Spatial Frequency Reuse Research Articles

UE admittance and contention free resource allocation for interference mitigation in HetNet cognitive femtocells

Femtocells are designed to co-exist alongside macrocells providing higher spectrum efficiency, spatial frequency reuse, to name a few. However, when deployed in the two-tier architecture with macrocells, interference is imminent thereby it is necessary to mitigate the inherent co-tier and cross-tier interference. The integration of cognitive radio (CR) in femtocells introduces the ability of femtocells to dynamically adapt to varying network conditions through learning, adapting, and reasoning leading to informed decisions. This paper proposes a joint threshold power based admittance and contention free resource allocation scheme (known as Proposed SA) for interference mitigation in HetNet cognitive femtocells (CF). In the proposed SA, a CF sets a threshold value on the mutual interference between itself and a close-by mobile user equipment (MUE). To mitigate cross-tier interference, a CF classifies MUEs which fall above this threshold value (high interference value) as Undesired MUEs (UMUEs), whereas MUEs which fall below this threshold are classified as Desired MUEs (DMUEs). To mitigate co-tier interference, proposed SA introduces a scheduling engine which employs matching policy attributes and assigns resource blocks (RBs) of unique DMUEs to CFs to avoid any possible contention problems, thus providing improved co-tier interference. System level simulations have been performed to demonstrate working and effectiveness of proposed SA. Key performance indicators including choice of maximum transmit power for MUE, co and cross tier interference mitigation, as well impact of MUE mobility has been investigated. Performance analysis of the Proposed SA has also found that the scheme performs much better in relation to a random spectrum assignment (Random SA) scheme. The proposed SA caters the mobility of the MUEs very well allowing more and more admittance thereby providing improved interference results and making it a viable candidate for Femtocell Access points (FAPs) implementation.

Mapping spatial distribution of comm‐satellite's beam based on ground omni‐antennas

SummaryThe current satellite communications (SatComs) systems are composed of a large number of satellites, beams and terrestrial devices. Due to their multinode dynamic nature, the usage of frequency resources is variable, complex and difficult to characterize. In particular, with the development of satellite‐borne phased array antenna technology, SatCom beams carrying different frequencies are directionally and dynamically distributed in global scale. Mapping and locating the spatial beam distributions of communication satellite (comm‐satellite) are the bases of intersystem cofrequency interference mitigation and spatial frequency reuse. In this paper, we design a data selection–multiparameter fitting iteration (DS‐MFI) algorithm on the basis of ground‐based omnidirectional antennas. The proposed approach can effectively map the spatial distribution of comm‐satellite's beam, including satellite transmitter position, equal‐gain off‐axis angle, and beam pointing in azimuth and elevation. Simulation results verify the effectiveness of the proposed approach for satellites with fixed or steerable beams at different altitudes. Furthermore, the results become increasingly accurate as the dense of ground omni‐antenna increases.

Formation-of-Arrays Antenna Technology for High-Throughput Mobile Non-Terrestrial Networks

Effective integration of terrestrial and non-terrestrial segments is one of the key research avenues in the design of current and future wireless communication networks. To this aim, modern communication-satellite constellations intend to attain sufficiently high throughput in terms of bit rate per unit area on the ground by rather aggressive patterns of spatial frequency reuse. This goal calls for on-board narrow-beam antennas, whose size turns out to be in many cases incompatible with the size/mass and accommodation constraints of the hosting satellite. This paper investigates the attainable performance of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">large distributed arrays of antennas</i> implemented as the ensemble of a few to many simpler sub-antennas of smaller sizes, carried by one (small) satellite each. The sub-antennas can in their turn be implemented like (regular) 2D arrays of simple radiating elements, realizing an overall (distributed) antenna architecture that we call “formation of arrays” (FoA). The satellites that implement this radiating architecture need to be relatively close to each other and constitute a <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">formation</i> of flying objects, to be coordinated and controlled as a whole. In this paper, we develop a theoretical analysis of an FoA antenna, and we show how to take advantage of this new technology to improve network throughput in a multi-beam S-band mobile communication network with low-earth or geostationary orbiting satellites directly providing 5G-like communication services to hand-held user terminals.

