Signal Processing - November 2016 - 110

Table 2. The general assignment game algorithm (GA-alg).
Step 1: Initialization
1) Set t = 1, b ti, j = b min j, 6i ! P, 6j ! S .
2) Set g ti, j = 0, 6i ! P, 6j ! S .
3) Construct the list of all the sellers that are not matched denoted by
MATCHLISTs = {s j} nj = 1 (implying U t (s j) = (p 0, 0), 6s j ! S ).
Step 2: Buyer Demand of Goods or Service
1) Each s j ! MATCHLISTs announces its price-allocation number b ti, j
to all the unmatched buyers.
2) Set SLISTp = Q .
3) Each unmatched buyer p i, 6i ! P :
■
■

■

Determines its demand X i (b ti ) .
If X i (b ti ) ! Q , then p i is added to SLISTp and bids for s j
(g ti, j = 1) , where j = X i (b ti ), 6s j ! S .
Otherwise, p i does not bid, (g ti, j = 0, j ! S) and
U t (p i) = (s 0, 0).

Step 3: Sellers' Decision Making
1) For all s j ! S
■

If U t (s j) = p 0 and
t

U (s j) =

/ mi = 1

(p i l, b ti l-, j1) ,

g ti, j = 0 and b ti, j 2 b min j, 6i ! P

where

t-1
i l = random ({i * | g i*, j = 1, 6i * ! P}) .

Remove s j from MATCHLIST J .
t

Set g i l , j@ = 0 , where j @ = X i l (b it ) .
2) For all s j ! S
■

If

/ mi = 1 g ti,j 2 1,
Set b ti,+j 1 = b ti, j + e .
If s j " MATCHLISTs

sj is added to MATCHLISTs .
■

Else

/ mi = 1 g ti,j = 1,

t

U t (s j) = (p i, b ti, j) , where i = arg i* ! P g i*, j = 1.
Remove s j from MATCHLISTs .
3) For all s j ! S
■

t

If (U (s j) ! p 0 and
t+1
b i, j

=

t
b i, j, i

/ mi = 1 g ti,j = 0) or U t (s j) = (p 0, 0)

! P.

Set t = t + 1. If SLISTp ! Q , go to step 2; otherwise, go to step 4.
Step 4: End of the Algorithm

received a bid from only one buyer. In this case, the seller will
be matched with this node. The last iteration of the GA-alg is
denote by t End .

Competitive equilibrium
The requirements of a stable matching in previous sections
are defined with the general implication that none of the
two matched agents has a desire to leave their current
matching and make a new match. In the wireless networks,
if users are assumed as the agents in matching then the
focus of the network is to maximize the agents' satisfaction level. Although the final matching may be stable, it is
an important factor to investigate whether any of the
matched buyers prefer to be matched with another seller.
110

In this regard, it is convenient to present the competitive
equilibrium, defined as
■ Definition 7: The matching matrix X, and price-allocation
vector b, that are produced by the matching algorithms are
in competitive equilibrium if the following conditions
are satisfied:
1) for each s j, j ! S, if U 1 (s j) ! p 0 , then b ij $ c j
2) for each p i, i ! P, U 1 (p i) ! X i ^b i h
3) for each s j, j ! S, if U 1 (s j) = p 0, then b ij = c j,
where X i ^b i h is defined in a similar way to (3) but dropping
parameter t.
The conditions can be interpreted as follows. Condition 1
states that a matched seller always receives a nonnegative utility; condition 2 states that each buyer will be matched with the
seller that provides the highest positive utility; and condition 3
states that if a seller is not matched, then its price-allocation
number results in a zero utility. Note that based on Definition 7,
the competitive equilibrium concept is a special case of the
stable matchings.
However, the concept of competitive equilibrium needs
to be distinguished from stable matching. In stable matching there are no buyer-seller pairs who both prefer each
other over their current match, but in competitive equilibrium there is no buyer who prefers any seller over his/her current match. Competitive equilibrium is a feasible matching
outcome that guarantees that 1) there are no two agents who
are able to form a matching pair such that both would benefit better than their current state, and 2) there is no matched
agent who prefers to be unmatched. Competitive equilibrium has been widely studied in the literature [25], [26]. It
has been shown that a competitive equilibrium always exists
[26]. A competitive equilibrium can be stated by the matching matrix and the price vector. Based on this definition, the
following theorem and lemma are presented [8].
■ Theorem 3: The algorithm in Table 2 produces matching
and price-allocation matrices, which are in competitive
equilibrium for sufficiently small values of e.
Theorem 3 provides an important property of the matching algorithm, that when e is small enough, the outcome
of the algorithm will be in the competitive equilibrium.
Decreasing e will increase the number of iterations of the
matching algorithm in Table 2, so there is always a tradeoff
between the optimality and the complexity of the matching
algorithm in Table 2. The parameter e can be considered
as a controlling parameter for the network designer to balance between the convergence time and performance of the
matching algorithm.
■ Lemma 1: An algorithm that results in a competitive equilibrium also results in a stable matching.
Lemma 1 implies that competitive equilibrium covers the
stable matching. However, there are some outcomes of the
matching that are not competitive equilibrium.

Matching with externalities
In all the matching models discussed previously, the preferences of agents over each other is fixed over time. In such a

IEEE Signal Processing Magazine

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November 2016

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Table of Contents for the Digital Edition of Signal Processing - November 2016

Signal Processing - November 2016 - Cover1
Signal Processing - November 2016 - Cover2
Signal Processing - November 2016 - 1
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Signal Processing - November 2016 - Cover3
Signal Processing - November 2016 - Cover4
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