Data Compression for the ALICE Silicon Drift Detector

The problem faced when transmitting data coming from the ADC is a typical data compression one. The data to compress may be viewed as a bit stream array containing values in the integer range [0, 255]. A large amount of these values (about 95%) should be around 0 [Alice, 1995], even though the noise will make them generally different from 0. The charges may be imagined as isolated hills (with an approximate gaussian shape) on a (approximately) planar surface. <P> The characteristics required for the algorithm are: compression coefficient c03, which means a compression ratio C30 (where c=1/C=n0/ n1 where n0 is the number of bits exciting the algorithm and n1 is the number of bits entering the algorithm), high operating speed, easy hardware implementation, minimal size of the data structures used, low power consumption, simplicity and degree of lossiness of the algorithm tunable with parameters. <P> A compression algorithm is termed lossy if the decompressed data is not the original data, while it is called lossless if the decompressed data is equal to the data before the compression-decompression phases.