In this paper, we propose a spectrum sharing protocol between two overlapping
static ad hoc wireless networks where the primary and secondary networks consist
of $n$ and $m$ randomly distributed nodes respectively. The secondary network 
achieves spectrum access along with the primary network by allowing its nodes 
to relay the primary traffic. Taking advantage of the broadcast nature of 
wireless channels, the secondary nodes are able to forward primary and secondary 
packets simultaneously by transmitting a superimposed signal. We analyze the 
throughput and delay scaling performance of the proposed protocol and show that 
given $m\geq n$, the primary network is able to achieve a per-node throughput 
scaling which is better than that of a stand-alone network with $n$ nodes. At 
the same time, the secondary network achieves the same throughput scaling as 
a stand-alone network with $m$ nodes. We also derive the throughput-delay 
tradeoff for both the primary and secondary systems in this scenario.