Method for transmitting data via a wireless interface between a field device and a mobile device

Abstract

The invention relates to a method for transmitting data via a wireless interface between a field device (1) and a mobile device (2), comprising the following steps: - Providing a field device (1) with a computing unit (10) and a first wireless interface (30), and a mobile device (2) with a second wireless interface (40), wherein an internal power limit and a minimum connection robustness are stored in the field device (1), - Configuring first connection parameters with a first transmit power, a first redundancy and a first packet length, wherein the first transmit power corresponds to a maximum transmit power, the first redundancy to a minimum redundancy and the first packet length to a minimum packet length, so that the internal power limit is not exceeded by the field device (1),- Sending an initial advertising message (WN1) from the field device (1) via the first wireless interface (30) with the initial connection parameters, - Receiving the initial advertising message (WN1) from the mobile device (2) via the second wireless interface (40), - Sending an initial reply message (AN1) from the mobile device (2) to the field device (1).

Description

The invention relates to a method for transmitting data via a wireless interface between a field device and a mobile device, and to a system. In analytical measurement technology, particularly in water management, environmental analysis, and industrial applications (e.g., food technology, biotechnology, and pharmaceuticals), as well as for a wide variety of laboratory applications, measured parameters such as pH, conductivity, or the concentration of analytes (e.g., ions or dissolved gases) in a gaseous or liquid medium are of great importance. These parameters can be measured and / or monitored using electrochemical sensors, such as optical, potentiometric, amperometric, voltammetric, or coulometric sensors, or conductivity sensors. These sensors are typically connected to a transmitter, which processes the sensor signals and communicates them to, for example, a control center. One type of connection between the transmitter and the control center uses only two wires. In this case, the transmitter is also called a two-wire device. With such two-wire devices, the available power is severely limited, making them particularly suitable for use in potentially explosive atmospheres. These devices communicate using an energy-efficient HART protocol, which is designed for signals between 4 and 24 mA via a current loop between, for example, the control center and the two-wire device. The minimum available current is usually limited to 3.6 mA at a supply voltage of typically a maximum of approximately 17 V. This results in an available power of approximately 61 mW. Many devices also have their operating voltage further reduced to power additional components such as explosion protection resistors or other devices in the current loop. This further reduces the available power. For example, the Endress+Hauser iTEMP TMT72 transmitter can be operated with a minimum supply voltage of only about 10V, resulting in a minimum available power of only 36 mW. However, the SoCs currently used in many transmitters with integrated Bluetooth communication modules exhibit peak power consumption of up to approximately 30 mW for wireless communication, while on average they typically require significantly less than 1 mW for their communication tasks. While on average sufficient power from the current loop is available for all device functions of the transmitter except Bluetooth, only about 6 mW are briefly available for functions such as measuring the sensor value, calculations, and fieldbus communication, as the remainder is used for Bluetooth communication. The total power consumption of the device can therefore briefly exceed the power supplied by the current loop. To meet this short-term energy demand, energy is typically stored temporarily in an energy storage device (e.g., a capacitor). The size of the required energy storage device depends on the duration and magnitude of the power peaks. However, this has the disadvantage that additional or larger electronic components become necessary, and the power available in the transmitter is increased beyond that provided by the current loop. This makes it more difficult to meet explosion protection requirements (“Ex”). Another option would be to put the Bluetooth communication module into sleep mode for a greater proportion of the time to save energy. However, this has the disadvantage of negatively impacting the data rate and latency of the Bluetooth connection. It is therefore an object of the invention to propose a method which enables energy-saving operation of the transmitter and at the same time optimal data transmission. This problem is solved according to the invention by a method for transmitting data via a wireless interface between a field device and a mobile device according to claim 1. The method according to the invention comprises: - Providing a field device with a processing unit and a first wireless interface, and a mobile device with a second wireless interface, wherein an internal power limit and a minimum connection robustness are stored in the field device, - Configuring first connection parameters with a first transmit power, a first redundancy, and a first packet length, wherein the first transmit power corresponds to a maximum transmit power, the first redundancy to a minimum redundancy, and the first packet length to a minimum packet length, so that the internal power limit is not exceeded by the field device, - Sending a first advertising message from the field device via the first wireless interface with the first connection parameters, - Receiving the first advertising message from the mobile device via the second wireless interface, - Sending a first reply message from the mobile device to the field device.