阅读说明：本技术 多输入多输出发送和接收 (Multiple input multiple output transmission and reception ) 是由 戴凌龙 T·米尔 M·西迪奇 郝墨 R·麦肯齐 于 2020-04-06 设计创作，主要内容包括：公开了多输入多输出(MIMO)发送器、接收器和收发器、以及其它相关联的设备、系统和方法。特别地,本发明的多个方面和实施方式涉及MIMO发送器、接收器和收发器,所述MIMO发送器、接收器和收发器被实现为用于向基站(10)和/或移动站(15)和/或从基站(10)和/或移动站(15)发送信号的中继设备的模块,特别是当这种设备在移动载具和/或飞行器(13)上实现,并且特别是用于以所谓的“毫米波波段”的频率发送、接收和/或转发无线通信信号。在这种设备中,功率控制单元被配置为确定能量可用性度量和/或功率需求度量,并且作为响应,使切换单元在不同状态下将多个RF链连接到多个天线元件。(Multiple-input multiple-output (MIMO) transmitters, receivers and transceivers, and other associated devices, systems, and methods are disclosed. In particular, aspects and embodiments of the present invention relate to MIMO transmitters, receivers and transceivers implemented as modules of relay devices for transmitting signals to and/or from base stations (10) and/or mobile stations (15), in particular when such devices are implemented on mobile vehicles and/or aircraft (13), and in particular for transmitting, receiving and/or forwarding wireless communication signals at frequencies of the so-called "millimeter wave band". In such an apparatus, the power control unit is configured to determine an energy availability metric and/or a power demand metric and, in response, to cause the switching unit to connect the plurality of RF chains to the plurality of antenna elements in different states.)

1. A multiple-input multiple-output (MIMO) transmitter, the MIMO transmitter comprising:

a digital signal processor configured to pre-code a plurality of data streams;

a plurality of Radio Frequency (RF) chains, each RF chain configured to convey a precoded data stream from the digital signal processor to generate a signal representative of the data stream;

an antenna array comprising a plurality of antenna elements;

a switching unit configured to connect the plurality of RF chains to the plurality of antenna elements in one of a first state or a second state, wherein:

-in the first state, at least one of the plurality of RF chains is connected to a first subset of the plurality of antenna elements, and

-in the second state, the at least one of the plurality of RF chains is connected to a second subset of the plurality of antenna elements, wherein the first and second subsets relating to the at least one RF chain have different numbers of antenna elements; and

a power control unit configured to determine an energy availability metric and/or a power demand metric and, in response, cause the switching unit to connect the plurality of RF chains to the plurality of antenna elements in the first state or the second state.

2. The MIMO transmitter of claim 1, wherein the energy availability metric is a metric of or is a metric indicative of an amount of energy remaining in a power supply from which the transmitter is powered.

3. The MIMO transmitter of claim 1, wherein the energy availability metric is or is a metric indicative of a power level that a power source from which the transmitter derives power is capable of providing.

4. The MIMO transmitter of claim 1, wherein the energy availability metric is a metric of or indicates a voltage level that a power supply from which the transmitter derives power can support.

5. The MIMO transmitter of claim 1, 2, 3 or 4, wherein the power requirement metric is or is a metric indicative of a level of power required to be provided by a power supply from which the transmitter is powered.

6. A MIMO transmitter as claimed in any preceding claim, implemented on or as part of a relay node.

7. The MIMO transmitter of any one of the preceding claims, implemented on or as part of an unmanned vehicle.

8. A MIMO transmitter according to any preceding claim, implemented on or as part of an aircraft.

9. The MIMO transmitter of any one of the preceding claims, implemented on or as part of a vehicle having a battery power source.

10. A MIMO transmitter according to any of the preceding claims, wherein the first subset relating to the at least one RF chain comprises a single antenna element.

11. A multiple-input multiple-output (MIMO) receiver, the MIMO receiver comprising:

an antenna array comprising a plurality of antenna elements, each antenna element arranged to receive a wireless communication signal;

a switching unit configured to connect the plurality of antenna elements to a plurality of RF chains in one of a first state or a second state, wherein:

-in the first state, at least one of the plurality of RF chains is connected to a first subset of the plurality of antenna elements, and

-in the second state, the at least one of the plurality of RF chains is connected to a second subset of the plurality of antenna elements, wherein the first and second subsets relating to the at least one RF chain have different numbers of antenna elements;

each RF chain is configured to pass signals received from a subset of antenna elements to which the RF chain is connected to generate a digital signal;

a digital signal processor configured to receive the digital signals generated from each RF chain and perform a combination of these signals to generate a plurality of data streams; and

a power control unit configured to determine an energy availability metric and/or a power demand metric and, in response, cause the switching unit to connect the plurality of RF chains to the plurality of antenna elements in the first state or the second state.

12. A MIMO system comprising a MIMO transmitter according to any of claims 1 to 10 and a MIMO receiver according to claim 11.

13. A method of operating a multiple-input multiple-output (MIMO) transmitter, the method comprising:

performing precoding on the plurality of data streams at the digital signal processor;

communicating the precoded data stream from the digital signal processor via each of a plurality of Radio Frequency (RF) chains to generate a signal representative of the data stream;

configuring a switching unit to connect the plurality of RF chains to a plurality of antenna elements of an antenna array in one of a first state or a second state, wherein:

-in the first state, at least one of the plurality of RF chains is connected to a first subset of the plurality of antenna elements, and

-in the second state, the at least one of the plurality of RF chains is connected to a second subset of the plurality of antenna elements, wherein the first and second subsets relating to the at least one RF chain have different numbers of antenna elements; and

determining an energy availability metric and/or a power demand metric and, in response, causing the switching unit to connect the plurality of RF chains to the plurality of antenna elements in the first state or the second state.

