U.S. patent application number 09/780948 was filed with the patent office on 2001-09-13 for filtering method to allow fdd and tdd operation in pcs transreceivers.
Invention is credited to Barabash, Darrell W., Morris, Russell A..
Application Number | 20010021178 09/780948 |
Document ID | / |
Family ID | 22125582 |
Filed Date | 2001-09-13 |
United States Patent
Application |
20010021178 |
Kind Code |
A1 |
Barabash, Darrell W. ; et
al. |
September 13, 2001 |
Filtering method to allow FDD and TDD operation in PCS
transreceivers
Abstract
A transreceiver allows efficient operation in a full or
half-duplex TDD or FDD system. The preferred transreceiver includes
a common set of filters used for both FDD (Frequency Division
Duplex) and TDD (Time Division Duplex) operation in a given range
of frequencies thereby reducing circuitry count and implementation
costs. Thus, the transreceiver of the present invention can operate
in FDD operation or TDD operation.
Inventors: |
Barabash, Darrell W.;
(Grapevine, TX) ; Morris, Russell A.; (Keller,
TX) |
Correspondence
Address: |
LYON & LYON LLP
SUITE 4700
633 WEST FIFTH STREET
LOS ANGELES
CA
90071-2066
US
|
Family ID: |
22125582 |
Appl. No.: |
09/780948 |
Filed: |
February 9, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09780948 |
Feb 9, 2001 |
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09075415 |
May 8, 1998 |
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6212172 |
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Current U.S.
Class: |
370/277 ;
370/280; 370/330; 370/489; 455/76 |
Current CPC
Class: |
H04B 1/00 20130101; H04B
1/44 20130101; H04B 1/406 20130101; H04B 1/56 20130101; H04B 1/52
20130101 |
Class at
Publication: |
370/277 ;
370/280; 370/330; 370/489; 455/76 |
International
Class: |
H04B 007/00 |
Claims
We claim:
1. A transreceiver architecture comprising: an antenna capable of
transmitting and receiving signals; a forward channel filter,
having a signal input end and a signal output end, said forward
channel filter tuned to permit passage of forward channel
frequencies and electrically coupled at said signal input end to
said antenna; a reverse channel filter, having a signal input end
and a signal output end, said reverse channel filter tuned to
permit passage of reverse channel frequencies and electrically
coupled at said signal input in to said antenna in parallel with
said signal input end of said forward channel filter; a TDD
transmit switch having an open and closed position and having a
signal input end and signal output end, said signal input end
electrically coupled to said signal output end of said forward
channel-filter; an FDD-TDD switch having an open and closed
position and having a signal input end and signal output end said
signal input end electrically coupled to said output end of said
forward channel filter and in parallel with said input end of said
TDD transmit switch and said signal output end electrically coupled
to said signal output end of said reverse channel filter; and a TDD
receive switch having an open and closed position and having a
signal input end and signal output end, said signal input end
electrically coupled to said signal output end of said reverse
channel filter and electrically coupled to said output end of said
FDD-TDD switch.
2. A transreceiver architecture as in claim 1 wherein said forward
channel filter and said reverse channel filter comprises a
frequency duplexer having a frequency duplexer signal input end and
having a plurality of frequency duplexer signal output ends, said
frequency duplexer input end electrically coupled to said antenna
and having one of said plurality of said frequency duplexer signal
output ends electrically coupled with said input end of said TDD
transmit switch and having one of said plurality of said frequency
duplexer signal output ends electrically coupled with said input
end of said TDD receive switch.
3. A transreceiver architecture as in claim 1 wherein said output
end of said TDD transmit switch is connectable to a low-noise
amplifier.
4. A transreceiver architecture as in claim 1 or 3 wherein said
output end of said TDD receive switch is connectable to an
amplifier.
