Multicarrier Wireless Research Articles

Automatic Modulation Recognition in Wireless Multi-carrier Wireless Systems with Cepstral Features

Automatic digital modulation recognition (ADMR) has become an interesting problem in wireless communication systems with various civil and military applications. In this paper, an ADMR algorithm is proposed for both orthogonal frequency division multiplexing and multi-carrier code division multiple access systems using discrete transforms and mel-frequency cepstral coefficients (MFCCs). The proposed algorithm uses one of the discrete cosine transform, discrete sine transform, and discrete wavelet transform with MFCCs to extract the modulated signal coefficients, and uses also either a support vector machine (SVM) or an artificial neural network (ANN) for modulation classification. Simulation results show that the proposed algorithm provides higher recognition rates than those obtained in previous studies, in addition to a superiority of SVM performance compared to ANN performance at low signal-to-noise ratios.

Price‐based spectrum sharing and rate allocation in the downlink of multihop multicarrier wireless networks

The author addresses the problem of subcarrier sharing with discrete rate allocation in the downlink of multicell and multihop orthogonal frequency division multiple access networks. The co-channel interference makes the problem computationally intractable. The author therefore models the problem as a non-cooperative game among the transmitting nodes with smaller scale problems. Each problem is solved using dual decomposition. Moreover, to mitigate the degradation effect of co-channel interference in this game, the author additionally proposes a price-based game. This game charges the nodes for their transmit power on subcarriers. Numerical results demonstrate that price-based game outperforms the non-cooperative game as a result of distributed interference avoidance. In addition, both the games with subcarrier sharing achieve higher sum-rate in comparison with resource allocation schemes with no subcarrier sharing.

Pre-Equalization in the Downlink of a Multicarrier Wireless Network Under Utility and Sum-Rate Optimization

This paper studies the problem of downlink pre-equalization in a multicarrier wireless network under utility and sum-rate maximization. The network utility depends on two main factors: an efficiency mapping which is a function of the signal-to-interference-noise ratio (SINR), and the power of the pre-equalization variables. Meanwhile, the sum-rate index is constructed by the summation of a logarithmic function of the SINRs of the active users. The network utility and sum-rate maximization problems are formulated here by assuming that the data estimation at the mobile units (MUs) is carried out by a simple matched filter. The optimal solutions are derived in this work for the pre-equalization factors by following a strategy that is distributed with respect to the channel state information (CSI) and data rates, but centralized with respect to the spreading sequences of all active users. The construction of these optimal solutions requires in each case a two step procedure. First, the optimal SINR is computed for the maximum utility and sum-rate solutions based on the efficiency mapping and on the bound of the transmission power, respectively. Then, exploiting the induced diversity by the multiple subcarriers, the pre-equalization algorithms cancel the multiple-access interference (MAI) and channel distortions, minimize the transmission power and achieve the optimal SINR after signal detection. A comprehensive numerical evaluation is presented at the end of the paper to validate the analytical derivations. Applications of the proposed pre-equalization schemes could be associated among others to cellular communication systems, and wireless networks of actuators.

Efficient pre‐equalisation strategies for the downlink of a multi‐carrier code division multiple‐access wireless network

In this study, the problem of optimal synthesis of pre-equalisation factors for a multi-carrier code division multiple-access wireless network is studied under different quality of service (QoS) restrictions and performance objectives. The downlink is particularly addressed, where the QoS is evaluated by the signal-to-interference-noise ratio (SINR) after signal detection by matched filtering. First, the minimum energy formulation under inequality QoS constraints is analysed, and it was concluded that the optimal performance is always achieved at the lower bounds. Next, the minimisation of the peak magnitude of the pre-equalisation factors was addressed by an optimal synthesis scheme through the infinity norm, where a linear programming strategy is proposed by using an upper bound. Finally, by combining the minimum energy and minimum peak strategies, the minimisation of an upper bound on the peak-to-average-power ratio (PAPR) is suggested, which can be solved through quadratic programming by incorporating the QoS constraints. The new synthesis schemes take into account two important transmitter-based properties: peak magnitude and PAPR. These ideas were extensively validated in simulation, where the synthesis schemes were compared by Monte Carlo tests at different load and noise levels, and objective SINRs.

