CN108206713B

CN108206713B - Beamforming in a multiple-input multiple-output system

Info

Publication number: CN108206713B
Application number: CN201611169450.9A
Authority: CN
Inventors: 赵昆; 蔡振浩; 王磊; 张勋勇; 徐洋; 郭伟
Original assignee: Nokia Shanghai Bell Co Ltd
Current assignee: Nokia Shanghai Bell Co Ltd
Priority date: 2016-12-16
Filing date: 2016-12-16
Publication date: 2021-04-27
Anticipated expiration: 2036-12-16
Also published as: WO2018109562A1; CN108206713A

Abstract

The invention provides a multiple-input multiple-output communication method in a transmitter, which comprises the following steps: performing baseband beamforming on the transverse data stream to obtain a longitudinal data stream; and performing radio frequency beamforming on the longitudinal data stream. In addition, the invention also provides a corresponding transmitter, a base station and the like.

Description

Beamforming in a multiple-input multiple-output system

Technical Field

The present invention relates to beamforming in a wireless network, and more particularly, to a method, apparatus, and system for beamforming in a massive mimo system.

Background

Multiple-input multiple-output (MIMO) communication systems use multiple antennas at both the transmitter and receiver of a wireless network to improve signal performance (e.g., spectral efficiency, link reliability, etc.) by exploiting spatial diversity. More specifically, MIMO significantly increases data throughput and link range without requiring additional bandwidth or increased transmit power. Large antenna systems using MIMO technology are commonly referred to as massive MIMO (M-MIMO) systems, which typically have a larger number of serving antennas than the number of active terminals they serve. These additional antennas may concentrate energy in a smaller spatial area, contributing to improved throughput and radiated energy efficiency. M-MIMO is a special case of multi-user MIMO (MU-MIMO) with narrow transmission beams that can serve multiple users simultaneously. Other advantages of M-MIMO include the widespread use of inexpensive low power components, reduced latency, simplified Medium Access Control (MAC) layer, robustness to intentional interference, etc.

Verizon organizes the technical Forum in the United states, specifically discussing the 5G specification (also known as V5G) prior to 3GPP, such as V5G.211-213 for the physical layer. The Massive multiple input multiple output (Massive MIMO, or M-MIMO) of V5G is applicable to Radio Frequency (RF) beamforming to layout and implement for millimeter wave (mmWave) frequency bands above 6 GHz.

In china, both the Ministry of Industry and Informatization (MIIT) and the largest mobile operator in china, China Mobile (CMCC), wish to perform 5G tests first on the sub-6GHz band or less (sub-6GHz), e.g. the 3.5GHz band. However, currently there is a lack of M-MIMO solutions for 3.5GHz, since existing beamforming methods are not applicable for 3.5 GHz.

Although the academic world and the enterprise world continuously research the M-MIMO, the system design is far away from the optimization, and many practical problems still need to be solved.

Disclosure of Invention

According to an embodiment of the first aspect of the present disclosure, there is provided a mimo communication method in a transmitter, including: performing baseband beamforming on the transverse data stream to obtain a longitudinal data stream; and, performing radio frequency beamforming on the longitudinal data stream.

According to one embodiment, the weights of the baseband beamforming and the weights of the radio frequency beamforming are designed to be close to full baseband beamforming weights.

According to one embodiment, the transverse data streams include N layer 1 data streams, and the step of baseband beamforming the transverse data streams to obtain the longitudinal data streams includes: performing baseband precoding on the N layer 1 data streams to obtain M groups of antenna port data; transmitting the M groups of antenna port data from the baseband layer 1 to radio frequency to form M groups of longitudinal data streams; the step of radio frequency beamforming the longitudinal data stream comprises: and performing radio frequency beam forming on the M groups of longitudinal data streams to form antenna data.

According to one embodiment, the M sets of antenna port data include a first subset and a second subset, wherein the antenna port data in the first subset carries data for users falling in a first beam and the antenna port data in the second subset carries data for users falling in a second beam.

According to an embodiment of a second aspect of the present disclosure, there is provided a transmitter for mimo communication, including: a first apparatus configured to perform baseband beamforming on a transverse data stream to obtain a longitudinal data stream; and a second apparatus configured to perform radio frequency beamforming on the longitudinal data stream.

According to one embodiment, the lateral data streams comprise N layer 1 data streams, the first apparatus comprising: a first unit, configured to perform baseband precoding on the N layer 1 data streams to obtain M groups of antenna port data; a second unit configured to transmit the M groups of antenna port data from baseband layer 1 to radio frequencies, forming M groups of longitudinal data streams; the second device is configured to perform radio frequency beamforming on the M groups of longitudinal data streams to form antenna data.

