Digital Signal Processing Reference
In-Depth Information
Ta b l e 1 . 1
SDR Forum's
5-tier concept [7]
Tier
Name
0
Hardware Radio
1
Software Controlled Radio
2
Software Defined Radio
3
Ideal Software Radio
4
Ultimate Software Radio
1.2.2 The Software-Defined Radio Solution
As mentioned above, only flexible radios enable the AAA paradigm, as their flexi-
bility allows them to operate in any environment and under any user request. This
observation gave birth to the concept of Software Radio (SR), an extremely flexible
radio. Today, the SR-concept is well established, but the ultimate SR (uSR) is still
not in reach. According to the SDRForum such an uSR accepts fully programmable
traffic and control information, supports operation over a broad range of frequen-
cies and can switch from one air-interface to another in milliseconds [6]. Though
the uSR might not yet be in reach, the research community has already made signif-
icant advances to increase the hardware flexibility.
In Table
1.1
, the initial 5-tier concept of the SDRForum is presented [7]. The
early radios were baseline radios with fixed functionality, called Hardware Radios
(HRs). Today, it may be argued that virtually all modern wireless communications
equipment can be classified as Software Controlled Radios. These radios implement
the signal path using application-specific hardware, i.e., the signal path is essentially
fixed. A software interface may allow certain parameters to be changed in software.
For most applications, the state-of-the-art flexible radios are Software Defined Ra-
dios (SDRs) (i.e. Tier 2). These radios allow the signal path to be reconfigured in
software without requiring any hardware modifications. As the uSR is considered
to be the
blue-sky
vision of SDR, the next target is the ideal Software Radio (iSR).
Compared to a standard SDR, an iSR implements much more of the signal path in
the digital domain. Ultimately, programmability would extend to the entire system
with Analog/Digital Conversion (ADC) taking place at the antenna.
1.3 Increasing the Policy Flexibility
Regulatory bodies are being pushed to define spectrum access policies more flex-
ible. The Dynamic Spectrum Access (DSA) concept, the ultimate goal of flexible
spectrum access, ideally could realize the optimal usage of the spectrum.
