JP2007174652A - Grouping method of pilot sub-carriers in orthogonal frequency division multiple access system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a grouping method of pilot sub-carriers in an orthogonal frequency division multiple access (OFDMA) system, and to provide a channel inferring method based thereon. <P>SOLUTION: With respect to a user (u), sub-carriers inside a pilot symbol are grouped. In this case, all the number of pilot sub-carrier groups and the number of pilot symbols for the user (u) are variable, and the number of subcarriers in each pilot sub-carrier group for the user (u) is identical. Here, the range of (u) is from 1 to U, where U is the number of all users in the OFDMA system. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to the field of wireless communication technology, and more particularly to a pilot subcarrier grouping method in an orthogonal frequency division multiple access (OFDMA) system.

Around the 60s of the 20th century, orthogonal frequency division multiplexing (OFDM) systems were already submitted as a kind of high-speed transmission technology in wireless communication systems. In recent years, OFDM systems have been realized by the rapid development of digital signal processing technology and ASIC technology, and OFDM technology has attracted widespread attention again. Currently, with the development of mobile communication systems, personal mobile communication terminals that can support various new services have already been provided to users. Since these services require transmission of a large amount of data, higher bit transmission rates are required in mobile communication systems. In an ordinary single carrier system, using a higher bit transmission rate makes it difficult to receive signals efficiently due to severe frequency selective fading and intersymbol interference (ISI) of the radio channel. The OFDM technology has the ability to suppress ISI and can provide high frequency spectrum efficiency, so it is regarded as one of the transmission technologies most likely to be adopted in next-generation wireless mobile communication systems. OFDM technology is already widely applied in various fields such as digital user lines, digital audio / video broadcasting, wireless local area network (WLAN) and wireless metropolitan area network (WMAN). The OFDMA system is a multi-user communication system based on OFDM technology. The basic principle of the OFDMA system is to divide the entire OFDM subcarriers into a number of subcarrier groups, where the subcarrier groups are called subchannels. Different users can use different subchannels at the same time. The OFDMA system inherits the benefits of OFDM and at the same time has a more flexible data transmission rate. In an OFDMA system, in order to better estimate the channel parameters, a small number of subcarriers are also used for transmission of pilot information and are called pilot subcarriers. On the other hand, a subcarrier used for data transmission is called a data subcarrier. In current OFDMA systems, the grouping of pilot symbols for subcarriers is not related to a specific user. For example, when performing uplink (Up-Link) channel estimation, pilot symbol subcarriers are grouped into the same size, but different channel characteristics for different users are considered in the grouping method for the pilot symbol subcarriers. Therefore, the grouping must be fixed based on the maximum multipath delay time of the system. Therefore, the number of uplink users and / or the number of antennas that can be supported simultaneously is relatively small and fixed and does not change.

  The present invention has been made in view of the above, and has as its main object to provide a pilot subcarrier grouping method in an OFDMA system that can simultaneously support a larger number of users and / or antennas in the OFDMA system. To do.

  In order to achieve the above object, the technical method of the present invention is realized as follows.

A pilot subcarrier grouping method in an OFDMA system,
For user u, subcarriers in pilot symbols are grouped, where the number of pilot subcarrier groups in user u and the number of pilot symbols are all variable, and the number of subcarriers in each pilot subcarrier group in user u is variable. The number of carriers is the same.

  Here, the range of u is 1 to U, and U is the total number of users in the OFDMA system.

  When the maximum Doppler [0] frequency shift of the radio channel increases in the OFDMA system, the maximum value of the number of pilot symbols is reduced.

  When the number of users and / or the number of antennas that need to be supported simultaneously in the OFDMA system increases, the number of pilot symbols is increased.

  When the frequency spectrum efficiency needs to be increased in the OFDMA system, the number of pilot symbols is reduced.

The number of pilot symbols is P, and the minimum number of pilot symbols is

And the maximum number of pilot symbols is

And the maximum Doppler [0] frequency shift of the radio channel in the OFDMA system is

And the range of P is

It is.

Maximum multipath delay time for user u

The minimum number of pilot subcarrier groups for the user u

Increase, and

And

Is a power of 2.

  When the number of users and / or the number of antennas that need to be supported simultaneously in the OFDMA system increases, the number of pilot subcarrier groups for each user is reduced.

