Temporal Analysis of Measured LOS Massive MIMO Channels with Mobility

The first measured results for massive multiple-input, multiple-output (MIMO) performance in a line-of-sight (LOS) scenario with moderate mobility are presented, with 8 users served by a 100 antenna base Station (BS) at 3.7 GHz. When such a large number of channels dynamically change, the inherent propagation and processing delay has a critical relationship with the rate of change, as the use of outdated channel information can result in severe detection and precoding inaccuracies. For the downlink (DL) in particular, a time division duplex (TDD) configuration synonymous with massive MIMO deployments could mean only the uplink (UL) is usable in extreme cases. Therefore, it is of great interest to investigate the impact of mobility on massive MIMO performance and consider ways to combat the potential limitations. In a mobile scenario with moving cars and pedestrians, the correlation of the MIMO channel vector over time is inspected for vehicles moving up to 29 km/h. For a 100 antenna system, it is found that the channel state information (CSI) update rate requirement may increase by 7 times when compared to an 8 antenna system, whilst the power control update rate could be decreased by at least 5 times relative to a single antenna system.Comment: Accepted for presentation at the 85th IEEE Vehicular Technology Conference in Sydney. 5 Pages. arXiv admin note: substantial text overlap with arXiv:1701.0881

Open source software radio platform for research on cellular networked UAVs: It works!

Cellular network-connected unmanned aerial vehicles (UAVs) experience different radio propagation conditions than radio nodes on the ground. Therefore, it has become critical to investigate the performance of aerial radios, both theoretically and through field trials. In this article, we consider low-altitude aerial nodes that are served by an experimental cellular network. We provide a detailed description of the hardware and software components needed to establish a broadband wireless testbed for UAV communications research using software radios. Results show that a testbed for innovation in UAV communications and networking is feasible with commercial off-the-shelf hardware, open source software, and low-power signaling.This work was in part supported by NSF award CNS-1939334.Peer ReviewedPostprint (author's final draft

Rate-Splitting Multiple Access: The First Prototype and Experimental Validation of its Superiority over SDMA and NOMA

In multi-user multi-antenna communications, it is well-known in theory that Rate-Splitting Multiple Access (RSMA) can achieve a higher spectral efficiency than both Space Division Multiple Access (SDMA) and Non-Orthogonal Multiple Access (NOMA). However, an experimental evaluation of RSMA's performance, relative to SDMA and NOMA, is missing in the literature, which is essential to address the ongoing debate between RSMA and NOMA over which is better suited to handle most efficiently the available resources and interference in 6G. In this paper, we address this critical knowledge gap by realizing the first-ever RSMA prototype using software-defined radios. Through measurements using our prototype, we empirically solve the modulation and coding scheme limited sum throughput maximization problem for RSMA, SDMA and NOMA for the two-user multiple-input single-output (MISO) scenario over (a) different pairs of line-of-sight channels that vary in terms of their relative pathloss and spatial correlation, and with (b) different channel state information quality. We observe that RSMA achieves the highest sum throughput across all these cases, whereas SDMA and NOMA are effective only in some cases. Furthermore, RSMA also achieves better fairness at a higher sum throughput than both SDMA and NOMA.Comment: major revisions of IEEE Transactions on Wireless Communication

USAGE OF 5G IN UAV MISSIONS FOR ISR

Traditionally, UAVs operate on a one-to-one transmission mode where the UAVs have one data link between one ground command and control station. Therefore, the radius at which the UAV can travel is limited. The bandwidth of the traditional link is limited to less than 8Mbps and the quality of the video is below 1080p. 4G technology has been applied to the UAV data link to solve some of these more traditional problems. However, the 4G data link also comes with its own limitations such as downlink interference and can only be useful in scenarios with a high delay tolerance. 5G technology solves the spatial coverage problem by increasing the number of antenna modules and fusing the antenna module and radio hardware. The result is a three-dimensional beam. The UAV itself can be used as a base station for the 5G network, so that all ground stations can be connected as the UAV continues its flight path. UAVs can also be used as aerial nodes in a larger swarm network to offer coverage over larger areas. Additionally, the use of the OpenStack architecture can allow the Navy to customize protocols as desired. The proposed research includes investigating how current UAV to ship/shore communications are conducted. The objective of this thesis is to determine if 5G communications are possible between UAV and ship/shore assets, to successfully connect a UAV to the 4G and possibly 5G network and to determine if UAVs can send data between each other to the ground station.Lieutenant Commander, United States NavyApproved for public release. Distribution is unlimited

