TIME-SLAP COMMUNICATION SYSTEM

Description

Technical field

[0001] The invention relates to a system for communication with a radio tag. background

[0002] A system mentioned above is known, for example, from DE 44 39 074 A1. According to this document, all radio tags must be in their active state at the time a preamble is transmitted in order to enable synchronous data transmission to the radio tags in their assigned time slots. This measure has low energy and system efficiency. Furthermore, WO 2010 / 004349 A1 discloses a system in which the radio tags are assigned to individual time slots. For synchronization with the communication station, the station transmits a preamble. This preamble contains several data packets that indicate a deviation from a reference time for the synchronous state between the communication station and the radio tag.The radio tags go from a sleep state to an active state at a time defined by their internal time base and within the time span of the preamble occurrence, and then receive one of the data packets. Using the respective received data packet and the deviation from the reference time encoded therein, the radio tags' internal time base is corrected in order to reset the next wake-up time and thus maintain a synchronous state with the communication station. However, the preamble used has proven disadvantageous because it causes a relatively high data volume. US 2011 / 0316676 A1 discloses a system in which a series of RFID tags are interrogated by an "interrogator." The RFID tags are designed to wake up periodically and check whether a wake-up signal intended for them, transmitted by the interrogator, is present.The interrogator is designed to transmit a sleep command to the RFID tags, if necessary, which specifies how long the RFID tags should sleep. Furthermore, US 2012 / 0326846 A1 discloses a system in which radio tags communicate with a communication station, whereby non-synchronous radio tags are addressed and synchronized during a "buffer time" within a time slot cycle. This system has proven disadvantageous, among other things, due to the necessity of the "buffer time."

[0003] The invention aims to provide a system that avoids the problems discussed above. Summary of the invention

[0004] This object is achieved by a system according to claim 1.

[0005] The subject of the invention is therefore a system comprising a communication station for communicating with a number of radio tags using a time slot communication method, in which a number of time slots are available for communication in a repeating sequence per time slot cycle and each time slot is identified by a unique time slot symbol, wherein the communication station is designed to transmit a synchronization data signal comprising the time slot symbol for the currently available time slot, and a radio tag, wherein the radio tag is designed to change from a sleep state to an active state at a wake-up time, and to receive the synchronization data signal in the active state, and, if the received time slot symbol indicates a time slot intended for it,for defining a new wake-up time corresponding to the next occurrence of the time slot intended for it in a time slot cycle following the currently existing time slot cycle, wherein the communication station is designed to embed command data in the synchronization data signal, with the aid of which a command can be transmitted to a radio tag in a time slot intended for said radio tag, and the radio tag, if the received time slot symbol indicates a time slot intended for it, is designed to evaluate the synchronization data signal with regard to the contained command data and to execute the command, wherein the radio tag is designed to execute a command as a multiple time slot command over several time slots, and wherein the communication station is designed toto instruct the radio tag in the time slot designated for it by means of a command about a further wake-up time, wherein the radio tag is designed to process this command and to switch to the active state at the further wake-up time imposed by the communication station, so that the radio tag is available for data transmission with the communication station in a time slot corresponding to the further wake-up time.

[0006] The measures according to the invention have the advantage that synchronization between the communication station and a radio tag is detected, maintained, and ensured during system operation in the simplest yet extremely robust way possible. Unlike with known measures, all radio tags no longer need to be in their active state at a specific time in order to remain synchronized with the time grid of the time slot communication method defined by the communication station. Likewise, the reception and evaluation of data indicating a temporal deviation from a reference time can be dispensed with, which has proven to be very complex in terms of both processing this data and the data volume during communication with the communication station.According to the invention, it is sufficient for each radio tag participating in communication with the communication station to know the time slot symbol indicating its designated time slot. Each of the radio tags thus individually orients itself to the occurrence of a time slot symbol relevant to it, identifies the relevant time slot symbol, and defines its next wake-up time.

[0007] It is entirely sufficient for the time slot symbol to uniquely identify the respective time slot, e.g., with a time slot identifier unique to each time slot. Further information encoded in the synchronization data signal, as discussed in relation to the known measures, is not necessary to operate a radio tag synchronously with the communication station. The radio tag establishes its synchronism with the communication station solely by recognizing the time slot symbol, which appears at the expected time or within an expected time window and indicates the time slot intended for it.

[0008] Once the radio tag has established its synchronism as previously discussed, it is generally sufficient for it to return to the sleep state, because the next wake-up time is automatically determined from the time frame of the time slot communication method known to it. Defining the new wake-up time can therefore be limited to restarting a time control stage (e.g., a timer) of the radio tag with the timing parameters previously used to switch from the sleep state to the active state. The radio tag can then return to the sleep state and remain there until it is triggered by the time control to wake up again and switch from the sleep state to the active state at the new wake-up time in the next time slot cycle.However, the radio tag does not necessarily have to remain in sleep mode for the remainder of its assigned time slot; it can also process other tasks in an active state during the time slot or even the time slot cycle. The previously discussed time control then operates in the background, independent of its other activities. The new wake-up time can be defined by specifying an absolute or relative time, such as relative to the time of occurrence of the synchronization data signal, relative to the time at which the sleep state is resumed after the active state, or relative to the time at which the synchronization data signal ends.However, defining the new wake-up time can also be understood as the duration of the sleep state following the active state in which the time slot symbol was received, or the sum of the durations of the sleep state and the active state, or the sum of the durations of several such state sequences, determining the new wake-up time. Since each radio tag operates its own timing stage and exemplary variations in the behavior of the respective electronic components cannot be ruled out, defining the new wake-up time can also include compensation for a drift in the time base that is unique to each radio tag.For this purpose, for example, a time difference between the expected occurrence of the synchronization data signal with the time slot symbol indicating the time slot assigned to the respective radio tag and the actual occurrence can be measured in the radio tag and taken into account in the timing control stage to correct its timing. However, compensation is only used when synchronism is detected. However, if a different time slot symbol is received instead of the expected time slot symbol, synchronism is not present, and the radio tag would have to perform a resynchronization, which will be discussed below.

[0009] In the time slot communication method, m time slots (e.g., 255 time slots) are used within n seconds, e.g., 15 seconds. The n seconds form a time slot cycle. In this time slot communication method, m time slots are available within a time slot cycle for communication with the radio tags. Each of the radio tags can be assigned to one of the time slots, although multiple radio tags can also be assigned to a specific time slot.

[0010] A radio tag essentially has a radio communication stage, also called a transceiver, and a interacting logic stage that provides the logical function of a tag. The logic stage can, for example, be implemented entirely in hardware or have a microprocessor and memory chips or a microcontroller with integrated memory chips so that software stored in the memory chips can be processed. A tag can receive a radio signal with the help of its radio communication stage, process the received data contained in the radio signal with the help of the logic stage and, if necessary, generate response data with the help of the logic stage and transmit this response data again as a radio signal via the radio communication stage. The radio communication stage has means for radio communication and for converting analog signals into digital signals and vice versa.