Spatial multiplexing and optical PAM4 quadruple the date rate in optical fiber systems.

This endeavor demonstrates a two-channel spatial division multiplexed (SDM) system and combines it with an all-optical four-level pulse amplitude modulation (PAM4) scheme to quadruple the data rate and presents the experimental setup, system model, as well as key results. The system initially introduces spatial reuse of optical frequencies in a single-core multimode optical fiber by transmitting two SDM channels, where both operate at 1310nm. It then complements the two SDM channels with an all-optical PAM4 scheme to enable 2bits/symbol and 40Gbps optical transport while using only 10Gbps sources. Since all sources operate at the same wavelength, it effectively achieves PAM16 efficiencies at the given wavelength. The system accomplishes these results without the use of dedicated PAM4 chipsets.

Uplink Interference and Performance Analysis for Megasatellite Constellation

Satellite communications play an important role in future Internet of Things (IoT) networks, and megasatellite constellations can further provide global coverage and high-quality services for IoT communications. In the megaconstellation, large-scale satellites are launched to enhance the capacity. However, the dense distribution of satellites brings intraconstellation interference, limiting the performance. In order to evaluate the restriction of interference caused by system parameters, such as the scale of constellation or the frequency reuse factor, we investigate uplink intraconstellation interference and performance of the megasatellite constellation. First, a multibeam polar constellation with uplink spatial frequency reuse is assumed. Then, the interference model is constructed considering the antenna gain of interfering user terminals and multibeam satellites, where the details of the satellite-fixed frequency reuse scheme and coordinates of co-frequency cells are provided. To evaluate the performance, expressions of outage probability, ergodic capacity, and sum ergodic capacity are driven. The analytical results disclose the impact of system design on the performance, and the accuracy of analysis results is obtained through extensive simulation evaluation. The results show that sum ergodic capacity achieves highest in the case of full frequency reuse for the frequency-limited constellation system, and it gets a linear growth at first but then keeps flat with a trend of fluctuating downward as the scale increases; therefore, the impact of the scale should be considered when constructing megaconstellations.

Spatial Compression of Sensing Information for Exploiting the Vacant Frequency Resource Using Radio Sensors

Recently, broadband wireless communication has been significantly enhanced; thus, frequency spectrum scarcity has become an extremely serious problem. Spatial frequency reuse based on the spectrum database is attracting significant attention. The spectrum database collects the wireless environment information, such as the radio signal strength indicator (RSSI), estimates the propagation coefficient for the propagation loss and shadow effect, and finds a vacant area where the secondary system uses the frequency spectrum without harmful interference to the primary system. To collect RSSI from the radio environ-mental monitor, which is a radio sensor, wireless sensor networks are required. However, a large number of RSSIs should be gathered because numerous sensors are spread over the wireless environment. In this paper, a data compression technique based on spatial features, such as buildings and houses, is proposed. Using a computer simulation and an experimental evaluation, we confirm that the proposed compression successfully reduces the size of the RSSI and restores the original RSSI in the recovery process.

D2D data offloading in vehicular environments with optimal delivery time selection

Within the framework of a Device-to-Device (D2D) data offloading system for cellular networks, we propose a Content Delivery Management System (CDMS) in which the instant for transmitting a content to a requesting node, through a D2D communication, is selected to minimize the energy consumption required for the transmission. The proposed system is particularly fit to highly dynamic scenarios, such as vehicular ones, where the network topology changes at a rate which is comparable with the order of magnitude of the delay tolerance. We present an analytical framework able to predict the system performance, in terms of energy consumption, considering concurrent requests for contents with different popularity. We validate the analytical model through simulations, and provide a thorough performance evaluation of the proposed CDMS, in terms of energy consumption and spectrum use. The proposed CDMS can be configured in two ways: (i) either use I2D transmissions only as a last resort, if it is not possible to serve request through D2D offloading within the limit of the delay tolerance; or (ii) include the possibility for the Base Stations (BSs) to transmit contents even before the deadline, if this is found to be more energy efficient from the point of view of the overall energy consumption, renouncing a portion of the offloading opportunities. The proposed scheme is benchmarked against a plain classic cellular scheme, a cellular (I2D only) scheme with optimal Infrastructure-to-Device (I2D) transmission scheduling for delay-tolerant applications, and a D2D data offloading scheme (proposed in previous works) in which the D2D transmission is performed as soon as a close-by device with the required content is found (i.e., without optimizing the transmission instant). We implemented a quite detailed simulator complete of Radio Resource Management (RRM) over the MAC layer of a multi carrier system, in a multi-cell scenario. Our results show that the proposed CDMS can induce a reduction of an order of magnitude, i.e. 90% or higher, of the energy consumed by the devices to implement D2D offloading, with respect to the benchmark D2D offloading scheme. At the same time, we observed a reduction of the energy consumption of the overall system in the order of 30%, under conservative assumptions. Finally, the system induces a remarkable degree of spatial frequency reuse, thus reducing the overall spectrum occupation.

