KR101083575B1 - Method for Allocating Pilot - Google Patents

Abstract

According to an aspect of the present invention, a pilot allocation method for uniformly distributing pilots in a wireless communication system includes: assigning pilots to a resource block including a plurality of sub resource blocks; A method, comprising: dividing each sub-resource block into blocks into virtual first and second regions; Assigning first and second pilots to be symmetrical to each other on a central subcarrier of the first region; And allocating third and fourth pilots to be symmetrical to each other on a central subcarrier of the second region.

MIMO, pilot, batch, assignment, pattern, channel, estimation

Description

Pilot assignment method {Method for Allocating Pilot}

TECHNICAL FIELD The present invention relates to wireless communication systems and, more particularly, to pilot assignment in wireless communication systems.

The Institute of Electrical and Electronics Engineers (IEEE) 802 committee is planning to develop a technical standard for IEEE 802. 16m, a technology standard that is one step ahead of the current mobile WiMAX as the next-generation standard of WiBro / Mobile WiMAX. Aims at 100 Mbps for mobile and 1 Gbps for fixed.

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 (Pilot) . A pilot is a signal component that can be used to estimate the state of a channel in wireless or wired communication, and is implemented by transmitting a predetermined sequence known to both a base station or a terminal when radio waves are transmitted through an unknown channel.

On the other hand, the pilot is also used for the above-described channel estimation in IEEE 802.16m, and various pilot patterns usable in IEEE 802.16m have been proposed. First, FIG. 1A is a pilot pattern used for two reception antennas on a Partial Usage Subchannel (PUSC) region of an uplink period in IEEE 802.16e. As shown in FIG. 1A, one sub-resource block is used. Block) is composed of four subcarriers in three OFDMA symbols, and the pilot 100 for the first antenna in one sub-resource block is the first subcarrier in the first OFDMA symbol and the fourth in the third OFDMA symbol. The pilot 110 for the second antenna is allocated on the first subcarrier in the third OFDMA symbol and the fourth subcarrier in the first OFMDA symbol.

In addition to the pilot pattern shown in FIG. 1A, a pilot pattern for allocating eight pilots in a sub-resource block consisting of eight subcarriers in three OFDMA symbols as shown in FIG. 1B, and three as shown in FIG. 1C A pilot pattern for allocating six pilots in a sub-resource block consisting of nine subcarriers in an OFDMA symbol has been presented.

However, in the case of the pilot pattern shown in Figs. 1A and 1B, the pilot distribution is uniform and efficient channel estimation can be performed, but the ratio of data to total tone is only two thirds in one sub-resource block. There is a problem that the amount of data transmission is not large.

Meanwhile, in the case of the pilot pattern shown in FIG. 1C, the ratio of data to total tones is 7/9 in one sub-resource block, so that the data transmission amount can be increased compared to the pilot patterns shown in FIGS. 1A and 1B. As the number of pilots increases together, not only does the overhead increase due to the pilots increase, but also the maximization of the frequency diversity gain is hindered when the size of the sub-resource block is commutated. There is a problem.

SUMMARY OF THE 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 pilots to uniformly distribute pilots in a wireless communication system.

Another object of the present invention is to provide a method for allocating pilots so that channel estimation can be efficiently performed and data transmission can be increased.

In addition, another object of the present invention is to provide a method for allocating a pilot to a server resource block sized to maximize frequency diversity gain.

A pilot allocation method according to an aspect of the present invention for achieving the above object is a method for allocating a pilot to a resource block consisting of a plurality of sub resource blocks (Sub Resource Block), Dividing the sub-resource block into blocks into virtual first and second regions; Assigning first and second pilots to be symmetrical to each other on a central subcarrier of the first region; And allocating third and fourth pilots to be symmetrical to each other on a central subcarrier of the second region.

In this case, the sub-resource block may consist of six subcarriers in three OFDMA symbols, and each of the first and second regions may consist of three subcarriers in three ODMA symbols. The block may consist of four or five sub resource blocks.

