Load balancing and resource allocation in C-RAN

First part of our series of articles on our collaboration with Télécom SudParis about the architectures of cloud access networks.

The background

Current wireless networks have a flat topology whose performance is guaranteed only by the presence of macro cells using low frequencies bands between 700 MHz and 2.6 GHz. This architecture is very costly for the operators in terms deployment and operation of the base stations; since each one of them must have its own Baseband Processing unit and its own Backhaul fiber link to be connected to the core network. Another problem is the under-utilization of the resources in case where the user traffic in the macro cell is low.

With the increase of the data rates demands and the evolution of the type of services requested by the users, 4G and 5G wireless networks topology have to be much denser using different frequency bands (low, medium and high). This densification aims at meeting the various requirements of these emerging new services in terms of data rates, latency and reliability.

Cell frequency coverage

The medium and high bands (more than 3GHz), have a larger bandwidth and provide higher capacities but at the cost of coverage reduction. In order to achieve the desired coverage level, and respect the service continuity constraints, cells densification becomes mandatory to ensure coexistence of 2G, 3G, 4G and 5G cellular technologies. This may generate a high level of interference between neighboring cells (frequency reuse, harmonic interference, cross layer interference in TDD mode) and an increase of the number of handovers (intercells and interRAT).

C-RAN architectures

In order to address these issues, access networks have adopted new cloud architecture called C-RAN where the base station signal processing units, which were previously located at the station itself, are deported to the cloud in a centralized infrastructure called BBU pool. This centralization allows a better overview of all deployed macro and micro stations, for more efficient coordination of their signal processing, power control and interference management.

In this architecture, a base station is composed of two remote entities: RRH (Remote Radio Head) and BBU pool (BaseBand Unit) interconnected through an optical fiber link called Fronthaul.

Cloud-RAN architecture

The gains of this architecture are multiple:

  • Better spectral efficiency and better interference management
  • Network densification supporting massive MIMO
  • Significant cost savings, as only one signal processing element would be required for a large number of antennas

Issues and solutions

However, the problems of the interference management and resource allocation between the different users and cells in the C-RAN, must be addressed in a dynamic real time manner in order to ensure better performance. Thus, we are working with Telecom Sud Paris on a research project to overcome these issues and we have proposed:

  • Solutions for load balancing and dynamic resource allocation between neighboring cells while applying inter-cell interference cancellation techniques, namely: Inter-cell Interference Coordination (ICIC) and Coordinated Multipoints (CoMP).
  • A study of Fronthaul dimensioning and C-RAN capacity in terms of the number of aggregated RRHs for different functional splits levels allowing ICIC and CoMP mechanisms at the BBU pool while taking into account users’ end-to-end latency constraints.

The goal of this project is to ensure the rollout of denser C-RAN networks supporting a larger number of RRH that are dynamically managed to maximize network capacity while minimizing interference. Our strategy aims also at reducing network deployment costs (CAPEX) and operating costs (OPEX).

Contact: innovation@ davidson.fr

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