Rabin encryption and a secure ownership transfer protocol based on the difficulty of factorization of a public key use a small public exponent. Such encryption requires random number padding. The Coppersmith's shortpad attack works effectively on short padding, thereby allowing an adversary to extract the secret message. However, the criteria for determining the appropriate padding size remains unclear. In this paper, we derived the processing-time formula for the shortpad attack and determined the optimal random-padding size in order to achieve the desired security.

The Rabin cryptosystem has been proposed protect the unique ID (UID) in radio-frequency identification tags. The Rabin cryptosystem is a type of lightweight public key system that is theoretically quite secure; however it is vulnerable to several side-channel attacks. In this paper, a crashing modulus attack is presented as a new fault attack on modular squaring during Rabin encryption. This attack requires only one fault in the public key if its perturbed public key can be factored. Our simulation results indicate that the attack is more than 50 percent successful with several faults in practical time. A complicated situation arises when reconstructing the message, including the UID, from ciphertext, i.e., the message and the perturbed public key are not relatively prime. We present a complete and mathematically rigorous message reconstruction algorithm for such a case. Moreover, we propose an exact formula to obtain a number of candidate messages. We show that the number is not generally equal to a power of two.

A new fault attack, double counting attack (DCA), on the precomputation of 2t-ary modular exponentiation for a classical RSA digital signature (i.e., RSA without the Chinese remainder theorem) is proposed. The 2t-ary method is the most popular and widely used algorithm to speed up the RSA signature process. Developers can realize the fastest signature process by choosing optimum t . For example, t=6 is optimum for a 1536-bit classical RSA implementation. The 2t-ary method requires precomputation to generate small exponentials of message. Conventional fault attack research has paid little attention to precomputation, even though precomputation could be a target of a fault attack. The proposed DCA induces faults in precomputation using instruction skip technique, which is equivalent to replacing an instruction with a no operation in assembly language. This paper also presents a useful position checker tool to determine the position of the 2t-ary coefficients of the secret exponent from signatures based on faulted precomputations. The DCA is demonstrated to be an effective attack method for some widely used parameters. DCA can reconstruct an entire secret exponent using the position checker with 63=26-1) faulted signatures in a short time for a 1536-bit RSA implementation using the2t-ary method. The DCA process can be accelerated for a small public exponent (e.g., 65537). To the best of our knowledge, the proposed DCA is the first fault attack against classical RSA precomputation.

The heterogeneous radio system is one approach to cognitive radio and a great candidate for creating a new fundamental network that improves the efficiency of frequency resource usage. In this paper, our target is to aggregate the adaptive link of multiple radio systems into a single rich link. Generally, time delays differ among multiple different radio systems, which cause the TCP performance to deteriorate. We propose two schemes to avoid the degradation. The first is delay adjustment and the second is TCP customizing. The delay adjustment scheme eliminates the time delay difference among multiple or between two links, while the customized TCP scheme performs the function to turn the slow start process of TCP on/off adaptively. When the slow start process is turned off, the congestion window is updated for the effective throughput, based on estimation from the radio environment information instead of the slow start process.

Channel occupancy is key information to realize efficient operation of the wireless system. Channel occupancy can be defined as the time occupancy ratio in the case of Wireless LAN (WLAN). We propose a novel passive method to estimate the time occupancy ratio of WLAN. The proposed method produces greater improvement in estimation accuracy compared with that of conventional methods. In this paper, we introduce the definition of the time occupancy ratio as the utilization index of a WLAN radio resource. Then, details of the proposal are introduced. Finally, the excellent evaluation results executed on an experimental system are introduced even when many loss packets exist.

This paper introduces the latest status of our undergoing project aiming at reliable communications by heterogeneous wireless networks. This project is one of the new Research and Development (R & D) projects in Japan to attain the efficient use of the precious and scarce radio spectrum resources. A test-bed facility has been developed and their features, specifications and some experimental results are also described. Our project focuses on cooperative heterogeneous wireless networks to improve the reliability of the radio communication links while ensuring efficient use of radio spectrum resources.