14. A method of operating a multiple-input multiple-output (MIMO) receiver, the method comprising:

receiving a wireless communication signal at each of a plurality of antenna elements of an antenna array;

configuring a switching unit to connect the plurality of antenna elements to a plurality of RF chains in one of a first state or a second state, wherein:

-in the first state, at least one of the plurality of RF chains is connected to a first subset of the plurality of antenna elements, and

-in the second state, the at least one of the plurality of RF chains is connected to a second subset of the plurality of antenna elements, wherein the first and second subsets relating to the at least one RF chain have different numbers of antenna elements;

each RF chain is configured to pass signals received from a subset of antenna elements to which the RF chain is connected to generate a digital signal;

receiving the digital signals generated from each RF chain at a digital signal processor and combining the signals to generate a plurality of data streams; and

determining an energy availability metric and/or a power demand metric and, in response, causing the switching unit to connect the plurality of RF chains to the plurality of antenna elements in the first state or the second state.

15. A method of operating a multiple-input multiple-output (MIMO) transceiver system, the method comprising performing the method of claim 13 and the method of claim 14.

Technical Field

The present invention relates to multiple-input multiple-output (MIMO) transmitters, receivers and transceivers, and other related devices, systems, and methods. In particular, the preferred embodiments relate to MIMO transmitters, receivers and transceivers implemented as modules of relay devices for transmitting signals to and/or from base stations and/or mobile stations, in particular when these devices are implemented on mobile vehicles and/or aircraft, and in particular for transmitting, receiving and/or forwarding wireless communication signals at frequencies in the so-called "millimeter wave band".

Background

Millimeter wave (mmWave) wireless communication systems are receiving increasing attention because they are expected to meet the increasing bandwidth demands of wireless devices. The term "millimeter wave band" generally refers to frequencies from about a few gigahertz (e.g., 3.0GHz) to several hundred gigahertz, while millimeter wave systems typically operate in the 30GHz-300GHz frequency band. This is a much larger band than the sub-6GHz band currently used for Long Term Evolution (LTE) networks and can therefore support a larger bandwidth than existing systems currently operating in the sub-6GHz band can support.

One problem associated with millimeter wave communications is the relatively high free space path loss that may be experienced. Such path loss can result in severe attenuation of signals that experience blockage (e.g., due to buildings or other large objects affecting the "line of sight" between the base station and the mobile station with which it may attempt to communicate) or long-range communications.

One approach to address this problem is to implement millimeter wave communications within or using a multiple-input multiple-output (MIMO) system, which may be implemented on relay nodes that may be located at fixed locations or may themselves be implemented on mobile, possibly aircraft (e.g., Unmanned Aerial Vehicles (UAVs) or "drones"), allowing signals to be relayed over and/or around line-of-sight obstacles, such as buildings. Such a scenario is illustrated in fig. 1, which shows a so-called UAV assisted millimeter wave MIMO system.

In such a system, as shown in fig. 1, the UAV 13 may act as a movable relay node between a Base Station (BS)10 and one or more Mobile Stations (MSs) 15 (labeled as users with mobile devices in this example), which Mobile Stations (MSs) 15 may not be able to be in line-of-sight communication with the base station 10 due to obstructions, such as a building 12.

The relatively short wavelength of millimeter wave communications enables the antenna spacing of the antenna elements in the antenna array of a MIMO system (i.e., involving a transmitter, receiver, or transceiver and/or other components) to be reduced, and thus enables a relatively large antenna array (e.g., containing 256 to 1024 antenna elements) to be packaged in a relatively small physical size (compared to that achievable when operating in the sub-6GHz band). These large antenna arrays can effectively compensate for the high path loss caused by the high frequency communication of millimeter waves.

Nonetheless, there are challenges to implementing millimeter wave MIMO systems in practice.

Traditionally, MIMO systems have been implemented with all-digital precoding. Fig. 2 shows an example MIMO transmitter with all-digital precoding.

In this example, the transmitter 200 includes a digital precoder 202 and a plurality of Radio Frequency (RF) chains (generally designated 204) coupled to the digital precoder 202. Each RF chain is coupled to an antenna (generally designated 208). In the example shown here, each RF chain is coupled to a respective antenna through an amplifier, generally designated 206.

The digital precoder 202 receives a plurality of data streams, generally designated 210, and operates to control the amplitude and phase of each received data stream to achieve a transmit beam from the antenna 208 having a desired direction and gain. The data stream, once precoded, is passed through the RF chain 204. Each RF chain may support a single antenna element. The respective RF chains operate to convert the digitally precoded data streams into analog signals for transmission by the respective antennas 208. Each RF chain typically includes transceiver circuitry for generating analog signals from a received digitally precoded data stream. For example, the transceiver circuitry may include a digital-to-analog (DAC) converter (and possibly an analog-to-digital (ADC) converter, e.g., if the device is a MIMO transceiver), a mixer, and a frequency converter. The output signal generated by each RF chain is then amplified by a respective amplifier 206 and transmitted from a respective antenna 208.

All-digital precoding offers a high level of design choice and enables high data rates and low interference between different data streams. However, it also typically requires a dedicated RF chain for each antenna. For millimeter wave MIMO systems, as described above, where the number of antennas is typically large, this requirement may result in undesirably high hardware costs and power consumption. These problems are typically associated with many types of millimeter wave MIMO systems, and may be associated with UAV assisted millimeter wave MIMO systems, as these millimeter wave MIMO systems typically (when in use) cannot be connected to a battery that the UAV must carry or a power source other than a power source such as a solar panel power source, the performance of which may be variable and/or limited by factors such as weather, time, and location, meaning that energy and/or power may be limited or restricted, or unreliable. This means that a trade-off may need to be found between performance and power consumption (or energy consumption).

Although millimeter wave signals may experience problems such as severe path loss, penetration loss, and rain fade compared to signals in the current cellular band (3G or LTE), advantageously, as described above, the shorter wavelengths of millimeter wave frequencies enable more antennas to be packaged in the same physical size, which makes them particularly suitable for large-scale spatial multiplexing and highly directional beamforming. This has led to the emergence of massive multiple-input multiple-output (or "massive MIMO") concepts for millimeter wave communication.

