Method and system for transmitting/receiving data in a communication system

Provided are a system and a method for transmitting/receiving data in a communication system. The method includes calculating a processing matrix of a transmission unit for transmitting data, a processing matrix of a reception unit for receiving the data, a channel matrix formed by a plurality of transmission antennas and a plurality of reception antennas, and a parameter of the transmission data, when the data to be transmitted to the plurality of reception antennas via the plurality of transmission antennas is generated; determining a minimum value of a Minimum Mean Square Error (MMSE) according to the calculated matrixes and parameter; and transmitting/receiving the data using an MMSE multiplexing scheme based on the determined minimum MMSE value.

PRIORITY

This application claims priority under 35 U.S.C. §119(a) of a Korean Patent Application filed in the Korean Intellectual Property Office on Feb. 7, 2006 and assigned Serial No. 2006-11672, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to a communication system, and in particular, to a method and system for transmitting/receiving data in a Multi-Input Multi-Output (MIMO) communication system.

2. Description of the Related Art

The key issue in communication is how efficiently and reliably is it possible to transmit data through a channel. In the next generation multimedia communication system, there is ongoing research to meet the need for a high-speed communication system capable of processing and transmitting a variety of information such as image and radio data, beyond the early voice-oriented service, because it is essential to increase the system efficiency using a channel coding scheme suitable for the system.

However, a wireless channel environment in the communication system, unlike the wired channel environment, suffers inevitable errors due to several factors, such as multipath interference, shadowing, radio attenuation, time-varying noise, interference, fading, and the like, and occurrence of the errors causes information loss. The information loss brings considerable distortion on actual transmission signals, causing a reduction in the entire performance of the communication system. Generally, in order to reduce information loss, various error control techniques are used according to channel characteristics to increase system reliability, and the most typical error control technique uses error correction codes.

Further, in order to remove communication instability due to fading, a diversity scheme is used, and the diversity scheme is roughly classified into a time diversity scheme, a frequency diversity scheme, and an antenna diversity scheme, i.e. space diversity scheme.

The antenna diversity scheme, a scheme using multiple antennas, is classified into a reception antenna diversity scheme using a plurality of reception antennas, a transmission antenna diversity scheme using a plurality of transmission antennas, and a Multiple Input Multiple Output (MIMO) scheme using a plurality of reception antennas and a plurality of transmission antennas.

In the MIMO communication system, Space-Time Coding (STC) determines what data it will transmit for each of the plurality of transmission antennas, and each of the reception antennas receives the signal transmitted from each of the transmission antennas and performs STC decoding thereon. The STC coding is implemented with a space-time transmit diversity technique for encoding the same data in different formats to transmit the same data via different transmission antennas, or a spatial multiplexing technique for transmitting different data via different transmission antennas.

Generally, in the spatial multiplexing technique, an STC-coded signal is decoded at a receiver using a joint or separate detection scheme. The joint detection scheme should take into account not only the signal transmitted from one transmission antenna, but also the signals transmitted from other transmission antennas. Due to this characteristic, multiplexing techniques such as Minimum Mean Square Error (MMSE), and Zero-Forcing (ZF)-based Joint-Channel Diagonalization (JCD), are well known as a multiplexing scheme for using the spatial multiplexing MIMO communication system.

Among the multiplexing techniques, the JCD-based multiplexing technique obtains higher data throughput compared with the MMSE-based multiplexing technique at a high Signal-to-Noise Ratio (SNR). On the contrary, at a low SNR, the MMSE-based multiplexing technique can obtain higher throughput performance compared with the JCD-based multiplexing technique. However, because the communication system generally multiplexes data using one multiplexing technique, it cannot use a multiplexing technique corresponding to a varying SNR in a time-varying wireless channel environment, causing performance degradation. In addition, the MMSE and JCD-based multiplexing techniques considerably increase in the system complexity, as the number of transmission antennas and the number of reception antennas increase.

SUMMARY OF THE INVENTION

It is, therefore, an aspect of the present invention is to address at least the problems and/or disadvantages described above-herein and to provide at least the advantages described below. Accordingly, an aspect of the present invention is to provide a method and system for transmitting/receiving data in a communication system.

Another aspect of the present invention is to provide a data transmission/reception method and system for preventing degradation of system performance while reducing system complexity in a MIMO-based communication system.

According to an aspect of the present invention, there is provided a method for transmitting/receiving data in a communication system. The method includes calculating a processing matrix of a transmission unit for transmitting data, a processing matrix of a reception unit for receiving the data, a channel matrix formed by a plurality of transmission antennas and a plurality of reception antennas, and a parameter of the transmission data, when the data to be transmitted to the plurality of reception antennas via the plurality of transmission antennas is generated; determining a minimum value of a Minimum Mean Square Error (MMSE) according to the calculated matrixes and parameter; and transmitting/receiving the data using an MMSE multiplexing scheme based on the determined minimum MMSE value.