This paper presents field experiment results for rotational orthogonal frequency division multiplexing (R-OFDM) transmission and demonstrates that R-OFDM is superior to conventional OFDM even in actual radio transmission. R-OFDM is a multi-carrier transmission scheme proposed by the authors. It is characterized by the use of rotational code division multiplexing that enables OFDM to obtain suitable frequency diversity gain. The authors previously implemented R-OFDM on a 100 MHz bandwidth testbed system and evaluated it in the laboratory. Measured results were in good agreement with simulation results. In addition, although the laboratory measurements made it clear that R-OFDM is superior to OFDM, the results assumed the typical radio channel conditions provided by a fading simulator. In order to confirm the effectiveness of R-OFDM, field experiments are indispensable. Therefore, this paper conducts field experiments with a measurement vehicle driven under conditions where OFDM demands frequency diversity. When the coverage of R-OFDM is measured, coverage with a packet error rate (PER) of 1% with OFDM is expanded by 12%. In addition, the measured PER performance against the measured signal-to-noise power ratio (SNR) clarifies that, by using R-OFDM, the SNR required to obtain a PER of 1% can be reduced by 3.3 dB compared with OFDM. Furthermore, OFDM throughput under severe SNR conditions can be improved by R-OFDM and R-OFDM throughput achieves 1.6 times as large as OFDM throughput.

Orthogonal frequency division multiple access (OFDMA) systems have recently drawn considerable attention as potential candidates for future generation cellular systems. To achieve proportional fairness among users while improving user's satisfaction in the upper layer, e.g. application and transmission control protocol (TCP) layers, we propose a novel multi-layer optimization approach for packet scheduling in OFDMA-based cellular systems, whereby the scheduler is designed not only based on optimization of the quality-of-service (QoS) class in the application layer, and fairness over users, but also based on the optimization of the throughput performance in the TCP layer. Simulations are conducted using TCP applications with the ultra mobile broadband (UMB) air interface numerology. Simulation results show that the proposed packet scheduling achieves up to 27.3% improvement over the proportional fairness scheduler in terms of the average system TCP throughput in the TCP layer, when resource usable rate for TCP applications is lower. Meanwhile, the proposed packet scheduling also performs with comparable fairness in the physical layer relative to the proportional fairness scheduler.

This paper presents field experiments on open-loop precoding multiple input multiple output (MIMO) using a testbed targeting International Mobile Telecommunication - Advanced (IMT-Advanced) systems. Open-loop MIMO is realized by applying Rotational OFDM (R-OFDM) to MIMO transmission. MIMO R-OFDM is more robust with respect to correlated channels than conventional open-loop MIMO-OFDM as was shown by the authors in a previous study. MIMO R-OFDM is implemented in a testbed targeting IMT-Advanced systems and is evaluated in a mobile environment. The antenna spacings are changed, i.e. the correlation coefficients between two antennas are changed, then the validity of MIMO R-OFDM is evaluated. The results of the field experiment reveal that MIMO R-OFDM is effective when the transmitter antenna spacings are decreased. The maximum cumulative distribution function (CDF) gain of MIMO R-OFDM with respect to conventional MIMO-OFDM is 6 % when the antenna spacing of the transmitter is same as the wave length of the carrier. In addition, it was also found that the rotational angle should be determined based not only on modulation order and coding rate, but also on the correlation coefficients between transmitter and receiver antennas.

This paper presents an experimental evaluation of open-loop precoding MIMO (multiple input multiple output) using a testbed targeted at IMT-Advanced systems. Open-loop MIMO is realized by applying rotational OFDM (R-OFDM), that is previously proposed by authors, to MIMO transmission. MIMO R-OFDM is more robust with respect to correlated channels than conventional open-loop MIMO-OFDM, because it optimizes the distances between the constellation points using simple phase rotation. The angle of phase rotation depends on the modulation orders and coding rate, hence the receiver does not need to feed the CSI (channel state information) back to the transmitter. In this paper, MIMO R-OFDM is implemented in a testbed targeted at IMT-Advanced systems, it is then evaluated experimentally and by computer simulations. The results of the evaluation reveal that MIMO R-OFDM is effective in correlated channels, and the gain in terms of the CIR (carrier to interference ratio) with respect to conventional MIMO OFDM to achieve PER (packet error rate) = 0.01 is about 1.5 dB when MIMO R-OFDM is used in correlated channels.

