KR101730730B1 - OFDM System and Method for power allocation using the same - Google Patents

Abstract

The present invention relates to an OFDM system and a power allocation method using the same.
According to an OFDM system and a power allocation method using the OFDM system according to the present invention, in a power allocation method of an OFDM system including a receiving end and a transmitting end using multiple antennas, the transmitting end and the receiving end calculate a weight and bit information on a channel state as a codebook Receiving a training signal from the receiving terminal; receiving, by the transmitting terminal, a training signal from the receiving terminal; receiving feedback information on bit information according to a channel state of each of a plurality of subcarriers included in the training signal from the receiving terminal; Allocating power by applying a weight corresponding to the bit information, and transmitting data through the reallocated power for each subchannel corresponding to the subcarrier group.
According to the present invention, feedback information is generated based on a codebook, and power is allocated differently for each subcarrier group according to channel conditions, thereby improving reliability and unnecessary overhead in a wireless communication system experiencing a wireless channel environment.

Description

[0001] OFDM SYSTEM AND POWER ALLOCATION METHOD USING THE SAME [0002]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an OFDM system and a power allocation method using the OFDM system. More particularly, the present invention relates to an OFDM system for reallocating power according to feedback information indicating a channel state in a wireless communication environment and a power allocation method using the same.

In recent wireless communication systems, high transmission rate and reliability are required in the proposed power and bandwidth. Accordingly, a MIMO-OFDM system combining OFG (Orthogonal Frequency Division Multiplexing) technology with high band efficiency and MIMO (Multiple-Input Multiple-Output) wireless technology system capable of improving data rate is used.

In a wireless communication environment, distortion and attenuation of a transmission signal occur due to multipath fading. In this case, distortion and attenuation of the signal cause difficulty in restoring the original signal at the receiving end.

The easiest way to overcome this difficulty is to increase the transmission power of the system. However, since systems such as LTE (Long Term Evolution) and Wi-Fi (Wireless Fidelity) There is a limit to heightening.

That is, since reliability is secured as a system while using limited power, a method of reallocating power according to the channel state is used.

At this time, it is necessary to use feedback information in order to grasp the channel information. Although it is possible to know a lot of channel information by sending a lot of feedback information from the receiving end to the transmitting end, it can reduce the transmission rate of the channel by generating overhead in communication.

Therefore, a technique of grouping adjacent subcarriers and allocating power according to channel information for each subcarrier group using a codebook including channel information and a weight is required in order to minimize feedback information.

The technology to be a background of the present invention is disclosed in Korean Patent No. 10-1024510 (published on Mar. 31, 2011).

SUMMARY OF THE INVENTION The present invention provides an OFDM system for reallocating power according to feedback information indicating a channel state in a wireless communication environment and a power allocation method using the OFDM system.

According to an aspect of the present invention, there is provided a method of allocating power in an OFDM system including a receiving end and a transmitting end using multiple antennas, the transmitting end and the receiving end including weight and bit information for a channel state, Receiving a training signal from the receiving terminal; receiving, by the transmitting terminal, a training signal from the receiving terminal; receiving feedback information on bit information according to a channel state of each of a plurality of subcarriers included in the training signal from the receiving terminal; Allocating power by applying a weight corresponding to the bit information, and transmitting data through the reallocated power for each subchannel corresponding to the subcarrier group.

The bit information is made up of N bits, and the codebook is grouped by dividing a maximum value and a minimum value of a predetermined channel state into ^2N groups, and a reciprocal of a median value of the corresponding group is selected as the weighting factor .

Wherein the receiver measures the SINR while receiving the training signal and feeds back bit information using the codebook with N = 3 if the SINR is lower than the reference value, and if the SINR is equal to or greater than the reference value, So that bit information can be fed back.

The step of reallocating the power may reallocate the normalized power value (W _i ) to each corresponding subcarrier through the following equation.

는 i번째 서브캐리어에 대응하는 가중치(weighting factor)를 나타낸다. Here, FFTSize is the total number of subcarriers, P (N _i ) is the transmission power before allocation of the i-th subcarrier, P (N _c ) is the total transmission power,

Represents a weighting factor corresponding to the i-th subcarrier.

