  In this paper, we propose a new relaying protocol for large multihop networks
combining the concepts of cooperative diversity and opportunistic relaying. The
cooperative relaying protocol is based on two diversity mechanisms, incremental
redundancy combining and repetition combining. We assume that nodes in the
large multihop network are modeled by a homogeneous Poisson Point Process and
operate under Rayleigh fading and constant power transmission per node. The
performance of the proposed relaying protocol is evaluated through the progress
rate density (PRD) of the multihop network and compared to the conventional
multihop relaying with no cooperation. We develop an analytic approximation to
the PRD based on the concept of decoding cells. The protocol parameters are
optimized to maximize the PRD of network. We show that the cooperative relaying
protocol provides significant throughput improvements over conventional
relaying with no cooperation in a large multihop network. It is also shown that
incremental redundancy combining provides a higher gain in PRD relative to
repetition combining. The gain in PRD has near constant value at all values of
the path loss exponent and is monotonic in diversity order.
