Can a New Approach to Wireless Beat Shannon’s Law?

on July 28, 2011

For the past 60 years, electrical engineers have understood the hard limits that physics imposes on the data capacity of any channel. The law, formulated by Claude Shannon of Bell Telephone Labs, says that the data capacity, in bits per second, is a function of the bandwidth, the signal strength, and the noise in the channel.

Shannon's law formula
Shannon's Law (Wikipedia)

No one has yet found a way to break Shannon’s law, but Rearden Companies, the brainchild of Steve Perlman, who is behind the bandwidth-bending OnLive online games service, claims to have found a way to cheat significantly. A paper by Perlman and Rearden Principal Scientist Antonio Forenza, describes a technology called Distributed-Input-Distributed-Output (DIDO).

Normally, when a wireless channel, such as a connection to a Wi-Fi access point, is shared by two or more users, each user can only get a fraction of the channel’s capacity. But DIDO allows each user to communicate, in theory, up to the full Shannon limit of the channel.

The explanation for just how this works is complicated, but the technology uses array of antennas to create a non-interfering path between an access point and a user. Shannon’s law applies not to a particular piece of bandwidth but to each channel. Traditionally, we have thought of the two as the same, but DIDO spearates the concept and allows the link between the access point and each user to function as an independent channel within the dame physical bandwidth.

Normally, I am deeply skeptical about claims of fundamental scientific breakthroughs. My skepticism is mitigated by what Perlman has already accomplished with OnLive, which moves gaming data across internet connections with an efficiency that no one thought possible. Clearly, this guy knows how to move bits.

Don’t expect to see DIDO deployed anytime in the very near future. It requires significant changes to network design.. including interposing a DIDO data center between an internet source and an access point to encode data as well as sophisticated new antennas.  But it does hold real promise to to reduce the growing crunch on our wireless airspace.