Osamu Muta

Weighting Factor Estimation Method for Peak Power Reduction Based on Adaptive Flipping of Parity Bits in Turbo-Coded OFDM Systems

In this paper, we propose a weighting factor (WF) estimation method for peak power reduction (PPR) based on adaptive flipping of parity carriers in a turbo-coded orthogonal frequency-division multiplexing (OFDM) system. In this PPR scheme, the peak-to-average power ratio of a turbo-coded OFDM signal is reduced with adaptive flipping of the phase of the parity carriers corresponding to the WFs. At the receiver, the WFs are estimated at a turbo decoder by exploiting the redundancy of an error-correcting code using no extra side information. The proposed WF estimation method is based on an iterative decoding of the turbo code, i.e., the turbo decoder provides not only error correction capability but the WF estimation function as well. When the proposed WF estimation method is used for the system using a turbo code with constraint length K = 4 and a code rate of R = 1/2, the instantaneous power of the OFDM signal at the complementary cumulative distribution function of 10-4 can be reduced by about 2.1 dB through the application of the PPR scheme. When the bit error rate (BER) performance is evaluated as a function of the peak signal-to-noise power ratio (PSNR), the proposed method achieves better BER performance than the case without the PPR in an attenuated 12-path Rayleigh fading condition. The improvements in BER performance as a function of PSNR are about 1.1, 2.0, and 2.1 dB at BER = 10-4 for turbo-coded OFDM signals using QPSK, 16-state quadrature amplitude modulation (QAM), and 64-state QAM schemes, respectively.

Game Theory Meets Wireless Sensor Networks Security Requirements and Threats Mitigation: A Survey

We present a study of using game theory for protecting wireless sensor networks (WSNs) from selfish behavior or malicious nodes. Due to scalability, low complexity and disseminated nature of WSNs, malicious attacks can be modeled effectively using game theory. In this study, we survey the different game-theoretic defense strategies for WSNs. We present a taxonomy of the game theory approaches based on the nature of the attack, whether it is caused by an external attacker or it is the result of an internal node acting selfishly or maliciously. We also present a general trust model using game theory for decision making. We, finally, identify the significant role of evolutionary games for WSNs security against intelligent attacks; then, we list several prospect applications of game theory to enhance the data trustworthiness and node cooperation in different WSNs.

Iterative interference alignment in macrocell-femtocell networks: A cognitive radio approach

The deployment of femtocells in current and future communication systems promises an effective solution for limited indoor coverage problem and a possible gateway for mobile data offloading. In this paper, we cast a cognitive interference alignment approach (IA) suitable for heterogeneous cellular networks with a mixed macrocell and femtocell deployment Specifically, in our approach a restricted waterfilling (RWF) algorithm is used to maximize the downlink data rate, while reserving some eigenmodes for giving the femtocell basestations the opportunity to do their transmissions even at high signal-to-noise power ratio (SNR) for the macrocell basestation. Additionally, both the cross-tier and co-tier interference is to be aligned at each femtocell users receiver using an Iterative Reweighted Least Squares(IRLS) algorithm. The simulation results show that the proposed IA approach provides an improved sum rate for the femtocell users, compared to the conventional IA techniques, like, the leakage minimization approach and the nuclear norm based rank constraint rank minimization approach.

A peak power reduction scheme based on reversal of parity-bits for a block-coded OFDM signal

We propose a peak power reduction (PPR) scheme based on the reversal of parity-bits for a block-coded OFDM signal. In our PPR scheme, the entire parity-check block of the codeword is adaptively reversed, symbol-by-symbol, so as to minimize the PAPR of the OFDM-signal. At the receiver, the original codeword can be restored with sufficient accuracy by checking the syndrome of the received codeword and protecting a significant-bit of the codeword from transmission error. When (7,4), (31,21) and (31,26) BCH codes are employed, the PAPR of the OFDM signal, at the CCDF (complementary cumulative distribution function) of 10/sup -4/, can be reduced by about 2.8, 2.5 and 2.0 dB, respectively, by applying the PPR scheme while achieving approximately the same BER performance as the case without PPR in an exponentially decaying 6-path Rayleigh fading condition.

Peak Power Reduction Method Based on Structure of Parity-Check Matrix for LDPC Coded OFDM Transmission

In this paper, we propose a peak power reduction method for LDPC coded OFDM system, where transmit data sequence is grouped into several clusters based on structure of a low density parity-check matrix and the phase or each cluster is adjusted so as to minimize PAPR of OFDM signal by multiplying weighting factors (WFs). At the receiver, WFs are estimated with sufficient accuracy by exploiting the decoding property of LDPC code. The proposed method can be applied to not only systematic coded signal but also non-systematic one. Computer simulation results show that, when LDPC code with code-rate of R ap 1/2 is used, PAPR of OFDM signal can be reduced by about 2.4 dB without significant degradation in BLER performance as compared to perfect WF estimation in attenuated 12-path Rayleigh fading condition.