[0011] Such a radio tag can have an energy storage device, such as a battery or a solar panel coupled with a rechargeable battery, for its power supply. In order to operate as energy-efficiently as possible, the radio tags have different operating states. In the active state, a radio tag has a relatively high energy consumption. The active state occurs, for example, when sending or receiving data, during display updates, when measuring battery voltage, etc. In the sleep state, in contrast, there is relatively low energy consumption. Preferably, as many electronic components as possible are disconnected from the power supply or shaded, or at least operated in a mode with the lowest possible energy consumption. The active state occurs primarily in the time slot designated for the radio tag for communication with the communication station. In the active state, the radio tag, for example,a receive state in order to receive commands and, if necessary, receive data from the communication station and process them with the help of the logic stage. In the active state, transmit data can also be generated with the help of the logic stage and communicated to the communication station. Outside of the time slot designated for the radio tag, the radio tag is primarily operated in the energy-saving sleep state. In the sleep state, the logic stage or the time control stage only performs those activities that are necessary for timing the timely wake-up so that the radio tag is ready to receive the synchronization data signal and / or to communicate with the communication station at the next designated time slot.In order to operate energy-efficiently and thus achieve the longest possible service life of the radio tag, the basic operating strategy is to keep the synchronous radio tag in sleep mode for as long as possible and to operate it in the active state for the shortest possible period of time only when absolutely necessary for the purpose of data transmission with the communication station.

[0012] The communication station can be a standalone device with server functionality. Preferably, the communication station will form an interface between wired communication with, for example, a data processing device (e.g., a server) and wireless, radio-based communication with the radio tags.

[0013] In order to be available for communication with the communication station, the radio tags can first register with the communication station or be assigned to it.

[0014] Further, particularly advantageous embodiments and developments of the invention emerge from the dependent claims and the following description.

[0015] The measures according to the invention not only ensure synchronization between the communication station and a radio tag in a simple manner, but also allow a radio tag that has entered an asynchronous state to be easily returned to the temporal scheme of the time slot communication method, i.e. to be synchronized again. For this purpose, such an asynchronous radio tag does not change periodically, as would be the case in a synchronous state, but rather, for example, changes from its sleep state to its active state once at any desired point in time and remains in this active state in readiness to receive. If nothing is received within a certain period of time, such as the duration of a time slot, it changes back to the sleep state and repeats the reception attempt at a different time. As soon as a synchronization data signal is received, the time slot symbol is evaluated.The time slot symbol received in this process most likely indicates a time slot not intended for it, which is determined autonomously by the radio tag. The radio tag knows the systematic occurrence of the time slot symbols and, after evaluating the received time slot symbol, can independently decide whether it can expect the time slot intended for it to occur within the current time slot cycle (first case) or only in the following time slot cycle (second case). For the first case, the radio tag is designed to define a new wake-up time in the current time slot cycle that corresponds to the next occurrence of the time slot intended for it. By evaluating the received time slot symbol and knowing the systematic occurrence of the time slot symbols, the radio tag determines that the time slot intended for it will occur within the current time slot cycle.For the second case, the radio tag is configured to define a new wake-up time corresponding to the next occurrence of the time slot designated for it in the time slot cycle following the current time slot cycle. By evaluating the received time slot symbol and knowing the systematic occurrence of the time slot symbols, the radio tag determines that the time slot designated for it will no longer occur in the current time slot cycle because it already occurred in this time slot cycle in the past. As discussed in the introduction to the synchronous state, the aforementioned timing control is also used for this type of definition of the new wake-up time, whereby the timing control is now operated with the timing parameter with which the desired entry into the synchronous state is achieved.The timing parameter to be selected for the radio tag results from the inherent knowledge of the time slot communication method used, i.e. it is determined by the logic level.

[0016] The radio tag defines the correct wake-up time for the respective radio tag based on the parameters of the time-slot communication method. These parameters can be queried or transmitted by the communication station during registration, or they can be pre-programmed into the radio tag. In both cases, it is advisable for the radio tag to have a memory level for storing the parameters of the time-slot communication method, and for the radio tag to be configured to access and consider these parameters for defining the new wake-up time.The parameters can represent all details of the timing of the time slot communication process, such as parameters relating to time sequences for communicating between the communication station and the radio tag, parameters relating to predefined times or time periods, but also parameters relating to the basic structure of the time slot communication process, such as the number of time slots, the duration of a time slot, the duration of the time slot cycle, or also as parameters the explicitly specified time slot symbols for identifying the individual time slots or algorithms for calculating the time slot symbols.Using these parameters, an asynchronous radio tag can easily and autonomously determine whether, based on the just-received time slot symbol, the time slot assigned to it is still expected within the current time slot cycle, or whether the time slot assigned to it in the current time slot cycle already belongs to the past and, consequently, the next time slot assigned to it will not occur until the next time slot cycle. The affected radio tag calculates the new wake-up time in the active state, switches to the sleep state, and switches to the active state at the calculated wake-up time, receives the time slot symbol of the time slot assigned to it, and then returns to the synchronous state.If no further activities are expected from it in the current time slot, it will only switch back to the active state in the next time slot cycle in order to receive the synchronization data signal in the time slot designated for it.

[0017] According to a further aspect of the invention, the radio tag may comprise a memory stage for storing a representation of the time slot symbol indicating the time slot intended for it.

[0018] The two memory levels (memory level for storing parameters and memory level for storing representation) can be implemented on a single memory chip or by separate ones. They can be located in different memory areas within this memory chip and be subject to different access rights. However, they can also be implemented with different memory modules, for example, due to security considerations.

[0019] It has proven advantageous if the representation of the time slot symbol is formed using a hardware address of the radio tag that uniquely identifies the radio tag and is immutably programmed into the second memory level. This reliably prevents unwanted, and sometimes even fraudulent, manipulation of the radio tags. Since each radio tag has a unique hardware address, it is also possible to create an assignment to a time slot following a strict and unalterable pattern.

[0020] Particularly preferably, said representation of the time slot symbol is realized by the least significant bits or the least significant byte of the hardware address, whereby this group of bits used must be capable of mapping at least the number of time slots existing in the time slot cycle. For example, with 256 time slots, only the least significant 8 bits or one byte are required, and with 128 time slots, only the least significant 7 bits of the hardware address are required. In this context, it should also be mentioned that it is advantageous if the number of time slots corresponds to a power of 2.

[0021] It should be noted that the representation of the time slot symbol or the time slot symbol itself can also be formed from a combination of the previously mentioned hardware address and another pre-programmed value.

[0022] The radio tag is designed to check whether a time slot symbol known to it matches the one present when the synchronization data signal is received. The check can be carried out, for example, with the aid of an algorithm which, when software describing the algorithm is executed on a processor of the radio tag, provides a test result. The algorithm can, for example, convert the received time slot symbol to the representation known to the radio tag and then perform a comparison. The radio tag can, however, also convert the other way around, starting from the representation known to the radio tag, to an expected time slot symbol and then compare the received time slot symbol with the expected time slot symbol. However, it is advantageous if a simple comparison between two, for examplebinary coded symbols because this can be done very quickly and with relatively low energy consumption at the processor level by a simple register comparison.

[0023] In principle, a unique identification defined in advance in the system can be used for each time slot. However, it has proven particularly advantageous if the communication station is configured to generate the time slot symbol as the consecutive number ("slot ID") of the respective time slot according to its occurrence in the order of the time slots in the time slot cycle. Thus, in each time slot cycle, the first time slot is assigned the number 1, the second time slot the number 2, and so on. This allows a time slot symbol to be generated as simply as possible, avoiding complex algorithms, and also resulting in minimal data traffic during data transmission from the communication station to the radio tag. Only a single data packet needs to be sent, which serves for synchronization.Thus, the total data volume available per time slot or per time slot cycle is barely affected by the transmission of the time slot symbol. Channel occupancy is therefore optimized because the number of data packets per time slot or per time slot cycle required for synchronization is as small as possible. The number of time slots that occur in the time slot cycle ultimately determines the number of bits required to generate the respective time slot number (i.e., to number them) and form the data packet required for synchronization. Because each bit can indicate two states, it is advantageous if the number of time slots per time slot cycle is a power of 2. Consequently, the time required to receive the time slot symbol can also be correspondingly short, which has a positive effect on the energy balance of the radio tag.Especially when parts of the hardware address are used on the radio tag side as a representation of the time slot symbol known to the radio tag, checking whether the received time slot symbol matches the stored time slot symbol can be performed quickly and easily. The radio tags synchronize themselves with the communication station or the time grid of the time slot communication method defined by it in the simplest possible way using the time slot number.

