VEHICULAR COMMUNICATION SYSTEM

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 Some users may be located in moving vehicles, e.g., trams, buses, and trains. A promising solution to provide such users with high speed 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 from pilot signal transmissions in order 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Outdated channel estimates are a problem when moving relays are used in vehicles travelling at high speeds. A solution to the problem with outdated channel information is discussed by M. Sternad et.al.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 an improved handling of backhaul traffic for moving relays.

SUMMARY

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

This object is obtained by a communication system comprising a network node and a vehicle arranged to move with a velocity v in a direction D. The network node comprises a node control unit. The vehicle comprises a vehicle control unit, a predictor antenna arranged on a front section of the vehicle, and one or more main antennas arranged on a rear section of the vehicle, whereby the one or more main antennas are arranged to trail the predictor antenna when the vehicle moves in direction D. The communication system is arranged to estimate channel state information, CSI, based on radio transmission between the network node and the predictor antenna, and to configure radio transmission of data between the network node and the one or more main antennas based on the CSI. The communication system is arranged to determine a time difference between a time instant when the predictor antenna is located at a reference location and a time instant when a main antenna is located at the reference location, and to delay the radio transmission of data based on the determined time difference.

The robustness and data throughput capabilities of the disclosed system is increased in that the vehicle comprises a predictor antenna arranged on a front section of the vehicle, and one or more main antennas arranged on a rear section of the vehicle, whereby the one or more main antennas are arranged to trail the predictor antenna when the vehicle moves in direction D. This set-up enables the main antenna to use channel estimates obtained by radio transmission via the predictor antenna. Conditions for radio transmission of data between the network node and the vehicle are improved by the delaying of the radio transmission of data based on the determined time difference, since the data transmission will then occur when the main antenna is close to the reference location, i.e., where the estimated CSI is the most relevant.

According to aspects, the predictor antenna and/or the main antenna are antenna arrays comprising a plurality of antenna elements arranged for beamforming based on the CSI.

According to aspects, the communication system is arranged to attempt a first transmission of data between the network node and a first main antenna out of the main antennas, and to attempt a first re-transmission of the data between the network node and a second main antenna out of the main antennas in case the first transmission is not successful, where the second main antenna is located at a larger distance from the predictor antenna than the first main antenna.

Thereby, the communication system becomes more robust since re- transmissions are provided for with accurate CSI. The CSI used for the first transmission of data can be re-used for the first re-transmission, which reduces overhead in that no new CSI needs to be estimated for the first re- transmission. Also, advantageously, the re-transmissions do not occupy the first main antenna which instead can be used for transmission of additional data, which further reduces overhead. Since the second main antenna is located at a larger distance from the predictor antenna than the first main antenna, a longer delay from CSI estimation by the predictor antenna to the re-transmission is possible, which allows for the re-transmission mechanism to complete its operation before the second main antenna reaches the reference location.

According to aspects, the communication system is arranged to determine a transmission delay of the first transmission based on a time difference between a first time instant when the predictor antenna is located at a reference location and a second time instant when the first main antenna is located at the reference location, and arranged to determine a transmission delay of the first re-transmission based on a time difference between the first time instant and a third time instant when the second main antenna is located at the reference location.

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, and also for data re-transmission by the second main antenna. Overhead related to estimating CSI is reduced due to the re-using of estimated CSI for data transmission and for data re- transmission.

According to aspects, the node control unit is arranged to determine one or more calibration parameters associated the one or more main antennas. The one or more calibration parameters are arranged to compensate for differences in antenna characteristics between the predictor antenna and corresponding main antennas.

The reliability, accuracy, and relevance of CSI estimated using the predictor antenna for data transmission using a main antenna is increased due to the compensation of differences by calibration.

There are also disclosed herein network nodes, vehicles, antenna systems, methods 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 a shows a schematic view of a communication system arranged for communication between a network node and a moving vehicle;

Figure 1 b illustrates an antenna system;

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

Figure 3 is a diagram illustrating transmissions in a communication system;

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;

Figures 7-9 are flowcharts illustrating methods described herein.

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 array.

