WO2019158179A1

WO2019158179A1 - Channel estimation for vehicular communication systems

Info

Publication number: WO2019158179A1
Application number: PCT/EP2018/053466
Authority: WO
Inventors: Behrooz MAKKI; Mona HASHEMI
Original assignee: Telefonaktiebolaget Lm Ericsson (Publ)
Priority date: 2018-02-13
Filing date: 2018-02-13
Publication date: 2019-08-22

Abstract

A method for configuring radio transmission between a network node (130) comprising a first node antenna (131) and a vehicle (101) moving with a velocity V in a direction D, the vehicle comprising a predictor antenna (110) and at least one main antenna (120), wherein the at least one main antenna is arranged to trail the predictor antenna as the vehicle moves in the direction D, the method comprising; estimating (S1) a first channel state information, CSI, value (h1b) between the first node antenna (131) and the predictor antenna (110), based on radio transmission between the first node antenna (131) and the predictor antenna (110) when located at a first location (141), estimating (S2) a second CSI value (h1a) between the first node antenna (131) and a main antenna (120) based on radio transmission between the first node antenna (131) and the main antenna (120) when located at a second location (142) trailing the first location (141) in direction D, predicting (S4) a third CSI value between the first node antenna (131) and the main antenna (120) when located at the first location (141) based on the first and on the second CSI value (h1a, h1b), and configuring (S5) radio transmission of data between the first node antenna (131) and the main antenna (120) when located at the first location (141) based on the predicted third CSI value.

Description

TITLE

CHANNEL ESTIMATION FOR VEHICULAR COMMUNICATION SYSTEMS

TECHNICAL FIELD

The present disclosure relates to a communication system comprising a network node arranged to communicate with a moving vehicle using two or more antennas.

BACKGROUND

Mobile wireless broadband users may not always be stationary. On the contrary, some users may be located in rapidly moving vehicles, e.g., trams, buses, and trains. A promising solution to provide such users with high velocity wireless access involves moving relays. Such moving‘cells’ are discussed by Y. Sui et.al. in "Moving cells: a promising solution to boost performance for vehicular users", IEEE Communications Magazine, vol. 51 , no. 6, pp. 62-68, June 2013. A moving cell refers to a local access point placed inside the moving vehicle and configured to serve broadband users inside the vehicle via short-range transceivers. The access point (also called the moving relay) connects to a core network via a backhaul link using antennas mounted on top of the vehicle.

Advanced antenna systems comprising antenna arrays may be used to increase throughput in backhaul links. Such systems use estimates of channel state information (CSI) obtained, e.g., from pilot signal transmissions to provide beamforming and spatial multiplexing which allows for increased data rates. However, pilot signal transmission is an overhead which consumes communication resources. Excessive use of pilot signal transmission is a drawback of many advanced communication systems due to the incurred overhead.

Outdated channel estimates are a problem when moving relays are used in vehicles travelling at high velocity. A solution to the problem with outdated channel information is discussed by M. Sternad et.al. in "Using predictor antennas for long-range prediction of fast fading for moving relays," 2012 IEEE Wireless Communications and Networking Conference Workshops (WCNCW), Paris, 2012, pp. 253-257.

However, there is still a need for improvements in channel estimation for communication systems involving moving vehicles. SUMMARY

It is an object of the present disclosure to provide a robust high-velocity wireless communications link between a network node and a moving vehicle.

This object is obtained by a method for configuring radio transmission between a network node comprising a first node antenna and a vehicle moving with a velocity V in a direction D. The vehicle comprises a predictor antenna and at least one main antenna. The at least one main antenna is arranged to trail the predictor antenna as the vehicle moves in the direction D. The method comprises;

estimating a first channel state information, CSI, value between the first node antenna and the predictor antenna, based on radio transmission between the first node antenna and the predictor antenna when located at a first location,

estimating a second CSI value between the first node antenna and a main antenna based on radio transmission between the first node antenna and the main antenna when located at a second location trailing the first location in direction D,

predicting a third CSI value between the first node antenna and the main antenna when located at the first location based on the first and on the second CSI value, and configuring radio transmission of data between the first node antenna and the main antenna when located at the first location based on the predicted third CSI value.

Since the prediction is based on both the first and on the second CSI values the third CSI value is predicted with increased accuracy and robustness compared to a scenario where the third CSI value is predicted only based on the first CSI value.

According to aspects, the method comprises estimating a fourth CSI value between the first node antenna and the main antenna when located at the first location, based on an extrapolation of the second CSI value to the first location.

The extrapolation may be implemented by, e.g., a Kalman or Wiener filter. This extrapolation enables estimation of the fourth CSI value independently of the predictor antenna. This independent estimation can be used to increase robustness of the third CSI value prediction, or to detect occurrence of large errors in the estimated second CSI value. According to aspects, the predicting comprises predicting the third CSI value based on a weighted combination of the first CSI value and the fourth CSI value, wherein weights are determined based on velocity V and direction D.

Advantageously, the weighted combination can be adapted based on accuracy of the component estimates. For instance, if the vehicle is moving rapidly, then an extrapolation of the second CSI value may be less accurate, and should be given less weight. When the velocity is lower, the extrapolation of the second CSI value may be more accurate, and should be higher weight. This increases robustness of the predicted third CSI value.

According to aspects, the method comprises assigning a radio transmission frequency band resource for radio transmission between the network node and the vehicle based on the velocity V.

The accuracy of extrapolated channel estimates may, in addition to vehicle velocity, also be dependent on carrier frequency. A high carrier frequency often implies more uncertain extrapolated estimates, while the reverse is true for lower carrier frequencies. This effect is due to the different wavelengths at different carrier frequencies. As will be discussed below, CSI estimation based on extrapolation is often more accurate when transmission frequency bands comprise lower frequencies, and less accurate when frequency bands comprising higher frequencies are used. By assigning radio transmission frequency bands based on velocity improvements in the extrapolated CSI estimates can be obtained, thereby leading to improvements in accuracy and robustness of the third CSI estimate.

According to aspects, the configuring comprises configuring radio transmission of data between the first node antenna and the predictor antenna when located at the third location based on an extrapolation of the first CSI value to the third location.

