I'm no expert on pcie signaling, but I have some general idea, problems are how to take care of the electromagnetic noise, that's why PCIe uses differential pa

I'm no expert on pcie signaling, but I have some general idea, problems are how to take care of the electromagnetic noise, that's why PCIe uses differential pairs wiring (both positive and negative wires are next to each other on board) instead of single-ended (single wire with common ground, negative) which were used in original PCI and PCI-X so the if some noise hits the first wire, same noise hits the second differential wire. improvements in coding and decoding the signals with error correction also help recovering any errors caused by the electromagnetic noise.