Using Cognitive Radio as Solution for Brazilian
National Broadband Planning
Luciano Mendes, Ricardo Silva Jr, João Melo, Lucas Chaves, Marco Ferrero and Ricardo Dias
[email protected], { augustosilva, joaopedro, chaves, marco.ferrero, radias}@gee.inatel.br
Instituto Nacional de Telecomunicações - Inatel
Av. Joao de Camargo, 510 Santa Rita do Sapucaí, MG, Brazil - 37540-000
Abstract – Brazilian Digital Television system is on
transition from an analog service to a digital service.
Commercial DTV transmission has started on
December 2006 and the analog switch off (ASO) is
expected to December 2016. In this mean while, each
broadcaster in Brazil is allowed to occupy two UHF
channels: one for the analog signal and other one for
the digital signal. After the ASO, the analog channel
will be returned to government and new services are
expected to be offered. Also, Brazilian Government
has launched the Brazilian National Broadband
Planning, aiming to deploy broadband Internet
access for any Brazilian citizen. The challenges to
accomplish this objective are huge because of the
economic aspects, the continental size of Brazil, the
infrastructure available and the interest from both
telecommunications companies and broadcasters.
The aim of this paper is to present this complex
scenario and propose the use of the IEEE 802.22
standard as an economic and technical solution to
complete the National Broadband Planning in
Brazil.
Keywords - IEEE 802.22, Cognitive Radio, Spectrum
Sensing, Brazilian National Broadband Planning.
1. INTRODUCTION
Today, Brazil is living a digital transformation, where
traditional analog services are being switched to its
digital version. An important example was the television
system that has became digital in 2007. The advent on
an interactive digital television system, the price
reduction of computers and the continuous growth of
the computational capacities of mobile devices are
pushing the demand for broadband Internet access. In
response to this demand, the Brazilian Federal
Government has launched the Brazilian National
Broadband Planning (BNBP) [1], which aims to provide
broadband Internet access for the entire country at a low
cost until 2014. This goal is very audacious for a
colossal country like Brazil, which lacks of
telecommunications infrastructure in several regions,
such as North, Central-west and Northeast regions [2].
The use of fibber optics is a feasible solution to provide
the backbone infrastructure [3]. Cellular mobile
technologies, such as HSDPA [4], WiMAX [5] and LTE
[5] can be used with wired solution, like ADSL [6] and
DOCIS [7], to provide the last mile access in areas with
high population density. However, Brazil has huge areas
with very low population density, i.e. the Amazon
region, where the technologies mentioned above are not
economic feasible. The small area coverage (typical less
than 20km) and the use of licensed frequencies are some
of the key factors that restrict the use of conventional
technologies to attend low populated areas.
The use of cognitive radios and the opportunistic access
of the spectrum seem to be a solution to achieve the
objectives of the BNBP. The use of the vacant spectrum
as a secondary service, allied with a coverage area of
more than 50km makes the IEEE 802.22 standard [8] a
feasible economic solution to provide broadband
Internet access in these regions. Nevertheless, there are
huge challenges in deploying this technology. The first
challenge is the fact that this technology is very
immature and it has never been use in large scale
anywhere in the word. Also, the TV broadcasters that
are expanding the DTV coverage in whole country are
very suspicious about the capacity of the base stations
and the user's devices in sensing the presence of the TV
signal and change the channel in a short period of time.
The aim of this paper is to present a proposal to use the
cognitive radio technology of the IEEE 802.22 standard
as a solution to provide the broadband Internet access in
Brazil. A simulation tool to analyze the performance of
a spectrum sensing algorithm has been developed and
will also be presented. This simulation tool can be used
to test, evaluate and compare the efficiency of different
algorithms that may be implemented in this platform.
In order to achieve these objectives, this paper is
organized as follows: Section 2 brings the social,
geographic, technical and economical aspects in Brazil
today, Section 3 shows the Brazilian National
Broadband Planning (BNBP) objectives and Section 4
presents the IEEE 802.22 standard and how this
technology can be employed to accomplish the BNBP.
