Beaulieu series approach to optimal UMTS RACH preamble detection estimation

• US 20050254604A1
• Filed: 04/18/2005
• Published: 11/17/2005
• Est. Priority Date: 04/16/2004
• Status: Active Grant

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Friedmann, Arnon A., Livingston, Frank C., Tanrikulu, Oguz, MacMullan, Samuel J.
• Granted Patent: US 7,394,875 B2
• Time in Patent Office: Days
• US Class Current: 375/340
• CPC Class Codes: H04B 1/70755 Setting of lock conditions, e.g. threshold

Abstract

A method for preamble detection in mobile unit to base unit wireless telephony sets a preamble detection threshold based upon a Beaulieu series computation dependent upon preamble correlation data. This preamble detection threshold adjusts for noise by assuming the noise is additive White Gaussian noise (AWGN) with a known variance. The method determines the threshold for achieving a probability of false detection of the preamble from noise input of less than 0.001.

Claims

1. A method of radio frequency message preamble detection comprising the steps of:

receiving in-phase and quadrature input samples of the radio frequency message;

coherently accumulating a first predetermined number of said in-phase and quadrature input samples;

forming an absolute value of the coherently accumulated input samples;

non-coherently combining a second predetermined number of said absolute values of said coherently accumulated input samples;

selecting a preamble detection threshold τ

according to the equation;

$\widehat{\mathrm{\tau <br><br>}}=\frac{1}{16<br><br>N_B}<br><br>\underset{j=1}{\overset{N_B}{\sum <br><br>}}<br><br>\underset{i=1}{\overset{16}{\sum <br><br>}}<br><br>\frac{{C_{{\hat{N}}_{\mathrm{nca}},\hat{W}}<br><br>\left(Z_{n,\mathrm{nca}}\right)}_{j,i}}{{\mathrm{\xi <br><br>}}_{i,W,N_{\mathrm{nca}}}}$

where;

N_B is a number of preamble detection attempts;

C_{{circumflex over (N)}nca,Ŵ}

is a fixed constant depending on {circumflex over (N)}_nca and Ŵ

;

{circumflex over (N)}_nca is the equivalent number of coherent packets;

Ŵ

is the equivalent search window;

(Z_n,nca)_j,i is the non-coherently combined values; and

ξ

_i,W,Nnca is the expected value of (Z_n,nca)_j,i; and

detecting a preamble in the radio frequency message employing said selected preamble detection threshold τ

.

2. The method of claim 1, wherein:

said constant C_{{circumflex over (N)}nca,Ŵ}

is selected from the table;

W = 512W = 1024N_nca = 1N_nca = 2N_nca = 4N_nca = 8N_nca = 1N_nca = 2N_nca = 4N_nca = 85.1046747.76917912.1550909.7563815.2218107.95216812.39860320.086897

according to the selected values of W and N_nca.

3. The method of claim 1, wherein:

said step of selecting said preamble detection threshold τ

further includes

selecting said preamble detection threshold τ

for a first 10 samples according to the equation;

$\mathrm{\tau <br><br>}=\frac{1}{16<br><br>t}<br><br>\underset{j=1}{\overset{t}{\sum <br><br>}}<br><br>\underset{i=1}{\overset{16}{\sum <br><br>}}<br><br>\frac{{C_{{\hat{N}}_{\mathrm{nca}},\hat{W}}<br><br>\left(Z_{n,\mathrm{nca}}\right)}_{j,i}}{{\mathrm{\xi <br><br>}}_{i,W,N_{\mathrm{nca}}}}$

forming an instantaneous preamble detection threshold {circumflex over (τ

)} for following samples according to the equation;

$\widehat{\mathrm{\tau <br><br>}}=\frac{1}{16}<br><br>\underset{i=1}{\overset{16}{\sum <br><br>}}<br><br>\frac{{C_{{\hat{N}}_{\mathrm{nca}},\hat{W}}<br><br>\left(Z_{n,\mathrm{nca}}\right)}_{j,i}}{{\mathrm{\xi <br><br>}}_{i,W,N_{\mathrm{nca}}}}$

modifying a preamble detection threshold {circumflex over (τ

)}_k according to the following infinite impulse response (IIR) filter;

{circumflex over (τ

)}_k=(1−

α

){circumflex over (τ

)}_k-1+α

{circumflex over (τ

)}

where α

=¼

.

4. A method of radio frequency message preamble detection comprising the steps of:

receiving in-phase and quadrature input samples of the radio frequency message;

coherently accumulating a first predetermined number of said in-phase and quadrature input samples;

forming an absolute value of the coherently accumulated input samples;

non-coherently combining a second predetermined number of said absolute values of said coherently accumulated input samples;

selecting a preamble detection threshold {circumflex over (τ

)} according to the equation;

$\widehat{\mathrm{\tau <br><br>}}=C_{{\hat{N}}_{\mathrm{nca}}<br><br>\widehat{,W}}<br><br>\sqrt{\frac{4096}{N_{\mathrm{nca}}}<br><br>\tilde{Z}}$

where;

C_{{circumflex over (N)}nca,Ŵ}

is a fixed constant depending on {circumflex over (N)}_nca and Ŵ

;

{circumflex over (N)}_nca is the equivalent number of coherent packets;

Ŵ

is the equivalent search window; and

{tilde over (Z)} is a mean power estimate value calculated for a first 80 256-chip power estimate outputs N, by the equation;

$\hat{Z}=\frac{\underset{n=1}{\overset{N}{\sum <br><br>}}<br><br>x_n^2+y_n^2}{N}$

where;

x_n and y_n are the respective in-phase and quadrature input samples, and for following samples modified according to the following infinite impulse filter (IIR) filter;

{tilde over (Z)}_k=(1−

α

){tilde over (Z)}_k-1+α

{tilde over (Z)}

where α

= 1/16.

5. The method of claim 4, wherein:

said constant C_{{circumflex over (N)}nca,Ŵ}

is selected from the table;

W = 512W = 1024N_nca = 1N_nca = 2N_nca = 4N_nca = 8N_nca = 1N_nca = 2N_nca = 4N_nca = 85.1046747.76917912.1550909.7563815.2218107.95216812.39860320.086897

according to the selected values of W and N_nca.