According to a third aspect of the present disclosure, a base station is provided, wherein the foregoing transmitter is included.

According to a fourth aspect of the disclosure, a mimo communication network is provided, which includes the foregoing base station.

Compared with the prior art, the method, the device or the system provided by the embodiment of the invention has the following advantages: 1. by combining baseband (digital) beamforming with radio frequency (analog) beamforming, the advantages of the two are combined; 2. the existing V5G specification is compatible and utilized to the maximum extent; 3. a feasible M-MIMO solution is provided for sub-6 GHz.

Drawings

Other features, objects and advantages of the invention will become more apparent upon reading the following detailed description of non-limiting embodiments thereof, made with reference to the accompanying drawings in which:

FIG. 1 illustrates an exemplary communication system to which methods and apparatus according to embodiments of the present invention may be applied;

FIG. 2 is a simplified flow diagram of a method of communication according to an embodiment of the present invention;

FIG. 3 is a schematic block diagram of a transmitter in accordance with an embodiment of the present invention;

fig. 4 is a system diagram of beamforming in a multi-user multiple-input multiple-output system according to an embodiment of the invention;

fig. 5 is an antenna pattern in a massive mimo system according to an embodiment of the present invention;

fig. 6 is a schematic diagram of a transmitter with beamforming functionality according to an embodiment of the present invention;

fig. 7 is a schematic diagram of an antenna module according to an embodiment of the invention;

fig. 8a-8b are diagrams illustrating simulation results of beamforming according to embodiments of the present invention.

The same or similar reference numbers in the drawings identify the same or similar elements.

Detailed Description

Before discussing exemplary embodiments in more detail, it should be noted that some exemplary embodiments are described as processes or methods depicted as flowcharts. Although a flowchart may describe the operations as a sequential process, many of the operations can be performed in parallel, concurrently or simultaneously. In addition, the order of the operations may be re-arranged. The process may be terminated when its operations are completed, but may have additional steps not included in the figure. Further, the processes may correspond to methods, functions, procedures, subroutines, and the like.

The term "computer device" may also be referred to as a "computer" in this context, and refers to an intelligent electronic device capable of executing predetermined processes such as numerical calculation and/or logic calculation by running a predetermined program or instruction, and may include a processor and a memory, wherein the processor executes a pre-stored instruction stored in the memory to execute the predetermined process, or the predetermined process is executed by hardware such as ASIC, FPGA, DSP, or a combination thereof. Computer devices include, but are not limited to, servers, personal computers, laptops, tablets, smart phones, and the like.

The computer equipment comprises user equipment and network equipment. Wherein the user equipment includes but is not limited to computers, smart phones, PDAs, etc.; the network device includes, but is not limited to, a single network server, a server group consisting of a plurality of network servers, or a Cloud Computing (Cloud Computing) based Cloud consisting of a large number of computers or network servers, wherein Cloud Computing is one of distributed Computing, a super virtual computer consisting of a collection of loosely coupled computers. Wherein the computer device can be operated alone to implement the invention, or can be accessed to a network and implement the invention through interoperation with other computer devices in the network. The network in which the computer device is located includes, but is not limited to, the internet, a wide area network, a metropolitan area network, a local area network, a VPN network, and the like.

It should be noted that the user equipment, the network device, the network, etc. are only examples, and other existing or future computer devices or networks may also be included in the scope of the present invention, and are included by reference.

The methods discussed below, some of which are illustrated by flow diagrams, may generally be implemented by hardware, software, firmware, middleware, microcode, hardware description languages, or any combination thereof. When implemented in software, firmware, middleware or microcode, the program code or code segments to perform the necessary tasks may be stored in a machine or computer readable medium such as a storage medium. The processor(s) may perform the necessary tasks.

Specific structural and functional details disclosed herein are merely representative and are provided for purposes of describing example embodiments of the present invention. The present invention may, however, be embodied in many alternate forms and should not be construed as limited to only the embodiments set forth herein.

It will be understood that, although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element may be termed a second element, and, similarly, a second element may be termed a first element, without departing from the scope of example embodiments. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.

It will be understood that when an element is referred to as being "connected" or "coupled" to another element, it can be directly connected or coupled to the other element or intervening elements may be present. In contrast, when an element is referred to as being "directly connected" or "directly coupled" to another element, there are no intervening elements present. Other similar words used to describe relationships between elements should be interpreted in a similar manner (e.g., "between" as compared to "directly between", "adjacent to" as compared to "directly adjacent to", etc.).