Photonic-Based RF Transceiver for UWB Multi-Carrier Wireless Systems

In this paper an all-optical system exploitable as the core structure for a photonic-based RF transceiver is presented. The proposed scheme is able to simultaneously perform either up- or down-conversion of multiple frequency Ultra-Wide Band (UWB) RF signals, employing a single Mode-Locking Laser (MLL). The system has been experimentally demonstrated and tested by up- and down-converting orthogonal frequency division multiplexing (OFDM) signals over a bandwidth of about 4 GHz. The scheme’s performance has been validated by measuring the error vector magnitude (EVM) of the OFDM signals over the whole considered RF spectrum (from 5 GHz to 26.5 GHz), both in up-conversion and in down-conversion. The measurements show negligible power penalties, lower than 0.5 dB. Since the proposed scheme can act either as an up- or down-converter, and it is composed by easily integratable devices, two identical structures can be combined on a single integrated platform, sharing a single MLL, to build a compact and efficient UWB transceiver.

Estimation of FBMC/OQAM Fading Channels Using Dual Kalman Filters

We address the problem of estimating time-varying fading channels in filter bank multicarrier (FBMC/OQAM) wireless systems based on pilot symbols. The standard solution to this problem is the least square (LS) estimator or the minimum mean square error (MMSE) estimator with possible adaptive implementation using recursive least square (RLS) algorithm or least mean square (LMS) algorithm. However, these adaptive filters cannot well-exploit fading channel statistics. To take advantage of fading channel statistics, the time evolution of the fading channel is modeled by an autoregressive process and tracked by Kalman filter. Nevertheless, this requires the autoregressive parameters which are usually unknown. Thus, we propose to jointly estimate the FBMC/OQAM fading channels and their autoregressive parameters based on dual optimal Kalman filters. Once the fading channel coefficients at pilot symbol positions are estimated by the proposed method, the fading channel coefficients at data symbol positions are then estimated by using some interpolation methods such as linear, spline, or low-pass interpolation. The comparative simulation study we carried out with existing techniques confirms the effectiveness of the proposed method.

Optimal pre‐equalisation for wireless multi‐carrier code division multiple access systems under quality of service requirements

This work addresses an optimal pre-equalisation scheme to provide power and phase compensation in multi-carrier code division multiple access wireless systems under quality of service (QoS) restrictions. Two assignation schemes are studied: independent and uniform pre-equalised transmission (IPT and UPT) per subcarrier. First, the QoS was quantified in terms of the signal-to-interference noise ratio (SINR) after using a linear detector in the receiver. The SINR expressions for IPT and UPT were explicitly derived, to highlight their dependence on the pre-equalisation factors. These relations are exploited to derive analytical procedures to obtain the required pre-equalisation factors that satisfy an objective SINR per active user. The author's proposal for IPT achieves the lowest power while requiring a simple detector independent of the channel state information (CSI). For IPT, two minimum norm solutions are derived by translating the SINR restrictions into linear equations: one based on spectral factorisation, and a second one based on a simultaneous zero-forcing effect plus an energy scaling. On the other hand, for UPT, multi-user detectors like zero-forcing (ZF) and minimum-mean-square error (MMSE) have to be employed at the receiver to achieve a solution to the QoS requirements. In the numerical evaluations, IPT attained roughly a 2.5–3% reduction in the overall transmission power compared to UPT with ZF and MMSE by varying the objective SINR and noise variance. Although this reduction is further expanded as the number of active users increases, achieving a reduction in transmission power larger than 50% for a fully-loaded system.

Radio resource allocation algorithms for multi-service OFDMA networks: the uniform power loading scenario

Adaptive Radio Resource Allocation is essential for guaranteeing high bandwidth and power utilization as well as satisfying heterogeneous Quality-of-Service requests regarding next generation broadband multicarrier wireless access networks like LTE and Mobile WiMAX. A downlink OFDMA single-cell scenario is considered where heterogeneous Constant-Bit-Rate and Best-Effort QoS profiles coexist and the power is uniformly spread over the system bandwidth utilizing a Uniform Power Loading (UPL) scenario. We express this particular QoS provision scenario in mathematical terms, as a variation of the well-known generalized assignment problem answered in the combinatorial optimization field. Based on this concept, we propose two heuristic search algorithms for dynamically allocating subchannels to the competing QoS classes and users which are executed under polynomially-bounded cost. We also propose an Integer Linear Programming model for optimally solving and acquiring a performance upper bound for the same problem at reasonable yet high execution times. Through extensive simulation results we show that the proposed algorithms exhibit high close-to-optimal performance, thus comprising attractive candidates for implementation in modern OFDMA-based systems.

