mmWave Wireless Research Articles

Efficient dynamic relay probing and concurrent backhaul link scheduling for mmWave cellular networks

Exploiting the enormous chunks of mmWave spectrum between 30 GHz and 300 GHz have the potential to facilitate gigabit rate services to the future 5G cellular networks, and help in alleviating the current spectrum crisis. Conventional backhaul links such as Digital Subscriber Line (DSL) and Asymmetric Digital Subscriber Line (ADSL) have been proved to be a major bottleneck in satisfying these high data rate demands of indoor user equipments associated with traditional Femto Base Stations (FBS). One possible solution is to deploy higher capacity optical fiber cable to satisfy such demands. However, it is a costly and non-flexible solution. Thus, mmWave wireless backhaul links can be utilized at the FBSs. But due to their high-frequency, mmWave carrier signals are highly susceptible to obstacles and thus suffer a high attenuation in signal strength when passed through the obstacles. In order to alleviate the losses incurred due to blockages and to improve the signal reachability, in this paper, we propose an efficient distributed mode selection and dynamic relay probing scheme. We also propose an efficient scheduling scheme, for scheduling wireless backhaul links, which works jointly with the proposed mode selection and relay probing scheme to further improve the system throughput. Our proposed scheduling scheme permits non-interfering links to schedule and transmit concurrently. An expression for calculating the expected number of concurrent transmissions for our proposed scheduling scheme is derived and validated. Through extensive simulations under various system parameters, we have demonstrated the superiority of our proposed mode selection and relay probing scheme over the fixed relay probing scheme.

Adaptive Virtual Waveform Design for Millimeter-Wave Joint Communication–Radar

Joint communication and radar (JCR) waveforms with fully digital baseband generation and processing can now be realized at the millimeter-wave (mmWave) band. Prior work has proposed a mmWave wireless local area network (WLAN)-based JCR that exploits the WLAN preamble for radars. The performance of target velocity estimation, however, was limited. In this paper, we propose a virtual waveform design for an adaptive mmWave JCR. The proposed system transmits a few non-uniformly placed preambles to construct several receive virtual preambles for enhancing velocity estimation accuracy, at the cost of only a small reduction in the communication data rate. We evaluate JCR performance trade-offs using the Cramer-Rao Bound (CRB) metric for radar estimation and a novel distortion minimum mean square error (MMSE) metric for data communication. Additionally, we develop three different MMSE-based optimization problems for the adaptive JCR waveform design. Simulations show that an optimal virtual (non-uniform) waveform achieves a significant performance improvement as compared to a uniform waveform. For a radar CRB constrained optimization, the optimal radar range of operation and the optimal communication distortion MMSE (DMMSE) are improved. For a communication DMMSE constrained optimization with a high DMMSE constraint, the optimal radar CRB is enhanced. For a weighted MMSE average optimization, the advantage of the virtual waveform over the uniform waveform is increased with decreased communication weighting. Comparison of MMSE-based optimization with traditional virtual preamble count-based optimization indicated that the conventional solution converges to the MMSE-based one only for a small number of targets and a high signal-to-noise ratio.

Energy efficiency maximization in mmWave wireless networks with 3D beamforming

In this paper, we address the problem of 3D beamforming (3DBF) in millimeter wave (mmWave) wireless networks. In particular, we study the impact of base station (BS) antenna tilt angle optimization on the energy efficiency (EE) of mmWave networks under two different scenarios: a homogeneous network consisting of multiple macro base stations (MBSs), and a heterogeneous network where several femto base stations are added within the coverage areas of the MBSs. First, by adopting a stochastic geometry approach, we analyze the coverage probability of both scenarios that incorporate 3DBF. Then, we derive the EE of the networks as a function of the MBS antenna tilt angle. Next, optimization problems are formulated to maximize the EE of the networks by optimizing the tilt angle. Since the computational complexity of the optimal solution is very high, near-optimal low-complexity methods are proposed for solving the optimization problems. Simulation results show that in the mmWave networks, the 3DBF technique with optimized tilt angle can considerably improve the EE of the network. Also, the proposed low complexity approach presents a performance close to the optimal solution but with a significant reduced complexity.

