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

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

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

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

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

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

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

Assumptions 8

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

Negative Utility of Femtocells

Address Negative Utility Issue (Naïve) Worst-case IR Reserve Price 4 Payment 2

Imprecision Loss New Issue (Naïve): Imprecision Loss 12 Imprecision Loss (IL): Percentage of utility loss Due to Imprecision: 100% No Imprecision Loss Reserve Price Payment 2 No Imprecision Loss

Problem Definition 13 Imprecision Loss No Imprecision Loss Reserve Price Payment 2 No Imprecision Loss

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

Multiple Reserve Prices In Imprecise Valuation Auction Two Reserve Prices 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%

Algorithm Sketch 16

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 #4S1S S1 S1 S2 S2 17

Simulation Result Precise Valuation – Near Optimal 18

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