Performance Evaluation of a Power Management Scheme for Disruption Tolerant Network

Abstract

Disruption tolerant network (DTN) is characterized by frequent partitions and intermittent connectivity. Power management issue in such networks is challenging. Existing power management schemes for wireless networks cannot be directly applied to DTNs because they assume the networks are well-connected. Since the network connectivity opportunities are rare, any power management scheme deployed in DTNs should not worsen the existing network connectivity. In this paper, we design a power management scheme called context-aware power management scheme (CAPM) for DTNs. Our CAPM scheme has an adaptive on period feature that allows it to achieve high delivery ratio and low delivery latency when used with Prophet, a recently proposed DTN routing scheme. Via simulations, we evaluate the performance of the CAPM scheme when used with the Prophet routing scheme in different scenarios e.g. different traffic load, node speeds and sleep patterns. Our evaluation results indicate that the CAPM scheme is very promising in providing energy saving (as high as 80%) without degrading much the data delivery performance.

Appendix

Average t_access:

$$t_{access} = \overline T _B + t_s $$

(5)

$\overline {T_B }$ is the average backoff time, t_s is the average time the channel is sensed busy because of a successful transmission.

$\overline {T_B }$ can be computed as follows:

$$\overline T _B = \frac{{\alpha \left( {W_{\min } \beta - 1} \right)}}{{2q}} + \frac{{1 - q}}{q}t_c $$

(6)

q:

the success probability that a packet experiences when it is transmitted.

t _c :

the average time the channel is sensed busy due to a collision in the channel.

W_min is the minimum contention window size, and α, β are defined in Eqns (8) and (9).

t _s : can be computed as

$$\begin{aligned} t_s = RTS + SIFS + \tau + CTS + SIFS + \tau + H + E\left\{ P \right\} \\ + SIFS + \tau + ACK + DIFS + \tau \\ \end{aligned} $$

(7)

where τ is the probability that a node transmits in a randomly chosen slot time, H is the packet header transmission time, E{P} is the average packet transmission time. RTS, CTS, SIFS, DIFS, ACK are parameters related to the 802.11 MAC protocol [13].

Equation for computing each variable:

$$\alpha = \sigma p_i + t_c p_c + t_s p_s $$

(8)

$$\beta = \frac{{q - 2^m \left( {1 - q} \right)^{m + 1} }}{{1 - 2\left( {1 - q} \right)}}$$

(9)

$$q \approx \frac{{\left( {W_{\min } + 1} \right)^2 }}{{\left( {W_{\min } + 1} \right)^2 + 2W_{\min } \left( {n - 1} \right)}}$$

(10)

$$t_c = RTS + DIFS + \tau $$

(11)

$$P_{tr} = 1 - \left( {1 - \tau } \right)^{n - 1} $$

(12)

$$P_{suc} = \frac{{\left( {n - 1} \right)\tau \left( {1 - \tau } \right)^{n - 2} }}{{1 - \left( {1 - \tau } \right)^{n - 1} }}$$

(13)

$$p_s = P_{tr} P_{suc} $$

(14)

$$p_i = 1 - P_{tr} $$

(15)

$$p_c = P_{tr} \left( {1 - P_{suc} } \right)$$

(16)

Equations [14],[15], and [16] are used in Eqn [8].

Equations [8]–[11] are used in Eqn [6].

$$p = \frac{{2W_{\min } \left( {n - 1} \right)}}{{\left( {W_{\min } + 1} \right)^2 + 2W_{\min } \left( {n - 1} \right)}}$$

(17)

$$\tau = \frac{{2\left( {1 - 2p} \right)}}{{\left( {1 - 2p} \right)\left( {W_{\min } + 1} \right) + pW_{\min } \left( {1 - \left( {2p} \right)^m } \right)}}$$

(18)

Eqn (17) is used in Eqn (18), and Eqn (18) is used in Eqn (7)

n :

number of nodes

σ :

slot size of the backoff timer

Using the parameter values in Table 4, we obtain t_access and hence obtain θ′ to be approximately 0.3 θ for medium traffic load.

Table 4 Physical layer parameters