HSIC (Hybrid Self Interference Cancellation)

Hybrid Self Interference Cancellation (HSIC) is a technology used in wireless communication systems to cancel the self-interference between the transmitted and received signals in full-duplex communication. In a full-duplex communication system, both transmission and reception happen simultaneously on the same frequency. Therefore, it is crucial to cancel the self-interference signal, which arises due to the transmitted signal being leaked into the receiver path. This self-interference can be several orders of magnitude stronger than the desired signal and severely limits the performance of the communication system. HSIC is one of the most promising techniques to overcome this problem.

In this article, we will discuss the working principle of HSIC, its advantages, and limitations, and its applications in wireless communication systems.

Working Principle of HSIC

HSIC is a hybrid approach that combines both analog and digital processing to cancel the self-interference signal. The analog processing is performed at the RF front-end, while the digital processing is performed at the baseband. The main idea behind HSIC is to use a self-interference cancellation (SIC) loop to generate an estimate of the self-interference signal, which is then subtracted from the received signal to cancel out the self-interference.

The SIC loop consists of two parts: an analog cancellation circuit and a digital cancellation filter. The analog cancellation circuit cancels out a portion of the self-interference signal by generating an estimate of the self-interference signal that is added back to the transmitted signal with a phase and amplitude adjustment. The analog cancellation circuit can be implemented using various techniques, such as the use of directional couplers or phase shifters.

The digital cancellation filter uses the estimated self-interference signal from the analog cancellation circuit to further cancel the self-interference signal. The digital cancellation filter can be implemented using various techniques, such as Finite Impulse Response (FIR) filters or Adaptive Filters. The digital cancellation filter can be trained to improve its performance over time.

The HSIC system can be implemented using different architectures, such as the hybrid RF-digital architecture or the RF self-interference cancellation (RF-SIC) architecture. In the hybrid RF-digital architecture, the analog cancellation circuit is located at the RF front-end, and the digital cancellation filter is located at the baseband. In the RF-SIC architecture, both the analog and digital cancellation circuits are located at the RF front-end.

Advantages of HSIC

HSIC has several advantages over other self-interference cancellation techniques, such as analog cancellation and digital cancellation.

One of the main advantages of HSIC is its ability to cancel out the self-interference signal in real-time. This is important for full-duplex communication systems, where the self-interference signal can be several orders of magnitude stronger than the desired signal. Real-time cancellation of the self-interference signal enables the system to operate at a higher Signal-to-Interference-plus-Noise Ratio (SINR), which improves the performance of the communication system.

Another advantage of HSIC is its ability to cancel out the self-interference signal in a wide range of operating conditions. The analog cancellation circuit can cancel out a portion of the self-interference signal, while the digital cancellation filter can further cancel out the remaining self-interference signal. The digital cancellation filter can adapt to the changing operating conditions, such as changes in the channel conditions or the transmitted power, to improve the performance of the system.

HSIC also has a low power consumption compared to other self-interference cancellation techniques. This is because HSIC uses a hybrid approach that combines both analog and digital processing, which reduces the complexity of the system and the power consumption.

Limitations of HSIC

Despite its advantages, HSIC has several limitations that need to be addressed.

One of the main limitations of HSIC is its sensitivity to the phase and amplitude errors in the analog cancellation circuit. The accuracy of the estimated self-interference signal depends on the accuracy of the phase and amplitude adjustments in the analog cancellation circuit. Any errors in these adjustments can result in a degraded performance of the HSIC system.

Another limitation of HSIC is its complexity and cost. The hybrid approach of HSIC requires the implementation of both analog and digital processing, which increases the complexity and cost of the system. The implementation of the analog cancellation circuit also requires additional RF components, such as directional couplers or phase shifters, which further increases the cost of the system.

HSIC also requires a high-performance Analog-to-Digital Converter (ADC) and Digital-to-Analog Converter (DAC) to ensure the accuracy of the estimated self-interference signal and the cancellation filter. The high-performance ADC and DAC are expensive and can increase the power consumption of the system.

Applications of HSIC

HSIC has several applications in wireless communication systems, such as in cellular networks, Wi-Fi networks, and satellite communication systems.

In cellular networks, HSIC can be used to improve the performance of full-duplex communication systems, such as in LTE-Advanced Pro and 5G systems. HSIC can enable full-duplex communication in small cells and in-device relays, which can improve the capacity and coverage of the cellular network.

In Wi-Fi networks, HSIC can be used to enable simultaneous transmission and reception in the same frequency band, which can improve the throughput and efficiency of the network. HSIC can also enable the deployment of Wi-Fi networks in environments where interference is high, such as in dense urban areas.

In satellite communication systems, HSIC can be used to enable full-duplex communication between the ground station and the satellite. This can improve the capacity and efficiency of the satellite communication system and enable the deployment of new services, such as real-time video streaming and remote sensing.

Conclusion

HSIC is a promising technology for cancelling self-interference in full-duplex communication systems. HSIC uses a hybrid approach that combines both analog and digital processing to cancel out the self-interference signal. HSIC has several advantages over other self-interference cancellation techniques, such as real-time cancellation, wide operating range, and low power consumption. However, HSIC also has some limitations, such as sensitivity to phase and amplitude errors, complexity, and cost. HSIC has several applications in wireless communication systems, such as in cellular networks, Wi-Fi networks, and satellite communication systems.