Finally, Section 6 draws the conclusion of this paper.
2. BRAZILIAN BACKGROUND
In order to understand the importance of the BNBP it is
necessary to know some aspects of the Brazilian society
today. The geography, cultural, technological and
economic aspects of the Brazilian society will be briefly
presented in the next subsections to allow the reader to
have a general idea about the impact BNBP in this
country and the challenges that must be overcame to
deploy this system.
a. Geographic aspects
Brazil is a continental size country. With 8.514.876,599
km2 [2], it is the fifth largest country in the word, after
Russia, Canada, China and USA. The 26 states and the
federal district that compose the Federative Republic of
Brazil are organized in five regions: North, Northeast,
Southeast, Central-west and South. Table 1 presents the
states that compose each region, the total area of each
region with its population density [2]. Figure 1
illustrates the regions in Brazil.
Table 1. Description of the regions in Brazil.
Population
Area
Region
States
Density
2
[km ]
[Inhab/km2]
Roraima, Acre,
Amazonas,
North
Rondônia, 3,853,575.624
4.12
Pará, Amapá
and Tocantins
Mato Grosso,
Moto Grosso
Centraldo Sul, Goiânia 1,606,366.787
8.75
west
and Federal
District.
Maranhão,
Piauí, Sergipe,
Ceará, Rio
Grande do
Northeast
1,554,387.725
34.15
Norte, Paraíba,
Alagoas,
Bahia, and
Pernambuco.
São Paulo, Rio
de Janeiro,
Southeast Minas Gerais 924,596.056
69.63
and Espírito
Santo.
Rio Grande do
South Sul, Paraná and 563,802.077
48.57
Santa Catarina.
It is easy to conclude from Figure 1 and Table 1 that the
population in Brazil is concentrate in South and
Southeast regions. North region, which corresponds to
the Amazon Rain Forest, is the largest one in Brazil
with the lowest population density.
Figure 1. Regions of Brazil.
São
Paulo,
that
has
the
most
effective
telecommunication infrastructure in Brazil, is 3,971 km
always from Manaus, the largest city in the North
region. Usually, satellite links are employed as backhaul
solution for Internet access in North region.
b. Penetration and influence of TV and Internet
services
Television sets are present in 96% of the Brazilian
houses [2]. Another important information is that only
17% of the population has pay TV (satellite or cable)
[9]. It means that people use their television set to watch
free broadcasting program. In fact, free television
broadcasting program are the main entertainment of a
large portion of the Brazilian population. The
broadcasting programs also works as social glue in the
Brazilian society because the same programs are
watched by people from different regions, different
economic power and different ethnic group.
Internet access in Brazil is also growing, but the
penetration of computer connected to the Internet is still
modest. Today, 26% of the houses have at least one
computer and 73.9 million people access Internet using
desktop, smartphones, notebooks or tablet [10].
Thus, it is clear that free broadcasting television
programs have a huge impact on the life of the Brazilian
people. Internet, however, has a much large potential to
affect the life of a person than television. In an
information era, as the one we live today, information
access and education to allow a person to process this
information are a key point to guarantee the
development of a country.
c. Economics, Technological and Political aspects
Brazil has adopted the ISDB-T (Integrated Services of
Digital Broadcasting – Terrestrial) [11]. The robustness
against multipath time-variant channels provided by the
orthogonal frequency division multiplexing (OFDM)
and the possibility to simultaneously broadcast High
Definition (HD) signals for fixed reception and Low
Definition (LD) signals for mobile reception due the
band-segmented transmission (BST) are the main
reasons for adoption of this DTV standard in Brazil. The
DTV standard in Brazil employs a local developed
middleware, called Ginga [12], that allow interactive
TV. Ginga allows the broadcaster to develop
applications that request an interaction with the viewer.
