LTE Relay vs. LTE Repeater: Key Differences Explained

This article clarifies the differences between LTE relays and LTE repeaters, outlining their functionalities, advantages, and disadvantages. Understanding these distinctions is crucial for optimizing LTE network performance and coverage.

LTE Repeater: Simple Signal Amplification

An LTE repeater essentially acts as a power amplifier for the received signal from an LTE eNB (evolved NodeB, or base station). It amplifies this signal and retransmits it to UEs (User Equipments, i.e., mobile devices).

The problem with this approach is that it amplifies everything, including noise. Consequently, the Signal-to-Noise Ratio (SNR) doesn’t improve and can even degrade due to the amplification of noise along with the signal. This limits the effectiveness of repeaters in areas with weak signals or high noise levels.

Figure 1 (described as depicting LTE repeater operations, but missing from the provided text) illustrates this process. The repeater simply boosts the existing signal, whether it’s good or bad.

LTE Relay: Intelligent Signal Processing

An LTE relay, particularly LTE relay type-1, is a more sophisticated device than a repeater. It not only amplifies the signal but also incorporates Forward Error Correction (FEC) functionality. This makes it a more intelligent solution for extending LTE coverage.

Figure 2 (missing from the provided text but described as showing LTE relay type-1 basics) outlines the following steps:

• RF signal down conversion (RF to baseband): Converts the radio frequency signal to a baseband signal for processing.
• Demodulation and decoding (FEC decoder): Extracts the data from the signal and corrects errors using FEC.
• Modulation and encoding (FEC encoder): Encodes and modulates the corrected data for retransmission.
• RF signal up conversion (baseband to RF): Converts the baseband signal back to a radio frequency signal.
• RF Power Amplification: Amplifies the RF signal for transmission.

By decoding and re-encoding the signal, the LTE relay significantly reduces errors. This leads to an improved SNR compared to a repeater. As a result, LTE relays can be deployed at the cell edge, where signals are weak and noisy.

LTE relays support both half-duplex and full-duplex modes, as well as in-band and out-band signaling modes.

LTE Relay Type-2: Data Regeneration

LTE relay type-2 (depicted in Figure 3, but the figure itself is missing from the provided text) is similar to type-1 but includes additional processing steps:

• Data regeneration processing: After decoding, the data is regenerated to further improve signal quality.
• Data transmission processing: Processing occurs before encoding and modulation to optimize transmission.

In essence, Type-2 goes a step further in cleaning up the data before retransmission.

Key Differences Summarized

The table below highlights the functional differences:

A key advantage of both LTE repeaters and LTE relays over a traditional LTE Base Station (eNB) is that they do not require backbone connectivity to relay the signal back to UEs. This makes them easier and cheaper to deploy in certain situations.

LTE Relay Type-1 Details

An LTE relay Type-1 cell operates with its own unique physical cell ID. It transmits its own synchronization channels and reference symbols, distinct from the donor cell (the main LTE eNB).

UEs receive scheduling information and HARQ (Hybrid Automatic Repeat Request) feedback directly from the relay node and transmit their control channels (SR, CQI, ACK, etc.) to the relay node.

LTE Relay Type-2 Details

LTE relay Type-2 does not have a separate Physical Cell ID and doesn’t create new cells. It can transmit PDSCH (Physical Downlink Shared Channel) but cannot transmit CRS (Cell-specific Reference Signals) or PDCCH (Physical Downlink Control Channel). This makes it less visible to the network compared to a Type-1 relay.

Conclusion

While both LTE repeaters and relays aim to extend coverage, LTE relays offer superior performance due to their signal processing capabilities. By understanding these differences, network engineers can select the optimal solution for specific deployment scenarios.