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Intelligent Radio: Cognitive Radio
Yang Zhang
Abstract: Cognitive radio (CR) is a new intelligent radio technology, which provides
users with high quality of service (QoS) through dynamic access spectrum and can
greatly improve the existing low efficiency of spectrum utilization. This paper mainly
summarizes the research status of CR, and introduces the key technologies in CR, such
as spectrum detection, spectrum management and power control. The application of CR
in ultra-wideband, mesh network and wireless area network is briefly summarized.
Key words: cognitive radio, spectrum management, power control
I. INTRODUCTION
At present, with the rapid growth of wireless communication service, available
spectrum resources become more and more scarce. Through the adoption of advanced
wireless communication theory and technology, such as link adaptive technology,
multi-antenna technology and other efforts to improve spectrum efficiency, but found
that the global authorized frequency band, especially the signal transmission
characteristics of good low frequency band spectrum utilization is very low. To improve
the spectrum efficiency, the researchers adopted advanced wireless communication
theories and technologies, such as link adaptation technology, multi-antenna technology,
etc., but found that the global licensed frequency bands, especially the low frequency
band spectrum with good signal propagation characteristics, are extremely efficient low.
In the United States, a large number of studies by the Federal Communications
Commission (FCC) indicate that spectrum utilization is extremely unbalanced. Some
unlicensed frequency bands are crowded and some licensed frequency bands are often
idle. Therefore, in recent years, the spectrum sharing technology which can realize the
reuse of non-renewable spectrum resources has been widely concerned. Cognitive radio
(CR), as a more intelligent spectrum sharing technology, can effectively use idle
spectrum. Theoretically, CR allows multi-dimensional spectrum multiplexing in time,
frequency and space, which will greatly reduce the constraints of spectrum and
bandwidth limitations on the development of wireless technology[1]
II. OVERVIEW OF THE CR KEY TECHNOLOGIES
A. SPECTRUM MANAGEMENT
Spectrum management can effectively improve spectrum utilization. The authors
of [2] proposed an opportunistic spectrum sharing protocol that exploits the situation
when the primary system is incapable of supporting its target transmission rate. They
studied the joint optimization of the set of subcarriers used for cooperation, subcarrier
pairing, and subcarrier power allocation such that the transmission rate of the secondary
system is maximized, while helping the primary system, as a higher priority, to achieve
its target rate. Simulation results demonstrated the performance of the proposed
spectrum sharing protocol as well as the win-win solution for the primary and secondary
systems.
The authors of [3] proposed an opportunistic spectrum sharing protocol where the
secondary system can access to the licensed spectrum of the primary system based on
full-duplex (FD) cooperative OFDM relaying. They studied the joint optimization of
subcarriers and power allocation in both two phases such that the transmission rate of
the secondary system is maximized while the primary system can achieve its target
transmission rate. Simulation results demonstrated the performance of the proposed
spectrum sharing protocol as well as its benefit to both primary and secondary system.
The authors of [4] proposed a different way to optimize the performance of
cooperative spectrum sensing by designing the relaying function. Simulation results
demonstrated that the proposed protocols achieve much better performance over the
existing protocols.
The authors of [5] sought for optimal resource allocation at the source and the
relay, including power allocation over different subcarriers at secondary source/relay
nodes and subcarrier pairing at the secondary relay station. They also proposed a
suboptimal low-complexity algorithm to trade performance for computational
complexity. The simulation results showed that the suboptimal scheme yields very close
performance to the joint optimization algorithm.
The authors of [6] proposde an opportunistic spectrum sharing protocol where the
secondary system can access to the licensed spectrum of the primary system based on
full-duplex (FD) cooperative OFDM relaying.
B. POWER CONTROL
Power control can effectively reduce signal interference in wireless
communication system.
The authors of [7] proposed the interference constraint which ensures that the
quality of service (QoS) standards for primary users is considered and a non-
cooperative game power control model. Simulation results verified the stability and
superiority of the novel algorithm in flat-fading channel environments.