The predictor antenna facilitates accurate prediction of the wireless propagation channel between the network node antenna and a main antenna mounted on the vehicle even at high vehicle speeds. This is possible since the main antenna trails the predictor antenna. If the predictor antenna passes a first location at a first time instant, the main antenna will pass very close to the first location after a short period of time at a second time instant. Thus, a channel estimate or determination of channel state information (CSI) made between a remote antenna, such as an antenna of the network node, and the predictor antenna at the first time instant will be valid for the channel between the remote antenna and the main antenna at the second time instant when the main antenna passes the first location.

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.

Fig. 1 a 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 one or more main antennas 120a, 120b, 120c arranged on a rear section 112 of the vehicle. Due to the relative arrangement of antennas on the vehicle, the one or more main antennas are 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, hi , h2, h3, h4 based on radio transmission between the network node 130 and the predictor antenna 110, and to configure radio transmission of data between the network node 130 and the one or more main antennas 120a, 120b, 120c based on the CSI.

The modular moving relay network results in better channel quality prediction, compared to the cases with the 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 speeds 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.

It is appreciated that radio channels corresponding to CSI values hi , h2, h3, and h4 are correlated in time. With reference to Fig. 1 b, suppose the predictor antenna 110 is used for estimating CSI at a location 141 at a given time instant. The first main antenna 120a is located at another location 142 at the time instant, but will pass the same location 141 after some delay. When this happens, i.e., when the first main antenna passes location 141 , then the CSI estimated by the reference antenna will be valid for transmission using the first main antenna. Consequently, the CSI denoted hi , h2, h3, h4 in Fig. 1 a and 1 b will assume equal or similar values, but at different time instants.

In other words, if the CSI values are written as functions of time, then;

hi (t0)=h2(t0+d1 )=h3(t0+d1 +d2)=h4(t0+d1 +d2+d3), where to is the time instant when the predictor antenna passes some location, such as a reference location 141 , d1 is the time delay relative to until the first main antenna passes the reference location 141 , i.e., the time it takes for the first main antenna 120a to go from location 142 to location 141. Then, d2 is the time delay between the first main antenna 120a passing the reference location 141 and the second main antenna 120b passing the reference location, and d3 is the time delay between the second main antenna 120b passing the reference location and the third main antenna 120c passing the reference location. It is appreciated that equality does not necessarily hold in the above expression, and that correlation between CSI values follow the above discussed principles. It is also appreciated that exact knowledge of CSI value is not necessary for communication between two locations using antenna arrays.

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). 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 typical speeds of transportation vehicles, the CSI soon becomes outdated affecting the link adaptation and beamforming quality.

Looking again at Fig. 1 a, the communication system 100 is arranged to determine a time difference between a time instant when the predictor antenna 110 is located at a reference location 140 and a time instant when a main antenna 120a, 120b, 120c is located at the reference location, and to delay the radio transmission of data based on the determined time difference.

Conditions for radio transmission of data between the network node and the vehicle are improved by the delaying of the radio transmission of data based on the determined time difference, since the data transmission will then occur when the main antenna is close to the reference location where the estimated CSI is most relevant.

According to aspects, the node control unit 135 and/or the vehicle control unit 115 are/is arranged for estimation of CSI, configuration of radio transmission, and determining of the time difference.

The delaying is, according to some aspects, performed by the node control unit 135, and according to some other aspects by the vehicle control unit 115. The amount of time to delay transmission is, according to some aspects, determined based on velocity v and direction D, and on a known distance between the predictor antenna 1 10 and the main antenna 120a, 120b, 120c. Given the distance to travel, e.g., from location 142 to location 141 , the time taken is computable from the velocity v.

In other words, according to aspects, the time difference is determined based on direction D, velocity v, and on a distance between the predictor antenna and a main antenna.

The amount of time to delay transmission can also be determined based on correlation between the predictor antenna and the one or more main antennas. Suppose the predictor antenna estimates CSI corresponding to a channel hi from a node antenna 131 to reference location 140. The vehicle control unit and/or the node control, unit may then estimate CSI using pilot symbol transmission between the node antenna 131 and the one or more main antennas 120a, 120b, 120c. The time delay between pilot symbol transmissions from a main antenna which yield CSI having maximum correlation with the CSI estimated using the predictor antenna can be used to derive the vehicle velocity v. In other words, the CSI estimated using the main antenna is likely to exhibit large correlation with the CSI estimated using the predictor antenna when the main antenna passes the location where the predictor antenna estimated the CSI.

