This paper describes a differential fault analysis (DFA) attack against CLEFIA. The proposed attack can be applied to CLEFIA with all supported keys: 128, 192, and 256-bit keys. DFA is a type of side-channel attack. This attack enables the recovery of secret keys by injecting faults into a secure device during its computation of the cryptographic algorithm and comparing the correct ciphertext with the faulty one. CLEFIA is a 128-bit blockcipher with 128, 192, and 256-bit keys developed by the Sony Corporation in 2007. CLEFIA employs a generalized Feistel structure with four data lines. We developed a new attack method that uses this characteristic structure of the CLEFIA algorithm. On the basis of the proposed attack, only 2 pairs of correct and faulty ciphertexts are needed to retrieve the 128-bit key, and 10.78 pairs on average are needed to retrieve the 192 and 256-bit keys. The proposed attack is more efficient than any previously reported. In order to verify the proposed attack and estimate the calculation time to recover the secret key, we conducted an attack simulation using a PC. The simulation results show that we can obtain each secret key within three minutes on average. This result shows that we can obtain the entire key within a feasible computational time.

Femto cell systems have been the one of the key technologies for ubiquitous networks, and some of them are already serviced by manufacturers. Femto base stations are deployed randomly and without pre-planning, so the femto system has a wider variation in topology than cellular networks. Therefore, a specialized resource assignment algorithm is essential for efficient performance of the femto cell. In this paper, we propose a realtime channel assignment algorithm for adapting to the varying environments, including new cell deployment or power switch off. Our algorithm is a form of a sequential graph coloring problem which outperforms other fixed allocation algorithms. Simulation results show realtime assignment has better performance than the fixed allocation when the wireless environment changes faster than the tracking operation time.

This letter deals with the time-domain estimation of time-varying channels in orthogonal frequency-division multiplexing (OFDM) systems. The general complex exponential basis expansion model (GCE-BEM) is used to capture the time variation of the channel within an OFDM block. The design criterion of optimal training for OFDM systems in time-varying channels is derived. This optimal training enables the complete elimination of the interference from data symbols and minimizes the noise effect on channel estimation. The design criterion can be used for both pilot symbol aided modulation (PASM) and superimposed training OFDM systems over time-varying channels.

In conventional preamble based channel estimation in OFDM/offset QAM (OFDM/OQAM) system, both the even index subcarriers and the odd index subcarriers are with identical value selected from { 1 } respectively to avoid inter-carrier interference (ICI), if and only if channel frequency response in neighbor few subcarriers remain invariable. However, it requires larger coherent bandwidth. In this paper, we propose an effective preamble design with ICI cancellation for channel estimation in OFDM/OQAM system. With this structure, we only utilize even (or odd) index of subcarriers as reference signal to avoid ICI, and then the channel information of remaining subcarriers can be estimated by the interpolation approach. Based on the sampling theorem, the mean square error (MSE) performance of the proposed preamble design is analyzed, where channel estimation performance is same for all subcarriers. Simulation and analytical results demonstrate that the proposed preamble design with ICI cancellation method outperforms the conventional one in term of channel estimation accuracy in OFDM/OQAM system.

In this paper, we study the performance of dual hop relaying in which the best relay selected by partial relay selection will help the source-destination link to overcome the channel impairment. Specifically, closed-form expressions for outage probability, symbol error probability and achievable diversity gain are derived using the statistical characteristic of the signal-to-noise ratio. Numerical investigation shows that the system achieves diversity of two regardless of relay number and also confirms the correctness of the analytical results. Furthermore, the performance loss due to partial relay selection is investigated.

A scan chain is one of the most important testing techniques, but it can be used as side-channel attacks against a cryptography LSI. We focus on scan-based attacks, in which scan chains are targeted for side-channel attacks. The conventional scan-based attacks only consider the scan chain composed of only the registers in a cryptography circuit. However, a cryptography LSI usually uses many circuits such as memories, micro processors and other circuits. This means that the conventional attacks cannot be applied to the practical scan chain composed of various types of registers. In this paper, a scan-based attack which enables to decipher the secret key in an AES cryptography LSI composed of an AES circuit and other circuits is proposed. By focusing on bit pattern of the specific register and monitoring its change, our scan-based attack eliminates the influence of registers included in other circuits than AES. Our attack does not depend on scan chain architecture, and it can decipher practical AES cryptography LSIs.

Interleaved Frequency Division Multiple Access (IFDMA) is a modulation scheme that achieves a frequency diversity gain and establishes a frequency orthogonal channel. In multicarrier modulation schemes such as orthogonal frequency division multiplexing (OFDM), a pilot signal is dispersed over the frequency and time domains and thus the estimated channel transfer function can track the fluctuations that occur in the time and frequency domains. This pilot signal is referred to as a scattered pilot signal. However, the scattered pilot signal has not yet been applied to IFDMA. In this paper, we propose a scattered pilot signal for IFDMA. The problem with the proposed scattered pilot signal is that it increases the peak to average power ratio of the transmitted signal. Therefore, we also propose three peak-to-average power ratio (PAPR) reduction schemes for the IFDMA symbols including the scattered pilot signal. A computer simulation shows that the proposed pilot signal achieves a highly accurate channel estimation under various channel conditions and that the proposed reduction shemes significantly reduce the PAPR.

