GB2471287A

GB2471287A - Communication message congestion control for the nodes of an intelligent transport system.

Info

Publication number: GB2471287A
Application number: GB0910810A
Authority: GB
Inventors: Hisashi Manabe
Original assignee: NEC Europe Ltd
Current assignee: NEC Europe Ltd
Priority date: 2009-06-23
Filing date: 2009-06-23
Publication date: 2010-12-29
Also published as: GB0916801D0; GB2471347A; GB0910810D0

Abstract

Disclosed is a communication system for a vehicle-to-vehicle communication network, ie an intelligent transport system (ITS) in which message congestion control is done by the nodes of the system. The nodes can communicate to each other and have means to determine the level of message congestion in the communication channel. A node that determines that the congestion level has reached or passed a threshold for that node, generates and transmits a signal requesting that a congestion control procedure be started. Other nodes that receive the signal initiate the requested congestion control procedure. The nodes that receive the signal may also determine the congestion level at that node and then if the level has reached or passed a threshold pass on the congestion control procedure requesting signal. The congestion control procedure may be to modify transmission power, the interval between messages and the size of the data packets.

Description

Communication System The present invention relates to communication networks and devices, and in particular but not exclusively to the provision of wireless access in vehicular environments (WAVE). The invention has particular although not exclusive relevance to so called intelligent transportation system communication networks.

The provision of wireless access in vehicular environments (WAVE) I dedicated short range communications (DSRC) for emerging Intelligent Transportation Systems (ITS) is becoming increasingly important and has many potential applications including, for example: systems for providing vehicles with emergency warnings from other vehicles in the vicinity (e.g. in the case of an emergency stop, accident, breakdown or the like); various collision avoidance applications; automated congestion and other road I parking charging systems; and inter-vehicle co-operative adaptive cruise control.

A frame-work for wireless communications required to support ITS is provided for by IEEE 802.11 p, which is an amendment to the IEEE 802.11 standard which sets out a number of enhancements to the standard aimed at supporting data communications between high-speed vehicles and between the vehicles and the roadside infrastructure in the associated ITS band (e.g. 5.9 GHz in the US and -5.8 GHz in Japan, and Europe).

In ITS, vehicle-to-vehicle communication will use a carrier sense multiple access protocol with collision avoidance (CSMAICA) which is a Media Access Control (MAC) protocol in which a communication node checks for the presence or absence of communication traffic on the communication channel, and transmits its data if the channel is free or delays transmission if the channel is busy. Accordingly, as more vehicles use the same communication channel, the channel becomes congested and this can result an inherent increase in the delay before a node can access the channel for transmission. Thus, congestion can represent a serious issue for vehicle-to-vehicle communication, especially for the transmissions of time-sensitive information such as safety' related information including, for example, emergency

I

alerts. In such examples, longer access delay times are highly undesirable and, ideally, should be prevented.

In order to cater for the expected large-scale provision of vehicle-to-vehicle communication capabilities in future vehicles, therefore, these communication congestion issues need to be addressed. Current proposals for addressing these issues, however, are based on flawed assumptions and as a result fail to address the congestion issues adequately. For example, current proposals assume that if a vehicle based communication node detects signal (communication) congestion in the channel it will reduce the rate at which it transmits its messages and/or reduce transmission power and that all other vehicle based communication nodes in the vicinity (and contributing to the signal congestion) will also detect the signal congestion and, accordingly, will also reduce their transmission rates and/or power, thereby reducing the signal congestion in the communications channel. However, there are situations in which this assumption does not hold and, accordingly, vehicle based communication nodes may remain in a congested state because of communications from other nodes in the vicinity which have failed to detect the signal congestion.

Accordingly, preferred embodiments of the present invention aim to provide methods and apparatus which overcome or at least alleviate the above issues.

According to one aspect of the present invention there is provided a communication node for communicating with at least one further communication node of a communication network over a communication channel, the communication node comprising: means for determining a congestion level in the communication channel; means for generating, in dependence on said determined congestion level, a signal for requesting initiation of a congestion control procedure; and means for transmitting said signal for requesting initiation of a congestion control procedure to said at least one further communication node.

The communication node may comprise means for initiating a congestion control procedure which may be operable to initiate a first congestion control procedure in dependence on said determined congestion level. The means for initiating a congestion control procedure may be operable to initiate the first congestion control procedure after said signal for requesting initiation of a congestion control procedure has been sent to said at least one further communication node.

The communication node may comprise means for receiving a signal for requesting initiation of a congestion control procedure from a further communication node, and the means for initiating a congestion control procedure may be operable to initiate a second congestion control procedure in response to receipt of said signal from said further communication node.

According to another aspect of the present invention there is provided a communication node for communicating with at least one further communication node over a communication channel, the communication node comprising: means for receiving a signal requesting initiation of a congestion control procedure from a further communication node; and means for initiating, in response to receipt of said signal, a congestion control procedure.

The communication node may comprise means for determining a congestion level in the communication channel, may comprise means for generating, in dependence on said determined congestion level, a signal for requesting initiation of a congestion control procedure; and may comprise means for transmitting said signal for requesting initiation of a congestion control procedure to at least one further communication node. The means for initiating a congestion control procedure may be further operable to initiate the congestion control procedure in dependence on said determined congestion level.