[0024] In principle, the synchronization data signal could be formed exclusively by the time slot symbol, and other communication parameters required for communication between the communication station and a radio tag, such as address data for addressing a tag or command data for transmitting commands, could be separated from the synchronization data signal. Since, as discussed previously, the time slot symbol is an extremely compact indicator for synchronizing communication within the system, it is advisable to embed additional information into the synchronization data signal in addition to the time slot symbol, which will be discussed below.

[0025] Therefore, according to a further aspect of the invention, the communication station is designed to embed address data in the synchronization data signal, with the aid of which address data a number of radio tags can be individually addressed per time slot intended for said radio tags, and the radio tag, if the received time slot symbol indicates a time slot intended for it, is designed to evaluate the synchronization data signal with regard to the address data contained therein and to check whether it is individually addressed.

[0026] Analogous to the use of the hardware address of a radio tag in conjunction with the time slot symbol, it is also advantageous if the communication station is designed to generate the address data using one or more bits or bytes of a hardware address of the radio tag that uniquely identifies a radio tag, in particular by omitting the least significant bits or the least significant byte. In the present system, the hardware address of the radio tag is therefore used to uniquely address each radio tag. On the one hand, the least significant bits or the least significant byte define which time slot is intended for the radio tag. Thus, a relatively large number of radio tags can be assigned to exactly one time slot in order to remain synchronized with this time slot and also be individually addressable within this time slot.The individual addressing of a specific radio tag is now performed using additional bits or bytes of the radio tag's individual hardware address. This measure also represents a significant contribution to system efficiency because the affected radio tag, which is currently in the active state to receive the time slot symbol, does not have to temporarily switch to the sleep state and then switch back to the active state at a later point in time in the current time slot to check whether address data is present. Rather, during this relatively short active phase, all radio tags simultaneously listening for the synchronization data signal can determine whether they are addressed or not.

[0027] Analogous to what was previously stated regarding the embedding of address data, a further significant contribution to system efficiency is achieved if the communication station is configured to embed command data into the synchronization data signal, with the aid of which a command can be transmitted to a radio tag in a time slot designated for said radio tag, and - if the received time slot symbol indicates a time slot designated for it, the radio tag is configured to evaluate the synchronization data signal with regard to the contained command data and to execute the command. For example, without individual addressing, a command can be transmitted to all radio tags assigned to a specific time slot, which command is then executed by a relatively large group of radio tags.

[0028] In principle, the radio tag could perform a standardized (predefined) task simply by recognizing its individual address, without having to receive an explicit command. However, it has proven particularly advantageous if address data for addressing an individual radio tag and command data for transmitting a command to this individual radio tag are transmitted, and the radio tag is configured to evaluate the command data and execute the command when individually addressed using the address data. This allows a command to be transmitted for a single radio tag in a sometimes relatively large group of radio tags.

[0029] According to a further aspect of the system, it is advantageous that the radio tag is configured to execute a command as a single time-slot command and to complete the executed command within a single time slot in which the command was received. This allows for rapid and compact processing of commands submitted to the radio tag via the communication station. Such single time-slot commands can, for example, be a so-called "PING" command, which only checks whether a specific radio tag exists, or an internal processing command that generates as little external data traffic as possible, such as a switching command for switching from one memory page to another. A memory page is a logical area (an address range) in memory in which, for example, data for an image is stored.With the single time slot command, no data for processing (e.g. data that is used for display, etc.) is transmitted by the radio tag to the radio tag, but only commands that may lead to internal processing of data or cause the radio tag to transmit information to the communication station.

[0030] In this context, it has also proven advantageous if the radio tag is configured to generate confirmation data upon completion of the executed command and to transmit the confirmation data in the time slot in which the command was received. Thus, data traffic resulting from the confirmation remains limited to the time slot in which the command was transmitted. Subsequent time slots remain unloaded, which has a positive effect on system performance.

[0031] Furthermore, a radio tag can be configured to transmit the confirmation data in a first part (e.g., the first half or the first third) of the time slot, which is located temporally following the synchronization data signal and leaves a second, adjoining part of the time slot untouched before the occurrence of the synchronization data signal of the following time slot. This structural or temporal division of the time slot takes into account the fact that confirmation data often requires only a short transmission time and therefore the remaining, namely the second part (e.g., the second half or the second and third thirds) of the respective time slot is unhindered for further data traffic.

[0032] In general, it should be noted at this point that the duration of each part of the time slot does not have to be defined by a fixed value, but can result dynamically from the respective configuration or use of the time slot.

[0033] In a system where, for example, 256 time slots of 58.6 milliseconds each exist during a 15-second time slot cycle, 2 to 5 radio tags can easily be individually addressed per time slot and individual tasks can be delegated to them using a single time slot command. Therefore, if multiple radio tags are assigned a task per time slot and it is consequently expected that all of these radio tags will report the aforementioned confirmation data in the current time slot, it is advantageous if each radio tag follows a specific ordering principle.For this purpose, the radio tag is designed to evaluate not only its own address, but also the address of the other addressed radio tag(s) if multiple radio tags are addressed using the address data, and to transmit its confirmation data within a time window designated for the transmission of confirmation data at the time that corresponds to the order in the group of addressed radio tags determined for it by the identified addresses. Since the communication station, as the task initiator, has knowledge of the addressed radio tags, only minimal data traffic is required to transmit the confirmation data. Adhering to the ordering principle, the communication station knows exactly in which order and consequently at what time or for what period each of the radio tags involved transmits its confirmation data.

[0034] In order to transmit larger amounts of data between the communication station and a radio tag, for which the duration of one time slot would not be sufficient, the radio tag is designed to execute a command as a multiple time slot command across several time slots. The processing of such commands can take place in adjacent time slots or in time slots that are not immediately adjacent. For example, a component of the command can be the number of time slots to be used or the identification of the time slots or time slot groups to be used. The time slots used can be limited to one time slot cycle or be located across several time slot cycles. From the perspective of the radio tag, such multiple time slot commands can, for example,the download of a large amount of data from the communication station but also the upload of such amounts of data to the communication station. Analogous to the single time slot command, the multiple time slot command does not transmit any data for processing (e.g. data that is used for display, etc.) by the radio tag to the radio tag, but only commands that may lead to internal data processing and / or cause the radio tag to receive or send data at a later time. After receiving the multiple time slot command, the radio tag can return to its energy-saving sleep state and then autonomously switch to the active state at the time at which the data transfer to it is carried out.During data transmission, no further command communication is required, and in particular no further addressing of the radio tag is necessary, since the communication station has already defined the data transmission system to the radio tag in advance by transmitting the multiple time slot command. For a radio tag with, for example, a display, the time at which the radio tag is addressed to receive data to be displayed is therefore completely decoupled from the actual time at which the data to be displayed is transmitted. The transmission of data to be displayed can be started at any time in the current or a different time slot. The transmission of the data to be displayed can extend over different time slots of a time slot cycle or even over several time slot cycles.

