KR101470642B1 - Receiver and method of restoring data - Google Patents

Abstract

A method for restoring data in a wireless communication system capable of redundantly allocating wireless resources to a plurality of users. The method includes receiving a received signal, obtaining a log likelihood ratio (LLR) by using the channel gain of the interference signal and the transmission power of the interference signal as noise and using the signal gain to calculate a signal-to-interference ratio, and using the LLR And restoring the data. Even when a collision occurs between different users, it is possible to restore the data without increasing the overhead of the system by reducing the amount of calculation required for LLR acquisition. Thus, the overall system performance can be improved.

Multiple Access, CDMA, OCHMA, ORHMA, LLR

Description

RECEIVER AND METHOD OF RESTORING DATA BACKGROUND OF THE INVENTION [0001]

The present invention relates to a wireless communication system, and more particularly, to a receiver and a data restoration method.

The next generation multimedia wireless communication system, which has been actively researched recently, requires a system capable of processing various information such as video and wireless data and transmitting the initial voice-oriented service. The purpose of a wireless communication system is to allow multiple users to communicate reliably regardless of location and mobility.

There are a wide variety of multiple access schemes that allow multiple users to communicate. The multiple access scheme can be divided into a fixed allocation scheme and a dynamic allocation scheme. The fixed allocation scheme allocates a radio resource to a specific user. For example, fixed allocation schemes include Frequency Division Multiple Access (FDMA), Time Division Multiple Access (TDMA), and Code Division Multiple Access (CDMA). In the fixed allocation scheme, since different radio resources are allocated to different users, collision does not occur. However, when there is no data to be transmitted by the user, the allocated radio resources are not used. The dynamic allocation method is a method of allocating radio resources only to users having data to be actually transmitted. The dynamic allocation scheme includes a scheduling based scheme and a contention based scheme. The scheduling-based scheme is to schedule radio resources to be allocated to a user by a central control device such as a base station. The scheduling based method also does not cause conflicts between different users. However, the scheduling based scheme has a disadvantage that overhead required for management becomes large. The collision-based method is a method in which a user who has data to be transmitted accesses without using scheduling. For example, Aloha (ALOHA) and Carrier Sense Multiple Access (CSMA) are examples of collision-based methods. The collision-based approach can cause conflicts because different users can use the same radio resources at the same time.

Recently, OCHMA (Orthogonal Code Hopping Multiple Access) and ORHMA (Orthogonal Resource Hopping Multiple Access) have been developed as a next generation multiple access scheme. CDMA is a scheme in which each user uses a specified orthogonal code. OCHMA is a method of periodically hopping orthogonal codes to change orthogonal codes allocated to users. While CDMA can accommodate as many users as the number of orthogonal codes, OCHMA has the advantage of accommodating more users than the number of orthogonal codes. The ORHMA periodically hops the radio resource to change the radio resource allocated to the user. The radio resource may be not only orthogonal codes but also frequency, phase, time, and the like. The OCHMA or ORHMA system has the advantage of efficiently using limited radio resources, but there is a problem that a collision may occur between different users.

Therefore, there is a need for a receiver and a data recovery method capable of improving reception performance in a wireless communication system in which collision between different users such as an OCHMA or an ORHMA system may occur.

SUMMARY OF THE INVENTION The present invention provides a receiver and a data recovery method capable of improving reception performance when a collision occurs between different users.

In one aspect, a method is provided for recovering data in a wireless communication system capable of redundant assignment of wireless resources to a plurality of users. The method includes receiving a received signal, obtaining a log likelihood ratio (LLR) by using the channel gain of the interference signal and the transmission power of the interference signal as noise and using the signal gain to calculate a signal-to-interference ratio, and using the LLR And restoring the data.

In another aspect, a receiver is provided. Wherein the receiver comprises: a receive antenna for receiving a received signal; an LLR detector for obtaining a LLR by using a channel gain of an interference signal and a transmit power of the interference signal as noise and calculating a signal-to-interference ratio; And a channel decoder for decoding the received signal.

Even when a collision occurs between different users, it is possible to restore the data without increasing the overhead of the system by reducing the amount of calculation required for LLR acquisition. Thus, the overall system performance can be improved.

The following techniques can be used in various wireless communication systems. Wireless communication systems are widely deployed to provide various communication services such as voice, packet data, and the like.