The training signal Y can be expressed by the following equation.

Here, N _c is the sub-channel, Nn is the n-th Gaussian corresponding to the total number, w _n is an n-normalization factor, X _n is an n th subcarrier of the second sub-carrier symbols, Hn is the n-th subcarrier of the subcarriers It represents noise.

According to another embodiment of the present invention, in an OFDM system including a receiving end and a transmitting end using multiple antennas, the transmitting end includes a codebook storage for storing weight values and bit information for channel states in the form of a codebook, And a receiver for receiving the feedback information from the receiver and for receiving the bit information according to a channel state for each of a plurality of subcarriers included in the training signal, And the communication unit transmits data through the reallocated power for each subchannel corresponding to the subcarrier group.

According to the present invention, feedback information is generated based on a codebook, and power is allocated differently for each subcarrier group according to channel conditions, thereby improving reliability and unnecessary overhead in a wireless communication system experiencing a wireless channel environment.

1 is a diagram for explaining OFDM communication between a receiving end and a transmitting end using multiple antennas according to an embodiment of the present invention.
2 is a diagram for explaining grouping of adjacent subchannels in an OFDM system according to an embodiment of the present invention.
3A and 3B are diagrams illustrating a 3-bit codebook and a 4-bit codebook according to an embodiment of the present invention.
4 is a configuration diagram illustrating a transmitting terminal according to an embodiment of the present invention.
5 is a flowchart illustrating a process of reallocating power in a transmitter according to an embodiment of the present invention.
6A and 6B are diagrams illustrating the bit error probability of the SISO-OFDM scheme, the conventional scheme, the MIMO-OFDM scheme, and the conventional scheme, among the embodiments of the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings, which will be readily apparent to those skilled in the art. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. In order to clearly illustrate the present invention, parts not related to the description are omitted, and similar parts are denoted by like reference characters throughout the specification.

Throughout the specification, when an element is referred to as "comprising ", it means that it can include other elements as well, without excluding other elements unless specifically stated otherwise.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily carry out the present invention.

1 is a diagram for explaining OFDM communication between a receiving end and a transmitting end using multiple antennas according to an embodiment of the present invention.

In FIG. 1, a transmitter and a receiver receive a training signal (training signal) and estimate the state of the channel. At this time, each channel is independent and remains static until the next transmission is transmitted I suppose.

First, a transmitting terminal performs power control of data to be transmitted on a bit-by-bit basis and transmits the data to a receiving end using several antennas.

Upon receipt of the signal, the receiving end confirms the channel state, generates feedback information based on the promised codebook information in advance, and transmits the generated feedback information to the transmitting end.

The feedback information includes information on a variable modulation technique according to the state of the channel. Therefore, the receiving end transmits the feedback information to the transmitting end. The transmitter that receives the feedback information reallocates the power according to the channel state in the variable modulation block.

2 is a diagram for explaining grouping of adjacent subchannels in an OFDM system according to an embodiment of the present invention.

2 is a graph showing the amplitudes of adjacent subchannels in an OFDM system. At this time, if we look at the shape of the graph, the amplitude at n-1, n, n + 1 has a similar value at n + 100. That is, it can be seen that adjacent subcarriers have values of channel amplitudes similar to those of non-adjacent subcarriers. Therefore, as shown in FIG. 2, adjacent subcarriers having similar channel amplitude values are grouped into the same group (A, B, C, D,?, N, M) .

Here, the range of values of the similar channel amplitudes can be easily changed by the manager later according to the amplitude type of the subchannels, and the adjacent subcarriers having the value of the channel amplitude included in the set range can be grouped into the same group have.

By grouping the subcarriers as described above, feedback information for grasping channel information can be minimized accordingly, so that sufficient feedback information can be transmitted while reducing the incidence of overhead in communication.

The channel state described below includes the amplitude of the channel. For convenience of explanation, the state value of the channel is used in the same meaning as the amplitude value of the channel.

