Evaluating Different Solutions to Design Fault Tolerant Systems with SRAM-based FPGAs

The latest SRAM-based FPGA devices are making the development of low-cost, high-performance, re-configurable systems feasible, paving the way for innovative architectures suitable for mission- or safety-critical applications, such as those dominating the space or avionic fields. Unfortunately, SRAM-based FPGAs are extremely sensitive to Single Event Upsets (SEUs) induced by radiation. SEUs may alter the logic value stored in the memory elements the FPGAs embed. A large part of the FPGA memory elements is dedicated to the configuration memory, whose content dictates how the resources inside the FPGA have to be used to implement any given user circuit, SEUs affecting configuration memory cells can be extremely critics. Facing the effects of SEUs through radiation-hardened FPGAs is not cost-effective. Therefore, various fault-tolerant design techniques have been devised for developing dependable solutions, starting from Commercial-Off-The-Shelf (COTS) SRAM-based FPGAs. These techniques present advantages and disadvantages that must be evaluated carefully to exploit them successfully. In this paper we mainly adopted an empirical analysis approach. We evaluated the reliability of a multiplier, a digital FIR filter, and an 8051 microprocessor implemented in SRAM-based FPGA’s, by means of extensive fault-injection experiments, assessing the capability provided by different design techniques of tolerating SEUs within the FPGA configuration memory. Experimental results demonstrate that by combining architecture-level solutions (based on redundancy) with layout-level solutions (based on reliability-oriented place and route) designers may implement reliable re-configurable systems choosing the best solution that minimizes the penalty in terms of area and speed degradation.     

InAlSb/InAs/AlGaSb Quantum Well Heterostructures for High-Electron-Mobility Transistors

Heterostructures for InAs-channel high-electron-mobility transistors (HEMTs) were investigated. Reactive AlSb buffer and barrier layers were replaced by more stable Al_0.7Ga_0.3Sb and In_0.2Al_0.8Sb alloys. The distance between the gate and the channel was reduced to 7–13 nm to allow good aspect ratios for very short gate lengths. In addition, n⁺-InAs caps were successfully deposited on the In_0.2Al_0.8Sb upper barrier allowing for low sheet resistance with relatively low sheet carrier density in the channel. These advances are expected to result in InAs-channel HEMTs with enhanced microwave performance and better reliability.     

A 0.18 μm CMOS direct down-converter for highly integrated 3G receivers

This paper presents the design of a high dynamic range direct down-converter for 3G cell-phone applications. The mechanisms responsible for second-order intermodulation distortion are discussed in details, leading to the following design strategy: the transconductor is degenerated by means of an RC filter, an LC network resonating at RF frequency loads the switching pair and carefully matched resistors are used in the output load. Prototypes realized in 0.18 μm CMOS show: +78 dBm IIP2 minimum among 40 samples, +10 dBm IIP3, 4 nV/√Hz input-referred noise density while burning only 4 mA from 1.8 V.     

MIMO MRC Systems with and without Multiuser Diversity

In this paper, we consider the multiple-input multiple-output (MIMO) wireless systems employing maximal ratio combining (MRC) in the absence and presence of multiuser diversity. First, using the well-known moment generating function-based analysis approach, we derive the error performance of the MIMO MRC systems without multiuser diversity over spatially correlated fading channels. Second, we present the average capacity of MIMO MRC systems with multiuser diversity. Numerical results demonstrate the accuracy of our analytical expressions.     

Scheduling Algorithms and Throughput Maximization for the Downlink of Packet-Data Cellular Systems with Multiple Antennas at the Base Station

The capacity-achieving coding scheme for the multiple-input multiple-output (MIMO) broadcast channel is dirty-paper coding. With this type of transmission scheme the optimal number of active users that receive data and the optimal power allocation strategy are highly dependent on the structure of the channel matrix and on the total transmit power available. In the context of packet-data access with adaptive transmission where mobile users are equipped with a single receive antenna and the base station has multiple transmit antennas, we study the optimal number of active users and the optimal power allocation. In the particular case of two transmit antennas, we prove that the optimal number of active users can be a non-monotonic function of the total transmit power. Thus not only the number of users that should optimally be served simultaneously depends on the user channel vectors but also on the power available at the base station transmitter. The expected complexity of optimal scheduling algorithms is thus very high. Yet we then prove that at most as many users as the number of transmit antennas are allocated a large amount of power asymptotically in the high-power region in order to achieve the sum-capacity. Simulations confirm that constraining the number of active users to be no more than the number of transmit antennas incurs only a marginal loss in spectral efficiency. Based on these observations, we propose low-complexity scheduling algorithms with sub-optimal transmission schemes that can approach the sum-capacity of the MIMO broadcast channel by taking advantage of multiuser diversity. The suitability of known antenna selection algorithms is also demonstrated. We consider the cases of complete and partial channel knowledge at the transmitter. We provide simulation results to illustrate our conclusions.     

