KR101476204B1 - Method For Transmitting Signals Using Modified Codeword-Layer Mapping Table - Google Patents

Abstract

We describe how to efficiently define the mapping relationship between code words and layers in a multi-antenna system, and how to transmit signals using them.

Modulating a predetermined bit block in accordance with each of the one or more code words to generate a modulation symbol stream for each codeword and then modulating the modulation symbols according to each of the one or more codewords in accordance with any combination of predetermined mapping combinations. Mapping a modulation symbol to a layer and mapping the codeword to a layer until the number of the layers is at most 8 and the number of codewords is at most 4, And the number of layers to which one codeword is mapped is limited to a number less than or equal to a ratio corresponding to a ratio of the total number of layers divided by the total number of codewords.

Codeword, Layer, Stream

Description

[0001] The present invention relates to a codeword-layer mapping scheme,

The following description relates to a method for effectively defining a mapping relationship between a codeword and a layer in a multi-antenna system, and using the same to transmit a signal.

In short, MIMO is short for "Multi-Input Multi-Output", so far it has been removed from using one transmit antenna and one receive antenna to improve transmit and receive data efficiency by employing multiple transmit antennas and multiple receive antennas How can you say. That is, a technique for increasing the capacity or improving the performance by using multiple antennas at the transmitting end or the receiving end of the wireless communication system. Here, MIMO is referred to as multiple antennas.

1 is a block diagram of a general multi-antenna (MIMO) communication system.

As shown in FIG. 1, if the number of transmission antennas is increased to N _{T and the} number of reception antennas is increased to N _R simultaneously, unlike the case where a plurality of antennas are used only in a transmitter and a receiver, The transmission capacity is increased. As a result, the transmission rate can be improved and the frequency efficiency can be remarkably improved. The transmission rate in accordance with the increase of the channel transmission capacity can theoretically increase by the multiplication of the maximum rate R _O when one antenna is used and the rate rate R _I multiplied by the following.

That is, for example, in a MIMO communication system using four transmit antennas and four receive antennas, the transmission rate can be four times the theoretical one in comparison with the single antenna system. Since the theoretical capacity increase of such a multi-antenna system has been proved in the mid-90s, various techniques have been actively researched so far to improve the actual data transmission rate. Some of these technologies have already been used for the third generation mobile communication and next generation wireless LAN And the like.

The research trends related to multi-antennas to date include information theory studies related to calculation of multi-antenna communication capacity in various channel environments and multiple access environments, research on wireless channel measurement and modeling of multi-antenna systems, and improvement of transmission reliability and transmission rate And research on space-time signal processing technology for various applications.

The multi-antenna technique has a spatial diversity scheme that increases transmission reliability using symbols that have passed through various channel paths, and a scheme that simultaneously transmits a plurality of data symbols using a plurality of transmission antennas to improve a transmission rate And can be divided into a spatial multiplexing method. In addition, research on how to appropriately combine these two approaches and obtain their respective advantages is also a subject of much research recently.

In order to explain the communication method in the multi-antenna system more specifically, it can be expressed as follows when it is mathematically modeled. As shown in FIG. 1, it is assumed that there are N _T transmit antennas and N _R receive antennas.

First of all, with respect to a transmission signal, if there are N _T transmission antennas, the maximum number of information that can be transmitted is N _T , which can be expressed by the following vector.

에 있어 전송 전력을 달리 할 수 있으며, 이때 각각의 전송 전력을 P ₁,P ₂,…,

라 하면, 전송 전력이 조정된 전송 정보는 다음과 같은 벡터로 나타낼 수 있다.On the other hand, each transmission information s ₁ , s ₂ , ... ,

And the transmission power of each of them is P ₁ , P ₂ , .... ,

, The transmission information whose transmission power is adjusted can be expressed by the following vector.

를 전송 전력의 대각행렬 P 를 이용하여 다음과 같이 나타낼 수 있다.Also,

Can be expressed as follows using the diagonal matrix P of transmit power.

에 가중치 행렬 W 가 적용되어 실제 전송되는 N _T 개의 송신신호(transmitted signal) x₁,x₂,…,

가 구성되는 경우를 고려해 보자. 여기서, 가중치 행렬은 전송 정보를 전송 채널 상황 등에 따라 각 안테나에 적절히 분배해 주는 역할을 수행한다. 이와 같은 전송 신호 x₁,x₂,…,

를 벡터 x를 이용하여 다음과 같이 나타낼 수 있다. 이때, 신호 벡터 x로 다음과 같이 표시하기로 한다. 여기서 w _ij 는 i 번째 송신안테나와 j 번째 정보간의 가중치를 의미하며, 행렬로 W 로 표시하기로 한다. W 는 가중치 행렬(Weight Matrix) 또는 프리코딩 행렬(Precoding Matrix)이라고 불린다.On the other hand,

N _T transmitted signals x ₁ , x ₂ , ..., x n, to which the weight matrix W is applied, ,

. Here, the weight matrix plays a role of appropriately distributing the transmission information to each antenna according to the transmission channel condition and the like. The transmission signals x ₁ , x ₂ , ... ,

Can be expressed as follows using the vector x . At this time, the signal vector x is expressed as follows. Where w _ij Denotes the weight between the i- th transmit antenna and the j- th information, and is denoted by W as a matrix. W is called a weight matrix or a precoding matrix.