[0035] If the multiple timeslot command relates to data transmission from the communication station to the radio tag, it is advantageous if the communication station is designed to transmit the total data divided into several time slots, with one or more data packets being transmitted as part of the total data per time slot and a second part of the respective time slot, adjacent to a first part of the time slot, being used for data transmission. In the present case, analogous to the discussions regarding the single timeslot command, only the second part (e.g. the second half) of the time slot is used in order to leave the other, namely the first, part of the time slot untouched for other activities. The same applies, mutatis mutandis, to data transmission from the radio tag to the communication station.

[0036] In order to indicate to the communication partner that in a series of time slots required to process the multiple time slot command, a partial task is being processed in the respective time slot, it is advantageous if the radio tag is designed to generate and transmit partial confirmation data in each time slot in which the multiple time slot command is executed.

[0037] In a particularly preferred embodiment of the system, the radio tag is configured to transmit the partial confirmation data in said second part following the received data packet and before the end of the respective time slot. Thus, all data traffic resulting from the multiple time slot command is consolidated in the second part of the time slot.

[0038] Depending on the design of the radio tags involved in the system, the communication station is also configured to receive and process the confirmation data in a designated reception time slot. Thus, confirmation data for the single-time slot command is received in the reception window corresponding to the first part of the respective time slot, and confirmation data for the multiple-time slot command is received in the reception window corresponding to the second part of the respective time slot.

[0039] In a preferred embodiment of the system, the previously described command processing options are combined. Consequently, the communication station is designed to address a second radio tag using the address data for a time slot intended for the processing of a multiple time slot command by a first radio tag, and to transmit a single time slot command to the second radio tag using the command data. This allows not only the transmission of larger amounts of data between the communication station and the first radio tag, but also the commissioning of a second radio tag with activities or tasks that only generate a low data volume in radio traffic with the communication device. Data transmission with the respective radio tag is handled in different parts of the relevant time slot.

[0040] According to a further aspect of the system, the communication station is configured to instruct a radio tag in its designated time slot, using a command, about a further wake-up time that does not correspond to a time slot usually assigned to it, so that the radio tag is available for data transmission with the communication station in a time slot other than its usual time slot in the time slot communication method. Complementing this, the radio tag is also configured to process this command and switch to the active state at the wake-up time imposed by the communication station. This measure is important if communication with a specific radio tag is forced by the communication station with high (highest) priority.The affected radio tag now synchronizes itself using the time slot symbol, which indicates a time slot not normally assigned to it. After processing the request received in this unusual time slot, the affected radio tag returns to its usual time slot and, once resynchronized, is ready to communicate with the communication station in the synchronous state.

[0041] To enable an independent search for a communication station, the radio tag is designed to check repeatedly for a period of time corresponding to the duration of the time slot cycle, in particular extended by a portion of said duration, whether a synchronization data signal can be received. If the synchronization data signal is absent, the radio channel is changed and the reception test is repeated. Since each communication station occupies a different radio channel, the consequence for a searching tag in the absence of a synchronization data signal is that either no communication station exists for the radio channel in question or such a communication station is outside its range, and consequently, another communication station must be sought.This process can be continued until a possibility of communication with a communication station has been found and the radio tag has been registered there and is then available in the system.

[0042] This search for a communication station can be simplified if the radio tag is designed to limit a search for a synchronization data signal to a group of predetermined radio channels, in particular those radio channels that were previously transmitted by a communication station when the radio tag was in contact with this communication station. This measure is useful for a radio tag that is newly integrated into the system, but is particularly preferred for an already integrated radio tag that has been moved and, as a result of the movement, lost the communicative connection with its communication station. Limiting the search to known radio channels is an energy-saving method and also helps to avoid collisions with radio channels that are predominantly occupied by other devices, such as a conventional WLAN (Wireless Local Area Network).

[0043] To ensure the simplest and most automatic installation of a new communication station in an existing system, it is advantageous if the communication station is designed to check all available radio channels, especially those pre-programmed for its operation, during commissioning to determine whether the respective radio channel is being used by another communication station or whether the respective radio channel is unused. If such an unused radio channel is present, it is used for communication with the radio tags assigned to it or to be assigned to it. An already occupied radio channel is recognized by the presence of the synchronization data signal from another communication device in the radio channel.

[0044] A system according to the invention can comprise a plurality of communication stations, which are located at different locations, for example, and each communication station can be assigned a group of radio tags by selecting the radio channel assigned to the communication station. Thus, groups of radio tags can be managed in the system in a simple and robust manner, with the same time slot communication method being used for each group of radio tags, but on different channels from group to group.

[0045] According to a preferred embodiment of the system, the radio tag has a display unit for displaying an image, wherein the image is structured into image planes and each image plane is represented by image plane data, wherein the radio tag is configured to individually receive the image plane data and to compile the image by superimposing the image planes, and wherein the communication station is configured to transmit the respective image plane data in a cross-time slot communication with the radio tag. This measure has the advantage that only the image plane in which changes occur needs to be selectively transmitted from the communication station to a radio tag. This measure represents a significant contribution to system and energy efficiency because the amount of data to be transmitted is relatively small compared to the amount of data that would need to be transmitted for the entire image content.In addition, the compression of the image data for each image layer to be transmitted can be optimized, thus minimizing the amount of data to be transmitted. This is possible because an image layer to be transmitted typically contains large "white" or "transparent" areas, for which a very high compression rate is achieved. Since the amount of data to be transmitted is thus reduced to the absolute minimum to perform an image update, this measure has a highly beneficial effect on the service life of the radio tags because their energy requirements and consumption are kept to a minimum by minimizing activity.

[0046] In this context, the radio tag can be configured to modify an existing image by receiving at least one new image layer of the image and generating the new appearance of the image by replacing an already existing image layer of the image with the just-received image layer. The commands discussed above can be used here. For example, the download of the image data of an image layer from the communication station to the radio tag can be processed using a multiple time slot command, in which the image data of the affected image layer is stored in a new memory page in the radio tag.Once the download is complete, a single time slot command can be used to switch from another memory page previously used to create the said image plane of the image to the new memory page in order to use the said image plane to composite the image with its other image planes.

[0047] According to a preferred embodiment, the radio tag is designed to process images in which the image levels have the following meanings: first or second frequency of change in image content; first or second color of image content; first or second information category of image content. This allows implementations tailored to the specific application area of ​​the system, with combinations of the meanings of the levels also being possible. More than two image levels, e.g., three, four, or five image levels, are also possible.

[0048] According to such a preferred embodiment, the system implements an electronic price display system and a display unit of the radio tag serves to display product or price information, etc.

[0049] In all cases where a display unit is used, the display unit can be implemented using LCD technology, for example, but preferably also electronic ink technology (also called E-Ink as a synonym for electronic paper).

[0050] According to a further aspect of the system, the radio tag is configured to transition from the sleep state to the active state at a wake-up time with a lead time before the occurrence of the synchronization data signal. This measure ensures that the radio tag as a whole, or in other words, all of its components required to receive and process the synchronization data signal, are fully operational, thus preventing partial reception of the synchronization data signal, which would then likely be impossible to meaningfully evaluate.

[0051] The lead time can be chosen so that it is a first fraction of the time slot duration. For example, it can be between 0.1% and 10% of the time slot duration.