On efficient radio resource calendaring in cloud radio access network

We propose in this paper a radio resource allocation scheme in the context of Cloud-based Radio Access Networks (C-RAN) run by a single operator. We specifically leverage bandwidth calendaring, a technique that allows shifting bulk data transfers, typically of large size with less stringent real-time constraints, to future epochs when the network is less congested. In particular, we propose an auction-based framework for bandwidth calendaring, where the C-RAN operator, as the spectrum auctioneer, runs an auction with its users, with the aim of maximizing its revenue. The auction-based mechanism takes as input the set of the users’ bids and outputs the calendaring and pricing decisions. We first formulate the calendaring problem using Integer Linear Programming (ILP) and the pricing problem using the Vickrey Clarke Groves (VCG) pricing scheme. We further make use of the Bayesian settings to compute the optimal revenue. Due to the exponential time induced by the NP-hardness of the ILP formulation, we propose an effective approach that satisfies desired auction properties such as individual rationality and truthfulness while achieving a sub-optimal revenue, in polynomial time. We explicitly evaluate the impact of mobile systems features such as spatial frequency re-use and interference among mobile users, and study their impact on the overall system’s performance. Extensive simulations, conducted in representative network scenarios, demonstrate the effectiveness of our proposal in improving the performance of C-RAN scheduling.

Interference Range-Reduced Cooperative Multiple Access with Optimal Relay Selection for Large Scale Wireless Networks.

Cooperative communication improves the link throughput of wireless networks through spatial diversity. However, it reduces the frequency reuse of the entire network due to the enlarged link interference range introduced by each helper. In this paper, we propose a cooperative medium access control (MAC) protocol with optimal relay selection (ORS-CMAC) for multihop, multirate large scale networks, which can reduce the interference range and improve the network throughput. Then, we investigate the performance gain achieved by these two competitive factors, i.e., the spatial frequency reuse gain and spatial diversity gain, in large scale wireless networks. The expressions of maximum network throughput for direct transmissions and cooperative transmissions in the whole network are derived as a function of the number of concurrent transmission links, data packet length, and average packet transmission time. Simulation results validate the effectiveness of the theoretical results. The theoretical and simulation results show that the helper can reduce the spatial frequency reuse slightly, and spatial diversity gain can compensate for the decrease of the spatial frequency reuse, thereby improving the network throughput from the viewpoint of the whole network.

A Tutorial on IEEE 802.11ax High Efficiency WLANs

While celebrating the 21st year since the very first IEEE 802.11 “legacy” 2 Mbit/s wireless local area network standard, the latest Wi-Fi newborn is today reaching the finish line, topping the remarkable speed of 10 Gbit/s. IEEE 802.11ax was launched in May 2014 with the goal of enhancing throughput-per-area in high-density scenarios. The first 802.11ax draft versions, namely, D1.0 and D2.0, were released at the end of 2016 and 2017. Focusing on a more mature version D3.0, in this tutorial paper, we help the reader to smoothly enter into the several major 802.11ax breakthroughs, including a brand new orthogonal frequency-division multiple access-based random access approach as well as novel spatial frequency reuse techniques. In addition, this tutorial will highlight selected significant improvements (including physical layer enhancements, multi-user multiple input multiple output extensions, power saving advances, and so on) which make this standard a very significant step forward with respect to its predecessor 802.11ac.

