KR101091972B1 - Fast optimal discrete bit-loading method for ofdm-based systems - Google Patents

Abstract

The present invention relates to a modulation technique in an orthogonal frequency division multiplexing system (OFDM). More specifically, the present invention relates to a case where a transmission error deteriorates temporarily according to a situation in each channel of an orthogonal frequency division multiplexing system, thereby increasing a bit error rate. By quickly grasping and increasing the transmission in a channel with a good transmission environment, it is possible to satisfy the target data rate by applying the modulation technique in each channel quickly and selectively according to the situation of each channel even in the frequent change of the channel environment. The present invention relates to a channel-specific modulation scheme selection method for satisfying target data rates and energy constraints in an orthogonal frequency division multiplexing system.

OFDM, modulation, bit error rate, signal-to-noise ratio

Description

A method for selecting an optimal channel-by-channel modulation scheme that satisfies the target data rate and energy constraints in orthogonal frequency division multiplexing systems {FAST OPTIMAL DISCRETE BIT-LOADING METHOD FOR OFDM-BASED SYSTEMS}

The present invention relates to a modulation technique in an orthogonal frequency division multiplexing system (OFDM). In particular, when each channel environment of an orthogonal frequency division multiplexing system is changed, the modulation technique is applied to the changed channel environment to improve the transmission rate of the target data. The present invention relates to a method for selecting an optimal channel modulation method that satisfies target data rates and energy constraints in an orthogonal frequency division multiplexing system.

Orthogonal Frequency Division Multiplexing (OFDM) is a modulation scheme that multiplexes one frequency band into multiple orthogonal narrowband carriers, provided that there is a sufficiently large guard interval between consecutive OFDM symbols. Intersymbol interference (ISI) is eliminated so that the frequency band can be used efficiently. In addition, by dividing one channel into orthogonal subchannels, the frequency-selective fading channel is changed to a frequency-non-selective fading channel, and each subchannel is faded. Will have a stronger nature.

As such, the efficient use of channels having mutual orthogonality in high-speed transmission of data using orthogonal frequency division multiplexing plays a very important role in increasing transmission efficiency of wireless communication.

However, in the channels that transmit data by such orthogonal frequency division multiplexing, the transmission environment deteriorates temporarily depending on the wireless communication situation, and thus an error occurrence rate, that is, a bit error rate (BER) often increases. Done. As such, increasing the bit error rate in a specific channel may cause a deterioration of the overall data rate using the orthogonal frequency division multiplexing as well as the corresponding channel, thereby reducing transmission efficiency.

Since the wireless communication environment is very dynamic, it is required to quickly select a modulation method suitable for the communication environment of each channel for efficient data communication. In particular, the modulation scheme becomes more complicated as more channels transmit data, and many studies are being conducted on various methods for efficiently performing the modulation for improving the data rate.

Accordingly, the problem to be solved by the present invention is to reduce the amount of data to be transmitted by quickly grasping that the transmission environment is temporarily deteriorated due to the situation in each channel of the orthogonal frequency division multiplexing system, thereby increasing the bit error rate, and relatively transmitting. By increasing the amount of data transmitted in a channel having a good environment, it is possible to satisfy the target data rate while satisfying the bit error rate (BER) of each channel.

The problem to be solved by the present invention is not limited to the above-mentioned problem. Other objects and advantages of the invention will be more clearly understood by the following description.

The present invention for achieving the above object,

Allocating an optimal bit for each channel satisfying a target data rate and energy constraint using a water-filling solution;

Calculating an optimal bit already rounded up or down to satisfy integer bit allocation and channel-specific maximum bit allocation allowance constraints required by an orthogonal frequency division multiplexing system, and then comparing the maximum bit allocation allowance with a maximum bit allocation allowance;

And allocating additional bits or removing the extra bits to satisfy the target data rate.

