Transmission method

Abstract

A transmission method with a plurality of transmitters and one receiver, wherein the transmission takes place in frames, each frame having a number N of time slots, comprising the steps: e) Sending multiple data packets from more than one sender to the receiver within a frame, where the multiple data packets from the one sender within the one frame are repetitions; f) Receipt of the data packets by the recipient; g) Identifying a data packet part that was received individually within a time slot and decoding the identified data packet part; h) Removing repetitions of the identified data packet portion within the frame; where in at least one frame the start of at least one data packet does not coincide with the start of a time slot.

Description

[0001] The present invention relates to a transmission method, and in particular a slotted grant-free Aloha transmission method. Furthermore, the present invention relates to a system for implementing such a transmission method.

[0002] With increasing demands on the availability of wireless transmissions, the requirement for receivers to simultaneously process transmissions from a large number of transmitters also increases. In many applications, a single receiver thus faces a multitude of transmitters sending data packets to the receiver via a wireless medium. In particular, there is no coordination between the transmitters, and the transmissions follow the grant-free access paradigm, allowing each transmitter to autonomously decide whether to send data within a MAC (Medium Access Control) frame. Specifically, a slotted random access protocol is used, so that (i) Sender transmits multiple replicas or repetitions of their data packets in the frame, (ii) time slot and data packets have the same duration and (iii) when a data packet is decoded at the receiver, all replicas of that data packet are removed to suppress interference.

[0003] The state of the art for grant-free Aloha transmissions with replicas is divided into slotted and unslotted approaches. Slotted Aloha schemes consist of dividing the time dimension into units called time slots, which are as long as the packet duration. A predefined number of time slots defines a frame. Examples of slotted schemes include Contention Resolution Diversity Slotted Aloha (CRDSA), which can be considered a special case of the Irregular Repetition Slotted Aloha (IRSA) scheme. In CRDSA, the number of replicas to be sent by each sender is fixed a priori, whereas in IRSA, each sender transmits a number of replicas according to a predefined distribution. The senders are time-synchronized, and each sender randomly selects the time slots within the frame in which the data packet to be transmitted and its replicas are placed. Transmissions occur only at the beginning of each time slot.Each data packet contains information about the location of all other copies / replicas. With this approach, data packet collisions occur at the receiver when two or more packets from different senders are received in the same time slot. If the receiver can capture a data packet in a collision-free time slot, it can be decoded, and the copies / replicas of the data packet from the received signal are deleted or subtracted. The receiver iteratively searches for collision-free time slots or replicates that can be captured for decoding and applies successive interference deletion.

[0004] One of the main limitations of the slotted random access protocol approach is that each sender transmits its data packets and replicas only at the beginning of one of the time slots, with the duration of the time slot corresponding to the packet duration. This conventional frame scheme, where data packets are only transmitted at the beginning of time slots, leads to complete overlap of interfering replicas. This can result in inefficient resource utilization and suboptimal system performance, especially since data packets that cannot be decoded due to the overlap must be retransmitted in a subsequent frame.

[0005] The state of the art is known from: - CLAZZER, Federico; KISSLING, Christian; MARCHESE, Mario: Enhancing contention resolution aloha using combining techniques. In: IEEE Transactions on Communications (T-COMM), Vol. 66, 2018, H. 6, pp. 2576-2587. ISSN 1558-0857 (E); 0090-6778 (P). https: / / doi.org / 10.1109 / TCOMM.2017.2759264 - DE GAUDENZI, Riccardo [et al.]: Asynchronous contention resolution diversity ALOHA: Making CRDSA truly asynchronous. In: IEEE Transactions on Wireless Communications, Vol. 13, 2014, H. 11, pp. 6193-6206. ISSN 1536-1276. https: / / doi.org / 10. 1109 / TWC.2014.2334620 - DE 10 2018 204 730 B3

[0006] The object of the present invention is to provide a transmission method with increased transmission efficiency.

[0007] The problem is solved by a transmission method according to claim 1 and a system for implementing such a transmission method according to claim 15.