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and/or "comprising," when used herein, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.

It should also be noted that, in some alternative implementations, the functions/acts noted may occur out of the order noted in the figures. For example, two figures shown in succession may, in fact, be executed substantially concurrently, or the figures may sometimes be executed in the reverse order, depending upon the functionality/acts involved.

The present invention is described in further detail below with reference to the attached drawing figures.

In the millimeter-wave band, radio-frequency beamforming uses LENs antennas or phased-array antennas to form beams in antenna sub-modules (sub-modules). The number of radio frequency Transceivers (TRX) is much smaller than the total number of antennas. However, in the frequency band of 6GHz or less (hereinafter also referred to as sub-6GHz), the number of antennas is much smaller than that of millimeter waves because the size of the antenna for the low frequency band is large. Therefore, improved signal processing algorithms are used for baseband (BB) beamforming.

Baseband beamforming was chosen for 8 antennas and 20MHz bandwidth in 4G, but with 5G there would be 64 or more antennas and up to 100MHz bandwidth, and Fronthaul (frontlaul) in the product would not provide support.

Example embodiments of the present disclosure, i.e., communication systems that support beamforming gain using large antenna arrays and M-MIMO operation, will be described below in a specific context. The present disclosure may be applied to standard-compliant communication systems, such as communication systems compliant with third generation partnership project (3GPP), IEEE 802.11, etc., technical standards, and non-standard-compliant communication systems supporting M-MIMO operation.

Fig. 1 illustrates an example communication system 100. The communication system 100 may be used to communicate data. The communication system 100 may include an evolved nodeb (enb)110 having a coverage area 101, a plurality of User Equipments (UEs) 120, and a backhaul network 130. eNB110 may include any component capable of providing wireless access by establishing uplink (dashed lines) and/or downlink (solid lines) connections with UEs 120, such as base stations, nodeb (nb), Access Points (AP), home base stations, micro cells, relay nodes, and other wireless-enabled devices. UE 120 may include any component capable of establishing a wireless connection with eNB110, such as a subscriber, handset, mobile Station (STA), terminal, user, or other wireless-enabled device. Backhaul network 130 may be any component or collection of components that allow for the exchange of data between eNB110 and a remote end (not shown). In some embodiments, the communication system 100 may include various other wireless devices, such as relays, low power nodes. It should be understood that although the communication system may employ multiple enbs capable of communicating with a large number of UEs, only one eNB and two UEs are shown here for simplicity. As shown in fig. 1, eNB110 may communicate with UE 120 using M-MIMO. In a communication system using M-MIMO, the number of transmit antennas used by the eNB will exceed the number of UEs being served simultaneously, thereby achieving UE isolation and data coverage through beamforming gain. Typically, an eNB may be considered to be using MMIMO when the number of transmit antennas used by the eNB exceeds 8. In general, as the number of transmit antennas of an eNB increases, communication links (e.g., M-MIMO, multi-user MIMO (MU-MIMO), etc.) and communications with UEs may become easier to establish. A high ratio of transmit antennas to simultaneously served UEs may achieve wider coverage, while a low ratio of transmit antennas to simultaneously served UEs may achieve greater throughput. Thus, the communication system can trade throughput for coverage (and vice versa) by adjusting the number of active UEs scheduled to receive simultaneous transmissions. In particular, system information (e.g., control information, scheduling information, etc.) is typically broadcast to many UEs at different spatial locations, and therefore, it is particularly desirable to maintain a uniform wave radiation pattern for multiple broadcast channels so that an acceptable signal-to-noise ratio (SNR) can be maintained throughout the coverage area of a cell. And, for UEs that do not perform the initial random access procedure, the network does not need to know their location; thus, the large coverage of the broadcast channel may simplify the initial random access procedure described above. In general, a broadcast channel is a broadcast transmission that propagates throughout or substantially throughout the coverage area of a cell. In contrast, unicast signals may gain the performance advantage of beamforming gain by spatial selectivity, such as by achieving a higher signal-to-noise ratio (SNR) at the intended receiver location at the expense of a lower SNR at other locations. In other words, a unicast signal is sent to a particular UE, or to a group of UEs for which the signal is tagged, or in other cases, to a subset of all possible recipients.