1 shows a wireless communication system.

1, a wireless communication system includes a mobile station (MS) 10 and a base station 20 (BS). The terminal 10 may be fixed or mobile and may be referred to by other terms such as a User Equipment (UE), a User Terminal (UT), a Subscriber Station (SS), a wireless device, The base station 20 generally refers to a fixed station that communicates with the terminal 10 and may be referred to in other terms such as a Node-B, a Base Transceiver System (BTS), an Access Point Can be called. One base station 20 can provide services for at least one cell. A cell is an area where the base station 20 provides communication services. Generally, a downlink means communication from a base station to a terminal, and an uplink means communication from a terminal to a base station.

The multiple access scheme used in the wireless communication system may be Orthogonal Code Hopping Multiple Access (OCHMA), Orthogonal Resource Hopping Multiple Access (ORHMA), or the like. In addition, a multiple access scheme capable of redundantly allocating limited radio resources to a plurality of users can be used.

The wireless communication system may be a Single Input Single Output (SISO) system or a Single Input Multiple Output (SIMO) system as well as a Multiple Input Multiple Output (MIMO) system or a Multiple Input Single Output (MISO) system. The MIMO technique improves the transmission / reception efficiency of data by using multiple transmission antennas and multiple reception antennas, and includes spatial diversity, spatial multiplexing, and beamforming.

2 is a block diagram illustrating a transmitter.

Referring to FIG. 2, the transmitter 100 includes a channel encoder 110 and a mapper 120. The transmitter 100 may be part of a base station in the downlink or a part of the terminal in the uplink.

The channel encoder 110 encodes data according to a predetermined coding scheme to form coded data. The coding scheme in the channel encoder 110 is not limited, and turbo codes, low-density parity-check codes (LDPC), and the like can be used.

The mapper 120 maps the coded data into symbols representing positions on a signal constellation. This is called a transmission data symbol. The transmit data symbols are transmitted via the transmit antennas.

The modulation scheme in the mapper 120 is not limited and may be m-Phase Shift Keying (m-PSK) or m-Quadrature Amplitude Modulation (m-QAM). For example, m-PSK may be binary phase shift keying (BPSK), quadrature phase shift keying (QPSK), or 8-PSK. The m-QAM may be 16-QAM, 64-QAM, or 256-QAM.

3 shows an example of 16-QAM constellation.

Referring to FIG. 3, the I-axis represents an in-phase component and the Q-axis represents a quadrature component. Qn (1? N? 16, n is a natural number) is a symbol coordinate number for identifying a transmission data symbol of 16-QAM constellation. The 4-bit coded data is mapped to each transmission data symbol.

4 is a block diagram illustrating a receiver in accordance with an embodiment of the present invention.

4, the receiver 200 includes an LLR detector 210 (LLR) and a channel decoder 220. The LLR detector 210 detects the LLR (LLR) The receiver 200 may be part of a terminal in the downlink, or may be part of a base station in the uplink.

The receiver 200 receives the reception signal through the reception antenna. The received signal includes an interference signal, which is a user signal different from the data in which the receiver 200 is a desired signal. The user signal is a signal transmitted to the user and corresponds to the data to be restored by the receiver. The interference signal is a signal transmitted to another user who has been allocated the same radio resource as the user and has a collision.

The LLR detector 210 acquires the LLR using the received signal received via the antenna. The channel decoder uses LLR to decode and recover the data.

5 is a flowchart illustrating a data restoration method according to another embodiment of the present invention.

Referring to FIG. 5, a receiver receives a reception signal through a reception antenna (S110). The received signal includes a data signal and an interference signal. The receiver obtains the LLR using the channel gain of the interference signal and the transmission power of the interference signal from the reception signal (S120). The receiver reconstructs the data using the obtained LLR (S130).

First, the LLR acquisition method will be described in the case where no collision occurs.

The received signal is represented by r, and can be expressed by the following equation.

Where h is the channel gain of the user signal, S is the transmission data symbol of the user signal, and n is the noise. When the modulation scheme of the transmitter mapper is the 16-QAM constellation shown in FIG. 3, the transmission data symbol S of the user signal is S? {Q1, Q2, ... , Q16}. The noise n may be additive white Gaussian noise (AWGN).

