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, 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 a time division multiple access method and each time slot 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 shared radio channel in a time-coordinated manner, and wherein, starting from a start time slot, the distance between free time slots and 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, and that subsequently, in a second counting loop, the distance between free time slots and an occupied time slot is counted in a second direction opposite to the first direction, and the respective distance is stored in a second data structure associated with the time slot, wherein, when a time slot is occupied, the counting loops are reset, and that the distances of the individual time slots stored in the first and second data structures are multiplied with one another and stored as a product in a third data structure,where a maximum value in the third data structure represents the greatest possible distance between two occupied time slots and the time slot with the greatest possible distance is output as the best possible time slot for data transmission of the network participant.

Description

[0001] The invention relates to a method for determining time slots in a wireless communication system according to the preamble of the first patent claim.

[0002] 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 moving objects, also called tags, such as tablets or mobile phones, can be determined.

[0003] 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.

[0004] There are various multiplexing methods for controlling anchor access to the single available transmission channel. A frequently used method is TDMA (time division multiple access).

[0005] Here, the time is divided into several time slots, whereby it is determined in which time slot an anchor is allowed to transmit.

[0006] 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 not practical for large installations with many anchors. Furthermore, manual configuration makes the system inflexible when it comes to adding or removing anchors during use.

[0007] A very simple automated approach is to randomly assign a time slot. This involves randomly selecting a time slot and then checking whether it's free. If many of the available slots are already occupied by anchors, the random allocation can often fail, consuming significant computing time. Therefore, a more systematic approach is necessary.

[0008] Transmitted UWB signals are received and processed in the receivers. This process requires a certain amount of processing time 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. Even with manual allocation, this would be a further disadvantage in terms of practicality, in addition to the lack of flexibility.

[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 power 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 the document 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] WO 00 / 74428 A1 discloses a method and apparatus for allocating radio resources, which is intended to provide a user with consecutive time slots in a cellular radio system with minimized signal load in the system. To this end, 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. Such a method requires powerful hardware to cope with the increased computational effort. Such a solution is not feasible on battery-operated microdevices.

[0014] The object of the invention is to develop a method for determining time slots in a wireless communication system, which assumes the assignment of a communication device to a time slot, whereby an optimal distribution of the communication devices to the available time slots is to take place with the lowest possible computational effort.

[0015] This problem is solved by the features of the first patent claim.

[0016] Advantageous embodiments result from the subclaims.

[0017] The method relates to the determination of time slots in a wireless communication system, wherein the communication system is designed in the form of a UWB network and 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 using 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. 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 0 such that a 0 is assigned to an occupied time slot in the respective data structure. The distances of the individual time slots stored in the first and second data structures are multiplied with one another 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.

[0018] 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.

[0019] 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 in this embodiment of the tag, since these tags do not actively access the channel.

[0020] The start time slot for the beginning of the counting is chosen randomly in an initial design, but can also be determined in advance.

[0021] Preferably, an anchor and / or tag selects the time slot that has 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.

[0022] 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.

[0023] 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.

[0024] Advantageously, the number of time slots specified by the variable n is divided into periodically recurring sections in the form of frames, each frame consisting of n time slots.

[0025] The present 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.

[0026] Furthermore, a balanced memory and processing load in the nodes is achieved and long communication pauses during network synchronization are avoided.

[0027] The method according to the invention is suitable for any radio network. In particular, the method can be used advantageously in UWB networks.

[0028] The invention is explained in more detail below using an embodiment and associated drawings.

[0029] They show: Fig. 1 a representation of an exemplary time slot assignment and with a first counting loop with associated diagram, Fig. 2 a diagram according to Fig. 1, Fig. 3 a representation of the exemplary time slot assignment and a second counting loop with associated diagram, Fig. 4 a diagram according to Fig. 3, Fig. 5 the multiplication of the first and second data structure Fig. 6 a diagram according to Fig. 5.

[0030] Fig. 1 shows an exemplary allocation of time slots within a frame m with a number of n = 8 (0 to 7) time slots zn. According to Fig. 1, time slot z0 is occupied by anchor A1, and time slot z5 is occupied by anchor A2. Time slot z0 is defined as the starting slot. The distance between the occupied time slots zn is counted by a counting loop s1 in a first direction from slot z0 toward slot z7, with each distance being stored in a first data structure d1.

[0031] The distances are shown in the diagram according to Fig. 2. According to the exemplary embodiment, time slot z0 has the distance 0 stored in data structure d1, since this time slot z0 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 integer array. Time slot z5 is occupied by anchor A2, which sets the distance to 0 and stores it 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 stored.

[0032] The Fig. 3 shows a representation of the occupancy of the time slots zn according to Fig. 1 with a count in the opposite direction using the second counting loop s2. The determined distances are stored in a second data structure d2. The start time slot is defined by the time slot z7.

[0033] This results in counting starting from time slot z7 with a distance of 1. Time slot z6 has a distance of 2. Since time slot z5 is occupied by anchor A2, the distance of this time slot is set to 0.

[0034] Subsequently, starting from time slot z5, the distance for time slots z4 to z0 is determined in the counting direction of the counting loop s2, whereby time slot z0 is occupied by armature A1 and thus sets the counting loop s2 to 0.

[0035] From the distances stored in the second data structure d2, the diagram results according to Fig. 4. The individual time slots zn are shown horizontally, and the distance to the next occupied time slot zn is indicated vertically. The time slots occupied by anchors A1 and A2 are represented by a 0 in the diagram.

[0036] Fig. 5 shows the frame m according to the Fig. 1 to 4 with the corresponding first and second data structures d1, d2. Frame m consists of the 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 each other, 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.

[0037] The product of the distances results in a maximum of 6 for the time slots z2 and z3. The determined products of the multiplications of the time slots are shown in the Fig. 6 shown.

[0038] This means 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. List of reference symbols A1 first anchor 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 z0 Time slot 0 z1 Time slot 1 z2 time slot 2 z3 time slot 3 z4 Time Slot 4 z5 Zeitslot 5 z6 Zeitslot 6 z7 Zeitslot 7

Claims

[1] Method for determining time slots in a wireless communication system, wherein the communication system is designed in the form of a UWB network and 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 shared radio channel in a time-coordinated manner, characterized bythat, 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 (s1), 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 is stored in a second data structure (d2) associated with the time slot (zn), wherein, in the case of an occupied time slot, the counting loops (s1, s2) are reset to 0 in such a way that a 0 is assigned to an occupied time slot in the respective data structure (d1, d2), and that the distances of the individual time slots (zn) stored in the first and second data structures (d1, d2) are compared with one another multiplied 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 by 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, whereby 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 by that the communication system has network participants without a slot selector in the form of tags without transmit functionality. [4] Method according to claim 1, characterized by that the start time slot for the beginning of the counting is chosen randomly. [5] Method according to claim 1, characterized by 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 by 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] Method according to claim 6, characterized by that if several maximum values ​​are determined in the third data structure (d3), a time slot (zn) with a maximum value in the third data structure (d3) is randomly selected. [8] Method according to one of the preceding claims, characterized by that the first, second and third data structures (d1, d2, d3) are arrays of type integer. [9] Method according to one of the preceding claims, characterized by that the time slots (zn) are divided into periodically recurring sections in the form of frames (m).

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