According to another aspect of the present invention there is provided a system (e.g. an intelligent transport system (ITS)) comprising first and second communication nodes each operable for communication over a communication channel, the first communication node comprising: means for determining a congestion level in the communication channel; means for generating, in dependence on said determined congestion level, a signal for requesting initiation of a congestion control procedure; and means for transmitting said signal for requesting initiation of a congestion control procedure to said second communication node; and the second communication node comprising: means for receiving said signal requesting initiation of a congestion control procedure from said first communications node; and means for initiating, in response to receipt of said signal, a congestion control procedure.

The (or each) congestion control procedure may comprise modifying at least one of a transmission power, an interval between transmitted signals, and/or the size of transmitted data packets.

According to another aspect of the present invention there is provided a method performed by a communication node of a communication network which communication node is operable for communication with at least one further communication node over a communication channel, the method comprising: determining a congestion level in the communication channel; generating, in dependence on said determined congestion level, a signal for requesting initiation of a congestion control procedure; and transmitting said signal for requesting initiation of a congestion control procedure to at least one further communication node of said communication network.

The method may further comprise initiating a congestion control procedure in dependence on said determined congestion level.

According to another aspect of the present invention there is provided a method performed by a communication node of a communication network which communication node is operable for communication with at least one further communication node over a communication channel, the method comprising: receiving a signal requesting initiation of a congestion control procedure from the further communication node; and initiating, in response to receipt of said signal, a congestion control procedure.

The communication node may comprise a means for identifying a preferred/optimum congestion control level. The preferred/optimum congestion control level may represent a preferred level of congestion control to be applied either by the communication node identifying the preferred/optimum congestion control level or the further communication node. Accordingly, the congestion control request may comprise information identifying the preferred/optimum congestion control level.

The (or each) congestion control procedure may comprise a procedure for reducing the contribution of the communication unit to (signal) congestion. For example, the congestion control procedure may comprise modifying at least one of a transmission power (e.g. decreasing transmission power for reducing congestion), an interval between transmitted signals (e.g. increasing the interval for reducing congestion), and the size of transmitted data packets (e.g. reducing the packet size for reducing congestion).

The first and second congestion control procedures may use the same or a different procedure for reducing the contribution of the communication unit to (signal) congestion.

The congestion control procedure may be initiated in dependence on the determined congestion level (for example, when the determined congestion level or a parameter indicative of the congestion level indicates a congested situation -possibly by exceeding a predetermined threshold). The congestion control procedure may also be initiated in response to receipt of a signal from a further communication node requesting the initiation.

The congestion control procedure may be initiated in dependence on a reduction in the determined congestion level (and possibly a predetermined criteria or plurality of criteria). In this case, the (or each) congestion control procedure may be operable to reduce an existing level of congestion control, for example by modifying at least one of a transmission power (e.g. increasing transmission power), an interval between transmitted signals (e.g. decreasing the interval), and the size of transmitted data packets (e.g. increasing the packet size).

Communication between units may be via a shared frequency resource but use signals separated in time. Communication between units may use a shared time resource with signals separated in frequency. Communication between units may use signals separated in both frequency and time.

The communication network may form an (or part of an) intelligent transport system (ITS).

Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings in which: Figure 1 is a simplified illustration of a vehicle based communication network; Figure 2 schematically illustrates the main components of a vehicle based communication unit forming part of the network shown in Figure 1; Figure 3 is a flow diagram illustrating operation of an exemplary implementation of the vehicle based communication unit of Figure 2; and Figures 4a to 4e are sequential time interval diagrams illustrating the benefits of a preferred implementation of the vehicle based communication unit of Figure 2.

Overview Figure 1, is a simplified illustration of a vehicle based communication network generally at 2. The vehicle based network 2 comprises an ad-hoc' network including a plurality of vehicles 4-1 to 4-8 (generally 4') each provided with a respective communication unit 6-1 to 6-8 (generally 6'), and a plurality of road-side' communication units 8-1, 8-2 (generally 8') forming part of a wider communication infrastructure (not shown).

The communication units 6, 8 are configured for wireless communication with one another (including vehicle-to-vehicle V2V', vehicle-to-infrastructure V21', and infrastructure-to-vehicle 12V' communication) using a short/medium range communication protocol suitable for supporting intelligent transportation system (ITS) applications. The communication units may, for example, be operable to communicate with one another using a medium access control (MAC) protocol, for example a contention based multiple access mechanism such as a carrier sense multiple access protocol with collision avoidance (CSMNCA). The protocol may, for example, comprise a protocol which is compatible with the so called Dedicated Short Range Communications (DSRC) and/or Wireless Access in a Vehicular Environment (WAVE) related standards (for example the IEEE 802.11 standard as amended by IEEE 802.llp).

The vehicle based communication units 6 employ a method of congestion control in which a congestion control request signal is transmitted by a communication node 6 of one vehicle (when signal congestion is detected by that communication unit 6), to the communication units 6 of other vehicles, just prior to initiation of a congestion control procedure aimed at reducing its contribution to signal congestion. The communication units 6 of the other vehicles that receive the congestion control request activate their own congestion control procedure aimed at reducing their contribution to signal congestion. In this way improvements in congestion control are achieved at times when efficient congestion control is particularly critical.

Vehicle Based Communication Units Figure 2 schematically illustrates the main components of the vehicle based communication unit 6 shown in Figure 1.