- Receiving the first reply message from the field device, - Determining an initial signal strength and packet error rate based on the initial reply message by the processing unit, - Determining an initial connection robustness between the field device and the mobile device based on the initial signal strength and packet error rate by the processing unit, - Comparing the initial connection robustness with the minimum connection robustness, - Sending an initial data message with the initial connection parameters if the initial connection robustness is less than or equal to the minimum connection robustness, - Configuring a second connection parameter with a second transmit power, a second redundancy, and a second packet length, where the second transmit power is less than the first transmit power, the second redundancy is greater than the first redundancy, and the second packet length is greater than the first packet length.so that the internal performance limit is not exceeded by the field device, and sending the first data message with the second connection parameters if the first connection robustness is greater than the minimum connection robustness. The method according to the invention makes it possible to provide optimal data transmission while simultaneously adhering to a desired energy consumption. According to one embodiment of the invention, the first wireless interface and the second wireless interface are Bluetooth Low Energy modules and are each suitable for transmitting at a first data rate or at a second data rate, wherein the second data rate is greater than the first data rate, wherein the first connection parameters further include the first data rate and the second connection parameters further include the second data rate. According to a further embodiment of the invention, the first connection parameters have a first redundancy bit count and the second connection parameters have a second redundancy bit count, wherein the first redundancy bit count is greater than the second redundancy bit count. According to one embodiment of the invention, the first connection parameters have a first telegram length and the second connection parameters have a second telegram length, wherein the first telegram length is shorter than the second telegram length. According to one embodiment of the invention, an algorithm, energy model or fault model configures the second connection parameters when the first connection robustness is greater than the minimum connection robustness. According to one embodiment of the invention, after sending the first data message, all previously performed steps are repeated until the first connection robustness is less than or equal to the minimum connection robustness. According to one embodiment of the invention, the first data message has a first phase position, and the method further comprises receiving the first data message at the mobile device, sending a second data message with a second phase position, receiving the second data message at the field device, evaluating the first phase position and the second phase position, and determining a distance between the field device and the mobile device based on the evaluation. According to one embodiment of the invention, the computing unit stores a transmission time when sending the first data message, and the method further comprises receiving the first data message at the mobile device, sending a second data message, receiving the second data message at the field device, storing a reception time of the second data message at the field device by the computing unit, determining a signal propagation time based on the transmission time and the reception time, and determining a distance between the field device and the mobile device based on the signal propagation time. The above-mentioned problem is further solved by a system according to claim 9. The system according to the invention comprises: - a field device with a first wireless interface, - a mobile device with a second wireless interface, wherein an internal power limit is stored in the field device, wherein the system is suitable for carrying out the method according to the invention. According to one embodiment of the invention, the first wireless interface and the second wireless interface are each a Bluetooth interface, preferably a Bluetooth Low Energy interface. The invention is explained in more detail with reference to the following description of the figures. Figure 1 shows a schematic representation of a system according to the invention for carrying out the method according to the invention. Figure 2 shows a flowchart of the method according to the invention for optimizing energy consumption and reliability of the connection. Figure 1 schematically depicts a system 100 according to the invention, comprising a field device 1 and a mobile device 2. The field device 1 includes a first computing unit 10, a second computing unit 20, and a first wireless interface 30 for communication with a second wireless interface 40 