The higher the accuracy requirement for radio channel estimation, the greater the number of pilot subcarrier groups for each user.

here,

Is the maximum multipath delay time of the u th user,

Is the minimum number of pilot subcarrier groups in the u th user,

Is the maximum number of pilot subcarrier groups in the u th user,

Is the number of subcarrier groups in the u th user, and

Is a power of 2,
N is the number of subcarriers in the OFDM symbol.

  The method further includes selecting one pilot subcarrier within each subcarrier group belonging to the same or different pilot symbols for each antenna at user u.

  When the base station has no information about the user channel in advance, one pilot subcarrier is randomly selected in each subcarrier group belonging to the same or different pilot symbol for each antenna in the user u, and the other in this user The same pilot subcarrier as that of the other antenna or the antenna of another user may not be selected.

  When the base station has information about the user channel, for each antenna at user u, one pilot sub at a position where there is no narrow band interference or where the narrow band interference is weak within each subcarrier group belonging to the same or different pilot symbols. In addition to selecting a carrier, it should satisfy the condition not to select the same pilot subcarrier as other antennas for this user and antennas for other users.

The method is
Perform LS channel estimation for pilot position of antenna k at user u,

Obtain LS channel estimation results at pilot positions, where the range of k is

And

Is the number of antennas for user u,

Is the number of subcarrier groups in the u th user, and

Is step A, which is a power of 2, and

Map the LS channel estimation results at one pilot position into one OFDM symbol,

And

here,

N is the number of subcarriers of the OFDM symbol, P is the number of pilot symbols, t is a time domain variable, n is a frequency domain variable, step B,

When

Complete frequency domain channel response of antenna k at user u by interpolating the LS channel estimation results at the pilot positions of

Where

Further includes step C, which is the minimum number of pilot subcarrier groups in the u-th user.

The method is
Perform LS channel estimation for pilot position of antenna k at user u,

Obtain LS channel estimation results at pilot positions, where the range of k is

And

Is the number of antennas for user u,

Is the number of subcarrier groups in the u th user, and

Is step A, which is a power of 2, and

Map the LS channel estimation results at one pilot position into one OFDM symbol,

And

here,

N is the number of subcarriers of the OFDM symbol, P is the number of pilot symbols, t is a time domain variable, n is a frequency domain variable, step B,

When

Channel estimation at the first subcarrier position in each subcarrier by interpolating the LS channel estimate at the pilot position

And

Step C is
Obtained by interpolation

Channel estimation at the first subcarrier position in one subcarrier group

Against

Perform channel inverse fast Fourier transform IFFT to estimate channel impulse response in time domain of antenna k at user u

And

Step D is

Truncate to zero padding

Step E to get

Perform N-point fast Fourier transform FFT on the complete frequency domain channel response of antenna k at user u

And step F.

The interpolation calculation is a linear interpolation calculation.

  As can be seen from the above technical method, in the present invention, when subcarriers in pilot symbols are grouped for each user u in the OFDMA system, the number of pilot subcarrier groups and the number of pilot symbols in user u are all variable. And the number of subcarriers in each pilot subcarrier group for user u is the same. At the same time, in the present invention, the number of pilot symbols is determined based on the maximum Doppler [0] frequency shift of the radio channel, the number of users and / or antennas that need to be supported simultaneously in the system, and the frequency spectral efficiency requirement in the system. Configure and configure the number of pilot subcarrier groups for each user based on the number of users and / or antennas that need to be supported simultaneously in the system, accuracy requirements for radio channel estimation, and the maximum multipath delay time for each user To do. Therefore, the present invention achieves a compromise between the number of users and / or antennas that can be supported simultaneously in the system and the frequency spectrum efficiency requirement in the system, and the number of users and / or antennas that can be supported simultaneously in the system. And an eclectic balance between the accuracy requirements for radio channel estimation. Thus, as many users and / or antennas as possible can be supported simultaneously by dynamic changes to the number of pilot symbols and the number of pilot subcarrier groups in different users. Also, in the present invention, all antennas for all active users can be used by grouping pilot subcarriers and selecting pilot subcarriers within each group, using some frequency resources allocated to each user. The complete frequency domain channel response can be obtained.

