Optical Fiber and WLAN - Essay Example

? Wireless Networks Wireless Ethernet networks were accepted several years ago, as traditional connectivity solutions were replaced by robust wireless connectivity solutions. Although, several industrial protocols utilized standardized Ethernet physical layer that facilitated automation protocols to be transmitted via wireless media Commercial off the Shelf (COTS) (Brandt, Piggin 2006). For instance, Ethernet and Internet Protocol Technology, as the Common Industrial Protocol (CIP) has the provision of an autonomous media that will utilize TCP/IP on an application layer for message automation of the OSI model (Brandt, Piggin 2006). Previously, there were issues associated with control by using Ethernet. Currently, there are also some concerns associated with wireless Ethernet today, as traditional wireless applications tends to be information based. Although, in specific situations, control is possible by addressing: Slow updating process enables retries that may result in an iterative response on switches communicating within wireless access points that may recover from many error types. The design of the application safeguards link losses The transmission control protocol ensures data integrity Noise or interference immunity is added by modulation methods and techniques Secondary routes ensures high availability Quality of Service (QoS) enables traffic controlling An application can be divided in to three separate groupings i.e. System configuration, data monitoring and application process control. Likewise, system configuration includes a modification of some 100 milliseconds among data packets and it is not available to the user and numerous solutions are available. Secondly, for data monitoring, where alteration of a 100 millisecond delay is acceptable with advised caution, again numerous solutions are available. Likewise, in the process of input and output I/O utilization of a wireless control, there is a probability for variance of some 100 millisecond packets that is acceptable in general. The design and development of a Wireless network emphasize on geographical are coverage along with the provision of an access point, as demands for traffic and quality of services must be met. Likewise, to fulfill all the objectives, wireless network design must have a mechanism that will make the frequency spectrum narrow in an efficient manner (Al-Hunaity 2011). However, working on an efficient frequency use, one point must be addressed i.e. GSM mobile and wireless network users will use the same medium i.e. air and that may result in in an interference or obstruction of frequencies, if design is not adequate (Al-Hunaity 2011). Wireless LAN utilizes radio frequencies or electromagnetic waves for carrying signals to the source or destination similar to Amplitude Modulation AM, frequency modulation FM or Frequency Division Multiple Access FDMA. FDMA allocates the available frequency range in to small ranges that are also called sub-frequencies. After dividing the sub frequencies, each sub frequency is utilized as a stand-alone frequency and is called as a channel. The Federal Communications Commission (FCC) has defined Wireless LAN standards by IEEE 802.11. The IEEE 802.11 standard is defined by the Institute of Electrical and Electronics Engineers Incorporated. Likewise, overviews of wireless LAN standards are demonstrated below (Al-Hunaity 2011): IEEE 802.11 (legacy mode) standard was defined in 1997, as it talks about two bandwidth rates i.e. 1 Megabits per second (Mbps) and 2 Megabits per second (Mbps) operational in a 2.4 GHz frequency hopping spread spectrum (FHSS) and in the direct sequence spread spectrum (DSSS). IEEE 802.11a is operational on a 5 GHz unlicensed spectrum and utilize frequency band Orthogonal Frequency Division Multiplexing (OFDM) that offers a maximum data transfer rates of 54 Mbps. Moreover, it also offers 12 channels that are non-interference along with 4 outdoor channels and 8 indoor channels. IEEE 802.11b standard is operational on a 2.4 GHz unlicensed frequency spectrum that offers a maximum data rate of 11 Mbps. Likewise, this standard divides the band further to 11 separate channels, as 11 channels are available in north America and 13 channels are in Europe. IEEE 802.11g standard is also operational on a 2.4 GHz unlicensed frequency spectrum that uses frequency band Orthogonal Frequency Division Multiplexing and offers a maximum data rate of Mbps. The other