In one aspect the present invention describes an electronic circuit for transmitting voice packet data over a wireless network with an upstream transmission mode and a downstream transmission mode. -HCCA is reacted with alcohol to give a racemic -HCCA ester, which is then reacted with an enzyme with enantioselectivity, whereby either R-form or S-form of the racemate is hydrolyzed. The plurality of synchronization codes are used to identify the code group of the TDD base station.