12 Questions
What is the main reason for the redesign of both the radio network and the core network in 3GPP?
To improve the performance of UMTS
What is the primary challenge with increasing the carrier bandwidth in UMTS?
The shorter a transmission step, the greater the impact of multipath fading on the received signal
What is the impact of multipath fading on the received signal?
It causes parts of the signal of a previous transmission step to overlap with the radio signal of the current transmission step
What is the main reason for the poor scalability of WCDMA?
The time between two transmission steps has to decrease
What is the result of the redesign of both the radio network and the core network by 3GPP?
Long-Term Evolution (LTE)
Why does the receiver in UMTS see several copies of the signal arriving at different times?
Due to radio waves bouncing off objects on the way from transmitter to receiver
What technology does LTE use to overcome the effects of multipath fading?
Orthogonal Frequency Division Multiplexing (OFDM)
How does LTE split a data stream to reduce the multipath effect?
By transmitting it over many slow data streams simultaneously
What is the minimum bandwidth specified for LTE?
1.25 MHz
What technology allows the base station to transmit several data streams over the same carrier simultaneously in LTE?
Multiple Input Multiple Output (MIMO) transmissions
Which duplexing method does LTE use in most parts of the world including Europe and the Americas?
Frequency Division Duplex (FDD)
What is the maximum datarate that can be achieved under very good signal conditions in a 20-MHz carrier?
Beyond 100 Mbit/s
Study Notes
Evolution of Mobile Networks
- 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).
Limitations of UMTS
- 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.
Improvements in LTE
- 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 Device Capabilities
- 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.
LTE Transmission Modes
- 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.
Learn about how LTE overcomes multipath fading with a different air interface involving Orthogonal Frequency Division Multiplexing (OFDM) in telecommunications.
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