The data provided by the viewer are sent to the
broadcaster data center through the Internet, using an
interactive channel [13]. In mobile devices, the cellular
system is the obvious solution to obtain an interactive
channel, but cellular system can be also the only
solution for fixed interactive channels in many different
places in Brazil. These news services, besides the high
definition of audio and video delivered by DTV system,
are promising to make the free open air television in
Brazil be even more popular.
The ASO in Brazil is programmed to happen in 2016. In
this mean time, the broadcasters are allowed to occupy
two UHF channels: one for analog transmission and
another for digital transmission. After the ASO, the
analog channels will be returned for the Federal
Government that is planning to use this frequency bands
to provide personal communication, such as mobile
Internet access. Educational, health care and social
programs are also going to use the future available UHF
frequencies. The broadcaster, however, consider that the
UHF channels must be reserved for broadcasting
services and shall not be employed to provide
communication services. The main reasons pointed by
the broadcaster to keep the UHF channels reserved for
broadcasting services are: i) upgrade form 2k (HDTV 1920x1080 pixels) to 4k (Ultra HDTV - 3840×2160
pixels), ii) broadcasting of 3D signals and iii) transition
from the actual DTV standard to a future standard.
Since the penetration of open air free TV is extremely
high, the broadcaster’s lobbyists always efficiently
pressure the Federal Government.
During the adoption the ISDB-T standard, Brazil was
also migrating from the 2nd generation of cellular phone
system based on GSM (Global System for Mobile
communication) [14] to the 3rd generation based on
HSDPA (High Speed Downlink Packet Access) [15]
technology. The high data rates provided by the 3G
technology, the advent of low prices smartphones
subsidized by telecommunication operator and the
services compatible with mobile platforms (such as
Facebook, Google Picasa, Myspace, Tweeter, Orkut and
others) collaborated with the growth of mobile Internet
access in Brazil. The UHF channels that will be
available after the ASO are being considered as the
solution to provide high data rate Internet access for the
exponential growing number of mobile users.
Therefore, the interests on the UHF bandwidth that will
be available after the ASO are growing for both:
broadcaster and telecommunication operators. In this
scenario, a digital communication system that allows an
opportunistic use of the available spectrum can be a
solution to accommodate the interests of both sectors.
3. THE NATIONAL BROADBAND PLANNING
We are living an information era, where the Internet
access is a key factor to achieve personal and collective
success. The Brazilian Federal Government has
launched and public and private initiative that aims to
popularize the broadband Internet access in Brazil
before 2014, promoting the increasing of the
communication infrastructure and offering opportunities
for the population to join this digital world. This
initiative has been called the Brazilian National
Broadband Planning [1] and it aims to:
• Increase Internet penetration;
• Promote the electronic government (e-gov) services;
• Contribute with the Future Internet;
• Contribute with national development of new
industries, mainly focused in Information and
Communication Technologies (ICT) and;
• Stimulate the internal economy.
It is clear that the BNBP aims not only the economical
aspects of the ICT development. It also aims the social
development of the Brazilian society, which is aligned
with the WSIS (World Summit on the Information
Society) [16] that aims to interconnect every school,
hospital, health care centers, government agencies,
scientific and development research institutes, museums
and public libraries in the world, in order to guarantee
radio and television access for 100% of the worldwide
population and Internet access for 50% of the
worldwide population by 2015. The BNBP stimulates
the private sector to be the driver for this broadband
access expansion, but the Government can complement
the actions of the private sector, mainly to guarantee a
reduction of the social and regions inequalities. It is
important to notice that the Internet access is not
uniform in Brazil. In fact, it is possible to divide the
Internet access in three different scenarios: i) Large
Cities, where the infrastructure is appropriated; ii) Small
Cities, where the infrastructure is being provided by the
private sector, but with a large latency and; iii) Rural,
Remote and Boundaries Areas, where the Internet
access can only be provided through public services.
The BNBP has different tools to incentive the
broadband Internet access in each scenario.
