Because of the ability to improve channel capability effectively, an MIMO system has received much attention during researches of Long-Term Evolution (LTE) and Advanced Long-Term Evolution (LTE-A).
A beam forming technology operates mainly by controlling a beam direction. A beam in a characteristic direction is obtained utilizing an antenna array structure, and a user terminal is distinguished according to a location of the user terminal so as to realize multiplexing of the same time and frequency resources by multiple users, thus obtaining evident beam energy gain, improving cell coverage and a capability of the MIMO system, reducing interference of the MIMO system, increasing the capability of the MIMO system, improving link reliability and increasing peak rate. At the same time, the beam forming technology can control a beam by utilizing the direction with the strongest user signals so as to perform data transmission by using several strongest paths in a multipath channel environment. The beam forming technology is more applicable to open suburbs and can be also applied in complicated urban environments. The beam forming technology is especially applicable to a short antenna space (e.g. 0.5λ), which is beneficial for controlling beam orientation.
In a single-user MIMO mode, multiple data streams can be transmitted by multiple layers at the same time by designing appropriate weight vectors of a transmitting antenna and a receiving antenna. In addition, data of multiple layers can be transmitted in parallel and interference among layers can be eliminated. In a multi-user MIMO mode, a direction of a beam subjected to the beam forming can be designed by designing appropriate weight vectors of a transmitting antenna and a receiving antenna and signals of multiple users are distinguished, so as to eliminate interference among users.
The current beam forming technology is mainly applied to a data stream of a single-layer. For the single-user MIMO mode, a terminal side directly performs beam forming for an uplink data stream to be transmitted and transmits the uplink data stream subjected to the beam forming to a base station side, wherein the uplink data stream to be transmitted is an uplink data stream of a single layer.
For the Third Generation Partnership Project (3 GPP) Release 10 (Rel-10) standard which will start to be proposed soon, the number of antennae at the base station side of the MIMO system will be increased to more than 8, and the number of antennae at the terminal side will be increased to more than 4. So for the beam forming technology, the number of layers used in the beam forming needs to be controlled. An existing single-layer beam forming technology needs to be extended into a multi-layer beam forming technology, so as to adequately and reasonably utilize space channel resources.
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