2 1 Introduction
though this trend turns into a significant increase in component count and bill of
materials (BoM), the final product price can be kept or even reduced, partially thanks
to the huge number of terminals sold [Abid07, Gian09]. Indeed, the rate at which
new functionalities are introduced in a mobile terminal will soon exceed the rate of
miniaturization in packaging. Therefore, addressing this challenge implies redefining
the concept of wireless hand-held terminals, evolving from a pure hardware-based
to a combination of hardware- and software-based radio [Abid07, Rube07, Gian09,
Kits09, Ru09]. As first envisaged by Mitola [Mito95], an ideal software-defined-
radio (SDR) should be a universal radio platform which can be programmed to steer
any band, tune a channel of any bandwidth, and receive any modulation, all with
reasonable constraints, while ensuring the required quality of service as well as
guaranteeing privacy and security [Abid07].
In addition to allowing mobile terminals to easily accommodate emerging stan-
dards via either software or firmware upgrade [Ru09], the implementation of the SDR
concept will enable the so-called cognitive radio (CR) paradigm [Mito95, Cabr06,
Rube07]. Essentially, CR-based technology enableswireless networksand hand-held
terminals to use the RF spectrum in a dynamic manner—instead of a fixed manner as
it is used today. As a result, a more efficient use of the licensed/unlicensed spectrum
is achieved, with reduced interferences and/or at a lower power consumption. In-
deed, in the near future, SDR-based mobile terminals implementing CR technology
will be capable of dynamically sensing their spectral environment and of exploit-
ing the captured information to change their transmission/reception parameters in
order to improve the communication link and to reduce the energy consumed on
the fly [Rube07]. CR mobile phones must therefore be smart enough to incorpo-
rate cognitive (spectrum sensing) capabilities and flexible enough to be dynamically
programmed according to the information obtained from their interaction with the
environment [Cabr06]. This approach is completely different from the fixed spec-
trum assignment policy followed by today’s mobile telecom systems, in which a large
portion (around 85%) of the assigned radio spectrum is used sporadically while the
remaining bands are truly busy at any given time. It is important to mention here
that reducing power dissipation will also make the use of alternative energy sources
possible, thus making solar-cell powered cellphones a reality [Rube07]. By means
of embedding additional sensorial capabilities, mobile terminals could also act as
healthcare devices, making emergency calls in case they detect problems in the vital
signs of the user (patient). Moreover, mobile terminals including cognitive abilities
can be used in domotic applications, allowing users to remotely control their home
appliances, etc.
However, the current situation in most commercial smartcellphones is farfrom the
universal radio platform defined by the CR/SDR paradigm, where the digitization
is close to the antenna and most of the processing is performed by a high-speed
general-purpose digital signal processor (DSP). As an illustration, Fig. 1.1 shows the
block diagram of an ideal SDR transceiver—as it was originally conceived by Mitola
[Mito95]—in which the RF signal coming in from the antenna is directly digitized by
an analog-to-digital converter (ADC). Hence, many functions like frequency tuning
我的内容管理
展开
