The invention relates to a vehicle tire pressure monitoring system. Further, the invention relates to a method for tire pressure monitoring of a vehicle. A vehicle tire pressure monitoring (TPM) system includes a TPM sensor inside each tire with a RF transmitter. The TPM system also includes a vehicle based central controller/receiver. A TPM sensor inside the tire senses the tire pressure information and transmits TPM information in a TPM signal via its RF transmitter. The vehicle based TPM system controller/receiver receives the TPM signal from the TPM sensor RF transmission and relays the information to the a vehicle control module. When the TPM sensor senses low tire pressure, the vehicle control module will be alerted via the TPM signal.

It is desirable to identify which tire has low pressure, i.e., to associate a TPM signal with a tire location (front-left (FL), front-right (FR), rear-left (RL), rear-right (RR)).

A vehicle tire pressure monitoring system is provided that comprises a vehicle- based central controller with at least one receiving antenna and at least one tire pressure monitoring sensor with at least one transmitting antenna, wherein a multiple in and multiple out antenna system is provided that is assigned to the vehicle-based central controller as well as the at least one tire pressure monitoring sensor.

A method for tire pressure monitoring of a vehicle is provided, wherein a vehicle tire pressure monitoring system is used, with the following steps:

Measuring tire pressure inside a tire by a tire pressure monitoring sensor assigned to the tire, and

Transmitting the information with regard to the tire pressure measured to a vehicle-based central controller via the tire pressure monitoring sensor by using a multiple in and multiple out antenna system established between the tire pressure monitoring sensor and the vehicle-based central controller.

The multiple in and multiple out antenna system may be established by the antennas of the vehicle-based central controller, namely the receiving antennas, and the antennas of the at least one tire pressure monitoring sensor, namely the transmitting antennas. Accordingly, two receiving antennas and two transmitting antennas may be provided that establish a 2x2 communication, in particular a 2x2 communication matrix, also called channel matrix.

According to an aspect, the vehicle tire pressure monitoring system is configured to analyze the signals exchanged between the vehicle-based central controller and the at least one tire pressure monitoring sensor so as to provide location information of the at least one tire pressure monitoring sensor. The signals are exchanged between the transmitting antennas and the receiving antennas of the respective components of the vehicle tire pressure monitoring system. Thus, the signals are assigned to the multiple in and multiple out antenna system since the respective antennas of the multiple in and multiple out antenna system are used for exchanging the signals.

For instance, the vehicle-based central controller has at least two receiving antennas. The vehicle-based central controller may have a receiver. The receiver processes the signals received by the at least one receiving antenna.

The at least one tire pressure monitoring sensor may have at least two transmitting antennas.

The at least one tire pressure monitoring sensor has a transmitter. The transmitter provides the signals to be transmitted via the at least one transmitting antenna.

The transmitting antennas are polarized orthogonally with respect to each other. Hence, a first antenna of the tire pressure monitoring sensor may be a horizontal antenna whereas a second antenna of the tire pressure monitoring sensor may be a vertical antenna. Another aspect provides that the vehicle tire pressure monitoring system is configured to determine a coupling matrix describing the communication between the vehicle-based central controller and the at least one tire pressure monitoring sensor. The coupling matrix is used for mathematically defining the communication of the participants of the multiple in and multiple out antenna system, namely the vehicle-based central controller and the at least one tire pressure monitoring sensor, in particular the respective antennas assigned thereto.

Particularly, the number of cells of the coupling matrix determined corresponds to the number of tire pressure monitoring sensors. Accordingly, the coupling matrix may have four cells in case of four tire pressure monitoring sensors that might be assigned to each tire of a typical vehicle.

Further, each cell of the coupling matrix determined may correspond to a matrix, wherein the dimension of the matrix corresponds to the number of the antennas assigned to the vehicle-based central controller and the number of the antennas assigned to each tire pressure monitoring sensor. In case of three receiving antennas and two transmitting antennas (per tire pressure monitoring sensor), each cell has a dimension of 3x2, namely six.

In case of four tire pressure monitoring sensors each having two transmitting antennas communicating with three receiving antennas, four cells, namely matrixes, are provided each having a dimension of 3x2.

The vehicle tire pressure monitoring system may be configured to gather phase and amplitude information of the signals exchanged, and wherein the vehicle tire pressure monitoring system is configured to use the phase and amplitude information gathered for calculating the coupling matrix. The matrix is calculated based on the signal information gathered, namely the phase and amplitude information.

Another aspect provides that the tire pressure monitoring system is configured to determine the distance and signal arrival angles from the at least one tire pressure monitoring sensor by evaluating the coupling matrix. The coupling matrix describing the communication via the multiple in and multiple out antenna system can be analyzed appropriately so as to gather the respective information.

Hence, the respective tire pressure monitoring sensor can be located easily. As already mentioned, the signals exchanged between the vehicle-based central controller and the at least one tire pressure monitoring sensor are analyzed so as to provide location information of the at least one tire pressure monitoring sensor. Particularly, a coupling matrix is determined that describes the communication between the vehicle-based central controller and the at least one tire pressure monitoring sensor, namely the communication via the multiple in and multiple out antenna system.

Accordingly, the distance and signal arrival angles from the at least one tire pressure monitoring sensor may be determined.