5. A transreceiver architecture comprising: an antenna capable of
transmitting and receiving signals; a forward channel filter,
having a signal input end and a signal output end, said forward
channel filter tuned to permit passage of forward channel
frequencies and said signal input end electrically coupled to said
antenna; a reverse channel filter, having a signal input end and a
signal output end, said reverse channel filter tuned to permit
passage of reverse channel frequencies and said signal input end
electrically coupled to said antenna in parallel with said signal
input end of said forward channel filter; a TDD transmit switch
having an open and closed position and having a signal input end
and signal output end, said signal input end electrically coupled
to said signal output end of said forward channel filter; a first
TDD switch having an open and closed position and having a signal
input end and signal output end said signal input end electrically
coupled both to said output end of said forward channel filter and
to said input end of said TDD transmit switch; a second TDD switch
having an open and closed position and having a signal input end
and signal output end, said signal input end electrically coupled
to said signal output end of said first TDD switch, said signal
output end electrically coupled to said signal output end of said
reverse channel filter; a bandpass filter having a signal input end
and a signal output end, said filter electrically coupled at said
signal input end to said antenna and said signal output end
electrically coupled to said signal output end of said first TDD
switch and electrically coupled to said signal input end of said
second TDD switch; and a TDD receive channel switch having an open
and closed position and having a signal input end and signal output
end, said signal input end electrically coupled both to said signal
output end of said reverse channel filter and said signal output
end of said second TDD switch.
6. The transreceiver architecture as in claim 5 wherein said
forward channel filter and said reverse channel filter are replaced
by a frequency duplexer having a frequency duplexer signal input
end and having a plurality of frequency duplexer signal output
ends, said frequency duplexer input end electrically coupled to
said antenna and having one of said plurality of said frequency
duplexer signal output ends electrically coupled in with said input
end of said TDD transmit switch and electrically coupled with said
input end of said first TDD switch and having one of said plurality
of said frequency duplexer signal output ends electrically coupled
in parallel with said input end of said TDD receive switch and with
said output end of said second TDD switch.
7. A transreceiver architecture as in claim 5 wherein said output
end of said TDD transmit switch is connectable to a low-noise
amplifier.
8. A transreceiver architecture as in claim 5 or 7 wherein said
output end of said TDD receive switch is connectable to an
amplifier.
9. A transreceiver architecture as in claim 6 wherein said output
end of said TDD transmit switch is connectable to a low-noise
amplifier.
10. A transreceiver architecture as in claim 6 or 9 wherein said
output end of said TDD receive switch is connectable to an
amplifier.
Description
FIELD OF THE INVENTION
[0001] The field of the invention pertains to wireless
communication transreceivers including, more particularly,
transreceivers capable of FDD and TDD operation.
DESCRIPTION OF RELATED ART
[0002] One method of providing duplex communication is through use
of FDD (Frequency Division Duplex) protocols in which frequency
allocations in the PCS band is split into a forward sub-band and a
reverse sub-band. This split can accommodate FDD where transmission
is limited to one of the sub-bands. However, this split presents a
problem to coexisting TDD (Time Division Duplex) systems which
transmit and receive on the same frequency and can use either of
the frequency sub-bands for transmission.
[0003] Shown in FIG. 1 is a known implementation of a TDMA-FDD
system, such as PCS-1900 or IS-136 with a switch placed between the
radio and the antenna. The switch, placed before the forward and
reverse channel filters, selectively routes the RF signal path
either to the receiver or from the transmitter in response to the
mode of the transreceiver (either transmit or receive). The
receiver subsystem will typically employ a bandpass filter tuned to
the forward channel, and the transmitter subsystem will typically
employ a filter tuned to the reverse channel. As a result of this
switch placement, only the forward channel path or only the reverse
channel path may be selected. This configuration precludes
transmission and reception in both the forward channel frequency
band or the reverse channel frequency band, thereby limiting the
available frequency bands for a TDD system. Other known
implementations remove the switch entirely to allow simultaneous
transmit and receive (e.g., IS-54 and IS-19) but are still limited
to different frequencies.
