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Performance Evaluations

In this section, the performance of the proposed incentive scheme is evaluated. We introduce the simulation setup and show the performance comparison with discussions.

Simulation Setup

In the simulation, there are 20 nodes with a transmission radius of 50 m, which are uniformly deployed in an area of 1km x 1 km. Each node moves at a speed uniformly spread in [0.5, 2.5] m/s with the random direction model. Therefore, according to [35], the average contact rate of two nodes is 0.37 contacts per hour to determine the contact time of each pair of nodes for the simulation in MATLAB.

The source node generates bundles with a uniform time interval of 10 min, and the size of each bundle is 2 MB. We set the buffer size of each node to 30 MB. The TTL of the bundle is 6 h. The destination of the bundle is randomly selected from the other nodes except source nodes. The energy of each node decreases according to Ere = e-Xt Emax, where X = 0.2. Moreover, the weight parameters are a = 0.3, в = 0.3, and y = 0.4. Table4.1 lists the parameter values in this simulation.

The social ties among mobile nodes are generated by using the BA model [36], which can generate a scale-free social network model. Each simulation runs for 12h and is repeated ten times. Every node has an initial virtual currency of 100 and pays the corresponding currency for each delivered bundle.

Table 4.1 Parameters

Parameter

Value

N: the number of users in the network

20

Bumax: the maximum buffer of each node

30 MB

Emax: the maximum energy of each node

2000 w

TTL: the time-to-live value of a bundle

6h

{a, в, y}: the weight parameters in (4.4)

{0.3,0.3,0.4}

a: the section threshold of each node

0.7

k: the change of status

3

{e, &>}: the weight parameters in (4.7)

{0.5,0.5}

v: the patience coefficient of the buyer

0.6

i: the patience coefficient of the seller

0.6

{Tb , Rs}: the costs associated with the transmission and recepition of bundle, respectively

{0,0}

The following metrics are used to compare different delivery schemes:

  • delivery ratio the proportion of the bundles that have been delivered to the bundles being created;
  • delivery delay the average delivery time that is used to deliver bundles from the source to the destination.
 
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