| [A1]. |
F. Babich, M. Comisso, M. D'Orlando, and L. Manià,
“Interference Mitigation on WLANs Using Smart Antennas”, Kluwer - Wireless Personal Communications Journal,
Vol. 36, No. 4, pp. 387 - 401, Mar. 2006. Abstract—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. |
| [A2]. | M.
Comisso and R. Vescovo,
“Exploitation of Spatial Channel Model for Antenna Array Synthesis”, Electronics Letters, Vol. 42, No. 19, pp.
1079 - 1080, 14th Sep.
2006. Abstract—A technique to modify the radiation pattern of an antenna array in order to reject interference in a certain angular region is proposed. This technique exploits the knowledge of the spatial channel model, derived from recent measurements, to properly choose the position of a certain number of nulls. The method of projections is used to modify the excitation phases in order to synthesize the array pattern. |
| [A3]. | M.
Comisso and R. Vescovo,
“Multi-Beam Synthesis with Null Constraints by Phase Control for Antenna
Arrays of Arbitrary Geometry”, Electronics Letters, Vol. 43, No. 7, pp.
374 - 375,
29th Mar. 2007. Abstract—A novel synthesis technique for antenna arrays of arbitrary geometry is proposed. Imposing equal excitation amplitudes and modifying only the excitation phases, the method is able to produce patterns endowed with multiple main lobes and nulls in assigned directions. The technique is quite simple and requires low CPU time. |
| [A4]. | F. Babich, M. Comisso, M. D’Orlando, and L. Manià,
“Performance Evaluation of Distributed Wireless Networks Using Smart Antennas in Low-Rank Channel”,
IEEE Transactions on Communications, Vol. 55, No. 7,
pp.
1344 - 1353, Jul. 2007. Abstract—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 the paper, the performance degradation due to the small channel angular spreads and to 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, able to exploit the interferer suppression capabilities of smart antennas, together with realistic models for the antenna and the channel behaviors. |
| [A5]. | F.
Babich and M. Comisso, “Optimum Contention Window for 802.11 Networks
Adopting Directional Communications”, Electronics Letters, Vol.
44, No. 16, pp. 994 - 995, 31st Jul. 2008. Abstract—A theoretical method is presented for evaluating the minimum contention window that maximises the throughput of an 802.11 network in which the use of directional or smart antennas enables the simultaneous coexistence of multiple communications between different node pairs. A simplified approach, derived from the complete analysis and validated by simulations, is proposed in order to reduce the complexity of the exact calculation. |
| [A6]. | M. Comisso,
“Theoretical and Numerical Analysis of the Resonant Behavior of the Minkowski Fractal Dipole Antenna”,
IET Microwaves, Antennas and Propagation, Vol. 3, No.
3, pp. 456 - 464,
Apr. 2009. Abstract—This paper investigates the resonant behavior and the size reduction capabilities of the Minkowski fractal dipole antenna. The antenna is analyzed at each resonant frequency by considering the radiation efficiency and the fractional bandwidth. Besides, this study proposes a method for deriving the approximate positions of the resonant frequencies of the Minkowski dipole at each fractal iteration. The presented analysis is based on the inductive circuit model and is validated by simulations. Moreover, in order to quantify the advantages provided by the Minkowski geometry, the proposed study performs a comparison with the generalised Koch dipole in terms of fractal dimension and lacunarity. |
| [A7]. | F. Babich, M. Comisso, and L. Manià,
“Performance Comparison of Advanced Antenna Systems for Wireless Mesh Routers in an
Outdoor Environment”, International Journal of Pervasive Computing and
Communications, Vol. 5, No. 3,
pp.
249 - 271, May 2009. Abstract—The objective of this paper is the comparison between the low-cost switched-beam antennas and the more expensive adaptive antennas in a Wireless Mesh Network (WMN) scenario. 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. The analysis is validated through simulation. The paper includes a thorough examination of benefits and crucial implementation issues concerning the adoption of multiple antennas on mesh routers. Besides, the theoretical model is used to investigate 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. |
| [A8]. | F.
Babich and M. Comisso,
“Throughput and Delay Analysis of 802.11-Based Wireless Networks Using Smart and Directional Antennas”,
IEEE Transactions on Communications, Vol. 57, No. 5,
pp.
1413 -
1423, May 2009. Abstract—This paper proposes a mathematical framework for comparing the performance of wireless networks based on the IEEE 802.11 standard, employing switched-beam, directional and adaptive antennas. The analysis adopts detailed models for the antenna system behavior and the propagation environment, taking into account multipath and interference. The purpose of this study is to determine the number of simultaneous communications that may be sustained by adopting advanced antenna systems, and to investigate, by analysis and simulation, the resulting performance improvements, in terms of throughput and packet delay. Both saturated and non-saturated traffic conditions are treated. Suitable 802.11 Medium Access Control (MAC) layer parameter settings, able to exploit smart and directional antenna capabilities for maximizing the throughput, are also discussed. |
| [A9]. | M.
