| 摘要 |
A mobile communications network includes respective first and second stations 1,2, one of which is a base station and the other of which is a mobile station. A first channel transmits signals from the first station to the second station and a second channel transmits signals from the second station to the first station. The network is one in which the uplink and downlink channel characteristics can validly be assumed to be the same or similar, for example a UTRA TD-CDMA network having a TDD mode. At the second station 2, channel estimation is carried out for the first channel. When a preselected change in communications-channel characteristics between the first and second stations is detected (e.g. based on the first channel FER), in response to such detection a predetermined control signal CS, embodying the channel estimate EST for the first channel, is transmitted from the second station to the first station. The control signal is received at the first station and employed to derive a channel estimate EST for the second channel. Thus, it is not necessary to provide the first station with its own channel estimation facility. In another embodiment (Fig. 6), when a change is detected in channel characteristics the predetermined control signal is transmitted via the second channel and comprises a known sequence of symbols such as a midamble and is used by a channel estimator in the first station to produce a channel estimate for the second channel directly. May be used for asymmetric data transmission, wherein the midamble is only added to the channel having the lowest data throughput requirement. |
