| 摘要 |
<p>A spread spectrum processing system (10) that employs wide bandwidth spread spectrum radio transmissions overlaid over the existing cellular voice signals to simultaneously provide additional cellular services without causing objectionable interference to current users of the cellular voice channels. The spread spectrum radio transmissions also support a large number of low rate digital messages. Both vehicle location and messaging functions are obtained without sacrificing any of the existing voice channel capacity. The cell site processor (40) is designed to share the existing cellular frequencies, real estate, antenna towers, antennas (31), and low noise amplifiers (32) used in the cell site radio frequency receiver chain. The only additional cell site equipment is the spread spectrum signal processor (3240 The processing system provides a means for achieving vehicle location accuracies that are improved by greater than two orders of magnitude over that which is possible by the current transmissions in that band. It provides a means of achieving transmit power control of the vehicle transmitter (11, 12) to combat the extremely large variation (dynamic range) of radio signal path loss to the receiving sites. It also provides a means of excising at the receiver the excessively strong conventional voice cellular signals that are not under power control which ordinarily might interfere with the successful reception of the new broadband signals. <IMAGE></p> |