Comisso and R. Vescovo,
“Fast Iterative Method of Power Synthesis for Antenna Arrays”, IEEE Transactions on Antennas and Propagation,
Vol. 57, No. 7, pp. 1952 - 1962, Jul. 2009. Abstract—A fast and simple method of power synthesis for antenna arrays of arbitrary geometry is presented. The method adopts an auxiliary function having the desired amplitude pattern and a generic phase pattern, and determines in closed form the array pattern approximating the auxiliary function in both amplitude and phase. A cost function involving the auxiliary function and the approximating pattern is minimized by modifying the phase pattern of the auxiliary function, using a simple and fast iterative technique. Once the optimal phase pattern has been found, the array pattern approximating the corresponding auxiliary function is the synthesized pattern. The proposed method allows to satisfy stringent requirements on the amplitude pattern, including multi-beam synthesis and radiation suppression within large angular regions. Numerical results show the effectiveness of the algorithm and are compared to those obtained using other existing methods. In order to achieve a more significant comparison such methods have been properly modified to improve their performances. Such comparison shows that the presented algorithm allows a significant reduction of CPU time with respect to the other considered methods, as well as a weaker dependence on the starting point. Finally, the presented method is extended in such a way as to reduce the Dynamic Range Ratio (DRR) of the array excitations. |
| [A10]. | M. Comisso,
“On the Use of Dimension and Lacunarity for Comparing the Resonant Behavior of Convoluted Wire Antennas”,
Progress In Electromagnetics Research,
Vol. 96, pp. 361 - 376, 2009. Abstract—This paper analyzes the possibility to use dimension and lacunarity for comparing the resonant behavior of different convoluted wire antennas, including prefractal dipoles. Since previous studies have proved that the Hausdorff fractal dimension is not suitable for antenna comparison purposes, this work proposes the adoption of a different approach for evaluating the dimension by using the measurement at scale d, which is more suitable for analyzing real phenomena. The results provided by this measure are compared to those obtained by using the average lacunarity. The objective is to verify if, given two convoluted wire dipoles, the dimension and the average lacunarity provide sufficient information to infer which dipole exhibits the lower resonances. |
| [A11]. | F. Babich, M. Comisso, and L. Manià,
“Sustainable Simultaneous Communications in Ad-Hoc Networks Using Smart Antenna Systems”,
ACM Wireless Networks, Vol. 15, No. 8, pp. 1074 - 1085, Nov. 2009. Abstract—This paper 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 paper examines the influence of the transmission policy of the control and data packets of the MAC layer on the number of simultaneous communications. |
| [A12]. | F.
Babich and M. Comisso,
“Theoretical Analysis of Asynchronous Multi-Packet Reception in 802.11 Networks”,
IEEE Transactions on Communications, Vol. 58, No. 6,
pp.
1782 - 1794, Jun. 2010. Abstract—This paper proposes a mathematical framework for evaluating the throughput of an 802.11 distributed wireless network when the system allows multi-packet reception in asynchronous operating mode. Differently from previous studies on multi-packet reception, which assume a certain synchronization between the different sources at the beginning of the respective transmissions, this work theoretically analyzes a fully distributed scenario, where each node can access to the medium in a completely asynchronous way. More precisely, a new transmission can begin in a channel where other nodes are already communicating as long as the current channel load is within a given threshold. The proposed framework consists of a single source, 802.11 specific model, which generalizes a previously presented analytical model, and a novel network model, which is adopted to evaluate the theoretical performance in terms of throughput. The novel model, which includes the synchronous scenario as a particular case, is employed to investigate the influence of the number of allowed communications, of the load threshold, and of the minimum contention window on the network performance. Furthermore, the theoretical analysis is used to evaluate the throughput in presence of Rayleigh fading and noise when error correcting codes are adopted. |
| [A13]. | F.
Babich and M. Comisso, “Optimum Contention Window for 802.11 Networks
Adopting Directional Communications”, Electronics Letters, Vol. 46, No.
21, pp. 1468 - 1470, 14th Oct. 2010. Abstract—Some issues concerning the use of a nonuniform backoff on the throughput and the successful packet delay of an 802.11 network are discussed. The transient and steady-state behaviours of the single node and of the whole network are investigated in non-saturated traffic conditions. |
| [A14]. | M.
