KR20090119156A - A power allocation scheme of sub-carriers over interference for down-link ofdma system - Google Patents

Abstract

PURPOSE: A method of allocating power a downlink sub carrier due to interference in a downlink OFDMA(Orthogonal Frequency Division Multiple Access) system is provided to induce an unequal environment of interference when interference due to another adjacent user is large at a cell boundary or in a wireless communication system, thereby improving receiving performance. CONSTITUTION: A base station produces an interference value about each subscriber terminal(S10). A cell interference value in a sub carrier about frames is distributed(S20). The frames include a current frame. The frames are frames in a section corresponding to a size of a sliding window. A pseudo random pattern is generated to make unequal power of the carrier. Power due to the generated pseudo random pattern is allocated to the sub carrier(S30). Each terminal performs SINR(Signal to Interference and Noise Ratio) weighting through interference estimation(S40).

Description

A Power Allocation Scheme of Sub-carriers over Interference for Down-link OFDMA System

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to cellular systems or wireless communication systems that have a lot of interference, and in particular, broadband wireless communication systems such as orthogonal frequency division multiple access (OFDMA) systems. The present invention relates to a method for mitigating interference between co-channels by neighboring cells.

In a cellular environment, Orthogonal Frequency Division Multiple (OFDM) transmission scheme maintains orthogonality between subcarriers and has a strong advantage in intra-cell interference, but when using a frequency reuse factor of 1, Intercell interference of a cell can be very large in the cell overlap region. Therefore, many researches have been conducted on techniques for mitigating, avoiding, and eliminating the effects of co-channel interference from adjacent cells.

However, the ongoing interference cancellation technique is burdened by estimating the channel of the signal from the adjacent cell as well as the channel of the cell to which the UE belongs, and it is difficult to effectively remove the interference when the interference comes from several cells.

That is, in an OFDMA system that does not estimate the interference from neighboring cells, if the amount of interference is unknown, a method of averaging the amount of interference on a subcarrier is used, which is suitable for an environment without power control. As an effect of averaging inter-cell interference, FH-OFDMA Frequency Hopping-Orthogonal Frequency Division Multiple Access (FH) technology is in the spotlight. However, when there are many terminals having different powers at cell boundaries, the interference between cells becomes uneven, and thus there is a disadvantage in that the method of averaging does not function properly.

Accordingly, the present invention has been made to solve the above problems, and improves reception performance by inducing a non-uniform environment of interference when the interference from a cell boundary or other adjacent users is large in a cellular system or a wireless communication system with a lot of interference. An object of the present invention is to provide a downlink subcarrier power allocation method according to interference in an OFDMA system that can be implemented.

Another object of the present invention is to allocate the power according to the pseudorandom pattern allocated based on the calculated neighbor cell interference to induce an uneven environment, thereby reducing the interference between the same channel by adjacent cells. A downlink subcarrier power allocation method is provided.

It is still another object of the present invention to induce an uneven environment of interference to create an interference environment using a predetermined pseudorandom pattern, thereby reducing the algorithm and complexity of accurate interference estimation and reducing the overhead of power control. To provide a downlink sub-carrier power allocation method according to the.

In the OFDMA system according to the present invention for achieving the above object, the downlink subcarrier power allocation method according to the interference is characterized by an Orthogonal Frequency Division Multiple Access (OFDMA) system using a frequency reuse factor of 1 and A method for mitigating interference between same channels by adjacent cells in the same broadband wireless communication system, the method comprising: (A) a base station calculating an interference value received by each subscriber station based on signals received from each subscriber station in every slot in each frame (B) dispersing cell interference values on subcarriers for frames of a section corresponding to the size of the sliding window, including the current frame, based on the calculated neighbor cell interference; and (C) Based on the distributed interference value, a pseudo random pattern is generated to have an uneven shape of power of subcarriers. (D) allocating power of the generated pseudo random pattern to subcarriers, and (E) each terminal is used for interference estimation by using a subcarrier allocated with a pseudo random pattern transmitted from the base station. And performing a Signal to Interference and Noise Ratio (SINR) weighting through this.

Preferably, the step (A) is characterized by calculating the difference between neighbor subcarriers from the signals received from each terminal to calculate the interference value of the neighbor cell.

