The NeXt Generation/Dynamic Spectrum Access/ Cognitive Radio Wireless Network 8/6/2014 LTEC 4550 Jose L Ortiz Jr Abstract The increased popularity in mobile devices has made the available spectrum used by those devices a precious commodity. In its current state, a large portion of the bandwidth goes unused while a smaller portion of the spectrum is nearing its capacity to provide service per the quality of service standard. This is largely due to the fact that the current model for assigning the available frequencies is by governmental agency static frequencies to use on a long term basis in specific geographical locations. The frequency is then only accessible by licensed used even when it is not being used making it inefficient. A proposed solution would be the use of NeXt Generation network, cognitive radio communications or dynamic spectrum access in order to make use of the unused frequencies. A proposed solution to the issue of the mismanagement of the allocated frequencies is the use of cognitive radio networks and dynamic spectrum access which are being coined NeXt Generation networks. This would allow owners of licensed frequencies to allow unlicensed users access to the unused spectrum for a fee. The problem exists on how to govern how companies charged for the use of its reserved bandwidth in a fair manner. Furthermore, how can companies that gain access to the licensed guarantee they will release access to the bandwidth when a licensed user requires access. This is a problem that can be solved by implementing new protocols but this poses a problem to the quality of service those using borrowed frequencies can provide. The last problem that would need to be addressed would what kind of hardware would be needed to allow devices to dynamically switch from not only an available frequency but an optimum frequency. It has been proposed that companies which have license to these regional area allow providers to lease or pay for use of the unused bandwidth. The question is what would be a fair way to allow providers to gain access and governing how much is charged to these companies which affect the end users. What has been proposed has been a system of where wireless regional area network providers, or WRANs, would bid on the available bandwidth in order to keep prices competitive and fair. This would specifically be used to useful in utilizing unused TV radio spectrum in order to provide access to the unused bandwidth to their users. The bidding process is recommended to be performed as a sealed double bid auction to be used by those TV providers with available bandwidth. It would require for the owners of the licensed spectrum to provide an amount it is willing to allow unlicensed access to. From there the WRANs would provide two figures to the licensed user, the amount of bandwidth desired and the amount they are willing to pay for access. This figure would be determined by the WRAN in which to allow them to provide their users a good balance between service provided and cost. The bandwidth owner then decides how to best accept bids based on the proper allotment of their available bandwidth at the highest selling price. This will give the owners incentive to allow unlicensed access as well as ensure that WRANs meet their service level agreement to their customers. This is detailed in the latest offering by the IEEE in the 802.22 for their working group on wireless regional area networks. The other issue with implementing a dynamic spectrum/cognitive radio or the coined NeXt Generation network, also known as xG network, is the protocols involved with the monitoring of stable and available frequencies. Another issue to address is the protocols involved with disengaging these networks when required by licensed users. The two main components of these types of protocols would be those that are that of allowing devices to have cognitive capability and re-configurability. Cognitive capability refers to the ability for a device to capture or sense radio signals from its environment. This is done not only by monitoring the power in some of the frequencies but by more sophisticated methods that capture temporal and spatial variations in the radio environment. When this capability is allowed then it allows for a device to avoid interference with other users and more specifically licensed users wishing to access the bandwidth. The ability to interpret these variations will allow for the detection of unused spectrum based on the specific time and location of the device. The other portion of these protocols requires a device to use the spectrum awareness to allow it to reconfigure itself dynamically based on this information to select the best spectrum available. The device should be configured to allow it to communicate in various frequencies not just one that belongs to the licensed user. This is really important when WRAN is in essential when sharing the spectrum with other licensed users that have first rights to the spectrum. The protocol has to have the ability to detect when a licensed user is trying to make use of the bandwidth they are currently using as well as keep track of other available frequencies to engage. There are three parts that are critical to these protocols that will facilitate communication from the users from the WRAN between their main network and the unlicensed networks. They are cognitive radio access, cognitive radio ad hoc access and primary network access. Having cognitive radio access is important because it allows the user to connect to a base station for not only their main base station but also those WRAN providers gained access to as unlicensed users. The cognitive network then encompasses not only the services provided by their main provided by their provider but also the network they are allowed access to as unlicensed users. The cognitive radio ad hoc access would allow end users to connect to each other via their main network or even through the unlicensed network. The protocol should be able to recognize which network the other device is currently connected to. Lastly, the device should still be able to first connect to their main network but also allow their medium access control, or MAC, to be adaptive and allow it to roam over different networks. The important part of all three functions to allow the cognitive radio to dynamically make use of the unused licensed spectrum so long as a licensed user is not making use of it. This makes the ability to acknowledge a frequency being used or even predicting when a frequency is about to be used that more important. What cognitive radio has to account for in order to offer the ability to dynamically switch from one frequency to another is recognizing the availability of white space. White space is also known as spectrum hole or the unused portion of the spectrum that can be utilized. What makes the concept of dynamic spectrum access or cognitive radio networking possible is the ability to recognize the unused spectrum and dynamically move from one unused frequency to another. It is in this function that the ability to monitor which frequencies are being used becomes that much more critical. This however cannot be accomplished without the proper hardware that would allow these protocols to perform the scans and frequency switches needed to maintain connectivity. In a generic hardware configuration, a receiver with dynamic spectrum access or cognitive radio network capabilities would need two main components to make it function properly. The first is a radio front end that would be able to receive a signal, amplify the signal, mix it and A/D convert the signal. The other portion would be a traditional baseband processing unit that is common to ones found in existing devices. Since the second portion is standard on devices, the focus for dynamic spectrum access/cognitive radio is on the front end receive as it will have specific components. They are as follows: radio frequency filter, low noise amplifier, mixer, voltage-controlled oscillator, phase lock loop, channel selection filter and automatic gain control. The radio frequency filter will allow the device to select a specific band via the bandpass filtering. The low noise amplifier will amplify the selected band and minimize the noise component at the same time. Once the band or frequency is been selected and amplified, the mixer will mix the signal with the local generated frequency which can then be interpreted by the baseband. Since different frequencies require different power levels, a voltage-controlled oscillator is needed in order to provide the needed for the internal signal to mix with the incoming signal before it is passed to the baseband. In order to maintain connectivity with the selected band, a phase lock loop is required which will also help the device produce precise frequencies in a fine resolution. The channel selector filter is used to select the desired channel to be used for communicating and filtering out adjacent channels to minimize interference. Although there are two types of channel selector filter available, this example refers to the super heterodyne receiver which uses the bandpass filtering which is also used by the radio frequency filter. The automatic gain control maintains the power level of the amplifiers constant over the large levels of available frequencies. This will adjust to match the power level required to match a given frequency. Even though the spectrum is currently being used in an inefficient manner, there have been several attempts to address the issue with dynamic spectrum and cognitive radio networks solutions. However, although there has been research done on these concepts more is required to truly make use of those idle frequencies in order to alleviate some of the strains data consumption is placing on those high traffic bandwidths. Many believe that cognitive radio networks or coined NeXt Generation Networks will provide “the ultimate spectrum-aware communication paradigm” if it is ever implemented. It remains to be seen if the recent advancements in technology will help make these concepts a reality. References Akyildiz, I., & Lee, W., & Vuran, M., & Mohanty, S. (2006). 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