On the other hand, the above-described transmission signal x can be divided into a case of using spatial diversity and a case of using spatial multiplexing.

When spatial multiplexing is used, different signals are multiplexed and transmitted, so that the elements of the information vector s have different values. On the other hand, when spatial diversity is used, the same signal is transmitted through multiple channel paths So that the elements of the information vector s all have the same value.

Of course, a method of mixing spatial multiplexing and spatial diversity can be considered. That is, for example, the same signal may be transmitted through three transmit antennas using spatial diversity, and the remaining signals may be transmitted by spatial multiplexing.

는 벡터로 다음과 같이 표현 하기로 한다. If there are N _R receive antennas, the received signals y ₁ , y ₂ , ... ,

Is expressed as a vector as follows.

Meanwhile, when a channel is modeled in a multi-antenna communication system, a channel can be classified according to a transmission / reception antenna index, and a channel passing from a transmission antenna j to a reception antenna i is denoted by h _ij . Here, note that the order of indexes of h _ij is the index of the receiving antenna and the index of the transmitting antenna.

These channels can be grouped together and displayed in vector and matrix form. An example of a vector representation is as follows.

2 is a diagram illustrating channels from N _T transmit antennas to receive antenna i .

As shown in FIG. 2, a channel arriving from a total of N _T transmit antennas to receive antenna i can be expressed as follows.

In addition, when using a matrix expression as the expression (7) represents all the channel passes through the N _R receive antennas from the N _T transmit antennas can be expressed as:

을 벡터로 표현하면 다음과 같다.Since the actual channel is added with additive white Gaussian noise (AWGN) after passing through the channel matrix H as described above, the white noise n ₁ , n ₂ , ... added to each of the N _R reception antennas ,

Is expressed as a vector as follows.

Through the above equation modeling, the received signal can be expressed by the following equation.

The above description has focused on the case where a multi-antenna communication system is used for a single user. However, it is possible to acquire multiuser diversity by applying the multi-antenna communication system to a plurality of users, and a brief description will be given below.

Fading channels are a major cause of poor performance of well-known wireless communication systems. The channel gain value changes according to time, frequency, and space, and the lower the channel gain value, the greater the performance degradation becomes. Diversity, one of the ways to overcome fading, exploits the fact that the probability of multiple independent channels all having low gain values is very low. Meanwhile, a codeword used in the multi-antenna communication system will be described as follows.

In a typical communication system, a receiver uses a forward error correction code to code the information sent from the transmitter in order to correct the error experienced by the channel. The receiver demodulates the received signal and then decodes the error correction code to recover the transmission information. Through this decoding process, the error on the received signal caused by the channel is corrected.

All error correction codes have a maximum correctable limit at the time of channel error correction. That is, if the received signal has an error exceeding the limit of the error correcting code, the receiver can not decode it with errorless information. Therefore, the receiving end needs a basis for determining whether there is an error in the decoded information. In this way, a special type of encoding process is required for error detection separately from error correction encoding. CRC (Cyclic Redundancy Check Code) is widely used as the error detection code.

CRC is one of coding methods used for error detection rather than error correction. In general, transmission information is encoded using CRC, and then forward error correction code is used for CRC-encoded information. One unit that is often encoded by applying CRC and error correction codes is called a " codeword ".

On the other hand, when multiple pieces of transmission information are received in a superposed manner, a performance improvement can be expected by using an interference cancellation type receiver. There are cases where multiple transmission information is received in a superposed manner, for example, a multi-antenna (MIMO) technique, a multiuser detection technique, or a multi-code technique. The interference cancellation structure will be briefly described as follows.

Demodulates / decodes the first information from the entire received signal, which is once superimposed with a plurality of information, and then removes information related to the first information from the entire received signal. Thus, the second signal is demodulated / decoded with the first information removed from the received signal. In the demodulation / decoding of the third signal, the first information and the second information are removed from the first received signal, and the fourth and subsequent signals are demodulated / decoded by repeating the above process. The method of continuously removing the demodulated / decoded signal from the received signal to improve the performance of the subsequent demodulation / decoding process is also referred to as a successive interference cancellation (SIC) method.

In order to use the interference cancellation scheme such as the SIC, the demodulated / decoded signal removed from the received signal must be error-free. If there was an error, error propagation will occur which will continue to have a bad influence on demodulation / decoding of all subsequent signals.

The interference cancellation technique as described above can also be used in multi-antenna technology. When the interference cancellation technique is used, multiple transmission information is transmitted over multiple antennas. That is, when the spatial multiplexing technique is used, an interference cancellation technique can be used while detecting each transmission information.

However, as described above, in order to minimize the error propagation phenomenon occurring at the time of interference cancellation, it is preferable to discriminate whether the demodulated / decoded signal is missing, and then selectively remove the interference. The CRC mentioned above is a practical means for judging the error of each transmission information. Usually, the unit of information that has passed through such CRC encoding is called "codeword ". Therefore, as a more practical method, the interference cancellation technique is used not only when there are a plurality of transmission information but also when there are a plurality of code words.