Preferably, the pseudo random pattern of step (D) is generated as a pattern for allocating a large power to a terminal having a small interference value and a small power to a terminal having a large interference value.

Another feature of the downlink subcarrier power allocation method according to interference in the OFDMA system according to the present invention for achieving the above object is an Orthogonal Frequency Division Multiple Access (OFDMA) system using a frequency reuse factor of 1 A method of mitigating interference between co-channels by adjacent cells in a broadband wireless communication system, the method comprising: generating a pseudo random pattern using a predetermined random pattern such that power of subcarriers is uneven; Allocating power of the generated pseudo random pattern to subcarriers, each terminal is used for interference estimation by using a subcarrier allocated with a pseudo random pattern transmitted from the base station and through this signal to interference and noise ratio (SINR) Performing weighting.

을 사용하여 랜덤하게 수행하여 산출하는 것을 특징으로 한다.(이때 x : 간섭전력이다.)Preferably the random pattern is a conditional expression

It is characterized by calculating by performing randomly using (where x is the interference power).

In the OFDMA system according to the present invention as described above, the downlink subcarrier power allocation method due to interference has the following effects.

First, when the interference caused by the cell boundary of the cellular system or other adjacent users in the wireless communication system is large, there is an effect that can improve the reception performance by inducing an uneven environment of interference.

Second, by allocating power of a pseudo random pattern based on adjacent cell interference, which is calculated as the transmission power of the subcarriers, to the subcarriers, interference between the same channels by adjacent cells can be mitigated.

Third, by allocating the transmission power of the subcarriers by using a predetermined pseudo random pattern, the predetermined pattern can be used for interference estimation, and the diversity gain can also be obtained rather than averaging the interference.

Fourth, the received information can be improved by the channel compensation through the Signal to Interference and Noise Ratio (SINR) weighting.

Other objects, features and advantages of the present invention will become apparent from the following detailed description of embodiments with reference to the accompanying drawings.

A preferred embodiment of a downlink subcarrier power allocation method according to interference in an OFDMA system according to the present invention will be described with reference to the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but can be implemented in various different forms, only the embodiments to complete the disclosure of the present invention and complete the scope of the invention to those skilled in the art. It is provided to inform you.

First Example

1 is a flowchart illustrating a downlink subcarrier power allocation method due to interference in an OFDMA system according to a first embodiment of the present invention.

Referring to FIG. 1, in a cellular system or a high interference environment using frequency reuse coefficient 1, first, an interference value received by each subscriber station based on signals received from each subscriber station in all slots in each frame is determined. It calculates (S10). In this case, as the method of calculating the interference value, various methods such as a modulation method and channel coding such as a method of directly calculating data or a method of calculating a preamble may be used. For example, the difference between neighbor subcarriers is obtained from the signals received from each subscriber station to calculate the interference value of the neighbor cell.

Subsequently, cell interference values on subcarriers for the frames corresponding to the size of the sliding window including the current frame are distributed based on the calculated neighbor cell interference (S20). For example, if the current frame is the i + 3 th frame and the sliding window size is “3 frames”, three previous frames including the current frame i + 3 th frame, that is, the i + 3 th frame, i + 2 Distribute the interference value on the subcarrier for the 1 st frame and the i + 1 th frames.

Based on the distributed interference value, a pseudo random pattern is generated to have an uneven form of power of the subcarrier, and the power according to the generated pseudo random pattern is allocated to the subcarrier (S30). In this case, it is preferable that the generated pseudo random pattern allocates a large power to a terminal having a small interference value and allocates a small power to a terminal having a large interference value.

Each terminal uses this information transmitted from the base station to use the interference estimation and through this performs a Signal to Interference and Noise Ratio (SINR) weighting (S40).

2nd Example

In the first embodiment, when generating a pseudo random pattern, the neighbor cell interference value is calculated and the pseudo random pattern is generated such that the power of the subcarriers is uneven based on the calculated neighbor cell interference value. In the second embodiment, when generating a pseudo random pattern, the power of the subcarriers is uneven using a predetermined random pattern.

2 is a block diagram illustrating a downlink subcarrier power allocation method due to interference in an OFDMA system according to a second embodiment of the present invention.