Although the principle of precoding may be substantially the same regardless of the carrier frequency, it is generally impractical to use conventional all-digital precoding schemes for large-scale antenna arrays. This is because the implementation of all-digital precoding typically requires a dedicated RF chain (including high resolution digital-to-analog converters, mixers, etc.) for each antenna element, which is prohibitive from both a cost and power consumption perspective at millimeter wave frequencies. Such a configuration presents challenges for implementation of massive MIMO systems, as the large number of power-consuming and costly RF chains can make the energy consumption and hardware cost of massive MIMO systems prohibitive.

To address this problem, a "hybrid" precoding technique (i.e., partially digital, partially analog) has recently been proposed for mmwave massive MIMO systems. The key idea is to separate the functionality of a conventional digital precoder into a small-sized digital precoder (implemented by a small number of RF chains) and a large-sized analog precoder (implemented by a large number of Phase Shifters (PS)) to increase the antenna array gain.

Generally, millimeter-wave communications are applied to line-of-sight (LOS) dominated scenarios because millimeter-wave signals are sensitive to blocking (i.e., compared to longer wavelength communication techniques), but to mitigate the negative impact of blocking, UAVs may be used for millimeter-wave massive MIMO systems (as discussed above with respect to fig. 1). In such UAV assisted mm wave systems, the channels from the Base Station (BS)10 to the UAV 13 and from the UAV 13 to each Mobile Station (MS)15 may be line of sight, and the transmission range and coverage may be extended. Similar to a conventional millimeter wave massive MIMO system, precoding plays an important role in UAV assisted millimeter wave massive MIMO systems to compensate for high path loss due to high antenna array gain.

Hybrid precoding can be achieved by two typical architectures, namely (a) a "fully-connected" architecture and (b) a "sub-connected" architecture (and possibly involving multiple "more-connected" and "less-connected" architectures between these two extremes). A "fully connected" architecture is one in which: where each RF chain is connected to all antennas (or all antenna elements of an antenna array or sub-array) via a network of elements including phase shifters. A fully connected architecture may provide near optimal overall rate performance, but at the expense of high power consumption due to a large number of phase shifters. Since the number of base station antennas can be very large, a fully connected architecture requires a large number of phase shifters. In contrast, a "sub-connection" architecture is one in which: where each RF chain is connected to only a subset of antennas (possibly only one antenna) via a phase shifter network. This may save power consumption compared to a fully connected architecture, but suffers from performance degradation.

Fig. 3 illustrates two precoding architectures (or "states") commonly used for hybrid precoding purposes in mmwave massive MIMO systems, namely (a) a fully-connected architecture and (b) a sub-connected architecture.

An analog precoder 30a with a fully connected architecture (as shown in part (a) of fig. 3) includes a plurality of phase shifters (generally designated 34a) and a plurality of RF combiners (generally designated 36 a). Each RF combiner is coupled to an antenna element (generally designated 38 a).

The analog precoder 30a receives a plurality of analog signals (via inputs generally designated 32 a) from an RF chain between itself and the digital precoder. The phase shifter 34a operates to control the phase of each received RF chain analog signal. Each RF combiner 36a operates to combine the precoded analog signals and map the combined signals to a corresponding antenna 38 a.

In this fully connected architecture (i.e., as shown in part (a) of fig. 3), N38a ═ N36 a; n38a is more than or equal to N32 a; n34a — N32a × N38a, where N32a is the number of input RF chains, N34a is the number of phase shifters, N36a is the number of RF combiners, and N38a is the number of antenna elements.

An analog precoder 30b with a sub-joint architecture (as shown in part (b) of fig. 3) includes a plurality of phase shifters (generally designated 34b) divided into subsets according to antenna elements (generally designated 38 b). Each of the input RF chain signals (received via respective inputs generally designated 32 b) is connected to only a subset of the phase shifters 34 b. In this sub-connection architecture (i.e., as shown in part (b) of fig. 3), N38b ═ N34 b; n38b ═ Ls × N32 b; n38a is more than or equal to N32 b; ls ≧ 1, where N32b is the number of input RF chains, N34b is the number of phase shifters, N38b is the number of antennas, and Ls is the size of the subset (number of phase shifters in each subset).

In MIMO transmitters, receivers and transceivers in general, and in particular MIMO transmitters, receivers and transceivers associated with UAV assisted millimeter wave massive MIMO systems, it is desirable to provide higher overall rate performance, but as noted above, the amount of power or energy available (particularly on the UAV) may be limited (i.e., on the UAV, power is typically provided by an onboard power source (e.g., a battery) or via solar panel devices, and thus is typically a constrained resource). If the UAV has a battery as its power source, this will typically limit the total amount of energy available before it needs to be charged (which typically involves the UAV returning to a location on the ground), and will typically have a limit on the level of power it can provide (which may be variable, may not be reliable, and is typically reduced). Even with solar-based power sources, while this may avoid or postpone the need for the UAV to land for charging, there are often variable limits on the level of power that can be provided on the UAV. These factors impact the applicability of current hybrid precoding techniques related to UAV assisted mmwave massive MIMO systems.

Therefore, in view of the above, there is a need to develop a new hybrid precoding architecture design for UAV assisted mmwave massive MIMO systems.

With reference to various previous disclosures, a paper entitled "UAV air-to-ground channel characterization for mmWave systems" (Vehicular Technology reference (VTC-face), 2017IEEE 86th) by Wahab Khawaja, Ozgur Ozdemir, and Ismail guven discusses characterization of the millimeter wave air-to-ground (AG) channel for UAV communications to study the behavior of the AG millimeter wave band at different frequencies using ray tracing simulations.

A paper entitled "Relay Hybrid Precoding Design in Millimeter-Wave Massive MIMO Systems" (IEEE Transactions on Signal Processing, vol.66, No.8, pp.2011-2026,15April 15,2018) by x.xue, y.wang, l.dai, and c.mass discusses a Relay Hybrid Precoding Design in a mmwave Massive MIMO system.