On the other hand, the number of rows and columns of the channel matrix H indicating the state of the channel is determined by the number of transmitting / receiving antennas. The number of rows as the channel matrix H is shown earlier becomes equal to the number N _R of the reception antennas, the number of columns becomes equal to the number N _T transmit antennas. That is, the channel matrix H is N _R x N _T matrix.

In general, the rank of a matrix is defined as the minimum number of independent rows or columns. Thus, the rank of the matrix can not be greater than the number of rows or columns. For example, the rank ( H ( H )) of the channel matrix H is limited as follows.

Another definition of the rank is defined as the number of eigenvalues that are not zero among the eigenvalues when the matrix is subjected to eigenvalue decomposition. Similarly, when the rank is SVD (Singular Value Decomposition), it can be defined as the number of non-zero singular values. Therefore, the physical meaning of a rank in a channel matrix is the maximum number that can transmit different information in a given channel.

Let's define each of the different information sent using the multi-antenna technique as a "transport stream" or simply a "stream". Such a "stream" may be referred to as a "Layer ". Then, the number of transport streams can not be larger than the maximum number of channels that can send different information.

If the channel matrix is H , this can be represented as follows.

Here, "# of streams" represents the number of streams. Note, however, that one stream may be transmitted over more than one antenna.

A correspondence method between a stream and an antenna will be described as a classification of a multi-antenna technique as follows. A spatial diversity scheme may be used for transmission through a plurality of antennas of one stream, and a spatial multiplexing scheme may be used for a case where a plurality of streams are transmitted through several antennas. Of course, a hybrid of spatial diversity and spatial multiplexing is possible.

Next, the relationship between codewords and streams in a multi-antenna communication system will be described.

3 is a diagram for explaining the relationship of antennas, streams, and codewords in a MIMO communication system.

There are various ways to correspond codewords and streams. A typical method is as follows: once the codeword (s) are generated as shown in Fig. 3, each codeword is again associated with the transport stream (s) via a "codeword- And is transmitted through a transmission antenna through a "stream-antenna mapping module ".

Among these processes, the part for determining the combination of the codeword and the stream to be mainly described here is a portion indicated by a bold line in FIG.

Ideally, the correspondence between codewords and streams can be freely set. That is, one codeword may be divided into several streams, and multiple codewords may be combined and transmitted in one stream. However, since combining several codewords serially serially is regarded as a kind of encoding, in the following description, a meaningful combination is limited to a case where one codeword corresponds to one or more streams do. It should be apparent to those skilled in the art, however, that the present invention can also be applied to a case where the above-described features are separately distinguished.

Therefore, in the following description, it is assumed that one codeword corresponds to one or more streams unless otherwise specified. Therefore, if all of the information is transmitted through the encoding process, the following relationship is formally established.

Here, "# of codewords" is the number of codewords, and "# of streams"

In summary, the above equations (11) to (13) can be collectively summarized as follows.

In this way, we can see the following facts. That is, when there is a limitation on the number of transmitting / receiving antennas, the maximum number of streams is limited. In addition, when the number of codewords is limited, the minimum number of streams is limited.

Due to the correlation between the codeword and the stream, if the number of antennas is limited, the maximum number of streams and codewords is limited, thereby allowing a limited number of codewords and streams to be combined.

This combination of codeword and stream is required in both uplink and downlink. For example, suppose that a multi-antenna technique is applied in the downlink for convenience of explanation. At this time, precise demodulation / decoding is possible only when the combination used in the information transmission among the combination of the entire codeword and the stream is precisely indicated on the receiving side in the information transmission using the multi-antenna technique in the downlink.

Also, it is necessary to inform, for example, a combination of the entire codeword and stream combination, even when transmitting the control information in the uplink. More specifically, for the multi-antenna technology, the transmitter needs to know the channel and state of the receiver. To this end, the receiver must inform the receiver of various control information through the uplink. For example, on the receiving side, considering the various states of the receiver, such as the measured channel and buffer state, a combination of the preferred codeword and stream, a Channel Quality Indicator (CQI) Information such as a precoding matrix index (PMI) should be informed. Of course, the details of the control information may vary depending on the multi-antenna technique used. However, the fact that the combination of codewords and streams preferred over the uplink does not change.

As another example, if the multiple antenna technique is applied in the uplink, the description of the above example is the same as that only the transmission link is mutually exchanged, and the combination and the preferred combination of the entire combination between the codeword and the stream are used. In displaying such a combination of codewords and streams, if it can be expressed in an effective way with a smaller number of bits, it is a great gain in efficient transmission of control information. Therefore, there is a demand for research on effective display methods of such codewords and streams.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a MIMO communication system, and more particularly, to a codeword and layer combination display method, a layer mapping method and a data transmission method using the same.

That is, it is an object of the present invention to provide a method for limiting the number of combinations of codewords and streams by a reasonable method and reducing the number of bits of information for representing the codewords.

It is another object of the present invention to provide a data processing method for effectively dividing one codeword into one or more layers when data is transmitted through multiple transmit antennas in a wireless communication system.