According to some aspects, the communication system 100 is arranged to attempt a first transmission of data between the network node 130 and a first main antenna 120a out of the main antennas, and to attempt a first re- transmission of the data between the network node 130 and a second main antenna 120b out of the main antennas in case the first transmission is not successful, where the second main antenna 120b is located at a larger distance from the predictor antenna 110 than the first main antenna 120a.

This feature provides for an increased backhaul transmission efficiency in that pilot transmission overhead is reduced while robustness to transmission errors is increased. The communication system becomes more robust since re-transmissions are provided for with accurate CSI. However, the CSI used for the first transmission of data is re-used for the first re-transmission, which reduces overhead in that no new CSI needs to be estimated for the first re- transmission. Also, advantageously, the re-transmissions do not occupy the first main antenna which instead can be used for transmission of additional data which further reduces overhead. Since the second main antenna is located at a larger distance from the predictor antenna than the first main antenna, a longer delay from CSI estimation by the predictor antenna to the re-transmission is possible, which allows for the re-transmission mechanism to complete its operation before the second main antenna reaches the reference location. Again, according to aspects, the transmissions and re- transmissions are configured by the node control, unit 135 and/or the vehicle control, unit 115.

According to aspects, the communication system 100 is arranged to determine a transmission delay of the first transmission based on a time difference between a first time instant when the predictor antenna 110 is located at a reference location 140 and a second time instant when the first main antenna 120a is located at the reference location 140, and arranged to determine a transmission delay of the first re-transmission based on a time difference between the first time instant and a third time instant when the second main antenna 120b is located at the reference location 140. This way the re-use of CSI is optimized since the predictor antenna, the first main antenna, and the second main antenna are all located in approximately the same location when the transmissions take place. Thus, the CSI estimated using the predictor antenna become highly relevant for data transmission using the first and second main antennas. In other words, referring back to the discussion above, if the CSI values are written as functions of time;

h1 (t0)=h2(t0+d1 )=h3(t0+d1 +d2)=h4(t0+d1 +d2+d3), where to corresponds to the time instant when pilots are transmitted for CSI estimation, suitable transmission delays for data transmission between the node antenna 131 and vehicle antennas correspond to time values d1 , d2, and d3, respectively.

The re-transmission may be repeated any number of times, each re- transmission using a main antenna located further away from the predictor antenna than the predictor antenna. In other words, the communication system is arranged to attempt a second re-transmission of the data between the network node 130 and a third main antenna 120c out of the main antennas in case the first re-transmission is not successful, where the third main antenna 120c is located at a larger distance from the predictor antenna 110 than the second main antenna 120b.

Also, the communication system is arranged to determine a transmission delay of the second re-transmission based on a time difference between the first time instant and a fourth time instant when the third main antenna 120c is located at the reference location 140.

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. Towards this end, according to some aspects, the node control unit 135 is arranged to determine one or more calibration parameters associated the one or more main antennas, wherein the one or more calibration parameters are arranged to compensate for differences in antenna characteristics between the predictor antenna 110 and corresponding main antennas 120a, 120b, 120c. 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.

Fig. 1 a shows a network node 130 comprising a node antenna 131 and a node control unit 135. The network node is arranged to communicate with a vehicle 101 moving in a direction D at a velocity v. The vehicle comprises a predictor antenna 110 arranged on a front section 111 of the vehicle and one or more main antennas 120a, 120b, 120c arranged on a rear section 112 of the vehicle, whereby the one or more main antennas are arranged to trail the predictor antenna when the vehicle moves in direction D. The node control unit 135 is arranged to obtain information related to a time difference between a first time instant when the predictor antenna is located at a reference location 140 and a second time instant when a main antenna is located at the reference location. The node control unit 135 is arranged to estimate channel state information, CSI, based on pilot transmission between the node antenna 131 and the predictor antenna 110, and to configure data transmission between the node antenna 131 and the one or more main antennas 120a, 120b, 120c arranged on the vehicle, based on the CSI, the node control unit 135 being arranged to determine a delay time amount based on the time difference, and to delay the data transmission by the delay time amount.

Consequently, the vehicle 101 shown in Fig 1 a is suitable for the communication system 100 discussed above. Examples of vehicles include, e.g., cars, trucks, trains, subway cars, motorcycles, and other vehicles and objects moving with high velocity.

