KR20140098913A - Method for Interference Alignment in Multi Cell Mutually Interfering MIMO Multiple Access Channles - Google Patents

Method for Interference Alignment in Multi Cell Mutually Interfering MIMO Multiple Access Channles Download PDF

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KR20140098913A
KR20140098913A KR1020130010969A KR20130010969A KR20140098913A KR 20140098913 A KR20140098913 A KR 20140098913A KR 1020130010969 A KR1020130010969 A KR 1020130010969A KR 20130010969 A KR20130010969 A KR 20130010969A KR 20140098913 A KR20140098913 A KR 20140098913A
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South Korea
Prior art keywords
base station
cell
channel
dof
users
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KR1020130010969A
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Korean (ko)
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김동구
채혁진
장진영
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연세대학교 산학협력단
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
    • H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
    • H04B7/0413—MIMO systems
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L5/00—Arrangements affording multiple use of the transmission path
    • H04L5/003—Arrangements for allocating sub-channels of the transmission path
    • H04L5/0058—Allocation criteria
    • H04L5/0062—Avoidance of ingress interference, e.g. ham radio channels

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  • Engineering & Computer Science (AREA)
  • Signal Processing (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Mobile Radio Communication Systems (AREA)

Abstract

Disclosed is an interference alignment method in a multi-cell mutual interference MIMO multiple access channel. The disclosed method includes determining a transmission symbol based on a mode switching pattern; and transmitting the determined transmission symbol. Same symbols are transmitted in same alignment blocks. The disclosed method can achieve optimal DoF without requiring channel information in a transmitter at two cell SIMO IFMAC.

Description

[0001] The present invention relates to an interference sorting method for a multi-cell mutual interference MIMO multiple access channel,

To an interference alignment method in a multi-cell inter-island MIMO multiple access channel.

The maximum DoF in the downlink multi-antenna MISO broadcast channel is

Figure pat00001
. here
Figure pat00002
Is the number of antennas of the base station,
Figure pat00003
The
Figure pat00004
Lt; th > user. In order to achieve this DoF, it is necessary to suppose that the transmitter must know the channel state information at transmitter (CSIT) completely. If the CSIT is quantized, the number of feedback bits proportional to SNR . With high quantization complexity and high feedback amounts, this technique is difficult to implement in real systems.

Research has been conducted to achieve one or more DoFs without CSIT on MISO downlink and interfering channels. In this study, it was shown that the optimum DoF can be achieved when the channel has a special type of coherence block structure without CSIT. However, this special block fading structure is hard to occur in a random fading environment. In another study, a technique has been proposed for achieving one or more DoFs by constructing the mentioned block fading structure through antenna switching in a static fading channel.

The single-cell uplink channel is different from the downlink. In a multi-user uplink channel, the optimal DoF is equal to the DoF achievable in the downlink due to the duality. However, the optimal DoF can easily be achieved by zero-forcing at the receiver without feedback of the channel information. Therefore, it is relatively easy to achieve the optimal DoF in the uplink than in the downlink. Consider a multi-cell uplink. In case of simply zero-forcing neighbor cell interference in a multi-cell uplink, the DoF obtained is not different from that of a single cell. Therefore, a new transmission scheme is required to obtain DoF beyond zero forcing in a multi-cell environment.

In another study, there is a study on optimal DoF in two cell SIMO IFMAC. In order to obtain more than DoF that can be achieved in a single cell, we propose an interference sorting scheme that aligns the transmitted symbols to a neighboring cell base station in a limited space by extending the symbols over time, Respectively. As the number of users increases, it is possible to achieve an interference free DoF, but each user must know the channel information of all users in order to achieve such DoF. However, this causes excessive feedback overhead.

The present invention proposes a method for achieving optimal DoF without channel information in a transmitter in a two-cell SIMO IFMAC.

According to a preferred embodiment of the present invention, there is provided a method of determining a transmission mode, the method comprising: determining a transmission symbol based on a mode switching pattern; And transmitting the determined transmission symbols, wherein the same symbols are transmitted in the same alignment block, and the other symbols are transmitted in another alignment block.

According to the present invention, an optimal DoF can be achieved without channel information in a transmitter in a two-cell SIMO IFMAC.