Hereinafter, a codebook shared by a transmitter and a receiver according to an embodiment of the present invention will be described with reference to FIGS. 3A and 3B. FIG.

FIG. 3A is a diagram illustrating a 3-bit codebook according to an embodiment of the present invention, and FIG. 3B is a diagram illustrating a 4-bit codebook.

For convenience of explanation, in FIGS. 3A and 3B, it is assumed that the minimum amplitude value of the channel is 0 and the maximum amplitude value is 2.5.

First, a codebook is composed of a pre-appointment between a transmitting end and a receiving end. Since the minimum amplitude value of the channel is 0 and the maximum amplitude value of the channel is a random value, a value corresponding to 99% of CDF (Cumulative Distribution Function) is determined through simulation.

The codebook is divided into 2 ⁿ parts according to n bits, and the weighting factor for allocating the power of the codebook is determined by the reciprocal of the median value of the range of the channel.

That is, a small power is allocated to a subcarrier having a good channel state, and a high power is allocated to a subcarrier having a poor channel state, thereby flattening the channel state.

Such a codebook may be generated at the receiving end, and the receiving end may transmit at least one generated codebook to the transmitting end to share. At this time, the transmitter may generate a codebook and transmit the codebook to the receiver.

After sharing and storing the codebook, the receiving end generates the feedback information based on the codebook through the training signal received from the transmitting end.

For example, assuming that the channel state value of the training signal is 1.35 Amplitude, the receiver first determines that the amplitude of the channel is within the range of the codebook, and determines the feedback value.

3A, when the 3-bit codebook is used, the channel state value 1.35 is in the minimum and maximum range of the channel, the corresponding weighting factor is 0.7692 and the bits are 010. If a 4-bit codebook is used as shown in FIG. 3B, The weighting factor corresponding to the channel amplitude of 1.35 is 0.7477 and the bits are 0010.

At this time, the feedback information sent from the receiving terminal indicates bit values (010) in the case of 3 bits and 0010 in the case of 4 bits.

If the receiving end transmits the feedback information including the value of bits to the transmitting end, the transmitting end knows the weighting factor based on the shared codebook and reallocates power to the data accordingly.

If the SINR is equal to or greater than the reference value, the receiving end measures the SINR while receiving the training signal. If the SINR is less than the reference value, Can be fed back.

That is, if the channel state is bad, a 3-bit codebook having a relatively wide channel state interval per group can be selected to transmit data more accurately. If the channel state is good, a high transmission rate is maintained even if the channel is finely divided. A codebook of 4 bits having a relatively narrow channel state interval can be selected.

Thus, the selection of the N-bit codebook can be variably selected depending on the channel state.

4 is a configuration diagram illustrating a transmitting terminal according to an embodiment of the present invention.

The transmission terminal 100 includes a codebook storage unit 110, a communication unit 120, and a power allocation unit 130.

The codebook storage unit 110 stores weight values and bit information for channel states in the form of a codebook.

At this time, the bit information consists of N bits and stores at least one codebook according to each bit information.

The codebook storage unit 110 receives the results of the simulation with the receiving end through the communication unit 120, and can generate and store the same codebooks through the same method. The codebook generated at the receiving end is received through the communication unit 120 and stored .

The communication unit 120 transmits the training signal to the receiving end and receives feedback information on the bit information according to the channel state for each of a plurality of subcarriers included in the training signal from the receiving end.

Then, the communication unit 120 transmits the data through the reallocated power from the power allocation unit 130 for each subchannel corresponding to the subcarrier group.

The power allocation unit 130 re-allocates power by applying a weight through a pre-stored codebook corresponding to the corresponding bit information for each of a plurality of sub-carrier groups.

5 is a flowchart illustrating a process of reallocating power in a transmitter according to an embodiment of the present invention.

Hereinafter, it is assumed that the process of generating the codebook described above is omitted and the receiving end stores the same codebook as the transmitting end.

First, the transmitting terminal 100 stores weight values and bit information for channel states in a codebook form (S510).

