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). NeXt Generation/Dynamic
Spectrum Access/Cognitive Radio Wireless Networks: A Survey. Computer Networks
50. 2127-2159.
Akyildiz, I., & Lee, W., & Vuran, M., & Mohanty, S. (2008) A Survey on Spectrum
Management in Cognitive Radio Networks. IEEE Communications Magazine. 40-48.
Niyato, D. (2009). Dynamic Spectrum Access in IEEE 802.22 – Based Cognitive Wireless
Networks: A Game Theoretic Model for Competitive Spectrum Bidding and Pricing.
IEEE Wireless Communications. 16-23.