Comisso and R. Vescovo,
“3D Power Synthesis with Reduction of Near-Field and Dynamic Range Ratio for Conformal Antenna Arrays”, IEEE Transactions on Antennas and Propagation,
Vol. 59, No. 4, pp. 1164 - 1174, Apr. 2011. Abstract—A simple method of power synthesis for 3D radiation patterns of conformal antenna arrays is presented. The method enables to synthesize a desired far-field pattern simultaneously controlling the dynamic range ratio (DRR) of the array excitations and the electric field amplitude in a given region of interest close to the antenna. The power synthesis problem is reduced to a field synthesis one by introducing an auxiliary phase pattern, which is incorporated in a cost function together with the desired far-field pattern, the array pattern, the near electric field amplitude, and the array excitations. Such cost function is minimized by iteratively modifying the auxiliary phase pattern and the array excitations. Applications of the proposed method to conformal arrays of different geometries show that accurate results are obtained also in presence of stringent requirements and within acceptable CPU times, even when hundreds of elements are involved. |
| [A15]. | F. Babich, M. Comisso, A. Dorni, F.
Barisi, M. Driusso, and A. Manià, “Discrete-Time Simulation of Smart
Antenna Systems in Network Simulator-2 Using MATLAB and Octave”, Simulation:
Transactions of The Society for Modeling and Simulation International,
Vol. 87, No. 11, pp. 932 - 946, Nov. 2011. Abstract—This paper presents two platforms that exploit the scalability properties of network simulator-2 (ns-2) for the discrete-event simulation of a telecommunication network, and the modeling capabilities of two development tools for the discrete-time implementation of adaptive antenna arrays at PHYsical (PHY) layer. The two tools are the proprietary software MATLAB and the open source one Octave, which are both used to implement the physical antenna system, the beamforming algorithm, the channel coding scheme, and the multipath and fading statistics. The adopted approach enables to model in detail the antenna radiation pattern generated by each network node, thus improving the accuracy of the Signal to Interference Ratio (SIR) estimated at the receiver. This study describes the methods that can be adopted to interface MATLAB and Octave with ns-2, discussing the advantages and disadvantages that characterize the integration of the two tools with ns-2. The proposed numerical platforms, which can be interfaced with any wireless network supported by ns-2, are used to investigate the possibility to exploit smart antenna systems in a Wireless Mesh Network (WMN) for enabling the coexistence of multiple simultaneous communications. |
| [A16]. | F. Babich, M. Comisso, E. Valentinuzzi,
A. Dorni, A. Suriano, and M. Davanzo, “Numerical and Experimental Characterization of Antenna Positioning in a Dual-Radio Mesh Router”,
AEU International Journal of Electronics and Communications, Vol.
66, No. 3, pp. 255 - 261, Mar. 2012. Abstract—This paper investigates the influence of the position of the antennas in a dual-radio mesh router by characterizing the router components from an electromagnetic point of view. Since the behavior of a wireless router equipped with multiple devices and antennas can be affected by mutual coupling among several close conducting bodies, numerical and experimental tests are carried out to provide some suggestions for an accurate positioning of the antennas. A reference configuration is implemented in an electromagnetic Computer-Aided Design (CAD) simulator. The most significant numerical results are validated by performing a campaign of measurements in anechoic chamber and deploying a testbed for the derivation of the experimental values of throughput, return loss, power density, and directivity. |
| [B1]. | F. Babich, M. Comisso, M. D’Orlando,
and A. Dorni, “Deployment of a Reliable 802.11e Experimental Setup for
Throughput Measurements”,
Wiley Wireless Communications and Mobile Computing, accepted for
publication, 2011. Abstract—This paper describes an experimental setup for measuring the throughput of an 802.11 network that supports Quality of Service (QoS) mechanisms, addressing some issues concerning the comparison between experimental and theoretical results. The setup is an ad hoc network in which the nodes implement the Multiband Atheros Driver for Wireless Fidelity (MADWiFi). There are three main contributions of this study. The first one describes the adjustments to the MADWiFi source code that guarantee the control of the QoS parameters in ad hoc mode. The second contribution aims to provide a practical method for verifying if the backoff generated by a given wireless card is uniformly distributed, as dictated by the 802.11 standard. This represents a key point when theoretical and experimental results must be compared, since many vendors adopt nonuniform backoff distributions in their commercial cards. As a third contribution, this paper presents a theoretical nonsaturated analysis that provides the throughput and the successful packet delay of an 802.11 network supporting QoS in presence of nonuniform backoff. The throughput derived from this analysis using a uniform backoff, which is included in the proposed model as a particular case, is compared to the measurements provided by the deployed setup. |
| [C1]. | F. Babich, M. Comisso, M. D'Orlando, and L. Manià,
“Performance Evaluation of MANETs Using Smart Antennas in Multipath Fading
Environment”, in 2nd IEEE International Symposium on Wireless
Communication Systems (ISWCS), Siena, Italy, pp. 327 - 331, 5-7 Sep. 2005. Abstract—This paper investigates the performance of a MANET where nodes are equipped 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 called 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 a 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. |
| [C2]. | F.