Embodiments of the present invention provide a composite beamforming solution that combines radio frequency beamforming (analog) with baseband beamforming (digital) under the limitations of fronthaul (frontaul). Using rf beamforming is different from 4G because in 4G only baseband beamforming is used, which not only saves forward transmission capacity (FH capacity) and the number of transceivers. Based on the theory of "Hybrid Digital and Analog Beamforming Design for Large-Scale Antenna Arrays" by Foad Sohrabi and Wei Yu and published in IEEE Journal of Selected pics in Signal Processing, volume 3, volume 10, at 2016.4, the inventors of the present disclosure have discovered that if the number of I/Q or RF transmit antennas is greater than twice the number of layer 1(L1) (transverse) data streams, the system Design will ensure that this conforming Beamforming scheme achieves similar performance as full baseband Beamforming.

According to an embodiment of the present invention, as shown in the flow of method 2 in fig. 2, in step 220, the transmitter of the base station 120 processes the horizontal layer 1 data stream by baseband (digital) beamforming to obtain a vertical data stream, and then, in step 240, performs radio frequency beamforming on the obtained vertical data stream. Therefore, better design flexibility is provided for the selection of the baseband algorithm and the design of the radio frequency beam. Theoretically, the CPRI should transmit data not less than twice the number of layer 1 data streams to achieve better performance in the composite system, and therefore, in the embodiment, it is considered that the CPRI I/Q number is equal to 2 times the number of layer 1 data streams.

Preferably, the weights of the baseband beamforming and the weights of the radio frequency beamforming described above are designed to be close to the full baseband beamforming weights to match the overall performance of the full baseband beamforming.

Preferably, the horizontal data stream includes N layer 1 data streams, and the step of performing baseband beamforming on the horizontal data stream to obtain the vertical data stream in step 220 includes: performing baseband precoding on the N layer 1 data streams to obtain M groups of Antenna Port (AP) data; and transmitting the M groups of antenna port data from the baseband layer 1 to radio frequency to form M groups of longitudinal data streams.

Preferably, the step S240 of performing rf beamforming on the longitudinal data stream includes: and performing radio frequency beam forming on the M groups of longitudinal data streams to form antenna data.

Preferably, the above-mentioned M sets of Antenna Port (AP) data include a first sub-set and a second sub-set, wherein the antenna port data in the first sub-set carries data of users falling into the first beam, and the antenna port data in the second sub-set carries data of users falling into the second beam.

Fig. 4 shows a composite beamforming system for MU-MIMO according to an embodiment of the present invention. In real products, baseband beamforming is generally considered to have the same meaning as digital beamforming in an experimental environment, while radio frequency beamforming has the same meaning as analog beamforming in an experimental environment. In the schematic diagram of fig. 4, the number of data streams, the forwarding capacity, the number of rf transceivers and the number of antennas can be defined normally, and there are many design choices to design a system with near-optimal performance and suitable complexity.

In the specification of V5G, CSI-RSs for 16 interfaces are defined for beamforming of layer 1 signals of the baseband. Also in the specification of V5G, a beam rs (brs) is defined for radio frequency (analog) beamforming.

In china, MIIT and CMCC currently assume that a large-scale MIMO system uses 128 antennas and 64 transceivers in a base station, and thus, 16 data streams (layers) are required to obtain the peak throughput requirement. Such an antenna pattern is shown in fig. 5.

According to one embodiment of the invention, forwarding uses 32 antenna ports, i.e., 32I/Q data paths from layer 1 to radio frequency, which is half of an all-digital scheme. Fig. 6 is a schematic diagram of a transmitter with beamforming function according to an embodiment of the present invention, wherein the aforementioned composite beamforming approach is applied, and there are 16 transversal/layer 1 data streams (0-15), which are subjected to baseband beamforming in the MU-MIMO module to obtain 32 sets of antenna port data (AP0-AP 31). Wherein, the weight of the baseband precoding/beamforming can be obtained by CSI-RS based on PMI/ZF or by EBB/ZF algorithm based on UL SRS reciprocity (reciprocity). The 32 sets of antenna port data are then transmitted from baseband layer 1 to radio frequencies. At the radio frequency module, 32 groups of AP data are subjected to Analog Beamforming (ABF) to obtain 8 paths of antenna data, AD0-AD 7.

The beam weights representing the beam identifications are stored in advance in the ABF as alternative beams. Thanks to BRS, each antenna interface knows the UE's preferred beam identity.

In an antenna module, see fig. 7, antenna ports 0-15 need only carry data for users falling within beam id a, and correspondingly antenna ports 16-31 need only carry data for users falling within beam id B. Through ABF, the data of the beam mark A and the data of the beam mark B are added, so that each beam mark is formed by all the longitudinal antennas, and the beam design is more flexible. This is also referred to as fully connected analog beamforming. Referring to fig. 7, for example, AP Ox W _ abf0..7+ AP16x W _ abf64..71 ═ AD 0..7 is also applied to AP1 and AP17, and the like.

