Apparatus and method for estimating channels in mobile communication system by using hidden pilots

• US 20080084943A1
• Filed: 09/21/2007
• Published: 04/10/2008
• Est. Priority Date: 09/22/2006
• Status: Abandoned Application

• Current Assignee: Samsung Electronics Co. Ltd.
• Original Assignee: Samsung Electronics Co. Ltd.
• Inventors: Yun, Sang-Boh, Kwon, Young-Hoon, Jung, Sung-Yoon
• Application Number:
  US11/903,504
• Publication Number:
  US 20080084943A1
• Time in Patent Office: Days
• US Class Current: 375/260
• CPC Class Codes: H04L 27/261 Details of reference signals
• CPC Class Codes: H04L 27/2613 Structure of the reference signals
• CPC Class Codes: H04L 5/023 Multiplexing of multicarrier modulation signals multicarrier modulation H04L27/2601

Abstract

Provided is an apparatus and method for estimating channels in a mobile communication system by using hidden pilots. In a method for transmitting data in the mobile communication system, a precoding signal and a hidden pilot are generated using a sequence with auto & cross-correlation characteristics. A user signal is modulated in a predetermined modulation scheme and is precoded using the precoding signal. The hidden pilot is added to the precoded signal. Therefore, a waste of bandwidth due to the use of the conventional pilot signal is reduced and a data rate is increased, thereby increasing the overall transmission efficiency of the system and reducing the PAPR002E.

Claims

1. A method for transmitting data in a mobile communication system, comprising the steps of:

modulating a symbol data to be transmitted in a predetermined modulation scheme;

generating a hidden pilot using a sequence with auto and cross-correlation characteristics;

precoding the modulated data with the precoding signal having the auto and cross-correlation characteristics; and

adding the hidden pilot to the precoded signal.

2. The method of claim 1, further comprising the steps of:

mapping the signal having the hidden pilot added thereto to a subcarrier allocated to the corresponding user; and

inverse fast Fourier transform (IFFT)-processing the signal mapped to the subcarrier, prior to transmission.

3. The method of claim 1, wherein the precoding signal is generated using a poly-phase sequence.

4. The method of claim 1, wherein the mobile communication system transmits to a target receiver an information whether the system precodes the modulated data.

5. The method of claim 4, further comprising the step of:

transmitting the information whether the system precodes the modulated data through a MAC (medium access control) layers.

6. The method of claim 1, wherein the sequence is a polyphase sequence expressed as the following equation:

$C=\left[c_0,c_1,\mathrm{\dots <br><br>}<br><br>\text{\hspace{1em}<br><br>},c_{N_1-1}\right]$ $c_i=\left[c_i<br><br>\left(0\right),c_i<br><br>\left(1\right),\mathrm{\dots <br><br>}<br><br>\text{\hspace{1em}<br><br>},c_i<br><br>\left(N_1-1\right)\right]$ $c_i<br><br>\left(n\right)=\frac{1}{\sqrt{N_1}}<br><br>\exp <br><br>\left[\mathrm{j2\pi <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>\left(s<br><br>\left(n\right)/p+\mathrm{i<br><br>}·<br><br>n/N_1\right)\right]$

where s(n) denotes a p-nary sequence with a length of N₁=p^r−

1, p is a prime number, r is an integer greater than 1, c_i denotes a polyphase sequence generated using the sequence s(n), C denotes a polyphase sequence set including a total of N₁ polyphase sequences c_i,

wherein the precoding signal is generated using the (N₁−

1) polyphase sequences and the hidden pilot is generated using the remaining one polyphase sequence.

7. The method of claim 1, further comprising the step of:

inserting a CP (cyclic prefix) in the modulated symbol data

8. An apparatus for transmitting data in a mobile communication system, comprising:

a modulator for modulating a user signal in a predetermined modulation scheme;

a precoder for precoding the modulated user signal using a precoding signal generated using a sequence with auto and cross-correlation characteristics; and

a adder for adding a hidden signal, generated using the sequence, to the precoded signal.

