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LTE relay vs LTE repeater | difference between LTE relay and LTE repeater

This page LTE relay vs LTE repeater describes difference between LTE relay and LTE repeater. It mentions benefits of LTE relay over LTE base station(eNB) and mentions basics and types of LTE relay. LTE relay specifications are mentioned in LTE advanced 3GPP standard Rel.10 version.

LTE repeater

LTE repeater

LTE repeater does just power amplification of the received signal from LTE eNB or LTE Base Station. After amplification it transmits the signal back to the UEs(User Equipments) or Mobile Subscribers. Due to this received weak signal along with noise power also gets amplified. Due to this noise amplification, SNR(Signal to Noise Ratio) will not be improved and further gets degraded. LTE repeater operations have been depicted in figure-1.

LTE relay basics and types

LTE relay type1

LTE relay is different than LTE repeater as it not only does amplification but also incorporate FEC functionality. Following are the steps involved in LTE relay as shown in the figure-2. This is known as LTE relay type-1.
• RF signal down conversion (RF to baseband).
• Demodulation and decoding (FEC decoder)
• modulation and encoding (FEC encoder)
• RF signal up conversion (baseband to RF)
• RF Power Amplification

As LTE relay does amplification after decoding errors are reduced to great extent. Hence SNR will be improved compare to LTE repeater.

Due to this LTE relay can be used even at the edge of the cell boundry where signals are weak and more noisy compare to other cell areas. LTE relay supports half duplex and full duplex modes. It also supports inband and outband signaling modes.

LTE relay type2

The other type of relay is LTE relay type-2 as depicted in figure-3. Following are the operations involved in this type of relay. All the functionalities are similar to LTE relay type-1. In addition following two steps are added.
• After decoding, data regeneration processing is carried out.
• data transmission processing is carried out before it is encoded and modulated.

Following table summarizes the difference between features of all these LTE devices. The benefits of LTE repeater and LTE relay compare to LTE Base Station(i.e. eNB) is that backbone connectivity is not required unlike LTE Base Station before relaying the signal back to the UEs.

Feature LTE eNB LTE repeater LTE relay
SNR improvement Yes No Yes
Backbone connectivity Yes No No
FEC Encoding, decoding Yes No Yes
Modulation, Demodulation Yes No Yes
RF Amplification Yes Yes Yes

LTE relay Type-1

This type-1 relay cell will have physical cell ID of its own. It transmits its own unique sync. channels, ref. symbols etc. These parameters are different compare to donor cell i.e. main LTE eNB.

Here UE will receive scheduling information and HARQ feedback directly from relay node(i.e. LTE relay) and transmits its control channels to the relay node. Control channels include SR, CQI, ACK etc.

LTE relay Type-2

This relay node will not have separate Physical Cell ID. Hence it will not create any new cells. It has capability to transmit PDSCH but can not transmist CRS and PDCCH.

Refer basic function of repeater used in VHF, UHF and microwave communication.

LTE Related Links

LTE tutorial  LTE terminologies  LTE system basics  LTE UE categories  LTE Frequency Bands  EARFCN vs frequency   LTE frame structure  FDD LTE vs TDD LTE 

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