[0004] While a transreceiver operable in FDD or TDD could employ
duplexers, or dual filters, for FDD operation plus an additional
filter and switch for TDD operation, since either the TDD or FDD
mode uses its own set of filters, one set of components will be
under utilized rendering the system cost inefficient.
SUMMARY OF THE INVENTION
[0005] The present invention comprises a transreceiver architecture
that allows a common set of filters to be used for either FDD
(Frequency Division Duplex) or TDD (Time Division Duplex) operation
in a given range of frequencies, thereby reducing circuitry count
and implementation costs. Accordingly, the present invention allows
operation in a full or half-duplex TDD or FDD system.
[0006] In a preferred embodiment of the invention, switches are
incorporated after the forward and reverse channel filters to
create three paths controlled by predetermined logic. This
configuration permits use of both the forward and reverse channel
filters for a TDD system and combines the forward and reverse
channel filters to create a filter that can pass both frequency
sub-bands. These single device frequency duplexers are often
commercially available, thereby allowing for ease in implementation
and cost reduction.
[0007] Some frequency allocation plans, such as those in the USA,
often have a frequency band between the transmit and receive
regions. In the USA, this frequency band can be referred to as the
"unlicensed frequency band" and can be used for TDD only. An
alternative preferred embodiment comprises an additional filter to
allow exploitation of multiple frequency bands for transmission and
reception.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1 is a known TDMA-FDD transreceiver architecture.
[0009] FIG. 2 is a schematic diagram of a transreceiver of the
present invention.
[0010] FIG. 3 is a schematic diagram of a second transreceiver of
the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0011] Referring to FIG. 1, the known TDMA-FDD capable architecture
depicts an antenna 1 electrically coupled to forward channel
filters 2 and reverse channel filters 3, each tuned to a different
frequency F.sub.1 and F.sub.2 respectively. Thus, in the known FDD
transreceiver the switch 4 will be placed in the Rx position to
connect the antenna to channel filter 2 to receive signals and will
be placed in the Tx position to connect the antenna 1 to the
reverse channel filter 3 to transmit signals. While more than one
antenna and more than one set of forward and reverse channels will
usually be employed, only one set is described herein for
simplicity and efficiency. Alternatively, the antenna 1 can be
split into a receive and transmit antenna, each individually
connected to a respective filter (not shown).
[0012] As the preferred dual mode FDD/TDD transreceiver, depicted
in FIG. 2, the forward channel filter 11 and the reverse channel
filter 12 are tuned to different frequencies F.sub.1 and F.sub.2
respectively, both connected to the antenna 10 without the typical
Tx/Rx switch 4 interposed between them. Instead, a TDD-Tx switch 13
is interposed in a receive path 20 between the forward channel
filter 11 and the low-noise amplifier 16. Also, a TDD/Rx switch 14
is interposed in the transmit path 22 between the reverse channel
filter 12 and the power amplifier 17. Additionally, an FDD/TDD
switch 15 is interposed in TDD path 24 between the receiver and
transmit paths 20 and 22 respectively. When the dual mode FDD/TDD
transreceiver is operating in the full or half duplex FDD mode, as
dictated by the Boolean equations for the switch states, the TDD/Tx
switch 13 will be closed, the FDD-TDD switch 15 will be open and
the TDD/Rx switch 14 will be closed. The result is that the
diplexer function created by the forward channel filter 11 and the
reverse channel filter 12 passes the portion of the signal in the
F.sub.1 frequency ranges through the TDD/Tx switch 13 to the
low-noise amplifier 16 and into the receive channel. In the
transmit mode, the output of the transmitter channel is passed
through the TDD/Rx switch 14 to the reverse channel filter 12 and
is transmitted by the antenna 10. This functionality represents
classical FDD operation.
[0013] Although the filters and switches may be described having
input and output ends, signals are being propagated in both
directions. Thus, although input and output ends may be described,
such labels are for references and orientation purposes.
