Interference cancellation technique for channel estimation in OFDM receivers
An interference cancellation technique is implemented in a receiver adapted for determining an estimation of interferences when receiving an OFDM signal made of packets. Each packet includes a first training field, a second training field, a first header field, a second header field and a data field. The receiver detects a first symbol value of the first header field, and a second symbol value of the second header field, the first and the second header fields having been modulated using different modulation schemes. The estimation of interferences is determined using the first and the second symbol values.
1. A method for determining an estimation of interferences when receiving an Orthogonal Frequency-Division Multiplexing (OFDM) signal made of packets, each packet including at least one training field, at least two header fields and a data field, the method comprising:
detecting a first symbol value (D1) of a first header field and a second symbol value (D2) of a second header field, said first and second header fields belonging to said at least two header fields, and said first and second header fields having been transmitted after being modulated using different modulation schemes, respectively; and
determining said estimation of interferences from said first and second symbol values,
wherein the determining of said estimation consists in solving a system of two linear equations, wherein re_int and im_int are respectively a real part and an imaginary part of said estimation:
{
D
1
=
±
1
+
re_int
+
j
·
im_int
D
2
=
±
j
+
re_int
+
j
·
im_int
.
2. The method according to claim 1 , wherein said different modulation schemes are Binary Phase-Shift Keying (BPSK) and Quadrature Binary Phase-Shift Keying (QBPSK).
3. The method according to claim 1 , wherein said estimation is determined for each subcarriers of said OFDM signal.
4. The method according to claim 1 , wherein said first and second header fields are selected among said at least two header fields according to the modulation mode of said OFDM signal.
5. The method according to claim 1 , wherein when said modulation mode is High-Throughput Greenfield Format (HT-GF), said first symbol value D1 is stored and compensated by estimations for Carrier Frequency Offset (CFO), Sampling Frequency Offset (SFO), time recovery and channel equalization when they are established.
6. The method according to claim 1 , further comprising correcting said signal by cancelling interferences according to said estimation.
7. A non-transitory computer-readable medium encoded with a computer program comprising program instructions which when loaded into a data processing circuitry cause the data processing circuitry to execute the method according to claim 1 .
8. A receiver adapted for determining an estimation of interferences when receiving an Orthogonal Frequency-Division Multiplexing (OFDM) signal made of packets, each packet including a first training field, a second training field, at least two header fields and a data field, the receiver comprising:
circuitry for detecting a first symbol value of a first header field and a second symbol value of a second header field, said first and second header fields belonging to said at least two header fields and said first and second header fields having been transmitted after being modulated using different modulation schemes, respectively; and
circuitry for determining said estimation of interferences from said first and second symbol values,
wherein said circuitry for determining said estimation is adapted to solve a system of two linear equations, wherein re_int and im_int are respectively a real part and an imaginary part of said estimation:
{
D
1
=
±
1
+
re_int
+
j
·
im_int
D
2
=
±
j
+
re_int
+
j
·
im_int
.
9. The receiver according to claim 8 , wherein said modulation scheme are Binary Phase-Shift Keying (BPSK) and Quadrature Binary Phase-Shift Keying (QBPSK).
10. The receiver according to claim 8 , wherein said estimation is determined for each subcarriers of said OFDM signal.
11. The receiver according to claim 8 , wherein circuitry for detecting selects said first and second header fields among said at least two header fields according to the modulation mode of said OFDM signal.
12. The receiver according to claim 8 , wherein when said modulation mode is High-Throughput Greenfield Format (HT-GF), said circuitry for detecting stores said first symbol value and compensates it by estimations for Carrier Frequency Offset (CFO), Sampling Frequency Offset (SFO), time recovery and channel equalization when they are established.
13. The receiver according to claim 8 , further comprising circuitry for correcting said signal by cancelling interferences according to said estimation.