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RE: stds-802-16: sub10. Proposal for the Duplexing Scheme
I agree that both FDD and TDD have pros and cons; both should be allowed to
evolve towards better spectrum usage and accessibility to the subscribers.
However, as shown in our contribution to ETSI TM4 of last week, I can confirm
that a "cellular" type asynchronous TDD system is perfectly feasible with a good
level of frequency reuse.
Remi Chayer [mailto:email@example.com]
Harris Corporation - Microwave Communications Division
Tel.: (514) 421-8360
Fax: (514) 421-0979
From: Eli Pasternak [mailto:EliP@bridgewave.com]
Sent: Wednesday, December 22, 1999 1:01 PM
To: 'firstname.lastname@example.org'; email@example.com
Subject: RE: stds-802-16: sub10. Proposal for the Duplexing Scheme
When comparing TDD vs. FDD, a more thorough study is required. It may be
found that TDD is preferred in some frequency bands and for some
applications and FDD is preferred elsewhere. While TDD has the promise of
flexibility and economy, as discussed in Vicente Quilez message below, TDD
has its drawbacks, of which I am going to discuss briefly a few.
TDD asymmetric bandwidth allocation flexibility is reduced in a multiple
cell environment, when T/R timing must be coordinated.
TDD requires higher peak power than FDD, which is expensive at high
TDD needs a quiet period between transmit and receive for variance in time
of arrival of signals from terminals at different distances.
TDD is less proven in wireless broadband access and is not suitable to many
frequency bands around the wold as currently allocated and regulated.
The pros and cons of each method should be studied carefully before a
conclusion can be drawn.
Eli Pasternak, CTO
BridgeWave Communications Inc.
249 Humboldt Ct.
Sunnyvale, CA 94089
Sent: Wednesday, December 22, 1999 3:09 AM
Subject: stds-802-16: sub10. Proposal for the
When comparing TDD and FDD duplexing alternatives,
considerations are relevant:
1. TDD allows asymmetrical traffic: When dealing with
traffic flow, as it is today for Internet-based data
traffic, in which
the volume of information sent in the downlink
direction is much
higher as compared to the corresponding volume sent in
direction, TDD allows to fully exploit the usage of the
(i.e. radiochannels), while in the FDD case this
asymmetry can not be
matched in an efficient manner, given the inherent
of FDD. This asymmetrical characteristic depends on the
application, but it is very significative, specially
for SoHo and
Residential markets, because these market segments are
the ones which
are reflected best in the client-server model
2. TDD provides more flexibility for spectrum usage:
spectrum is an increasingly scarce resource. More and
more often, it
is difficult to obtain paired bands available for new
TDD can make use of both paired and unpaired slots in
while FDD necessarily has to match paired bands. In
particular TDD is
the chosen duplexing approach for the US MMDS band,
possibly the most
important frequency band for IEEE 802.16sub10.
3. TDD provides better economies: A switch is cheaper
duplexer, and this has had a direct impact for the cost
of the CPE
equipment, the key element when computing the global
cost per user.
Therefore TDD-based systems will inherently provide
than FDD-based systems. Economy is always very
important, but it is
particularly key for SoHo and Residential markets,
given the continuos
trend of tremendous reduction costs of competing
technologies such as
4. TDD allows to concentrate most of the air interface
related-process in the infrastructure, as channel
behaviour can be
extrapolated from uplink into downlink and viceversa.
partitioning open the possibility for further improving
for CPE equipment
Based on the reasons above, it is proposed than IEE
a TDD duplexing scheme