A Utility Maximization Framework for Fair and Efficient Multicasting in Multicarrier Wireless Cellular Networks

Multicast/broadcast is regarded as an efficient technique for wireless cellular networks to transmit a large volume of common data to multiple mobile users simultaneously. To guarantee the quality of service for each mobile user in such single-hop multicasting, the base-station transmitter usually adapts its data rate to the worst channel condition among all users in a multicast group. On one hand, increasing the number of users in a multicast group leads to a more efficient utilization of spectrum bandwidth, as users in the same group can be served together. On the other hand, too many users in a group may lead to unacceptably low data rate at which the base station can transmit. Hence, a natural question that arises is how to efficiently and fairly transmit to a large number of users requiring the same message. This paper endeavors to answer this question by studying the problem of multicasting over multicarriers in wireless orthogonal frequency division multiplexing (OFDM) cellular systems. Using a unified utility maximization framework, we investigate this problem in two typical scenarios: namely, when users experience roughly equal path losses and when they experience different path losses, respectively. Through theoretical analysis, we obtain optimal multicast schemes satisfying various throughput-fairness requirements in these two cases. In particular, we show that the conventional multicast scheme is optimal in the equal-path-loss case regardless of the utility function adopted. When users experience different path losses, the group multicast scheme, which divides the users almost equally into many multicast groups and multicasts to different groups of users over nonoverlapping subcarriers, is optimal .

Digital multicarrier modulation techniques for high data rates multimedia applications in present and future wireless communication systems

To accommodate high performance and high bit rates for multimedia applications in present and future wireless communication systems, it is essential that modulation techniques applied in this scenario are able to support high data rates upto and above 200 Mbps. To meet the increased demand of higher bit rates, the wireless systems are incorporating the multi-carrier modulation techniques ,such as FFT based MCM which is also known as conventional OFDM and wavelet transform based MCM. Wireless multicarrier modulation is a technique of transmitting data by dividing the input data stream into parallel sub-streams that are each modulated and multiplexed onto the channel at different carrier frequencies. In this paper, we studied the performance of DWT based MC-CDMA and FFT based MC- CDMA modulations for transmission over wireless fading channels. This scheme is shown to be overall quite similar to FFT based OFDM modulation, but with some interesting additional features and improved characteristics. Results shows that DWT based MC- CDMA modulation has better bit error rate (BER) performance than conventional FFT based CDMA without cyclic prefix (CP) for all signal-to-noise ratios and also outperforms FFT based CDMA for low signal-to-noise ratio values.

Joint Access Point Selection and Power Allocation for Uplink Wireless Networks

We consider the distributed uplink resource allocation problem in a multi-carrier wireless network with multiple access points (APs). Each mobile user can optimize its own transmission rate by selecting a suitable AP and by controlling its transmit power. Our objective is to devise suitable algorithms by which mobile users can jointly perform these tasks in a distributed manner. Our approach relies on a game theoretic formulation of the joint power control and AP selection problem. In the proposed game, each user is a player with an associated strategy containing a discrete variable (the AP selection decision) and a continuous vector (the power allocation among multiple channels). We provide characterizations of the Nash Equilibrium of the proposed game, and present a set of novel algorithms that allow the users to efficiently optimize their rates. Finally, we study the properties of the proposed algorithms as well as their performance via extensive simulations.