As shown, the communication unit comprises receiver circuitry 20 and transmitter circuitry 22 respectively operable to receive signals from and to transmit signals to other vehicle based or road-side communication units 6, 8 via one or more antennae 24. As shown, the vehicle based communication unit 6 also includes an intelligent transport system (ITS) management processor 26 which is operable to control operation of the vehicle based communication unit 6 including, for example, operation of the receiver and transmitter circuitry 20, 22, interaction with a user via suitable input/output units 28 (e.g. loudspeaker, display, user control pad or the like), and the acquisition of vehicle information, via a corresponding sensor and navigation system interface 29, from vehicle mounted sensors and a vehicle based navigation system such as a global navigation satellite system (GNSS). For example, the interface 29 of the communication unit 6 may interface with an automotive navigation terminal (e.g. a GNSS) either directly or indirectly via an in-vehicle Local Area Network (LAN) and may obtain from it current position, speed, direction and acceleration information for the vehicle. The interface 29 may also receive inputs from other vehicle mounted sensors that provide similar or other vehicle related information. The management processor 26 operates in accordance with software instructions stored within memory 30, which software instructions comprise, amongst other things, an operating system 31.

The vehicle based communication unit 6 also includes, amongst other things, a received signal analysis module 32, a transmitter power control module 34, a congestion status analysis module 36, a congestion reduction control module 38, and a signal generation module 40.

The received signal analysis module 32 is operable to process signals received from the other communication units 6, 8, to analyse the contents of the signals, and to initiate appropriate responses to receipt of the signal when required. The transmitter power control module 34 is operable to control the power used by the transmitter to transmit signals to other communication units 6, 8 and, accordingly, to control the effective range of the transmitted signals. The congestion status analysis module 36 is operable to monitor the usage of the communication channel (or channels) used for vehicle-to-vehicle, vehicle-to-infrastructure and/or infrastructu re-to-vehicle communications, and to identify a communication congestion level within the channel (or channels). The congestion reduction control module 38 is operable to initiate congestion reduction procedures, to enforce (increase) or moderate (decrease) a level of congestion control being applied, or to initiate termination of a congestion control procedure in dependence upon the congestion level within the channel (or channels) as identified by the congestion status analysis module 36. The signal generation module 40 is operable to generate signals for communication to other communication units 6, 8. The signals generated typically carry, for example: regular messages carrying vehicle related information such as stored identification information (e.g. vehicle ID), and information acquired from the GNSS via the sensor and navigation system interface 29; alert messages for alerting or warning other users to a potentially hazardous situation (e.g. a vehicle breakdown); and other such messages.

In one embodiment, for example an on-board unit (OBU) for Safety-ITS will identify the location of the vehicle in which it is installed by GNSS and then broadcast the self-location-information (e.g. latitude, longitude, altitude) by embedding the location information into a signal (often referred to as a beacon) as one of the parameters of the signal. The broadcasting of this location information allows other vehicles that receive the signal to determine the location of the vehicle that broadcast the signal.

Similarly, location information for other vehicles nearby is obtained from beacon messages received from those other vehicles. Accordingly, in operation, when congestion is detected by the congestion status analysis module 36, the congestion reduction control module 38 initiates generation of the congestion control request signal by the signal generation module 40 for broadcast by the transmitter circuitry 22, just prior to initiation of the congestion control procedure. In response to receiving the congestion control request, the congestion reduction control module 38 in the communication unit 6 of each other vehicle 4 activates a corresponding congestion control procedure for that vehicle.

In this example, the congestion control procedure typically comprises a procedure for reducing the contribution of the communication unit 6 to signal congestion by reducing the transmission power as controlled by the transmission power control module 34 (thereby reducing the range of the transmitted signals and decreasing the number of vehicles that will receive the transmitted signals). In other examples, the congestion control procedure may comprise increasing the interval between transmitted signals (thereby reducing the number of signals transmitted per unit time), and/or reducing the size of the transmitted data packets (thereby reducing the amount of data transmitted per unit time).

It will be appreciated that some or all of the functionality of the various modules of the vehicle based communication unit 6 may be provided by dedicated hardware circuits and/or that some or all of the functionality may be provided by the management processor 26 operating in accordance with software instructions, stored within memory 30 and arranged to provide the corresponding functionality.

Signal Congestion Reduction Figure 3 is a flow diagram illustrating operation of an exemplary implementation of a vehicle based communication unit 6 to assist a reduction in communications congestion (e.g. when several communication units 6 are within range of one another).

As described above, the congestion status analysis module 36 is operable to monitor congestion on communications channel(s) to determine a communication congestion level within a channel (or channels) over which signals are being transmitted and/or received. In accordance with this embodiment, the congestion status analysis module 36 measures parameters indicative of the level of congestion as shown at step Sb in Figure 3. In this implementation, the congestion status analysis module 36 is operable to determine a communication congestion level based on measurements of a channel usage parameter.

Furthermore, the congestion status analysis module 36 is operable to provide an indication of the prevailing signal congestion conditions (for example, based on a comparison of the congestion level, or a congestion parameter, with one or more predetermined thresholds stored in memory 30) to the congestion reduction control module 38.

The congestion reduction control module 38 is operable to monitor the prevailing conditions indicated by the congestion status analysis module 36 to determine, at step S12, when the channel is under congestion.

Conditions Indicative of Congestion at Step S12 In the event that the communication channel is deemed to be under congestion, the congestion status analysis module 36 notifies the congestion reduction control module 38 to initiate a congestion reduction procedure.

