Method for determining time slots in a wireless communication system

Abstract

The invention relates to a method for determining time slots in a wireless communication system in the form of a radio network with synchronization tasks, wherein the communication system comprises a plurality of network subscribers having a transmission functionality, wherein a radio channel provided by the network subscribers is divided, by the time division multiplexing method of time-division multiple access, into individual times slots for sequential data transfer and each time slot can be occupied by a network subscriber, wherein each network subscriber having transmission functionality comprises a slot selector by means of which the network subscriber accesses the shared radio channel with temporal coordination and wherein, proceeding from a starting time slot, the distance of free time slots from an occupied time slot is counted in a first direction in a first counting loop and the distance of each time slot is stored in a first data structure and subsequently the distance of free time slots from an occupied time slot is counted in a second direction, which is opposite to the first direction, in a second counting loop and each distance is stored, in association with the time slot, in a second data structure, wherein, in the case of an occupied time slot, the time loops are reset to a value of 0, and wherein the distances of the individual time slots stored in the first and second data structures are multiplied by each other and are stored, as a product, in a third data structure, and wherein a maximum value in the third data structure represents the greatest possible distance between two occupied time slots and the time slot having the greatest possible distance is output as the best possible time slot for the data transfer of the network subscriber.

Description

[0001] Method for determining time slots in a wireless communication system

[0002] The invention relates to a method for determining time slots in a wireless communication system, in particular in a radio network with synchronization tasks according to the preamble of the first patent claim.

[0003] For radio positioning in buildings, especially indoors, networks for locating mobile devices are known. They use ultra-wideband (UWB) technology for communication between individual network nodes. Such positioning networks typically consist of several stationary reference stations, also called beacons or anchors, which form the infrastructure of an indoor positioning environment. Within such an infrastructure, the position of mobile objects, also called tags, such as tablets or mobile phones, can be determined.

[0004] The radio-based data transmission between the anchors and also between anchors and tags usually takes place via radio over a fixed transmission channel in the air.

[0005] Various multiplexing methods exist to regulate anchor access to the single available transmission channel. A frequently used method is TDMA (time division multiple access).

[0006] Here, the time is divided into several time slots, whereby it is determined in which time slot an anchor is allowed to transmit.

[0007] Anchors can be assigned to time slots in a variety of ways. For example, time slots can be manually defined prior to installation, although this is impractical for large installations with many anchors. Furthermore, manual configuration makes the system inflexible when it comes to adding or removing anchors during use.

[0008] A very simple automatic option is the random allocation of a time slot. This involves randomly selecting a time slot and then checking whether it is free. If many of the available slots are already occupied by anchors, the random allocation can often fail, consuming a lot of computing time. Therefore, a more systematic approach is necessary. Transmitted UWB signals are received and processed in the receivers. This process requires a certain amount of time for processing in both the transmitter and the receiver. To minimize the load, the available transmission channel should be used as evenly as possible. The occupied time slots within the transmission channel should therefore be as far apart as possible. This is not possible with random allocation of time slots. In addition to the lack of flexibility, this would also be a further disadvantage with manual allocation in terms of practicality.

[0009] Publication WO 98 / 23106 A2 describes a method and a base station system for configuring a radio interface between a mobile station and a base station of a time-division multiplexed mobile radio system for packet data transmission. In this case, several time slots in the downlink direction are combined into a signaling block for several mobile stations. However, this does not ensure an optimal spacing between two time slots, which can lead to reduced transmission performance and interference with the secondary channels.

[0010] WO 99 / 23844 A2 discloses a method and device for transmitting data packets. Data transmission occurs using time-division multiplexing, with the base station transmitting the highest supported data rate to a mobile station in each time slot.

[0011] Another time-division multiplexing method is known from the document DE 696 20 781 T2.

[0012] A method for selecting the best receiving antenna from two or more receiving antennas is known from DE 691 01 733 T2. A time-division multiplex radio communication system containing a mobile radio station is described, with a time slot designated for each station. The received signal strength for each antenna is measured during a time slot immediately preceding the time slot designated for the station in question, and the antenna is selected based on these signal strengths. Measuring and evaluating the signal strength requires increased computing power and time.