By using both main and predictor antennas for data transmission, data throughput is increased, which is an advantage compared to known systems using predictor antennas only for channel estimation.

According to aspects, the configuring comprises configuring radio transmission of data between the first node antenna and the main antenna when located at the first location using a first lobe width, and configuring radio transmission of data between the first node antenna and the predictor antenna when located at the third location using a second lobe width larger than the first lobe width.

This way robustness is increased in that data traffic via the predictor antenna is transmitted using a wider lobe while the main antenna data traffic is transmitted using a narrower lobe. The CSI used for data transmission to the predictor antenna is often of reduced accuracy compared to the CSI used for data transmission to the main antenna, since the main antenna CSI is based on both the first and on the second CSI values, while the predictor antenna CSI is based only on extrapolation of the first CSI value. The wider lobe compensates to some extent for the expected CSI estimation quality degradation at the predictor antenna compared to the main antenna.

According to aspects, the configuring comprises determining a time difference between a time instant when the predictor antenna is located at the first location and a corresponding time instant when the main antenna is located at the first location, and delaying the radio transmission of data between the first node antenna and the main antenna when located at the first location based on the determined time difference.

This way the relevance of CSI estimated using the predictor antenna is maintained despite delays such that the estimated CSI can be used for data transmission by the first main antenna.

According to aspects, the method is also applicable for configuring additional radio transmission between a further network node comprising a second node antenna and the vehicle. The method then comprises;

estimating a fifth CSI value between the second node antenna and the predictor antenna, based on radio transmission between the second node antenna and the predictor antenna when located at a first location,

estimating a sixth CSI value between the second node antenna and the main antenna based on radio transmission between the second node antenna and the main antenna when located at a second location trailing the first location in direction D predicting a seventh CSI value between the second node antenna and the main antenna when located at the first location based on the fifth and on the sixth CSI value, and

configuring joint radio transmission of data between the first and second node antennas and the main antenna when located at the first location based on the third and on the seventh CSI value.

This set-up using additional radio transmission involving a further network node increases robustness and data throughput beyond that obtained by the single network node system. By utilizing several network nodes during communication, diversity gains are obtained.

There are also disclosed herein network nodes, vehicles, antenna systems and computer programs associated with the above-mentioned advantages.

Generally, all terms used herein are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to "a/an/the element, apparatus, component, means, step, etc." are to be interpreted openly as referring to at least one instance of the element, apparatus, component, means, step, etc., unless explicitly stated otherwise. The steps of any method disclosed herein do not have to be performed in the exact order disclosed, unless explicitly stated.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure will now be described more in detail with reference to the appended drawings, where:

Figure 1 shows a schematic view of a communication system arranged for communication between a network node and a moving vehicle;

Figure 2 shows a schematic view of a communication system arranged for communication between a network node and a moving train;

Figure 3 shows a schematic view of a communication system arranged for communication between a plurality of network nodes and a moving vehicle;

Figure 4 is a diagram illustrating transmissions in a communication system;

Figure 5 shows one example of a computer program product comprising computer readable means; Figure 6 is a schematic diagram showing a control unit;

Figure 7 is a flowchart illustrating methods described herein.

Figure 8 illustrates a frequency allocation. DETAILED DESCRIPTION

Aspects of the inventive concept will now be described more fully hereinafter with reference to the accompanying drawings, in which certain embodiments of the inventive concept are shown. Aspects of the inventive concept may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided by way of example so that this disclosure will be thorough and complete, and will help convey the scope of the inventive concept to those skilled in the art. Like numbers refer to like elements throughout the description. Any step or feature illustrated by dashed lines should be regarded as optional.

The techniques disclosed herein are aimed at developing a modular moving relay setup associated with improved channel prediction quality and link reliability for communication between a network node connected to a core network and a moving vehicle. The proposed setup comprises communication involving a predictor antenna and one or more main antennas mounted on the vehicle.

The predictor antenna and/or the main antenna may according to aspects comprise a plurality of antenna elements in an antenna to make an antenna array or an antenna matrix. Herein, when discussing antennas, any type of antenna is applicable unless a specific type is specified.

With reference to Fig. 1 , the predictor antenna 110 facilitates accurate prediction of the wireless propagation channel between the network node antenna 131 and a main antenna 120 mounted on the vehicle 101 even at high vehicle velocity. This is possible since the main antenna 120 trails the predictor antenna 110. If the predictor antenna passes a first location 141 at a first time instant t, the main antenna will pass very close to the first location 141 after a short period of time d at a second time instant t+d. Thus, a channel estimate or determination of channel state information (CSI) made between a remote antenna, such as the antenna 131 of the network node 130, and the predictor antenna 110 at the first time instant t will be valid for the channel between the remote antenna 131 and the main antenna 120 at the second time instant t+d when the main antenna passes the first location 141.

The proposed setup is applicable for both frequency division duplex (FDD) and time division duplex (TDD) schemes as well as for both uplink and downlink transmission. To further improve the CSI used for data transmission, the CSI obtained by use of the predictor antenna is complemented by extrapolated CSI obtained by radio transmission involving the main antenna. Furthermore, to improve data throughput, the prediction antenna is used for data transmission in addition to its use for obtaining channel state information.

There are several advantages associated with using also the main antenna for channel prediction, despite the potentially high velocity of the moving vehicle. For instance, pilot transmission represents and overhead which is not desired. The sparser the pilot transmission is, the lower the quality of the estimated CSI becomes overall. The CSI estimated directly after pilot transmission is accurate, but becomes outdated as time passes. To improve CSI estimation, extrapolation in time can be performed. Flowever, as will be shown below, such extrapolation suffers from vehicle velocity considered in light of the wavelengths used for radio transmission. Therefore, to complement channel estimation, and to reduce requirements on pilot transmission duty cycles, the main antenna is also involved in the channel estimation.

