Reconfigurable Baseband Processing for Wireless Communications - Adaptive Signal Processing in Wireless Communications - page 462

15.3.2 Cognitive Radio
In November 2002, the Federal Communications Commission (FCC) in the United
States released a report [18] aimed at improving the management of spectrum resources
in the United States. The report concluded that the current spectrum scarcity problem
is largely due to the strict regulation on spectrum access. Spectrum measurements con-
ducted by the FCC indicated that only small portions of the spectrum are heavily used,
while other frequency bands are either partially used or unoccupied most of the time.
So, spectrum utilization can be improved by making it possible for an unlicensed user
(secondary user) to access the spectrum that is not occupied by the licensed user (pri-
mary user). The unlicensed user has the awareness of the spectrum and adapts its trans-
mission accordingly on a noninterference basis. This spectrum access and awareness
scheme is referred to as cognitive radio by the FCC.
The idea of cognitive radio was first presented by Joseph Mitola III in his paper [40],
where he proposed that cognitive radio can enhance the personal wireless service by a
radio knowledge representation language (RKRL). This language represents knowledge
of radio at all aspects, from transmission to application scenarios, in such a way that
automated reasoning about the needs of the user is supported. Cognitive radio thus is
able to autonomously observe and learn the radio environment, generate plans, and even
correct mistakes. A comprehensive conceptual architecture of cognitive radio was later
presented in [31], where cognitive radio was thought to be a final point of the software-
defined radio platform evolution: a fully reconfigurable radio that changes its communi-
cation functions depending on network and user demands. Recently, cognitive radio has
become a very hot topic due to its impact on future spectrum policy, which could fun-
damentally change the current status of radio communication. At the Berkeley Wireless
Research Center (BWRC), a dedicated Cognitive Radio Research (CRR) project is in
progress. Their motivation is to improve the spectrum utilization by opportunistic use
of the spectrum, which is the same as the FCC's initiative. Spectrum pooling is investi-
gated in [50]. The basic idea is that a secondary user can dynamically access the licensed
band by switching on and off OFDM subcarriers to avoid interference to the licensed user
(primary user). The cognitive radio project at Virginia Tech does not specifically aim to
improve spectrum utilization. This project is based on the observation that cognitive
radio distinguishes itself by awareness and learning. In [10], a genetic algorithm-based
cognitive engine is proposed to learn its environment and respond with an optimal
adaptation. The European Union 6th Framework End-to-End Reconfigurability (E2R)
project studies reconfigurability, software-defined radio, and cognitive radio. The key
objective of the E2R project is to devise, develop, and test the architectural design of
reconfigurable devices and supporting system functions for users, application and
service providers, operators, and regulators in the context of heterogeneous systems.
Although the project does not specifically address cognitive radio, dynamic spectrum
allocation and evolution from software-defined radio to cognitive radio have been envi-
sioned. In parallel with the ongoing research projects around the world, international
standardization organizations also have proposals to improve the spectrum utilization.
An example is IEEE 802.22, which is a new standard for a cognitive point-to-point (P2P)
air interface for spectrum sharing with television bands.