Massive MIMO performance evaluation based on measured propagation data (1403.3376v3)

Abstract: Massive MIMO, also known as very-large MIMO or large-scale antenna systems, is a new technique that potentially can offer large network capacities in multi-user scenarios. With a massive MIMO system, we consider the case where a base station equipped with a large number of antenna elements simultaneously serves multiple single-antenna users in the same time-frequency resource. So far, investigations are mostly based on theoretical channels with independent and identically distributed (i.i.d.) complex Gaussian coefficients, i.e., i.i.d. Rayleigh channels. Here, we investigate how massive MIMO performs in channels measured in real propagation environments. Channel measurements were performed at 2.6 GHz using a virtual uniform linear array (ULA) which has a physically large aperture, and a practical uniform cylindrical array (UCA) which is more compact in size, both having 128 antenna ports. Based on measurement data, we illustrate channel behavior of massive MIMO in three representative propagation conditions, and evaluate the corresponding performance. The investigation shows that the measured channels, for both array types, allow us to achieve performance close to that in i.i.d. Rayleigh channels. It is concluded that in real propagation environments we have characteristics that can allow for efficient use of massive MIMO, i.e., the theoretical advantages of this new technology can also be harvested in real channels.

• The paper demonstrates that increasing antenna counts significantly improve channel orthogonality by reducing the singular value spread in measured Massive MIMO systems.
• The research employs practical ULA and UCA measurements at 2.6 GHz to compare LOS and NLOS propagation, validating theoretical sum-rate capacity predictions.
• The findings highlight Massive MIMO's potential for high-capacity communications and offer practical insights for optimizing array structures in real-world networks.

Evaluation of Massive MIMO Performance with Measured Propagation Data

The paper explores the real-world performance of Massive MIMO systems, which are critical to enhancing network capacities in multi-user scenarios. By equipping base stations with a large number of antennas, Massive MIMO can simultaneously serve multiple single-antenna users in the same time-frequency resource. Prior studies largely relied on theoretical channels with i.i.d. complex Gaussian coefficients. This research aims to bridge the gap between theory and practice by evaluating Massive MIMO using channels measured in real propagation environments.

Methodology and Measurements

Channel measurements were conducted at 2.6 GHz using two distinct array types with 128 ports each: a virtual uniform linear array (ULA) and a practical uniform cylindrical array (UCA). The paper offers a comprehensive examination of channel behavior across various propagation conditions: line-of-sight (LOS), non-line-of-sight (NLOS), and scenarios where users are spaced far apart.

Numerical Evaluation and Results

The research analyzes performance using metrics like singular value spread and sum-rate capacity achieved through dirty-paper coding (DPC). Key findings include:

• Singular Value Spreads: There is a noticeable decline in the singular value spread as the number of antennas increases, indicating improved orthogonality among user channels. This enhancement is vital for efficient spatial separation of signals.
• Sum-Rate Capacities: Despite the challenging propagation conditions, such as closely placed users with LOS, the ULA and UCA demonstrate the potential to achieve a significant portion of the capacity predicted by i.i.d. Rayleigh channels. In NLOS and distributed user scenarios, the performance closely aligns with theoretical predictions.

Array Structures and Their Implications

The ULA, with its expansive aperture, offers superior angular resolution compared to the UCA, leading to better user channel decorrelation. Nonetheless, in environments where users are widely distributed, the UCA's compact design still capitalizes on its structural properties to yield competent performance.

Conclusion and Implications

The paper concludes that Massive MIMO's theoretical advantages can be operationalized in real-world environments. As antenna numbers grow, the system gains better user orthogonality and channel stability, crucial for reliable high-capacity communications.

Speculations for Future Developments

This research sets a foundation for exploring practical implementations of Massive MIMO. With advancements in low-cost hardware enabling large antenna deployments, future work can delve into optimizing array structures, accounting for mutual coupling, and addressing hardware imperfections.

The implications for AI and network infrastructure are significant, promising robust, high-efficiency communication systems capable of supporting the ever-growing demands of wireless services. Moving forward, the integration of these findings into practical standards and equipment will be pivotal.