of the mobile device 2. The first processing unit 10 and the second processing unit 20 are connected to exchange instructions and / or data, as indicated by the double arrow in Fig. 1. For example, the two processing units are connected via a bidirectional, wired communication interface. The second processing unit 20 is capable of performing computational tasks, such as creating or processing packets and cryptographic calculations. The first processing unit 10 is also connected to the first wireless interface 30 to send commands and / or data to the first wireless interface 30. The first wireless interface 30 is preferably a Bluetooth module, particularly advantageously a so-called "Bluetooth Low Energy" module, or a module for wireless communication using other protocols (e.g., ZigBee, Wireless HART, or a communication protocol based on the IEEE 802.15.4 transmission protocol, etc.). The first wireless interface 30 can be located in the same system-on-a-chip as one or both processing units, or it can be implemented as a separate IC. The field device 1 is suitable for connection to an external power source 3, which has an external power level, and for operation at an internal power level, where the internal power level is less than or equal to the external power level. The external power source 3 is, for example, a current loop with a current of 4 to 20 mA. The current loop is only shown abstractly in Fig. 1. The external power level is, for example, between 36 mW and 61 mW. Of course, the field device 1 is also suitable for operation with an internal power source, such as a battery. However, operating the field device 1 without a battery has the advantage that the field device 1 can be used, for example, in an explosion-proof environment without additional effort. Furthermore, no batteries need to be replaced over the lifetime of the field device 1. The field device 1 is preferably a two-wire device suitable for communicating with a control center via the current loop using the HART protocol and simultaneously being supplied with power. Field device 1 is connected, for example, to a sensor 4, which supplies electrical signals, such as voltage potentials, to field device 1. These signals are processed by field device 1 and sent via the current loop to the control center and / or via the first wireless interface 30 to mobile device 2. System 100 preferably includes a signal amplifier 6, also called a repeater, which is suitable for amplifying a signal exchanged between the field device 1 and the mobile device 2, or for increasing the range by transmitting the signals via two separate stages (so-called "hops"). The signal amplifier / repeater 6 thus enables communication over greater distances. The following describes the inventive method for transmitting data via the wireless interface 30 between a field device 1 and a mobile device 2. In particular, a first data message DN1 is to be transmitted from the field device 1 to the mobile device 2. The first data message DN1 preferably has a predetermined number of payload bits and a predetermined number of redundancy bits. First, the system 100 described above is provided, which includes the field device 1 with a computing unit 10 and a first wireless interface 30, as well as a mobile device 2 with a second wireless interface 40, wherein an internal performance limit is stored in the field device 1. Range during connection setup: Subsequently, a first advertising message WN1 is sent from field device 1 via the first wireless interface 30. This first advertising message WN1 is a so-called "advertising message," meaning a kind of notification that field device 1 exists and that, for example, sensor data can be retrieved from field device 1. One could also call it an advertisement. This first advertising message WN1 contains, for example, information about the serial number of field device 1, the device name, and / or the sensor(s) 4 connected to field device 1. Furthermore, the first advertising message WN1 is received by the mobile device 2 via the second wireless interface 40. It is assumed that the mobile device 2 is, of course, within the range of the signal (here the first advertising message WN1) sent by the field device 1. When transmitting advertising messages, various connection parameters, such as transmission power and the number of packets, can be varied. The lowest possible energy consumption of the field device can be achieved by sending advertising messages as infrequently as possible and with the lowest possible transmission power. However, a reduced range can be problematic. For example, if a Bluetooth device is mounted on a tank at a great height, the range may not be sufficient to wirelessly reach smartphones / tablets on the ground with reduced transmission power. This prevents both the establishment of a connection and the reception of broadcast data transmitted via advertising and scanning. Therefore, if no connection has yet been established, it is advisable to send the so-called advertising packets necessary for detecting the device's presence, i.e., in this case, for example...The first advertising message WN1 is always sent with high, preferably maximum, transmission power. However, this means that with a limited energy budget, only a reduced number of packets can be sent per unit of time (e.g., within one minute). For example, if 60 packets can be sent per unit of time at maximum transmission power, then 600 packets could have been sent per unit of time at minimum