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ACI (Adjacent carrier interference)

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Adjacent carrier interference (ACI) is a common phenomenon in wireless communication systems where the signal from a carrier interferes with the signal from an adjacent carrier. ACI is one of the most significant sources of interference in radio communication, and it can degrade the quality of a wireless signal, causing errors, signal distortion, and even complete loss of signal. In this article, we will discuss the causes of ACI, its impact on wireless communication systems, and methods to mitigate ACI.

Causes of ACI

ACI is caused by the non-linearity of the radio frequency (RF) components in a wireless communication system. Non-linear components do not respond linearly to the input signal, which causes them to generate harmonics and intermodulation products. Harmonics are frequencies that are multiples of the original frequency, while intermodulation products are frequencies that are generated by the mixing of two or more frequencies.

In a wireless communication system, adjacent carriers are separated by a frequency spacing, also known as the channel spacing. The channel spacing is determined by the regulatory body that governs the use of the radio spectrum, and it is typically set to be large enough to prevent interference between adjacent carriers. However, when a non-linear component in the system generates a harmonic or an intermodulation product that falls within the channel spacing of an adjacent carrier, it can cause interference, which is referred to as ACI.

The impact of ACI on wireless communication systems

ACI can significantly degrade the performance of a wireless communication system, leading to reduced throughput, lower data rates, and poor quality of service. The impact of ACI depends on several factors, including the magnitude of the interference, the frequency spacing between the interfering and interfered carriers, and the sensitivity of the receiver to interference.

In a wireless communication system, the receiver is typically more susceptible to interference than the transmitter, as it is responsible for extracting the useful information from the received signal. If the interference caused by ACI is significant, the receiver may be unable to extract the information from the received signal, resulting in errors and loss of data. This can be particularly problematic in wireless systems that require high data rates and low error rates, such as mobile broadband and video streaming.

Methods to mitigate

ACI There are several methods to mitigate ACI in wireless communication systems. These methods can be classified into two categories: pre-processing techniques and post-processing techniques.

Pre-processing techniques aim to reduce the level of interference before it enters the receiver. The most common pre-processing techniques include:

  1. Filtering: Filters are used to remove unwanted frequencies from the signal before it enters the receiver. Filters can be implemented in the transmitter, the receiver, or both.
  2. Frequency planning: Frequency planning is the process of allocating frequency bands to different carriers in a way that minimizes interference. Frequency planning can be done by the system designer or by the regulatory body that governs the use of the radio spectrum.
  3. Power control: Power control is the process of adjusting the transmission power of the transmitter to minimize interference. Power control can be implemented at the system level or at the user level.

Post-processing techniques aim to reduce the impact of interference after it has entered the receiver. The most common post-processing techniques include:

  1. Equalization: Equalization is the process of compensating for the distortion caused by ACI. Equalization can be implemented in the receiver using digital signal processing techniques.
  2. Interference cancellation: Interference cancellation is the process of removing the interference from the received signal. Interference cancellation can be implemented using adaptive filtering techniques.
  3. Diversity techniques: Diversity techniques involve using multiple antennas or multiple channels to improve the signal-to-noise ratio and reduce the impact of interference.

Conclusion

ACI is a common phenomenon in wireless communication systems, and it can significantly degrade the performance of the system. ACI is caused by the non-linearity of RF components in the system, which generates harmonics and intermodulation products that interfere with adjacent carriers.

To mitigate ACI, there are several pre-processing and post-processing techniques that can be employed. Pre-processing techniques aim to reduce the level of interference before it enters the receiver, while post-processing techniques aim to reduce the impact of interference after it has entered the receiver. These techniques include filtering, frequency planning, power control, equalization, interference cancellation, and diversity techniques.

In addition to these techniques, there are other measures that can be taken to reduce the impact of ACI. These measures include using narrowband channels, increasing the channel spacing between adjacent carriers, improving the linearity of RF components, and using advanced modulation techniques that are more robust to interference.

In conclusion, ACI is a significant source of interference in wireless communication systems, and it can have a significant impact on the performance of the system. However, there are several techniques and measures that can be employed to mitigate ACI and improve the performance of the system. By carefully designing and implementing these techniques and measures, it is possible to minimize the impact of ACI and ensure reliable and high-quality wireless communication.