User-Centric C-RAN Architecture for Ultra-Dense 5G Networks: Challenges and Methodologies

Ultra-dense networks (UDNs) constitute one of the most promising techniques for supporting the 5G mobile system. By deploying more small cells in a fixed area, the average distance between users and access points can be significantly reduced; hence, dense spatial frequency reuse can be exploited. However, severe interference is the major obstacle in UDNs. Most contributions deal with the interference by relying on cooperative game theory. This article advocates the application of dense user-centric C-RAN philosophy to UDNs, thanks to the recent development of cloud computing techniques. Under dense C-RAN, centralized signal processing can be invoked for supporting CoMP transmission. We summarize the main challenges in dense user-centric C-RANs. One of the most challenging issues is the requirement of the global CSI for the sake of cooperative transmission. We investigate this requirement by only relying on partial CSI, namely, on inter-cluster large-scale CSI. Furthermore, the estimation of the intra-cluster CSI is considered, including the pilot allocation and robust transmission. Finally, we highlight several promising research directions to make the dense user-centric C-RAN become a reality, with special emphasis on the application of big data techniques.

Two-Color Scheme for a Multi-Beam Satellite Return Link: Impact of Interference Coordination

The return link of broadband satellite systems has recently received more attention due to the spread of multi-beam antennas which enable spatial frequency reuse, and thus increase drastically the number of users that can potentially be served by one satellite. While interference isolation has so far been the way to go, with regular four-color frequency reuse scheme, there is a growing interest in densifying the frequency usage as is being done in cellular networks. In this paper, we address the return link radio resource allocation challenges, from spectral resource allocation to user scheduling, including modulation and coding scheme (MODCOD) selection. Our contributions highlight the potential gains of a two-color scheme and shed light on several levers to reap its benefits through interference management. We first consider the possibility to use a two-color scheme, while keeping the MODCOD selection and the scheduling local to each beam and we show that even though it yields a potential performance gain (+16%) with respect to the state of the art (SoA) (based on four colors), it is not viable due to a very high-block loss rate. Therefore, we propose a simple—yet fast and efficient—coordinated MODCOD selection process that alleviates the need of estimating interference and reduces drastically decoding failures. This coordination step offers significant gains (+58%) over the SoA, while leaving the per beam scheduler unchanged. Finally, we formulate a joint user scheduling and MODCOD selection problem across all beams and propose an offline heuristic to solve it efficiently. We obtain a 83% gain with respect to the SoA, but with higher computational complexity. Still, it confirms the great potential of coordinated scheduling.

Improving QoS of VANET Using Adaptive CCA Range and Transmission Range both for Intelligent Transportation System

Connectivity and spatial frequency reuse are very important performance influencing factors in Vehicular Ad-hoc NETwork (VANET). In proposed work connectivity in VANET is measured in terms of Vehicular Average Connected Coverage (VACC). Interference on road is measured in terms of Average Highly Interference Region ratio (AvgHIR). A new Adaptive Transmission and Clear Channel Assessment (CCA) Power scheme (ATCCAPsch) is proposed. ATCCAPsch varies Transmission Range (TR) along with CCA range to improve VACC, AvgHIR, spatial frequency reuse and hence overall QoS performance of VANET. ATCCAPsch performs its operations based on selected threshold “MINimum Transmission Range of Vehicle ( $$minTR_{v\_sel}$$ )” and “Required Number of Neighbours ( $$RNNgb_{sel}$$ )”. Comprisal of $$minTR_{v\_sel}$$ and $$RNNgb_{sel}$$ is done in the definition of VANET’s Multi-Objective optimization Problem (VANET-MOP). VANET Multi-Objective optimization Model (VANET-MOM) is defined and implemented to solve VANET-MOP to determine $$RNNgb_{sel}$$ and lower bound of $$minTR_{v\_sel}$$ ( $$lbhvh\_minTR_{v\_sel}$$ ). VANET-MOM incorporates ATCCAPsch in another newly proposed algorithm “VATCCAPschSim” to evaluate VACC and AvgHIR. Multi Objective Optimization (MO-Opt) tool “gamultiobj” is used to serve the purpose. Performance of proposed ATCCAPsch is verified in NS-3 simulator for single channel and infrastructureless VANET. ATCCAPsch decreased mean delay per hop by 1.86, 25.9 and 16.8% for given MAXimum Transmission Range of Vehicle ( $$maxTR_{v}$$ ) 250, 400 and 1000 m resp. as compared to Fixed Transmission and CCA Power SCHeme (FTCCAPsch). ATCCAPsch is also enhancing other Quality of Services (QoS) like packet delivery ratio, delay and jitter of VANET.