transmission power. Sending at maximum transmission power can cause high latency during connection establishment—meaning it may take a long time for the smartphone to successfully receive the first data message DN1 from the field device and exchange the message pairs necessary for establishing a connection. This problem can be alleviated according to the invention by the following procedure: The majority of the advertising packets, i.e., the advertising messages, are transmitted with low transmission power. At the same time, individual, less frequent advertising packets are transmitted with high transmission power. The term "rare" here refers, for example, to 1 packet out of 100 packets, preferably 1 packet out of 200 packets, or even fewer. This results in only a slight increase in average energy consumption and therefore only a slight impact on the latency during connection establishment. At the same time, remote devices can still establish a connection, albeit with increased latency. Furthermore, when using Bluetooth, so-called Extended Advertising can be used for even greater ranges.This is only compatible with newer devices that support Bluetooth 5 or later, but it allows the use of a Coded Physical Layer with Forward Error Correction even during connection setup (which includes advertising). This range-optimized connection setup method is preferably enabled or disabled by the user to adapt the device to the requirements regarding range, throughput, and latency. Adaptive adjustment of connection parameters: After receiving the advertising message WN1, a first reply message AN1 is sent from mobile device 2 to field device 1. The first reply message AN1 includes, for example, a request for further data from the field device. Furthermore, the reply message can be used to request a synchronous connection between the two devices, enabling the exchange of further packet pairs after this synchronization. The configuration of the connection parameters, both during asynchronous message exchange (called "advertising and scanning" in Bluetooth Low Energy) and in a synchronous connection, determines the energy consumption of the wireless communication. This, in turn, determines the performance of the wireless connection. The required transmit power, in turn, essentially determines the necessary configuration of the connection parameters. The following describes methods aimed at adaptively estimating the necessary transmit power and, based on this, optimizing the relevant connection parameters. Estimation of transmission power: If no synchronous connection yet exists, i.e., if advertising and reply messages are being exchanged, the first processing unit 10 or the second processing unit 20 determines an initial distance E1 between the field device 1 and the mobile device 2. This initial distance corresponds to an initial connection quality or initial connection robustness. With unobstructed communication, the connection quality and robustness are generally high at short distances. Determining the initial distance E1 is based on the first response message AN1. Preferably, the first response message AN1 includes an initial transmit signal strength and / or a packet error rate. To determine the initial distance E1, the signal strength, also known as the Received Signal Strength Indicator (RSSI), of the received initial reply message AN1 is preferably determined. The RSSI is expected to be between -30 and -90 dBm. Signal strength is considered excellent if values ​​close to -30 dBm are avoided, and signal strength is considered very poor if values ​​close to -90 dBm are reached. The initial distance E1 is estimated based on the signal strength. For example, if the RSSI is close to -30, the distance is assumed to be very short. If the RSSI is close to -90, the distance is assumed to be very long. Preferably, to determine the signal strength of the first reply message AN1 in the field device 1, an original transmit signal strength, with which the first reply message AN1 was sent from the mobile device 2, is stored, and / or the original transmit signal strength is appended to or included in the first reply message AN1. In this case, it is possible to determine the first distance E1 based on the signal strength and the original transmit signal strength. It is assumed here that there are no obstacles on the transmission path. The initial transmission signal strength of the first reply message AN1 is preferably at its maximum. This is particularly advantageous because mobile device 2 has fewer energy limitations. Preferably, the packet error rate of the first reply message AN1 is also determined. A high packet error rate suggests a long distance; a low packet error rate suggests a short distance. The packet error rate is determined, for example, by evaluating a cyclic redundancy check (CRC) of the received packet contents. The first distance E1 can then be estimated based on the determined packet error rate or the determined RSSI of the first response message AN1. If a synchronous connection is already established, the distance can also be determined using RSSI and packet error rate. According to an alternative and / or complementary embodiment, the first distance E1 is determined based on the phase or signal time-of-flight measurement carried out during a connection established after the exchange of the advertising messages (known as channel sounding when using Bluetooth). When measuring signal propagation times, the field device 1 determines an