KR101030871B1 - Method for Allocating Pilot - Google Patents

Abstract

A pilot allocation method according to an aspect of the present invention for uniformly distributing pilots in a MIMO system is a method of allocating pilots in a resource block including 18 subcarriers and 6 symbols. Assigning pilots for the first transmit antenna on subcarrier indexes 2, 8, and 15, and assigning pilots for the second transmit antenna on subcarrier indexes 3, 9, and 16 It is characterized by.

MIMO, pilot, batch, allocation, pattern, channel, estimation

Description

Pilot Allocation Method {Method for Allocating Pilot}

The present invention relates to a wireless communication system supporting the MIMO scheme, and more particularly, to a pilot allocation in a wireless communication system supporting the MIMO scheme.

The IEEE 802 committee is planning to develop a technical standard for IEEE 802. 16m, which is an advanced technology standard than the current mobile WiMAX, as the next-generation standard of WiBro / Mobile WiMAX. The IEEE 802.16m is 100Mbps for mobile and 1Gbps for fixed. Aim for transmission.

Even in the IEEE 802.16m, as in the conventional IEEE 802.16e, the terminal or the base station must estimate the channel to recover the information data transmitted from the base station or the terminal, the channel estimation is performed using a pilot symbol do. The pilot is a signal component that is a basis for estimating the state of a channel in wireless or wired communication, and is implemented by transmitting a predetermined sequence known to both the base station or the terminal when radio waves are transmitted through an unknown channel.

On the other hand, in the IEEE 802.16m, a pilot is used for channel estimation. In the IEEE 802.16m, the pilot pattern is not defined in detail yet, so the pilot pattern presented in IEEE 802.16e may be used.

1 is a diagram showing a pilot pattern presented in IEEE 802.16e. As shown, IEEE 802.16e subtracts the pilot symbol 100 for the first antenna and the pilot symbol 110 for the second antenna to 1, 4, 7, 10, 13, and 16 subs. It can be seen that the six pilots are allocated to each antenna so as to be allocated to the carriers, but not to overlap each pilot in the same symbol.

However, in the case of the pilot pattern as shown in Figure 1, it can be seen that the distribution of the pilot is not uniform on the symbol axis and the subcarrier axis. As described above, if the distribution of the pilot is not uniform, there is a problem in that a good performance cannot be exhibited in channel estimation when the transmitting entity of the pilot moves at a low speed or a high speed.

Disclosure of Invention The present invention has been made in view of the above-described problems, and it is a technical object of the present invention to provide a method for allocating a pilot to have a uniform distribution of a pilot in a MIMO system.

Another object of the present invention is to provide a method for estimating a channel using a pilot allocated according to the above-described pilot allocation method.

A pilot allocation method according to an aspect of the present invention for achieving the above object is a method of allocating pilots in a resource block consisting of 18 subcarriers and 6 symbols, on the 1 and 4 symbol index, 2, Allocating pilots for the first transmit antenna on the 8th and 15th subcarrier indexes, and assigning pilots for the second transmit antennas on the 3rd, 9th, and 16th subcarrier indexes. .

Here, pilots for the first and second antennas and uplink data transmitted through the first and second antennas are allocated to the resource block.

In one embodiment, the first and second transmit antennas are arranged in the same terminal, or the first and second transmit antennas are characterized in that arranged in different terminals.

Meanwhile, the pilot allocation method may be applied to a frame defined in IEEE 802.16m.

According to another aspect of the present invention, a method for allocating a pilot may include: allocating first pilots to a first resource block transmitted through a first antenna; Allocating second pilots to a second resource block transmitting over a second antenna, wherein the resource block consists of a plurality of virtual sub resource blocks, the virtual sub resource block comprising one pilot .

A pilot allocation method according to another aspect of the present invention for achieving the above object is a plurality of virtual resources on the basis of the symbol axis and the sub-carrier axis (Resource Block) to which the pilot and data are allocated Dividing into subblocks of; And assigning a pilot set for first and second transmit antennas to each of the virtual subblocks, and assigning the pilot set to a central region based on a symbol axis and a subcarrier axis within each subblock. .

