KR20080040108A - Modulation and coding scheme selection method and user scheduling method using the same - Google Patents

Abstract

An MCS(Modulation and Coding Scheme) determination method and a user scheduling method using the same are provided to raise a multi-user diversity gain and improve a transmission rate by determining an MCS level using an estimated error rate. An MCS determination method includes the steps of: predicting an error rate of a symbol at a scheduler(110); and determining an MCS of a symbol using the error rate at the scheduler. The MCS determination step maintains the error rate below a predetermined value and determines the MCS to maximize frequency efficiency. The frequency efficiency is acquired by RT=RClog2M at a channel encoder(120-1), where RT denotes a frequency efficiency, RC denotes a code rate, and M denotes a modulation size. The MCS determination step determines the MCS to maximize a throughput of a transmission antenna irrespective of the error rate.

Description

Modulation and coding scheme selection method and user scheduling method using the same

1 is an exemplary diagram illustrating a mobile communication system.

2 is a block diagram illustrating a transmitter according to an embodiment of the present invention.

3 is a block diagram illustrating a receiver according to an embodiment of the present invention.

4 is an exemplary diagram showing peripheral points in 16-QAM.

5 is a graph showing goodput versus SNR according to the simulation result.

The present invention relates to a modulation and coding scheme determination method and a user scheduling method using the same, and more particularly, to a modulation and coding scheme determination method for improving link performance and a user scheduling method using the same.

In the current wireless communication system, various transmission / reception schemes are emerging for the purpose of high quality and high capacity data transmission using limited frequency resources. In addition, there is an increasing demand for an effective countermeasure against fading phenomenon occurring in a wireless channel for high-speed multimedia data transmission.

Recently, MIMO (Multiple Input Multiple Output) technology using multiple transmit / receive antennas to be applied to the next generation mobile communication system for ultra-high speed multimedia data transmission and Orthogonal Frequency Division Multiplexing (OFDM) technology that can efficiently cope with frequency selective characteristics of channels Research is going on in many ways.

A representative example of the MIMO technology is a spatial division multiplexing (SDM) technique. This allows the transmitting end to transmit different data through each transmitting antenna, and the receiving end to distinguish the transmission data through appropriate signal processing such as interference cancellation and diversity technology. It is well known that the channel capacity increases linearly when the number of transmit / receive antennas is increased simultaneously using such a MIMO system. Therefore, multi-antenna technology will be an essential research task for current wireless communication systems requiring high data rates.

In order to effectively transmit high-speed data in a wireless channel, it is necessary to overcome frequency selective fading caused by inter-symbol interference or multipath interference of the wireless channel. The OFDM technique can effectively remove the frequency selective nature of the channel. In addition, compared with conventional frequency division multiplexing (FDM), the use of multiple carriers having mutually orthogonality can increase the spectral efficiency and inverse fast fourier transform (IFFT) and FFT (FFT) Fast Fourier Transform can be used for high speed implementation. Therefore, the OFDM technique is actively studied as a transmission method of the next generation wireless system.

As a means to further increase the performance of the system, a closed loop system structure that provides a feedback channel from the receiving end to the transmitting end has attracted attention. When channel state information (hereinafter referred to as CSI) is provided at a transmitter, performance of the system can be maximized by adjusting various system parameters. Adaptive Modulation and Coding (AMC) scheme increases the link performance by adjusting the transmit power level, modulation level and / or channel coding rate at the transmitter using current channel state information. It is a technique to let. If the CSI is known to the transmitting end, the data transmission rate can be maximized through the AMC method. If the channel condition is good, the data transmission rate can be increased, and if there is a deterioration of the channel, the data transmission rate can be reduced to support efficient transmission, and consequently, the average transmission rate can be increased.

However, the load is too high to measure and return the current CSI for all channels, and performance may degrade if there is user mobility. Therefore, a criterion for determining a modulation and coding scheme (hereinafter referred to as MCS) is required.

On the other hand, a cellular system has multiple users in one cell. A performance gain can be obtained by supplying information to a plurality of users having different channel gains at an appropriate time, which is called a multiuser diversity gain. In addition, the performance of the system can be improved by applying the AMC technique to multiple users. There is a need for a technique of determining MCS for multiple users and efficiently scheduling each user to increase multiuser diversity gain.

