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Software Requirements Specification (SRS)

Cooperative Adaptive Cruise Control : Team 2


Alex Crimin, Project Manager

Joseph Hollopter, Customer Liaison

Roy Barnes, Artifacts Manager

Chengzhu Jin, Project Facilitator

Jimmy Mkude, Security Engineer


Mr. Bill Milam, Ford Motor Company


Dr. Betty Cheng

1 Introduction

Cooperative Adaptive Cruise Control (CACC) is a system that Ford Motor Company will be utilizing in their commercial vehicles to provide increased convenience and safety for drivers using cruise control. Cooperative Adaptive Cruise Control allows the vehicle to communicate with other similarly equipped vehicles. They can share up-coming road conditions, current speeds, and directions of travel. This is information that can help the vehicle to adjust its speed autonomously. With this system, vehicles can move as one platoon. As a group, they can adjust and maintain their speed. This SRS will detail how the system functions and thoroughly model the system with various diagrams.

1.1 Purpose

To clearly communicate with the customer all requirements that need to be satisfied for the embedded CACC system to operate as intended. This SRS will show a clear indication of how the different subsystems of the CACC system should interact with one another. This will give Ford Motor Company developers a point of reference to begin designing and building the CACC system.

1.2 Scope

Cooperative Adaptive Cruise Control (CACC) assists the driver of the vehicle it is embedded in by supplying information about impending road conditions, and taking autonomous actions in response to these conditions. CACC is an embedded automotive system, which allows for the system to make real-time decisions and control the vehicle in a timely fashion. The GPS Network System of CACC is used to collect information from and transmit information to other vehicles on the road that are near. The radar sensing, radio communication, and forward-looking camera are sensors that the system uses to absorb information about the surrounding environment. An electronic throttle and vehicle brakes are the actuators used to maintain the speed of the vehicle, as well as slow or stop the vehicle in emergency situations. The vehicle controller will coordinate these subsystems, retrieving input from the sensors, processing the information, and sending appropriate signals to the actuators.

1.3 Definitions, Acronyms, and Abbreviations

The following table includes descriptions of keywords and acronyms used in this document.

Table 1 : Definitions




Anti-Lock Brake System. This is a pre-existing subsystem in the vehicle that actuates the brakes when there is a dangerous loss of wheel traction.


Adaptive Cruise Control. This is a subsystem of CACC that allows the vehicle to autonomously adjust its speed when obstacles are detected using radar and camera sensors.


Bit Error Ratio. This is a measure of performance for the GPS network system. See [1] in section 6 (References) for more information.


Basic Safety Message. A type of message that may be transmitted from vehicle-to-vehicle between embedded CACC network transmitters in the form of an identification key. This type of message key is used to notify following vehicles of impending safety issues. See [11] in section 6 (References) for more information.


Cooperative Adaptive Cruise Control. This is the embedded automotive system being described by this document.


Cooperative Awareness Message. A type of message that may be transmitted from vehicle-to-vehicle between embedded CACC network transmitters in the form of an identification key. This type of message key is used as general communication between vehicles. See [11] in section 6 (References) for more information.

DSRC standards

Dedicated Short Range Communications standards. See [5] in section 6 (References) for more information.


embedded Hardware Security Module. This module verifies the authenticity of incoming network message keys. See [11] in section 6 (References) for more information.

Following Vehicle

This is a CACC enabled vehicle directly behind the vehicle.


Global Positioning System. This is used to get the current position and velocity of vehicle. See [4] in section 6 (References) for more information.


Independent Monitoring Function. This is function of the CACC system vehicle controller that monitors the successful completion of OS tasks.

Leading Vehicle

This is a vehicle at the front of a platoon.




miles-per-hour. All relative speeds in the system will be in units of mph.


Operating System. This Provides the environment for which the programs of the system can run. See [2] in section 6 (References) for more information.


A collection of 2-8 vehicles that are all communicating using the CACC system.



Target Vehicle

This refers to the vehicle directly in front of the vehicle that the CACC system detects.


User Interface. This is where the user interacts with the CACC system.


Vehicle Controller. This is the system controller. It is composed of the main, speed, and platoon controllers.

V2X Standards

Standardized methods for secure vehicle-to-vehicle communication. See [11] in section 6 (References) for more information.

1.4 Organization

The following is the table of contents for this SRS document.

2 Overall Description......Page 5

2.1 Product PerspectivePage 5

2.2 Product Functions...Page 5

2.3 User Characteristics...Page 5

2.4 Constraints...Page 6

2.5 Assumptions and Dependencies..Page 7

3 Specific Requirements....Page 7

Functional Requirements...Page 7-13

Nonfunctional Requirements.Page 13

4 Modeling Requirements..Page 14

Use-Case Diagram..Page 15

Use-Case Diagram Documentation..Page 16 - 22

Domain Model (Class Diagram)....Page 23Class Diagram Data Dictionary.....Page 24 - 35

Scenarios and Sequence Diagrams.Page 41 - 43

State Diagram.....Page 39 - 43

State Diagram Textual Description...Page 44 - 51

Prototype.......Page 52 - 55

References....Page 56

Point of Contact........Page 57

2 Overall Description

In this section, certain background information that is needed to understand the functionality of the CACC system is outlined. The context of the product, the goal of product functions, expectations for users, possible constraints, assumptions about the environment, and potential future features are all addressed.

2.1 Product Perspective

The CACC system will be embedded in certain automotive vehicles. It is a standalone system, although it is part of the vehicle as a whole. It comprises various subsystems, such as an existing ACC system, and an array of sensors and actuators that may be used by other systems in the vehicle, such as the rain sensing wipers. It is not a system that can be retroactively added to a vehicle that was previously unequipped with CACC. The CACC system is to be used at speeds greater than or equal to 25 mph, and it is meant to be used in the presence of other vehicles, where lateral control from the driver is only required during emergency situations. As such, the CACC system is most well suited for usage on main highways and freeways.

2.2 Product Functions

This is a summarization of the major functions that the CACC system will perform.

Maintain a constant forward speed, as specified by the driver. [8]

Detect vehicles or objects ahead, and adjust the forward speed accordingly.

Effectively communicate with other CACC-equipped vehicles.

Join or create new platoons.

Leave or disband platoons.

2.3 User Characteristics

Users are expected to be licensed drivers. Users are expected to be able to operate a vehicle. Users are expected to know how to communicate with and use the CACC system, so they must have knowledge of the dashboard display output, and input methods, such as steering wheel buttons. Users are not expected to have any sort of knowledge about the internal workings of the CACC system. Users do not need to possess any specialized skills for the operation of the CACC system.

2.4 Constraints

The following are the safety and functional constraints that have been applied to the design of the CACC system.

The platoon size will not exceed eight vehicles.

A platoon must contain at least two vehicles.

CACC will not be enabled at speeds less than 25 mph, and there is no upper bound on the speed it may be set to.

If there is a subsystem failure, the full system will be disabled (see section 3, Specific Requirements, for more details).

All local traffic laws must be obeyed, except for speed limits. The vehicle driver will command the speed.

The system may not cause the vehicle to behave in a reckless or dangerous manner, which could possibly cause harm to the driver, or others on the road.

Braking and acceleration force will not exceed the vehicle limits as defined in its performance envelope.

Damage must be mitigated in the event of an impending collision. (see section 3, Specific Requirements, for more details).

The system must be able to effectively communicate messages to the driver through the dashboard scree