1. Field of the Invention
The present invention relates to a transmission system and more particularly, to a method of transmitting and receiving data streams using a plurality of antennas. Although the present invention is suitable for a wide scope of applications, it is particularly suitable for grouping a plurality of antennas into sub-groups of antennas based on an antenna combination having a maximum data throughput and transmitting such information. Moreover, it is suitable for transmitting a plurality of data streams based on weight values for each antenna. The related arts do not show such features of applying weight values to transmitting antennas and grouping antenna combinations to determine a combination having a maximum data throughput.
2. Discussion of the Related Art
In a transmission diversity (Tx diversity) scheme, a single data stream is transmitted using at least two antennas via independent channel. The signals corresponding to the data stream suffer different channel environment and are received in a receiving antenna. In a receiving end, the signals suffering different channel are combined and decoded. Because it is more efficient to decode combined signals than a single signal, the receiving end can acquire efficiency in decoding, called diversity gain.
As another aspect of diversity scheme, a spatial multiplexing method has been proposed. In the spatial multiplexing system, at least two independent data streams are transmitted using at least two transmitting antennas respectively. In a receiving end, at least two antennas are introduced, and each antenna receives at least two signals simultaneously. Therefore, the received signals must be recovered separately with a detection algorithm for each signal. The separated signal is decoded independently. In this method, each signal is transmitted independently so different modulation or coding scheme is applicable to each signal.
In the existing diversity schemes, data streams are transmitted via a fixed set of antennas without regard to a potentially more efficient and effective antenna combination. As a result, transmission may suffer inefficiency and delays due to underutilization of antennas and overuse of other antennas. Moreover, time and resources could be wasted. Therefore, the amount of data transmitted suffers.
For example, in a system having four antennas in a transmitting end which are set to transmit data stream 1 from antennas 1 and 2 and data stream 2 from antennas 3 and 4, other antenna configuration is not considered. If antennas 1 and 2 have strong signal strength compared to antennas 3 and 4, yet data stream 1 does not have much data to transmit whereas data stream 2 does, the fixed configuration would cause delays in transmitting data stream 2 due to weak signals and data overload. On the contrary, antennas 1 and 2 do not have much data to transmit, resulting in underutilization of resources.
Another disadvantage of the existing diversity scheme is that antenna signal strengths are not considered prior to transmitting data through them. In other words, data is transmitted through an antenna regardless of the transmission rate of that antenna. As a result, inefficient as well as ineffective data transmission could occur. In addition, the amount of data transmitted suffers.
For example, in a system having two antennas, the transmission signal strength of antenna 1 is strong while antenna 2 has weak signal strength. By transmitting a data stream through both antennas, the transmission in antenna 2 would suffer and considered inefficient.