FIRST AND SECOND TERMINAL DEVICES OF A RADIO NETWORK AND METHOD FOR OPERATING THE FIRST AND SECOND TERMINAL DEVICES

Description

State of the art

[0001] The invention relates to a first and a second terminal of a wireless network and to methods for operating the first and the second terminal.

[0002] According to a CSMA / CA (Carrier Sense Multiple Access / Collision Avoidance) protocol, a radio channel is only accessed if it has previously been identified as free. This procedure is used, for example, for IEEE 802.11p, which is a vehicle-specific adaptation of IEEE 802.11.

[0003] EP 2 288 190 A1 discloses a network node of an ad hoc network for motor vehicles. In a vehicular ad hoc network (VANET), a transceiver node is arranged in a vehicle. The node includes a protocol stack comprising an application layer, a link layer, and a congestion control layer arranged between the application layer and the link layer. The congestion control layer transmits short messages between the application layer and the link layer. The short messages are defined according to a standard for the VANET, and the congestion control layer optimizes a network-wide tariff allocation for the short messages.

[0004] US 2009 / 0122738 A1 discloses a method for distributing a packet to a plurality of mobile nodes. The method includes receiving a packet containing at least a message, a sender identifier, a location of a sender, an identifier for a relay node, and a distance from the sender and the relay node; determining whether a node receiving the packet is the relay node; and immediately distributing the packet to a plurality of mobile nodes if the receiving node is the relay node. If the receiving node is not the relay node, the method further includes the steps of waiting a predetermined period of time, determining whether a packet containing the same message is received from another sender within the period of time, and distributing the packet to a plurality of mobile nodes if a packet containing the same message is not received within the period of time.The distributed packet contains an identifier for a subsequent relay node.

[0005] US 2004 / 0071154 A1 discloses a technique that enables a common communication medium to achieve a higher data rate while maintaining low latency under lossy conditions. Disclosure of the invention

[0006] According to a first aspect, a first vehicle-mounted terminal for radio communication in a radio network according to claim 1 is provided.

[0007] Advantageously, the absence of subsequent communication after the expiration of the first time period by a second terminal device is interpreted as meaning that the first data was not received correctly. Consequently, the channel access procedure that has already been performed is used to initiate a retransmission of the first data after the expiration of the second time period, which is longer than the first time period. This prevents a retransmission of the channel access procedure. In the event of subsequent communication originating from the second terminal device, the first data is not retransmitted by the first terminal device. Consequently, a retransmission of the channel access procedure is prevented, thus increasing spectral efficiency.

[0008] An advantageous embodiment is characterized in that the channel access procedure, before a channel access which includes the transmission of the first data, checks whether the radio channel is free for a monitoring period, decrements a randomly selected backoff number for each time slot of the radio channel which is recognized as free, and uses the first data for the first time when the backoff number reaches a threshold value of, for example, zero and the radio channel is free.

[0009] This CSMA-CA (Carrier Sense Multiple Access / Collision Avoidance) procedure prevents conflicting channel accesses. By waiting for the initial time period and then checking whether the radio channel is free, the previously executed channel access procedure is not executed again before the first data is sent again.

[0010] An advantageous embodiment is characterized in that the first time period (SIFS; PIFS) is a short interframe space or a PCF interframe space.

[0011] Advantageously, the first time period is chosen to be so short that no other terminal than the second terminal, which follows the first terminal for communication, can successfully arbitrate the radio channel.

[0012] An advantageous embodiment is characterized in that the second time period (PIFS; DIFS) is a PCF interframe space or a DCF interframe space.

[0013] Advantageously, the second time period is chosen to be so short that the first terminal device can still detect an incorrect transmission of the first data and can resend the first data before another terminal device successfully accesses the radio channel.

[0014] A second aspect of this description relates to a method for operating a first vehicle-side terminal of a radio network according to claim 5.

[0015] A third aspect of this description relates to a second vehicle-mounted terminal for radio communication in a radio network according to claim 6.