The low Internet penetration in Brazil has two main
reasons. The first one is the monthly subscription cost
that can drive a significant percentage of the family
monthly income. This factor can be minimized by
development public policies that aim to reduce the cost
of the monthly fee for Internet access. The second factor
is the backhaul limitation that reduces the overall
bandwidth available for Internet access. This limitation
also implies in the cost of the service, since the demand
is very high, but the offer is restricted to the limited
capacity of the backhaul. This situation is critical for the
North region, but it is also a problem for communities
that are located a part of the large center in the others
regions in Brazil. The low diversity in the last mile
access technologies is one factor that reduces the
number of people with Internet access. ADSL,
DOCSYS and 3G cellular system covers the areas
where the population density is relatively high, but these
technologies don’t cover areas with small population
density. Thus, the development of new technological
solutions to allow the coverage of low density areas and
that increases the overall capacity of the backhaul in
Brazil is stimulated.
The BNBP has several goals and tasks that must be
accomplished by 2014. Table 2 presents a summary of
these goals.
Table 2. BNBP goals for 2014.
Service
Goal
Individual Fixed
a) 30 millions broadband connections.
Internet Access.
a) 100% of Federal, State and
Municipal Administration units;
b) 100% of public schools (more than
70,000 rural schools must be
connected);
c) 100% of heath care center and
hospitals (more than 177,000 units
Collective Fixed
must be connected);
Internet Access.
d) 100% of public libraries (more than
10,000 units to be connected);
e) 100% of public security centers
(more than 14,000 units to be
connected)
f) Implement more 100,000 new
public data centers.
a) Implement 60 millions mobile
Mobile access.
broadband connections.
The challenges to achieve the goals presented in Table 2
are huge, mainly for the North, Northeast and Centralwest regions. Some mechanisms have been created by
the Federal Government to minimize the barriers in this
process. One set of mechanisms is directed to stimulate
the private investments on the telecommunication
market, allowing the introduction of new players and
reducing the bureaucracy for financing the sector. This
set of mechanisms aims to encourage the competition in
the sector, which reduces the prices of the services and
increase the number of subscriptions. Other set of
mechanisms is directed to reduce the taxes on
telecommunication services and clarify the regulations
aspects to use the licensed bandwidths at 450MHz,
2.5GHz and 3.5GHz for telecommunications services.
The total amount of resources (public and private)
estimated to achieve the goals presented in the BNBP is
around US$ 28 billion. The government budget to be
applied in the BNBP is estimated to be US$ 3.2
billion/year. Thus, it is clear that the BNBP is a key
program for the Brazilian Government and it is the main
program that is stimulating the telecommunication
market in Brazil.
4. IEEE 802.22 STANDARD
The IEEE 802.22 WRAN (Wireless Regional Area
Network) [17] is the first wireless communication
standard based on the concept of cognitive radio. The
purpose of this standard is to provide broadband
connectivity to areas of low population density using the
open channels in the TV spectrum, a frequency range of
54MHz to 862MHz. This standard establishes a
coverage radius from 17km up to 50 km, depending on
the channels conditions, data rate, number of users and
parameters employed in the physical layer, such as
modulation, coding rate, time guard interval,
transmission power, sensibility of the receivers, etc. The
IEEE 802.22 WRAN topology has an architecture based
on cellular system, where the Base Station (BS)
connects the Consumer Premises Equipments (CPEs)
and manages the system. The BS uses the CPE to
perform measurements of signal levels at various
channels in the spectrum. These measurements are
collected and processed by the base station determines
all actions that shall be performed. The IEEE 802.22
can operate with LOS (Line of Sight) or NLOS (Non
Line of Sight). The minimum data rate of the system is
1.5 Mbit/s for the downstream link (BS to the CPE) and
384 kbit/s for the upstream link (CPE to BS). The BS
can support up to 255 CPEs. Figure 2 presents a
systemic architecture of an IEEE 802.22 WRAN.
Figure 2. Systemic architecture of an IEEE 802.22
WRAN.