High Capacity Fiber-Connected Wireless MIMO Communication

There will be more and more users while beyond-5G (B5G) and 6G bring more wireless applications. Current cellular communication networks assign specific serving boundaries for each radio, which becomes a limitation when too many users work with one radio simultaneously. By physically distributing radios. user’s service can be more uniform. Radio-over-fiber is a promising enabling technology for distributed antenna systems.To have several tens of Gbit/s data rate, we need to apply millimeter-wave (mm-wave) frequency band in radio-over-fiber (RoF). However, mm-wave signals have weak penetration and high propagation loss. Hence, beamforming and/or multiple-input-multiple-output (MIMO) technology become necessary for mm-wave RoF to overcome those drawbacks.This thesis introduces an automatic distributed MIMO (D-MIMO) testbed with a statistical MIMO capacity analysis for an indoor use case. Raytracing-based simulations also predicts the indoor case to make a comparison. The statistical MIMO capacity analysis shows that D-MIMO has a higher and more uniform capacity than co-located MIMO (C-MIMO) in measurements and simulations.Next, a mm-wave sigma-delta-over-fiber (SDoF) link architecture is proposed for MIMO applications. In the implementation of this link, a QSFP28 fiber link connects a central unit with a remote radio unit with four bandpass sigma-delta-modulation (BPSDM) bitstreams. The remote radio unit generates four mm-wave signals from four BPSDM signals and feeds a linear array antenna. The measurement characterizes the remote radio head at each stage and concludes that this proposed link can reach 800 Msym/s data rate with -0.5 dBm output bandpower.Furthermore, the proposed link is demonstrated with digital beamforming and multi-user MIMO (MU-MIMO) functionalities. The digital beamforming function reaches 700 Msym/s with -25 dB error vector magnitude (EVM) results by improving the received bandpower in comparison to (single-input-single-output) SISO results. The MU-MIMO function serves two independent users at 500 Msym/s symbol rate and satisfies 3GPP requirements at 1 m over-the-air distance.In conclusion, this thesis proves that D-MIMO has a higher and more uniform capacity than C-MIMO by statistical analysis from measurements and simulations. The proposed novel mm-wave SDoF link can pave the way for future D-MIMO applications

Decentralized Ultra-Reliable Low-Latency Communications through Concurrent Cooperative Transmission

