Spectral Coexistence Research Articles

A New Paradigm for Spectrum Sharing Between Cellular Wireless Communications and Radio Astronomy Systems

This paper proposes a new paradigm for spectrum sharing between cellular wireless communications (CWC) and radio astronomy systems (RAS). In contrast to the existing paradigm of geographical and spectral isolation between CWC and RAS, this paper develops a three phase spectrum access, which enables geographical and spectral coexistence between CWC and RAS. Shared spectrum access zone (SSAZ) is created around the RAS site and CWC cells within the SSAZ follow the three phase spectrum access scheme while those outside the SSAZ have full spectrum access. In addition, system characteristics-based improved spectrum sharing is developed. Furthermore, a built-in fine tuning mechanism is presented for addressing mismatches between design and practical environments as well as for facilitating service evolutions. Performance evaluation results demonstrate that the proposed paradigm offers 1) certain guaranteed spectrum access to RAS, which is impossible in the existing paradigm, 2) capability to handle higher peak and mean traffics to CWC under spectrum restructuring of both CWC and RAS bands, and 3) overall improved spectrum utilization.

Constrained radar waveform design algorithm for spectral coexistence

The design problem of radar waveform to enhance target delectability while ensuring spectral compatibility is considered. Precisely, an iterative sequential optimisation algorithm is developed to jointly optimise signal-to-interference-plus-noise ratio and stopband frequency energy. In each iteration of the proposed algorithm, the multidimensional optimisation problem is turned into multiple one-dimensional optimisation problems with closed-form solutions. Finally, the computational cost and objective value of the proposed algorithm in comparison with the existing method is assessed.

Spectral Coexistence of MIMO Radar and MIMO Cellular System

This paper details designing the precoder of a MIMO-radar spectrally-coexistent with a MIMO cellular system. Spectrum sharing with zero or minimal interference is achieved by using, respectively, the conventional switched null space projection (SNSP) or the newly proposed switched small singular value space projection (SSSVSP). Loss in radar target localization capability due to precoding can be compensated by using SSSVSP instead of SNSP to some extent but increasing the number of radar antenna elements is more effective.

On Spectral Coexistence of CP-OFDM and FB-MC Waveforms in 5G Networks

Future 5G networks will serve a variety of applications that will coexist on the same spectral band and geographical area in an uncoordinated and asynchronous manner. It is widely accepted that using cyclic prefix-orthogonal frequency division multiplexing (CP-OFDM), the waveform used by most current communication systems, will make it difficult to achieve this paradigm. Especially, CP-OFDM is not adapted for spectral coexistence because of its poor spectral localization. Therefore, it has been widely suggested to use filter bank-based multicarrier (FB-MC) waveforms with enhanced spectral localization to replace CP-OFDM. Especially, FB-MC waveforms are expected to facilitate coexistence with legacy CP-OFDM-based systems. However, this idea is based on the observation of the power spectral density of FB-MC waveforms only. In this paper, we demonstrate that this approach is flawed and show that interference between FB-MC and CP-OFDM systems should be rated on precise estimation of the error vector magnitude. Our analysis, which is confirmed through simulations on both flat and frequency selective channels and software radio implementation, shows that the interference caused by FB-MC waveforms on CP-OFDM receivers is multiple orders of magnitude higher than expected in the literature. Finally, our results show that using FB-MC waveforms does not facilitate coexistence with CP-OFDM-based systems to a high extent.

On the spectral coexistence of GSO and NGSO FSS systems: power control mechanisms and a methodology for inter‐site distance determination

SummaryThe coexistence of geostationary satellite orbit (GSO) and non‐GSO (NGSO) fixed satellite service systems within the same spectrum to enhance the spectrum efficiency in Ka band has attracted many interests lately. However, the coexistence of GSO‐NGSO satellite systems with limited shared spectrum can cause in‐line interference from a satellite to other satellite's earth terminals. In this context, this contribution investigates three possible power control approaches to mitigate the in‐line interference caused by an NGSO satellite to the GSO earth terminal, while the NGSO satellite is crossing the GSO satellite's illumination zone. Moreover, three types of interference mitigation techniques, namely, range‐based, traffic‐aware, and cognitive power control techniques are investigated. Furthermore, to increase the spectrum efficiency of the GSO‐NGSO fixed satellite service terrestrial network, we formulate and solve an optimization problem with the objective of minimizing the inter‐site distance between earth user‐terminals. More specifically, we find the minimum distance from a GSO earth terminal, where an NGSO earth terminal can be implemented subject to minimizing received interference level at the victim system. Finally, our comparative results show that the cognitive power control technique performs the best in protecting the victim receiver from the in‐line interference. Copyright © 2016 John Wiley & Sons, Ltd.