At the same time, according to the present invention, the base station can select a corresponding pilot subcarrier for the user in a self-adaptive manner based on the distribution situation of the narrowband interference. This avoids or reduces the effects of narrowband interference and increases channel estimation performance. Furthermore, in the present invention, since the channel estimation algorithm can be selected in a self-adaptive manner based on the number of pilot subcarrier groups used by the user, it is possible to give consideration to both performance and complexity of channel estimation.

  In order to further clarify the objects, technical methods and merits of the present invention, the present invention will be described in more detail with reference to the drawings and specific embodiments.

  The main idea of the present invention is that by dynamically changing the number of pilot symbols and the number of pilot subcarrier groups in different users, the number of users and / or antennas that can be supported simultaneously in the system and the frequency spectral efficiency requirement in the system. Achieves a balance between the number of users and / or antennas that can be supported simultaneously in the system and the accuracy of radio channel estimation, thereby increasing the number of users and / or antennas in an OFDMA system. It is to be able to support at the same time.

  Hereinafter, the algorithm of the present invention will be described in detail, and first, a symbol will be defined.

N is the number of subcarriers in the OFDM symbol,
P is the number of pilot symbols,
U is the number of users in the OFDMA system

Is the number of groups that group pilot subcarriers in the u th user, where

Is a power of 2, u = 1,2, ..., U,

Is the number of subcarriers included in each subcarrier group in the u th user, u = 1, 2,..., U,

Is the number of antennas for the u-th user, u = 1, 2,.

Is the maximum multipath delay time of the u th user, u = 1,2, ..., U,
First, for each user u, subcarriers in pilot symbols are grouped, where the number of pilot subcarrier groups and the number of pilot symbols in user u are variable, and in each pilot subcarrier group in user u The number of subcarriers is the same. Here, the range of u is 1 to U, and U is the total number of users in the OFDMA system.

That is, first, it is necessary to group the subcarriers in P pilot symbols for each user. That is, N subcarriers of the same size

Divided into individual groups, the number of subcarriers in each group

It is.

  FIG. 1 is a diagram illustrating pilot subcarrier grouping according to an embodiment of the present invention. As shown in FIG. 1, it is a schematic diagram of one data frame. The data frame includes two parts of pilot and data, the data part is located after the pilot part, and the pilot part includes P OFDM pilot symbols in total.

Each subchannel within P pilot symbols is grouped for each user channel condition, eg, maximum multipath delay time, where the same user has the same subcarrier grouping method for different pilot symbols. is there. That is, N subcarriers of the same size

Divided into individual groups, the number of subcarriers in each group

Is to do. Here, the number of pilot symbols P and the number of subcarrier groups

Are all dynamically variable.

  The value of the number of pilot symbols P is determined by the rate of change with time of the radio channel, the number of users and / or antennas that need to be supported simultaneously in the system, and the frequency spectral efficiency of the system.

The faster the radio channel changes with time, that is, the maximum Doppler [0] frequency shift.

The larger the is, the theoretical maximum of P

Should be smaller,

The filling,
The more users and / or antennas that need to be supported simultaneously in the system, the larger the value of P should be, and the fewer users and / or antennas that need to be supported simultaneously in the system As a result, the value of P can be reduced.

  The higher the frequency spectrum efficiency requirement in the system, the smaller the value of P should be, and the lower the frequency spectrum efficiency requirement in the system, the larger the value of P can be.

As you can see from the above, the value of P is

Should be in the range of

  Here, it is necessary to take an eclectic idea about the magnitude of the specific value of P based on different system requirements. That is, an eclectic idea is taken with respect to a specific value of P based on the balanced relationship between the number of users and / or the number of antennas supported simultaneously and the frequency spectrum efficiency.

Number of subcarrier groups in uth user

The value of is the maximum multipath delay time of the radio channel

And the number of users and / or antennas that need to be supported simultaneously in the system and the channel estimation accuracy.

The larger the value of, the greater the number of subcarrier groups

The theoretical minimum of

Becomes larger,

Should satisfy and

Is a power of 2.

The more users and / or antennas that need to be supported simultaneously in the system,

Should be reduced, and the fewer users and / or antennas that need to be supported simultaneously in the system,

The value of can be increased.