A paper entitled "Phase Shifters vs Switches: An Energy efficient perfect on Hybrid Beamforming" (IEEE Wireless Communications Letters, vol.8, No.1, February 2019) by s.payami, n.m.balabraumanya, c.masouros and m.selathurai discusses how Hybrid Beamforming architectures offer the prospect of exploiting the advantages of massive MIMO systems by combining Phase Shifters, Switches or a combination thereof, and solves the design problems of such architectures from An Energy Efficiency Perspective, provides closed form expressions to compare various Hybrid Beamforming architectures, and yields the optimal number of antennas required to maximize Energy Efficiency.

The article by Shahar Stein and Yonina C.Eldar entitled "Hybrid Analog-Digital Beamforming for Massive MIMO Systems" (available online at https:// axiv.org/pdf/1712.03485. pdf) discusses how Massive MIMO Systems and Hybrid Beamforming can help exploit potential array gains without using dedicated RF chains for each antenna. It considers the data phase in a massive MIMO communication process, where the transmitter and receiver use fewer RF chains than antennas, and examines several different full-connection and half-connection schemes.

A paper entitled "partial-active Conjugate Beamforming for LoS Massive MIMO Communications" (IEEE Access PP (99):1-1, October 2018) by Wendong Liu, Zhuocheng Wang, Jian Jienfei Cao and Sheng Chen proposes Partially Activated Conjugate Beamforming (PACB) for Massive MIMO Communications, in which the line-of-sight (LoS) channel is dominant. Unlike conventional conjugate beamforming, which activates all antenna elements to radiate signals, the proposed PACB activates only a small portion of the antennas by exploiting the spatial structure of the LoS channel to mitigate inter-user interference and improve downlink spectral efficiency.

Referring now to the prior patent literature, chinese application CN107809274 relates to a hybrid precoding method based on a novel phase shift switching network.

US9967014(Park et al) relates to an apparatus, method and system for beamforming in an antenna system.

Disclosure of Invention

According to a first aspect of the present invention, there is provided a multiple-input multiple-output (MIMO) transmitter, comprising:

a digital signal processor configured to pre-code a plurality of data streams;

a plurality of Radio Frequency (RF) chains, each RF chain configured to convey a precoded data stream from a digital signal processor to generate a signal representative of the data stream;

an antenna array comprising a plurality of antenna elements;

a switching unit configured to connect the plurality of RF chains to the plurality of antenna elements in one of a first state or a second state, wherein:

-in a first state, at least one RF chain of the plurality of RF chains is connected to a first subset of the plurality of antenna elements, and

-in a second state, at least one RF chain of the plurality of RF chains is connected to a second subset of the plurality of antenna elements, wherein the first subset and the second subset relating to the at least one RF chain have a different number of antenna elements; and

a power control unit configured to determine an energy availability metric and/or a power demand metric and, in response, cause the switching unit to connect the plurality of RF chains to the plurality of antenna elements in the first state or the second state.

By virtue of the stated features, the preferred embodiments may switch between at least a first state and a second state in response to a determination by the power control unit of an energy availability metric and/or a power demand metric.

In response to such a determination of the energy availability metric and/or the power demand metric, the switching unit may be configured to switch the states relating to only one, some or all of the plurality of RF chains in order to place the MIMO transmitter in a so-called fully-connected state or a sub-connected state, or (in case of more than two states) in a "more-connected" or "less-connected state" depending on such a determination.

There may be more than two states associated with a particular RF chain, the RF chain in question being connected to different subsets of the plurality of antenna elements in each state, the different subsets having different numbers of antenna elements ranging from only one antenna element to all possible antenna elements.

An RF chain may include entities including, but not limited to, an analog-to-digital converter, a digital-to-analog converter, at least one phase shifter, and at least one filter, the entities of a particular RF chain being configured to perform respective functions related to a data stream provided to the RF chain and/or a signal generated by the RF chain.

According to a preferred embodiment, the energy availability measure may be or be a measure indicative of one or more of the following:

-the amount of energy remaining in the power supply from which the transmitter derives power;

-a power level that can be provided by a power source from which the transmitter derives power; and

the voltage level that the power supply from which the transmitter derives power can support.

According to a preferred embodiment, the power demand metric may be a measure of the power level required to be provided by the power source from which the transmitter derives power or a measure indicative of the power level required to be provided by the power source from which the transmitter derives power.

The energy availability metric may be measured directly from the current state of the power source, or may be estimated or predicted based on its past measurements. It may depend on or be based on current and/or past measurements of the amount of energy remaining in the power supply and/or current and/or past measurements of the power level provided by the power supply and/or current and/or past measurements of the voltage level supported by the power supply. It may be based on current and/or past measurements of electrical characteristics of the power supply, such as voltage, current, and/or internal resistance measurements.

The power demand metric may be measured directly from a current power level provided by the power supply to the transmitter and/or other device, or may be estimated or predicted based on past measurements thereof. It may depend on or be based on information indicative of predicted future demand or changes in future demand in relation to the transmitter and/or other devices (e.g., the system or vehicle on which the transmitter is implemented).

According to a preferred embodiment, the MIMO transmitter may be implemented on or as part of a relay node.

According to a preferred embodiment, the MIMO transmitter may be implemented on or as part of an unmanned vehicle.

According to a preferred embodiment, the MIMO transmitter may be implemented on or as part of an aircraft.

According to a preferred embodiment, the MIMO transmitter may be implemented on or as part of a vehicle having a battery power source.

Alternatively or in addition to a relay node, vehicle or other system on or as part thereof (where the MIMO transmitter is implemented using battery power), the relay node, vehicle or other system may use a generator such as solar energy, a wind turbine or the like.

When the MIMO transmitter is implemented on a relay node and/or a vehicle, the power demand metric may depend on a direct measurement of the current power level provided by the power supply to the relay node and/or the vehicle in question, or may be estimated or predicted based on its past measurements. It may depend on or be based on information indicating a predicted future demand or a change in future demand in relation to the power that needs to be provided to the relay node and/or the vehicle in question.

