LTE Aida Botonjić Aida Botonjić Tieto 1
Why LTE? Applications: Interactive gaming DVD quality video Data download/upload Targets: High data rates at high speed Low latency Packet optimized radio access technology Goals: Improving efficiency Lowering costs Reducing complexity Improving services Making use of new spectrum opportunities and better integration with other open standards (such as WLAN and WiMAX) Aida Botonjić Tieto 2
Introduction November 2004, 3GPP Rel8: Long-term Evolution (LTE) Related specifications are formally known as the evolved UMTS terrestrial radio access (E-UTRA) and evolved UMTS terrestrial radio access network (E-UTRAN) LTE encompasses the evolution of: - the radio access through the E-UTRAN - the non-radio aspects under the term System Architecture Evolution (SAE) Entire system composed of both LTE and SAE is called the Evolved Packet System (EPS) Aida Botonjić Tieto 3
Network Architecture IP Service Network Cost efficient two node architecture Fully meshed approach with tunneling mechanism over IP network Access gateway (AGW) Enhanced Node B (enb) AGW AGW S1 S1 S1 S1 IP Transport Network enb X2 enb X2 enb X2 enb X2 enb Aida Botonjić Tieto 4
Network Elements Aida Botonjić Tieto 5
Protocol overview Control Plane User Plane UE enb MME UE enb NAS NAS NAS RRC RRC Handovers RRC RRC PDCP RLC MAC PHY PDCP RLC MAC PHY Ciphering Radio bearers Segmentation Logical channels HARQ Transport channels Modulation, coding Physical channels PDCP RLC MAC PHY PDCP RLC MAC PHY Aida Botonjić Tieto 6
Frame structure LTE: One radio frame, T f = 307200 T s =10 ms One slot, T slot = 15360 T s = 0.5 ms #0 #1 #2 #3 #18 #19 One subframe WCDMA/HSPA: One radio frame, 10 ms One slot, 2/3ms #0 #1 #2 #3 #13 #14 One subframe, 2ms Aida Botonjić Tieto 7
Channel Dependent Scheduling and Link adaptation Frequency-domain & Time-domain adaptation Focus transmission power to each user s best channel portion Adaptive modulation (QPSK, 16QAM, 64QAM) Aida Botonjić Tieto 8
LTE PHY Main Technologies MIMO Multiple Input Multiple Output OFDM Orthogonal Frequency Division Multiplexing N Tx Transmit Antennas N Rx Receive Antennas Aida Botonjić Tieto 9
LTE PHY - MIMO Basics Minimum antenna requirement: 2 at enodeb 2 Rx at UE Transmission of several independent data streams in parallel => increased data rate The radio channel consists of N Tx x N Rx paths Theoretical maximum rate increase factor = Min(N Tx x N Rx ) Aida Botonjić Tieto 10
LTE PHY - OFDM Basics Sub-carriers are orthogonal All the sub-carriers allocated to a given user are transmitted in parallel. The carrier spacing is 15kHz Aida Botonjić Tieto 11
Requirement comparison Requirement HSPA (Rel 6) LTE Peak data rate 14 Mbps DL 5.76 Mbps UL 5% packet call throughput 64 Kbps DL 5 Kbps UL Averaged user throughput Control plane capacity 900 Kbps DL 150 Kbps UL User plane latency 50 ms 5 ms Call setup time 2 sec 50 ms 100 Mbps DL 50 Mbps UL 3-4x DL / 2-3x UL improvement 3-4x DL / 2-3x UL improvement > 200 users per cell (for 5MHz spectrum) Broadcast data rate 384 Kbps 6-8x improvement Mobility Up to 250 km/h Up to 350 km/h (500 km/h for wider bandwidths) Bandwidth 5 MHz 1.25, 2.5, 5, 10, 15, 20 MHz Aida Botonjić Tieto 12
Feature comparison Feature HSPA (Rel 6) LTE minimum TTI size 2 ms 1 ms Modulation HARQ DL: QPSK, 16 QAM UL: QPSK Async DL, Sync UL DL: QPSK, 16 QAM, 64 QAM UL: 16 QAM Async DL, Sync UL Fast scheduling TDS (time domain) TDS and FDS (frequency domain) Aida Botonjić Tieto 13
Scalable bandwidth Conclusion Downlink and uplink peak data rates are 100 and 50 Mbit/s respectively for 20 MHz bandwidth. MIMO OFDM At least 200 mobile terminals in the active state for 5MHz bandwidth. If bandwidth is more than 5MHz, at least 400 terminals should be supported. PHY key technologies enable higher spectral efficiency, peak rate and lower latency Aida Botonjić Tieto 14