Transmit antenna selection in a mobile wireless device

Methods and apparatuses to select a transmit antenna in a mobile wireless device connected to a wireless network are described. The mobile wireless device monitors received signal characteristics through first and second antennas and switches antennas based on the monitored signal characteristics and on an assessment of the sufficiency of available transmit power headroom to accommodate data transmissions in the uplink direction. Sufficiency is determined based on one or more criteria including achievable data rate throughput, quality of service, grade of service, an amount of data buffered, an amount of resources allocated by the wireless network and a number of "power up" commands received by the mobile wireless device during a pre-determined time interval.