According to aspects, the node control unit 135 is arranged to configure a first transmission of data between the node antenna 131 and a first main antenna 120a out of the main antennas, and to configure a first re- transmission of the data between the node antenna 131 and a second main antenna 120b out of the main antennas in case the first transmission is not successful, where the second main antenna 120b is located at a larger distance from the predictor antenna 110 than the first main antenna 120a.

Fig. 1 a also shows a vehicle 101 arranged to move with a velocity v in a direction D, the vehicle comprising a predictor antenna 110 arranged on a front section 111 of the vehicle and one or more main antennas 120a, 120b, 120c arranged on a rear section 112 of the vehicle, whereby the one or more main antennas are arranged to trail the predictor antenna when the vehicle moves in direction D. The vehicle comprises a vehicle control unit 115 arranged for estimating channel state information, CSI, based on pilot transmission between a network node 130 and the predictor antenna, and to configure a data transmission between the network node and a first main antenna based on the CSI, and to configure a data re-transmission between the network node and a second main antenna based on the CSI if the data transmission is not successful, wherein the first main antenna is located closer to the predictor antenna than the second main antenna.

There is also shown an antenna system 150 for mounting on a vehicle 101 comprising a predictor antenna 110 arranged to be mounted on a front section of the vehicle and one or more main antennas 120a, 120b, 120c arranged to be mounted on a rear section of the antenna system, whereby the one or more main antennas are arranged to trail the predictor antenna when the antenna system moves in a direction D.

One example of the vehicle 101 is illustrated in Fig. 2, where the vehicle is a train moving in direction D with velocity v. The train 200 comprises a predictor antenna array 110 located at the front section of the train, and a number of main antenna arrays located to the rear of the predictor antenna. Because of the fact that 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-speed robust and efficient wireless backhaul is provided for wireless broadband users located on the train.

In the following, an example of a signalling procedure for an FDD downlink setup is given. Flowever, the same procedure can be adapted for the cases with uplink connection and/or TDD-based systems.

Considering Fig. 3, the network node 130 first sends pilot signals to the predictor antenna 110. Then, the moving relay 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 perform user scheduling.

These information quantities are then fed back to the core network as CSI feedback. Also, depending on the vehicle speed and the antennas spaces, the moving relay may request for a variable delay such that the main antenna is at the same position as the predictor antennas when they receive the data signal, as discussed above. Receiving the feedback, the core network and or the network node performs link adaptation/beamforming and sends the data to the selected main antennas. Depending on the message decoding condition, an acknowledgement or negative acknowledgement (ACK/NACK) signal is sent from the data-gate antennas to the core-network, and the retransmissions are performed using main antenna arrays located further away from the predictor antenna, as discussed above, passing the same position as the predictor antenna was in when originally estimating the CSI. The retransmissions continue until the message is correctly decoded or all mounted sets of backup antennas are used. In the example of Fig. 3, one failed transmission attempt was experienced using a first main antenna 120a, while the first re-transmission attempt was successful to the second main antenna 120b.

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

Note that, as shown in Fig. 2, installing antenna matrices for message transfer and retransmissions facilitates the selection of the appropriate set of antennas with respect to the vehicle direction. Also, to reduce the coupling effect, it may be advantageous to provide sufficient space between the antenna sets. Flowever, depending on the vehicle speed, the information transfer is appropriately delayed by the core network to guarantee that the different antennas reach the same position as the predictor antennas when they receive and/or transmit the information signal comprising data.

Fig. 4 shows an uplink example. The vehicle first transmits pilots using the predictor antenna 110 to the network node 130, which provides CSI feedback comprising estimated CSI values. A variable delay is then used such that the first main antenna has time to reach the location where the CSI was estimated, When the first main antenna reaches the correct location, data transmission takes place using the estimated CSI. In this example the first transmission was not successful so the network node transmits a‘NACK’ signal (not acknowledged) back to the vehicle. The vehicle again uses a variable delay such that the second main antenna 120b reaches the location corresponding to the estimated CSI. When this happens a re-transmission of data is performed using the second main antenna 120b, which in this case was successful. The network node therefore transmits an ACK (acknowledgement) signal to the vehicle.

