Vehicles are increasingly getting connected with 5thGeneration (SG) cellular connectivity, and are expected to be connected to 6thGeneration (6G) in the future. One of the key challenges of enabling cellular connectivity in a vehicle is radio frequency (RF) cabling from the sharkfin antennas on the top of the vehicle to modem placed inside the vehicle. Such placement of antennas is needed to negate the impact of out-to-in (O2I) losses introduced by a car body. Cost of the cabling can particularly be a concern as cellular systems utilize higher bands. In this paper we study using optically transparent and transmissive meta-surface(s) on windows of a vehicle to eliminate/mitigate the O2I loss. This can eliminate need for RF cable. To do so, we determine the 3-dimensional O2I loss of a Volkswagen Atlas sports utility vehicle (SUV) through measurements in an anechoic chamber. Next, based on this measured O2I loss and the proposed theoretical link model for a transmissive meta-surface we perform link-level analysis of the in-car antenna system with meta-surfaces installed on various glass surfaces. We analyze actively controlled and fixed design meta-surfaces. Our results show that actively controlled meta-surfaces (controlled with full channel information) of desired dimension and placed on the driver and passenger side window can recover the O2I losses in almost all cases. We additionally show that an in-vehicle antenna with fixed design meta-surface (i.e., with fixed refraction angle) can negate the O2I loss to be within 3 dB 90% of the time.

Low-resolution digital-to-analog and analog-to-digital converters (DACs and ADCs) have attracted considerable attention in efforts to reduce power consumption in millimeter wave (mmWave) and massive MIMO systems. This paper presents an information-theoretic analysis with capacity bounds for classes of linear transceivers with finite quantization. The transmitter modulates symbols via a unitary transform followed by a DAC and the receiver employs an ADC followed by the inverse unitary transform. If the unitary transform is set to a discrete Fourier transform (DFT) matrix, the model naturally captures filtering and spectral constraints. In particular, this model allows studying the impact of quantization on out-of-band (OOB) emission constraints. The out-of-band emission constraints are defined using a “spectrum mask” in practical wireless systems. All transmissions need to meet the OOB constraint to allow other services and technologies to operate in adjacent bands.In the limit of a large random unitary transform, it is shown that the effect of quantization can be precisely described via an additive Gaussian noise model. This model in turn leads to simple and intuitive expressions for the power spectrum of the transmitted signal and a lower bound to the capacity with quantization. Comparison with non-quantized capacity and a capacity upper bound that does not make linearity assumptions suggests that while low resolution quantization has minimal impact on the achievable rate at typical parameters in 5G systems, satisfying OOB emissions is potentially much more of a challenge.

Low-resolution digital-to-analog and analog-to-digital converters (DACs and ADCs) have attracted considerable attention in efforts to reduce power consumption in millimeter wave (mmWave) and massive MIMO systems. This paper presents an information-theoretic analysis with capacity bounds for classes of linear transceivers with quantization. The transmitter modulates symbols via a unitary transform followed by a DAC and the receiver employs an ADC followed by the inverse unitary transform. If the unitary transform is set to an FFT matrix, the model naturally captures filtering and spectral constraints which are essential to model in any practical transceiver. In particular, this model allows studying the impact of quantization on out-of-band emission constraints. In the limit of a large random unitary transform, it is shown that the effect of quantization can be precisely described via an additive Gaussian noise model. This model in turn leads to simple and intuitive expressions for the power spectrum of the transmitted signal and a lower bound to the capacity with quantization. Comparison with non-quantized capacity and a capacity upper bound that does not make linearity assumptions suggests that while low resolution quantization has minimal impact on the achievable rate at typical parameters in 5G systems today, satisfying out-of-band emissions are potentially much more of a challenge.

