KR20070063850A - Method for determining transmission rate in communication system - Google Patents

Abstract

A method for determining a transfer rate in a communication system is provided to allocate an exact MCS(Modulation and Coding Scheme) level to mobile stations by receiving the channel states reported from mobile terminals, adding an interference level to the values of the reported channel states on the basis of a previously stored interference level table based on the number of mobile stations, and determining an MCS level. A base station transmits reference signals, such as preamble signals, to mobile stations(202). Then the base station receives CQI(Channel Quality Information) from mobile stations and demodulates it(204). The base station executes scheduling and determines the number of mobile stations to which data are to be transmitted(206). The base station selects an interference level equivalent to the determined number from a previously stored interference level table based on the number of mobile stations(208). The base station determines a CINR(Carrier to Interference and Noise) in consideration of the selected interference level and allocates an MCS level according to the determined CINR(210).

Description

How to determine the rate in a communication system {METHOD FOR DETERMINING TRANSMISSION RATE IN COMMUNICATION SYSTEM}

1 is a graph showing the amount of interference according to the number of mobile stations and the moving speed in the present invention

2 is a flowchart illustrating a process of allocating an MCS level of a mobile station by a base station according to an embodiment of the present invention.

The present invention relates to a communication system, and more particularly, to a method for determining a transmission rate of a mobile station.

In general, current mobile communication systems have evolved to provide high-speed, high-quality wireless data packet communication systems for providing data services and multimedia services beyond the initial voice-oriented services. In addition, a third generation mobile communication system currently divided into an asynchronous method such as 3GPP (3rd Generation Partnership Project, hereinafter referred to as '3GPP') and a synchronous method such as 3GPP2 is standardized for high-speed, high-quality wireless data packet service. Work is being done.

This standardization work is a representative proof of the effort to find a solution for a high speed, high quality wireless data packet transmission service of 2Mbps or more in the third generation mobile communication system. In addition, the fourth generation mobile communication system is based on providing more high speed and high quality multimedia services.

Meanwhile, in the wireless mobile communication system, a factor that hinders high-speed and high-quality data service is usually due to a channel environment. The channel for the wireless communication includes power change, shadowing, movement of the terminal, and frequent speed of the received signal generated by fading in addition to white noise such as AWGN (Additive White Gaussian Noise). The channel environment changes frequently due to the Doppler effect, interference caused by other users, and multipath signals.

Accordingly, in order to provide the high speed and high quality wireless data packet service in wireless communication, a method for effectively overcoming the above-mentioned obstacles is required.

One such method is an adaptive modulation and coding (AMC) technique and an adaptive antenna system (hereinafter referred to as AAS).

First, the AMC scheme is an efficient link adaptation scheme for data transmission. Unlike the conventional power control scheme, the AMC scheme is a link adaptation scheme that changes a transmission rate other than a transmission power according to a channel environment. Here, the rate is determined by a modulation and coding scheme (hereinafter referred to as 'MCS') level, the base station is referred to as channel quality information (hereinafter referred to as 'CQI') fed back by the mobile station. MCS level to be applied to the mobile station is determined. For example, the mobile station can obtain a CQI by measuring a carrier to interference and noise ratio (hereinafter referred to as "CINR") of a downlink signal.

Therefore, in the system using the AMC scheme, the data transmission rate is increased because the higher order modulation scheme and the higher code rate are applied to the mobile station having a good channel, that is, a channel in a relatively good state. However, the data rate is lowered because the low-order modulation scheme and the low code rate are applied to a mobile station having a relatively poor channel, that is, a channel in a relatively poor state.

Next, the AAS technique is a technique for forming a transmission and reception beam pattern in a desired direction using a plurality of smart antennas. The beam pattern is formed to have the highest gain in the direction of the mobile station, and may form N antenna beam patterns when there are N mobile stations, for example.

In an AAS system using multiple beam patterns, a base station receives a channel state from multiple mobile stations and transmits a signal by multiplying each antenna array by a weight vector. Thus, the weight vector is a value that reflects the channel state of each mobile station. Ideally, each of the mobile stations receives only the beampattern signal transmitted by the base station toward it, and the signals transmitted to the other mobile stations are canceled out. However, in an actual channel environment, a time delay occurs until the mobile station reports the channel status to the base station and transmits a signal according to the reported channel condition. In this case, when the channel environment is constantly changing, the mobile station can receive not only its own signal but also a signal transmitted to another mobile station, which acts as interference. The amount of interference increases as the number of mobile stations increases.

