iDEAL: Incentivized Dynamic Cellular Offloading via Auctions Wei Dong1 Joint work with Swati Rallapalli1, Rittwik Jana2, Lili Qiu1, K.
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Transcript iDEAL: Incentivized Dynamic Cellular Offloading via Auctions Wei Dong1 Joint work with Swati Rallapalli1, Rittwik Jana2, Lili Qiu1, K.
iDEAL: Incentivized Dynamic Cellular
Offloading via Auctions
Wei Dong1
Joint work with
Swati Rallapalli1, Rittwik Jana2, Lili Qiu1, K. K. Ramakrishnan2,
Leonid V. Razoumov2,Yin Zhang1, Tae Won Cho2
1The
University of Texas at Austin
2 AT&T Labs – Research
1
INFOCOM 2013
Motivation
Cellular network overloaded
Traffic is highly dynamic
Time (s)
Cellular demand variation
2
Large peak-to-average traffic
ratio
• Over 5 times in this
example
=>
Too costly to provision based
on the peak demand
Alternative?
ISPs augment cellular networks on their own
Wi-Fi
Femtocell
Insufficient as a long-term solution
High deployment cost
High management cost
Interferes with existing infrastructure
3
Our approach
Cellular provider purchases bandwidth on
demand from 3rd party resources
Wi-Fi, femtocell, or other cellular resources
Incentivize cellular offloading via auctions
Effective price discovery
Avoids long-term contracts
Cut cost by leveraging the competition
4
Unique challenges
Diverse spatial coverage
Traffic uncertainty
Non-truthful bidding and collusion
5
Cellular offloading as a reverse auction
Auction conducted periodically
Cellular provider (A): buyer
Hotspots: sellers
A
Hotspots submit bids
Cellular provider (A) serves as
auctioneer
A sector is divided into regions based
on location of hotspots
Objective: satisfy A’s traffic while
minimizing the total cost
Cost = cellular cost + hotspots cost
6
R1
R2
R3
Naïve solution
Limited competition
R1
R2
Auction 2
Demand 2
Auction 1
Demand 1
Cellular resource
7
Cellular resource as a virtual bidder
Inter-region competition
iDEAL overview
Two phases of iDEAL
Allocation: determine how to allocate cellular
resources and 3rd party resources to minimize cost
Pricing: determine payment to 3rd party
resource owners
8
Global static allocation
Input: di, ei, λj, pj, F(z)
Output: xj, ci, z
𝑗 𝑝𝑗
Minimize:
∗ 𝑥𝑗 + 𝐹(𝑧)
Total cost: Wi-Fi + cellular
Subject to:
[C1]
[C2]
𝑗:𝑓 𝑗 =𝑖 𝑥𝑗 + 𝑐𝑖
𝑚 𝑐𝑖
𝑖=1 𝑒 = 𝑧
𝑖
= Satisfy
𝑑𝑖 ∀𝑖
= 1,2,
…both
, 𝑚Wi-Fi and cellular
the demand
with
Translate cellular resource usage into spectrum
[C3] 0 ≤ 𝑥𝑗 ≤ λ𝑗 ∀𝑗 = 1,2,Never
… , 𝑛buy more than offered
[C4] 0 ≤ 𝑐𝑖 ∀𝑖 = 1,2, … , 𝑚
9
Global dynamic allocation
Traffic in different regions may peak at different times
Have multiple possible demand vectors
Optimize for the worst case
[C1-dynamic]
[C2-dynamic]
𝑗:𝑓 𝑗 =𝑖 𝑥𝑗 + 𝑐𝑖𝑘 =
𝑚 𝑐𝑖𝑘
𝑖=1 𝑒 = 𝑧 ∀𝑘
𝑑𝑘𝑖 ∀𝑘 𝑎𝑛𝑑 𝑖
𝑖
Benefits
Efficiently leverage cellular resource on demand
Avoid provisioning for the peak in each region
10
iDEAL pricing
VCG principle
Pay the winners the opportunity cost
Payment to winner w = the extra amount that other bidders could
sell if w is not present
iDEAL pricing
Apply VCG over the whole sector as one auction
Global opportunity cost
Captures inter- and intra-region competition
11
iDEAL pricing: Example
r: amount of resource
v: valuation of a single unit
d: demand
Allocation if 1 is
not there
r:1 v:$1.5
Optimal
allocation
Consider hotspot 1
Value sold by
others: $1.5
The “local
opportunity
cost” is $9
12
Value sold by
others: $3.5
1
r:1 v:$1
3
r:1 v:$9
Region 1 (d: 1)
2
r:1 v:$2
Global
opportunity
cost: $2
Region 2 (d:1)
1. Global opportunity cost captures inter-region competition and lowers cost
2. Payment is higher than bid
Economic properties
Theorem 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).
