As of today, orthogonal frequency division multiplexing (OFDM) has been the dominant technology for broadband multicarrier communications. However, in certain applications such as cognitive radios and uplink of multiuser multicarrier systems, where a subset of subcarriers is allocated to each user, OFDM may be an undesirable solution. In this article, we address the shortcomings of OFDM in these and other applications and show that filter bank multicarrier (FBMC) could be a more effective solution. Although FBMC methods have been studied by a number of researchers, and some even before the invention of OFDM, only recently has FBMC been seriously considered by a few standard committees.

OFDM Versus Filter Bank Multicarrier

CVXGEN is a software tool that takes a high level description of a convex optimization problem family, and automatically generates custom C code that compiles into a reliable, high speed solver for the problem family. The current implementation targets problem families that can be transformed, using disciplined convex programming techniques, to convex quadratic programs of modest size. CVXGEN generates simple, flat, library-free code suitable for embedding in real-time applications. The generated code is almost branch free, and so has highly predictable run-time behavior. The combination of regularization (both static and dynamic) and iterative refinement in the search direction computation yields reliable performance, even with poor quality data. In this paper we describe how CVXGEN is implemented, and give some results on the speed and reliability of the automatically generated solvers.

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CVXGEN: a code generator for embedded convex optimization

With the rapid proliferation of new technologies and services in the wireless domain, spectrum scarcity has become a major concern. The allocation of the Industrial, Medical and Scientific (ISM) band has enabled the explosion of new technologies (e.g. Wi-Fi) due to its licence-exempt characteristic. The widespread adoption of Wi-Fi technology, combined with the rapid penetration of smart phones running popular user services (e.g. social online networks) has overcrowded substantially the ISM band. On the other hand, according to a number of recent reports, several parts of the static allocated licensed bands are under-utilized. This has brought up the idea of the opportunistic use of these bands through the, so-called, cognitive radios and cognitive radio networks. Cognitive radios have enabled the opportunity to transmit in several licensed bands without causing harmful interference to licensed users. Along with the realization of cognitive radios, new security threats have been raised. Adversaries can exploit several vulnerabilities of this new technology and cause severe performance degradation. Security threats are mainly related to two fundamental characteristics of cognitive radios: cognitive capability, and reconfigurability. Threats related to the cognitive capability include attacks launched by adversaries that mimic primary transmitters, and transmission of false observations related to spectrum sensing. Reconfiguration can be exploited by attackers through the use of malicious code installed in cognitive radios. Furthermore, as cognitive radio networks are wireless in nature, they face all classic threats present in the conventional wireless networks. The scope of this work is to give an overview of the security threats and challenges that cognitive radios and cognitive radio networks face, along with the current state-of-the-art to detect the corresponding attacks. In addition, future challenges are addressed.

A Survey on Security Threats and Detection Techniques in Cognitive Radio Networks

In this article we have shown that receding horizon control offers a straightforward method for designing feedback controllers that deliver good performance while respecting complex constraints. A designer specifies the RHC controller by specifying the objective, constraints, prediction method, and horizon, each of which has a natural choice suggested directly by the application. In more traditional approaches, such as PID control, a designer tunes the controller coefficients, often using trial and error, to handle the objectives and constraints indirectly. In contrast, RHC con trollers can often obtain good performance with little tuning. In addition to the straightforward design process, we have seen that RHC controllers can be implemented in real time at kilohertz sampling rates. These speeds are useful for both real-time implementation of the controller as well as rapid Monte Carlo simulation for design and testing purposes. Thus, receding horizon control can no longer be considered a slow, computationally intensive policy. Indeed, RHC can be applied to a wide range of control problems, including applications involving fast dynamics.

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Receding Horizon Control

Due to their numerous advantages, communications over multicarrier schemes constitute an appealing approach for broadband wireless systems. Especially, the strong penetration of orthogonal frequency division multiplexing (OFDM) into the communications standards has triggered heavy investigation on multicarrier systems, leading to re-consideration of different approaches as an alternative to OFDM. The goal of the present survey is not only to provide a unified review of waveform design options for multicarrier schemes, but also to pave the way for the evolution of the multicarrier schemes from the current state of the art to future technologies. In particular, a generalized framework on multicarrier schemes is presented, based on what to transmit, i.e., symbols, how to transmit, i.e., filters, and where/when to transmit, i.e., lattice. Capitalizing on this framework, different variations of orthogonal, bi-orthogonal, and non-orthogonal multicarrier schemes are discussed. In addition, filter designs for various multicarrier systems are reviewed considering four different design perspectives: energy concentration, rapid decay, spectrum nulling, and channel/hardware characteristics. Subsequently, evaluation tools which may be used to compare different filters in multicarrier schemes are studied. Finally, multicarrier schemes are evaluated from the perspective of practical implementation aspects, such as lattice adaptation, equalization, synchronization, multiple antennas, and hardware impairments.

