preamble.

In this case, the long preamble2 of the second transmission signal TX2 transmitted after the SIGNAL field is different from the long preamble1 of the first transmission signal TX1 in which 32 guard intervals are inserted before two symbols. By inserting 16 guard intervals per symbol, the IEEE 802.11a reception method can be used as it is.

According to the present invention, MIMO information is loaded on the reserved bits of SIGNAL of the frame format of the MIMO-OFDM WLAN having compatibility with the OFDM technology standard based on OFDM, so that the compatibility between the WLAN technology standard mode and the MIMO mode is facilitated.

In addition, since the MIMO information is transmitted through the SIGNAL field, the receiver can quickly and easily determine the transmission signal mode. In addition, by inserting MIMO additional information after SIGNAL, information necessary to implement MIMO-WLAN system can be transmitted, and LENGTH included in SIGNAL can be appropriately changed according to transmission rate and amount of additional information to ensure compatibility with existing WLAN system. Can be.

On the other hand, since each transmit antenna transmits the long preamble used in the existing WLAN system in a time division manner, the receiving side of the MIMO-WLAN system applies the same channel estimation method used in the existing WLAN system in the same manner as the channel of each transmit antenna. Can be estimated sequentially.

In addition, since each transmitting antenna transmits the short preamble in the same form or in the form of a cyclic shift, the receiving side estimates the magnitude of the sum of the signals transmitted from all transmitting antennas and performs AGC. An effective AGC can be achieved for a DATA section in which multiple antennas simultaneously transmit signals.

According to the present invention, MIMO information is carried in the reserved bits of the SIGNAL field in the data packet frame format of the MIMO-WLAN having compatibility with the WLAN technology standard based on OFDM, so that the WLAN technology standard mode and the MIMO mode are easily compatible. Information is transmitted through the SIGNAL field, so the receiver can quickly determine the transmission signal mode.

In addition, by inserting the MIMO additional information after the SIGNAL field of the data packet, information necessary for implementing the MIMO-WLAN system can be transmitted, and the LENGTH included in the SIGNAL field can be appropriately changed according to the transmission rate and the amount of additional information. Can ensure compatibility.

On the other hand, since each transmit antenna transmits the long preamble used in the existing WLAN system in a time division manner, the receiving side of the MIMO-WLAN system applies the same channel estimation method used in the existing WLAN system in the same manner as the channel of each transmit antenna. Can be estimated sequentially.

Therefore, according to the present invention, it is compatible with the existing WLAN technology standard mode and can implement a high data rate, so that it can be used for services such as real-time transmission of high-definition video.

Although the preferred embodiments of the present invention have been illustrated and described above, the present invention is not limited to the specific embodiments described above, and the present invention is not limited to the specific embodiments of the present invention without departing from the spirit of the present invention as claimed in the claims. Anyone skilled in the art can make various modifications, as well as such modifications are within the scope of the claims.

Claims (7)

In the multiple signal configuration method in a Multiple Input Multiple output-Wireless LAN (MIMO-WLAN) system for transmitting a data packet as a plurality of signals through a plurality of antennas, Configuring the data packet such that the data packet includes a preamble required for data packet transmission, a SIGNAL, an additional information section required for data packet transmission of the MIMO-WLAN system, and a service data unit; Distributing data of the preamble and the SIGNAL to at least one of the plurality of signals: Distributing data of the additional information section to at least one of the plurality of signals; And And distributing the data of the service data unit to at least one of the plurality of signals. The method of claim 1, And the data of the additional information section includes information on the number of the plurality of signals of the MIMO-WLAN system.  The method of claim 1, And the data of the additional information section includes a transmission scheme of the MIMO-WLAN system. The method of claim 1, And the data of the additional information section includes a data rate of the MIMO-WLAN system. The method of claim 1, The data of the additional information section comprises a training signal for channel estimation of the MIMO-WLAN system. The method of claim 1, In the data packet forming step, the additional information section is located before the service data unit. The method of claim 1, And the data of the SIGNAL includes LENGTH_N data for calculating time information necessary for the data packet transmission according to the transmission rate of the MIMO-WLAN system.

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