What is the difference between 5G NR and 4G LTE?
The studies of 5G NR (New Radio) in 3GPP started in 2015 and later became the first NR specifications in Release 15 in 2018 focusing on the use cases eMBB (enhanced Mobile Broadband) and URLLC (Ultra-Reliable and Low Latency Communication). For the third IMT-2020 use case mMTC (massive Machine Type Communication), there is already a well-defined LTE standard in form of NB-IoT. The NR carrier is also designed to support overlapping LTE based mMTC as well as sidelink communication (in Release 16) supporting direct communication between devices such as vehicle to vehicle (V2V) in- and out-of-network and communication between various wearables.
4G LTE radio was introduced in 2009 and has after that evolved to offer higher data rates and spectrum efficiency as well as support for low-cost devices with very long battery life time for machine type communication such as different types of sensors. LTE has also reduced the air-interface latency. In particular, the TTI (transmission time interval) reduction enables shorter channel state information and hybrid automatic repeat request (HARQ) feedback times, thereby leading to a more accurate rate control which results in a more efficient use of air interface resources and a higher perceived user throughput and system capacity. The evolution of LTE will be able to further support 5G use cases and makes LTE an integral part of the 5G radio access solution.
However, NR has a radio structure that makes it compatible with LTE but better prepared for future technology solutions and use cases such as higher spectral efficiency, traffic capacity and shorter user plane latency.
Unlike LTE, NR is band-agnostic and in R15 supports mm-wave frequencies up to 52,6 GHz enabling high traffic capacity and eMBB. The drawback of high frequency bands is however higher radio channel attenuation with less coverage. Though this can partly be compensated for with multi-antenna transmission and beamforming, lower frequency transmission for coverage will still be important in 5G.
Mobile communication networks rely on downlink transmission for cell detection, broadcast of system information and channel estimation. This always-on transmission impacts the limit of network energy performance and can cause interference to other cells, especially in a dense 5G network. Therefore an ultra-lean design principle is used in NR where e.g. reference signals only are present when data are transmitted. Unlike LTE, NR does not include cell-specific reference signals but instead it relies on user-specific demodulation reference signals for channel estimation which also supports beamforming and multi-antenna transmission.
Another feature in NR is that rather than being backward compatible, NR is forward compatible by maximizing the amount of time and frequency resources left blank for future new types of transmission. NR supports a flexible OFDM numerology with subcarrier spacing from 15 kHz up to 240 kHz and a scalable TTI to support low latency transmission. But NR also supports a “mini-slot” with a transmission over a fraction of a slot for immediate transmission of data for URLLC. This “mini-slot” is also helpful in unlicensed spectrum where the transmitter must ensure that the radio channel is not occupied by another transmission since the transmission can start immediately without waiting for the start of a slot.
Low-latency support in NR is also supported by redesigning MAC (Medium Access Control) and RLC (Radio Link Control) protocols to enable processing without knowing the amount of data to transmit. NR RLC does not support in-sequence delivery to reduce delays since packets do not have to wait for retransmission of an earlier missing packet before being delivered to higher layers.
Both LTE and NR uses OFDM as the waveform due to its ease of exploiting the time and frequency domains. But unlike LTE, which only uses DFT-precoded OFDM in the uplink which forms single-carrier signals and thus generates lower power consumption, the NR also uses non-DFT-precoded OFDM to support same transmission schemes in both uplink and downlink.
NR also supports receiver-bandwidth adaptation to reduce the receiver device energy consumption and a small bandwidth to monitor control channels and receive data and to only open up a wideband receiver to support very high data rates.
In LTE two different frame structures, FDD and TDD are used, while in NR the frame structure supports both half-duplex and full-duplex such as TDD and FDD.
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Until next time,
The Apis IP-Solutions Team