According to an embodiment, when the pilot allocation method is applied to a 2ⅹ2 MIMO system, the first and fourth pilots are pilots for a first antenna, and the second and third pilots are first It is characterized by being a pilot for two antennas. In this case, pilots for the same antenna among the first to fourth pilots may be allocated on different OFDMA symbols, and the first and second antennas may include one terminal, one base station, different terminals, And an antenna disposed at any one of different base stations.

In another embodiment, when the pilot allocation method is applied to a 4x4 MIMO system, the first pilot is a pilot for a first antenna, and the second pilot is a pilot for a second antenna. The third pilot may be a pilot for a third antenna, and the fourth pilot may be a pilot for a fourth antenna.

In another embodiment, when the pilot allocation method is applied to a 4x4 MIMO system, a fifth pilot and a sixth pilot on a second subcarrier and a third subcarrier in a second OFDMA symbol within the first region. Assigning each; And allocating a seventh pilot and an eighth pilot on the first subcarrier and the second subcarrier in a second OFDMA symbol, respectively, in the second region, wherein the first and seventh pilots are respectively assigned to the first and seventh pilots. A pilot for one antenna, the second and eighth pilots for a second antenna, the third and fifth pilots for a third antenna, and the fourth and sixth pilots for a fourth antenna. It is characterized in that the pilot.

In another embodiment, when the pilot allocation method is applied to a 4x4 MIMO system, a fifth pilot and a sixth pilot on a first subcarrier and a third subcarrier in a second OFDMA symbol within the first region. Assigning each; And allocating a seventh pilot and an eighth pilot on a first subcarrier and a third subcarrier in a second OFDMA symbol, respectively, in the second region, wherein the first and fourth pilots are assigned to the first and fourth pilots. A pilot for one antenna, the second and third pilots for a second antenna, the fifth and seventh pilots for a third antenna, and the sixth and eighth pilots for a fourth antenna It is characterized in that the pilot.

Meanwhile, in the above-described embodiments, the resource block may be a distributed resource block to which permutation is applied. In this case, the permutation may be performed in units of the sub-resource block. do.

In an embodiment, the resource block is a resource block included in a subframe for uplink transmission.

According to another aspect of the present invention, a pilot allocation method includes a second subcarrier and a third OFDMA symbol in a first OFDMA symbol of at least one first sub-resource block constituting a resource block for first antenna transmission. Assigning a pilot on a fifth subcarrier in the carrier; And allocating pilots on a second subcarrier in the third OFDMA symbol and the fifth subcarrier in the first OFDMA symbol of the at least one second sub resource block configuring the resource block for second antenna transmission. The sub-resource block is comprised of six subcarriers within three OFDMA symbols.

In one embodiment, the first sub-resource block and the second sub-resource block may be the same sub-resource block.

As described above, according to the present invention, by uniformly distributing pilots, channel estimation can be efficiently performed, and the number of data tones can be increased without increasing the number of pilots, thereby increasing overhead due to the increase of pilots. There is an effect that can be prevented.

In addition, the present invention has the effect of maximizing the frequency diversity gain by increasing the data transmission amount and adjusting the size of one resource block.

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

First, before the detailed description of the present invention, it is necessary to look at the structure of the frame specified in the Institute of Electrical and Electronics Engineers (IEEE) 802.16m, the frame structure defined in the IEEE 802.16m will be described with reference to FIG. Let's do it.

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 sub-frame 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 blocks (Resource Block), these resource blocks are again a plurality of sub resource blocks (Sub Resource Block) It can be configured as.

Herein, the resource block includes a localized resource block and a distributed resource block. The localized resource block is a resource block to which permutation is not applied. Output) is a resource block that can be used.

Meanwhile, the distributed resource block is a resource block to which permutation is applied and is a resource block capable of mitigating interference by averaging interference through permutation.

