MotionCast: on the capacity and delay tradeoffs

In this paper, we define multicast for ad hoc network through nodes' mobility as <i>MotionCast</i>, and study the capacity and delay tradeoffs for it. Assuming nodes move according to an independently and identically distributed (i.i.d.) pattern and each desires to send packets to <i>k</i> distinctive destinations, we compare the capacity and delay in two transmission protocols: one uses 2-hop relay algorithm without redundancy, the other adopts the scheme of redundant packets transmissions to improve delay while at the expense of the capacity. In addition, we obtain the maximum capacity and the minimum delay under certain constraints. We find that the per-node capacity and delay for 2-hop algorithm <i>without redundancy</i> are Θ(1/<i>k</i>) and Θ(<i>n</i>log <i>k</i>), respectively; and for 2-hop algorithm <i>with redundancy</i> they are Ω(1/(<i>k</i>√<i>n</i>log <i>k</i>)) and Θ(√<i>n</i>log <i>k</i>), respectively. The capacity of the 2-hop relay algorithm without redundancy is better than the multicast capacity of static networks developed in [3] as long as <i>k</i> is strictly less than <i>n</i> in an order sense; while when <i>k</i>=Θ(<i>n</i>), mobility does not increase capacity anymore. The ratio between delay and capacity satisfies <i>delay/rate</i> ≥ <i>O</i>(<i>nk</i>log <i>k</i>) for these two protocols, which is smaller than that of directly extending the fundamental tradeoff for unicast established in [1] to multicast, i.e., <i>O</i>(<i>nk</i>²).