[0052] According to a further aspect of the system, the radio tag is configured to assume the active state for a reception period that is longer than the transmission period of the synchronization data signal. This measure has the advantage of ensuring that the entire synchronization data signal can be reliably received. The current reception period to be used can be fixed for all reception processes in the synchronous state. However, the duration of the active state can also be dynamically adapted to the respective drift based on the drift of the radio tag's time base determined with the aid of the occurrence of the synchronization data signal, possibly including the aforementioned lead time. The reception period can also be limited by detecting the disappearance of the synchronization data signal.

[0053] To ensure optimal reception conditions, the radio tag in such a system can also be configured to maintain the active state assumed for receiving the synchronization data signal with a lag time after receiving the synchronization data signal. The lag time can be defined, for example, by the predefined duration of the active state or can even be dynamically adjusted according to the current drift or reception conditions.

[0054] The duration of the lag time can be selected so that it is a second fraction of the duration of a time slot. It can, for example, be between 0.1% and 10% of the duration of the time slot. The duration of the lag time can be identical to the duration of the lead time or different from it.

[0055] It has proven particularly advantageous for the communication station to be configured to transmit the synchronization data signal at the beginning of each time slot. This measure ensures that the beginning of a time slot can be identified very precisely for the radio tag, that the drift of the radio tag's internal time base can be compensated for right at the beginning of the time slot, and consequently, all further activities of the radio tag within the respective time slot can proceed with the best possible synchronization with the time base of the communication station, and that the full remaining length of the time slot is available for said further activities.

[0056] With a view to achieving the most structured yet flexible communication possible between the communication station and a radio tag, it has proven advantageous if the communication station is designed to embed confirmation time data in the synchronization data signal, with the aid of which a confirmation time can be determined within the time slot at which confirmation data is expected from the radio tag, and the radio tag is designed to transmit the confirmation data at the specified time. This is particularly advantageous if several radio tags have been addressed in a time slot and an individual confirmation time is communicated for all of them. Each of the radio tags can then, for example,After receiving the synchronization data signal, execute a command, switch to the energy-saving sleep state and only switch back to the active state at the individually defined confirmation time and send out its confirmation data, and then switch back to the sleep state as quickly as possible. The specification of the confirmation time in the synchronization data signal therefore represents a measure for improving the energy efficiency of the radio tag as well as a measure for avoiding collisions and thus has a lasting effect on its lifetime. The confirmation time data can specify an absolute time in the time slot measured from its start or a length of time in the sleep state, e.g. based on a preceding event, such as the end of the synchronization data signal, which can be detected by the radio tag, or the end of the active state.

[0057] A further aspect of the invention relates to the assignment of a plurality of radio tags to a plurality of communication stations. In order to achieve the most balanced distribution of assignments between the radio tags and the communication stations, it has proven advantageous if a data processing device, e.g., a server, is configured to decide which of the radio tags may connect to which communication station. The basis for this decision can be an existing distribution of connections in the system, which is to be optimized with regard to newly added radio tags. However, there can also be a fixed, predefined connection scheme that has been defined in advance and is to be implemented.

[0058] To enable the most dynamic system possible, it can be advantageous if a data processing device, e.g., a server, is configured to cause a radio tag to terminate an existing connection with one of the communication stations and establish a connection with another communication station. The server can then react to an unbalanced distribution of radio tags and proactively influence and change the assignment of radio tags to communication stations to achieve optimal load balancing.

[0059] These and other aspects of the invention are apparent from the figures discussed below. FIGURES SHORT DESCRIPTION

[0060] The invention will be explained in more detail below with reference to exemplary embodiments in the accompanying figures. In the various figures, identical components are provided with identical reference numerals. They show schematically: Fig. 1 shows a system according to the invention; Fig. 2 shows a distribution of radio channels for the system; Fig. 3 shows a block diagram of an electronic price display sign; Fig. 4 shows an assembly of an image; Fig. 5 shows a first state diagram; Fig. 6A shows a second state diagram; Fig. 6B shows a first data structure; Fig. 7A shows a second state diagram; Fig. 7B shows a second data structure; Fig. 8 shows a third state diagram; Figs. 8B-8C show a third and a fourth data structure. DESCRIPTION OF THE EMBODIMENTS

[0061] In the Figure 1An electronic price display system is shown as an inventive system 1 for communicating according to a time slot communication method, which is installed in the premises of a retail establishment. For reasons of clarity, a representation of the premises and their equipment has been omitted from the figures. The system 1 has a server 2, a first and a second communication station 3 and 4 (hereinafter referred to as station), and a number of eight radio tags 7 - 14 (hereinafter referred to as ESL for Electronic Shelf Label). The server is housed in office premises and is connected to the stations 3 and 4 via a wired communication line (LAN) L. The stations 3 and 4 are in contact with the ESLs 7-14 via radio signals. The stations 3 and 4 are mounted on the ceiling at different positions in a sales room.ESLs 7–14 are mounted on shelves corresponding to products, for which price and product information are displayed using the ESLs 7–14. The product information is transmitted from server 2 to stations 3 and 4, and from there communicated individually to the individual ESLs 7–14.

[0062] Each station 3, 4 covers a radio area, with a first radio area boundary 5 of station 3 and a second radio area boundary 6 of station 4 indicated by area. The radio areas have an overlap area in which the ESLs 9 - 11 are arranged.

[0063] When commissioning System 1, stations 3 and 4 were started one after the other. Each station 3 or 4 knows the preferred radio channels for operating System 1 with the channel numbers 3, 5, 8, 9 and 10. This is shown in the Figure 2shown in which different frequency bands 15 - 22 are represented by channel numbers K. Frequency bands 15, 16 and 17 are available for operation of a conventional WLAN. The frequency bands 18, 19, 20 - 22 preferred for operation of system 1 correspond to channel numbers 3, 5, 8 - 10 and do not overlap with the WLAN frequency bands 15 - 17. Station 3 automatically selected the radio channel with channel number 3 because this was the first to be checked to see whether it was already occupied by another station. Station 4 automatically selected the radio channel with channel number 5 because, when checking for free radio channels, it found that the radio channel with channel number 3 was already occupied and the next free radio channel was identified as the one with channel number 5. However, the assignment of the radio channels can also be fixed.

[0064] As soon as the ESLs 7 - 14 are brought into the respective radio range of station 3 or 4, they determine that radio signals from the corresponding stations 3 or 4 exist in one or more radio channels. ESLs 7 and 8 establish a connection to the first station 3. ESLs 12 - 14 establish a connection to the second station 4. ESLs 9 - 11 determine that both stations 3 and 4 are available to them. Each ESL 9 - 10 now checks the reception quality of the radio signals received from the respective station 3, 4 and decides on the station 3 or 4 for which the best reception quality was determined in order to establish a connection with it in the respective radio channel (channel number 3 or 5).However, this decision-making process can also be performed by stations 3 and 4, whereby the stations check the respective reception quality of a communication with ESLs 9-11 and communicate among themselves as to which of them will establish a connection with which of the ESLs 9-11, because more favorable communication conditions exist for the respective ESL 9-11. However, the decision-making process regarding the assignment between ESLs 9-11 and stations 3, 4 can also be outsourced to server 2, as this server is in contact with stations 3, 4. As part of the connection establishment between the respective ESLs 7-14, radio channels are first selected (also known as a "channel scan"), an assessment of the reception quality on the respective radio channel is performed if necessary, and then unique hardware addresses of the ESLs 7-14 are transferred to the station 3, 4 selected for communication.Thus, each station 3, 4 knows the ESLs 7 - 14 assigned to it. This initial assignment between station 3, 4 and ESLs 7 - 14 is passed on to server 2.