The presented communication system 100 may optionally involve a further network node 330 as will be discussed in connection to Fig. 3 below. The diversity obtained by using a further network node for communication with the vehicle results in further improvements in robustness and data throughput since diversity gains are obtained. Fig. 1 shows a schematic view of a communication system 100 arranged for communication between a network node 130 and a moving vehicle 101. The vehicle 101 is arranged to move with a velocity v in a direction D. The network node 130 comprises a node control unit 135. The vehicle comprises a vehicle control unit 115, a predictor antenna 110 arranged on a front section 111 of the vehicle, and a main antenna 120 arranged on a rear section 112 of the vehicle. Control units in general will be discussed below in connection to Fig. 6. Due to the relative arrangement of antennas on the vehicle, the main antenna is arranged to trail the predictor antenna when the vehicle moves in direction D. The communication system 100 is arranged to estimate channel state information, CSI, based on radio transmission between the network node 130 and the predictor antenna 110, and between the network node and the main antenna. The modular moving relay network shown in Fig. 1 provides better channel quality prediction, compared to the cases with state-of-the-art prediction schemes based on, e.g., Wiener or Kalman prediction methods. As a result, advanced beamforming and link adaptation schemes can be utilized even at high vehicle velocity or carrier frequencies. Further advantages associated with moving relays according to the present teaching include;

1 ) Compared to the cases with direct radio links between users on the vehicle and the network node, less path loss/shadowing, and higher line-of-sight (LOS) connection probability are expected for the moving relay-core network connections. Also, the penetration loss through vehicle windows is omitted. Thus, higher channel quality is experienced in the backhaul link compared to individual radio links between wireless broadband users and the network node when connecting directly.

2) Unlike regular wireless handheld devices, such as user equipment (UE), moving relays are less limited by, e.g., size, power and complexity. As a result, advanced signal processing and antenna techniques can be effectively exploited to improve the system performance.

3) It is appreciated that handover may be necessary between several network nodes as the vehicle travels in direction D. The wireless devices served by a moving relay may be served as a group. Group handover can then be performed by the moving relay which, compared to the case where each wireless device connects to the core network individually, can reduce the handover failure probability significantly.

Fig. 1 shows three different radio channels with corresponding CSI values; h1 b is associated with a first CSI value relevant for a channel between the network node antenna 131 and the location denoted 141 ; h1 a is a second CSI value relevant for a channel between the network node antenna 131 and the location denoted 142; h1 c is a CSI value relevant for a channel between the network node antenna 131 and the location denoted 140.

It is appreciated that radio channels corresponding to CSI values h1 b, h1 a and h1 c are correlated in time. Suppose the predictor antenna 110 is used for estimating CSI at a location 141 at a given time instant. The main antenna 120 is then located at another location 142 at the given time instant, but will pass the location denoted as 141 after some delay. When this happens, i.e., when the main antenna passes the location denoted 141 , then the CSI estimated by the predictor antenna 110 will be valid for transmission using the main antenna 120.

In more detail, a prediction horizon of T seconds can be expressed as its equivalent to prediction over space in terms of carrier wavelengths according to

p_s=T^*f_d=(T^*v^*f_c)/C [wavelengths].

Here, P_s is the prediction horizon over space (in terms of wavelength), f_d denotes the maximal Doppler frequency (in Hz), v and C are the velocity of the vehicle and the light (in m/s), respectively, and f_c represents the carrier frequency (in Hz). Known Kalman prediction based schemes are known to provide adequate accuracy for a prediction range in space corresponding to 0.1 -0.3 carrier wavelengths. Considering a transmission control loop delay of, say, 5 ms (including the delay for channel prediction, feedback, scheduling, and precoding) and carrier frequency 1.5 GHz, 0.1 -0.3 wavelength prediction ahead corresponds to vehicle velocities of 14-42 km/h. Consequently, for a typical velocity of transportation vehicles, the CSI soon becomes outdated affecting the link adaptation and beamforming quality.

The network node 130 shown in Fig. 1 comprises a first node antenna 131 arranged for radio communication with vehicle 101. This node antenna may comprise a single radiating antenna element, or may comprise a plurality of antenna elements in an antenna array or antenna matrix. The vehicle is shown as moving with a velocity V in a direction D. The vehicle comprises a predictor antenna 110 and at least one main antenna 120. The at least one main antenna is arranged to trail the predictor antenna as the vehicle moves in the direction D. The network node comprises a node control unit 135 which will be discussed in more detail below in connection to Fig. 6. The node control unit is arranged to;

estimate a first channel state information, CSI, value h1 b between the first node antenna 131 and the predictor antenna 110, based on radio transmission between the first node antenna 131 and the predictor antenna 110 when located at a first location 141 ,

estimate a second CSI value h1 a between the first node antenna 131 and a main antenna 120 based on radio transmission between the first node antenna 131 and the main antenna 120 when located at a second location 142 trailing the first location 141 in direction D,

predict a third CSI value h1f between the first node antenna 131 and the main antenna 120 when located at the first location 141 based on the first and on the second CSI value h1 b, hi a, and

configure radio transmission of data between the first node antenna 131 and the main antenna 120 when located at the first location 141 based on the predicted third CSI value h1f.

This way, any data transmission using the predicted third CSI value becomes more robust in that the predicted third CSI is based on both the first and on the second estimated CSI values.

Estimation of CSI by pilot transmission is known and will not be discussed in detail here.

According to aspects, the node control unit 135 is also arranged to configure radio transmission of data between the first node antenna and the predictor antenna 110 when located at the third location 140 based on an extrapolation hi e of the first CSI value h1 b to the third location 140.

By using the predictor antenna 110 also for data transmission, the data throughput is increased compared to existing systems only using the predictor antenna for pilot symbol transmission.

According to aspects, the node control unit 135 is furthermore arranged to estimate a fourth CSI value hid between the first node antenna 131 and the main antenna 120 when located at the first location 141 , based on an extrapolation of the second CSI value h1 a to the first location 141.

