Long Term Evolution (LTE)

Long Term Evolution (LTE)  Long-Term Evolution (LTE) is a standard for high-speed wireless communication for mobile devices and data terminals, based on the GSM/EDGE and UMTS/HSPA (High Speed Packet Access) technologies. GSM (Global System for Mobile communication) EDGE (Enhanced Data rates for GSM Evolution) UMTS (Universal Mobile Telecommunications Service) HSPA (High Speed Packet Access) WCDMA (Wideband CDMA) GPRS (General Packet Radio Services) HSCSD (High-Speed Circuit-Switched Data)  

Cellular Network Generations: Analog cellular telephony. 2G: Digital cellular telephony. 3G: High-speed digital cellular telephony (including video telephony). 4G: IP-based voice, data, and multimedia telephony (at faster data rates than 3G).

The Source of “G”:

Evolution of Mobile Communications: From 1G to 4G

The Multiple Access Problem: FDMA: TDMA: CDMA: Data Signal PN Sequence Tx Signal

Evolution of Mobile Communications: From 2G to 3G

GSM Evolution: From 2G to 3G Dedicate up to 4 timeslots for data connection ~ 50 kbps Good for real-time applications (but inefficient) HSCSD EDGE Enhanced Data Rates for Global Evolution 3x improvement in data rate ~ 384 kbps Can fall back to GMSK for greater distances General Packet Radio Services Data rates up to ~ 115 kbps Max: 8 timeslots used as any one time Packet switched (Efficient, but variable delays) GPRS GSM 9.6kbps (one timeslot) WCDMA

Evolution of Mobile Communications: From 1G to 4G

Outlines: Motivation LTE Performance Requirements Key Features of LTE OFDM & SC-FDMA LTE Network Architecture Multiple Antenna Techniques LTE-A Specifications Summary

Motivation: Need for higher data rates and greater spectral efficiency: Can be achieved with HSDPA/HSUPA ((High Speed Packet Access)  and/or new air interface defined by 3GPP (3rd Generation Partnership Project) LTE Need for Packet Switched optimized system: Evolve UMTS towards packet only system Need for high quality of services: Use of licensed frequencies to guarantee quality of services Reduce control plane latency & round trip delay Need for cheaper infrastructure: Simplify architecture (reduce number of network elements)

LTE Performance Requirements: Data Rate: Downlink peak data rate of 100Mbit/s in a 20MHz downlink spectrum. Uplink peak data rate of 50Mbit/s in a 20MHz uplink spectrum. Mobility: Optimized for low mobility (0-15km/h) but supports high speed. Latency: user plane < 5ms control plane < 50 ms The control plane is the part of a network that carries signaling traffic and is responsible for routing.

LTE Performance Requirements: Improved spectrum efficiency. Improved broadcasting. IP-optimized. Scalable bandwidth: 20MHz, 15MHz, 10MHz, 5MHz and <5MHz Co-existence with legacy standards: Users can transparently start a call or transfer of data in an area using an LTE standard, and when there is no coverage, continue the operation using GSM/GPRS or W-CDMA-based UMTS.

LTE Key Features: Multiple access scheme: Adaptive modulation: Downlink: OFDMA (Orthogonal frequency-division multiple access) Uplink: SC-FDMA (Single-carrier FDMA) Adaptive modulation: DL modulations: QPSK, 16QAM, and 64QAM UL modulations: QPSK and 16QAM Bandwidth scalability: For efficient operation in differently sized allocated spectrum bands. Multiple Antenna (MIMO) technology: For enhanced data rate and performance. Power control and link adaptation. Implicit support for interference coordination.

OFDMA:

OFDMA & SC-FDMA (for QPSK symbols):

Adaptive Modulation:

LTE-A Network Architecture: Packet Data Network (PDN)  Packet Data Network (PDN)  LTE-A Network Architecture: Evolved Packet Core (EPC) eNBs (evolved NodeBs) as base stations Policy and Charging Rules Function (PCRF) Mobility Management Entity (MME)  Packet Data Network (PDN) E-UTRA is the air interface of 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE) 

MIMO:

Comparison of 3G & LTE-A Specifications:

LTE-A Specifications:

Summary: LTE-A is a highly optimized, spectrally efficient, mobile OFDMA solution built from the ground up for mobility. It allows operators to offer advanced services and higher performance for new and wider bandwidths. It is based on a flattened IP-based network architecture that improves network latency. It is compatible with existing 3GPP networks. It leverages the benefits of existing 3G technologies and enhances them further with additional antenna techniques (such as higher-order MIMO).