Multi-criteria ranking based greedy algorithm for physical resource block allocation in multi-carrier wireless communication systems

A computationally efficient algorithm, referred to as the multi-criteria ranking based greedy (MCRG) algorithm, is proposed for physical resource block (PRB) allocation in multi-carrier wireless communications systems, where the users' utilities are ranked with multiple criteria. The MCRG algorithm not only outperforms the previous single criterion ranking based greedy algorithm in terms of throughput and outage probability, but also provides a near optimal performance, irrespective of whether the channel frequency response (CFR) or bit error rate (BER) or throughput optimisation utilities are used. In particular, when the MCRG algorithm is used to optimise the CFR utility, the overall computational complexity is kept at a very low level, without sacrificing the performance. To further reduce the overall computational complexity, a selectivity ratio is included in the MCRG algorithm, where greedy PRB allocation is applied only to a selection of users with lower multi-criteria ranking.

Analysis of Best Channel Feedback and Its Adaptive Algorithms for Multicarrier Wireless Data Systems

Multiuser diversity techniques are used in multicarrier data systems to enhance downlink cell throughput. This requires downlink channel information from the users that is opportunistically used by a base station to send data to the users with good channel condition. Channel feedback from the user to the base station incurs high overhead especially when many users are in the cell and each user needs to report channel information over multiple channels, as in OFDMA systems. To reduce the quantity of feedback information without significant throughput degradation, a practical strategy is to deliver feedback on a partial set of channels with the best channel quality. We call it best feedback, and this reporting scheme carried out for best four or five among 24 channels has been already adopted in the IEEE 802.16e standard. Considering real feedback conditions, we investigate the performance of a best feedback scheme and derive the optimal number of channels for which information needs to be fed back to keep the throughput gap (compared to a full feedback scheme) within a target margin. From the optimal condition, we propose an adaptive best feedback algorithm, where the number of reported channels is adjusted to adapt to the number of users in the cell. We also propose an adjusted periodic feedback algorithm, where users are divided into groups and scheduling is carried out group by group, so a user can report feedback information when his group is scheduled, thereby reducing the frequency of feedback transmission. To support differentiated performance, we further propose heterogeneous feedback algorithms where users are divided into heterogeneous groups, each with a different group size or a different feedback period. Numerical results validate our analysis and provide meaningful insights into the design of various channel feedback schemes.

Scheduling Algorithms for Multicarrier Wireless Data Systems

We consider the problem of scheduling multicarrier wireless data in systems such as IEEE 802.16 (WiMAX). Each scheduling decision involves assigning carriers to users for each time slot, subject to the constraint that each carrier is assigned to at most one user, but multiple carriers can potentially be assigned to the same user. One important aspect of our problem is that a scheduler knows the channel rates across all users and all carriers whenever a scheduling decision is made. This “global” information may give a potential for enhancing performance via an optimized allocation of carriers to users. We analyze this problem in a situation where finite queues are fed by a data arrival process. The well-known MaxWeight algorithm for the single-carrier setting maximizes the product of queue size and service rate. We focus on how to adapt MaxWeight to the multicarrier setting. If the same objective is pursued, more service than needed may be assigned to drain a queue, thereby creating wastage. While a simple variant in the objective forbids this wastage, it turns an easy-to-compute old objective into an intractable new objective. We state the hardness of the new optimization problems and propose several extremely simple algorithms with provable performance bounds. We conclude with supporting simulation examples.

McWiLL—A New Mobile Broadband Access Technology for Supporting Both Voice and Packet Services

As an evolution from Synchronous Code Division Multiple Access (SCDMA), McWiLL (Multi-Carrier Wireless Information Local Loop) mobile broadband access technology was proposed to work with Next Generation Networks (NGNs) to offer various content-rich services. Several core state-of-the-art technologies used in McWiLL mobile broadband access system are introduced in this paper, such as smart antennas, CS-OFDMA (Code Spreading Orthogonal Frequency Division Multiple Access), adaptive modulation, dynamic channel allocation, make-before-break handoff, and fraud protection, etc. These key techniques allow McWiLL to support a large coverage, high spectrum efficiency (up to 3 bit/s/Hz), a homogeneous service quality between high and low rate traffics, low cost terminals, and high mobility applications. McWiLL was designed in particular to suit for its applications in hostile environments due to its superb interference cancellation capability, special frame structure design, and dynamic channel assignment scheme.

