EP4331314A1

EP4331314A1 - A vehicular wireless channel access method

Info

Publication number: EP4331314A1
Application number: EP21722200.9A
Authority: EP
Inventors: Maria Bezmenov
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2021-04-28
Filing date: 2021-04-28
Publication date: 2024-03-06
Also published as: WO2022228667A1

Abstract

A wireless channel access method (8a, 8b) based on wireless channel collision avoidance, comprising: receiving (10a, 10b), at a first item of user equipment (UE1), a first measured quantity transmitted from a second item of user equipment (UE2) at the second position, detecting (12a, 12b), at the first item of user equipment (UE1) located at the first position, that the second item of user equipment (UE2) located at the second position has transmitted data via a wireless channel shared by the first and second items of user equipment, and declaring (14a, 14b), at the first item of user equipment (UE1), the presence of a transmission opportunity for the first item of user equipment (UE1) to transmit data over the wireless channel to a second, or further item of user equipment at a first time, wherein the first time is dependent on the first measured quantity.

Description

A vehicular wireless channel access method

Technical Field

This specification relates to a wireless channel access method based on wireless channel collision avoidance, and an associated apparatus, system, and computer readable medium.

Background

Channel access in wireless communications concerns the problem of how first and second wireless terminals can access and share a common wireless resource. Carrier Sense Multiple Access with Collision Avoidance ( CSMA/CA ) is a wireless channel multiple access protocol in which first and second wireless terminals that conventionally operates in layer 2 (Data Link Layer) of the OSI model. In CSMA/CA, a wireless terminal wishing to transmit first on the shared channel first listens to the shared channel to sense whether, or not, another wireless terminal is transmitting on the share channel. If the wireless terminal wishing to transmit senses another transmission on the shared channel from another wireless terminal, the wireless terminal wishing to transmit waits for a period of time before listening again for an opportunity to transmit on the shared wireless channel.

In the context of, for example, vehicular wireless access (such as 802. lip for adding wireless access to vehicular environments, LTE-V2X, or its successor NR-V2X from 3GPP), wireless channel multiple access protocols may be further improved.

Summary

According to a first aspect, there is provided a wireless channel access method based on wireless channel collision avoidance, comprising: receiving, at a first item of user equipment, a first measured quantity transmitted from a second item of user equipment at the second position; detecting, at the first item of user equipment located at the first position, that the second item of user equipment located at the second position has transmitted data via a wireless channel shared by the first and second items of user equipment; and declaring, at the first item of user equipment, the presence of a transmission opportunity for the first item of user equipment to transmit data over the wireless channel to a second, or further item of user equipment at a first time, wherein the first time is dependent on the first measured quantity and that the second item of user equipment has transmitted data. An effect is that a first item of user equipment and a second item of user equipment may communicate more reliably. The emergent effect of the wireless channel access method is that a first item of user equipment bases the declaration of a transmission opportunity from the first item of user equipment at least partially on an objectively measurable variable transmitted from the second item of user equipment. This means that packet collisions between users within communication range of the first item of user equipment can be avoided. For example, the period of time that the first item of user equipment should wait for the presence of a transmission opportunity may be a function of the distance separating the first item of user equipment from the second item of user equipment. When several items of user equipment generate waiting time for the transmission opportunity according to the same function and objectively measurable variable, a distributed sending order is created, and thus indirectly reservation, based on the objectively measurable variable (such as a relative distance between the first and second items of user equipment).

According to a second aspect, there is provided an item of user equipment configured to perform vehicular wireless channel access based on wireless channel collision avoidance, comprising non -transitory computer readable media comprising machine readable instructions which, when executed, cause the item of user equipment to execute the method according to the first aspect or its embodiments, and a processor configured to load and to execute the machine readable instructions.

According to a third aspect, there is provided a system configured to perform wireless channel access based on wireless channel collision avoidance comprising a first item of user equipment located at a first position, a second item of user equipment located at a second position. The first item of user equipment is configured to detect that a second item of user equipment has transmitted data via a wireless channel. The second item of user equipment is configured to transmit, to the first item of user equipment, a first measured quantity transmitted from the second item of user equipment at the second position. The first item of user equipment is configured to declare at the first item of user equipment the presence of a transmission opportunity for the first item of user equipment to transmit data over the wireless channel to the second, or a further item of user equipment at a first time, wherein the first time is dependent on the first measured quantity. According to a fourth aspect, there is provided a computer readable medium comprising machine readable instructions configured to cause a processor to perform the method according to the first aspect or its embodiments.

Brief Description of the Figures

Exemplary embodiments are depicted in the figures, which are not to be construed as limiting the claims, and are explained in greater detail below.

Fig. 1 schematically illustrates a wireless channel access method according to the first aspect. Fig. 2 schematically illustrates a wireless channel access method according to an embodiment. Fig. 3 schematically illustrates a system configured to perform wireless channel access between vehicles comprised in a vehicle platoon according to an example.

Fig. 4 schematically illustrates an example of the time variance of a channel access function at three items of User Equipment according to an embodiment.

Fig. 5 schematically illustrates the same examples of the time variance of a channel access function at three items of User Equipment according to the embodiment of Fig. 4 on separate graph axes.

Fig. 6 schematically illustrates User Equipment according to the second aspect.