In this case, the codebook can be generated as shown in FIGS. 3A and 3B, and can be received and stored in the receiving terminal in the same way as the codebook stored by the receiving end.

Next, the transmitting terminal 100 transmits the training signal to the receiving terminal (S520).

Here, the training signal Y can be expressed by the following equation (1).

Here, N _c is the sub-channel, Nn is the n-th Gaussian corresponding to the total number, w _n is an n-normalization factor, X _n is an n th subcarrier of the second sub-carrier symbols, Hn is the n-th subcarrier of the subcarriers It represents noise.

The transmitting terminal 100 receives bit information according to channel conditions for each of a plurality of subcarriers included in the training signal from the receiving terminal (S530). When the transmitter 100 receives the bit information, it can check the weights and the channel amplitudes of the subcarriers inversely through the codebook.

The transmitting terminal 100 re-allocates power by applying a weight corresponding to the corresponding bit information for each of a plurality of subcarrier groups (S540).

At this time, the transmitting end 100 can re-allocate the normalized power value W _i to each corresponding subcarrier through Equation (2).

는 i번째 서브캐리어에 대응하는 가중치(weighting factor)를 나타낸다. Here, FFTSize is the total number of subcarriers, P (N _i ) is the transmission power before allocation of the i-th subcarrier, P (N _c ) is the total transmission power,

Represents a weighting factor corresponding to the i-th subcarrier.

As described above, according to the embodiment of the present invention, reliability can be improved by allocating power differently for each subcarrier within the power available through normalization.

The transmitting terminal 100 transmits the data through the reallocated power for each subchannel corresponding to the subcarrier group (S550).

Hereinafter, the bit error probability difference between the OFDM system and the conventional system according to the embodiment of the present invention will be described with reference to FIGS. 6A and 6B.

6A and 6B are diagrams illustrating the bit error probability of the SISO-OFDM scheme, the conventional scheme, the MIMO-OFDM scheme, and the conventional scheme, among the embodiments of the present invention.

Here, the conventional technique is a method of transmitting data without feedback information, which indicates a method of allocating the same power to all subcarriers without considering the channel state.

First, in FIG. 6A, the FFT size is 256, the QPSK scheme is used, the Rayleigh channel and the 3-bit codebook are used for the wireless channel.

FIG. 6A is a graph illustrating a bit error rate (BER) for an SISO-OFDM scheme and an SNR (dB) of an existing scheme in an embodiment of the present invention. In the proposed SISO-OFDM method according to the embodiment of the present invention, a group (4) of four subcarriers, a group of sixteen subcarriers, a group of 32 subcarriers, (□), respectively, into 2 ⁿ subcarrier groups.

)보다 SNR(dB)의 값이 커질수록 비트 오류 확률(BER)이 낮은 것을 알 수 있다.Referring to the graph of FIG. 6A, the techniques proposed in the embodiment of the present invention (*,?,?,?

, The bit error probability (BER) is lower as the value of SNR (dB) becomes larger.

In addition, it can be seen that the BER performance is improved as the grouping of 32, 16, and 4 is smaller than that of grouping 64 subcarriers. Particularly, in the case of grouping four subcarriers as in the embodiment of the present invention (*), a gain of 5 dB SNR is obtained compared with the conventional method.

Next, FIG. 6B shows a BER graph between the MIMO-OFDM scheme proposed in the present invention and the conventional scheme. In FIG. 6, the FFT size is 256, 16QAM, and the radio channel is a Rayleigh channel and a 4-bit codebook.

In the technique proposed in the embodiment of the present invention, a group (2) is divided into two subcarriers, a group (4) is divided into four subcarriers, and a group (□) is divided into 8 subcarriers.

) 보다 SNR(dB)의 값이 커질수록 비트 오류 확률(BER)이 낮은 것을 알 수 있다.6B, the techniques proposed in the embodiment of the present invention (,,,,))

, The bit error probability (BER) is lower as the value of SNR (dB) becomes larger.