The present invention grasps the deterioration of a channel's transmission environment for high-speed data transmission in an orthogonal frequency division multiplexing system, lowers the modulation method on a channel temporarily causing a poor transmission environment, and modulates a method on another channel having a good transmission environment. By performing the process of increasing the speed, the energy constraints of the entire subchannels can be satisfied and the target transmission rate can be satisfied even in an environment in which the channel situation changes frequently.

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

1 is a control flowchart of a method for selecting an optimal channel-by-channel modulation method that satisfies a target data rate and an energy constraint in an orthogonal frequency division multiplexing (OFDM) system according to the present invention.

Allocating an optimal bit for each channel that satisfies a target data rate and energy constraint using a water-filling solution (S1-S6);

In order to satisfy the target data rate, a process of allocating an additional bit or removing an extra bit is performed.

In the OFDM-based system according to the present invention, the total energy used to transmit while satisfying the target data rate and energy constraint of the system while the average bit error rate (BER) is maintained at a specific value required for all subchannels. Efforts are made to minimize this, which is represented by Equation 1 below.

는 제i번째 채널에 할당되는 파워,

는 제i번째 채널에 할당되는 비트 수,

은 목표 데이터 전송률,

은 에너지 제약,

는 채널에 할당될 수 있는 최대 비트 수를 나타낸다.here,

Is the power allocated to the i th channel,

Is the number of bits allocated to the i-th channel,

Is the target data rate,

Silver energy constraint,

Represents the maximum number of bits that can be allocated to the channel.

According to the channel gain-to-noise ratio (CNR), the number of bits bi for the i-th channel is calculated using Equation 2 below.

는 제i번째 채널에 대한 비트의 수를 나타내고,

는 채널 게인 대 잡음비인 CNR의 값을 나타내며,

는 SNR 갭(GAP)을 나타낸다.

는 시스템에서 사용되는 코딩 스킴(coding scheme)과 요구되는 비트 에러율(BER)에 의해 정해진다.here,

Represents the number of bits for the i th channel,

Represents the value of the channel gain-to-noise ratio, CNR,

Represents the SNR gap (GAP).

Is determined by the coding scheme used in the system and the required bit error rate (BER).

Using Equation 2, the power e _i allocated to the sub-channel i can be obtained as shown in Equation 3 below.

Using Equation 3, Equation 1 and Lagrange, the optimization problem can be expressed as Equation 4 below.

When Equation 4 is differentiated with respect to the number of bits allocated to each sub-channel, N equations can be obtained as shown in Equation 5 below.

By calculating both N + 1 [Equations] in [Equation 5] and [Equation 1], the optimal solution for each channel can be obtained as shown in [Equation 6].

Equation 6 needs to be modified to apply to an actual system. Since the maximum number of bits that can be allocated for each channel is predetermined and an integer bit must be allocated for each subchannel, Equation 7 below can be used.

Referring to FIG. 1, a process of allocating an optimal number of bits for each subchannel according to a subchannel state while satisfying a target data rate and energy constraint in an OFDM-based system will now be described in detail.

For optimal bit allocation, an optimal bit b (i) that satisfies the target data rate and energy constraint is calculated using a water-filling solution. The optimal bit b (i) is a bit that can be allocated to subchannel i and can be obtained using Equation 6 above (S1).

Equation (7) may be used to satisfy the allowance constraints on the integer bit allocation required by the orthogonal frequency division multiplexing system and the maximum bit allocation that can be allocated for each channel.

Subsequently, in order to obtain a subchannel used in the process of determining a subchannel to perform a bit add or remove operation to satisfy the target bit rate described below, the computed result bit and the optimal bit obtained in the first step S1. And difference (prior (i) = b (i) -b ^* (i)) is obtained (S3).

Thereafter, whenever bits are allocated to each subchannel, they are accumulated and summed in a variable called Sum. (S4)

Thereafter, the above process is repeated until bits are allocated to all subchannels (S5).

