WO2018052167A1 - Multi-beam code division multiple access communication method and device for performing same - Google Patents

Abstract

A multi-beam code division multiple access communication method and a device for performing the same are disclosed. According to one embodiment, the multi-beam multiple access communication method comprises the steps of: allocating a corresponding spreading code to a user transmission signal; and spreading, among a plurality of beams, the user transmission signal to which the spreading code is allocated, and transmitting the same.

Description

Multiple beam code division multiple access communication method and apparatus for performing the same

The following embodiments are related to a multi-beam code division multiple access communication method and apparatus for performing the same.

Conventional multi-user multi-input multi-output (MU-MIMO) technology is an interference presubtraction technique that removes multi-user interference before transmitting from the base station. The base station accurately knows channel state information (CSI) of all UEs. In some cases, theoretically, the multi-user interference can be completely eliminated. However, in the case where UE mobility exists in the actual system or the accuracy of the feedback CSI is not guaranteed, the accuracy of the interference presubtraction is impaired. The interference is severe and this is fatal to the overall system capacity and quality of service (QoS).

Embodiments can provide a transmission / reception technique for overcoming multi-user interference in an MU-MIMO system composed of a base station having a plurality of transmit antennas and user terminals having a plurality of receive antennas.

Embodiments provide a method of code division multiplexing in a beam region other than time using multiple beams and decoding by using a code assigned to each UE at each UE, thereby eliminating interference. Multi-user interference can be overcome without channel state information feedback (CSI feedback).

Embodiments are robust to rapid channel changes, such as UE mobility, face blocking, etc., compared to the existing MU-MIMO technology, and can achieve transmission quality of a high MU-MIMO system.

A multi-beam multi-access communication method according to an embodiment includes allocating a spreading code corresponding to a user transmission signal, and spreading and transmitting a user transmission signal to which a spreading code is assigned, among a plurality of beams. Can be.

The spreading code corresponding to the user transmission signal may be orthogonal to the spreading code corresponding to another user transmission signal.

According to an embodiment, a transmission apparatus for multi-beam multi-access communication may include a spreading precoder for allocating a spreading code corresponding to a user transmission signal, and spreading a user transmission signal assigned with a spreading code between a plurality of beams. It may include a beamformer for transmitting.

The spreading code corresponding to the user transmission signal may be orthogonal to the spreading code corresponding to another user transmission signal.

A multi-beam multi-access communication method according to another embodiment may include estimating a channel estimate for an effective channel, and detecting a transmission signal based on the channel estimate and an assigned spreading code.

The transmission signal may be transmitted by being assigned a corresponding threading code and spreading the plurality of beams.

Each of the stradding codes included in the code matrix may be orthogonal to each other.

In another embodiment, a receiving apparatus for multi-beam multi-access communication includes a channel estimator for estimating a channel estimate for an effective channel, and a signal for detecting a transmission signal based on the channel estimate and a spreading code assigned to the receiving apparatus. It may include a detector.

The transmission signal may be transmitted by being assigned a corresponding threading code and spreading the plurality of beams.

Each of the stradding codes included in the code matrix may be orthogonal to each other.

1 shows an example of an SDMA-based MU-MIMO system.

2 shows another example of an SDMA-based MU-MIMO system.

3 shows an MU-MIMO system based on analog beamforming.

4 shows a hybrid beamforming based MU-MIMO system.

5 shows baseband / RF beamforming and hybrid precoding.

FIG. 6 illustrates the effect of CI precoding on a beam pattern through an example of the method shown in FIG. 5.

FIG. 7 shows the effect of CI precoding in a beam pattern through another example of the method shown in FIG. 5.

8 is a conceptual diagram illustrating a multiple beam code division multiple access technique according to an embodiment.

9 illustrates a Multi-Beam CDMA system according to an embodiment.

10 is a diagram for describing a signal model, according to an exemplary embodiment.

FIG. 11 is a diagram for describing a transmission signal radiation pattern through Multi-Beam CDMA. FIG.

12 is a block diagram of a UE receiver according to an embodiment.

13 is a diagram for explaining a simulation environment.

14 shows an example of a simulation result.

15 shows another example of simulation results.

