METHOD FOR DETECTING A CPE ALERT SIGNAL OF A TELECOMMUNICATION SYSTEM BY UTILIZING AN ENERGY RATIO

Abstract

A method for detecting a Customer Premises Equipment (CPE) alert signal of a telecommunication system in a Customer Premises Equipment of the telecommunication system includes: detecting a first signal energy at a first frequency; detecting a second signal energy at a second frequency; comparing a total received signal energy with a summation of at least the first signal energy and the second signal energy to generate a comparison result; enabling a first detecting procedure or a second detecting procedure for detecting the CPE alert signal according to the comparison result; and transmitting an ACK signal to a telephone service provider of the telecommunication system when the CPE alert signal is detected.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to signal detection in a telecommunication system, and more particularly to a method for an adaptive detection of a CPE alert signal by utilizing an energy ratio.

2. Description of the Prior Art

In addition to conventional telecommunication systems, a call waiting system is used in the U.S.A., which has a standard TIA/EIA-777. The TIA (Telecommunications Industry Association) standards describe the requirements for Caller ID capable Customer Premises Equipment (CPE) under both on-hook (type-1) and off-hook (type-2) modes. Please refer to FIG. 1, which is a flowchart illustrating operation of a prior art call waiting mechanism. The telephone service provider 10 is used to provide communication services for a plurality of CPEs 12, 14, 16. Assume that the CPE 12 is currently communicating with the CPE 14 on line 1 through the telephone service provider 10. If the CPE 16 wants to communicate with the CPE 14 on line 2, the telephone service provider 10 will activate the call waiting mechanism for notifying the CPE 14. Firstly, the telephone service provider 10 temporarily blocks the speech sounds outputted from the CPE 12 from reaching the CPE 14, and sends a CPE alert signal (CAS) to the CPE 14 during this period.

Please refer to FIG. 2, which is a diagram illustrating the composition of the CAS signal. As shown in FIG. 2, the CAS signal is composed of two DTMF (Dual Tone Multi-Frequency) signals S₁ and S₂, where one DTMF signal S₁ has a frequency of about 2130 Hz, and the other DTMF signal S₂ has a frequency of approximately 2750 Hz.

After detecting the CAS signal transmitted from the telephone company 10, the CPE 14 automatically stops outputting speech sounds for a short period of time, and transmits an ACK signal to the telephone service provider 10 in response to the CAS signal. After receiving the ACK signal outputted from the CPE 14, the telephone service provider 10 starts transmitting information related to the CPE 16 (e.g., the phone number of the CPE 16) to the CPE 14. Once the CPE 14 successfully receives the incoming information related to the CPE 16 the call waiting operation is finished.

Please note that, during the process of transmitting the CAS signal to the CPE 14, although speech sounds outputted from the CPE 12 are blocked, the CPE 14 continues to output speech sounds. Both the CAS signal and the speech sounds share the same frequency band. The outgoing speech sounds will cause interference to the incoming CAS signal. As a result, the interference imposed upon the CAS signal means the prior art call waiting mechanism may fail to correctly detect the CAS signal. Therefore, detection of the CAS signal becomes an important issue for a telecommunications system.

SUMMARY OF THE INVENTION

It is therefore one of the objectives of the claimed invention to provide an adaptive method for detection of a CPE alert signal of a telecommunication system by utilizing an energy ratio, to solve the above problem.

The claimed invention discloses a method for detecting a Customer Premises Equipment (CPE) alert signal of a telecommunication system in a Customer Premises Equipment of the telecommunication system. The method comprises: detecting a first signal energy at a first frequency; detecting a second signal energy at a second frequency; comparing a total received signal energy with a summation of at least the first signal energy and the second signal energy to generate a comparison result; enabling a first detecting procedure or a second detecting procedure for detecting the CPE alert signal according to the comparison result; and transmitting an ACK signal to a telephone service provider of the telecommunication system when the CPE alert signal is detected.

This present invention can adopt different CAS detection criteria to meet different detection conditions, such as the above-mentioned non-speech condition and speech condition. Obviously, the adaptive method of the present invention is capable of optimizing the performance of detecting the CAS signal in a telecommunication system.

These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flowchart illustrating operation of a prior art call waiting mechanism.

