Spectrum sharing can take a number of forms, and limits on the amount of sharing yield lesser value for end users and service providers.
In India, spectrum sharing also takes the form of mobile operators agreeing to allow other carriers access to licensed frequencies, so long as reciprocity is available. In other words, one carrier might agree to share frequencies within a single band (800 MHz, for example).
That format tends to limit the value of spectrum sharing, since not all mobile service providers, for example, own spectrum in all the relevant bands, and mobile operators cannot share across frequency bands (sharing within 800 MHz is permitted, sharing between 800 MHz and 2.1 GHz is not allowed).
So any limits on sharing necessarily limit the impact of sharing, for end users and service providers.
Wi-Fi has been the classic case of shared access, as well as the classic case of unlicensed access. One might argue the “no limits except interference” approach has spectacularly affected the entire access market.
The Wi-Fi ecosystem now embraces virtually all apps, all devices and all access settings. In fact, Wi-Fi is among the essential features for any appliance, and the de facto “inside the building” distribution choice as well.
Other spectrum sharing efforts likewise will have impact more or less directly on the degree of allowable sharing.
More recently, there is new thinking on shared access using TV White Spaces, which essentially are frequencies otherwise allocated for use by TV broadcasters, but which might actually be unused in many markets.
In the United States, a new form of sharing will be enabled in the 3.5 GHz band, with existing licensed users retaining primary access, but with commercial entities able to obtain licenses for secondary use, while some spectrum will also be available for unlicensed use, on a best effort basis, by devices and users, so long as primary and secondary licensees are not using the spectrum, at any place and at the same time.