This extrapolation is, according to some aspects based on Kalman filtering. The fast fading can be well predicted from noisy past/present channel measurements; for frequency-selective fading broadband channels, a powerful linear prediction of complex channel coefficients is obtained by Kalman predictors. With reasonably low implementation complexity, Kalman predictors utilize known reference signals and estimated models of the fading statistics over time and frequency to predict the channel quality in the subsequent slots. To optimize transmit beamforming, both the channel amplitude and the phase are required. Thus, the Kalman predictor needs to predict the complex channel coefficient. Since the third CSI value h1f is predicted based on pilot transmission using both the predictor and the main antenna via extrapolation, the result becomes more stable and can also be expected to be more accurate. For instance, in case the first CSI value is of low quality, this can be detected and compensated for since the first CSI value will differ from the extrapolated fourth CSI value by an amount.

According to other aspects, the node control unit 135 is arranged to predict the third CSI value based on a weighted combination of the first CSI value h1 b and the fourth CSI value hid, wherein weights are determined based on velocity V and direction D. Consequently, in case the vehicle is moving at a high velocity, the predicted third CSI value will be more heavily based first CSI value obtained from the predictor antenna, and less based on the extrapolated value, while a more slow-moving vehicle can put higher weight on the extrapolated fourth CSI value.

According to an example, the third CSI value is predicted as the first CSI value h1 b in case a product of velocity V and a carrier frequency fc associated with the radio transmission exceeds a pre-determ ined threshold T, and as the fourth CSI value hid otherwise. This way a predictor of CSI with reduced complexity is obtained, in that the prediction is merely based on the operations of thresholding and selecting.

According to another example the communication system is arranged for assigning a radio transmission frequency band resource for radio transmission between the network node 130 and the vehicle 101 based on the velocity V.

Referring to the discussion on prediction horizon above, this feature is advantageous in that the higher the frequency of radio transmission, the more sensitive the system is to spatial distance when it comes to channel estimates. Consequently, it is more difficult to predict CSI values using extrapolation by, e.g., Kalman filtering for fast moving vehicles communicating at higher center frequencies. However, by assigning a radio transmission frequency band resource for radio transmission based on V, these effects can be alleviated. This feature will be discussed in more detail below in connection to Fig. 8.

According to aspects, the node control unit 135 is arranged to assign a radio transmission frequency band resource corresponding to a first carrier frequency fd for transmission between the network node 130 and a vehicle associated with velocity V1 , and assigning a radio transmission frequency band resource corresponding to a second carrier frequency fc2 smaller than fd for transmission between the network node 130 and a vehicle associated with a velocity V2 higher than velocity V1.

According to further aspects, the node control unit 135 is arranged to assign a radio transmission frequency band resource corresponding to a first carrier frequency fd for transmission between the network node 130 and the main antenna 120, and assigning a radio transmission frequency band resource corresponding to a second carrier frequency fc2 smaller than fd for transmission between the network node 130 and the predictor antenna 110.

According to aspects, the node control unit 135 is arranged to configure radio transmission of data between the first node antenna 131 and the main antenna 120 when located at the first location 141 using a first lobe width, and configuring radio transmission of data between the first node antenna 131 and the predictor antenna 110 when located at the third location 140 using a second lobe width larger than the first lobe width.

According to aspects, the node control unit 135 is arranged to determine a time difference between a time instant when the predictor antenna 110 is located at the first location 141 and a corresponding time instant when the main antenna 120 is located at the first location 141 , and delaying S53 the radio transmission of data between the first node antenna 131 and the main antenna 120 when located at the first location 141 based on the determined time difference.

Fig. 1 also shows a vehicle 101 arranged to move with a velocity V in a direction D, the vehicle comprising a predictor antenna 110 and at least one main antenna 120, wherein the at least one main antenna is arranged to trail the predictor antenna as the vehicle moves in the direction D, the vehicle being arranged for radio communication with a network node 130 comprising a first node antenna 131 , the vehicle comprises a vehicle control unit 115 arranged to;

predict a third CSI value between the first node antenna 131 and the main antenna 120 when located at the first location 141 based on the first and on the second CSI value h1 b, h1a, and

configure radio transmission of data between the first node antenna 131 and the main antenna 120 when located at the first location 141 based on the predicted third CSI value.

It is appreciated that antenna characteristics of the predictor antenna may not be exactly equal to the one or more main antennas. For instance, the antenna surroundings, including objects in near field, may differ between the different antennas. Such differences may need to be compensated for. Towards this end, according to some aspects, the node control unit 135 and/or the vehicle control unit 115 is arranged to determine one or more calibration parameters associated with the main antenna and with the predictor antenna, wherein the one or more calibration parameters are arranged to compensate for differences in antenna characteristics between the predictor antenna 110 and the main antenna 120. For instance, a calibration parameter may comprise a vector of values describing a difference in antenna diagram between the predictor and a main antenna. A calibration parameter may also comprise a gain difference between antennas. A calibration parameter may furthermore comprise a difference in antenna diagrams between two antennas. In general, a calibration parameter is a parameter such that a CSI value estimated using a predictor antenna can be modified to fit another main antenna by taking the calibration parameter into account.

In other words, the node control unit 135 and/or the vehicle control unit 155 is arranged to determine one or more calibration parameters associated with the at least one main antenna 120, wherein the one or more calibration parameters are arranged to compensate for differences in antenna characteristics between the predictor antenna 110 and the at least one main antenna 120.

One example of the vehicle 101 is illustrated in Fig. 2, where the vehicle is a train 200 moving in direction D with velocity v. The train 200 comprises a predictor antenna 110 located at the front section of the train, and a number of main antennas located to the rear of the predictor antenna. Because the train travels on fixed rails, the main antennas will pass almost exactly the same location as the predictor antenna after a delay corresponding to velocity v and the distance between antennas on the train. Thus, high-velocity robust and efficient wireless backhaul is provided to wireless broadband users located on the train.

