VoLTE: Differentiating the Voice Calls?

Aricent recently hosted a webinar titled Monetizing VoLTE – How to provide HD voice/video services over LTE while minimizing costs and risks. In this webinar our experts discussed how you can implement a high performance VoLTE solution spanning User Equipment (UE) (IMS Client), RAN (eNodeB), Core (EPC) and IMS Servers. They also discussed critical issues such as GSMA IR92 compliance for IMS client and EPC, audio specific QoS implementation for eNodeB and policy control on IMS servers. Our experts also provided insights into how you can customize your VoLTE solution to cater to a specific market based on the number of subscribers.

Please click here to view the archived version of the webinar.

R Ezhirpavai, AVP technology, Aricent, answers some of the questions asked during the webinar.

What are the challenges for voice calls over cellular systems?  How does VoLTE overcome those challenges?
The major inhibitors for Voice over cellular system are:

•   Latency in voice
•   Quality of service

LTE provides the ability to reduce the latency as required latency in data over the air is 10-25 ms for LTE and it is around 100ms for 3G. So latency of voice is not seen in VoLTE. It provides end to end quality of service due to better bandwidth control and guaranteed services. This can thus be even used to deliver high definition (HD) voice and video over LTE.

How can an operator increase ARPU in a mobile only environment with VoLTE?
Using VoLTE, one can combine multiple multi-media services like presence, IM, file transfer, image sharing and video along with voice. With 3G circuit switched (CS) traffic using low-end phones having only one radio channel, either CS voice call or data can be transferred at a time. So these multi-media applications could not be supported using 3G. These value added applications can help in increasing ARPU.

How do you envision the decrease in OPEX with VoLTE HD voice?
Using VoLTE, there would be a single network for providing the voice, data and multi-media applications. Common nodes need to handle charging policy, authentication etc. On the other hand with 3G, there were 2 parallel networks – one for voice and one for data. Also the 3G was not an all IP network. These factors reduce the number of network nodes thereby reduces the maintenance of the network, overall reducing the OPEX for the operators.

One of the biggest problems with voice, from a user perspective, is echo, or noise problems, what will HD Voice do about these issues where there is even higher frequency response for voice?
The echo cancellation procedures and noise suppression help in reducing these issues in IMS networks. These have been used in VoLTE as well.

As a new operator is it possible to start an LTE network without having backward support for the older legacy application?
A new operator would need older legacy interfaces if and only if it would need roaming support to a non LTE coverage area. Otherwise a new operator can support LTE network without providing any support for legacy applications.

Can the public safety deployment have mobility if so how is that accomplished?
Yes, in public safety networks, the mobility can be supported with the local EPC networks which are available at disaster site or with centralized EPC networks. The mobility is supported in the same way as commercial networks, but with common EPC nodes.

How do you offer quality VoIP services at the cell edges, which are constrained both of data capacity and in-building coverage?
At cell edges, the voice can still be provided because of the higher control of QoS. The voice can be normal voice rather than higher definition voice, and higher bandwidth consuming data applications can be assigned lower bandwidth through policy control.

What is the latest status of standardization and knowledge of roaming for VoLTE?
The VoLTE is defined by GSMA IR.92 and is a frozen speciation. Roaming agreements are still being discussed by operators and has not yet been well defined.

Is HD Voice inherent to VoLTE or is HD voice an add-on feature to VoLTE?
HD Voice is an add-on feature to VoLTE. GSMA IR92 mandates to support Adaptive Multi-Rate (AMR) narrow band speech codecs in the UE for normal VoLTE call. If wideband speech communication is offered, then UE need to prefer AMR wideband codecs if it is already supported by the UE. Enabling or disabling certain codecs is restricted to SDP negotiation between UE,  policy control rules as defined in PCRF, and codecs supported by MRFC network server.  Supporting of HD voice can also be controlled by service provider and also based upon UE capability to support wideband AMR codecs.

What is the bit rate requirement?
The conversational voice in VoLTE is streamed either using AMR narrow band or AMR wide band codecs. Both AMR narrow band and AMR Wide-band are multi-mode codecs, which support wide range of bit-rates. For e.g. AMR codecs supports eight narrow band speech encoding modes with bit rates between 4.75 and 12.2 kbps whereas AMR-WB supports nine wide band speech coding modes with respective bit rates ranging from 6.6 to 23.85 kbps. The encoded speech data will be part of RTP/UDP/IP payload. VoLTE mandates to support RoHC to further compress RTP/UDP/IP header for minimizing the bandwidth usage of a voice call on LTE network.

How realistic is it to setup a LTE network for streaming Video over RTP/UDP in place of regular TV.
For simple streaming of data to a group of users like for regular TV, Aricent’s view is that eMBMS shall be used rather than VoLTE. This would have better optimized radio usage. VoLTE would be used for peer to peer video.

How does the MMTel client for VoLTE in the device interwork with VoLTE LTE device, which also supports CSFB?
The MMTel applications provide voice supplementary services in IMS networks for VoLTE. On the other hand when there is a handover to CS due to no LTE coverage, this call has to be handed over using SRVCC to CS network. The MMTel applications of IMS networks can continue to provide the services even when user moves to CS networks.

Are there any new data codecs written for this technology? 
GSMA IR92 specifies support for Adaptive Multi-Rate (AMR) narrow band and AMR wide-band codec as part of VoLTE. These codecs are already available today. They have corresponding IETF and 3GPP specification for implementation on both UE and network. However, a service provider can customize its implementation to use other codecs considering inter-operability with other clients and quality to the end user. UE can use dynamic payload during call negotiation procedure for establishing the voice call with these customized codecs.

How would VoLTE help in freeing up spectrum load for operators?
VoLTE would use the LTE spectrums that are different from 3G spectrums. Hence with VoLTE, the 3G spectrums load would be reduced due to load offloading to LTE.

Can you elaborate on what must be added in a handset to enable VoLTE services?
Enabling VoLTE in a handset is primarily distributed among the following components of the handset.

  • LTE UE Base-Band Modem: This component primarily interacts with eNodeB over radio access network.
  • IMS signalling Module: This component primarily interacts with IMS server over the IMS APN based bearer as created for IMS signalling procedures.
  • Media Engine: This component interacts with hardware devices like microphone, speaker and streams conversational voice over RTP/UDP/IP using either a narrow-band or wide-band codec.
  • Telephony manager/phone application: Phone application is end-user application, which is used to dial
    and receive a call.

Leave a Reply

Your email address will not be published. Required fields are marked *