Method of determining an acquisition indicator bit in a communication system

Abstract

A method of determining an acquisition indicator bit AIs at a receiver in a communication system which includes receiving multiplexed acquisition indicator bits y=B×AI+n, where B is the signature matrix known at both base station and UE, AI is all the acquisition indicator bits and n represents noise. Next, an estimated value of the acquisition indicator bit AÎMMSE (s) as a function of ∑j ⁢ ⁢BT⁡(s,j)×y⁡(j) is calculated, where BT(s,.) is the s-th row vector of the transposed matrix BT for acquisition indicator bit AIs. Finally, the acquisition indicator bit AIs is set as follows: AIs=−1, if AÎMMSE (s)

Description

BACKGROUND AND SUMMARY OF THE INVENTION

The present invention relates generally to communication systems of coded data and, more specifically, to an improvement in determining an acquisition indicator bit at a receiver in a communication system.

Although the present invention will be described with respect to 3^rd generation wideband code division multiple access (3G WCDMA) system, the same method can be used for determining an acquisition bit AI_s at a receiver in other communication systems. General and specific references will also be made to the 3G WCDMA standard 3GPP TS 25.211, Physical channels and mapping of transport channels onto physical channels (FDD) (Release 4) and 3GPP TS 25.213, “Spreading and modulation (FDD)” (Release 4).

In 3^rd generation CDMA systems, physical connections between UE (User Equipment) and base stations are established through the Physical Random Access Channel (PRACH) and Acquisition Indicator Channel (AICH). The UE transmits PRACH signal that carries the RACH preamble and message to a base station, to request a connection. When the base station recognizes a PRACH preamble, it responds with AICH to UE to indicate if the connection request is granted. An example of the AICH from 3GPP TS 25.211 is shown in FIG. 1.

Upon the AICH reception, the problem is to estimate the AI_s based on the received real valued symbols a₀, a₁, . . . , a₃₁ which are transmitted through AICH, where AI_s ε{−1,0,1} and s=0,1, . . . , 15. An AI_s of 0 indicates that the signature s is not a member of the set of available signatures. An AI_s of 1 indicates a positive acknowledgement, and an AI_s of −1 indicates a negative acknowledgement. At the base station, AI_s is code multiplexed with others, {AI_n: n≠s}, by the following formula: $\begin{array}{cc}{a}_j=\sum _{s=0}^{15}{\mathrm{AI}}_s{b}_{s,j},j=0,1,\dots ,31,& \left(1\right)\end{array}$ where {b_s,j: j=0,1, . . . 31} are given in Table 21 in 3GPP TS 25.211 and shown below in the example as B

The present invention is a method of determining an acquisition indicator bit AI_s at a receiver in a communication system. The method includes receiving multiplexed acquisition indicator bits y=B×AI+n, where B is the signature matrix known at both base station and UE, AI is the set of all the acquisition indicator bits and n represents noise, for example, AWGN (additive white Gaussian noise). Next, an estimated value of the acquisition indicator bit $A{\hat{I}}_{\mathrm{MMSE}}\left(s\right)\mathrm{as}a\mathrm{function}\mathrm{of}\sum _j^{}{B}^T\left(s,j\right)\times y\left(j\right)$ is calculated, where B^T (s,.) is the s-th row vector of the transposed matrix B^T for acquisition indicator bit AI_s. Finally, the acquisition indicator bit AI_s is set as follows: AI_s=−1, if AÎ_MMSE (s)<R AI_s═0, if R≦AÎ_MMSE (s)<U AI_s=1, if AÎ_MMSE (S)≧U, where R and U are decision thresholds.

The constants R and U may be equal absolute values, for example, −0.5 and 0.5, respectively. The estimated value AÎ_MMSE (s) is calculated by $A{\hat{I}}_{\mathrm{MMSE}}=\frac{1}{\left(32+{\hat{\sigma }}^2\right)}\sum _{j=0}^{31}{B}^T\left(s,j\right)\times y\left(j\right).$ The method is performed without forming a matrix B or B^T and is performed in software.

These and other aspects of the present invention will become apparent from the following detailed description of the invention, when considered in conjunction with accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of the structure of the acquisition indicator channel AICH of the 3G WCDMA system defined in 3GPP TS 25.211.

