International Journal of Distributed Sensor Networks
Sink node
1
2
M
M−1
CT DT CT DT
···
CT DT CT DT
Sink
Node 1 Node 2
Node M
F : Typical data acquisition system and time slot assignment.
node, the transmit power
𝑑
𝑖
of node satises ()toachieve
the packet data transmit rate []:
𝑑
𝑖
≥
1
𝑖,𝑗
2
𝐼
𝑝
/𝑊
−1.
()
For presentation brevity,
𝑖,𝑗
is dened as
𝑖,𝑗
=|
𝑖,𝑗
|
2
/
(
0
).
2.2. MS-CTDMA MAC Protocol. To maximize the sensor
network lifetime, which is dened as the network working
time until one sensor node uses up its energy, we proposed
MS-CTDMA protocol. Introducing sleep mechanism into
sensor node’s idle state can reach low network energy con-
sumption, but it also prolongs average packet delay. And the
cooperative transmission could average power consumption
over sensor nodes to lengthen the network lifetime. For
example, as shown in Figure ,
𝑀−1,𝐷
is greater than
1,𝐷
and
𝑖,𝑗
denotes the distance between node and .Sonode
−1drains up its energy faster than node under the same
trac load. rough combining cooperative relay strategy
with sleep mode, the source node gets benet of lowering its
transmit power with the help of the relay node. e key idea
of our proposed protocol is to eciently utilize each node’s
transmit power in its idle state by choosing to sleep or to
cooperate, so as to maximize network lifetime.
Each node is in one of the following states: init state, busy
state, setup state, closedown state, sleep state or cooperation
state. e state transition diagram is depicted in Figure .A
node is said to be in sleep state when it turns o the radio
transreceiver to save its battery energy. In a sensor node’s
cooperation state, the idle node acts as the relay node to
savethesourcenode’senergyconsumptionbycooperative
transmission based on source node selection, not relay node
selection.
Initially each node starts out with the initial state. In this
state the sensor node completes initialization and waits for the
packet arrival. If the sensor has data to transmit, it transfers
to the busy state. During the busy state, this node acts as
thesourceterminal. is listening to the cooperative relay
request (CREQ) from other idle sensor nodes by signaling
packet. en sends the negotiation (CNEG) message back
to the request relay node. Once a request sensor node selects
as its cooperative target and replies to by cooperative
acknowledgement (CACK), and this relay node establish
the cooperative relay link to help to transmit. Aer all
Queue length
Busy state
Setup state
Packet arrives
Sleep
state
Cooperation
Closedown
Init state
Busy state: service its own data trac
Setup state: cooperative negotiation stage
Cooperation state: cooperative transmission stage
Sleep state: enter the sleep mode
Closedown state: release the cooperative transmission
state
state
equal to 0
Queue length
larger than N
F : State transition diagram of each sensor node.
packets in data buer have been sent out, the node changes
back to the idle state, where it can be a relay node or go
into sleep mode according to the following steps. If it were a
relay node, rst, enters the setup state to select the optimal
by broadcasting CREQ. If successfully nds the source
node from other nodes, it transfers to the cooperative state.
Otherwise, fails to nd an appropriate and turns o the
radio to go into the sleep state. Aer sleep or cooperation,
reexamines the queue length. If there is not enough trac
coming and the data buer size is less than which denotes
the predened threshold, maintains the cooperative or
sleep status. On the contrary, if ’s data buer size grows
larger than ,itgoestotheclosedownstateandreleasesthe
cooperative relay link or sleep mode. e node turns to be a
source node to transmit its own data trac until the next idle
state is satised.
e criterion to choose optimal source node for is
vital for the mixed transmission strategy. e mixed strategy
tries to give a tradeo between the network lifetime and
packet delay determined by considering the multiple impor-
tant elements: the residual battery energy, the channel state
information at the physical layer, the incoming trac load at
the MAC layer, and the packet delay for a dierent trac type.
During the same constant time interval, if the predened
threshold is increasing, the number of entering setup
state is decreasing. In other words, the overhead for sleep or
cooperation is reducing. For the same reason, the long-sleep
time
𝑠
or cooperative time
𝑐
leads to low overhead. But
these energy saving behaviors also incur lengthy packet delay.
3. Vacation Queue Model for MS-CTDMA
e
𝑋
//1vacation queue model with -policy multiple
exhaustive vacations is explored to analyze the performance
of MS-CTDMA protocol in this section. e access mecha-
nism of MS-CTDMA is coincident with the -policy vaca-
tionqueuemodelinherently.eidlestateinMS-CTDMA
can be modeled by the vacation state in
𝑋
//1vacation
queue model.
Here, we assume that the trac data buer size is
unlimited, which is reasonable when analyzing the average