Flexible Spectrum Use Research Articles

Fast Convolution Based Complexity Reduction in Universal Filtered Multi-Carrier Systems

The Universal Filtered Multi-Carrier (UFMC) is a derivative of the Orthogonal Frequency Division Multiplexing (OFDM) scheme. It is considered as a candidate waveform for 5G. The considerably high computational complexity restricts the usage of UFMC based systems. This complexity is caused by the filtration process in the system. Since the flexible and efficient use of non-continuous unused spectrum for different network deployment strategies is important in the next generation communication, the selection of UFMC is inevitable because of its improved performance over OFDM and the Filter Bank Multi-Carrier (FBMC) systems. Hence, it is essential to reduce the complexity of a UFMC system. In this paper, we propose a Fast Convolution (FC) based UFMC system. The technique makes use of smaller FFTs and overlapped data frames. The proposed FC-UFMC system achieves a computation minimisation higher than 95% for systems having 64 or more fully utilised sub-channels compared to similar UFMC systems. The Peak to Average Power Ratio (PAPR) for the FC-UFMC system has a 2.27 dB improvement over the UFMC system. The BER performance of the FC-UFMC system in AWGN and ITU-R channels models are superior or similar to the corresponding UFMC system. The paper also presents the relationship of BER dependence on Signal to Noise Ratio (SNR) and Side Lobe Attenuation (SLA) of the sub-band filter.

Spectrum sharing analysis for unlicensed use in 6 GHz using Risk-Informed Interference Assessment

In October of 2018, the FCC proposed new rules for opening 1.2 GHz of spectrum in the 6 GHz band, from 5925 to 7125 MHz, for unlicensed Wireless Local Area Networks (WLAN) devices. The objective is to allow WLAN in the 6 GHz band while sharing the spectrum with current incumbents. The traditional spectrum sharing approach relies on the worst-case scenario analysis of single events of severe consequences, regardless of their probability of occurrence, which leads to over-conservative use of the spectrum. Risk-Informed Interference Assessment (RIIA) is a quantitative approach that can be successfully applied for spectrum sharing analysis. Based on statistical analysis, RIIA estimates the probability and the consequence of interference. The objective is to allow flexible use of spectrum without being overprotective. It has been applied to a few coexistence studies in the last years and has shown great potential in providing informed insight to spectrum sharing analysis. To date, however, it has not been yet applied to coexistence studies in the 6 GHz band. In this work, we apply RIIA to analyze coexistence between WLAN and each type of incumbent service in this band and propose spectrum sharing mechanisms to reduce the probability of harmful interference. To facilitate sharing in the 6 GHz band, the FCC has divided it into four sub-bands, from U-NII-5 to U-NII-8, and proposed mitigation rules for each of them depending on the incumbents. This band is allocated to Broadcast Auxiliary Service (BAS) and Cable Television Relay Service (CARS) fixed and mobile links, Fixed Satellite Service (FSS) and fixed point-to-point links. These systems use narrow beamwidth antennas located at elevated heights, while WLANs employ low-power transmitters, mostly indoors, and, typically, omnidirectional antennas at few meters above the ground, which suggests the possibility that little energy from the incumbent links is perceptible on the ground and vice versa. To investigate this hypothesis, we apply RIIA to quantify the level of risk and its consequences to both, incumbent links and WLANs devices. Our analysis is based upon a four-step method. First, we make an inventory of all significant harmful interference hazards, in our case, 6 GHz Wi-Fi APs or incumbent links that could cause co-channel interference to the incumbents or Wi-Fi devices, respectively. Second, we define the interference protection criteria for each of them as consequence metrics to characterize the severity of hazards. Third, the likelihood and consequence of each hazard are analyzed. Using Monte Carlo simulations, we calculate the likelihood of downlink and aggregate interference from/to current incumbents to/from future WLANs and, using an interference protection criterion, determine if this interference can be tolerable. Finally, the likelihood-consequence results are aggregated and compared for different scenarios. This approach provides detailed coexistence analysis between WLAN and incumbent services in the 6 GHz band using the RIIA methodology. The results suggest that there is a low risk of harmful interference to terrestrial incumbent links in the U-NII-6 and U-NII-8 bands, which consider low-power indoor APs only. For the U-NII-5 and U-NII-7 bands, considering outdoor APs transmitting at full power, the probability of harmful interference ranges from low to high, depending on the scenario. To reduce this risk, it is suggested to implement a mitigation technique. In the case of a satellite incumbent, coexistence is possible without the need of mitigation techniques. Ultimately, this work will provide decision-makers with information regarding the risks associated with coexistence in the 6 GHz band.