Specific structural or functional descriptions of the embodiments according to the inventive concept disclosed herein are merely illustrated for the purpose of describing the embodiments according to the inventive concept, and the embodiments according to the inventive concept. These may be embodied in various forms and are not limited to the embodiments described herein.

Embodiments according to the inventive concept may be variously modified and have various forms, so embodiments are illustrated in the drawings and described in detail herein. However, this is not intended to limit the embodiments in accordance with the concept of the present invention to specific embodiments, and includes modifications, equivalents, or substitutes included in the spirit and scope of the present invention.

Terms such as first or second may be used to describe various components, but the components should not be limited by the terms. The terms are only for the purpose of distinguishing one component from another component, for example, without departing from the scope of the rights according to the inventive concept, the first component may be called a second component, Similarly, the second component may also be referred to as the first component.

When a component is referred to as being "connected" or "connected" to another component, it may be directly connected to or connected to that other component, but it may be understood that other components may be present in between. Should be. On the other hand, when a component is said to be "directly connected" or "directly connected" to another component, it should be understood that there is no other component in between. Expressions describing relationships between components, such as "between" and "immediately between" or "directly neighboring", should be interpreted as well.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. As used herein, the terms "comprise" or "having" are intended to designate that the stated feature, number, step, operation, component, part, or combination thereof is present, but one or more other features or numbers, It is to be understood that it does not exclude in advance the possibility of the presence or addition of steps, actions, components, parts or combinations thereof.

Unless defined otherwise, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art. Terms such as those defined in the commonly used dictionaries should be construed as having meanings consistent with the meanings in the context of the related art, and are not construed in ideal or excessively formal meanings unless expressly defined herein. Do not.

Hereinafter, exemplary embodiments will be described in detail with reference to the accompanying drawings. However, the scope of the patent application is not limited or limited by these embodiments. Like reference numerals in the drawings denote like elements.

1 shows an example of an SDMA-based MU-MIMO system.

Referring to FIG. 1, a MU-MIMO system based on a spatial division multiple access (SDMA) may perform operations for spatial multiplexing and multi-user diversity.

For example, a base station can service multiple users simultaneously via N _T transmit antennas.

In addition, when the number of users is large, the base station can schedule its transmission to users in favorable channel fading conditions in order to improve the throughput of the system. To maximize performance, the base station can select a group of users with good spatial separations.

However, the SDMA-based MU-MIMO system may have a problem about interference pre-subtraction. Since there is no coordination between the receivers, channel diagonalization is completely performed by the transmitter. Complete channel state information may be available at the transmitter. Requires high complexity dirty paper coding (DPC), reduced throughput, or channel inversion precoding with reduced higher tx power, and block diagonalization Can be.

2 shows another example of an SDMA-based MU-MIMO system.

Referring to FIG. 2, beamforming (BF) is an optimal strategy for providing services to multiple users at once, but has a reduced complexity relative to DPC. When the beamforming vectors are optimally selected, the channel sum rate of the BF approaches the channel sum rate of the DPC when the number of users goes to infinity. However, RBF (Random Beamforming) is approaching the optimal channel rate of the DPC gradually when K is large (C = M log log K), but actually K <100 for M = 4. Low performance on values. Since beamforming weights do not match the user channel, ZF beamforming is generally power inefficient. The high cost and power consumption of mixed signal components does not currently enable fully digital baseband precoding with semiconductor technology.

In addition, i) a large number of antennas requiring a large training overhead, ii) complete channel state information is difficult to achieve because of the small SNR before beamforming in the mmWave case.

3 shows an MU-MIMO system based on analog beamforming.

Referring to FIG. 3, analog beamforming controls the phase of a signal transmitted to each antenna through a network of analog phase shifters and is implemented in a radio frequency (RF) domain. It has been adopted in commercial indoor mmWave communication standards such as IEEE 802.11 ad (WigG at 60 GHz) and IEEE 802.15.3c (mmwave-based alternative PHY 802.15.3 WPAN).

The proposed algorithm is beam space MIMO in which adaptive beamforming algorithms, multi-resolution codebooks, and discrete fourier transform (DFT) beamforming vectors are used.

