Uplink CoMP under a Constrained Backhaul and Imperfect Channel Knowledge (1002.3356v1)

Abstract: Coordinated Multi-Point (CoMP) is known to be a key technology for next generation mobile communications systems, as it allows to overcome the burden of inter-cell interference. Especially in the uplink, it is likely that interference exploitation schemes will be used in the near future, as they can be used with legacy terminals and require no or little changes in standardization. Major drawbacks, however, are the extent of additional backhaul infrastructure needed, and the sensitivity to imperfect channel knowledge. This paper jointly addresses both issues in a new framework incorporating a multitude of proposed theoretical uplink CoMP concepts, which are then put into perspective with practical CoMP algorithms. This comprehensive analysis provides new insight into the potential usage of uplink CoMP in next generation wireless communications systems.

• The paper provides a framework and numerical analysis of uplink CoMP strategies, evaluating their performance and backhaul trade-offs under constrained backhaul and imperfect channel state information.
• It systematically evaluates CoMP strategies like DAS-C and DIS, revealing DAS-C's superiority in strong interference and assessing advanced coding benefits and complexity.
• Analysis shows CoMP gain increases with decreasing CSI quality at cell edges and highlights practical trade-offs between backhaul usage and performance gains.

Uplink CoMP under Constrained Backhaul and Imperfect Channel Knowledge

The paper contributes a thorough investigation into the practical and theoretical aspects of Coordinated Multi-Point (CoMP) transmission in uplink scenarios, focusing specifically on the challenges posed by constrained backhaul infrastructure and imperfect channel state information (CSI). CoMP technology is fundamental in advancing mobile communication systems by mitigating inter-cell interference, potentially enhancing spectral efficiency and fairness, particularly in urban environments where such interference is prevalent.

Key Contributions

The paper's primary offering is a framework that bridges various theoretical CoMP concepts with real-world algorithms, augmented by numerical insights to elucidate their applicability in next-generation wireless systems. This approach addresses two predominant obstacles in CoMP deployment: the demand for extensive backhaul and the detrimental effects of suboptimal CSI.

Analysis of Performance Trade-offs

The work systematically evaluates several CoMP strategies, including Distributed Interference Subtraction (DIS), Compressed Interference Forwarding (CIF), Distributed Antenna Systems with both centralized (DAS-C) and decentralized decoding (DAS-D), across different scenarios characterized by UE locations. Such evaluations reveal valuable insights into these strategies' rate-backhaul trade-offs, identifying DAS-C as notably superior in scenarios of strong interference due to its centralized approach.

Additionally, the paper critically examines the potential benefits and complexity issues related to advanced coding techniques like Wyner-Ziv and Slepian-Wolf source coding and superposition coding (SPC). While source coding appears to offer substantial gains in specific interference scenarios, SPC generally manifests minor benefits, questioning its pragmatic utilization considering the added complexity.

Impact of Imperfect CSI

An interesting revelation is that the relative gain of CoMP at the cell-edge increases with decreasing CSI quality—a consequence of the array gain, which allows the system to capitalize more effectively on estimated channels when interference is significant. Conversely, towards the cell-center, CoMP's efficacy diminishes due to the challenge of estimating weaker interference links accurately.

Practical Considerations

The paper emphasizes the trade-off inherent in CoMP strategies between efficient backhaul usage and achieving maximal performance gains. It compares the theoretical concepts with practical algorithms and posits that while iterative BS cooperation may be marginally beneficial, the complexity introduced may not justify its implementation. Also highlighted is the significance of distributional requirements of CSI, which can affect the practicality of implementing certain CoMP strategies.

Future Directions

The investigation suggests further research into hybrid schemes combining aspects of DIS and DAS-C to achieve optimal performance across varying interference scenarios, particularly focusing on enhancing adaptability and addressing the practical challenges related to CSI distribution and mitigating the latency and redundancy in iterative cooperation approaches.

In conclusion, the paper delivers a comprehensive exploration of uplink CoMP strategies, providing both theoretical insight and practical implications crucial for deploying advanced CoMP techniques in future mobile networks efficiently. The detailed analysis and proposed solutions offer a solid foundation for overcoming existing barriers to maximizing the potential of CoMP in enhancing wireless communication systems.