Over 100 Gbit/s/ch high-speed optical transmission is required to achieve the high capacity networks that can meet future demands. The coherent receiver, which is expected to yield high frequency utilization, is a promising means of achieving such high-speed transmission. However, it requires a high-speed Analog to Digital Converter (ADC) because the received signal bandwidth would be over several tens or hundreds of GHz. To solve this problem, we propose a band-divided receiver structure for wideband optical signals. In the receiver, received wideband signals are divided into a number of narrow band signals without any guard band. We develop a band-divided receiver prototype and evaluate it in an experiment. In addition, we develop a real-time OFDM demodulator on an FPGA board that implements 1.5 GS/s ADCs. We demonstrate that the band-divided receiver prototype with its real-time OFDM demodulator and 1.5 GS/s ADC can demodulate single polarization 12 Gbit/s OFDM signals in real-time.

An optimal selection criterion of the modulation and coding scheme (MCS) for maximizing spectral efficiency is proposed in consideration of the signaling overhead of mobile WiMAX systems with a hybrid automatic repeat request mechanism. A base station informs users about the resource assignments in each frame, and the allocation process generates a substantial signaling overhead, which influences the system throughput. However, the signaling overhead was ignored in previous MCS selection criteria. In this letter, the spectral efficiency is estimated on the basis of the signaling overhead and the number of transmissions. The performance of the proposed MCS selection criterion is evaluated in terms of the spectral efficiency in the mobile WiMAX system, with and without persistent allocation.

This paper proposes a windowed-sinc function based peak-to-average power ratio (PAPR) reduction scheme for applying the polar transmitter techniques to orthogonal frequency division multiplexing (OFDM), where the high PAPR problem occurs. The proposed algorithm mitigates the effect of excessive suppression due to successive peaks or relatively high peaks of a signal, which is often observed when applying the conventional peak windowing scheme. The bit error rate (BER) and error vector magnitude (EVM) performances are measured for various window types and lengths. The simulation results demonstrate that the proposed algorithm achieves significant improvement in terms of BER and PAPR reduction performance while maintaining similar spectrum performance compared to the conventional peak windowing scheme.

Multi-core processors have been attracting a great deal of attention. In the domain of signal processing for communications, the current trends toward rapidly evolving standards and formats, and toward algorithms adaptive to dynamic factors in the environment, require programmable solutions that possess both algorithm flexibility and low implementation complexity. Reconfigurable architectures have demonstrated better tradeoffs between algorithm flexibility, implementation complexity, and energy efficiency. This paper presents a reconfigurable homogeneous memory-based FFT processor (MBFFT) architecture integrated in a single chip to provide hybrid SISO/MIMO OFDM wireless communication systems. For example, a reconfigurable MBFFT processor with eight processing elements (PEs) can be configured for one DVB-T/H with N=8192 and two 802.11n with N=128. The reconfigurable processors can perfectly fit the applications of Software Defined Radio (SDR) which requires more hardware flexibility.

We describe a concept and realization of distance-adaptive (DA) resource allocation in spectrum-sliced elastic optical path network (SLICE). We modify the modulation format and cross-connection bandwidth of individual fixed-bit rate optical paths to optimize performance with respect to transmission distance. The shorter paths are allocated a smaller amount of resources which allows reducing the spectrum occupied by the channel. We show in calculation a reduction in required spectral resources of more than 60% when compared to the traditional traffic allocation schemes based on ITU-T grid. The concept is verified experimentally.

In this paper, a novel receiver architecture is proposed for multiple-input-multiple-output (MIMO) systems; the proposed architecture helps achieve superior performance in multipath fading channels when the number of layered streams exceeds the number of receiving antennas. In this architecture, the concept of “virtual channel” is adopted to attain diversity gain even when successive detection is applied for reducing computational complexity, while orthogonal frequency division multiplexing (OFDM) is employed to combat multipath fading. Actually, successive detection is carried out in all possible virtual channels, and the virtual channel with the minimum error probability is detected with the assistance of the maximum a-posteriori (MAP) decoder in the architecture. In addition, soft input and soft output (SISO) iterative detection is introduced in the virtual channel estimation scheme. The performance of the proposed architecture is verified by computer simulations. This architecture can be implemented with lesser complexity than that in maximum likelihood detection (MLD), but the gain in the former case exceeds that in the latter by 4.5 dB at the BER of 10-3 for 42 MIMO-OFDM.