According to an aspect of the present invention, there is provided a method of mapping a code word to a layer in a multi-antenna system, the method comprising: modulating a predetermined bit block according to each of the one or more code words, Generating a modulation symbol stream; Mapping modulation symbols according to each of the one or more code words to one or more of the layers according to any combination of predetermined mapping combinations; And transmitting the layer-mapped modulation symbols,

The predetermined mapping combination specifies a mapping relationship between each codeword and a layer until the number of layers is at most 8 and the number of codewords is at most 4, and the number of layers to which one codeword is mapped Is a combination limited to a number less than or equal to a ratio of the total number of layers divided by the total number of codewords.

In addition, the predetermined mapping combination may be a combination in which the number of layers to which one code word is mapped is set to be as equal as possible.

Also, the predetermined mapping combination may be a combination in which the number of layers to which one codeword is mapped is limited to 1, 2, 4, 6 and 8, or the number of layers to which one codeword is mapped is 1, 2, 3 , 4, 6, and 8, respectively.

In addition, the predetermined mapping combination may define one code word-layer mapping according to the number of layers, and for a specific number of layers, a mapping combination for retransmission using the specific number of layers May be included.

According to the above-described embodiments of the present invention, it is possible to limit the total number of combinations of code words and streams through a reasonable method, thereby effectively reducing the signaling overhead.

Hereinafter, preferred embodiments according to the present invention will be described in detail with reference to the accompanying drawings. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following detailed description, together with the accompanying drawings, is intended to illustrate exemplary embodiments of the invention and is not intended to represent the only embodiments in which the invention may be practiced.

The following detailed description includes specific details in order to provide a thorough understanding of the present invention. However, those skilled in the art will appreciate that the present invention may be practiced without these specific details. In some instances, well-known structures and devices are omitted or shown in block diagram form around the core functions of each structure and device in order to avoid obscuring the concepts of the present invention. In the following description, the same components are denoted by the same reference numerals throughout the specification.

The present invention intends to provide a method for reducing the number of bits of information for reasonably limiting the total number of combinations of codewords and streams as described above. To do this, we first look at the number of possible combinations from the relationship between the codeword and the stream, and then how to reasonably limit the number of such combinations.

If the number of transmit / receive antennas and the number of codewords is limited, the maximum number and minimum number of streams are determined from Equation (14).

In the following, the number of antennas is limited to 8, but the same restriction can be applied even when the number of antennas is 16 or more. If the number of transmission / reception antennas is 8, for example, the number of streams and code words can be a maximum of 8. On the other hand, if the number of codewords is limited, the minimum possible number of streams is limited. If the number of codewords is two, the number of streams is at least equal to two. Thus, if the number of transmit and receive antennas is eight and the number of codewords is two, then the number of possible streams is two, three, four, five, six, seven, and eight.

Recently, in 3GPP LTE (3 ^rd Generation Partnership Project Long Term Evolution), the number of codewords is limited to two and the number of antennas is limited to four. Accordingly, in the following description, it is intended to focus on the case where the number of codewords is two, three, four, and the number of antennas is eight.

If the number of streams is 8 and the maximum number of codewords is 4, the total combination of possible codewords and streams is shown in Table 1.

The order of the codewords in all of the following tables, including Table 1, is not important. It is important to know how many codewords are transmitted rather than the order of codewords. When the streams are mapped to antennas again, the mappings to the antennas are changed according to the order of the streams. When precoding is used, the mappings are also changed in accordance with the order of the relationships with the corresponding weight vectors However, according to the research result in 3GPP LTE, since the difference in performance is small according to the fixed order of the streams, the stream will not be considered in the same order as codewords in the present invention.

For the sake of convenience, CW and S shall be used as abbreviations of "codeword" and "stream" in the following tables including Table 1 above. That is, CW4 means that the number of codewords is four, and S8 means that the number of streams is eight. Numbers separated by a semicolon (;) indicate the number of streams mapped to each codeword. That is, (2: 3) means that two streams are mapped to the first codeword and three streams are mapped to the second codeword.

On the other hand, in Table 1, when the number of maximum usable codewords is four, the number of usable codewords is one to four. CW1 to CW4 denote the case where all the 1 to 4 codewords are available. In other words, in the following description, CWX-CWY is to be displayed when X number of possible code words are possible.

It is also possible to have one or more combinations of specific streams mapped to each code word to represent a combination of all possible codewords and streams. For example, when using CW1-CW4, the possible combinations of CW2 and S7 are (1; 6), (2; 5), and (3; This means that when seven streams are mapped using two codewords (1; 6), one stream is mapped to the first codeword and six streams are mapped to the second codeword. Similarly, (1; 1; 2; 2) maps four streams of codewords, one stream for the first and two codewords, and two streams for the third and fourth codewords, You can say that it maps the stream. (1; 2; 1; 2) and (1; 1; 2; 2) can be used with the same meaning.

In Table 1, the tables divided by the double lines represent combinations of various codewords. That is, the first leftmost part of Table 1, consisting of the left part of the first double line, is the case where the number of codewords of all numbers up to CW1-CW4 is possible. Part of the second table, separated by the first double line and the second double line, is where CW1, CW2, and CW4 are used, except when three code words are used. Likewise, the third part means that up to three codewords are used up to CW1-CW3, and the last part shows cases where up to two codewords are used.

