CDMA vs. CDMA
by John C. Tanner
Nine contenders, but will anyone really win?
Nine 3G cellular proposals have been submitted to the
ITU for its IMT-2000 standard, and just about all of them
are based on CDMA. What are the differences? And
why isn't Qualcomm smiling?
The IMT-2000 war is well under way. And like any keenly
contested economic battle, “war” is not too strong a term to
describe it. Despite some 15 IMT-2000 proposals submitted
to the International Telecommunication Union at the end of
June last year, the industry is drawing battle lines between
what are regarded as the top two competing proposals:
European/Japanese backed W-CDMA and US-backed
cdma2000.
To keep things in perspective, not all of these 15 proposals
are directly competing with each other. The ITU's proposed
IMT-2000 “family” of systems envisions a global network from
the micro/pico cell level to macrocellular and all the way up
to global satellite “anywhere, anytime” connectivity. This can
conceivably be covered by one harmonized standard as far
up as the macrocellular terrestrial level, but the satellite
component of IMT-2000 is technologically separate from the
terrestrial air interface. As such, five of the 15 IMT-2000
proposals are strictly for the satellite component of the
IMT-2000 “family”, and are competing only amongst
themselves.
Of the 10 terrestrial proposals, the European DECT cordless
access standard has been submitted essentially as a
micro/pico cell component of IMT-2000 for applications like
wireless PBXs. European standards body ETSI claims
DECT's third-generation incarnation can meet the ITU's
bandwidth requirements for indoor and pedestrian
environments – 2 Mbps for stationary users, and 384 kbps
for pedestrian users walking within the campus or workplace
environment, for example – but can't meet the vehicular user
requirements of 144 kbps since DECT by design is not a
wide-area wireless network technology.
The other nine
That leaves the other nine third-generation cellular
technologies proposed for the terrestrial IMT-2000 network,
which have since become eight after proponents of two US
proposals decided to harmonize their respective technologies
into a single standard in September. W-CDMA is actually
represented in two separate proposals – there's pure
W-CDMA backed by Japan's Association of Radio Industry
Broadcasters (ARIB), and UTRA from ETSI, which is actually
a hybrid standard based on Japan's W-CDMA technology
and Europe's original UMTS platform for third-generation
GSM. So, take away the W-CDMA and cdma2000 interests,
and you have five additional 3G technologies that are being
greatly overshadowed by the war between W-CDMA and
cdma2000.
And there's a fairly good reason for that, the journalistic
appeal of a nasty corporate cat fight over IPR and regional
barriers to entry notwithstandng: all but one of them are
variants on the same basic theme of W-CDMA vs.
cdma2000. The exception is UWC-136, the 3G IS-136
technology submitted by the US-based Universal Wireless
Communications Consortium, and the only proposal based
solely on TDMA. The other four, however, are all rooted in
CDMA technology. And the differences between them can all
basically be traced back to the primary technological
differences between W-CDMA and cdma2000 – making the
political battle between proponents of those two standards
even harder to ignore.
US air assault
In fact, it's the political landscape of the IMT-2000 race that
seems more interesting than the technologies themselves.
For example, the US submitted a whopping four proposals
for terrestrial 3G cellular: CDG's cdma2000, the UWCC's
UWC-136, and two other CDMA-based technologies –
wireless multimedia and messaging services wideband
CDMA (WIMS W-CDMA), and North American wideband
CDMA (NA:W-CDMA).
WIMS W-CDMA was developed by AT&T Wireless Labs,
Hughes Network Systems, InterDigital Communications, OKI
America and GoldenBridge Technologies, and endorsed by
the American TIA standards body. NA:W-CDMA is the
brainchild of the North American GSM Alliance and backed
by ANSI's T1 standards group.
And those are the main differences between them. Beyond
that, the technological similarities between key system
requirements are striking. Both utilize DS-CDMA multiple
access, a 4.096 Mcps chip rate for a minimum 5-MHz
channel, asynchronous base station timing, 10-ms frame
length, adaptive rate vocoder support – the list goes on and
on. There are minor differences, but they are minor enough
that the TIA and T1 bodies elected in September to
harmonize the two proposals into a single standard called
wideband packet CDMA (WP-CDMA).
What's even more striking is the key similarities between
WP-CDMA (and the two standards that created it) and the
W-CDMA and UTRA proposals from Japan and Europe,
which themselves are nearly identical. The multiple access
techniques, basic chip rates, base station timing and frame
length are all the same, and only when broken down into
minute details and simulation test results are the differences
noticeable.
Why the US is pushing so many 3G standards is somewhat
open to interpretation. The official reason has to do with the
US government's supposed philosophy that competing
multiple 3G standards will ultimately produce a stronger
standard.
Ambassador David Aaron, under-secretary for international
trade at the US Commerce Department, reiterated that
position in a letter to UWCC chairman and wireless systems
vice president of SBC Communications Gregory Williams in
November. Aaron stated that the submission of four
competing 3G standards was “[c]onsistent with this overall
market-based approach to standards development”.
Dig at ETSI
Some industry observers also consider it a veiled slap at the
ETSI harmonized-standard approach. The US has been
critical of Europe for submitting one 3G proposal devised
largely by European wireless vendors that effectively shut out
competing standards from other countries before the
IMT-2000 evaluation process had even begun.
ETSI director general Karl Heinz Rosenbrock dismisses
such accusations, pointing out in a letter to the US
government's Subcommittee on Trade that, in the first place,
“major North American manufacturers (e.g. Lucent, Nortel,
Motorola) are members of ETSI via their European affiliates,”
and in the second place, “the major part of the registered
essential [GSM] Intellectual Property Rights emanate from
US companies.”