An object of the present invention is to provide a modulation and coding scheme determination method for determining a modulation and coding scheme for user data according to channel conditions.

Another object of the present invention is to provide a user scheduling method for selecting a plurality of user data according to channel conditions.

According to an aspect of the present invention, a modulation and coding scheme determination method is provided. The modulation and coding determination method predicts an error rate of a symbol and determines an MCS (Modulation and Coding Scheme) of the symbol using the error rate. By determining the MCS through the error rate of the symbol, the transmission rate according to the quality of service can be efficiently obtained.

According to another aspect of the present invention, there is provided a user scheduling method for scheduling user data for a plurality of users to access. The user scheduling method obtains a transmission rate supported by a transmission antenna and an error rate of a stream, and selects the user data to be transmitted to the transmission antenna using the error rate and the transmission rate. The user data is modulated and coded according to a modulation and coding scheme determined by the transmission rate.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. Like numbers refer to like elements throughout.

1 is an exemplary diagram illustrating a mobile communication system.

Referring to FIG. 1, a mobile communication system includes a base station (BS) 10 and a plurality of UEs 20. Mobile communication systems are widely deployed to provide various communication services such as voice and packet data.

The base station 10 generally refers to a fixed station that communicates with the terminal 20. Other terms such as node-B, base transceiver system (BTS), and access point (access point) terminology).

The terminal 20 may be fixed or mobile and may be called by other terms such as a mobile station (MS), a user terminal (UT), a subscriber station (SS), and a wireless device.

Downlink (downlink) means communication from the base station 10 to the terminal 20, uplink (uplink) means communication from the terminal 20 to the base station 10. In downlink, a transmitter may be part of the base station 10 and a receiver may be part of the terminal 20. In contrast, in uplink, the transmitter may be part of the terminal 20 and the receiver may be part of the base station 10. The base station 10 may include a plurality of receivers and a plurality of transmitters, and the terminal 20 may include a plurality of receivers and a plurality of transmitters.

2 is a block diagram illustrating a transmitter according to an embodiment of the present invention.

Referring to FIG. 2, the transmitter 100 includes a scheduler 110, a channel encoder 120-1,..., 120 -Nt, an interleaver 130-1,..., 130 -Nt. ), Mapper (140-1, ..., 140-Nt) and OFDM modulator (150-1, ..., 150-Nt).

The scheduler 110 receives data for K users and rearranges the data into Nt streams according to a scheduling method. K is the number of users and Nt is the number of transmit antennas 160-1, ..., 160-Nt. Due to problems such as the number of transmit antennas and the transmit power, all users cannot use resources simultaneously. The scheduler 110 selects the appropriate user and turns it into a stream to increase the multi-user diversity gain for the Multiple Input Multiple Output (MIMO) system. In addition, the scheduler 110 receives feedback information from the receiver 200 (200 of FIG. 3) and determines a modulation and coding scheme (hereinafter referred to as MCS) for each stream, and the channel encoder 120-1, ... 120-Nt) and mapper 140-1, ..., 140-Nt so that the stream is modulated and coded according to a predetermined coding scheme and modulation scheme. A method of determining the MCS level in the scheduler 110 and a method of scheduling user data will be described later.

The channel encoders 120-1,..., 120 -Nt receive the stream, encode the data according to a coding scheme determined by the scheduler 110, and form coded data. The channel encoders 120-1,..., 120 -Nt may add error detection bits such as cyclic redundancy check (CRC) to the stream, and add extra code for error correction. The error correction code may be, for example, a convolutional code or a turbo code. The interleavers 130-1, ..., 130-Nt mix the encoded data to reduce the noise effect from the channel.

The mapper 140-1,..., 140 -Nt modulates the interleaved coded data according to a modulation scheme determined by the scheduler 110 to provide modulation symbols. That is, the encoded data are mapped to modulation symbols representing positions according to amplitude and phase constellation by the mappers 140-1,..., 140 -Nt. The modulation scheme determined by the scheduler 110 may be variously changed and may be m-quadrature phase shift keying (m-PSK) or m-quadrature amplitude modulation (m-QAM). For example, m-PSK may include BPSK or 8-PSK as well as QPSK. m-QAM may include 256-QAM as well as 16-QAM or 64-QAM.