FIG. 2 is a flow chart of a method of determining an acquisition indicator bit AI_s incorporating the principles of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The method of the present invention, which is performed at the receiver of a communication system, is illustrated in FIG. 2. The input signal y is received at 10. An estimated acquisition indicator (AÎ_ML(s)) is calculated from the input signal y. The resulting estimated acquisition indicator corresponding to a signature index s, AÎ_ML(s) is then used for determining an acquisition indicator bit AI_s having one of the values −1,0,1. The decided acquisition indicator bit is outputted at 16. The details of the method are described as follows:

In matrix form, equation (1) can be expressed as $\begin{array}{cc}\begin{array}{c}a=B\times \mathrm{AI},\\ \mathrm{where}\\ a={\left[a_0,a_1,\dots ,a_{31}\right]}^T,\\ B=\left[\begin{array}{ccccc}{b}_{0,0}& b_{1,0}& b_{2,0}& \cdots & b_{15,0}\\ b_{0,1}& b_{1,1}& b_{2,1}& \cdots & b_{15,1}\\ ·& ·& ·& ·& ·\\ ·& ·& ·& ·& ·\\ b_{0,31}& b_{1,31}& b_{2,31}& \cdots & b_{15,31}\end{array}\right],\\ \mathrm{and}\\ \mathrm{AI}={\left[{\mathrm{AI}}_0,{\mathrm{AI}}_1,\dots ,{\mathrm{AI}}_{15}\right]}^T.\end{array}& \left(2\right)\end{array}$

The received soft bits from a rake receiver can be modeled as y=a+n

• • or y=B×AI+n,  (3) where n denotes noise, for example, the AWGN.

The maximum likelihood estimator for the unknown acquisition indicator, AÎ_ML, in equation (3) is well known (see S. M. Kay, Fundamentals of Statistical Signal Processing (Estimation Theory), Prentice Hall) and is given by AÎ_ML=(B^T×B)⁻¹×B^T×y.  (4) Due to orthogonality (see Table 21 in 3GPP TS 25.211), B^T×B=32×I_16×16,  (5) where I_16×16 is the identity matrix with dimension 16.

Thus, equation (4) can be reduced to $\begin{array}{cc}A{\hat{I}}_{\mathrm{ML}}=\frac{1}{32}\times B^T\times y.& \left(6\right)\end{array}$

It is assumed that the table index, s, for AICH signature patterns is equivalent to the one for the RACH preamble signatures from Table 3 in 3GPP TS 25.213. In other words, the index s is known at the user equipment UE so that only the portion corresponding to s of equation (6) is of interest.

Let T_s(y) be a statistic corresponding to an index s, given y $\begin{array}{cc}{T}^s\left(y\right)=A{\hat{I}}_{\mathrm{ML}}\left(s\right)=\frac{1}{32}\sum _{j=0}^{31}{B}^T\left(s,j\right)\times y\left(j\right),& \left(7\right)\end{array}$ where B^T(s,.) denotes the s-th row vector of the matrix BT.

Assuming uniform prior for the following hypotheses, H₋₁: AI_s=−1, H₀: AI_s=0 H₁: AI_s=1, s=0,1, . . . , 15, the 3-arry MAP decision rule (see S. M. Kay, Fundamentals of Statistical Signal Processing (Detection Theory), Prentice Hall) is to decide AI_s=−1, if T^s(y)<R AI_s=0, if R≦T^s(y)<U AI_s=1, if T^s(y)≧U, where U and R are constants. The {H_i, i=−1,0,1} denote the hypotheses that the acquisition indicator bit is i. Assuming perfect channel, the constants R and U may be equal absolute values, for example, −0.5 and 0.5, respectively.

To improve the estimation, an MMSE (Minimum Mean Square Error) estimator that is given by the following may be used AÎ_MMSE=(B^T×B+{circumflex over (σ)}² I)⁻¹×B^T×y,  (8) where {circumflex over (σ)}² represents the estimated noise variance at the receiver. The MMSE estimator is the solution that takes into account the background noise.

