Sian-Jheng Lin

VCPSS: A two-in-one two-decoding-options image sharing method combining visual cryptography (VC) and polynomial-style sharing (PSS) approaches

This paper presents a novel method to combine two major branches of image sharing: VC and PSS. n transparencies are created for a given gray-valued secret image. If the decoding computer is temporarily not available at (or, not connected to) the decoding scene, we can still physically stack any t received transparencies (t≤n is a threshold value) to get a vague black-and-white view of the secret image immediately. On the other hand, when the decoding computer is finally available, then we can get a much finer gray-valued view of the secret image using the information hidden in the transparencies. In summary, each transparency is a two-in-one carrier of the information, and the decoding has two options.

New Space Shift Keying Modulation with Hamming Code-Aided Constellation Design

A modulation scheme that maps the information onto the antenna indices, such as space shift keying (SSK) and its generalized form (namely, generalized SSK or GSSK), presents an attractive option for the emerging large-scale MIMO system due to the reduced algorithm and hardware cost. In this letter, we present a new modulation scheme in this category, where we propose use of the Hamming code construction technique to systematically design the constellation. An illustrative example and experimental studies demonstrate that the proposed scheme introduces rich design flexibility and achieves better transmission rate, performance, and power tradeoffs with comparable hardware costs as compared with existing schemes.

Flip visual cryptography (FVC) with perfect security, conditionally-optimal contrast, and no expansion

This paper proposes a flip visual cryptography (FVC) scheme with perfect security, conditionally optimal contrast, and no expansion of size. The proposed FVC scheme encodes two secret images into two dual-purpose transparencies. Stacking the two transparencies can reveal one secret image. Flipping one of the two transparencies and then stacking with the other transparency can reveal the second secret image. The proposed scheme is proved to have conditionally optimal contrast: its contrast is optimal if the double-secrets non-expanded FVC scheme is required to have perfect security. The perfect security is also proved.

Energy Efficient Transmission over Space Shift Keying Modulated MIMO Channels

Energy-efficient communication using a class of spatial modulation (SM) that encodes the source information entirely in the antenna indices is considered in this paper. The energy-efficient modulation design is formulated as a convex optimization problem, where minimum achievable average symbol power consumption is derived with rate, performance, and hardware constraints. The theoretical result bounds any modulation scheme of this class, and encompasses the existing space shift keying (SSK), generalized SSK (GSSK), and Hamming code-aided SSK (HSSK) schemes as special cases. The theoretical optimum is achieved by the proposed practical energy-efficient HSSK (EE-HSSK) scheme that incorporates a novel use of the Hamming code and Huffman code techniques in the alphabet and bit-mapping designs. Experimental studies demonstrate that EE-HSSK significantly outperforms existing schemes in achieving near-optimal energy efficiency. An analytical exposition of key properties of the existing GSSK (including SSK) modulation that motivates a fundamental consideration for the proposed energy-efficient modulation design is also provided.

A Probabilistic Model of

The (t, n) visual cryptography (VC) is a secret sharing scheme where a secret image is encoded into n transparencies, and the stacking of any t out of n transparencies reveals the secret image. The stacking of t - 1 or fewer transparencies is unable to extract any information about the secret. We discuss the additions and deletions of users in a dynamic user group. To reduce the overhead of generating and distributing transparencies in user changes, this paper proposes a (t, n) VC scheme with unlimited n based on the probabilistic model. The proposed scheme allows n to change dynamically in order to include new transparencies without regenerating and redistributing the original transparencies. Specifically, an extended VC scheme based on basis matrices and a probabilistic model is proposed. An equation is derived from the fundamental definitions of the (t, n) VC scheme, and then the (t, ∞) VC scheme achieving maximal contrast can be designed by using the derived equation. The maximal contrasts with t = 2 to 6 are explicitly solved in this paper.