The OFDM modulators 150-1, ..., 150-Nt convert the input symbols into OFDM symbols. The OFDM modulators 150-1,..., 150 -Nt may perform Inverse Fast Fourier Transform (IFFT) on the input symbols and convert them into time domain samples. A cyclic prefix (CP) may be added to the OFDM symbol. The OFDM symbols output from the OFDM modulators 150-1, ..., 150-Nt are converted into analog signals and transmitted through the antennas 160-1, ..., 160-Nt.

3 is a block diagram illustrating a receiver according to an embodiment of the present invention.

Referring to FIG. 3, the receiver 200 includes an OFDM demodulator 220-1,..., 220 -Nr, a channel estimator 230-1,..., 230 -Nr, and an equalizer 240-1. , Descheduler 250, demapper 260, deinterleaver 270, channel decoder 280, and AMC controller 290. Here, Nr is the number of reception antennas 210-1, ..., 210-Nr.

The signals received from receive antennas 210-1, ..., 210-Nr are digitized and converted into symbols in the frequency domain by OFDM demodulators 220-1, ..., 220-Nr. The OFDM demodulators 220-1,..., 220 -Nr may remove a CP from an input signal and perform a fast fourier transform (FFT). The channel estimators 230-1,..., 230 -Nr estimate the channel information. Equalizers 240-1, ..., 240-Nr equalize the symbols using the estimated channel information.

The inverse scheduler 250 extracts the corresponding user stream from the input signal. The demapper 260, the deinterleaver 270, and the channel decoder 280 provide the channel encoders 120-1,..., 120 -Nt, the interleaver 130-1, of the transmitter 100 for the corresponding stream. 130-Nt) and mappers 140-1, ..., 140-Nt.

The AMC controller 290 receives the channel quality estimated by the channel estimators 230-1,..., 230 -Nr, and converts the channel quality into feedback information, which is a form known in advance, between the scheduler 110 and the transmitter 100. Send to.

Hereinafter, an MCS determination method and a user scheduling method according to an embodiment of the present invention will be described. The AMC technique using the determined MCS adaptively controls the transmission rate and / or power level for each user according to feedback information.

Hereinafter, it is assumed that MIMO channels are not spatially related to each other, and the number Nr of receive antennas is equal to the number Nt of transmit antennas. The output of the equalizer 240 of the receiver 200 separates the total Nt stream. The user data sequence transmitted through the i th antenna is called an i th stream. The channel state is static during one packet transmission, and each transmission is said to experience a different channel state. The feedback channel is assumed to be error free.

When the CP is longer than the channel delay spread, the output r _n of the n th subcarrier at the j th reception antenna in each time slot after performing the FFT is expressed by Equation 1 below.

은 n번째 부반송파에서 i번째 송신 안테나와 j번째 수신 안테나 사이의 채널 주파수 응답을 나타내고,

은 복소수 차원(complex dimension)당 분산(variance)

을 갖는 독립적이고 동일하게 분포되는(independent and identically distributed) 복소 부가 가우시안 잡음(complex additive Gaussian noise)을 나타내고,

은 분산

을 갖는 i번째 송신 안테나에서의 송신 심벌을 나타낸다. x_n의 총 파워는

이라 하고, Nt 송신 안테나에 걸쳐 동일하게 분포된다. here,

Denotes the channel frequency response between the i th transmit antenna and the j th receive antenna on the n th subcarrier,

Is the variance per complex dimension

Represents complex and additive additive Gaussian noise with independent and identically distributed

Silver dispersion

The transmission symbol in the i th transmit antenna having? The total power of x _n

This is equally distributed over the Nt transmit antenna.

라고 할 수 있다.

은 i번째 송신 안테나에서 j번째 수신 안테나로의 l번째 탭(tap)에서 시간 영역 채널 임펄스 응답이다.

은 영 평균(zero mean)을 갖는 복소 가우시안에 독립적이다.When the channel impulse response is time invariant during transmission, the channel frequency response of the received signal is

It can be said.

