Scattered pilot pattern and channel estimation method for MIMO-OFDM systems
A method and apparatus are provided for reducing the number of pilot symbols within a MIMO-OFDM communication system, and for improving channel estimation within such a system. For each transmitting antenna in an OFDM transmitter, pilot symbols are encoded so as to be unique to the transmitting antenna. The encoded pilot symbols are then inserted into an OFDM frame to form a diamond lattice, the diamond lattices for the different transmitting antennae using the same frequencies but being offset from each other by a single symbol in the time domain. At the OFDM receiver, a channel response is estimated for a symbol central to each diamond of the diamond lattice using a two-dimensional interpolation. The estimated channel responses are smoothed in the frequency domain. The channel responses of remaining symbols are then estimated by interpolation in the frequency domain.
1. A method of transmitting symbols using Orthogonal Frequency Division Multiplexing, OFDM, frames at an OFDM transmitter having at least two transmitting antennas, the OFDM frames having a time domain and a frequency domain, each OFDM frame comprising a plurality of OFDM symbols in the time domain, and a plurality of sub-carriers in the frequency domain, the method comprising the steps of:
transmitting, on an OFDM symbol, pilot symbols corresponding to the first antenna using a scattered pattern; and
transmitting, on the OFDM symbol, pilot symbols corresponding to the second antenna using the scattered pattern, wherein the pilot symbols for the first antenna correspond to a first code and the pilot symbols for the second antenna correspond to a second code.
2. The method of claim 1 , further comprising transmitting the pilot symbols with a power level which is dynamically adjusted as a function of a modulation type applied to the sub-carriers carrying data.
3. The method of claim 1 , wherein the first and second codes are space time block codes.
4. The method of claim 1 , further comprising applying an inverse fast Fourier transform to the pilot symbols.
5. The method of claim 1 , wherein the scattered pattern is a diamond lattice pattern.
6. The method of claim 1 , further comprising transmitting data symbols from the first and second antenna of the OFDM transmitter.
7. The method of claim 1 , wherein the scattered pattern is scattered in time and frequency.
8. The method of claim 1 , wherein each OFDM frame includes a preamble.
9. A device for transmitting pilot symbols using Orthogonal Frequency Division Multiplexing, OFDM, frames at an OFDM transmitter having at least two transmitting antennas, the OFDM frames having a time domain and a frequency domain, each OFDM frame comprising a plurality of OFDM symbols in the time domain, and a plurality of sub-carriers in the frequency domain, comprising:
a first antenna of the OFDM transmitter;
a second antenna of the OFDM transmitter; and
one or more processors configured to:
cause transmission via the first antenna, on an OFDM symbol, pilot symbols corresponding to the first antenna using a scattered pattern; and
cause transmission via the second antenna, on the OFDM symbol, pilot symbols corresponding to the second antenna using the scattered pattern, wherein the pilot symbols for the first antenna correspond to a first code and the pilot symbols for the second antenna correspond to a second code.
10. The device of claim 9 , the one or more processors further configured to cause transmission of the pilot symbols with a power level which is dynamically adjusted as a function of a modulation type applied to the sub-carriers carrying data.
11. The device of claim 9 , wherein the first and second codes are space time block codes.
12. The device of claim 9 , the one or more processors further configured to apply an inverse fast Fourier transform to the pilot symbols.
13. The device of claim 9 , wherein the scattered pattern is a diamond lattice pattern.
14. The device of claim 9 , the one or more processors further configured to cause transmission of data symbols from the first and second antenna of the OFDM transmitter.
15. The device of claim 9 , wherein the scattered pattern is scattered in time and frequency.
16. The device of claim 9 , wherein each OFDM frame includes a preamble.
17. A non-transitory computer readable medium for transmitting symbols using Orthogonal Frequency Division Multiplexing, OFDM, frames at an OFDM transmitter having at least two transmitting antennas, the OFDM frames having a time domain and a frequency domain, each OFDM frame comprising a plurality of OFDM symbols in the time domain and a plurality of sub-carriers in the frequency domain, the computer readable medium storing instructions to cause a processor to perform operations comprising:
transmitting, on an OFDM symbol, pilot symbols corresponding to the first antenna using a scattered pattern; and
transmitting, on the OFDM symbol, pilot symbols corresponding to the second antenna using the scattered pattern, wherein the pilot symbols for the first antenna correspond to a first code and the pilot symbols for the second antenna correspond to a second code.