[0013] From the publication WO 00 / 74428 A1 a method and a device for

[0014] Allocation of radio resources is known, which is intended to provide a user with consecutive time slots in a cellular radio system with minimized signal load in the system. Available time slots are allocated by searching for free time slots within a frame, with time slots being regrouped to obtain adjacent free time slots. For this purpose, the distance to the beginning or end of a frame is recorded and evaluated for each time slot. Such a method requires powerful hardware to cope with the increased computational effort. Such a solution is not feasible on battery-operated microdevices.

[0015] The object of the invention is to develop a method for determining time slots in a wireless communication system. This method assigns a communication device to a time slot, ensuring optimal distribution of the communication devices across the available time slots with the least possible computational effort. Furthermore, peak loads during data processing and communication pauses are to be reduced or avoided.

[0016] This problem is solved with the features of the first patent claim.

[0017] Advantageous embodiments arise from the subclaims.

[0018] The method relates to the determination of time slots in a wireless communication system, wherein the communication system has a plurality of network participants with a transmission functionality, wherein a radio channel provided by the network participants is divided into individual time slots for sequential data transmission by means of the time division multiple access method, and each time slot can be occupied by a network participant. According to the invention, each network participant with transmission functionality has a slot selector, by means of which the network participant accesses the divided radio channel in a time-coordinated manner, wherein, starting from a start time slot, the distance from free time slots to an occupied time slot is counted in a first direction in a first counting loop, and the respective distance of each time slot is stored in a first data structure.Subsequently, in a second counting loop, the distance from free time slots to an occupied time slot is counted in a second direction opposite to the first direction, and the respective distance is assigned to the time slot and stored in a second data structure. When a time slot is occupied, the counting loops are reset to a value of 0. The distances of the individual time slots stored in the first and second data structures are multiplied and stored as a product in a third data structure. A maximum value in the third data structure represents the greatest possible distance between two occupied time slots. The time slot with the greatest possible distance is output as the best possible time slot for data transmission by a network participant.

[0019] In an advantageous embodiment, the network participants are stationary reference stations in the form of anchors and / or mobile objects in the form of tags with transmission functionality, wherein each anchor and / or tag has its own time slot as the transmission time and wherein the anchors and / or tags select a free time slot.

[0020] In a further advantageous embodiment, the communication system comprises additional network participants without a slot selector in the form of tags without transmit functionality. The slot selector is not necessary with this tag configuration, since these tags do not actively access the channel.

[0021] In a first embodiment, the starting time slot for counting is randomly selected, but can also be predetermined. The counting loop is continuous and restarts from a previously defined initial value for each occupied time slot. In one embodiment of the method, an occupied time slot is assigned an initial value of 0, and the adjacent time slot is assigned a 1. If the counting loop begins with a free time slot, this time slot is assigned a 1 as the initial value. The value of the numerical sequence increases by 1 with each time slot until an occupied time slot is determined. This occupied time slot is assigned a 0, which restarts the counting from the beginning. This applies to both the first counting loop and the second counting loop, which counts in the opposite direction.

[0022] Preferably, an anchor and / or tag selects the time slot with the maximum value in the third data structure. If multiple maximum values ​​are determined in the third data structure, a time slot with a maximum value in the third data structure can be randomly selected. This ensures time-balanced network communication by allocating new slots with the greatest possible distance from already occupied slots.

[0023] The first, second, and third data structures can be integer arrays. Preferably, a 0 is assigned to an occupied time slot in the data structure. Two variables are used to calculate the distances: the first variable, n, specifies the maximum number of time slots, and the second variable, M, specifies the positions of the already occupied time slots. The third data structure stores the calculated distance of each time slot to an occupied time slot directly or indirectly adjacent to it.

[0024] By specifying the occupied time slots, it is possible to reserve a simple pre-allocation of non-vacant time slots, for example for system services, without any procedural adjustments.