Is the time domain channel impulse response at the l th tap from the i th transmit antenna to the j th receive antenna.

Is independent of a complex Gaussian with zero mean.

은 다음 수학식 2와 같이 나타낼 수 있다.The receiver 200 detects Nt transmission signals by the equalizer matrix W _n from the received signals. That is, the output from the nth subcarrier after applying the equalizer 240 in the receiver 200

May be expressed as in Equation 2 below.

When w _{n , i} is an i-th row of W _n , and h _{n , i} are i-th column of H _n , the output of the i-th stream is expressed by Equation 3 below.

을 갖는 간섭 및 잡음이다. 총 분산

은 다음 수학식 4와 같다. The last two elements of equation (3) are the total variance

With interference and noise. Total dispersion

Is as shown in Equation 4 below.

Accordingly, the signal to interference plus noise ratio (SINR) at the output of the equalizer for the i th stream in the n th subcarrier is expressed by Equation 5 below.

Meanwhile, in the equalizer 240, two linear equalizers, a zero-forcing equalizer (ZFE) or a minimum mean square error equalizer (MMSE), may be considered.

ZFE uses channel inverse transform to remove interference from other streams. According to the ZFE method, the equalizer matrix W _n ^ZFE may be represented by Equation 6 below.

는 에르미트 전치(Hermitian transpose)를 나타낸다.here,

Denotes Hermitian transpose.

The MMSE equalizer matrix W _n ^MMSE can be expressed by Equation 7 below.

는

단위 행렬(identity matrix)이다. ZFE는 간단하지만 잡음 증대를 겪을 수 있으므로, 일반적으로 MMSE가 좀더 나은 성능을 보일 수 있다. here,

Is

It is an identity matrix. ZFE is simple but can experience increased noise, so MMSE can generally perform better.

Hereinafter, a method of determining the MCS will be described.

The user data stream transmitted from the transmitter 100 via the transmit antennas 160-1,..., 160 -Nt is selected by the scheduler 110. The scheduler 110 determines a modulation and coding scheme (MCS) according to a predetermined criterion for each stream.

Each stream by the scheduler 110 passes through the channel encoders 120-1,..., 120 -Nt and the mapper 140-1,..., 140 -Nt. Hereinafter, R _c denotes a code rate and d _H denotes a minimum Hamming distance. Channel encoders 120-1, ..., 120-Nt employ Rate Compatible Punctured Convolutional Codes (RCPC), with higher code rates puncturing from mother code at code rate 1/2. period) is said to be punctured by p.

라 할 때, i번째 스트림의 순간적인 에러율(error rate)은 다음 수학식 8과 같이 추정될 수 있다. 여기서 에러율은 심벌에 대한 채널 오차를 말하며, 이하에서 설명을 보다 명확하게 하기 위해 비트 에러율(bit error rate)로 한다. 당업자라면 에러율을 FER(Frame Error Rate)이나 BLER(Block Error Rate) 등 다른 형식으로 용이하게 바꿀 수 있을 것이다. SINR vector

In this case, the instantaneous error rate of the i-th stream may be estimated as in Equation 8. In this case, the error rate refers to a channel error for a symbol, and a bit error rate is referred to below for clarity. Those skilled in the art will be able to easily change the error rate to other formats such as Frame Error Rate (FER) or Block Error Rate (BLER).

Here, N (d) represents the total input weight of the error event at the hamming distance d, and P (d, Ω _i ) is the average code between the codewords at the hamming distance d. Word PEP (pairwise error probability). In a single carrier system, if the channel is modeled as a Rayleigh or Rician distribution, P (d, Ω _i ) can be calculated accurately.

By estimating the instantaneous error rate of the symbol for each transmit antenna (160-1, ..., 160-Nt) it can determine the MCS level. The error rate may be estimated on OFDM symbols rather than on the entire subchannel. However, in the OFDM-based mobile communication system, P (d, Ω _i ) may be very complicated to accurately calculate due to the frequency selectivity of the channel. In order to calculate the error rate of Equation 8, a method of estimating an error rate will be described below.

P (d, Ω _i ) for the SINR vector Ω _i for each stream can be obtained as shown in Equation 9 below.

