This paper presents a novel decoding strategy called combined iterative demapping/decoding (CIDD), for coded M-ary biorthogonal keying-based direct sequence ultra-wideband (MBOK DS-UWB) systems. A coded MBOK DS-UWB system consists of a convolutional encoder, an interleaver, and an MBOK DS-UWB pulse mapper. CIDD improves the error rate performance of MBOK DS-UWB systems by applying the turbo principle to the demapping and decoding processes at the receiver side. To develop the CIDD, a soft-in/soft-out MBOK demapping algorithm, based on the max-log-MAP algorithm, was derived. Simulation results showed that using CIDD siginificantly improved the error rate performance of both static and multipath fading channels. It was also shown that the computational complexity of CIDD is comparable to that of the Viterbi decoding used in [133,171]8 conventional convolutional coding.

In this paper, we propose a transmitter structure in digital QAM systems where pre-compensator compensates for nonlinearity with "memory effects" at the output amplifier. The nonlinearity is modeled as a linear time-invariant filter cascaded by memoryless nonlinearity (Wiener model), whereas the pre-compensator comprises an FIR-type adaptive filter that follows a memoryless predistorter based on a series expansion with orthogonal polynomials for digital QAM data. The predistorter and the adaptive filter of the pre-compensator are stochastically and directly adapted using the error signal. The theoretically optimum parameters of the predistorter are approximately solved whence the steady-state mean square compensation error is calculated. Simulations show that the proposed pre-compensator can be adapted to achieve a sufficiently small compensation error, restoring the original QAM constellation through linearization and equalization of the nonlinearity with memory effects.

Direct manipulation by hand is an intuitive and simple way of positioning objects in an immersive virtual environment. However, this technique is not suitable for making precise adjustments to virtual objects in an immersive environment because it is difficult to hold a hand unsupported in midair and to then release an object at a fixed point. We therefore propose an alternative technique using a virtual 3D gearbox widget that we have designed, which enables users to adjust values precisely. We tested the technique in a usability study along with the use of hand manipulation and a slider. The results showed that the gearbox was the best of the three techniques for precise adjustment of small targets, in terms of both performance data and subject preference.

Recently, with the explosive growth of communication technologies, group oriented services such as teleconferencing and multi-player games are increasing. Access to information is controlled through secret communication using a group key shared among members, so efficient updating of group keys is vital to maintaining secrecy of large and dynamic groups. In this paper, we employ (2,4)-tree as a key tree, which is a height balanced tree, to reduce the number of key updates caused by joins or leaves of members. Specifically, we use the CBT (Core Based Tree) to determine the network configuration of the group members to reflect that onto the structure of the key tree. This allows for more efficient updates of group keys when splitting or merging of subgroups occurs by network failure or recovery.

In many cryptosystems incorporating human beings, the users' limited memories and their indifference to keeping the systems secure may cause some severe vulnerability of the whole systems. Thus we need more studies on personal entropy, from an information theoretical point of view, to capture the characteristics of human beings as special information sources for cryptosystems. In this paper, we discuss and analyze the use of personal entropy for generating cryptographic keys. In such a case, it is crucially important to precisely evaluate the amount of personal entropy that indicates the actual key length. We propose an advanced key generation scheme based on the conventional graphical passwords proposed in [12]. We improve them to make the most of the secret information extracted in one drawing, i.e., we incorporate the on-line pen pressure and pen inclination information in addition to utilize more secret information. We call the scheme dynamic graphical passwords, and propose a practical construction of them. We also show a precise way of quantifying their entropy, and finally, as an experimental result, we can generate a key of over 110-bit long, using the data of a single drawing. When quantifying their entropy, we need to precisely evaluate the entropy of graphical passwords as well as that of the on-line information of pen movements. We need to precisely evaluate the entropy of graphical passwords by considering the users' biased choices of their graphical passwords. It is expected that they tend to choose their passwords that are memorable as easily as possible, thus we quantify the burden of memorizing each graphical password by the length of its description using a special language based on [12]. We improve the approach in [12] by more directly reflecting how easily each graphical password can be memorized.

In this paper we study the large deviation property for chaotic binary sequences generated by one-dimensional maps displaying chaos and thresholds functions. We deal with the case when nonlinear maps are the r-adic maps. The large deviation theory for dynamical systems is useful for investigating this problem.