Single carrier (SC)-FDMA has been adopted by 3GPP as the radio access scheme for the uplink of long term evolution (LTE). The uplink Layer 1 / Layer 2 (L1/L2) control signalling information consists of ACK/NACK and channel quality indicator (CQI) etc. Frequency hopping based uplink L1/L2 control channel structures for ACK/NACK and CQI are agreed. This paper proposes user equipment (UE, i.e., handset or mobile terminal) specific cyclic shift (CS) setting based on the agreed hopping structure in order to achieve further interference averaging effect and diversity effect. The simulation results show that proposed UE-specific CS hopping can provide additional intra and inter-subframe interference randomization effect and hence additional gain compared to the case without further CS hopping.

This paper presents the experimental results of rotational orthogonal frequency division multiplexing (R-OFDM) performance with a turbo decoder implemented in an IMT-Advanced testbed. Taking into account recent advances in research and development toward realization of the IMT-Advanced system era, the authors are developing the testbed. The R-OFDM is multi-carrier transmission scheme and previously proposed by the authors. Its feature is to use rotational code division multiplexing that enables OFDM to obtain suitable frequency diversity gain. However, the previous work is only predicated on computer simulation. In this paper, the R-OFDM is implemented on the testbed and experimentally evaluated by distorting the R-OFDM signal on radio wave with a fading simulator. When packet error rate is measured, it is verified that measurement results are in good agreement with simulation results. The measured deterioration of required carrier-to-interference power ratio (CIR) is suppressed by about 0.5 dB compared with the simulation. The experimental results also demonstrate that the R-OFDM can reduce the required CIR of OFDM even without T2 decoder by about 1.1 dB.

In this contribution, an optimal inter-antenna and subblock shifting and inversion (IASSI) scheme exploiting additional degrees of freedom brought by multiple antennas and subblocks is proposed to alleviate peak-to-average power ratio (PAPR) problem of MIMO-OFDM systems. In order to reduce the complexity of proposed scheme, two suboptimal schemes based on sequential search and transformation are presented. Besides, combination of IASSI and matrix transform is proposed, which takes advantage of low autocorrelation characteristic of constant amplitude zero autocorrelation (CAZAC) sequence to further reduce PAPR. Simulation results show that IASSI improves PAPR reduction performance compared with existing PAPR reduction scheme. And when combined with orthogonal matrix transform utilizing CAZAC sequence, further gain can be obtained. All these proposed methods provide flexible tradeoff between satisfied PAPR reduction performance and cost of implementation.

Aiming at actual evaluation of IMT-Advanced system performance using field tests, this paper presents a developed IMT-Advanced testbed system with transmission bandwidth of 100 MHz. IMT-Advanced supports the "new capability of systems beyond IMT-2000" as indicated by the ITU-R van diagram [1] and requires a peak data rate of 1 Gbps with low mobility. In consideration of the enhanced IMT-2000 systems undergoing standardization, orthogonal frequency division multiple access (OFDMA) with multi-input multi-output (MIMO) are also promising technologies in the IMT-Advanced system. In addition, in order to meet the requirements for IMT-Advanced, the system seems to have about 100 MHz bandwidth with the aid of MIMO transmission. The developed system is based on the above prediction regarding the IMT-Advanced era, which is a more reliable prediction compared with previous studies, and the goals of this development are to provide a more realistic transmission performance, judgment criteria for operators introducing new air interfaces, and to explore new applications. In addition, the testbed enables us to conduct feasibility studies of rotational OFDM (R-OFDM) and the twin turbo decoder, which is our previous work [2] [3]. This paper performs pre-experiments before field tests, and verifies that the testbed transmits signals with 100 MHz bandwidth and the coverage providing a throughput of more than 100 Mbps without MIMO will reaches about 650 m.