1 shows a SIMO IFMAC system model;
FIG. 2 illustrates a structure of an alignment block according to an embodiment of the present invention. FIG.
3 is a diagram showing an example of a mode switching pattern.
4 is a diagram illustrating a mode switching pattern according to an embodiment of the present invention.
5 is a diagram illustrating a transmission symbol pattern according to an embodiment of the present invention.
FIG. 6 is a diagram showing the mode switching patterns of FIG. 4 rearranged in an arbitrary time order; FIG.
7 is a diagram of a method for assigning pilot patterns through grouping where channel estimation time interference is reduced based on a user's location.

While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that the invention is not intended to be limited to the particular embodiments, but includes all modifications, equivalents, and alternatives falling within the spirit and scope of the invention. Like reference numerals are used for like elements in describing each drawing.

Hereinafter, embodiments according to the present invention will be described in detail with reference to the accompanying drawings.

The user transmits data only to the serving cell. Thus causing interference to neighboring cells.

These channels

Figure pat00005
SIMO IFMAC, and Fig. 1 is a diagram showing a SIMO IFMAC system model.

the reception signal of the i < th > base station at time t can be expressed by the following equation (1).

Figure pat00006

In Equation (1)

Figure pat00007
The
Figure pat00008
Th cell
Figure pat00009
From the first user
Figure pat00010
Th base station,
Figure pat00011
silver
Figure pat00012
Th cell
Figure pat00013
Th user's transmit symbol,
Figure pat00014
Additive white Gaussian noise (AWGN),
Figure pat00015
The
Figure pat00016
Th cell
Figure pat00017
From users
Figure pat00018
Th < / RTI > base station. ≪ RTI ID = 0.0 &
Figure pat00019
.

DoF is defined as follows.

Figure pat00020

DoF means the number of streams that can be transmitted interference free with the slope of channel capacity at high SNR. The maximum DoF in SIMO IFMAC has been studied conventionally, as follows. .

In a two-cell SIMO IFMAC, the sum of DoF of two base stations for time-varying channels is:

Figure pat00021

In Equation (2)

Figure pat00022
Denotes the DoF of the k-th user in the i-th cell, and 1 (*) denotes the indicator function.

In Equation (2), if the number of users is sufficiently large

Figure pat00023
Can be obtained.

However, to achieve this DoF, every user must know all the other users' channels, and every hour the channel should be independent. If the feedback channel capacity is limited, a rate loss occurs due to channel inaccuracy.

In the following, we propose a B-IA that obtains channel capacity without CSIT in two cell IFMAC through mode switching of reconfigurable antenna.

Blind IA with staggered antenna switching for two cells (M, K) 2 IFMAC

In a two-cell (M, K) 2 SIMO IFMAC, each base station antenna

Figure pat00024
Assuming that the channel is independent and the coherence time of the channel is sufficiently long so that the statistical properties of the channel change only by mode switching, the B The sum DoF of -IA is as follows.

Figure pat00025

At this time, if K is a multiple of M, the achievable DoF of B-IA is equal to the optimal DoF.

Hereinafter, a transmission / reception technique for attaining the DoF of Equation (3) will be described. First, the number of users per cell is divided into a case where the number of users per cell is equal to or greater than M / 2 and a case where the number of users per cell is equal to or less than M / 2. If the number of users per cell is less than or equal to M / 2, since the base station has M antennas, the symbols of its own cell and neighbor cell user can be easily classified as a zero forcing receiver. Therefore, the achievable DoF is 2K.

If the number of users per cell is larger than M / 2, the user can not receive all the symbols in a single time domain without interfering with the existing receiving antenna with M single modes.

Here, it is assumed that M antennas are reconfigurable antennas each having L preset modes. It is assumed that the channels are independent of each other in the preset mode m. Also assume that the correlation time of the channel is long enough so that the channel only changes by mode switching.

The present invention proposes a B-IA scheme in the above SIMO IFMAC. The basic principle of B-IA in SIMO IFMAC is the same as in B-IA of MISO BC channel. In order to decode a desired symbol, the receiver performs mode switching, in which the adjacent receiver (the receiver receiving interference) receives in a fixed mode and the adjacent cell signal is aligned in a limited spatial dimension align. In the MISO BC channel, the B-IA receives the MX1 symbol repetitively M times in order to receive the MX1 symbol. In IFMAC, the symbols of K users are expressed as L =

Figure pat00026
Figure pat00027
Repeatedly. In this case, when mode switching is performed L times when M reconfigurable antennas are activated, the Rank of the L-time / K-user composite channel matrix becomes K, and K repeated transmission symbols can be decoded. Equation 4 represents the reception signal of the base station 1 omitting the AWGN.

