Catálogo de publicaciones - libros

In general, it requires lots of complicated and expensive processing functions to find the exact location of a mobile target. For example, Ubiquitous Robotic Companion (URC) system should be equipped with powerful resources or be given an aid from the external servers to find its location for itself. Sensor network that consists of inexpensive low-power sensors can provide an efficient solution to find the exact location of such a mobile target at a low price. In such applications, if all sensor nodes have to always wake up to find location of the mobile robot, we have to pay a lot of waste of resources such as battery power and channel utilization. In this paper, we propose a cheap and energy efficient location tracking method of a mobile robot by minimizing the number of sensor nodes participating in the task of target tracking.

Constraint specific wireless sensor networks need energy efficient and secure communication mechanisms. In this paper we propose Lightweight Security protocol (LSec) that fulfils both requirements. LSec provides authentication and authorization of sensor nodes with simple secure key exchange scheme. It also provides confidentiality of data and protection mechanism against intrusions and anomalies. LSec is memory efficient that requires 72 bytes of memory storage for keys. It only introduces 74.125 bytes of transmission and reception cost per connection.

In this paper, a new class of space-time block codes achieving full-rate and full spatial diversity for QAM is proposed when using any odd transmit antennas over quasi-static Rayleigh fading channels. Like the conventional A-ST-CR codes [10], the proposed codes are constructed by serially concatenating the constellation-rotating precoders [7]-[9] with the Alamouti scheme [3]. Computer simulations show that for the case of QPSK, the best code in this class achieves approximately 1.5dB larger coding gain than the existing ST-CR code [8], [9] for both 3 and 5 transmit antennas at average SER=10 and for the case of 16-QAM, 3dB for 3 transmit antennas. The codes possessing quasi-orthogonal characteristic are also included in this class, allowing simple ML decoding with virtually no performance loss compared to the best code in the class.

Group-orthogonal multi-carrier code division multiple access (GO-MC-CDMA) has recently been proposed as a promising technique for the uplink segment of wireless systems. In this paper we propose and analyze a related scheme, group-orthogonal multi-carrier code division multiplexing (GO-MC-CDM), suitable for the downlink segment. The proposed receiver is shown to offer a similar bit error rate (BER) performance as the downlink version of GO-MC-CDMA at a fraction of its computational complexity. An analytical expression for the BER when using maximum likelihood (ML) detection is derived providing valuable insight into the parameters affecting the system performance and providing a basis for its optimization. Simulation results using parameters and channel models aiming at the next generation of wireless systems are provided confirming the analytically derived results.

In this work we study ultra wideband (UWB) communications over dense multipath channels using orthogonal pulse position modulation (PPM) for data modulation and time-hopping (TH) for code modulation. We consider the effects of the multiple access interference (MUI) in asynchronous spread spectrum multiple access (SSMA) based on random TH codes. We consider a realistic multipath channel to analyze the effects of the transmission rate in the number of users for different bit error rate (BER) values.

This paper discusses an adaptive modulation technique combined with space-frequency block coded OFDM(SFBC OFDM) over frequency selective channels and evaluates the performance in terms of the outdated channel state information(CSI) in mobile environments. This paper employs the Alamouti’s diversity scheme in multiple input multiple output OFDM (MIMO OFDM) and an adaptive modulation with enhanced performance. Adaptive modulation scheme shows very attractive performance when the CSI is perfect. The CSI for bit loading in MIMO OFDM can be obtained from the singular value decomposition(SVD) of MIMO channel. But, SFBC OFDM system based on Alamouti’s diversity scheme does not require the SVD process. Through various simulations, the performance of SFBC OFDM employing adaptive modulation is compared with that of fixed modulation. Also, in adaptive modulation scheme, the effects of the outdated CSI under mobile environments are shown

Spreading-Interleaved Frequency Division Multiple Access (IFDMA) providing code domain multiplexing for one IFDMA channel shows improved spectrum efficiency and good compatibility with CDMA systems while maintaining advantages of IFDMA systems. A generalized Rake receiver for Spreading-IFDMA is proposed in this paper, which combines jointly de-repetition, equalization, and de-spreading processing. Similar to the conventional CDMA systems, the guard interval in Spreading-IFDMA symbols is not necessary, which means that spectrum efficiency can be further improved over IFDMA systems. With digital simulations and performance analysis, the proposed generalized Rake receiver demonstrates better BER performance, robustness, and lower computational complexity.

To guarantee secure communication in wireless sensor networks, secret keys should be securely established between sensor nodes. Recently, an efficient security mechanism was proposed for large-scale distributed sensor networks by Zhu, Setia, and Jajodia. In their scheme, each node uses a single initial key to establish pair-wise keys and erases the key after key setup. If the key is compromised during key setup, however, the entire network will be compromised. Therefore, the performance overhead during key setup is very important for the speedy key establishment. In this paper, we propose a modified scheme which reduces the performance overhead during key setup and has provable security after key setup.

The envisioned sensor network architecture where some of the nodes may be mobile poses several new challenges to this special type of ad hoc wireless network. Recently, researchers have proposed several data dissemination protocols based on some hierarchical structure mainly constructed by a source node to support mobile sinks. However, such a source-initiated hierarchical structure results in significant resource consumption as the number of source-sink pairs are increased. Additionally, stimulus mobility aggravates the situation, where several sources may build a separate data forwarding hierarchy along the stimulus moving path. In this paper, we propose a new data dissemination protocol that exploits “Quadtree-based network space partitioning” to provide more efficient routing among multiple stimuli and sink nodes. Simulation results show that our work significantly reduces average energy consumption while maintaining comparably higher data delivery ratio.

Geographic routing for ad hoc and sensor networks has gained a lot of momentum during the last few years. In this scheme routes are created locally by each individual node, just based on the position of the destination and its local neighbors. To do that, a node selects its best neighbor (according to some metric) out of those being closer than itself to the destination. This operation is called . When a node has no such neighbors, it enters into mode. However, for face routing to work properly, the underlying graph needs to be planarized by removing crossing edges, which may eventually be very good from the routing metric point-of-view. In this paper, we introduce a new localized scheme to build a planar in a simple and efficient way, with low control overhead. The produced allows to be executed, without the need to remove any of the original links in the network. Thus, the best links according to the routing metric can still be used, Our simulation results show that by performing face routing over the virtual spanner, we manage to enhance the routing performance both for greedy-face-greedy routing and face routing between a 40 to 60% compared to existing planarity tests.