Fig. 3 illustrates a scenario where a further network node 330 takes part in the communication with the moving vehicle 101. The further network node is arranged for additional radio transmission between the further network node 330 comprising a second node antenna 331 and the vehicle 101. The further network node comprises a further node control unit 335 arranged to;

estimate a fifth channel state information, CSI, value h2b between the second node antenna 331 and the predictor antenna 110, based on radio transmission between the second node antenna 331 and the predictor antenna 110 when located at a first location 141 ,

estimate a sixth CSI value h2a between the second node antenna 331 and the main antenna 120 based on radio transmission between the second node antenna 331 and the main antenna 120 when located at a second location 142 trailing the first location 141 in direction D,

predict a seventh CSI value between the second node antenna 331 and the main antenna 120 when located at the first location 141 based on the fifth and on the sixth CSI value h2b, h2a, and

configure joint radio transmission of data between the first and second node antennas 131 , 331 and the main antenna 120 when located at the first location 141 based on the third and on the seventh CSI value.

The channels associated with the main antenna 120 is in general, as discussed above, predicted accurately. As a result, the main antenna 120 may be served using relatively narrow beams, and/or relatively high carrier frequencies and often at high data rates. On the other hand, the network nodes 130 and 330 have less accurate prediction of the channels between them and the predictor antenna 110 and, consequently, serve it by relatively lower data rates, and/or wider beams and/or at lower carrier frequencies.

Using joint vehicle velocity and Kalman-based or Wiener-based channel prediction information and carrier frequency adaptation as well as smart beamforming, all of which have been discussed above, improvements in the channel prediction quality and reduction in the beamforming mismatch probability are obtained. Moreover, carrier frequency adaptation improves the prediction quality, reduces the interference and allows exploitation of frequency diversity. Also, coordinated transmission by the plurality of network nodes allows exploitation of network diversity where each radio link can compensate for other links as selective link outage occurs. As a result, the system reliability of a system such as that illustrated in Fig. 3 is improved considerably compared to known systems.

The network node 130 and the further network node 330 are shown in Fig. 3 as connected 340, e.g., by fast fiber connection. As a result, the network nodes can share information about estimated CSI, channel quality, and exchange other messages. Th network nodes are also able to coordinate radio transmissions to the vehicle 101.

An example operation involving the network node 130 and the further network node 330 will now be described. Long codewords for transmission to the vehicle 101 are divided into two or more shorter sub-codewords, each one sent to one of the vehicle antennas via a different network node antenna 131 , 331. Then, by combining the signals received from different network nodes, the vehicle control unit 115 may decode the received signals corresponding to the different sub-codewords jointly, and forward the decoded codeword to a recipient of the codeword, i.e., a user, inside the vehicle 101. Assume that at time T the main 120 and the predictor 110 antennas are at positions a and b, respectively, as shown in Fig. 3. The vehicle 101 uses its velocity information V and the vehicle control unit 115 to find a range of carrier frequencies, or radio transmission frequency bands, for which Kalman prediction has sufficiently high quality and/or accuracy. Then, the vehicle control unit 115 selects two available carrier frequencies, denoted as f1 and f2 in Fig. 8, with f 1 <f2 for channel estimation and/or data transmission to the main and to the predictor antennas, respectively. This is due to the fact that the prediction horizon of the Kalman predictor depends on the product of the vehicle velocity and the carrier frequency. In order to improve the prediction horizon at high speeds, the carrier frequency is reduced.

Fig. 8 shows a schematic illustration of the carrier frequency selection procedure. By broadcasting short radio signals, the vehicle control unit informs the network nodes about the carrier frequencies they should work on. It is appreciated that, according to some aspects, the carrier frequency selection rule is optimized as a function of the vehicle velocity offline and stored in a table before data transmission. Then, depending on the vehicle velocity, the vehicle control unit 115 sends, e.g., an index of the appropriate frequencies to the network nodes. Also, using these carrier frequencies is motivated by the fact that the CSI of the main antenna is predicted by both predictor antenna and Kalman prediction while CSI for the predictor antenna uses only prediction, and also because the use of two frequencies increases the frequency diversity/reduces the interference.

The network node 130, working at frequency band f 1 , sends pilot signals and receives quantized CSI feedback from the vehicle to estimate h1 b(t) as function of time t, i.e., the channel from network node 130 to an antenna located in position b. Also, the further network node 330, working at frequency band f2, follows the same procedure to estimate h2a(t) and h2b(t), i.e., the channels from the further network node 330 to antennas located in positions a and b, respectively. Moreover, optionally, the vehicle control unit 115 informs the network nodes 130, 330, about its position and velocity as well as the users data requests status which is used for user scheduling. Finally, depending on the vehicle velocity and the antenna spacing on the vehicle, and based on the predictor antenna concept, the vehicle 101 may request for an extra delay D to make sure that the main antenna array reaches point b when it receives the message signal, or data radio transmission. Receiving the feedback, the network nodes 130, 330, jointly perform link adaptation/beamforming and send the data to both the predictor antenna 110, and to the main antenna 120. Details of the CSI estimation and prediction will now be discussed according to an example operation. Define a total control loop delay as a time interval between when the network node starts sending pilot signals and the time the data transmission takes place, and denote it by d. The further network node 330 first utilizes CSI estimated for h2a(t) and Kalman prediction to find h^~2b(t+6+A|h2a(t)), i.e., the prediction of the channel seen by the main antenna as it receives the message signal at point b given h2a(t). Then, the final prediction of the channel seen by the main antenna 120 at time t+d+D is decided based on both h2b(t) and on h^~2b(t+d+A|h2a(t)), coming from the predictor antenna concept and the Kalman prediction, respectively. Various functions can be defined to combine these different quantities, for instance,

where hf2a(t+6+A) is the final prediction of the channel from the further network node 330 to the main antenna array, based on both predictor antenna and Kalman prediction techniques. Also, w is a constant weighting factor selected based on the vehicle velocity/carrier frequency. Another example of combination function is

with Q being a threshold. Here, the further network node 330 selects one of the results of the predictor antenna or Kalman prediction techniques based on the vehicle velocity/carrier frequency. In this way, the presence of two antennas improves the channel prediction quality for the main antenna and, as a result, the further network node 330 can use narrow beams to serve the main antenna (possibly) with high rates.

The network node 130, on the other hand, uses only h1 b(t) to predict h^~ 1 c(t+6+A|h1 b(t)) by Kalman or Wiener filter prediction, where c is the position of the predictor antenna when it receives a data transmission at time t+d+D. Thus, the network node has less accurate prediction of the channel between the network node 130 and the predictor antenna at location c. Finally, the vehicle control unit accumulates the signals received by different antennas, jointly decodes them and forwards the message to the users of interest inside the vehicle.