According to another aspect of the present invention, there is provided a system for transmitting/receiving data in a communication system. The system includes a transmitter for calculating a processing matrix of a transmission unit for transmitting data, a processing matrix of a reception unit for receiving the data, a channel matrix formed by a plurality of transmission antennas and a plurality of reception antennas, and a parameter of the transmission data, when the data to be transmitted to the plurality of reception antennas via the plurality of transmission antennas is generated, determining a minimum value of a Minimum Mean Square Error (MMSE) according to the calculated matrixes and parameter, and transmitting/receiving the data using an MMSE multiplexing scheme based on the determined minimum MMSE value.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention provides a method and system for transmitting/receiving data in a communication system, for example, in at least one of a reception antenna diversity scheme-based communication system using a plurality of reception antennas, a transmission antenna diversity scheme-based communication system using a plurality of transmission antennas, and a Multiple Input Multiple Output (MIMO)-based communication system using a plurality of reception antennas and a plurality of transmission antennas. Although the present invention will be described herein with reference to the MIMO communication system by way of example, the data transmission/reception method and system provided in the present invention can be applied to other communication systems.

In addition, the present invention provides a data transmission/reception method and system in a communication system, for improving data throughput and system performance in the full Signal-to-Noise Ratio (SNR) interval for a time-varying wireless channel environment, and reducing the system complexity in the communication system. Further, the present invention provides a data transmission/reception method and system using a hybrid-multiplexing technique that can make use of merits of multiplexing techniques such as Minimum Mean Square Error (MMSE), and Zero-Forcing (ZF)-based Joint-Channel Diagonalization (JCD), as the optimal multiplexing technique for use in the spatial multiplexing MIMO communication system.

FIG. 1is a diagram illustrating a structure of a transceiver in a communication system.

Referring toFIG. 1, a transmitter100includes an encoder111, a modulator113and a Radio Frequency (RF) processor115, and a receiver150includes an RF processor151, a demodulator153and a decoder155. If information data that the transmitter100desires to transmit is generated, the information data is delivered to the encoder111. The encoder111encodes the information data into a coded symbol using a predetermined coding scheme, and outputs the coded symbol to the modulator113. The modulator113modulates the coded symbol into a modulation symbol using a predetermined modulation scheme, and outputs the modulation symbol to the RF processor115. The RF processor115performs RF processing on the signal output from the modulator113, and transmits the RF-processed signal over the air via an antenna ANT.

The signal transmitted over the air by the transmitter100is received at the receiver150via an antenna ANT, and the received signal is delivered to the RF processor151. The RF processor151performs RF processing on the received signal, and outputs the RF-processed signal to the demodulator153. The demodulator153demodulates the signal output from the RF processor151using a demodulation scheme corresponding to the modulation scheme applied by the modulator113of the transmitter100, and outputs the demodulated signal to the decoder155. The decoder155decodes the signal output from the demodulator153using a decoding scheme corresponding to the coding scheme applied by the encoder111of the transmitter100, and outputs the decoded signal as the finally restored information data.

FIG. 2is a diagram illustrating a structure of a transceiver in a communication system according to the present invention. It is assumed inFIG. 2that the transceiver of the communication system includes KTtransmission units with N transmission antennas, and K reception units with N{R,K}reception antennas.

Referring toFIG. 2, in a communication system according to the present invention, a transmitter200includes KTtransmission units210-1,210-2, and210-K, NTsummers, each of which sums up the data that the transmission units210-1,210-2, and210-K desire to transmit, and transmits the summed data via one antenna, and NTantennas for transmitting the data output by the NTsummers over the air, and a receiver250includes K reception units260-1,260-2and260-K, N{R,K}antennas included in the K reception units260-1,260-2and260-K, respectively, for receiving the signals transmitted by the transmitter200over the air, and N{R,K}summers for summing up Gaussian noises to cancel the noises included in the signals received via the N{R,K}antennas.

If data X1, X2, . . . , XKthat the transmitter200desires to transmit is generated, the data X1, X2, . . . , XKis delivered to its associated transmission units210-1,210-2and210-K, respectively, and the transmission units210-1,210-2and210-K each perform transmission processing T1, T2, . . . , TKon the provided data X1, X2, . . . , XK. Thereafter, the transmitter200sums up the data on which the transmission units210-1,210-2and210-K performed transmission processing T1, T2, . . . , TK, using the N{R,K}summers, in order to transmit the data to the reception units260-1,260-2and260-K, and then transmits the summed data

∑k=1K⁢Tk⨯k
over the air via the NTantennas. Here, the transmitter200recognizes channel status information depending on its feedback channel status received from the receiver250, and transmits the data over the air according to the recognized channel status information.

