Overview of Full-Dimension MIMO in LTE-Advanced Pro
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paper_title: Noncooperative Cellular Wireless with Unlimited Numbers of Base Station Antennas

paper_content:

A cellular base station serves a multiplicity of single-antenna terminals over the same time-frequency interval. Time-division duplex operation combined with reverse-link pilots enables the base station to estimate the reciprocal forward- and reverse-link channels. The conjugate-transpose of the channel estimates are used as a linear precoder and combiner respectively on the forward and reverse links. Propagation, unknown to both terminals and base station, comprises fast fading, log-normal shadow fading, and geometric attenuation. In the limit of an infinite number of antennas a complete multi-cellular analysis, which accounts for inter-cellular interference and the overhead and errors associated with channel-state information, yields a number of mathematically exact conclusions and points to a desirable direction towards which cellular wireless could evolve. In particular the effects of uncorrelated noise and fast fading vanish, throughput and the number of terminals are independent of the size of the cells, spectral efficiency is independent of bandwidth, and the required transmitted energy per bit vanishes. The only remaining impairment is inter-cellular interference caused by re-use of the pilot sequences in other cells (pilot contamination) which does not vanish with unlimited number of antennas.
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paper_title: Full-dimension MIMO (FD-MIMO) for next generation cellular technology

paper_content:

This article considers a practical implementation of massive MIMO systems [1]. Although the best performance can be achieved when a large number of active antennas are placed only in the horizontal domain, BS form factor limitation often makes horizontal array placement infeasible. To cope with this limitation, this article introduces full-dimension MIMO (FD-MIMO) cellular wireless communication system, where active antennas are placed in a 2D grid at BSs. For analysis of the FD-MIMO systems, a 3D spatial channel model is introduced, on which system-level simulations are conducted. The simulation results show that the proposed FD-MIMO system with 32 antenna ports achieves 2-3.6 times cell average throughput gain and 1.5-5 times cell edge throughput gain compared to the 4G LTE system of two antenna ports at the BS.
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paper_title: Full dimension mimo (FD-MIMO): the next evolution of MIMO in LTE systems

paper_content:

Full dimension MIMO has attracted significant attention in the wireless industry and academia in the past few years as a candidate technology for the next generation evolution toward beyond fourth generation and fifth generation cellular systems. FD-MIMO utilizes a large number of antennas placed in a 2D antenna array panel for realizing spatially separated transmission links to a large number of mobile stations. The arrangement of these antennas on a 2D panel allows the extension of spatial separation to the elevation domain as well as the traditional azimuth domain. This article discusses features and performance benefits of FD-MIMO along with the ongoing standardization efforts in 3GPP to incorporate FD-MIMO features in the next evolution of LTE. Furthermore, a design of a 2D antenna array, which plays a key role in the implementation of FD-MIMO, is also discussed. Finally, in order to demonstrate the performance benefits of FD-MIMO, system-level evaluation results are provided.
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paper_title: Field trial and future enhancements for TDD massive MIMO networks

paper_content:

Massive MIMO is one of the promising techniques to improve the spectral efficiency and network performance in future 5G networks. Compared to FDD, it is relatively easier to realize downlink massive MIMO for TDD as downlink channel information can be obtained via uplink-downlink channel reciprocity. This paper provides our field test results of massive MIMO system with a base station prototype equipped with 64 transmit antennas. Significant throughput gain is observed by performing 3D-beamforming to current LTE-Advanced handsets by using standard-transparent Multiuser(MU) MIMO techniques. With the massive MIMO base station prototype, MU-MIMO is realized by multiplexing maximum of eight handsets in spatial domain considering both azimuth and elevation directions. In addition to the field trial test results, future potential enhancements for TDD massive MIMO system are discussed. Evaluation results of evaluating some enhancements on uplink reference signal are provided.
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paper_title: Noncooperative Cellular Wireless with Unlimited Numbers of Base Station Antennas

paper_content:

A cellular base station serves a multiplicity of single-antenna terminals over the same time-frequency interval. Time-division duplex operation combined with reverse-link pilots enables the base station to estimate the reciprocal forward- and reverse-link channels. The conjugate-transpose of the channel estimates are used as a linear precoder and combiner respectively on the forward and reverse links. Propagation, unknown to both terminals and base station, comprises fast fading, log-normal shadow fading, and geometric attenuation. In the limit of an infinite number of antennas a complete multi-cellular analysis, which accounts for inter-cellular interference and the overhead and errors associated with channel-state information, yields a number of mathematically exact conclusions and points to a desirable direction towards which cellular wireless could evolve. In particular the effects of uncorrelated noise and fast fading vanish, throughput and the number of terminals are independent of the size of the cells, spectral efficiency is independent of bandwidth, and the required transmitted energy per bit vanishes. The only remaining impairment is inter-cellular interference caused by re-use of the pilot sequences in other cells (pilot contamination) which does not vanish with unlimited number of antennas.
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paper_title: A Leakage-Based Precoding Scheme for Downlink Multi-User MIMO Channels

paper_content:

In multiuser MIMO downlink communications, it is necessary to design precoding schemes that are able to suppress co-channel interference. This paper proposes designing precoders by maximizing the so-called signal-to-leakage-and-noise ratio (SLNR) for all users simultaneously. The presentation considers communications with both single- and multi-stream cases, as well as MIMO systems that employ Alamouti coding. The effect of channel estimation errors on system performance is also studied. Compared with zero-forcing solutions, the proposed method does not impose a condition on the relation between the number of transmit and receive antennas, and it also avoids noise enhancement. Simulations illustrate the performance of the scheme
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paper_title: MIMO broadcast channels with finite rate feedback

paper_content:

Multiple transmit antennas in a downlink channel can provide tremendous capacity (i.e. multiplexing) gains, even when receivers have only single antennas. However, receiver and transmitter channel state information is generally required. In this paper, a system where the receiver has perfect channel knowledge, but the transmitter only receives quantized information regarding the channel instantiation is analyzed. Simple expressions for the capacity degradation due to finite rate feedback as well as the required increases in feedback load per mobile as a function of the number of access point antennas and the system SNR are provided.
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paper_title: Antenna Grouping based Feedback Compression for FDD-based Massive MIMO Systems

paper_content:

Recent works on massive multiple-input multiple-output (MIMO) have shown that a potential breakthrough in capacity gains can be achieved by deploying a very large number of antennas at the base station. In order to achieve the performance that massive MIMO systems promise, accurate transmit-side channel state information (CSI) should be available at the base station. While transmit-side CSI can be obtained by employing channel reciprocity in time division duplexing (TDD) systems, explicit feedback of CSI from the user terminal to the base station is needed for frequency division duplexing (FDD) systems. In this paper, we propose an antenna grouping based feedback reduction technique for FDD-based massive MIMO systems. The proposed algorithm, dubbed antenna group beamforming (AGB), maps multiple correlated antenna elements to a single representative value using predesigned patterns. The proposed method modifies the feedback packet by introducing the concept of a header to select a suitable group pattern and a payload to quantize the reduced dimension channel vector. Simulation results show that the proposed method achieves significant feedback overhead reduction over conventional approach performing the vector quantization of whole channel vector under the same target sum rate requirement.
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Title: Overview of Full-Dimension MIMO in LTE-Advanced Pro

Section 1: Key Features of FD-MIMO Systems
Description 1: Discuss the key features of FD-MIMO systems, including a large number of basestation antennas, two dimensional active antenna array, 3D channel propagation, and new pilot transmission with CSI feedback.

Section 2: Increase the Number of Transmit Antennas
Description 2: Explain the significance of increasing the number of transmit antennas in FD-MIMO systems and the challenges related to CSI acquisition.

Section 3: 2D Active Antenna System (AAS)
Description 3: Describe the introduction of the active antenna with a 2D planar array and the benefits of 3D beamforming.

Section 4: 3D Channel Environment
Description 4: Discuss the design considerations for maximizing performance in realistic 3D channel environments, including height-dependent pathloss and elevation angular-spread of departure (ESD).

Section 5: RS Transmission for CSI Acquisition
Description 5: Highlight the evolution of reference signal (RS) schemes from LTE to LTE-Advanced systems and the use of beamformed CSI-RS in FD-MIMO.

Section 6: System Design and Standardization of FD-MIMO Systems
Description 6: Provide an overview of the system design and standardization efforts for FD-MIMO systems, focusing on deployment scenarios, TXRU structures, and new RS strategies.

Section 7: Deployment Scenarios
Description 7: Outline typical deployment scenarios for FD-MIMO systems, such as 3D urban macro and micro scenarios.

Section 8: Antenna Configurations
Description 8: Detail the antenna configurations for FD-MIMO systems, including the number of elements in vertical and horizontal directions and polarization considerations.

Section 9: TXRU Architectures
Description 9: Describe the TXRU (transceiver unit) architectures and their role in controlling the gain and phase of individual antenna elements.

Section 10: New CSI-RS Transmission Strategy
Description 10: Discuss the strategies for transmitting CSI-RS, including conventional non-precoded and beamformed CSI-RS transmissions.

Section 11: CSI Feedback Mechanisms for FD-MIMO Systems
Description 11: Explore various CSI feedback mechanisms, such as composite codebook, beam index feedback, partial CSI-RS with dimensional feedbacks, and adaptive CSI feedback.

Section 12: Performance of FD-MIMO System
Description 12: Analyze the performance of FD-MIMO systems through system-level simulations under realistic multicell environments, using metrics like spectral efficiency for cell average and cell edge.