Efficient general secure multiparty computation (MPC) protocols were previously proposed, and the combination with the efficient auction circuits achieves the efficient sealed-bid auctions with the full privacy and correctness. However, the combination requires that each bidder submits ciphertexts of bits representing his bid, and their zero-knowledge proofs. This cost amounts to about 80 multi-exponentiations in usual case that the bid size is 20 bits (i.e. about 1,000,000 bid prices). This paper proposes sealed-bid auction protocols based on the efficient MPC protocols, where a bidder can submit only a single ciphertext. The bidder's cost is a few multi-exponentiations, and thus the proposed protocols are suitable for mobile bidders. A novel technique for the realization is a bit-slicing conversion by multiple servers, where a single ciphertext for a bid is securely converted into ciphertexts of bits representing the bid.

Optimistic coding is a coding in which we require the existence of reliable codes for infinitely many block length. In this letter we consider the optimistic source coding theorems for a general source Z from the information-spectrum approach. We first formulate the problem to be considered clearly. We obtain the optimistic infimum achievable source coding rate Tε (Z) for the case where decoding error probability εn is asymptotically less than or equal to an arbitrarily given ε [0,1). In fact, Tε (Z) turns out to be expressed in a form similar to the ordinary infimum achievable source coding rate. A new expression for Tε (Z) is also given. In addition, we investigate the case where εn = 0 for infinitely many n and obtain the infimum achievable coding rate.

Computer systems are constantly under attack and illegal access is a constant threat which makes security even more critical. A system can be broken into and secret information, e.g. decryption key, may be exposed, resulting in a total break of the system. Recently, a new framework for the protection against such key exposure problem was suggested and was called, Key-Insulated Encryption (KIE). In our paper, we introduce a novel approach to key insulated cryptosystems that offers provable security without computational assumptions. For the model of Information-Theoretically Secure Key-Insulated Encryption (ISKIE), we show lower bounds on required memory sizes of user, trusted device and sender. Our bounds are all tight as our concrete construction of ISKIE achieves all the bounds. We also extend this concept further by adding an extra property so that any pair of users in the system is able to communicate with each other and still have the same security benefits as the existing KIE based on intractability assumptions. We called this, Dynamic and Mutual Key-Insulated Encryption (DMKIE), and concrete implementations of DMKIE will be shown as well. In the end, we discuss the relationship of DMKIE against Key Predistribution Schemes (KPS) and Broadcast Encryption Schemes (BES), that is, we show that DMKIE can be constructed from either KPS or BES.

We propose use of QR factorization with sort and Dijkstra's algorithm for decreasing the computational complexity of the sphere decoder that is used for ML detection of signals on the multi-antenna fading channel. QR factorization with sort decreases the complexity of searching part of the decoder with small increase in the complexity required for preprocessing part of the decoder. Dijkstra's algorithm decreases the complexity of searching part of the decoder with increase in the storage complexity. The computer simulation demonstrates that the complexity of the decoder is reduced by the proposed methods significantly.

Iterative decodings used for turbo codes, concatenated codes and LDPC codes have been the main current of Coding Theory. Many researches have been done to improve the structure, algorithms and so on. But, the iterative process itself was not so much improved. On the other hand, in the field of nonlinear analysis, various iterative methods have been studied for nonlinear mappings. We consider the iterative decodings as nonlinear discrete dynamical systems in mathematics and apply iterative processes called Mann type iteration to the iterative decoding process. We will show, by using monotone operator theory, that the proposed method has more extensive stable domain than that of the conventional iterative process. Moreover, we will see the effect of proposed method in computer simulations.

The PN triangle method has a great significance in processing tessellation at the hardware level without software assistance. Despite its significance, however, the conventional PN triangle method has certain defects such as inefficient GE operation and degradation of visual quality. Because the method tessellates a curved surface according to the user-defined fixed LOD (Level Of Detail). In this paper, we propose adaptive tessellation of PN triangles using minimum-artifact edge linking. Through this method, higher efficiency of tessellation and better quality of scene are obtained by adaptivity and minimum-artifact edge linking, respectively. This paper also presents a hardware architecture of a PN triangle method using adaptive LOD, which is not a burden for overall 3D graphics hardware.

A novel multiple programming method for a phase change nonvolatile random access memory (NVRAM) is proposed. The resistance of the chalcogenide semiconductors (phase change materials, e.g. SeSbTe) stacked on the memory cell is controlled by the number of the applied current pulses, and we have observed experimentally 4-valued resistance in the range of 42 k-2.1kΩ at the SeSbTe discrete memory cell. On the basis of this experimental results, the 4-valued memory circuit was designed with CMOS 0.35 µm process. It has been confirmed with a circuit simulation that the multi-bit read circuit proposed works successfully under a read cycle operation over 100 MHz at 3.3 V supply voltage and the read operation is completed within 3 nsec.

