Method of beamforming on FACH
Original Publication Date: 2001-Jul-01
Included in the Prior Art Database: 2003-Jul-23
The use of smart antennas is currently foreseen for almost all mobile communications systems. Therefore, solutions for efficiently exploiting the benefits of smart antennas are of high importance. Especially for low chip rate TDD / 1.28 Mcps TDD, smart antennas are seen as a key feature to increase spectral efficiency. Beamforming greatly reduces intra-cell as well as inter-cell interference. Beamforming is performed in the physical layer. The calculation of an optimized beamforming pattern for the downlink is based on uplink transmissions of the involved UEs. This concept is already feasible in the current standards for 3rd generation mobile communication systems. However, mainly solutions for dedicated channels have been discussed so far. Beamforming on FACH (a common downlink channel) has also been thought of, but no concrete concepts have been proposed so far. FACH can be used to convey information relevant for all UEs (e.g. scheduling information for system information on BCCH), as well as UE specific information (e.g. small packets on DTCH). MAC Headers depend on the logical channel type, that is transported on FACH. Depending on which kind of information is to be transmitted on FACH, beamforming might not be applicable and an omnidirectional pattern would be needed in order to reach all UEs. With the current protocol architecture, Node B functionality is restricted to layer 1. Therefore, no knowledge about the type of information on FACH is available in the Node B. Therefore, beamforming on FACH is quite difficult to realize. The problem described has not been solved so far and this contribution seeks to propose a possible way for beamforming on FACH. There is a hook for the possibility to use beamforming on FACH in 3GPP specification TS 25.302, but no detailed solutions are available. Node B has no knowledge about the contents of the transport block sets which it receives from MAC.