As described above, in the following description of the present invention, in order to efficiently show the mapping relationship even in the combination of various codewords, it is assumed to be expressed in a bundle as shown in Table 1 for convenience.

If the codewords CW1 to CW2 are used from Table 1, it is possible to display a maximum of 5 bits (2 ⁴ <24 <2 ⁵ ) if all combinations are allowed without any restriction. Also, if CW1-CW3 is used, maximum 6 bits (2 ⁵ <40 <2 ⁶ ) can be displayed if all combinations are allowed without any restrictions. Furthermore, if CW1-CW4 is used up to 6 bits (2 ⁵ <52 <2 ⁶ ) can be displayed. The combination of CW1, CW2, and CW4 is also referred to as a table, and the combination is considered in a manner similar to the above three cases, so detailed calculations and additional explanations will be omitted.

In Table 1, since it is possible to represent all possible combinations, it is possible to express a plurality of combinations in arbitrary codewords and arbitrary streams. However, in the following, some restrictions are applied to reduce the total number of possible combinations.

1. If there is no limit on the number of codewords that can be mapped to a stream

Let's start with a case where there is no limit on the number of possible codewords in a single stream representation. That is, the number of codewords representing one stream is represented in various cases.

1-A) How to allocate as many streams as possible to one codeword

The first method is to allocate as many streams as possible to one codeword of all codewords. That is, the possible codewords in which one stream is allocated to the remaining codewords are shown in Table 2 below.

When the codewords CW1 to CW2 are used, a maximum of 4 bits (2 ³ <15 <2 ⁴ ) is displayed. If CW 1 to CW 3 are used, a maximum of 5 bits (2 ⁴ <21 <2 ⁵ ) Can be expressed by the following formula. Furthermore, if CW1-CW4 is used up to 5 bits (2 ⁴ <26 <2 ⁵ ) can be displayed. The present embodiment is characterized in that a pattern for mapping one stream to one codeword is repeated, which is simple in implementation. That is, when the codeword-layer mapping relation is set as shown in Table 2, the hardware implementation for transmitting CW1 can be maintained regardless of the number of codewords.

1-B) Assigning as many streams as possible to each codeword

As a second method, we propose a method to map the stream to a similar number to the entire codeword. As discussed in 3GPP LTE, when four streams are mapped to two codewords, two streams are mapped to one codeword, which can be expressed as (2; 2). As described above, it is possible to obtain a gain using SIC more efficiently than when mapping the same number of streams to each codeword as possible. This will be described in more detail.

4 is a diagram for explaining an advantage of the case where the number of streams mapped to each codeword is the same according to an embodiment of the present invention.

FIG. 4 illustrates an example of mapping two codewords into four streams. A case where CW1 is mapped to one stream (stream 1) and CW2 is mapped to three streams (streams 2 to 4) as shown in Fig. 4 (a) will be described. If CW1 is mapped to stream 1 and then removed from the entire received signal, the signal removed from the entire received signal is small and the SIC gain obtained in decoding for CW2 received through the three streams is small. In addition, when the CW2 signal received through the three streams is first decoded and subtracted from the entire signal, the SIC gain can not be obtained when decoding the CW2 signal received through the three streams.

On the other hand, when the number of streams to be mapped per code word is set to be the same or as close as possible, as shown in FIG. 4B, the SIC gain can be acquired more efficiently in each decoding.

The above-described mapping method can be considered to be extended even when two or more code words are used. That is, five streams can be mapped to two codewords (2; 3) and three codewords (1; 1; 1). Table 3 summarizes the results.

When the codewords CW1 to CW2 are used from Table 3, the maximum 4 bits (2 ³ <15 <2 ⁴ ) are displayed and when the CW 1 to CW 3 is used, the maximum 5 bits (2 ⁴ <21 <2 ⁵ ) have. Furthermore, if CW1-CW4 is used up to 5 bits (2 ⁴ <26 <2 ⁵ ) can be displayed.

1-C) Assigning only one or even streams to each codeword

The third method is to limit the number of streams mapped to each codeword to one or an even number. That is, an odd number of streams other than 1 are not mapped to the codeword. In this case, unlike Table 2 and Table 3, it can be seen from Table 4 that the number of combinations can be reduced compared to Table 1 although streams having the respective codewords can have one or more combinations.

If the codewords CW1 to CW2 are used from Table 4, they can be expressed by a maximum of 4 bits (2 ³ <15 <2 ⁴ ), and if CW 1 to CW 3 are used, they can be expressed by a maximum of 5 bits (2 ⁴ <21 <2 ⁵ ) have. Furthermore, if CW1-CW4 is used up to 5 bits (2 ⁴ <26 <2 ⁵ ) can be displayed.

1-D) A method of allocating the number of streams allocated to each codeword by limiting the total number of streams divided by the total number of codewords

The present embodiment proposes a method of limiting the number of streams mapped to one codeword to the number corresponding to a ratio obtained by dividing the total number of streams by the total number of codewords. Since the number of codewords is odd and the number of streams is an even number, the number of streams mapped per codeword can be expressed by the following equation.

That is, the maximum number of streams is 8 when the codeword is 1, 4 is the maximum when the codeword is 2, 3 is the maximum when the codeword is 3, and 2 when the codeword is 4.

