2. 1 Voice Quality Enhancements

3. 2 Outline Acoustic and network echo Noise Reduction (NR) Mobile Cross-talk Control (MCC) Noise Level Compensation (NLC)

4. 3 Causes of echo Reflection Delay

5. 4 Echo in telecommunications systems Network (or PSTN, or electrical) echo –Generated by electrical reflection of the signal Acoustic echo –Generated by acoustic reflection of the audio signal

6. 5 Electrical (PSTN) Echo 4-wire transmission network Hybrid 2-wire subscriber line PSTN subscriber Echo PSTN: Public Switched Telephone Network Mismatching in the impedance

7. 6 Acoustic Echo Loudspeaker Microphone

8. 7 Acoustic Echo Control - Terminals Terminals are different in terms of –Size –Design –Internal design of Acoustic Echo Cancellation

9. 8 Pure delay and End Path Delay time Echo Path Delay (EPD) G.168 Pure delay Example of an impulse response of an echo path

10. 9 Different Echo type characteristics PSTN echo (Electrical echo) time 64 ms time >5-10 ms 120-320 ms MS echo (Acoustic echo)

11. 10 Echo tolerance Echo Return Loss (ERL) dB Echo Tolerance Curve Tolerable Intolerable Delay (msec) Analog Networks Digital Networks Satellite 200300

12. 11 Mobile Cross-talk Control (MCC) Acoustic Echo Control Digital cellular subscriber PSTN subscriber Digital Cellular System Network echo ECP Mobile services Switching Center Acoustic echo Network Echo Canceller Mobile Cross-talk Control

13. 12 Noise Reduction (NR) Reduce the background noise on the mobile side ECP: Echo Canceller in Pool PSTN: Public Switched Telephone Network PSTN subscriber Digital Cellular System Network echo Mobile Switching Center Digital cellular subscriber Mobile side ECP

14. 13 Noise Reduction (NR) Reduce the background noise on the PSTN side ECP: Echo Canceller in Pool PSTN: Public Switched Telephone Network PSTN subscriber Digital Cellular System Network echo Mobile Switching Center Digital cellular subscriber ECP

15. 14 Noise Level Compensation (NLC) Improves audibility in noisy environment ECP NLC