  In wireless ad hoc networks, distributed nodes can collaboratively form an
antenna array for long-distance communications to achieve high energy
efficiency. In recent work, Ochiai, et al., have shown that such collaborative
beamforming can achieve a statistically nice beampattern with a narrow main
lobe and low sidelobes. However, the process of collaboration introduces
significant delay, since all collaborating nodes need access to the same
information. In this paper, a technique that significantly reduces the
collaboration overhead is proposed. It consists of two phases. In the first
phase, nodes transmit locally in a random access fashion. Collisions, when they
occur, are viewed as linear mixtures of the collided packets. In the second
phase, a set of cooperating nodes acts as a distributed antenna system and
beamform the received analog waveform to one or more faraway destinations. This
step requires multiplication of the received analog waveform by a complex
number, which is independently computed by each cooperating node, and which
enables separation of the collided packets based on their final destination.
The scheme requires that each node has global knowledge of the network
coordinates. The proposed scheme can achieve high throughput, which in certain
cases exceeds one.