Let G=(V,E) be a graph of order n. A Hamiltonian cycle of G is a cycle that contains every vertex in G. Two Hamiltonian cycles C1= and C2= of G are independent if u1=v1 and ui ≠ vi for 2 ≤ i ≤ n. A set of Hamiltonian cycles {C1, C2, , Ck} of G is mutually independent if its elements are pairwise independent. The mutually independent hamiltonicity IHC(G) of a graph G is the maximum integer k such that for any vertex u of G there are k mutually independent Hamiltonian cycles of G starting at u. For the n-dimensional burnt pancake graph Bn, this paper proved that IHC(B2)=1 and IHC(Bn)=n for n ≥ 3.

One-time signature schemes have been used as an important cryptographic tool for various applications. To generate a signature on a message, the state-of-the-art one-time signature requires roughly one hash function evaluation and one modular multiplication. We propose a new one-time signature scheme for short messages that needs only one integer multiplication (i.e., without modular reduction or hash function evaluation). Theoretically, our construction is based on a generic transformation from identification protocols secure against active attacks into secure one-time signature schemes for short messages, where the Fiat-Shamir technique is not used. To obtain efficient instantiation of the transformation, we prove that the GPS identification protocol is secure against active attacks, which may be of independent interest.

In this letter we present efficient iterative frequency domain equalization for single-carrier (SC) transmission systems with insufficient cyclic prefix (CP). Based on minimum mean square error (MMSE) criteria, iterative decision feedback frequency domain equalization (IDF-FDE) combined with cyclic prefix reconstruction (CPR) is derived to mitigate inter-symbol interference (ISI) and inter-carrier interference (ICI). Computer simulation results reveal that the proposed scheme significantly improves the performance of SC systems with insufficient CP compared with previous schemes.

A 10-Gbit/s-class ac-coupled average-detection-type burst-mode receiver (B-Rx) with an ultra fast response and a high tolerance to the long consecutive identical digits has been developed. Key features of the circuit design are the baseline-wander common-mode rejection technique and the inverted distortion technique adopted in the limiting amplifier to cope with both the fast response and the high tolerance. Our B-Rx with newly developed limiting amplifier IC achieved a settling time of less than 150 ns, a sensitivity of -29.8 dBm, and a dynamic range of 23.8 dB with a 231-1 pseudo random bit sequences. Moreover, we also describe several potential B-Rx applications. We achieved better performance by applying the proposed systems to our B-Rx.

This letter provides a tight upper bound on the bit error rate (BER) over the Nakagami-m fading channel for the dual carrier modulation (DCM) scheme, which is adopted by the multi-band orthogonal frequency division multiplexing (MB-OFDM) ultra-wideband (UWB) system. Its tightness is verified with the existing result for Rayleigh fading channel, i.e., for m=1, which would be also valid for a more general fading environment.

A planar circularly-polarized (CP) small antenna is proposed. To obtain a low profile configuration, a co-planar waveguide (CPW) structure is employed. Circular polarization is achieved using a curved stub that generates current distribution in a direction orthogonal to the current distribution from the patch. Using meander lines and a series gap capacitance, a 70% size reduction is achieved compared to a half-wavelength resonant antenna. To the best of the authors' knowledge, the proposed antenna is the smallest CP antenna using CPW technology. The measured 3 dB axial ratio bandwidth is 8.3% from 3.83 GHz to 4.16 GHz, and a 1.6 dBic gain and 89% efficiency are achieved.

It is important to find an efficient design-for-testability methodology that satisfies both security and testability, although there exists an inherent contradiction between security and testability for digital circuits. In our previous work, we reported a secure and testable scan design approach by using extended shift registers that are functionally equivalent but not structurally equivalent to shift registers, and showed a security level by clarifying the cardinality of those classes of shift register equivalents (SR-equivalents). However, SR-equivalents are not always secure for scan-based side-channel attacks. In this paper, we consider a scan-based differential-behavior attack and propose several classes of SR-equivalent scan circuits using dummy flip-flops in order to protect the scan-based differential-behavior attack. To show the security level of those SR-equivalent scan circuits, we introduce a differential-behavior equivalent relation and clarify the number of SR-equivalent scan circuits, the number of differential-behavior equivalent classes and the cardinality of those equivalent classes.

An unsupervised algorithm is proposed for learning overcomplete topographic representations of nature image. Our method is based on Independent Component Analysis (ICA) model due to its superiority on feature extraction, and overcomes the weakness of traditional method in fast overcomplete learning. Besides, the learnt topographic representation, resembling receptive fields of complex cells, can be used as descriptors to extract invariant features. Recognition experiments on Caltech-101 dataset confirm that these complex cell descriptors are not only efficient in feature extraction but achieve comparable performances to traditional descriptors.