According to still another aspect of the present invention, there is provided a method of estimating a channel using a pilot pattern to which a pilot is allocated according to a pilot allocation method in a MIMO system. Calculating a channel response of a channel to which the pilot is allocated by using pilots for the first and second transmit antennas included in the sub-blocks constituting the block; And estimating a channel response for all channels to which the pilot is not assigned using the channel response.

As described above, according to the present invention, since the pilot can be uniformly allocated in the MIMO system, the performance can be improved when the channel is estimated using the pilot even when the speed of the terminal is low and high. .

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

The pilot allocation method according to the present invention described below is applicable to a wireless communication system supporting a multi-input multi-output (MIMO) scheme, and hereinafter, it will be described on the assumption that it is 2 ⅹ 2 MIMO for convenience of description. In this case, the transmission data is to be transmitted through two transmission antennas (first and second transmission antennas).

First, before the detailed description of the present invention, it is necessary to look at the structure of the frame defined in IEEE 802.16m, the frame structure defined in IEEE 802.16m will be described with reference to FIG.

2 is a diagram showing a frame structure defined in IEEE 802.16m. As shown in FIG. 2, IEEE 802.16m defines a super frame 200 having a size of 20 ms, and one super frame 200 has four radio frames having a size of 5 ms. 210). In addition, each radio frame 210 is composed of eight sub-frames (Sub Frame, 220). Each subframe 220 may be allocated for either downlink transmission or uplink transmission. At this time, each subframe 220 is composed of six OFDM symbols 230, the frequency axis is composed of a plurality of resource tiles (Resource Tile) or a resource block (Resource Block).

In this case, the size of the resource block is composed of 18 subcarriers and 6 symbols, 12 subcarriers and 6 symbols, 10 subcarriers and 6 symbols or 20 subcarriers And two symbols. Hereinafter, the allocation of pilot symbols will be described on the assumption that the size of the resource block is composed of 18 subcarriers and 6 symbols.

3 is a flowchart showing a pilot allocation method according to an embodiment of the present invention. As shown, first, a resource block is divided into a plurality of regions based on a symbol axis and a subcarrier axis (S300). Here, the resource block is a block constituting the frame presented in IEEE 802.16m, and a pilot block and data are allocated to the resource block.

As already mentioned in the description of FIG. 2, the frame structure presented in IEEE 802.16m includes a plurality of super frames 200 having a size of 20 ms, and one super frame 200 has a size of 5 ms. 4 radio frames (210), each radio frame 210 is composed of eight sub-frames (Sub Frame, 220).

The resource block is included in each subframe, and the size of the resource block includes 18 subcarriers and 6 symbols, 12 subcarriers and 6 symbols, or 10 subcarriers and It may consist of six symbols or 20 subcarriers and two symbols. The present invention may be applied to a resource block including 18 subcarriers and 6 symbols among resource blocks of various sizes.

In one embodiment, to allocate a pilot, the present invention may divide one resource block into six regions having the same size. That is, since the resource block includes 18 subcarriers and 6 symbols, as shown in FIG. 4A, each region 410 may include 6 subcarriers and 3 symbols.

Meanwhile, the above-described resource block refers to a resource block included in an uplink subframe for collaborative spatial multiplexing (CSM) transmitted from a terminal to a base station among subframes presented in IEEE 802.16m.

Referring back to FIG. 3, pilots of the first and second transmit antennas to be allocated to each region 410 are grouped into one set (S310). In this case, in grouping pilots for the first and second transmit antennas into one pilot set, two subcarriers adjacent to each other on the same symbol index are one pilot for the first antenna and one pilot for the second antenna. Group pilots so that they can be allocated on the index.
Here, the first and second transmit antennas may be arranged in the same terminal, but in the modified embodiment, the first and second transmit antennas may be arranged in separate terminals, respectively.

delete

Thereafter, the center region is determined as a position to allocate one pilot set in each region 410 based on the symbol axis and the subcarrier axis (S320). As described above, since the pilots included in one pilot set are grouped so that they can be allocated on two adjacent subcarrier indexes on the same symbol index, the center region to which each pilot set is to be allocated is also adjacent to each other on the same symbol index. It consists of two subcarrier indices.

