Bring on the BER

April 24, 2006 - 0 Comments

What the heck is a BER? A long time ago I was in a group interview for a candidate ASIC engineer. Generally these are *really* interesting interviews since there is often logic questions asked, design questions, plus normal interview questions. The candidate was an absolute powerhouse – he nailed every question without breaking a sweat. Out of the blue a guy that I worked with asked a question about how do you compensate for photons affecting bits as they go through the ASIC.For the first time in the interview the guy paused and said,”I don’t know, but I do know that the likelihood of this happening to any packet would be something like 10-400th power.”For those of you reading from the cheap seats- That is a very low bit error rate. The Bit error rate for a standard Ethernet cable is considerably higher, something like 10-23rd or something like that. We who dwell in the wireless world would salivate for such performane- and I mean salivate. That’s cause the air, by its very nature, is a medium that’s prone environmental variables that ultimately impact the throughput and performance of the wireless network. Obi-one Kenobi, er, Bob Friday, has said that the Bit Error Rate for wireless is about 10-6th. That means that you are going to have a lot more packets with errors in it, and this is one of the reasons why your performance in wireless doesn’t equal your wireline network. Beyond the inherent unreliable air, you are also competing with other devices that operate in the same spectrum. That doesn’t help either. There are new technologies that will help compensate, a prime example is MIMO, which uses multiple antennas – just because a signal was weak, or blocked, from one antenna doesn’t mean that the other antenna had the same problem. What does a high BER mean for you? Well if you are surfing to to check on the player personnal activities of the Raiders – who they are picking up to compensate for the bad year that they had last year. Chances are that the BER isn’t going to be a problem- That’s the beauty of TCPIP, and the 802.11 MAC. If you are at the edge of a cell, you may see your client connect and disconnect, but that is more because of signal strength. Hopefully the Raiders won’t have a high BER when making their decisions. However, if you are make a voice call, and you have an abnormally high BER, then it may sound like your ear is next to a bowl of Rice Krispies- You know.. Snap, Krackle and Pop. There are no retransmissions for UDP based applications.We can improve technology, and believe me we afre working on it, but we will never be able to overcome physics.

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