The signals transmitted over the air by the transmitter200are received at the receiver250via N antennas that are included in each of the K reception units260-1,260-2and260-K, and the received signals are delivered to their associated summers. Then the summers sum up Gaussian noises n1, n2, . . . , nKto cancel the noises included in the received signals, and then delivers the summed signals to the reception units260-1,260-2and260-K. The reception units260-1,260-2and260-K each perform reception processing on the received signal

Hk⁢∑j=1K⁢Tj⁢xj+nk,
and generate output signals {tilde over (X)}1, {tilde over (X)}2, {tilde over (X)}K. Herein, the output signal {tilde over (X)}Kcan be expressed as set forth in Equation (1).

In Equation (1), Hkdenotes a channel matrix formed between the transmitter200with NTtransmission antennas and the receiver250with K reception units260-1,260-2and260-K including N{R,K}reception antennas, and RkHdenotes a reception processing matrix performed by the K reception units260-1,260-2and260-K.

Equation (1) can be rewritten as set forth in Equation (2).

If a channel matrix, a transmission processing matrix and a reception processing matrix are defined as their weighting matrixes H=[H1H. . . HKH], T=[T1. . . Tk], and R=blockdiag[R1H, . . . , RkH], respectively, then Equation (2) can simply be expressed as set forth in Equation (3).
{tilde over (x)}=RHHTx+RHn(3)

In Equation (3), {tilde over (x)}=[{tilde over (x)}1H. . . {tilde over (x)}KH], x=[x1H. . . xKH], n=[n1H. . . nKH], E[xxH]=IL, E[•] denotes an expectation function, and ILdenotes an identity matrix of a region L. The transmission weighting matrix T satisfies Equation (4) due to the limit of transmission power.
E└∥Tx∥2┘=tr(THT)PT(4)
In Equation (4), ∥•∥ denotes a vector 2-norm, tr(•) denotes a trace operation, and PTdenotes the total transmission power used for data transmission in the transmitter200. In this manner, the receiver250performs reception processing on the data transmitted by the transmitter200using Equation (3).

In the communication system according to the present invention, the minimum MMSE value for using the MMSE multiplexing technique for the output signal on which the reception processing of Equation (3) was performed can be defined as set forth in Equation (5) that satisfies conditions as set forth in Equation (6) based on Equation (4).

Herein, as the transmission weighting matrix T of Equation (4) is conditions for the limit of transmission power as described above, if Equation (3) is substituted in Equation (5), i.e. if Equation (3) is substituted for {tilde over (x)}kof Equation (5), Equation (6) can be expressed as set forth in Equation (7).

The minimum MMSE value defined as set forth in Equation (7) can be calculated through a Lagrangian function as shown in Equation (8).

In Equation (8), λ denotes a Lagrange multiplier, and Λkdenotes a non-negative JCD effective channel gain. Accordingly, the MMSE multiplexing technique based on the minimum MMSE value defined as set forth in Equation (7) can obtain high data throughput at the high SNR, as well as at the low SNR. That is, the MMSE multiplexing technique based on the minimum MMSE value defined as set forth in Equation (7) according to the present invention can reduce the system complexity and improve the system performance in the full SNR interval. In the foregoing equations, Λkdenotes a weight of information symbols xK, i.e. Λkdenotes a product of an effective channel gain matrix D obtained through ZF processing and a power control weighting matrix E of the transmitter, and β denotes a scaling factor which is a parameter of a transmission signal transmitted from the transmitter200, and is a transmitter weight parameter which is calculated as a weight of the transmitter, found through Zero-Forcing at the receiver.

Utilizing Equation (8), the transmission processing matrix TK, the reception processing matrix RKand the scaling factor β can be expressed as set forth in Equation (9), Equation (10) and Equation (11), respectively.

Herein, σk2denotes a variance of Gaussian noises nKobtained by the summers of the receiver250by summing up the received signals to cancel the noises included in the signals received via the N{R,K}antennas, and an average of the Gaussian noises nKis 0.

An algorithm for calculating the optimal transmission processing matrix TK, reception processing matrix RKand scaling factor β satisfying Equation (9), Equation (10) and Equation (11), respectively, is as follows. In this algorithm, λβ2of Equation (9) is given as ξ.

In the foregoing algorithm, ν denotes λβ2, and the present invention calculates the optimal transmission processing matrix TK, reception processing matrix RKand scaling factor β satisfying conditions of Equation (9), Equation (10) and Equation (11) by performing the algorithm, and then determines the minimum MMSE value that satisfies Equation (6) and is defined in Equation (7), using Equation (8). That is, in the communication system according to the present invention, the data transmission/reception system calculates the optimal transmission/reception processing according to the channel environment formed by a plurality of transmission/reception antennas, and determines the minimum MMSE value through the calculated transmission/reception processing. Thereafter, the data transmission/reception system transmits/receives data using the MMSE multiplexing technique based on the determined minimum MMSE value.

As can be understood from the foregoing description, the present invention calculates the optimal transmission/reception processing according to the channel environment formed by a plurality of transmission/reception antennas, determines the minimum MMSE value through the calculated transmission/reception processing, and transmits/receives data using the MMSE multiplexing technique based on the determined minimum MMSE value, thereby reducing the system complexity and improving the system performance.