[0065] Subsequently, a second assignment is established between each ESL 7-14 and exactly one product. The server ultimately obtains knowledge of where in the salesroom, on which shelf, and at which shelf position each ESL 7-14 is (or should be) located because it also knows the corresponding position of the products, which is represented by a planogram.

[0066] In the Figure 3A block diagram of the ESL 7 is shown, representative of the ESLs 7 - 14 used in the system, which are all identically constructed. The ESL 7 has a radio module 24, a processor 25 for processing data, controlling operating states, and providing functions, a memory 26 for storing data and programs, and a display 27 implemented using energy-saving electronic ink technology for displaying product information. The radio module 24 is used for radio-based communication with stations 3 and 4, respectively. Receive data is generated from received radio signals and transferred to the processor 25, or transmit data transferred by the processor 25 is converted into radio signals. The data stored in the memory 26 can be assigned to both the processor 25 and the display 27. The selected representation also does not differentiate between the type of memory (ROM, EEPROM, RAM, etc.).) it is or how the memory 26 is logically or physically assigned to the processor 25 and / or the display 27. The selected representation also omits the representation of connections such as signal and / or data lines between the functional blocks 24-27, as well as a representation of the energy storage device (in this case, a battery).

[0067] Memory 26 stores image data BD for generating an image using display 27, wherein image data BD indicates a first image plane of the image with first plane data ED1 and a second image plane of the image with second plane data ED2, hardware address data HAD for indicating the hardware address of the ESL, and parameter data PD relating to the parameterization of the time slot communication method. It should be noted at this point that additional image planes may also be present.

[0068] The hardware address data HAD comprises four bytes B3, B2, B1, B0, where B0 is the least significant byte of the hardware address.

[0069] With the help of the processor 25, the various layer data ED1 and ED2 are combined in the ESL 7 to form the entire image. Both the first and second layer data ED1, ED2 represent image information for each pixel. However, for both image layers, specific image information is defined as "transparent," "background," or "background color." Therefore, the individual image layers can be overlaid pixel by pixel, thus creating the overall image by superposing the image content at identical coordinates of the pixels from different image layers. The images are in bitmap format, but they can also be available in other formats such as JPG, etc.

[0070] This image structure is in the Figure 4shown schematically. A first image level 28, represented by the first level data ED1, essentially contains static image information 29 about a product, whereby this static image information is only changed when the ESL 7 is assigned to a different product. The static image information 29 concerns, for example, descriptive text about the product. All other image areas are defined as "transparent." A second image level 30, represented by the second level data ED2, essentially contains dynamic image information 31, which changes relatively frequently compared to the static image information, for example, daily or several times a day or even weekly. The dynamic image information 31 concerns, for example, the price of the product or information about the validity of an offer, such as the start date and end date or times or other conditions linked to the offer. All other image areas are defined as "transparent."An overall image 32 represented by the image data BD, which was generated by superimposing each pixel of the first image plane 28 and a pixel of the second image plane 30 that corresponds exactly to it, shows both the static and the dynamic image information 29, 32 and the areas remaining between them that are marked as "transparent".

[0071] With the ESL 7, the entire image data BD can be received at once in compressed form, decompressed, and stored in memory 26. This can happen, for example, during the initial transmission of the entire image. However, the process is relatively lengthy and consequently requires a relatively high amount of energy. Once the image exists in the ESL 7, a partial update of the image is more efficient because this can be handled in a more energy-efficient manner. For this purpose, the ESL 7 can receive the image layer to be updated (e.g., the second image layer 30) separately from the other image layer already stored in memory 26 (e.g., the first image layer 28), decompress it, and store it in memory 26. The newly created second layer data ED2 is then accessed internally (switching from one memory page to another) in order to reconstruct the entire image 32.

[0072] The ESL 7 also has a timing control stage 33, which can be implemented as a standalone hardware component or at least partially with the aid of the processor 25. It generates a time base typical for the ESL and uses this time base to control the timing (entering and exiting) of the states of the ESL 7. The timing is controlled, for example, using timing parameters that are inherently known to the timing control stage and / or provided by the processor.

[0073] The following will be done with the help of Figure 5 - 8 The time slot communication method used in System 1 is discussed. Only the ESLs 7 - 9 assigned to the first stage 3 are discussed, with analogous discussions also applying to the ESLs 11 - 14 assigned to the second station 4. In the Figure 5 - 8In the state diagrams shown, time t is plotted on the abscissa axis. The states Z of each component of system 1 considered in the discussion are plotted on the ordinate axis. The diagrams thus show the temporal progression of the state.

[0074] In all Figure 5 - 8The top state sequence shows the states of level 3, countersigned by ST. During a time slot cycle duration DC (e.g. 15 seconds), N time slots Z1 ... ZN (e.g. 256) with identical time slot duration DS (e.g. approx. 58 milliseconds) are available. During the time slot cycle duration DC, level 3 alternates between a transmit state T and an idle state R. The transmit state T is always assumed at the start of a time slot Z1 ... ZN and maintained for a synchronization data signal duration DSD (or transmission time duration DSD of the synchronization data signal SD) in order to send the respective applicable time slot symbol ZS1, ZS2, ... ZSN with the respective synchronization data signal SD. The consecutive number of the respective time slot Z1 ... ZN in the order in which the time slots Z1 ... ZN occur is used as the respective time slot cycle symbol ZS1 ... ZSN.Consequently, the first time slot Z1 is denoted in hexadecimal notation (marked by "Hex") with the time slot symbol Hex 00, the second time slot Z2 with the time slot symbol Hex 01, etc., and the last time slot ZN (in this example, the two hundred and fifty-sixth time slot Z256) with the time slot symbol Hex FF.

[0075] The following describes the hardware addresses of ESLs 7–9, which are specified in hexadecimal notation (most significant byte on the left = fourth byte B3; third byte B2; second byte B1; least significant byte on the right = first byte B0). The hardware addresses of ESLs 7–9 would remain unchanged during real operation of System 1. However, in order to discuss various aspects of System 1 with a manageable number of ESLs, different hardware addresses are sometimes assigned to the ESLs of System 1 from figure to figure, or individual or multiple ESLs are omitted from the discussion.

[0076] For the Figure 5 The hardware address of the first ESL is 7 Hex B2:00:01:00, the second ESL is 8 Hex B2:00:01:01, and the third ESL is 9 Hex B2:00:02:00. The fourth ESL, 10, is ignored.

[0077] For the Figure 6 The hardware addresses of the first ESL are 7 Hex B2:00:01:00, the second ESL is 8 Hex B2:00:02:00, and the third ESL is 9 Hex B2:00:03:00. The fourth ESL, 10, is ignored.

[0078] For the Figure 7 The hardware address of the first ESL 7 is Hex B2:00:01:00. The remaining three ESLs 8 - 10 are ignored.

[0079] For the Figure 8 The hardware addresses of the first ESL are 7 Hex B2:00:01:00, the second ESL is 8 Hex B2:00:01:01, the third ESL is 9 Hex B2:00:02:01 and the fourth ESL is 10 Hex B2:00:03:01.

[0080] In System 1, the least significant byte B0 of the respective ESL 7-10 is used to identify a time slot occurring within the time slot communication process, which is intended for the respective ESL 7-10. With the exception of the least significant byte B0, the remaining three bytes B1-B3 of the hardware address are used to individually address an ESL 7-10 in the time slot Z1...ZN designated for the respective ESL.