Phase shifters are digitally controlled and have quantized phase values and adaptive gain control that cannot be implemented.

This limitation limits the ability to perform complex processing to manage interference between users, thus limiting the possibility of analog-only beamforming solutions related to baseband precoding.

4 shows a hybrid beamforming based MU-MIMO system.

Referring to FIG. 4, hybrid precoding includes a combination of analog and digital processing inspired by the complete radio frequency and power consumption of mixed signal hardware.

Joint processing provides higher channel rate compared to analog dedicated beamforming solutions and approaches the performance of uncontrained digital unforming with relatively small codebooks.

As described with reference to FIGS. 1 to 4, in the existing MU-MIMO system, an interference presubtraction / avoidance method should be applied at a base station based on accurate channel information in order to eliminate multi-user interference. Real-time channel feedback for a large number of UEs lacks realism due to excessive overhead. Low resolution feedback to reduce overhead inevitably leads to inaccurate precoding and beamforming, resulting in UE interference. As the effectiveness of interference presubtraction is greatly impaired in a fast fading environment, a new MU-MIMO scheme capable of controlling UE interference without relying on CSI feedback is needed.

FIG. 5 shows baseband / RF beamforming and hybrid precoding. FIG. 6 shows the effect of channel inversion (CI) precoding on a beam pattern through an example of the method shown in FIG. 5, and FIG. 7 is shown in FIG. 5. Another example of the proposed method illustrates the effect of CI precoding on the beam pattern.

Multi-user interference can be overcome when the base station knows the channel information (CSI) of all UEs correctly, but it is difficult to overcome the multi-user interference in a situation where UE mobility exists or the accuracy of the fed back CSI is not guaranteed. This is critical for overall system capacity and QoS.

8 is a conceptual diagram illustrating a multiple beam code division multiple access technique according to an embodiment.

Referring to FIG. 8, unlike the existing schemes of dividing a spatial resource into a plurality of beams and assigning independent beams to each UE and applying precoding to pre-remove inter-beam interference, the proposed scheme is specific. Spreading may be applied between a plurality of beams having AoDs, and interference may be removed and symbol detection may be performed by a code assigned to each UE at each UE. The technique of applying spreading between these beams may be referred to as a multi-beam multiple access method (Multi-beam CDMA (MB-CDMA)).

In the multiple beam multiple access method, all UEs may use a plurality of beams simultaneously but use orthogonal codes so that signals (eg, UE streams) of UEs can be distinguished. Through this, problems such as overhead due to channel feedback of the existing schemes and multi-user interference due to channel information error can be solved.

In the multi-beam multi-access method, unlike the conventional method of transmitting different UE streams for each beam, one UE stream simultaneously uses multiple beams, and assigns a unique spreading code to each UE stream. Spread transmission on multiple beams.

The multi-beam multiple access method is a more robust technique than the existing MU-MIMO technique of interference presubtraction using the same frequency resource, and may be a key technique for guaranteeing system capacity and QoS. In other words, since the multi-beam multiple access technology is an open-loop technology, it is robust to CSI change and there is no saturation of channel capacity.

The multi-beam multiple access method may have the following benefits.

(1) Spatial coding overcomes multi-user interference without CSI feedback

(2) Robust to abrupt channel changes such as UE mobility, face blocking, etc.

(3) mitigate the effects of beam instability and interference

(4) In an unintended receiver, beam spread signals are received as low power noise

(5) Privacy by pseudo random code.

9 illustrates a multi-beam CDMA system according to an embodiment, FIG. 10 illustrates a signal model according to an embodiment, and FIG. 11 illustrates a transmission signal radiation pattern through multi-beam CDMA. 9 to 11, the multi-beam multiple access system 10 may include a transmitting device 100 and a receiving device 200. The receiving device 200 may mean a UE receiver.

The transmitting device 100 may include a spreading precoder 110 and a beamformer 130. Spreading precoder 110 may be used to spread-transmit the transmit signal, ie, the UE stream, over multiple beams.

The spreading precoder 110 may allocate a spreading code corresponding to each of the transmission signals. That is, each spreading signal may be assigned a unique spreading code. In this case, spreading codes corresponding to each of the transmission signals may be orthogonal to each other.

