Patent Application
20080013573
The present invention is hereinafter described in detail with reference to accompanying drawings and embodiments.
In embodiments of the present invention, synchronous pilots including odd synchronous pilots and even synchronous pilots are inserted in a frame, and signals of inverse values are transmitted on the odd synchronous pilots and the even synchronous pilots; thus the frame synchronization is accomplished according to the odd synchronous pilots and the even synchronous pilots.
Referring to
The frame consisting of 8 OFDM symbols may reduce the time required for the frame synchronization; moreover, carriage of the PCS by 8 OFDM symbols may improve the time diversity and the flexibility of program carriage and transmission.
In
Table 2 shows carrier indices for the synchronous pilot carriers in an OFDM symbol in accordance with the locations in the 2 K mode and 4 K mode. The minimum distance separating two synchronous pilots are at least 15 sub-carriers and the distribution of the synchronous pilots is generally average. In
Other distributions of the synchronous pilots may be similar to that in Table 2 and will not be described in detail herein.
To facilitate the frame synchronization, the synchronous pilots are divided into odd synchronous pilots and even synchronous pilots. Specifically, the synchronous pilots in OFDM symbols 2 and 5 are the odd synchronous pilots, corresponding to the circles filled with rightward biases in
A reference sequence transmitted on the useful sub-carriers may be generated by a Pseudo Random Binary Sequence (PRBS) generator. For example, generate a sequence W, and take the sequence W as the reference sequence. Each useful sub-carrier bears one bit of the sequence W, i.e., W, where i=0˜nSubCrrNum−1. The polynomial for the PRBS generator may be X16+X12+X3+X+1, and the operation of the PRBS generator includes: initialize the PRBS generator for each OFDM symbol and generate nSubCrrNum bits, specifically, the initialization sequence is set to be all 1.
The polynomial for the PRBS generator is not limited to the above form and may also be X11+X2+1, etc. In other words, the reference sequence transmitted on the useful sub-carriers is not limited, as long as it is known and consistent at the transmitter and receiver.
Implement a BPSK modulation to the Wi to get a complex modulation symbol Ci. The detailed modulation process is given as follows:
Re{C
i}=2×(2×Wi−1),Im{Ci}=0
For the nSubCrrNum useful sub-carriers of an OFDM symbol, the signals on the synchronous pilot sub-carriers are Ci and the signals on the data sub-carriers are reassigned to the actually transmitted signals. In order to make the power gains of the pilot constellations higher than those of the data constellations, the powers of the pilot constellations are normalized to values larger than 16/9, such as 4. The powers of the pilot constellations may also be normalized to other values larger than those of the data constellations, such as 64/25. The pilot constellations herein include the synchronous pilot constellations and the scattered pilot constellations. The signals on the scattered pilots Sk=Ck, where kε{k=Kmin+3×[(3×n+1)mod4]+12×p|pεZ, p≧0, kε[Kmin, Kmax]};
the signals on the even synchronous pilots Va=Ca;
the signals on the odd synchronous pilots Vb=Cb, i.e., the signals on the odd synchronous pilots and the signals on the even synchronous pilots have inverse values.
The numerical values of a and b are shown in Table 2.
According to the above frame structure and pilot insertion pattern, the process of frame synchronization is hereinafter described. As shown in
Step 401: read 2 consecutive OFDM symbols, A and B, perform a correlation operation for A and B according to the following formula to obtain a correlation value ρ(k0),
where R(u, v) denotes a complex modulation symbol in OFDM symbol u at sub-carrier v, conj(R) denotes the complex conjugate of R, kc
Step 402: take k0 as the integral frequency offset K when k0 makes the absolute value of ρ(k0), i.e., the value of |ρ(k0)| reaches the maximum value.
If the integral frequency offset is K, there is a maximum value of |ρ(k0)| at k0=K, i.e., k0 corresponding to the maximum value of |ρ(k0)| is the integral frequency offset, K, where
where
Step 404: perform the frame synchronization according to signs of the real parts of the 5 ρ(K) obtained through the 5 times of correlation calculations.
The 5 ρ(K) are the correlation values obtained through the correlation calculations of A and B, B and C, C and D, D and E, and E and F, respectively.
Since the signals on the odd synchronous pilots and those on the even synchronous pilots have inverse values, there will be positive real parts and negative real parts of the ρ(K) when performing the correlation calculations.
To facilitate the frame synchronization, a relationship between the signs of the real parts of the correlation values and the locations of the OFDM symbols in the frame may be established in advance. Thus, after m consecutive OFDM symbols are read and the correlation calculations are performed to obtain m−1 correlation values, the frame synchronization may be performed according to the signs of the real parts of the correlation values and the relationship established in advance.
In this embodiment, the frame synchronization may be accomplished by reading 6 consecutive OFDM symbols. The relationship between the signs of the real parts of the correlation values between the 6 consecutive OFDM symbols in the frame and the locations of the 6 consecutive OFDM symbols in the frame is shown in
After the frame synchronization, the locations of the scattered pilots may be determined according to the distribution of the scattered pilots, and the channel estimation and demodulation and decoding may be performed after the determination of the locations of the scattered pilots.
It should be noted that the number and the distribution of the synchronous pilots and the scattered pilots may be adjusted according to the practical situations and are not limited to the above description. Moreover, the distribution of the odd synchronous pilots and the even synchronous pilots are also not limited to the above scheme and may also adopt other distributions as far as it is convenient for the frame synchronization. For example, the synchronous pilots in the OFDM symbols 3 and 6 may be taken as the odd synchronous pilots and the synchronous pilots in the OFDM symbols 0, 1, 2, 4, 5, and 7 may be taken as the even synchronous pilots. Table 3 needs to be adjusted in thus a case.
In addition, the frame structure may also be adjusted according to practical demands. For example, 16 OFDM symbols are included in a frame, and the pilot insertion pattern is designed and the frame synchronization is performed in terms of such a frame structure.
The foregoing is only the preferred embodiments of the present invention and is not for use in limiting the invention. Any modification, equivalent replacement or improvement made under the spirit and principles of this invention is included in the protection scope of the present invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2006 10098788.X | Jul 2006 | CN | national |