Figure pat00028

While the first base station receives the transmission symbols while switching modes as described above, the second base station receives the signals without mode switching. This can be expressed by the following equation (5).

Figure pat00029

Assuming that K is a multiple of M for convenience, the rank of the channel matrix is K in Equation (4). However, in Equation (5), the rank of the channel matrix is M. Thus, the interference signal is aligned to the undesired receiver in the M dimensional signal space. The difference from B-IA in MISO BC is that M antennas of the receiver simultaneously switch modes.

Next, the antenna mode switching pattern of each base station and the symbol transmission pattern of each user should be determined.

<Mode switching pattern>

As shown in Equations (4) and (5), in order to receive symbols of K users, it is necessary to perform L times repeated transmission symbols and L times of reception mode switching. Let's call it an 'alignment block' for decoding K symbols. FIG. 2 is a view showing the structure of an alignment block according to an embodiment of the present invention. The length of one alignment block is L, and the required receiver performs mode switching a total of L times while the required user repeatedly transmits the same symbol L times, and the unrequested receiver maintains the same mode. The alignment block can be divided into part 1 of length L-1 and part 2 of length 1, and part 2 is naturally determined to be one mode not used in part 1 in that the required receiver uses all of the L modes . Therefore, the part 1 of the alignment block should be designed first. Part 1 should be considered in designing that the alignment block of the base station 1 and the alignment block of the base station 2 are overlapped. In other words, the modes in the alignment block of the base station 1 are reused in the mode of the alignment block of the base station 2. For example, base station 1 has a mode from 1 to L-1 in the alignment block, where a particular mode a can be reused in the mode of the alignment block of base station 2. When there are L-1 preset modes for each base station, the length of part 1 is (L-1) ^ 2 when it is designed to overlap with each other. For convenience of description, base station 1 assumes that each alignment block is sequentially connected, and that each alignment block in base station 2 has symbols distributed at L-1 intervals. In the opposite case, the same DoF can be achieved. As mentioned above, the alignment block was originally L-length, but the last mode was separated because it was automatically determined by the previous L-1 mode. Therefore, a total of 2 (L-1) symbol extensions are needed when collecting the last modes of each alignment block. This is shown in FIG. In each alignment block, each base station can receive K symbols. So the achievable DoF

Figure pat00030
.

<Transmission symbol pattern>

The transmission symbols are determined according to the mode switching pattern. In Part 1, users at each base station repeatedly transmit the same symbol in the alignment block of each base station, and transmit different symbols in different alignment blocks. Therefore, each user transmits L-1 different symbols repeatedly L-1 times. Here, the symbol pattern to be transmitted differs according to the arrangement block structure described above by the users of the base station 1 and the users of the base station 2. The users of the base station 1 repeatedly transmit the same symbol L-1 successively in the part 1 and the users of the base station 2 repeatedly transmit the same symbols dispersed at the interval of L-1.

In part 2, the symbols transmitted in the alignment block of part 1 are transmitted one more time. Since the number of alignment blocks in Part 1 is L-1 per cell, in Part 2, each user transmits L-1 symbols one more time. At this time, the transmission symbol of Part 2 is transmitted without interference since it is used to remove interference in a neighboring cell. For example, when users of base station 1 transmit a symbol of part 2, users of base station 2 should not transmit any symbols. The opposite is true. While the base station 1 transmits the symbol of part 2, the base station 2 performs mode switching according to the last symbol pattern of the alignment block to eliminate the interference of the alignment blocks of part 1.

3 is a diagram showing an example of a mode switching pattern.

The mode switching pattern and the transmission symbol pattern are unique, but the alignment block is maintained even if the order changes according to time. The detailed explanation will be specifically described in the following examples.