FIG. 2 is a diagram illustrating the composition of the CAS signal.

FIG. 3 is a flowchart illustrating operation of detecting a CAS signal according to an embodiment of the present invention.

DETAILED DESCRIPTION

As interference to the incoming CAS signal will occur when there are outgoing speech sounds from the CPE, the method of the present invention utilizes an adaptive detection system which first determines whether or not there are outgoing speech sounds, and then adaptively selects predetermined thresholds for determining whether or not a CAS signal is received.

Please refer to FIG. 3, which is a flowchart illustrating operation of detecting a CAS signal according to an embodiment of the present invention. The operation of detecting the CAS signal of a telecommunication system can be summarized by: detecting a first signal energy at a first frequency; detecting a second signal energy at a second frequency; comparing a total received signal energy with a summation of at least the first signal energy and the second signal energy to generate a comparison result; and enabling a first detecting procedure or a second detecting procedure for detecting the call alert signal according to a comparison result.

In step 300, an energy ratio ER of the summation of the first signal energy A (i.e., the energy of the DTMF signal S₁ shown in FIG. 2) and the second signal energy B (i.e., the energy of the DTMF signal S₂ shown in FIG. 2) to the total received signal energy T is determined. A and B are determined by digital Fourier transforms, or by using narrow band filters. In a truly linear system, the total received signal energy T will be equal to the sum of the first signal energy A and the second signal energy B. When speech sounds are outputted from the CPE, however, the total received signal energy will be equal to the sum of A, B and the speech signal S. Therefore, the present invention uses an energy ratio ER (A+B/T) and compares this ratio with a threshold K to adaptively select thresholds for determining whether or not the CAS signal is received. The total received signal energy T is determined using an ADC sampling output data X(n) for a sample period L/F, where F is the sample rate.

$T=\sum _{n=0}^{L-1}X_n^2,$

where L is the decision length.

Also, A and B may be calculated by ADC output data X_n, and Fourier transform.

$A={\sum _{n=0}^{L-1}X_n{}^{-j2\pi n/f_1}}^2,$

where f1 is 2130 Hz.

$B={\sum _{n=0}^{L-1}X_n{}^{-j2\pi n/f_2}}^2,$

where f2 is 2750 Hz.

For a simplified system, the following equations may be taken,

$T^{\prime }=\sum _{n=0}^{L-1}X_n,$

where L is the decision length.

$A^{\prime }=\sum _{n=0}^{L-1}X_n{}^{-j2\pi n/f_1},$

where f1 is 2130 Hz.

$B^{\prime }=\sum _{n=0}^{L-1}X_n{}^{-j2\pi n/f_2},$

where f2 is 2750 Hz.

In the simplified system, the following method and related thresholds K, L1, L2, L3, L4, α1 and α2 can also be used. The simplified equation's A′, B′, and T′ are more easily calculated by “Cordic” processors, or equivalent narrow-band filters.

K can be a value approximately between 0.3 and 0.7. The particular selection of K will depend on false alarm rate requirements specified by individual CPE manufacturers.

The comparison between ER and K generates a comparison result, which is used for the adaptive selection of thresholds. If the energy ratio ER is greater than the threshold K (i.e. S component of T is small), step 310 is performed to detect the CPE alert signal; and if the energy ratio ER is not greater than the threshold K (i.e. S component of T is large), step 320 is performed to detect the CPE alert signal.

In step 310, the frequency energy level FL and the two-frequency energy difference TW are examined. Step 310 first compares the first signal energy A with a first frequency energy level L₁ and then compares the second signal energy B with a second frequency energy level L₂. L₁ and L₂ are according to the standards of TIA-777. L₁=−36 dbm and L₂=−36 dbm. This is because the TIA-777 standards require a signal level of −32 dbm to be received when the signal is quiet. If the first signal energy A is greater than the first frequency energy level L₁ and the second signal energy B is greater than the second frequency energy level L₂, step 310 then determines whether the CAS signal occurs in the telecommunication system, by checking whether the signal ratio A/B of the first signal energy A to the second signal energy B falls in a predetermined range where the limits are 1/α₁ and α₁. α₁ is also a value according to the TIA-777 standards, and is taken in this example as 8 db. When a signal is quiet, TIA-777 standards require a twist of 6 db to be received. If the first signal energy A is greater than the first frequency energy level L₁, the second signal energy B is greater than the second frequency energy level L₂, and the signal ratio A/B falls in the predetermined range, the method of the present invention determines that the CAS signal exists (step 330). In the following, the method of the present invention goes back to step 300 for monitoring the occurrence of a next CAS signal.