Iterative Relay Scheduling With Hybrid ARQ Under Multiple User Equipment (Type II) Relay Environments

In this paper, we propose an iterative relay scheduling with hybrid ARQ (IRS-HARQ) scheme, which realizes fast jump-in/successive relaying and subframe-based decoding under the multiple user equipment (UE) relay environments applicable to the next-generation cellular systems (e.g., LTE-advanced and beyond). The proposed IRS-HARQ aims to increase the achievable data rate by iteratively scheduling a relatively better UE relay closer to the end user in a probabilistic sense, provided that the relay-to-end user link should be operated in an open-loop and transparent mode. The latter is due to the fact that not only there are no dedicated control channels between the UE relay and the end user, but also a new cell is not created. Under this open-loop and transparent mode, our proposed protocol is implemented by partially exploiting the channel state information based on the overhearing mechanism of acknowledge/negative acknowledge for HARQ. Further, the iterative scheduling enables UE-to-UE direct communication with proximity that offers spatial frequency reuse and energy saving.

Resource Allocation Based on Channel Sensing and Spatial Spectrum Reuse for Cognitive Femtocells

A cognitive femtocell is a new small cell based on a smart home base station to solve the spectrum-scarcity problem. Recently, dedicated resource allocation for cognitive femtocell to mitigate co-channel interference is extensively researched. However, the cognitive femtocell may suffer from the lack of frequency resource for its users due to high data traffic load of the macrocell. We propose a novel resource allocation and power control mechanism using spatial frequency reuse and spectrum sensing, which enables femto users in the cognitive femtocell to obtain more feasible resource. We analyze and evaluate the performance gain of the proposed scheme. Although data traffic load of the macrocell increases, the capacity of the cognitive femtocell can be maintained appropriately by the proposed resource allocation and power control scheme and it is shown that the performance is improved compared to that of the conventional scheme.

Adaptive De-Coupling and Multi-BS Association in Heterogeneous Networks

This paper proposes a novel method for maximizing the spatial frequency reuse in cellular networks by exploiting the possibility to simultaneously associate each user to multiple base-stations (BSs). To this end, the proposed technique presents a criterion for determining when a user should be associated with one or more BSs and whether the uplink and downlink should be decoupled, based on minimizing the average interference power across the network. To minimize the effect of interference that may occur due to increasing the spatial frequency reuse, the proposed association methods are integrated with an overlap checking scheme to insure that the resources are orthogonalized between the interfering BSs and user equipments. The results show that significant performance improvements can be attained by the proposed scheme in comparison with other benchmark techniques.

Mobility-Aware Modeling and Analysis of Dense Cellular Networks With $C$ -Plane/ $U$ -Plane Split Architecture

The unrelenting increase in the population of mobile users and their traffic demands drive cellular network operators to densify their network infrastructure. Network densification shrinks the footprint of base stations (BSs) and reduces the number of users associated with each BS, leading to an improved spatial frequency reuse and spectral efficiency, and thus, higher network capacity. However, the densification gain comes at the expense of higher handover rates and network control overhead. Hence, user’s mobility can diminish or even nullifies the foreseen densification gain. In this context, splitting the control plane ( $C$ -plane) and user plane ( $U$ -plane) is proposed as a potential solution to harvest densification gain with reduced cost in terms of handover rate and network control overhead. In this paper, we use stochastic geometry to develop a tractable mobility-aware model for a two-tier downlink cellular network with ultra-dense small cells and $C$ -plane/ $U$ -plane split architecture. The developed model is then used to quantify the effect of mobility on the foreseen densification gain with and without $C$ -plane/ $U$ -plane split. To this end, we shed light on the handover problem in dense cellular environments, show scenarios where the network fails to support certain mobility profiles, and obtain network design insights.

