Choosing the Right Audio Codecs for VoIP over cdma2000 ... · Choosing the Right Audio Codecs for VoIP over cdma2000 Networks: ... • Requirements for VoIP over cdma2000 networks
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• Match or exceed the quality of existing CS voice services.• One-way delay equivalent to CS voice services is desirable.• Match or exceed the capacity of CS voice over cdma2000 1x.• Interoperability with other cellular and fixed networks to avoid
transcoding is desirable.• The evolutionary path should include an overlap period with the
existing CS voice services to allow for smooth transition.• Reasonable robustness and tolerance with respect to packet loss and
jitter in the IP networks.• Use and enhancement of IMS architecture to control and manage
SIP/SDP based sessions and signaling.• Some enhancements in the mobility management to overcome the
limitations on the real-time services such as VoIP (e.g., handoffs).• Compliance with regulatory services and requirements.
VMR-WB is the only 3GPP2 standard codec with flexible DTX capabilityVMR-WB is the only 3GPP2 standard codec with both wideband and narrowband processing capabilities
VMR-WB is the only 3GPP2 standard codec that is interoperable with UMTS/AMR-WB codec at 12.65, 8.85, and 6.6 kbps
Our simulation methodology uses those parameters specified in the strawman [1,2] except
• Channel model• Channel model B only was studied as some concerns were raised regarding the percentage of channel model A
users in mixed channel environment
• Outage criteria• Based on long-term FER
• Requirement: Less than 3% of all users in the system have long-term FER higher than 1%
• EVRC codec was used for the cdma2000 1x simulation.
[1] "1xEV-DO Evaluation Methodology (V1.4)," C30-20031002-004, 3GPP2 WG3 DO Ad Hoc Group, October 2, 2004
[2] "1xEV-DV Evaluation Methodology – Addendum (V14)," 3GPP2 WG5 Evaluation Ad Hoc, June 16, 2003
* Note: The existing EVRC standard codec does not include DTX capability and this number represents only an estimate, should a DTX mechanism similar to that of VMR-WB be used for EVRC.
3224292422Channel B
VMR-WB
Mode 4
(with DTX)
VMR-WB
Mode 0
(with DTX)
EVRC*
[Benchmark]
(with DTX)
EVRC
[Benchmark]
(No DTX)
VoIP over 1x EV-DO Rev. A w/o RX Diversity (users/sector)cdma2000 1x Circuit-switched w/o RX Diversity
(users/sector)Channel Model
VMR-WB mode 4 offers superior wideband quality while performing statistically equivalent to EVRCin narrowband operation, operating at an average data rate that is 8% lower than that of EVRC.
VoIP over cdma2000 networks is promising and can take off as early as 2H 2006 as an add-on service.
cdma2000 1x system capacity and voice service quality can be matched or exceeded with certain assumptions. The use of RX diversity with 1xEV-DO Rev. A is one way to further increase the capacity gains.
Harmonization of VoIP services across various cellular/fixed networks can be facilitated through the use of interoperable codecs
(e.g., UMTS/AMR-WB, CDMA/VMR-WB), resulting in more efficient network design and operation by eliminating the transcoding.
The 3GPP2 standard wideband/narrowband multimode speech codec,VMR-WB, provides unique functionalities that are
ESSENTIAL to the success of VoIP over cdma2000 networks.
3GPP2 VMR-WB standard offers superior quality, DTX capability, and interoperability with UMTS/AMR-WB,
at a system capacity that is comparable to that offered by other existing 3GPP2 standard codecs.
• Narrowband speech codec: A vocoder that operates with 8 kHz sampled input/output speech signals that are band-limited to 300-3400 Hz.
• Wideband speech codec: A vocoder that operates with 16 kHz sampled input/output speech signals that are band-limited to 50-7000 Hz. The expanded audio bandwidth results in more intelligibility and naturalness and substantially improved quality of the speech signals.
• Discontinuous transmission (DTX): A mechanism that suppresses the encoding and transmission of inactive (silence) intervals in a speech signal, thus reducing the output data rate of the vocoder. Silence speech intervals are perceptually less significant and therefore the impact on speech quality is minimal.
• Transcoding: Extra decoding and encoding functions at the gateways to enableconnection of different codecs at the end points. This process adds to the overall delay and degrades the speech quality.
• Interoperability: Capability of a vocoder to decode the speech data encoded by another codec without incorporating any transcoding mechanism.
• Multimode speech coding: Tradeoff between voice quality and system capacity through the use of multiple encoding schemes each operating at different bit rate.