KR20040056987A - Method for sub-channel allocation of OFDM and its program stored recording medium - Google Patents

Abstract

PURPOSE: A method for allocating sub-channels in OFDM communication and a recoding medium for storing an allocation program are provided to form a simple bit-loading algorithm by using a modulation/demodulation level as feedback information. CONSTITUTION: A base station receives modulation/demodulation levels and average receiving S/N ratios from each terminal(S1). Users are sorted according to the average receiving S/N ratios(S2). Sub-channels are selected by using the maximum modulation/demodulation level and the maximum average receiving S/N ratio after the users are sorted according to the average receiving S/N ratio(S3). The selected sub-channels are assigned to the users(S4-S7).

Description

Method for sub-channel allocation of OFDM and its program stored recording medium in orthogonal frequency division multiplexing

The present invention relates to a method for allocating subchannels in orthogonal frequency division multiplexing communication and a recording medium storing the program, and more particularly, to orthogonal frequency division multiplexing for user-based power control while reducing the amount of feedback information in a multi-user environment. A subchannel allocation method in communication and a recording medium in which the program is stored.

Each terminal used in a wireless channel environment has a different wireless channel environment, and each subcarrier of each terminal has a different channel environment.

In general, an orthogonal frequency division multiplexing (OFDM) system uses an adaptive modulation and coding scheme (AMC) suitable for a channel environment for each subcarrier of each terminal to increase spectrum efficiency per user.

That is, for a subcarrier having a good wireless environment, a channel encoder having a low code rate and a higher-order modulation scheme capable of transmitting several bits at the same time are selected. However, for a subcarrier having a relatively poor wireless environment, a low order modulation scheme such as a channel coder having a high code rate and a binary phase shift keying (BPSK) modulation scheme is selected.

The adaptive modulation and coding (AMC) algorithm for the OFDM system of the embodiment according to the prior art is as follows.

The transmitter determines the modulation and demodulation scheme and the error correction code based on the received signal to noise ratio (SNR) information of the receiver.

In one embodiment, the bit loading algorithm in the Discrete Multitone Modulation (DMM) system feeds back channel information of all subcarriers and selects an appropriate modulation method for each subcarrier to have an optimal performance.

However, in the above bit loading algorithm, the modulation and demodulation and error correction codes of each subcarrier are not determined at one time, but only one bit is allocated through one calculation, and the process is repeatedly performed to allocate the transmission bits of all subcarriers.

When the transmission bit allocation is made through such an iterative calculation process, the bit loading algorithm according to the prior art is relatively easy to implement when there are few users, but the complexity and difficulty of implementation are increased as the number of subcarriers and the number of users increases. There is this.

In addition, the bit loading algorithm according to the related art uses the received signal-to-noise ratio as feedback information to first increase the symbol energy of the subchannel that requires a minimum to increase one bit, and then perform one operation of lowering one bit.

Thus, the bit loading algorithm according to the prior art generates an optimal result through an EF (Efficientizing) algorithm that preferentially reduces the symbol energy of the subchannel, which can reduce the most symbol energy, and performs power control for each subcarrier in a multi-user environment. Improve performance.

However, since the bit loading algorithm according to the related art requires an accurate reception signal-to-noise ratio, feedback information is increased, and the complexity of the multi-user environment is very difficult to design the system.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to implement a simple bitloading algorithm using the modulation and demodulation level as feedback information, thereby significantly reducing the amount of feedback information and at the same time reducing the amount of bitloading calculation and system complexity. A method of allocating subchannels in orthogonal frequency division multiplexing and a recording medium storing the program are provided to ensure system performance.

1 is a flowchart illustrating a subchannel allocation method in orthogonal frequency division multiplexing according to an embodiment of the present invention.

FIG. 2 is a graph showing the performance result of bit loading according to FIG.

3 is a graph illustrating PER performance of an OFDMA system to which power control for each subcarrier and power control for each user are applied.

4 is a graph illustrating power usage performance of an OFDMA system to which power control for each subcarrier and power control for each user are applied.