[0008] The transmission method of the present invention serves to transmit data packets from a plurality of senders to a single, common receiver. This is, in particular, a slotted Aloha transmission protocol, wherein the transmission takes place in frames. Each frame has a number N of time slots, the time slots dividing the transmission time or the time axis into discrete segments. In particular, the length of the frames is identical. Likewise, the length of the individual time slots and the number N of time slots are constant for each frame. According to the invention, the method comprises the following steps: a) Sending multiple data packets from more than one sender to the receiver within a frame, where the multiple data packets from the one sender within the one frame are repetitions; b) Receiving the data packets by the recipient; c) Identifying a data packet part that was received individually and decoding the identified data packet part; d) Removing repetitions of the identified data packet portion within the frame.

[0009] According to the invention, at least one data packet in at least one frame of the transmission does not begin with the start of a time slot. In particular, the start of the data packet transmission in the at least one frame is independent of the start of the time slot. This increases the number of times within a frame at which a data packet transmission can begin, so that with a random distribution of data packets from multiple senders within a frame, there is statistically less overlap, and thus non-overlapping or collision-free data packet segments can be identified, which are then decoded by the receiver. This increases the probability of being able to decode more data packets per frame, especially under high load, i.e., with many simultaneous senders. Retransmission of the same data packet can thus be avoided, and efficient transmission can be ensured.

[0010] In this context, the data packet components can be either a section of the received data packet or the entire data packet. Transmission occurs primarily via wireless or radio transmission. Each sender can transmit exactly one data packet per frame to the receiver, with the data packets from a single sender within a frame being repetitions. This means the information to be transmitted in the frame can be decoded by the receiver by decoding exactly one data packet. All other data packets in the same frame from the same sender contain only the same information, are redundant, and can be ignored by the receiver.

[0011] This means that the data packet part is received individually, that the data packet part is collision-free within the frame, or without temporal overlap with a data packet part from another sender.

[0012] Preferably, steps c) and d) are repeated until no individually received data packet parts can be identified in the frame. This iteratively identifies all data packet parts that can be decoded because they are collision-free within a single time slot of the respective frame. Remaining data packet parts in the frame that cannot be decoded are discarded by the receiver and must be retransmitted by the sender in a subsequent frame.

[0013] Preferably, the transmitters are synchronized. In particular, the transmitters are time-slot synchronized.

[0014] Preferably, the senders transmit the data packets randomly within the frame. In particular, the possible start times for the transmission of a data packet within the frame are chosen randomly by the respective senders.

[0015] Preferably, each data packet contains information about the location of its repetitions in the respective frame.

[0016] Preferably, the transfer method is an Aloha transfer method, and in particular a grant-free slotted Aloha transfer method. This can preferably be a CRDSA transfer method or an IRSA transfer method.

[0017] Preferably, in more than one frame, and especially in every frame, the start of at least one data packet does not coincide with the start of a time slot. This increases the number of possible start times for the respective data packets in more than one frame, thereby reducing overlap or collisions of the data packet components within the corresponding frame.

[0018] Preferably, depending on the number of data packets transmitted within a frame, the start of at least one data packet may not coincide with the start of a time slot. This allows, particularly when high utilization is required (i.e., a large number of simultaneous senders and thus a large number of data packets within a frame), the number of possible start times for data packet transmission within the frame to be increased. Therefore, especially under increased load, it is possible to dynamically deviate from the usual grant-free slotted Aloha transmission method and increase the number of possible start times within the frame for data packet transmission. In particular, the number of data packets transmitted within a previous frame can be used as a basis for this.

[0019] Preferably, S denotes the number of possible start times of a data packet within a frame, where S < N or S > N is chosen. In particular, S = N denotes the case of conventional grant-free slotted Aloha transmission methods, since in this case the number of possible start times of a data packet within a frame exactly matches the number of time slots. S can also be understood as the number of sub-time slots (S > N) or super-time slots (SN). <N) innerhalb des Frames. Der gleiche Sender kann nicht innerhalb desselben Subzeitslots bzw. Superzeitslots seine Datenpakete senden. Für den Fall S<N kann insbesondere eine weitere Randomisierung erfolgen hinsichtlich dem Startzeitpunkt einer Übertragung innerhalb dem jeweiligen Superzeitslot.

[0020] Preferably, S is given by: S=αβN, where α denotes a slot coefficient and β a slot ratio. S ∈ ℕ. In particular, β denotes the ratio between the length of the frame's time slot and the selected sub-time slots or super-time slots. α and β are known for all senders and the receiver.