The congestion reduction control module 38 is operable, on identifying that the communication channel is under congestion, to determine an appropriate congestion control level for other vehicle based communication units 6 within range of the transmitter 22 of the communication unit 6 which identified the congested status (step S14). The congestion control level is indicative of the extent to which congestion control should preferably be applied by other vehicle based communication units 6 in the vicinity. The congestion reduction control module 38 is further operable to notify the signal generation module 40 of the determined congestion control level, thereby to initiate generation and transmission of a congestion control request.

As shown at step S16, the signal generation module 40 is operable, on receipt of information identifying the required congestion control level, to generate the congestion control request, including an indication of the required congestion control level, and to initiate broadcast, by the transmitter circuitry 22, of the congestion control request to other vehicle based communication units 6 in the vicinity.

Prior to enforcing (increasing) an existing level of congestion control (or initiating congestion control) as described previously, the unit 6 ensures that any existing congestion control can be stepped-up (increased/reinforced). Accordingly, the congestion reduction control module 38 is further operable, at step S19, to determine if the current level of congestion control for its own' vehicle 4 (i.e. the vehicle 4 in which the unit 6 that has detected the congestion is installed) has reached (or exceeded) a maximum level (for example, by reference to a maximum congestion control' flag or by comparison with a maximum congestion control level stored in memory 30). If the existing level of congestion control has reached (or exceeded) the maximum level, then the congestion reduction control module 38 simply returns to congestion monitoring (step S10) without a further reinforcement in the level of congestion control employed.

In the event that the existing level of congestion control has not reached (or exceeded) the maximum level, the congestion reduction control module 38 is operable to determine an appropriate (increased) congestion control level for its own vehicle 4 (step S20) and to initiate a reinforcement in the level of congestion control accordingly (step S22) by stepping up the level of congestion control applied, towards the maximum congestion control level for the unit 6. The determined congestion control level is dependent on an optimum congestion control level (e.g. the congestion control level determined at step S14) and the maximum congestion control level for the unit 6.

As described above, there are a number of different ways in which the congestion reduction control module 38 may be operable to implement the reinforcement of the congestion control. In the present embodiment, for example as described above, the congestion reduction control module 38 is operable to reinforce the level of congestion control by initiating a reduction in transmitter power by the transmitter power control module 34 (referred to as transmitter power control (TPC)').

Accordingly, the range of the transmitter is decreased and hence any communication units 6 which, as a result of the power reduction, become located outside the new range will receive fewer signals (less communications traffic) thereby reducing the signal congestion on those other communication units 6.

In another embodiment, as mentioned above, the congestion reduction control module 38 is operable to initiate an increase in the interval between the signals generated by the signal generation module 40 (referred to as signal interval control (SIC)') for transmission by the transmitter circuitry 22. Accordingly, the number of signals sent by the transmitter per unit time, and received by other communication units 6, 8 within range, is decreased thereby reducing signal traffic and hence congestion for the other communication units 6, 8.

In another embodiment, as mentioned above, the congestion reduction control module 38 is operable to initiate a reduction in the size of message packets generated by the signal generation module 40 (referred to as message size control (MSC)') for transmission by the transmitter circuitry 22. Accordingly, the amount of data sent by the transmitter per unit time, and received by other communication units 6, 8 within range, is decreased thereby reducing congestion for the other communication units 6, 8.

After the congestion reduction control level has been increased the congestion reduction communication unit 6 then returns to congestion monitoring as described with reference to step Sb.

Conditions not Indicative of Congestion at Step S12 In the event that the conditions do not indicate the communication channel to be congested at step S12, the congestion status analysis module 36 is operable, at step S24, to monitor for receipt of an indication from the signal analysis module 32, that a congestion control request has been received from another vehicle based communication unit 6. It will be appreciated that, although shown sequentially, this monitoring may be carried out substantially in parallel with congestion monitoring rather than after a specific determination that the communication channel is deemed not to be congested.

The congestion status analysis module 36 is operable, in the event that a congestion control request has been received from another vehicle based communication unit 6, to initiate a request based congestion control procedure which essentially follows steps S19 to S22 as described above and will not, therefore, be described again.

As described previously, there are number of different ways in which the congestion reduction control module 38 may be operable to implement the increase in congestion control including, for example TPC, SIC or MSC. The method employed for congestion reduction may be dependent on the contents of the congestion control request message, which may be configured to include an explicit (or implicit) indication of a preferred type of congestion reduction.

After the congestion reduction control level has been increased the congestion reduction control module 38 then returns to congestion monitoring (step Sb).

The congestion reduction control module 38 is operable, in the event that a congestion control request has not been received from another vehicle based communication unit 6, to determine if its own communication unit 6 is currently subject to a level of congestion control (step S26). If it is not, then the control module 38 returns to the monitoring step SlO described above.

Otherwise, the congestion reduction control module 38 is operable to monitor the prevailing congestion conditions indicated by the congestion status analysis module 36 to determine whether or not the level of congestion control to which the communication unit 6 is subject, may be moderated based on a predetermined set of criteria (step S28).

In this embodiment, the predetermined set of criteria for reducing (moderating) congestion control are set to ensure that oscillation between different levels of congestion control (e.g. between increasing and decreasing congestion control) is avoided. The criteria may include, for example, a requirement that the prevailing congestion level has been stable for a predetermined length of time, before allowing the level of congestion control to be moderated. The criteria of S28 may alternatively or additionally include criteria based on the number of vehicle based communication units 6 in the vicinity. For example, if the number of vehicles in the vicinity is 30 when congestion is indicated at S12, the criteria of step S28 may be met when the number of vehicle based communication units 6 drops to 25 (thereby avoiding oscillation resulting from a smaller change in the number of vehicle based communication units 6 in the vicinity).