Considering the proposed coordinated setup, the following points are interesting to note:

While there is presented a setup for the cases with two fiber-connected network nodes/antenna arrays/sub-codewords, the setup can be adapted to the cases with arbitrary numbers of network nodes/antenna arrays/sub-codewords. Particularly, the antenna arrays can be served by a single network node, e.g., having different sectors, at the cost of reduced network diversity.

While there is presented a case with high- and low-rate sub-codewords, this is not a necessary assumption. For instance, the same sub-codewords can be sent by the network nodes, and the vehicle control unit can perform, e.g., maximum ratio combining of the two copies of the signal. In the following, an example of a signaling procedure for an FDD downlink setup is given. However, the same procedure can be adapted for the cases with uplink connection and/or TDD-based systems.

Considering Fig. 4, a network node 130 first sends pilot signals to the predictor antenna 110 and to the main antenna 120. Then, the moving relay or vehicle control unit uses the received pilot signals, and possibly also the vehicle position, velocity and direction as well as any data requests to estimate the channel quality, and possibly also performs user scheduling.

These information quantities are then fed back to the core network as CSI feedback. Also, depending on the vehicle velocity and the antenna spaces, the moving relay may request for a frequency dependent scheduling of transmissions, as discussed above. Receiving the feedback, the core network and/or the network node performs link adaptation/beamforming and sends the data to the predictor and main antennas. Depending on the message decoding condition, an acknowledgement or negative acknowledgement (ACK/NACK) signal may be sent from the vehicle antennas to the network node.

According to aspects, the predictor antenna consists of n antennas and the main antennas comprise antenna element matrices of size N*N. The operations may then further comprise selecting n out of N*N antennas in the main antenna matrices for communication based on the estimated CSI.

Fig. 5 shows one example of a computer program product 510 according to the present disclosure comprising computer readable means 530. On this computer readable means 530, a computer program 520 can be stored, which computer program 520 can cause a processing circuitry 610 and thereto operatively coupled entities and devices, such as the communications interface 620 and the storage medium 630, to execute methods according to embodiments described herein. The computer program 520 and/or computer program product 510 may thus provide means for performing any steps of a control node as herein disclosed, i.e., such as control unit 135 or control unit 115.

In the example of Fig. 5, the computer program product 510 is illustrated as an optical disc, such as a CD (compact disc) or a DVD (digital versatile disc) or a Blu- Ray disc. The computer program product 510 could also be embodied as a memory, such as a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM), or an electrically erasable programmable read-only memory (EEPROM) and more particularly as a non-volatile storage medium of a device in an external memory such as a USB (Universal Serial Bus) memory or a Flash memory, such as a compact Flash memory. Thus, while the computer program 520, is here schematically shown as a track on the depicted optical disk, the computer program 520, can be stored in any way which is suitable for the computer program product 510.

There is disclosed herein a computer program 520 for configuring radio transmission between a network node 130 comprising a first node antenna 131 and a vehicle 101 moving with a velocity V in a direction D, the vehicle comprising a predictor antenna 110 and at least one main antenna 120, wherein the at least one main antenna is arranged to trail the predictor antenna as the vehicle moves in the direction D, the computer program comprising computer code which, when run on a node control unit 135 and/or a vehicle control unit 115, causes the node control unit 135 and/or vehicle control unit 115 to;

There is also disclosed herein a computer program product 510 comprising a computer program 520 according to claim 12, and a computer readable storage medium 530 on which the computer program is stored. Fig. 6 schematically illustrates the components of a control unit 600, such as control unit 135 or control unit 115. according to embodiments. The control unit 600 comprises processing circuitry 610, a communication interface 620, and storage medium 630. In general terms, the control unit comprises functional modules, where each functional module may be implemented in hardware or in software. The processing circuitry 610 may thus be arranged to from the storage medium 630 fetch instructions as provided by a functional module and to execute these instructions, thereby performing any steps of the control unit as disclosed herein.

According to an example, the functional units may comprise;

an estimating unit for estimating a first channel state information, CSI, value h1 b between the first node antenna 131 and the predictor antenna 110, based on radio transmission between the first node antenna 131 and the predictor antenna 110 when located at a first location 141 ,

an estimating unit for estimating a second CSI value h1 a between the first node antenna 131 and a main antenna 120 based on radio transmission between the first node antenna 131 and the main antenna 120 when located at a second location 142 trailing the first location 141 in direction D,

a predicting unit for predicting S4 a third CSI value between the first node antenna 131 and the main antenna 120 when located at the first location 141 based on the first and on the second CSI value h1 b, h1a, and

a configuration unit for configuring S5 radio transmission of data between the first node antenna 131 and the main antenna 120 when located at the first location 141 based on the predicted third CSI value.

The control unit 600 may be provided as a standalone device or as a part of at least one further device. For example, the control unit may be provided in a wireless device, in a vehicle 101 , or in a network node 130.

Fig. 7 is a flowchart illustrating methods as described herein, and in particular methods corresponding to operations of the network nodes and vehicles discussed in connection to Figs. 1 -4. There is shown a method for configuring radio transmission between a network node 130 comprising a first node antenna 131 and a vehicle 101 moving with a velocity V in a direction D. The vehicle comprises a predictor antenna 110 and at least one main antenna 120, wherein the at least one main antenna is arranged to trail the predictor antenna as the vehicle moves in the direction D. The method comprises

estimating S1 a first channel state information, CSI, value h1 b between the first node antenna 131 and the predictor antenna 110, based on radio transmission between the first node antenna 131 and the predictor antenna 110 when located at a first location 141 ,

estimating S2 a second CSI value h1 a between the first node antenna 131 and a main antenna 120 based on radio transmission between the first node antenna 131 and the main antenna 120 when located at a second location 142 trailing the first location 141 in direction D,

predicting S4 a third CSI value between the first node antenna 131 and the main antenna 120 when located at the first location 141 based on the first and on the second CSI value h1 b, h1 a, and

configuring S5 radio transmission of data between the first node antenna 131 and the main antenna 120 when located at the first location 141 based on the predicted third CSI value.