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 520a, 520b, 520c can be stored, which computer program 520a, 520b, 520c 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 520a, 520b, 520c 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.

With reference to Fig. 1 and Fig. 9, there is also disclosed herein a method performed by a vehicle control unit in a vehicle 101 arranged to move with a velocity v in a direction D. The vehicle comprises a predictor antenna 110 arranged on a front section 111 of the vehicle and one or more main antennas 120a, 120b, 120c arranged on a rear section 112 of the vehicle, whereby the one or more main antennas are arranged to trail the predictor antenna when the vehicle moves in direction D. The method comprises estimating Sb1 channel state information, CSI, based on pilot transmission between a network node 130 and the predictor antenna,

configuring Sb2 data transmission between the network node and a first main antenna based on the CSI, and

configuring Sb3 a data re-transmission between the network node and a second main antenna based on the CSI if the data transmission is not successful, wherein the first main antenna is located closer to the predictor antenna than the second main antenna.

Thus, there is disclosed herein a computer program 520a for operating a communication system 100 comprising a network node 130 and a vehicle 101 arranged to move with a velocity v in a direction D, the vehicle comprising a vehicle control unit 115, a predictor antenna 110 arranged on a front section 111 of the vehicle, and one or more main antennas 120a, 120b, 120c arranged on a rear section 112 of the vehicle, whereby the one or more main antennas are arranged to trail the predictor antenna when the vehicle moves in 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 channel state information, CSI, hi , h2, h3, h4 based on radio transmission between the network node 130 and the predictor antenna 110, configure radio transmission of data between the network node 130 and the one or more main antennas 120a, 120b, 120c based on the CSI,

determine a time difference between a time instant when the predictor antenna 110 is located at a reference location 140 and a time instant when a main antenna 120a, 120b, 120c is located at the reference location, and delay the radio transmission of data based on the determined time difference. There is also disclosed herein a computer program 520b for operating a network node 130 comprising a node antenna 131 and a node control unit 135, for communicating with a vehicle 101 moving in a direction D at a velocity v, the vehicle comprising a predictor antenna 110 arranged on a front section 111 of the vehicle and one or more main antennas 120a, 120b, 120c arranged on a rear section 112 of the vehicle, whereby the one or more main antennas are arranged to trail the predictor antenna when the vehicle moves in direction D, the computer program comprising computer code which, when run on a node control unit 135, causes the node control unit 135 to:

obtain information related to a time difference between a first time instant when the predictor antenna is located at a reference location 140 and a second time instant when a main antenna is located at the reference location, estimate channel state information, CSI, based on pilot transmission between the node antenna 131 and the predictor antenna 110, configure data transmission between the node antenna 131 and the one or more main antennas 120a, 120b, 120c arranged on the vehicle, based on the CSI,

determine a delay time amount based on the time difference, and

delay the data transmission by the delay time amount.

There is furthermore disclosed herein a computer program 520c for operating a vehicle 101 arranged to move with a velocity v in a direction D, the vehicle comprising a predictor antenna 110 arranged on a front section 111 of the vehicle and one or more main antennas 120a, 120b, 120c arranged on a rear section 112 of the vehicle, whereby the one or more main antennas are arranged to trail the predictor antenna when the vehicle moves in direction D, the computer program comprising computer code which, when run on a vehicle control unit 115, causes the vehicle control unit 115 to:

estimate channel state information, CSI, based on pilot transmission between a network node 130 and the predictor antenna,

configure data transmission between the network node and a first main antenna based on the CSI, and

configure a data re-transmission between the network node and a second main antenna based on the CSI if the data transmission is not successful, wherein the first main antenna is located closer to the predictor antenna than the second main antenna.

Thus, Fig. 5 shows a computer program product 510 comprising a computer program 520a, 520b, 520c according to the present teaching, and a computer readable storage medium 530 on which the computer program is stored.

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 520a, 520b, 520c, is here schematically shown as a track on the depicted optical disk, the computer program 520a, 520b, 520c, can be stored in any way which is suitable for the computer program product 510.

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 channel state information, CSI, hi , h2, h3, h4 based on radio transmission between the network node 130 and the predictor antenna 110,

a transmission unit for configuring radio transmission of data between the network node 130 and the one or more main antennas 120a, 120b, 120c based on the CSI,

a determining unit for determining S3 a time difference between a time instant when the predictor antenna 110 is located at a reference location 140 and a time instant when a main antenna 120a, 120b, 120c is located at the reference location, and

a delay unit for delaying S4 the radio transmission of data based on the determined time difference.