In the event that the criteria for reducing congestion control have been met, the congestion reduction control module 38 is operable to determine an appropriate (reduced) congestion control level for its own vehicle 4 (step S30) and to initiate a moderation in the level of congestion control accordingly (step S18) by stepping down the level of congestion control applied, towards no congestion control for its own unit 6.

There are a number of different ways in which the congestion reduction control module 38 may be operable to implement the moderation in congestion control. In the present embodiment, for example, the congestion reduction control module 38 is operable to moderate the level of congestion control by initiating an increase in transmitter power by the transmitter power control module 34 (TPC). Accordingly, the range of the transmitter is increased and hence any communication units 6 which, as a result of the power increase, become located within the new range will begin to receive signals from the communication unit 6 once again.

In another embodiment, the congestion reduction control module 38 is operable to initiate a decrease in the interval between the signals generated by the signal generation module 40 (SIC) for transmission by the transmitter circuitry 22.

Accordingly, the number of signals received from the communication unit 6, by other communication units 6, 8 within range, is increased once again.

In another embodiment, the congestion reduction control module 38 is operable to initiate an increase in the size of the message packets generated by the signal generation module 40 (MSC) for transmission by the transmitter circuitry 22.

Accordingly, the amount of data received from the communication unit 6, by other communication units 6, 8 within range, is increased once again.

It will be appreciated that the congestion reduction control module 38 may be operable to implement any suitable mechanism for moderating the level of congestion control applied and may use any appropriate combination of such mechanisms (at different times or substantially simultaneously) to optimise the level of congestion control. It will be further appreciated that moderating the congestion control level may comprise removing all congestion control to which the communication unit 6 was previously subject.

After the congestion reduction control level has been moderated in this way, or in the event that the criteria for reducing congestion control have not been met at step S28, the communication unit 6 returns to congestion monitoring substantially as described with reference to step SlO.

Benefits and Advantages Some of the benefits I advantages of the various embodiments are illustrated in Figures 4(a) to 4(e). Figures 4(a) to 4(c) comprise a set of sequential time interval diagrams illustrating operation of an exemplary intelligent transport system in which only some of the technical features described for the communication units are implemented. Figures 4(a), 4(d) and 4(e), on the other hand, illustrate operation of an intelligent transport system in which the vehicle communication units comprise the features of at least one of the embodiments described.

Figure 4(a) -Time Point I In Figure 4(a) the systems are shown in an initial state (or first time point) in which there are seven vehicles (Vi to V7) at different distances relative to one another (as illustrated by arrow A') and each having an associated vehicle communication unit 6 (not shown). Each vehicle communication unit 6 has a respective transmitter range represented by arrows BI' to B7' which is a function of transmitter power. The vertical line (Cl to C7) through each vehicle (VI to V7) may be visualised as a virtual antenna' for that vehicle indicating the capability of the corresponding communication unit to receive messages from other vehicles (VI to V7) in dependence on their transmitter range (BI to B7).

In Figures 4(a) to 4(e), a circle at the intersection between a range arrow (BI to B7) for the communication unit 6 of a first vehicle (VI to V7) and a vertical line (CI to C7) through (or virtual antenna' for) a second vehicle (VI to V7) is indicative of the second vehicle's communication unit being able to receive messages from the first vehicle's communication unit.

As seen in Figure 4(a), for example: vehicle VI is capable of receiving messages from just one other vehicle (vehicle V2); vehicle V2 is capable of receiving messages from four other vehicles (VI, V3, V4 and V5); vehicle V3 is capable of receiving messages from four other vehicles (V2, V4, V5 and V6); vehicle V4 is capable of receiving messages from four other vehicles (V2, V3, V5 and V6); vehicle V5 is capable of receiving messages from four other vehicles (V2, V3, V4 and V6); vehicle V6 is capable of receiving messages from four other vehicles (V3, V4, V5 and V7); and vehicle V7 is capable of receiving messages from just one other vehicle (V6).

The number of communication units from which a particular vehicle may receive messages (and shown at the top of the corresponding vertical line (CI to C7)) is indicative of channel usage for the associated communication unit 6 with higher numbers indicating a greater chance of channel congestion. In the illustrated systems of Figures 4(a) to 4(e), for ease of explanation, it is assumed that the channel becomes congested when the number of communication units from which a particular vehicle may receive messages reaches five. It will be appreciated, however, that in practical applications the number of communication units communicating using a particular channel before congestion occurs may be much larger, for example thirty or more units 6, depending on how the communication channel is being used, the nature of messages being sent, etc. Figure 4(b) -Time Point 2 -exemplary ITS Figure 4(b) shows the situation at a second time point for the exemplary intelligent transport system.

In Figures 4(a) to 4(e) vehicles V2 to V7 are moving at substantially the same speed whilst vehicle VI (shown with diagonal hatching) is moving faster. Accordingly, as shown in Figure 4(b) at the second (later) time point, vehicle VI is closer to the other vehicles (vehicles V2 to V7) and, accordingly, the communication units 6 of vehicle V3 and vehicle V4 are now within transmitter range Bi as illustrated by the solid black circles on vertical lines C2 and C3.