[0081] In the Fig. 5It is shown that the first ESL 7 is in the more synchronous state. It awakens from its sleep state S at a first wake-up time TA1 and changes to its ready-to-receive active state E with a relatively short lead time DV before an expected occurrence of a synchronization data signal SD. It receives the synchronization data signal SD during a reception period DE with the first time slot symbol ZS1 (Hex 00). By comparing the least significant byte B0 of its hardware address (Hex 00) with the received time slot symbol ZS1, it determines that the first time slot Z1 intended for the first ESL 7 is indicated (matching the bytes to be compared: B0 of the hardware address and the first time slot symbol ZS1).Retains the parameters of the time control stage 33 used to control wake-up for the wake-up in the subsequent time slot cycle for the purpose of defining the new wake-up time and switches back to the sleep state S with a relatively short lag time DN. After the specified sleep state dwell time DR has elapsed, it wakes up as scheduled at the new (second) wake-up time TA2 with the aforementioned lead time VD before the renewed start of the first time slot cycle Z1. The same applies analogously to the second ESL 8, which, like the first ESL 7, is in the synchronous state.

[0082] The third ESL 9 is in the asynchronous state prior to a synchronization time TSY, which is indicated by the dashed arrow 34 running parallel to the time axis. It wakes up at a randomly selected first wake-up time TA1 and changes from its sleep state S to the ready-to-receive active state E. It waits in this state until the next occurrence of the synchronization data signal SD is received, whereby in this case, the second time slot symbol ZS2 (Hex 01) is received.The third ESL 9 recognizes, based on the least significant byte B0 (Hex 00) of its hardware address, that the time slot designated for it in the current time slot cycle already belongs to the past and, consequently, the next time slot with the time slot symbol Hex 00 is not expected until the next time slot cycle. It calculates that the currently detected time slot Z2 is one time slot apart from its original time slot Z1, which is subsequently referred to as the time slot difference. In the third ESL 9, the timing control stage 33 is now programmed such that the new wake-up time TA2, as with an ESL in a synchronous state with the aforementioned lead time DV, occurs before the occurrence of the first time slot Z1 of the subsequent time slot cycle.The expected dwell time DSA in the sleep state S is calculated as follows: sleep state dwell time DR (in the synchronous state) minus the time slot duration DS multiplied by the time slot difference (in this case, the value 1). Thus, the third ESL 9 is back in the synchronous state, which is indicated by the solid-line arrow 35, and switches from the active state E to the sleep state S. After the dwell time DAS has elapsed, it switches back to its active state E at the new wake-up time TA2.

[0083] With the help of the Figure 6AThe individual addressing of ESLs 7–9 and the individual commissioning of these ESLs 7–9 using single time slot commands are discussed. Only the first time slot Z1 is shown, embedded between two synchronization data signals SD. Station 3 embeds address data AD, command data CD, and confirmation time data ZD in the synchronization data signal SD of the first time slot Z1. The first ESL 7 is individually addressed using address data AD Hex B2:00:01, the second ESL 8 is individually addressed using address data AD Hex B2:00:02, and the third ESL 9 is individually addressed using address data AD Hex B2:00:03. Using command data CD, a "PING" command is transmitted to the first ESL 7, a "PING" command to the second ESL 8, and a "SWPAG2" command to the third ESL 9. These instructions are single time slot instructions which are processed immediately after their decoding in the respective ESL 7 - 9 with negligible time expenditure.The two "PING" commands are used to test whether the addressed ESL 7, 8 responds with ACD confirmation data, i.e., whether it exists or is even responding and synchronized. The "SWAPG2" command is used to cause the third ESL 9 to switch from a (first) current memory page to a second memory page, for example, to change the image displayed on display 27, as described in connection with the... Figure 4was discussed. In addition, the synchronization data signal SD transmits a confirmation time for the first ESL 7 by specifying a first idle time period DR1, for the second ESL 8 by specifying a second idle time period DR2, and for the third ESL 9 by specifying a third idle time period DR3. The reference point for the three idle time periods DR1 - DR3 is always the end of the reception time period DE. The data structure transmitted with the help of the synchronization data signal SD at the beginning of the first time slot Z1 is shown in the Fig. 6B visualized.

[0084] Instead of the individual rest periods DR1 - DR3, maximum response times can also be specified, which result from the sum of the respective rest period DR1 - DR3 and the time period for submitting the confirmation data ACD.

[0085] According to the Figure 6Aall three ESLs 7 - 9 recognize that they are synchronous because the first time slot symbol Z1 indicates the time slot assigned to them (least significant byte B0 of the hardware address is Hex 00 for all three ESLs 7 - 9). Checking the address data AD shows that each ESL 7 - 9 is individually addressed (existence of the remaining three bytes B1 - B3 of the respective hardware address in the address data AD). The commands intended for the respective ESL 7 - 9 are decoded and immediately executed, and the individual confirmation data ACD are transmitted to station 3 after the expiration of the individual rest periods DR1 ... DR3 and after the end of the reception period DE. Station 3 is ready to receive the confirmation data ACD during a station reception period SDE.The complete processing of the single time slot commands including the communication of the confirmation data ACD takes place in a first part 36 of the time slot Z1, so that a second part 37 is available for other tasks, such as the processing of multiple time slot commands, whereupon in the . Figures 7 to 8 has been discussed in detail.

[0086] In the Figure 7AThe processing of a multiple time slot command is shown, in which the first ESL 7 receives total data (e.g. relating to an entire image to be displayed or even just one image plane of the image) broken down into three data packets DAT1 - DAT3 from station 3 over three adjacent time slots Z1 - Z3. With the help of the synchronization data signal SD, the first ESL 7 detects its synchronous state and that it is individually addressed (addressee Hex B2:00:01), receives and decodes a "DATA_INIT" command instructing it to receive the three data packets DAT1 - DAT3 in said time slots Z1 - Z3, and at the end of the reception period DE goes into the sleep state S for a first wait period DW1, whereby the first wait period DW1 expires at the end of the first half of the time slot duration DS.At the beginning of the second part 37 of the first time slot Z1, station 3 enters its transmit state T, and the first ESL 7 enters its ready-to-receive active state E, so that it receives the first data packet DAT1 during a data transmission period DT. It then confirms the successful reception using partial confirmation data ACD1 during a confirmation period DA, during which station 3 is also in the receive state E. The confirmation period DA ends before the end of the first time slot Z1. After the confirmation time period DA has expired, the first ESL 7 remains in the sleep state S for a second waiting period DW2, which lasts until the end of the first part 36 of the second (subsequent) time slot Z2. At the beginning of the second part 37 of the second time slot Z2, the station 3 goes into its transmit state T and the first ESL 7 into its ready-to-receive active state E, so that it receives the second data packet DAT2 during a data transmission period DT.The same applies to the third time slot Z3, at the end of which the data transmission is terminated. Each successfully transmitted data packet DAT1 - DAT3 is confirmed using the partial confirmation data ACD1 - ACD3. The data structure transmitted using the synchronization data signal SD at the beginning of the first time slot Z1 is shown in the following figure. Fig. 7B visualized.

[0087] With the help of the Figure 8AA data transmission using a combination of a multiple time slot command and three single time slot commands is discussed. The first ESL 7 uses the synchronization data signal SD to detect its synchronous state (least significant byte B0 of the hardware address is Hex 00) and that it is individually addressed (address data Hex B2:00:01). It receives and decodes a "DATA_INIT" command, which instructs it to receive three data packets DAT1 - DAT3 in the time slots Z1 - Z3. The data structure transmitted using the synchronization data signal SD at the beginning of the first time slot Z1 is shown in the Fig. 8B The data transfer from station 3 to the first ESL 7 is analogous to the discussion of the Figure 7A .

