4Long Term Evolution (LTE) and LTE‐Advanced Pro
4.1 Introduction and Overview
Despite constant evolution, the Universal Mobile Telecommunications System (UMTS), as described in Chapter 3, has reached a number of inherent design limitations in a manner similar to GSM and GPRS at the end of the 1990s. The Third Generation Partnership Project (3GPP), the organization of mobile device manufacturers, infrastructure developers and mobile network operators responsible for the GSM and UMTS specification, hence decided to once again redesign both the radio network and the core network. The result is commonly referred to as ‘Long Term Evolution’ or LTE for short and has been included in 3GPP Release 8. The main improvements over UMTS are in the areas described below.
When UMTS was designed, it was a bold approach to specify an air interface with a carrier bandwidth of 5 MHz. Wideband Code Division Multiple Access (WCDMA), the air interface chosen at that time, performed very well within this limit. Unfortunately, it does not scale very well. If the bandwidth of the carrier is increased to attain higher transmission speeds, the time between two transmission steps has to decrease. The shorter a transmission step, the greater the impact of multipath fading on the received signal. Multipath fading can be observed when radio waves bounce off objects on the way from transmitter to receiver, and hence the receiver does not see one signal but several copies arriving at different times. As a ...
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