Incentives - Peer-to-Peer Computing: Applications, Architecture, Protocols, and Challenges - page 109

5.3 Incentive Issues in Wireless P2P Systems
Wireless P2P systems [Hsieh and Sivakumar, 2004] are proliferating in
recent years. Thanks to the widely available hot-spot wireless environments,
users handheld devices can work with each other in an ad hoc and impromptu
manner. As will be evident in this section, many techniques designed for wired
environments are also applied in a wireless system in a similar manner. Nev-
ertheless, there is a unique challenge in a wireless environment, namely the
connectivity issue. Furthermore, there is also one more dimension of cost in-
curred in each wireless P2P user—the energy expenditure, which is of prime
concern to the user as wireless devices are largely powered by batteries.

5.3.1 Routing and Data Forwarding
In a wireless P2P system, the connectivity among peers is itself a boot-
strap sharing problem. Indeed, if wireless users are unwilling to cooperate
in performing routing and data forwarding, the wireless network can become
partitioned so that service providers cannot be reached by potential service
consumers. In view of this critical challenge, there has been a plethora of im-
portant research results related to incentive issues for ad hoc routing and data
forwarding. In the following, we briefly cover several interesting techniques
that are based on payment mechanisms, auction mechanisms, reputation sys-
tems, and game theoretic modeling.
Ileri et al. [Ileri et al., 2005] proposed a payment-based scheme for enticing
devices to cooperate in forwarding data for other devices in the network. The
payment is not in monetary terms but in terms of bits-per-Joule. Specifically,
the utility of a user i in the network is defined as:

T i (p i )
p i

u i (p i ) = (5.40)

where u i is the utility, p i is the transmit power, and T i is the throughput.
That is, the utility is equal to the average amount of data received per unit
energy expended, also in bits-per-Joule.
The payment system also involves an access point in the wireless network.
Specifically, the access point also tries to maximize its revenue by using two
parameters, and λ, judiciously. Here, λ is the unit price of service provided
by the access point to any device in the network. On the other hand, is the
unit reimbursement the access point provides to any device which has helped
forward other devices' tra c. The access point's revenue is therefore given by:

T ef f−f or
ja

ρ = λT in i − (5.41)

all users i all forwarders j

is the service provided by the access point to user i and T ef f−f or
ja

where T in i