18. The computer readable medium of claim 17 , the operations further comprising transmitting the pilot symbols with a power level which is dynamically adjusted as a function of a modulation type applied to the sub-carriers carrying data.
19. The computer readable medium of claim 17 , wherein the first and second codes are space time block codes.
20. The computer readable medium of claim 17 , the operations further comprising applying an inverse fast Fourier transform to the pilot symbols.
21. The computer readable medium of claim 17 , wherein the scattered pattern is a diamond lattice pattern.
22. The computer readable medium of claim 17 , the operations further comprising transmitting data symbols from the first and second antenna of the OFDM transmitter.
23. The computer readable medium of claim 17 , wherein the scattered pattern is scattered in time and frequency.
24. The computer readable medium of claim 17 , wherein each OFDM frame includes a preamble.
25. A method for receiving symbols using Orthogonal Frequency Division Multiplexing, OFDM, frames transmitted from an OFDM transmitter having at least two transmitting antennas, the OFDM frames having a time domain and a frequency domain, each OFDM frame comprising a plurality of OFDM symbols in the time domain and a plurality of sub-carriers in the frequency domain, the method comprising the steps of:
receiving, on an OFDM symbol, pilot symbols corresponding to the first antenna using a scattered pattern; and
receiving, on the OFDM symbol, pilot symbols corresponding to the second antenna using the scattered pattern, wherein the pilot symbols for the first antenna correspond to a first code and the pilot symbols for the second antenna correspond to a second code.
26. The method of claim 25 , further comprising receiving the pilot symbols with a power level which is dynamically adjusted as a function of a modulation type applied to the sub-carriers carrying data.
27. The method of claim 25 , wherein the first and second codes are space time block codes.
28. The method of claim 25 , further comprising estimating a channel based on the received pilot symbols.
29. The method of claim 25 , wherein the scattered pattern is a diamond lattice pattern.
30. The method of claim 25 , further comprising receiving data symbols from the first and second antenna of the OFDM transmitter.
31. A User Equipment (UE) for receiving pilot symbols using Orthogonal Frequency Division Multiplexing, OFDM, frames transmitted from an OFDM transmitter having at least two transmitting antennas, the OFDM frames having a time domain and a frequency domain, each OFDM frame comprising a plurality of OFDM symbols in the time domain and a plurality of sub-carriers in the frequency domain, comprising:
a receiver configured to:
receive, on an OFDM symbol, pilot symbols corresponding to the first antenna using a scattered pattern; and
receive, on the OFDM symbol, pilot symbols corresponding to the second antenna using the scattered pattern, wherein the pilot symbols for the first antenna correspond to a first code and the pilot symbols for the second antenna correspond to a second code.
32. The device of claim 31 , the receiver further configured to receive the pilot symbols with a power level which is dynamically adjusted as a function of a modulation type applied to the sub-carriers carrying data.
33. The device of claim 31 , wherein the first and second codes are space time block codes.
34. The device of claim 31 , the UE further comprises a processor configured to estimate a channel based on the received pilot symbols.
35. The device of claim 31 , wherein the scattered pattern is a diamond lattice pattern.
36. The device of claim 31 , the receiver further configured to transmit data symbols from the first and second antenna of the OFDM transmitter.
37. A non-transitory computer readable medium for receiving symbols using Orthogonal Frequency Division Multiplexing, OFDM, frames transmitted from an OFDM transmitter having at least two transmitting antennas, the OFDM frames having a time domain and a frequency domain, each OFDM frame comprising a plurality of OFDM symbols in the time domain and a plurality of sub-carriers in the frequency domain, the computer readable medium storing instructions to cause a processor to perform operations comprising:
receiving, on an OFDM symbol, pilot symbols corresponding to the first antenna using a scattered pattern; and
receiving, on the OFDM symbol, pilot symbols corresponding to the second antenna using the scattered pattern, wherein the pilot symbols for the first antenna correspond to a first code and the pilot symbols for the second antenna correspond to a second code.
38. The computer readable medium of claim 37 , the operations further comprising receiving the pilot symbols with a power level which is dynamically adjusted as a function of a modulation type applied to the sub-carriers carrying data.
39. The computer readable medium of claim 37 , wherein the first and second codes are space time block codes.
40. The computer readable medium of claim 37 , the operations further comprising estimating a channel based on the received pilot symbols.
41. The computer readable medium of claim 37 , wherein the scattered pattern is a diamond lattice pattern.
42. The computer readable medium of claim 37 , the instructions further comprising receiving data symbols from the first and second antenna of the OFDM transmitter.