Weighted-fairness in message rate based congestion control for vehicular systems

#The specification relates to vehicular communication systems. In particular, the specification relates to a system and method for synchronously updating message rates to control communication congestion, where the message rates converge to weighted fair rates for different vehicles in a distributed manner.

#Vehicles usually communicate with each other using Dedicated Short Range Communications (“DSRC”) channels specially designed for automotive use. It has been well known that congestion mitigation on the DSRC channels is one of the priorities in moving DSRC towards deployment. Existing message rate based congestion control strategies converge all the vehicles participating in congestion control to the same steady state message rates. In some scenarios, different steady message rates for different vehicles are desired. For example, ambulances and police cars engaged in emergency services travel at a much higher speed than private vehicles, and can be more prone to accidents. Therefore, practically it may be desirable that such vehicles transmit messages at a higher rate than the rates used by private vehicles. However, the existing message rate based congestion control strategies cannot achieve different steady message rates for different vehicles.

#The specification overcomes the deficiencies and limitations of the prior art at least in part by providing a system and method for implementing congestion control for vehicles based at least in part on weighted fair message rates where the weighted fair message rates are calculated in a distributed manner. The system comprises a measurement module, a calculation module and a determination module. The measurement module measures a channel busy ratio describing a fraction of time during which a channel is busy. The calculation module calculates a ratio error by comparing the measured channel busy ratio with a target channel busy ratio. The determination module determines a first parameter value for a first vehicle based at least in part on a ratio of weights. The determination module determines a message rate for the first vehicle based at least in part on the ratio error and the first parameter value. The message rate describes a speed for transmitting messages from the first vehicle.

#The specification is illustrated by way of example, and not by way of limitation in the figures of the accompanying drawings in which like reference numerals are used to refer to similar elements.

#FIG. 1 is a high-level block diagram illustrating a system for implementing congestion control for vehicles based at least in part on weighted fair message rates according to one embodiment.

#FIG. 2 is a block diagram illustrating a vehicle system in detail according to one embodiment.

#A system and method for implementing congestion control for vehicles based at least in part on weighted fair message rates is described below. In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the specification. It will be apparent, however, to one skilled in the art that the embodiments can be practiced without these specific details. In other instances, structures and devices are shown in block diagram form in order to avoid obscuring the specification. For example, the specification is described in one embodiment below with reference to user interfaces and particular hardware. However, the description applies to any type of computing device that can receive data and commands, and any peripheral devices providing services.

#Reference in the specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment.

#Some portions of the detailed descriptions that follow are presented in terms of algorithms and symbolic representations of operations on data bits within a computer memory. These algorithmic descriptions and representations are the means used by those skilled in the data processing arts to most effectively convey the substance of their work to others skilled in the art. An algorithm is here, and generally, conceived to be a self consistent sequence of steps leading to a desired result. The steps are those requiring physical manipulations of physical quantities. Usually, though not necessarily, these quantities take the form of electrical or magnetic signals capable of being stored, transferred, combined, compared and otherwise manipulated. It has proven convenient at times, principally for reasons of common usage, to refer to these signals as bits, values, elements, symbols, characters, terms, numbers or the like.