According to the present embodiment, the total combination can be expressed as shown in Table 5 by applying Equation (15).

When codewords CW1 to CW2 are used as shown in Table 5, up to four streams can be mapped per one codeword, and a maximum of 4 bits (2 ³ &lt; 14 &lt; 2 ⁴ ) CW1-CW3 can be used to map up to three streams per codeword, so it can be represented by a maximum of 5 bits (2 ⁴ <18 <2 ⁵ ). Finally, when CW1-CW4 is used, up to 4 bits (2 ³ <14 <2 ⁴ ) can be expressed because a maximum of 4 streams can be mapped per codeword.

1-E) How to limit the number of possible streams to 1,2,3,4,6,8

On the other hand, even if a maximum of eight streams are supported, since odd numbers are unlikely to appear except for a channel rank of 1, the number of streams can be represented by only one stream and the number of streams can be represented by an even number of streams. However, since 3GPP LTE supports 3 streams already, it can be shown that the number of streams is 1,2,3,4,6,8 only. In the examples of Tables 2 to 5 The following applies.

Table 6 above shows a method in which the number of streams 1, 2, 3, 4, 6, and 8 is used in Table 2. When the codewords CW1 to CW2 are used, a maximum of 4 bits (2 ³ <11 <2 ⁴ ) can be displayed. When CW 1 to CW 3 is used, a maximum of 4 bits (2 ³ <15 <2 ⁴ ) can be displayed. Furthermore, if you use up to CW1-CW4, you can display up to 5 bits (2 ⁴ <18 <2 ⁵ ).

Table 7 above shows a method in which only the stream numbers 1, 2, 3, 4, 6, and 8 are used in Table 3. If the codewords CW1 to CW2 are used, they can be displayed with a maximum of 4 bits (2 ³ <11 <2 ⁴ ) and a maximum of 4 bits (2 ³ <15 <2 ⁴ ) if CW1-CW3 is used. Furthermore, if you use up to CW1-CW4, you can display up to 5 bits (2 ⁴ <18 <2 ⁵ ).

Table 8 shows a method in which only the stream numbers 1, 2, 3, 4, 6, and 8 are used in Table 4. In this case, if the codewords CW1 to CW2 are used, they can be displayed with a maximum of 4 bits (2 ³ <12 <2 ⁴ ) and a maximum of 5 bits (2 ⁴ <18 <2 ⁵ ) if CW1-CW3 is used . Furthermore, if CW1-CW4 is used up to 5 bits (2 ⁴ <22 <2 ⁵ ) can be displayed.

Table 9 above shows a method in which only the stream numbers 1, 2, 3, 4, 6, and 8 are used in Table 5. In this case, if the codewords CW1 to CW2 are used, the maximum 4 bits (2 ³ <11 <2 ⁴ ) are displayed, and if CW1-CW3 is used, the maximum 4 bits (2 ³ <13 <2 ⁴ ) can be displayed. Furthermore, if CW1-CW4 is used up to 4 bits (2 ³ <11 <2 ⁴ ) can be displayed.

1-F) Limiting the number of possible streams to 1,2,4,6,8

On the other hand, in 3GPP LTE, three streams are considered because four streams are supported. However, in the present invention, all the odd streams except for one stream are limited It is also possible. Tables 10 to 13 below show the method of limiting the number of streams to 1, 2, 4, 6, and 8 in Tables 1 to 5 summarized above.

Table 10 above shows a method in which only the stream numbers 1, 2, 4, 6, and 8 are used in Table 2. When the codewords CW1 to CW2 are used, it is possible to display up to 4 bits (2 ³ <9 <2 ⁴ ) when CW 1 to CW 3 is used, (2 ³ <12 <2 ⁴ ). Furthermore, up to 4 bits (2 ³ <15 <2 ⁴ ) can be displayed when using up to CW1-CW4.

Table 11 above shows a method in which only the stream numbers 1, 2, 4, 6, and 8 are used in Table 3. If the codeword-stream combination is set as shown in Table 11, a maximum of 4 bits (2 ³ <9 <2 ⁴ ) can be displayed if the codewords CW 1 to CW 2 are used, 2 ³ <12 <2 ⁴ ). Furthermore, up to 4 bits (2 ³ <15 <2 ⁴ ) can be displayed when using up to CW1-CW4.

Table 12 shows a method in which only the stream numbers 1, 2, 4, 6, and 8 are used in Table 4. When a codeword-stream combination is set as shown in Table 12, a maximum of 4 bits (2 ³ <10 <2 ⁴ ) is displayed if the codewords CW 1 to CW 2 are used and a maximum of 4 bits ³ &lt; 15 &lt; 2 ⁴ ). Furthermore, if CW1-CW4 is used up to 5 bits (2 ⁴ <19 <2 ⁵ ) can be displayed.

Table 13 above shows a method in which only the stream numbers 1, 2, 4, 6, and 8 are used in Table 5. When a codeword-stream combination is set as shown in Table 13, up to 4 bits (2 ³ <9 <2 ⁴ ) are displayed if the codewords CW 1 to CW 2 are used, and up to 4 bits ³ &lt; 10 &lt; 2 ⁴ ). Furthermore, up to 4 bits (2 ³ <9 <2 ⁴ ) can be displayed when using up to CW1-CW4.