According to a preferred embodiment, the first subset relating to at least one RF chain may comprise a single antenna element.

According to a second aspect of the present invention, there is provided a multiple-input multiple-output (MIMO) receiver, comprising:

an antenna array comprising a plurality of antenna elements, each antenna element arranged to receive a wireless communication signal;

a switching unit configured to connect the plurality of antenna elements to a plurality of RF chains in one of a first state or a second state, wherein:

-in a first state, at least one RF chain of the plurality of RF chains is connected to a first subset of the plurality of antenna elements, and

-in a second state, the at least one of the plurality of RF chains is connected to a second subset of the plurality of antenna elements, wherein the first and second subsets related to the at least one RF chain have different numbers of antenna elements;

each RF chain is configured to pass signals received from a subset of antenna elements to which the RF chain is connected to generate a digital signal;

a digital signal processor configured to receive the digital signals generated from each RF chain and perform a combination of these signals to generate a plurality of data streams; and

a power control unit configured to determine an energy availability metric and/or a power demand metric and, in response, cause the switching unit to connect the plurality of RF chains to the plurality of antenna elements in the first state or the second state.

According to a third aspect of the present invention, there is provided a MIMO system comprising a MIMO transmitter according to the first aspect and a MIMO receiver according to the second aspect.

According to a fourth aspect of the present invention, there is provided a method of operating a multiple-input multiple-output (MIMO) transmitter, the method comprising:

performing precoding on the plurality of data streams at the digital signal processor;

communicating the precoded data stream from the digital signal processor via each of a plurality of Radio Frequency (RF) chains to generate a signal representative of the data stream;

configuring a switching unit to connect the plurality of RF chains to a plurality of antenna elements of an antenna array in one of a first state or a second state, wherein:

-in the first state, at least one of the plurality of RF chains is connected to a first subset of the plurality of antenna elements, and

-in the second state, the at least one of the plurality of RF chains is connected to a second subset of the plurality of antenna elements, wherein the first and second subsets relating to the at least one RF chain have different numbers of antenna elements; and

determining an energy availability metric and/or a power demand metric and, in response, causing the switching unit to connect the plurality of RF chains to the plurality of antenna elements in the first state or the second state.

According to a fifth aspect of the present invention, there is provided a method of operating a multiple-input multiple-output (MIMO) receiver, the method comprising:

receiving a wireless communication signal at each of a plurality of antenna elements of an antenna array;

configuring a switching unit to connect the plurality of antenna elements to a plurality of RF chains in one of a first state or a second state, wherein:

-in the first state, at least one of the plurality of RF chains is connected to a first subset of the plurality of antenna elements, and

-in the second state, the at least one of the plurality of RF chains is connected to a second subset of the plurality of antenna elements, wherein the first and second subsets relating to the at least one RF chain have different numbers of antenna elements;

each RF chain is configured to pass signals received from a subset of antenna elements to which the RF chain is connected to generate a digital signal;

receiving the digital signals generated from each RF chain at a digital signal processor and combining the signals to generate a plurality of data streams; and

determining an energy availability metric and/or a power demand metric and, in response, causing the switching unit to connect the plurality of RF chains to the plurality of antenna elements in the first state or the second state.

According to a sixth aspect of the present invention there is provided a method of operating a multiple-input multiple-output (MIMO) transceiver system, the method comprising performing the method according to the fourth aspect and the method according to the fifth aspect.

The various options and preferred embodiments described above in relation to the first aspect also apply in relation to the second, third, fourth, fifth and sixth aspects.

Drawings

Preferred embodiments of the present invention will now be described with reference to the accompanying drawings, in which:

FIG. 1 is a UAV assisted millimeter wave MIMO system;

FIG. 2 shows an example of an all-digital precoded MIMO transmitter;

FIG. 3 illustrates two hybrid precoding implementations that are typically used for the purpose of hybrid precoding in millimeter wave massive MIMO systems;

FIG. 4 illustrates a system configuration suitable for providing hybrid precoding for UAV assisted millimeter wave massive MIMO systems;

FIG. 5 illustrates elements of a MIMO transmitter and elements interacting therewith in accordance with a preferred embodiment;

fig. 6 illustrates a decision making process that may be used by a power control unit of a MIMO transmitter or a MIMO receiver in accordance with a preferred embodiment; and

FIG. 7 is a block diagram of a computer system suitable for use in the operation of an embodiment of the present invention.

Detailed Description

A method and apparatus according to a preferred embodiment will be described with reference to the accompanying drawings.

The preferred embodiments will be described primarily with reference to a UAV-mounted relay having a MIMO transmitter that transmits signals received from a source (such as base station 10 in fig. 1) to one or more destinations (such as mobile station 15 in fig. 1). It should be understood that this description applies in a corresponding manner generally to "mirrored" embodiments, such as UAV-mounted relays having MIMO receivers that transmit signals received from a source (such as the mobile station 15) to a destination (such as the base station 10), and to UAV-mounted relays having MIMO transceivers that transmit signals in both directions. It should be understood that this description also applies generally to embodiments such as MIMO transmitters, receivers, and transceivers that are not mounted on a UAV or other such vehicle or relay. Although the following description focuses primarily on links between UAVs (acting as relays) and multiple mobile stations, the same principles are equally applicable to links between UAVs and base stations. Furthermore, while potentially varying power availability and the possible need (or desire) to be able to switch between more energy-consuming (and typically higher data rates) and more energy-efficient (typically lower data rates) states are generally not an issue for issues related to fixed ground entities (such as base stations) as compared to issues related to airborne and/or mobile devices (such as UAVs acting as unidirectional or bidirectional relays), ground entities (such as base stations) may have similar needs to switch between higher and lower power states in certain scenarios, so embodiments of the invention may also be applied to such entities (e.g., ground base stations that are used only as, for example, transmitters).