Detailed Description

Vehicular wireless access is regulated according to protocols that are planned, or in development, such as 802. lip for adding wireless access to vehicular environments, LTE- V2X, or its successor NR-V2X from 3GPP. For example, channel access in 802. lip is based on CSMA/CA. When a first item of user equipment (such as a vehicle comprising user equipment UE1) wishes to transmit a packet, the wireless channel for transmission must first be observed (sensed) by the first item of user equipment. If the wireless channel is perceived to have been unused for a predefined period of time, the user equipment can transmit the packet, in a so-called transmission opportunity. If, within the predefined period of time, the channel is transmitted on by other items of user equipment, the first item of user equipment must postpone its transmission. The amount of time that the first item of user equipment must postpone its transmission for is regulated using a backoff procedure.

An example of a backoff procedure is exponential backoff, or binary exponential backoff. One example of a backoff function is that any number in the interval [0, CW] is chosen, and assigned to the backoff counter configured to count down in integer intervals. For each successive timeslot, as long as the shared wireless channel is observed to be unoccupied, the backoff counter is reduced by one integer from the value initially assigned to the backoff counter. For example, in an 802. lip wireless channel having a bandwidth of 10MHz, each free timeslot has a duration of 13us. Therefore, in that example, the backoff counter is decremented by 1 every 13us.

If the shared wireless channel is perceived to be busy, the backoff counter is not reduced. Following a period where the shared wireless channel is occupied, a predefined period of time must elapse before the counter can be reduced again. If the backoff counter reaches zero, the user equipment can transmit the packet. In this example, the predefined time. And the value CW in the interval [0, CW] can optionally be based on the priority category of the data to be sent by the user equipment.

The OFDM-based (Orthogonal Frequency-Division Multiplexing) LTE-V2X and NR-V2X standards divide the shared wireless channel into resource blocks in terms of time and frequency. Several resource blocks within a time window are combined into sub channels. During data transmission, at least one subchannel is used, but sometimes several sub channels are used in the same window for transmission.

Aspects of the LTE-V2X and NR-V2X standards base channel access on semi-persistent scheduling (SPS). SPS enables users to attach periodicity information to their transmissions, indicating when they will return to the same subchannel. By specifying the periodicity in this way, resource blocks are periodically reserved for a user by one or more items of user equipment monitoring the wireless channel and the broadcast periodicity information of the SPS transmissions. Each item of user equipment monitors the shared wireless channel, and each item of user equipment comprises a counter indicating how often the reserved resource blocks are used. The number of repetitions of each user can be selected from a predefined interval. The reservation period is reduced, for example, by one each time an item of user equipment observes that a reserved resource of the wireless channel has been used. If the internal counter of an item of user equipment reaches zero, the item of user equipment chooses new wireless resources for transmission. Subchannel is reserved by other users are excluded.

Conventional CSMA/CA is not sensitised to objectively measurable parameters measurable at the items of user equipment, such as the location of one item of user equipment relative to another item of user equipment. However, variations in channel conditions between items of user equipment can affect channel access. These considerations are becoming more important with the rise of inter-vehicle communication. For example, a platoon of vehicles on a road in which one car has a different relative location (is accelerating) compared to a group of other cars presents a complicated channel situation. A challenge with channel access is that packet collisions occur when two or more packets of data are sent and arrive at one receiver. In this case, error-free reconstruction of both packets is not possible. A distinction may be drawn between a case where both senders of the colliding data packets are within communication range of each other, and a case where the senders of the colliding data packets are not within communication range of each other. The latter case is referred to as the “hidden node problem”.

In LTE-V2X and NR-V2X, collisions are reduced using SPS as described above. Resources in the shared wireless channel are reserved in advance for the entire duration of the transmission of data packet so that the shared wireless channel is inaccessible to other users in the reserved periods. However, due to irregularities in the data packet generation, it may be that resources reserved in advance cannot be used. This leads to reduced channel utilisation due to the fact that resources have been reserved for the entire transmission. In the event of failure, a lot of resources are reserved for the entire transmission. However, the existing SPS protocol takes a long time to react to changes in the data packet generation, or arrangements in the vehicle distribution.

In 802. lip, reservations are not made a priori. Instead, collisions in the shared wireless channel are reduced by only sending from an item of user equipment when the shared wireless channel is perceived as unused. In order to prevent the collision of multiple other items of user equipment trying to access the channel at the end of the transmission, a random component is added to the waiting time of each of the other items of user equipment. In this scenario, hidden node collisions cannot be prevented.

Accordingly, the flexibility and fast response time of the 802. lip, and the reliability of a reservation -based protocol are both desirable in vehicular wireless communications. Wireless channel multiple access protocols may be further improved.

Fig. 1 schematically illustrates a wireless channel access method according to the first aspect. According to the first aspect, there is provided a wireless channel access method 8a, 8b based on wireless channel collision avoidance, comprising: receiving 10a, 10b, at a first item of user equipment UE1, a first measured quantity transmitted from a second item of user equipment UE2 at the second position; detecting 12a, 12b, at the first item of user equipment UE1 located at the first position, that the second item of user equipment UE2 located at the second position has transmitted data via a wireless channel shared by the first and second items of user equipment; and declaring 14a, 14b, at the first item of user equipment UE1, the presence of a transmission opportunity for the first item of user equipment UE1 to transmit data over the wireless channel to a second, or further item of user equipment at a first time, wherein the first time is dependent on the first measured quantity and that the second item of user equipment UE2 has transmitted data.

The wireless channel access method according to the first aspect may be applied to the LTE- V2X, NR-V2X, and 802. lip “side link” channels, for example.

Therefore, the time period that a UE waits for when attempting to access a shared wireless channel at a first item of user equipment UE1 is, according to this approach, calculated using a metric or quantity originally measured at a second item of user equipment UE2 remote from the first item of user equipment UE2. The back-off period the first item of user equipment UE1 defining the opportunity for the first item of user equipment U1 to transmit over the shared wireless channel is not merely dependent on the function applied by the first item of user equipment UE1 , also on an external parameter that is transmitted to the first item of user equipment UE1 from the second item of user equipment UE2.