The present invention has been made to solve the above problems, and an object of the present invention is to predict the amount of interference in advance in consideration of the number of mobile stations in a communication system using a smart antenna, and to apply it when MCS level allocation In providing.

The first method of the present invention for achieving the above object; In a communication system, a method of determining a modulation and coding scheme of a mobile station by a base station, the method comprising: preliminarily retaining predicted interference amount information according to the number of mobile stations; receiving channel quality information from the mobile station; Determining a number of mobile stations, selecting an interference amount corresponding to the identified number of mobile stations, and determining a modulation and coding scheme (MCS) of the mobile station in consideration of the selected interference amount and the channel quality information. Process.

The second method of the present invention for achieving the above object; In a communication system, a method in which a mobile station is assigned a modulation and coding scheme level, the method comprising: receiving a reference signal from a base station, measuring channel strength and transmitting channel quality information to the base station; And a step of assigning a modulation and coding scheme (MCS) level in consideration of the estimated interference amount according to the number of mobile stations and the channel quality information.

The second method of the present invention for achieving the above object; In a communication system, a method in which a mobile station is assigned a modulation and coding scheme level, the method comprising receiving a reference signal from a base station, measuring the reference signal strength, and referring to the amount of interference compared to the number of mobile stations already held, And transmitting the reflected channel quality information to the base station, and receiving a modulation and coding scheme (MCS) level from the base station.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description, only parts necessary for understanding the operation of the present invention will be described, and other background art will be omitted so as not to distract from the gist of the present invention.

In the present invention, the base station predicts the amount of interference corresponding to the number of mobile stations in advance, and reflects the predicted amount of interference to set the modulation and coding scheme (hereinafter, referred to as 'MCS') of the mobile stations. Decide That is, the base station may hold the interference amount information corresponding to the number of mobile stations in advance, and may refer to the interference amount information when allocating the MCS level, or the mobile station holds the interference amount information in advance, and when the channel state is reported to the base station, the interference amount The report may reflect the information.

The present invention is applicable to all communication systems, preferably to a communication system using a smart antenna. Therefore, hereinafter, a communication system using a smart antenna will be described as an example.

In a communication system using the smart antenna, a signal received by a base station from a mobile station may be represented by Equation 1 below.

In Equation 1, Y _u denotes a signal received from a u-th mobile station, H _{u, M} denotes an M-th array channel of the u-th mobile station, and S _u denotes a signal transmitted by the u-th mobile station. N _M is the noise of the M-th array, and U is the total number of mobile stations.

If Equation 1 is expressed as a vector representation, it is represented by Equation 2 below.

here,

,

,

,

,

In Equation 2, the weight vector W _{u, M is} multiplied to separate only the signal of the u-th mobile station. The weight vector W _{u, M} is multiplied by Equation 3 below.

When there are N mobile stations in the current cell, a signal received from the first mobile station may be represented by Equation 4 below.

를 제외한 나머지는 제거되어야만 하는 간섭 성분들이다. In Equation 4, only a signal including S ₁ and a signal including noise are signals related to the first mobile station, and the remaining signals are interference signals received from other mobile stations. Therefore, in Equation 4

The rest except for are interference components to be removed.

If the base station indicates a carrier to interference and noise ratio (hereinafter referred to as "CINR") of the signal received from the first mobile station is represented by the following equation (5).

In Equation 5, I _C represents the amount of interference signals from other cells.

The base station does not consider the interference component corresponding to the denominator of Equation 5 when determining the data rate of each mobile station, that is, the MCS level according to the channel state reported by the mobile station. Therefore, even if the base station determines the MCS level of the mobile station according to the channel state reported by the mobile station, performance deterioration occurs by allocating the MCS level without reflecting the channel state at the time of assigning the MCS level.