The LLR acquisition method used by the LLR detector includes a maximum likelihood (ML) method and a MAX method.

The LLR obtained using the ML scheme can be expressed by the following equation.

Where N ₀ is the noise spectral density.

The LLR obtained using the MAX method can be expressed by the following equation.

The MAX method is a method of obtaining an approximate value of the ML method. There is no significant difference between the MAX method and the ML method.

Hereinafter, an LLR acquisition method will be described when a collision occurs.

The received signal is represented by r, and can be expressed by the following equation.

Here, g is the channel gain of the interference signal, and I is the transmission data symbol of the interference signal. When the modulation scheme of the interference signal is the 16-QAM constellation shown in FIG. 3, the transmission data symbol I of the interference signal is I? {Q1, Q2, ... , Q16}.

When two users using 16-QAM collide, the LLR obtained using the ML scheme can be expressed by the following equation.

When two users using 16-QAM collide, the optimal LLR calculation must be based on the number of all cases of signal combinations that two users can send. Therefore, in the case of a collision between two users using 16-QAM, 16 × 16 = 256 exponential terms must be included.

In addition, when the wireless communication system is a MIMO system, a receiver can receive a reception signal through multiple reception antennas.

If the collided user uses two receive antennas, the LLR obtained using the ML scheme can be expressed by the following equation.

Here, r is the received signal vector, h is the channel gain vector of the user signal, and g is the channel gain vector of the interference signal. Received signal vector _{r = [r 1, r 2} ] T, a channel gain vector of the reconstructed signal is _{h = [h 1, h 2} ] T, a channel gain vector of the interfering signal is _{g = [g 1, g 2} ] T .

When each collided user uses multiple receive antennas, the channel information to be considered in the LLR calculation is increased by the number of receive antennas.

As described above, when the ML scheme uses a high modulation scheme such as 16-QAM and 32-QAM, the LLR calculation amount increases exponentially when multiple users collide with each other when using multiple antennas. If the amount of computation is increased, it becomes overhead to the receiver, leading to transmission delay. Thus, the overall system performance may be degraded. Particularly, in the next generation communication, there is a need for an LLR detection method that requires a high data transmission rate and can reduce the amount of calculation required for obtaining LLR because MIMO technology is attracting attention.

Hereinafter, a new LLR detection method that can reduce the amount of calculation required for LLR acquisition is referred to as an LC (Low Complexity) method. When the transmission data symbol of the interference signal collides with the transmission data symbol of the user signal, the LC method does not consider the number of cases included in the collided symbol in the LLR calculation. Also, the channel gain of the collided interference signal and the transmission power of the interference signal are regarded as noise and used for the calculation of the signal-to-noise ratio.

The LLR obtained using the LC method can be expressed by the following equation.

Here, P is the transmission power of the interference signal causing the collision.

If the collided user uses two reception antennas, the LLR obtained using the LC scheme can be expressed by the following equation.

Thus, when calculating the LLR by the LC method, the number of the exponential terms to be included in the LLR calculation is equal to the number of the exponential terms of the ML system when the collision does not occur. The number of exponential terms of the ML method is 126 when the collision occurs, and it can be seen that the amount of LLR calculation is significantly reduced in the LC method.

Therefore, even when collision occurs between different users, it is possible to restore the data without increasing the overhead of the system by reducing the amount of calculation required for LLR acquisition. Thus, the overall system performance can be improved.

Hereinafter, a simulation result of the reception performance of the receiver and the reception method will be described. The data transmitted in the simulation is encoded using a turbo code. The coding rate is 1/3. In addition, data encoded through encoding is mapped to transmission data symbols of a 16-QAM modulation scheme. The transmission environment assumes that there are two users in the AWGN environment. The collision rate (CR) between two users is assumed to be 0, 0.1, 0.3, or 0.5. The detection method for the received signal uses ML method, MAX method, and LC method. Through simulation, we analyze the change of frame error rate (FER) performance according to the change of collision probability of each detection method.

FIG. 6 is a graph illustrating a frame error rate according to bit energy vs. noise power ratio when each user has one receive antenna. The graph x axis is the bit energy to noise power ratio (E _b / N ₀ ) and the y axis is the frame error rate (FER). The unit of bit energy to noise power ratio is decibel (dB).