There is a trend towards flexible radios which are able to cope with a range of wireless communication standards. For the integrated processing of widely different signals -- including single-carrier, multi-carrier, and spread-spectrum signals -- monolithic baseband receivers need universal formats for the signal representation and channel description. We consider a reconfigurable receiver architecture building on concepts from time-frequency (TF) signal analysis. The core elements are TF signal representations in form of a Gabor expansion along with a compatible parameterization of time-variant channels. While applicable to arbitrary signal types, the TF channel parameterization offers similar advantages as the frequency domain channel description employed by orthogonal frequency-division multiplexing receivers. The freedom in the choice of the underlying analysis window function and the scalability in time and frequency facilitate the handling of diverse signal types as well as the adaptation to radio channels with different delay and Doppler spreads. Optimized window shapes limit the inherent model error, as demonstrated using the example of direct-sequence spread-spectrum signaling.

In the centralized polling mode in IEEE 802.16e, a base station (BS) polls mobile stations (MSs) for bandwidth reservation in one of three polling modes; unicast, multicast, or broadcast pollings. In unicast polling, the BS polls each individual MS to allow to transmit a bandwidth request packet. This paper presents an analytical model for the unicast polling of bandwidth request in IEEE 802.16e networks over Gilbert-Elliot error channel. We derive the probability distribution for the delay of bandwidth requests due to wireless transmission errors and find the loss probability of request packets due to finite retransmission attempts. By using the delay distribution and the loss probability, we optimize the number of polling slots within a frame and the maximum retransmission number while satisfying QoS on the total loss probability which combines two losses: packet loss due to the excess of maximum retransmission and delay outage loss due to the maximum tolerable delay bound. In addition, we obtain the utilization of polling slots, which is defined as the ratio of the number of polling slots used for the MS's successful transmission to the total number of polling slots used by the MS over a long run time. Analysis results are shown to well match with simulation results. Numerical results give examples of the optimal number of polling slots within a frame and the optimal maximum retransmission number depending on delay bounds, the number of MSs, and the channel conditions.

This paper proposes new techniques to simulate a MIMO propagation channel using the ray-tracing method for the purpose of decreasing the computational complexity. These techniques simulate a MIMO propagation channel by substituting the propagation path between a particular combination of transmitter and receiver antennas for all combinations of transmitter and receiver antennas. The estimation accuracy calculated using the proposed techniques is evaluated based on comparison to the results calculated using imaging algorithms. The results show that the proposed techniques simulate a MIMO propagation channel with low computational complexity, and a high level of estimation accuracy is achieved using the proposed Vector-Rotation Approximation technique compared to that for the imaging algorithm.

An OFDMA based channel access scheme is proposed for dynamic spectrum access to utilize frequency spectrum efficiently. Though the OFDMA based scheme is flexible enough to change the bandwidth and channel of the transmitted signals, the OFDMA signal has large PAPR (Peak to Average Power Ratio). In addition, if the OFDMA receiver does not use a filter to extract sub-carriers before FFT (Fast Fourier Transform) processing, the designated sub-carriers suffer large interference from the adjacent channel signals in the FFT processing on the receiving side. To solve the problems such as PAPR and adjacent channel interference encountered in the OFDMA based scheme, this paper proposes a novel dynamic channel access scheme using overlap FFT filter-bank based on single carrier modulation. It also shows performance evaluation results of the proposed scheme by computer simulation.

Channel estimation is a key baseband processing task in wireless systems. Filtering or smoothing algorithms can improve the accuracy of channel estimates and the Discrete Cosine Transform (DCT) can be used for this purpose. By using the DCT, performance will be improved compared to the straight-forward approach of per subcarrier estimation (PSE). However, the complexity of the DCT is not negligible. This paper proposes a low-complexity channel estimation scheme using the DCT. Simulation results show that the performance is improved by more than 1dB compared with PSE in MIMO-OFDM system.

This paper describes a novel channel allocation scheme that enables data to be collected from observation points throughout the ultra-wide area covered by a satellite communication system. Most of the earth stations in the system acquire pre-scheduled type data such as that pertaining to rainfall and temperature measurements, but a few of them acquire event-driven type data such as that pertaining to earthquakes. Therefore, the main issue pertaining to this scheme is how to effectively accommodate demand for the channels by a huge number of earth stations with limited satellite frequency bandwidth regardless of their acquired data types. To tackle this issue, we propose a channel allocation scheme built on a pre-assigned scheme to gather pre-scheduled type data but that also includes an additional procedure to gather event-driven type data reliably. Performance evaluations show that the proposed scheme achieves higher throughput and lower packet loss rate than conventional schemes.