The code matrix C for the spreading code used for spreading may be a matrix satisfying Equation 1 below as L × K matrix (L ≧ K). Here, L may be the length of a spreading code, and K may be the number of transmission signals in a spreading group, that is, the number of UE streams.

Here, H is a channel matrix, C is a spreading matrix, and α is an arbitrary constant and may be a positive number.

Is the K x K matrix,

It is an off-diagonal term of, and may satisfy Equation 2 below.

Here, F may mean Frobenius norm.

That is, each of the transmission signals may be assigned a unique spreading code through the spreading precoder 110.

The beamformer 130 may spread and transmit the transmission signals to which the spreading code is assigned among the plurality of beams. For example, the beamformer 130 may spread the transmission signals allocated with the spreading code between the plurality of beams based on the beamforming weight. When defined as, s2, ..., sK) ^ T, the signal transmitted through the N _T antennas when spreading to L different beams in the spatial domain using a code matrix C is represented by It can be expressed as 3.

The signal received at the antennas of the k-th UE may be expressed as Equation 4.

In this case, the radiation pattern of the transmission signal through the multi-beam CDMA may be as shown in FIG.

12 is a block diagram of a UE receiver according to an embodiment.

Referring to FIG. 12, the UE receiver 200 may include a channel estimator 210 and a signal detector 230.

The channel estimator 210 can estimate the channel estimate for the effective channel. The signal detector 230 may detect a transmission signal transmitted from the transmission apparatus 100 based on a channel estimate for an effective channel and a spreading code assigned to the UE receiver 200, that is, a code vector. .

Channel estimate and code vector for the effective channel at the kth UE

Suppose we know that the transmission signal

Detection can be performed in a variety of ways, including maximum-likelihood detection. Thus, the signal

Can be obtained.

The received signal may be expressed as Equation 5.

The maximum-likelihood detection rule may be expressed as shown in Equation 6.

Where U is

Is a set of possible values.

Hereinafter, the simulation result through Multi-Beam CDMA will be described.

13 is a view for explaining a simulation environment, the simulation environment is shown in Table 1.

14 shows an example of a simulation result.

Sector capacity was calculated by summing the channel capacities of K UEs in each sector. In both Sector 1 and Sector 2, it can be seen that the MB-CDMA scheme has higher sector capacity than the conventional scheme.

15 shows another example of simulation results.

The sector capacities of individual technologies according to channel feedback accuracy were observed. In both Sector 1 and Sector 2, the MB-CDMA scheme shows the performance independent of the channel feedback error, whereas the ZF-BD scheme shows that the sector capacity decreases significantly when the dispersion of the channel feedback error is more than 10 ^-4 . Can be.

The apparatus described above may be implemented as a hardware component, a software component, and / or a combination of hardware components and software components. For example, the devices and components described in the embodiments are, for example, processors, controllers, arithmetic logic units (ALUs), digital signal processors, microcomputers, field programmable gate arrays (FPGAs). Can be implemented using one or more general purpose or special purpose computers, such as a programmable logic unit (PLU), a microprocessor, or any other device capable of executing and responding to instructions. The processing device may execute an operating system (OS) and one or more software applications running on the operating system. The processing device may also access, store, manipulate, process, and generate data in response to the execution of the software. For convenience of explanation, one processing device may be described as being used, but one of ordinary skill in the art will appreciate that the processing device includes a plurality of processing elements and / or a plurality of types of processing elements. It can be seen that it may include. For example, the processing device may include a plurality of processors or one processor and one controller. In addition, other processing configurations are possible, such as parallel processors.

The software may include a computer program, code, instructions, or a combination of one or more of the above, and configure the processing device to operate as desired, or process it independently or collectively. You can command the device. Software and / or data may be any type of machine, component, physical device, virtual equipment, computer storage medium or device in order to be interpreted by or to provide instructions or data to the processing device. Or may be permanently or temporarily embodied in a signal wave to be transmitted. The software may be distributed over networked computer systems so that they may be stored or executed in a distributed manner. Software and data may be stored on one or more computer readable recording media.

