Mitigating interference and signal disruptions in wireless communication

Introduction

Wireless communication uses radio waves to transmit data between devices, providing convenience and flexibility in an increasingly connected world. Wireless communication systems' smooth and reliable operation is vital for various applications, including mobile phones, IoT devices, autonomous vehicles, and critical infrastructure like emergency services and military communications. Wireless communication is considered by many as the backbone of the modern world.

Advancements in communication come with accompanying challenges like random interference. Increased co-channel and adjacent channel interference results in dropped calls, slow data throughput, and signal latency. Interference also affects non-cellular networks such as public safety systems, air-traffic radar, and critical failures. An increasing number of intelligent evolutionary algorithms are under exploration to tackle these problems. This article will delve into mitigating Interference and Signal Disruptions in Wireless Communication.

Understanding interference in wireless communication

Interference is a phenomenon that modifies or disrupts a signal when it travels from the source to the destination via a channel. Interference also means an addition of unwanted signals to the desired signal. This disturbance may impede, debase, or limit the effectiveness of the channel. Interference can occur in any communication system and is unpredictable because of its randomness/uncertainty.

Figure 1: The concept of interference in communication systems

Types of interference in wireless communication

Co-channel interference (CCI) - Interference in wireless systems that transmit signals at the same frequency is called co-channel interference.
Adjacent channel interference (ACI) - Interference in wireless systems caused by adjacent frequency signals.
Electromagnetic interference - The electromagnetic signals emitted by various systems and devices interfere with the desired signals of wireless communication systems.
Sound interference - There can be constructive as well as destructive interference caused by sound waves in speakers and other sound-producing devices.
Light interference - Light waves can interfere with communication systems transmitting signals through other mediums.
Inter-carrier interference - In telecommunications, the orthogonal frequency-division multiplexing (OFDM) subcarriers lose orthogonality and cause intercarrier interference (ICI).
Inter symbol interference - The time delay in OFDM symbols traveling from the transmitting end to the receiving end results in the spreading out of OFDM symbols and they interfere with consecutive OFDM symbols.

Impact of interference on signal quality and reliability

Reduced signal quality: Interference disrupts data transmission, causing errors that necessitate the retransmission of data packets. Consequently, this process increases latency and diminishes the overall data transfer rate.
Latency amplification: Interference introduces delays that can significantly impact real-time applications, affecting the user experience in video conferencing, online gaming, and more.
Signal dropouts: This occurs when interference reaches a critical level, causing the signal to vanish completely. This unfortunate occurrence can lead to dropped calls and a disruption in data connectivity.

Techniques to mitigate interference in wireless communication /mitigation strategy

Zero forcing equaliser: This linear equaliser reduces inter symbol interference. Equaliser is a better filter alternative for channels with unknown characteristics to correct for Rayleigh fading-induced inter-symbol interference. The Rayleigh fading model yields a Rayleigh-distributed random variable for the channel response. An LTI filter with transfer function T(Y) is the linear equaliser circuit in this method. The equaliser outputs the original signal since the transfer function T(Y) is the channel impulse response's inverse. Zero Forcing Equaliser forces the inter-symbol interference component at the equaliser's output response to zero. Eye diagrams of the equaliser's input and output signals indicate that inter-symbol Interference is gone.

Conventional filtering: These filters handle interference outside the operation band well. However, they are ineffective against direct interference in the operation band. The figure below depicts how a standard filter passes in-band and out-of-band interference.

Figure 2: Receiver-chain interference representation. This method filters out-of-band interference but not in-band interference

Frequency hopping spread spectrum (FHSS): This approach bounces a narrow band signal to a new centre frequency or channels. The total operational bandwidth should be higher than the signal bandwidth because a signal can hop to many frequencies. Jammers must either cover the entire jumping band or focus on a few channels. If the jammer covers all hopping channels, the number of hops reduces its energy received. FHSS architecture can avoid jammers that are entirely concentrated on a few channels if their channels are known.

Direct sequence spread spectrum (DSSS) : This approach directly multiplies the narrowband transmitted signal by a wider-bandwidth spreading sequence. This distributes the transmitted signal over greater bandwidths. CDMA is an effective DSSS communication that provides strong spreading gain against interference with bandwidth similar to signals of interest. The conventional spread spectrum design at the digital baseband leaves the RF front end vulnerable to high-power in-band interference. This strategy must be implemented in RF for strong interference mitigation.

Transmit power and window control (TPWC): It reduces inter-user interference. In CDMA cellular packet systems, TPWC is proposed. Conventional transmit power management creates inter-user interference and reduces system capacity. Transmit Power and Window management (TPWC) solves these drawbacks. Flexible scheduling in packet-based data transfer is used. This method allows packet-based data transmission during transmit windows when the power needed to transmit the packet is less than a threshold. Thus, average transmitted power and inter-user interference decrease, but transmission delay increases. The transmit power reduction is calculated from simulations. The following method is for downlink systems but can be applied to uplink systems.

Channel allocation algorithm: Adjacent cells cause Co-channel interference in cognitive radio (CR) networks. The Channel Allocation Algorithm reduces CR network Co-channel interference. A cluster-based multi-cell CR network assumes no two cells can select the same channel simultaneously. Cells have orthogonal narrowband subcarriers. The desired data rate and degree of interference are evaluated while assigning resources to cells in a cluster. In this algorithm, the channels available at a cell are allocated to satisfy capacity, and then the cell with the highest necessary data rate and the least interfering channel is allocated. This approach assigns one channel per cell and subcarriers to secondary CR users. Allocating unused channels to another cluster reduces channel reallocation and is favourable. Simulation results demonstrate algorithm efficiency.

Electromagnetic shielding using chemical compounds: Electromagnetic shielding confines or stops electromagnetic energy. The shield material reflects radiation for EMI shielding. Metals are utilised for EMI shielding because free electrons interact with electromagnetic fields. Electroless plating coats devices with metal. EMI shielding also involves absorption. Chemical compounds include Barium ferrite adorned reduced graphene oxide nanocomposite, Carbon black, and silicone rubber mixes absorb microwaves and are lightweight, making them useful for reducing electromagnetic interference. These materials interact with the electromagnetic field via electric and magnetic dipoles. Devices are covered with chemical compounds. However, the studies do not specify which material to utilise at different frequencies.