07-07-2012, 12:22 PM
Mobile wireless networks
[attachment=27086]
INTRODUCTION
Mobile wireless networks are receiving an increasing interest due to possibility of ubiquitous communications they offer. In particular, mobile ad hoc networks (MANETs) enable users to maintain connectivity to the fixed network or exchange information when no infrastructure, such as a base station or an access point, is available. This is achieved through multi hop communications, which allow a node to reach far away destinations by using intermediate nodes as relays.
The selection and maintenance of a multi hop path, however, is a fundamental problem in MANETs. Node mobility, signal interference and power outages make the network topology frequently change as a consequence, the links along a path may fail and an alternate path must be found. To avoid the degradation of the system performance, several solutions have been proposed in the literature, taking into account various metrics of interest. A method that has been advocated to improve routing efficiency is to select the most stable path so as to avoid packet losses and limit the latency and overhead due to path reconstruction.
In this work, we focus on the stability of a routing path, which is subject to link failures caused by node mobility. We define the path duration as the time interval from when the route is established until one of the links along the route becomes unavailable, while we say that a path is available at a given time instant t when all links along the path are active at time t. Then, our objective is to derive the probability of path duration till time t and the probability of path availability at time t.
Clearly, the probabilities of path duration and path availability strongly depend on the mobility pattern of the network nodes. Indeed, the path duration (availability) is determined by the duration (availability) of its links, which on its turn depends on the movement of a node with respect to the other. To characterize the nodes position with respect to each other, we need the spatial distribution of a single node over time. One would like to be able to evaluate these quantities in presence of various mobility models, however the analysis is extremely difficult even under simple mobility patterns Here we focus on bi-dimensional random mobility and we consider nodes moving according to the Random Direction (RD) mobility model.
The main contributions of our work are as follows.
We derive for the first time an expression for the transform of the distribution of a node moving according to the RD model. This expression can be numerically inverted to obtain the temporal evolution of the probability density function of the node position, given an assigned initial condition. Closed-form expressions for the temporal evolution of the distribution moments can also be derived directly from the transform.
We propose a simple, approximate expression for the probability of link availability under the RD model, which leverages the derivation of the second moment of the node spatial distribution. Our findings suggest that, as time proceeds, the probability of link availability under a generic mobility model can be obtained through a similar approximation. The same approach can be applied to the computation of the probability of path duration.
Based on our results on the probabilities of link availability and link duration, we study
the same metrics for multi hop paths, again in the case of RD mobility. We discuss the validity of the link independence assumption, which is widely used, and compare it against refined assumption that accounts for link correlation. We observe that the link
independence assumption provides sufficiently accurate results.
We show how our analysis can be exploited to improve the efficiency of traffic routing in
MANETs. In particular, we show how to select the optimal route in terms of path availability and how to determine the optimal number of hops between source and destination, taking into account the initial distance between the nodes. We then propose an approach to find and select routes, which accounts for the expected data transfer time over the path and allows to reduce the overhead of reactive routing protocols.
MOBILE COMPUTING
Mobile communication refers to the conversation established between two users at two different places with their handheld equipment. Mobile computing offers significant benefits for organizations that choose to integrate the technology into their fixed organizational information system. Mobile computing is made possible by portable computer hardware, software, and communications systems that interact with a non-mobile organizational information system while away from the normal, fixed workplace.
Mobile computing is a versatile and potentially strategic technology that improves information quality and accessibility, increases operational efficiency, and enhances management effectiveness. A detailed analysis, supported by selective presentation of published literature, is used to elucidate and support these asserted benefits of mobile computing. Additionally, a set of heuristics called the MOBILE framework is developed.
Mobile computing is a form of human–computer interaction by which a computer is expected to be transported during normal usage. Mobile computing has three aspects: mobile communication, mobile hardware, and mobile software. The first aspect addresses communication issues in ad-hoc and infrastructure networks as well as communication properties, protocols, data formats and concrete technologies. The second aspect is on the hardware, e.g., mobile devices or device components. The third aspect deals with the characteristics and requirements of mobile applications
The advantages of mobile computing are tremendous and manifold:
• Location Flexibility: We no longer need to stay plugged in to a specific location for performing computing activities. Mobile computing allows you unprecedented flexibility to move about and perform computing activities at the same time.
• Saves Time: Mobile computing technology is just the thing to use such transit time more effectively! Mobile computing also allows to instantly connect with your family anywhere and anytime.
• Enhanced Productivity: Increased work flexibility is directly proportionate to enhanced work productivity - the fact that you can do your work from any place you want, without waiting for, and making efforts to, get access to computing facility translates into people being able to do more work with greater flexibility. This is the reason why most companies these days offer home-computing access to employees.
• Ease of Research: Mobile computing and the flexibility offered by it enable students as well as professionals to conduct in-depth research on just about any topic or subject even when on the go.
• Entertainment: With rapid growth of internet facility, wireless networks play an important role. Static information can be downloaded through DVDs, CDs, whereas the up-to-date information of any appropriate location can be supplied by wireless networks.