As used in this document, the phrase "millimeter wave band" refers to frequencies from about a few gigahertz (e.g., 3.0GHz) to several hundred gigahertz. Radio waves in the cellular band may have less propagation loss and provide better coverage, but a relatively small number of antennas may also be used. On the other hand, radio waves in the millimeter wave band may suffer from higher propagation losses, but make them well suited for small form factor high gain antenna or antenna array designs.

Fig. 4 illustrates, by way of example, a system configuration suitable for providing hybrid precoding on a UAV, suitable for assisting mmwave massive MIMO system usage with respect to a UAV.

The source (which may be a base station, such as BS 10 in fig. 1) has a hybrid precoder 40, the hybrid precoder 40 having multiple antennas (generally 408) and may include multiple RF transceiver and transmitter circuits (not shown). The antenna may include an array of antenna sub-arrays. Thus, each antenna shown may represent a sub-array comprising one or more antennas. Each antenna sub-array is configured to beamform signals transmitted to and received from the sub-array. Transmitter (TX) processing circuitry encodes, multiplexes, and digitizes the outgoing baseband data to generate a processed baseband signal. The RF transceiver receives the outgoing processed baseband signal from the transmitter processing circuitry, up-converts the baseband signal to an RF signal, and performs RF pre-coding on the RF signal transmitted via antenna 408.

The destination, which may be a mobile station such as one of those shown as MS 15 in fig. 1, has a hybrid combiner 45, which hybrid combiner 45 has multiple antennas (generally 458) and may include multiple RF transceiver and receiver circuits (not shown).

An RF transceiver at the destination receives incoming RF signals, such as signals transmitted by a base station, from antenna 458. The RF transceiver performs RF combining (i.e., beamforming at the various sub-arrays) and downconverts the incoming RF signals to generate baseband signals. The baseband signal is sent to Receiver (RX) processing circuitry, which generates a processed baseband signal by filtering, decoding, and digitizing the baseband signal. The RX processing circuitry then typically sends the processed baseband signals to a controller/processor (not shown) for further processing.

At the UAV, as shown in fig. 4, the system has a first channel 42 from the source (e.g., base station 10) to the UAV 43 and a second channel 44 from the UAV 43 to the destination (e.g., mobile station 15). Hybrid precoding at the base station and hybrid combining at the mobile station may be performed as described above. Therefore, the following explanation focuses on the hybrid precoding process at the UAV 43. For simplicity, this explanation is provided primarily in relation to the case where the source is the Base Station (BS)10 and the destination is the Mobile Station (MS)15, but it should be understood that elements on the UAV 43 may also process signals traveling in the opposite direction (i.e., from the mobile station 15 to the base station 10).

First, a receive analog combiner 420 is used for signals from base station 10 received at antenna 428. The digital precoder 430 (if the UAV is configured to process signals in both directions, i.e., from BS 10 to MS 15 and from MS 15 to BS 10, the digital precoder 430 may be a functional block of a digital precoder/combiner) then processes the signals into baseband. Next, the analog precoder 440 is used to forward signals transmitted at the UAV to the mobile station via the antenna 448 of the analog precoder 440 and the antenna 458 on the mobile station hybrid combiner. This is a generic hybrid precoding process for UAV assisted mmwave massive MIMO systems. However, we now explain in detail the proposed technique with switches and phase shifters, which allows to implement a fully connected architecture and a sub-connected architecture at the UAV, and to switch between the two architectures according to the requirements explained with reference to fig. 5.

Compared to hybrid precoding at the base station 10 and the mobile station 15, the hybrid precoding method of the UAV assisted system proposed here is very different from the hybrid precoding method of the conventional MIMO millimeter wave system. The present explanation will focus on the "amplify-and-forward" UAV of a mmwave massive MIMO system with no direct link between the source and destination, as shown in fig. 5. For simplicity, we will consider a scenario where there is no non line of sight (NLOS) communication, so all channels are line of sight (LOS). For precoding, we assume that the channel 42 (i.e., the channel between the source 40 (e.g., base station 10) and the UAV 43 (or other such relay 13)) and the channel 44 (i.e., the channel between the UAV 43 (or other such relay 13) and the destination 45 (e.g., mobile station 15)) are known at the source, UAV, and destination. In a practical system, Channel State Information (CSI) received at the UAV may be obtained via training from the source to the UAV, and CSI received at the destination may be obtained via training from the UAV to the destination. The CSI is then shared with a transmitter at the UAV via feedback from the UAV to the source, and the CSI transmitted at the source is shared by feedback from the UAV to the destination.

As described above, conventional hybrid precoding techniques are not universally applicable due to power limitations at the UAV. Thus, unlike these prior art techniques, the technique employed here uses a combination of a Phase Shifter (PS) (generally 554) and an energy efficient switch (generally 552).

Before continuing with the discussion of the overall functionality of the elements shown in fig. 5, it is noted that two RF chains (generally 54) are shown, labeled "RF chain 1" and "RF chain 2", and four antennas 558 are shown, labeled TX1, TX2, TX3, and TX 4. Between the two RF chains 54 and the four antennas 558 is a switching unit 550 of the analog precoder 55. The switching unit (shown within the dashed box) comprises eight switches 552, each of which functions in relation to the connection of one of the eight phase shifters 554. The eight connections are paired with respective ones of the four antennas 558 via four RF combiners 556. In fig. 5, the connections from/to RF chain 1 are shown as solid lines, while the connections from/to RF chain 2 are shown as dashed lines — this is to facilitate (in the figure) identification of the RF chains associated with the respective connections.

In addition, each switch in fig. 5 is labeled with an "s-number" or "switch-number," the s-number indicating which RF chain and which antenna are connected (or disconnected) via the switch. Thus, switch number s11, when closed, connects RF chain 1 to antenna TX1, and switch number s24, when closed, connects RF chain 2 to antenna TX 4.

