Source: https://patents.google.com/patent/US20060182015A1/en
Timestamp: 2018-12-19 14:07:19
Document Index: 658514871

Matched Legal Cases: ['§ 119', 'Application No.10', 'art 272', 'art 272', 'art 272', 'art 282', 'art 283', 'art 283', 'art 287', 'art 283', 'art 287', 'art 287', 'art 287', 'art 287', 'art 287', 'art 287', 'art 288', 'art 288']

US20060182015A1 - OFDM signal receiving apparatus and method for estimating common phase error of OFDM signals using data subcarriers - Google Patents
OFDM signal receiving apparatus and method for estimating common phase error of OFDM signals using data subcarriers Download PDF
US20060182015A1
US20060182015A1 US11339455 US33945506A US2006182015A1 US 20060182015 A1 US20060182015 A1 US 20060182015A1 US 11339455 US11339455 US 11339455 US 33945506 A US33945506 A US 33945506A US 2006182015 A1 US2006182015 A1 US 2006182015A1
US11339455
US7577206B2 (en )
This application claims the priority under 35 U.S.C. § 119 of Korean Patent Application No.10-2005-0006583, filed on Jan. 25, 2005 in the Korean Intellectual Property Office, the contents of which is incorporated herein in its entirety by reference.
In general, the CPE can be estimated using phase rotation generated in the pilot subcarriers because it is a common phase error generated in all subcarriers. The CPE may equal a value, Δ{circumflex over (φ)}r, obtained by estimating the quantity of phase rotation generated in carriers due to a residual frequency offset and can be represented as follows: Δ ⁢ ⁢ ϕ ^ r = tan - 1 ⁡ [ ∑ k ∈ P ⁢ R k · S k * ] , P = { - 21 , - 7 , + 7 , + 21 } [ Equation ⁢ ⁢ 1 ]
wherein k represents a subcarrier index and Sk and Rk respectively denote a transmitted (expected) value and a received value with respect to the pilot subcarriers.
The channel measurement unit 270 (FIG. 2) includes the channel estimator 271 and a good subcarrier indexing part 272. The channel estimator 271 continuously estimates the channel from the fast-Fourier-transformed signal to generate the channel coefficients Hk corresponding to to respective subcarriers. Each channel coefficient Hk corresponds to the magnitude of channel frequency response associated with (is proportional to) the power of each subcarrier. The good subcarrier indexing part 272 calculates the mean |{overscore (H)}|2 of the powers of the channel coefficients Hk as a channel reference value (step S42). The mean |{overscore (H)}|2 of the powers of the channel coefficients Hk is defined in Equation 2 as follows:  H _  2 = 1 52 ⁢ ∑ k = - 26 , k ≠ 0 26 ⁢  H k  2 [ Equation ⁢ ⁢ 2 ]
where k is a subcarrier index (ranging from −26 to 26), and the absolute values of the channel coefficients Hk are proportional to the powers of the respective subcarriers. In Equation 2, it is assumed that the number of effective subcarriers is known to be 52. Thus, the FFT length used in the system is 64 but there are 52 effective subcarriers. Furthermore, 4 of the 52 effective subcarriers are pilot subcarriers and 48 of them are data subcarriers.
The good subcarrier indexing part 272 indexes as good subcarriers, the plurality of subcarriers for which the powers of each of their corresponding channel coefficient Hk generated by the channel estimator 271 are larger than half of the mean |{overscore (H)}|2, as shown in Decision 3, to generate the CSI about the index k (S43).  H k  2 >  H _  2 2 ? [ Decision ⁢ ⁢ 3 ]
The pilot extraction part 282 outputs pilot subcarriers (judged to be “good” subcarriers) based on their having channel coefficient powers larger than half of the mean |{overscore (H)}|2 as the “good” pilot subcarriers Rk based on the CSI (step S44). Here, pilots having “bad” channel characteristics (those not having channel coefficient powers larger than half of the mean |{overscore (H)}|2) are eliminated in order to improve CPE estimation accuracy.