Concerning the reception 10a, 10b of the first measured quantity at the first item of user equipment UE1, as an example, the first measured quantity transmitted from the second item of user equipment UE2 is any objectively measurable quantity. As an example, the grid coordinates of the second location of the second item of user equipment UE2 can be obtained via a satellite navigation system (GPS, Galileo, GLONASS, for example) of the second item of user equipment UE2 installed in a vehicle. The second item of user equipment UE2 may transmit the grid coordinates to the first item of user equipment UE1, optionally with the time of transmission referenced using a time stamp. The first item of user equipment UE1 receives the grid coordinates transmitted from the second item of user equipment UE2. The first item of user equipment UE1 also comprises a satellite navigation system and so the first item of user equipment UE1 is also aware of its grid coordinates (position).

An embedded computer in the first item of user equipment UE1 may compute the linear distance separating the first and second items of user equipment. The linear distance varies as a function of time. For example, if the second item of user equipment UE2 is in a vehicle that is accelerating ahead of the vehicle comprising the first item of user equipment UE1. Therefore, the linear distance monotonically increases as a function of time. The grid coordinate transmitted from the second item of user equipment UE2 is an example of a measured quantity.

In an example, the first measured quantity (such as the grid coordinate) is transmitted from the second item of user equipment UE2 to the first item of user equipment UE1 via a side link channel between the first and second items of user equipment. Alternatively, the first measured quantity may be relayed from the second item of user equipment UE2 to the first item of user equipment UE1 via a base station (sometimes also referred to as an eNB, not illustrated). The first measured quantity may be transmitted on an independent portion of the wireless resource that is not the subject of the wireless channel access method.

Concerning the detection 12a, 12b of the fact that the second item of user equipment U E2 has transmitted via the shared wireless resource, similar channel sensing techniques applied using the CSMA/CA algorithm may be used.

Concerning declaring 14a, 14b the presence of a transmission opportunity for the first item of user equipment UE1, the first time is dependent on the first measured quantity and that the second item of user equipment UE2 has transmitted data. For example, at the time that the first item of user equipment UE1 senses that another item of user equipment has transmitted in the shared wireless channel, the first item of user equipment UE1 may compute a future time, or time range, at which a transmission opportunity of the first item of user equipment U El exists. The future time, or time range is, an example, a function of the first measured quantity received from the second item of user equipment UE2.

Alternatively, the first item of user equipment U El may initiate an iterative process at the instant that the first item of user equipment UE1 senses another item of user equipment transmitting in the shared wireless channel. The iterative process is defined, or parameterised, according to the first measured quantity. Therefore, the future time at which the iterative process approaches a value indicating that a transmission opportunity is available is dependent on the first measured quantity and the time at which the second item of user equipment is sensed transmitting in the shared wireless channel by the first item of user equipment UE1. Further options for the first measured quantity, and the method of computing the presence of the transmission opportunity, will be discussed below.

It is not essential that the first item of user equipment UE1 transmits in all circumstances. For example, a technical benefit is achieved if the first item of user equipment U El transmits during a time when the shared wireless channel is not occupied by a transmission from another item of user equipment because a collision will not occur, or the probability of collision is reduced. A technical benefit is also achieved if the first item of user equipment UE1 does not transmit during a time when the shared wireless channel is occupied by transmission from another item of user equipment. In the former case, a transmission from the first item of user equipment UE1 is more likely to be received correctly. In the latter case, transmissions from other items of user equipment in the proximity of the first item of user equipment U El are less likely to be interrupted.

According to an embodiment, the first measured quantity is the second position of the second item of user equipment UE2.

The first measured quantity obtained at the second item of user equipment UE2 may, for example, be a quantity defined in a cooperative awareness message CAM transmitted from the second item of user equipment UE2 or vehicle, and measured by the vehicle containing the first item of user equipment UE1. For example, the first measured quantity may be the second position of the second item of user equipment UE2 defined in terms of a grid reference, the heading, speed, lane position, drive direction, longitudinal acceleration, lateral acceleration, vertical acceleration, curvature (rate of turning), yaw rate, steering wheel angle data as measured in a vehicle containing the second item of user equipment UE2. Optionally, the second item of user equipment UE2 may detect these quantities using integral accelerometers and/or a satellite communication sensor. Optionally, in the case that the satellite communication sensor is non-functional, the second item of user equipment UE2 may send as the position estimate calculated from the last known grid reference obtained using satellite communication sensor. Optionally, in the case that the satellite communication sensor is non-functional, the second item of user equipment UE2 may relay as the position estimate a location estimate of the second item of user equipment UE2 from a local base station (eNB) in communication with the second item of user equipment UE2.

Cooperative Awareness Messages (CAMs) are defined in the document “Intelligent Transport Systems (ITS), Vehicular Communications, Basic Set of Applications, Part 2: Specification of Cooperative Awareness Basic Service” ETSI EN 302 637-2 VI.4.1 (2019-04).

According to an embodiment at least the first measured quantity is transmitted to the first item of user equipment UE1 from the second item of user equipment UE2 according to at least one of: position information of the second item of user equipment UE2 comprised in the transmission from the second item of user equipment UE2, cooperative awareness message CAM data transmitted by at least the second item of user equipment UE2, cooperative perception messaging CPM transmitted by at least the second item of user equipment UE2, time stamp information and/or geographical coordinate data comprised in the transmission from at least the second item of user equipment UE2.

Fig. 2 schematically illustrates a wireless channel access method according to an embodiment.