The IEEE 802.22 WRAN nodes must use only the
vacant channels, also called white spaces. The primary
users, such as TV broadcasters, wireless microphones
and any other service that has the premise of the
spectrum utilization, shall not suffer any interference
from an IEEE 802.22 node. Thus, every IEEE 802.22
node senses the spectrum and reports to the BS about
the vacant and occupied channels at its specific position.
Beacons signals shall be used to inform the presence of
very low power users, such as wireless microphone
[17]. Each CPE shall have two antennas: an
omnidirectional antenna that is used to sense the
spectrum; and a directional antenna that is used for
communication with the BS. High gain directional
antennas with LOS link can be used to obtain a long
distance communication in this scenario. The
omnidirectional antennas shall be used outdoors for
accurate monitoring of the spectrum.
Figure 3 presents a simplified block diagram of the
physical layer of the IEEE 802.22 standard. The
physical layer of this standard is deeply based on the
physical layer of the IEEE 802.16 standard (Wi-MAX)
[5].
Figure 3. Simplified block diagram of the physical layer
of the IEEE 802.22 standard.
The data to be transmitted must be coded to protect it
from the errors introduced by the channel. Two
concatenates codes are employed: an outer Reed
Solomon RS (204,188,8) shortened code [18] and an
inner convolution punctured code [18]. Optionally, the
inner code can be a Turbo convolution code [19] or a
Low Density Parity Check code [20]. Interleavers are
also employed to increase the performance of the coding
scheme in frequency-selective time-variant channels.
The channel encoded bits are mapped into a Quadrature
Amplitude Modulation with M symbols (M-QAM) [21].
Orthogonal Frequency Division Multiplexing (OFDM)
[22] is used to transmit the mapped data with robustness
against multipath channels. Pilot subcarriers are
introduced in the OFDM symbol to allow the receiver to
synchronize with the transmitter. The pilot subcarriers
are also employed to estimate the channel frequency
response and also can be used by the cognitive engine of
the radio to estipulate the best configuration for a
particular channel condition. Table 3 summarizes the
different transmission modes possible in this standard.
The cognitive engine is responsible for sensing the
spectrum in order to define which channels are available
for communication and which channel are occupied by a
primary user. The cognitive engine also defines the best
operation mode for a specific channel condition.
Adaptive modulation techniques are employed to
guarantee that the parameters used in the
communication link can be changed without loss of
information.
Table 3. Transmission modes of the IEEE 802.22.
Physical
Layer
Mode
Modulation
1
BPSK
2
3
4
5
6
7
8
9
10
11
12
13
14
QPSK
QPSK
QPSK
QPSK
QPSK
16 – QAM
16 – QAM
16 – QAM
16 – QAM
16 – QAM
64 – QAM
64 – QAM
64 – QAM
Code
Rate
---1/2
1/2
2/3
3/4
5/6
1/2
2/3
3/4
5/6
1/2
2/3
3/4
5/6
Peak
Data Rate
(Mb/s)
Spectral
Efficiency BW
(6MHz)
4.54
0.76
1.51
4.54
6.05
6.81
7.56
9.08
12.10
13.61
15.13
13.61
18.15
20.42
22.69
0.25
0.76
1.01
1.13
1.26
1.51
2.02
2.27
2.52
2.27
3.03
3.40
3.78
The spectrum management provides information for the
cognitive engine about the current policies that must be
considered by the system, depending on its position.
This ensures that the cognitive radio does not operate
illegally from the standpoint of the political spectrum
[23].
The Cognitive Radio Medium Access Control (CRMAC) is responsible to manage the communication
link. The CR-MAC is responsible to change the
communication channel if a primary user is detected.
The transmission power control is also realized by the
CR-MAC, which must guarantee that the desired
covered area has reached without interfering in any
primary user or other IEEE 802.22 networks (selfexistence). The BS controls the channel access of all
CPEs connected to it. The CRMAC uses a synchronous
timing structure based on frames that are grouped into a
structure called a superframe. Figure 4 shows the frame
structure used in IEEE 802.22 WRAN standard.
Figure 4. Frame structure employed in the CR-MAC.
