University | Computer Science  

    Circus Family hiJaC Case Study   


The purpose of the CDx is to detect potential collisions of aircrafts located by a radar device. This is a   modified version of the original CDx, providing a concurrent execution of computation of detection and also exploiting the features of SCJ Level 1. Our aim with the concurrent CDx is, most of all, to provide a genuine and more representative Level 1 application. Due to the novelty of the SCJ paradigm and technology, such applications are still diffcult to come by in the public domain.

This SCJ program uses a simple cyclic executive, and embeds the assumption that the radar device collects a frame of aircraft positions that becomes available for input to the program periodically. In each
iteration, the CDx :

(1) reads a frame; (2) carries out a voxel hashing step that maps aircrafts to voxels;  (3) checks for collisions of aircrafts in each voxel; (4) records and reports the number of detected collisions.

A voxel is a volumetric element; all voxels together subdivide the entire space. The voxels in the CDx superimpose a coarse 2-dimensional grid on the x-y plane with the height of a voxel extending along the entire z-axis. Thus, the altitude of aircrafts is abstracted away during voxel hashing in step (2). This reduces the number of necessary collision tests between aircrafts. After mapping aircrafts to the voxels that are intersected by their interpolated trajectories, it is sufficient to test for possible collisions
of aircrafts within each voxel.

 The concurrent CDx consists of a single mission that instantiates seven handlers. Figure 1 and Figure 2 present two UML diagrams that illustrate the design.




1. Download CDx code from here or follow the instructions to get it from the hiJaC tools here.

2 Build CDx simply by the command 'make' and run it by 'make run'. However, before that, you first make sure that RTSJ RI and a fix for SCJ have been installed.  

Any problem when installing or running CDx, please contact Frank Zeyda ( or Kun Wei (

Technical Report of the Refinement Strategy

1. Download the technical report for the refinement strategy from here as a PDF.



       Department of Computer Science

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       Tel: 01904 325500 | Fax:01904 325599                                                                                                 Last updated on 6 July 2012