14 research outputs found
Performance Enhancement of Ultra Wideband WPAN using Narrowband Interference Mitigation Techniques
A new promising technique adopted by 4G community is ultra-wideband technology, which offers a solution for high bandwidth, high data rate, low cost, low power consumption, position location capability etc. A conventional type of UWB communication is impulse radio, where very short transient pulses are transmitted rather than a modulated carrier. Consequently, the spectrum is spread over several GHz, complying with the definition of UWB. Currently, the Rake receiver used for spread spectrum is considered a very promising candidate for UWB reception, due to its capability of collecting multipath components. Since UWB signals occupy such a large bandwidth, they operate as an overlay system with other existing narrowband (NB) radio systems overlapping with their bands. In order to ensure a robust communication link, the issue of coexistence and interference of UWB systems with current indoor wireless systems must be considered. Ultra Wideband technology with its application, advantages and disadvantages are discussed in detail. Design of UWB short pulse and a detail study IEEE 802.15.3a UWB channel models statistical characteristics have been analyzed through simulation. Simulation studies are performed and improved techniques are suggested for interference reduction in both Impulse Radio based UWB and Transmitted Reference type of UWB system. Modified TR-UWB receiver with UWB pulse design at transmitter end and notch filtering at receiver’s front end proved to be more efficient in single NBI, multiple NBI and WBI suppression. Extensive simulation studies to support the efficacy of the proposed schemes are carried out in the MATLAB. Bit error rate (BER) performance study for different data rates over different UWB channel models are also analyzed using proposed receiver models. Performance improvement of TR-UWB system is noticed using the proposed techniques
Global path planning for multiple AUVs using GWO
In global path planning (GPP), an autonomous underwater vehicle (AUV) tracks a predefined path. The main objective of GPP is to generate a collision free sub-optimal path with
minimum path cost. The path is defined as a set of segments, passing through selected nodes
known as waypoints. For smooth planar motion, the path cost is a function of the path length,
the threat cost and the cost of diving. Path length is the total distance travelled from start to end
point, threat cost is the penalty of collision with the obstacle and cost of diving is the energy
expanse for diving deeper in ocean. This paper addresses the GPP problem for multiple AUVs in
formation. Here, Grey Wolf Optimization (GWO) algorithm is used to find the suboptimal path
for multiple AUVs in formation. The results obtained are compared to the results of applying
Genetic Algorithm (GA) to the same problem. GA concept is simple to understand, easy to
implement and supports multi-objective optimization. It is robust to local minima and have wide
applications in various fields of science, engineering and commerce. Hence, GA is used for this
comparative study. The performance analysis is based on computational time, length of the path
generated and the total path cost. The resultant path obtained using GWO is found to be better
than GA in terms of path cost and processing time. Thus, GWO is used as the GPP algorithm
for three AUVs in formation. The formation follows leader-follower topography. A sliding mode
controller (SMC) is developed to minimize the tracking error based on local information while
maintaining formation, as mild communication exists. The stability of the sliding surface is verified by Lyapunov stability analysis. With proper path planning, the path cost can be minimized
as AUVs can reach their target in less time with less energy expanses. Thus, lower path cost
leads to less expensive underwater missions
Adaptive sliding mode formation control of multiple underwater robots
This paper proposes a new adaptive sliding mode control scheme for achieving coordinated motion control of a group of autonomous underwater vehicles with variable added mass. The control law considers the communication constraints in the acoustic medium. A common reference frame for velocity is assigned to a virtual leader dynamically. The performances of the proposed adaptive SMC were compared with that of a passivity based controller. To save the time and traveling distance for reaching the FRP by the follower AUVs, a sliding mode controller is proposed in this paper that drives the state trajectory of the AUV into a switching surface in the state space. It is observed from the obtained results that the proposed SMC provides improved performance in terms of accurately tracking the desired trajectory within less time compared to the passivity based controller. A communication consensus is designed ensuring the transfer of information among the AUVs so that they move collectively as a group. The stability of the overall closed-loop systems are analysed using Lyapunov theory and simulation results confirmed the robustness and efficiency of proposed controller
Formation control of underwater vehicles using Multi Agent System
This paper proposes the development of a formation control algorithm of multiple acoustic
underwater vehicles by employing the behaviour of autonomous mobile agents under a proposed
pursuit. A robust pursuit is developed using the distributed consensus coordinated algorithm
ensuring the transfer of information among the AUVs. The development of robust pursuit based
on characteristics of multi-agent system is for solving the incomplete information capabilities in
each agent such as asynchronous computation, decentralized data and no system global control.
In unreliable and narrow banded underwater acoustic medium, the formation of AUVs based
distributed coordinated consensus tracking can be accomplished under the constant or varying
virtual leader’s velocity. Further, the study to achieve tracking based on virtual leader AUV’s
velocity is extended to fixed and switching network topologies. Again for mild connectivity,
an adjacency matrix is defined in such a way that an adaptive connectivity is ensured between
the AUVs. The constant virtual leader vehicle velocity method based on consensus tracking
is more robust to reduce inaccuracy because no accurate position and velocity measurements
are required. Results were obtained using MATLAB and acquired outcomes are analysed for
efficient formation control in presence of the underwater communication constraints