는 각 d개의 비트 위치들 간의 카티시안(Cartesian) 곱이고,

는 j번째 비트가 b인 m-QAM 성상에서 신호점들의 부분 집합이고, m=log₂M 이다.here,

Is a Cartesian product between each d bit positions,

Is a subset of the signal points in the m-QAM constellation where j th bit is b, and m = log ₂ M.

Assuming ideal interleaving and gray mapping, Equation 9 may be expressed as Equation 10 below.

In computing Equation 10, most error events are due to a misjudgement of v _k , which is the neighboring points around x _k . The peripheral point v _k is where x _k and the j th bit are different.

4 is an exemplary diagram showing peripheral points in 16-QAM. In the case of j = 1, the dark points represent the points at which the first bit position is one.

Referring to Figure 4, there are three types of transitions that characterize each error event. The A1 point has two peripheral points with different first bit positions. The A2 point has three peripheral points with different first bit positions. On the other hand, the A3 point has no peripheral point that differs in the first bit position. In the case of j = 1 and 2, there are four points similar to the A3 point, and in the case of j = 3 and 4, there are no points similar to the A3 point.

Q ₁ and Q ₂ are defined as in Equation 11 below.

은 모든 j에 대해 고려할 때 3(2Q₁ + 3Q₂)/8 로 구할 수 있다. Q(x)를

로 정의할 때, 다음 수학식 12와 같이 간략화할 수 있다.For 16-QAM

Can be found as 3 (2Q ₁ + 3Q ₂ ) / 8 when all j are considered. Q (x)

When defined as, it can be simplified as shown in the following equation (12).

도 각각 Q₁+Q₂ 와 (28Q₁ + 49Q₂)/48 로 구할 수 있다. 즉

은 ρ_n,i의 함수로써 쉽게 계산할 수 있고, 에러율의 계산도 간단히 가능하다.For QPSK and 64-QAM

Can be obtained as Q ₁ + Q ₂ and (28Q ₁ + 49Q ₂ ) / 48, respectively. In other words

Can be easily calculated as a function of ρ _{n, i} , and the error rate can be calculated simply.

The transmission rate at each transmission is selected from an AMC table that defines the modulation and coding scheme according to each MCS level. That is, the transmission rate is determined according to the modulation scheme and coding scheme selected.

과 크기

인 M_l-QAM 신호 집합으로 이루어진다고 한다. Assume that the k-th user transmits the data stream through the i-th transmit antenna, and the AMC table supports the total l _max MCS level. Each MCS level l (l = 1, ..., l _max ) is code rate

And size

It is said to consist of the M _l -QAM signal set.

로 구할 수 있다. 주파수 효율이 클수록 송신율은 높아진다. 주어진 SINR 벡터 Ω_i에 대해, 주파수 효율 R_T(l)에 대한 손실 함수(cost function)은 다음 수학식 13과 같이 정의할 수 있다.The spectral efficiency supported by MCS level l is

Can be obtained as The higher the frequency efficiency, the higher the transmission rate. For a given SINR vector Ω _i , the cost function for the frequency efficiency R _T (l) can be defined as in Equation 13.

Where p _l is the puncturing period of the code.

Equation 13 is used to determine the MCS as an error rate estimation equation. The error rate may be calculated by the receiver 200 through the channel quality information and sent to the transmitter 100 as feedback information. Alternatively, the transmitter 100 receiving the channel quality information may calculate the error rate.

To determine the MCS level using the error rate, the following methods are possible.

One embodiment is an error rate limiting method for determining MCS under error rate limiting. In this case, the AMC scheme can determine the transmission rate according to the current channel state while maintaining the error rate below the required error level. That is, the error rate limiting method may be expressed as in Equation 14 below.

Where P _e is the required error rate. That is, the error rate limiting method estimates the error rate of each stream at every instant, and selects the MCS having the maximum frequency efficiency under the limitation of P _e , where the obtained error rate is a threshold. The transmission rate can be maximized while keeping the error rate below the threshold. This method is suitable for transmissions requiring reliability such as collision control in the Internet Protocol (IP) layer.