Referring to FIG. 6, when the collision probability is 0.1, in order to have the same frame error rate, the LC scheme should increase the noise power ratio to bit energy by about 1 dB over the ML scheme or the MAX scheme. That is, when the impulse probability is 0.1, the LC method has a power difference of about 1 dB from the ML method or the MAX method. When the collision probability is 0.3, in order to have the same frame error rate, the LC method should increase the noise power ratio to bit energy by about 2 dB over the ML method or the MAX method. If the collision probability is 0.5, the LC method should increase the noise power ratio to about 4 dB compared to the ML method or the MAX method in order to have the same frame error rate.

FIG. 7 is a graph illustrating a frame error rate according to a bit energy vs. noise power ratio when each user has two receive antennas. The graph x axis is the bit energy to noise power ratio (E _b / N ₀ ) and the y axis is the frame error rate (FER). The unit of bit energy to noise power ratio is decibel (dB).

Referring to FIG. 7, when the collision probability is 0.1, in order to have the same frame error rate, the LC method should increase the noise power ratio to bit energy by about 0.5 dB over the ML method or the MAX method. When the collision probability is 0.3, the LC method should increase the noise power ratio to about 2.5dB compared to the ML method or the MAX method in order to have the same frame error rate. If the collision probability is 0.5, the LC method should increase the noise power ratio to bit energy by about 4.5 dB over the ML method or MAX method in order to have the same frame error rate.

As we have seen, the LC scheme should increase the bit energy to noise power ratio to have the same frame error rate as the ML scheme or the MAX scheme. However, when the collision probability is lower than 0.5, the bit energy to noise power ratio to be increased is an acceptable level of the system. Also, in the actual ORHMA system, there is hardly a case where the collision probability is 0.5. Therefore, the LC method can reduce the overhead of the system by dramatically reducing the amount of calculation without any performance degradation.

All of the functions described above may be performed by a processor such as a microprocessor, a controller, a microcontroller, an application specific integrated circuit (ASIC), etc. according to software or program code or the like coded to perform the function. The design, development and implementation of the above code will be apparent to those skilled in the art based on the description of the present invention.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those skilled in the art that various changes and modifications may be made therein without departing from the spirit and scope of the invention. You will understand. Therefore, it is intended that the present invention covers all embodiments falling within the scope of the following claims, rather than being limited to the above-described embodiments.

1 shows a wireless communication system.

2 is a block diagram illustrating a transmitter.

3 shows an example of 16-QAM constellation.

4 is a block diagram illustrating a receiver in accordance with an embodiment of the present invention.

5 is a flowchart illustrating a data restoration method according to another embodiment of the present invention.

6 is a graph illustrating a frame error rate according to the bit energy vs. noise power ratio when the receiving antenna is one.

FIG. 7 is a graph illustrating a frame error rate according to a bit energy vs. noise power ratio when two receiving antennas are used.

Claims (4)

A method of restoring data in a wireless communication system capable of redundantly allocating radio resources to a plurality of users, Receiving a received signal; Obtaining a log likelihood ratio (LLR) using the channel gain of the interference signal and the transmission power of the interference signal as noise and using the signal gain to calculate a signal-to-interference ratio; And And restoring the data using the LLR, The wireless communication system is an ORHMA (Orthogonal Resource Hopping Multiple Access) system, The LLR

. Q denotes a channel gain of the data, n denotes a number of coordinates of a 16-QAM (Quadrature Amplitude Modulation) constellation, N0 denotes a noise spectral density, g denotes a channel gain of the data, P is the channel gain of the interference signal, and P is the transmission power of the interference signal. delete delete A receiver operating in an ORHMA (Orthogonal Resource Hopping Multiple Access) system, A receiving antenna for receiving a received signal; An LLR detector for calculating an LLR by using a channel gain of an interference signal and a transmission power of the interference signal as a noise and calculating the signal-to-interference ratio; And And a channel decoder for decoding the data signal using the LLR, The LLR

≪ / RTI > Q denotes a channel gain of the data, n denotes a number of coordinates of a 16-QAM (Quadrature Amplitude Modulation) constellation, N0 denotes a noise spectral density, g denotes a channel gain of the data, P is the channel gain of the interference signal, and P is the transmission power of the interference signal.

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