As seen in Figure 4(b), therefore: vehicle VI is now capable of receiving messages from three other vehicles (V2, V3, V4); vehicle V2 is still capable of receiving messages from four other vehicles (VI, V3, V4 and V5); vehicle V3 is now capable of receiving messages from five other vehicles (VI, V2, V4, V5 and V6); vehicle V4 is also now capable of receiving messages from five other vehicles (VI, V2, V3, V5 and V6); vehicle V5 is capable of receiving messages from four other vehicles (V2, V3, V4 and V6); vehicle V6 is still capable of receiving messages from four other vehicles (V3, V4, V5 and V7); and vehicle V7 is still capable of receiving messages from just one other vehicle (V6).

Accordingly, vehicles V3 and V4 are now capable of receiving messages from five other vehicles and, for illustrative purposes, are therefore assumed to be subject to congestion.

Unlike, the communication units 6 described above the communication units 6 of the exemplary intelligent transport system are not configured to carry out step S16 in Figure 3 in which a congestion control request is generated and transmitted to other communication units 6 in the vicinity, or step S24 in which a congestion control request is received from other communication units 6 (e.g. based on the assumption that all vehicles contributing to congestion will be able to accurately detect the onset of congestion). Thus, on detection of the congestion which occurs at time point 2, the communication units 6 of vehicles V3 and V4 initiate their own congestion reduction control procedures only (nominally to reduce their own contribution to any congestion).

Figure 4(c) -Time Point 3 -exemplary ITS Figure 4(c) shows the situation at a third time point after the communication units 6 of vehicles V3 and V4 have initiated their own congestion reduction control procedures. As seen in Figure 4(c), the communication unit 6 of each of vehicles V3 and V4 (horizontally and vertically hatched) has reduced its transmitter power and, accordingly, vehicles VI, V2 and V6 are no longer within range (as illustrated by the dotted circles).

As seen in Figure 4(c), therefore: vehicle VI is once again capable of receiving messages from just one other vehicle (V2); vehicle V2 is now capable of receiving messages from just two other vehicles (VI and V5); vehicle V3 is still capable of receiving messages from five other vehicles (VI, V2, V4, V5 and V6); vehicle V4 is also still capable of receiving messages from the five other vehicles (VI, V2, V3, V5 and V6); vehicle V5 is still capable of receiving messages from four other vehicles (V2, V3, V4 and V6); vehicle V6 is now capable of receiving messages from just two other vehicles (V5 and V7); and vehicle V7 is still capable of receiving messages from just one other vehicle (V6).

However, at time point 2, most of the communication units 6 contributing to the congestion seen by the communication units 6 of vehicles V3 and V4 (those of vehicles VI, V2, V5, V6) are not under congestion and so have not taken any action to reduce congestion. Accordingly, the communication units 6 of vehicles V3 and V4 remain under congestion at time point 3. Furthermore, the action taken by the communication units 6 of vehicles V3 and V4 has reduced signal traffic to the communication units of vehicles VI, V2 and V6. Hence, congestion control action by the communication units of vehicles VI, V2 and V6, which might otherwise help to alleviate congestion for the communication units 6 of vehicles V3 and V4, becomes less likely.

Thus, after the congestion is detected, the action of one vehicle based communication unit 6 to activate congestion reduction control (TPC, SIC and/or MSC) for the vehicle 4 in which it is located does not resolve the local congestion.

More specifically, the assumption that all other vehicle based communication units 6 nearby will detect the congestion using the same standardised procedures, and take appropriate congestion reduction action (TPC, SIC and/or MSC), thereby to decrease radio channel usage, does not hold.

As illustrated, a communication unit 6 for a vehicle 4 located at an edge of a region of road traffic congestion may not detect the congestion because the threshold for such detection is not reached. Thus, the radio channel usage causing congestion is not resolved despite the congestion reduction control for the vehicle experiencing the congestion being activated. This issue is compounded because the approach of vehicles to a region of road traffic congestion (where vehicle to vehicle collisions are more likely) is one of the most important situations in which road-safety ITS applications need to work correctly. However, in systems based on the exemplary ITS, such applications may not work effectively because the radio channel usage is high at the edge of road traffic congestion with associated increases in channel access delay. This means the vehicle-to-vehicle communication is delayed, and safety-related information, such as vehicle-location information, sent over the communication channel will be obsolete by the time the information is received.

Figure 4(d) -Time Point 2 -embodiment ITS Figure 4(d) shows the situation at the second time point for the intelligent transport system according to an embodiment, that comprises the vehicle based communication units 6 as described previously.

As described previously, in Figures 4(a) to 4(e) vehicles V2 to V7 are moving at substantially the same speed whilst vehicle VI (shown with diagonal hatching) is moving faster. Accordingly, as shown in Figure 4(d) at the second time point, vehicle VI is closer to the other vehicles (vehicles V2 to V7) and, accordingly, the communication units 6 of vehicle V3 and vehicle V4 are now within transmitter range BI as illustrated by the solid black circles on vertical lines C2 and C3.

As seen in Figure 4(d), therefore: vehicle VI is now capable of receiving messages from three other vehicles (V2, V3, V4); vehicle V2 is still capable of receiving messages from four other vehicles (VI, V3, V4 and V5); vehicle V3 is now capable of receiving messages from five other vehicles (VI, V2, V4, V5 and V6); vehicle V4 is also now capable of receiving messages from five other vehicles (VI, V2, V3, V5 and V6); vehicle V5 is capable of receiving messages from four other vehicles (V2, V3, V4 and V6); vehicle V6 is still capable of receiving messages from four other vehicles (V3, V4, V5 and V7); and vehicle V7 is still capable of receiving messages from just one other vehicle (V6).