Coexistence of Power-Controlled Cellular Networks With Rotating Radar

In this paper, we study spectral coexistence between rotating radar and power-controlled cellular networks in radar bands. For two systems to spectrally coexist, they must be able to operate effectively without causing harmful electromagnetic interference to each other. Very short radar-cellular system separation distances are required during 83.3% of time due to the narrow main beam width of the rotational radar antenna. We propose a spatio-temporal analytical approach with adaptive base station (BS) power control for adjacent spectrum sharing between the two systems. We develop a new model for the aggregate interference from power-controlled cellular BSs using log-normal approximation. The cellular system is allowed to transmit at high power when the radar antenna's main beam is pointing elsewhere from it. On the other hand, the cellular system reduces its transmit power only for a short period when the radar directional antenna main beam is pointing toward it. We use the degradation of the radar signal-to-interference plus noise ratio and cellular outage probability as our performance metrics. Numerical results show that power control of cellular BS highly reduces separation distance between the BS and radar, while yielding marginal degradation of outage performance. In addition, the mathematical results given by the log-normal approximation closely follow our simulated results. Detail system level assessments and investigations are presented to comprehensively understand secondary access to this band opportunistically.

Energy Efficiency Strategy in D2D Cognitive Networks Using Channel Selection Based on Game Theory and Collaboration

The growth of Device-to-Device (D2D) communications and the extensive use of Wireless Sensor Networks (WSNs) bring new problems such as spectral coexistence and spectrum saturation. Cognitive Radio (CR) appears as a paradigm to solve these problems. The introduction of CR into WSNs as a solution to the spectrum utilization problem could be used not only to increase the reliability of communications, but also to optimize energy consumption. The contribution of this paper is a cognitive lightweight strategy based on game theory and collaboration proposed to save energy consumption in Cognitive Wireless Sensor Networks (CWSNs). The proposed strategy takes advantage of the two main capabilities of CWSNs, the ability to adapt communication parameters, specifically channel allocation, and collaboration among devices. The decision making is modeled through a light noncooperative game designed for low resources networks. Despite the fact that the game used is a noncooperative game, the decision process takes advantage of the collaboration among CWSN nodes in a distributed way. Simulations over Castalia Simulator have been carried out in order to validate the strategy in different scenarios with different interference schemes showing increases in energy savings around 50% depending on the scenario.

Successive QCQP Refinement for MIMO Radar Waveform Design Under Practical Constraints

The authors address the problem of designing a waveform for multiple-input multiple-output (MIMO) radar under the important practical constraints of constant modulus and waveform similarity. Incorporating these constraints in an analytically tractable manner is a longstanding open challenge. This is due to the fact that the optimization problem that results from signal-to-interference-plus-noise ratio (SINR) maximization subject to these constraints is a hard non-convex problem. The authors develop a new analytical approach that involves solving a sequence of convex quadratically constrained quadratic programing (QCQP) problems, which they prove converges to a sub-optimal solution. Because an improvement in SINR results via solving each problem in the sequence, they call the method Successive QCQP Refinement (SQR). Furthermore, the proposed SQR method can be easily extended to incorporate emerging requirements of spectral coexistence, as shown briefly in this paper. The authors evaluate SQR against other candidate techniques with respect to SINR performance, beam pattern, and pulse compression properties in a variety of scenarios. Results show that SQR outperforms state-of-the-art methods that also employ constant modulus and/or similarity constraints while being computationally less burdensome.

A new radar waveform design algorithm with improved feasibility for spectral coexistence

Radar signal design in a spectrally crowded environment is currently a challenge due to the increasing requests for spectrum from both military sensing applications and civilian wireless services. The goal of this paper is to improve a previously devised algorithm for the synthesis of optimized radar waveforms fulfilling spectral compatibility with overlaid licensed radiators. The new technique achieves an enhanced spectral coexistence with the surrounding electromagnetic environment through a suitable modulation of the transmitted waveform energy, which was kept fixed at the maximum level in the previously devised algorithm. At the analysis stage, the waveform performance is studied in terms of trade-off among the achievable Signal to Interference Plus Noise Ratio (SINR), spectral shape, and the resulting Autocorrelation Function (ACF), also in situations where the previous technique cannot be applied.