According to an embodiment, the first time is obtained by: computing 16, at the first item of user equipment UE1, a first value of a first channel access function of the first item of user equipment UE1, wherein the first value of the first channel access function is computed at least partially according to the first measured quantity, updating 18, at the first item of user equipment UE1, the first channel access function as a function of time starting from the first value; and if 20, after an elapsed time interval, the first channel access function has reached a second value, declaring 14b the presence of the transmission opportunity.

According to an embodiment, the first channel access function is implemented as an integer counter that is incremented or decremented in steps from the first value of the first channel access function to the second value of the first channel access function, wherein each increment or decrement of the counter is triggered per slot of a channel access protocol of the first item of user equipment UE1.

As an example, a counter operated by the first item of user equipment UE1 may be initialised according to the value of the first measured value received from the second item of user equipment U E2. For example, if the second item of user equipment U E2 is 100 m distant from the first item of user equipment UE1, the counter may be initialised at 100. If the second item of user equipment UE2 is 200 m distant from the first item of user equipment UE1, the counter may be initialised at 200. The counter at the first item of user equipment UE1 that is decremented by “1” after each shared wireless channel timeslot has elapsed. In this example, when the counter reaches a value of “0”, the first item of user equipment UE1 declares a transmission opportunity to itself. For example, an application layer process operated by UE1 may execute the counter and declare the transmission opportunity.

Following transmission of a packet of data (MAC PDU), the counter may be reset or recalculated. If the first item of user equipment UE1 does not transmit a packet of data in its transmission opportunity, the counter may be reset or re-calculated. In this example, the first channel access function is a negative linear function of time, with the gradient and starting value dependent on the first measured quantity transmitted from the second item of user equipment UE2. As will be explained, many other functions may be used.

According to an embodiment, the method further comprises: obtaining, at the first item of user equipment UE1, an item of data 23, 25, 27 for transmission, wherein the item of data is generated by the first item of user equipment UE1 and is for transmission via the wireless channel to the second, or a further item of user equipment; and if the presence of a transmission opportunity to transmit data over the wireless channel has been declared at the first item of user equipment U El, transmitting the item of data 23, 25, 27 from the first item of user equipment UE1 to the second, or further item of user equipment.

Fig. 3 schematically illustrates a system configured to perform wireless channel access between vehicles comprised in a vehicle platoon along a straight road, according to an example. Of course, this example is not limiting and the shared wireless channel access technique discussed herein may be applied to vehicles disposed in a variety of positions, for example travelling around a bend or a corner, parked in various locations in a car park, and the like.

In Fig. 3, user equipment UE1, UE2, UE3, and UE4 comprise a linear platoon travelling along the left lane of the road 22 in a direction from left to right of the page. A positive distance between UE1 and UE2 is denoted di2. A negative distance from UE2 to UE1 is denoted -d2i. A positive distance from UE2 to UE3 is denoted d23. A negative distance from UE3 to UE2 is denoted -d32. A positive distance from UE2 to UE4 is denoted d24. A negative distance from UE4 to UE2 is denoted -d42. A positive distance from UE3 to UE4 is denoted d34. A negative distance from UE4 to UE3 is denoted -d43.

Fig. 4 schematically illustrates an example of the time variance of a channel access function at three items of User Equipment UE2, UE3, UE4 illustrated in Fig. 3 according to an embodiment.

In the example of Fig. 4, it is assumed that a first measured quantity is available, and continuously updated at UE2-UE4. For example, CAM messages are assumed to be continuously transmitted by UE2-UE4 containing, in this example, location data obtained by GPS at each of UE2-UE4.

Fig. 4 comprises three time axes. The upper time axis illustrates when a MAC PDU is received in a transmit buffer of a respective item of user equipment UE2, UE3, UE4. At time point 23, a MAC PDU is received in the transmit buffer of UE2. At time point 25, a MAC PDU is received in the transmit buffer of UE3. At time point 27, a MAC PDU is received in the transmit buffer of UE4. Whether or not the respective MAC PDUs are instantly transmitted, or are buffered, depends on the wireless channel access method according to the examples discussed herein.

The middle time axis of Fig. 4 defines when the shared wireless channel is occupied (in other words, the time that which is possible for an item of user equipment to sense that the shared wireless channel is occupied). During time range 24, the second item of user equipment UE2 is transmitting a MAC PDU in the shared wireless channel. During time range 26, the fourth item of user equipment U E4 is transmitting a MAC PDU in the shared wireless channel. During the time range 28, the third item of user equipment UE3 is transmitting a MAC PDU in the shared wireless channel.

In this example, the lower time access of Fig. 4 is a superimposed representation of the value of a first instance 30, second instance 32, and third instance 34 of the same channel access function. In this example, the first instance of the channel access function 30 is calculated or tracked by the second item of user equipment UE2. The second instance of the channel access function 32 is calculated or tracked by the third item of user equipment U E3. The third instance of the channel access function 34 is calculated or tracked by the fourth item of user equipment UE4. As noted above, it is only necessary for each item of user equipment to execute its own copy of the channel access function according to sensing occurring at that item of user equipment. If a large number of items of user equipment execute the function according to the first aspect, an emergent CSMA/CA effect is provided. It is not essential that one item of user equipment tracks the function outputs (or counters) relevant to all other items of user equipment.