[0025] Advantageously, the number of time slots specified by the variable n is divided into periodically recurring sections in the form of frames, with each frame consisting of n time slots. In one embodiment, the first counting loop can start at the beginning of the frame and count upwards toward the end of the frame. The second counting loop counts from the end of the frame toward the beginning. Upon detection of an occupied time slot, the counting loop is set to 0.

[0026] This method allows for the use of battery-powered microdevices with low memory and computational complexity. The computational methods require only simple, energy- and memory-efficient calculations.

[0027] Furthermore, a balanced memory and processing load in the nodes is achieved, as well as the avoidance of long communication pauses during network synchronization. This is an added value, especially with regard to UWB networks.

[0028] The method according to the invention is suitable for any radio network with synchronization tasks. The method can particularly preferably be used in UWB networks for locating mobile devices.

[0029] The method according to the invention achieves time-balanced communication while avoiding load peaks during data processing in UWB networks. By avoiding long communication pauses, a high level of synchronization fidelity is achieved and maintained within the network. This is an important aspect when using UWB networks for locating mobile devices in particular.

[0030] The invention is explained in more detail below using an exemplary embodiment and the accompanying drawings. They show:

[0031] Figure 1 shows an illustration of an exemplary time slot allocation and with a first counting loop with associated diagram, Figure 2 shows a diagram according to Figure 1,

[0032] Figure 3 shows an example of the time slot allocation and a second

[0033] Counting loop with associated diagram, Figure 4 a diagram according to Figure 3,

[0034] Figure 5 the multiplication of the first and second data structure

[0035] Figure 6 is a diagram according to Figure 5.

[0036] Figure 1 shows an example of the allocation of time slots in a radio network with synchronization tasks, in particular a positioning network, within a frame m with a number of n = 8 (0 to 7) time slots zn. According to Figure 1, time slot zO is allocated an anchor A1, and time slot z5 is allocated an anchor A2. Time slot zO is defined as the start slot. The distance between the allocated time slots zn is counted by means of a counting loop s1 in a first direction from slot zO toward slot z7, with each distance being stored in a first data structure d1. Figure 1 shows that when a time slot (zO, z5) is allocated, counting loop s1 stores a 0 in data structure d1. Subsequently, counting loop s1 is incremented by 1 for each free time slot.

[0037] The distances are shown graphically in the diagram in Figure 2. According to the exemplary embodiment, time slot zO has the distance 0 stored in data structure d1, since this time slot zO is occupied by anchor A1. According to the first counting loop s1, time slot z1 has the distance 1 to anchor A1, time slot z2 has the distance 2, time slot z3 has the distance 3 and time slot z4 has the distance 4. The distances are stored using an array of type integer. Time slot z5 is occupied by anchor A2, which means that the distance is set to 0 and stored in the first data structure d1. Subsequently, counting is carried out again for time slots z6 and z7 and the distance 1 or 2 is determined and saved.

[0038] Figure 3 shows a representation of the occupancy of time slots zn according to Figure 1, with counting in the opposite direction using the second counting loop s2. The determined intervals are stored in a second data structure d2. The starting time slot is defined as time slot z7. This results in counting beginning at time slot z7 with an interval of 1. Time slot z6 has an interval of 2. Since time slot z5 is occupied by anchor A2, the interval of this time slot is set to 0.

[0039] Subsequently, starting from time slot z5, the distance for time slots z4 to zO is determined in the counting direction of counting loop s2, whereby time slot zO is occupied by armature A1 and thus sets counting loop s2 to 0.

[0040] The distances stored in the second data structure d2 result in the diagram shown in Figure 4. The individual time slots zn are shown horizontally, and the distance to the next occupied time slot zn is shown vertically. The time slots occupied by anchors A1 and A2 are represented by a 0 in the diagram.

[0041] According to the invention, the first and second data structures d1 and d2 are further processed to determine the optimal time slot according to Figure 5.

