Experimental investigations on detection of terahertz radiation are presented. We used plasma wave instability phenomenon in nanometer Silicon field effect transistor. A 30 nm gate length transistor was illuminated by THz radiation at room temperature. We observe a maximum signal near to the threshold voltage. This result clearly demonstrates the possibility of plasma wave THz operation of these nanometer scale devices. The response was attributed to a non resonant detection. We also demonstrate the possibility to observe a resonant detection on the same devices.

For hybrid Multimedia-on-Demand (MoD) systems which support broadcast, batch and interactive services, the charging scheme employed plays an important role in the delivery of good service quality to users, while also determining the revenue generated for the service provider. In this letter a new charging scheme is proposed. This scheme provides the same quality of service to the users as previous charging schemes while providing higher revenue. Numerical results are presented to evaluate the performance of the new charging scheme in comparison with previous schemes.

Expressions are presented for the probability of target detection and the measurement accuracy of the detection, taking into account the effects of antenna beam-pointing error. Evaluation of these expressions requires numerical integration, which is computationally expensive. Approximate but analytic and efficient expressions are also presented. Numerical examples are given to present the relative accuracy of our analytic approximations.

To obtain large capacity, high quality mobile satellite communication systems in the future, we must use a multi-beam that can cope with extremely high levels of frequency reuse. This paper describes a novel resource allocation algorithm for multi-beam satellite communication systems that can dynamically adapt to maximum communication capacity without compromising quality. The algorithm combines two resource allocation schemes that enable it to contend with the ever-changing user distribution and inter-beam interference conditions. The first scheme optimizes the resources amongst beams. To minimize interference, the optimal constraint conditions are clarified when all clusters share and occupy the same bandwidth completely. These constraints are used in the optimization algorithm. The second scheme manages the various required resources and adapts them to the beam gain and interference levels at various user locations within a single beam. We propose a fixed power adaptive modulation scheme to obtain stable communications. This two-layered scheme can satisfactorily allocate multi-beam satellite resources to contend with the increasing communication capacity and still improve the quality.

Coexisting with many concurrent narrowband services, the performance of UWB systems will be affected considerably by them. Specifically, IEEE 802.11a systems which operate around 5 GHz and overlap the band of UWB signals will interfere with UWB systems significantly. In this paper, a novel narrow-band interferences (NBI) suppression technique based on singular value decomposition (SVD) algorithm for a direct sequence ultra-wideband (DS-UWB) communication system is presented. SVD is used to approximate the interferences which then are subtracted from the received signals. The proposed technique is simple and robust. Simulation results show that the proposed new technique is very effective.

Adaptive transmission methods improve the performance of wireless communication system by adjusting parameters like modulation, code-rate, and power depending on the channel state adaptively. In this letter, we consider the adaptive code-rate OFDM system in which code-rate of each subcarrier is adapted optimally. RCPC code is used to obtain different code-rate for each subcarrier. Performance analysis shows that 3-6 dB SNR gain or up to 30-50% data rate increase is achieved at bit error rate 10-6.

This paper proposes a new class of parallel branch-and-bound (B&B) schemes. The main idea of the scheme is to focus on the functional parallelism instead of conventional data parallelism, and to support such a heterogeneous and irregular parallelism by using a collection of autonomous agents distributed over the network. After examining several implementation issues, we describe a detail of the prototype system implemented over eight PC's connected by a network. The result of experiments conducted over the prototype system indicates that the proposed parallel processing scheme significantly improves the performance of the underlying B&B scheme by adaptively switching exploring policies adopted by each agent participating to the problem solving.

A 32-bit embedded RISC microcontroller core targeted for automotive, industrial, and PC-peripheral applications has been developed to offer the smaller code size, lower-latency instruction and interrupt processing needed for next-generation microcontrollers. The 360 MIPS/400MFLOPS/200 MHz core--based on the Harvard bus architecture--uses 0.13/0.15-µm CMOS technology and consists of a CPU, FPU, and register banks. To reduce the size of the control programs, new instructions have been added to the instruction set. These new instructions, as well as an enhanced C compiler, produce object files about 25% smaller than those for a previous designed core. A dual-issue superscalar structure consisting of three- or five-stage pipelines provides instruction processing with low latency. The cycle performance is thus an average of 1.8 times faster than the previous designed core. The superscalar structure is used to save 19 CPU registers in parallel when executing interrupt processing. That is, it saves the 19 CPU registers to the resister bank by accessing four registers at a time. This structure significantly improves interrupt response time from 37 cycles to 6 cycles.

