iDEAL: Incentivized Dynamic Cellular Offloading via Auctions

Wei Dong1Joint work withSwati Rallapalli1, Rittwik Jana2, Lili Qiu1, K. K. Ramakrishnan2, Leonid V. Razoumov2, Yin Zhang1, Tae Won Cho2

1The University of Texas at Austin2 AT&T Labs Research

INFOCOM 2013iDEAL: Incentivized Dynamic Cellular Offloading via Auctions1Motivation2Cellular network overloaded

Traffic is highly dynamic

Large peak-to-average traffic ratioOver 5 times in this example=>Too costly to provision based on the peak demand

Time (s)Cellular demand variationAlternative?3ISPs augment cellular networks on their ownWi-FiFemtocell

Insufficient as a long-term solutionHigh deployment costHigh management costInterferes with existing infrastructure

Our approach4Cellular provider purchases bandwidth on demand from 3rd party resources Wi-Fi, femtocell, or other cellular resources

Incentivize cellular offloading via auctionsEffective price discoveryAvoids long-term contractsCut cost by leveraging the competition

Their approach is similar to the nave solution we are going to talk about laterWe are the first to use auction to support offload to a variety of resources, and consider dynamic demandIn order to achieve that, a few unique challenges need to be addressed4Unique challengesDiverse spatial coverage

Traffic uncertainty

Non-truthful bidding and collusion5Cellular offloading as a reverse auction6Auction conducted periodicallyCellular provider (A): buyerHotspots: sellers

Hotspots submit bidsCellular provider (A) serves as auctioneerA sector is divided into regions based on location of hotspotsObjective: satisfy As traffic while minimizing the total costCost = cellular cost + hotspots cost

R1

R2

R3

AWe first formulate the problem as a reverse auction.Reverse auction means sellers bid to the buyer, in our case

We look at one cellular sector, which can be further partitioned to different regions, each region may have a few hotspots and each region, depend on its location, may have different spectrum efficiency

Mention the challenge, diverse spatial coverage6Nave solution7

Auction 1Demand 1Auction 2Demand 2Limited competitionCellular resourceCellular resource as a virtual bidder Inter-region competitionR1R2The details of the independent auctions?How do you introduce the inter-region competition?

Based on this observation we introduce XXX7iDEAL overview8Two phases of iDEALAllocation: determine how to allocate cellular resources and 3rd party resources to minimize cost

Pricing: determine payment to 3rd party resource owners Global static allocation9Satisfy the demand with both Wi-Fi and cellularTranslate cellular resource usage into spectrumNever buy more than offeredTotal cost: Wi-Fi + cellularFirst propose a global static allocation, that doesnt consider the demand uncertainty prevision for the peak in each region9Global dynamic allocation1010iDEAL pricing11VCG principle Pay the winners the opportunity costPayment to winner w = the extra amount that other bidders could sell if w is not present

iDEAL pricingApply VCG over the whole sector as one auctionGlobal opportunity costCaptures inter- and intra-region competition

VCG is a well known auction scheme that .

One reason we choose VCG is its truthfulSecond reason is it captures as the opportunity cost is not only affected by bids within the winners own region, but also bids from other regions, and thats important because Next we use an example to show how inter-region competition helps to lower cost11iDEAL pricing: Example12132

Region 1 (d: 1)Region 2 (d:1)r:1 v:$1r:1 v:$9r:1 v:$2r:1 v:$1.5Optimal allocationAllocation if 1 is not thereValue sold by others: $3.5

Global opportunity cost: $2The local opportunity cost is $9r: amount of resourcev: valuation of a single unitd: demand Global opportunity cost captures inter-region competition and lowers costPayment is higher than bidConsider hotspot 1Value sold by others: $1.512Economic properties13Theorem 1: Truth-telling is optimal.

Theorem 2: iDEAL is efficient (i.e., winners are the bidders with lowest valuation).

