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AML TURBO EQUALIZATION FOR SPACE TIME BLOCK CODED SYSTEMS

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P. Xiao, R. A. Carrasco, I. Wassell
 The use of multiple antennas in combination with advanced detection techniques, such as turbo equalization is an effective means for a communication system to provide high quality and high data rate services. Alamouti’s space-time block code (STBC) with two transmit antennas and one or two receive antennas over frequency selective multiple-input, multipleoutput (MIMO) channel is considered in this paper. The maximum likelihood detection for the studied system is investigated and shown to be prohibitive for implementation. In order to reduce the complexity, we propose a turbo equalization scheme based on the approximate maximum likelihood (AML) algorithm. The proposed scheme is shown to provide large performance gains compared to the original Alamouti algorithm and the conventional linear minimum mean square error (MMSE) based turbo equalization for the STBC coded systems.

ANALYSIS OF A CLUSTERED STDMA MAC PROTOCOL FOR WIRELESS SENSOR NETWORKS

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I. Martinez, J. Altuna, V. Acha, L.M. Arnaiz
Due to the distributed nature of sensor networks, the development of an appropriate medium access control (MAC) protocol must fulfil certain features to work properly in applications with quality of service (QoS) requirements. The performance needed by these applications can only be obtained with an ideal centralized implementation of the protocol, but this centralized architecture breaks the ad hoc concept of sensor networks. Therefore, there is a dichotomy between the performance we need and the network distributed nature we have. From another point of view, contention-based MAC protocols are not suitable for traffic with QoS requirements because of the blocking effect that they produce in MAC queues when the offered load is increased. The result of merging these two problems, the architecture and the MAC protocol, shows that, for sensor networks, we need a collision-free protocol with a better performance than the distributed one but not breaking the ad hoc concept. A comparison between a totally distributed and a clustered collision-free STDMA protocol is presented in this work. We prove that a collision-free protocol can be implemented with a clustered architecture where the efficiency of a collision-free centralized protocol and the dynamic nature of a sensor network are merged. When analysing the connection reliability the obtained results indicate that the clustered protocol performs 30% better than the distributed one using 60º directional antennas.

DS-CDMA PN CODE ACQUISITION IN RAYLEIGH FADING CHANNEL

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J. A. Obiebi, M. Y. Sharif, J. Sharp
 In this paper, an adaptive double dwell PN code acquisition circuit suitable for use in DS-CDMA systems is proposed. The adaptive nature of the circuit is based on the cell averaging constant false alarm rate technique. It is analysed in a Rayleigh fading channel taking into consideration the effect of Doppler shift, multiple access interference and frequency offset. Expressions are derived for detection probability, false alarm rate and mean acquisition time. Numerical analysis showed that the proposed method is more robust to noise conditions than a non-adaptive method. Moreover, the proposed method uses less hardware components.

DYNAMIC CLUSTERING FOR HIGH SPEED MOBILE AD HOC NETWORKS

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A. Baburam, F.H. Ali, E. Stipidis
 The intrinsic properties of logical classification of nodes into clusters in Mobile Ad hoc Networks (MANETs), offers several benefits such as improved bandwidth utilisation, scalability, and mobility management. An important prerequisite to such benefits is the formation of stable clusters even in the presence of node mobility. By clustering nodes using carefully selected similarity criteria and reducing the cluster reaffiliations experienced by nodes, the stability of the clusters can be improved. To resolve these issues, this paper presents a mobility adaptive clustering algorithm called Relative Mobility Clustering (RMC). By employing simple yet effective mobility related parameters of speed, angle of motion, location, and spatial orientation of nodes, each node in RMC makes autonomous clustering decisions to create and maintain efficient non-overlapped multihop clusters. Results from extensive simulations affirm the properties and benefits of the RMC algorithm and shows its ability to adapt effectively to changes in high speed ad hoc network. Finally, improvement in the stability of the clusters formed using RMC, is shown by comparing it against the Distributed Mobility Adaptive Clustering Algorithm (DMAC).

INFORMATION AND COMMUNICATIONS TECHNOLOGY SIGNIFICANCE IN HEALTH CARE: USER PERCEPTION

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 A. M. Oddershede, R. A. Carrasco

This paper addresses user perception regarding the significance of Information and Communication Technology (ICT) support in healthcare processes. Nowadays, most actions oriented to the improvement of operation and quality of health service depends upon the level of the ICT system available. However, there is scarce evidence from the perspective of health agents on the effect of having a suitable ICT system infrastructure for each event. Moreover, the implementation of new technology competes for funding available for health institutions’ resources and to simply introduce all of them is impossible. A case study using a multi-criteria approach was carried out involving three categories of Chilean hospitals. Empirical data was collected comprising diverse health representatives. The main contribution is the development of a decision-making model by the use of the Analytic Hierarchy Process (AHP) to reflect ICT system provision connotation and the identification of the high priority dimensions in a healthcare service.

