LTE Air Interface and OFDM in Telecommunications

What is the main reason for the redesign of both the radio network and the core network in 3GPP?

What is the primary challenge with increasing the carrier bandwidth in UMTS?

What is the impact of multipath fading on the received signal?

What is the main reason for the poor scalability of WCDMA?

What is the result of the redesign of both the radio network and the core network by 3GPP?

Why does the receiver in UMTS see several copies of the signal arriving at different times?

What technology does LTE use to overcome the effects of multipath fading?

How does LTE split a data stream to reduce the multipath effect?

What is the minimum bandwidth specified for LTE?

What technology allows the base station to transmit several data streams over the same carrier simultaneously in LTE?

Which duplexing method does LTE use in most parts of the world including Europe and the Americas?

What is the maximum datarate that can be achieved under very good signal conditions in a 20-MHz carrier?

UMTS is approaching its design limitations, similar to GSM and GPRS in the past.
3GPP redesigned the radio network and core network, resulting in Long-Term Evolution (LTE).

UMTS was designed with a carrier bandwidth of 5 MHz, which is limiting for higher transmission speeds.
WCDMA, the air interface chosen for UMTS, does not scale well with increased bandwidth.
Multipath fading, caused by radio waves bouncing off objects, affects signal reception and increases with shorter transmission steps.

LTE uses Orthogonal Frequency Division Multiplexing (OFDM) to overcome multipath fading.
OFDM transmits data over many narrowband carriers of 180 kHz each, reducing multipath effects.
LTE devices can adapt to different bandwidths (1.25 MHz to 20 MHz) and must support all bandwidths.
In a 20-MHz carrier, datarates beyond 100 Mbit/s can be achieved under good signal conditions.

LTE devices have a high baseline, supporting flexible bandwidth and Multiple Input Multiple Output (MIMO) transmissions.
MIMO allows for simultaneous transmission of multiple data streams, increasing datarates under good signal conditions.

In most parts of the world, LTE uses Frequency Division Duplex (FDD) to separate uplink and downlink transmissions.
In some regions, Time Division Duplex (TDD) is used, where uplink and downlink transmissions use the same carrier and are separated in time.