1. Research Challenges for Wireless Internet Access (some thoughts) David K. Y. Yau Purdue University Department of Computer Science

2. Why Less is More (wireless vs wireline) Everyone wants residential broadband access –Pay bills, shop, entertainment, ICQ, skype, … –Reality: 12% of U.S. households have it (Korea 50%; Hong Kong 25%; Japan 6%; Sweden 15%) –Access is still expensive; “remote areas” aren’t covered Citywide WiFi clouds –$20--$50K per square mile to build (1/4 of high speed cables) –Quick installation: one square mile in 1/2 day –Low maintenance/operation costs: routers put on rooftops and hung off lamp posts So, let’s do multihop wireless; I.e., wireless mesh network –ADSL, cable modem, WiMax Internet gateway

4. Wireless Cities Chaska, Minnesota –One of 29 Wi-Fi clouds in U.S. –$18K people, 16 square miles –Built in a few weeks at cost of $600K –Service charge $15.99 / month Wi-Fi clouds being planned for larger cities –Philadelphia, Austin, Portland, Chicago, Tokyo, Taiwan, …

5. Will it fly? Who knows? –Small scale easy; But large scale? Challenges in the large –Spectrum and bandwidth quality and interference –Security and privacy –Incentives –Etc, etc –And their interactions too

6. What is a Wireless “Link”? Not quite a neighbor or not abstraction –Most links have intermediate loss rates –SNR, distance, range, etc, not good predictor of delivery probability –Multipath fading matters; interference between radios and their assigned channels matters; small vs large time scale interference matters –Simple math models don’t work -- how to predict and characterize channel quality and capacity? How to provide QoS? How to be fair?

7. Security and Privacy If Wi-fi clouds fly, communities will naturally form –Community this and that (school, interest group, support group, political group) –Cooperative this and that (caching, routing, packet repair) –Community/cooperation should share what’s needed and no more (Tom routes my packets, but he shouldn’t read them) How to define trust and minimal shared knowledge? (E.g., Yao’s millionnaires problem) How to enforce it at low cost? (Trust set up on the fly, high speed authentication, etc) Wireless is about uninterfered spectrum use –How to ensure fair play? Regulations? Courtesy in unlicensed bands?

8. Incentives Large enough cloud will have multiple owners and independent players –Needed for low cost mesh to have coverage –Natural course of expansion –Competition, competition, competition Why should people cooperate? –Free riders and tragedies of the commons well known –People chip in for good reasons Selfish, but rational (most people) –Need protocols and infrastructure to reward good behaviors and discourage bad ones

9. Possible Incentive Protocol Feature 1: Contribution aware –Good citizens get good service Feature 2: Handle heterogeneous players –They fit different utility functions Shares of service proportional to utility weighted prior contributions Management infrastructure for contributions important Original design for wireline network; Interactions with wireless MAC protocol can present challenges

11. Thanks for listening Questions / comments?