Emerging cyber-physical systems demand for communication technologies that enable seamless interactions between humans and physical objects in a shared environment. This thesis proposes decentralized URLLC (dURLLC) as a new communication paradigm that allows the nodes in a wireless multi-hop network (WMN) to disseminate data quickly, reliably and without using a centralized infrastructure. To enable the dURLLC paradigm, this thesis explores the practical feasibility of concurrent cooperative transmission (CCT) with orthogonal frequency-division multiplexing (OFDM). CCT allows for an efficient utilization of the medium by leveraging interference instead of trying to avoid collisions. CCT-based network flooding disseminates data in a WMN through a reception-triggered low-level medium access control (MAC). OFDM provides high data rates by using a large bandwidth, resulting in a short transmission duration for a given amount of data. This thesis explores CCT-based network flooding with the OFDM-based IEEE 802.11 Non-HT and HT physical layers (PHYs) to enable interactions with commercial devices. An analysis of CCT with the IEEE 802.11 Non-HT PHY investigates the combined effects of the phase offset (PO), the carrier frequency offset (CFO) and the time offset (TO) between concurrent transmitters, as well as the elapsed time. The analytical results of the decodability of a CCT are validated in simulations and in testbed experiments with Wireless Open Access Research Platform (WARP) v3 software-defined radios (SDRs). CCT with coherent interference (CI) is the primary approach of this thesis. Two prototypes for CCT with CI are presented that feature mechanisms for precise synchronization in time and frequency. One prototype is based on the WARP v3 and its IEEE 802.11 reference design, whereas the other prototype is created through firmware modifications of the Asus RT-AC86U wireless router. Both prototypes are employed in testbed experiments in which two groups of nodes generate successive CCTs in a ping-pong fashion to emulate flooding processes with a very large number of hops. The nodes stay synchronized in experiments with 10 000 successive CCTs for various modulation and coding scheme (MCS) indices and MAC service data unit (MSDU) sizes. The URLLC requirement of delivering a 32-byte MSDU with a reliability of 99.999 % and with a latency of 1 ms is assessed in experiments with 1 000 000 CCTs, while the reliability is approximated by means of the frame reception rate (FRR). An FRR of at least 99.999 % is achieved at PHY data rates of up to 48 Mbit/s under line-of-sight (LOS) conditions and at PHY data rates of up to 12 Mbit/s under non-line-of-sight (NLOS) conditions on a 20 MHz wide channel, while the latency per hop is 48.2 µs and 80.2 µs, respectively. With four multiple input multiple output (MIMO) spatial streams on a 40 MHz wide channel, a LOS receiver achieves an FRR of 99.5 % at a PHY data rate of 324 Mbit/s. For CCT with incoherent interference, this thesis proposes equalization with time-variant zero-forcing (TVZF) and presents a TVZF receiver for the IEEE 802.11 Non-HT PHY, achieving an FRR of up to 92 % for CCTs from three unsyntonized commercial devices. As CCT-based network flooding allows for an implicit time synchronization of all nodes, a reception-triggered low-level MAC and a reservation-based high-level MAC may in combination support various applications and scenarios under the dURLLC paradigm

Efficient DSP and Circuit Architectures for Massive MIMO: State-of-the-Art and Future Directions

Massive MIMO is a compelling wireless access concept that relies on the use of an excess number of base-station antennas, relative to the number of active terminals. This technology is a main component of 5G New Radio (NR) and addresses all important requirements of future wireless standards: a great capacity increase, the support of many simultaneous users, and improvement in energy efficiency. Massive MIMO requires the simultaneous processing of signals from many antenna chains, and computational operations on large matrices. The complexity of the digital processing has been viewed as a fundamental obstacle to the feasibility of Massive MIMO in the past. Recent advances on system-algorithm-hardware co-design have led to extremely energy-efficient implementations. These exploit opportunities in deeply-scaled silicon technologies and perform partly distributed processing to cope with the bottlenecks encountered in the interconnection of many signals. For example, prototype ASIC implementations have demonstrated zero-forcing precoding in real time at a 55 mW power consumption (20 MHz bandwidth, 128 antennas, multiplexing of 8 terminals). Coarse and even error-prone digital processing in the antenna paths permits a reduction of consumption with a factor of 2 to 5. This article summarizes the fundamental technical contributions to efficient digital signal processing for Massive MIMO. The opportunities and constraints on operating on low-complexity RF and analog hardware chains are clarified. It illustrates how terminals can benefit from improved energy efficiency. The status of technology and real-life prototypes discussed. Open challenges and directions for future research are suggested.Comment: submitted to IEEE transactions on signal processin

Emerging Prototyping Activities in Joint Radar-Communications

The previous chapters have discussed the canvas of joint radar-communications (JRC), highlighting the key approaches of radar-centric, communications-centric and dual-function radar-communications systems. Several signal processing and related aspects enabling these approaches including waveform design, resource allocation, privacy and security, and intelligent surfaces have been elaborated in detail. These topics offer comprehensive theoretical guarantees and algorithms. However, they are largely based on theoretical models. A hardware validation of these techniques would lend credence to the results while enabling their embrace by industry. To this end, this chapter presents some of the prototyping initiatives that address some salient aspects of JRC. We describe some existing prototypes to highlight the challenges in design and performance of JRC. We conclude by presenting some avenues that require prototyping support in the future.Comment: Book chapter, 54 pages, 13 figures, 10 table