Data compression and transmission algorithms for CMS FRPC muon chambers

The CMS (compact muon solenoid) will have a forward resistive plate chamber (FRPC) to identify muons, measure their transverse momenta, p /sub t/, and determine the bunch crossing from which they originate. The trigger algorithm is based on the muon pattern comparator (PACT). The actual hit pattern is compared to a set of predefined possible hit patterns for a muon with definite transverse momentum. When a match is found, the muon transverse momentum is determined at the same time. For that, the synchronized bit signals from four layers of the RPCs have to be brought to one processor. A huge interconnection network is needed to fulfill this task. To reduce the cost of the links transmitting data from the detector to the control system, we propose two compression/decompression systems for the data transmission based on both the SPC (segment-position-compression) method and the RLE (run-length-encoding) method with bunch crossing time information. The ideas for such systems are simulated and discussed. (8 refs).