adjacent channel interference (ACI)

Understanding Adjacent Channel Interference (ACI) in Electrical Systems

Adjacent channel interference (ACI) is a common issue in wireless communication systems, particularly those using frequency division duplex (FDD). It occurs when the signal from an adjacent frequency band interferes with the desired signal, impacting its quality and reliability. This interference can be categorized as either in-band or out-of-band ACI, depending on the relationship between the interfering signal's center frequency and the desired signal's bandwidth.

In-band ACI arises when the center frequency of the interfering signal falls within the bandwidth of the desired signal. This means the interfering signal directly overlaps with the desired signal, causing significant disruption and degradation. Imagine two radio stations broadcasting on adjacent frequencies. If the signals bleed into each other, the listener on one frequency might hear both broadcasts, making it difficult to distinguish the desired information.

Out-of-band ACI, on the other hand, occurs when the center frequency of the interfering signal lies outside the bandwidth of the desired signal. However, the interfering signal's energy can still spill over into the desired signal's bandwidth due to factors like imperfect filtering or non-ideal transmitter characteristics. While less severe than in-band ACI, out-of-band interference can still introduce noise and distortions, affecting the quality of the received signal.

Causes and Mitigation of ACI:

Several factors can contribute to ACI, including:

• Limited channel spacing: In systems with high frequency reuse, the channels are close together, increasing the chance of interference.
• Non-ideal filtering: Imperfect filters in transmitters and receivers allow signal energy to leak into adjacent channels.
• Nonlinear amplification: Non-linear amplifiers can generate spurious frequencies that can interfere with other channels.
• Inter-modulation distortion: When multiple signals combine in a non-linear system, new frequencies can be generated, leading to interference.

Mitigating ACI is crucial for ensuring reliable communication. Several techniques are employed:

• Frequency planning: Carefully choosing frequency assignments to minimize the possibility of interference.
• Improved filtering: Using better filters in transmitters and receivers to reduce out-of-band emissions.
• Adaptive equalization: Employing algorithms to compensate for the effects of ACI on the received signal.
• Power control: Adjusting the power levels of transmitters to minimize interference to adjacent channels.

Understanding and addressing ACI is crucial for achieving high-quality wireless communication in modern systems. By employing appropriate mitigation techniques, engineers can minimize the impact of interference and ensure seamless and reliable data transmission.