that is related to wireless LAN is a FSO (Free Space Optics) network. The hardware selection for FSO network is “MRV TS800 /155” transceiver for supporting medium range connections. The “MRV TS800 / 155” supports data rates up to 1 to 155 Mbps and can connect with the other transceiver up to around 600 meters (, MRV Laser Links - Free Space Optic laser links up to 10Gbps - FSO Point to Point laser Links MRV TereScope ). However, the most significant aspect for deploying FSO is the direction and height of FSO transceivers. Moreover, the transceivers must be installed adjacent to the other transceiver and in the line of sight for establishing connectivity. Cost for each transceiver varies by vendor name and model and is below 5000 $ for each transceiver. Fig 1.2 shows the placement and direction of FSO transceivers sending and receiving data on a 60 to 100 GHz frequency range. The radio frequency solution is quite achievable. As the organizations require wireless connectivity ‘access points’ are of major concern. ‘Access points’ can be deployed to connect devices equipped with wireless technology. ‘Access points’ transmits and receive radio signals adjacent to a network hub over a limited distance. However, distance varies from different model types and the technology adopted. An IEEE 802.11n wireless network standard is recommended for connecting all the city government offices. 802.11n supports transmission speeds up to 150 Mbps and beyond. 802.11n works on 2.4 GHz and 5 GHz frequency bands (802.11n definition from PC magazine encyclopedia). Cisco is recommended for the Wi-Fi solution. Three major devices that are associated for implementing the wireless fidelity solution are: Cisco 4400 wireless LAN controller Cisco Aironet 1500 Series Access points Cisco 3300 Series Mobility Services Engine Radio over Fiber Networks NGA abbreviated as next generation access network technology is been motivated by Nielsen’s Law concluding the usage of Internet access bandwidth increasing almost double for every 21 months. Moreover, bandwidth access for end users may reach 1 GB per day by 2015 and 10 GB per day by the end of 2020 (Parker, Walker et al. 2010). Likewise, research and studies associated with NGA incorporates convergence with different technologies and the wireless convergence is addressed by Radio over Fiber (Parker, Walker et al. 2010). A fiber radio network consists of two different domains, one is optical and the other one is wireless. The wavelength division multiplexing (WDM), in the optical domain is used to combine a number of wavelengths together in order to send them through a network known as fiber-optic network. Hence the growing use of available fiber bandwidth and maximizing total data throughput, a single CO supply each remote radio BS and has access to divide optical wavelength, therefore to accomplish the requirements of future bandwidth wireless. From CO to BS a separate optical wavelength is allocated in the downlink. However, it can be used in the uplink route as BS to CO. On the contrary, a channel offset method can be used or downlink and uplink channels can be interleaved because, by using the identical wavelength in both the directions is not necessary. The main aspect that determines the type of that optical network and the tools used in CO and BS is that whether the data designed for the BS is sent at the baseband or at intermediate-or radio-frequency(IF and RF). The WDM is engage in multiplexing numerous wavelengths and transfers them into a single fiber. However, recent technology allows only one to two hundred channels to be transported in a single fiber, attaining Tb/s whole capacity. If, in a fiber-radio network WDM is used then every BS is allocated a wavelength. A particular WDM network requires a wavelength and selective optical components that can add, subtract, or multiply channels. This mechanism is imperfect hence, unwanted optical signal generates as, it cannot remove undesired channels that lead to optical crosstalk. However, the closest wavelength channels can be rejected by the optical mechanism by 30dB or more. If the channels powers are unequal the left over signals will be present. Therefore, this kind of crosstalk is known as heterodyne or in homodyne. And in simple words it is called as inter-channel crosstalk or out –of band crosstalk. This kind of crosstalk is at a different wavelength hence, it does not damage the network performance. If the crosstalk signal is at the same