The y-axis of the bottom graph of Fig. 4 represents the value of each of the first to third instances of the channel access function 30, 32, 34. In an example, CMAX is a limit value that the instances of the channel access function are reset to upon sensing or detecting transmissions from other UEs, for example. In the illustrated example, the first to third instances of the channel access function 30, 32, 34 have the same limit value CMAX. AS will be explained subsequently, each of the first to third instances of the channel access function 30, 32, 34 may use a different limit value based on objectively measured values, measured locally at each of the corresponding items of user equipment. For example, the limit value CMAX at each corresponding item of user equipment may be based on an objectively measurable parameter. For example, the objectively measurable parameter could be an optically measurable feature such as the light intensity, scene content, or vehicle traffic density proximate to a corresponding item of U E, or time of data packet reception, or the channel busy ratio at corresponding UEs.

For the purposes of illustration, Fig. 4 is based on the assumption that no vehicle has been present for a large number of slots, corresponding to time interval 40. Therefore, all instances of the channel access function across UE2-UE4 have a value of “0”.

Then, UE2 generates a packet of data 23. Because the first instance of the channel access function at UE2 has a value of “0”, UE2 is allowed transmit the packet of data as soon as it receives it from an application of UE2. Therefore, the packet of data 23 is provided to the radio interface of UE2 for transmission with no buffering or delay. During time period 41, the packet of data 23 is transmitted in channel access opportunity 24.

UE3 and UE4 are sensing the shared wireless channel, and thus detect the transmission of the packet of data 23 during channel access opportunity 24. Once detected, UE3 and UE4 recalculate their respective instances of the channel access function (in the optional case where the channel access function is defined by an integer counter, UE3 and UE4 recalculate their counters). In this example, the recalculation occurs based on the distance between UE2 and the respective UE3 or UE4 receiving the transmission from UE2. The result of the recalculation is illustrated in time range 41 of Fig. 4. UE3’s instance of the channel access function 32 has a lower value C(d23) compared to UE4’s instance of the channel access function 34, because the distance between U E2 and U E3 is smaller than the distance between UE2 and UE4.

After the transmission 24 from UE2 is complete, UE2 sets its counter to, in this example, CMAX. The effect of the distributed shared wireless channel access algorithm up to this point is, therefore, that UE3, which is closest in a positive direction to the item of user equipment UE2 last sensed transmitting on the shared wireless channel, has the shortest time to wait before a transmission opportunity is available at U E3. The item of user equipment U E4, which is furthest in a positive direction from the item of user equipment UE2 last sensed transmitting on the shared wireless channel, has the next greatest time to wait before a transmission opportunity is available at UE4. The item of user equipment UE2, which was the most recent item of user equipment to transmit, has the longest amount of time to wait before a transmission opportunity is next available at UE2.

As soon as UE2 has reinitialised (reset) its instance of the channel access function to the limit value such as CMAX, the first 30, second 32, and third 34 instances of the channel access function at the corresponding items of user equipment UE2, UE3, and UE4 are calculated. In the illustrated example, the channel access function is a decreasing linear function starting from different C value is dependent on the starting value of the first 30, second 32, and third 34 instances. Therefore, the illustrated example shows that the first 30, second 32, and third 34 instances of the channel access function are decremented in unison as time advances. This may correspond to each item of user equipment UE2, UE3, and UE4 decrementing an integer counter from different starting values.

During time period 42, the first 30, second 32, and third 34 instances of the channel access function are counting down, but none have reached a value (in the example, “C=0”) enabling a transmission opportunity to be declared at any of the items of user equipment UE2, UE3, and UE4. Accordingly, the fourth item of user equipment UE4 generates a packet of data 25 for transmission from UE4. However, the value of the third instance of the channel access function 34 defining when UE4 may transmit the packet of data 25 indicates that a transmit opportunity is not currently available. Accordingly, the packet of data 25 is buffered at UE4. This means that the shared wireless channel remains free to other users.

At time Ti, the second instance of the channel access function 32 defining UE3’s channel access capability reaches “0”. This means that a transmit opportunity is declared at UE3 by, for example, firmware operating inside UE3. Optionally, other items of user equipment sensing the channel may maintain a shadow instance of UE3’s channel access function to enable predictive scheduling at other items of user equipment, for example, but this is optional. However, at this point, UE3 does not have a data packet waiting for transmission. Therefore, UE3 changes or resets the second instance 32 of the channel access function. Optionally, UE3 may change or reset the second instance 32 of the channel access function to a reset value which is not the limit value CMAX. In the illustrated example, UE3 changes or resets the second instance 32 of the channel access function to the limit value CMAX. Therefore, the shared wireless channel remains free. The data packet 25 buffered at U E4 thus remains untransmitted by U E4, because during time period 43, the value of the third instance 34 of the channel access function maintained by UE4 does not indicate the presence of a transmission opportunity into the shared wireless channel from UE4.

As time advances, the items of user equipment continue to recalculate their instances of the channel access function. At time T2, the third instance 34 of the channel access function maintained by UE2 reaches “0”, and UE4 sends its buffered packet. Accordingly, arrow 29 represents the delay between the arrival of data packet 25 in the buffer of UE4, and the transmission 26 of that data packet 25 on the shared wireless channel.

During time period 43, a third data packet 27 is generated by UE3, but the third data packet 27 must be buffered because the value of the second instance 32 of the channel access function maintained by UE3 does not indicate that UE3 has a transmission opportunity.

During time period 44, UE2 and UE3 detect or sense the transmission of the packet 25 on the shared wireless channel. Accordingly, the recalculation of the first 30 and second 32 instances of the wireless channel access function is triggered, respectively at UE2 (C(-d24)) and UE3 (C(- d34)). Since UE2 is further away from UE4 as compared to the distance between UE4 and UE3, the first instance 30 of the channel access function maintained by UE2 is smaller than the second instance 32 of the channel access function maintained by UE3. As illustrated, the recalculation of the respective instances of the channel access function occurs at the beginning of the channel access period of UE4. As an alternative example, the recalculation could occur as soon as UE4 has finished transmitting.