Another embodiment is a rate maximizing scheme for maximizing the total throughput regardless of the average error rate at the receiver 200. The rate maximization scheme requires another loss function that represents the expected yield at the receiver. Expected yield can be obtained as in Equation 15 through Equation 13.

을 최대화하도록 결정된다. 에러율을 포함하는 수율을 최대화하도록 MCS 레벨을 결정하여 송신율을 최대로 할 수 있다. 이 방식은 WWW(World Wide Web)이나 FTP(File Transfer Protocol) 등과 같은 고속 전송에 적합하다고 할 수 있다. MCS level for packet transmission is expected yield

Is determined to maximize. The transmission rate can be maximized by determining the MCS level to maximize the yield including the error rate. This method is suitable for high speed transmission such as the World Wide Web (WWW) or the File Transfer Protocol (FTP).

Hereinafter, a user scheduling method according to an embodiment of the present invention will be described. Consider a multiuser environment using multiuser diversity. Multi-user diversity gain may increase with the number of users simultaneously accessing the base station.

It is assumed that all users have the same channel state as the received SNR. K users are said to be connected to the base station, and each user is said to have enough data streams in the waiting queue. The transmission rate supported by the i th transmit antenna for user k (k = 1, .., K) is referred to as R _{k , i} . The transmission rate is determined by the MCS selected.

을 갖는 사용자를 선택할 수 있다. 송신 안테나별로 최대의 송신율을 갖는 사용자를 선택하고, 이를 통해 MCS 레벨을 결정하여 다중사용자 다이버시티 이득을 높인다.In one embodiment, the base station has the highest transmission rate reported from all users for the i < th > transmit antenna.

You can select a user with. The user having the maximum transmission rate is selected for each transmission antenna, and the MCS level is determined through this to increase the multiuser diversity gain.

의 최대값을 갖는 사용자를 선택할 수 있다. R_k는

을 나타내고, R_{avg ,k}는 이전 시간 슬롯에서 사용자에게 제공된 데이터률의 이동 평균(moving average)이다. 이는 모든 사용자에게 대략 동일한 수의 시간 슬롯을 제공하지만 가장 좋은 채널 상태를 갖는 사용자에게 송신을 할당한다. 이 방식은 사용자의 이동성이 큰 시간 선택적 환경에 보다 적합할 수 있다. In another embodiment, the base station is

You can select the user with the maximum value of. R _k is

R _{avg , k} is a moving average of the data rates provided to the user in the previous time slot. This gives approximately all users the same number of time slots but assigns transmissions to the users with the best channel conditions. This approach may be more suitable for a time selective environment in which a user's mobility is large.

과

의 합은 사용자 측에서 계산되어 기지국으로 보내질 수 있다. 즉 송신률과 에러율을 수신기(200)에서 계산하여 송신기(100)로 귀환시켜 귀환 정보량을 줄인다. 만약 충분한 사용자들이 패킷 전송을 동시에 요청하는 경우 각 안테나에서 패킷을 송신하기를 원하는 적어도 하나의 사용자가 존재할 수 있다. 이 경우 선택된 안테나에 따라

의 최대값만을 보고함으로써 귀환 정보의 양을 줄일 수 있다. Transmission rate

and

The sum may be calculated at the user side and sent to the base station. That is, the transmission rate and the error rate are calculated by the receiver 200 and fed back to the transmitter 100 to reduce the amount of feedback information. There may be at least one user who wants to transmit a packet at each antenna if enough users request packet transmission at the same time. In this case, depending on the antenna selected

By reporting only the maximum value of, we can reduce the amount of feedback information.

5 is a graph showing goodput versus SNR according to the simulation result. N _t = N _r = 4, and K = 20 users transmit packets simultaneously. Consider an OFDM system with N = 64 subcarriers and 16 samples of CP length. Assume an exponentially decreasing channel profile of 5-tap for all users, and the total transmit power P is 2. The AMC table used in the simulation is shown in Table 1 below.

l R _T ( l ) R _C Modulation One 0.75 bps / Hz 3/4 BPSK 2 1 bps / Hz 1/2 QPSK 3 1.5 bps / Hz 3/4 QPSK 4 2 bps / Hz 1/2 16-QAM 5 2.5 bps / Hz 5/8 16-QAM 6 3 bps / Hz 3/4 16-QAM 7 3.5 bps / Hz 7/12 64-QAM 8 4 bps / Hz 2/3 64-QAM 9 4.5 bps / Hz 3/4 64-QAM 10 5 bps / Hz 5/6 64-QAM

