Spreading Signals in the Wideband Limit

Abstract-- Wideband communications are asymptotically impossible with signals that are spread over a very wide band and are transmitted over a multipath channel unknown ahead of time, if the signal to noise ratio (snr ) during communications is too low. This work exploits the recently discovered connection between mutual information and minimum mean square error (I-mmse) to bound the achievable data-rate of spreading signals in wideband settings, and to conclude that the achievable data-rate diminishes as the bandwidth increases due to channel uncertainty if the signal to noise ratio during active transmission is too low. The result applies to all spreading modulations, i.e. signals that are spread almost uniformly over the bandwidth available to the communication system, with snr during active transmission that is o log (W/L) W/L . The result holds for communications over channels where the number of paths L is unbounded but sub-linear in the bandwidth W.

• Type: Journal
• Year: 2008
• Where: CORR
• Authors: Elchanan Zwecher, Dana Porrat
• Keywords: Achievable Data-rate, Communications, CORR 2008, Education, Multipath Channel