Next Generation Fiber-Wireless Fronthaul for 5G mmWave Networks

mmWave radio, although instrumental for achieving the required 5G capacity KPIs, necessitates the need for a very large number of access points, which places an immense strain on the current network infrastructure. In this article, we try to identify the major challenges that inhibit the design of the Next Generation Fronthaul Interface in two upcoming distinctively highly dense environments: in Urban 5G deployments in metropolitan areas, and in ultra-dense Hotspot scenarios. Second, we propose a novel centralized and converged analog Fiber-Wireless Fronthaul architecture, specifically designed to facilitate mmWave access in the above scenarios. The proposed architecture leverages optical transceivers, optical add/drop multiplexers and optical beamforming integrated photonics towards a Digital Signal Processing analog fronthaul. The functional administration of the fronthaul infrastructure is achieved by means of a packetized Medium Transparent Dynamic Bandwidth Allocation protocol. Preliminary results show that the protocol can facilitate Gb/s-enabled data transport while abiding to the 5G low-latency KPIs in various network traffic conditions.

Energy Beamforming in Wireless Powered mmWave Sensor Networks

This paper studies the beneficial combination of wireless power transfer and millimeter-wave (mmWave) communications in wireless sensor networks. In particular, an mmWave wireless powered sensor network is considered, where the access point (AP) employs beamforming techniques to transfer energy to the sensors of a selected sector of the cell. The served sensors harvest and store energy from the received signal, and use it to power their uplink transmissions. We consider a random energy beamforming scheme but also propose several intelligent schemes that steer the beam to specific areas of the cell by considering the sensors' locations. This setup is investigated from a large-scale point-of-view where spatial randomness is considered with the aid of Poisson point processes. The performance of the network is described in terms of the energy outage probability and the beam outage probability. We show that, depending on the scenario, each of the considered energy beamforming schemes can provide significant gains to the network's performance. Finally, we study an event monitoring application of our theoretical framework, where the active sensors observe a random event in the network and the AP attempts to estimate it based on the received information; this scenario is evaluated in terms of the estimation's mean squared error.

Relay Assisted Concurrent Scheduling to Overcome Blockage in Full-Duplex Millimeter Wave Small Cells

The millimeter wave (mmWave) has been extensively utilized for its rich spectrum resource. With the development of self-interference (SI) cancellation technology, full-duplex (FD) communications have become possible recently. In order to get larger network capacity, we introduce FD communications into mmWave wireless network. However, mmWave links are easily blocked by obstacles, and the blockage makes some flows fail to be transmitted directly. For the communication problems of shadow coverage area, a relay path selection algorithm is proposed to select optimal multi-hop paths for these blocked flows. This proposed algorithm not only can relay the blocked flows by other unblocked links, but also select the appropriate relay paths to minimize transmission time of the entire transmission process. To further improve the system transmission efficiency, we develop a concurrent scheduling algorithm by using FD communications. The scheduling algorithm continuously schedules the links until the throughput requirements of flows are accommodated. Through extensive simulations at 60 GHz mmWave wireless network, the proposed scheme can solve the problem for a certain degree of blocked flows and complete the transmission with the least time consumption. Compared with other existing schemes, the proposed scheme shows superior performances on relaying capability and scheduling duration.