Channel coding employs a 16-state punctured convolutional code. Simulate transmissions over 10,000 frames to measure system yield. In addition to the AMC scheme, it implements an Automatic Repeat Request. Goodput is employed to measure the performance of the AMC method. Goodfoot is to count the bits of information in a decoded frame with the correct Cyclic Redundancy Check (CRC).

Referring to FIG. 5, a single input single output (SISO) system uses a maximum likelihood demapper rather than a linear equalizer. As the SNR increases, the scheme according to the invention shows better performance gains and performance gains over SISO systems.

The rate maximizing scheme shows the highest transmission rate, although it does not meet the required average error rate. Whether BER constarint or transmission maximization, MMSE performs better than ZFE. In ZFE, the SINR calculated at the output of the equalizer degrades due to noise amplification and the AMC scheme determines the MCS level as a function of SINR, so the transmission rate selected by ZFE is generally lower than the transmission rate by MMSE.

In general, the SNR required to increase the frequency efficiency while satisfying the error rate limit increases as the desired frequency efficiency increases. This makes the expected error rate of the MCS level under the error rate limit under high frequency efficiency easily much lower than the required error rate. In the high frequency efficiency region, the transmission rate maximization scheme can improve yield by considering only expected yields among AMC sets.

As shown in the graph, the performance difference between the two determination schemes occurs more than in the region of about 90% of the maximum possible transmission rate. Ie larger in the low frequency efficiency range. In addition, ZFE requires greater SNR to select higher frequency efficiency, and thus shows more performance improvement than MMSE by adopting a transmission rate maximization scheme.

The invention can be implemented in hardware, software or a combination thereof. In hardware implementation, an application specific integrated circuit (ASIC), a digital signal processing (DSP), a programmable logic device (PLD), a field programmable gate array (FPGA), a processor, a controller, and a microprocessor are designed to perform the above functions. , Other electronic units, or a combination thereof. In the software implementation, the module may be implemented as a module that performs the above-described function. The software may be stored in a memory unit and executed by a processor. The memory unit or processor may employ various means well known to those skilled in the art.

Although the present invention has been described above with reference to the embodiments, it will be apparent to those skilled in the art that the present invention may be modified and changed in various ways without departing from the spirit and scope of the present invention. I can understand. Therefore, the present invention is not limited to the above-described embodiment, and the present invention will include all embodiments within the scope of the following claims.

As described above, according to the present invention, the error rate is estimated, the MCS level is determined using the estimated error rate, and user data is scheduled. Multi-user diversity gain can be increased, and transmission rate can be improved.

Claims (10)

Predicting an error rate of a symbol; And And determining a modulation and coding scheme (MCS) of the symbol using the error rate. The method of claim 1, Determining the MCS is And determining the MCS to maximize frequency efficiency while maintaining the error rate below a predetermined value. The method of claim 2, The frequency efficiency is

Modulation and coding method determination method to obtain. R _T is the frequency efficiency, R _C is the code rate, and M is the modulation size. The method of claim 1, Determining the MCS is And determining the MCS to maximize throughput of the transmit antenna regardless of the error rate. The method of claim 4, wherein The yield is

Modulation and coding method determination method to obtain. Where R _i is yield, R _C is code rate, M is modulation size, and BER is the error rate. The method of claim 1, Wherein the error rate is a bit error rate. A user scheduling method for scheduling user data for a plurality of users to access, Obtaining a transmission rate supported by the transmitting antenna and an error rate of the stream; Selecting the user data to transmit to the transmission antenna using the error rate and the transmission rate; Modulating and coding the user data according to a modulation and coding scheme determined by the transmission rate. The method of claim 7, wherein And a plurality of transmit antennas. The method of claim 7, wherein And the error rate is returned from the receiving end to the transmitting end. The method of claim 7, wherein The transmission rate is a user scheduling method that is sent from the receiving end to the transmitting end.

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