The higher the accuracy requirement for channel estimation,

Should be increased and the lower the accuracy requirement for channel estimation,

The value of can be reduced.

As you can see from the above,

The value of

Should be in the range of

here,

It is necessary to take an eclectic idea based on different system requirements. That is, based on a balance between the number of users and / or antennas supported simultaneously and the channel estimation accuracy.

Eclectic consideration is taken for the specific value of.

Therefore, the number of users and / or antennas that can be supported simultaneously in the system

There is a constraint condition.

As can be seen, in order to support as many users and / or antennas as possible simultaneously, the value of P is increased and / or within the permitted range of channel conditions, and / or

The value of may be decreased. In order to support as many users and / or antennas as possible, taking into account the exponential fading characteristics of the radio channel,

The theoretical minimum value of

It may be smaller, for example

It can be. In this way, it is clear that the channel estimation performance is reduced to some extent, but the number of users and / or antennas simultaneously supported by the system can be increased.

  After completing the dynamic grouping of subcarriers based on the above description, pilot subcarriers are further selected within the corresponding subcarrier group for each antenna for each user. Each antenna in user u can occupy one subcarrier in each subcarrier group and can occupy only one subcarrier, but the subcarrier group is located in any one of P pilot symbols. be able to.

  FIG. 2 is a diagram for selecting pilot subcarriers in a corresponding subcarrier group for each antenna in each user according to an embodiment of the present invention. As can be seen from FIG. 2, each antenna in each user should occupy one pilot subcarrier in each corresponding pilot subcarrier group, and only one pilot subcarrier can be occupied, and all users The pilot subcarrier positions of all the antennas in should not overlap each other.

  At the same time, when the selection of pilot subcarriers within each subcarrier group of user u is controlled by the base station, there are two cases.

  When in the communication establishment stage, the base station often has no information about the user channel, where the base station randomly assigns one pilot subcarrier within each subcarrier group for each antenna at user u. To ensure that it does not overlap with the antenna's pilot subcarriers for existing users.

  When in a continuous phase of communication, the base station often has information about the user channel, and the base station then uses each subcarrier for each antenna at user u based on the distribution of narrowband interference. One pilot subcarrier is selected within the group. The channel estimation performance is enhanced by avoiding selecting pilot subcarriers at the position of narrowband interference as much as possible on the premise of ensuring that they do not overlap with the pilot subcarriers of the antenna of the current user.

  FIG. 3 is a comparison between prior art and selecting pilot subcarriers within a corresponding subcarrier group for each antenna for each user according to an embodiment of the present invention. As can be seen from FIG. 3, in the prior art, when selecting the pilot subcarrier, the influence of the narrowband interference was not taken into account, so there is a possibility that the narrowband interference may occur at the selected pilot subcarrier position. It is clear that the performance of the channel estimation will be affected. On the other hand, if the pilot subcarrier selection method according to the present invention is adopted, the influence of narrowband interference can be effectively avoided or reduced, thereby improving the channel estimation performance.

  After completing the dynamic grouping of subcarriers and selection of subcarriers, dynamic channel estimation can be performed. Here, an appropriate channel estimation algorithm may be selected based on the number of subcarrier groups in the user.

  FIG. 4 is a flowchart of uplink channel estimation in a self-adaptive MIMO-OFDMA system according to an embodiment of the present invention. In this embodiment, the OFDMA system is assumed to be a self-adaptive multiple-input multiple-output orthogonal frequency division multiple access (MIMO-OFDMA) system. In the MIMO system, by arranging a plurality of antennas on both sides of transmission and reception, the capacity of the radio communication system can be doubled without increasing the signal frequency spectrum bandwidth. Self-adaptive MIMO-OFDMA systems are generally applied to quasi-static or slow fading environments. In the system, the base station can dynamically allocate channel resources based on the channel conditions of each user. That is, the number of subcarriers and the number of antennas used for each user are all dynamically variable. In order to achieve full dimension self-adaptation, the base station needs to know the complete frequency domain channel response of all antennas in all active users.

  As shown in FIG. 4, uplink channel estimation in the self-adaptive MIMO-OFDMA system according to the present invention includes the following steps.