wavelength as of desired signal than the additional damaging crosstalk occurs. As a result, so called phase-induced interferometry noise (PIIN) occurred that is referred as intra-channel or homodyne or in-band crosstalk. Furthermore, it cannot be filtered since it is at the same wavelength as desired signal. Hence, the attendance of this optical crosstalk in the fiber-radio networks of WDM performance of network will be affected. If the subcarrier multiplexing is used than the type of modulation design is important to determine the level of optical crosstalk. Through (DWDM) technique that is, dense wavelength division multiplexing technique, an enormous bandwidth of fiber would be preferred as a medium to support and provide all the requirements related to BS in an optical fiber network infrastructure. In recent times an easy method was projected to increase spectral competence by optical frequency interleaving. The method is to design an optical modulation that is either double side hand (DSB) or single side hand (SSB). Hence, this technique determines no signal splitting because it is based on reflective filter add drops that allows multiple channels to share the spectrum and low insertion losses. In telecommunication applications the use of highly birefringent Bragg gratings (Hi-Bi FGB) has shown us its benefits and growing concentration that lead us to a new level of radio over fiber networks. However, the two kinds of self-governing peaks of Hi-Bi gratings that is firmly spaced and containing each orthogonal polarization are not optimized for this application but the bandwidth, spacing and the major restrictions are mainly verified. Suppose a signal from RoF signal modulator and the data at the mm-wave frequency if passes through the Hi-Bi FBG we notice the output that is the carrier and the signal in two different polarization. The advantages of the ROF are: Short attenuation loss Huge bandwidth Resistance to radio frequency interference Effortless installation and maintenance Condensed power consumption Flexibility in operations. The distribution of high frequency microwave signals through electrical lines or in open space is difficult and expensive. The losses occur due to absorption and reflection increases in the open space. Impedance gets higher with the frequency in electrical lines. The optical fiber recommends huge bandwidth. It offers low attenuation and hence, includes three transmission windows namely 850nm, 1310nm and 1550nm wavelengths. The combined bandwidth of three windows for a single SMF optical fiber is more than 50THz. To release more and more bandwidth from an optical fiber advanced techniques should be used like, Optical Time Division Multiplexing (OTDM), Dense Wavelength Division Multiplex (DWDM), the Erbium Doped fiber Amplifier (EDFA) for 1550nm window. For microwave transmission, resistance to electromagnetic interference is an asset of an optical fiber communication because; signals are transmitted through fiber in the form of light. Even for short connections fiber cables are chosen at mm-waves due to the high resistance. The resistance is eavesdropping hence, it is one of the significant characteristics of optical fiber communication related to RFI immunity because, and it offers safety and privacy. Difficult and costly equipment are reserved in RoF systems at SC’s thereby making distant base stations simpler. In fact, the techniques used in RoF systems remove the desire of local oscillator and other equipment at the remote stations. In this situation an RF amplifier, a photo detector, and an antenna makes the RS equipment. At SC, modulation and switching tools are kept in several RS as a result; smaller and lighter RS successfully reduces the cost of installation and maintenance. Due to the huge number of site antennas simple installation, cost free and easy maintenance of RS is extremely significant for mm-wave systems. Condensed power utilization results in the simpler RS’s with reduced equipment. At the central SC, majority of complex and difficult equipment are used. The RoF distribution system does not provide any benefits in terms of flexibility in operations. If, depending upon microwave generation technique the Rof system can be made signal format transparent. Firstly, to create a transparent system, intensity modulation and direct detection (IMDD) technique must be used to activate as a linear system. Secondly, it is possible to allocate if the modulation, switching and other functions