If the sum of bits allocated to all subchannels satisfies the target data rate and the energy constraint, the process is terminated (S6).

However, if the comparison result is not satisfied, as described in the following description, the sub-channel is first found, and then a series of processes of allocating or removing bits are further performed and then terminated.

If bits are allocated to each subchannel through Equation 7, the target data rate may not be satisfied. In this case, an evaluation criterion for first allocating or removing bits to several subchannels is required to satisfy a target data rate, which can be determined using Equation 8 below.

Equation (8) means that the larger the Prior value of one subchannel, the less energy is required to allocate 1 bit compared to other subchannels.

If the sum of bits allocated to all subchannels is less than the target transmission rate, if the fryer value is determined to be impossible by assigning additional bits to the largest subchannel, it is determined that it is not possible. Set the value back to the minimum value (MIN) (S7-S9).

If the check result indicates that additional bits can be allocated to the kth subchannel, the additional bits are allocated to the kth subchannel, and then the sum of the bits allocated to all the subchannels corresponds to the target bit. According to the result of the check, the process returns to step S7 of selecting a corresponding subchannel for allocating the additional bit or terminates the processing (S10, S11).

However, if the sum of bits allocated to all subchannels is larger than the target bit amount, if the fryer value is determined to be impossible by removing the bit of the k-th subchannel having the smallest value, the fryer of the subchannel is determined to be impossible. Set the value of (Prior) back to the maximum value (MAX) (S12-S14).

If it is determined that bit removal is possible in the kth subchannel, the bit is removed from the kth subchannel, and then the sum of bits allocated to all subchannels matches the target bit. Accordingly, the process returns to the step S12 of selecting the corresponding subchannel for removing the bit or terminates the process (S15, S16).

As a result, through the above-described series of processes, the average bit error rate of all channels can be satisfied with the required bit error rate, and the target data rate can be quickly satisfied while satisfying the energy constraint.

As a result, the amount of transmitted data is increased and decreased by rapidly adapting to a changing environment in a wireless communication environment with a large change in communication environment, thereby preventing the degradation of the overall data rate and enabling a user to perform optimal communication.

Although the preferred embodiment of the present invention has been described in detail above, the scope of the present invention is not limited thereto, and may be implemented in various embodiments based on the basic concept of the present invention defined in the following claims. Such embodiments are also within the scope of the present invention.

1 is a flowchart illustrating a method for selecting an optimal channel-specific modulation scheme satisfying a target data rate and energy constraint in an orthogonal frequency division multiplexing system according to the present invention.

Claims (3)

A first step of allocating an optimal bit for each channel satisfying a target data rate and an energy constraint using a water-filling solution; The second process of rounding up or down the optimal bits already obtained to satisfy the integer bit allocation and channel-specific maximum bit allocation allowance constraints required by orthogonal frequency division multiple systems, and then comparing the maximum bit allocation allowance ; For all subchannels, an evaluation criterion (prior) is obtained in which the energy required to allocate one bit is smaller than that of other subchannels, so that the sum of bits allocated to all subchannels is smaller than a target transmission rate and the evaluation value If an additional bit can be allocated to this largest subchannel, an additional bit can be allocated to that channel, and if a sum of bits allocated to all subchannels is larger than a target transmission rate and bits can be removed from a subchannel having the smallest evaluation value. The third step of repeating the operation of removing the bits from the channel as long as the condition is allowed to satisfy the target data rate; and the target data rate and energy constraints in the orthogonal frequency division multiplexing system comprising: How to choose the best channel-specific modulation scheme. 10. The method of claim 1, wherein the channel comprises subchannels. The method of claim 1, wherein the channel satisfies a target data rate and energy constraint in an orthogonal frequency division multiplexing system. The method of claim 1, wherein the third process further comprises selecting a subchannel to which bits are allocated or removed to satisfy the target data rate. A method for selecting an optimal channel modulation method that satisfies energy constraints.

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