initial time interval, also called signal propagation time, between sending a message and receiving a reply message, assuming known latencies for packet processing and response. The propagation speed is assumed to be that of air. Using the propagation speed and the initial time interval, the initial distance is then calculated. In phase-based measurement using Bluetooth Channel Sounding, one of the two communication participants (field device or mobile device) sends a message with a known phase. The receiver responds with a message whose phase is identical to the phase measured in the incoming packet. If the phase of a received reply message is measured at different frequencies, the distance between the field device and the mobile device can be calculated. Adaptive adjustment of connection parameters: After the initial distance E1 has been determined using one of the two techniques described above, the required transmit power, data rate of the wireless interface, redundancy of the payload, the number of payload bytes per packet, and the interval at which packets are exchanged are determined. First, the procedure for adjusting these connection parameters, as shown in Fig. 2, is described. Then, the effect of each connection parameter to be adjusted is described in detail. An algorithm is used to adjust the connection parameters. The algorithm, which finds the optimized settings, works as follows (see Fig. 2). First, it starts with the most energy-intensive but most robust configuration of connection parameters. This guarantees maximum transmission range, i.e., the maximum possible distance between the field device and the mobile device. Based on the estimated first distance E1, measured attenuation or packet error rate, and an error model, it is estimated whether the communication with these connection parameters is sufficiently robust, i.e., whether it exhibits a minimum level of connection robustness. If this is not the case, the required communication robustness, i.e., the minimum connection robustness, cannot be achieved, and the algorithm concludes with the most robust configuration supported by the wireless interface 30.However, if the required robustness (minimum connection robustness) is achieved, it is checked whether a more energy-efficient configuration of the connection parameters exists that is supported by the wireless interface 30. The next most energy-efficient configurations are examined with regard to the transmit power, the physical layer (also called Phy), and the number and length of packets per connection interval. Here, a connection interval is defined as an exchange of a message sent by field device 1 and received by field device 1. At the same time, only those configurations are permitted for which a fault model shows that the required robustness is still achieved. If no more energy-efficient configuration achieves the required robustness (minimum connection robustness), the previous configuration is retained and the algorithm is modified. Otherwise, the next most energy-efficient configuration of the connection parameters supported by the wireless module is selected again, and the process described above is followed. This continues until the most energy-efficient configuration that exhibits the required robustness is identified. Since this method is based on error models, the algorithm can perform multiple iterations and find the most favorable configuration without requiring stepwise adjustments to the wireless interface 30 connection parameters. Because models can only approximate reality, iterative adjustment and measurement of robustness data, i.e., connection robustness (based on packet error rate and received power), is also possible. Furthermore, both approaches can be combined. Since the mobile device 2 can move away from the field device 1 at any time, or change its location so that the line of sight between the two devices is at least partially obscured, the described procedure for adjusting the connection parameters at runtime is continuously repeated. The connection parameters affect the wireless interface 30 and its energy consumption as follows. The transmit power determines the packet error rate and range. Higher transmit power potentially reduces the error rate and increases the range. The physical layer used also influences the range of the wireless connection. For example, Bluetooth uses different physical layers with different data rates: 1 Mbit / s and 2 Mbit / s. At a higher data rate, packets require less transmission time. Sending a certain number of bytes through the first wireless interface (30) is also shortened, which in turn reduces energy consumption. However, this also reduces the transmission range and its robustness against interference. Similarly, corrupted symbols can be corrected after reception using forward error correction (FEC). In Bluetooth, this is achieved, for example, through the use of the "Coded Phy S2" (double redundancy) and "Coded Phy S8" (eightfold redundancy) options.Thus, in "Coded Phy S2," two redundancy bits are introduced per data bit, and in "Coded Phy S8," eight redundancy bits are introduced per data bit. This reduces the data rate and increases energy consumption. However, the range and interference immunity are significantly improved. The "Physical Layer" can therefore be selected depending on the desired data rate, robustness, and energy-optimized transmission power. Complementary to defining the physical layer (and thus the rate at which bits are