The structure of the pilot allocated according to the above-described pilot allocation method is shown in FIG. 4B. As shown, the pilot 420 for the first transmit antenna and the pilot 430 for the second transmit antenna are grouped into one pilot set 440, with one pilot set 440 in each region 410. It can be seen that is assigned to the central region with respect to the symbol axis and the sub-carrier axis within the).

More specifically, the pilots 420 for the first antenna are allocated on the subcarrier indexes 2, 8, and 15 on the symbol indexes 1 and 4, respectively, and the pilot 430 for the second antenna. It can be seen that they are allocated on the 3, 9, and 16 subcarrier index on the 1 and 4 symbol index, respectively.

In the above-described embodiment, it is described that a resource block is divided into a plurality of regions, the pilots for each transmit antenna are grouped into a pilot set, and then the center portion of each region is determined as the location where the pilot set is placed. To illustrate that the pilots for each transmit antenna are arranged to be uniformly distributed on the time axis (symbol axis) and the frequency axis (subcarrier axis) within one resource block. Rather than dividing into multiple regions or grouping the pilots for each transmit antenna into one pilot set, the pilots for the first antenna directly subcarriers 2, 8, and 15 on symbol 1 and 4 symbol indices Assign on the index, respectively, the pilots for the second antenna 3, 9 on symbol 1 and 4 symbol index , And it could be directly allocated to the 16 sub-carrier index.

That is, since the above-described plurality of regions may be regarded as a virtually set block for allocating pilots, the present invention therefore allocates first pilots to a first resource block transmitted through a first antenna, and a second antenna. Second pilots are allocated to the second resource block transmitted through the first and second resource blocks, and the virtual sub-resource block includes a plurality of virtual resource blocks. Could be.

Hereinafter, a method of estimating a channel using the pilot pattern as shown in FIG. 4B will be described in more detail with reference to FIGS. 4C and 4D. In FIG. 4C, only a method of estimating a channel with a first transmitting antenna using a pilot for a first transmitting antenna will be described for convenience of description, and a pilot of each region is set to 0 to distinguish a pilot for each region. The numbers from 1 to 5 were assigned. In the following description, it is assumed that one resource block includes a plurality of virtual subblocks as described above.

Each subblock is used to calculate a response to the channel in which the pilot is located by using a pilot disposed in the center of each subblock, and then, as shown, all channels included in the subblock including the pilot. By estimating the response of as the channel response for the channel in which the pilot is located, estimate all the channels included in each sub-block.

In the above-described embodiment, it has been described as estimating all channels included in the corresponding subblock using one pilot included in each subblock. However, in the modified embodiment, the pilot pattern as shown in FIG. 4B is illustrated. As shown in FIG. 4D, a resource block having a subframe includes two virtual subblocks consisting of nine subcarriers and six symbols, and a channel response of the pilot included in each subblock, for example, the first subblock. In the case of block 410, all channels included in the sub-block are estimated by calculating an average value of the channel response calculated using the pilots 0, 1, 3, and 4 included in the first sub-block 410. can do.

In another embodiment, rather than estimating the channel for each of the plurality of sub-blocks constituting one resource block, by calculating the average value of the channel response calculated by using all the pilots included in one resource block to the corresponding resource block All included channels can be estimated.

In the above-described embodiment, one resource block is composed of six virtual subblocks, and a pilot is assigned to the center portion of each subblock. However, in the modified embodiment, one resource block has two resource blocks. It may consist of four virtual sub-blocks, and the pilot may be arranged in the central portion of each sub-block. A pilot pattern assigned a pilot according to the pilot allocation method according to the modified embodiment will be described in detail with reference to FIGS. 5 and 6.