Hereinafter, a pilot allocation method according to an embodiment of the present invention will be described with reference to FIGS. 3 to 5. 3 is a flowchart illustrating a method of allocating pilot when the pilot allocation method according to an embodiment of the present invention is applied to a wireless communication system in a 2ⅹ2 MIMO environment.

As shown, first, a plurality of sub-resource blocks included in one resource block are divided into two virtual regions having the same size (S300). At this time, one sub-resource block may be composed of six sub-carriers in three OFDMA symbols, as shown in Figure 4a, which is two virtual regions included in one resource block (410a ~ 410d) Each of the first region 420 and the second region 422 may be composed of three subcarriers within three OFDMA symbols.

In one embodiment, as shown in FIG. 4A, one resource block 400 may consist of four sub-resource blocks 410a-410d, in which case one resource block 400 is It may consist of 24 subcarriers in three OFDMA symbols.

In FIG. 4A, one resource block is described as being composed of four sub-resource blocks. However, in a modified embodiment, the resource block may be composed of various number of sub-resource blocks instead of four sub-resource blocks.

Meanwhile, the above-described resource block may be a resource block included in an uplink subframe for CSM (Collaborative Spatial Multiplexing) transmitted from a terminal to a base station among the subframes proposed in IEEE 802.16m. It may be a distributed resource block that can be applied. In one embodiment, in performing permutation on distributed resource blocks, permutation may be performed in units of sub-resource blocks constituting the resource block.

In the present invention, since the interference and fading experienced by each sub-resource block are different from each other by performing permutation for each sub-resource block, the interference and fading are averaged and thus frequency diversity gain ( Frequency Diversity Gain).

Here, frequency diversity refers to a method of transmitting the same communication information on several frequencies to prevent fading occurring in the propagation process of radio waves. Specifically, the frequency diversity means that the reception characteristics are different for each frequency. By using this method, a good reception signal is selected or different signals are combined to prevent fading.

Referring back to FIG. 3, the first and second pilots are allocated on the center subcarrier of the first region so that the first pilot for the first antenna and the second pilot for the second antenna are symmetric with each other (S310). . That is, since the first region is composed of three subcarriers in three OFDMA symbols, in the first region, the first pilot is allocated on the second subcarrier in the first OFDMA symbol and in the third OFDMA symbol. The second pilot is allocated on the second subcarrier.

In this case, the first and second antennas may be antennas disposed in different terminals, but the first and second antennas may be antennas disposed on the same terminal.

Thereafter, a third pilot and a fourth pilot are allocated on the center subcarrier of the second region so that the fourth pilot for the first antenna and the third pilot for the second antenna are symmetric with each other, but the pilot for the same antenna is Do not allocate on the same symbol (S320).

That is, since the second region consists of three subcarriers in three OFDMA symbols, a third pilot is allocated on the second subcarrier in the first OFDMA symbol in the second region, and the third OFDMA symbol The fourth pilot is allocated on the second subcarrier in the terminal. In this case, since pilots for the same antenna should not be allocated on the same symbol, if the first pilot for the first antenna is allocated on the first OFDMA symbol in the first region, the first pilot for the first antenna is used. Four pilots should be allocated on the third OFDMA symbol in the second region.

A pattern of pilots allocated according to the above-described pilot allocation method in one sub resource block is shown in FIG. 4B. As shown, the first pilot 430 for the first antenna in the first region 420 is assigned to the second subcarrier in the first OFDMA symbol, and the second pilot 440 for the second antenna is It is allocated on the second subcarrier in the third OFDMA symbol.

In addition, in the second region 422, the third pilot 450 for the second antenna is assigned to the second subcarrier in the first OFDMA symbol, and the fourth pilot 460 for the first antenna is assigned to the third OFDMA. It is assigned to the second subcarrier in the symbol.

Therefore, the pilot pattern when one resource block is composed of four sub resource blocks is as shown in FIG. 4C. 4C, since four pilots and 14 data tones are allocated to each sub-resource block, one resource block includes 16 pilots and 56 data tones.