Minimum Autocorrelation Spreading Codes

Intersymbol Interference (ISI) always appears when the communication channel is a multi-path channel. Many methods are used to reduce the effect of ISI. In this paper we focus on the autocorrelation property of the spreading codes and the role it plays in minimizing the ISI effect, where we obtain the spreading codes with minimum autocorrelation property. The results of comparing the average autocorrelation of the obtained codes with that of the well known Hadamard codes show a great enhancement in the performance, where for example, for codes of length 8 a gain of 408% was achieved at one shift, and for codes of length 16 a gain of 530% was achieved at one shift. Ahmad I. Amayrah was born in Amman in 1976. He received his Master of Science in Electrical Engineering from University of Jordan in 2003. He works as a lecturer in Al-Balqaa' University Abdallah K. Farraj was born in Amman in 1977. He earned his Bachelor of Science and Master of Science degrees in Electrical Engineering from University of Jordan, Amman, Jordan. He is currently working towards a PhD degree at the Department of Electrical and Computer Engineering, Texas A&M University. He is a fellow of the Graduate Teaching Academy, Texas A&M University, and he was awarded the Fulbright Scholarship for the 2005–2006 and 2006–2007 academic years.     

Trapdoor Hard-to-Invert Group Isomorphisms and Their Application to Password-Based Authentication

In the security chain the weakest link is definitely the human one: human beings cannot remember long secrets and often resort to rather insecure solutions to keep track of their passwords or pass-phrases. For this reason it is very desirable to have protocols that do not require long passwords to guarantee security, even in the case in which exhaustive search is feasible. This is actually the goal of password-based key exchange protocols, secure against off-line dictionary attacks: two people share a password (possibly a very small one, say a 4-digit number), and after the protocol execution, they end up sharing a large secret session key (known to both of them, but nobody else). Then an adversary attacking the system should try several connections (on average 5000 for the above short password) in order to be able to get the correct password. Such a large number of erroneous connections can be prevented by various means. Our results can be highlighted as follows. First we define a new primitive that we call trapdoor hard-to-invert group isomorphisms, and give some candidates. Then we present a generic password-based key exchange construction that admits a security proof assuming that these objects exist. Finally, we instantiate our general scheme with some concrete examples, such as the Diffie-Hellman function and the RSA function, but more interestingly the modular square-root function, which leads to the first scheme with security related to the integer factorization problem. Furthermore, the latter variant is very efficient for one party (the server). Our results hold in the random-oracle model.     

A novel rate control algorithm for video coding based on fuzzy-PID controller

Rate control algorithms (RCAs) aim to achieve the best visual quality under the minimum bit rate and the limited buffer size. A self-parameter-tuning fuzzy-PID controller is proposed to reduce the deviation between the target buffer level and the current buffer fullness. Fuzzy logic is used to tune each parameter of the proportional-integral-derivative controller by selecting appropriate fuzzy rules through simulation in H.264/advanced video coding (AVC). To control the quality fluctuation between consecutive frames, a quality controller is adopted. The proposed RCA has been implemented in an H.264/AVC video codec, and our experimental results show that the proposed algorithm achieves smooth target bits while enabling better buffer control and visual quality.     

Optically- and Electrically-Stimulated Terahertz Radiation Emission from Indium Nitride

Indium nitride is a novel narrow band gap semiconductor. The material is a potential strong source of terahertz frequency electromagnetic radiation with applications in time-domain terahertz spectroscopy and imaging systems. This article reviews recent experimental research on terahertz emission from the binary compound semiconductor indium nitride excited by near-infrared laser beams or microseconds electrical pulses. Advantages of indium nitride as terahertz radiation source material are discussed. It is demonstrated that different mechanisms contribute to the emission of terahertz radiation from indium nitride. The emission of up to 2.4 μW of THz radiation power is observed when InN is excited with near-infrared femtosecond laser pulses at an average power of 1 W.     

Dissipativity Analysis and Stabilization for Stochastic Systems with Repeated Scalar Nonlinearities and Applications

This paper investigates the problem of exponential dissipativity for stochastic systems with repeated scalar nonlinearities. The nonlinear system is described by a state equation containing a repeated scalar nonlinearity, which typically appears in recurrent neural networks. Attention is focused on the exponential dissipativity analysis of stochastic systems with repeated scalar nonlinearities with respect to quadratic supply rates. Passive and non-expansive property of stochastic systems with repeated scalar nonlinearities is also characterized. Moreover, a controller has been designed to make the stochastic systems with repeated scalar nonlinearities asymptotically stable. A Marketing-Production system and a Chua circuit are given to illustrate the effectiveness of the proposed design method.