Software-defined radio tunes in

[David Farber <dave () farber net>]

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From: Dewayne Hendricks <dewayne () warpspeed com>
Reply-To: <dewayne () warpspeed com>
Date: Fri, 04 Mar 2005 06:25:41 -0800
To: Dewayne-Net Technology List <dewayne-net () warpspeed com>
Subject: [Dewayne-Net] Software-defined radio tunes in

[Note:  A very good general technical article on SDR for the lay
reader.  DLH]

Software-defined radio tunes in
By David Marsh, Contributing Technical Editor -- 3/3/2005
EDN
<http://www.edn.com/article/CA505082.html>

AT A GLANCE SUMMARY

 €   SDR (software-defined radio) promises operators massive cost
reductions.
 €   Cognitive radio will soon furnish bandwidth on demand.
 €   SDR forces re-evaluation of superhet and direct-conversion
technologies.
 €   Carrier-speed data converters are beginning to emerge.

Until recently an expensive R&D exercise, SDR (software-defined radio)
is finally breaking cover. The last few months have seen a flurry of
product announcements‹from application-specific semiconductors to the
first software-driven radio to gain approval from the FCC (Federal
Communications Commission). The US military has a big interest here,
having earmarked as much as $25 billion for SDR development through the
JTRS (Joint Tactical Radio System) initiative. Its objective is to
support some 33 waveform profiles from 2 MHz to 55 GHz‹one of which
includes some of the cellular standards‹with one platform, rather than
requiring a truckload of transceivers and a patch system to enable
cross-agency communications. As JTRS overseer, the US Department of
Defense is now working with agencies in Canada, Japan, Sweden, and the
United Kingdom to foster this development. In the wider world of
commerce, the technology similarly promises to shrink operators' costs
and increase service-provision flexibility by using a generic,
reprogrammable hardware platform. So, what's the truth behind the
banner headlines, and how soon will designers benefit from taking a
software approach to a technology that's traditionally rooted in analog
hardware?

First off, it's worth reviewing what differentiates an SDR system from
contemporary telecommunications technologies, such as the CDMA
(code-division multiple access) and GSM (global system for mobile)
variants that serve most of today's cell phones. CDMA and GSM systems
already carry extensive programmable hardware for tasks that range from
managing base-station links to baseband processing within individual
cell phones. According to the FCC, SDR's definition is disarmingly
simple: "In a software-defined radio, functions that were formerly
carried out solely in hardware, such as the generation of the
transmitted signal and the tuning and detection of the received radio
signal, are performed by software that controls high-speed signal
processors." Similarly, the SDR Forum defines an SDR device as one that
functions independently of carrier frequencies and can operate within a
range of transmission-protocol environments. Architecturally, these
definitions suggest transceivers that perform upconversion and
downconversion between baseband and RF exclusively in the digital
domain, reducing the RF interface to a transmit-channel power
amplifier, low-noise amplifier for the receive path, and minimal analog
filtering (Figure 1).

  The generic nature of the hardware appeals to military and commercial
operators alike, because it prevents operators from being locked into
any one system supplier. Crucially, SDR will make it possible to
upgrade a network simply by loading new software. Given estimates of $1
billion to upgrade a 2G (second-generation) network to 3G, this move
enables massive savings in new equipment purchases and shortens the
10-year average network lifetime that previous economic models dictate.
Moreover, base stations will become protocol-aware and capable of
bridging otherwise-incompatible networks‹an increasingly desirable
technical goal as global operators consolidate their operations. (The
politics are currently something else.) Such bridges will blur today's
distinction between networking and telecommunications to the point
that, say, a W-CDMA (wideband-CDMA) handset will be able to tap into a
local WiMax infrastructure to gain broadband data access. Ultimately,
handset manufacturers will use a common global platform, enabling
manufacturing economies of scale that will reduce hardware costs to
make their products competitive with today's single-band and multiband
phones. The revenue stream for mobile devices will move from
connectivity to a true service-provision model, with
bandwidth-on-demand serving subscribers' needs from voice to video and
allowing operators to dynamically share bandwidth among network
resources.

  Today, this grand vision is some way off due to formidable hardware
and software obstacles. In the meantime, industry insiders agree that
SDR will evolve in phases that reflect increasing technical ability in
areas such as DSP and converter ICs, power management, and
network-infrastructure design. From the software side, developers
desire a common framework that enables and promotes portability (see
sidebar "SCA standardizes software development"). The SDR Forum's
predictions show commercial 3G telecommunications maturing by 2008 and
beginning to move into 4G services around 2010. It identifies SDR
opportunities opening with 2.5G services, such as the EDGE (enhanced
data for GSM evolution) packet-switched service, which is operational
in North America and beginning to roll out in Europe. The technology's
commercial uptake is mostly starting with base-station manufacturers,
such as Vanu, which recently became the first company to receive FCC
approval for its software radio.

[snip]

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