Data sharing among wireless client devices in cooperative manner with minimum transmissions

Abstract

A group of nearby wireless end devices such as mobile phones can benefit a fast service to satisfy their required packets by cooperating to exchange their packets after receiving collectively from a common base station. This problem can be formulated as a coding and transmission scheme and solved by the linear network coding. We propose a balanced coding and transmission (BCT) scheme that assigns suitable clients to find and transmit linear combinations of the received packets. The goals of our scheme are to minimize the total number of transmissions, to maintain fairness on the number of transmissions among the participants in the cooperative group and to maintain the limited energy resources until all members satisfy their needs. Moreover, we also introduce transmission scheme with physical layer network coding (BCTS/PNC) for the same problem to further reduce the required transmission time slots and accomplish the data exchange process in short time. We present the performance of the schemes and discussion in terms of the fairness, the number of transmissions and the completion time by testing with various simulation parameters and scenarios.

Appendix: upper and lower bounds on the number of transmissions

In this Section, the upper and lower bounds from Rouayheb et al. (2010) are described.

The minimum number of transmissions is greater or equal to $n-n_{min}$ where n is the number of packets and $n_{min}$ is the minimum number of packets held by a client, i.e., $n_{min} = \min _{1\le i\le k}n_i$. If all clients initially have the same number of packets $n_{min} < n$, i.e., $n_i = n_{min}$ for $i = 1, \ldots , k$ clients, then the minimum number of transmissions is greater than or equal to

$$\begin{aligned} n-n_{min}+1 \end{aligned}$$

(1)

The upper bound on the minimum required number of transmissions is less than or equal to

$$\begin{aligned} \min _{1\le i\le k} \lbrace |\overline{X_i} |+ \max _{1\le j\le k} |\overline{X_j} \cap X_i |\rbrace \end{aligned}$$

(2)

for $|\mathbb {F} |\ge k$. Each client $c_i$ initially holds a subset $X_i$ of packets in $X = \lbrace x_1,\cdots , x_n\rbrace$, i.e., $X_i \subseteq X$. And $n_i = |X_i |$ denotes the number of packets initially available to client $c_i$, and $\overline{X_i} = X \setminus X_i$.