Babich, M. Comisso, M. D'Orlando, and F. Vatta, “Distortion Estimation Algorithms (DEAs) for Wireless Video Streaming",
in IEEE Global Telecommunications Conference (GLOBECOM), San Francisco,
California (USA), pp.
1 - 5, 27 Nov.-1 Dec. 2006.
Abstract—This paper proposes three methods to estimate the distortion deriving from packet losses in wireless video communication. The proposed models take into account the short-term properties of the encoded video sequences and the properties of the wireless links. A suitable set of functions is adopted to model the distortion envelope resulting from multiple losses. The performance of the employed models, which depends on the average Packet Loss Rate (PLR), is compared with the actual distortion, evaluated by decoding the received sequence with a properly designed, robust decoder. Numerical results confirm the accuracy of the proposed models, that are able to closely approximate the actual Mean Square Error (MSE) behavior for a wide range of loss rates. Some applications of the proposed algorithms are also presented in the paper. |
| [C3]. | M. Comisso,
F. Babich, M. D’Orlando, and L. Manià,
“Simultaneous Communications in Ad-Hoc Networks Using Smart Antennas in Multipath Environment”,
in IEEE Global Telecommunications Conference (GLOBECOM), San Francisco,
California (USA), pp.
1 - 6, 27 Nov.-1 Dec. 2006 (Best Student Paper Award
Finalist). Abstract—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. |
| [C4]. |
F. Babich, M. Comisso, and L. Manià,
“Multi-Antenna Techniques for Wireless Mesh Networks in an Outdoor Environment”,
in IEEE International Conference on Communications (ICC),
Glasgow, Scotland (UK), pp. 4961 - 4966, 24-28 Jun. 2007. Abstract—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. |
| [C5]. | F.
Babich and M. Comisso, “Channel Coding and Multi-Antenna Techniques for Distributed Wireless Networks",
in IEEE Global Telecommunications Conference (GLOBECOM), Washington,
DC (USA), pp. 4180 - 4184, 26-30 Nov. 2007.
Abstract—This paper investigates the influence of channel coding on the performance of a distributed wireless network in which the nodes are equipped with multiple antennas. Different coded modulation techniques and antenna systems are taken into consideration and compared, assuming an outdoor environment. More precisely, the proposed study compares the performance of wireless networks adopting convolutional codes, already adopted in the 802.11a physical layer standard, with the performance that may be achieved by adopting more efficient coding techniques. A realistic channel model including Rayleigh fading and Laplacian power azimuth spectrum is adopted, and code performance comparison is performed using both simple switched-beam antenna systems and more complex fully adaptive smart antennas. |
| [C6]. |
F. Babich and M. Comisso,
“Throughput Maximization in 802.11 Wireless Networks Employing Adaptive Antenna Arrays”,
in IEEE International Conference on Communications (ICC), Beijing,
China, pp. 4549 - 4553, 19-23 May 2008. Abstract—This paper proposes a mathematical framework for evaluating, in saturated and non-saturated traffic conditions, the performance of an 802.11 wireless network in which the nodes are equipped with adaptive antenna systems. The analysis, validated by simulations, adopts detailed models for the antenna behavior and the propagation environment, taking into account multipath and interference. The developed model is used to investigate the proper parameter settings that lead to throughput maximization, providing a simplified method to obtain the optimum contention window when adaptive arrays are employed. |
| [C7]. | M.
Comisso and R. Vescovo,
“Fast Power Pattern Synthesis with Near-Field Control for Antenna Arrays”,
in IEEE Antennas and Propagation Society (AP-S) International Symposium, Charleston,
South Carolina (USA), pp.
1 - 4, 1-5 Jun. 2009. Abstract—In this paper we propose a fast iterative method of power synthesis that enables to reduce the electric field amplitude in a given region of interest close to the antenna. The method can be applied to antenna arrays of arbitrary geometry and requires a low CPU time. |
| [C8]. | M. Comisso,
“Considerations on the Use of Lacunarity for Comparing the Resonant Behavior of Different Convoluted Wire Antennas”,
in IEEE Antennas and Propagation Society (AP-S) International Symposium, Charleston,
South Carolina (USA), pp.
1 - 4, 1-5 Jun. 2009. Abstract—This paper investigates the possibility of using lacunarity to compare the resonant behavior of different convoluted (prefractal and non-prefractal) wire dipoles. More precisely, the purpose is to verify whether, given two convoluted wire dipoles having the same height and the same total length, the average lacunarity provides sufficient information to infer which dipole exhibits the lower resonances. |
| [C9]. | F.