In the above-described embodiment, it is described that partitioning one sub-resource block into two virtual regions and then assigning pilots for each antenna indicates that the pilots for each antenna are located in the time axis (symbol) within one sub-resource block. Axis) and a frequency axis (subcarrier axis), which are arranged to be uniformly distributed. In a modified embodiment, one sub-resource block is not divided into two virtual regions. The first pilot and the fourth pilot are allocated to the second subcarrier in the first OFDMA symbol and the fifth subcarrier in the third OFDMA symbol of the first sub resource block constituting one resource block for antenna transmission. The second subcarrier in the third OFDMA symbol of the second sub-resource block and the fifth in the first OFDMA symbol for two-antenna transmission A second pilot and a third pilot may be allocated respectively on the subcarriers. In this case, the first and second sub-resource blocks may be different resource blocks but may also be the same resource blocks.

5 is a diagram showing a simulation result of the performance of the above-described pilot allocation method. FIG. 5A is a simulation result when the above-described pilot allocation method is applied to a terminal moving at a low speed, and FIG. 5B is a diagram showing a simulation result when the above-mentioned pilot allocation method is applied to a terminal moving at a high speed.

As shown in FIGS. 5A and 5B, in the case of the pilot allocation method according to the present invention, the number of pilots is reduced compared to those of FIGS. It can be seen that the performance is superior to the pilot allocation method shown in FIG. As described above, in the pilot allocation method according to the present invention, since the ratio of the data tone to the total tone is 7/9 in one resource block, the performance of the channel estimation is almost equal while the data estimation is performed in comparison with FIGS. 1A and 1B. Increasing the number of tones can increase the amount of data transmission.

In addition, the pilot allocation method according to the present invention shows the same data rate as the pilot pattern shown in Figure 1c, but the pilot number is smaller than the pilot pattern shown in Figure 1c can reduce the overhead according to the pilot number, of course, Since the size of the sub-resource block is smaller than that shown in FIG. 1C, it is possible to maximize the frequency diversity gain when performing permutation.

Meanwhile, in the above-described embodiment, the pilot allocation method has been described as being applied to the uplink of the wireless communication system in the 2 환경 2 MIMO environment. However, in the modified embodiment, the above-described pilot allocation method is the uplink of the wireless communication system in the 4ⅹ4 MIMO environment. May be applied to the link.

Specifically, referring to FIG. 6, within the first region 650, the first pilot 610 for the first antenna is allocated on the second subcarrier in the first OFDMA symbol and the first for the second antenna. The second pilot 620 allocates to the second subcarrier in the third OFDMA symbol. Further, in the second region 660, the third pilot 630 for the third antenna is allocated on the second subcarrier in the first OFDMA symbol, and the fourth pilot 640 for the fourth antenna is third Assign on the second subcarrier in the symbol.

In FIG. 6, one pilot is used for each of the four antennas, but in another embodiment, two pilots may be used for each of the four antennas. A method of assigning two pilots to each of four antennas will be described in detail with reference to FIGS. 7 and 8.

First, as shown in FIG. 7, one resource block 700 includes five sub resource blocks 710a to 710e including six subcarriers within three OFDMA symbols. It can be seen that two pilots are allocated to each antenna. Specifically, in each sub-resource block, the first pilot 740a for the first antenna, the fifth pilot 760a for the third antenna, and the second pilot for the second antenna in the first region 720. 750a consecutively allocates each on the second subcarrier in the first to third OFDMA symbols, and assigns a sixth pilot 770a for the fourth antenna on the third subcarrier in the second OFDMA symbol do.

Meanwhile, in the second region 730, the seventh pilot 740b for the first antenna is allocated on the first subcarrier in the second OFDMA symbol, and the third pilot 760b for the third antenna, An eighth pilot 750b for two antennas and a fourth pilot 770b for a fourth antenna are sequentially allocated on the second subcarrier in the first to third OFDMA symbols.