Satellite Internet is one of the most important networks for emergency communications because of its tolerant of disasters such as earthquake. Therefore, satellite Internet has received considerable attention over recent years. However, most standard implementations of TCP congestion control method perform poorly in satellite Internet due to its high bit error rate and long propagation delay. This paper proposes a new TCP congestion control method called TCP-STAR to improve the throughput over satellite Internet. TCP-STAR has three new mechanisms, namely Congestion Window Setting (CWS) based on available bandwidth, Lift Window Control (LWC), and Acknowledgment Error Notification (AEN). CWS can resist the reduction of the transmission rate when data losses are caused by bit error. LWC is able to increase the congestion window quickly based on the estimated available bandwidth. AEN can avoid the reduction of the throughput by mis-retransmission of data. The mis-retransmission is caused by ack losses or delay. Simulations show that TCP-STAR can obtain the best throughput comparing with other TCP variants (TCP-J and TCP-WestwoodBR). Furthermore, we found that the fairness of TCP-STAR is a little lower than that of TCP-WestwoodBR. However, the fairness of TCP-STAR is equal to TCP-J.

This paper focuses on the design and the performance evaluation of a p-persistent transmission control protocol that can enhance the IEEE 802.11 MAC, namely the p-persistent IEEE 802.11 DCF. Unlike the well-known p-persistent CSMA for modeling the legacy IEEE 802.11 MAC, the proposed protocol truly exploits the p-persistent transmission capability for this MAC. Moreover, the protocol is not restricted to IEEE 802.11 and, in fact, it can be executed on the top of a pre-existent access protocol without introducing additional overhead. When considered with WLAN, this protocol can optimize the throughput of the wireless network by setting the optimal transmission probability in the IEEE 802.11 MAC according to the throughput calculation given in this paper. The key characteristics of this protocol are represented by its simplicity, integration with the Standard, complete distribution, absence of modifications to the original IEEE 802.11 MAC frame format, and no requirement of extra messages being shared by the cooperating nodes. Analysis and simulation results confirm the effectiveness of the p-persistent protocol in achieving the optimal throughput and in improving the frame delay. In addition, the protocol can be easily extended to be a distributed priority mechanism, which requires further research.

Usually an FIR filter is used to model the physical paths in an active noise control system. However, the order of the filter to be modeled is a key factor for determining the computational load for the adaptive algorithms associated with active noise control (ANC), particularly for multi-channel algorithms. In this letter, the relationships among the filter's order, the plant modeling error and the location of poles for the transfer functions of the physical paths in an ANC system are theoretically examined and numerical examples are given to verify the theoretical results.

We extend the adaptive-order rational Arnoldi algorithm for multiple-inputs and multiple-outputs (MIMO) interconnect model order reductions. Instead of using the standard Arnoldi algorithm for the SISO adaptive-order reduction algorithm (AORA), we study the adaptive-order rational global Arnoldi (AORGA) algorithm for MIMO model reductions. In this new algorithm, the input matrix is treated as a vector form. A new matrix Krylov subspace, generated by the global Arnoldi algorithm, will be developed by a Frobenius-orthonormal basis. By employing congruence transformation with the matrix Krylov subspace, the one-sided projection method can be used to construct a reduced-order system. It will be shown that the system moment matching can be preserved. In addition, we also show that the transfer matrix residual error of the reduced system can be derived analytically. This error information will provide a guideline for the order selection scheme. The algorithm can also be applied to the classical multiple point MIMO Pade approximation by the rational Arnoldi algorithm for multiple expansion points. Experimental results demonstrate the feasibility and the effectiveness of the proposed method.

