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 base station using a first plurality of processing paths to transmit OFDM signals, the OFDM base station neighboring an adjacent OFDM base station using a second plurality of processing paths to transmit OFDM signals, the OFDM frames having a time domain and a frequency domain, each of the OFDM frames 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:
for each processing path, transmitting scattered pilot symbols using a respective scattered pattern in time-frequency, wherein the respective scattered pattern is offset from a scatted pattern of the adjacent OFDM base station.
2. The method of claim 1 , wherein at least one of the OFDM frames includes a preamble.
3. The method of claim 1 , wherein transmitting scattered pilot symbols comprises:
transmitting scattered pilot symbols in a respective location within the scattered pattern on a same sub-carrier.
4. The method of claim 1 , wherein transmitting scattered pilot symbols in an identical scattered pattern in time-frequency comprises:
transmitting scattered pilot symbols at locations that form at least one diagonal arrangement in time-frequency.
5. The method of claim 1 , further comprising transmitting the scattered pilot symbols with a power level greater than a power level of data symbols, depending upon a value reflective of channel conditions.
6. The method of claim 1 , further comprising transmitting the scattered pilot symbols with a power level which is dynamically adjusted to ensure sufficiently accurate reception as a function of a modulation type applied to sub-carriers carrying data.
7. The method of claim 1 , wherein the scattered pattern in time-frequency includes a first plurality of pilot symbols, each pilot symbol of the first plurality of pilot symbols spaced six subcarriers apart.
8. The method of claim 7 , wherein the scattered pattern in time-frequency includes a second plurality of pilot symbols, each pilot symbol of the second plurality of pilot symbols spaced six subcarriers apart, the second plurality of pilot symbols offset from the first plurality of pilot symbols by three subcarriers.
9. The method of claim 8 , wherein the second plurality of pilot symbols is offset in time from the first plurality of pilot symbols.
10. The method of claim 1 , wherein the offset is in at least one of time or frequency.
11. The method of claim 1 , wherein the adjacent OFDM base station transmits, for each of its plurality of processing paths, a scattered pattern of pilot symbols in time-frequency.
12. A base station comprising:
a memory;
at least two processing paths; and
at least one processor communicatively coupled with the memory and configured to:
cause transmission of Orthogonal Frequency Division Multiplexing (OFDM) signals in OFDM frames using the at least two processing paths, wherein the OFDM frames have a time domain and a frequency domain, and each of the OFDM frames comprises a plurality of OFDM symbols in the time domain and a plurality of sub-carriers in the frequency domain; and
for each of the at least two processing paths, cause transmission of scattered pilot symbols using a respective scattered pattern in time-frequency, wherein the respective scattered pattern is offset from a scatted pattern of an adjacent OFDM base station, wherein the adjacent OFDM base station uses a second plurality of processing paths to transmit OFDM signals.
13. The base station of claim 12 , wherein at least one of the OFDM frames includes a preamble.
14. The base station of claim 12 , wherein the scattered pilot symbols are transmitted in a respective location within the scattered pattern on a same sub-carrier.
15. The base station of claim 12 , wherein the scattered pilot symbols are transmitted at locations that form at least one diagonal arrangement in time-frequency.
16. The base station of claim 12 , wherein the at least one processor is further configured to cause transmission of the scattered pilot symbols with a power level greater than a power level of data symbols, depending upon a value reflective of channel conditions.
17. The base station of claim 12 , wherein the at least one processor is further configured to cause transmission of the scattered pilot symbols with a power level which is dynamically adjusted to ensure sufficiently accurate reception as a function of a modulation type applied to sub-carriers carrying data.
18. The base station of claim 12 , wherein the scattered pattern in time-frequency includes a first plurality of pilot symbols, each pilot symbol of the first plurality of pilot symbols spaced six subcarriers apart.
19. The base station of claim 18 , wherein the scattered pattern in time-frequency includes a second plurality of pilot symbols, each pilot symbol of the second plurality of pilot symbols spaced six subcarriers apart, the second plurality of pilot symbols offset from the first plurality of pilot symbols by three subcarriers.