Babich, M. Comisso, A. Dorni, F. Barisi, and A. Manià, “The Simulation of
Smart Antennas in Network Simulator-2 Using MATLAB”, in IEEE
International Workshop on Computer Aided Modeling and Design of
Communication Links and Networks (CAMAD), Pisa, Italy, pp.
1 - 5, 12 Jun. 2009
(Best Paper Award). Abstract—This paper presents an extension for network simulator-2 (ns-2) that enables the simulation of adaptive antennas in realistic channel conditions using MATLAB. A hybrid discrete-event discrete-time approach is adopted to exploit the scalability properties of ns-2 for the network simulation, and the modeling capabilities of MATLAB for the physical layer implementation. The developed package takes into account the physical antenna system and the signal processing algorithm to model in detail the antenna radiation pattern generated by each network node. The wireless propagation model of ns-2, which typically accounts only for path-loss attenuation and shadowing, is modified to include the Power Azimuth Spectrum (PAS), thus improving the accuracy of the estimated Signal to Interference plus Noise Ratio (SINR) at each node in presence of multipath. The proposed numerical model, which can be interfaced with any wireless network supported by ns-2, is used to evaluate the throughput of a Wireless Mesh Network (WMN). |
| [C10]. | F. Babich, M. Comisso, M. D'Orlando, and A. Dorni,
“Quality of Service in 802.11 Networks: Modeling and Experimental Evaluation”,
in IEEE International Conference on Communications (ICC), Dresden,
Germany, pp.
1 - 5, 14-18 Jun. 2009. Abstract—This paper proposes a mathematical framework for evaluating, in saturated and non-saturated traffic conditions, the performance of an 802.11 wireless network in which the nodes are equipped with adaptive antenna systems. The analysis, validated by simulations, adopts detailed models for the antenna behavior and the propagation environment, taking into account multipath and interference. The developed model is used to investigate the proper parameter settings that lead to throughput maximization, providing a simplified method to obtain the optimum contention window when adaptive arrays are employed. |
| [C11]. | M.
Comisso and R. Vescovo, “Fast 3D Power Synthesis for Antenna Arrays with
Dynamic Range Ratio Reduction”,
in IEEE International Conference on Electromagnetics in Advanced
Applications (ICEAA), Turin, Italy, pp.
218 - 221, 14-18 Sep. 2009. Abstract—This paper proposes a fast method of 3D power synthesis for antenna arrays of arbitrary geometry, which also allows to reduce the Dynamic Range Ratio (DRR) of the array excitations. The method adopts an auxiliary phase pattern in order to reduce the power synthesis problem to a field synthesis one. A cost function involving the desired far-field pattern and the amplitudes of the array excitations is iteratively minimized by modifying the auxiliary phase pattern and the array excitations. Numerical results show that the method, which requires a low CPU time, allows to satisfy stringent pattern requirements, while enabling the control of the DRR by a proper selection of the weights inserted in the cost function. |
| [C12]. | F.
Babich and M. Comisso, “Analysis of Asynchronous Multi-Packet Reception in
802.11 Distributed Wireless Networks",
in IEEE Global Telecommunications Conference (GLOBECOM), Honolulu,
Hawaii (USA), pp.
1 - 6, 30 Nov.-4 Dec. 2009.
Abstract—This paper proposes a mathematical framework for evaluating the throughput of an 802.11 Distributed Wireless Network (DWN) when the system allows Multi-Packet Reception (MPR) in asynchronous operating mode. Differently from previous studies on MPR, which assume a certain synchronization between the different sources at the beginning of the respective transmissions, this work analyzes a fully distributed scenario, where each node can access to the medium in a completely asynchronous way. More precisely, a new transmission may begin in an already busy channel, as long as the current channel load is within a given threshold. The presented model, which includes the synchronous scenario as a particular case, is employed to investigate the influence of the number of allowed communications, of the load threshold, and of the minimum contention window on the network performance. |
| [C13]. | F.
Babich, M. Comisso, A. Dorni, and M. Driusso, “Open Source Simulation of
Smart Antenna Systems in Network Simulator-2 Using Octave”, in IEEE
International Symposium on Wireless Pervasive Computing (ISWPC), Modena,
Italy, pp.
51 - 56, 5-7 May 2010. Abstract—This paper presents a simulation platform that exploits the scalability properties of network simulator-2 (ns-2) for the discrete-event simulation of a telecommunication network, and adopts the open source tool Octave for the discrete-time implementation of adaptive antenna arrays. The physical antenna system, the beamforming algorithm, and the multipath statistic are modeled in detail to accurately estimate the Signal to Interference Ratio (SIR) at each receiving node. This study describes the methods that can be used to interface Octave with ns-2 and compares the developed solution to an existing one, based on the proprietary tool MATLAB, discussing the advantages and disadvantages that characterize the two platforms. |
| [C14]. | F.