Single RF-Chain Beam Training for MU-MIMO Energy Efficiency and Information-Centric IoT Millimeter Wave Communications

In a multi-user multiple-input multiple-output (MU-MIMO) communication system, multiple RF (radio frequency) chains are generally connected corresponding to the antenna elements. However, the system complexity, hardware cost, and energy consumption are challenging while using many RF chains. In addition, an information-centric Internet of Things (IoT) will be significant to guarantee fast service demand for radio access in the fifth generation (5G) mmWave wireless systems. In this paper, a new beam training method based on a single RF chain is proposed to overcome these challenges by using the downlink–uplink and downlink–downlink beam training techniques to establish the elite users’ subset group which can be trained in a single training time slot. Additionally, the users’ subset mechanism is implemented by selecting an arbitrary function to guarantee the convergence. Moreover, the proposed techniques are compared with the conventional full search method regarding searching time, cost, and complexity. Different user subset functions are modeled, evaluated, and compared with the existing ones with respect to effective channel gain and average system capacity. The simulation results show that the proposed method can achieve a significant system performance, and the single RF chain is serviceable for a large number of users when connected with a maximum of 64 antenna elements at the BS. The proposed method can also be implemented in a massive MU-MIMO system by using multiple RF chains in which each RF chain is connected to a group of 64 antenna elements. This work is applicable in 5G mmWave communications, which require robust infrastructure to meet the future IoT service demand in 5G hot scenarios.

Energy-Efficient Full-Duplex Concurrent Scheduling Based on Contention Graph in mmWave Backhaul Networks

In the fifth generation (5G) era, dense deployment of small cells and full-duplex (FD) technology applications are two key features of millimeter-wave (mmWave) wireless communication systems, which offer the opportunity to meet the explosive growth of data service requirements. It is the beamforming and advances in analog as well as digital self-interference (SI) cancellation schemes that improve the network capacity in mmWave wireless backhaul networks. To achieve power saving and further network performance optimization, we propose a FD concurrent transmission mechanism employed in a mmWave backhaul network. Contention graph is constructed in consideration of multi-user interference (MUI), SI, and FD transmission constraints. Then flow-grouping and power control algorithms are proposed based on the contention graph. We evaluate the performance of the proposed algorithm in terms of energy consumption, achievable network throughput, and energy efficiency. The impact of the interference threshold on the system performance is also investigated when the distribution of base stations (BSs), traffic loads, and maximum transmission powers change. Simulation results illustrate that with proper SI cancellation and interference threshold, the proposed concurrent mechanism outperforms time-division multiple access (TDMA), half-duplex (HD) concurrent transmission, and FD concurrent transmission without power control.

Integrated Use of Licensed- and Unlicensed-Band mmWave Radio Technology in 5G and Beyond

The 3GPP standardization rapidly moves forward with studies of a wide-bandwidth waveform as well as an adaptation of the emerging 5G new radio (NR)-based access to the unlicensed spectrum (NR-U). One of the basic architectures for NR-U involves carrier aggregation of an anchor-licensed-NR carrier and a secondary carrier in unlicensed spectrum, which altogether allows for seamless traffic offloading in scenarios where multi-gigabit data rates are required. While today's research on NR-U addresses mostly physical- and protocol-layer aspects, a system-level performance of the NR-U offloading mechanisms has not been investigated thoroughly. In this paper, we develop a mathematical queuing-theoretic framework that is mindful of the specifics of millimeter-wave (mmWave) session dynamics and may serve as a flexible tool for the analysis of various strategies for the integrated use of licensed and unlicensed mmWave bands in terms of the session drop probability and system utilization. To illustrate this, we select three distinct strategies (based on sequential service, probabilistic offloading, or proportional splitting), and complement our mathematical models with a detailed performance evaluation in a representative massive augmented/virtual reality scenario. Based on this quantitative analysis of the selected schemes, we conclude that proportional splitting of traffic between the two mmWave bands leads to a better performance. We believe that the contributed mathematical analysis can become an important building block in further system development and service optimization across many usage scenarios.

Millimeter-Wave Radio Channels vs. Synthetic Beamwidth.