With (8), (4) can be reduced to $\begin{array}{cc}A{\hat{I}}_{\mathrm{MMSE}}=\frac{1}{\left(32+{\hat{\sigma }}^2\right)}\times B^T\times y.& \left(9\right)\end{array}$ Let T^s(y) be a statistic corresponding to an index s, given y $\begin{array}{cc}{T}^s\left(y\right)=A{\hat{I}}_{\mathrm{MMSE}}\left(s\right)=\frac{1}{\left(32+{\hat{\sigma }}^2\right)}\sum _{j=0}^{31}{B}^T\left(s,j\right)\times y\left(j\right),& \left(10\right)\end{array}$

As an illustrative example, let AI₀=−1, AI₁=−1, AI₂=1, AI₃=−1, AI₄=−1, AI₅=−1, AI₆=−I, AI₇=−1, AI₈₌₋₁, AI₉=−1, AI₁₀=0, AI₁₁=−1, AI₁₂=−1, AI₁₃=−1, AI₁₄=−1, and AI₁₅=0.

Since AI is defined by AI=[AI₀ AI₁ AI₂ AI₃ AI₄ AI₅ AI₆ AI₇ AI₈ AI₉ AI₁₀ AI₁₁ AI₁₂ AI₁₃ AI₁₄ AI₁₅]{circumflex over ( )}T, where T denote the transpose, that is $\begin{array}{c}\mathrm{AI}=[-1\\ -1\\ 1\\ -1\\ 1\\ -1\\ -1\\ -1\\ -1\\ -1\\ 0\\ -1\\ -1\\ -1\\ -1\\ 0].\end{array}$ The matrix B (of size 32×16) in (2) is given by $\begin{array}{c}B=[1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1\\ 1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1\\ 1,-1,1,-1,1,-1,1,-1,1,-1,1,-1,1,-1,1,-1\\ 1,-1,1,-1,1,-1,1,-1,1,-1,1,-1,1,-1,1,-1\\ 1,1,-1,-1,1,1,-1,-1,1,1,-1,-1,1,1,-1,-1\\ 1,1,-1,-1,1,1,-1,-1,1,1,-1,-1,1,1,-1,-1\\ 1,-1,-1,1,1,-1,-1,1,1,-1,-1,1,1,-1,-1,1\\ 1,-1,-1,1,1,-1,-1,1,1,-1,-1,1,1,-1,-1,1\\ 1,1,1,1,-1,-1,-1,-1,1,1,1,1,-1,-1,-1,-1\\ 1,1,1,1,-1,-1,-1,-1,1,1,1,1,-1,-1,-1,-1\\ 1,-1,1,-1,-1,1,-1,1,1,-1,1,-1,-1,1,-1,1\\ 1,-1,1,-1,-1,1,-1,1,1,-1,1,-1,-1,1,-1,1\\ 1,1,-1,-1,-1,-1,1,1,1,1,-1,-1,-1,-1,1,1\\ 1,1,-1,-1,-1,-1,1,1,1,1,-1,-1,-1,-1,1,1\\ 1,-1,-1,1,-1,1,1,-1,1,-1,-1,1,-1,1,1,-1\\ 1,-1,-1,1,-1,1,1,-1,1,-1,-1,1,-1,1,1,-1\\ 1,1,1,1,1,1,1,1,-1,-1,-1,-1,-1,-1,-1,-1\\ 1,1,1,1,1,1,1,1,-1,-1,-1,-1,-1,-1,-1,-1\\ 1,-1,1,-1,1,-1,1,-1,-1,1,-1,1,-1,1,-1,1\\ 1,-1,1,-1,1,-1,1,-1,-1,1,-1,1,-1,1,-1,1\\ 1,1,-1,-1,1,1,-1,-1,-1,-1,1,1,-1,-1,1,1\\ 1,1,-1,-1,1,1,-1,-1,-1,-1,1,1,-1,-1,1,1\\ 1,-1,-1,1,1,-1,-1,1,-1,1,1,-1,-1,1,1,-1\\ 1,-1,-1,1,1,-1,-1,1,-1,1,1,-1,-1,1,1,-1\\ 1,1,1,1,-1,-1,-1,-1,-1,-1,-1,-1,1,1,1,1\\ 1,1,1,1,-1,-1,-1,-1,-1,-1,-1,-1,1,1,1,1\\ 1,-1,1,-1,-1,1,-1,1,-1,1,-1,1,1,-1,1,-1\\ 1,-1,1,-1,-1,1,-1,1,-1,1,-1,1,1,-1,1,-1\\ 1,1,-1,-1,-1,-1,1,1,-1,-1,1,1,1,1,-1,-1\\ 1,1,-1,-1,-1,-1,1,1,-1,-1,1,1,1,1,-1,-1\\ 1,-1,-1,1,-1,1,1,-1,-1,1,1,-1,1,-1,-1,1\\ 1,-1,-1,1,-1,1,1,-1,-1,1,1,-1,1,-1,-1,1].