The data extraction part 283 outputs data subcarriers having real components Re(Yk) and imaginary components Im(Yk) larger than half of a maximum mapping level according to the constellation among data subcarriers. The data extraction part 283 selects and outputs as the “good” data subcarriers Yk those among the good subcarriers (having channel coefficient Hk powers larger than half of the mean |{overscore (H)}|2 based on the CSI (step S46)), that satisfy Condition 4 as follows:
IF ({k is “good subcarrier”}&{Re(Yk)>(maximum size)/2}&{Im(Yk)>(maximum size)/2}), THEN k is “selected” [Condition 4]
The second CPE determination part 287 (FIG. 3) first performs phase compensation on the good data subcarriers Yk (extracted by the data extraction part 283) by using the first CPE {circumflex over (φ)}c (S47). Then, the second CPE determination part 287 determines mapping levels Gk according to the constellation for the data subcarriers phase-compensated by the first CPE {circumflex over (φ)}c (step S48), and as shown in Equation 5. In Equation 5, Π represents a symbol decision making process according to the constellation (such as 256-QAM). G k = ∏ 256 - QAM ⁢ ( Y k ⁢ ⅇ - j ⁢ ⁢ ϕ ^ c ) , k ⁢ ⁢ is ⁢ ⁢ “ selected ” [ Equation ⁢ ⁢ 5 ]
When the mapping levels Gk are determined, the second CPE determination part 287 (FIG. 3) generates the quantity of phase rotation for the good data subcarriers Yk as the second CPE {circumflex over (φ)}c,data based on the mapping levels Gk (step S49), and as shown in Equation 6. ϕ ^ c , data = tan - 1 ( ∑ k ⁢ ⁢ is ⁢ ⁢ “ slected ” ⁢ Y k ⁢ G k * ) [ Equation ⁢ ⁢ 6 ]
Here, the second CPE determination part 287 (FIG. 3) limits the range of the calculated second CPE {circumflex over (φ)}c,data. Thus, the second CPE determination part 287 determines whether the second CPE {circumflex over (φ)}c,data is larger than half of the minimum phase between neighboring points (for example, 15.4° in 64-QAM and 7.64° in 256-QAM) in the constellations shown in FIG. 5 or FIG. 6 (S50). When the second CPE {circumflex over (φ)}c,data is larger than half of the minimum phase between neighboring points, the second CPE determination part 287 restricts the second CPE {circumflex over (φ)}c,data to half of the minimum phase between neighboring points (step S51). When the second CPE {circumflex over (φ)}c,data is not larger than half of the minimum phase between neighboring points, the second CPE determination part 287 outputs the quantity of phase rotation calculated according to Equation 6 unchanged.
The final determination part 288 (FIG. 3) generates the final CPE {circumflex over (φ)}c,final from the first CPE {circumflex over (φ)}c and the second CPE {circumflex over (φ)}c,data , and based on a decision step S52 For example, when the number (m) of the good data subcarriers is larger than the number of pilot subcarriers used in the system (S52), the final determination part 288 generates the mean of the first CPE {circumflex over (φ)}c and the second CPE {circumflex over (φ)}c,data as the final CPE {circumflex over (φ)}c,final (S53), as shown in Equation 7. ϕ c , final = 4 * ϕ ^ c + m * ϕ ^ c , data 4 + m [ Equation ⁢ ⁢ 7 ]
an equalizer configured to equalize an received baseband signal;
a Common Phase Error (CPE) estimation unit configured to estimate good pilot subcarriers and good data subcarriers from the equalized signal based on the CSI, and to calculate a second CPE from the estimated data subcarriers
3. The OFDM signal receiver of claim 1, wherein:
the Common Phase Error (CPE) estimation unit is further configured to calculate a first CPE from the estimated pilot subcarriers.
4. The OFDM signal receiver of claim 3, wherein:
the Common Phase Error (CPE) estimation unit is further configured to combine the first and second CPEs and to generate a final CPE.
5. The OFDM signal receiver of claim 4, further comprising:
a CPE compensation unit configured to compensate the phase of the equalized signal by the final CPE and outputting the phase-compensated signal.