In particular, each subcarrier (,,)) grouped into 8 and 4 does not show a larger performance difference than the conventional scheme as the SNR increases. However, the subcarriers grouped by 2 have a SNR gain of about 3 dB .

According to the embodiment of the present invention, feedback information is generated based on a codebook, and power is allocated differently for each subcarrier group according to channel conditions, thereby improving reliability and reducing unnecessary overhead in a wireless communication system experiencing a wireless channel environment have.

While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. Accordingly, the true scope of the present invention should be determined by the technical idea of the appended claims.

100: Transmitter 110: Codebook storage
120: communication unit 130: power allocation unit

Claims (10)

In a power allocation method of an OFDM system including a receiving end using a multiple antenna and a transmitting end
The transmitter and receiver may store the weight and the bit information of the channel state in the form of a codebook,
The transmitting end transmits a training signal to the receiving end,
Receiving, from the receiving end, bit information according to a channel state for each of a plurality of subcarriers included in the training signal;
Allocating power by applying a weight corresponding to the corresponding bit information for each of a plurality of subcarrier groups, and
And transmitting data through the reallocated power for each subchannel corresponding to the subcarrier group,
The bit information is composed of N bits,
Wherein the codebook is grouped by dividing a maximum value and a minimum value of a predetermined channel state into ^2N groups and a reciprocal of a median value of the group is selected as the weighting factor. delete The method according to claim 1,
The receiver measures the SINR while receiving the training signal,
And if the SINR is less than the reference value, feeds back bit information using the codebook having N = 3 and feeds back bit information using the codebook having N = 4 if the SINR is equal to or greater than the reference value. The method according to claim 1,
The step of reallocating the power comprises:
A power allocation method of an OFDM system for reallocating normalized power values (W _i ) to respective subcarriers using the following equation:

Here, FFTSize is the total number of subcarriers, P (N _i ) is the transmission power before allocation of the i-th subcarrier, P (N _c ) is the total transmission power,

Represents a weighting factor corresponding to the i-th subcarrier. The method according to claim 1,
Wherein the training signal (Y) comprises a power assignment method of an OFDM system comprising:

Here, N _c is the sub-channel, Nn is the n-th Gaussian corresponding to the total number, w _n is an n-normalization factor, X _n is an n th subcarrier of the second sub-carrier symbols, Hn is the n-th subcarrier of the subcarriers It represents noise. In an OFDM system including a receiving end using multiple antennas and a transmitting end
The transmitting end transmits,
A codebook storage unit for storing weight values and bit information for channel states in a codebook form,
A communication unit for transmitting a training signal to the receiving end and feedbacking bit information according to channel conditions for each of a plurality of subcarriers included in the training signal from the receiving end;
And a power allocator for allocating power by applying a weight corresponding to the corresponding bit information for each of a plurality of subcarrier groups,
Wherein,
Data is transmitted through the re-allocated power for each sub-channel corresponding to the sub-carrier group,
The bit information is composed of N bits,
Wherein the codebook is grouped by dividing a maximum value and a minimum value of a predetermined channel state into ^2N groups and a reciprocal of a median value of the group is selected as the weighting factor. delete The method according to claim 6,
The receiver measures the SINR while receiving the training signal,
And feedback the bit information using the codebook with N = 3 if the SINR is lower than the reference value, and feed back bit information using the codebook with N = 4 if the SINR is equal to or greater than the reference value. The method according to claim 6,
The step of reallocating the power comprises:
An OFDM system for reallocating normalized power values (W _i ) to respective subcarriers through the following equation:

Here, FFTSize is the total number of subcarriers, P (N _i ) is the transmission power before allocation of the i-th subcarrier, P (N _c ) is the total transmission power,

Represents a weighting factor corresponding to the i-th subcarrier. The method according to claim 6,
The training signal (Y) is an OFDM system comprising:

Here, N _c is the sub-channel, Nn is the n-th Gaussian corresponding to the total number, w _n is an n-normalization factor, X _n is an n th subcarrier of the second sub-carrier symbols, Hn is the n-th subcarrier of the subcarriers It represents noise.

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