First, as shown in FIG. 5, one resource block is composed of two virtual subblocks 500 composed of nine subcarriers and six symbols, and a first transmission is performed within each subblock 500. Three pilots 510 for the antenna and three pilots 520 for the second transmit antenna are alternately assigned so as not to overlap each other on the subcarrier indexes (number 4 and 13 subcarrier indexes) of the center portion. .

Specifically, the pilots 510 for the first transmit antennas are allocated on symbol 0, 2, and 4 symbol indexes on subcarrier indexes 4 and 13, respectively, and the pilot 520 for the second transmit antennas. It can be seen that they are allocated on symbol indexes 1, 3, and 5 on subcarrier indexes 4 and 13, respectively.

Next, as shown in FIG. 6, one resource block is composed of two virtual subblocks 600 composed of nine subcarriers and six symbols, and a first transmission is performed in each subblock 600. Three pilots 610 for the antenna are allocated on three subcarrier indices adjacent to each other on the same symbol index, and three pilots 620 for the second transmit antenna have a pilot 610 for the first transmit antenna. It is allocated on three subcarrier indices adjacent to each other on the assigned symbol index and the neighboring symbol index.

Specifically, the pilots 610 for the first transmit antennas are allocated on subcarrier indexes 3, 4, and 5 on symbol 2, and the pilots 620 for the second transmit antenna are symbol 3 On the 3rd, 4th, and 5th subcarrier index on the index.

As shown in FIG. 5 and FIG. 6, the pilot allocation method according to the modified embodiment is also the same as the pilot allocation method shown in FIGS. 3 to 4. Allocate the pilots so that the pilots for are uniformly distributed.

Meanwhile, the pilot allocation method according to another embodiment of the present invention may allocate the pilot as shown in FIGS. 7 and 8.

First, referring to FIG. 7, it can be seen that only one pilot is disposed on the same symbol in one virtual sub-block 700. Looking at the pilot pattern in detail, two pilots 710 for the first transmit antenna are allocated on subcarrier indexes 3 and 12 on symbol 0 and subframes 4 and 13 on symbol 2, respectively. Two are allocated on the carrier index, and the other two are allocated on the subcarrier indexes 5 and 14 on the symbol index 4.

Next, two pilots 720 for the second transmit antenna are allocated on subcarrier indexes 3 and 12 on symbol 1, and 2 on subcarrier indexes 4 and 13 on symbol 3, respectively. The other two are allocated on the 5th and 14th subcarrier indexes on the 5th symbol index.
Next, referring to FIG. 8A, it can be seen that the pilot 810 for the first transmit antenna and the pilot 820 for the second transmit antenna are allocated on symbol indexes adjacent to each other on the same subcarrier index. Specifically, the pilot 810 for the first transmit antenna is allocated on the 0, 4, 8, 9, 13, and 17 subcarrier indexes on the symbol index 2, respectively, and the second transmission is performed. It can be seen that the pilot 820 for the antenna is allocated on subcarrier indexes 0, 4, 8, 9, 13, and 17 on symbol index 3, respectively.

On the other hand, in the case of having a pilot pattern as shown in Figure 8a, as shown in Figure 8b, it is possible to estimate the channel by using the interpolation (Interpolation) and copy (Copy) technique. Specifically, as shown in FIG. 8B, first, the resource block is composed of a virtual subblock 800 composed of nine subcarriers and six symbols.

delete

Subsequently, a response for a channel to which a pilot is allocated in the corresponding subblock is calculated, and the channel located on the same symbol as the pilots using the corresponding channel response exists, for example, on the first interval 830. In the case of the channel, the channel is estimated by interpolation based on the channel responses of the pilots 0 and 1, and the channel responses of the pilots 1 and 2 are estimated for the channel existing on the second section 840. The channel is estimated through the based interpolation.

Then, by copying the channel response of each channel located on the same symbol as the channel to which the pilot is assigned and determining the channel response of all channels located on the same subcarrier as each channel, all channels included in the corresponding subblock. Estimate the channel of.

9 is a diagram illustrating performance of channel estimation of a pilot pattern allocated according to the pilot allocation method of the present invention described above.

