1. EasyBid: Enabling Cellular Offloading via Small Players Zhixue Lu 1, Prasun Sinha 1 and R. Srikant 2 1 The Ohio State University 2 Univ. of Illinois at Urbana-Champaign 1

2. Cellular Data Keeps Increasing 2 Mobile Data Increases more than 60% Annually Small Cells (Femtocells) Increase Spectrum Reuse

3. Femtocells: the Concept Small in-home Cellular Base Station – connects to the service provider’s network through owner’s broadband network Femtocell Broadband Router Internet Core Network Femtocell Gateway 3

4. Femtocells: the Facts To Deploy Cellular Base Stations – Site, Backbone and Power Supply – Costly to deploy 7.9 Million Femtocells Deployed by 2013 – Almost all are residential and enterprise (small owners) Femtocells Acquiring Access to these Femtocells is Important 4

5. Proposed Incentive Mechanism: Auction Why Auction? : Fair and Efficient Two Types of Auctions – Forward Auction: buyers bid – Reverse Auction: sellers bid Consider a Reverse Auction Model – Buyer: the wireless service provider (WSP) – Sellers: the femtocell owners – Reason: most owners have only one femtocell 5

6. Background Desired Properties of Auctions – Truthfulness: bidders cannot get higher utility by lying – Individual Rationality: utility of any bidder ≥0 Common Auction Mechanisms – Secondary price auction – Reserve price based secondary auction 6

7. Imprecise Valuation: an Ignored Problem Existing Works Assume Precise Valuations Valuations of Femtocell Owners Depend On: – Cost of extra broadband traffic, electricity usage – Degree of overload/delay tolerance – Wiliness to provide service – May vary over time Hard to Precisely Estimate + + No Delay! = ? 7

8. Assumptions 8

9. Basic Form of Auctions in the Paper Consider Reserve-Price based Secondary Auction – Secondary auction: truthful with precise valuations – Reserve price: eliminate errors (uncertainties) in payments How It Works – Consider one seller a time – WSP sets a reserve price x – The Femtocell owner places its bid – Auction succeeds and pay x to the owner if the bid ≤ x – Utility of WSP is G-x, G: the savings of the WSP on each unit of data offloading 9

10. Negative Utility of Femtocells 10 0 8 6 4 2

11. Address Negative Utility Issue (Naïve) Worst-case IR 11 0 8 10 6 Reserve Price 4 Payment 2

12. Imprecision Loss New Issue (Naïve): Imprecision Loss 12 Imprecision Loss (IL): Percentage of utility loss Due to Imprecision: 100% No Imprecision Loss 0 8 10 6 4 Reserve Price Payment 2 No Imprecision Loss

13. Problem Definition 13 Imprecision Loss No Imprecision Loss 0 8 10 6 4 Reserve Price Payment 2 No Imprecision Loss

14. Solution: Multiple Reserve Prices Example: 2-reserve-price Approach: – if bid ∈ [0,4), approve and pay $8 – if bid ∈ [4,10], approve with probability 2/3 and pay $10 if it is approved Truthful and IR with Precise Valuations 04 S1 S1 S2 S2 10 Payments: P i Approval Ratios: R i 14 Segments: S i

15. Multiple Reserve Prices In Imprecise Valuation Auction Two Reserve Prices 0 4 10 6 No Imprecision Loss Imprecision Loss No Imprecision Loss S1 S1 S2 S2 15 WSP’s Expected Utility4.0 vs. 3.6 (Naïve) Imprecision Loss25% vs. 100% Percent of Sellers in IL Range40% vs. 40%

16. Algorithm Sketch 16

17. Example $8 Seller #1 $6 $1 $3 B C D E Seller #2 Seller #3 Seller #4 A SellerSeg#RatioPmt #1S1S1 18 #2S2S2 2/310 #3S2S2 2/310 #4S1S1 18 0 4 10 6 S1 S1 S2 S2 17

18. Simulation Result Precise Valuation – Near Optimal 18

19. Summary EasyBid: A Reverse Auction Mechanism for Acquiring Access to Femtocells – Introduce the notion of Perceived Valuation, Partial Truthfulness, and Imprecision Loss to characterize the quality of auctions with imprecise valuations. – Present heuristic algorithms to maximize the WSP’s utility while satisfying given constraints on partial truthfulness and imprecision loss. 19