In this embodiment, if either the first signal energy A is not greater than the first frequency energy level L₁ or the second signal energy B is not greater than the second frequency energy level L₂, the method of the present invention directly judges that there is no CAS signal, and then goes back to step 300 to continue monitoring the occurrence of the CAS signal. Please note that in this embodiment the first frequency energy level L₁ is equal to the second frequency energy level L₂.

In step 320, the frequency energy level FL and the two-frequency energy difference TW are examined. Step 320 first compares the first signal energy A with a third frequency energy level L₃ and then compares the second signal energy B with a fourth frequency energy level L₄. L₃ and L₄ are according to the standards of TIA-777. In this embodiment, L₃ is recommended to be −29 dbm and L₄ is recommended to be −29 dbm, although both values can be as large as −24 dbm. If the first signal energy A is greater than the third frequency energy level L₃ and the second signal energy B is greater than the fourth frequency energy level L₄, step 320 further determines if the CAS signal occurs in the telecommunication system. In other words, step 320 checks if the signal ratio A/B of the first signal energy A to the second signal energy B falls in a predetermined range where the limits are 1/α₂ and α₂. α₂ is also a value according to the TIA-777 standards, and is taken in this example as 6 db. If the first signal energy A is greater than the third frequency energy level L₃, the second signal energy B is greater than the fourth frequency energy level L₄, and the signal ratio A/B falls in the predetermined range, the method of the present invention determines that the CAS signal exists (step 330). In the following, the method of the present invention goes back to step 300 for monitoring the occurrence of a next CAS signal.

In this embodiment, if either the first signal energy A is not greater than the third frequency energy level L₃ or the second signal energy B is not greater than the fourth frequency energy level L₄, the method of the present invention directly judges that there is no CAS signal, and then goes back to step 300 to continue monitoring the occurrence of the CAS signal.

Please note that in a preferred embodiment the first frequency energy level L₁ is equal to the second frequency energy level L₂, and the third frequency energy level L₃ is equal to the fourth frequency energy level L₄. In addition, the third frequency energy level L₃ is greater than the first frequency energy level L₁, and the second signal ratio α₂ is greater than the first signal ratio α₁. However, in other embodiments, the first frequency energy level L₁ is not limited to being equal to the second frequency energy level L₂, and the third frequency energy level L₃ is not limited to being equal to the fourth frequency energy level L₄. For example, in an alternative design, these frequency energy levels L₁, L₂, L₃, L₄ are not identical to each other, but the third frequency energy level L₃ is still required to be greater than the first frequency energy level L₁, and the fourth frequency energy level L₄ is still required to be greater than the second frequency energy level L₂.

Using the method of the present invention, the CPE 14 shown in FIG. 1 selects one criterion out of two available criteria according to the signal-to-noise ratio (SNR). That is, step 300 is used to measure the SNR corresponding to signals at frequencies 2130 Hz and 2750 HZ. If a user of the CPE 14 shown in FIG. 1 does not talk when the telephone service provider 10 passes the CAS signal to the CPE 14, the measured SNR is sure to be high. In other words, the energy ratio ER is greater than the threshold K. Therefore, the following step 310 using lower frequency energy levels L₁, L₂ is activated to check the existence of the CAS signal. On the other hand, if a user of the CPE 14 shown in FIG. 1 talks when the telephone service provider 10 passes the CAS signal to the CPE 14, the measured SNR is sure to be low. In other words, the energy ratio ER is not greater than the threshold K. Therefore, the following step 320 using higher frequency energy levels L₃, L₄ is activated to check the existence of the CAS signal. In addition, both steps 310, 320 further check the signal ratio A/B to improve the detection accuracy.

In contrast to the prior art, the present invention can adopt different CAS detection criteria to meet different detection conditions, such as the above-mentioned non-speech condition and speech condition. Obviously, the adaptive method of the present invention is capable of optimizing the performance of detecting the CAS signal in a telecommunication system.

Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.

