define the time and frequency implementation methods. The 3GPP specifications are structured as releases, whereby each release includes features added to the previous release. Table 4-1 outlines the 3GPP releases and the associated mobile technology for each of them. Note that this table is very much simplified SO as not to introduce excessive amounts of new terminology and acronyms. If you are not familiar with these technologies, "Chapter 10. Mobile Timing Re- quirements", discusses them in some detail. Table 4-1 3GPP Releases Milestone lease 3G specifications taken from a consolidation of the underlying GSM specifications combined with the development of a new RAN 3G (UMTS) with all IP core network High Speed Downlink Packet Access (HSDPA) High Speed Uplink Packet Access (HSUPA) HSPA+ or evolved HSPA, sometimes marketed as 3.5G Long Term Evolution (LTE) LTE broadcast (enhanced Multimedia Broadcast Multicast System, known as eMBMS), Voice over LTE (VoLTE), LTE positioning LTE-Advanced, Carrier Aggregation (CA), and advanced multiple input and multiple output (MIMO) antenna technology Coordinated Multipoint (CoMP) FDD-TDD Carrier Aggregation (CA) LTE-Advanced Pro, IoT technologies, LTE in unlicensed bands Enhanced Licensed Assisted Access (LAA) allowing LTE to use 5-GHz unlicensed spectrum (also used by Wi-Fi) for uplink and downlink 5G Phase 1, introducing the first IMT-2020 enhancements within existing spectrum; also includes as- pects of machine-type communications (MTC) and IoT 5G Phase 2, completing the initial 5G for IMT-2020 submission Under development over the 2021-22 period (schedule may be further affected by COVID-19) and in- cludes enhancements to 5G (discussed in following text) Studies just beginning as of time of writing (early 2021) 3GPP uses a system of parallel releases to provide a stable platform for implementation while at the same time allowing the addition of new features. A release not only contains the newly implemen- ted features but builds upon the previous releases to ensure backward