Device-to-Device (D2D) Communications: Why do we need it for public safety?

D2D communication means that devices talk to each other to garner opportunities to perform end-to-end communications or transfers. A typical and old example people use to describe D2D is that why do our mobile phones have to synchronize and communicate with the base station if they are very close to each other, perhaps in the same room. The D2D argument has been to exploit such situations and harvest more out of the scarce spectrum by not bothering the spectrum with connections to the base station(s).

The D2D argument goes even further.. What if our devices can do this opportunistic talking to each other over multiple hops. That will extend the reach of the base stations (and hence the Internet), right? Yes, this is true. However, not so easy. Many innovations across the protocol stack as well as hardware front end are needed. In our recently funded NSF project, we are taking a stab at research challenges involved in reaching such an environment where devices talk to each other, and further, share their wireless connectivity/resources pervasively: https://sites.google.com/site/pss4psc

Like most other NSF projects, the concept of "pervasive sharing" is risky and draws easy criticism from our peers. Why would providers be willing to share their preciously licensed spectrum bands with the customers of other providers? Why would a user be incentivized for allowing his/her phone to relay traffic for others, which clearly involves privacy risks and exposure to more cyber-attacks? How would you handle the heterogeneity of the wireless connections? -- which I call "substrates" to make up something larger and good. The questions go on and on..

I guess one simple answer is the "larger good"! If there is a larger good that threatens everybody, then, history shows, people are motivated for sharing. Sharing and cooperation happen more when the fate of the whole system or the ship is in danger. Public safety is an example case.. Safety of the public and the people is important and everybody, eventually, cares about it. I think notions like pervasive sharing or D2D make sense for these types of larger goods.

Further, I do think that, given the literally exponential growth (I don't use the term "exponential" to attract attention, but use it carefully.) of mobile data demand, our wireless communication infrastructure is in danger. We, as the whole community, need to find a solution and cooperate. Cut-throat competition when improving a system's performance helps until a point. But, beyond a point, just like thrashing in operating systems' multi-programming level (a textbook classic), competition degrades what we can collectively achieve. That is the point when regulations incentivizing sharing are needed.

Folks have recognized this need for sharing and cooperation in spectrum management a while back.. Tethering is now part of almost all phones, which allow sharing of data plans with devices nearby. Going further, opengarden.com designed an app that allows mostly peer-to-peer sharing of wireless connectivity among devices. The power of cyber-sharing and openness is unprecedented. Yet, achieving it as a profitable business/system is hard.

Yet another case where D2D communication and sharing makes sense is disastrous scenarios. Here is a recent incident showing how D2D could have helped responding to an emergency in metro: http://www.firefighterclosecalls.com/news/fullstory/newsid/216435  We had reports indicating that crowdsourcing via D2D communications helped catch Boston Marathon: http://www.cnn.com/2013/04/24/opinion/kessler-digital-forensics

More could be done for public safety by employing D2D communications -- perhaps catch the bombers even before they detonate the bombs. Establishing common sense is what we need to do. But, that common sense requires more seamless D2D and more sharing.. To the level that it may have to be pervasive.

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