Pilot design for wireless system
View Patent ↗The description herein relates to pilot designs for an Orthogonal Frequency Division Multiplexing (OFDM) based communication system. In the preferred embodiment, the communication system is one operating according to the IEEE 802.16m, or WiMax, standard. In general, an OFDM transmitter operates to insert pilot symbols into a resource of a transmit frame according to a predetermined staggered pilot symbol pattern defining pilot symbol locations within the resource of the transmit frame. The predetermined pilot symbol pattern is defined such that pilot symbols are located at or near time boundaries of the resource, at or near frequency boundaries of the resource, or both. By doing so, when generating a channel estimate for the communication channel between the OFDM transmitter and an OFDM receiver based on the pilot symbols, extrapolations needed to estimate the channel near the boundaries of the resource are optimized, thereby improving overall channel estimation accuracy.
1. An Orthogonal Frequency Division Multiplexing (OFDM) receiver comprising:
receiver circuitry adapted to process a received OFDM signal to provide symbols for a resource of a transmit frame; and
a channel estimator implemented in hardware and adapted to:
receive the symbols from the receiver circuitry; and
extract one or more pilot symbols from the symbols for the resource of the transmit frame according to a predetermined staggered pilot symbol pattern including one or more of a group consisting of: pilot symbol locations located at or near each time boundary of the resource and pilot symbol locations located at or near each frequency boundary of the resource,
wherein the pilot symbol locations located at or near each time boundary of the resource comprises one of:
pilot symbol locations less than or equal to two OFDM symbols from a first time boundary of the resource and pilot symbol locations less than or equal to two OFDM symbols from a second time boundary of the resource; or
pilot symbol locations in an OFDM symbol at a first time boundary of the resource and pilot symbol locations in an OFDM symbol at a second time boundary of the resource; and
wherein the pilot symbols located at or near each frequency boundary of the resource comprises one of:
pilot symbol locations less than or equal to three sub-carriers from a first frequency boundary of the resource and pilot symbol locations less than or equal to three sub-carriers from a second frequency boundary of the resource; or
pilot symbol locations at a sub-carrier at a first frequency boundary of the resource and pilot symbol locations at a sub-carrier at a second frequency boundary of the resource.
2. An Orthogonal Frequency Division Multiplexing (OFDM) receiver comprising:
receiver circuitry adapted to process a received OFDM signal to provide symbols for one or more modern sub-frames of a transmit frame and symbols for a legacy sub-frame neighboring a modern sub-frame of the one or more modern sub-frames within the transmit frame; and
a channel estimator implemented in hardware and adapted to:
receive the symbols from the receiver circuitry;
extract at least one pilot symbol from the symbols in the legacy sub-frame;
extract at least one pilot symbol from the symbols for the one or more modern sub-frames according to a predetermined staggered pilot symbol pattern for the one or more modern sub-frames; and
generate channel estimates for the one or more modern sub-frames based on the at least one pilot symbol extracted from the one or more modern sub-frames and the at least one pilot symbol extracted from the legacy sub-frame.
3. The OFDM receiver of claim 2 wherein the legacy sub-frame precedes the one or more modern sub-frames in the transmit frame, and the modern sub-frame neighboring the legacy sub-frame is a first modern sub-frame of the one or more modern sub-frames in the transmit frame.
4. The OFDM receiver of claim 3 wherein the predetermined staggered pilot symbol pattern begins at a time offset from a starting time boundary of the first modern sub-frame, the time offset being greater than two OFDM symbols.
5. The OFDM receiver of claim 4 wherein the predetermined staggered pilot symbol pattern is a uniform pilot symbol pattern starting after the time offset from the starting time boundary of the first sub-frame.
6. The OFDM receiver of claim 5 wherein the time offset is such that last pilot symbol locations defined by the predetermined staggered pilot symbol pattern are at or near an ending time boundary of a last modern sub-frame.
7. A method implemented, at least in part, in hardware, the method comprising:
receiving at least one Orthogonal Frequency Division Multiplexing (OFDM) signal;
processing the at least one OFDM signal effective to provide one or more symbols for one or more modern sub-frames of a transit frame and one or more symbols for a legacy sub-frame neighboring a modern sub-frame of the one or more modern sub-frames within the transmit frame;
extracting one or more pilot symbols from the one or more symbols in the legacy sub-frame;
extracting one or more pilot symbols from the symbols for the one or more modern sub-frames according to a predetermined staggered pilot symbol pattern for the one or more modern sub-frames; and
generating channel estimates for the one or more modern sub-frames based on the one or more pilot symbols extracted from the one or more modern sub-frames and the one or more pilot symbols extracted from the legacy sub-frame.
8. The method of claim 7 , wherein the legacy sub-frame precedes the one or more modern sub-frames in the transmit frame, and the modern sub-frame neighboring the legacy sub-frame is a first modern sub-frame of the one or more modern sub-frames in the transmit frame.
9. The method of claim 8 , wherein the predetermined staggered pilot symbol pattern begins at a time offset from a starting time boundary of the first modern sub-frame, the time offset being greater than two OFDM symbols.
10. The method of claim 9 , wherein the predetermined staggered pilot symbol pattern is a uniform pilot symbol pattern starting after the time offset from the starting time boundary of the first sub-frame.
11. The method of claim 10 , wherein the time offset is such that last pilot symbol locations defined by the predetermined staggered pilot symbol pattern are at or near an ending time boundary of a last modern sub-frame.
12. A hardware device embodying one or more executable instructions that are configured to:
process at least one Orthogonal Frequency Division Multiplexing (OFDM) signal effective to provide one or more symbols for one or more modern sub-frames of a transmit frame and one or more symbols for a legacy sub-frame neighboring a modern sub-frame of the one or more modern sub-frames within the transmit frame;
extract one or more pilot symbols from the one or more symbols in the legacy sub-frame;
extract one or more pilot symbols from the one or more symbols for the one or more modern sub-frames according to a predetermined staggered pilot symbol pattern for the one or more modern sub-frames; and
generate channel estimates for the one or more modern sub-frames based on the one or more pilot symbols extracted from the one or more modern sub-frames and the one or more pilot symbols extracted from the legacy sub-frame.
13. The hardware device of claim 12 , wherein the legacy sub-frame precedes the one or more modern sub-frames in the transmit frame, and the modern sub-frame neighboring the legacy sub-frame is a first modern sub-frame of the one or more modern sub-frames in the transmit frame.
14. The hardware device of claim 13 , wherein the predetermined staggered pilot symbol pattern begins at a time offset from a starting time boundary of the first modern sub-frame, the time offset being greater than two OFDM symbols.
15. The hardware device of claim 14 , wherein the predetermined staggered pilot symbol pattern is a uniform pilot symbol pattern starting after the time offset from the starting time boundary of the first sub-frame.
16. The hardware device of claim 15 , wherein the time offset is such that last pilot symbol locations defined by the predetermined staggered pilot symbol pattern are at or near an ending time boundary of a last modern sub-frame.
17. The hardware device of claim 13 , wherein the one or more executable instructions included on the one or more hardware devices comprise firmware.
18. The hardware device of claim 13 , wherein at least one hardware device comprises a Field Programmable Gate Array (FPGA).
19. The hardware device of claim 13 further configured to utilize at least one channel estimate of the channel estimates to correct signal degradation associated with at least one OFDM signal of the one or more OFDM signals.
20. The hardware device of claim 13 further configured to generate channel estimates based, at least in part, on comparing at least one pilot symbol extracted from the one or more modern sub-frames or at least one pilot symbol extracted from the legacy sub-frame with at least one expected pilot symbol.