  This paper investigates optimal caching placement for wireless femto-caching
network. The average bit error rate (BER) is formulated as a function of
caching placement under wireless fading. To minimize the average BER, we
propose a greedy algorithm finding optimal caching placement with low
computational complexity. Exploiting the property of the optimal caching
placement which we derive, the proposed algorithm can be performed over
considerably reduced search space. Contrary to the optimal caching placement
without consideration of wireless fading aspects, we reveal that optimal
caching placement can be reached by balancing a tradeoff between two different
gains: file diversity gain and channel diversity gain. Moreover, we also
identify the conditions that the optimal placement can be found without running
the proposed greedy algorithm and derive the corresponding optimal caching
placement in closed form.
