Deployments of millimeter wave systems suffer from increased propagation and blockage losses that lead to a focus on small cell coverage. With an increased densification of such systems, cooperative transmissions are possible at a user equipment (UE) from multiple transmission reception points (TRPs) and with repeater nodes (e.g., relay UEs, intelligent reflecting surfaces, reflectarrays) in the vicinity of a certain UE. In this context, this work proposes and studies the performance of a class of directional beam steering and co-phasing schemes that leverage the existing set of beam steering solutions for point-to-point transmissions. To benchmark the performance of the proposed schemes, an unrealizable upper bound to the SNR is first established. We then quantify the SNR gap between the proposed directional schemes and the unrealizable upper bound via theory and numerical studies and show that the proposed solutions are of low complexity and comparable performance to the unrealizable upper bound.

Hand and body blockage are known to result in significant performance degradation at millimeter wave carrier frequencies. A number of prior works have proposed statistical models to capture the spatial region lost due to blockage and the associated losses incurred in signal strength over this region. In particular, it is understood that while a hard hand grip can lead to substantial losses, a more relaxed/looser hand grip can lead to moderate losses. However, all these works consider only the signal strength degradation with blockage mitigation mechanisms consisting of densification of the network and the use of more antenna modules at the user equipment end. In practice, the number of antenna modules in a user equipment may be limited leading to the need for more novel blockage mitigation strategies. Towards this goal, in this work, we show that the presence of the hand on top/near an antenna module can distort the observed amplitude and phase of the array response. We also show that a non-directional analog beamforming codebook enhancement can de-randomize some of the phase distortions and recover some of the gains lost due to the hand with a directional beamforming codebook.

The ongoing commercial deployment of millimeter wave systems brings into focus a number of practical issues in form factor user equipment (UE) design. With wavelengths becoming smaller, antenna gain patterns becoming directional, and link budgets critically dependent on beamforming, it becomes imperative to use a number of antenna modules at different locations of the UE for good performance. While more antennas/modules can enhance beamforming array gains, it comes with the trade-off of higher component cost, power consumption of the associated radio frequency circuitry, and a beam management overhead in learning the appropriate beam weights. Thus, the goal of a good UE design is to provide robust spherical coverage corresponding to good array gains over the entire sphere around the UE with a low beam management overhead, complexity, and cost. The scope of this paper is to study the implications of two popular commercial millimeter-wave UE designs (a face and an edge design) on spherical coverage. We show that the analog beam codebooks can result in good performance for both the designs, and the edge design provides a better trade-off in terms of robust performance (with hand blockage), beam management overhead, implementation complexity from an antenna placement standpoint, and cost.

There has been a strong interest in understanding hybrid precoding tradeoffs for millimeter wave (mmW) multi-input multi-output (MIMO) systems. A common assumption in most of these works is that the analog part of the hybrid precoder can only be designed with phase shifters. The consequent search for analog and digital precoding matrices is solved with different black box-type optimization algorithms. In contrast, this work motivates an analog precoding structure at the base-station end that can be realized with both phase shifters and gain controls. Such a structure is necessary for interference management in multi- user transmissions and is easily realized with low complexity and cost. We then propose a feedback framework of the top-P beams over a beam alignment phase from each user. This framework allows the base-station to reconstruct the channel matrix between it and each user, and to manage interference with a simple zeroforcing solution. Such a structured solution is implemented with the amplitude and phase control of the analog part of the hybrid precoder. We finally illustrate the performance improvement with the proposed solution over simpler constructions such as beam steering that can be implemented with phase shifters alone.

Given the cost and complexity associated with the deployment of a large number of radio frequency (RF) chains in millimeter wave (mmW) multi-input multi-output (MIMO) systems, this paper addresses the question of network efficiency considerations for hybrid precoding. We first establish the relevance of directional precoding structures as a low-complexity and robust solution to meet the data rate demands of single-user MIMO systems relative to the more complex and less robust eigen-mode-based precoding structures. Key to the relevance of the directional precoding structures is the sparsity of the mmW channel coupled with higher antenna dimensionality affordable due to smaller wavelengths. We then leverage the directional structure of the channel to propose a simple class of directional schedulers that offers a low-complexity and yet approximately fair separation plane in the user space. We then compare the performance of single-user precoding schemes with multi-user precoding schemes and show that from network efficiency considerations, it would be more worthwhile to expend the RF chain resource on multi-user transmissions.

