In this paper, we propose a low-power technique, called RF power gating, which consists in varying the active time ratio (ATR) of the RF front end at a symbol time scale. This technique is especially well suited to adapt the power consumption of the receiver to the performance needs without changing its architecture. The effect of this technique on the bit error rate (BER) performances is studied for a basic estimator in the specific case of minimum-shift keying signaling. A system-level energy model is also derived and discussed to estimate precisely the power reduction based on the characteristics and the power consumption of each block. This model allows highlighting the different contributors of the power reduction. The BER results and the energy model are finally merged to determine the best ATR meeting the design constraints. Applying this technique to the IEEE 802.15.4 standard, this paper shows that an ATR of 20% is a good tradeoff to meet the packet error rate constraint while maximizing the energy reduction ratio. Using typical block power consumptions, an energy reduction ratio around 20% can be reached. Even better energy reduction ratios (~60%) are also achievable when most of the blocks are power-gated.

In this paper, the impact on the bit error rate (BER) of the periodic non-uniform sampling implied by a power-gated analog-to-digital converter (ADC) is addressed in the specific case of a binary CPFSK receiver. Analytical and simulated lower bounds of the BER in an additive white Gaussian noise channel for several phase-based estimators are presented and discussed together with their dependency on the sampling synchronization. The main results are summarized in a practical abacus for Minimum Shift-Keying (MSK) modulation. Finally, the proposed techniques are evaluated against the IEEE 802.15.4 specification in MSK mode and lead to an active time ratio of the ADC of only 10% or less. Application of the proposed technique to a more competitive IEEE 802.15.4 compliant architecture available in the literature is also presented.

The emergence of new criteria specifically adapted to multidatabase systems, in response to constraints imposed by global serializability, leads to restrictive hypotheses in order to ensure correctness of executions. This is the case with the two level serializability presented in [6], that ensures strongly correct executions if transaction programs are Local Database Preserving (LDP). The main drawback of the LDP hypothesis is that it relies on rigorous programming. The principal objective of this paper has been to suppress this drawback while conserving the strong correctness of 2LSR executions We propose defining precisely the notion of value dependencies, and managing them so as not to impose the LDP property.

An integrated approach to concurrency control adaptively allows classical pessimistic (two-phase locking) or optimistic (using certification) approaches. The principles for a distributed integrated method controlling both locking and optimistic transactions are defined. The implementation of these principles leads to a method for constructing the serialization order of transactions, using their conflicts. This dynamic construction prevents the systematic rejection of old (long) readers, as in the multiversion methods. On the other hand, applying Thomas' rule to control the write conflicts permits the presence of old (long) writers.>

This paper introduces, as an optimistic concurrency control method, a new certification method by means of intervals of timestamps, usable in a distributed database system. The main advantage of this method is that it allows a chronological commit order which differs from the serialization one (thus avoiding rejections or delays of transactions which occur in usual certification methods or in classical locking or timestamping ones). The use of the dependency graph permits both classifying this method among existing ones and proving it. The certification protocol is first presented under the hypothesis that transactions' certifications are processed in the same order on all the concerned sites; it is then extended to allow concurrent certifications of transactions.