Building and expanding an LTE network does not usually happen overnight. It tends to be a gradual process where new cells and capacity are added in line with business and subscriber demand. Providing LTE, voice over LTE (VoLTE), and voice handover is a fundamental part of next-generation mobile networks, where voice handover to legacy systems is a key enabler while LTE coverage continues to be spotty.
LTE networks and the VoLTE services built on top of them need to coexist with legacy circuit-switched networks and ensure handover to the legacy network when LTE radio coverage is insufficient.
Such handover needs to be well engineered with performance levels that are comparable to the IRAT handover for voice calls procedures available in circuit-switched networks today – with voice interruption of less than 0.3s and a success rate that is greater than 99 percent.
Experiments using Ericsson commercial products and Qualcomm test phones with commercial chipsets show that the 3GPP-specified SRVCC handover mechanism can meet the requirements for performance standards to ensure seamless service, greatly reducing the number of dropped calls.
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