A feature of the subchannel allocation method in orthogonal frequency division multiplexing according to the present invention for achieving the above object is a) a base station receives a modulation / demodulation level and an average received signal-to-noise ratio from each terminal, Classifying users according to noise ratio; b) when the users are classified in step a), selecting a subchannel according to one-to-one correspondence between the highest value of the modulation level and the maximum value of the average received signal-to-noise ratio; And c) assigning the subchannel selected in step c) to the corresponding user.

The step of allocating the subchannel in step c) cancels the allocation of the selected subchannel when another subchannel is already assigned to the corresponding user, and allocates the selected subchannel when the subchannel of the corresponding user is empty. .

In step c), when the subchannel allocation is completed to the corresponding user, checking whether all the subchannels are allocated or all the subchannels are completed to all the users is finished.

In the step c), classifying the user may perform power control for each user according to the average received signal to noise ratio.

On the other hand, the characteristics of the recording medium that stores a program for implementing a subchannel allocation method in orthogonal frequency division multiplexing communication, the base station receives the modulation and demodulation level and the average received signal-to-noise ratio from each terminal, the user according to the average received signal-to-noise ratio A first function of sorting; A second function of selecting a corresponding subchannel by associating a maximum value of the modulation / demodulation level with a maximum value of the average received signal-to-noise ratio when users are classified through the first function; And a third function of allocating a subchannel selected through the second function to a corresponding user.

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

1 is a flowchart illustrating a subchannel allocation method in orthogonal frequency division multiplexing according to an embodiment of the present invention.

As shown in Fig. 1, in the method of the embodiment according to the present invention, a base station first receives a modulation / demodulation level and an average received signal-to-noise ratio (SNR) from a terminal (S1), and classifies users according to the average received SNR. )

In this case, since the base station uses the predetermined modulation and demodulation level having the discrete value as the feedback information instead of the received SNR having the continuous value, the system performance becomes independent of the amount of the feedback information.

For example, assuming that the number of bits needed to represent the received SNR is N, and the number of bits for representing the modulation and demodulation and error correction codes is M, then M representing a discrete value than N representing a continuous value is generally Fewer bits are required. Therefore, the base station receives a small amount of feedback information from the terminal.

The base station performs bit loading in one-to-one correspondence between the highest value and the maximum value of the average received SNR among the modulation and demodulation levels received from the terminal (S3).

As such, since the base station uses a simple bit loading method that corresponds directly to one transmission bit number according to the received SNR, the modulation and demodulation and error correction codes of one subcarrier can be determined by one calculation. Complexity is greatly reduced.

It is determined whether the subchannel selected by the above bit loading is assignable to the corresponding user. If the subchannel is not allocated to the user and is empty, the base station allocates the subchannel to the corresponding user (S4, S5).

However, if the subchannel is already assigned to the user, the base station cancels the subchannel allocation to allocate the subchannel to another user.

In this way, when all subchannels are allocated or subchannels are assigned to all users, the base station terminates all subchannel allocation processes. (S7) However, the base station still has a subchannel to be allocated or a subchannel. If there is still a user who wants to assign the process, the process returns to the step S3.

On the other hand, the base station performs power control using the average received SNR for each user, unlike the conventional method of performing power control for each subcarrier.

Therefore, since the base station receives feedback information of the average received SNR rather than the received SNR from the terminal, the amount of feedback information can be significantly reduced.

In addition, in Orthogonal Frequency Division Multiplexing, the user does not use a single subcarrier but multiple subcarriers. Therefore, the power control calculation amount and the amount of memory are greatly reduced when the user performs power control rather than power control for each subcarrier. The complexity of can be reduced.

FIG. 2 is a graph showing the performance results of bit loading according to FIG. 1, in which an existing optimal adaptive modulation / demodulation (AMC) bit loading algorithm in an OFDM system when there is one user and a method of an embodiment according to the present invention. The packet error rate (PER) performance is shown in FIG.

As shown in FIG. 2, in order to support PER 10 ^-2 , the performance of the existing optimal bit loading algorithm and the bit loading algorithm of the embodiment according to the present invention show a difference of about 1 db.

However, considering the complexity of the system and the amount of feedback information, the method of the embodiment according to the present invention can be said to be a bit loading algorithm suitable for an OFDMA system for multi-user support.

3 is a graph illustrating PER performance of an OFDMA system to which power control for each subcarrier and power control for each user are applied.