The method according to the embodiment may be embodied in the form of program instructions that can be executed by various computer means and recorded in a computer readable medium. The computer readable medium may include program instructions, data files, data structures, etc. alone or in combination. The program instructions recorded on the media may be those specially designed and constructed for the purposes of the embodiments, or they may be of the kind well-known and available to those having skill in the computer software arts. Examples of computer-readable recording media include magnetic media such as hard disks, floppy disks, and magnetic tape, optical media such as CD-ROMs, DVDs, and magnetic disks, such as floppy disks. Magneto-optical media, and hardware devices specifically configured to store and execute program instructions, such as ROM, RAM, flash memory, and the like. Examples of program instructions include not only machine code generated by a compiler, but also high-level language code that can be executed by a computer using an interpreter or the like. The hardware device described above may be configured to operate as one or more software modules to perform the operations of the embodiments, and vice versa.

Although the embodiments have been described by the limited embodiments and the drawings as described above, various modifications and variations are possible to those skilled in the art from the above description. For example, the described techniques may be performed in a different order than the described method, and / or components of the described systems, structures, devices, circuits, etc. may be combined or combined in a different form than the described method, or other components. Or even if replaced or substituted by equivalents, an appropriate result can be achieved.

Therefore, other implementations, other embodiments, and equivalents to the claims are within the scope of the claims that follow.

Claims (14)

1. Assigning a spreading code corresponding to the user transmission signal; And

   Spreading and transmitting a user transmission signal assigned with a spreading code between a plurality of beams

   Multiple beam multiple access communication method comprising a.
2. The method of claim 1,

   And a spreading code corresponding to the user transmission signal is orthogonal to a spreading code corresponding to another user transmission signal.
3. The method of claim 1,

   The allocating step,

   Allocating a spreading code corresponding to the user transmission signal using a code matrix

   Including,

   And the code matrix satisfies the following equation.

   

   Where C is the code matrix, H is the channel matrix, α is a constant, K is the number of user transmitted signals,

   

   Is

   

   The off-diagonal term of.
4. In the transmitting device for multi-beam multiple access communication,

   A spreading precoder for assigning a spreading code corresponding to the user transmission signal; And

   Beamformer for spreading and transmitting a user transmission signal assigned a spreading code between a plurality of beams

   Transmission device comprising a.
5. The method of claim 4, wherein

   And a spreading code corresponding to the user transmission signal is orthogonal to a spreading code corresponding to another user transmission signal.
6. The method of claim 4, wherein

   The spreading precoder,

   Assigns a spreading code corresponding to the user transmission signal using a code matrix,

   And the code matrix satisfies the following equation.

   

   Where C is the code matrix, H is the channel matrix, α is a constant, K is the number of user transmitted signals,

   

   Is

   

   The off-diagonal term of.
7. Estimating a channel estimate for the effective channel; And

   Detecting a transmission signal based on the channel estimate and the assigned spreading code

   Multiple beam multiple access communication method comprising a.
8. The method of claim 7, wherein

   And the transmission signal is transmitted by being assigned a corresponding threading code and spreading among the plurality of beams.
9. The method of claim 8,

   The spreading signal is assigned the spreading code using a code matrix,

   And the code matrix satisfies the following equation.

   

   Where C is the code matrix, H is the channel matrix, α is a constant, K is the number of transmission signals,

   

   Is

   

   The off-diagonal term of.
10. The method of claim 9,

    And each of the stradding codes included in the code matrix is orthogonal to each other.
11. In the receiving device for multi-beam multi-access communication,

    A channel estimator for estimating a channel estimate for the effective channel; And

    A signal detector for detecting a transmission signal based on the channel estimate and the spreading code assigned to the receiving device

    Receiving device comprising a.
12. The method of claim 11,

    And the transmission signal is transmitted by being assigned a corresponding threading code and being spread among a plurality of beams.
13. The method of claim 12,

    The spreading signal is assigned the spreading code using a code matrix,

    And the code matrix satisfies the following equation.

    

    Where C is the code matrix, H is the channel matrix, α is a constant, K is the number of transmission signals,

    

    Is

    

    The off-diagonal term of.
14. The method of claim 13,

    And each of the stradding codes included in the code matrix is orthogonal to each other.

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