At the same time, while the US government talks of
competing standards, two have already consolidated, and
UWC-136 is decidedly next in line. UWC-136, of course, has
little in common with any W-CDMA proposal, but what little
there is to be found is quite valuable.
Specifically, UWC-136's approach to high-speed data is
compatible with GSM's enhanced EDGE technology, and
with no realistic hope of a fully TDMA-based 3G standard,
the UWCC is already cooperating with both ETSI and North
American GSM Alliance.
With WP-CDMA and UWC-136 aligning more or less with
W-CDMA/UTRA, cdma2000 is essentially the only US
standard likely to be competing with W-CDMA – particularly
given Qualcomm's well-publicized stand-off with virtually
everybody else over IPR squabbles.
Korean fence-straddling
Meanwhile, South Korea's TTA has submitted two 3G
cellular submissions of its own that seem to play both sides
of the IPR fence. Korea is Asia's largest market for 2G IS-95
networks, and as such has an interest in the success of
cdma2000 or something compatible to it. At the same time,
major Korean players like Samsung Electronics and LGIC
have collaborated extensively with NTT DoCoMo in
developing W-CDMA.
As such, TTA's CDMA I (multiband synchronous DS-CDMA)
resembles cdma2000 – not as closely as the W-CDMA
proposals resemble each other, but close enough on key
elements such as the basic 3.6864-Mcps chip rate and
synchronous base station timing, which other differences not
so drastic that the two standards couldn't be harmonized.
TTA's CDMA II (asynchronous DS-CDMA), meanwhile, is as
similar to W-CDMA/UTRA as any other competing W-CDMA
variant, barring its own minor idiosyncrasies.
Finally, even China's 3G proposal, time division synchronous
CDMA (TD-SCDMA), albeit the most idiosyncratic of all the
CDMA-based submissions, is a sort of lost cousin to ETSI's
UTRA standard. TD-SCDMA's chip rate of 1.1136 Mcps over
a proposed bandwidth per channel of 1.2 MHz and a frame
length of 5 ms (8 slots) has little to do with either the
W-CDMA or cdma2000 camps. However, while TD-SCDMA
seems designed more as a low-mobility WLL technology, its
hybrid access approach utilizing TDMA and CDMA gives it a
potential in-road to cooperation with UTRA, which also
combines both techniques.
W-CDMA's numbers advantage
What all this amounts to is a potentially grim outlook for
cdma2000 in the IMT-2000 standardization process. Of the
seven 3G CDMA cellular air interface proposals, only one
has the potential to cooperate with the CDG on cdma2000 –
Korea's CDMA I. The rest are more likely to side with
W-CDMA, which means cdma2000 will have to take on half
of Korea, most of the US, and all of Europe, Japan and China
at the ITU Technical Group 8/1 table from now until March
1999, when the final evaluations are due.
And that won't be easy with Qualcomm playing hardball over
the IPR issue. Qualcomm claims to hold patents to all of the
essential key elements to any given 3G CDMA standard,
and refuses to license any IPR to W-CDMA, UTRA, CDMA II
or WP-CDMA.
Qualcomm has been accused, particularly by Ericsson, of
trying to make cdma2000 the default 3G standard by
refusing to license CDMA to anyone else, but Qualcomm
vice president of government affairs William Bold denies this
is the case. “Ericsson sort of goes back and forth on this
position,” he says. “On some days, they say we don't hold
the central IPR, other days, they say we are in a position to
blackmail the industry.”
What Qualcomm objects to, Bold says, is W-CDMA's
deliberate incompatibility to 2G cellular systems. For
example, cdma2000's 3.6864 Mcps chip rate is
backwards-compatible to 2G IS-95 – W-CDMA's 4.096 Mcps
chip rate, which ETSI claims provides more efficient use of a
5-MHz channel, is not backwards-compatible to any 2G air
interface. There is also an ongoing argument over base
station synchronization – cdma2000, like IS-95, relies on
GPS for synchronization. But W-CDMA proponents are
skittish about using GPS, partially because it makes indoor
base stations much harder to synchronize, and partially
because GPS is a military technology controlled by the US,
a country known for exerting leverage on uncooperative
neighbors in difficult times.
Qualcomm's motive
However, Qualcomm's objections are clearly not entirely void
of self-interest. For a start, it has spent an incredible amount
of energy, alongside the CDG, hyping and evangelizing 2G
CDMA and convincing operators to adopt it over rival GSM –
not an easy sell at a time when operators are already trying
to second-guess what 3G technology they should consider,
and even harder when the odds-on favorite isn't compatible
with IS-95. Moreover, operators who have already adopted
IS-95 won't be very happy to discover they've just installed a
system that can't be upgraded without a major overhaul.
However, how much all of this will matter in the end is
anyone's guess. As with other standards battles, the ITU is
unlikely to pick one proposal intact. Indeed, the ITU has
specified it will select the key characteristics that will
comprise the IMT-2000 air interface. At the same time, the
ITU has specified that compatibility with 2G land networks –
not the 2G air interface – is essential to the IMT-2000
standard, which would lend considerable weight to
W-CDMA-related proposals.
The ITU also will not consider any proposal with unresolved
IPR disputes, which is what cdma2000 may well be banking
on. Indeed, Qualcomm's Bold says that, in light of the IPR
stipulation, “presumably W-CDMA will never become a
standard.” The ITU goes further, suggesting that neither
W-CDMA or cdma2000 can be an IMT-2000 standard if the
dispute continues. But that doesn't mean Qualcomm isn't
willing to work something out, says Bold, who describes
Qualcomm's IPR as an incentive for everyone to work out a
compromise.
However, no one outside the CDG sees it that way, and
Qualcomm's IPR hold-out strategy is a gambit that could
well alienate it from the rest of the industry outside of the US
even more than it already is.
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