Cell based echo cancellation technique for transmitting voice over ATM network
... Echo is caused by the reflections that happen in the hybrid circuit. Hybrid echo is the primary source of echo generated from the Public Switched Telephony Network (PSTN) [1]. This electrically generated echo is created as voice signals and transmitted across the network via the hybrid circuit at the two wire/four wire PSTN conversion points, reflecting energy back to the speaker from the four-wire circuit. ...
... Based on the above plot, the average ERLE achieved is 34.4 dB. The similar band limited white noise has been used for the following simulation in Fig.5 Table I Based on the above results shown in table [1], it can be seen clearly that the performance of the ADPCM is hand in hand with the performance of the PCM. The ADPCM which only uses 32kbps for transmission will therefore help save bandwidth and at the same time preserve the voice quality without much degradation. ...
In today's modern telephony network, VoIP is fast emerging as one of the main communication techniques. However, the performance and the quality of VoIP is affected by echo. In this paper, a packet based echo canceller (PBEC) is introduced, as a solution to cancel echo in the VoIP network. PBEC can replace the current echo cancellers, which are located in the public switched telephony network (PSTN) central switches. The operating principle of the PBEC is explained and its advantages highlighted. The performance of the PBEC operating using different speech codecs is also studied. Using the PBEC, a maximum ERLE of 37.39 dB has been achieved when used with the pulse code modulation (PCM) based speech codec. From the simulation results, it can be also shown that the performance of the adaptive differential pulse code modulation (ADPCM) clearly matches the performance of the PCM based speech codec.
... The analogue section of the network is the cause of echo and is due to reflections that happen in the hybrid circuit. Hybrid echo is the primary source of echo generated from the Public Switched Telephony Network (PSTN) [1]. This electrically generated echo is created as voice signals and transmitted across the network via the hybrid circuit at the two-wire/four-wire PSTN conversion points, reflecting energy back to the speaker from the four-wire circuit. ...
In today's modern telephony network, VoIP is fast emerging as one of the main communication techniques. However, the performance and the quality of VoIP are affected by echo. Packet Based Echo Canceller (PBEC) is introduced, as a solution to cancel echo in the VoIP network. PBEC can replace the current echo cancellers, which are located in the Public Switched Telephony Network (PSTN) central switches. The operating principle of the PBEC is explained and its advantages are highlighted. The performance of the PBEC using different speech codecs is also studied. Using the PBEC, a maximum Echo Return Loss Enhancement (ERLE) of 37.39 dB has been achieved when used with the Pulse Code Modulation (PCM) based speech codec. From the simulation results, it can be seen that the performance of the Adaptive Differential Pulse Code Modulation (ADPCM) clearly matches the performance of the PCM based speech codec. The other major problem affecting the VoIP network is the issue of packet loss. This issue of packet loss has been successfully addressed in this paper by the insertion of random values. With the insertion of random values, the ERLE increases by 4.81 dB compared to when there is no insertion of random value. The PBEC with the utilization of random values would make the VoIP a better communication tool.
In today's modern telephony network, VoIP is fast emerging as one of the main communication technique. However, the performance and the quality of VoIP are affected by echo. Packet based echo canceller (PBEC) is introduced, as a solution to cancel echo in the VoIP network. PBEC can replace the current echo cancellers, which are located in the public switched telephony network (PSTN) central switches. The operating principle of the PBEC is explained and its advantages are highlighted. Simulations have been done with variable amount of network delay using the PBEC and PSTN based echo cancellation system. The PBEC has performed better than the PSTN based echo cancellation system when simulated with variable amount of network delay time. The PBEC had a 2.25 dB advantage over the PSTN based echo cancellation system when simulated with 400 ms of network delay time
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