Babich, M. Comisso, and A. Dorni, “A Practical Method for Verifying the
Uniformity of the Backoff Distribution in 802.11 Network Cards”, in IEEE International Conference on Communications (ICC), Cape
Town, South Africa, pp.
1 - 5, 23-27 May 2010. Abstract—Recent studies have revealed that many vendors implement nonuniform backoff distributions in their commercial 802.11 Network Interface Cards (NICs) in order to obtain a better performance in particular scenarios. Therefore, in many cases, the backoff behavior of the cards can be not adherent to the 802.11 standard specifications. By consequence, the theoretical and the experimental performance of an 802.11 distributed network, including throughput and packet delay, may not coincide because the real backoff behavior of the adopted cards is different from the expected one. This paper presents a practical method for verifying if the backoff generated by a given 802.11 NIC is uniformly distributed, as dictated by the 802.11 standard, or not. The proposed method is based on the comparison between the theoretical and the experimental statistics of the time between two successfully transmitted packets. Thus it does not require intrusive measurements inside the chipset and can be performed using a simple open source software platform. |
| [C15]. | A. Dorni, F. Babich, and M. Comisso,
“Numerical Implementation of Multi-Packet Reception for the IEEE
802.11 MAC/PHY Layers”, in EuroNF Workshop on Wireless and Mobility
in the Network of the Future, Como (Italy), 21-22 Jun. 2010.
Abstract—This paper presents a PHYsical (PHY) and Medium Access Control (MAC) layer design that enables Multi-Packet Reception (MPR) in an 802.11 network. The 802.11 stations are equipped with smart antenna systems and adopt efficient coding techniques to support multi-hop communications in a multipath-fading affected channel. The introduced MAC layer modifications are minimal and provide asynchronous access to the medium as long as the number of ongoing communications lies within a given threshold. The numerical investigations are performed by using an ad-hoc developed hybrid discrete-time discrete-event simulation platform, which is based on the integration between network simulator-2 (ns-2) and MATLAB. |
| [C16]. | M.
Comisso and R. Vescovo, “Fast 3D Pattern Synthesis for Conformal Antenna
Arrays with Cross-Polarization Reduction”, in IEEE Antennas and Propagation Society (AP-S) International Symposium, Toronto,
Ontario (Canada), pp.
1 - 4, 11-17 Jul. 2010. Abstract—This paper presents a fast iterative method for 3D pattern synthesis of conformal arrays that is able to generate a desired co-polar pattern simultaneously reducing the cross-polar one. |
| [C17]. | F. Babich, M. Comisso, and A. Dorni, “A PHY Design for Asynchronous Multi-Packet Reception in 802.11 Heterogeneous Networks”, in IEEE
Vehicular Technology Conference (VTC), Budapest, Hungary, pp.
1 - 5, 15-18 May
2011. Abstract—This paper presents a PHYsical (PHY) layer design that enables Multi-Packet Reception (MPR) in an 802.11 network using advanced antenna systems without modifying the 802.11 MAC layer. The proposed scheme is designed for an asynchronous scenario, in which a node can access to the medium as long as the number of ongoing communications lies within a given threshold, and considering an heterogeneous network, in which the antenna system can be different for each node. The proposed PHY approach guarantees the coexistence of the legacy 802.11 stations, which use a single omnidirectional antenna, with the stations equipped with more advanced antenna systems. The developed solution is implemented in an hybrid discrete-time discrete-event simulation platform obtained integrating MATLAB and network simulator-2 (ns-2), in order to explore the system performance for different network topologies and in presence of multipath-fading. |
| [C18]. | M. Comisso and R. Vescovo, “Fast
Power Synthesis for Reconfigurable Arrays with Dynamic Range Ratio
Reduction”, in IEEE International Conference on Electromagnetics in
Advanced Applications (ICEAA), Turin, Italy, pp.
374 - 377, 12-17 Sep. 2011. Abstract—This paper presents a fast method of power synthesis for reconfigurable conformal antenna arrays that allows one to generate a set of desired radiation patterns, each transformable into any of the others by modifying only the phase of each array element, while reducing the Dynamic Range Ratio (DRR) of the excitation amplitudes of the array elements. The method adopts a set of auxiliary phase patterns to reformulate the original power synthesis problem as a field synthesis one. A functional involving the desired amplitude patterns and the array excitations is iteratively minimized by updating the phase patterns and the excitations. The results show that the method allows beam scanning operations involving also the suppression of multiple fixed interference regions, with acceptable CPU times. |
| [C19]. | G. Buttazzoni, M. Comisso, and R.
Vescovo, “Deterministic and Stochastic Methods for the Synthesis of
Large-Scale Antenna Arrays”, in IEEE International Conference on
Electromagnetics in Advanced Applications (ICEAA), Turin, pp.
