A wireless data communication system has a first station or mobile unit is
linked to a second station configured as an access unit to support packet
communication, voice or data, where the voice packets are transmitted in
the Continuously Aware Mode (CAM) mode while other packets are buffered
by the access point and held until asked for by the first station when in
a Power Saving-Poll (PSP) mode. A monitoring apparatus at the access
point monitors all transmitted packets and sorts the packets to the
mobile unit according to CAM or PSP mode. Voice packets are sent out
immediately to the mobile unit. Other packets are stored at the access
point. The packet arrival rate may vary during transmission and due to
random packet delays introduced by propagation characteristic and
processing apparatus. The packet arrival rate and delays are taken into
account by the first station in an algorithm to determine and extend the
normal safe period in which the station receiver may be powered off.