are executed at centralized SC. Band pass filters Bandpass filters currently gaining a lot of attention in academic as well as industrial domains associated with wireless networks. Subsequently, in the United States, FCC has approved the unlicensed use of UWB spectrum, research analyst are now focusing for the development of UWB bandpass filters (Zhu 2012). In a typical functionality of a UWB transmitter, the source data is modulated, multiplexed and encoded on the chip level. Likewise, the multiplexed pulse is generated by the UWB antenna after amplification and redesigning at the package level (Zhu 2012). Identical to narrowband transmission systems, there is a requirement of filter blocks that are used for eliminating or minimizing unnecessary signals and noise from the transmission systems of the UWB. Likewise, UWB transmission systems broadcasts signals to a massive frequency range that broadcasts the transmission in individual bands. Although for indoor UWB hand held based system, devices are operational with a bandwidth of 10 dB with a frequency of 3.1 to 10.6 GHz (Zhu 2012). Ultra-wideband (UWB) communications technology defines many benefits such as low power and high data transmission rates can be achieved in short distance such as Personal Area Network (PAN). Likewise, UWB is also suitable for long distance applications requiring long range such as radar devices (Alahyari, Shahrjerdi et al. 2011). For co-existence with current wireless networks with the UWB systems, acceptable bandwidth with the provision of efficient filers is vital. Likewise, design is not small of such filters, as there are methods that are adopted for this purpose. For instance, “Two types of suspended strip line ultra-wideband bandpass filters are described in Menzel et.al., (2005), one based on a standard lumped element (L-C) filter concept including transmission zeroes to improve the upper passband slope, and a second one consisting of the combination of a low-pass and a high-pass filter.” (Alahyari, Shahrjerdi et al. 2011). Moreover, another method is to “design utilized embedding individually designed highpass structures and lowpass filters (LPF) into each other, followed by an optimization for tuning in-band performance” (Alahyari, Shahrjerdi et al. 2011). PIN Photodiode The intrinsic type, p-type and n-type semiconductors includes in a pin photodiode. Firstly I indicate the intrinsic type that is the simplest type of semiconductors (Pin Photodiode on an Atomic Scale. 2002). It is made up of extremely purified elements includes in the group IV, for example silicon (SC) and germanium (GE). Such elements comprise four electrons in their outer most orbits allowing them to form a crystalline structure. Hence, to complete the outer most shell they obtained four electrons from neighboring atoms thus completing the outer orbit of eight electrons as the most stable shell (Pin Photodiode on an Atomic Scale. 2002). A stable shell means that there are no free electrons resulting in the zero conductivity at 0k. The free electrons as compared to the electrons present in orbit possess high level of energy. The energy level of orbital electrons is known as in valance band while the energy level of free electrons are considered as in conduction band moreover, the difference between these two energy is denoted by Eg,.The amplified thermal energy concludes the probability of granting maximum energy to some electrons that will leave the orbit and become carrier electrons. Likewise, these carrier electrons are demonstrated by circles in the conduction band (Pin Photodiode on an Atomic Scale. 2002). For every electron that turns out to be a carrier electron, it leaves a vacant space behind and is represented by open circles in the valence band. However, the Fermi level is still lingers between the valence and conduction levels. Moreover, the n-type layer is constructed by replacing few group IV atoms associated with intrinsic semiconductor that are donated by group V atoms. For instance, ‘Si’ is considered as an intrinsic semiconductor and ‘As’ is represented as a donor. Let’s assume that Si atom is taken over by the donor, resulting in total available valence electrons equal to 9. However, at lower temperatures, as utilize total 9 electrons for completion of the outermost shell. Likewise, the ninth electron is bonded with the ‘As’ atom nucleus coulomb. When the temperature rises, a minor energy is utilized for the 9th electron for becoming a carrier