That is, in the pilot pattern illustrated in FIG. 7, one pilot may be allocated to each antenna in each of the first and second regions, but the pilots may be located far apart without allocating pilots for the same antenna on the same symbol. You can see that it is allocated. As such, when allocating pilots, one resource block includes 8 pilots and 10 data tones for each sub-resource block. As a result, one resource block includes 40 pilots and 50 data tones.

Next, referring to FIG. 8, similar to the pilot pattern illustrated in FIG. 7, one resource block 800 includes five sub resource blocks 810a to 810e composed of six subcarriers within three OFDMA symbols. It can be seen that two pilots are allocated to each antenna in each of the sub-resource blocks 810a to 810e.

In the case of the pilot pattern shown in FIG. 8, specifically, the third pilot 860a for the third antenna in the first region 820 is allocated on the first subcarrier in the second OFDMA symbol, and the first antenna Sequentially assign each of the first pilot 840a for the second pilot 850a for the second antenna and the second subcarrier in the first OFDMA symbol and the third OFDMA symbol for the fourth antenna for the fourth antenna. The pilot 870a is assigned on the third subcarrier in the second OFDMA symbol.

Meanwhile, in the second region 830, the fifth pilot 860b for the third antenna is allocated to the first subcarrier in the second OFDMA symbol, and the eighth pilot 850b and the first for the second antenna are allocated. Each of the seventh pilot 840b for the antenna is sequentially allocated on the second subcarrier in the first OFDMA symbol and the third OFDMA symbol, and the sixth pilot 870b for the fourth antenna is 3 in the second OFDMA symbol. On the first subcarrier.

In the case of the pilot pattern shown in FIG. 8, one pilot for each antenna is allocated to each of the first and second regions in the same manner as the pilot pattern shown in FIG. 7, but the pilots for the same antenna are not allocated on the same symbol. It can be seen that the pilots are assigned to be far apart. As such, when pilots are allocated, each sub-resource block includes 8 pilots and 10 data tones. As a result, one resource block includes 40 pilots and 50 data tones.

Meanwhile, in the above-described embodiments, the pilot allocation method of the present invention has been described as being applied to a MIMO system. However, in another embodiment, the pilot allocation method of the present invention may be applied to a single input single output (SISO) system. Specifically, referring to FIG. 9, when the pilot allocation method of the present invention is applied to a SISO system, four pilots 920a to 920d in a sub resource block 910 including six subcarriers in three OFDMA symbols. ) On the second subcarrier and the fifth subcarrier in the first OFDMA symbol and the second subcarrier and the fifth subcarrier in the third OFDMA symbol so that the respective pilots 920a to 920d are uniformly distributed. Each of the pilots 920a to 920d is allocated. In this case, since one resource block 900 includes four sub-resource blocks 910a to 910d, the resource block 900 includes 16 pilots and 56 data tones.

The above-described pilot allocation method can be implemented in the form of program instructions that can be executed by various computer means and recorded in a computer-readable recording medium. In this case, the computer-readable recording medium may include program instructions, data files, data structures, and the like, alone or in combination. On the other hand, the program instructions recorded on the recording medium may be those specially designed and configured for the present invention or may be available to those skilled in the art of computer software.

Computer-readable recording media include magnetic media such as hard disks, floppy disks, and magnetic tape, optical media such as CD-ROMs, DVDs, and magnetic disks, such as floppy disks. -Magneto-Optical Media, and hardware devices specifically configured to store and execute program instructions, such as ROM, RAM, flash memory, and the like. 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 data structure, or the like.

In addition, program instructions include not only machine code generated by a compiler, but also high-level language code that can be executed by a computer using an interpreter or the like. The hardware device described above may be configured to operate as one or more software modules to perform the operations of the present invention, and vice versa.

On the other hand, those skilled in the art will understand that the present invention described above can be implemented in other specific forms without changing the technical spirit or essential features.

For example, in the above-described embodiment, the pilot allocation method of the present invention has been described as being applied to the uplink of the wireless communication system. However, the modified embodiment may also be applied to the downlink.