We present an attractive approach for OFDM transmission using an adaptive pre-FFT equalizer, which can select ICI reduction mode according to channel condition, and a degenerated-inverse-matrix-based channel estimator (DIME), which uses a cyclic sinc-function matrix uniquely determined by transmitted subcarriers. In addition to simulation results, the proposed system with an adaptive pre-FFT equalizer and DIME has been laboratory tested by using a software defined radio (SDR)-based test bed. The simulation and experimental results demonstrated that the system at a rate of more than 100 Mbps can provide a bit error rate of less than 10-3 for a fast multi-path fading channel that has a moving velocity of more than 200 km/h with a delay spread of 1.9 µs (a maximum delay path of 7.3 µs) in the 5-GHz band.

An exact expression of error rate is developed for maximal ratio combining (MRC) in an independent but not necessarily identically distributed frequency selective Nakagami fading channel taking into account inter-symbol, co-channel and adjacent channel interferences (ISI, CCI and ACI respectively). The characteristic function (CF) method is adopted. While accurate analysis of MRC performance cannot be seen in frequency selective channel taking ISI (and CCI) into account, such analysis for ACI has not been addressed yet. The general analysis presented in this paper solves a problem of past and present interest, which has so far been studied either approximately or in simulations. The exact method presented also lets us obtain an approximate error rate expression based on Gaussian approximation (GA) of the interferences. It is shown, especially while the channel is lightly faded, has fewer multipath components and a decaying delay profile, the GA may be substantially inaccurate at high signal-to-noise ratio. However, the exact results also reveal an important finding that there is a range of parameters where the simpler GA is reasonably accurate and hence, we don't have to go for more involved exact expression.

Alamouti's orthogonal space-time block code (OSTBC) is a simple yet important technique to take advantage of transmit diversity to mitigate fading channel effects. In this paper, we analyze the effects of time-selective channels and channel estimation errors on the bit error rate (BER) performance of Alamouti's OSTBC. We develop an analytical expression of the BER performance for the linear decoding with minimum mean squared error (MMSE) channel estimates in place of the true channel. Based on the expression, we derive a BER performance limit in decision-directed mode where the channel is tracked with Kalman filtering. Numerical examples are provided to validate our analysis and to see the impact of time-selective fading and channel estimation errors on the BER performance.

This paper describes a proposed propagation estimation method and TCP/IP-based evaluations for mobile communications employing a stratospheric platform. To estimate a wireless channel, a realistic and detailed description of its physical environment must be accurately defined. Therefore, a building distribution model characterizing the physical environment in areas in Japan is presented. The analyses of the propagation estimation method are based on the "ray-tracing" model. The results from the proposed method are derived depending on elevation and azimuth angles. In order to validate our results, comparisons between the proposed method and our previous measurement are made for a typical semi-urban area in Japan. The comparisons show close agreement between the estimation results and the measurement results. Finally and interestingly, we present communication performance evaluations based on TCP/IP protocol by using the results achieved from our channel estimation with semi-analytical and simulation approach.

In orthogonal frequency division multiplexing (OFDM) system, a guard interval (GI) is used to remove the inter-symbol interference (ISI) due to a multipath channel. It is difficult to set an optimal GI length in the environment whose multipath varies. In this paper, we propose a variable guard interval based on the estimated maximum delay of a multipath channel. The maximum delay is estimated from a channel impulse response (CIR), which is estimated by a preamble symbol. However, since the estimated CIR includes the noise, it is difficult to decide the optimal GI. In order to solve the problem, we introduce the method which selects the path whose signal to noise ratio is high. Additionally, the information of the optimal GI length is required to be transmitted from a receiver to a transmitter. In this paper, we use an acknowledgment (ACK) frame for the feedback of the GI information.

Multiple-input-multiple-output (MIMO) wireless systems can not always have full spatial multiplexing gain due to the channel correlation problem caused by various factors such as the coupled antenna elements, and the key-hole effect of the propagation environment. In this paper, we proposed a channel reconfiguration technique to combat the rank deficiency problem of the involved MIMO wireless channels that can not afford high-order multiplexing gains. In the proposed approach, each mobile station can simultaneously receive several independent data streams from multiple base stations through a set of MMSE-based receive beamformers to suppress the multiple access interferences. Making use of the receive beamforming, which virtually produce the effect of a single antenna at each receive mobile, makes the transmit base station possible to reconfigure the MIMO downlink channel and then pre-cancel the co-channel interferences. The proposed signal processing mechanism that iteratively optimized the MMSE receive weights and the transmit precoders, which brings the reconfigured MIMO system about the high data throughput seen only with indoor MIMO systems having rich wireless channels. It is shown that as compared to the conventional MIMO system, the M4 system can achieve a significantly higher capacity which is proportional to the number of the linked base stations.

The joint source-channel coding problem is considered. The joint source-channel coding theorem reveals the existence of a code for the pair of the source and the channel under the condition that the error probability is smaller than or equal to ε asymptotically. The separation theorem guarantees that we can achieve the optimal coding performance by using the two-stage coding. In the case that ε = 0, Han showed the joint source-channel coding theorem and the separation theorem for general sources and channels. Furthermore the ε-coding theorem (0 ≤ ε <1) in the similar setting was studied. However, the separation theorem was not revealed since it is difficult in general. So we consider the separation theorem in this setting.