The Best Questions About Mobile/Wireless Network Structures

a. Please use diagrams to illustrate the following WSN structures. Briefly describe

the major characteristics for each of them.

(i.) Star network

star topology

(ii.) Mesh Network

mesh topology

(b) In a larger size WSN, star-mesh hybrid network structure is often used. Please

justify why such a structure is beneficial.

The upsides of hybrid technology in WSNs are given beneath: –

Dependable communication as there is no failure due to a single point

Less power utilization when contrasted with mesh technology

Numerous substitute paths for nodes in this sort of situation.

This is a more versatile network

Problem 2. WSN Issue and Challenges

(a) Please describe the phenomenon of multi-path radio propagation in Wireless

networks and the cause of it.

A)    Multipath Radio Propagation in WSN

Multiple copies of a signal could make completely different phases. If phases add destructively, the amplitude relative to noise declines, creating detection tougher.

Multipath propagation will bring about to interference which will scale back the signal to noise ratio and scale back bit error rates for digital signals. One reason for a degradation of the signal quality is that the multipath attenuation already represented. But there are alternative ways in which within which multipath propagation will degrade the signal and have an effect on its integrity.

One of the ways} which is especially obvious once driving during an exceedingly in an automotive and paying attention to an FM radio. At certain points the signal can become distorted and seem to break up. This arises from the very fact that the signal is frequency modulated and at any given time, the frequency of the received signal provides the instant voltage for the audio output. If multipath propagation happens, then 2 or a lot of signals can seem at the receiver. One is that the direct or line of sight signal, and another could be a mirrored signal. As these can make completely different times thanks to the different path lengths, they’ll have completely different frequencies, caused by the very fact that the 2 signals are transmitted by the transmitter at slightly completely different times. Consequently once the 2 signals area unit received along, distortion will arise if they need similar signal strength levels.

Another type of multipath propagation interference that arises once digital transmissions area unit used is thought as put down image Interference, ISI. This arises once the delay caused by the extended path length of the mirrored signal. If the delay is critical proportion of an emblem, then the receiver could receive the direct signal that indicates one a part of the image or one state, and another signal that is indicating another logical state. If this happens, then the info are often corrupted.

In order to fulfill the necessities to transmit giant amounts of information over a radio channel, it’s necessary to decide on the foremost applicable type of signal bearer format. One type of signal lends itself to radio knowledge transmissions in the effects surroundings wherever reflections is also gift is Orthogonal Frequency Division Multiplex, OFDM. An OFDM signal contains an oversized variety of carriers, every of that are modulated with an occasional bit rate knowledge stream. During this method the 2 getting necessities for top rate transmission, to fulfill the capability necessities, and low bit rate to fulfill the inter-symbol interference necessities are often met.

Multipath propagation is a problem for any radio communications system. starting from the short vary wireless communications like Wi-Fi although the cellular and longer vary knowledge schemes like WiMAX although to VHF links wherever troposheric propagation could have an effect on the signal path, through to HF systems victimization the region for reflections. All told of those systems, the consequences of multipath propagation are often seen and seasoned. Any type of communications, so should be able to accommodate the consequences of the multipath propagation in a method or another.


(b) How does the multipath phenomenon affect the radio quality and the wireless

network capacity? Briefly explain your answer.

In radio detection and ranging process, multipath causes ghost targets to seem, deceiving the radar receiver. These ghosts are significantly pesky since they move and behave just like the traditional targets (which they echo), and then the receiver has problem in uninflected the proper target echo. These issues are often overcome by incorporating a ground map of the radar’s surroundings and eliminating all echoes that seem to originate below ground or on top of a definite height.


In digital radio communications (such as GSM) multipath will cause errors and have an effect on the standard of communications. The errors are attributable to inter-symbol interference (ISI). Equalizers are typically accustomed correct the isi. As an alternative, techniques like orthogonal frequency division modulation and rake receivers could also be used.


In a GPS receiver, Multipath result will cause a stationary receiver’s output to point as if it were at random jumping regarding or creeping. When the unit is moving the jumping or creeping is hidden, however it still degrades the displayed accuracy.

Problem 3. Mobile OS

a) Most of today’s Operating Systems, including many mobile platforms (e.g., iPhone OS and Android) use the Microkernel architecture. Please explain the benefit of using such an architecture for support a mobile platform.

A microkernel architecture could be compressed to a “very measured accumulation of utilization unbiased deliberations whereupon can be constructed vigorous, adaptable and dynamic applications” and brings the accompanying and non-select advantages to programming executions:

Measured quality



Better footprint impression administration

Less demanding improvement, unit testing, upkeep and movability

Service division has the focal point that if one Service (called a server) fizzles others can in any case work so unwavering quality is the essential feature.