[0016] According to the invention, the radio channel used is a dedicated radio channel reserved exclusively for the transmission of consecutive packets according to a packet train, wherein the packet train comprises a number of data items that are not immediately consecutive in time, which originate from different terminals and for which only the first of the participating terminals performs a channel access procedure, wherein the first data and its retransmission are part of the packet train. Advantageously, a channel access procedure is carried out once by the first terminal, the first data are sent, and all subsequent transmissions or transmissions of second data in the sense of a packet train advantageously do not require a further channel access procedure. The second data of the packet train originates from a respective terminal. The further transmissions all depend on the first successful channel access procedure.As a result, data from different end devices is sent using a single access procedure, significantly reducing data transmission latency for multi-hop communication. Overall, spectral efficiency is improved.

[0017] The second data serves two functions: First, it forms an ACK for the receipt of the first data, so that the first device receives confirmation of receipt of the first data from the second device. Second, the second data contains information for the third device.

[0018] An advantageous embodiment is characterized in that the second data are determined as a function of the first data.

[0019] An advantageous embodiment is characterized in that the time period is a short interframe space or a PCF interframe space.

[0020] It is advantageous to choose a time period that is so short that no other terminal device can successfully arbitrate the radio channel.

[0021] An advantageous embodiment is characterized in that the second terminal is designed to wait a further period of time after the end of the transmission of the second data, to check after the expiry of the further period of time whether the radio channel is occupied, and to transmit the second data again via the radio channel after the expiry of an additional period of time after the end of the previously carried out transmission of the second data if the radio channel is not occupied after the expiry of the additional period of time.

[0022] Advantageously, the absence of subsequent communication by a third terminal after the additional time period has elapsed is interpreted as meaning that the second data was not received correctly. Consequently, the channel access procedure already performed on the first terminal is used to initiate a retransmission of the second data after the additional time period has elapsed. This prevents a retransmission of the channel access procedure. In the event of subsequent communication originating from the third terminal, the second terminal does not retransmit the second data. Consequently, a retransmission of the channel access procedure is prevented, thus increasing spectral efficiency.

[0023] Furthermore, this ensures that all end devices are provided with the necessary information in the specified sequence. In the event of an error, the affected end device can immediately initiate measures to ensure the operational safety of the vehicle (e.g., emergency braking or maintaining a new minimum distance from the vehicle in front).

[0024] A fourth aspect of this description relates to a method for operating a second vehicle-side terminal of a radio network according to claim 10.

[0025] Further features and advantages can be found in the following description and the figures in the drawing. The figures show: Figure 1 shows a schematic perspective view of an exemplary traffic situation; Figure 2 shows a schematic flow diagram; and Figures 3-6 each show a schematic channel diagram.

[0026] Figure 1shows a schematic perspective view of an exemplary traffic situation. Each vehicle V1, V2, V3 comprises a terminal device NN1, NN2, NN3, which together form an ad hoc radio communication network VANET. Of course, other infrastructure units, particularly stationary ones such as traffic lights, can also comprise a terminal device in the sense of one of the terminal devices NN1 to NN3.

[0027] Each of the terminal devices NN1, NN2, NN3 comprises a data bus B1, B2, B3, which connects at least one processor P1, P2, P3, a memory M1, M2, M3, and a radio module C1, C2, C3. At least one antenna A1, A2, A3 is connected to the radio module C1, C2, C3. The respective radio module C1, C2, C3 is configured to transmit and receive radio signals according to the ad hoc radio communication network VANET via the antenna A1, A2, A3. A computer program in the sense of a computer program product is stored on the memory M1, M2, M3. The computer program is designed to carry out the method steps set out in this description, in particular with the aid of the at least one processor P1, P2, P3, the at least one memory M1, M2, M3 and the at least one radio module C1, C2, C3, and to communicate with further terminals via the at least one antenna A1, A2, A3.Alternatively or additionally, the processors P1, P2, P3 are implemented as ASICs to carry out the described method steps.