The digital pre-coder 51 takes input from the analog combiner and applies sub-carrier dependent digital pre-coding before passing the pre-coded signal to the Inverse Fast Fourier Transform (IFFT) stage. The signal for each RF chain passes through an "M-point inverse fast fourier transform" module 52, where M is the number of subcarriers that convert the frequency domain signal to a time domain digital signal. Each symbol passed from the M-point IFFT 52 then has a cyclic prefix added by the "add CP" block 53 and then passed to the applicable RF chain 54. The RF chain will typically include the following functions: digital-to-analog (DAC) conversion, mixers, and frequency converters. The digital module may be used to convert the baseband signal into the RF domain. (Note that for a receiver, the reverse order and set of functions would typically be used, e.g., DAC is replaced by an analog-to-digital converter (ADC) and IFFT is replaced by a Fast Fourier Transform (FFT) module.)

The signal from the RF chain 54 is passed to the switching unit 550. If the switch "sXn" is closed, the signal from "RF chain X" will be passed to the antenna "TXn" via an associated phase shifter 554 and combiner 556. If switch "sXn" is open, no signal is passed from "RF chain X" to antenna "TXn". In this case, the relevant phase shifter may be turned off.

It is clear that both the fully-connected and the sub-connected architectures are thus possible, with the switching between them being performed in a specific way different from the existing hybrid precoding techniques.

As previously mentioned, sometimes performance may be high priority, while energy consumption is less important, so the UAV may operate in a fully connected (or more connected) mode and be able to provide higher overall rate performance. At other times, for example, when power consumption becomes a priority (e.g., if service requirements are low, or if battery power is low, or if the UAV determines or is told that it needs to remain running for a longer period of time than previously expected), it may switch to the sub-connection (or less connection) architecture by utilizing an additional switch incorporated in the new system.

It is noted that, in addition to a "fully-connected" architecture, in which each RF chain is connected to all antennas (or all antenna elements of an antenna array or sub-array), and one or a series of "sub-connected" architectures, in which each RF chain is connected to only a subset of antennas (possibly only one antenna), an architecture is also possible in which one or more antenna elements are no longer connected to any RF chain.

Referring in more detail to fig. 5, power control unit 50 performs the task of determining an "energy availability metric" and/or a "power demand metric" and, in response to either or both (or a change in either or both), may indicate or cause switching unit 550 to change architecture to a more connected architecture or a less connected architecture by connecting or disconnecting one or more RF chains to or from one or more antenna elements. In this example, a Switch Control Unit (SCU)58 (shown as part of the power control unit 50 for convenience) performs the task of controlling the switch 552 in the switching unit 550, but the SCU 58 need not be a functional module of the power control unit 50-it may be a separate module, or its functionality may be integrated into the power control unit 50. The SCU 58 in this example is connected to a power monitoring unit 56 having one or more power monitoring sensors that continuously monitor the available power resources at the UAV, and may also obtain information about data requirements from a data rate measurement unit 57 (e.g., an admission control unit). As with SCU 58, power monitoring unit 56 and data rate measurement unit 57 are shown as modules of power control unit 50 for convenience, but either or both may be separate modules communicating with power control unit 50 by telemetry (wired or wireless) or otherwise, or may be functionally integrated into power control unit 50. Based on the data power and/or energy data it obtains (by itself or externally), the power control unit 50 then makes a notification decision of which architecture to use, and then causes the SCU 58 to configure the switch 552 in the switching unit 550 for the selected architecture.

Typically the UAV/drone uses a telemetry system to report various aspects of the drone status, so the power control unit 50 may use the data obtained thereby to determine an energy availability metric, depending on which a possible decision to switch the architecture to a more connected architecture or a less connected architecture is made. The battery indication may be given as a percentage (or estimated percentage) of the known maximum level of the amount of energy remaining in the battery or a percentage (or estimated percentage) of the maximum power that the battery is still capable of providing, and may be based on measurements of current, voltage or internal resistance. Furthermore, data obtained from antennas, phase shifters, amplifiers or other electronic components of the signal processing or transmitting portion of the on-board drone system, or other components of the drone (such as motors) may be used by the power control unit 50 to determine power demand metrics from which decisions may be made to switch the architecture to a more connected architecture or a less connected architecture.

A simple battery monitoring device may be used which sends a message when one or more voltage level thresholds are exceeded, for example it may be used as a trigger to switch to a different (less connected) level of the sub-connected architecture when the voltage decreases, or may be used to switch to a different (more connected) architecture, for example when the battery is charged (e.g. using solar energy).

Depending on the battery percentage level or other aspects, the remaining flight duration may be calculated/estimated, for example, if the expected/indicated flight time is extended (or vice versa), a decision to switch to a less connected architecture may be triggered, or if the battery percentage level begins to decrease faster than previously estimated (e.g., an increase in traffic rate requires more radio processing, resulting in a shorter battery life), a switch to a less connected architecture may be triggered to restore the flight duration to a previous expectation.

Although in this example the communication between the SCU 58 and the power monitoring unit 56 and the data rate measurement unit 57 mainly involves the SCU 58 receiving input from the power monitoring unit 56 and/or the data rate measurement unit 57, it is possible that some control feedback requests from the SCU 58 send information, e.g. at the correct frequency or based on relevant thresholds, so the channel 59 between the SCU 58 and the power monitoring unit 56 and the data rate measurement unit 57 is represented as a double-headed arrow.

The basic process that may be used in accordance with the present embodiment is illustrated in fig. 6, which shows the decision making process of the power control unit 50 and the SCU 58 shown in the exemplary embodiment of fig. 5. An event may be activated by: periodic review by system or architecture; by a specific message from a power monitoring sensor in the power monitoring unit 56 (i.e., in the power control unit 50 of the UAV or otherwise) or connected to the power monitoring unit 56 or from a data rate measurement unit 57 (e.g., an admission control unit); or otherwise.

The power control unit 50 then determines whether a change in state or architecture is required. If so, a dedicated message requesting the change may be used.

Alternatively, a determination that a state or architecture may need to be changed may be triggered, for example, by exceeding a threshold. For example, if the UAV determines or is indicated to need to remain airborne for an additional period of time (e.g., another two minutes), and such an increase requires or will take a total time that exceeds a threshold (e.g., a 5 hour threshold), this may trigger a decision that a state or architecture needs to be changed, or a determination needs to be made as such.