In‐line interference mitigation techniques for spectral coexistence of GEO and NGEO satellites

SummaryThe interest towards the deployment of Low Earth Orbit (LEO)/Medium Earth Orbit (MEO) satellite systems in several frequency bands is increasing due to the requirement of low latency for real‐time systems and high demand of broadband data. When the number of usable Non‐Geostationary (NGEO) satellites, that is, LEO/MEO in space, increases, the frequency coexistence between the NGEO satellite systems with the already existing geostationary (GEO) satellite networks becomes a requisite. In this context, it is crucial to explore interference mitigation techniques between GEO and NGEO systems in order to allow their spectral coexistence. More specifically, in the coexistence scenario of GEO and NGEO satellite networks, in‐line interference may be a serious problem, especially in the equatorial region. In this paper, we provide several frequency sharing studies in the context of the coexistence of an NGEO satellite link with another NGEO/GEO satellite link. Furthermore, we carry out interference analysis between GEO and MEO satellite systems considering the case of the O3b satellite system and propose an adaptive power control technique for both the uplink and downlink scenarios in order to mitigate the in‐line interference. Moreover, we suggest several cognitive solutions for mitigating the in‐line interference and provide future research issues. Copyright © 2014 John Wiley & Sons, Ltd.

Cognitive beamhopping for spectral coexistence of multibeam satellites

SUMMARYHerein, the spectral coexistence scenario of two multibeam satellites over a common coverage area is studied where a primary satellite produces larger beams while a secondary satellite has smaller beams. A novel cognitive beamhopping satellite system is proposed assuming that the secondary gateway is aware of the primary's beamhopping pattern. The performance of the proposed system is evaluated and compared with that of conventional multibeam and beamhopping systems in terms of throughput. It is shown that the proposed system significantly enhances the spectral efficiency (SE) in comparison to other systems. Furthermore, a power control technique is applied on the secondary transmission in order to adhere to the primary's interference constraint. It is noted that the total SE increases with the number of secondary users in the full frequency reuse approach. Moreover, the exclusion zone (EZ) principle is applied to exploit the regions in which the secondary system can operate without causing harmful interference to the primary system. It is shown that the EZ radius of 8.5 dB is sufficient to protect the primary system perfectly with a significant gain in SE. Finally, it is shown that power control and the EZ methods are suitable for lower and higher values of secondary aggregated interference, respectively. Copyright © 2014 John Wiley & Sons, Ltd.

Interference Studies Between Adjacent Satellite Communications Systems operating Above 10 GHz and Using Power Control as Fade Mitigation Technique

Interference problems are arising from the spectral coexistence between satellite communication networks that operate at frequencies above 10 GHz and particularly when they employ power control as fade mitigation technique. This situation is aggravated due to tropospheric propagation phenomena. In this frequency range, rain attenuation is considered to be the dominant tropospheric fading mechanism. The conditional acceptable intersystem interference probability of the Carrier-to-Interference Ratio of a satellite terminal interfered by an adjacent satellite network is defined as a figure of merit and analytically calculated taking into account a physical-mathematical model for the rainfall medium. The correlated propagation fading phenomena over multiple slant paths are accurately incorporated. The proposed model is flexible and can be applied on a global scale since it incorporates the local climatic conditions concerning the point rainfall rate and the spatial rainfall inhomogeneity. Useful numerical results of the proposed model are obtained and the impact of various crucial operational and geometrical parameters of satellite networks' coexistence is examined. The numerical results have been also verified through simulations using a multi-dimensional rain attenuation synthesizer. Finally, simple and easy-calculated formulas for the satellite communication designers for back of the envelope computations are given.

Hybrid UWB and WiMAX radio-over-multi-mode fibre for in-building optical networks

In this paper the use of hybrid WiMedia-defined ultra-wideband (UWB) and IEEE 802.16d WiMAX radio-over-fibre is proposed and experimentally demonstrated for multi-mode based in-building optical networks with the advantage of great immunity to optical transmission impairments. In the proposed approach, spectral coexistence of both signals must be achieved with negligible mutual interference. The experimental study performed addressed an indoor configuration with 50 μm multi-mode fibres (MMF) and 850 nm vertical-cavity surface-emitting laser (VCSEL) transmitters. The results indicate that the impact of the wireless convergence in radio-over-multi-mode fibre (RoMMF) is significant for UWB transmissions, mainly due to MMF dispersion and electrooptical (EO) devices with limited bandwidth. On the other hand, WiMAX transmission is feasible for a 300 m MMF and 30 m wireless link in the presence of UWB, with −31 dBm WiMAX EVM.