(t,n)

In this paper, we consider a two-way relay network in which two users exchange messages through a single relay using a physical-layer network coding (PNC) based protocol. The protocol comprises two phases of communication. In the multiple access (MA) phase, two users transmit their modulated signals concurrently to the relay, and in the broadcast (BC) phase, the relay broadcasts a network-coded (denoised) signal to both users. Nonbinary and binary network codes are considered for uniform and nonuniform pulse amplitude modulation (PAM) adopted in the MA phase, respectively. We examine the effect of different choices of symbol mapping (i.e., mapping from the denoised signal to the modulation symbols at the relay) and bit mapping (i.e., mapping from the modulation symbols to the source bits at the user) on the system error-rate performance. A general optimization framework is proposed to determine the optimal symbol/bit mappings with joint consideration of noisy transmissions in both communication phases. Complexity-reduction techniques are developed for solving the optimization problems. It is shown that the optimal symbol/bit mappings depend on the signal-to-noise ratio (SNR) of the channel and the modulation scheme. A general strategy for choosing good symbol/bit mappings is also presented based on a high-SNR analysis, which suggests using a symbol mapping that aligns the error patterns in both communication phases and Gray and binary bit mappings for uniform and nonuniform PAM, respectively.

Visual Cryptography Scheme With Dynamic Group

Reversible information-embedding (RIE) is a technique transforming host signals and the message into the stego-signals, and the stego-signals can be losslessly reversed to the host signals and the message. We consider the conditions: 1) the host signals are composed of gray-scale independent and identically distributed (i.i.d.) samples; 2) the mean squared error is adopted as the measure of distortion; and 3) the procedure is a scalar approach, i.e., the encoder only reads a host signal and then outputs the corresponding stego-signal in each iteration. In this paper, we propose an iterative algorithm to calculate the signal transition probabilities approximating the optimal rate-distortion bound. Then we propose an explicit implementation to embed a message in an i.i.d. host sequence. The experiments show that the proposed method closely approaches the expected rate-distortions in i.i.d. gray-scale signals. By the image prediction model, the proposed method can be applied to gray-scale images.

Symbol and Bit Mapping Optimization for Physical-Layer Network Coding with Pulse Amplitude Modulation

In this paper, we present a new basis of polynomial over finite fields of characteristic two and then apply it to the encoding/decoding of Reed-Solomon erasure codes. The proposed polynomial basis allows that h-point polynomial evaluation can be computed in O(hlog2(h)) finite field operations with small leading constant. As compared with the canonical polynomial basis, the proposed basis improves the arithmetic complexity of addition, multiplication, and the determination of polynomial degree from O(hlog2(h)log2log2(h)) to O(hlog2(h)). Based on this basis, we then develop the encoding and erasure decoding algorithms for the (n=2r, k) Reed-Solomon codes. Thanks to the efficiency of transform based on the polynomial basis, the encoding can be completed in O(nlog2(k)) finite field operations, and the erasure decoding in O(nlog2(n)) finite field operations. To the best of our knowledge, this is the first approach supporting Reed-Solomon erasure codes over characteristic-2 finite fields while achieving a complexity of O(nlog2(n)), in both additive and multiplicative complexities. As the complexity leading factor is small, the algorithms are advantageous in practical applications.

The Scalar Scheme for Reversible Information-Embedding in Gray-Scale Signals: Capacity Evaluation and Code Constructions

The detection problem of the space shift keying (SSK) signaling and its generalized form (namely, generalized SSK or GSSK) in the emerging large-scale multiple-input multiple-output (MIMO) systems is discussed in this paper. First, we explicitly formulate the tree search and column search detection schemes achieving optimal maximum likelihood (ML) performance, and discuss their pros and cons in the context of large MIMO systems where the size of the GSSK modulation alphabet increases significantly. Secondly, we propose two useful suboptimal detection methods for large MIMO systems and large-alphabet GSSK signaling based on convex relaxation, which induce an approximately 2-4 dB performance penalty as shown through experimental results.

Novel Polynomial Basis and Its Application to Reed-Solomon Erasure Codes

Regenerating codes represent a class of block codes applicable for distributed storage systems. The [n, k, d] regenerating code has data recovery capability while possessing arbitrary k out of n code fragments, and supports the capability for code fragment regeneration through the use of other arbitrary d fragments, for k ≤ d ≤ n - 1. Minimum storage regenerating (MSR) codes are a subset of regenerating codes containing the minimal size of each code fragment. The first explicit construction of MSR codes that can perform exact regeneration (named exact-MSR codes) for d ≥ 2k - 2 has been presented via a product-matrix framework. This paper addresses some of the practical issues on the construction of exact-MSR codes. The major contributions of this paper include as follows. A new product-matrix framework is proposed to directly include all feasible exact-MSR codes for d ≥ 2k - 2. The mechanism for a systematic version of exact-MSR code is proposed to minimize the computational complexities for the process of message-symbol remapping. Two practical forms of encoding matrices are presented to reduce the size of the finite field.