Lucio Mania

Interference Mitigation on WLANs Using Smart Antennas

This paper investigates the performance of a fixed Wireless LAN in which nodes are equipped with fully adaptive smart antennas. The considered smart antenna system is a uniform circular array of microstrip patch elements in which the weights are updated using the unconstrained LMS algorithm. The behavior of a new directional MAC protocol for spatial multiplexing is analyzed and compared with IEEE 802.11 DCF. The paper purpose is the evaluation of interference and multipath effects on SDMA, using realistic models for the channel and for the smart antenna system. The link model takes into account path loss, cochannel interference and multipath, using a modified Jakes model. Results show that the performance of the WLAN are strictly dependent on the interferer characteristics and on the angular spread of the channel.

Multi-Antenna Techniques for Wireless Mesh Networks in an Outdoor Environment

This paper investigates the behavior of a wireless mesh network in which the nodes are equipped with a multiple antenna system. The objective of this study is the comparison of the low-cost switched-beam antennas with the more expensive fully adaptive smart antennas. The analysis and the simulations are performed together with some considerations regarding the advantages and the practical possibilities of employing multi-antenna systems on mesh routers. The analytical and the numerical results are derived employing realistic antenna radiation patterns and a proper spatial channel model.

Performance Evaluation of Distributed Wireless Networks Using Smart Antennas in Low-Rank Channel

This paper investigates the performance of a distributed wireless network in which the nodes are equipped with fully adaptive smart antennas. The main goal is the evaluation of the influence that the geometrical configuration of the antenna array has on network throughput and packet delay. Analysis and simulations are performed to study the relationship between the geometry of the antenna array and the network topology. In this paper, the performance degradation due to both the small-channel angular spreads and the speed of mobile nodes is investigated. The results, which hold for the low-rank channel model only, extend to this specific case previous results obtained in ideal channel conditions. The study adopts an access scheme, previously proposed for ad-hoc networks, which is able to exploit the interferer suppression capabilities of smart antennas, together with realistic models for the antenna and the channel behaviors.

WLC02-5: Simultaneous Communications in Ad-Hoc Networks Using Smart Antennas in Multipath Environment

This paper analyzes the maximum number of simultaneous communications that can be sustained by an ad-hoc network in which the nodes are equipped with fully adaptive smart antennas. The study proposes an analytical model for the evaluation of the performance of ad hoc networks which includes multipath together with some characteristics of the access scheme. The main goal is the analysis of the relationship between the angular spread of the channel and the transmission policy ruled at MAC layer. Moreover, in the paper, it is examined the influence of the spatial channel model on network performance.

Performance Evaluation of MANETs Using Smart Antennas in Multipath Fading Environment

This paper investigates the performance of a MANET where nodes are equiped with fully adaptive smart antennas. The physical antenna system is a uniform circular array and the signal processing unit, employing LMS algorithm uses a reference signal to update the antenna weights. A comparison between a MAC protocol call selective CSMA with cooperative nulling (SCSMA/CN) and 802.11 DCF shows that higher throughput can be obtained exploiting efficient SDMA schemes. The objective of this paper is to extend, via simulations, the considerations on interferer suppression capabilities of smart antennas in more severe channel conditions. So, the link model takes into account path loss, cochannel interference and multipath fading, using modified Jakes model. Simulation results show the performance degradation due to increase of angular spread in multipath channels due to difficulties of smart antennas in placing nulls towards undesired directions. Moreover, this paper puts into evidence the effects of fading on network throughput in mobility scenario

The Antenna Phase Center in Satellite Radio-Doppler Geodetic Systems

In this paper, we consider the role of the antenna phase center in geodetic measurements based on satellite systems. To this end, we first of all clarify the mechanism through which errors arise, due to the lack of knowledge of the location of the phase center of the receiving antenna. Then, we recall briefly the procedure which can be used for finding the location of the phase center of a single antenna and we tackle the problem of finding the location of the equivalent phase center in systems consisting of two and three antennas working at different frequencies. These multiple antenna systems seem to be very promising for cutting down the errors due to the ionospheric refraction. The analytical procedure presented in the paper for solving the abovementioned problem is very general and simple and leads to results which display clearly the geometrical properties characterizing the location of the phase center of multiple antenna systems.

Sustainable simultaneous communications in ad-hoc networks using smart antenna systems

This article proposes an analytical model for evaluating the number of simultaneous communications that can be sustained by an ad-hoc network in which the nodes are equipped with fully adaptive smart antennas. The presented mathematical framework adopts realistic models for the antenna radiation pattern and the channel behavior, and is able to take into account the network topology and the characteristics of the medium access control (MAC) protocol in the spatial domain. The model is employed to investigate the impact of the spatial channel model and of the angular spread on network performance. Additionally, this article examines the influence of the transmission policy of the control and data packets of the MAC layer on the number of simultaneous communications.

Effects of the Diode Junction Capacitance on the Conversion Loss of Microwave Mixers

The theory of the frequency down-converters, which use sinusoidally driven exponential junction diode, is reviewed here with the purpose of investigating the effects of the junction Capacitance on the conversion loss. The analysis deals With single-ended mixers, both in the Z and Y configurations. Their performances are compared with those obtained from the same configurations of mixers using a purely resistive (PR) exponential diode, in cases of both short-circuited and open-circuited image frequency. This comparison shows that the junction capacitance modifies strongly the behavior of the single-ended mixer compared tothe case of purely resistive diodes. It is pointed out that, when the junction capacitance may not be neglected, and the image frequency is either open- or short-circuited, good performance can still be achieved from a sinusoidally driven Y mixer. On the contrary, the sinusoidally driven Z mixer, which Operates better than the Y mixer when the effect of the junction capacitance may be neglected, is strongly deteriorated, and it becomes worse than the Y mixer.

Performance comparison of advanced antenna systems for wireless mesh routers in an outdoor environment

Purpose – The purpose of this paper is to compare the low‐cost switched‐beam antennas and the more expensive adaptive antennas in a wireless mesh network (WMN) scenario.Design/methodology/approach – A mathematical framework is adopted in order to determine, for the two antenna systems, the number of sustainable simultaneous communications and the achievable throughput of a backbone WMN in a realistic outdoor environment.Findings – The paper includes a thorough examination of benefits and crucial implementation issues concerning the adoption multiple antennas on mesh routers.Originality/value – The paper investigates the relationship between the antenna system and the adopted channel coding technique, to determine the set‐up that may offer the best compromise between performance and complexity.

A simulation study of packet access protocols for microcellular systems

The paper presents a simulation study of reservation random access (RRA) protocols for microcellular systems. The considered protocols are based on collision resolution techniques. Previous analytical evaluations show that these techniques represent a suitable solution for handling mixed traffic, consisting of speech and data, because they allow one to decouple the speech access procedure from the data access one. In the previous analytical works, a single cell scenario has been considered, assuming a radio channel with capture and errors. We present a simulation study that validates the analytical model, and extends the study to cellular scenarios. Different reuse factors are considered. The simulation includes the reservation traffic that affects the performance noticeably. The study presented is restricted to speech users only. The results of the simulation study about in-slot, decoupling RRA protocols in a cellular system with Rayleigh fading and shadowing are included.