In the spatial domain, the beam identity a and the beam identity B are designed to be orthogonal to each other. The UE in beam identity a is not interfered by the UE in beam identity B and vice versa. And the UE in the same beam identifier realizes spatial multiplexing through an MU-MIMO means.

The simulation results based on the 3D beam pattern are shown in fig. 8a, and fig. 8B shows the simulation results of beam id a and beam id B. It should be noted that further algorithm optimization and beam design may bring about further changes in the above results.

Fig. 3 shows a transmitter 3 for mimo communication, comprising: a first device 32 configured to perform baseband beamforming on the transverse data stream to obtain a longitudinal data stream; and a second device 34 configured to perform radio frequency beamforming on the longitudinal data stream.

Preferably, the weights of the baseband beamforming and the weights of the radio frequency beamforming are designed to be close to the full baseband beamforming weights.

Preferably, the transverse data stream comprises N (e.g., the aforementioned 16, streams 0-15) layer 1 data streams, and the first device 32 comprises: a first unit 322 configured to perform baseband precoding on the N layer 1 data streams, and obtain M groups (e.g., the aforementioned 32, AP0-31) of antenna port data; a second unit 324 configured to transmit the M groups of antenna port data from baseband layer 1 to radio frequency, forming M groups of longitudinal data streams; the second device 34 is configured to perform radio frequency beamforming on the M sets of longitudinal data streams to form antenna data.

Preferably, the M groups of antenna port data include a first subgroup and a second subgroup, wherein the antenna port data in the first subgroup carries data of users falling into the first beam, and the antenna port data in the second subgroup carries data of users falling into the second beam.

It is noted that the present invention may be implemented in software and/or in a combination of software and hardware, for example, the various means of the invention may be implemented using Application Specific Integrated Circuits (ASICs) or any other similar hardware devices. In one embodiment, the software program of the present invention may be executed by a processor to implement the steps or functions described above. Also, the software programs (including associated data structures) of the present invention can be stored in a computer readable recording medium, such as RAM memory, magnetic or optical drive or diskette and the like. Further, some of the steps or functions of the present invention may be implemented in hardware, for example, as circuitry that cooperates with the processor to perform various steps or functions.

It will be evident to those skilled in the art that the invention is not limited to the details of the foregoing illustrative embodiments, and that the present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein. Any reference sign in a claim should not be construed as limiting the claim concerned. Furthermore, it is obvious that the word "comprising" does not exclude other elements or steps, and the singular does not exclude the plural. A plurality of units or means recited in the system claims may also be implemented by one unit or means in software or hardware. The terms first and second, etc. are used to denote names, but not any particular order.

While exemplary embodiments have been particularly shown and described, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the claims. The protection sought herein is as set forth in the claims below.

Claims

1. A multiple-input multiple-output communication method in a transmitter, comprising:

performing baseband beamforming on the N transverse data streams to obtain longitudinal data streams, wherein:

performing baseband precoding on the N transverse data streams to obtain M groups of antenna port data;

transmitting the M groups of antenna port data from the baseband layer 1 to radio frequency to form M groups of longitudinal data streams;

the M groups of antenna port data comprise a first subgroup and a second subgroup, wherein the antenna port data in the first subgroup bear the data of the users falling into the first beam, and the antenna port data in the second subgroup bear the data of the users falling into the second beam; and

and performing radio frequency beam forming on the M groups of longitudinal data streams.

2. The method of claim 1, wherein the weights of the baseband beamforming and the weights of the radio frequency beamforming are designed to approximate full baseband beamforming weights.

3. A transmitter for multiple-input multiple-output communication, comprising:

a first apparatus, configured to perform baseband beamforming on N horizontal data streams to obtain a vertical data stream, where the first apparatus specifically includes:

a first unit, configured to perform baseband precoding on the N transverse data streams to obtain M groups of antenna port data;

a second unit configured to transmit the M groups of antenna port data from baseband layer 1 to radio frequencies, forming M groups of longitudinal data streams;

a second device configured to perform radio frequency beamforming on the M sets of longitudinal data streams.

4. The transmitter of claim 3, wherein the weights of the baseband beamforming and the weights of the radio frequency beamforming are designed to approximate full baseband beamforming weights.

5. A base station comprising a transmitter as claimed in claim 3 or 4.

6. A multiple-input multiple-output communication system comprising the base station of claim 5.