Referring to FIG. 2, first, a pseudo random pattern generated by a pseudo random pattern (PRP) generator 20 in a cellular system or a high interference environment using frequency reuse coefficient 1 is applied to each cell and each user (terminal). To generate the power of the subcarrier. At this time, each cell or users 10 has a unique assignment value α such as its cell number.

Subsequently, a pseudo random pattern (PRP (n)) generated by the pseudo random generator 20 is combined with the power generated by the power generator 30 according to a unique allocation value for each cell, thereby corresponding to each cell or each user. The subcarrier power is transmitted by increasing the power difference of the subcarriers according to the interference.

In this case, as shown in FIG. 4, the pseudo random generator 20 sums the interference power x from 1 using Equation 1 as a conditional expression of a predetermined pattern h [n] through the pseudo random generator 20. By randomly calculating the difference between the two cells, the interference between each other in the same channel between adjacent cells is made uneven during transmission.

In this case, x is the interference power.

By using Equation 1, a pseudo random pattern for increasing a difference in transmission power of a subcarrier can be made various.

FIG. 5 is a diagram illustrating an embodiment according to power allocation of a subcarrier signal when the dispersion magnitude β of an interference signal is 0.5 through the structure of FIG. 2.

Referring to FIG. 5, when the average signal power of the subcarrier and the signal power of the interference are fixed to 1, the power of the signal can be allocated as follows by the dispersion magnitude of the interference. That is, it is possible to assign a probability of 1/2 = 1.7071 and a remaining probability of 1/2 = 0.2929.

In this case, the size of the allocated signal affects adjacent cells or users by assigning a signal size of interference as follows. That is, the probability is assigned to 1/2 probability = 1.7071 and the remaining 1/2 probability = 0.2929 to affect.

At this time, by using the pseudo-random pattern corresponding to the interference by varying the magnitude of the transmission power of the subcarrier, when looking at the size of the signal for interference, the probability that the signal is larger than the interference is 1/4, the probability is equal to 1/2.

As such, rather than allocating the same signal power of the subcarriers, the subcarrier signal may be allocated with a different size to correspond to the dispersion of interference, thereby improving reception performance.

In addition, if the channel size of the neighbor cell is known and the channel assignment can be performed accordingly, the performance of the neighbor cell can be further improved by adjusting the distribution of interference on the neighbor cell. That is, when channel allocation is performed in order to know the estimated channel value of the neighbor cell and maximize the performance of the neighbor cell, the performance of the neighbor cell can be maximized by allocating interference to the subcarrier having the smallest channel value.

As described above, when a pseudo random pattern that induces an uneven environment of interference between cells through a base station is allocated to subcarrier power and transmitted, each terminal uses this information transmitted from the base station to use for interference estimation and through this SINR. Signal to Interference and Noise Ratio weighting is performed (S40).

In this case, as shown in FIG. 3, each terminal can know information about its pseudo random pattern through the interference preamble signal 50 transmitted from the base station. Therefore, even if an accurate interference estimation is not made, if a pseudo random pattern PRP (n) corresponding to its own allocation value α is allocated using a pseudo random pattern estimate through the pseudo random pattern estimator 60, Signal to Interference and Noise Ratio (SINR) weighting is performed using this. If the estimated pseudo random pattern is not a pattern corresponding to the unique allocation value α of the corresponding terminal, the pseudo random pattern corresponding to the pseudo random pattern is stored using a pseudo random pattern lookup table in which a pseudo random pattern corresponding to the unique allocation value is stored in advance. Is detected and allocated to the transmit power of the subcarrier.

As a result, when the difference in the transmission power of subcarriers is increased and an uneven amount of interference becomes large, diversity gain can be obtained rather than averaging the interference, and through SINR weighting using interference estimation or pseudo random pattern information It can improve the received performance.

The magnitude of the signal power using the pseudo random pattern is compared with the average, compared with the average size of the signal allocated to a constant size in the Rayleigh Fading channel and the average of the signal allocated power using the pseudo random pattern. The magnitudes are 0.8822 and 0.7879, respectively, excluding the effects of Rayleigh fading, and the magnitudes of the signals are similar.

FIG. 6 is a graph showing a bit error rate (BER) performance according to a change in signal to noise ratio (SNR), and FIG. 7 is a graph showing a frame error rate according to a change in signal to noise ratio (SNR).