High-gain narrow-beam antennas or beamformed antenna arrays will likely be used in millimeter-wave (mmWave) bands and 5G to mitigate the high path loss. Since many multipath components may be excluded by the narrow beam, the mmWave radio channel (consisting of the transmit antenna, the propagation channels, and the receive antenna) strongly depends on the beamwidth, orientation, and shape of the narrow beam. In this article, a procedure is proposed to measure and model the channels vs. synthetic beamwidth. Based on experimental data collected at 60 GHz in an indoor hallway/lobby scenario, the results show that the number of multipath components and the delay dispersion of the channel are significantly reduced by the narrow beams. In addition, the path loss can be decreased by more than 20 dB with an optimized beam-center orientation. The impact of the study on future 5G mmWave system design is discussed, including frequency reuse, antenna design, receiver design, equalization, and link budget.

Millimeter-Wave-Based Fiber-Wireless Bridge System for 8K UHD Video Streaming and Gigabit Ethernet Data Connectivity

In this paper, we introduce an end-to-end and real-time seamless fiber-wireless (Fi-Wi) bridge system, for gigabit Ethernet standard data connectivity and 8K standard video streaming. The proposed end-to-end Fi-Wi bridge system consists of seamless integration of 2 × 20-km intermediate frequency-over-fiber (IFoF) and 96-GHz millimeter-wave (mmWave) wireless links. Using our system, zero packet loss of 36 compressed 8K standard videos streaming is successfully achieved for different values of mmWave attenuation levels, ranging from 35 to 55 dB. We also demonstrate the transmission of Ethernet frames at 5-Gbps capacity on the Fi-Wi bridge with 20 meters mmWave wireless link, where 8% error vector magnitude can be attained. We then investigate and evaluate the degradation caused by the IFoF and mmWave links characteristics on the overall system performance. Furthermore, we estimate analytically the attainable mmWave transmission range for different weather conditions. The obtained results demonstrate the potentials of our proposed Fi-Wi bridge systems to provide high data and reliable transmission for areas lacking fiber infrastructure and for live broadcasting relay of 8K based TV programs.

A ROF Access Network for Simultaneous Generation and Transmission Multiband Signals Based on Frequency Octupling and FWM Techniques

We report a radio-over-fiber (ROF) access network with multiple high-repetive frequency mm-wave signals generation utilizing a dual-parallel Mach-Zehnder modulator (DP-MZM) and an semiconductor optical amplifier (SOA) for multiple base stations (BSs). In the scheme, at the central station (CS), signal and pump with frequency interval of 8fRF are generated by properly adjusting the parameters of the DP-MZM. After FWM in a SOA, new converted optical signals are obtained. Two tones of the optical signals are selected by using tunable optical filter (TOF), which are then sent into a photodiode (PD) to generate multiple mm-wave signals with different frequencies (8fRF, 16fRF, and 24fRF) for different BSs. Based on the proposed scheme, the mm-wave signals with frequencies of 20, 40, and 60 GHz carrying 2.5 Gb/s signal by a 2.5GHz RF signal have been generated by numerical simulation. Simulation results show that the proposed ROF system architecture with multiple-frequency millimeter-wave signals generation serving multiple BSs can work well. This scheme can raise the capacity of ROF system, reduce the requirement of the repetitive frequency of the driven RF signal, and support multiple mm-wave wireless access for BSs.

Millimeter-Wave Multibeam Endfire Dual-Circularly Polarized Antenna Array for 5G Wireless Applications

A broadband multibeam endfire dual-circularly polarized (CP) antenna array using dielectric-loaded stepped slot antennas for millimeter-wave (mmWave) applications is proposed. First, a dual-CP endfire antenna element is designed for broadband mmWave applications. Additional loaded dielectric is utilized to improve the interelement isolation, the polarization purity, and the gain performance. Second, a substrate integrated waveguide (SIW) feeding network is designed for multibeam array applications. The broadband $4\times 4$ SIW Butler matrix, interconnections, and transitions are designed and applied in the antenna array. Third, mutual coupling and its influence on the array performance are investigated. Additional air gaps between elements are designed for axial ratio performance enhancement. Finally, the proposed multibeam array is designed, fabricated, and measured. The fabricated prototype achieves wide impedance bandwidth of 29.3% with the interbeam isolation greater than 15 dB, and a wide axial ratio bandwidth of 22.5%. The proposed multibeam endfire dual-CP antenna array would be a very attractive candidate for 5G mmWave wireless applications.