The author of [8] put forward a new cost function power control game theory
algorithm under the restriction of interference temperature threshold. The power control
problem was transformed into an interference-limited multi-constrained nonlinear
programming problem and the distributed algorithm of the model was given.
In [9], Multi-users’ power allocation was studied based on the analysis of multiple
interference temperature limitation of the power model and multi-user access power
control. The power allocation issue was converted into a multiconstrained nonlinear
programming problem with the interference temperature limitation and then an
improved simulated annealing genetic algorithm was proposed to solve this problem.
Simulation results showed that the improved simulated annealing genetic algorithm has
better accuracy and convergence performance.
In [10], a joint optimization algorithm for cognitive radio (CR) network based on
centralized spectrum sharing is proposed. A more practical scenario where the primary
users (PU) transmit signals with multiple levels of power is studied in CR network. To
reduce the computational complexity, a low complexity suboptimal power allocation
algorithm is investigated. By solving the objective function, the optimal allocation of
bandwidth and power are achieved.
Based on a Space-Time Block Coding Multi-Carrier Code Division Multiple
Access (STBC MC-CDMA) system, a Asynchronous Distributed Pricing (ADP)
Algorithm was studied in [11], in which the cognitive radio(CR) users announces a
price that reflect other users’ compensation paid.
An algorithm of power control in two-tier heterogeneous networks is proposed in
[12]. The authors consider femtocell base stations (FBSs) dense deployment in the
macrocell base station (MBS) coverage, the MBS dynamically estimates total uplink
interference of femtocell user equipments (FUEs). In order to cope with interference
issues, the MBS decides the transmit power of macrocell user equipment (MUE)
according to the uplink power budget.
C. OTHER TECHNOLOGIES
In [13], the authors used the multi-carrier code division multiple access (MC-
CDMA) network as the cognitive radio platform, based on shannon information theory
and the non-cooperative game model, designed a new utility function, and the nash
equilibrium of the new utility function was proved. In [14], k-channel connectivity was
defined to derive a CR network that remains connected whenever any k −1 channels are
occupied concurrently. The authors proposed both centralized and distributed topology
control algorithms to ensure both the k-channel-connected and conflict-free properties.
In [15], an optimization algorithm that joints bandwidth and power allocation of
hybrid spectrum sharing is proposed in CR. According to the location variation of
cognitive user (CU) that adopt the random waypoint based mobility models, the state
of CU can switch between Underlay spectrum sharing model and Overlay spectrum one.
In [16], the price-based power allocation for femtocells underlaying a macrocell
heterogeneous cellular network is investigated. By exploiting interference pricing
mechanism, we formulate the interference management problem as a Stackelberg game
and make a joint utility optimization of macrocells and femtocells. Specially, the energy
consumption of macrocell users and the transmission rate utility of femtocell users are
considered in this utility optimization problem.
III. TYPICAL APPLICATION OF CR
The introduction of CR technology into the research and design of UWB system
can improve the spectrum sharing, effectively suppress the narrowband interference,
coexist with other systems better, and potentially improve the spectrum utilization, data
transmission rate and performance of the whole UWB system.
The combination of CR technology and wireless Mesh networks can be used for
wireless broadband access in densely populated cities because of its ability to improve
spectrum utilization. When the backbone of a wireless Mesh network is composed of
cognitive access points and fixed relay points, the coverage of a wireless Mesh network
can be greatly increased.
IEEE 802.22 is the first world standard based on CR technology, and IEEE802.22
working group has established CR technology as the core technology of wireless area
network (WRAN). The IEEE 802.22 working group has authorized the development of
a co-operating point-to-multipoint air interface standard for the spectrum on which
existing broadcast television is located for the CR based WRAN.
IV. CONCLUSION
CR technology is the "Next Big Thing" of wireless communication technology
after software defined radio (SDR), which attracts great attention from relevant
researchers. This paper mainly summarizes the current research status of CR key
technology, and briefly introduces the typical application of CR technology.
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