9. The apparatus of claim 8, further comprising:

a subcarrier mapper for mapping the signal having the hidden pilot added thereto to a subcarrier allocated to the corresponding user; and

an inverse fast Fourier transform (IFFT) processor for IFFT-processing the signal mapped to the subcarrier.

10. The apparatus of claim 8, wherein the sequence is a polyphase sequence expressed as the following equation:

$C=\left[c_0,c_1,\mathrm{\dots <br><br>}<br><br>\text{\hspace{1em}<br><br>},c_{N_1-1}\right]$ $c_i=\left[c_i<br><br>\left(0\right),c_i<br><br>\left(1\right),\mathrm{\dots <br><br>}<br><br>\text{\hspace{1em}<br><br>},c_i<br><br>\left(N_1-1\right)\right]$ $c_i<br><br>\left(n\right)=\frac{1}{\sqrt{N_1}}<br><br>\exp <br><br>\left[\mathrm{j2\pi <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>\left(s<br><br>\left(n\right)/p+\mathrm{i<br><br>}·<br><br>n/N_1\right)\right]$

where s(n) denotes a p-nary sequence with a length of N₁=p^r−

1, p is a prime number, r is an integer greater than 1, c_i denotes a polyphase sequence generated using the sequence s(n), and C denotes a polyphase sequence set including a total of N₁ polyphase sequences c_i,

wherein the precoding signal is generated using the (N₁−

1) polyphase sequences and the hidden pilot is generated using the remaining one polyphase sequence.

11. A method for receiving data in a mobile communication system, comprising the steps of:

removing a cyclic prefix (CP) from a receive (RX) signal; and

removing the remaining signal except a hidden pilot of a self-user from the CP-removed RX signal using a cyclic hidden pilot, and estimating a channel using only the hidden pilot of a self-user.

12. The method of claim 11, further comprising the steps of:

fast Fourier transform (FFT)-processing the CP-removed RX signal;

subcarrier-demapping the FFT-processed signal;

removing the hidden pilot from the subcarrier-demapped signal using the estimated channel; and

detecting a signal using the estimated channel.

13. The method of claim 12, wherein the channel estimating step and the signal detecting step are performed using a minimum mean square error (MMSE) scheme.

14. The method of claim 11, wherein the hidden pilot is generated using a polyphase sequence with auto &

cross-correlation characteristics.

15. The method of claim 11, wherein the step of removing the remaining signal from the CP-removed RX signal is performed by multiplying the Hermitian of the cyclic hidden pilot as the following equation:

$B_{k^{\mathrm{\prime <br><br>}}}^H<br><br>A_{k,i}\to <br><br>0,\forall <br><br>\mathrm{i<br><br>}\in <br><br>\left[1,M\right]<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{and}<br><br>\text{\hspace{1em}<br><br>}<br><br>k\in <br><br>\left\{1,K\right]$ $B_{k^{\mathrm{\prime <br><br>}}}^H<br><br>B_k\to <br><br>\{\begin{array}{ccc}\mathrm{cI},& k^{\mathrm{\prime <br><br>}}=k& \left(c<br><br>\text{;<br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{constant}\right)\\ 0,& k^{\mathrm{\prime <br><br>}}\ne <br><br>k& \text{\hspace{1em}<br><br>}\end{array}$

where B_k denotes a circulant matrix whose first column is [b_k^T(i), 0, . . . , 0]^T, that is, the cyclic hidden pilot, b_k=F^HΨ

_kt_k, t_k denotes an N×

1 hidden pilot, Ψ

_k denotes a P×

N subcarrier mapping matrix of a user k, F^H denotes a P×

P IFFT matrix, A_k,i denotes a column-wise circulant matrix using the i^th column of A_k, K denotes the total number of users, M denotes a modulation order, k denotes a user index from the standpoint of a transmitting side, and k′

denotes a user index from the standpoint of a receiving side, wherein the k^th user data transmitted by the transmitting side is the data of the k′

^th user.