It is noted that the power monitoring sensors may monitor the power requirements or status of the MIMO transmitter or repeater (or components thereof) and/or the power requirements of the UAV as a whole (or components thereof), and/or may directly monitor the current or ongoing status of the onboard power supply, for example.

Referring to fig. 6, once the system is in active (i.e. after power-up, take-off or another such "start" step s 60), the process in this example may be activated by the power monitoring unit 56 and/or one or more sensors in or monitored by the admission control unit, the power monitoring unit 56 sending a message regarding a change in power consumption requirements (step s61) and the admission control unit sending a message regarding a change in resource requirements and/or importance (step s 62). One (or both) of these messages may trigger a decision as to whether a change in state or architecture is required (step s 64). If not, the process returns to waiting for a message.

If it is determined at step s64 that a change of state or architecture is required, the power control unit 50 determines what architecture should be selected (step s 66). In this example, this is based on power and performance requirements. Energy efficiency will favor the most (or more) sub-connection configuration, while performance enhancement will favor the most (or more) fully-connected configuration. The power control unit 50 may select one of these extreme cases, or a configuration between the two extreme cases.

If the selected configuration is different from the currently used configuration, the SCU 58 in the power control unit 50 instructs the associated switch 552 in the switching unit 550 to open or close. It may (generally simultaneously) notify the digital precoder 51 of a change in configuration, but during the switching process itself, the main function is to instruct the switching unit 550 to open or close the appropriate switch 552. It can be seen that if all switches are closed, switches s24 and s23 of RF chain 2 and switches s13 and s14 of RF chain 1 are open, causing a change from the fully connected architecture to the sub-connected architecture. For example, the power control unit 50 may only indicate the analog precoder 55, with the analog precoder 55 passing an indication of the change to the digital precoder 51. Furthermore, when a particular switch 552 is open, the associated connection between the RF chain 54 and the antenna 558 will be broken, and thus the phase shifter 554 in question may be turned off while the antenna 558 in question may remain on for data transmission.

The following scenario is provided as an example of how embodiments of the present invention may work. First, the MIMO transmitter (or receiver or transceiver) in the UAV 13 operates in a fully connected architecture that provides high data rate requirements as needed. For example, it may be in peak hours, where the data demand may be higher. With the arrival of off-peak hours, the data rate requirements may be reduced and high data rate requirements are no longer needed, at which point it may be appropriate to switch to a sub-connection architecture in order to conserve energy while still maintaining operation at lower data rate requirements. The switching process may be described as follows (with reference to the numbered elements in fig. 5):

(i) if the power control unit 50 determines that it is appropriate or necessary to switch from the fully-connected architecture to the sub-connected architecture, the RF chain 1 will only be connected with the transmit antenna elements TX1 and TX 2. For this purpose, switches s13 and s14 are switched off. By doing so, the fully connected architecture is converted to a sub-connected architecture, and RF chain 1 is connected only to TX1 and TX2, which are disconnected from TX3 and TX 4.

(ii) If the power control unit 50 decides that it is appropriate to switch back to the fully connected configuration, switches s13 and s14 are turned on. By doing so, RF chain 1 reconnects with TX3 and TX4, resulting in a fully connected architecture that can provide higher data rates but at the cost of higher power consumption.

In this way, the preferred embodiments provide hybrid precoding techniques for UAV assisted mmwave massive MIMO systems. In this technique, two precoding architectures (full-concatenation and sub-concatenation) are combined. Additional units (i.e., the SCU 58, the power monitoring unit 56 (including or in communication with sensors to sense current requirements, etc.)) are used as part of the power control unit 50 to allow determination of when to switch between the two architectures, which can be accomplished using a low cost switch 552, which can be implemented in conjunction with the current architecture. In practical deployments of UAV assisted mmwave massive MIMO systems, this may provide a better tradeoff between overall rate performance and energy consumption.

FIG. 7 is a block diagram of a computer system suitable for operation of an embodiment of the present invention. A Central Processing Unit (CPU)702 is communicatively connected to a data memory 704 and an input/output (I/O) interface 706 via a data bus 708. The data store 704 may be any read/write storage device or combination of devices, such as a Random Access Memory (RAM) or a non-volatile storage device, and may be used to store executable data and/or non-executable data. Examples of non-volatile storage devices include disk or tape storage devices. The I/O interface 706 is an interface of a device for data input or output, or both data input and output. Examples of I/O devices that may be connected to I/O interface 706 include a keyboard, a mouse, a display (e.g., a monitor), and a network connection.

As long as the described embodiments of the invention are implementable, at least in part, using software to control a programmable processing device, such as a microprocessor, digital signal processor or other processing device, data processing apparatus or system, it will be appreciated that a computer program for configuring a programmable device, apparatus or system to carry out the foregoing methods is envisaged as an aspect of the invention. For example, a computer program may be implemented as source code or compiled to be implemented on a processing device, apparatus, or system, or may be implemented as object code.

Suitably, the computer program is stored on a carrier medium in machine or device readable form, e.g. solid state memory, magnetic memory such as a magnetic disk or tape, optically or magneto-optically readable memory such as a compact disk or digital versatile disk, etc., and the processing device configures it for operation with the program or a portion thereof. The computer program may be provided from a remote source embodied in a communication medium such as an electronic signal, radio frequency carrier wave or optical carrier wave. Such carrier media are also contemplated as aspects of the present invention.

It will be appreciated by persons skilled in the art that whilst the invention has been described in conjunction with the above exemplary embodiments, the invention is not limited thereto and that there are many possible variations and modifications which fall within the scope of the invention.

The scope of the present invention may include other novel features or combinations of features disclosed herein. The applicant hereby gives notice that new claims may be formulated to such features or combinations of features during the prosecution of the present application or of any such further applications derived therefrom. In particular, with reference to the appended claims, features from dependent claims may be combined with those of the independent claims and features from respective independent claims may be combined in any appropriate manner and not merely in the specific combinations enumerated in the claims.