Interference alignment for spectral coexistence of heterogeneous networks

The coexistence of heterogeneous networks within the same spectrum for enhancing the spectrum efficiency has attracted large interest lately in the research community. Furthermore, the research interest towards the deployment of small cells and multibeam satellites is increasing due to high capacity, easier deployment and higher energy efficiency. However, due to the scarcity of available spectrum and the requirement of additional spectrum for these systems, small cells need to coexist with macrocells and multibeam satellites need to coexist with monobeam satellites within the same spectrum. In this context, this contribution investigates an underlay spectral coexistence mechanism which exploits an interference alignment (IA) technique in order to mitigate the interference of cognitive transmitters towards the primary receivers in a normal uplink mode. More specifically, three types of IA techniques, namely static, uncoordinated and coordinated are investigated. The performance of the IA technique is evaluated and compared with primary only, resource division and no-mitigation techniques in terms of sum-rate capacity, primary to secondary rate ratio and primary rate protection ratio. It is shown that the coordinated IA technique perfectly protects the primary rate in both terrestrial and satellite coexistence scenarios.

Joint IR-UWB Power Spectral Lines and Interference Suppression Based on Coded Auxiliary Independent Signaling in Presence of Pulse Attenuation and Timing Jitter

This paper deals with spectral shaping problem in impulse radio ultra-wideband systems based on coded auxiliary independent signaling (AIS), as a modified version of transmitted-reference approach. In this manuscript, the main contribution includes a unified theoretical framework for spectral analysis which is, not only able to address all effective parameters in the emergence of spectral lines and coexistence issues, but also provides a convex optimization based method. This can produce AIS-aided signals using random process characteristics as optimization variables. In particular, the specific novelty insights of this paper are as follows: (i) to propose a new signal model, where each transmitted symbol is represented by a preamble AIS pulse followed by a set of transmitted data pulses that are synthesized in accordance with a codeword design and within this context, the preamble signal is designed to eliminate spectral lines via an adaptive monitoring of data-stream statistics as the optimal policy; (ii) to exploit the proposed spectral optimization strategies to maximize spectral flexibility.

Theoretical Investigation into Spectral Coexistence of CDMA and TDMA Systems

The scarcity of available radio spectrum presently limits the extension of modern multimedia systems. This paper presents a theoretical investigation into the possibility of using a frequency overlay of a narrowband Code Division Multiple Access (CDMA) System and a Time Division Multiple Access (TDMA) System to provide a greater spectral efficiency. This paper shows that under certain conditions the two systems can operate in the same frequency band and in the same area with a considerable improvement in the overall capacity of the whole system.

Quality of Service of Broadband Fixed Wireless Access QPSK Channels Interfered by Adjacent Terrestrial Links

A physical model is presented concerning the quality of service (QoS) statistics of broadband fixed wireless access (BFWA) QPSK channels interfered by adjacent terrestrial links operating at the same frequency. The QoS is quantified in terms of the bit-error probability (BEP) of the link. BFWA networks of current interest are mainly operated above 10 GHz assuming line-of-sight (LoS) connection between the base station and the subscriber terminal. In these network configurations, rain attenuation is the dominant fading mechanism and its statistical behavior severely aggravates the nominal interference environment due to the spatial inhomogeneity of rain. The BEP of a coherent QPSK demodulator in the presence of Gaussian noise, cochannel interference and rain attenuation is determined and is related to the relevant performance masks recommended by ITU-R. Numerical results of the proposed model examine how the frequency of operation, the clear-sky interference levels, the length of the interfering path and the climatic conditions affect the QoS of BFWA channels. The spectral and spatial coexistence of BFWA networks and point-to-point links is investigated

Radio resource sharing games: enabling QoS support in unlicensed bands

Distributed quality of service support in wireless networks that are sharing unlicensed frequency bands is an increasingly significant research problem. The spectral coexistence of dissimilar radio systems has to be addressed in the near future in concerning the widely deployed IEEE 802.11 wireless local area networks and other future radio systems operating in unlicensed or opportunistically used frequency bands. The competition between independent wireless networks for allocating a common shared radio channel is modeled in this article as a stage-based game model: players, representing wireless networks, interact repeatedly in radio resource sharing games, without direct coordination or information exchange. Solution concepts derived from game theory allow the analysis of such models under the microeconomic aspects of welfare. Decisions players repeatedly have to make are about when and how often to attempt medium access. In multistage games the players apply strategies in order to maximize their observed utility as a summarizing value for successfully supported quality of service. Strategies determine whether competing radio networks cooperate or ignore the presence of other radio networks. The traffic requirements of a player thereby decide which strategy is adequate to guarantee quality of service.