[0021] Preferably, a data packet is reconstructed from multiple repetitions. In particular, a data packet is constructed by combining the decoded, identified data packet parts, wherein the data packet parts originate from different data packets of the same sender within the same frame. For example, if two data packet parts from the same sender are identified and decoded within a frame, the entire data packet can be recombined from the two decoded, identified data packet parts. The individual data packet parts can be present at different times and, in particular, not consecutively within the frame.

[0022] Preferably, the data packet and its repetition do not overlap in time within a frame.

[0023] Preferably, the duration of the data packet and its repetition correspond to the duration of a time slot. Even if the start of a data packet does not coincide with the start of a particular time slot, it is still preferred that the length of the data packet corresponds to the duration of the time slot.

[0024] In a further aspect of the present invention, a system is provided comprising a receiver and a plurality of transmitters, wherein the system is configured to carry out the transmission method as described above.

[0025] The invention will now be explained in more detail with reference to preferred embodiments and the accompanying figures.

[0026] They show: Fig. 1 a system according to the present invention, Fig. 2 a flowchart of the transmission method according to the present invention, Fig. 3 a schematic representation of the transmission method according to the present invention and Fig. 4 A schematic representation of the transmission method according to the state of the art.

[0027] The following refers to Fig. 1. Fig. Figure 1 shows a system 100 with a large number of transmitters 120. In the example of the Fig. Figure 1 shows the transmitters 120 as user terminals. However, the present invention is not limited to this, so that all other possible transmitters, such as IoT devices, vehicles, or the like, can also be considered. All transmitters 120 wirelessly transmit data to a common receiver 110. This receiver can be a base station, an access point, or the like.

[0028] Fig. Figure 2 shows the schematic sequence of the procedure for transmitting data from a multitude of senders 120 to a common receiver 110 in a system according to the Fig. 1. Transmission occurs in frames, each frame having a number N of time slots. Preferably, the transmission method is an Aloha transmission method, and in particular a grant-free slotted Aloha transmission method. This can preferably be a CRDSA transmission method or an IRSA transmission method.

[0029] In step S01, several data packets from more than one sender are sent to the receiver within one frame, with the multiple data packets from the one sender within the one frame being repetitions.

[0030] In step S02, the data packets are received by the receiver.

[0031] In step S03, at least one data packet part is identified, in particular by the receiver, which were received individually, and the identified data packet part is decoded, in particular by the receiver.

[0032] In step S04, the repetitions of the identified data packet portion within the frame are removed.

[0033] In at least one frame, the start of at least one data packet does not coincide with the start of a time slot. This increases the number of possible times within a frame at which a data packet can be transmitted. As a result, with a random distribution of data packets from multiple senders within a frame, there is statistically less overlap, allowing for the identification of non-overlapping or collision-free data packet segments, which are then decoded by the receiver. This increases the probability of decoding more data packets per frame, especially under high load, i.e., with many simultaneous senders. Retransmission of the same data packet can thus be avoided, ensuring efficient transmission.

[0034] The following refers to the Fig. 3. Fig. Figure 3 shows a single frame of the transmission between transmitters 1-5 and the common receiver. In this example, the frame is... Fig. The signal is divided into 6 time slots, slots 1 to 6. Data packet 1 from sender 1 is collision-free. It does not begin in slot 3, but extends from slot 3 to slot 4. Because data packet 1 is collision-free, it can be decoded by the receiver. Subsequently, data packet 2, which is a repetition of data packet 1, is deleted or subtracted from the received signal. Thus, data packet 3 in slot 6 of sender 5 is again collision-free and can be decoded by the receiver. Similarly, data packet 4 in slot 1 of sender 5, which is a repetition of data packet 3, is deleted. Finally, data packet 5 from sender 3 is collision-free in slot 1 and can be decoded by the receiver. Similarly, data packet 6 from sender 3 is deleted.Data packet part 7A is then collision-free in slot 2, allowing it to be decoded. Similarly, data packet part 9A from sender 2 can be deleted from slot 5. Likewise, data packet part 9B from sender 2 is collision-free in slot 5, allowing it to be decoded by the receiver. From the two data packet parts 7A and 9B, the entire transmitted data packet from sender 2 can be decoded or reconstructed. After decoding the second data packet part 9B, data packet part 7B from sender 2 is deleted from slot 2. Subsequently, data packet parts 8A or 8B can be decoded. Thus, all data packets in the displayed frame can be completely decoded and received. Repeated transmission of individual data packets from each sender is therefore unnecessary.