transmitted in a message), an initial message length is defined based on the initial distance E1. Defining the initial message length determines the number of payload bytes in the transmitted messages. The Bluetooth standard also allows the interface to optionally handle particularly long packets through the use of the so-called Data Length Extension (DLE). The advantage of long telegrams, i.e., an initial data message DN1 with a large initial data length, is that the ratio between protocol overhead and payload becomes more favorable with longer telegrams. However, if a bit is transmitted incorrectly when using a physical layer without FEC, the entire message is discarded and must be retransmitted. While some errors can be corrected when using FEC, an excessively high bit error rate will result in uncorrectable errors, and the entire packet must be retransmitted. This retransmission significantly increases energy consumption. The bit error rate depends, among other things, on the attenuation in the wireless channel and thus also on the distance between sender and receiver. The longer a telegram is, the higher the probability that it contains at least one incorrectly transmitted bit, given a certain bit error rate. At short distances and low bit error rates on the radio channel, longer telegrams are therefore advantageous with regard to energy consumption. At greater distances and thus higher bit error rates, shorter packet lengths are more advantageous. For a given bit error rate, the lowest possible energy consumption is always determined by an optimal combination of the physical layer used and the packet length. The optimal combination in a given situation can be calculated at runtime using mathematical models. For this reason, the physical layer and the packet length, i.e., the initial data length, are preferably continuously optimized at runtime by the first processing unit 10. Advantageously, a communication protocol is used which, on the sender side, first splits a serial byte stream into individual datagrams of variable size and then, on the receiver side, reassembles these variable-size datagrams, initiating a retransmission if individual datagrams are lost. The use of such a data link layer allows application protocols at a higher layer to continue to be used regardless of the length of the packets transmitted wirelessly. This means that at the application layer, both long transmission distances with short datagrams and short transmission distances with longer datagrams can be used without the application itself having to change the size of the data being transmitted. Subsequently, an initial data rate is set based on the initial distance E1. The first processing unit 10 modifies the packet rate, i.e., the number of messages per unit of time. When using Bluetooth, this is achieved by defining a period. If no connection exists, the advertising messages are exchanged at approximately this period. Once a connection is established, the "Connection Interval" is set accordingly. After each Connection Interval, either one or more packet pairs can be exchanged between the field device and the mobile device. If a longer packet length than supported by the Bluetooth standard or the radio hardware is available, multiple packet pairs can be exchanged consecutively. The optimal number of packets is also determined by the energy model. By adaptively adjusting the transmit power, data rate, and redundancy of the physical layer, as well as the message length, packet rate, and number of consecutive packet pairs, the lowest possible energy consumption for wireless communication is achieved while still maintaining optimal performance. The energy saved in this way is invested, firstly, in a higher rate of message exchange at the same energy consumption, thus reducing the latency of the wireless connection. Secondly, some of the saved power is available to the device for other functions unrelated to wireless communication. The procedure described above is preferably repeated regularly, as the mobile device 2 may have moved, rendering the initial distance E1 no longer valid. Therefore, as described above for determining the initial distance E1, a second distance E2, or second connection robustness, is determined. This involves, for example, exchanging a second advertising message WN2, a second reply message AN2, and a second data message DN2. The procedure shown in Fig. 2 can preferably be modified to eliminate the need for error models: Instead of evaluating the adjustment of the connection parameters using a model-based approach, the wireless interface parameter can also be adjusted, and the received signal power and packet error rate can be monitored during runtime. If the power is too low or the error rate too high, the system reverts to the previous configuration. The proposed method increases the data rate of Bluetooth devices and reduces their latency by adjusting the transmission power to the required transmission power. This leads to higher performance, or, with the same power budget, to increased robustness (connection reliability) of the communication. Reference symbol list 1 Field device 2 Mobile device 3 External power source 4 Sensor 5 Memory 6 Signal amplifier 10 First processing unit 20 Second processing unit 30 First wireless interface 40 Second wireless interface 100 System AN1 First reply message AN2 Second reply message DN1 First data message DN2 Second data message E1 First distance E2 Second distance WN1 First advertising message WN2 Second advertising message