The focus of this work is on cost and complexity- induced rank-constrained precoding for millimeter- wave (mmW) multi-input multi-output (MIMO) systems. The higher antenna dimensionality and sparse channel structure of mmW systems motivate directional precoding schemes over more complex and less robust eigen-mode-based precoding schemes. Building on a prior work that illustrated the superiority in design, robustness and performance of a directional rank-1 beamformer, this work considers higher-rank directional precoding structures for mmW systems. It is shown that directional precoders continue to enjoy similar properties in single-user MIMO (SU-MIMO) systems. But from a network efficiency consideration, it would be more worthwhile to expend the radio frequency (RF) chain resource on multi-user transmissions. Towards this goal, a directional scheduler and different directional beamforming structures are proposed here. These structures are shown to result in significant performance improvement over higher-rank SU-MIMO schemes.

For the development of new 5G systems to operate in bands up to 100 GHz, there is a need for accurate radio propagation models at these bands that currently are not addressed by existing channel models developed for bands below 6 GHz. This document presents a preliminary overview of 5G channel models for bands up to 100 GHz. These have been derived based on extensive measurement and ray tracing results across a multitude of frequencies from 6 GHz to 100 GHz, and this document describes an initial 3D channel model which includes: 1) typical deployment scenarios for urban microcells (UMi) and urban macrocells (UMa), and 2) a baseline model for incorporating path loss, shadow fading, line of sight probability, penetration and blockage models for the typical scenarios. Various processing methodologies such as clustering and antenna decoupling algorithms are also presented.

This paper presents and compares two candidate large-scale propagation path loss models, the alpha-beta-gamma (ABG) model and the close-in (CI) free space reference distance model, for the design of fifth generation (5G) wireless communication systems in urban micro- and macro-cellular scenarios. Comparisons are made using the data obtained from 20 propagation measurement campaigns or ray- tracing studies from 2 GHz to 73.5 GHz over distances ranging from 5 m to 1429 m. The results show that the one-parameter CI model has a very similar goodness of fit (i.e., the shadow fading standard deviation) in both line-of-sight and non-line-of-sight environments, while offering substantial simplicity and more stable behavior across frequencies and distances, as compared to the three-parameter ABG model. Additionally, the CI model needs only one very subtle and simple modification to the existing 3GPP floating-intercept path loss model (replacing a constant with a close-in free space reference value) in order to provide greater simulation accuracy, more simplicity, better repeatability across experiments, and higher stability across a vast range of frequencies.

The millimeter-wave (mm-Wave) frequency band ~30-300 GHz has received significant attention lately as a prospective band for 5G systems. Millimeter-wave frequencies have traditionally been used for backhaul, satellite and other fixed services. While these bands offer substantial amount of bandwidth and opportunity for spatial multiplexing, the propagation characteristics for terrestrial mobile usage need to be fully understood prior to system design. Towards this end, this paper presents preliminary indoor measurement results obtained using a channel sounder equipped with omni- and directional antennas at 2.9 GHz and 29 GHz as a comparative study of the two bands. The measurements are made within a Qualcomm building in Bridgewater, NJ, USA, for two separate floors, each representing a different yet representative type of office plan. We present measurements and estimated parameters for path loss, excess delay, RMS delay and analyze the power profile of received paths. In addition, we present several spherical scans of particular links to illustrate the 3-D angular spread of the received paths. This work represents initial results of an ongoing effort for comprehensive indoor and outdoor channel measurements. The measurements presented here, along with cited references, offer interesting insights into propagation conditions (e.g. loss, delay/angular spread etc.), coverage and robustness for mobile use of millimeter-wave bands. We believe additional extensive measurement campaigns in diverse settings by academia and industry would help facilitate the generation of usable channel models.

In this work we present a unified analysis of the capacity and performance gains attainable by oversampling at the receiver in the temporal and spatial domains under multiple transmit antennas through a linear algebra approach. We quantify the increase in dimensionality gain beyond the spreading factor and illustrate the increase in system performance.

We demonstrate the performance gains attainable through the aid of oversampling in an asynchronous direct sequence code division multiple access (CDMA) system. In chip-rate sampled systems with spreading factor N/spl acute/, the dimensionality of the system is N, limiting the number of supportable users. We show that oversampling increases the dimensions beyond this factor. The increased dimensionality allows the support of more users or a higher separation between existing users. We formulate an optimization problem over user delays and spreading codes that achieves maximum system performance. This forced-asynchronous CDMA system creates a novel area of optimization with immediate implications on code and system design.

In this paper, we evaluate the performance of the minimum energy wireless network, which seeks to provide global connectivity in an ad hoc network while maintaining overall minimum energy for communications. The properties and advantages of employing multi-hop communication over a direct peer-to-peer communication system are illustrated and the performance of such a network is characterized. The blockage percentage for throughput and the overall power consumption are also quantified via simulation.