Adaptive pilot structure to assist channel estimation in spread spectrum systems
View Patent ↗The present invention relates generally to methods for generating a dynamic pilot symbol structure in spread spectrum communication systems, and in particular to the use of pilot symbols by user equipment in channel estimation. In one form, the method includes, allocating basic pilot symbols ( 402 ) at the beginning of each data chunk ( 404, 406 ) and spread over the plurality of sub-carrier frequencies; and selectively replacing data symbols ( 408 ) in each data chunk ( 400 ) with adaptive pilot symbols ( 410 ) according to the speed of the user equipment.
1. A method of generating a pilot symbol in a spread spectrum communication systems, wherein data is transmitted between a base station and user equipment in the spread spectrum communication system in data chunks in which data symbols are transmitted in parallel on a plurality of sub-carrier frequencies and at regular temporal positions during a transmission time interval, the method including the steps of:
allocating basic pilot symbols at the beginning of each data chunk and spread over the plurality of sub-carrier frequencies; and
selectively replacing data symbols in each data chunk with adaptive pilot symbols according to the speed of the user equipment,
wherein the adaptive pilot symbols are evenly distributed in the data chunk in the time domain.
2. The method according to claim 1 , wherein the adaptive pilot symbols are evenly distributed in the data chunk in the frequency domain.
3. The method according to claim 1 , wherein the step of selectively replacing data symbols with adaptive pilot symbols includes:
at a central sub-carrier frequency of the data chunk, inserting the adaptive pilot symbols along the time domain separated by a temporal distance 2×N T where:
N
T
=
⌊
1
2
·
f
D
·
T
sym
⌋
where
⌊
⌋
is
a
round
down
to
the
nearest
integer
where f D is the Doppler frequency measured at the user equipment in Hz, and
where T sym is the data symbol duration in seconds.
4. The method according to claim 3 , wherein a first adaptive pilot symbol is inserted at the central sub-carrier frequency at a temporal distance of N T from the basic pilot symbols.
5. The method according to claim 3 , wherein the step of selectively replacing data symbols with adaptive pilot symbols further includes inserting the adaptive pilot symbols at subcarrier frequencies spaced from each other by a frequency spacing N F where:
N
F
=
⌊
1
2
·
Δ
f
·
τ
max
⌋
where
⌊
⌋
is
a
round
down
to
the
nearest
integer
where Δf is the sub-carrier bandwidth in Hz, and
where τ max is the maximum delay spread in seconds.
6. The method according to claim 5 , wherein τ max is a cyclic prefix length.
7. The method according to claim 5 , wherein adaptive pilot symbols inserted in consecutive sub-carrier frequencies are temporally offset by the temporal distance N F .
8. The method according to claim 3 , and further including the step of:
performing data symbol puncturing or reducing data symbol repetition prior to insertion of the adaptive pilot symbols.
9. The method according to claim 3 , wherein a number N ADAPTIVE — PILOT — SYM of adaptive pilot symbols to be inserted within a data chunk is determined from the expression
N
ADAPTIVE_PILOT
_SYM
=
⌈
1
2
×
⌈
N
subcarrier
per
chunk
N
F
⌉
×
⌊
N
symbols
per
TTI
per
subcarrier
N
T
⌋
⌉
where:
N subcarrier per chunk =a number of subcarriers per data chunk; and
N symbols per TTI per subcarrier =a number of symbols per Transmission Time Interval (TTI) per subcarrier.
10. The method according to claim 9 , wherein, when N T is greater than number of symbol per TTI on a single carrier, then adaptive pilot symbols is not required to be inserted.
11. The method according to claim 1 , and further including the step of:
generating pilot symbol information identifying the location of the adaptive pilot symbols in the data chunk to enable the user equipment to use the adaptive pilot symbols for channel estimation.
12. The method according to claim 11 , wherein the pilot symbol information is encoded to reduce the number of bits transmitted to the user equipment.
13. The method according to claim 12 , wherein the pilot symbol information is self-decodable by the user equipment.
14. The method according to claim 11 , wherein the pilot symbol information is transmitted prior to transmission of the pilot symbols and data chunks to enable detection of the adaptive pilot symbols by the user equipment.
15. The method according to claim 1 , wherein the data chunks are transmitted from the base station to the user equipment using Orthogonal Frequency Division Multiplexing.
16. The method according to claim 1 , wherein the spread spectrum communication system conforms to LTE/Super 3G systems standards developed by the 3 rd Generation Partnership Project (3GPP).