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 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 multi carrier (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 PSD of FB-MC waveforms only. In this paper, we demonstrate that this approach is flawed and show what metric should be used to rate interference between FB-MC and CP-OFDM systems. Finally, our results show that using FB-MC waveforms does not facilitate coexistence with CP-OFDM based systems to a high extent.Comment: Manuscript submitted for review to IEEE Transactions on Wireless Communication

Modeling Interference Between OFDM/OQAM and CP-OFDM: Limitations of the PSD-Based Model

To answer the challenges put out by the next generation of wireless networks (5G), important research efforts have been undertaken during the last few years to find new waveforms that are better spectrally localized and less sensitive to asynchronism effects than the widely deployed Cyclic Prefix Orthogonal Frequency Division Multiplexing (CP-OFDM). One of the most studied schemes is OFDM-Offset Quadrature Amplitude Modulation (OFDM/OQAM) based on the PHYDYAS filter pulse. In the recent literature, spectrum coexistence between OFDM/OQAM and CP-OFDM is commonly studied based on the Power Spectral Density (PSD) model. In this paper, we show that this approach is flawed and we show that the actual interference injected by OFDM/OQAM systems onto CP-OFDM is much higher than what is classically expected with the PSD based model in the literature. We show that though using OFDM/OQAM in secondary systems is still advantageous, it brings limited gain in the context of coexistence with incumbent CP-OFDM systems.Comment: 7 pages, 9 figures, ICT 201

TACT: A Transfer Actor-Critic Learning Framework for Energy Saving in Cellular Radio Access Networks

Recent works have validated the possibility of improving energy efficiency in radio access networks (RANs), achieved by dynamically turning on/off some base stations (BSs). In this paper, we extend the research over BS switching operations, which should match up with traffic load variations. Instead of depending on the dynamic traffic loads which are still quite challenging to precisely forecast, we firstly formulate the traffic variations as a Markov decision process. Afterwards, in order to foresightedly minimize the energy consumption of RANs, we design a reinforcement learning framework based BS switching operation scheme. Furthermore, to avoid the underlying curse of dimensionality in reinforcement learning, a transfer actor-critic algorithm (TACT), which utilizes the transferred learning expertise in historical periods or neighboring regions, is proposed and provably converges. In the end, we evaluate our proposed scheme by extensive simulations under various practical configurations and show that the proposed TACT algorithm contributes to a performance jumpstart and demonstrates the feasibility of significant energy efficiency improvement at the expense of tolerable delay performance.Comment: 11 figures, 30 pages, accepted in IEEE Transactions on Wireless Communications 2014. IEEE Trans. Wireless Commun., Feb. 201

An optimal architecture for a multi-standard reconfigurable radio: A network theory re-formulation

International audienceWe provide a procedure for identifying an architecture for a multistandard reconfigurable radio that is optimal in view of cost and performance (latency) considerations. We examine the trade-off between installing complex self-contained components providing high performance at a high cost (as well as size and weight), versus invoking simpler, reusable low level modules, which reduces cost but increases system latency. In the present work, we show that the the problem of finding an optimal design for a multi-standard reconfigurable radio can be reformulated as a “network design problem”. This reformulation provides a wealth of results, algorithms, and experience already available in the scientific literature. We explain the reformulation, give a simple but realistic design example, and discuss some algorithms available in the network design literature

From a Configuration Management to a Cognitive Radio Management of SDR Systems

International audienceThis paper proposes a functional management architecture for Cognitive Radio systems. It relies on a previously defined configuration management architecture for multi-standard SDR systems, and complement it to support cognitive radio features. This paper explains the requirements of Cognitive Radio systems in terms of reconfiguration, smartness and sensing capabilities. A configuration management architecture capable of dealing with the hardware heterogeneity and a wide range of reconfiguration scenarios expected with SDR systems is presented. The management is distributed over the system and a hierarchical dependency is set on 3 layers, each having a different level of knowledge of the system and the associated hardware constraints of the elements it supervises. Then a cognitive management functional architecture is derived from the previous one, copying the 3 layers of hierarchy. The roles of the elements of each layer are discussed, as well as their respective interactions and their relationships with the elements of the configuration management architecture

Closed-form approximations of the peak-to-average power ratio distribution for multi-carrier modulation and their applications

International audienceThe theoretical analysis of the peak-to-average power ratio (PAPR) distribution for an orthogonal frequency division multiplexing (OFDM) system, depends on the particular waveform considered in the modulation system. In this paper, we generalize this analysis by considering the generalized waveforms for multi-carrier (GWMC) modulation system based on any family of modulation functions, and we derive a general approximate expression for the cumulative distribution function (CDF) of its PAPR, for both finite and infinite integration time. These equations allow us to directly find the expressions of the PAPR distribution for any particular functions and characterize the behaviour of the PAPR distribution associated with different transmission and observation scenarios. In addition to that, a new approach to formulating the PAPR reduction problem as an optimization problem, is presented in this study

Closed-form Approximations of the PAPR Distribution for Multi-Carrier Modulation Systems

International audienceThe theoretical analysis of the Peak-to-Average Power Ratio (PAPR) distribution for an Orthogonal Frequency Division Multiplexing (OFDM) system, depends on the particular waveform considered in the modulation system. In this paper, we generalize this analysis by considering the Generalized Waveforms for Multi-Carrier (GWMC) modulation system based on any family of modulation functions, and we derive a general approximate expression for the Cumulative Distribution Function (CDF) of its continuous and discrete time PAPR. These equations allow us to directly find the expressions of the PAPR distribution for any particular family of modulation functions, and they can be applied to control the PAPR performance by choosing the appropriate functions