Due to the heavy reliance of millimeter-wave (mmWave) wireless systems on directional links, beamforming (BF) with high-dimensional arrays is essential for cellular systems in these frequencies. Thus, performing the array processing in a power-efficient manner is a fundamental challenge. Analog and hybrid BF require few analog-to-digital and digital-to-analog converters (ADCs and DACs), but can only communicate in a small number of directions at a time, limiting directional search, spatial multiplexing, and control signaling. Digital BF enables flexible spatial processing but must be operated at a low quantization resolution to stay within reasonable power levels. This decrease in quantizer resolution distorts the received as well as the transmitted signal. To assess the effect of coarse quantization at the receiver, this paper presents a system level analytic framework based on a simple additive quantization noise model (AQNM). The analysis verified through extensive simulations reveals that at moderate resolutions (3-4 bits per ADC), there is negligible loss in downlink cellular capacity from quantization. In essence, the low resolution ADCs limit the high SNR, where cellular systems typically do not operate. For the transmitter, it is shown that DACs with 4 or more bits of resolution can support high order modulations, and do not violate the adjacent carrier leakage limit set by 3rdGeneration Partnership Project (3GPP) New Radio (NR) standards for cellular operations. In fact, our findings suggest that low resolution digital BF architectures can be a power-efficient alternative to analog or hybrid BF for both transmitters and receivers at millimeter-wave.

Extending cellular services to remote locations on the globe is a key challenge for next generation cellular systems. Base stations mounted on high altitude platform systems (HAPS) are currently used to extend 4G LTE cellular services to remote areas. Due to the availability of large blocks unlicensed spectrum in the millimeter wave (mmWave) bands, mmWave systems can operate over bandwidths much higher than the congested sub-6 GHz bands. In this paper we study the system level implications of using mmWave BSs on HAPS for air to ground cellular communication systems. It is well known that mmWave links, unlike LTE, are power limited. Moreover, mmWave systems are conventionally designed for small cell applications. Thus to get large coverage with mmWave HAPS poses an interesting design challenge. In this work we show that even when sufficient link budgets are available, coverage by a mmWave based HAPS will be limited due to the design of the physical random access channel (PRACH). To overcome this, we propose a novel re-transmission mechanism for PRACH sequences. As illustrated through simulations, the proposed algorithm can potentially double the coverage area.

The millimeter-wave (mmWave) frequencies have attracted considerable attention for fifth generation (5G) cellular communication as they offer orders of magnitude greater bandwidth than current systems. However, the medium access control (MAC) layer may need to be significantly redesigned to support the highly directional transmissions, and the demand for ultra-low latencies and high peak rates expected in mmWave communication. To address these challenges, we present a novel mmWave MAC layer frame structure with a number of enhancements, including flexible, highly granular transmission times, dynamic control signal locations, extended messaging, and the ability to efficiently multiplex directional control signals. Analytic formulas are derived for the utilization and control overhead as a function of control periodicity, number of users, traffic statistics, signal-to-noise ratio, and antenna gains. Importantly, the analysis can incorporate various front-end MIMO capability assumptions-a critical feature of mmWave. Under realistic system and traffic assumptions, the analysis reveals that the proposed flexible frame structure design offers significant benefits over designs with fixed frame structures similar to current 4G long-term evolution. It is also shown that the fully digital beamforming architectures offer significantly lower overhead compared with analog and hybrid beamforming under equivalent power budgets.

The increasing demand of data, along with the spectrum scarcity, are motivating a urgent shift towards exploiting new bands. This is the main reason behind identifying mmWaves as the key disruptive enabling technology for 5G cellular networks. Indeed, utilizing new bands means facing new challenges; in this context, they are mainly related to the radio propagation, which is shorter in range and more sensitive to obstacles. The resulting key aspects that need to be taken into account when designing mmWave cellular systems are directionality and link intermittency. The lack of network level results motivated this work, which aims at providing the first of a kind open source mmWave framework, based on the network simulator ns-3. The main focus of this work is the modeling of customizable channel, physical (PHY) and medium access control (MAC) layers for mmWave systems. The overall design and architecture of the model are discussed in details. Finally, the validity of our proposed framework is corroborated through the simulation of a simple scenario.