In other words, when the SNR is small, as shown in FIG. 6, if the interference is uneven due to a difference in transmission power, the higher the concentration of the specific subcarrier, the better the performance, and the higher the SNR, the higher the performance. As shown in FIG. 7, it can be seen that the frame error rate (FER) performance is excellent as the subcarrier power dispersion is increased.

As such, the present invention can improve the average SNR to maximize the frame error rate performance in a given channel environment.

Although the technical spirit of the present invention described above has been described in detail in a preferred embodiment, it should be noted that the above-described embodiment is for the purpose of description and not of limitation. In addition, those skilled in the art will understand that various embodiments are possible within the scope of the technical idea of the present invention. Therefore, the true technical protection scope of the present invention will be defined by the technical spirit of the appended claims.

1 is a flowchart illustrating a downlink subcarrier power allocation method due to interference in an OFDMA system according to a first embodiment of the present invention.

2 is a block diagram illustrating a downlink subcarrier power allocation method due to interference in an OFDMA system according to a second embodiment of the present invention.

FIG. 3 is a block diagram illustrating a process of estimating interference using pseudo random pattern information of a terminal in FIG. 2. FIG.

4 is a block diagram illustrating in detail the structure of the pseudo random generator of FIG.

FIG. 5 is a diagram illustrating an embodiment according to power allocation of a subcarrier signal when the dispersion magnitude of the interference signal is 0.5 through the structure of FIG.

6 is a graph showing the BER (Bit Error Rate) performance according to the SNR (Signal to Noise Ratio) change

7 is a graph illustrating frame error rates according to changes in signal to noise ratio (SNR).

* Explanation of symbols for main parts of the drawings

10: cell or user (terminal) 20: pseudo random pattern generator

30: power generator 40: combiner

50: interference preamble 60: pseudo random pattern estimator

70: Comparator 80: Pseudo Random Pattern Lookup Table

90: interference pseudo random pattern 100: SINR weighting

Claims (7)

In a broadband wireless communication system such as an orthogonal frequency division multiple access (OFDMA) system using a frequency reuse factor of 1, a method for mitigating interference between adjacent channels by adjacent cells, (A) a base station calculating an interference value received by each subscriber station based on signals received from each subscriber station in every slot in each frame; (B) dispersing cell interference values on subcarriers for frames of a section corresponding to the size of the sliding window, including the current frame, based on the calculated neighbor cell interference; (C) generating a pseudo random pattern such that the power of subcarriers has an uneven shape based on the distributed interference value; (D) a method for allocating downlink subcarrier power according to interference in an OFDMA system, comprising allocating power of the generated pseudo random pattern to subcarriers. Each terminal further uses the subcarrier to which the pseudo-random pattern transmitted from the base station is allocated for interference estimation, and performs SINR (Signal to Interference and Noise Ratio) weighting. A downlink subcarrier power allocation method according to interference in an OFDMA system. The method of claim 1, The method (A) of the downlink subcarrier power allocation method according to the interference in the OFDMA system, characterized in that for calculating the interference value of the adjacent cell by obtaining the differences between the adjacent subcarriers from the signals received from each terminal. The method of claim 1, The downlink subcarrier according to the interference in the OFDMA system, wherein the pseudo random pattern of step (D) is generated by assigning a large power to a terminal having a small interference value and a small power to a terminal having a large interference value. Power allocation method. In a broadband wireless communication system such as an orthogonal frequency division multiple access (OFDMA) system using a frequency reuse factor of 1, a method for mitigating interference between adjacent channels by adjacent cells, Generating a pseudo random pattern using a predetermined random pattern such that the power of the subcarriers is uneven; Allocating power of the generated pseudo random pattern to subcarriers; Each terminal is used for the interference estimation using a subcarrier assigned a pseudo-random pattern transmitted from the base station and through this perform a signal to interference and noise ratio (SINR) weighting (weighting) Downlink subcarrier power allocation method according to interference in the system. The method of claim 5, wherein The random pattern is a conditional expression

The downlink subcarrier power allocation method according to the interference in the OFDMA system, characterized in that it is performed by using a random. (X is the interference power) The method of claim 5, wherein The generated pseudo-random pattern is generated by assigning a large power to a terminal having a small interference value and a small power to a terminal having a large interference value. The downlink subcarrier power allocation method according to the interference in the OFDMA system, characterized in that it is generated. .

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