16. The method of claim 12, wherein the hidden pilot is removed from the subcarrier-demapped signal using the following equation:

X_k(i)=D_H,kP_ks_k(i)+(D_H,k−

{circumflex over (D)}_H,k)t_k+w_F,k(i)

where D_H,k denotes a matrix obtained by diagonalizing the channel frequency responses of a k^th user, {circumflex over (D)}_H,k denotes a matrix obtained by diagonalizing the frequency responses of the estimated channel, the hidden pilot is removed by making the D_H,k be 0 using the D_H,k, P_k denotes an (N×

M)-sized precoding signal, s_k(i) denotes an (M×

1)-sized i^th symbol block including a total of M modulation symbols generated by modulating data of a user k in an M-ary PSK modulation scheme, t_k denotes an N×

1 hidden pilot, and w_F,k(i) denotes a noise signal.

17. The method of claim 16, wherein the hidden pilot and the precoding signal satisfy the following equation:

$P_k<br><br>P_k^H=\frac{M}{N}<br><br>I_N,t_k<br><br>t_k^H=\frac{P_t}{N}<br><br>I_N,P_k^H<br><br>P_k=I_M$

where P_t denotes TX power allocated to the hidden pilot, N denotes the number of subcarriers allocated to the k^th user, and M denotes a modulation order.

18. An apparatus for receiving data in a mobile communication system, comprising:

a CP remover for removing a cyclic prefix (CP) from a receive (RX) signal; and

a channel estimator for removing the remaining signal except a hidden pilot of a self-user from the CP-removed RX signal using a cyclic hidden pilot, and estimating a channel using only the hidden pilot of a self-user.

19. The apparatus of claim 18, further comprising:

a receiver for fast Fourier transform (FFT)-processing the CP-removed RX signal, subcarrier-demapping the FFT-processed signal, removing the hidden pilot from the subcarrier-demapped signal using the estimated channel, and detecting a signal using the estimated channel; and

an inverse precoder for inverse-precoding the detected signal using an inverse precoding signal corresponding to a precoding signal of a transmitting side.

20. The apparatus of claim 19, wherein the hidden pilot is generated using a polyphase sequence with auto &

cross-correlation characteristics.

21. The apparatus of claim 19, wherein the hidden pilot and the precoding signal satisfy the following equation:

$P_k<br><br>P_k^H=\frac{M}{N}<br><br>I_N,t_k<br><br>t_k^H=\frac{P_t}{N}<br><br>I_N,P_k^H<br><br>P_k=I_M$

where P_t denotes TX power allocated to the hidden pilot, N denotes the number of subcarriers allocated to the k^th user, and M denotes a modulation order.

22. An apparatus for transceiving data in a mobile communication system, comprising:

a receiving apparatus for estimating a channel using only a preamble, decoding a receive (RX) signal using the estimated channel, transmitting feedback information for transmission of a hidden pilot to a transmitting apparatus if there is an error in the decoding operation, receiving a TX signal having a hidden pilot added thereto from the transmitting apparatus after MAP information including information, which indicates that the hidden pilot is to be added to a TX signal prior to transmission to the receiving apparatus, is received from the transmitting apparatus, estimating a channel using the added hidden pilot, and decoding an RX signal using the estimated channel; and

a transmitting apparatus for transmitting only a TX signal to the receiving apparatus, transmitting the MAP information to the receiving apparatus if the feedback information is received from the receiving apparatus, and transmitting the TX signal having the hidden pilot added thereto to the receiving apparatus.

23. The apparatus of claim 22, wherein the feedback information is a channel quality indicator (CQI) or a Negative ACKnowledgement (NACK) signal.

24. The apparatus of claim 22, wherein the hidden pilot is generated using a polyphase sequence with auto &

cross-correlation characteristics.