According to a further example, the functional units may comprise; a first transmission unit for attempting a first transmission of data between the network node 130 and a first main antenna 120a out of the main antennas, and

a first re-transmission unit for attempting a first re-transmission of the data between the network node 130 and a second main antenna 120b out of the main antennas in case the first transmission is not successful, where the second main antenna 120b is located at a larger distance from the predictor antenna 110 than the first main antenna 120a.

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. In particular, there is shown a method of operating a communication system 100 comprising a network node 130 and a vehicle 101 arranged to move with a velocity v in a direction D. The vehicle comprises a vehicle control unit 115, a predictor antenna 110 arranged on a front section 111 of the vehicle, and one or more main antennas 120a, 120b, 120c arranged on a rear section 112 of the vehicle. The one or more main antennas are arranged to trail the predictor antenna when the vehicle moves in direction D, the method comprises;

estimating S1 channel state information, CSI, hi , h2, h3, h4 based on radio transmission between the network node 130 and the predictor antenna 110, configuring S2 radio transmission of data between the network node 130 and the one or more main antennas 120a, 120b, 120c based on the CSI, determining S3 a time difference between a time instant when the predictor antenna 110 is located at a reference location 140 and a time instant when a main antenna 120a, 120b, 120c is located at the reference location, and delaying S4 the radio transmission of data based on the determined time difference. Consequently, the illustrated method performs the functions discussed above in connection with Figs. 1 -3.

According to aspects, the determining S3 comprises determining S31 the time difference based on direction D, velocity v, and on a distance between the predictor antenna and a main antenna.

The reasons for determining time difference include delaying transmissions by a corresponding amount, as discussed above. This improves performance in that data transmission can be performed using higher quality CSI.

According to aspects, the method further comprises;

attempting S5 a first transmission of data between the network node 130 and a first main antenna 120a out of the main antennas, and

attempting a first re-transmission of the data between the network node 130 and a second main antenna 120b out of the main antennas in case the first transmission is not successful, where the second main antenna 120b is located at a larger distance from the predictor antenna 110 than the first main antenna 120a.

The features related to re-transmission using main antennas located further away from the predictor antenna was discussed above in connection with, e.g., Fig. 1.

According to aspects, the method comprises determining SO one or more calibration parameters associated the one or more main antennas, and compensating for differences in antenna characteristics between the predictor antenna 110 and corresponding main antennas 120a, 120b, 120c based on the calibration parameters.

As noted above, 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, which is achieved by the above feature related to one o more calibration parameters. With reference to Fig. 1 and Fig. 8, there is also disclosed herein a method performed by a network node 130 comprising a node antenna 131 and a node control unit 135, for communicating with a vehicle 101 moving in a direction D at a velocity v, the vehicle comprising a predictor antenna 110 arranged on a front section 111 of the vehicle and one or more main antennas 120a, 120b, 120c arranged on a rear section 112 of the vehicle, whereby the one or more main antennas are arranged to trail the predictor antenna when the vehicle moves in direction D, the method comprises;

obtaining Sa1 information related to a time difference between a first time instant when the predictor antenna is located at a reference location 140 and a second time instant when a main antenna is located at the reference location,

estimating Sa2 channel state information, CSI, based on pilot transmission between the node antenna 131 and the predictor antenna 110,

configuring Sa3 data transmission between the node antenna 131 and the one or more main antennas 120a, 120b, 120c arranged on the vehicle, based on the CSI,

determining Sa4 a delay time amount based on the time difference, and delaying Sa5 the data transmission by the delay time amount.

According to aspects, the method comprises configuring Sa6 a first transmission of data between the node antenna 131 and a first main antenna 120a out of the main antennas, and configuring a first re-transmission of the data between the node antenna 131 and a second main antenna 120b out of the main antennas in case the first transmission is not successful, where the second main antenna 120b is located at a larger distance from the predictor antenna 110 than the first main antenna 120a.

Aspects of the inventive concept have mainly been described above with reference to a few embodiments. Flowever, as is readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the inventive concept, as defined by the below enumerated embodiments.