Theorem 3: iDEAL is individually rational (i.e., bidders of the auction will get non-negative utility). Understand collusions14Collusion strategiesSingle seller collusionMulti seller collusionIn both cases, they use Supply ReductionDrop losing bidsReduce the capacity offered in winning bids

Supply reduction: increases the opportunity cost drives up priceMitigating collusions15Dynamic demands make collusion hardInaccurate traffic prediction supply reduction may lead to missed winning opportunitiesBidding as a groupHotspots owned by same party bid as group considered one bidderRemoves competition within a groupno incentive for supply reductionInter-group competition retainedMulti seller collusion is unstableSeller has incentive to leave the bidding ring

Evaluation methodology16Sector reports3G HTTP sessions# of usersEvent driven trace playerDetailed aggregated traffic demandSector locationHotspot locationClusteringRegionsPricing plan of major ISPsBidsAuctionsComparison of truthful auctions17

Auction based approaches much better than fixed pricing given enough competitioniDEAL consistently beats other auction based approaches40 hotspots130 hotspotsFig. 2-417

40 hotspots130 hotspotsComparison of truthful auctions (cont.)18Global allocation efficiently allocates cellular resource to different regions.Dynamic global allocation avoids provisioning for peak demand in each region.Comparison of non-truthful auctions19

Value consumptionCostNon-truthful auctions invites gaming behaviorsGaming causes fluctuation and can increase costVCG in iDEAL is stable, efficient and low-costNon-truthful auctions: first price and uniform priceWe use some simple strategies to simulate gaming, they adjust their bid based on the results of previous rounds

Our gaming strategies are conservative, in reality can be worse19Collusion under dynamic demands20

50: 28% chance of higher utility 20: 5% chance

Significantly weakens the incentive to colludeUsed two different sizes of bidding ring: 20 and 50

Collusion: Bidding as a group21Group bidding removes competition between a sellers own hotspots and maintains the competition between different sellers, thus reducing the cost40 hotspots130 hotspotsConclusion22Design incentive framework for cellular offloadExplicitly account for diverse spatial coverage of different resourcesCope with dynamic trafficPromote truthfulnessProvably efficientGuard against collusions

Trace-driven simulations show iDEAL is efficient, low-cost and robust against collusionQ&AThank you23Backup slides24Practical Considerations25Supporting offloading to femtocells and dynamic roamingThe same framework applies to purchasing femtocells and other cellular resourcesHandle partially overlapping spatial coverage Revise the constraint [C1] to split the resources from the same provider into different regionsRelated Work26MeasurementBalasubramanian et al. report Wi-Fi is available for 11% time and 3G is available for 87% time but they are negatively correlatedLee et al. find Wi-Fi offload 65% traffic without delay and 83% with over 1-hour delayAuction based offloadingZhou et al. uses auction to incentivize mobile users to wait until they reach Wi-FiChen et al. uses auction to incentivize femtocell owners to share resourcesIgnore three unique challenges iDEAL addressesSimilar to local allocation in spiritDesign GoalsAccount for different spatial coverage of resources

Achieve high efficiency

Promote truthful bidding

Low cost

Guard against collusion27Mitigating Collusions (Cont.)28Stability of a multi-seller collusionWithout utility sharing, a seller has no incentive to conduct supply reductionFollows from the truthfulness of VCG and that in our system sellers submit sealed, separated bids

Utility sharing is hard to achieve in our systemHard to attribute utility change to collusionDemand and Wi-Fi availability is dynamicHard to validate other bidders behaviorSellers submit sealed separately bidsCan make it even harder via system designE.g. use delayed payment to further obfuscate the utility

Supporting Femtocell Offload29

Benefit of femtocells is large when there are fewer Wi-Fi hotspots16 femtocellsSupporting Dynamic Roaming30

When Wi-Fi is insufficient, dynamic roaming can significantly cut down cost even with a small amount of capacity40 hotspotsImplementation31Dynamic offloading involves three stepsIdentify a network to offloadSolved by iDEAL Automatic authenticationSolved by Hotspot 2.0The roaming partners are updated dynamically according to the offload decision from iDEAL.Seamless offload to maintain the existing sessionsAddressed by Dual Stack Mobile IP (DSMIP), DSMIPv6,

System Architecture32