  Multicast transmission, wherein the same packet must be delivered to multiple
receivers, is an important aspect of sensor and tactical networks and has
several distinctive traits as opposed to more commonly studied unicast
networks. Specially, these include (i) identical packets must be delivered
successfully to several nodes, (ii) outage at any receiver requires the packet
to be retransmitted at least to that receiver, and (iii) the multicast rate is
dominated by the receiver with the weakest link in order to minimize outage and
retransmission. A first contribution of this paper is the development of a
tractable multicast model and throughput metric that captures each of these key
traits in a multicast wireless network. We utilize a Poisson cluster process
(PCP) consisting of a distinct Poisson point process (PPP) for the transmitters
and receivers, and then define the multicast transmission capacity (MTC) as the
maximum achievable multicast rate per transmission attempt times the maximum
intensity of multicast clusters under decoding delay and multicast outage
constraints. A multicast cluster is a contiguous area over which a packet is
multicasted, and to reduce outage it can be tessellated into $v$ smaller
regions of multicast. The second contribution of the paper is the analysis of
several key aspects of this model, for which we develop the following main
result. Assuming $\tau/v$ transmission attempts are allowed for each
tessellated region in a multicast cluster, we show that the MTC is $\Theta(\rho
k^{x}\log(k)v^{y})$ where $\rho$, $x$ and $y$ are functions of $\tau$ and $v$
depending on the network size and intensity, and $k$ is the average number of
the intended receivers in a cluster. We derive $\{\rho, x, y\}$ for a number of
regimes of interest, and also show that an appropriate number of
retransmissions can significantly enhance the MTC.