3 is a simulation result of the PER performance of the downlink, using three modulation and demodulation schemes, one error correction code, and a modulation and demodulation level of transmission abandonment.

The power level for the power control is determined by simulation in accordance with the number of users. Power control levels of 1, 30, 60, and 90 users were used at 14 dB, 16 dB, 24 dB, and 26 dB, respectively. The results indicate that a system for complex subcarrier power control and simple user power control are available. The performance of the system shows little difference.

4 is a graph illustrating power usage performance of an OFDMA system to which power control for each subcarrier and power control for each user are applied.

4 is a result of simulating downlink power usage, and the power control level for each user uses the level as shown in FIG. 3.

According to the results, in the case of power control for each subcarrier, a power gain of about 3 dB is given, but considering the power loss according to the amount of feedback information of the uplink, a method of power control for each subcarrier is used in power usage. There is no guarantee that it will give a 3dB gain.

For example, in this simulation where 5 bits are used for the received SNR and 2 bits are used for the modulation / demodulation level, the feedback information required by the power control for each subcarrier is the number of users, the number of subcarriers, and 5 bits. The amount of feedback information required by the user is approximately 1/2 of the number of users, the number of subcarriers, the number of 2 bits + the number of users, and 5 bits, compared to the power control for each subcarrier.

Therefore, considering the amount of feedback information, the power control method for each subcarrier is further reduced by 3dB gain in the power used.

As such, considering the complexity of the system and the amount of feedback information, the method of the embodiment of the present invention employs a simple bitloading algorithm and user-specific power control, making it easier to implement an OFDMA system to support multiple users. can do.

The drawings and detailed description of the invention are merely exemplary of the invention, which are used for the purpose of illustrating the invention only and are not intended to limit the scope of the invention as defined in the appended claims or claims. Therefore, those skilled in the art will understand that various modifications and equivalent other embodiments are possible from this. Therefore, the true technical protection scope of the present invention will be defined by the technical spirit of the appended claims.

In the present invention, a subchannel allocation method and a recording medium storing the program in the orthogonal frequency division multiplexing communication use a modulation demodulation level as feedback information to implement a simple bitloading algorithm in which a received signal-to-noise ratio and a modulation / demodulation scheme correspond one-to-one. This reduces the amount of feedback information and reduces the complexity of bitloading calculations without compromising system performance.

In addition, the sub-channel allocation method and the recording medium in which the program is stored in the orthogonal frequency division multiplexing according to the present invention, the power for each user based on the average received signal-to-noise ratio instead of performing power control for each sub-carrier based on the received signal-to-noise ratio By performing the control, the system complexity is reduced, and the power control gain can be easily obtained with a small amount of feedback information.

Claims (5)

a) a base station receiving a demodulation level and an average received signal-to-noise ratio from each terminal, and classifying users according to the average received signal-to-noise ratio; b) when the users are classified in step a), selecting a subchannel according to one-to-one correspondence between the highest value of the modulation level and the maximum value of the average received signal-to-noise ratio; And c) assigning the subchannel selected in step c) to the corresponding user; Subchannel allocation method in orthogonal frequency division multiplexing comprising a. The method of claim 1, The step of allocating the subchannel in step c) cancels the allocation of the selected subchannel when another subchannel is already allocated to the corresponding user, and allocates the selected subchannel when the subchannel of the corresponding user is empty. A subchannel allocation method in orthogonal frequency division multiplexing, characterized in that. The method of claim 1, Orthogonal frequency division multiple communication comprising the step of terminating the sub-channel allocation process by confirming whether all sub-channels are allocated or all sub-channels are completed to all users when the sub-channel allocation is completed in the step c) Subchannel Allocation Method in. The method of claim 1, In the step a), the classifying a user may include performing power control for each user according to the average received signal-to-noise ratio. A first function of the base station receiving a demodulation level and an average received signal-to-noise ratio from each terminal, and classifying users according to the average received signal-to-noise ratio; A second function of selecting corresponding subchannels by matching the highest value of the modulation / demodulation level with the maximum value of the average received signal-to-noise ratio when the users are classified through the first function; And A third function of allocating a subchannel selected through the second function to a corresponding user; The recording medium in which the program is stored.