According to aspects, the method also comprises estimating S3 a fourth CSI value hid between the first node antenna 131 and the main antenna 120 when located at the first location 141 , based on an extrapolation of the second CSI value h1 a to the first location 141.

According to aspects, the predicting S4 comprises predicting S41 the third CSI value based on a weighted combination of the first CSI value h1 b and the fourth CSI value hid, wherein weights are determined based on velocity V and direction D.

According to aspects, the predicting S4 comprises predicting S42 the third CSI value as the first CSI value h1 b in case a product of velocity V and a carrier frequency fc associated with the radio transmission exceeds a pre-determ ined threshold T, and as the fourth CSI value hid otherwise.

According to aspects, the method further comprises assigning S6 a radio transmission frequency band resource for radio transmission between the network node 130 and the vehicle 101 based on the velocity V.

According to aspects, the assigning S6 comprises assigning S61 a radio transmission frequency band resource corresponding to a first carrier frequency fd for transmission between the network node 130 and a vehicle associated with velocity V1 , and assigning a radio transmission frequency band resource corresponding to a second carrier frequency fc2 smaller than fd for transmission between the network node 130 and a vehicle associated with a velocity V2 higher than velocity V1.

According to aspects, the assigning S6 comprises assigning S62 a radio transmission frequency band resource corresponding to a first carrier frequency fd for transmission between the network node 130 and the main antenna 120, and assigning a radio transmission frequency band resource corresponding to a second carrier frequency fc2 smaller than fd for transmission between the network node 130 and the predictor antenna 110.

According to aspects, the configuring S5 comprises configuring S52 radio transmission of data between the first node antenna 131 and the main antenna 120 when located at the first location 141 using a first lobe width, and configuring radio transmission of data between the first node antenna 131 and the predictor antenna 110 when located at the third location 140 using a second lobe width larger than the first lobe width.

According to aspects, the configuring S5 comprises determining S53 a time difference between a time instant when the predictor antenna 110 is located at the first location 141 and a corresponding time instant when the main antenna 120 is located at the first location 141 , and delaying S53 the radio transmission of data between the first node antenna 131 and the main antenna 120 when located at the first location 141 based on the determined time difference.

According to aspects, the method is also for configuring additional radio transmission between a further network node 330 comprising a second node antenna 331 and the vehicle 101 , the method further comprises;

estimating S71 a fifth channel state information, CSI, value h2b between the second node antenna 331 and the predictor antenna 110, based on radio transmission between the second node antenna 331 and the predictor antenna 110 when located at a first location 141 ,

estimating S72 a sixth CSI value h2a between the second node antenna 331 and the main antenna 120 based on radio transmission between the second node antenna 331 and the main antenna 120 when located at a second location 142 trailing the first location 141 in direction D, predicting S74 a seventh CSI value between the second node antenna 331 and the main antenna 120 when located at the first location 141 based on the fifth and on the sixth CSI value h2b, h2a, and

configuring S75 joint radio transmission of data between the first and second node antennas 131 , 331 and the main antenna 120 when located at the first location 141 based on the third and on the seventh CSI value.

According to aspects, the method also comprises determining S8 one or more calibration parameters associated with the at least one main antenna 120, wherein the one or more calibration parameters are arranged to compensate for differences in antenna characteristics between the predictor antenna 110 and the at least one main antenna 120.

Generally, the present disclosure also relates to a network node 130 comprising a first node antenna 131 arranged for radio communication with a vehicle 101 moving with a velocity V in a direction D, the vehicle comprising a predictor antenna 110 and at least one main antenna 120, wherein the at least one main antenna is arranged to trail the predictor antenna as the vehicle moves in the direction D, the network node comprising a

node control unit 135 arranged to;

predict a third CSI value between the first node antenna 131 and the main antenna 120 when located at the first location 141 based on the first and on the second CSI value h1 b, h1 a, and configure radio transmission of data between the first node antenna 131 and the main antenna 120 when located at the first location 141 based on the predicted third CSI value.

Generally, the present disclosure also relates to vehicle 101 arranged to move with a velocity V in a direction D, the vehicle comprising a predictor antenna 110 and at least one main antenna 120, wherein the at least one main antenna is arranged to trail the predictor antenna as the vehicle moves in the direction D, the vehicle being arranged for radio communication with a network node 130 comprising a first node antenna 131 , the vehicle comprising a vehicle control unit 115 arranged to;

predict a third CSI value between the first node antenna 131 and the main antenna 120 when located at the first location 141 based on the first and on the second CSI value h1 b, h1 a, and

Claims

1. A method for configuring radio transmission between a network node

(130) comprising a first node antenna (131 ) and a vehicle (101 ) moving with a velocity V in a direction D, the vehicle comprising a predictor antenna (110) and at least one main antenna (120), wherein the at least one main antenna is arranged to trail the predictor antenna as the vehicle moves in the direction D, the method comprising;

estimating (S1 ) a first channel state information, CSI, value (h 1 b) between the first node antenna (131 ) and the predictor antenna (110), based on radio transmission between the first node antenna (131 ) and the predictor antenna (110) when located at a first location (141 ), estimating (S2) a second CSI value (h1 a) between the first node antenna (131 ) and a main antenna (120) based on radio transmission between the first node antenna

(131 ) and the main antenna (120) when located at a second location (142) trailing the first location (141 ) in direction D, predicting (S4) a third CSI value (h1f) between the first node antenna (131 ) and the main antenna (120) when located at the first location (141 ) based on the first and on the second CSI value (h 1 b, h1 a), and

configuring (S5) radio transmission of data between the first node antenna (131 ) and the main antenna (120) when located at the first location (141 ) based on the predicted third CSI value.

2. The method according to claim 1 , comprising estimating (S3) a fourth CSI value (hid) between the first node antenna (131 ) and the main antenna (120) when located at the first location (141 ), based on an extrapolation of the second CSI value (H1A) to the first location (141 ).