GROUP LOCATION UPDATE SCHEME AND PERFORMANCE ANALYSIS IN MOBILE NETWORK

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F. Wang, Lai Tu

This paper proposes a new location update scheme for subscribers in an area where a large number of fast-moving users need to send update information frequently. The group location update (GLU) scheme in which a group location update is performed by a leader mobile terminal (LMT) instead of individual updates by every normal mobile terminal (NMT) has been proposed. Mobile terminals (MTs) in close vicinity spontaneously form a group and select a LMT to collect location information of NMTs and report in groups. We build a stochastic service system model to analyze the GLU scheme and individual location update (ILU) scheme in the view of channel access cost. Compared with the ILU scheme, the GLU scheme obviously increases channel capability and system throughput due to a significant reduction in signaling cost per update and the number of location updates. As user mobility increases or the number of users in the group increases, the advantage of the group update scheme improves.

OPTICAL WIRELESS AND RF WLAN LINKS FOR ETHERNET NETWORKING APPLICATIONS

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M. Gebhart, S. S. Muhammad, E. Leitgeb, E. Brandstatter, C. Chlestil

Optical Wireless and radio frequency WLAN links have very different characteristics for data transmission applications. We introduce both system concepts, the different aspects of the transmission channels and the regulatory background to point out the main advantages and challenges for each technology in this context. Even operated at nominally the same data rates in a most commonly used Ethernet network, point-to-point optical wireless links allow significantly higher data throughput as they can avoid a protocol change, which is necessary for an RF WLAN. This has a significant impact on service quality, especially in real-time applications.

MULTILEVEL DIGITAL PULSE INTERVAL MODULATION FOR OPTICAL WIRELESS COMMUNICATIONS

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Z. Ghassemlooy, N. M. Aldibbiat
 In this paper a new digital pulse time modulation scheme known as Multilevel Digital Pulse Interval Modulation (MDPIM), which is suitable for optical wireless communication systems, is introduced and its properties are investigated. Mathematical expressions for MDPIM signal, its bandwidth and transmission rate are derived, whereas its power spectral density (PSD) and the slot error rate performance are simulated. The performance of the proposed modulation scheme is analysed for different bit resolutions and the results are compared with other pulse modulation techniques such as PPM, DPIM and DH-PIM.

AVAILABILITY OF A SIMULATED 850 nm FSO / 58 GHz MMW HYBRID SYSTEM

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V. Kvicera, M. Grabner
Results of a propagation study on a free space optical link at 850 nm on an 850 m long path and on a parallel MMW 58 GHz link over 2-year period from August 2003 to July 2005 are presented. Individual attenuation events were compared with the concurrent meteorological situations and were classified according to the causes of their origin. The records of the observed attenuation events were statistically processed. Cumulative distributions of attenuation due to all hydrometeors together were obtained. It was shown that the cumulative distributions of attenuation obtained on the FSO path are much more stable than the cumulative distributions of attenuation on the MMW path which show a great year-to-year variability. Availability and diversity characteristics of the simulated FSO/MMW hybrid link were assessed. Much higher availability was achieved for the simulated FSO/MMW hybrid system than for the FSO link alone. Significant diversity gain was obtained for the percentages of time smaller than 1% and the diversity improvement factor reached significant values for attenuation greater than 10 dB. A few typical examples of attenuation events observed are given. It is shown that attenuation due to combination of fog with rain and fog with snow has also significant influence on availability of hybrid systems.

TRANSMISSION SCHEME AND ERROR PROTECTION FOR SIMPLEX LONG-DISTANCE ATMOSPHERIC FSO SYSTEMS

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H. Henniger, A. Gonzalez
Theoretical investigations and channel measurements clearly show that the atmospheric optical communication channel is often interrupted by strong and very slow fades. Using on/off keying modulation, synchronous communication schemes suffer from channel interruptions, therefore asynchronous datagram communication seems to be favourable. Furthermore the error protection codes must be able to cope with very long fades compared to the bit duration. For envisaged high data-rates, physical-layer bit wise coding can not deal with burst errors longer than codewords. Further, interleaver with technically feasible depth fail in splitting long burst errors produced by the slow fading. Therefore packet-layer coding with an implicitly longer codeword length can overcome this problem. Packet-layer coding performance investigations and code dimensioning are discussed in this paper.