Unlike the communication units 6 of the exemplary ITS, however, the communication units 6 of the embodiment are configured to carry out step S16 in Figure 3 in which a congestion control request is generated and transmitted to other communication units 6 in the vicinity (when congestion is detected), and step S24 in which a congestion control request is received from another communication unit 6. Thus, on detection of the congestion which occurs at time point 2, the communication units 6 of vehicles V3 and V4 generate and broadcast a congestion control request to other vehicles in the vicinity in addition to initiating their own congestion reduction control procedures.

Accordingly, on receipt of the congestion control request, the communication units 6 of vehicles VI, V2, V5 and V6 (circled) also initiate a congestion reduction control procedure (in addition to vehicles V3 and V4) in accordance with the procedures shown in Figure 3.

Figure 4(e) -Time Point 3 -embodiment ITS Figure 4(e) shows the situation after the communication units 6 of vehicles VI to V6 have initiated their congestion reduction control procedures at the third time point. As seen in Figure 4(e), the communication unit 6 of each of vehicles VI to V6 has reduced its transmitter power and, accordingly, the communication units 6 (of vehicles VI to V7) are no longer within range of the same number of other communication units.

As seen in Figure 4(e), for example: vehicle VI is now capable of receiving messages from just one other vehicle (V2); vehicle V2 is now capable of receiving messages from just two other vehicles (VI and V5); vehicle V3 is capable of receiving messages from just three other vehicles (V2, V4 and V5); vehicle V4 is capable of receiving messages from just two other vehicles (V3 and V5); vehicle V5 is capable of receiving messages from just two other vehicles (V3 and V4); vehicle V6 is capable of receiving messages from just one other vehicle (V7); and vehicle V7 is not capable of receiving messages from any other vehicle shown.

Accordingly, the communication units 6 of vehicles V3 and V4 are no longer subject to congestion because of the significant reduction in signal traffic.

It can be seen, therefore, that sending the congestion control request can advantageously allow other communication units 6 in the vicinity to take proactive steps to reduce congestion on behalf of the affected units. Furthermore, sending the congestion control request can advantageously allow signal traffic to be significantly reduced to the benefit of other communication units 6 (which may not be experiencing congestion) proactively before congestion occurs. These advantages can also potentially provide the additional advantage of ensuring that emergency vehicle-to-vehicle messages (and other road-safety related messages) continue to be successfully communicated to other vehicles in the immediate vicinity with less chance of congestion induced failure. This is particularly important because communication congestion is more likely to occur when road traffic congestion is at its highest and therefore when hazardous situations are more likely to occur.

Modifications and Alternatives A number of detailed embodiments have been described above. As those skilled in the art will appreciate, a number of modifications and alternatives can be made to the above embodiments whilst still benefiting from the inventions embodied therein.

In the above embodiments, a vehicle based telecommunications network was described. As those skilled in the art will appreciate, the signalling techniques described in the present application can be employed in other communications systems. Furthermore the vehicle based and road-side communication units may comprise any suitable communication nodes or devices, for example, dedicated vehicle communication units, mobile telephones, personal digital assistants, laptop computers, etc. In the embodiments described above, the vehicle based communication units each include transceiver circuitry. Typically this circuitry will be formed by dedicated hardware circuits. However, in some embodiments, part of the transceiver circuitry may be implemented as software run by the corresponding controller.

In the above embodiments, a number of hardware and/or software modules were described. As those skilled in the art will appreciate, where all or part of the module's functionality is provided in software, the software may be provided in compiled or un-compiled form and may be supplied to the communication units as a signal over a computer network, or on a recording medium. Whilst, part or all the functionality performed by the modules may be performed using one or more dedicated hardware circuits, the use of software modules is preferred as it facilitates the updating of the communication units in order to update their functionalities.

In the above embodiments the congestion status analysis module is described as being operable to determine a communication congestion level based on measurements of a channel usage parameter. The measurements may assess, for example, how many messages or how much data is being transmitted on the channel within in a predetermined period of time. Such measurements may be carried out at layer 2 (e.g. in MAC layer). It will be appreciated that the congestion status analysis module may alternatively or additionally determine a communication congestion level based on an assessment of the number of different vehicle based (and possibly road-side) communication units from which signals are being received.

Such measurements may, for example, be carried out at layer 3 (Network layer).

It will be appreciated, however, that the measurements may alternatively or additionally include other measurements from which a congestion level may be derived, for example measurements of the number of received signals having certain characteristics (e.g. as extracted / detected by the received signal analysis module 32).

It will be further appreciated that the congestion reduction control module 38 may be operable to implement any suitable congestion reduction mechanism and may use any appropriate combination of such mechanisms (at different times or substantially simultaneously) to optimise congestion reduction control. For example, the congestion reduction control module 38 may be operable to initiate a different mechanism (or combination of mechanisms) in response to a congestion reduction request than in response to a change in the prevailing congestion conditions. The congestion reduction control module 38 may also be operable to initiate a different mechanism when another mechanism has already been used (or has been used to a maximum permitted level). Furthermore, the congestion reduction control module 38 may be operable to initiate generation and transmission of a congestion control request requesting implementation of a different mechanism respectively to different vehicles. For example, a request for one mechanism may be sent to vehicles ahead of, and a request for a different mechanism sent to those vehicles behind, the vehicle making the request. Similarly, a request for one mechanism (e.g. TPC) may be sent to vehicles beyond a certain distance away and a request for a different mechanism (e.g. SIC and/or MSC) may be sent to vehicles which are closer.

