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

1 © 2005 CDG VoIP Summit San Diego, CA/February 2005/Sassan Ahmadi

Choosing the Right Audio Codecs for VoIP over cdma2000 Networks:

System capacity, Voice quality, Delay, and Transcoding issues

Dr. Sassan Ahmadi

NOKIA Inc.

[email protected]

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 withlower 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 RequirementITU-T E-Model

G.114_F010 100 200 300 400 50050

60

70

80

90

100

Nearly allusers

dissatisfied

Many usersdissatisfied

Some usersdissatisfied

Userssatisfied

Usersvery satisfied

Mouth-to-ear-delay/ms

E-m

odel

ratin

g R

ITU- G.114 – Determination of the effects of absolute one-way delay by the E-modelMaximum Perceptually Tolerable Delay


Mobile-to-Mobile DelayAn Example

EncoderEncoder 1xEV-DOModem

1xEV-DOModem

De-JitterBuffer

De-JitterBuffer

1xEV-DOModem

1xEV-DOModem 1xEV-DO RAN + PDSN1xEV-DO RAN + PDSN

1xEV-DO RAN + PDSN1xEV-DO RAN + PDSN

IP Network

DecoderDecoder

RL H-ARQ Delay

FL H-ARQ Delay (voice packet drop timer)

60 ms

80 ms

20 ms 20 ms

20 ms5 ms35 ms

5 ms20-60 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

YesYes33.758.55

13.3YesYesVMR-WB

YesNo35.58.55YesNoSMV

NoNo338.55YesNoEVRC

NoNo30.513.3YesNoQCELP13

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 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


System CapacitySimulation Parameters (1xEV-DO Rev. A)

Typically 1/16 of the total capacity is allocatedNot ModeledControl Channel

Overhead

ModeledH-ARQ

DisabledRLP Retransmission

ModeledMulti-user packet

Forward Link1%Target FER

Average compressed header size for IPv64 BytesRTP/UDP/IP Header Size

Inter-arrival time between voice packets

Fixed inter-arrival time of 20 msVoice traffic model

Timer starts from the time each voice packet arrives in

BS buffer80 msVoice packet drop timer

Error freeACK/NACK channel error

Error freeDRC channel error

ModeledPreamble detection error

As specified in [1]Channel BChannel model

CommentValueParameters

[1] "1xEV-DO Evaluation Methodology (V1.4)," C30-20031002-004, 3GPP2 WG3 DO Ad Hoc Group, October 2, 2004

Jakes103Pedestrian BB

FadingSpeed (km/h)# of FingersMulti-path Model

Channel Model


System CapacitySimulation 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

* 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.


Migration Path to VoIP over cdma2000 Networks

cdma2000 1x CS voice services

VoIP over cdma2000 Networks

2004 2005 2006 2007 20092008 2010 2011

VOIP as an add-on service VOIP as the main serviceCS 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


AppendixDefinitions

• 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.

Documents

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