Because UE4 is, at the end of time period 44, the latest item of user equipment to have transmitted, the third instance 34 of the channel access function maintained at UE4 is recomputed to a limit value. In this example, the limit value is CMAX.

During time period 45, the first 30, second 32, and third 34 instances of the channel access function are (in this example) decremented in unison. Accordingly, the first instance 30 reaches “0”, inaugurating time period 46 during which only UE2 has a declared opportunity to transmit. However, UE2 does not have any waiting data to transmit. During time period 47, the second instance of the channel access function 32 reaches “0”, enabling data packet 27 to be transmitted by UE3.

According to an embodiment, after transmitting the item of data 23, 25, 27 from the first item of user equipment UE1 to the further item of user equipment, resetting the first channel access function of the first item of user equipment U El to a limit value of the first channel access function.

According to an embodiment, there is provided: receiving, at the first item of user equipment UE1, an indication that a third item of user equipment UE3 located at a third position has transmitted via the wireless channel; recomputing, at the first item of user equipment U El, the first value of the first channel access function of the first item of user equipment UE1, wherein the first value of the first channel access function is computed at least partially according to a spatial relationship between the first item of user equipment UE1 and the third item of user equipment UE3.

According to an embodiment, there is provided detecting, at the first item of user equipment U El, that the first item of user equipment U El has missed an opportunity to transmit data over the wireless channel to the second, or further item of user equipment, and in response to the detection, resetting the first channel access function of the first item of user equipment UE1 to the limit value of the first channel access function.

According to an embodiment, the first channel access function of the first item of user equipment U El is a monotonic function of time, optionally selected from a linear function, or an exponential function, or a parabolic function. A skilled person will understand that a wide range of backup functions may be applied as the channel access function, and that the present specification is not limited to those stated.

In an example, the limit value of the channel access function, or at least individual instances of the channel access function at each item of user equipment, can be based on the channel busy ratio (channel utilisation). In an example, sensor data at each item of user equipment can be used to calculate the counter value. For example, camera, LIDAR, or lookup of traffic information on a real-time Internet traffic database can optionally be used to calculate the limit values of the channel access function at each item of user equipment. For example, in the case that an individual item of user equipment is in an area, e.g., on a road, with low vehicular traffic density, the limit value can be reduced. This has the effect that an instance of the channel access function used at that individual item of user equipment has a shorter backoff waiting interval, and thus may be provided with more frequent opportunities to access the shared wireless channel. This results in a higher channel capacity, because the user equipment spends less time waiting to access the channel.

In an example, the amount of data transmitted in the transmission opportunity is a function of the limit value.

For example, an instance of the channel access function may have a lower limit value if the associated item of user equipment has a large amount of data buffered. This has the effect that an item of user equipment that requires a large number of channel access opportunities (because there is a lot of data to send from it) generates an instance of the channel access function to be used at that individual item of user equipment has a shorter backoff waiting interval, and thus may be provided with more frequent opportunities to access the shared wireless channel, compared to items of user equipment that do not generate and buffer as much data. In an example, the channel access function applied by an item of user equipment may be different based on whether or not the ego vehicle is behind, or ahead of, the item of user equipment relative to a direction of travel of the vehicle comprising the item of user equipment.

An example, the algorithm may be configured to account for multi-lane motorways, intersections, or roundabouts. Accordingly, the channel access function is a function (for example, a trigonometric ratio) of the distance (component) of a respective UE perpendicular to the direction of travel y and a distance (component) of the respective UE in the direction of travel x. For example, the channel access function may be a function of the derivative of the distance perpendicular to the direction of travel and the distance in the direction of travel f(dx; dy). Alternatively, a radial f and distance r component can be decomposed such that the channel access function is f(dcf>; dr).

According to an embodiment, there is provided the first value of the first channel access function of the first item of user equipment UE1 is computed in an application layer of operating software of the first item of user equipment, and transferred to the MAC layer of the first item of user equipment UE1 following computation.

According to an embodiment, there is provided identifying, at the first item of user equipment UE1, whether the second item of user equipment UE2 is ahead of the first item of user equipment UE1, or is behind the first item of user equipment UE1, relative to a predefined direction of the first item of user equipment UE1; and applying a second channel access function, different to the first channel access function, if the second item of user equipment UE2 is behind the first item of user equipment UE1, and applying the first channel access function if the second item of user equipment UE2 is ahead of the first item of user equipment UE1.

Fig. 6 schematically illustrates User Equipment according to the second aspect.

According to the second aspect, an item of user equipment UE1 configured to perform vehicular wireless channel access based on wireless channel collision avoidance, comprises non-transitory computer readable media 52 comprising machine readable instructions which, when executed, cause the item of user equipment UE1 to execute the method according to the first aspect of its embodiment discussed above and a processor 54 configured to load and to execute the machine readable instructions. Fig. 6 schematically illustrates a wireless device 50 (User Equipment) in accordance with the second aspect. The wireless device 50 comprises non-transitory computer readable media 52 and a processor 54 capable of reading the non transitory computer readable media 52.

The wireless device 50 is configured to communicate wirelessly with other network nodes and base stations. Wireless communication embraces the transmission and reception of information using, as a carrier, electromagnetic waves and in particular radio waves. The wireless device may transmit according to a predefined schedule, according to a predefined trigger internal to the wireless device 50, or according to user demand. A skilled person will be aware of many examples of a wireless device such as a smart phone, mobile phone, a desktop or laptop computer, a laptop, a vehicle-installed wireless device.

