
108 Energy-Efficient Cooperative Wireless Communication and Networks
Denoted by LC
CL
, the link cost of the cooperative link is
LC
CL
=
N
i=1
P
i
=1
.
N
i=1
1
LC
i,D
. (8.8)
We assume that the packet size is a bits. Denote η
S
,η
i
to be the required
energy for
N
S
and R
i
to transmit a packet, respectively. Obviously we have
η
S
= LC
BL
×
a
W × log
2
(1 + SNR
min
)
, (8.9)
η
i
= P
i
×
a
W × log
2
(1 + SNR
min
)
. (8.10)
In Khandani et al. [54], all relays participate in cooperative transmis-
sion and relays
R
i
transmit with power P
i
given by (8.3). This s cheme is
not suitable for battery-powered ad hoc or sensor networks. According to
(8.10), good-channel-condition relays (i.e., those with