Which of the following statements are applicable to the technology of massive MIMO? (Select 3)

Massive MIMO (Multiple-Input Multiple-Output) is a key 5G technology that uses a large number of antennas at the base station. Its primary benefit is spatial multiplexing, which allows for the transmission of several independent data streams to different users simultaneously on the exact same frequency resources (A). This is enabled by precoding techniques that shape the transmitted signals, making the effective communication channels to different users nearly orthogonal, thus preventing the data streams from interfering with each other (B). While spatial multiplexing increases data rates in good conditions, massive MIMO systems can also employ transmit diversity in poor radio conditions. In this mode, the same data is sent across multiple antennas to improve signal reliability and robustness (D).

C. Sending data flows on different frequencies describes Frequency Division Multiplexing (FDM), not MIMO. The core advantage of MIMO is its ability to reuse the same frequency spectrum.

1. Larsson, E. G., Edfors, O., Tufvesson, F., & Marzetta, T. L. (2014). Massive MIMO for next generation wireless systems. IEEE Communications Magazine, 52(2), 186-195.

Section II-A, "Massive MIMO in a Nutshell," Paragraph 1: "The basic idea is to equip base stations (BSs) with a very large number of antennas... This enables the BS to serve many terminals simultaneously in the same time-frequency resource." (Supports Answer A).

Section II-B, "Favorable Propagation," Paragraph 1: "As the number of antennas at the BS, M, grows large, the channel vectors... to any pair of terminals become pairwise orthogonal." (Supports Answer B).

Section III-A, "Multiplexing and Diversity," Paragraph 1: Discusses the trade-off between spatial multiplexing gain and diversity gain, confirming that MIMO systems can be configured for either, with diversity being preferable for reliability. (Supports Answer D).

DOI: https://doi.org/10.1109/MCOM.2014.6736761

2. Nokia. (2020). 5G Technology Evolution. Nokia White Paper.

Page 10, Section "Massive MIMO": "Massive MIMO uses a large number of antenna elements... to create many individual beams to serve many users simultaneously within the same time and frequency resources." (Supports Answer A). The document further explains that this beamforming minimizes inter-user interference, which is a practical application of creating orthogonal channels. (Supports Answer B).

3. Tse, D., & Viswanath, P. (2005). Fundamentals of Wireless Communication. Cambridge University Press.

Chapter 7, "Spatial Multiplexing," Section 7.1, Page 292: "The basic idea of spatial multiplexing is to transmit independent data streams from the different transmit antennas simultaneously and in the same frequency band." (Supports Answer A).

Chapter 7, "Diversity," Section 7.2, Page 303: This section details how multiple antennas can be used for transmit diversity (e.g., Alamouti scheme) to combat fading and improve link reliability, especially in poor channel conditions. (Supports Answer D).