378 - 381, Italy,
12-17 Sep. 2011
(Invited Paper). Abstract—Given a large antenna array of arbitrary geometry, the problem of synthesizing S desired patterns is considered, with two requirements: (a) each pattern can be transformed into any of the others by phase-only control, that is, the excitation amplitude applied to each array element holds constant during the reconfiguration process, although it can be different from the other excitation amplitudes; (b) the dynamic range ratio of the excitation amplitudes must be minimized, or reduced below a prescribed threshold. To this aim, we first propose the use of two deterministic methods: the first one minimizes a cost function, while the second one is based on an intersection approach and exploits the method of projections. A third approach is also considered, which minimizes a fitness function by a genetic algorithm. Numerical results of the three methods are mutually compared. |
| [C20]. | F. Babich, M. Comisso, and A. Dorni, “Multi-Packet Communication in 802.11 Networks: A MAC/PHY Backward Compatible Solution”, in IEEE Global Telecommunications Conference (GLOBECOM), Houston,
Texas (USA), pp.
1 - 5, 5-9 Dec. 2011. Abstract—This paper presents a novel Medium Access Control (MAC) protocol for 802.11 networks in which the nodes can adopt smart antenna systems. The presented protocol is designed to satisfy two fundamental requirements: the exploitation of adaptive arrays to increase the network throughput and the backward compatibility of the novel scheme with the 802.11 MAC layer. The developed solution allows the simultaneous coexistence of multiple communications, while maintaining, for the legacy nodes, the same throughput levels achievable in the 802.11 standard. The performance and the backward compatibility of the proposed MAC protocol are tested in multipath-fading environment and considering heterogeneous scenarios, including 802.11 legacy stations together with nodes implementing the novel scheme and equipped with different antenna systems. |
| [C21]. | F. Babich, M. Comisso, and A. Dorni, “A
Novel SIR-Based Access Scheme for Multi-Packet Communication in 802.11
Networks”, in IEEE International Conference on Communications (ICC), Ottawa,
Canada, 10-15 Jun. 2012. Abstract—This paper proposes a novel Medium Access Control (MAC) protocol for enabling multiple simultaneous communications in 802.11 networks where the nodes can use adaptive antenna arrays. The presented scheme is backward compatible with the 802.11 standard and is designed for heterogeneous scenarios, where legacy and non-legacy nodes equipped with different antenna systems can coexist. The access rules are based on a local but accurate Signal-to-Interference Ratio (SIR) estimation and on the adoption of Low Density Parity Check (LDPC) codes, which enable each node to reliably estimate the result of the transmission attempt of all active nodes. The proposed scheme is compared to a previously developed one in noisy and multipath-fading environments. |
| [D1]. | M. Comisso, R. Vescovo, “Un
Algoritmo Veloce per la Sintesi di Potenza di Schiere di Antenne di
Geometria Arbitraria”, in Riunione Nazionale di Elettromagnetismo (RiNEM),
Lecce (Italy), 15-19 Sep. 2008.
Abstract—This paper presents a simple and fast power synthesis algorithm for antenna arrays of arbitrary geometry. The proposed technique is based on the use of an auxiliary radiation pattern, reproducing the desired amplitude pattern and having a generic phase pattern. Adopting an iterative approach, the phase pattern is optimized in such a way as to minimize the distance between the auxiliary pattern and the array pattern approximating it in amplitude and phase. The distance is defined using a mean-square weighted norm in order to better satisfy the required specifications on the desired amplitude pattern, including multi-beam and wide null synthesis. The proposed algorithm requires a low CPU time and is compared with a modified version of the method of successive projections. |
| [D2]. | F. Babich, M. Comisso, A. Dorni, F.
Barisi, M. Driusso, and A. Manià, “Discrete-Time Simulation of Smart
Antenna Systems in Network Simulator-2 Using MATLAB and Octave”, in
Workshop Reti.it, Bormio (Italy), 13-15 Jan. 2010.
Abstract—This paper presents a platform that exploits the scalability properties of network simulator-2 (ns-2) for the discrete-event simulation of a telecommunication network, and compares the modeling capabilities of two development tools for the discrete-time implementation of adaptive antenna arrays at PHYsical (PHY) layer. The two tools are the proprietary software MATLAB and the open source one Octave, which are both used to implement the physical antenna system, the beamforming algorithm, and the multipath statistic. This enables to model in detail the antenna radiation pattern generated by each network node, thus improving the accuracy of the Signal to Interference Ratio (SIR) estimated at the receiver. This study describes the methods that can be adopted to interface MATLAB and Octave with ns-2, discussing the advantages and disadvantages that characterize the integration of the two tools with ns-2. The proposed numerical platforms, which can be interfaced with any wireless network supported by ns-2, are used to investigate the possibility to exploit smart antenna systems in a Wireless Mesh Network (WMN) with minimum modifications to the IEEE 802.11 access mechanism. |
| [D3]. | F. Babich, M. Comisso, A. Dorni, E.
