Understanding Repeater Types: WiFi, LTE, Satellite, and More

We will explore repeater types used in wireless communication and networking systems, including WiFi repeaters, microwave repeaters, satellite repeaters, LTE repeaters, and optical repeaters. We will also differentiate between repeaters and amplifiers and discuss the advantages and disadvantages of using repeaters.

Introduction

As we know, every communication system has a limit on the distance it can transmit information. The coverage distance depends on the modules used at the transmitter side, such as the modulation scheme, amplifier, and data format of the signal. To increase the communication distance of a system, repeaters are used.

What is a Repeater?

• A repeater is a device that receives a signal and retransmits it after amplification.
• It may or may not perform frequency conversion before retransmission, depending on the application.
• It usually consists of a receiver, amplifier, frequency converter, and transmitter.
• In some systems, repeaters also perform baud rate conversion before retransmission.
• Repeaters are used for both wired mediums (e.g., telephone lines, fiber optic cables) and wireless mediums (e.g., satellite, microwave, WiFi, LTE).

Types of Repeaters in Networking and Wireless Communication Systems

Based on the data type they handle, repeaters are mainly divided into two types:

Analog Repeater

• Amplifies analog signals to boost their amplitude.
• Typically used in trunking systems that employ FDM multiplexers, which use multiple analog signals in the form of current or voltage. These signals can attenuate over the transmission medium.
• Consists of a linear amplifier and filters.

Digital Repeater or Digipeater

• Amplifies digital signals to compensate for losses over the medium.
• Digital signals can be in any binary format, such as NRZ, RZ, etc.
• Also known as a “Digipeater.”
• Aids in pulse reshaping, demodulation, decoding, and re-synchronization at the receiver end.

Let’s explore repeater types based on the technologies they serve, such as telephone lines, fiber optics, microwave links, satellite links, WLAN networks, LTE networks, and so on.

Microwave Repeater

In a microwave link, repeaters are used between the transmitting and receiving stations. Depending on the distance between them, there may be one or multiple repeater stations in between.

These repeaters use sensitive receivers, high-power transmitters, and high-mounted antennas. They are very effective at increasing the communication range of a microwave link.

In microwave relay stations, a repeater picks up the signal at one frequency, amplifies it, and retransmits it on another frequency to the next repeater in the chain. This process is repeated across a string of repeater stations to relay signals over greater distances. The distance between two repeater stations is usually 20 to 60 miles, and the antennas are mounted at very high altitudes.

Satellite Repeater

As we know, communication satellites are located about 36,000 km (22,369 miles) above the ground. Hence, repeaters used in satellites cover greater distances.

A satellite repeater receives the uplink signal from the ground, amplifies it, and performs frequency conversion to an appropriate downlink frequency before retransmitting it back to Earth.

It serves as a relay station in space, facilitating communication between two or more distant locations on Earth. The three functional modules—receiver, amplifier, and transmitter—are combined into one unit called a transponder in the satellite domain.

For example, a C-band satellite receives at 6 GHz and transmits at 4 GHz, using down conversion with a suitable LO (Local Oscillator) of 2225 MHz.

The main purpose of a satellite repeater is to extend the range and coverage of communication signals, helping to establish communication links over long distances, including across oceans, remote areas, and even between different continents. Satellite repeaters are used for various applications, such as telecommunications, remote sensing, GPS, disaster management, military, and defense.

Satellite repeaters ensure that signals remain strong and clear during their journey from the Earth to space and back.

WiFi Repeater | WLAN Repeater

A WiFi repeater is based on the IEEE 802.11 a/b/g/n standard.

It extends the coverage range supported by a WiFi router to a larger region, usually between two rooms.

WiFi repeaters operate either in the 2.4 GHz or 5 GHz band, as supported by the WLAN standard.

The 2.4 GHz band supports 14 frequency channels spaced at 5MHz apart. A WiFi router operating at 2.4 GHz receives a signal at one channel frequency (e.g., 2412 MHz) and transmits it on another channel frequency (e.g., 2422 MHz) after necessary amplification, as per the designed specification.

LTE Repeater

As shown in the figure, an LTE repeater receives a signal from an LTE eNB (e.g., base station) and re-transmits it after amplification towards UEs. Because it amplifies noise along with the signal, the SNR degrades.

As a result, an LTE relay is used, which has FEC (Forward Error Correction) functionalities in addition to amplification, helping to maintain the SNR.

Optical Repeater

Optical repeaters are used in fiber optic communication systems.

They receive optical signals in electrical form and perform reshaping and amplification operations before retransmission.

Because of the signal reconstruction before amplification, the signal is less distorted.

Difference between Repeater and Amplifier

Let’s understand the difference between a repeater and an amplifier:

• Amplifier: Amplifies the input signal to boost its amplitude on the same frequency. It does not involve any frequency conversion.
• Repeater: Amplifies the input signal and performs frequency conversion before retransmission. This means a repeater consists of an amplifier and a frequency converter.

Advantages and Disadvantages of Repeaters

Advantages

• Extends the distance typically covered by a wired or wireless medium.
• Does not affect network performance by performing its task on the signal appropriately.
• Repeaters are available that can use different mediums for reception and transmission.
• Does not increase or decrease network traffic.

Disadvantages

• It’s not possible to connect different network architectures using a repeater. A router or gateway is needed for this.
• The number of repeaters that can be used is limited between two endpoints. More repeaters can introduce noise, leading to packet collisions or problems in packet detection at the receiver.
• Repeaters do not perform segmentation of the network.
• Repeaters do not perform filtering of the data.

Conclusion

By amplifying and retransmitting signals, repeaters address challenges posed by signal attenuation, interference, and obstacles, resulting in improved wired and wireless connectivity and better user experiences.

Repeaters of various technologies and standards ensure seamless wireless communication and enable networking between various devices and systems.