Wideband Broadcasting: A Power-Efficient Approach to 5G Broadcasting

Efficient and flexible use of spectrum will be inherent characteristics of 5G communication technologies with native support of wideband operation with frequency reuse 1 (i.e., all transmit sites use all available frequency resources). Although not in the very first 5G release of 3GPP, it is expected that broadcast/multicast technology components will later be added and fully integrated in the 5G system. The combination of both wideband and frequency reuse 1 may provide significant gains for broadcast transmissions in terms of energy efficiency, since it is more efficient to increase capacity by extending the bandwidth rather than increasing the transmit power over a given bandwidth. This breaks with the traditional concept of terrestrial broadcast frequency planning, and paves the way to new potential uses of UHF spectrum bands for 5G broadcasting. This article provides insight into the fundamental advantages in terms of capacity, coverage, as well as power saving of wideband broadcast operation. The role of network deployment, linked to frequency reuse in the UHF band, and its influence on the performance of a wideband broadcasting system are discussed. The technical requirements and features that would enable such a power-efficient solution are also addressed.

SFAB: Spectrum Fragment Agile Broadcast in Cognitive Radio Networks

To improve spectrum utilization, cognitive radio (CR) is introduced to detect and exploit available spectrum resources autonomously. The flexible spectrum use imposes special challenges on broadcast because different CR devices may have different available spectrum fragments at different locations. The transmitter and the receivers have to agree on spectrum fragments that will be used for broadcast. There may not exist a common spectrum fragment that is available to all receivers. Most existing work assumes that a device operates only in a single channel and thus the sender has to broadcast multiple times in different channels to reach all receivers. The broadcast problem is studied as a channel rendezvous and minimum latency scheduling problem. Recent spectrum-agile designs have enabled a device to utilize partially occupied spectrum. We thus view a wideband channel as an aggregation of multiple narrow channels that can be evaluated independently. A spectrum fragment agile broadcast (SFAB) scheme is introduced in this paper to support efficient broadcast on fragmented spectrum. It aims at achieving spectrum agreement between the transmitter and the receivers efficiently and maximizing the channel width used for broadcast regardless of the spectrum availability differences at receivers. We validate the effectiveness of SFAB through implementation on the GNU Radio/USRP platform and use ns-2 simulations to evaluate the performance in large deployments.

The 5G candidate waveform race: a comparison of complexity and performance

5G will have to cope with a high degree of heterogeneity in terms of services and requirements. Among these latter, the flexible and efficient use of non-contiguous unused spectrum for different network deployment scenarios is considered a key challenge for 5G systems. To maximize spectrum efficiency, the 5G air interface technology will also need to be flexible and capable of mapping various services to the best suitable combinations of frequency and radio resources. In this work, we propose a comparison of several 5G waveform candidates (OFDM, UFMC, FBMC and GFDM) under a common framework. We assess spectral efficiency, power spectral density, peak-to-average power ratio and robustness to asynchronous multi-user uplink transmission. Moreover, we evaluate and compare the complexity of the different waveforms. In addition to the complexity analysis, in this work, we also demonstrate the suitability of FBMC for specific 5G use cases via two experimental implementations. The benefits of these new waveforms for the foreseen 5G use cases are clearly highlighted on representative criteria and experiments.

LTE broadcast and supplemental downlink enablers for exploiting novel service and business opportunities in the flexible use of the uhf broadcasting spectrum

This article reviews technology and business enablers for future flexible use concepts of the UHF broadcasting spectrum (470-790 MHz) by digital terrestrial TV and MBB. Flexible use of the UHF band aims to increase the efficiency of spectrum use in delivering fast-growing and converging mobile broadband, media, and TV content to meet changing consumer needs. Enabling technical factors are presented, and potential services are compared in order to identify similarities and differences in possible business model designs and scaling factors for developing successfully deployable services and regulatory concepts. The results indicate that several services meet basic requirements to scale, leveraging key existing assets and capabilities of LTE technologies and the business ecosystem while extending current business models beyond connectivity. Regulation and standardization forums can utilize the developed use case and service scenarios in analyzing the future of UHF spectrum and LTE broadcasting evolution. Furthermore, the flexible use concept has the potential to transform the business ecosystem around both BC and MBB by introducing new convergence opportunities for LTE's development toward 5G.