Energy efficient millimetre‐wave fronthaul and OFDMA resource optimisation in C‐RANs

Recently, millimetre-wave (mmWave) wireless fronthauls have been regarded as an effective solution to deploy remote radio heads with higher flexibility and efficiency in cloud radio access networks (C-RANs). Different from the traditional fibre fronthauls, in order to maximise the utilisation of the time-frequency resource, the mmWave wireless fronthauls are more expected to operate in a dynamic allocation manner. In this study, the energy efficient mmWave fronthaul and OFDMA resource optimisation in C-RANs is investigated. The TDMA-based fronthaul allocation mechanism is first presented and then the joint resource optimisation is formulated as an energy efficiency (EE) maximisation problem which is in the form of a mixed-integer non-linear fractional programming (MINLFP) problem. By taking advantage of the Dinkelbach method, the MINLFP problem is transformed into a subtractive optimisation problem and solved by using the Lagrange dual decomposition theory. Moreover, a maximal weighted bipartite graph matching approach is proposed to determine the optimal resource block allocation. Finally, extensive simulation results are provided to evaluate the EE performance of the proposed algorithm by comparing with several benchmark schemes, and it shows that the proposed algorithm can achieve great EE performance gain over the benchmark schemes.

Hybrid MIMO and Phased-Array Directional Modulation for Physical Layer Security in mmWave Wireless Communications

Millimeter-wave (mmWave) wireless communication system allows a compact antenna array with a large number of colocated elements, which enables flexible array design and beampattern synthesis. However, security is also particularly important but challenging for the fifth-generation (5G) wireless communications, as the broadcasting nature allows any receivers to have a copy of the transmitted signals. In this paper, we propose a hybrid multiple-input multiple-output (MIMO) phased-array time-modulated directional modulation (DM) scheme for physical layer security in mmWave wireless communications. The hybrid MIMO phased-array enjoys the advantages of MIMO in spatial diversity without sacrificing the main advantage of phased-array in coherent directional gain. The essence is to divide the transmit array into multiple subarrays. Each subarray can be used to form a directional beam, while all subarrays are jointly combined to work as an MIMO for higher angular resolution capabilities. More importantly, a time-modulated DM scheme is applied for the phased-MIMO to achieve physical layer security for mmWave wireless communications, even without the knowledge of the eavesdropper’s position information. The feasibility of the proposed scheme is verified by numerical results.

Swift-Link: A Compressive Beam Alignment Algorithm for Practical mmWave Radios

Next generation wireless networks will exploit the large amount of spectrum available at millimeter wave (mmWave) frequencies. Design of mmWave systems, however, is challenging due to strict power, cost and hardware constraints at higher bandwidths. To achieve a good SNR for communication, mmWave systems use large antenna arrays. Beamforming with highly directional beams is one way to use the antennas. As the channel changes over time, the beams that maximize the SNR have to be estimated quickly to reduce the training overhead. Prior work has exploited the observation that mmWave channels are sparse to perform compressed sensing (CS) based beam alignment with few channel measurements. Most of the existing CS-based algorithms, however, assume perfect synchronization and fail in the presence of carrier frequency offset (CFO). This paper presents Swift-Link, a fast beam alignment algorithm that is robust against the offset. Swift-Link includes a novel randomized beam training sequence that minimizes the beam alignment errors due to CFO and a low-complexity algorithm that corrects these errors. Even with strict hardware constraints, our algorithm uses fewer channel measurements than comparable CS algorithms and has analytical guarantees. Swift-Link requires a small output dynamic range at the analog-to-digital converter compared to beam-scanning techniques.