Channel estimation technique for MIMO-constant envelope modulation

The authors have proposed Multi-Input Multi-Output (MIMO)-Constant Envelope Modulation, (MIMO-CEM), as power and complexity efficient alternative to MIMO-OFDM, suitable for wireless backhaul network in which relay nodes are fixed in their positions. One of the major problems to withstand real application of MIMO-CEM is to estimate MIMO channel characteristics. The MIMO-CEM is based upon two contrary schemes; one is the nonlinear CEM modified Maximum Likelihood Sequence Estimator (MLSE) proposed by the authors, which needs accurate channel information to replicate the received signal passing through channel. The other is low resolution analog-to-digital converter (ADC), i.e., 1-bit in the default operation and 2 or 3 bits in the optional operations, which means that the received channel amplitude information may be completely or partially destroyed. These two contrary demands make MIMO-CEM channel estimation a big challenge; how we can accurately estimate the channel in these severe low ADC resolution conditions. We consider this issue through designing an efficient MIMO-CEM channel estimator based upon a block based adaptive filter. In addition, in order to speed up the parameter convergence rate in the proposed adaptive estimator, we design a correlator estimator as initial channel state estimation used in the adaptive estimator. We prove the effectiveness of the proposed MIMO-CEM channel estimation under different channel scenarios and different low ADC resolutions such as 1, 2 and 3-bit.

Joint Energy-Efficient Single Relay Selection and Power Allocation for Analog Network Coding with Three Transmission Phases

The multiple access broadcast (MABC) is an effective two phases transmission (2P) ANC protocol for the half-duplex (HD) communication mode. However, MABC does not make use of channel gain of the direct link (DL) no matter how strong it is. On the other hand, the time division broadcast (TDBC) is known as a three phases transmission (3P) protocol which enables transceivers to utilize DL and thus offers the possibility to achieve higher performance compared with the MABC at the expense of a reduced spectral efficiency due to the one extra transmission phase. In this paper, we investigate a joint single relay selection and power allocation schemes for energy-efficient wireless communication systems with analog network coding (ANC) for TDBC, where two-way relay channel with two end nodes and N parallel relay nodes is considered under an assumption of perfect channel-state information (CSI). Our objective is to minimize the total system transmit power consumption under quality-of-service (QoS) constraints for TDBC protocol with joint single relay selection and nodes power allocation. In addition, a zero-forcing based relay signal combining technique that combines the signals received at the 1st and 2nd transmission phases, also known as zero-forcing relay power allocation (ZF-RPA), is also investigated. Numerical simulation shows that the traditional VG-RPA is more energy-efficient than the ZF-RPA scheme for TDBC in cases with and without utilizing DL.

Wide-Band Cooperative Compressive Spectrum Sensing for Cognitive Radio Systems Using Distributed Sensing Matrix

In this paper, cooperative compressive spectrum sensing is considered to enable accurate sensing of the wide-band spectrum. The proposed algorithm is based on compressive sensing theory and aims to reduce the hardware complexity of the cognitive radio receiver by distributing the sensing work among groups of sensing nodes. The proposed algorithm classifies the cooperated sensing nodes into different sensing groups depending on the quality of the reporting channel between the sensing node and the fusion center (FC). To sense the wide- band analog signal and take a global decision about spectrum occupancy, each node uses its local sensing matrix, which is assigned to its sensing group and a part of a global sensing matrix at the FC. The size of the local sensing matrix of each sensing node,and consequently the contribution of this node in the overall measurement vector, depends on its sensing group. The FC classifies and rearranges the compressed data to formulate one global measurement vector which is used with a global sensing matrix to estimate the wide-band signal spectrum. The receiver operation characteristics (ROC) of the overall spectrum sensing system show that the proposed receiver provides more protection to primary users (higher detection probability) at the same secondary user throughput (probability of false alarm).

Static and dynamic channel estimation techniques for MIMO-Constant Envelope Modulation

The authors have proposed Multi-Input Multi-Output (MIMO)-Constant Envelope Modulation (MIMO-CEM), as power and complexity efficient alternative to MIMO-OFDM, suitable for wireless backhaul networks. One of the major problems to withstand real application of MIMO-CEM is to estimate MIMO channel characteristics. The MIMO-CEM is based upon two contrary schemes; one is nonlinear Maximum Likelihood Sequence Estimator (MLSE), which needs accurate channel information to replicate the received signal passing through it. The other is a low resolution analog-to-digital converter (ADC), e.g., 1-bit in the default operation that removes the received signal amplitude fluctuation. This paper considers channel estimation problem in MIMO-CEM. First, we propose a MIMO-CEM adaptive channel estimator, in static and quasi-static channel conditions, based upon Code Division Multiplexing (CDM) preambles transmission, where channel parameters are iteratively estimated by observing the received MIMO preambles. Then, we extended the proposed CDM preamble method to Decision Directed Channel Estimation (DDCE) to track MIMO-CEM channel in high Doppler frequency conditions and clarify the effectiveness of MIMO-CEM in dynamic channel conditions.

Effect of peak power suppression and adaptive predistortion on power amplification of an OFCDM signal

The OFCDM (orthogonal frequency and code division multiplexing) system is receiving attention to achieve a high data rate transmission for multimedia communication. A problem with the system is that PAPR (peak to average power ratio) of the OFCDM signal increases as the number of carriers increases. In this paper, we investigate peak reducing methods for OFCDM system with a predistorter power amplifier. We show that the peak reduction scheme and adaptive predistortion gives a high power efficiency and high linearity in power amplification of OFCDM signal.