AN2832 Freescale Semiconductor / Motorola, AN2832 Datasheet - Page 13

• Manufacturer Part Number: AN2832
• Description: Packet Telephony Remote Diagnostics on the StarCore SC140 Core
• Manufacturer: Freescale Semiconductor / Motorola

It is much more efficient to compute two data points in parallel. Another point of computation is N/2 – k, which
shares the same twiddle factor as point k:
Finally, the FFT/IFFT kernel has a triple nested loop, one loop for looping through the number of processing nodes
within a butterfly set, another for processing through the number of butterfly sets, and a third for looping through
the number of FFT/IFFT stages, which depends on the number of computation points. A pragma statement
provides the loop counter boundary range information to the compiler for more aggressive loop optimization.
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Remote diagnostics are an important maintenance application in packet telephony systems for monitoring, and
sometimes correcting, anomalies affecting performance of voice or data communication services. This application
note presents an intrusive remote diagnostic device that dynamically estimates and emulates hybrid circuits in
packet telephony systems. This device uses a robust FFT-based channel identification scheme to estimate the actual
impulse response h
h
results for this remote diagnostic device demonstrate the robustness of its contribution in packet telephony systems.
Finally, selected code optimization strategies make effective use of the key parallel architecture features of the
StarCore DSP. The remote diagnostic device was efficiently implemented and extensively tested in real time on the
Freescale StarCore-based DSP, requiring less than 2.0 million cycles per second (MCPS), on average, for a target
impulse response of up to 128 ms span. The remote diagnostic device was validated with a carrier-class network
echo canceller as it emulated various target impulse responses, regardless of the actual hybrid circuit(s) in the
system. This device is demonstrated to be a valuable component in developing and deploying packet telephony
systems, especially when proper control is provided over the communication network
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[1]
[2]
[3]
[4]
[5]
Freescale Semiconductor
t
(n) by injecting an echo signal based on the effective impulse response h
M. Bertocco and P. Paglierani, “In-Service Nonintrusive Measurement of Echo Parameters in Telephone-
Type Networks,” IEEE Transactions on Instrumentation and Measurement, vol. 47, no. 5, pp. 1322–1325,
1998.
T. Gänsler and G. Salomonsson, “Nonintrusive Measurements of the Telephone Channel,” IEEE
Transactions on Communications, vol. 47, no. 1, pp. 158–167, 1999.
ITU-T, Recommendation P.561: In-Service Non-intrusive Device–Voice Service Measurements, 2002.
R. A. Dyba, P. P. He, and L. F. C. Pessoa, Network Echo Cancellers and Motorola Solutions Using the
StarCore SC140 core, Freescale Application Note, AN2598/D, 2004.
ITU-T, Recommendation G.168: Digital Network Echo Canceller, 2002.
Conclusion
References
#pragma loop_count (1,64)
est
Packet Telephony Remote Diagnostics on the StarCore SC140 Core, Rev. 1
F
of a hybrid circuit and then dynamically emulate a target hybrid circuit impulse response
N 2 k
⁄
–
F
k
=
=
1
-- - G
2
1
-- - G
2
(
(
N 2 k
k
⁄
+
–
G ∗
+
N 2 k
G ∗
⁄
–
k
)
)
+
+
-- - G ∗
2
j
-- - G ∗
2
j
(
(
k
N 2 k
–
⁄
G
–
N 2 k
⁄
–
–
G
eff
k
)e
(n) = h
)e
–
–
j2π N 2 k
j2πk N
(
t
(n) – h
⁄
⁄
–
) N
est
⁄
. Typical performance
Equation 8
Equation 9
Conclusion
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