We design a DAB system using space-time coding for reliable transmission in the multipath fading channel. This letter assess the performance evaluation of space-time coded DAB system. For channel estimation in the space-time coded DAB system, we introduce two training sequences and derive the mean square error of each training sequence. We then represent the average symbol error rate of the space-time coded DAB system for the specific cases of two, three, four transmit antennas.

Estimating the parameters of a statistical distribution from measured sample values forms an essential part of many signal processing tasks. K-distribution has been proven to be an appropriate model for characterising the amplitude of sea clutter. In this paper, a new method for estimating the parameters of K-Distribution is proposed. The method greatly lowers the computational requirement and variance of parameter estimates when compared with the existing non-maximum likelihood methods.

We have proposed and theoretically verified a 2R (reshaping and regeneration) limiter circuit using continuous wave (CW) holding beam for cross-gain modulation (XGM) wavelength converter, through simulation. The gain clamping effect of semiconductor optical amplifier (SOA), which is caused by CW holding beam injected into SOA, was used to obtain the accurate optical gain and phase conditions for SOA's in 2R limiter circuit. XGM wavelength converter with the proposed 2R limiter circuit provides higher extinction ratio (ER) as well as more enhanced operation speed than any other wavelength converter. Our numerical results show that after the wavelength-converted signal from XGM wavelength converter passed the 2R limiter circuit, it was re-inverted with the improved ER of 30 dB at 5 Gb/s. In case of high-speed operation, great enhancement to decrease power penalty of about 12 dB was shown at 10 Gb/s.

This paper proposes a bandwidth allocation algorithm and a demand accommodation algorithm guaranteeing utility max-min fairness under bandwidth constraints. We prove that the proposed algorithms can fairly split network resources among connections and achieve call admission control considering the fairness among different types of applications. We then formulate three different network design problems to maximize the total utility of all customers, the number of users accommodated in the network, and the average utility of the customers accommodated in the network. To solve the problems, we extend the conventional network design algorithms considering utility max-min fair share, and numerically evaluate and compare their performance. Finally, we summarize the best algorithms to design the utility max-min fair share networks considering the operation policy of network providers.

In mobile cellular networks it is crucial to be able to use the available radio spectrum as efficiently as possible while providing a certain level of Quality of Service (QoS) for the users. Emergence of miscellaneous services has dramatically increased the complexity of this problem by creating a heterogeneous traffic environment. In this paper an efficient resource allocation scheme between two real-time services with different bandwidth requirements has been proposed for cellular networks with multimedia offered traffic and highly mobile users, which combines classical intera-cell resource borrowing concept with a novel inter-cell resource-sharing scheme between diverse classes of traffic. By assuming the heterogeneous offered traffic to be a combination of audio and video traffic types, through extensive simulations it will be shown that HCBA-UCB is capable of significantly improving audio teletraffic performance of the system while preserving fairness in service provision, i.e. without imposing additional expenses upon video QoS performance.

A multi-hop wireless local area network (LAN) is an ad-hoc wireless network that connects to the Internet backbone via an access point. Routing paths between mobile hosts and a fixed host can be divided into two sub-paths, wireless and wired. In this paper, we apply the Hierarchical Routing Tree (HRT) concept to finding wireless sub-paths. That is, by constructing an HRT, each mobile host can find a routing path to an access point (i.e., the HRT root) quickly and thus gain the access to Internet. In addition, we choose the Ad-hoc On-demand Distance Vector (AODV) routing protocol as a point-to-point routing method for sources and destinations located in the same ad-hoc network in order to improve upon a weakness in the HRT method. Numerical experiments are given to show the effectiveness of the hybrid routing method.

The window flow control based end-to-end TCP congestion control may cause unfair resource allocation among multiple TCP connections with different RTTs (round trip times) at a bottleneck link. In this paper, in order to improve this unfairness, we propose the active ECN which is an ECN based active queue mechanism (AQM). A bottleneck router with the proposed mechanism marks TCP segments with a probability which depends on the RTT of each connection. By enabling the TCP senders to reduce their transmission rate when their packets are marked, the proposed mechanism can realize the same transmission rate among TCP connections with different RTTs. Furthermore, the active ECN can directly mark ACKs from TCP receivers, while the conventional ECN marks TCP segments coming from the TCP senders. As a result, the queue length distribution at the bottleneck link gets stabilized, because the sender can quickly react to the marking according to variation of the queue length.