Truthful and Non-Monetary Mechanism for
Direct Data Exchange
I-Hong Hou, Yu-Pin Hsu, and Alex Sprintson
Direct Data Exchange in
Wireless D2D Communications
• Exchange data locally instead of getting all
packets from the base station
A,B
AB
A,B
Direct Data Exchange in
Wireless D2D Communications
• Exchange data locally instead of getting all
packets from the base station
A,B
AB
AB
A,B
Direct Data Exchange in
Wireless D2D Communications
• Exchange data locally instead of getting all
packets from the base station
AB
AB
A,B
AB
A,B
Direct Data Exchange in
Wireless D2D Communications
• Exchange data locally instead of getting all
packets from the base station
A
AB
AB
B
Direct Data Exchange in
Wireless D2D Communications
• Exchange data locally instead of getting all
packets from the base station
A
AB
A
B
B
Benefits of Wireless P2P
•
•
•
•
Exchange data locally requires less power
Reduce power consumption
Reduce interference
Increase spatial reuse and hence total
system capacity
• Challenge: How to provide incentives for
clients to cooperate?
Network Model
A B C
A B D
A D C
D B C
Need: D
Need: C
Need: B
Need: A
• Each client has all but one unique file, which it
needs
• The size of a file = Z bits
• All clients can communicate with each other
Incentive Model
A B C
A B D
A D C
D B C
v1 = 0.7
v2 = 0.6
v3 = 0.5
v4 = 0.1
• Each client has a secret valuation vi ≤1 for its
needed file
• Each client pays some transmission cost for the
amount of upload data
Incentive Model
A B C
A B D
A D C
D B C
v1 = 0.7
v2 = 0.6
v3 = 0.5
v4 = 0.1
• The goal of a client: Maximize net utility
vi1(receive file) - (amount of upload)/Z
Bidding Model
A B C
A B D
A D C
D B C
v1 = 0.7
v2 = 0.6
v3 = 0.5
v4 = 0.1
• Each client submits a bid bi to a broker
• The broker determines how much data a client
uploads, and what packets it should uploads
An Example
A B C
A B D
A D C
D B C
b1 = 0.8
b2 = 0.2
b3 = 0.9
b4 = 0.4
An Example
A B C
A B D
A D C
D B C
b1 = 0.8
b2 = 0.2
b3 = 0.9
b4 = 0.4
Upload
0.6Z
(A+B)
Upload
nothing
Upload
0.6Z
(A+D)
Upload
0.4Z
(B+D)
An Example
A B C
• D = (A+D)-A = (B+D)-B
• Can obtain all bits of D
b1 = 0.8
Upload
0.6Z
(A+B)
Upload
nothing
Upload
0.6Z
(A+D)
Upload
0.4Z
(B+D)
An Example
A B C
A B D
A D C
D B C
b1 = 0.8
b2 = 0.2
b3 = 0.9
b4 = 0.4
Upload
0.6Z
(A+B)
Upload
nothing
Upload
0.6Z
(A+D)
Upload
0.4Z
(B+D)
D
B
A
An Example
v1 = 0.7
v2 = 0.6
v3 = 0.5
v4 = 0.1
Upload
0.6Z
D
Upload
nothing
Upload
0.6Z
B
Upload
0.4Z
A
Net utility
0.7-0.6
=0.1
0
0.5-0.6
= -0.1
0.1-0.4
= -0.3
Goal of this Work
• Design a “truthful” broker policy
• Truthful: Every client maximizes its utility by
choosing bi = vi
• The policy should also achieve high total net
utility
Why not simply apply VCG
auction?
Auction
Each client submits a
bid
Wireless P2P
Each client submits a
bid
Auction
Each client submits a
bid
Auctioneer determines
who wins the auction,
and how much each
winner pays
Wireless P2P
Each client submits a
bid
Broker determines how
much a client uploads,
and who can download
its file
Comparable by treating uploads as payments,
clients that download files as winners
Auction
Each client submits a
bid
Auctioneer determines
who wins the auction,
and how much each
winner pays
Decisions on selecting
winners and payments
are independent
Wireless P2P
Each client submits a
bid
Broker determines how
much a client uploads,
and hence who can
download its file
Decision on upload
rates limits who can
download its file
Proposed Protocol
• Every client submits a bid bi
• Find the largest set S such that, for all i in S,
bi≥ 1/(|S|-1)
b1=0.7
b2=0.6
b3=0.6
• S = {1,2,3}, b1, b2, b3≥ 1/2
• S = {1,2,3,4}, b4< 1/3
• Largest set is {1,2,3}
b4=0.2
Proposed Protocol
• Every client submits a bid bi
• Find the largest set S such that, for all i in S,
bi≥ 1/(|S|-1)
• Every client in S uploads Z/(|S|-1) bits
containing a linear combination of all files that
other clients in S needs
• Each client in S receive Z bits, and hence can
obtain the file it needs
• Clients not in S do not obtain needed files
Theorem:
This protocol is truthful
Note: The broker is only conceptual. The policy
can be implemented in a distributed fashion by
letting each client run the broker policy.
Performance Analysis
• Sort clients such that b1≥b2≥b3≥…
• The set S must be the form of {1,2,…,n}
• Client i does not obtain its file only if bi<1/(i-1)
Theorem:
In terms of total net utility, the difference
between this protocol and one maximizing total
net utility is at most 1+1+1/2+1/3+…+1/(N-1),
where N is the number of clients
Numerical Results
• Assign vi to each client uniformly at random
from [0,1]
• Compare the difference in total net utility
between our proposed protocol and a
protocol that maximizes total net utility
Extension: Dependency Graph
• Some clients may not be able to exchange
file
– A client may miss some files that it does not need
– Some clients may be too far away to communicate
• Define a “dependency graph”
• Each client is a node in the graph
• Two nodes have an edge between them if the
two clients can exchange needed files
Solutions for Dependency
Graph
1. Find the largest clique such that every node
in the clique has bi≥ 1/(size of clique-1)
2. Each node in the clique uploads Z/(size of
clique-1) bits
3. Repeat Step 1
Theorem:
This protocol is truthful
Extension: Some Clients Need
the Same File
Need: A
bi =0.5
Need: A
bi =0.3
Need: A
bi =0.2
• Some clients need the same file
• Each client has all but one files
• Merge them into one, whose bid is (number
of merged clients)x(minimum bid)
• If they are selected in S, they divide the
amount of upload evenly
Extension: Some Clients Need
the Same File
Need: A
bi =0.5
Need: A
bi =0.3
Need: A
bi =0.2
• Some clients need the same file
• Each client has all but one files
• Merge them into one, whose bid is (number
of merged clients)x(minimum bid)
• If they are selected in S, they divide the
amount of upload evenly
Extension: Some Clients Need
the Same File
Need: A
bi =0.6
• Some clients need the same file
• Each client has all but one files
• Merge them into one, whose bid is (number
of merged clients)x(minimum bid)
• If they are selected in S, they divide the
amount of upload evenly
Summary
• Study the problem of direct data exchange
from the perspective of game theory
• While the game looks like an auction, results
of auction theory do not apply
• Propose a non-monetary protocol that is
truthful
• The protocol can be extended to various
scenarios