\end{array}$ For instance, b_0,0=1 and b_2,1=−1. The transposed B is then $\begin{array}{c}{B}^T=[1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,\\ 1,1,1,1,1,1,1,1,1,1,1,1,1,-1,-1,1,1,-1,-1,\\ 1,1,-1,-1,1,1,-1,-1,1,1,-1,-1,1,1,-1,-1,\\ 1,1,-1,-1,1,1,-1,-1,1,1,1,1,-1,-1,-1,-1,1,\\ 1,1,1,-1,-1,-1,-1,1,1,1,1,-1,-1,-1,-1,1,1,\\ 1,1,-1,-1,-1,-1,1,1,-1,-1,-1,-1,1,1,1,1,-1,\\ -1,-1,-1,1,1,1,1,-1,1,1,1,1,-1,-1,-1,-1,1,\\ 1,1,1,-1,-1,-1,-1,1,1,1,1,1,1,1,1,1,1,-1,\\ -1,-1,-1,-1,-1,-1,-1,1,1,1,1,1,1,1,1,-1,\\ -1,-1,-1,-1,-1,-1,-1,1,1,-1,-1,1,1,-1,-1,\\ -1,-1,1,1,-1,-1,1,1,1,1,-1,-1,1,1,-1,-1,\\ -1,-1,1,1,-1,-1,1,1,1,1,1,1,-1,-1,-1,-1,\\ -1,-1,-1,-1,1,1,1,1,1,1,1,1,1,-1,-1,-1,-1,\\ -1,-1,-1,-1,-1,1,1,1,1,1,1,-1,-1,-1,-1,\\ 1,1,-1,-1,1,1,1,1,-1,-1,1,1,-1,-1,-1,-1,\\ 1,1,-1,-1,1,1,1,1,1,-1,-1,1,1,1,1,1,1,1,\\ 1,1,1,1,1,1,1,1,1,-1,-1,-1,-1,-1,-1,-1,\\ -1,-1,-1,-1,-1,-1,-1,-1,-1,-1,1,1,-1,-1,\\ 1,1,-1,-1,1,1,-1,-1,1,1,-1,-1,-1,-1,1,\\ 1,-1,-1,1,1,-1,-1,1,1,-1-1,1,1,1,1,1,1,\\ -1,-1,-1,-1,1,1,1,1,-1,-1,-1,-1,-1,-1,-1,\\ -1,1,1,1,1,-1,-1,-1,-1,1,1,1,1,1,1,-1,-1,\\ -1,-1,1,1,1,1,-1,-1,-1,-1,1,1,-1,-1,1,1,1,\\ 1,-1,-1,-1,-1,1,1,1,1,-1,-1,1,1,1,1,1,1,1,\\ 1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,\\ -1,-1,-1,-1,1,1,1,1,1,1,1,1,1,1,-1,-1,1,1,\\ -1,-1,-1,-1,1,1,-1,-1,1,1,-1,-1,1,1,-1,-1,1,\\ 1,1,1,-1,-1,1,1,-1,-1,1,1,1,1,-1,-1,-1,-1,\\ -1,-1,-1,-1,1,1,1,1,-1,-1,-1,-1,1,1,1,1,1,1,\\ 1,1,-1,-1,-1,-1,1,1,-1,-1,-1,\\ -1,1,1,-1,-1,1,1,1,1,-1,-1,-1,-1,\\ 1,1,1,1,-1,-1,1,1,-1,-1,-1,-1,1,1]\end{array}$ From equation (3), a=B×AI. Note that the size of y, a, B. and AI are 32×1, 32×1, 32×16, and 16×1, respectively. The calculated a is then $\begin{array}{c}a=[-12\\ -12\\ 2\\ 2\\ -4\\ -4\\ -2\\ -2\\ 2\\ 2\\ 4\\ 4\\ -2\\ -2\\ -4\\ -4\\ 0\\ 0\\ 2\\ 2\\ 0\\ 0\\ -2\\ -2\\ 2\\ 2\\ 0\\ 0\\ -2\\ -2\\ 0\\ 0].\end{array}$

