Distributed-Input-Distributed-Output (DIDO) Wireless Technology


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Abstract

Distributed-Input-Distributed-Output (DIDO) wireless technology is a breakthrough approach that allows each wireless user to use the full data rate1 of shared spectrum simultaneously with all other users, by eliminating interference between users sharing the same spectrum. With conventional wireless technologies the data rate available per user drops as more users share the same spectrum to avoid interference, but with DIDO, the data rate per user remains steady at the full data rate of the spectrum as more users are added.
As a result, DIDO profoundly increases the data capacity of wireless spectrum, while increasing reliability and reducing the cost and complexity of wireless devices. DIDO deployment is far less expensive than conventional commercial wireless deployment, despite having vastly higher capacity and performance, and is able to use consumer Internet infrastructure and indoor access points.
The potential of DIDO is to have unlimited number of simultaneous users, all streaming high-definition video, utilizing the same spectrum that a single user would use with conventional wireless technology, with no degradation in performance, no dead zones, no interference between users, and no reduction in data rate as more users are added.

Spectrum capacity and Shannon’s Law

Ultimately, the reason we are limited in multiuser spectrum capacity using conventional wireless techniques is due to Shannon’s Law, which defines the maximum amount of error-free data rate that can be transmitted through a single communications channel for given amount of spectrum and noise level (the “spectrum capacity” of the channel).
For example, a cellular sector (which may span a kilometer) is essentially a single channel whose maximum data rate is limited by Shannon’s Law, and all of the users within that cell sector share that data capacity. As another example, all of the users in overlapping Wi-Fi networks at the same frequency share the Shannon-limited data capacity.

What is DIDO wireless?
Distributed-Input-Distributed-Output (DIDO) wireless technology is a new approach to multiuser wireless that allows the number and density of users in the same area to be steadily increased without additional users reducing the data rate of others. In other words, the shared spectrum capacity is not subject to Shannon’s law: as more users in a given area share the same wireless spectrum, the data rate per user does not decline. As a result, regardless of how many users are in a given area, each user is able to use the entire Shannon Limit of the channel, despite sharing the same spectrum.
We do not know of a theoretical limitation to how many users we can add to a DIDO system without a degradation in data rate per user. There certainly will be practical limitations with each era of technology evolution, but we have not yet come close to them. So far, as we’ve increased the number of simultaneous users in the same area to 10 (limited just by the number of hand-built radios we have) we have not seen any degradation in performance. So, while our demonstrated spectral capacity today is 10X the Shannon Limit, we expect we can get to 100X, and are optimistic that 1000X is achievable. But, until we start to see some degradation in performance as we add more users, we will not be able to predict how far it can go.