System Level Modeling and Optimization of the LTE Downlink

2. 3GPP Long Term Evolution2. 3GPP Long Term EvolutionIn its Release 8, Long Term Evolution (LTE) was standardized by the 3rd GenerationPartnership Project (3GPP) as the successor of the Universal Mobile TelecommunicationsSystem (UMTS) standard. LTE was designed from the start withthe assumption that all of the services would be packet-switched rather than circuitswitched, thus continuing the trend set from the evolution of Global Systemfor Mobile communications (GSM), to General Packet Radio Service (GPRS), EnhancedData Rates for GSM Evolution (EDGE), UMTS, and High-Speed PacketAccess (HSPA). During this evolution, it has been seen how the focus has beenmoving towards providing ubiquitous availability of broadband communications, aswell as the classical voice/text communication capabilities. From the early mobilepacket services, not only has throughput been dramatically increased, but also latencygreatly decreased [4, 9, 10]. Early 2G-based systems such as GPRS were ableto offer data transfer rates in the order of 10 kbit/s, while in its latest current iteration,HSPA can theoretically reach peak speeds of 80 Mbit/s by combining multiple5 MHz carriers and Multiple-Input Multiple-Output (MIMO) techniques [11–13].The combination of higher throughput requirements, lower latency, as well as affordability,given the needed non-linear evolution between traffic volume and cost [14],contributed to the requirements specified for LTE by 3GPP, which are summarizedin the following points [15–17]:ˆ Increased peak data rates of 100 Mbit/s in the Downlink (DL) and 50 Mbit/s inthe Uplink (UL), as well as improvements in cell edge and spectrum efficiency.ˆ Scalable bandwidthˆ Easy interworking with existing 3GPP systems and cost-effective migration toLTE, resulting in a reduced CAPital EXpenditure (CAPEX).ˆ Simplified network architecture allowing for a lower OPerational EXpenditure9