Cognitive radio frequency assignment with interference weighting and categorization

Cognitive radio is one of the technologies promoting flexible and efficient use of radio frequency spectrum, thus solving spectrum scarcity problem. Frequency assignment is an integral part of the cognitive radio spectrum management and a critical point of success or failure of the cognitive radio concept. In this paper, cognitive radio frequency assignment with a novel interference weighting and categorization is proposed, as an extension of the solution to the graph coloring problem. In our approach, the edge weights quantifying the interference potential are appended to the conflict graph, co- and adjacent channel interference are treated, and dynamically changing local lists of blocked frequencies are included. We propose the improved cognitive radio saturation metric for the dynamic vertex ordering and to introduce interference categorization which will reduce the communication overhead. Using the proposed model, resource manager can quantify individual interference components, as well as aggregate interference from multiple users, resulting in more knowledgeable frequency decisions. Generalization of the proposed model is suggested. The suggested generalization consists of the selection of the central frequency and optimal bandwidth to be used, according to the user requirements. We have developed interference-sensitive algorithms for minimizing the interference and maximizing the throughput, both in centralized and distributed implementation. The results show significant reduction of the interference, improved spectrum efficiency, and increase in network throughput, comparing to the benchmark algorithms.

Real-Time Demonstration of Optimized Spectrum Usage with LSA Carrier Aggregation

AbstractMobile broadband networks will face a tremendous growth in data traffic demand over the next 20 years. A key requirement for the evolution of radio access networks is the increase in the amount of spectrum and optimized spectrum usage, in order to meet future service demands. More efficient spectrum use will come with evolving technology features and novel spectrum sharing models. Candidates for technology improvements are higher order and massive MIMO systems, cooperative base stations and CoMP techniques, highly optimized resource allocation algorithms, network densification with inter-cell interference management and highly flexible carrier aggregation techniques to extend spectrum. In this paper, we will highlight carrier aggregation combined with flexible spectrum assignment and use of spectrum databases following novel licensing schemes. We give an overview of LSA activities, present a 3CA demonstration platform enabling the LSA concept and discuss its implementation constraints.

Spectrum Exploration and Exploitation for Cognitive Radio: Recent Advances

The lack of availability of radio spectrum for wireless communication purposes is becoming a serious problem as more wireless systems and services are being developed and operate in crowded spectral bands. The scarcity of useful radio spectrum is mainly due to the static allocation and rigid regulation of the spectrum use rather than the spectrum being actually fully in use. Flexible spectrum use and cognitive radio technologies provide an approach to alleviating this problem by allowing for secondary spectrum use while the spectrum is underutilized by its primary licensed users. Idle spectrum is a time-frequency-location varying resource. It is a resource that also depends on the relative locations of the primary and secondary receivers and transmitters as well as the instantaneous propagation conditions. By acquiring awareness about the current radio environment and the other spectrum users, cognitive radios can more efficiently exploit idle spectrum and manage interference. Doing so requires a means to explore the spectrum to identify high-quality and persistent local spectral resources and access and share them among a number of users while strictly controlling the interference caused to others, in particular, licensed primary users (PUs). Situational awareness about the state of the spectrum allows for optimal exploitation of underutilized spectrum. For example, idle subbands may be allocated, and waveform parameters may be chosen to maximize the sum-rate for the cognitive users while making sure no harmful interference is caused to the other users of the spectrum.

