Compressed Pulse Position Modulation Encoding Method for Infrared Local Area Networks
Original Publication Date: 1987-Feb-01
Included in the Prior Art Database: 2005-Feb-01
A technique is described whereby compressed pulse position modulation (CPPM) encoding provides signal symmetry, when used in conjunction with edge-coupled infrared local area network (LAN) data transmission circuitry. A method is described to reduce losses in edge-coupled systems, where losses of 6-8 dB are encountered [*]. In prior art, signal symmetry problems can occur when infrared transmission of data is influenced by devices, such as high frequency fluorescent bulbs, which produce infrared electrical noise in the 70 KHz range. The transmission signal rise and fall time may vary as much as 30%, causing the differentiated waveform to vary significantly in amplitude, as shown in Fig. 1. For this variance of rise times (30%), bit error rates may change within one order of magnitude.