2. If there is only one possible codeword in a stream

In the combination of codewords and streams mentioned above, it is possible to combine a plurality of codewords when representing one stream. For example, in Table 13, codewords supporting six streams in CW1-CW4 could be expressed in two of CW3 (2; 2; 2) and CW4 (1;

In the following description, the number of combinations is reduced by mapping one codeword to each stream. In other words, although the total number of combinations is reduced by decreasing the number of possible streams so far, the following will be the case of reducing the total number of combinations while using all streams.

As is well known, there is a disadvantage that the amount of feedback of the system increases when the number of codewords is increased, but there is an advantage that the performance can be improved. Therefore, if the number of streams is four or more, it can be mapped to CW4 if the system supports up to four codeword counts as the first method. As a second method, when the amount of feedback of the system is limited, when the number of streams is high, mapping is performed using four codewords as much as possible, while when the number of streams is small, mapping is performed using fewer codewords. That is, one codeword is used when the number of streams is 1, and four codewords are used when the number of streams is eight. The stream between them uniformly maps the case of using one codeword and the case of using four codewords evenly. In the following table, the gray areas are considered for retransmission.

Table 14 below applies the above limitation criteria to a method of mapping as many streams as possible to one codeword as shown in Table 2 above.

(1, 1) - (1, 3) is a method for using CW4 as much as possible for system performance, (2, 1) - (2, 3) is one for each of CW1 and CW2 The remaining streams minus the number of streams are evenly distributed in CW3 and CW4, and are mapped by dividing them into similar numbers.

In Table 15 below, (3,1) - (5,4) maps the number of streams that can be supported to CW2, CW3, and CW4 in a similar number considering the feedback amount of the system.

For example, in (4,1), S1 can be mapped to CW1, and S2 and S3 can be mapped to two codewords. In S4, S5 and S6, mapping is performed using three code words, and S7 and S8 can be mapped using four code words.

On the other hand, the number of bits that can be used according to the system can be changed depending on whether the retransmission case is considered together with the total number of codeword and stream mapping combinations. If the total number of combinations in parentheses is calculated by considering the retransmission as a codeword mapping and the total number of bits required for retransmission is calculated in the system, the total sum of values outside the parentheses is used as a necessary total combination Can be called water. Assignments for retransmissions are shown in gray in each table. Hereafter, the calculation of the number of bits required for the total combination is omitted, and the mapping of the codewords and streams as possible will be tabulated.

The reason why CW1, CW2, and CW4 are not shown in Table 14 is that three streams can not be mapped to four codewords.

Table 15 above maps streams of S1-S8 to CW2, CW3 and CW4 in a similar number as mentioned above. Tables 16 to 21 below show the mapping of codewords and streams as possible by applying the criteria shown in Table 3 to Table 5 above, and therefore duplication of explanations will be avoided.

2-A) How to allocate the number of possible streams by limiting to 1,2,3,4,6,8

Tables 6 to 9 limit the number of streams mapped to codewords to 1, 2, 3, 4, 6, 8 in order to reduce the total number of combinations. These limitations can also be applied to Tables 14 to 21 as shown in Tables 22 to 29 below. Because the number of possible streams is limited to 1, 2, 3, 4, 6, 8, the number of streams mapped to codewords CW3, CW4 is reduced. In other words. Since the number of streams such as 5 and 7 is limited, the possibility of mapping using a relatively large number of codewords is reduced.

In Table 22 to Table 29, when five retransmissions are required for two or less streams while five streams and seven streams are excluded, mappings of codewords and streams considering retransmission can be expressed by only three bits.

2-B) How to limit the number of possible streams to 1,2,4,6,8

In order to further reduce the total number of combinations following Tables 22 to 29, the number of streams mapped to code words is limited to 1, 2, 4, 6, and 8. Since the number of streams is already large, the number of odd streams including the case of using three streams is further strengthened. Since the basic application method is similar, additional description will be omitted.

In the Tables 30 to 37, when the number of retransmissions is three or less, three streams, five streams, and seven streams are excluded, the codeword and stream mappings considering retransmission can be expressed by only three bits.

In the above-described embodiments, a mapping method for minimizing the number of corresponding codeword-to-stream combinations among possible combinations according to a given number of codewords and a number of streams (or layers) has been described. Hereinafter, a method of efficiently processing data and transmitting signals under such a condition as described above will be described.

5 is a block diagram illustrating a method of transmitting a signal according to an embodiment of the present invention.

In a typical wireless communication system, channel coding is performed for reliable data transmission. Channel coding refers to coding the transmission information by using a forward error correction code in order to allow the receiver to correct an error experienced by the channel. As an example of such encoding, a turbo code can be used, and scrambling 501 is performed to transmit the encoded codewords through one or more physical channels.

The scrambled information bit blocks are input to the modulation mapper 502. The modulation mapper 502 performs modulation in various manners such as QPSK, 16 QAM, 64 QAM, and outputs a (complex) modulation symbol block (complex-valued modulation symbol) according to the type of the physical channel to be transmitted.