A superframe consists of 16 frames, each frame with a
fixed duration of 10ms. The structure of a superframe
starts with a superframe preamble followed by a frame
preamble and a superframe control header (SCH). It is
important to notice that each frame has a frame
preamble. The superframe is responsible for time
synchronization. The channel estimation is done once at
every frame. This procedure allows the receiver to
robustly decode the SCH and the messages in sequence.
Among the several important information carried by the
SCH, such as MAC address, flux control timing and
others, the silent period must be highlighted. The silence
period is the period of time that all nodes in the IEEE
802.22 must turn off the transmitter and sense the
channel, looking for a primary user. If a primary user is
detected, the BS is notified by the presence of this users
and it initiates the procedure to change the channel
frequency. The SCH is transmitted with a high degree of
robustness to allow an efficient decoding even at long
distances, which is important to ensure that neighbors
WRANs can sense the presence of a BS, avoiding
interference [24]. Discovering other WRAN networks
and coexistence is crucial; therefore it is important to
understand the coexistence beacon protocol (CBP).
Each frame is divided into subframes: downlink
subframes (DSF) and the uplink subframes (USF). A
coexistence window is added at the end of each
subframe. The USF specifies the coexistence
notifications (UCS – Urgent Coexistence Situation) and
the bandwidth requirements (BWR – Bandwidth
Requirements). The CPEs can use the UCS to notify the
BS that a primary user has been detected in the currently
used channel. presents the frames employed at the CRMAC layer of IEEE 802.22 standard.
Figure 5. Frame structure of the CR-MAC layer.
Spectral sensing is a fundamental function of a
cognitive radio system. The performance of the dynamic
allocation of radio spectrum depends on this function
[25]. Usually, spectrum sensing consists only in
measuring the RF power within a specific bandwidth,
but for a cognitive radio, spectrum sensing should be
provide more information about the signal that might
occupy this specific bandwidth. Also spectrum sensing
algorithms must be able to recognize the signal from the
primary system even under the worst conditions of
propagation, shadowing and fading, since one of the
main premises of the cognitive radio is that it cannot
interfere with the primary users. Thus, the faster the
sensing spectrum algorithms detect the primary users,
the smaller will be the interference caused by the
cognitive radio. These techniques should be able to
accurately identify the status of channel sensed,
identifying transmissions from the primary systems with
high probability. Furthermore, these algorithms should
also identify opportunities for transmissions with high
probability, i.e., maintaining a low probability of false
alarm, in which it classifies a channel as occupied when,
in fact, the channel is available. In order to maximize
the efficiency of the system, the spectrum sensing is
performed in two steps: coarse sensing and fine sensing.
Figure 6 illustrates this principle, where one can see that
the MAC layer will control the spectrum sensing in
order to maximize the probability of detection and
reducing the probability of false alarm.
Figure 6. Simplified block diagram of the sensing
technique: coarse sensing and fine sensing.
The coarse spectrum sensing detects if there are a signal
in the channel that is being used for communication.
This measurement is done in a short period of time and
it doesn’t distinguish the type of signal that is present in
the channel. The coarse spectrum sensing only points
the presence or absence of signals within the analyzed
spectrum.
The fine spectrum sensing is more complex than the
coarse spectrum sensing because this procedure aims to
characterize the signal that have been found by the
coarse spectrum sensing. The IEEE 802.22 standard
does not specifies a sensing technique. However, it is
necessary that the spectral sensing is in conformity with
the spectral sensing framework, which completely
specifies the inputs and outputs of the spectrum sensing
algorithm and its behavior. This framework specifies
that the CPEs must perform the spectrum sensing and
inform the BS about the presence of a signal. The BS
coordinates the coarse and fine sensing. Figure 7
presents the spectrum sensing framework, where it is
possible to verify the necessary input information and
the expected output information. The basic input
information is: channel number, bandwidth (6, 7 or 8
MHz), type of signal to be sensed (Analog TV, DTV,
microphone, etc.) and Pfa (false alarm Probability).
Figure 7. Spectrum sensing framework.
