VOLTE principals
The LTE voice solution is as follows:
-Voice solution based on dual-standby UEs:
A dual-standby UE is capable of receiving or sending signals in both E-UTRAN and GERAN or UTRAN. Dual-standby UEs automatically select GERAN or UTRAN to perform voice services and select E-UTRAN to perform data services. That is, the E-UTRAN provides dual-standby UEs with only data services.
-Voice solution based on CSFB:
In the initial phase of LTE network deployment, CSFB is a transitional solution to provide voice services for LTE users if the IMS is not yet deployed.With the CSFB
solution, when a UE initiates a CS service in the E-UTRAN, the MME instructs
the UE to fall back to the legacy CS domain of the GERAN or UTRAN before the UE
performs the service
-Voice solution based on the IMS :
This solution is used
in the mature stage of the LTE network when the IMS is deployed, With this solution, UEs can directly perform voice services in an
LTE network. This solution is also termed as the Voice over LTE (VoLTE) solution.
The LTE network must support SRVCC or PS handover to provide UEs running voice
services with continuous services when the UEs move out of an LTE network
VoLTE is the voice
service supported by the IP transmission network between calling/called UEs in
the E-UTRAN and the IMS. That is, with VoLTE, calling/called UEs in the LTE
network can perform voice services directly.
VoLTE provides UEs in the E-UTRAN with voice services, without the need of falling back to GERAN or UTRAN. VoLTE features the following characteristics:-Higher spectral efficiency
-Better user experience, such as lower access delay and better voice quality
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Network Architecture
MME: mobility management entity
S-GW: serving gateway
SGSN: serving GPRS support node
HSS: home subscriber
server
PCRF: policy and charging rule function
PDN Gateway: packet
data network gateway
IP multimedia subsystem (IMS) includes multiple
network elements (NEs). These NEs perform voice session control and multimedia
negotiation between the calling and called UEsSpeech Codec Scheme and Traffic Model
AMR
-AMR is an audio data compression scheme optimized for speech
coding and is now widely used in GERAN and UTRAN. AMR is classified into
adaptive multirate wideband (AMR-WB) and adaptive multirate narrowband
(AMR-NB).
AMR-NB has eight speech coding rates.
They are 12.2 kbit/s, 10.2 kbit/s, 7.95 kbit/s, 7.4 kbit/s,
6.7 kbit/s, 5.9 kbit/s, 5.15 kbit/s, and 4.75 kbit/s.
AMR-WB has nine speech coding rates.
They are 23.85 kbit/s, 23.05 kbit/s, 19.85 kbit/s, 18.25
kbit/s, 15.85 kbit/s, 14.25 kbit/s, 12.65 kbit/s, 8.85 kbit/s, and 6.6 kbit/s.
There are two VoLTE traffic states:
Talk spurts
During talk spurts, the uplink of UEs transmits voice packets or the downlink of UEs receives voice packets. Voice packets are transmitted at intervals of 20 ms, and the packet size is determined by the speech coding rate.
Silent period
During silent periods, the UE transmits silence insertion descriptor (SID) frames or receives SID frames at intervals of 160 ms. For different AMR speech codec rates, the SID frame sizes are all 56 bits.
The differences between talk spurts and silent period are as follows:
The size of voice frames is greater than the size of SID frames.
The interval between neighboring voice frames is different from the interval between SID frames.
The eNodeB distinguishes between voice frames and SID frames based on the preceding differences
G.711
G.711, also known as pulse code modulation (PCM), is
primarily used in fixed-line telephony. It supports a coding rate of 64 kbit/s.
G.729
G.729, known for the high voice quality and low delay, is
widely used in various domains of data communications. It supports a coding
rate of 8 kbit/s.
G.726
G.726 supports coding rates of 16 kbit/s to 40 kbit/s. The
most commonly used rate is 32 kbit/s. In actual application, voice packets are
sent at intervals of 20 ms.
The VOLTE Feature will be explained sooooon