[0028] The VANET network provides at least one ad hoc radio channel in the sense of radio resources. Each of the terminal devices NN1, NN2, and NN3 is configured, for example, according to the IEEE 802.11p standard, in particular IEEE 802.11p-2010 of July 15, 2010, which is incorporated into this description by reference. The IEEE 802.11p PHY and MAC functions provide services for upper-layer protocols for dedicated short-range communication (DSRC) in the USA and for cooperative ITS (C-ITS) in Europe. The terminal devices NN1, NN2, and NN3 communicate directly with each other via the ad hoc radio channel in the unlicensed frequency range. The ad hoc radio channel is accessed by the radio modules C1, C2, and C3 using a CSMA / CA (Carrier Sense Multiple Access / Collision Avoidance) protocol. The ad hoc radio channel and the ad hoc radio communication network VANET, for example, are defined by the IEEE standard "802.11p-2010 - IEEE Standard for Information Technology - Local and Metropolitan Area Networks - "Specific Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications Amendment 6: Wireless Access in Vehicular Environments", which is incorporated by reference. IEEE 802.11p is a standard extending the IEEE 802.11 WLAN standard. The goal of IEEE 802.11p is to establish radio technology in passenger vehicles and to provide a reliable interface for Intelligent Transport Systems (ITS) applications. IEEE 802.11p is also the basis for Dedicated Short Range Communication (DSRC) in the 5.85 to 5.925 GHz band.

[0029] To access the ad hoc radio channel, the terminal devices NN1, NN2, and NN3 use a listen-before-talk procedure. The LBT includes a backoff procedure that checks the occupancy of the ad hoc radio channel before transmitting. First, the terminal devices NN1, NN2, and NN3 listen to the radio channel and wait until the ad hoc radio channel AHCH is free after a period of time DIFS, known as the intermediate arbitration period, has elapsed. The ad hoc radio channel AHCH is considered free if a power level is lower than a threshold and no ad hoc preamble with a power level greater than a second threshold is detected. The ad hoc radio channel is occupied if the channel is detected as not free.

[0030] If the ad hoc radio channel is detected as free during the DIFS period, the backoff procedure begins. The terminal device NN1, NN2, or NN3 receives a transmission opportunity TXOP when a backoff counter expires. If the terminal device NN1, NN2, or NN3 detects the ad hoc radio channel as free, it will transmit data as long as a TXOP duration of the transmission opportunity has not expired.

[0031] The document "ETSI EN 302 663 V1.2.0 (2012-11)", incorporated herein by reference, describes the two lowest layers of ITS-G5 technology (ITS G5: Intelligent Transport Systems operating in the 5 GHz frequency band), the physical layer and the data link layer. Radio modules C1, C2, and C3, for example, implement these two lowest layers and corresponding functions according to "ETSI TS 102 687 V1.1.1 (2011-07)" to use the ad hoc radio channel. The following unlicensed frequency bands are available in Europe for use of the ad hoc radio channel, which is part of the unlicensed NLFB frequency band: 1) ITS-G5A for safety-related applications in the frequency range 5.875 GHz to 5.905 GHz; 2) ITS-G5B for non-safety-related applications in the frequency range 5.855 GHz to 5.875 GHz; and 3) ITS-G5D for the operation of ITS applications in the frequency range 5.055 GHz to 5.925 GHz.ITS-G5 enables communication between the terminals NN1, NN2, and NN3 outside the context of a base station. The ITS-G5 standard enables the immediate exchange of data frames and avoids the overhead required to set up a cellular network.

[0032] The document "ETSI TS 102 687 V1.1.1 (2011-07)", which is incorporated herein by reference, describes a "Decentralized Congestion Control Mechanism" for ITS-G5. The ad hoc radio channel is used, among other things, to exchange traffic safety and traffic efficiency data. The radio modules C1, C2, and C3, for example, implement the functions described in the document "ETSI TS 102 687 V1.1.1 (2011-07)". The applications and services of ITS-G5 are based on the cooperative behavior of the roadside terminals NN1, NN2, and NN3, which form the ad hoc network VANET (Vehicle Ad Hoc Network). The ad hoc network VANET enables time-critical applications in road traffic that require rapid information exchange to alert and assist the driver and / or vehicle in a timely manner. To ensure the smooth functioning of the ad hoc network VANET, "Decentral Congestion Control" (DCC) is used for the ad hoc radio channel of ITS-G5.DCC has functions located at multiple layers of the ITS architecture. DCC mechanisms are based on knowledge of the radio channel. Channel state information is obtained through channel probing. Channel state information can be obtained through the TPC (transmit power control), TRC (transmit rate control), and TDC (transmit data rate control) methods. These methods determine the channel state information in response to received signal level thresholds or preamble information from detected packets.