Recently, Yoon et al. exhibited the vulnerability of the smart-card-equipped password based authentication protocol proposed by Chien et al. to the Denning-Sacco attack. Furthermore, they also pointed out that the protocol does not provide the perfect forward secrecy. Accordingly, they presented an enhanced protocol to strengthen the security. This letter, however, demonstrates an interleaving attack on the Yoon et al.'s improved protocol and also discusses how to defend the protocol from the attack presented here.

Recent work has shown that the usage of multiple antennas at the transmitter and receiver in a flat fading environment results in a linear increase in channel capacity. But increasing the number of antennas induces the higher hardware costs and computational burden. To overcome those problems, it is effective to select antennas appropriately among all available ones. In this paper, a new antenna selection method is proposed. The transmit antennas are selected so as to maximize the channel capacity using the genetic algorithm (GA) which is the one of the general random search algorithm. The results show that the proposed GA achieves almost the same performance as the optimal selection method with less computational amount.

We study the configuration issue of three-stage multi-granularity optical cross-connects (MG-OXC) for the dynamic traffic model in all-optical networks. From the single node point of view, we propose a configuration algorithm to configure different granularity cross-connects for arrival sub-requests with different traffic types and bandwidths. The performance of the configuration algorithm is evaluated by simulation and, furthermore, is validated by experiment based on our flexible Multi-functional Optical Switching Testbed (MOST).

In this paper, the voice signal processing module has been designed using the micro processor for the use of fully implantable middle ear devices (F-IMEHD). The voice signal processing module for F-IMEHD should be designed to compensate for the hearing loss of hearing impaired person and have the flexibility for compensating various hearing threshold level. So, the voice signal processing module has been designed and implemented to present the various frequency characteristics using the low-power micro processor, MSP430F169. The different voice signal path to the inner ear entrance was considered so that two voice signal would be combined in-phase using an all pass filter with a constant time-delay to improve the vibration of the ossicles.

This paper proposes a simple and efficient method to numerically obtain the mapping degree deg(f, 0, B) of a C1 map f : Rn → Rn at a regular value 0 relative to a bounded open subset B ⊂ Rn. For practical application, this method adopts Aberth's algorithm which does not require computation of derivatives and determinants, and reduces the computational cost with two additional procedures, namely preconditioning using the coordinate transformation and pruning using Krawczyk's method. Numerical examples show that the proposed method gives the mapping degree with 2n+1 operations using interval arithmetic.

This paper proposes a novel UWB ranging scheme employing 1-bit ADCs and analog window bank for energy collection. For an appropriate 1-bit ADC process DC offset is exploited and removed via performing analog low pass filter. To improve ranging accuracy in presence of ambiguity, dual overlapped window banks designated as primary and auxiliary windows are utilized. Corresponding to the proposed ranging scheme, its performance is verified by conducting simulations in two types of channel conditions. The simulation results show that the proposed ranging scheme performs well even in condensed multipath environment and low SNR situation.

This paper proposes a new all digital dividing ratio changeable phase locked loop (D-DCPLL) using delay clock pulse that exhibits low output jitter characteristics compared with the conventional DCPLL. This is achieved by employing the delay clock pulse generated from the ring oscillator for the standard clock controlling the loop. This output jitter is always constant regardless of the frequency fluctuation of the delay clock, and the fluctuation coefficient has little effect on the output jitter. This circuit can expand the upper bound frequency of the lock-in range compared with conventional DCPLL when the permissible output jitter is identical. Furthermore, the proposed D-DCPLL can obtain an initial pull-in in one period of the input signal and the multiplication output signal of the constant pulse interval can be obtained by using the remainder control circuit.

With the advent of deep sub-micron era, there is a demand to consider the design closure problem in high-level synthesis. It is well known that the slack is an effective means of tolerating the uncertainties in operation delays. Previous work ever attempted to increase the usable slack based on a given initial schedule. Instead of the post-processing approach, this paper is the first attempt to the simultaneous application of operation scheduling and slack optimization. We use a 0-1 integer linear programming (0-1 ILP) approach to formally formulate the problem. Under the design constraints (timing and resource), our approach is applicable to two different objective functions: the maximization of the total usable slack and the maximization of the number of non-zero slack operations. Compared with previous work, our approach has the following two advantages: first, our approach guarantees the optimality; second, our approach is more suitable for the design space exploration.