Communicating over powerline media using spot beamforming
A system and method for communicating information through a powerline medium including at least three conductors, where the transmitter transmits at least two signals onto the powerline medium and the receiver receives one or more signals from the powerline medium. The transmitter adjusts the power transmitted into the powerline medium in order to set the adjusted transmit power to a predetermined level, e.g., a level that ensures power radiated from the powerline medium does not exceed a regulatory limit. The process of adjusting the transmit power may take into account a functional relationship between the transmitted power and properties of the channel.
1. A method for operating a transmitter in order to transmit information through a powerline medium that includes at least three conductors, the method comprising:
determining a power adjustment factor α based on data including channel-descriptive information, wherein the channel-descriptive information includes a channel estimate or parameters derived from the channel estimate, wherein the channel estimate is an estimate of a channel between two or more inputs of the powerline medium and one or more outputs of the powerline medium;
operating on a symbol s of a symbol stream to obtain two or more transmit values, wherein the symbol stream is determined by a stream of information bits, wherein said operating on the symbol s includes computing a transmit vector x by multiplying the symbol s by the power adjustment factor α and by a vector c, wherein the vector c is a column of a precoding matrix, wherein the precoding matrix is derived from the channel estimate, wherein the two or more transmit values are specified by respective components of the transmit vector x; and
transmitting the two or more transmit values, respectively, through the two or more inputs of the powerline medium, wherein the power adjustment factor α is determined so that power transmitted into the powerline medium is set to a predetermined value.
2. The method of claim 1 , wherein the power adjustment factor α is greater than one.
3. The method of claim 1 , wherein the power adjustment factor α is positive and less than one.
4. The method of claim 1 , wherein the powerline medium includes exactly three conductors, where said two or more inputs includes exactly two inputs.
5. The method of claim 1 , wherein the predetermined value is selected to ensure that power radiated from the powerline medium does not exceed a regulatory limit.
6. The method of claim 1 , wherein the predetermined value is selected to ensure that power transmitted into the powerline medium does not exceed a regulatory limit.
7. The method of claim 1 , wherein the precoding matrix is a matrix V in a singular value decomposition UDV* of the channel estimate.
8. The method of claim 1 , wherein the parameters derived from the channel estimate include a first angle and second angle that characterize the precoding matrix.
9. The method of claim 1 , wherein the parameters derived from the channel estimate include a magnitude and an angle that characterize the precoding matrix.
10. The method of claim 1 , wherein the data also includes measured impedance values of wire pairs in the powerline medium.
11. The method of claim 1 , wherein the precoding matrix is a unitary matrix.
12. A system for transmitting information through a powerline medium that includes at least three conductors, the system comprising:
a processing unit configured to determine a power adjustment factor α based on data including channel-descriptive information, wherein the channel-descriptive information includes a channel estimate or parameters derived from the channel estimate, wherein the channel estimate is an estimate of a channel between two or more inputs of the powerline medium and one or more outputs of the powerline medium;
a precoding unit configured to operate on a symbol s of a symbol stream to obtain two or more transmit values, wherein the symbol stream is determined by a stream of information bits, wherein said operating on the symbol s includes computing a transmit vector x by multiplying the symbol s by the power adjustment factor α and by a vector c, wherein the vector c is a column of a precoding matrix, wherein the precoding matrix is derived from the channel estimate, wherein the two or more transmit values are specified by respective components of the transmit vector x; and
an output unit configured to transmit the two or more transmit values, respectively, through the two or more inputs of the powerline medium, wherein the power adjustment factor α is determined so that power transmitted into the powerline medium is set to a predetermined value.
13. The system of claim 12 , wherein the powerline medium includes exactly three conductors, wherein said two or more inputs includes exactly two inputs.
14. The system of claim 12 , wherein the predetermined value is selected to ensure that power radiated from the powerline medium does not exceed a regulatory limit.
15. The system of claim 12 , wherein the precoding matrix is a matrix V in a singular value decomposition UDV* of the channel estimate.
16. The system of claim 12 , wherein the output unit is configured to transmit the two or more transmit values by incorporating each of the two or more transmit values into a corresponding one of two or more orthogonal frequency division multiplexing (OFDM) signals, and transmitting the two or more OFDM signals, respectively, through the two or more inputs of the powerline medium.
17. The system of claim 12 , wherein the precoding matrix is a unitary matrix.
18. The system of claim 12 , wherein the parameters derived from the channel estimate include a first angle and second angle that characterize the precoding matrix.
19. The system of claim 12 , wherein the parameters derived from the channel estimate include a magnitude and an angle that characterize the precoding matrix.
20. The system of claim 12 , wherein the data also includes measured impedance values of wire pairs in the powerline medium.