[0033] In the traffic situation shown, the first vehicle V1 is driving in front of the second vehicle V2 and the second vehicle V2 is driving in front of the third vehicle V3. In order to avoid rear-end collisions, for example, the first vehicle V1 transmits its currently determined braking distance and transmits this to the second vehicle V2 using the first data P1. Depending on the received data P1, the second vehicle V2 adjusts its distance from the first vehicle V1. The second vehicle V2 determines its own braking distance depending on the received first data P1, for example depending on the braking distance of the vehicle V1, and transmits the determined braking distance to the third vehicle V3 using data P2. The vehicle V3 determines data P3 in a similar way to vehicle V2 depending on the received data P2 and passes its own braking distance on to following vehicles using the data P3.

[0034] In another example, the first vehicle V1 detects an obstacle at a distance ahead and initiates braking. Information about the obstacle, such as its position and / or the information that emergency braking has been initiated, is transmitted to the following vehicle V2 via data P1. The vehicle V2 forwards the information received via data P1 unchanged to the third vehicle V3 via data P2.

[0035] Figure 2 shows a schematic flow diagram for operating the first terminal NN1 and the second terminal NN2 from Figure 1 A process 100 is provided for operating the first terminal NN1. A process 200 is provided for operating the second terminal NN2 or other terminals.

[0036] The first terminal NN1 and the second terminal NN2 determine the sequence of data P1, P2 to be sent in the form of data packets in a respective step 102 or 202. This sequence is, for example, preconfigured. In another example, however, a communication K takes place in advance to determine the sequence of data transmission. For example, the terminals NN1 and NN2 exchange CAM messages or DENM messages, which contain a position and direction of travel of the respective vehicle V1, V2. Figure 1 For example, by position and direction of travel, each vehicle V1, V2, V3 from Figure 1Determine the order in which vehicles V1, V2, and V3 travel in the direction of travel. Depending on the travel order of vehicles V1, V2, and V3, the sequence of data to be sent is determined, for example, in steps 102 and 202 by the respective terminal devices NN1 and NN2. This sequence can occur in the direction of travel or against the direction of travel and depends, for example, on the application. For coordinated braking, a chronological sequence against the direction of travel is useful. For coordinated starting, a chronological sequence against the direction of travel may be useful.

[0037] In step 104, initial data P1 is determined. In step 106, a backoff procedure is started, and a time period DIFS is waited for. The terminal device NN1 then randomly determines a value for a backoff number or a backoff counter. If, after a transmission from any terminal device, the medium is detected as free for the time period DIFS, the backoff number is decremented by one for each slot period following the time period DIFS and for which the channel continues to be detected as free. If the backoff number reaches zero and the channel is free, the terminal device is permitted to access the radio channel. After radio channel access is granted, the process switches to step 110 to send the determined data P1 on the radio channel.

[0038] In one example, the radio channel used is a dedicated radio channel reserved exclusively for the transmission of consecutive packets according to a packet train. A packet train comprises a number of non-contiguous data items originating from different terminals and for which only the first of the participating terminals has performed a channel access procedure. Alternatively or additionally, the data P1, P2 include a flag indicating this packet train communication. In another example, the presence of a packet train communication is derived from the data received or to be transmitted.

[0039] The second terminal NN2 is switched to receive in a step 204. If the data P1 is successfully received in step 204, the process switches to a step 208 according to a step 206. In step 206, a check is made as to whether the first data P1 was received correctly. In addition, a check is made as to whether the received data P1 originates from the first terminal NN1. For this purpose, an identifier of the first terminal NN1, which was determined in step 202, is used, for example. This identifier identifies the first terminal NN1 as the predecessor for sending the second data P2. This means that the second terminal NN2 must first receive the first data P1 from the first terminal NN1 in order to be permitted to send the second data P2.

