Anuj Puri

Channel estimation techniques based on pilot arrangement in OFDM systems

Channel estimation techniques for OFDM systems based on a pilot arrangement are investigated. Channel estimation based on a comb type pilot arrangement is studied through different algorithms for both estimating the channel at pilot frequencies and interpolating the channel. Channel estimation at pilot frequencies is based on LS and LMS methods while channel interpolation is done using linear interpolation, second order interpolation, low-pass interpolation, spline cubic interpolation, and time domain interpolation. Time-domain interpolation is obtained by passing to the time domain by means of IDFT (inverse discrete Fourier transform), zero padding and going back to the frequency domain by DFT (discrete Fourier transform). In addition, channel estimation based on a block type pilot arrangement is performed by sending pilots in every sub-channel and using this estimation for a specific number of following symbols. We have also implemented a decision feedback equalizer for all sub-channels followed by periodic block-type pilots. We have compared the performances of all schemes by measuring bit error rates with 16QAM, QPSK, DQPSK and BPSK as modulation schemes, and multipath Rayleigh fading and AR based fading channels as channel models.

What's decidable about hybrid automata?

Hybrid automata model systems with both digital and analog components, such as embedded control programs. Many verification tasks for such programs can be expressed as reachability problems for hybrid automata. By improving on previous decidability and undecidability results, we identify the precise boundary between decidability and undecidability of the reachability problem for hybrid automata. On the positive side, we give an (optimal) PSPACE reachability algorithm for the case of initialized rectangular automata, where all analog variables follow trajectories within piecewise-linear envelopes and are reinitialized whenever the envelope changes. Our algorithm is based on the construction of a timed automaton that contains all reachability information about a given initialized rectangular automaton. The translation has practical significance for verification, because it guarantees the termination of symbolic procedures for the reachability analysis of initialized rectangular automata. The translation also preserves the

Geographical routing using partial information for wireless ad hoc networks

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A study of channel estimation in OFDM systems

-languages of initialized rectangular automata with bounded nondeterminism. On the negative side, we show that several slight generalizations of initialized rectangular automata lead to an undecidable reachability problem. In particular, we prove that the reachability problem is undecidable for timed automata augmented with a single stopwatch.

Dynamical Properties of Timed Automata

This paper presents an algorithm for routing in wireless and ad hoc networks using information regarding the geographic location of the nodes. The algorithm, which is a new type of distributed, adaptive and asynchronous algorithm, is known as a geographical routing algorithm (GRA). The authors describe the GRA, and discuss it in relation to other routing algorithms in the literature. A system model and a problem statement are presented. Issues related to position information inaccuracy and inconsistency, and mobility are discussed, along with simulation results.

A wireless token ring protocol for intelligent transportation systems

The channel estimation techniques for OFDM systems based on pilot arrangement are investigated. The channel estimation based on comb type pilot arrangement is studied through different algorithms for both estimating channel at pilot frequencies and interpolating the channel. The estimation of channel at pilot frequencies is based on LS and LMS while the channel interpolation is done using linear interpolation, second order interpolation, low-pass interpolation, spline cubic interpolation, and time domain interpolation. Furthermore, the channel estimation based on block type pilot arrangement is performed by sending pilots at every sub-channel and using this estimation for a specific number of following symbols. We have also implemented a decision feedback equalizer for all sub-channels followed by periodic block-type pilots. We have compared the performances of all schemes by measuring bit error rate with 16QAM, QPSK and DQPSK as modulation schemes, and multipath Rayleigh fading and AR based fading channels as channel models.

A wireless token ring protocol for ad-hoc networks

Timed automata are an important model for specifying and analyzing real-time systems. The main analysis performed on timed automata is the reachability analysis. In this paper we show that the standard approach for performing reachability analysis is not correct when the clocks drift even by a very small amount. Our formulation of the reachability problem for timed automata is as follows: we define the set R*(T,Z0)=∩∈>0Reach(T∈, Z0 where T∈ is obtained from timed automaton T by allowing an ∈ drift in the clocks. R*(T,Z0) is the set of states which can be reached in the timed automatonT from the initial states in Z0 when the clocks drift by an infinitesimally small amount. We present an algorithm for computing R*(T,Z0)and provide a proof of its correctness. We show that R*(T,Z0)is robust with respect to various types of modeling errors. To prove the correctness of our algorithm, we need to understand the dynamics of timed automata—in particular, the structure of the limit cycles of timed automata.

Driving safely in smart cars

The wireless token ring protocol (WTRP) is a medium access control (MAC) protocol for wireless networks in intelligent transportation systems (ITS). It supports quality of service (QoS) in terms of bounded latency and reserved bandwidth. The WTRP is efficient in the sense that it reduces the number of re-transmissions due to collisions. It is fair in the sense that each station takes a turn to transmit and is forced to give up the right to transmit after transmitting for a specified amount of time. It is a distributed protocol that supports many topologies since not all stations need to be connected to each other or to a central station. It can be used with an admission control agent for bandwidth or latency reservations. The WTRP is robust against single node failure. The WTRP is designed to recover gracefully from multiple simultaneous faults. It has applications to inter-access-point coordination in ITS dedicated short-range communication (DSRC) and to safety-critical vehicle-to-vehicle networking.

Verification of Hybrid Systems using Abstractions

The wireless token ring protocol (WTRP) is a medium access control protocol for wireless networks in unmanned aerial vehicles. It supports quality of service in terms of bounded latency and reserved bandwidth. This quality of service guarantee is critical in mesh stability of the formation of the vehicles. The communication of the speed and the velocity of the lead vehicle to all other vehicles in the formation had been shown to be sufficient for mesh stability of the system. WTRP is efficient in the sense that it reduces the number of retransmissions due to collisions. It is fair in the sense that each station takes a turn to transmit and is forced to give up the right to transmit after transmitting for a specified amount of time. It is a distributed protocol that supports many topologies since not all stations need to be connected to each other or to a central station. It can be used with an admission control agent for bandwidth or latency reservations. WTRP is robust against single node failure. WTRP is designed to recover gracefully from multiple simultaneous faults.

MEWLANA-mobile IP enriched wireless local area network architecture

Addresses the following question: how does one know a proposed design for an automated vehicle/highway system (AVHS) is safe? In particular, can one prove that there can be no high relative velocity collision on the AVHS? The authors show that if the controllers in the vehicles satisfy a set of constraints, then the AVHS is safe. The problem of checking whether the controllers satisfy the constraints is equivalent to solving an optimal control problem.