Claims

A method for transmitting data via a wireless interface between a field device (1) and a mobile device (2), comprising the following steps: - Providing a field device (1) with a computing unit (10) and a first wireless interface (30), and a mobile device (2) with a second wireless interface (40), wherein the field device (1) has an internal power limit and a minimum link robustness; - Configuring initial link parameters with an initial transmit power, an initial redundancy, and an initial packet length, wherein the initial transmit power corresponds to a maximum transmit power, the initial redundancy to a minimum redundancy, and the initial packet length to a minimum packet length, such that the internal power limit is not exceeded by the field device (1); - Sending an initial advertising message (WN1) from the field device (1) through the first wireless interface (30) with the initial link parameters.- Receiving the first advertising message (WN1) from the mobile device (2) via the second wireless interface (40),- Sending a first reply message (AN1) from the mobile device (2) to the field device (1),- Receiving the first reply message (AN1) from the field device (1),- Determining a first signal strength and a first packet error rate based on the first reply message (AN1) by the processing unit (10),- Determining a first link robustness between the field device (1) and the mobile device (2) based on the first signal strength and the first packet error rate by the processing unit (10),- Comparing the first link robustness with the minimum link robustness,- Sending a first data message (DN1) with the first link parameters if the first link robustness is less than or equal to the minimum link robustness,- Configuring second link parameters with a second transmit power,a second redundancy and a second packet length, wherein the second transmit power is less than the first transmit power, the second redundancy is greater than the first redundancy and the second packet length is greater than the first packet length, so that the internal power limit is not exceeded by the field device (1), and sending the first data message (DN1) with the second connection parameters if the first connection robustness is greater than the minimum connection robustness. Method according to claim 1, wherein the first wireless interface (30) and the second wireless interface (40) are Bluetooth Low Energy modules and are each suitable for transmitting at a first data rate or at a second data rate, wherein the second data rate is greater than the first data rate, wherein the first connection parameters further comprise the first data rate and the second connection parameters further comprise the second data rate. Method according to claim 1 or 2, wherein the first connection parameters have a first redundancy bit count and the second connection parameters have a second redundancy bit count, wherein the first redundancy bit count is greater than the second redundancy bit count. Method according to one of the preceding claims, wherein the first connection parameters have a first telegram length and the second connection parameters have a second telegram length, wherein the first telegram length is smaller than the second telegram length. Method according to one of the preceding claims, wherein an algorithm, energy model or fault model configures the second connection parameters when the first connection robustness is greater than the minimum connection robustness. Method according to one of the preceding claims, wherein after sending the first data message (DN1) all previously performed steps are repeated until the first connection robustness is less than or equal to the minimum connection robustness. Method according to one of the preceding claims, wherein the first data message (DN1) has a first phase position, and the method further comprises receiving the first data message (DN1) at the mobile device (2), sending a second data message (DN2) with a second phase position, receiving the second data message (DN2) at the field device (1), evaluating the first phase position and the second phase position, and determining a distance between the field device (1) and the mobile device (2) based on the evaluation. A method according to one of the preceding claims, wherein the computing unit (10) stores a transmission time when sending the first data message (DN1), and the method further comprises receiving the first data message (DN1) at the mobile device (2), sending a second data message (DN2), receiving the second data message (DN2) at the field device (1), storing a reception time of the second data message (DN2) at the field device (1) by the computing unit (10), determining a signal propagation time based on the transmission time and the reception time, and determining a distance between the field device (1) and the mobile device (2) based on the signal propagation time. System (100) comprising, - a field device (1) with a first wireless interface (30), - a mobile device (2) with a second wireless interface (40), wherein an internal power limit is stored in the field device (1), wherein the system (100) is suitable for performing the method according to one of the preceding claims. System (100) according to claim 9, wherein the first wireless interface (30) and the second wireless interface (40) are each a Bluetooth interface, preferably a Bluetooth Low Energy interface.

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