Multiuser Detection For Asynchronous ARGOS Signals

In this paper, we investigate the application of multiuser detection techniques to a Low Polar Orbit (LPO) mobile satellite used in the ARGOS system. These techniques are used to mitigate the multiple access interference in the uplink transmission of the system. Unlike CDMA, due to the Doppler Effect, each signal has a different received carrier frequency and a different propagation delay. Multiuser detection techniques are proposed for asynchronous transmission in ARGOS system: the maximum likelihood detector, the conventional detector, and the sequential interference cancellation detector, as solutions to tackle the interference effects. Bit Error Rate performance graphs are shown for these techniques

Non Data Aided Parameter Estimation for Multi-User ARGOS Receivers

In this paper, parameter estimators are analyzed in the context of Successive Interference Cancelation (SIC) receivers for the ARGOS system. A Non Data Aided (NDA) feed forward estimator is proposed for the amplitude and the carrier phase parameters. Time delays are assumed to be known. A Window Accumulator (WA) is used to reduce the influence of the additive noise. In the presence of frequency offset, the window length L cannot be chosen arbitrarily large but an optimal length Lopt can be determined. However, because the estimator induces a different optimal length for each parameter, a trade-off must be made. We show that a window length of around 35 samples induces mean square errors (MSEs) lower than 0.012 for both parameters. The MSE of the proposed estimator is also compared to the Modified Cram´er Rao Bound (MCRB)

Leverage Bubbles

This paper investigates the relation between liquidity and asset prices. It shows that, when banks balance sheets are marked to market and banks are targeting a financial leverage level - a situation similar to current environment - formation of Leverage Bubble phenomenon and suggests a new regulation rule based on a Dynamic Leverage Ratio (DLR) rule.Financial crises, rational bubbles, Dynamic Leverage Ratio, mark to market accounting, asset pricing, macroprudential regulation, market liquidity.

Direct externalities, specific performance and renegotiation design

This paper examines how the model of De Fraja [Games and Economic Behavior, 1999] can be amended after Che [Games and Economic Behavior, 2000] negative result. We mainly show that the optimal level of investments can be obtained with the specific performance contract considered by De Fraja if the renegotiation process does not follow the Hart-Moore procedure but allocates an extreme bargaining power.incomplete contract hold-up

Impact of Imperfect Parameter Estimation on the Performance of Multi-User ARGOS Receivers

In this paper, we analyze the performance of Successive Interference Cancelation (SIC) receivers in the context of the ARGOS satellite system. Multi-user SIC receivers are studied in presence of imperfect estimates of signal parameters. We derive performance graphs that show the parameter ranges over which a successful demodulation of all users is possible. First, the graphs are derived in the context of perfect parameter estimation. Then, imperfect parameter estimation is considered. Erroneous estimations affect both the amplitude and the time delay of the received signal. Carrier frequencies are assumed to be accurately measured by the receiver. ARGOS SIC receivers are shown to be both robust to imperfect amplitude estimation and sensitive to imperfect time delay estimation

Specific Performance, Separability Condition and the Hold-Up Problem

Edlin and Reichelstein (1996) claim that an efficient solution to the hold-up problem can be implemented with a specific performance contract if a separability condition is satisfied, i.e. if the effect of investments and the effect of the state of the world enter the parties valuation functions in an additively separable manner. This note shows that this separability condition generates the same solution than if the valuation functions are independent of the sate of nature (proposition 1). This implies that a simple menu of prices that does not specify the level of trade can solve the hold-up problem (proposition 2). That is, specifying the terms of trade by writing a specific performance contract is useless with the separability condition.incomplete contract, specific performance, hold-up

Asymptotically Optimal Approximation Algorithms for Coflow Scheduling

Many modern datacenter applications involve large-scale computations composed of multiple data flows that need to be completed over a shared set of distributed resources. Such a computation completes when all of its flows complete. A useful abstraction for modeling such scenarios is a {\em coflow}, which is a collection of flows (e.g., tasks, packets, data transmissions) that all share the same performance goal. In this paper, we present the first approximation algorithms for scheduling coflows over general network topologies with the objective of minimizing total weighted completion time. We consider two different models for coflows based on the nature of individual flows: circuits, and packets. We design constant-factor polynomial-time approximation algorithms for scheduling packet-based coflows with or without given flow paths, and circuit-based coflows with given flow paths. Furthermore, we give an $O(\log n/\log \log n)$-approximation polynomial time algorithm for scheduling circuit-based coflows where flow paths are not given (here $n$ is the number of network edges). We obtain our results by developing a general framework for coflow schedules, based on interval-indexed linear programs, which may extend to other coflow models and objective functions and may also yield improved approximation bounds for specific network scenarios. We also present an experimental evaluation of our approach for circuit-based coflows that show a performance improvement of at least 22% on average over competing heuristics.Comment: Fixed minor typo