The wireless device may be configured for implementation of a 3GPP standard for device-to- device (D2D) communication, and in particular vehicle-to-vehicle (V2V) or vehicle-to- infrastructure (V2I) communication.

The wireless device 50 may further comprise a radio access module 58 communicatively coupled to the processor 54 and a wireless antenna 60. The wireless device 50 comprises an input interface 62 for receiving data to be transmitted, and an output interface 64 for communicating received data. The wireless device comprises a power source 56. In examples, the wireless device 50 may be referred to as a UE, a terminal, a radio network node, and the like. The wireless device may support at least device to device, internet of things, and V2X communications.

The wireless antenna 60 and radio access module 58 are configured to perform the physical layer functions of one or more radio access standards such as GSM (TM), WCDMA, WiFi (TM), Bluetooth (TM), LTE (TM), NR. The physical layer functions may be performed using an application-specific integrated circuit, software defined radio, and the like. Wireless antenna 60 may be integrated with, or separated from the wireless device 50. For example, the wireless antenna 60 may be mounted on the roof of a vehicle with which the wireless device 50 is integrated.

The non-transitory computer readable media 52 is configured to store a computer program, application, logic including machine code capable of being executed by the processor 54. The non-transitory computer readable media 52 includes RAM, ROM, EEPROM, and any other non-volatile device that stores that may be used by the processor 54. In examples, the processor 54 and the non-transitory computer readable media 52 are integrated on the same silicon die, or in the same packaging.

The power source 56 is optionally a battery integrated with the wireless device 50, a power source of a vehicle to which the wireless device 50 is integrated, and the associated power management circuitry.

The processor 54 optionally comprises one or more of a central processing unit, digital signal processor, application-specific integrated circuit, field programmable gate array, embedded microcontroller, microprocessor, capable of reading and executing instructions stored in the non-transitory computer readable medium 52. When the instructions stored in the non- transitory computer readable medium 52 are executed, the processor 54 implements a method of share wireless channel access orchestrated using the other components of the wireless device 50 as defined according to the first aspect or its embodiments.

According to a third aspect, there is provided a system configured to perform wireless channel access based on wireless channel collision avoidance comprising a first item of user equipment UE1 located at a first position, and a second item of user equipment UE2 located at a second position.

The first item of user equipment UE1 is configured to detect that a second item of user equipment UE2 has transmitted data via a wireless channel. The second item of user equipment UE2 is configured to transmit, to the first item of user equipment UE1, a first measured quantity transmitted from the second item of user equipment UE2 at the second position. The first item of user equipment UE1 is configured to declare at the first item of user equipment U El the presence of a transmission opportunity for the first item of user equipment UE1 to transmit data over the wireless channel to the second, or a further item of user equipment at a first time, wherein the first time is dependent on the first measured quantity and that the second item of user equipment UE2 has transmitted data.

According to an embodiment of the third aspect, each item of user equipment U El-U E4 of the system is comprised in a vehicle. Each item of user equipment UE1-UE4 is provisioned with, or has initialised, a counter within the set CUE = [0-CMAX]. The counter that each item of user equipment UE1-UE4 is provisioned with defines in how many slots of the shared wireless channel the corresponding item of user equipment can transmit. In an embodiment, the counter in each item of user equipment U El-U E4 is selected as a function of the geographical position. In an example, the value of the counter in each item user equipment is a function of whether, or not, the vehicle comprising the corresponding item user equipment is travelling in front of, or behind, and ego vehicle. In this example, all items of user equipment have the same function for calculating corresponding counter values based on whether, or not, the vehicle comprising the corresponding item of user equipment is travelling in front of, or behind, and ego vehicle.

For example, in the case that the last vehicle to transmit has a positive distance to the ego vehicle, the counter function should increase monotonically with the distance from the ego vehicle. This guarantees that vehicles having a smaller distance to the ego vehicle compared to the vehicle that was last heard, are heard first.

In the opposite case, if the vehicle that is “last heard” is behind the ego vehicle, the vehicles with the greatest distance to the ego vehicle are allowed to transmit again first. In this case, the selection of the counter can be performed by setting, for example, C= C_max - f(d), where C_max is the maximum possible counter value, d is the displacement to the ego vehicle, and f(.) is a channel access function. In an example, the function f(d) and the value of C_max can be optimised by mathematical modelling, computational simulation, or experimental trials so that the probability of hidden node collisions decrease, and resources in the shared wireless channel are used as efficiently as possible.

Accordingly, a wireless radio system according to the third aspect comprising items of user equipment configured to use the wireless channel access algorithm of the first aspect provides an emergent CSMA/CA approach in which the time interval defining a transmission opportunity of an individual item of user equipment is dependent on the arrangement of other items of user equipment in the proximity of the individual item of user equipment.

According to a fourth aspect, there is provided a computer readable medium comprising machine readable instructions configured to cause a processor to perform the method according to the first aspect, or the embodiments discussed above.

The examples provided in the drawings and described in the foregoing written description are intended for providing an understanding of the principles of this specification. No limitation to the scope of the appended claims is intended thereby. The present specification describes alterations and modifications to the illustrated examples. Only the preferred examples have been presented, and all changes, modifications and further applications to these within the scope of the specification are desired to be protected.

Claims

1. A wireless channel access method (8a, 8b) based on wireless channel collision avoidance, comprising: receiving (10a, 10b), at a first item of user equipment (UE1), a first measured quantity transmitted from a second item of user equipment (UE2) at the second position; detecting (12a, 12b), at the first item of user equipment (UE1) located at the first position, that the second item of user equipment (UE2) located at the second position has transmitted data via a wireless channel shared by the first and second items of user equipment; and declaring (14a, 14b), at the first item of user equipment (UE1), the presence of a transmission opportunity for the first item of user equipment (UE1) to transmit data over the wireless channel to a second, or further item of user equipment at a first time, wherein the first time is dependent on the first measured quantity and that the second item of user equipment (UE2) has transmitted data.