<MIMO IFMAC>

The present invention is based on the assumption that a user has N transmit antennas,

Figure pat00031
The present invention is also applicable to the case of having M receive antennas. The mode switching pattern of the base station in the MIMO IFMAC is the same as the switching pattern of the (M, NK) 2 SIMO IFMAC in which NK users per cell have a single transmit antenna. On the other hand, unlike the case of a single antenna, a terminal transmits N multi-streams simultaneously at N antennas at one time. That is, for one alignment block corresponding to FIG. 2, the terminal repeats N multi-streams L times. As a result, corresponding to the mode switching pattern of FIG. 3, the users of the base station 1 repeatedly transmit the Nx1 symbol vector in L-1 times in the part 1, and the users of the base station 2 distribute the Nx1 symbol vector in the L- Repeat transmission. In Part 2, the symbol vectors that were transmitted in Part 1 are transmitted one at a time, matching all users' alignment blocks.

<Channel Estimation>

The B-IA estimates the channel when the mode switching occurs at the base station, so that the base station performs channel estimation for each mode at least L times or more. Since the channel must not change during switching (i.e., during (L-1) 2 + 2 (L-1) symbol extensions), the pilot density for channel estimation may increase for B- This fact is signaled to the mobile station so that the pilot density can be increased and transmitted.

The number of users serving a single frequency tone is increased compared to the conventional uplink system. Because more users transmit pilot at the same time than existing uplink systems, pilot sequence or time and frequency transmission location scheduling is needed. Also, the pilot for channel estimation should be transmitted orthogonal to each user and each terminal antenna. If the number of users increases, orthogonal pilots may become insufficient. In such a case, the location information of the terminal can be grasped, and the users with less interference to the adjacent cells can be grouped to reuse and transmit the pilot.

&Lt; Embodiment of the present invention &

The number of antennas of the base station is 4, the number of modes of the base station antenna is 3, and the number of users per cell is 12, the embodiment of the present invention will be described in detail. The embodiments described below are for convenience of description and the present embodiment is not limited thereto. 4 is a view illustrating a mode switching pattern according to an embodiment of the present invention.

Transmission symbols are determined by the mode switching pattern, where users transmit the same symbol in the same alignment block and different symbols in different alignment blocks.

Figure pat00032
Is defined as a symbol vector to be transmitted in the nth alignment block of users in the i-th base station, the transmission symbol pattern of this embodiment is as shown in FIG. 5, and FIG. 5 shows a transmission symbol pattern according to an embodiment of the present invention FIG.

Also, the transmission switching pattern and the transmission symbol pattern are maintained as they are, even if the order changes according to time. FIG. 6 is a diagram showing the mode switching patterns of FIG. 4 rearranged in an arbitrary time order. The transmission symbols can also be transmitted in the same alignment block according to the rearranged mode switching pattern, and different symbols can be transmitted in different alignment blocks.

7 is a diagram of a method for allocating a pilot pattern through grouping in which channel estimation time interference is reduced based on a user's location. A cell boundary user that interferes with a neighbor cell can allocate a pilot to be orthogonal to the maximum, and a user located at a cell center and giving less interference to an adjacent cell can reuse the pilot. The position estimation of the UE can use information such as GPS or RSRP or CQI fed back from the user.

As described above, the present invention has been described with reference to particular embodiments, such as specific elements, and specific embodiments and drawings. However, it should be understood that the present invention is not limited to the above- And various modifications and changes may be made thereto by those skilled in the art to which the present invention pertains. Accordingly, the spirit of the present invention should not be construed as being limited to the embodiments described, and all of the equivalents or equivalents of the claims, as well as the following claims, belong to the scope of the present invention .

Claims (1)

Determining a transmission symbol based on a mode switching pattern;
And transmitting the determined transmission symbol,
Wherein the same symbol is transmitted in the same alignment block, and another symbol is transmitted in another alignment block.
KR1020130010969A 2013-01-31 2013-01-31 Method for Interference Alignment in Multi Cell Mutually Interfering MIMO Multiple Access Channles KR20140098913A (en)

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN108347271A (en) * 2018-01-11 2018-07-31 西安电子科技大学 A kind of distributed interference alignment neutralization implementation method of reachable system maximum degree of freedom
WO2024001874A1 (en) * 2022-06-30 2024-01-04 华为技术有限公司 Mode negotiation method and apparatus, device, system, and computer readable storage medium

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN108347271A (en) * 2018-01-11 2018-07-31 西安电子科技大学 A kind of distributed interference alignment neutralization implementation method of reachable system maximum degree of freedom
WO2024001874A1 (en) * 2022-06-30 2024-01-04 华为技术有限公司 Mode negotiation method and apparatus, device, system, and computer readable storage medium

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