Operation of the communication units has been described sequentially with reference to a flow diagram (Figure 3) for the purposes of clarity. It will be appreciated, however, that many of the steps need not run sequentially but may run in parallel with other steps.

It will be appreciated that although the sequential time interval diagrams (Figures 4(a) to 4(e)) illustrate the benefits of embodiments of the invention in which TPC is used to manage congestion levels, the same benefits follow for other implementations, for example in which SIC and/or MSC are used. In the case of SIC, for example, the length of arrows may be considered conceptually to represent the interval between signals but with longer arrows representing shorter intervals and vice versa.

The congestion control request may include information identifying the geographical position of the vehicle making the request, as acquired by the vehicle's GNSS. The antenna for the GPS may or may not be different from that of the communication unit. Location information may be broadcast to other nearby vehicles via vehicle to vehicle communication or infrastructure to vehicle communication. Similarly, geographical location information for other vehicles may be received with the congestion request in step S24 Various other modifications will be apparent to those skilled in the art and will not be described in further detail here.

Claims

Claims 1. An intelligent transport system (ITS) communication node for communicating with at least one further communication node over a communication channel, the communication node comprising: means for determining a congestion level in the communication channel; means for generating, in dependence on said determined congestion level, a signal for requesting initiation of a congestion control procedure; and means for transmitting said signal for requesting initiation of a congestion control procedure to said at least one further communication node.
2. A communication node as claimed in claim I further comprising means for initiating a congestion control procedure.
3. A communication node as claimed in claim 2 wherein the means for initiating a congestion control procedure is operable to initiate a first congestion control procedure in dependence on said determined congestion level.
4. A communication node as claimed in claim 3 wherein said means for initiating a congestion control procedure is operable to initiate said first congestion control procedure after said signal for requesting initiation of a congestion control procedure has been sent to said at least one further communication node.
5. A communication node as claimed in claim 2 to 4 further comprising: means for receiving a signal for requesting initiation of a congestion control procedure from a further communication node; wherein the means for initiating a congestion control procedure is operable to initiate a second congestion control procedure in response to receipt of said signal from said further communication node.
6. An intelligent transport system (ITS) communication node for communicating with at least one further communication node over a communication channel, the communication node comprising: means for receiving a signal requesting initiation of a congestion control procedure from a further communication node; and means for initiating, in response to receipt of said signal, a congestion control procedure.
7. A communication node as claimed in claim 6 further comprising: means for determining a congestion level in the communication channel; means for generating, in dependence on said determined congestion level, a signal for requesting initiation of a congestion control procedure; and means for transmitting said signal for requesting initiation of a congestion control procedure to at least one further communication node.
8. A communication node as claimed in claim 7 wherein the means for initiating a congestion control procedure is further operable to initiate the congestion control procedure in dependence on said determined congestion level.
9. A communication node as claimed in any of claims 2 to 8 wherein the (or each) congestion control procedure comprises modifying at least one of a transmission power, an interval between transmitted signals, and the size of transmitted data packets.
10. An intelligent transport system (ITS) comprising first and second communication nodes each operable for communication over a communication channel, the first communication node comprising: means for determining a congestion level in the communication channel; means for generating, in dependence on said determined congestion level, a signal for requesting initiation of a congestion control procedure; and means for transmitting said signal for requesting initiation of a congestion control procedure to said second communication node; and the second communication node comprising: means for receiving said signal requesting initiation of a congestion control procedure from said first communications node; and means for initiating, in response to receipt of said signal, a congestion control procedure.
II. A communication system as claimed in claim 10 wherein the congestion control procedure comprises modifying at least one of a transmission power, an interval between transmitted signals, and the size of transmitted data packets.
12. A method performed by a intelligent transport system (ITS) communication node which communication node is operable for communication with at least one further communication node over a communication channel, the method comprising: determining a congestion level in the communication channel; generating, in dependence on said determined congestion level, a signal for requesting initiation of a congestion control procedure; and transmitting said signal for requesting initiation of a congestion control procedure to at least one further communication node.
13. A method as claimed in claim 12 further comprising initiating a congestion control procedure in dependence on said determined congestion level.
14. A method performed by a intelligent transport system (ITS) communication node which communication node is operable for communication with at least one further communication node over a communication channel, the method comprising: receiving a signal requesting initiation of a congestion control procedure from the further communication node; and initiating, in response to receipt of said signal, a congestion control procedure.
15. A method as claimed in any of claims 12 to 14 wherein the congestion control procedure comprises modifying at least one of a transmission power, an interval between transmitted signals, and the size of transmitted data packets.
16. An intelligent transport system (ITS) communication node for communicating with at least one further communication node over a communication channel, the communication node comprising: a determiner operable to determine a congestion level in the communication channel; a generator operable to generate, in dependence on said determined congestion level, a signal for requesting initiation of a congestion control procedure; and a transmitter operable to transmit said signal for requesting initiation of a congestion control procedure to at least one further communication node.
17. An intelligent transport system (ITS) communication node for communicating with at least one further communication node over a communication channel, the communication node comprising: a receiver operable to receive a signal for requesting initiation of a congestion control procedure from a further communication node; and a controller operable to initiate, in response to receipt of said signal, a congestion control procedure.