  In step 401, subcarriers in pilot symbols are grouped for user u, where the number of pilot subcarrier groups and the number of pilot symbols in user u are variable and within each pilot subcarrier group of user u. The number of subcarriers is the same.

Here, first, subcarriers in pilot symbols are grouped for each user's channel condition, for example, the maximum multipath delay time, and among them, a subcarrier grouping method for different pilot symbols in the same user Are the same. That is, N subcarriers of the same size

Divided into individual groups, the number of subcarriers in each group

Is to do. Among them, the number of pilot symbols and the number of subcarrier groups

Are all dynamically variable.

  In step 402, pilot subcarriers are selected within a corresponding subcarrier group for each antenna for each user.

  Here, a pilot subcarrier is selected based on whether the base station has information on the user channel. When the base station has no information about the user channel in advance, it randomly selects one pilot subcarrier within each subcarrier group for each antenna at user u and does not even overlap with the pilot subcarrier of the antenna at the current user I can guarantee it. When the base station has information about the user channel, the base station selects one pilot subcarrier within each subcarrier group for each antenna at user u based on the distribution of narrowband interference. The channel estimation performance is enhanced by avoiding selecting pilot subcarriers at the position of narrowband interference as much as possible on the premise of ensuring that they do not overlap with the pilot subcarriers of the antenna of the current user.

In step 403, LS channel estimation is performed for the pilot position of antenna k at user u,

Obtain LS channel estimation results at pilot positions, where the range of k is

And

Is the number of antennas for user u,

Is the number of subcarrier groups in the u th user, and

Is a power of 2.

In step 404,

Map the LS channel estimation results at one pilot position into one OFDM symbol,

And

Where t is a time domain variable and

n is a frequency domain variable

N is the number of subcarriers of the OFDM symbol, and P is the number of pilot symbols.

  In step 405, it is determined whether the number of subcarrier groups is larger than the minimum value of the number of groups, and when the number of subcarrier groups is larger than the minimum value of the number of groups, step 406 and the subsequent steps are executed. When the number of groups is less than or equal to the minimum number of groups, step 409 and subsequent steps are executed.

In step 406,

Channel estimation at the first subcarrier position in each subcarrier group by interpolating the LS channel estimate at the pilot position

And

  Here, any interpolation calculation can be performed on the LS channel estimation value, and it is preferable to employ linear interpolation calculation.

Obtained by performing interpolation in step 407

LS channel estimation at the first subcarrier position in one subcarrier group

Against

Time domain channel impulse response estimation of antenna k at user u by performing IFFT transform of points

And

In step 408,

Truncate to zero padding

And

Perform an N-point FFT on the complete frequency domain channel response of antenna k at user u

Get.

In step 409,

Interpolate the LS channel estimation results at the pilot positions of to obtain the full frequency domain channel response of antenna k at user u, where

Is the minimum number of pilot subcarrier groups in the u-th user.

  Here, also in step 409, an arbitrary interpolation calculation can be performed on the LS channel estimation result, and similarly, a linear interpolation calculation is preferably employed.

  What should be explained in particular is as follows. The present invention applies not only to OFDMA systems, but also to single carrier frequency using discrete Fourier transform (DFT) and inverse discrete Fourier transform (IDFT) modules at the transmitter and frequency domain equalization (FDE) modules at the receiver The same applies to division multiple access (SC-FDMA) systems.

  The above are only preferred embodiments of the present invention and do not limit the protection scope of the present invention. Various modifications, equivalent switching, improvements and the like made within the spirit and principle of the present invention should all be included in the protection scope of the present invention.

FIG. 6 is a diagram illustrating grouping of pilot subcarriers according to an embodiment of the present invention. FIG. 6 is a diagram of selecting pilot subcarriers within a corresponding subcarrier group for each antenna for each user according to an embodiment of the present invention. FIG. 6 is a comparison of related prior art with selecting pilot subcarriers within a corresponding subcarrier group for each antenna at each user according to an embodiment of the present invention; 4 is a flowchart of uplink channel estimation in a self-adaptive MIMO-OFDMA system according to an embodiment of the present invention.

