Line code selection for 155.52 Mb/s data transmission on category 5 cable plant

EMI/EMC is a dominant problem encountered in high bit-rate (>100 Mb/s) transmission over unshielded twisted-pair cable (UTP) which leads to a novel set of line-code dependent tradeoffs affecting transceiver and cable plant complexity. To understand the tradeoffs, the authors examined the factors affecting RF emissions and susceptibility in both trellis-configured cable plant models and installed cable plant. An analytical model is presented that describes mode conversion by discontinuities in multi-pair UTP cable plant. Termination of the three dominant propagating modes produces consistently lower radiated emissions than other standard cable termination procedures. Cable plant parameters which predict good transmission do not assure satisfactory EMI performance. Radiated emissions from the trellis model occur in broad bands at 43, 53, 60, 70, and 80 MHz, and show a positive correlation with the transmit signal spectrum. For a given transmit level at 155 Mb/s, the emissions with MLT3 and BPR1 were 8-13 dB (10 dB typ) and 4-20 dB (13 dB typ) below NRZ levels, respectively. The authors also compared the performance of NRZ, MLT3, BPR1, and BPR4 line codes in an experimental 155 Mb/s link with 100 m of UTP5 by measuring the BER sensitivity to both injected noise and pseudo-random data sequence length. When the measured receiver penalty associated with three levels is included, MLT3, BPR1, and BPR4 offer 5-15 dB better performance over NRZ at 155 Mb/s, although implementation complexity is greater