From equation (3), the noise is assumed as the additive white Gaussian. Suppose the noise values are given by $\begin{array}{c}n=[0.1703\\ 0.3561\\ 0.2907\\ 0.2298\\ 0.0160\\ 0.2692\\ 0.2262\\ -0.1017\\ -0.1501\\ -0.1177\\ -0.5866\\ -0.0930\\ 0.0471\\ 0.1252\\ 0.5740\\ -0.1396\\ 0.2478\\ 0.3177\\ 0.3741\\ -0.3945\\ 0.0843\\ 0.0946\\ -0.4007\\ -0.2951\\ 0.4304\\ -0.0523\\ 0.1550\\ 0.0350\\ -0.2527\\ -0.2225\\ 0.1764\\ -0.3777].\end{array}$

Then from equation (3), the observed samples, y, is $\begin{array}{c}y=[-11.8297\\ -11.6439\\ 2.2907\\ 2.2298\\ -3.9840\\ -3.7308\\ -1.7738\\ -2.1017\\ 1.8499\\ 1.8823\\ 3.4134\\ 3.9070\\ -1.9529\\ -1.8748\\ -3.4260\\ -4.1396\\ 0.2478\\ 0.3177\\ 2.3741\\ 1.6055\\ 0.0843\\ 0.0946\\ -2.4007\\ -2.2951\\ 2.4304\\ 1.9477\\ 0.1550\\ 0.0350\\ -2.2527\\ -2.2225\\ 0.1764\\ -0.3777].\end{array}$

The y is the noisy version of the received acquisition indicator bits carried over AICH.

Assume that the signature index s is 2, then by equation (3), the AI₂ can be estimated as $\begin{array}{c}A{\hat{I}}_{\mathrm{ML}}\left(2\right)=\frac{1}{32}\sum _{j=0}^{31}{B}^T\left(2,j\right)\times y\left(j\right)=1/32*(1*\text{-}11.8297+\\ 1*\text{-}11.6439+1*2.2907+\dots \text{-}1*0.1764+\\ \text{-}1*\text{-}0.3777)=1.0434.\end{array}$ This is the multiplication of two vectors, the 3^rd row of B^T and y. Since AÎML (2) is greater than 0.5 using U=0.5, the decision can be made as AÎ(2)=1, which is matched with the initial setting, AI₂=1.

Although the present invention has been described and illustrated in detail, it is to be clearly understood that the same is by way of illustration and example only, and is not to be taken by way of limitation. The scope of the present invention are to be limited only by the terms of the appended claims.

Claims

1. A method of determining an acquisition indicator bit AIs at a receiver in a communication system, the method comprising: receiving multiplexed acquisition bits y=B×AI+n, where B is the signature matrix known at both base station and UE, AI is all the acquisition indicator bits and n represents noise; calculating an estimated value of the AI bit of interest AÎMMSE (s) as a function of ∑j⁢BT⁡(s,j)×y⁡(j),where BT(s,.) is the s-th row vector of the transposed matrix BT for acquisition indicator bit AIs; and setting the acquisition indicator bit AIs as follows: AIs=−1, if AÎMMSE (s)<R AIs=0, if R≦AÎMMSE (s)<U AIs=1, if AÎMMSE (s)≧U where R and U are decision thresholds.

2. The method according to claim 1, wherein R and U are equal absolute values.

3. The method according to claim 1, wherein R and U are −0.5 and 0.5, respectively.

4. The method according to claim 1, wherein the estimated value AÎMMSE (s) is calculated by

5. The method of claim 1, wherein the method is performed without forming a matrix B or BT.

6. The method of claim 1, wherein the method is performed in software.

7. A receiver including an interleaver or deinterleaver performing the method of claim 1.

8. The receiver of claim 7, wherein the receiver includes software for performing the method of claim 1.

9. The receiver of claims 7, wherein the method of claim 1 is performed in the receiver without forming a matrix B or BT.