The output information is: sensing mode (coarse or
fine), signal type, signal presence decision and
confidence metric. Also, multiple sensing can be
performed simultaneously [24].
In order to understand the principles of the spectrum
sensing, a computational simulation has been developed
using Matlab/Simulink [26]. Therefore, one can analyze
each step of the spectrum sensing algorithm, aiming to
understand how this procedure can define if the channel
is occupied or vacant. The simulation has been
conceived to allow an opportunistic use of the spectrum,
so the UHF TV licensed bandwidth has been
considered. In this case, each licensed users randomly
transmit at one specific channel. The CR-MAC senses
the overall spectrum and determines which channel is
vacant. Then, cognitive radio occupies the available
spectrum. If a primary user start to transmit in the same
channel that has been occupied by the cognitive radio,
the IEEE 802.22 senses the presence of this user and
inform the BS, which is responsible to coordinate the
change to other vacant channel. The energy detection
algorithm has been used in this simulation, but any other
algorithm can be developed and applied in this tool.
Figure 8 presents the complete block diagram of the
spectrum sensing simulator.
Figure 8. Complete block diagram of the spectrum
sensing simulator.
Figure 9 presents the simulation results where the 60
MHz vacant channel has been opportunistically
occupied by the cognitive radio.
Figure 9. Simulation result where the 60MHz vacant
channel has been opportunistically occupied by the
cognitive radio.
Since in Brazil there is a great conflict of interests for
the use of the UHF bandwidth after the ASO, it is clear
that the IEEE 802.22 standard can be used to
accommodate both the broadcaster’s interests and the
telecommunication operator’s interests. This standard
can also solve the BNBP challenge to provide
broadband access for low populated area. Since it can
operate as a secondary service, there is no need for
licensing the bandwidth. This means that small Internet
Service Providers (ISP) can use this technology to offer
broadband Internet access at low cost. The large
coverage area of the IEEE 802.22 standard allows an
economical feasible Internet service even for rural areas.
Also, public sector can employ this technique as a cheap
solution to deliver Internet access in regions where the
private sector does not cover.
Since technologies such as ADSL, DOCSIS, 3G,
WiMAX and LTE are being used to provide the last
mile connection in areas relatively high populated, it
seems that Cognitive Radio technology based on an
efficient spectrum sensing algorithm and opportunistic
spectrum allocation is the right solution to provide
broadband Internet access for the population of low
density areas in a continental developing country, like
Brazil.
5. CONCLUSIONS
Brazil is a colossal developing country that is emerging
as one of the future economic power. The Federal
Government is concerned about the low penetration of
the Internet access and its impact in the economy,
education and social development of the population.
The analog switch off can be seem as the solution to
allocate UHF bandwidth to provide wireless broadband
Internet access in areas sparsely populated. However,
the Brazilian broadcasters, based on the huge
penetration of free open air TV, are requesting the UHF
channels that are being used today to broadcast analog
TV to allow the evolution of the DTV system. Future
services, such as Ultra HDTV and 3D-HDTV are being
pointed as the drivers to use the UHF that will be
vacant.
In this conflict scenario, the IEEE 802.22 standard can
be a solution to attend the interests of both sectors.
Since the spectrum sensing and opportunistic spectrum
allocation protects the primary users and allows
secondary users to use vacant channels, it can be used
by telecommunication operators to provide wireless
broadband Internet access, while the broadcaster can
count on the UHF spectrum when the times come to
implement a second generation of the DTV system.
Besides, the cognitive radio technology allows small
ISP to provide wireless Internet access for low
populated areas, once it is possible to obtain large
coverage areas. It means that the IEEE 802.22 also
attends the requirements stated by the BNBP that aims
to largely popularize the Internet access in Brazil by
2014, when the Soccer World Cup will be hosted by this
country.
REFERENCES
[1] Átila Augusto Souto, Daniel Calvalcanti and
Roberto Pinto Martins, Um Plano Nacional para a
Banda Larga. Brasília, Brasil: Ministério das
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