Choosing the Right Audio Codecs for VoIP over cdma2000 Networks:
System capacity, Voice quality, Delay, and Transcoding issues
Dr. Sassan Ahmadi NOKIA Inc.
sassan.ahmadi@nokia.com
February 8, 2005
Outline
• Drivers and advantages of VoIP over cdma2000 networks
• Requirements for VoIP over cdma2000 networks
• Delay requirement
• Mobile-to-mobile delay, an example
• 3GPP2 standard codecs for VoIP
• System capacity
• Simulation parameters
• Simulation results
• Migration path to VoIP over cdma2000 networks
• Summary
• Appendix
• Definitions
Drivers and Advantages of VoIP over cdma2000 Networks
• VoIP drivers
• Efficient use of system bandwidth as well as flexible technology.
• The use of standard packet network components and protocols with lower costs.
• Migration toward all-IP network architecture in general and adoption of 1x EV-DO by cdma operators as the next cdma air interface in particular.
• VoIP is the simplest and most efficient path to convergence of the Next Generation Networks.
• VoIP facilitates the introduction of rich multimedia services.
• Integration of voice, data, and other multimedia services simplifies network design, operation, and management.
• Convergence of various cellular/wireless/fixed network services
Drivers and Advantages of VoIP over cdma2000 Networks
• Advantages of VoIP over CS voice services
• More flexible and efficient codec design
• The permissible encoding rates in existing cdma2000 codecs are restricted by the air-interface to either rate-set I or rate-set II.
• Discontinuous transmission cannot be used in cdma2000 CS voice services.
• Opportunity for cross-system interoperability.
• Opportunity for providing better voice quality.
• Existing cdma2000 CS voice services involve transcoding
• VoIP can offer transparent end-to-end transport, resulting in
• Lower end-to-end delay by eliminating transcoding
• Improving quality of service by avoiding quality degradation due to transcoding
• Reducing the complexity and cost of the gateways
• Ease of harmonization with other cellular/fixed network voice services
Requirements for VoIP over cdma2000 Networks
• 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.
Delay Requirement
ITU-T E-Model
G.114_F01
0 100 200 300 400 500
50 60 70 80 90 100
Nearly all users dissatisfied Many users dissatisfied Some users dissatisfied
Users satisfied
Users very satisfied
Mouth-to-ear-delay/ms
E-model rating R
ITU- G.114 – Determination of the effects of absolute one-way delay by the E -model
Maximum Perceptually Tolerable Delay
Mobile-to-Mobile Delay
An Example
Encoder
Encoder 1xEV-DO Modem 1xEV-DO Modem
De-Jitter Buffer De-Jitter
Buffer 1xEV-DO
Modem 1xEV-DO
Modem 1xEV-DO RAN + PDSN1xEV-DO RAN + PDSN 1xEV-DO RAN + PDSN 1xEV-DO RAN + PDSN
IP Network
Decoder Decoder
RL H-ARQ Delay
FL H-ARQ Delay (voice packet drop timer)
60 ms
80 ms
20 ms 20 ms
20 ms 5 ms
35 ms
20-60 ms 5 ms
15 ms
Transcoding delay has not been included ~ 40 ms
Included in capacity calculations
3GPP2 Standard Codecs for VoIP
Yes UMTS/AMR-WB
No No No
Interoperability with UMTS Codecs
Rate-Set I Rate-Set II
Rate-Set I Rate-Set I Rate-Set II
Operating cdma2000 Rate-Set
Yes Yes
33.75 8.55
Yes 13.3 Yes
VMR-WB
Yes No
35.5 8.55
Yes No
SMV
No No
33 8.55
Yes No
EVRC
No No
30.5 13.3
Yes No
QCELP13
Multimode Functionality
(Quality- Capacity Tradeoff) DTX
Capability Algorithmic
Delay (ms) Maximum
Source Bit Rate (kbps) Narrowband
Speech Processing
Capability Wideband
Speech Processing
Capability 3GPP2
Standard Codec
VMR-WB is the only 3GPP2 standard codec with flexible DTX capability
VMR-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
System Capacity
Simulation Parameters (1xEV-DO Rev. A)
Typically 1/16 of the total capacity is allocated Not Modeled
Control Channel Overhead
Modeled H-ARQ
Disabled RLP Retransmission
Modeled Multi-user packet
Forward Link 1%
Target FER
Average compressed header size for IPv6
4 Bytes RTP/UDP/IP Header Size
Inter-arrival time between voice packets
Fixed inter-arrival time of 20 ms
Voice traffic model
Timer starts from the time each voice packet arrives in
BS buffer 80 ms
Voice packet drop timer
Error free ACK/NACK channel error
Error free DRC channel error
Modeled Preamble detection error
As specified in [1]
Channel B Channel model
Comment Value
Parameters
Jakes 10
3 Pedestrian B
B
Fading Speed (km/h)
# of Fingers Multi-path
Model Channel Model
System Capacity
Simulation Results
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
32 24
29 24
22
Channel 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 EVRC in narrowband operation, operating at an average data rate that is 8% lower than that of EVRC.
Migration Path to VoIP over cdma2000 Networks
cdma2000 1x CS voice services
VoIP over cdma2000 Networks
2004 2005 2006 2007 2008 2009 2010 2011
VOIP as an add-on service VOIP as the main service CS voice as the main service
VoIP over Fixed Networks
Next Generation Networks
Summary
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.
Thank You
Appendix
Definitions
• 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 enable connection 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.