3. The method according to claim 2, wherein the predicting (S4) comprises predicting (S41 ) the third CSI value (h1f) based on a weighted combination of the first CSI value (h1 b) and the fourth CSI value (hid), wherein weights are determined based on velocity V and direction D.

4. The method according to claim 2, wherein the predicting (S4) comprises predicting (S42) the third CSI value (h1f) as the first CSI value (h1 b) in case a product of velocity V and a carrier frequency fc associated with the radio transmission exceeds a pre-determ ined threshold T, and as the fourth CSI value (hi d) otherwise.

5. The method according to any previous claim, comprising assigning (S6) a radio transmission frequency band resource for radio transmission between the network node (130) and the vehicle (101 ) based on the velocity V.

6. The method according to claim 5, wherein the assigning (S6) comprises assigning (S61 ) a radio transmission frequency band resource corresponding to a first carrier frequency fd for transmission between the network node (130) and a vehicle associated with velocity V1 , and assigning a radio transmission frequency band resource corresponding to a second carrier frequency fc2 smaller than fd for transmission between the network node (130) and a vehicle associated with a velocity V2 higher than velocity V1 .

7. The method according to any previous claim, wherein the assigning (S6) comprises assigning (S62) a radio transmission frequency band resource corresponding to a first carrier frequency fd for transmission between the network node (130) and the main antenna (120), and assigning a radio transmission frequency band resource corresponding to a second carrier frequency fc2 smaller than fd for transmission between the network node (130) and the predictor antenna (1 10).

8. The method according to any previous claim, wherein the configuring (S5) comprises configuring (S51 ) radio transmission of data between the first node antenna (131 ) and the predictor antenna (1 10) when located at the third location (140) based on an extrapolation (hi e) of the first CSI value (h 1 b) to the third location (140).

9. The method according to any previous claim, wherein the configuring (S5) comprises configuring (S52) radio transmission of data between the first node antenna (131 ) and the main antenna (120) when located at the first location (141 ) using a first lobe width, and configuring radio transmission of data between the first node antenna (131 ) and the predictor antenna (1 10) when located at the third location (140) using a second lobe width larger than the first lobe width.

10. The method according to any previous claim, wherein the configuring (S5) comprises determining (S53) a time difference between a time instant when the predictor antenna (110) is located at the first location (141 ) and a corresponding time instant when the main antenna (120) is located at the first location (141 ), and delaying (S53) the radio transmission of data between the first node antenna (131 ) and the main antenna (120) when located at the first location (141 ) based on the determined time difference.

11. The method according to any previous claim, for configuring additional radio transmission between a further network node (330) comprising a second node antenna (331 ) and the vehicle (101 ), comprising;

estimating (S71 ) a fifth channel state information, CSI, value (h2b) between the second node antenna (331 ) and the predictor antenna (110), based on radio transmission between the second node antenna (331 ) and the predictor antenna (110) when located at a first location (141 ),

estimating (S72) a sixth CSI value (h2a) between the second node antenna (331 ) and the main antenna (120) based on radio transmission between the second node antenna (331 ) and the main antenna (120) when located at a second location (142) trailing the first location (141 ) in direction D,

predicting (S74) a seventh CSI value between the second node antenna (331 ) and the main antenna (120) when located at the first location (141 ) based on the fifth and on the sixth CSI value (h2b, h2a), and

configuring (S75) joint radio transmission of data between the first and second node antennas (131 , 331 ) and the main antenna (120) when located at the first location (141 ) based on the third and on the seventh CSI value.

12. The method according to any previous claim, comprising determining

(S8) one or more calibration parameters associated with the at least one main antenna (120), wherein the one or more calibration parameters are arranged to compensate for differences in antenna characteristics between the predictor antenna (110) and the at least one main antenna (120).

13. A computer program (520) for configuring radio transmission between a network node (130) comprising a first node antenna (131 ) and a vehicle (101 ) moving with a velocity V in a direction D, the vehicle comprising a predictor antenna (110) and at least one main antenna (120), wherein the at least one main antenna is arranged to trail the predictor antenna as the vehicle moves in the direction D, the computer program comprising computer code which, when run on a node control unit (135) and/or a vehicle control unit (115), causes the node control unit (135) and/or vehicle control unit (115) to;

estimate a first channel state information, CSI, value (h1 b) between the first node antenna (131 ) and the predictor antenna (110), based on radio transmission between the first node antenna (131 ) and the predictor antenna (110) when located at a first location (141 ),

estimate a second CSI value (h1 a) between the first node antenna (131 ) and a main antenna (120) based on radio transmission between the first node antenna (131 ) and the main antenna (120) when located at a second location (142) trailing the first location (141 ) in direction D,

predict a third CSI value between the first node antenna (131 ) and the main antenna (120) when located at the first location (141 ) based on the first and on the second CSI value (h1 b, h1 a), and

configure radio transmission of data between the first node antenna (131 ) and the main antenna (120) when located at the first location (141 ) based on the predicted third CSI value.

14. A computer program product (510) comprising a computer program (520) according to claim 13, and a computer readable storage medium (530) on which the computer program is stored.

15. A network node (130) comprising a first node antenna (131 ) arranged for radio communication with a vehicle (101 ) moving with a velocity V in a direction D, the vehicle comprising a predictor antenna (110) and at least one main antenna (120), wherein the at least one main antenna is arranged to trail the predictor antenna as the vehicle moves in the direction D, the network node comprising a node control unit (135) arranged to;

16. A vehicle (101 ) arranged to move with a velocity V in a direction D, the vehicle comprising a predictor antenna (110) and at least one main antenna (120), wherein the at least one main antenna is arranged to trail the predictor antenna as the vehicle moves in the direction D, the vehicle being arranged for radio communication with a network node (130) comprising a first node antenna (131 ), the vehicle comprising a vehicle control unit (115) arranged to;

predict a third CSI value between the first node antenna (131 ) and the main antenna (120) when located at the first location (141 ) based on the first and on the second CSI value (h1 b, h1 a), and configure radio transmission of data between the first node antenna (131 ) and the main antenna (120) when located at the first location (141 ) based on the predicted third CSI value.