[0088] The three remaining ESLs 8-10 recognize at the beginning of the second time slot that they are synchronized because the second time slot symbol Z2 indicates the time slot assigned to them (least significant byte B0 of the hardware address is Hex 01 for all three ESLs 8-10). Checking the address data AD indicates that each ESL 8-10 is individually addressed (existence of the remaining three bytes B1-B3 of the respective hardware address in the address data AD). The commands assigned to the respective ESL 8-10 are decoded (in this case, three "PING" commands) and immediately executed, and the individual confirmation data ACD are transmitted to station 3 after the individual sleep periods DR1-DR3 have elapsed, as is required for the Figure 6A The data structure transmitted using the synchronization data signal SD at the beginning of the second time slot Z2 is shown in the Fig. 8C visualized.

[0089] As can be clearly seen, the three single-time slot commands and the multiple-time slot command in the second time slot T2 are processed virtually simultaneously with respect to the time unit "time slot," since the first part 36 of the second time slot Z2 is reserved for the single-time slot commands and the second part 37 for the multiple-time slot commands for the respective data communication. However, the assignment of the respective command type to the parts of the time slot 36 and 37 can also be reversed.

[0090] Finally, it should be noted once again that the figures described in detail above are merely exemplary embodiments that can be modified in a variety of ways by those skilled in the art without departing from the scope of the invention. For the sake of completeness, it should also be noted that the use of the indefinite articles "a" or "an" does not exclude the possibility that the relevant features may be present multiple times.

Claims

1. System (1), comprising - a communication station (3, 4) for communicating with a number of radio tags (7-14) in a time slot communication procedure, in which a number of time slots (Zl-ZN) per time slot cycle in a repeating sequence are available for communication, and each time slot (Zl-ZN) is characterized by a unique time slot symbol (ZS1-ZSN), wherein + the communication station is designed to send out a synchronization data signal (SD) comprising the time slot symbol (Zl-ZN) for the currently present time slot (Zl-ZN), and - a radio tag (7-14), the radio tag (7-14) being designed: + for changing from a sleep state (S) into an active state (E) at a wakeup instant (TA1), and + for receiving the synchronization data signal (SD) in the active state (E) and, + if the received time slot symbol (ZS1-ZSN) indicates a time slot (Zl-ZN) intended for it, for defining a new wakeup instant (TA2) corresponding to the next occurrence of the time slot (Zl-ZN) intended for it in a time slot cycle that follows the currently present time slot cycle, wherein + the communication station (3, 4) is designed to embed command data (CD) into the synchronization data signal (SD), with which a command can be transmitted to a radio tag (7-14) in a time slot (Zl-ZN) intended for said radio tag (7-14), and + the radio tag (7-14), if the received time slot symbol (ZS1-ZSN) indicates a time slot (Zl-ZN) intended for it, is designed to evaluate the synchronization data signal (SD) with respect to the contained command data (CD) and execute the command, wherein + the radio tag (7-14) is designed to execute a command as a multiple time slot command over multiple time slots (Zl-ZN), and wherein + the communication station (3, 4) is designed to use a command for instructing a radio tag (7-14) about another wakeup instant in the time slot (Z1-ZN) intended for it, wherein the radio tag (7-14) is designed to process this command and to switch into the active state (E) at the other wakeup instant imposed by the communication station (3, 4), so that the radio tag (7-14) is available for data transmission with the communication station (3, 4) in a time slot (Zl-ZN) corresponding to the other wakeup instant.

2. System (1) according to claim 1, wherein - the communication station (3, 4) is designed to embed address data (AD) into the synchronization data signal (SD), which can be used to individually address a number of radio tags (7-14) per time slot (Zl-ZN) intended for said radio tags (7-14), and - the radio tag (7-14), if the received time slot symbol (ZS1-ZSN) indicates a time slot (Zl-ZN) intended for it, is designed to evaluate the synchronization data signal (SD) with regard to the contained address data (AD), and to check whether it is individually addressed.

3. System (1) according to claim 2, wherein the radio tag (7- 14) is designed to evaluate the command data (CD) and to execute the command when said command is individually addressed by means of the address data (AD) .

4. System (1) according to any of the preceding claims, wherein - the radio tag (7- 14) is designed to execute a command as a single time slot command, and to conclude the executed command within a single time slot (Zl-ZN) in which the command was received.

5. System (1) according to claim 4, wherein - the radio tag (7-14), on conclusion of the executed command, is designed to generate confirmation data (ACD) and to deliver the confirmation data (ACD) in the time slot (Zl-ZN) in which the command was received.

6. System (1) according to claim 5, wherein - the radio tag (7-14) is designed to deliver the confirmation data (ACD) in a first part (36) of the time slot (Zl-ZN), which is chronologically localized after the synchronization data signal (SD), and leaves an ensuing second part (37) of the time slot (Zl-ZN) untouched prior to the occurrence of the synchronization data signal (SD) of the following time slot (Zl-ZN).

7. System (1) according to claim 5 or 6, when dependent on claim 2, wherein - the radio tag (7-14) is designed, when multiple radio tags (7-14) are addressed by means of the address data (AD), to evaluate not just its own address, but also those of the other addressed radio tag or tags (7-14), and to deliver its confirmation data (ACD) within a time window provided for delivering the confirmation data (ACD) at the instant corresponding to the sequence in the group of addressed radio tags (7-14) ascertained for it by the determined addresses.

8. System (1) according to any of the preceding claims, wherein the multiple time slot command relates to a data transmission from the communication station (3, 4) to the radio tag (7-14), and - the communication station (3, 4) is designed to transmit the overall data divided over multiple time slots (Zl-ZN), wherein one data packet (DAT1-DAT3) per time slot (Zl-ZN) is transmitted as part of the overall data, and the respective time slot (Zl-ZN) uses a second part (37) of the respective time slot (Zl-ZN) adjoining the first part (36) of the respective time slot (Zl-ZN) for data transmission.

9. System (1) according to any of the preceding claims, wherein - the radio tag (7-14) is designed to generate and deliver partial confirmation data (ACD1-ACD3) in each time slot (Z1-Z3) in which the multiple time slot command is executed.

10. System (1) according to claim 9, when dependent on claim 8, wherein - the radio tag (7-14) is designed to deliver the partial confirmation data (ACD1-ACD3) in the said second part (37) subsequent to the received data packet (DAT1-DAT3) and prior to the end of the respective time slot (Zl-ZN).

11. System (1) according to any of claims 5 - 7 or 9 - 10, wherein - the communication station (3, 4) is designed to receive and process the confirmation data (ACD; ACD1-ACD3) in a reception time window (SDE; DA) designated for this purpose.

12. System (1) according to any of claims 3-11, when dependent on claim 2, wherein - the communication station (3, 4) is designed to address a second radio tag (7-14) by means of the address data (AD) for a time slot (Zl-ZN) provided for processing a multiple time slot command by a first radio tag (7-14), and to transmit a single time slot command to the second radio tag (7-14) by means of the command data (CD).

13. System (1) according to any of the preceding claims, wherein the system (1) realizes an electronic price display system, and a display unit (27) of the radio tag (7-14) serves to display product and / or price information, etc.

14. System (1) according to any of the preceding claims, wherein - the communication station (3, 4) is designed to send out the synchronization data signal (SD) at the beginning of the respective time slot (Zl-ZN).