AD-HOC NETWORKS
A MANET is a type of ad hoc network that can change locations and configure itself on the fly. Because MANETS are mobile, they use wireless connections to connect to various networks. This can be a standard Wi-Fi connection, or another medium, such as a cellular or satellite transmission.
On wireless computer networks, ad-hoc mode is a method for wireless devices to directly communicate with each other. Operating in ad-hoc mode allows all wireless devices within range of each other to discover and communicate in peer-to-peer fashion without involving central access points (including those built in to broadband wireless routers).
To set up an ad-hoc wireless network, each wireless adapter must be configured for ad-hoc mode versus the alternative infrastructure mode. In addition, all wireless adapters on the ad-hoc network must use the same SSID (service set identifier) and the same channel number. An SSID is the name of a wireless local area network (WLAN). All wireless devices on a WLAN must employ the same SSID in order to communicate with each other.
An ad-hoc network tends to feature a small group of devices all in very close proximity to each other. Performance suffers as the number of devices grows, and a large ad-hoc network quickly becomes difficult to manage. Ad-hoc networks cannot bridge to wired LANs or to the Internet without installing a special-purpose gateway.
Ad hoc networks make sense when needing to build a small, all-wireless LAN quickly and spend the minimum amount of money on equipment. Ad hoc networks also work well as a temporary fallback mechanism if normally-available infrastructure mode gear (access points or routers) stop functioning.
Wi-Fi wireless networking supports two basic forms - so-called "infrastructure" mode and "ad-hoc" mode . Ad-hoc mode allows a Wi-Fi network to function without a central wireless router or access point. In a few situations, ad-hoc mode networking is preferable to the alternative infrastructure mode, but ad-hoc networks suffer from several key limitations as described here.
Wi-Fi devices in ad hoc mode offer minimal security against unwanted incoming connections. For example, ad-hoc Wi-Fi devices cannot disable SSID broadcast like infrastructure mode devices can. Attackers generally will have little difficulty connecting to your ad-hoc device if they get within signal range.
Signal strength indications accessible when connected in infrastructure mode will be unavailable to you in ad-hoc mode. Therefore, you will face some difficulty whenever re-positioning an ad-hoc device to achieve a better signal.
The Wi-Fi networking standards require only that ad-hoc mode communication supports 11 mbps band width. We should expect that Wi-Fi devices supporting 54 Mbps or higher in infrastructure mode, will drop back to a maximum of 11 Mbps when changed to ad-hoc mode. Ad-hoc mode should generally be viewed as "slower" than infrastructure mode for this reason.
[attachment=27086]
INTRODUCTION
Mobile wireless networks are receiving an increasing interest due to possibility of ubiquitous communications they offer. In particular, mobile ad hoc networks (MANETs) enable users to maintain connectivity to the fixed network or exchange information when no infrastructure, such as a base station or an access point, is available. This is achieved through multi hop communications, which allow a node to reach far away destinations by using intermediate nodes as relays.
The selection and maintenance of a multi hop path, however, is a fundamental problem in MANETs. Node mobility, signal interference and power outages make the network topology frequently change as a consequence, the links along a path may fail and an alternate path must be found. To avoid the degradation of the system performance, several solutions have been proposed in the literature, taking into account various metrics of interest. A method that has been advocated to improve routing efficiency is to select the most stable path so as to avoid packet losses and limit the latency and overhead due to path reconstruction.
In this work, we focus on the stability of a routing path, which is subject to link failures caused by node mobility. We define the path duration as the time interval from when the route is established until one of the links along the route becomes unavailable, while we say that a path is available at a given time instant t when all links along the path are active at time t. Then, our objective is to derive the probability of path duration till time t and the probability of path availability at time t.
Clearly, the probabilities of path duration and path availability strongly depend on the mobility pattern of the network nodes. Indeed, the path duration (availability) is determined by the duration (availability) of its links, which on its turn depends on the movement of a node with respect to the other. To characterize the nodes position with respect to each other, we need the spatial distribution of a single node over time. One would like to be able to evaluate these quantities in presence of various mobility models, however the analysis is extremely difficult even under simple mobility patterns Here we focus on bi-dimensional random mobility and we consider nodes moving according to the Random Direction (RD) mobility model.
The main contributions of our work are as follows.
We derive for the first time an expression for the transform of the distribution of a node moving according to the RD model. This expression can be numerically inverted to obtain the temporal evolution of the probability density function of the node position, given an assigned initial condition. Closed-form expressions for the temporal evolution of the distribution moments can also be derived directly from the transform.
We propose a simple, approximate expression for the probability of link availability under the RD model, which leverages the derivation of the second moment of the node spatial distribution. Our findings suggest that, as time proceeds, the probability of link availability under a generic mobility model can be obtained through a similar approximation. The same approach can be applied to the computation of the probability of path duration.
Based on our results on the probabilities of link availability and link duration, we study
the same metrics for multi hop paths, again in the case of RD mobility. We discuss the validity of the link independence assumption, which is widely used, and compare it against refined assumption that accounts for link correlation. We observe that the link
independence assumption provides sufficiently accurate results.