Accordingly, in the present invention, the base station measures the interference amount according to the number of mobile stations in the cell in advance, and allocates the correct MCS level to the mobile station in consideration of the measured interference amount when the MCS level is allocated. Here, the amount of interference measured in advance is a value obtained by a simulation result according to the characteristics of each system to be implemented, the base station holds the amount of interference mapped to the number of mobile stations 1: 1 in the form of a table, MCS level allocation The interference is removed by reflecting the amount of interference in the table.

1 is a graph showing a change in the amount of interference according to the number of mobile stations and the moving speed in the present invention.

Referring to FIG. 1, as the number of mobile stations increases, the amount of interference increases as a function in exponential form, and a mobile station moving at a higher speed (60 km / hour) than a mobile station moving at a low speed (3 km / hour) receives. It can be seen that the amount of interference is large.

The simulation environment from which the graph is derived is as follows.

Applicable Channels: Additive White Gaussian Noise (AWGN), PED-A, VEH-A

Mobile station speeds: 3 km / h and 60 km / h

Frame Type: AMC 1X6

Antenna type: Uniform Linear Array (ULA)

Number of mobile stations: 2-20

Cell radius: 1 km

Cell type: 3 sectors

2 is a flowchart illustrating a process of allocating an MCS level of a mobile station by a base station according to an embodiment of the present invention.

Referring to FIG. 2, in step 202, the base station transmits a reference signal, for example, a preamble signal, to a mobile station and proceeds to step 204. Here, the preamble may be an adaptive antenna system (AAS) preamble in the case of a communication system using a smart antenna. In step 204, the base station demodulates channel quality information (CQI) received from the mobile station and proceeds to step 206. In step 206, the base station determines scheduling of the mobile station to transmit data by performing scheduling (step 208). In step 208, the base station selects an interference amount value corresponding to the number of mobile stations to transmit data determined by the scheduling from the interference amount table according to the number of mobile stations already held, and proceeds to step 210. In step 210, the base station allocates the MCS level of the mobile station according to the CINR determined in consideration of the selected interference amount. The determined CINR may be represented by Equation 6 below.

In Equation 6, H ₁ and W ₁ represent channel response and weight vector of the corresponding mobile station, N is noise, I _c is interference from another cell, and C is the interference value selected from the table. Means. That is, the base station holds the amount of interference according to the number of mobile stations obtained by the simulation in the form of a table, and allocates the MCS level based on the CINR to which the amount of interference is added.

Meanwhile, in the detailed description of the present invention, specific embodiments have been described, but various modifications are possible without departing from the scope of the present invention. Therefore, the scope of the present invention should not be limited to the described embodiments, but should be defined not only by the scope of the following claims, but also by those equivalent to the scope of the claims.

As described above, according to the present invention, the base station reports the channel state from the mobile station, adds the amount of interference to the channel state value reported by the mobile station with reference to the interference amount table according to the number of mobile stations already held, and assigns the MCS level to the mobile station. By determining this, the correct MCS level assignment is possible.

Claims (6)

In a communication system, a method in which a base station determines a modulation and coding scheme of a mobile station, Preliminarily holding the estimated amount of interference according to the number of mobile stations, Receiving channel quality information from the mobile station; Determining the number of mobile stations scheduled at the present time; Selecting an amount of interference corresponding to the identified number of mobile stations; And determining the modulation and coding scheme (MCS) of the mobile station in consideration of the selected interference amount and the channel quality information. The method of claim 1, The interference amount information is predicted by a simulation result considering a system environment, and the system environment considers a moving speed of a mobile station. The method of claim 1, And transmitting a preamble signal to the mobile station. The method of claim 1, And the base station uses a smart antenna. In a communication system, a method in which a mobile station is assigned a modulation and coding scheme level, Receiving a reference signal from a base station, Transmitting channel quality information to the base station by measuring the reference signal strength; And a step of allocating a modulation and coding scheme (MCS) level in consideration of the estimated interference amount and the channel quality information according to the number of mobile stations from the base station. In a communication system, a method in which a mobile station is assigned a modulation and coding scheme level, Receiving a reference signal from a base station, Measuring the reference signal strength and transmitting channel quality information reflecting the amount of interference to the base station by referring to the amount of interference with respect to the number of mobile stations in advance; And a method of allocating a modulation and coding scheme (MCS) level from the base station.

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