[0040] In step 208, the second terminal NN2 determines the second data P2 for transmission. The second data P2 is determined, for example, depending on the received data P1. Alternatively, the data P2 is not determined depending on the data P1. However, the second data P2 is sent depending on the receipt of the data P1.

[0041] In a step 210, a time period SIFS or PIFS is waited after the end of the reception of the first data P1 from step 204. Once the time period SIFS or PIFS has expired, the transmission of the second data P2 is started in a step 212.

[0042] A step 220 following step 212 corresponds to a step 120, which is executed by the first terminal NN1. Step 120 follows step 110 in the sequence 100 and thus after the first transmission of the first data P1 over the radio channel.

[0043] After the end of the transmission of the first data P1, a first time period SIFS or PIFS is waited for according to a step 122. After this first time period has elapsed, a check is carried out in a step 124 whether the radio channel is free during a monitoring period between the expiration of the first time period SIFS or PIFS and the expiration of a second time period PIFS or DIFS, which begins after the end of the transmission of the first data P1. If this is the case, the first terminal NN1 begins to transmit the first data P1 again in a step 128. In a step 130, a check is carried out to determine whether the maximum number of transmission attempts has been reached. If this is the case, the method is terminated. If this is not the case, the process switches to step 122 in order to start another transmission attempt, if necessary.

[0044] Figure 3shows a schematic channel diagram. It shows the transmission of the first to third data P1 to P3, whereby only the first terminal NN1 waits for the time period DIFS to then execute the LBT (Listen-Before-Talk) procedure once according to steps 108 and 110 of Figure 2 The single execution of the procedure LBT is therefore sufficient for the respective data P1, P2, P3 to be sent from a respective terminal device NN1, NN2 and NN3 Figure 1 are sent via the radio channel, whereby the terminal devices NN2 and NN3 do not have to carry out a respective LBT procedure for sending the data P2 and P3.

[0045] The second terminal NN2 waits for the SIFS period after the end of the transmission of the first data P1, and then immediately after the SIFS period has ended, it sends the second data P2 over the radio channel. The third terminal NN3 proceeds in a similar manner to send the third data P3.

[0046] Figure 4shows a schematic channel diagram. In contrast to Figure 3 the second data P2 is not sent after the end of the SIFS period, which begins with the end of the initial transmission of the first data P1. The first terminal device NN1 detects this and immediately begins re-sending the first data P1 after the end of the PIFS period, which begins with the end of the initial transmission of the first data P1. Following the re-sending of the first data P1, the second terminal device NN2 begins re-sending the second data P2 after the end of the SIFS period.

[0047] Figure 5 shows a schematic channel diagram. In contrast to Figure 4 Instead of the time period PIFS, the time period DIFS is used to start a new transmission of the first data P1.

[0048] Figure 6 shows a schematic channel diagram. In contrast to the Figure 5Instead of the time period SIFS, the time period PIFS is used to start a subsequent data transmission of the data P2, P3 and, after the time period PIFS has elapsed, to check whether a subsequent data transmission is carried out by a terminal device such as P2 or not.

[0049] The SIFS time period is a short interframe space. The PIFS time period is a PCF interframe space, where PCF stands for point coordination function. The DIFS time period is a DCF interframe space, where DCF stands for distribution coordination function.

Claims

1. First vehicle-side terminal (NN1) for radio communication in a radio network, wherein the first vehicle-side terminal (NN1) is designed to determine first data (P1), to perform a channel access procedure for a radio channel, to send the first data (P1) over the radio channel, to wait for a first period (SIFS; PIFS) after the first data (P1) have finished being sent, to check, after the expiry of the first period (SIFS; PIFS), whether the radio channel is occupied, and to resend the first data (P1) over the radio channel after the expiry of a second period (PIFS; DIFS), which begins after the end of the previous sending of the first data (P1) and is longer than the first period (SIFS; PIFS), if the radio channel is not occupied after the expiry of the first period, characterized in that the radio channel that is used is a dedicated radio channel reserved exclusively for the transmission of successive packets in a packet train, wherein the packet train comprises a number of data (P1; P2) that are not directly successive in terms of time, that originate from different terminals (NN1; NN2) and for which only the first of the participating terminals (NN1) performs a channel access procedure, wherein the first data (P1) and the retransmission thereof are part of the packet train.