Particularly, the distance and signal arrival angles from the at least one tire pressure monitoring sensor are determined by evaluating the coupling matrix determined previously.

In general, the MIMO antenna system (multiple in and multiple out antenna system) provides TPM auto location functionality in a TPM system to provide the sensor location (tire location) identification function.

The multiple in and multiple out antenna system also enhances the radio frequency link, reduces the sensor battery power, and reduces the sensor size.

There are typically four TPM sensors in the vehicle, one associated with each tire.

The receiver of the vehicle tire pressure monitoring system may be configured to perform the steps mentioned above, namely analyzing the signals exchanged, determining the coupling matrix and/or evaluating the coupling matrix.

The foregoing aspects and many of the attendant advantages of the claimed subject matter will become more readily appreciated as the same become better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein Figure 1 schematically shows a vehicle tire pressure monitoring system according to the invention that is used for conducting a method for tire pressure monitoring of a vehicle according to the invention. Figure 1 shows a vehicle with a vehicle tire pressure monitoring system 10 that comprises a vehicle-based central controller 12 with a receiver and at least one receiving antenna B_Ant. In the shown embodiment, three receiving antennas B_Ant_1 - B_Ant_3 are assigned to the vehicle-based central controller 12. Further, the vehicle tire pressure monitoring system 10 comprises at least one tire pressure monitoring (TPM) sensor 14 with a transmitter. In the shown embodiment, two tire pressure monitoring sensors 14 are shown for the purpose of simple illustration even though typically four TPM sensors 14 are provided.

Each TPM sensor 14 has at least one transmitting antenna A_Ant. In the shown embodiment, the TPM sensor 14 has two transmitting antennas A_Ant_1 , A_Ant_2. However, each TPM sensor 14 may have multiple transmitting antennas from 1 to n.

The transmitting antennas A_Ant_1 , A_Ant_2 may be orientated orthogonally with respect to each other wherein the first transmitting antenna is a vertical one and the second transmitting antenna is a horizontal one.

The relationship between each sensor's transmitting antenna A_Ant and the receiving antennas B_Ant are governed by the following equations:

Cll Cll

C C21 C22 Eq . (2) C31 C32

"A" antennas are at the sensor side. "B" antennas are at the receiver side.

The C is a coupling matrix describing the communication between the vehicle- based central controller 12 and the TPM sensor(s) 14, namely the communication of a multiple in and multiple out antenna system 16 established by the respective antennas A_Ant, B_Ant. C parameters are associated with the relative location between the respective antennas A_Ant, B_Ant. It has signal amplitude (A) and phase (Θ) information.

Cll =Allei ⁹¹¹ Eq.(3) Amplitude (A) and phase (Θ) are associated with relative position/orientation between each sensor antenna A Ant and each vehicle antennas B Ant.

Cij 11 Cij_12

Cij Cij 21 Cij _22 Ed [4]

Cij_31 Cij_32 where [ij] can represent the location of the sensor 14.

For example, [1 1 ] can represent the front left; [12] can represent the front right;

[21 ] can represent the rear left and [22] can represent the rear right.

\Front Left(lY) Front Right(12)]

C= Eq. (5) Rear Left(21) Rear Right(22)

The whole system coupling matrix with four TPM sensors 14 is shown in Eq.

(6):

C11_H Cll_12 C12_ll C12_12 Cll_21 Cll_22 C12_21 C12_22 Cll_31 Cll_32 C12_31 C12_32

C = Eq. (6) C21_ll C21_12 C22_ll C22_12 C21_21 C21_22 C22_21 C22_22 C2131 C2132 C2231 C2232

Different TPM sensor's distance and orientation will have different coupling matrix C, due to their different orientation and distance relative to the vehicle antennas B_Ant.

By measuring the C matrix, the distance and signal arrival angles from the TPM sensor 14 can be determined. This correlation factor could be one that simply just uses amplitude information or TPM message reception rate.

By compare RSSI level or TPM capture rate, the location of the sensor 14 can be identified.

Accordingly, the vehicle tire pressure monitoring system 10 is configured to: - gather phase and amplitude information of the signals exchanged; to use the phase and amplitude information gathered for calculating the coupling matrix C describing the communication between the vehicle-based central controller 12 and the at least one tire pressure monitoring sensor 14; analyze the signals exchanged between the vehicle-based central controller 12 and the at least one tire pressure monitoring sensor 14 so as to provide location information of the at least one tire pressure monitoring sensor 14; - to determine the distance and signal arrival angles from the at least one tire pressure monitoring sensor 14 by evaluating the coupling matrix C.

In the coupling matrix C determined, the number of cells corresponds to the number of tire pressure monitoring sensors 14 of the vehicle tire pressure monitoring system 10. Each cell of the coupling matrix C determined corresponds to a matrix, and wherein the dimension of the matrix corresponds to the number of the receiving antennas B_Ant assigned to the vehicle-based central controller 12 and the number of the transmitting antennas A_Ant assigned to each tire pressure monitoring sensor 14. The MIMO antenna system 16 not only provides auto location performance, it also improves the RF communication by reducing the multipath and signal fading.

It also provides the best matching between the sensor antenna A_Ant and the vehicle antenna B Ant.

The MIMO antenna system 16 therefore can reduce the sensor output power, reduce the battery size, and reduce the sensor size, which increases the service life span of the TPM sensor 14.