Valentinuzzi, and A. Suriano, “Numerical and Experimental
Electromagnetic Characterization of Antenna Positioning in a Dual-Radio
Mesh Router”, in
Workshop Reti.it, Bormio (Italy), 13-15 Jan. 2010.
Abstract—This paper investigates the influence of the positions of the antennas on the performance of a dual-radio mesh router by performing a characterization of the router components from an electromagnetic point of view. Since the behavior of a wireless router equipped with multiple receiving devices and multiple antennas can be severely affected by problems of mutual coupling among several close conducting bodies, a study concerning the displacement of the antennas may help to reduce the possible performance degradations. To examine this issue, numerical and experimental tests are carried out for analyzing the electromagnetic behavior of the router in order to provide some suggestions for an accurate positioning of the antennas. In particular, a reference configuration is implemented in an electromagnetic CAD simulator and the obtained results are partly validated using an experimental setup reproducing the reference configuration. |
| [D4]. | A. Dorni, F. Babich, and M. Comisso,
“A MAC/PHY Simulation Platform for Multi-Packet Reception in 802.11
Networks”, in Riunione annuale GTTI, Brescia (Italy), 21-23
Jun. 2010.
Abstract—This paper presents an hybrid discrete-time discrete-event simulation platform, based on the integration between network simulator-2 (ns-2) and MATLAB, which implements a PHYsical (PHY) and Medium Access Control (MAC) layer design for enabling Multi-Packet Reception (MPR) in an 802.11 network using advanced antenna systems. In the proposed MPR scheme, which introduces minimal MAC layer modifications, a node asynchronously accesses to the medium as long as the number of ongoing communications lies within a given threshold. Heterogeneous scenarios are considered by taking into account distinct load thresholds for nodes equipped with different antenna systems. The simulated MAC/PHY design maintains backward compatibility with legacy 802.11 stations and is numerically tested in Wireless Mesh Networks (WMNs) in presence of multipath-fading and multihop communications. |
| [D5]. | M. Comisso, R. Vescovo, “Power
Synthesis with Reduction of Dynamic Range Ratio and Cross-Polarization
for Conformal Antenna Arrays”, in Riunione Nazionale di
Elettromagnetismo (RiNEM), Benevento (Italy), 6-10 Sept. 2010.
Abstract—This paper presents an algorithm for conformal antenna arrays that enables the synthesis of the co-polar array pattern, simultaneously reducing the amplitude of the cross-polar pattern and the dynamic range ratio (DRR) of the array excitations. The method, which is based on the minimization of a weighted cost function involving a power synthesis problem, requires low CPU times. Numerical results are provided to show the effectiveness of the proposed synthesis technique. |
| [D6]. | F. Babich, M. Comisso, and A. Dorni, “An
802.11-based MAC Protocol for Distributed Wireless Networks Using
Adaptive Antenna Arrays”, in
Workshop Reti.it, Cavalese (Italy), 12-14 Jan. 2011.
Abstract—This study presents a novel 802.11-based Medium Access Control (MAC) protocol for nodes that can adopt smart antenna systems. The presented scheme is designed to satisfy two main requirements: the exploitation of smart antenna systems to increase the network throughput and the backward compatibility with the 802.11 standard. The proposed protocol allows the simultaneous coexistence of multiple communications, while maintaining acceptable throughput levels for the 802.11 legacy nodes. The performance of the proposed MAC protocol is tested in multipath-fading environment, considering heterogeneous scenarios, including 802.11 legacy stations together with nodes implementing the novel scheme and equipped with different antenna systems. |
| [D7]. | F. Babich, M. Comisso, and A. Dorni, “A
Novel Access Scheme with Localization Capabilities for Multi-Packet
Communications in WiFi Networks”, in
Workshop Reti.it, Courmayeur (Italy), 11-13 Jan. 2012.
Abstract—This study presents a novel Medium Access Control (MAC) protocol for enabling multiple simultaneous communications in 802.11 networks in which the nodes can use smart antenna systems. The developed access scheme, which is backward compatible with the 802.11 standard, is designed for heterogeneous scenarios, where legacy and non-legacy nodes equipped with different antenna systems can coexist. The access rules are based on a local but accurate Signal-to-Interference Ratio (SIR) estimation and on the adoption of Low Density Parity Check (LDPC) codes, which enable each node to reliably estimate the result of the transmission attempt of all active nodes. The proposed scheme is compared to a previously developed one in noisy and multipath-fading environments. Furthermore, some issues concerning the problem of localization in 802.11 networks in presence of multi-antenna systems are discussed. |
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Last updated 03/06/2012