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.

1A-1C show a typical pilot pattern.

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 4C show pilot patterns allocated according to the pilot assignment method shown in FIG.

5A and 5B show simulation results for the performance of the pilot allocation method shown in FIG.

6 to 9 illustrate pilot patterns according to another embodiment of the present invention.

Claims (14)

A method of allocating a pilot to a resource block composed of a plurality of sub resource blocks, Dividing each of the sub-resource blocks into virtual first and second regions; And Allocating the first and second pilots to be symmetrical to each other on the center subcarriers of the first region, and allocating the third and fourth pilots to be symmetric to each other on the central subcarriers of the second region; And a pilot allocation method. The method of claim 1, And wherein the sub-resource block consists of six subcarriers in three OFDMA symbols, and each of the first and second regions consists of three subcarriers in three OFDMA symbols. The method of claim 1, And the resource block is composed of four or five sub-resource blocks. The method of claim 1, When the pilot allocation method is applied to a 2ⅹ2 Multi Input Multi Output (MIMO) system, the first and fourth pilots are pilots for a first antenna, and the second and third pilots are pilots for a second antenna. And a pilot allocation method. The method of claim 1, And pilots for the same antenna among the first to fourth pilots are allocated on different OFDMA symbols. 5. The method of claim 4, The first and second antennas may include an antenna type in which both the first and second antennas are arranged in one terminal, an antenna type in which both the first and second antennas are arranged in one base station, and the first and second antennas. 2. The pilot allocation method according to claim 1, wherein the antenna is any one of an antenna type arranged in different terminals, and an antenna type in which the first and second antennas are arranged in different base stations. The method of claim 1, When the pilot allocation method is applied to a 4x4 MIMO system, the first pilot is a pilot for a first antenna, the second pilot is a pilot for a second antenna, and the third pilot is a pilot for a third antenna. And the fourth pilot is a pilot for a fourth antenna. The method of claim 1, wherein the pilot allocation method is applied to a 4x4 MIMO system. Assigns a fifth pilot and a sixth pilot on a second subcarrier and a third subcarrier in a second OFDMA symbol in the first region, respectively, and includes a first subcarrier in a second OFDMA symbol in the second region and Allocating a seventh pilot and an eighth pilot on the second subcarrier, respectively, The first and seventh pilots are pilots for a first antenna, the second and eighth pilots are pilots for a second antenna, the third and fifth pilots are pilots for a third antenna, and a fourth And a sixth pilot is a pilot for the fourth antenna. The method of claim 1, wherein the pilot allocation method is applied to a 4x4 MIMO system. Assigns a fifth pilot and a sixth pilot on a first subcarrier and a third subcarrier in a second OFDMA symbol in the first region, respectively, and includes a first subcarrier in a second OFDMA symbol in the second region and Allocating a seventh pilot and an eighth pilot on the third subcarrier, respectively, The first and fourth pilots are pilots for a first antenna, the second and third pilots are pilots for a second antenna, the fifth and seventh pilots are pilots for a third antenna, and a sixth And an eighth pilot is a pilot for the fourth antenna. The method of claim 1, The resource block is a distributed resource block, The distributed resource block is defined as a resource block to which permutation is applied. The method of claim 10, The permutation is performed in units of the sub-resource block. The method of claim 1, And the resource block is a resource block included in a subframe for uplink transmission. As a method of assigning pilots, Allocating pilots on a second subcarrier in a first OFDMA symbol and at a fifth subcarrier in a third OFDMA symbol of at least one first sub-resource block constituting a resource block for first antenna transmission; And Allocating a pilot on a second subcarrier in a third OFDMA symbol and a fifth subcarrier in a first OFDMA symbol of at least one second sub-resource block constituting the resource block for second antenna transmission; , And the first and second sub-resource blocks consist of six subcarriers in three OFDMA symbols. The method of claim 13, And the first sub-resource block and the second sub-resource block are the same sub-resource block.

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