A Survey on Multicarrier Communications: Prototype Filters, Lattice Structures, and Implementation Aspects

This work is motivated by the needs in the doubly dispersive underwater acoustic (UWA) communication channels. We propose and develop the use of filterbank multicarrier (FBMC) technique for communications in the channels of interest. A novel cost function for optimization of the filterbank prototype filter, to achieve a robust performance in doubly dispersive channels, is proposed. A design algorithm that optimizes the proposed cost function is then developed. The developed FBMC technique is compared with the celebrated orthogonal frequency-division multiplexing (OFDM). Our study shows that in doubly dispersive channels, in terms of signal-to-interference-plus-noise ratio (SINR), FBMC outperforms OFDM by several decibels. The theoretical results are validated and confirmed to be applicable to UWA communications, by examining real data from an at-sea experiment (ACOMM10), off the coast of New Jersey in July 2010.

Filterbank Multicarrier Communications for Underwater Acoustic Channels

The Third Generation Partnership Project (3GPP) Long Term Evolution (LTE) radio standard has adopted a special form of orthogonal frequency division multiplexing (OFDM) method for the uplink of multiple access networks. This method which is called single carrier frequency division multiple access (SC-FDMA) applies a precoding to each user data set in each OFDM symbol to control its peak-to-average power ratio (PAPR). In this paper, we present a novel formulation of the SC-FDMA and explore possible mimicking the same method when filter bank multicarrier (FBMC) is used for transmission. We find that such direct application of SC-FDMA to FBMC systems is not successful. However, we show that FBMC techniques offer other opportunities that when used correctly lead to a significant reduction in PAPR.

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Single carrier frequency division multiple access (SC-FDMA) for filter bank multicarrier communication systems

Although orthogonal frequency division multiplexing (OFDM) has been the dominant technology for broadband communications in the past, a number of researchers have noted the shortcomings of OFDM in frequency-selective fast-fading channels, e.g., underwater acoustic channels. Hence, alternative systems that use filter banks for multicarrier (FBMC) modulation have been proposed. The widely studied FBMC systems use offset quadrature amplitude modulation (OQAM) or cosine modulated filter bank (CMFB) to maximize the transmission efficiency. However, unfortunately, such systems are not extendable to transmission over multiple-input multiple-output (MIMO) channels. The emphasis of this paper is on a class of FBMC systems in which data symbols are conventional QAM and, thus, support MIMO channels. Unlike OQAM/CMFB-based systems, the FBMC systems considered in this paper suffer some bandwidth loss. We develop a novel filter design that minimizes this bandwidth loss.

Isotropic filter design for MIMO filter bank multicarrier communications

Underwater acoustic (UWA) communication has been the topic of many recent research publications. Because of small ratio of the carrier frequency over the signal bandwidth, UWA channels may be categorized as super broadband channels. UWA channels are also highly dispersive in both time (because of widely spread multipaths) and frequency (because of fast variation of the gain of each path). In order to combat time dispersion of UWA channels, it has been proposed to deploy orthogonal frequency division multiplexing (OFDM) technique with a sufficiently long cyclic prefix (CP). Moreover, to keep the bandwidth efficiency of the transmission high, long OFDM symbols that are at least four times the length of the CP should be used. This leads to an OFDM system in which channel variation over each OFDM symbol may be unacceptably large, thus, results in a significant level of intercarrier interference (ICI). In this paper, we propose the use of a particular class of filter bank multicarrier (FBMC) systems that are optimized for robust performance in the doubly dispersive UWA channels. The FBMC method which we use is a particular implementation of the filtered multitone (FMT) that we have recently developed. Real data from an at-sea experiment (ACOMM10) are used to demonstrate the superior performance of the proposed FMT system over OFDM.

Filterbank multicarrier for underwater communications

Although orthogonal frequency division multiplexing (OFDM) communication systems that use inverse discrete Fourier (IDFT) for multicarrier modulation and discrete Fourier transform (DFT) for demodulation are dominantly adopted in the current broadband standards, there have been some reports in recent years that discuss the shortcomings of OFDM in highly mobile and/or multiple access environments. To resolve these problem, a number of authors have proposed a shift from OFDM to filterbank-based multicarrier techniques. This paper is also along the same line. We present a thorough study of filtered multitone (FMT)in time-varying frequency selective channels. We derive close-form equations for the optimum parameters of per tone fractionally spaced equalizers and also signal to interference plus noise ratio (SINR) and use these to evaluate FMT in typical wireless mobile environments.

Pooyan Amini

Papers

Filterbank Multicarrier Communications for Underwater Acoustic Channels

Single carrier frequency division multiple access (SC-FDMA) for filter bank multicarrier communication systems

Isotropic filter design for MIMO filter bank multicarrier communications

Filterbank multicarrier for underwater communications

Per-Tone Equalizer Design and Analysis of Filtered Multitone Communication Systems over Time-Varying Frequency-Selective Channels