Multi-cell Cooperation and interference Management

- Overview

Inter-cell interference (ICI) is a problem that affects the radio quality and throughput of cellular mobile communication systems. It can occur when neighboring cells use the same frequency resources, or when a user equipment (UE) moves away from a cell's center. 

ICI can cause issues for UEs at cell edges, where they may receive equally strong or weak signals from adjacent cells. This can make it difficult for the UE to receive downlink transmission. ICI can also increase as a UE moves away from a cell's center, as the received signal strength decreases and path-loss increases. 

To reduce ICI, technologies like Inter-Cell Interference Coordination (ICIC) can be used to coordinate transmissions between cells. ICIC can optimize the allocation of resources like frequency, power, or time to mitigate interference. 

Some techniques used in ICIC include:

• Frequency reuse: Using a higher reuse factor, like 3 or 7, can suppress ICI, but it can also reduce spectral efficiency.
• Fractional frequency reuse (FFR): Limiting transmissions in different parts of the cell edge to different parts of the spectrum channel.
• Interference randomization: Applying random scrambling or frequency hopping to randomize interference.

Please refer to the following for more information:

• Wikipedia: Inter-cell interference coordination

- Multi-cell Cooperation

Multi-cell cooperation, also known as coordinated multipoint (CoMP) transmission and reception, is a method to optimize resources across cells in wireless networks. It's considered an effective way to reduce interference and improve cellular system performance.

In CoMP systems, base stations (BSs) or evolved node Bs (eNBs) are grouped into clusters that work together. The eNBs in each cluster exchange information, process signals, and provide services to users jointly. For example, user equipment (UE) near the cell edge can be served by multiple base stations. The UE estimates channel state information (CSI) and sends it back to the BS. In a centralized architecture, a central unit uses this CSI feedback to schedule radio resources. In a distributed architecture, the cells exchange data and CSI over a signaling network.

The idea of CoMP is to evolve from the conventional single-cell multi-user system to a multi-cell multi-user system, so that the UEs close to the cell edge can be served by multiple base stations. In CoMP-enabled systems, the base stations (BS, also called evolved Node B – eNB) are grouped into cooperating set.

- Multi-cell Cooperation in 5G Networks

Multi-cell cooperation, also known as coordinated multipoint (CoMP) transmission and reception, is a method that helps 5G networks manage the growing demand for bandwidth and the increasing number of users. 

CoMP allows multiple base stations to serve user equipment (UE) that are close to the cell edge, which helps reduce inter-cell interference (ICI). ICI occurs when different cells use the same spectrum at the same time.

In CoMP-enabled systems, base stations (BS) are grouped into cooperating sets, or clusters, and exchange information with each other. The BSs then work together to process signals and provide services to users. CoMP clustering can be static, dynamic, or semi-dynamic. Dynamic clustering can be further divided into network centric and user centric.

5G networks also use multi-connectivity, which allows users to simultaneously use component carriers from different network nodes, such as base stations and WiFi access points. 

5G NR also uses PDCP duplication on top of multi-connectivity to improve data transmission reliability and latency. This method takes advantage of the frequency, temporal, and spatial diversity that multiple cells on different carrier frequencies can offer.

- Multi-tier Cooperative Architecture

With the growing demand for high bandwidth and high spectral efficiency, inter-cell interference (ICI) is becoming more and more severe, and ICI management plays an increasingly important role in mobile cellular networks. Existing ICI management schemes (4G/LTE mobile communication systems) may not be strong enough for 5G, which faces extremely severe ICI due to its ultra-dense network (UDN) topology.

Existing cellular wireless networks (4G/LTE) are facing fundamental challenges due to the exponential demand of mobile data traffic, the need of higher data rates, user coverage, lowering latency, and minimizing signaling overhead. In order to address these challenges, future cellular networks will require adopting a multi-cell multi-tier cooperative architecture. 

However, in multi-cell cooperation, the user equipment (UE) needs to estimate the channel state information (CSI) and feed it back to the base station (BS) scheduler for adaptive resource management. This results in a significant increase of signaling overhead and feedback latency into the cooperative networks. These overhead and latency are the two key challenges to achieve gains in coordinated multi-point (CoMP) operation. 

- Inter-cell Interference Coordination in 5G Ultra-dense Networks

The exponential growth in demand for mobile broadband communications has resulted in dense deployments of cellular networks with aggressive frequency reuse patterns. Fifth-generation (5G) networks are expected to overcome capacity and throughput challenges by adopting a multi-layer architecture in which multiple low-power base stations (BSs) are deployed within the coverage area of a macrocell. Therefore, inter-cell interference (ICI) caused by simultaneous use of the same spectrum in different cells poses a serious problem.

ICI reduces system throughput and network capacity, and negatively impacts cell edge users and overall system performance. Therefore, effective interference coordination techniques are required, especially for user-to-cell association and resource allocation, to mitigate the severe impact of ICI on system performance in 5G heterogeneous networks (HetNet).

This is to improve the quality of service (QoS) and maximize the system throughput, which is caused by the deployment of small base station coverage on the macro base station in the heterogeneous cellular network, which will be due to the different transmit power of different base stations in the downlink. As a result, the traffic load is unbalanced.

With the advancement of information and computer technology, the envisioned 5G wireless communication is expected to encompass unprecedented heterogeneous and ultra-dense communication environments. In-vehicle communication plays a vital role in 5G wireless networks and has been extensively studied in recent years due to its great potential in ensuring reliability and supporting smart transportation and various safety applications.

[More to come ...]