2. The method (8a, 8b) according to claim 1, wherein the first time is obtained by: computing (16), at the first item of user equipment (UE1), a first value of a first channel access function (30) of the first item of user equipment (UE1), wherein the first value of the first channel access function is computed at least partially according to the first measured quantity, updating (18), at the first item of user equipment (U El), the first channel access function as a function of time starting from the first value; and if (20), after an elapsed time interval, the first channel access function has reached a second value, declaring (14b) the presence of the transmission opportunity.

3. The method (8a, 8b) according to claims 1 or 2, wherein the first measured quantity is the second position of the second item of user equipment.

4. The method (8a, 8b) according to one of the preceding claims, further comprising: obtaining, at the first item of user equipment (UE1), an item of data (23, 25, 27) for transmission, wherein the item of data is generated by the first item of user equipment (UE1) and is for transmission via the wireless channel to the second, or a further item of user equipment; and if the presence of a transmission opportunity to transmit data over the wireless channel has been declared at the first item of user equipment (UE1), transmitting the item of data (23, 25, 27) from the first item of user equipment (UE1) to the second, or further item of user equipment.

5. The method (8a, 8b) according to one of claims 2 to 4, further comprising: after transmitting the item of data (23, 25, 27) from the first item of user equipment (UE1) to the further item of user equipment, resetting the first channel access function of the first item of user equipment (UE1) to a limit value of the first channel access function.

6. The method (8a, 8b) according to one of claims 2 to 5, further comprising: receiving, at the first item of user equipment (UE1), an indication that a third item of user equipment (UE3) located at a third position has transmitted via the wireless channel; recomputing, at the first item of user equipment (U El), the first value of the first channel access function of the first item of user equipment (UE1), wherein the first value of the first channel access function is computed at least partially according to a spatial relationship between the first item of user equipment (UE1) and the third item of user equipment (UE3)

7. The method (8a, 8b) according to one of claims 2 to 6, further comprising: detecting, at the first item of user equipment (U El), that the first item of user equipment

(U El) has missed an opportunity to transmit data over the wireless channel to the second, or further item of user equipment, and in response to the detection, resetting the first channel access function of the first item of user equipment (UE1) to a or the limit value of the first channel access function.

8. The method (8a, 8b) according to one of claims 2 to 7, wherein the first channel access function of the first item of user equipment (UE1) is a monotonic function of time, optionally selected from a linear function, or an exponential function, or a parabolic function.

9. The method (8a, 8b) according to one of claims 2 to 8, wherein the first channel access function is implemented as an integer counter that is incremented or decremented in steps from the first value of the first channel access function to the second value of the first channel access function, wherein each increment or decrement of the counter is triggered per slot of a channel access protocol of the first item of user equipment (UE1).

10. The method (8a, 8b) according to one of the preceding claims, wherein at least the first measured quantity is transmitted to the first item of user equipment (UE1) from the second item of user equipment (UE2) according to at least one of: position information of the second item of user equipment (UE2) comprised in the transmission from the second item of user equipment (UE2), cooperative awareness message (CAM) data transmitted by at least the second item of user equipment (UE2), cooperative perception messaging (CPM) transmitted by at least the second item of user equipment (U E2), time stamp information and/or geographical coordinate data comprised in the transmission from at least the second item of user equipment (UE2).

11. The method (8a, 8b) according to one of claims 2 to 10, wherein the first value of the first channel access function of the first item of user equipment (UE1) is computed in an application layer of operating software of the first item of user equipment (UE1), and transferred to the MAC layer of the first item of user equipment (UE1) following computation.

12. The method (8a, 8b) according to one of claims 2 to 11, further comprising: identifying, at the first item of user equipment (UE1), whether the second item of user equipment (UE2) is ahead of the first item of user equipment (UE1), or is behind the first item of user equipment, relative to a predefined direction of the first item of user equipment (UE1); and applying a second channel access function, different to the first channel access function, if the second item of user equipment (UE2) is behind the first item of user equipment (UE1), and applying the first channel access function if the second item of user equipment (U E2) is ahead of the first item of user equipment (U El).

13. An item of user equipment (UE1) configured to perform vehicular wireless channel access based on wireless channel collision avoidance, comprising: non-transitory computer readable media (52) comprising machine readable instructions which, when executed, cause the item of user equipment (UE1) to execute the method according to one of claims 1 to 12; and a processor (54) configured to load and to execute the machine readable instructions.

14. A system configured to perform wireless channel access based on wireless channel collision avoidance comprising: a first item of user equipment (UE1) located at a first position, and - a second item of user equipment (UE2) located at a second position; wherein the first item of user equipment (UE1) is configured to detect that a second item of user equipment (UE2) has transmitted data via a wireless channel; wherein the second item of user equipment (UE2) is configured to transmit, to the first item of user equipment (UE1), a first measured quantity transmitted from the second item of user equipment (UE2) at the second position; wherein the first item of user equipment (UE1) is configured to declare at the first item of user equipment (UE1) the presence of a transmission opportunity for the first item of user equipment (UE1) to transmit data over the wireless channel to the second, or a further item of user equipment at a first time, wherein the first time is dependent on the first measured quantity and that the second item of user equipment has transmitted data.

15. A computer readable medium comprising machine readable instructions configured to cause a processor to perform the method according to one of claims 1 to 12.