The tag collection algorithm in ISO/IEC 18000-7 has difficulty in collecting data from massive numbers of active RFID tags in a timely manner, so it should be improved to allow successful application in a wide variety of industrial fields. We propose two novel methods, a reduced-message method to improve the performance of data-tag collection and an efficient-sleep method to improve the performance of ID-tag collection. The reduced-message method decreases the slot size for a tag response by reducing the response size from the tag and reduces the number of commands issued from the reader. The efficient-sleep method utilizes redundant empty slots within the frame period to transmit sleep commands to the tags collected previously. We evaluated the performance improvement of tag collection by the proposed methods experimentally using an active RFID reader and 60 tags that we prepared for this study. The experimental results showed that the reduced-message method and the efficient-sleep method decreased the average tag collection time by 16.7% for data-tag collection and 9.3% for ID-tag collection compared with the standard tag collection. We also developed a simulation model for the active RFID system, reflecting the capture effect in wireless communication, and performed simulations to evaluate the proposed methods with a massive number of tags. The simulation results with up to 300 tags confirmed that the proposed methods could improve the tag collection performance, confirming the experimental results, even with larger numbers of tags.

This brief paper describes a background calibration algorithm for a pipelined ADC with an open-loop amplifier using a Split ADC structure. The open-loop amplifier is employed as a residue amplifier in the first stage of the pipelined ADC to realize low power and high speed. However the residue amplifier as well as the DAC suffer from gain error and non-linearity, and hence they need calibration; conventional background calibration methods take a long time to converge. We investigated the split ADC structure for its background calibration with fast convergence, and validated its effectiveness by MATLAB simulation.

We present a new structure for parallel affine projection (AP) filters with different step-sizes. By observing their error signals, the proposed alternating AP (A-AP) filter selects one of the two AP filters and updates the weights of the selected filter for each iteration. As a result, the total computations required for the proposed structure is almost the same as that for a single AP filter. Experimental results show that the proposed alternating selection scheme extracts the best properties of each component filter, namely fast convergence and small steady-state error.

We propose an improved TDoA (Time Difference of Arrival) localization scheme based on PSO (Particle Swarm Optimization) in UWB (Ultra Wide Band) systems. The proposed scheme is composed of two steps: the re-estimation of TDoA parameters and the re-localization of tag position. In both steps, the PSO algorithm is employed to improve the performance. In the first step, the proposed scheme re-estimates the TDoA parameters obtained by traditional TDoA localization to reduce the TDoA estimation error. In the second step, the proposed scheme with the TDoA parameters estimated in the first step, re-localizes the tag to minimize the location error. Simulation results show that the proposed scheme achieves better location performance than the traditional TDoA localization in various channel environments.

Quadratic congruence code (QCC)-based frequency-hopping and time-spreading (FH/TS) optical orthogonal codes (OOCs), and the corresponding expanded cardinality were recently studied to improve data throughput and code capacity. In this paper, we propose a new FH/TS two-dimensional (2-D) code using the QCC and the cubic congruence code (CCC), named as the QCC/CCC 2-D code. Additionally the expanded CCC-based 2D codes are also considered. In contrast to the conventional QCC-based 1-D and QCC-based FH/TS 2-D optical codes, our analysis indicates that the code capacity of the CCC-based 1-D and CCC-based FH/TS 2-D codes can be improved with the same code weight and length, respectively.

The detection of object categories with large variations in appearance is a fundamental problem in computer vision. The appearance of object categories can change due to intra-class variations, background clutter, and changes in viewpoint and illumination. For object categories with large appearance changes, some kind of sub-categorization based approach is necessary. This paper proposes a sub-category optimization approach that automatically divides an object category into an appropriate number of sub-categories based on appearance variations. Instead of using predefined intra-category sub-categorization based on domain knowledge or validation datasets, we divide the sample space by unsupervised clustering using discriminative image features. We then use a cluster performance analysis (CPA) algorithm to verify the performance of the unsupervised approach. The CPA algorithm uses two performance metrics to determine the optimal number of sub-categories per object category. Furthermore, we employ the optimal sub-category representation as the basis and a supervised multi-category detection system with χ2 merging kernel function to efficiently detect and localize object categories within an image. Extensive experimental results are shown using a standard and the authors' own databases. The comparison results reveal that our approach outperforms the state-of-the-art methods.