[0035] Alternatively, only complete repetitions of the received signal are removed. In this embodiment, after decoding data packet part 7A, data packet part 9A of the repetition is not deleted. Then, either data packet part 8B, data packet part 9B, or data packet part 10A can be decoded. The data packet of sender 4 can then be reconstructed from data packet parts 10A and 8B, and the data packet of sender 2 can be reconstructed from data packet parts 7A and 9B.

[0036] In the example of the Fig. In the case of 3, the number S of possible start times for the individual data packets is almost doubled. In the example of the Fig. 3. The data packets can be transmitted at 11 different start times. Since data packets cannot be transmitted across the frame boundary, a data packet cannot begin within slot 6, leaving 11 possible start times. The individual data packets transmitted by senders 1-5 are randomly distributed across these 11 times. This increases the probability of identifying non-overlapping or non-collision data packet segments and thus receiving the corresponding data packets. In particular, in the example of the Fig. 3 S are chosen to be S = 2N, where after time (N - 1 * (Data packet length) no longer allow data packets to begin.

[0037] The following refers to the Fig.Figure 4, which represents the prior art, shows that all data packets begin with their respective time slots, Slot 1 to Slot 6. The data packets do not extend across the slot boundaries, as is permissible under the present invention. To decrypt the user data, the receiver searches for a singleton slot, i.e., a time slot with a unique replica. Slot 2 contains a single transmission (data packet 1), and the receiver can decrypt this and subtract its copy / repeat (data packet 2) from Slot 6. In this way, Slot 6 now contains a single data packet (data packet 3), and Sender 5 is decoded, and both data packets are removed from Time Slot 6 (data packet 3) and Time Slot 1 (data packet 4). Similarly, User 3 is decoded, and the replicas (data packets 5 and 6) are removed. Now, Time Slot 3 and Time Slot 5 each contain two packets from the same sender.This is an example of a stop set that the receiver cannot decode. Users 2 and 4 are then declared as unsuccessfully decoded users, and the corresponding data packets must be resent in a subsequent frame.

Claims

[1] A transmission method with a plurality of transmitters and one receiver, wherein the transmission takes place in frames, each frame having a number N of time slots, comprising the steps: a) Sending multiple data packets from more than one sender to the receiver within a frame, where the multiple data packets from the one sender within the one frame are repetitions; b) Receiving the data packets by the recipient; c) Identifying a data packet part that was received individually and decoding the identified data packet part; d) Removal of repetitions of the identified data packet portion within the frame; wherein in at least one frame the start of at least one data packet does not coincide with the start of a time slot. [2] Transmission method according to claim 1, wherein steps c) and d) are repeated until no individual data packet parts can be identified in a time slot. [3] Transmission method according to claim 2, wherein the remaining data packet parts in the frame are discarded. [4] Transmission method according to any one of claims 1 to 3, wherein the transmitters are synchronized. [5] Transmission method according to any one of claims 1 to 4, wherein the transmitters send data packets randomly within a frame. [6] Transmission method according to any one of claims 1 to 5, wherein each data packet contains information about the location of its repetitions. [7] Transfer method according to any one of claims 1 to 6, wherein the transfer method is an Aloha transfer method, in particular a grant-free Aloha transfer method and preferably a CRDSA or IRSA transfer method. [8] Transmission method according to one of claims 1 to 7, wherein in more than one frame and in particular in each frame the start of at least one data packet does not coincide with the start of a time slot. [9] Transmission method according to any one of claims 1 to 8, wherein in a frame the start of at least one data packet does not coincide with the start of a time slot depending on the number of data packets sent within a frame. [10] Transmission method according to any one of claims 1 to 9, wherein S denotes the number of possible start times of a data packet within a frame, wherein S<N oder S> N. [11] Transmission method according to claim 10, wherein S results in S=αβN, where α denotes a slot coefficient and β a slot ratio, where α and β are known for all transmitters and the receiver. [12] Transmission method according to any one of claims 1 to 11, wherein a data packet is reconstructed from different repetitions. [13] Transmission method according to any one of claims 1 to 12, wherein the data packet and its repetitions do not overlap in time within one frame. [14] Transmission method according to any one of claims 1 to 13, wherein the time length of the data packet and its repetitions corresponds to the time length of a time slot. [15] System comprising a receiver and a plurality of transmitters, wherein the system is configured to carry out the transmission method according to any one of claims 1 to 14.

Images