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The essential aspects of LTE's PHY (Part 1)

Posted: 22 Jun 2010     Print Version  Bookmark and Share

Keywords:LTE PHY  physical layer  peak transmission rate 

The design of the LTE physical layer (PHY) is heavily influenced by requirements for high peak transmission rate (100Mbit/s DL/50Mbit/s UL), spectral efficiency and multiple channel bandwidths (1.25-20MHz). To fulfil these requirements, OFDM was selected as the basis for the PHY layer.

OFDM is a technology that dates back to the 1960s. It was considered for 3G systems in the mid-1990s before being determined too immature. Developments in electronics and signal processing since that time has made OFDM a mature technology widely used in such other access systems as 802.11 (Wi-Fi) and 802.16 (WiMAX) and broadcast systems (DAB/DVB). In addition to OFDM, LTE implements multiple-antenna techniques such as multiple input multiple output (MIMO), which can either increase channel capacity (spatial multiplexing) or enhance signal robustness (space frequency/time coding).

Together, OFDM and MIMO are two key technologies featured in LTE and constitute major differentiation over 3G systems, which are based on CDMA. This article presents an overview of the LTE physical layer, which in itself is a very large and feature-rich topic, particularly as there are different modes of operation (FDD/TDD) and different downlink and uplink access technologies (OFDMA, SC-FDMA), along with options and exceptions for each mode and access technology.

To narrow the scope, this technical article focuses on essential aspects of the physical layer for FDD mode, which is the dominant mode of operation and selected by incumbent mobile operators as it fits well into existing and perspective spectrum assignments. Furthermore, the topic of MIMO is left out. It is hoped that this tech paper serves as a useful introduction to practitioners involved in designing LTE based-networks and systems such as network engineers, product managers and technical managers.

View the PDF document for more information.





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