SoftMobile: control evolution for future heterogeneous mobile networks

Heterogeneous mobile networks, HMNs, with flexible spectrum use, densified cell deployment, and multi-layer multiple types of radio access technologies, are expected to be key to meeting the 1000 times increase of mobile data traffic in 2020 and beyond. The increasing complexity in HMNs renders the control and coordination of networks a challenging task. The control frameworks of current cellular networks, which were previously designed for sparse network deployment, hit the wall for HMNs. HMNs need good separation of control and data planes, and call for novel control methods to handle the highly complex dynamics therein. In this article, we first briefly review the control planes of 2G to 4G cellular networks, and then identify their constraints to support HMNs. We analyze the complexity in HMNs and examine enabling control technologies for HMNs. We believe new thinking is needed for efficient control of HMNs. SDN is a promising technology to solve complex control problems in the Internet. Principle-based control methods applied in SDN are promising to solve control problems in HMNs. Several SDN approaches have been proposed for mobile networks. However, most of them are targeted at mobile core networks. We propose an SDNbased control framework named SoftMobile to coordinate complex radio access in HMNs. The main features of SoftMobile are low-layer abstraction, separation of control and data planes, and network-wide high-layer programmable control. Important research problems in SDN for mobile networks are highlighted. We believe SDN for mobile networks will be the controlling evolution of future HMNs.

Emerging cognitive radio applications: A survey

Recent developments in spectrum policy and regulatory domains, notably the release of the National Broadband Plan, the publication of final rules for TV white spaces, and the ongoing proceeding for secondary use of the 2360-2400 MHz band for medical body area networks, will allow more flexible and efficient use of spectrum in the future. These important changes open up exciting opportunities for cognitive radio to enable and support a variety of emerging applications, ranging from smart grid, public safety and broadband cellular, to medical applications. This article presents a high-level view on how cognitive radio (primarily from a dynamic spectrum access perspective) would support such applications, the benefits that cognitive radio would bring, and also some challenges that are yet to be resolved. We also illustrate related standardization that uses cognitive radio technologies to support such emerging applications.

Empirical time and frequency domain models of spectrum use

Dynamic spectrum access (DSA) has been proposed as a solution to the spectrum scarcity problem. However, the models for spectrum use, that are commonly used in DSA research, are either limited in scope or have not been validated against real-life measurement data. In this paper we introduce a flexible spectrum use model based on extensive measurement results that can be configured to represent various wireless systems. We show that spectrum use is clustered in the frequency domain and should be modelled in the time domain using geometric or lognormal distributions. In the latter case the probability of missed detection is significantly higher due to the heavy-tailed behaviour of the lognormal distribution. The listed model parameters enable accurate modelling of primary user spectrum use in time and frequency domain for future DSA studies. Additionally, they also provide a more empirical basis to develop regulatory or business models.

Flexible spectrum use and better coexistence at the physical layer of future wireless systems via a multicarrier platform

C-N2-N- Company 2 bandwidth ABSTRACT In this article we propose a new multicarrier platform to optimize the efficiency of wireless operators' licensed hands and enable flexible shar- ing of licensed and unlicensed hands (in different spectral regions). This research, besides introduc- ing a high degree of flexibility of spectrum use for 4G systems, supports a recent FCC proposal that goes beyond suggesting improved spectral efficien- cy, and instead suggests innovative spectrum man- agement regulations. Specifically, this work presents a multicarrier platform capable of achiev- ing high spectral efficiency by the application of narrow orthogonal carriers, that enables flexible spectral sharing across different licensed and unli- censed bands via operator borrowingilending.

Legal and regulatory issues regarding spectrum rights trading

The FCC's historic “command-and-control” approach to spectrum management has contributed to spectrum scarcity, especially as it relates to spectrum below 3 GHz. This approach has also made it difficult for spectrum users to adjust their business plans to the needs of the marketplace. A more flexible regulatory regime would increase spectrum efficiency and foster innovation and new services. In order to promote more flexible use of spectrum, the authors recommend a number of regulatory and statutory changes, including (1) the elimination of use restrictions for new wireless allocations; (2) the replacement of existing use restrictions with power limits sufficient to minimize the potential for harmful interference; (3) the enactment of rules expressly allowing private parties to “contract around” established interference limits; and (4) the identification of “safe harbor” spectrum leasing arrangements that are deemed permissible under the FCC's license transfer of control requirements. The authors also recommend a number of statutory reforms, including granting the FCC express statutory authority to auction spectrum licenses held by private parties and assess spectrum fees upon users of auction-exempt spectrum.