| 摘要 |
A code division multiple access (CDMA) system wherein communication between a base station and a plurality of hand sets is effected at a common carrier frequency utilising time division duplex to afford accurate power control and to obviate the 'near far' problem. Preferably a pilot signal is added to the transmissions from the base station. This is used to sound the channel, providing a measure of the channel impulse response from base station to each hand set receiver. This information is then used to set up an inverse filter, which is applied to the receiver signal prior to detection. The detrimental effects of the channel can be removed, restoring orthogonality to a received code set and thus giving optimum capacity. In the reverse link a pilot can be used to predistort each hand set signal prior to transmission, according to the unique channel impulse response measurement made at each hand set. Since the filtering operations are assumed linear the order may be interchanged, and the base station receives each hand set signal with the detrimental effects of the channel precompensated. Orthogonality between hand set transmissions is therefore achieved at the base station receiver. Capacity is therefore balanced in forward and reverse links and the constraint of power control may be somewhat relaxed. |