Claims (15)

A pilot subcarrier grouping method in an orthogonal frequency division multiple access OFDMA system, comprising:
For user u, subcarriers in pilot symbols are grouped, where the number of pilot subcarrier groups in user u and the number of pilot symbols are all variable, and the subcarriers in each pilot subcarrier group in user u are variable. The number of carriers is the same,
Where u ranges from 1 to U, U is the total number of users in the OFDMA system,
This method characterized by that.   The method of claim 1, wherein the maximum number of pilot symbols decreases when the maximum Doppler [0] frequency shift of a radio channel increases in the OFDMA system.   The method of claim 1, wherein the number of pilot symbols is increased when the number of users and / or the number of antennas that need to be supported simultaneously in the OFDMA system increases.   The method of claim 1, wherein the number of pilot symbols is reduced when frequency spectrum efficiency needs to be increased in the OFDMA system. The number of pilot symbols is P, and the minimum number of pilot symbols is
And the maximum number of pilot symbols is
And the maximum Doppler [0] frequency shift of the radio channel in the OFDMA system is
And the range of P is
The method of claim 1, wherein: Maximum multipath delay time for user u
The minimum number of pilot subcarrier groups for the user u
Increase, and
And
The method of claim 1, wherein is a power of two.   The method of claim 1, wherein when the number of users and / or antennas that need to be supported simultaneously in the OFDMA system increases, the number of pilot subcarrier groups for each user is reduced.   The method of claim 1, wherein the higher the accuracy requirement for radio channel estimation, the larger the number of pilot subcarrier groups for each user. here,
Is the maximum multipath delay time of the u th user,
Is the minimum number of pilot subcarrier groups in the u th user,
Is the maximum number of pilot subcarrier groups in the u th user,
Is the number of subcarrier groups in the u th user, and
Is a power of 2,
N is the number of subcarriers in the OFDM symbol,
The method according to claim 1.   The method of claim 1, further comprising selecting one pilot subcarrier within each subcarrier group belonging to the same or different pilot symbols for each antenna at user u.   When the base station has no information about the user channel in advance, one pilot subcarrier is randomly selected in each subcarrier group belonging to the same or different pilot symbol for each antenna in user u, and the other in this user 11. The method according to claim 10, wherein the same pilot subcarrier as that of the antenna or the antenna of another user is not selected.   When the base station has information about the user channel, one pilot subcarrier in a position where there is no narrowband interference or where the narrowband interference is weak in each subcarrier group belonging to the same or different pilot symbol for each antenna in user u 11. The method according to claim 10, characterized in that a condition not to select the same pilot subcarriers as other antennas for the user and antennas for the other user should be satisfied. Perform LS channel estimation for pilot position of antenna k at user u,
Obtain LS channel estimation results at pilot positions, where the range of k is
And
Is the number of antennas for user u,
Is the number of subcarrier groups in the u th user, and
Is step A, which is a power of 2, and
Map the LS channel estimation results at one pilot position into one OFDM symbol,
And
,here,
N is the number of subcarriers of the OFDM symbol, P is the number of pilot symbols, t is a time domain variable, n is a frequency domain variable, step B,
When
Complete frequency domain channel response of antenna k at user u by interpolating the LS channel estimation results at the pilot positions of
Where
Is step C, which is the minimum number of pilot subcarrier groups in the u th user,
The method of claim 10, further comprising: Perform LS channel estimation for pilot position of antenna k at user u,
Obtain LS channel estimation results at pilot positions, where the range of k is
And
Is the number of antennas for user u,
Is the number of subcarrier groups in the u th user, and
Is step A, which is a power of 2, and
Map the LS channel estimation results at one pilot position into one OFDM symbol,
And
here,
N is the number of subcarriers of the OFDM symbol, P is the number of pilot symbols, t is a time domain variable, and n is a frequency domain variable, step B;
When
Channel estimation at the first subcarrier position in each subcarrier by interpolating the LS channel estimate at the pilot position
And
Step C is
Obtained by interpolation
Channel estimation at the first subcarrier position in one subcarrier group
Against
Perform channel inverse fast Fourier transform IFFT to estimate channel impulse response in time domain of antenna k at user u
And
Step D is
Truncate to zero padding
Step E to get
Perform N-point fast Fourier transform FFT on the complete frequency domain channel response of antenna k at user u
Step F to get
The method of claim 10, further comprising:   15. The method according to claim 13, wherein the interpolation operation is a linear interpolation operation.