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Energy Detection

Overview

The Energy Detection feature detects energy on a channel. You can use this feature for CPA when there is not a pattern to match available, or to report energy detection to the host application. To compensate for background noise and to filter out short energy bursts, you can set the sensitivity level and the scan duration (defined below).

You can determine these settings based upon the type of energy to be detected, and to some extent, by trial and error. After setting both levels, test to see if the desired energy is being detected, then adjust the settings as necessary.

For CPA, the Energy Detection feature determines only that a pattern has occurred. It does not distinguish tones. The Energy Detection class (Class 3) is composed of the most common call setup tones: Ringback, Double Ringback, Busy, and Reorder. You can add any pattern to this class, or use any other class for Energy Detection, with the following restrictions:

• The pattern must consist of alternating periods of tones and silence. Energy Detection recognizes a pattern by periods with energy (tone) and no energy (silence). Because Energy Detection must detect both tone and silence, it cannot detect a "pattern" that has tone but no silent interval.

• The Energy Detection DSP function can detect only tones from the default patterns defined for the Energy Detection class (Tone IDs 0, 1, 2, and 5). You can still use a pattern for Energy Detection that does not use one of these tones. To do so, you must change the Tone IDs in the pattern to one of those allowed, using the CPA Pattern Configure message.

Parameters

The following parameters configure energy detection:

• Sensitivity Level

• Scan Duration

• Completion Timer

Sensitivity Level

The Sensitivity Level is the amplitude above which the energy detector perceives a signal. Set the sensitivity level to detect and report energy that is greater than the prevailing background noise. When you expect a significant background noise, use the least sensitive setting (0 dBm). When you expect little background noise, use the most sensitive setting (-30 dBm).

Scan Duration

The Scan Duration is the repeating time interval over which the energy detector determines that energy is either Present or Not Present. Set the scan duration to be longer than expected energy bursts. You must use 20 millisecond intervals to set the scan duration, so energy is sampled for each 20 millisecond block within the specified duration.

The scan cycles repeat until the completion timer expires. The calculated energy level is the average over all blocks, as shown in Vocabulary Index File Format. If the calculated energy level exceeds the configured sensitivity level, energy is reported.

Figure 8-5 Scan Cycle

Completion Timer

The completion timer determines the maximum amount of time to scan for energy. Each scan cycle, as defined by the scan duration, is repeated until either energy is detected, or the completion timer expires. We recommend setting the completion timer for 3 to 4 times the scan duration, depending on the application. If the timer expires before energy is detected, the host receives a Call Processing Event message of "No Energy Detected."

Detection Methods

You can invoke Energy Detection in the following two ways:

• Interactively, with the DSP Service Request message

• As part of Call Progress Analysis

Interactive Energy Detection

You can invoke Energy Detection interactively, with the DSP Service Request message. Use the data bytes of the message to configure the sensitivity level, reporting mode, scan duration, and completion timer. The detected energy is reported to the host in a Call Processing Event message in one of two modes:

• Report Initial Energy Detection Only
The host receives a Call Processing Event of "Energy Result Report" with Data[0], indicating Energy Detected. Data[1] indicates the duration of the period of no energy. The DSP resource is then automatically released.

• Report All Energy Threshold Crossings
All of the following are reported: the initial energy detection, all subsequent changes, and the duration of the previous state’s ON or OFF interval.
When energy (A) is first detected, the host receives a Call Processing Event of "Energy Result Report" with Data[0] indicating "Energy Detected." Data[1] indicates the duration of the preceding period of no energy (D1).
When energy is no longer detected (B), the host receives a Call Processing Event message of "Energy Result Report" with Data[0] indicating "No Energy Detected." Data[1] indicates the duration of the preceding period of energy (D2).

Figure 8-6 Energy Result Report

The DSP resource remains attached and reports energy changes until the completion timer expires, or until the host sends a DSP Service Cancel 0x00BE message, or until the channel returns to an idle state.

Energy Detection as Call Progress Analysis

Energy Detection allows the CSP to perform Call Progress Analysis for frequencies not supported by the default CPA DSP load. The Energy Detection DSP function matches cadences, based on the reported energy levels. CPA Class 3 is pre-configured for Energy Detection, using the standard CPA tones of ringback, double ringback, busy, and re-order.

To accommodate unique requirements for matching cadences, you can modify these patterns or add new patterns to the class. The host can change the pattern cadence that energy detection scans for, using the CPA Pattern Configure message.

Configuration

See Configuring Energy Detection.

Digital Signal Processor