We show how our analysis can be exploited to improve the efficiency of traffic routing in
MANETs. In particular, we show how to select the optimal route in terms of path availability and how to determine the optimal number of hops between source and destination, taking into account the initial distance between the nodes. We then propose an approach to find and select routes, which accounts for the expected data transfer time over the path and allows to reduce the overhead of reactive routing protocols.
MOBILE COMPUTING
Mobile communication refers to the conversation established between two users at two different places with their handheld equipment. Mobile computing offers significant benefits for organizations that choose to integrate the technology into their fixed organizational information system. Mobile computing is made possible by portable computer hardware, software, and communications systems that interact with a non-mobile organizational information system while away from the normal, fixed workplace.
Mobile computing is a versatile and potentially strategic technology that improves information quality and accessibility, increases operational efficiency, and enhances management effectiveness. A detailed analysis, supported by selective presentation of published literature, is used to elucidate and support these asserted benefits of mobile computing. Additionally, a set of heuristics called the MOBILE framework is developed.
Mobile computing is a form of human–computer interaction by which a computer is expected to be transported during normal usage. Mobile computing has three aspects: mobile communication, mobile hardware, and mobile software. The first aspect addresses communication issues in ad-hoc and infrastructure networks as well as communication properties, protocols, data formats and concrete technologies. The second aspect is on the hardware, e.g., mobile devices or device components. The third aspect deals with the characteristics and requirements of mobile applications
The advantages of mobile computing are tremendous and manifold:
• Location Flexibility: We no longer need to stay plugged in to a specific location for performing computing activities. Mobile computing allows you unprecedented flexibility to move about and perform computing activities at the same time.
• Saves Time: Mobile computing technology is just the thing to use such transit time more effectively! Mobile computing also allows to instantly connect with your family anywhere and anytime.
• Enhanced Productivity: Increased work flexibility is directly proportionate to enhanced work productivity - the fact that you can do your work from any place you want, without waiting for, and making efforts to, get access to computing facility translates into people being able to do more work with greater flexibility. This is the reason why most companies these days offer home-computing access to employees.
• Ease of Research: Mobile computing and the flexibility offered by it enable students as well as professionals to conduct in-depth research on just about any topic or subject even when on the go.
• Entertainment: With rapid growth of internet facility, wireless networks play an important role. Static information can be downloaded through DVDs, CDs, whereas the up-to-date information of any appropriate location can be supplied by wireless networks.
AD-HOC NETWORKS
A MANET is a type of ad hoc network that can change locations and configure itself on the fly. Because MANETS are mobile, they use wireless connections to connect to various networks. This can be a standard Wi-Fi connection, or another medium, such as a cellular or satellite transmission.
On wireless computer networks, ad-hoc mode is a method for wireless devices to directly communicate with each other. Operating in ad-hoc mode allows all wireless devices within range of each other to discover and communicate in peer-to-peer fashion without involving central access points (including those built in to broadband wireless routers).
To set up an ad-hoc wireless network, each wireless adapter must be configured for ad-hoc mode versus the alternative infrastructure mode. In addition, all wireless adapters on the ad-hoc network must use the same SSID (service set identifier) and the same channel number. An SSID is the name of a wireless local area network (WLAN). All wireless devices on a WLAN must employ the same SSID in order to communicate with each other.
An ad-hoc network tends to feature a small group of devices all in very close proximity to each other. Performance suffers as the number of devices grows, and a large ad-hoc network quickly becomes difficult to manage. Ad-hoc networks cannot bridge to wired LANs or to the Internet without installing a special-purpose gateway.
Ad hoc networks make sense when needing to build a small, all-wireless LAN quickly and spend the minimum amount of money on equipment. Ad hoc networks also work well as a temporary fallback mechanism if normally-available infrastructure mode gear (access points or routers) stop functioning.
Wi-Fi wireless networking supports two basic forms - so-called "infrastructure" mode and "ad-hoc" mode . Ad-hoc mode allows a Wi-Fi network to function without a central wireless router or access point. In a few situations, ad-hoc mode networking is preferable to the alternative infrastructure mode, but ad-hoc networks suffer from several key limitations as described here.
Wi-Fi devices in ad hoc mode offer minimal security against unwanted incoming connections. For example, ad-hoc Wi-Fi devices cannot disable SSID broadcast like infrastructure mode devices can. Attackers generally will have little difficulty connecting to your ad-hoc device if they get within signal range.
Signal strength indications accessible when connected in infrastructure mode will be unavailable to you in ad-hoc mode. Therefore, you will face some difficulty whenever re-positioning an ad-hoc device to achieve a better signal.
The Wi-Fi networking standards require only that ad-hoc mode communication supports 11 mbps band width. We should expect that Wi-Fi devices supporting 54 Mbps or higher in infrastructure mode, will drop back to a maximum of 11 Mbps when changed to ad-hoc mode. Ad-hoc mode should generally be viewed as "slower" than infrastructure mode for this reason.