ACIR (Adjacent Channel Interference Ratio)

Last updated on Feb 23, 2023

Introduction

Adjacent Channel Interference Ratio (ACIR) is a metric that is used to measure the ability of a radio receiver to reject interference from adjacent radio channels. In radio communication systems, different radio channels are assigned to different users, services or applications. However, these channels are not completely isolated from each other and there is always some level of interference between adjacent channels. This interference can result in degradation of the quality of the received signal, which can affect the overall performance of the communication system. Therefore, it is important to measure the ACIR of a radio receiver to ensure that it can effectively reject interference from adjacent channels.

Concept of ACIR

The concept of ACIR can be understood by considering the frequency spectrum of a radio communication system. The frequency spectrum is divided into several bands, with each band assigned to a different user or service. The width of each band is called the channel bandwidth, and it is usually expressed in terms of hertz (Hz). The channel bandwidth determines the maximum data rate that can be transmitted over the channel. However, the channel bandwidth is not completely isolated from adjacent channels, and there is always some level of interference between them.

Adjacent channel interference occurs when the energy from a signal in an adjacent channel spills over into the receiver's bandwidth. This can happen when the receiver is not able to completely reject the interference from the adjacent channel. The ACIR is a measure of the ability of the receiver to reject this interference. It is defined as the ratio of the power in the desired channel to the power in the adjacent channel, both measured at the input of the receiver.

ACIR is expressed in decibels (dB) and is a measure of the attenuation of the adjacent channel interference. A higher ACIR value indicates that the receiver can effectively reject interference from adjacent channels and is therefore better able to receive the desired signal.

Factors affecting ACIR

The ACIR of a radio receiver is affected by several factors, including the bandwidth of the adjacent channel, the frequency separation between the channels, the modulation scheme used in the channels, and the sensitivity of the receiver. These factors can be briefly described as follows:

Bandwidth of adjacent channel: The wider the bandwidth of the adjacent channel, the greater the amount of interference that can spill over into the desired channel. Therefore, a narrower bandwidth of the adjacent channel can improve the ACIR of the receiver.
Frequency separation between channels: The greater the frequency separation between adjacent channels, the lower the amount of interference that can spill over into the desired channel. Therefore, a larger frequency separation between channels can improve the ACIR of the receiver.
Modulation scheme: The modulation scheme used in the adjacent channels can also affect the ACIR of the receiver. For example, if the adjacent channel uses a modulation scheme that is more complex than the desired channel, it can result in a higher level of interference. Therefore, it is important to use compatible modulation schemes in adjacent channels.
Sensitivity of the receiver: The sensitivity of the receiver refers to its ability to detect weak signals. A more sensitive receiver can detect weaker signals and can therefore reject interference more effectively. Therefore, a more sensitive receiver can have a higher ACIR.

Measurement of ACIR

The ACIR of a radio receiver can be measured using specialized equipment, such as a signal generator and a spectrum analyzer. The measurement process involves transmitting a test signal at a specific frequency and power level in the adjacent channel, while simultaneously monitoring the power level of the received signal in the desired channel. The ACIR is then calculated as the ratio of the power level in the desired channel to the power level in the adjacent channel.

Applications of ACIR

The ACIR metric is used in various applications in the field of radio communication. One important application is in the design and testing of radio receivers. By measuring the ACIR of a receiver, designers can ensure that the receiver is able to effectively reject interference from adjacent channels and provide high-quality signal reception. This is especially important in crowded radio frequency environments where multiple channels are in use simultaneously.

Another application of ACIR is in the licensing and allocation of radio frequency spectrum. Governments and regulatory bodies use ACIR as a metric to ensure that radio communication systems do not interfere with each other. By setting minimum ACIR requirements for different radio services, regulatory bodies can ensure that adjacent channels are not affected by interference, which can result in reduced quality of service for users.

ACIR is also used in the development of communication standards, such as those used in cellular networks. Communication standards often define minimum ACIR requirements for radio receivers to ensure compatibility between different systems and devices.

Conclusion

Adjacent Channel Interference Ratio (ACIR) is a metric that is used to measure the ability of a radio receiver to reject interference from adjacent radio channels. The ACIR is a measure of the attenuation of the adjacent channel interference, expressed in decibels (dB). The ACIR of a receiver is affected by several factors, including the bandwidth of the adjacent channel, the frequency separation between the channels, the modulation scheme used in the channels, and the sensitivity of the receiver. ACIR is used in various applications in the field of radio communication, including receiver design, spectrum allocation, and communication standards development. By ensuring that radio receivers have a high ACIR, communication systems can provide high-quality signal reception and reduce the risk of interference from adjacent channels.