Scattered pilot pattern and channel estimation method for MIMO-OFDM systems
View Patent ↗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 inserting pilot symbols into 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:
for a first antenna of the OFDM transmitter, inserting scattered pilot symbols in a scattered pattern in time-frequency by inserting a first set of pilot symbols in a first pattern in time-frequency and inserting a second set of pilot symbols in a second pattern in time-frequency at the same frequencies as the first pattern, offset by one OFDM symbol in the time domain; and
for a second antenna of the OFDM transmitter, inserting scattered pilot symbols using the same scattered pattern.
2. A method according to claim 1 , wherein each pilot symbol of the first set of pilot symbols is spaced six sub-carriers apart.
3. A method according to claim 1 , wherein the scattered pattern is a regular diagonal-shaped lattice.
4. A method according to claim 3 , wherein the regular diagonal shaped lattice is a diamond shaped lattice.
5. A 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.
6. A method according to claim 3 , wherein the regular diagonal-shaped lattice pattern comprises:
a first plurality of equally spaced sub-carrier positions;
a second plurality of equally spaced sub-carrier positions offset from said first plurality;
wherein the pilot symbols are inserted alternately in time using the first plurality of equally spaced sub-carrier positions and the second plurality of equally spaced sub-carrier positions.
7. An apparatus, comprising:
an Orthogonal Frequency Division Multiplexing, OFDM, transmitter having at least two transmit antennas, the OFDM transmitter being adapted to insert pilot symbols into 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, and configured to:
insert, using a first antenna of the OFDM transmitter, scattered pilot symbols in a scattered pattern in time-frequency by inserting a first set of pilot symbols in a first pattern in time-frequency and inserting a second set of pilot symbols in a second pattern in time-frequency at the same frequencies as the first pattern, offset by one OFDM symbol in the time domain; and
insert, using a second antenna of the OFDM transmitter, scattered pilot symbols using the same scattered pattern.
8. The apparatus according to claim 7 , wherein the pilot symbols are transmitted with a power level greater than a power level of data symbols.
9. The apparatus according to claim 8 , wherein the pilot symbols are transmitted with a power level greater than a power level of data symbols depending on a value reflective of channel conditions.
10. The apparatus according to claim 7 , further comprising an OFDM receiver configured to receive scattered pilot symbols in the scattered pattern for each transmitting antenna.
11. A User Equipment (UE), comprising:
one or more processors configured to:
receive, from a first antenna of an OFDM transmitter, scattered pilot symbols in a scattered pattern in time-frequency, wherein the scattered pattern includes a first set of pilot symbols in a first pattern in time-frequency and a second set of pilot symbols in a second pattern in time-frequency at the same frequencies as the first pattern, offset by one OFDM symbol in the time domain; and
receive, from a second antenna of the OFDM transmitter, scattered pilot symbols using the same scattered pattern.
12. The UE according to claim 11 , wherein each pilot symbol of the first set of pilot symbols is spaced six sub-carriers apart.
13. The UE according to claim 11 , wherein the scattered pattern is a regular diagonal-shaped lattice.
14. The UE according to claim 13 , wherein the regular diagonal shaped lattice is a diamond shaped lattice.
15. The UE according to claim 11 , one or more processors 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.
16. The UE according to claim 13 , wherein the regular diagonal-shaped lattice pattern comprises:
a first plurality of equally spaced sub-carrier positions;
a second plurality of equally spaced sub-carrier positions offset from said first plurality; and
wherein the pilot symbols are inserted alternately in time using the first plurality of equally spaced sub-carrier positions and the second plurality of equally spaced sub-carrier positions.
17. A method, comprising:
receiving, from a first antenna of an OFDM transmitter, scattered pilot symbols in a scattered pattern in time-frequency, wherein the scattered pattern includes a first set of pilot symbols in a first pattern in time-frequency and a second set of pilot symbols in a second pattern in time-frequency at the same frequencies as the first pattern, offset by one OFDM symbol in the time domain; and
receiving, from a second antenna of the OFDM transmitter, scattered pilot symbols using the same scattered pattern.
18. The method according to claim 17 , wherein each pilot symbol of the first set of pilot symbols is spaced six sub-carriers apart.
19. The method according to claim 17 , wherein the scattered pattern is a regular diagonal-shaped lattice.
20. The method according to claim 19 , wherein the regular diagonal shaped lattice is a diamond shaped lattice.
21. The method according to claim 17 , 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.
22. The method according to claim 19 , wherein the regular diagonal-shaped lattice pattern comprises:
a first plurality of equally spaced sub-carrier positions;
a second plurality of equally spaced sub-carrier positions offset from said first plurality; and
wherein the pilot symbols are inserted alternately in time using the first plurality of equally spaced sub-carrier positions and the second plurality of equally spaced sub-carrier positions.
23. A method of inserting pilot symbols into 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:
for a first antenna of the OFDM transmitter, inserting scattered pilot symbols in a scattered pattern in time-frequency by inserting pilot symbols corresponding to the first antenna in a first pattern in time-frequency; and
for a second antenna of the OFDM transmitter, inserting scattered pilot symbols using the scattered pattern by inserting pilot symbols corresponding to the second antenna, 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.
24. A device for inserting pilot symbols into 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:
for a first antenna of the OFDM transmitter, insert scattered pilot symbols in a scattered pattern in time-frequency by inserting pilot symbols corresponding to the first antenna in a first pattern in time-frequency; and
for a second antenna of the OFDM transmitter, insert scattered pilot symbols using the scattered pattern by inserting pilot symbols corresponding to the second antenna, 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.
25. A non-transitory computer readable medium for inserting pilot symbols into 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:
for a first antenna of the OFDM transmitter, inserting scattered pilot symbols in a scattered pattern in time-frequency by inserting pilot symbols corresponding to the first antenna in a first pattern in time-frequency; and
for a second antenna of the OFDM transmitter, inserting scattered pilot symbols using the scattered pattern by inserting pilot symbols corresponding to the second antenna, 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.