Filter Banks for Next Generation Multicarrier Wireless Communications

1Department of Communications Engineering, Tampere University of Technology, P.O. Box 553, 33101 Tampere, Finland 2Orange Labs, France Telecom, 4 Rue du Clos Courtel, B.P. 91226, 35512 Cesson Sevigne Cedex, France 3Department of Electrical and Computer Engineering, University of Utah, Salt Lake City, UT 84112-9206, USA 4Centre Tecnologic de Telecommunication de Catalunya (CTTC), Parc Mediterrani de la Tecnologia, Avinguda del Canal Olimpic, Casstelldefels, 08860 Barcelona, Spain

Pilot-Aided Carrier Frequency Estimation for Filter-Bank Multicarrier Wireless Communications on Doubly-Selective Channels

Multicarrier modulation techniques are currently the key technology in the area of high-data-rate transmission over wireless fading channels. Their considerable vulnerability to carrier frequency offsets, however, hinders their appealing features and demands adequate countermeasures. This paper contributes with a class of frequency estimation algorithms intended for filter bank burst-mode multicarrier transmission over time-frequency selective fading channels. All algorithms are derived from the maximum likelihood principle, exhibit a feedforward structure and are based on the use of pilot symbols scattered throughout the burst. The accuracy of the proposed schemes is investigated in typical mobile wireless scenarios, showing that they outperform maximum likelihood non-data-aided frequency recovery in spite of a substantially lower computational requirement.

Analytical prediction of spectral regrowth and correlated and uncorrelated distortion in multicarrier wireless transmitters exhibiting memory effects

Measurement of non-linearity effects in wireless transmitters had been always difficult under complex digitally modulated signals. On the other hand, blind time domain simulation of these effects is generally time consuming and insufficient. In this study, the authors present new frequency domain closed-form formulas for predicting the spectral regrowth in wireless communication systems/subsystems with fifth-order non-linearity exhibiting memory effects. Particularly, the suggested formulas estimate the power spectral density, as well as the undesirable adjacent-channel and co-channel emissions of the modelled device, under phase-aligned and randomly phase-modulated multitone excitations. In addition, they are able to predict the correlated and uncorrelated distortion powers separately. The efficiency and robustness of the proposed approach has been demonstrated by predicting the output of a laterally diffused metal oxide semiconductor Doherty-based power amplifier. The obtained results have been compared to measurements and those of time-domain simulators and have revealed good accuracy and time efficiency.

A New Effective and Efficient Measure of PAPR in OFDM

In multi-carrier wireless OFDM communication systems, a major issue is related to high peaks in transmitted signals, resulting in such problems as power inefficiency. In this regard, a common practice is to transmit the signal that has the lowest Peak to Average Power Ratio (PAPR). Consequently, some efficient and accurate method of estimating the PAPR of a signal is required. Previous literature in this area suggests a strong relationship between PAPR and Power Variance (PV). As such, PV has been advocated as a good measure of PAPR. However, contrary to what is suggested in the literature, our research shows that often low values of PV do not correspond to low values of PAPR. Hence, PV does not provide a sound scientific basis for comparing and estimating PAPR in OFDM signals. In this paper a novel, effective, and efficient measure of high peaks in OFDM signals is proposed, which is less complex than PAPR. The proposed measure, termed as Partial Power Variance (PPV), exploits the relationship among PAPR, Aperiodic Autocorrelation Co-efficient (AAC), and Power Variance (PV) of the transmitted signal. Our results demonstrate that, in comparison to PV, Partial Power Variance is a more efficient as well as a more effective measure of PAPR. In addition, we demonstrate that the computational complexity of PPV is far less than that of PAPR.

Adaptive mobile spot diffusing angle diversity MC-CDMA optical wireless system in a real indoor environment

In this paper, we introduce a mobile optical wireless (OW) multicarrier - code division multiple access (MC-CDMA) system that employs a new adaptive line strip multibeam system (ALSMS) with diversity detection. Our results indicate that a significant improvement in the bit error rate (BER) can be obtained in the presence of very directive noise, multipath propagation and shadowing typical in a real indoor environment. With transmitter and/or receiver mobility, ALSMS can improve the BER performance by almost 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-5</sup> with 2 active users, and increase the signal-to-noise ratio (SNR) by more than 13 dB compared to the unadaptive LSMS.