Thereafter, the modulation symbol blocks are input to the layer mapper 503. In the layer mapper 503, a layer is mapped to a layer according to any combination of predetermined mapping combinations.

For example, in the case where CW1-4 is available in Table 16, the case where the mapping combination shown at the bottom of the table is used will be described. If the number of layers is v , v is set to be equal to or less than the number of antennas. In addition, if one codeword is mapped to two or more layers, the modulation symbols corresponding to one codeword may be sequentially mapped (cyclically) to each layer and transmitted.

는 각 레이어당 심볼 개수를 의미하며, 예를 들어

는 인덱스 a를 가지는 레이어의 심볼 개수를 의미한다.

는 a번째 레이어에 매핑되는 i번째 심볼 비트를 나타내며,

는 a번째 코드워드의 i번째 변조 심볼을 나타낸다.In Table 38

Denotes the number of symbols per layer. For example,

Denotes the number of symbols of the layer having the index a.

Denotes an i-th symbol bit mapped to an a-th layer,

Denotes the i-th modulation symbol of the a-th codeword.

As shown in Table 38, the modulation symbols corresponding to each codeword are mapped to layers according to a predetermined codeword-stream mapping combination. The mapped symbols are mapped 505 to a frequency resource via precoding 504 and a signal mapped to a frequency resource is transmitted through an OFDM signal generator 506 to a plurality of antennas, .

Although not shown in FIG. 5, it is necessary for the transmitting side to perform signaling to inform the receiving side of what layer mapping rule the transmitted signal is to be transmitted. This signaling can be explicitly informed through 3-bit signaling that it is one of the eight combinations shown in Table 38, or may be combined with other control information for notification. It is also possible to implicitly inform the receiving side through a combination of other control information.

In the above description with reference to FIG. 5, the case where the mapping combination shown at the bottom of the case where CW1-4 is available in Table 16 has been specifically described, but all combinations of Tables 1 to 37 It is apparent to those skilled in the art that signals can be transmitted in the same manner.

The signal transmission method according to the above-described embodiment can be used for spatial multiplexing signal transmission and also for other transmission, in order to define a code word and a layer mapping relationship.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The foregoing description of the preferred embodiments of the present invention has been presented for those skilled in the art to make and use the invention. It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the present invention as defined by the following claims It can be understood that Accordingly, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

We have discussed the possibility of various combinations of codewords and streams in a MIMO communication system. That is, a combination of a codeword having a minimum number of codewords and a stream mapping in consideration of various possibilities and the ratio of codewords and layers among all possible combinations according to the total codeword and the number of layers is provided, and a data transmission method using the codeword and the stream mapping is provided . That is, in the 3GPP LTE, although a combination of two codewords and four streams are combined, the possibility of more codewords and streams must be taken into consideration for improving performance, and since the number of combinations of codewords and streams increases, By limiting the combination in the manner described above, it is possible to provide an efficient communication service by reducing the number of bits of information required to represent it.

Therefore, the above-described scheme can be used in various ways in the 3GPP LTE-A system, which is a development model of the 3GPP LTE system, and other next generation mobile communication systems.

The signal transmission method according to the above-described embodiment can be used for spatial multiplexing signal transmission and also for other transmission, in order to define a code word and a layer mapping relationship.

1 is a block diagram of a general multi-antenna (MIMO) communication system.

2 is a diagram illustrating channels from N _T transmit antennas to receive antenna i .

3 is a diagram for explaining the relationship of antennas, streams, and codewords in a MIMO communication system.

4 is a diagram for explaining an advantage of the case where the number of streams mapped to each codeword is the same according to an embodiment of the present invention.

5 is a block diagram illustrating a method of transmitting a signal according to an embodiment of the present invention.

Claims (6)

A method for mapping codewords to layers in a multi-antenna system, the method comprising: Modulating a predetermined bit block according to each of the one or more code words to generate a modulation symbol stream for each codeword; Mapping modulation symbols according to each of the one or more code words to one or more of the layers according to any combination of predetermined mapping combinations; And And transmitting the layer-mapped modulation symbols, Wherein the predetermined mapping combination comprises: A mapping relationship between each codeword and a layer is defined until a maximum number of the layers is 8 and a maximum number of the codewords is 4, Wherein the number of layers to which one codeword is mapped is limited to a number less than a number corresponding to a ratio of dividing the total number of layers by the total number of codewords. The method according to claim 1, Wherein the predetermined mapping combination comprises: Wherein the number of layers to which one codeword is mapped is set to be equal to the maximum. The method according to claim 1, Wherein the predetermined mapping combination comprises: Wherein the number of layers to which one codeword is mapped is limited to 1, 2, 4, 6, and 8, respectively. The method according to claim 1, Wherein the predetermined mapping combination comprises: Wherein the number of layers to which one code word is mapped is limited to 1, 2, 3, 4, 6, and 8, respectively. 5. The method according to any one of claims 1 to 4, Wherein the predetermined mapping combination comprises: Wherein a codeword-layer mapping is defined according to the number of each layer. 6. The method of claim 5, Wherein the predetermined mapping combination comprises: Further comprising a mapping combination for retransmission using the specific number of layers for a specific number of layers.

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