Claims

1. A method for detecting a Customer Premises Equipment (CPE) alert signal of a telecommunication system in a Customer Premises Equipment of the telecommunication system, the method comprising: detecting a first signal energy at a first frequency;detecting a second signal energy at a second frequency;comparing a total received signal energy with a summation of at least the first signal energy and the second signal energy to generate a comparison result;enabling a first detecting procedure or a second detecting procedure for detecting the CPE alert signal according to the comparison result; andtransmitting an ACK signal to a telephone service provider of the telecommunication system when the CPE alert signal is detected.

2. The method of claim 1, wherein the step of generating the comparison result further comprises: determining an energy ratio of the summation of at least the first signal energy and the second signal energy to the total received signal energy; andcomparing the energy ratio with a threshold to generating the comparison result.

3. The method of claim 2, wherein the step of detecting the CPE alert signal further comprises: if the energy ratio is greater than the threshold, performing the first detecting procedure to detect the CPE alert signal; andif the energy ratio is not greater than the threshold, performing the second detecting procedure to detect the CPE alert signal.

4. The method of claim 3, wherein the first detecting procedure comprises: comparing the first signal energy with a first frequency energy level and comparing the second signal energy with a second frequency energy level; andwhen the first signal energy is greater than the first frequency energy level and the second signal energy is greater than the second frequency energy level, determining that the CPE alert signal occurs in the telecommunication system.

5. The method of claim 4, wherein the first frequency energy level is equal to the second frequency energy level.

6. The method of claim 4, wherein the first detecting procedure further comprises: checking if a signal ratio of the first signal energy to the second signal energy falls in a predetermined range; andwhen the first signal energy is greater than the first frequency energy level, the second signal energy is greater than the second frequency energy level, and the signal ratio falls in the predetermined range, determining that the CPE alert signal occurs in the telecommunication system.

7. The method of claim 3, wherein the second detecting procedure comprises: comparing the first signal energy with a first frequency energy level and comparing the second signal energy with a second frequency energy level; andwhen the first signal energy is greater than the first frequency energy level and the second signal energy is greater than the second frequency energy level, determining that the CPE alert signal occurs in the telecommunication system.

8. The method of claim 7, wherein the first frequency energy level is equal to the second frequency energy level.

9. The method of claim 7, wherein the second detecting procedure further comprises: checking if a signal ratio of the first signal energy to the second signal energy falls in a predetermined range; andwhen the first signal energy is greater than the first frequency energy level, the second signal energy is greater than the second frequency energy level, and the signal ratio falls in the predetermined range, determining that the CPE alert signal occurs in the telecommunication system.

10. The method of claim 3, wherein the first detecting procedure comprises: comparing the first signal energy with a first frequency energy level and comparing the second signal energy with a second frequency energy level; andwhen the first signal energy is greater than the first frequency energy level and the second signal energy is greater than the second frequency energy level, determining that the CPE alert signal occurs in the telecommunication system; andthe second detecting procedure comprises:comparing the first signal energy with a third frequency energy level and comparing the second signal energy with a fourth frequency energy level; andwhen the first signal energy is greater than the third frequency energy level and the second signal energy is greater than the fourth frequency energy level, determining that the CPE alert signal occurs in the telecommunication system, wherein the third frequency energy level is greater than the first frequency energy, and the fourth frequency energy level is greater than the second frequency energy.

11. The method of claim 10, wherein the first frequency energy level is equal to the second frequency energy level, and the third frequency energy level is equal to the fourth frequency energy level.

12. The method of claim 10, wherein the first detecting procedure further comprises: checking if a first signal ratio of the first signal energy to the second signal energy falls in a first predetermined range; andwhen the first signal energy is greater than the first frequency energy level, the second signal energy is greater than the second frequency energy level, and the first signal ratio falls in the first predetermined range, determining that the CPE alert signal occurs in the telecommunication system; andthe second detecting procedure further comprises:checking if a second signal ratio of the first signal energy to the second signal energy falls in a second predetermined range; andwhen the first signal energy is greater than the third frequency energy level, the second signal energy is greater than the fourth frequency energy level, and the second signal ratio falls in the second predetermined range, determining that the CPE alert signal occurs in the telecommunication system, the first predetermined range covering the second predetermined range.