Wavelength independency of spatially multiplexed communication channels in standard multimode optical fibers

Spatial domain multiplexing (SDM), also known as space division multiplexing, adds a new degree of photon freedom to existing optical fiber multiplexing techniques by allocating separate radial locations to different channels of the same wavelength as a function of the input launch angle. These independent MIMO channels remain confined to their designated locations while traversing the length of the carrier fiber owing to helical propagation of light inside the fiber core. As a result, multiple channels of the same wavelength can be supported inside a single optical fiber core, thereby allowing spatial reuse of optical frequencies and multiplication of fiber bandwidth. It also shows that SDM channels of different operating wavelengths continue to follow an output pattern that is based on the input launch angle. As a result, the SDM technique can be used in tandem with wavelength division multiplexing (WDM), to achieve higher optical fiber bandwidth through increased photon efficiency and added degrees of photon freedom. This endeavor presents the feasibility of a hybrid optical fiber communication architecture in which the spectral efficiency of the combined system increases by a factor of “n” when each channel of an “ n ” channel SDM system carries the entire range of WDM spectra.

Combining Spot and Futures Markets: A Hybrid Market Approach to Dynamic Spectrum Access

Dynamic spectrum access is a new paradigm of secondary spectrum utilization and sharing. It allows unlicensed secondary users (SUs) to exploit the opportunistically underutilized licensed spectrum. Market mechanism is a widely used promising means to regulate the consuming behaviours of users and, hence, achieve the efficient allocation and consumption of limited resources. In this paper, we propose and study a hybrid secondary spectrum market consisting of both the futures market and the spot market, in which SUs (buyers) purchase underutilized licensed spectrum from a spectrum regulator (SR), either through predefined contracts via the futures market, or through spot transactions via the spot market. We focus on the optimal spectrum allocation among SUs in an exogenous hybrid market that maximizes the secondary spectrum utilization efficiency. The problem is challenging because of the stochasticity and asymmetry of network information. To solve this problem, we first derive an off-line optimal allocation policy that maximizes the ex ante expected spectrum utilization efficiency based on the stochastic distribution of network information. We then propose an online Vickrey-Clarke-Groves (VCG) auction that determines the real-time allocation and pricing of every spectrum based on the realized network information and the prederived off-line policy. We further show that with the spatial frequency reuse, the proposed VCG auction is NP-hard; hence, it is not suitable for online implementation, especially in a large-scale market. To this end, we propose a heuristics approach based on an online VCG-like mechanism with polynomial-time complexity, and further characterize the corresponding performance loss bound analytically. We finally provide extensive numerical results to evaluate the performance of the proposed solutions.

Combining spatial domain multiplexing and orbital angular momentum of photon-based multiplexing to increase the bandwidth of optical fiber communication systems

Spatial domain multiplexing/space division multiplexing (SDM) can increase the bandwidth of existing and futuristic optical fibers by an order of magnitude or more. In the SDM technique, we launch multiple single-mode pigtail laser sources of the same wavelength into a carrier multimode fiber at different angles. The launching angles decide the output of the carrier fiber by allocating separate spatial locations for each channel. Each channel follows a helical trajectory while traversing the length of the carrier fiber, thereby allowing spatial reuse of optical frequencies. We launch light from five different single-mode pigtail laser sources (of same wavelength) at different angles (with respect to the axis of the carrier fiber) into the carrier fiber. Owing to helical propagation, five distinct concentric donut-shaped rings with negligible crosstalk at the output end of the fiber were obtained. These SDM channels also exhibit orbital angular momentum (OAM), thereby adding an extradegree of photon freedom. We present the experimental data of five spatially multiplexed channels and compare them with simulated results to show that this technique can potentially improve the data capacity of optical fibers by an order of magnitude: A factor of five using SDM and another factor of two using OAM.