20. The base station of claim 19 , wherein the second plurality of pilot symbols is offset in time from the first plurality of pilot symbols.
21. The base station of claim 12 , wherein the offset is in at least one of time or frequency.
22. The base station of claim 12 , wherein the adjacent OFDM base station transmits, for each of its plurality of processing paths, a scattered pattern of pilot symbols in time-frequency.
23. A non-transitory computer-readable medium storing instructions that are operable when executed by data processing apparatus to perform operations comprising: transmitting Orthogonal Frequency Division Multiplexing (OFDM) signals in OFDM frames at an OFDM base station using a first plurality of processing paths, wherein the OFDM frames have a time domain and a frequency domain, and each of the OFDM frames comprises a for each processing path, transmitting scattered pilot symbols using a respective scattered pattern in time-frequency, wherein the respective scattered pattern is offset from a scattered pattern of an adjacent OFDM base station, wherein the adjacent OFDM base station uses a second plurality of processing paths to transmit OFDM signals.
24. The non-transitory computer-readable medium of claim 23 , wherein at least one of the OFDM frames includes a preamble.
25. The non-transitory computer-readable medium of claim 23 , wherein transmitting scattered pilot symbols comprises:
transmitting scattered pilot symbols in a respective location within the scattered pattern on a same sub-carrier.
26. The non-transitory computer-readable medium of claim 23 , wherein transmitting scattered pilot symbols in an identical scattered pattern in time-frequency comprises:
transmitting scattered pilot symbols at locations that form at least one diagonal arrangement in time-frequency.
27. The non-transitory computer-readable medium of claim 23 , the operations further comprising transmitting the scattered pilot symbols with a power level greater than a power level of data symbols, depending upon a value reflective of channel conditions.
28. The non-transitory computer-readable medium of claim 23 , the operations further comprising transmitting the scattered pilot symbols with a power level which is dynamically adjusted to ensure sufficiently accurate reception as a function of a modulation type applied to sub-carriers carrying data.
29. The non-transitory computer-readable medium of claim 23 , wherein the scattered pattern in time-frequency includes a first plurality of pilot symbols, each pilot symbol of the first plurality of pilot symbols spaced six subcarriers apart.
30. The non-transitory computer-readable medium of claim 29 , wherein the scattered pattern in time-frequency includes a second plurality of pilot symbols, each pilot symbol of the second plurality of pilot symbols spaced six subcarriers apart, the second plurality of pilot symbols offset from the first plurality of pilot symbols by three subcarriers.
31. The non-transitory computer-readable medium of claim 30 , wherein the second plurality of pilot symbols is offset in time from the first plurality of pilot symbols.
32. The non-transitory computer-readable medium of claim 23 , wherein the offset is in at least one of time or frequency.
33. The non-transitory computer-readable medium of claim 23 , wherein the adjacent OFDM base station transmits, for each of its plurality of processing paths, a scattered pattern of pilot symbols in time-frequency.
34. A telecommunication system, comprising: a first Orthogonal Frequency Division Multiplexing (OFDM) base station comprising: a first memory; a first plurality of processing paths; and at least a first processor communicatively coupled with the first memory and configured to cause transmission of OFDM signals using the first plurality of processing paths, a second Orthogonal Frequency Division Multiplexing (OFDM) base station, adjacent to the first OFDM base station comprising: a second plurality of processing paths; and at least a second processor communicatively coupled with the second memory and configured to: cause transmission of OFDM signals in OFDM frames using the second plurality of processing paths, wherein the OFDM frames have a time domain and a frequency domain, and each of the OFDM frames comprises a plurality of OFDM symbols in the time domain and a plurality of sub-carriers in the frequency domain; and for each of the first plurality of processing paths, cause transmission of scattered pilot symbols using a respective scattered pattern in time-frequency, wherein the respective scattered pattern is offset from a scattered pattern of the first OFDM base station.