[0042] Figure 5 shows frame m according to Figures 1 to 4 with the associated first and second data structures d1, d2. Frame m consists of time slots zn (n=0 to n=7). The data structures d1, d2, which were previously determined using the first and second counting loops s1, s2, are multiplied with one another, with the product of the values ​​of the first and second data structures d1, d2 of the individual time slots being saved in a third data structure d3. This results in a 0 in the third data structure d3 for the occupied time slots z0 and z5 with the anchors A1 and A2.

[0043] The product of the distances results in a maximum of 6 for time slots z2 and z3. The determined products of the time slot multiplications are shown in Figure 6. This shows that the optimal available time slot for a new anchor is time slot z2 or z3. Since time slots z2 and z3 have the same value in the third data structure, a random selection of time slot z2 or z3 can be performed by a new anchor or tag.

[0044] A1 first anchor

[0045] A2 second anchor d1 first data structure d2 second data structure d3 third data structure m frame n number of time slots per frame s1 first counting loop s2 second counting loop zn time slot zO time slot 0 z1 time slot 1 z2 time slot 2 z3 time slot 3 z4 time slot 4 z5 time slot 5 z6 time slot 6 z7 time slot 7

Claims

Patent claims 1 . A method for determining time slots in a wireless communication system in the form of a radio network with synchronization tasks, wherein the communication system has a plurality of network participants with a transmission functionality, wherein a radio channel provided by the network participants is divided into individual time slots (zn) for sequential data transmission by means of a time division multiple access method, and each time slot (zn) can be occupied by a network participant, wherein each network participant with transmission functionality has a slot selector by means of which the network participant accesses the divided radio channel in a time-coordinated manner, characterized in thatthat starting from a start time slot, the distance between free time slots (zn) and an occupied time slot (zn) is counted in a first direction in a first counting loop (s 1 ) and the respective distance of each time slot (zn) is stored in a first data structure (d1), and that subsequently, in a second counting loop (s2), the distance between free time slots (zn) and an occupied time slot (zn) is counted in a second direction opposite to the first direction, and the respective distance assigned to the time slot (zn) is stored in a second data structure (d2), wherein, in the case of an occupied time slot, the counting loops (s1, s2) are reset to a value of 0, and that the distances of the individual time slots (zn) stored in the first and second data structures (d1, d2) are multiplied with one another and stored as a product in a third data structure (d3),where a maximum value in the third data structure (d3) represents the greatest possible distance between two occupied time slots (zn) and the time slot (zn) with the greatest possible distance is output as the best possible time slot (zn) for data transmission of the network participant., 2. Method according to claim 1, characterized in that the network participants are stationary reference stations in the form of anchors (A1, A2) and / or mobile objects in the form of tags with transmission functionality, wherein each anchor (A1, A2) and / or tag has its own time slot (zn) as the transmission time and that the anchors (A1, A2) and / or tags select a free time slot (zn).

3. Method according to claim 1 or 2, characterized in that the communication system has network participants without a slot selector in the form of tags without transmission functionality.

4. Method according to claim 1, characterized in that the start time slot for the beginning of the counting is chosen randomly.

5. Method according to claim 1, characterized in that the start time slot for the beginning of the counting is determined in advance.

6. Method according to one of the preceding claims, characterized in that an anchor (A1, A2) and / or tag selects the time slot (zn) which has the maximum value in the third data structure (d3).

7. The method according to claim 6, characterized in that if several maximum values ​​are determined in the third data structure (d3), a random selection of a time slot (zn) with a maximum value in the third data structure (d3) takes place.

8. Method according to one of the preceding claims, characterized in that the first, second and third data structures (d1, d2, d3) are arrays of the integer type.

9. Method according to one of the preceding claims, characterized in that a 0 is assigned to an occupied time slot (zn) in the data structure.

10. Method according to one of the preceding claims, characterized in that the time slots (zn) are divided into periodically recurring sections in the form of frames (m).

11. Method according to one of the preceding claims, characterized in that the radio network with synchronization tasks is a UWB network.

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