First, Figure 9a, if the speed of low-speed terminals, that is, PEDB 3km / h in the case, (Packet Error Rate) The pilot pattern is shown PER 10- ^2, in Figure 4b, when compared to the pilot pattern shown in Figure 2 You can see that it shows about 2db better performance.

Next, in Figure 9b, if the speed of the high-speed terminal, that is, VEH-A 60km / h in the Figure when compared with the pilot pattern shown in Figure 2, a pilot pattern ² are 10- PER (Packet shown in Figure 4b, if Error rate) shows better performance about 2db.

The above-described pilot allocation method may also be implemented in the form of a program that can be executed using various computer means. In this case, the program for performing the pilot allocation method may be a hard disk, a CD-ROM, a DVD, a ROM, or a RAM. Or a computer-readable recording medium such as a flash memory.

Those skilled in the art to which the present invention pertains will understand that the present invention can be implemented in other specific forms without changing the technical spirit or essential features.

For example, some of the available patterns among the plurality of pilot patterns according to the above-described embodiment of the present invention may be determined in advance, and adaptively selecting a plurality of suitable pilot patterns according to a given environment. For example, in consideration of the moving speed of the terminal, when the speed of the terminal is greater than or equal to the first threshold, that is, when the speed of the terminal is high, it is determined to use a pilot pattern that exhibits excellent performance at high speed, and the speed of the terminal is less than the second threshold. In other words, when the speed of the terminal is low, it may be determined to use a pilot pattern having excellent performance at low speed.

In this case, the selection of the pilot pattern may be determined by the base station. For this, the base station may further include an apparatus for monitoring the speed of the terminal.

Therefore, it is to be understood that the embodiments described above are exemplary in all respects and not restrictive. The scope of the present invention is shown by the following claims rather than the detailed description, and all changes or modifications derived from the meaning and scope of the claims and equivalent concepts are included in the scope of the present invention. Should be.

1 shows a pilot pattern in a frame defined in IEEE 802.16e.

2 is a diagram showing the structure of a frame defined in IEEE 802.16m.

3 is a flowchart showing a pilot allocation method according to an embodiment of the present invention.

4A and 4B illustrate pilot patterns in accordance with one embodiment of the present invention.

4C and 4D illustrate a channel estimation method using the pilot pattern shown in FIG. 4B.

5 illustrates a pilot pattern according to another embodiment of the present invention.

6 illustrates a pilot pattern according to another embodiment of the present invention.

7 illustrates a pilot pattern according to another embodiment of the present invention.

8A illustrates a pilot pattern according to another embodiment of the present invention.

FIG. 8B is a view illustrating a channel estimation method using the pilot pattern shown in FIG. 8A.

FIG. 9 is a diagram showing the performance of channel estimation of the pilot pattern shown in FIG. 2 and the pilot pattern shown in FIG. 4B.

Claims (8)

A method of allocating pilots in a resource block consisting of 18 subcarriers and 6 symbols, Assign pilots for the first transmit antenna to subcarrier indexes 2, 8, and 15 of symbol indexes 1 and 4, and assign the second transmit antenna to subcarrier indexes 3, 9, and 16. And assigning pilots for the pilot. The method of claim 1, And a pilot for the first and second antennas and uplink data transmitted through the first and second antennas are allocated to the resource block. The method of claim 1, And the first and second transmit antennas are arranged in the same terminal. The method of claim 1, And the first and second transmit antennas are arranged in different terminals, respectively. Allocating first pilots to a first resource block transmitting over a first antenna; And Allocating second pilots to a second resource block transmitting over a second antenna, The resource block is composed of a plurality of virtual sub-resource block, the virtual sub-resource block comprises a pilot. The method of claim 5, And allocating the one pilot to a central region in a symbol index increment direction and a subcarrier index increment direction in the virtual sub-resource block. The method of claim 1, And the resource block is included in an uplink frame for collaborative spatial multiplexing (CSM). The method according to any one of claims 1 to 7, And the pilot allocation method is applied to a frame defined in IEEE 802.16m.

Images