13
Understand collusions
Collusion strategies
Single seller collusion
Multi seller collusion
In both cases, they use Supply Reduction
Drop losing bids
Reduce the capacity offered in winning bids
Supply reduction: increases the opportunity cost
drives up price
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Mitigating collusions
Dynamic demands make collusion hard
Inaccurate traffic prediction supply reduction may lead
to missed winning opportunities
Bidding as a group
Hotspots owned by same party bid as group
considered one bidder
Removes competition within a group
no incentive for supply reduction
Inter-group competition retained
Multi seller collusion is unstable
Seller has incentive to leave the bidding ring
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Evaluation methodology
Sector reports
# of users
Event driven trace player
3G HTTP sessions
Detailed aggregated traffic demand
Sector location
Clustering
Regions
Hotspot location
Pricing plan of major ISPs
16
Bids
Auctions
Comparison of truthful auctions
40 hotspots
130 hotspots
1. Auction based approaches much better than fixed pricing given enough competition
2. iDEAL consistently beats other auction based approaches
17
Comparison of truthful auctions (cont.)
40 hotspots
130 hotspots
1. Global allocation efficiently allocates cellular resource to different regions.
2. Dynamic global allocation avoids provisioning for peak demand in each region.
18
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
First price (KF 0.2)
First price (KF 0.5)
First price (KF 0.8)
Uniform price
iDEAL (static)
iDEAL
0
10
20
Round
19
30
Total cost
Total value consumption
Comparison of non-truthful auctions
40
50
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
First price (KF 0.2)
First price (KF 0.5)
First price (KF 0.8)
Uniform price
iDEAL (static)
iDEAL
0
10
20
30
Round
Value consumption
Cost
1. Non-truthful auctions invites gaming behaviors
2. Gaming causes fluctuation and can increase cost
3. VCG in iDEAL is stable, efficient and low-cost
40
50
Collusion under dynamic demands
• Used two different sizes of bidding ring: 20 and 50
50: 28% chance of higher utility
20: 5% chance
Significantly weakens the
incentive to collude
20
Collusion: Bidding as a group
40 hotspots
130 hotspots
Group bidding removes competition between a seller’s own hotspots and
maintains the competition between different sellers, thus reducing the cost
21
Conclusion
Design incentive framework for cellular offload
Explicitly account for diverse spatial coverage of different resources
Cope with dynamic traffic
Promote truthfulness
Provably efficient
Guard against collusions
Trace-driven simulations show iDEAL is efficient, low-cost and
robust against collusion
22
Q&A
Thank you
23
Backup slides
24
Practical Considerations
Supporting offloading to femtocells and dynamic roaming
The same framework applies to purchasing femtocells and other
cellular resources
Handle partially overlapping spatial coverage
Revise the constraint [C1] to split the resources from the same
provider into different regions
25
Related Work
Measurement
Balasubramanian et al. report Wi-Fi is available for 11% time and 3G is
available for 87% time but they are negatively correlated
Lee et al. find Wi-Fi offload 65% traffic without delay and 83% with
over 1-hour delay
Auction based offloading
Zhou et al. uses auction to incentivize mobile users to wait until they
reach Wi-Fi
Chen et al. uses auction to incentivize femtocell owners to share
resources
Ignore three unique challenges iDEAL addresses
Similar to local allocation in spirit
26
Design Goals
Account for different spatial coverage of resources
Achieve high efficiency
Promote truthful bidding
Low cost
Guard against collusion
27
Mitigating Collusions (Cont.)
Stability of a multi-seller collusion
Without utility sharing, a seller has no incentive to conduct supply
reduction
Follows from the truthfulness of VCG and that in our system sellers
submit sealed, separated bids
Utility sharing is hard to achieve in our system
Hard to attribute utility change to collusion
Demand and Wi-Fi availability is dynamic
Hard to validate other bidders’ behavior
Sellers submit sealed separately bids
Can make it even harder via system design
E.g. use delayed payment to further obfuscate the utility
28
Supporting Femtocell Offload
Benefit of femtocells is
large when there are
fewer Wi-Fi hotspots
16 femtocells
29
Supporting Dynamic Roaming
When Wi-Fi is
insufficient, dynamic
roaming can
significantly cut down
cost even with a small
amount of capacity
40 hotspots
30
Implementation
Dynamic offloading involves three steps
Identify a network to offload
Solved by iDEAL
Automatic authentication
Solved by Hotspot 2.0
The roaming partners are updated dynamically according to the offload
decision from iDEAL.
Seamless offload to maintain the existing sessions
Addressed by Dual Stack Mobile IP (DSMIP), DSMIPv6, …
31
System Architecture
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