The measured quality, adaptability and extensibility viewpoints are what I would consider the most critical ones of a microkernel-based execution. An exceedingly secluded architecture permits conventions to be divided from their executions and keeping up a level of freedom between the different modules and segments/ administrations (authorization of limits) of the framework. Adaptability awards you with element stacking and emptying of modules and extensibility gives the designers intends to augment the current framework with new convention or plans usage.

b) Multitasking has been a “standard” feature on computers such as servers, desktop, laptop, etc. However, earlier iPhone platforms, one of the most popular smart phone devices available on the market, lacked such feature. Please use examples to illustrate the challenges to support Multi-tasking in general, as well as specially on a mobile device.

Multitasking includes having the capacity to quickly switch between distinctive applications and to consolidate various wellsprings of data. Little mobile screens cutoff clients’ capacity to see content from diverse applications in the meantime, so present working framework support for multitasking concentrates basically on exchanging between distinctive applications. This builds clients’ memory load, so mobile originators must help clients analyze and quickly recover late things.

Some mobile designers have toyed with the thought of a split screen. Numerous Samsung gadgets have a multitasking mode that lets clients see two applications in the meantime. What’s more, in Windows 8 for tablets it is conceivable to show applications next to each other. Notwithstanding, I haven’t seen numerous Samsung or Windows 8 tablet clients exploiting this highlight in our client research, for a straightforward reason: it makes an officially little screen much littler and strengths clients to work in a significantly more minor window.

c) kexts or kernel extensions are widely used in Mac OS X. What is it used for? However, iPhone OS, a streamlined version of Mac OS X, doesn’t use it as often. Please explain why.

iOS, unfortunately, does not have kexts floating around the record system, but rather they are without a doubt present. The kernelcache can be unpacked to demonstrate the bit legitimate, alongside the kexts (all pressed in the __PRELINK_TEXT segment) and their plists (in the __PRELINK_INFO area).

The Cydia supplied kextstat does not deal with iOS. Unfortunately, the reason is that kextstat depends on kmod_get_info(…), which is a belittled (and as of late uprooted) API in late iOS and OS X adaptations. So, the kexts do exist. The option, jkextstat, does deal with late iOS adaptations. jkextstat can bring about some perplexity as it uses the executable name kextstat, like how calling g++ just dispatches gcc however with parameters to treat all .c documents as C++ records.

d) Abstraction Technique is widely applied to mobile OS design. Could you give two examples of abstraction used in the Android platform? Please justify your answer.

Platform Abstraction – Business Façade example, gives a brought together access crosswise over stages and digests the genuine stage executions into one, bound together API. The usage will contain stage particular code and even reference stage particular outside libraries

& Factory Abstraction that provides an interface for making families of connected or dependent objects while not specifying their concrete categories. A hierarchy that encapsulates: several potential platforms, and also the construction of a set of products.

Problem 4. Mobile Adaptation

A mobile platform may benefit from adaptive clocking control (i.e., adapting its execute speed based on the active computing load) because it helps save battery without penalize the performance. However, it is critical to have an accurate estimate of active computing load to benefit from such an approach.

(i)  Please suggest a method to estimate the computing load. (Hint: recall the process execution time estimate in “shortest job first” CPU scheduling scheme.

Web Farms are bunched frameworks intended to give high accessibility and superior web administrations. A web ranch is a gathering of recreated HTTP servers that answer web solicitations sent by a solitary purpose of access to the administration. To manage this undertaking the purpose of access executes a heap adjusting calculation to appropriate web demand among the gathering of servers. The present calculations gives a transient element design for this operation, yet some restorative activities (giving diverse session needs or circulated WAN forwarding) can’t be accomplished without a long haul estimation without bounds web load.

(ii) What’s the impact of an under-estimate of the active computing load?

The execution of direct ANC algorithm (FXLMS) corrupts because of the presence of nonlinearity sources. Thusly, NANC algorithm are required. Such calculations are used in adjusting nonlinear models, for example, truncated Volterra series, practical connection neural systems, bilinear channels, and the NARMAX model. The model request spoke to by the quantity of weights is a vital issue in equipment execution. It influences both the computational load and the memory prerequisites of the control calculation. Regularly, in polynomial models, for example, the Volterra, bilinear, and NARMAX models, the model request is situated to a vast quality bringing on over parameterization. Nonetheless, just a couple of parameters are prevailing to model the framework. In this manner, a few methods have been utilized to handle the over parameterization issue like akaike data basis (AIC) and bayesian data standard (BIC)


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