2. First terminal (NN1) according to Claim 1, wherein the channel access procedure, prior to a channel access operation that comprises sending the first data (P1), checks whether the radio channel is free for the length of a monitoring period (DIFS), decrements a randomly selected backoff number for each time slot, recognized as being free, of the radio channel, and sends the first data for the first time when the backoff number reaches a threshold value of for example zero and the radio channel is free.

3. First terminal (NN1) according to either of the preceding claims, wherein the first period (SIFS; PIFS) is a short interframe space and the second period (PIFS; DIFS) is a PCF interframe space or a DCF interframe space.

4. First terminal (NN1) according to either of Claims 1 and 2, wherein the first period (SIFS; PIFS) is a point coordination function interframe space and the second period (PIFS; DIFS) is a DCF interframe space.

5. Method for operating a first vehicle-side terminal (NN1) of a radio network, wherein the method comprises: determining first data (P1), performing a channel access procedure for a radio channel, sending the first data (P1) over the radio channel, waiting for a first period (SIFS; PIFS) after the first data (P1) have finished being sent, checking, after the expiry of the first period (SIFS; PIFS), whether the radio channel is occupied, and resending the first data (P1) after the expiry of a second period (PIFS; DIFS), which begins after the end of the previous sending of the first data (P1) over the radio channel and is longer than the first period (SIFS; PIFS), if the radio channel is not occupied after the expiry of the first period, characterized in that the radio channel that is used is a dedicated radio channel reserved exclusively for the transmission of successive packets in a packet train, wherein the packet train comprises a number of data (P1; P2) that are not directly successive in terms of time, that originate from different terminals (NN1; NN2) and for which only the first of the participating terminals (NN1) performs a channel access procedure, wherein the first data (P1) and the retransmission thereof are part of the packet train.

6. Second vehicle-side terminal (NN2) for radio communication in a radio network, wherein the second terminal (NN2) is designed to determine an identifier that identifies a first vehicle-side terminal (NN1) as a predecessor for sending second data (P2), to receive first data (P1) over a radio channel from the first terminal (NN1) having the identifier, to determine second data (P2), to wait for a period (SIFS; PIFS) after the first data (P1) have finished being received, and to send the second data (P2) over the radio channel without a channel access procedure when the period (SIFS; PIFS) has expired, wherein the first data (P1) and the second data (P2) form a packet train, wherein the first data (P1) and the second data (P2) comprise data (P1; P2) that are not directly successive in terms of time, that originate from different terminals (NN1; NN2) and for which only the first of the participating terminals (NN1) performs a channel access procedure.

7. Second terminal (NN2) according to Claim 6, wherein the second data (P2) are determined on the basis of the first data (P1).

8. Second terminal (NN2) according to Claim 6 or 7, wherein the period (SIFS; PIFS) is a short interframe space or a PCF interframe space.

9. Second terminal (NN2) according to one of Claims 6 to 8, wherein the second terminal (NN2) is designed to wait for a further period (SIFS; PIFS) after the second data (P2) have finished being sent, to check, after the expiry of the further period (SIFS; PIFS), whether the radio channel is occupied, and to resend the second data (P2) over the radio channel after the expiry of an additional period (PIFS; DIFS), which begins after the end of the previous sending of the second data (P2) and is longer than the further period (SIFS; PIFS), if the radio channel is not occupied after the expiry of the additional period.

10. Method for operating a second vehicle-side terminal (NN2) of a radio network, wherein the method comprises: determining an identifier that identifies a first vehicle-side terminal (NN1) as a predecessor for sending second data (P2), receiving first data (P1) over a radio channel from the first terminal (NN1) having the identifier, determining second data (P2), waiting for a period (SIFS; PIFS) after the first data (P1) have finished being received, and sending the second data (P2) over the radio channel without a channel access procedure when the period (SIFS; PIFS) has expired, wherein the first data (P1) and the second data (P2) form a packet train, wherein the first data (P1) and the second data (P2) comprise data that are not directly successive in terms of time, that originate from different terminals (NN1; NN2) and for which only the first of the participating terminals (NN1) performs a channel access procedure.