A 60 GHz Low Power Self-mixing Receiver in 65-nm CMOS for a Radio-Triggered Battery-Less Monolithic Wireless Sensor

With the growing attention at 60 GHz ISM band on millimeter-wave therapy for diseases treatment of sedative, anti-inflammatory actions or immune system stimulation, growing demand for new biomedical monitoring and treating systems with more bandwidth, high data rates and low power creates new challenges for 60 GHz body area network. Most smart wireless sensors wireless sensing operates on battery, which limits their life-time. To overcome this limitation, a system of radio-triggered batteryless monolithic wireless sensor based on mm-wave wireless power transfer technique is introduced in this work. From the system power budget analysis, it could support 10 bits communication within 10 cm, which would be sufficient for mm-wave wireless sensing application. Furthermore, it is identified that the receiver is power limited. Based on the system evaluation, an injection locked oscillator based self-mixing receiver is presented. In this architecture, the IJLO based LO scheme is used to save receiver power consumption. The sensitivity of the receiver is improved by applying the IJLO into the self-mixing architecture. This single chip receiver is implemented in a 65 nm CMOS technology. The DC power consumption of this receiver is only 16.4 mA from 1 V power supply. This power consumption is lower than other mm-wave receivers, which is an important step towards fully integrated monolithic sensor nodes.

Analysis and Comparison of High-Resolution GS/s Samplers in Advanced BiCMOS and CMOS

High-speed and high-resolution analog to digital converters (ADCs) (10+ bits) are essential components of modern wireless communication systems and mmWave radios. Their performance is often limited by the noise and distortion from the front-end samplers, the design of which can be challenging. Modern ADC design has moved heavily to scaled CMOS technologies due to its attractive digital and integration capabilities, but these processes face challenges of high fabrication costs, and diminishing analog performance that has to be bolstered by extensive digital calibration. On the other hand, BiCMOS processes have advanced and scaled sufficiently that they may be able to offer the best of the mixed signal world. This brief examines, both theoretically and through simulations, the design of samplers for high-speed, low-distortion in CMOS and BiCMOS for GS/s ADCs. Two fully differential samplers, with an equivalent sampling frequency of 5 GS/s and an input frequency range of up to 10 GHz, are designed in a 90-nm BiCMOS and a 28-nm CMOS process, respectively, and their distortion performance is analyzed, simulated, and compared.

Shadowing Correlation: Empirical Results for mm-Wave Wireless Links in Urban Street Canyons

To the best of our knowledge, this letter reports the first measurement campaign aimed at modeling the empirical large-scale/shadowing decorrelation distance in urban street canyons at 60 GHz. The observed path-loss exponents were close to Friis. Our results also show that the decorrelation distance is smaller than 40 wavelengths for the three tested scenarios. We also report that Zhang's model for the autocorrelation function of shadow fades provides a better fit than the Gudmundson's model.

SINR-based scheduling in multi-path multi-hop multi-radio multi-channel mmWave WPANs

Millimeter wave (mmWave) communications is a prospective candidate technology for multi-gigabit rates multimedia applications. To combat the severe propagation attenuation of mmWave, the high gain directional antenna is commonly employed at the nodes. Moreover, exploiting multiple radios over multiple channels is also a promising technology to improve the throughput and delay performance of mmWave communications. In this paper, considering the signal to interference plus noise ratio (SINR) constraint, we develop a multi-path multi-hop multi-radio multi-channel (MPMH-MRMC) concurrent transmission scheduling algorithm to fully exploit spatial reuse in mmWave wireless personal area networks (WPANs). The problem of MPMH-MRMC scheduling is formulated as a mixed-integer linear programming (MILP) to clear all the flows within a minimum number of time slots, which is generally NP-hard. We further propose a heuristic MPMH-MRMC scheme with low computational complexity to solve the problem. Finally, through extensive simulations, we demonstrate that MPMH-MRMC can significantly improve the network performance in terms of network throughput and transmission delay under various traffic patterns.