We evaluate the sink capacity of wireless code division
multiple access (CDMA) sensor networks with layered
architecture. We introduce a model of interference at a
sink considering two kinds of interference: multiple access
interference (MAI) and node interference (NI). We also
investigate the activity of sensor nodes around the sink in
relation to gathering data under a layered architecture.
Based on the interference model and the activity of sensor
nodes around the sink, we derive the failure probability of
the transmission from a source node located one hop away
from the sink using Gaussian approximation. Under the
requirement of 1% failure probability of transmission, we
determine the sink capacity, which is defined as the
maximum number of concurrent sensor nodes located one
hop away from the sink. We demonstrate that as the node
activity of the MAI decreases, the variation of the sink
capacity due to the node activity of the NI becomes more
significant. The analysis results are verified through
computer simulations.