electron. However, the electron of ‘As’ atom requires less energy as compare to other electrons. Laser Diode VCSEL VCSELs are basically laser semiconductors or can be called as laser diodes containing a monolithic laser resonator. The laser resonator is the component where emitted light moves forward from the device in a perpendicular direction straight to the chip surface. Likewise, the resonator is recognized by Bragg mirrors called as reflected lasers i.e. dispersed Bragg (, Encyclopedia of Laser Physics and Technology - vertical cavity surface-emitting lasers, VCSEL, semiconductor laser). Moreover, there is also a component that is called an active region i.e. gain structure composed of many significant wells with a thickness comprises of 2 to 3 micrometers (, Encyclopedia of Laser Physics and Technology - vertical cavity surface-emitting lasers, VCSEL, semiconductor laser). In general, the active region is charged with milliwats ranging from few or more. Likewise, it generates output power ranging from 0.5 to 5mW or maybe higher for supporting other multi- mode devices (, Encyclopedia of Laser Physics and Technology - vertical cavity surface-emitting lasers, VCSEL, semiconductor laser). Likewise, the current is injected via a ring electrode that enables the extraction of the output beam. VCSELs are known to have a quality beam that can be used for small areas, as it is limited to power output. However, for larger areas, avoidance of higher-order transverse modes is not possible, as the value is very small represented in terms of small length of resonator with few microns, likewise, a consistent pushing a large active region consisting a ring electrode. Besides, the short resonator finds easier to accomplish a sole frequency operation by integrating with wavelength tenability. Furthermore, VECSELs can also be modified with high frequencies in order to make it operational for optical fiber communication. Moreover, for a low power high quality beam VCSELs, a critical factor is a deviation of a low beam, as compared to the laser diodes along with beam profile that is symmetric. As a result, it is parallel to the output beam with an ordinary lens not possessing characteristics of a high numeric aperture (, Encyclopedia of Laser Physics and Technology - vertical cavity surface-emitting lasers, VCSEL, semiconductor laser). Moreover, a significant practical advantage of VCSELs, when comparing with edge-emitting semiconductor lasers differentiates it as immediately after growth, VCSELs can be tested i.e. prior to the slash of the wafer. As a result, issues can be addressed at an early stage and can be rectified accordingly. Additionally, there is a possibility of integrating wafer of VCSEL with optical element’s array i.e. collimation lenses. Likewise, the wafer is than diced and can be mounted on optical elements one by one for every VCSEL. As a result, laser products are manufactured with minimum cost. Bibliography AL-HUNAITY, M., 2011. New Channel Assignment Method for Access Points in Wireless LANs. International Journal of Computer Science Issues (IJCSI), 8(6), pp. 213-218. ALAHYARI, A., SHAHRJERDI, M., HABIBZADEH, A. and DOUSTI, M., 2011. Designing Tunable Narrowband Bandpass Filter Utilizing Neural Network And Converting It To Wideband Filter. Journal of Applied Sciences Research, 7(8), pp. 1526-1533. BRANDT, D. and PIGGIN, R., 2006. The right time and place [wireless LAN]. Computing & Control Engineering, 17(4), pp. 40-45. , Encyclopedia of Laser Physics and Technology - vertical cavity surface-emitting lasers, VCSEL, semiconductor laser . Available: http://www.rp-photonics.com/vertical_cavity_surface_emitting_lasers.html [4/4/2012, 2012]. , MRV Laser Links - Free Space Optic laser links up to 10Gbps - FSO Point to Point laser Links MRV TereScope . Available: http://www.digitalairwireless.com/mrv-terescope-fso.asp [4/4/2012, 2012]. PARKER, M.C., WALKER, S.D., LLORENTE, R., MORANT, M., BELTRAN, M., MOLLERS, I., JAGER, D., VAZQUEZ, C., MONTERO, D., LIBRAN, I., MIKROULIS, S., KARABETSOS, S. and BOGRIS, A., 2010. Radio-over-fibre technologies arising from the Building the future Optical Network in Europe (BONE) project. IET Optoelectronics, 4(6), pp. 247-259. Pin Photodiode on an Atomic Scale. 2002. Elements of Photonics, Volume II, 2, pp. 1151-1159. ZHU, S., LI, 2012. UWB Bandpass Filters. Microwave Bandpass Filters for Wideband Communications. http://eu.wiley.com/WileyCDA/WileyTitle/productCd-0470876611.html edn. Read More