In order to realize ultra low-latency mobile networks whose target is a unidirectional end-to-end latency of 10 milliseconds per IP packet, we proposed an adaptive error recovery scheme. The simulation results, which verified the effectiveness of the proposed scheme, need to be complemented by more realistic testing. Hence, we have implemented the proposed scheme using field programmable gate array (FPGA) and developed a testbed. The experimental evaluation results obtained using the testbed show similar IP packet error rate (IP PER) performances to those of the simulation results. Moreover, the IP PER performances with an end-to-end latency limitation (including transmission latency and processing latency) are firstly evaluated using the testbed. The experimental results verify the effectiveness of the proposed adaptive error recovery scheme using the testbed and indicate the possibility of realizing ultra low-latency mobile networks using the proposed error recovery scheme.

Aiming at high spectrum efficiency, this paper proposes the twin turbo decoder. The received symbol carried by multi-level modulation or MIMO (multi-input multi-output) transmission consists of two or more bits, and these bits share mutual information. However, the conventional likelihood estimation neglects this mutual information and deteriorates the estimation accuracy. This paper presents an alternative estimation method taking into account the above mutual information and applies our proposal to an iterative MAP (maximum a posteriori probability) decoder in order to improve its error correction capability. Computer simulations verify that the proposed scheme improves the PER (packet error rate) performance with the conventional method, and the required ESN0obtaining a PER of 1 % is improved by about 1.0 dB at maximum. Note that our proposed method is called the twin iterative decoder (twin turbo decoder) because it has double feedback loops

This paper proposes rotational orthogonal frequency division multiplexing (R-OFDM) transmission with multi-dimensional demodulator (MDD) and twin turbo decoder (T2D). R-OFDM uses rotational multi-carrier modulation (R-MCM), which provides suitable frequency diversity gain in any coding rates although coded OFDM cannot obtain it in high coding rates. In addition, by applying MDD to its receiver, R-OFDM does not cause inter symbol interference degrading multi-carrier code division multiplexing (MC-CDM) with Walsh code multiplexing (WCM). Then, aiming at high spectrum efficiency, T2D is also proposed. T2D is based on a turbo decoder and has the proposed likelihood estimation taking into account the mutual information between multiplexed bits in the identical received symbol. Computer simulations verify that the proposed scheme improves the packet error rate (PER) performance of not only MC-CDM with WCM, but also OFDM, and the required Es/N0of the OFDM obtaining a PER of 1% is improved by about 1.5 dB at the maximum.

This paper proposes a symbol mapping scheme on sub-carriers in use of MC-CDMA (multi carrier-code division multiple access) and LDPC (low-density parity-check) codes. Aiming at high spectrum efficiency, 16QAM modulation and LDPC codes with the PICW (progressively increased column-weight) are used here. The PICW-LDPC code is proposed in our previous studies and is proved to have better decoding performance as rate-compatible LDPC codes. By adopting the proposed symbol mapping method, the FER (frame error rate) performance of the PICW-LDPC code is improved, the required Es/N0is reduced by 0.12 dB in an AWGN channel. In order to improve FER performance in the multi-path channel, the proposed sub-carrier mapping is further applied, and the required Es/N0can also be reduced by 2.32 dB

An approach for automated modeling and verification of communication protocols is presented. A language that specifies the input/output behavior of protocol entities is introduced as the starting point of the approach, and verification of the linguistic specifications is discussed. Rules for conversion of the specifications into a Petri net model (based on a timed Petri net) are presented and illustrated by examples. This leads to a second level of verification on the net model. The approach is illustrated by its application to a part of the LAPD protocol.>

An approach for automated modeling and verification of communication protocols is presented. A language that specifies input/output behavior of protocol entities is introduced as the starting point, and some verification of the specifications is discussed. Further verification is aided by translation of the specifications to a timed Petri net model.>