7. The OFDM signal receiver of claim 6, wherein the predetermined symbol mapping format is one of QPSK, BPSK and QAM.
9. The OFDM signal receiver of claim 1, wherein the CPE estimation unit comprises:
a subcarrier estimator configured to estimate the good pilot subcarriers and good data subcarriers; and
a CPE determination part configured to calculate first and second CPEs and combining the first and second CPES to generate a final CPE.
10. The OFDM signal receiver of claim 9, wherein the subcarrier estimator comprises:
11. The OFDM signal receiver of claim 10, wherein the data extraction part is configured to generate the number of the good data subcarriers within the FFT length used in a system employing the OFDM signal receiver.
12. The OFDM signal receiver of claim 11, wherein the CPE determination part comprises:
a first CPE determination part configured to output the quantity of phase rotation with respect to the good pilot subcarriers as the first CPE;
a second CPE determination part configured to output the quantity of phase rotation with respect to the good data subcarriers as the second CPE; and
13. The OFDM signal receiver of claim 12, wherein the final CPE determination part outputs the mean of the first and second CPEs as the final CPE when the number of the good data subcarriers is larger than the number of pilot subcarriers used in the system employing the OFDM signal receiver; and outputs the first CPE as the final CPE when the number of the good data subcarriers is not larger than the number of pilot subcarriers.
14. The OFDM signal receiver of claim 12, wherein the second CPE determination part performs phase compensation on the good data subcarriers using the first CPE, determines mapping levels according to constellation, and generates as the second CPE the quantity of phase rotation with respect to the good data subcarriers referencing the determined mapping levels.
15. The OFDM signal receiver of claim 14, wherein the maximum value of the second CPE is restricted to half of the minimum phase between neighboring points in a constellation.
16. An OFDM signal receiving method comprising:
equalizing an received baseband signal;
estimating good pilot subcarriers and good data subcarriers from the equalized signal based on the CSI;
calculating a first common phase error CPE from the estimated pilot subcarriers;
and calculating a second common phase error CPE from the estimated data subcarriers.
combining the first and second CPEs to generate a final CPE; and
compensating the phase of the equalized signal by the final CPE.
20. The method of claim 18, further comprising demapping the phase-compensated signal according to a predetermined symbol mapping format.
21. The method of claim 20, wherein the predetermined symbol mapping format is one of QPSK, BPSK and QAM.
22. The method of claim 16, wherein generating the CSI comprises:
23. The method of claim 22, wherein the estimating the good pilot subcarriers and good data subcarriers comprises:
24. The method of claim 23, further comprising generating the number of the good data subcarriers existing in the FFT length used in a system employing the OFDM signal receiver.
generating as the first CPE the quantity of phase rotation with respect to the good pilot subcarriers;
generating as the second CPE the quantity of phase rotation with respect to the good data subcarriers; and
generating the mean of the first and second CPEs as the final CPE when the number of the good data subcarriers is larger than the number of pilot subcarriers used in the system employing the OFDM signal receiver, and generating the first CPE as the final CPE when the number of the good data subcarriers is not larger than the number of pilot subcarriers.
26. The method of claim 25, wherein generating the second CPE comprises:
27. The method of claim 26, wherein the maximum value of the second CPE is restricted to half of the minimum phase between neighboring points in a constellation.
US11339455 2005-01-25 2006-01-25 OFDM signal receiving apparatus and method for estimating common phase error of OFDM signals using data subcarriers Active 2027-09-08 US7577206B2 (en)
KR20050006583A KR100752641B1 (en) 2005-01-25 2005-01-25 Receiver and method for estimating common phase of Orthogonal Frequency Division Multiplexed signals using data subcarriers
KR2005-0006583 2005-01-25
US20060182015A1 true true US20060182015A1 (en) 2006-08-17
US7577206B2 US7577206B2 (en) 2009-08-18
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US11339455 Active 2027-09-08 US7577206B2 (en) 2005-01-25 2006-01-25 OFDM signal receiving apparatus and method for estimating common phase error of OFDM signals using data subcarriers
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DE (1) DE102006004119B4 (en)
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