The Voice over LTE (VoLTE) provides High Definition Voice over all IP networks. It enables simultaneous voice and data traffic on LTE. SK Telecom and LG Uplus in South Korea launched the world’s first VoLTE in August 2012. MetroPCS also launched VoLTE using the LG Connect smartphone in 2012. To fully deploy VoLTE services, seamless connection of an IP Multimedia Subsystem (IMS) and its associated Session Initiation Protocol (SIP) in a mobile environment is an essential factor. Thus, several technical features at the radio access protocol level are required.
Four technical features at the radio access protocol level that support seamless VoIP connection in a mobile environment are specified in LTE standard specifications: TTI bundling for HARQ (reduce the latency of data transmission by a smartphone), Discontinuous Reception (DRX: save the power consumption), Semi-persistent scheduling (SPS: reduce the scheduling overhead ) and Robust Header Compression (ROHC: reduce RTP/UDP/IP packet size).
TechIPm, LLC’s 4G LTE patent research for the US market identifies that there are total of 70 published applications and issued patents relating to four technical features at the radio access protocol level that supporting seamless VoIP connection. Nokia is the leading IPR holder followed by BlackBerry, Ericsson, Innovative Sonic, Qualcomm, Samsung, LG, ETRI, InterDigital and Motorola.
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