[0014] If it is desired to operate the dual mode TDD/FDD
transreceiver in the TDD mode, the FDD-TDD switch 15 will be
closed. In the TDD receive mode, the TDD-Tx switch 13 will be
closed and the TDD-Rx switch 14 will be open. In the TDD transmit
mode, the TDD-RX switch 14 will be closed and the TDD-Tx switch 13
will be open. Thus, while transmitting in the TDD-Tx mode, the
TDD-RX switch 14 is closed and the output of the transreceiver is
applied to both the reverse channel filter 12 and also the forward
channel filter 11 through the FDD-TDD switch 15. Thus signals in
both frequency ranges F.sub.1 and F.sub.2 will be passed to the
antenna 10 with minimal loss. When receiving, the portion of the
received signal in the forward frequency band F.sub.1 passes
through the forward channel filter 11 and the portion of the
received signal in the reverse frequency band F.sub.2 passes
through the receive channel through the LNA 16.
[0015] In the preferred embodiment, the forward channel and reverse
channel filters have a total electrical length between their filter
outputs that is either very small (e.g. less than .pi./20 radians)
or equal to n*.pi. radians where `n` is as small an integer as
possible. The reason for this is that filters are generally
reflective outside their passband and, in the case of typical radio
filters, behave as open circuits. An open circuit translated
through a transmission line whose electrical length is a multiple
of .pi. radians will still appear as an open circuit. Thus, a
signal that is in the forward passband will pass through the
forward channel filters 11 and the reverse channel filters 12 and
will appear as an open circuit. Since the transmission line will
appear as an open circuit, the signal is effectively rejected by
the circuit, i.e. will have no influence on the forward channel
filters 11. Should a filter behave as a short circuit, an
additional .pi./2 may be added to transform the short circuit to an
open circuit.
[0016] An alternative preferred arrangement is disclosed in FIG. 3.
The architecture operates in a similar manner as that shown in FIG.
2 except that an additional bandpass filter 19 permits the system
to operate in the TDD mode over an additional frequency band F3,
such as the "unlicensed frequency band".
[0017] As depicted in FIG. 3, the forward channel filter 11, the
reverse channel filter 12, and the unlicensed band filter 19 are
tuned to different frequencies F.sub.1, F.sub.2, and F.sub.3
respectively. Each filter can be connected to the antenna 10
without a Tx/Rx switch 4 interposed between them. Instead, a TDD-Tx
switch 13 is interposed in a receive path 30 between the forward
channel filter 11 and the low-noise amplifier 16. Also, a TDD/Rx
switch 14 is interposed in the transmit path 33 between the reverse
channel filter 12 and the power amplifier 17. Additionally, TDD
switch 34 is interposed in TDD path 31 between the forward channel
filter 11 and the unlicensed band filter 19. Finally, TDD switch 35
is interposed in TDD path 32 between the reverse channel filter 12
and the unlicensed band filter 19.
[0018] When the dual mode FDD/TDD transreceiver is operating in the
FDD mode, as dictated by the Boolean equations for the switch
states, the TDD/Tx switch 13 will be closed, both TDD switch 34 and
TDD switch 35 will be open and the TDD/Rx switch 14 will be closed.
The result is that the diplexer function created by the forward
channel filter 11 and the reverse channel filter 12 passes the
portion of the signal in the F.sub.1 frequency ranges through the
TDD/Tx switch 13 to the low-noise amplifier 16 and into the receive
channel. In the transmit mode, the output of the transmitter
channel is passed through the TDD/Rx switch 14 to the reverse
channel filter 12 and is transmitted by the antenna 10. This
functionality represents classical FDD operation.
[0019] If it is desired to operate the dual mode TDD/FDD
transreceiver in the TDD mode, unlicensed filter 19 can be included
with forward channel filter 11 and reverse channel filter 12 to
accommodate the "unlicensed" frequency band. In the TDD receive
mode, the TDD-TX switch 13 will be closed and the TDD-RX switch 14
will be open. With TDD switch 34 closed and TDD switch 35 open,
path 31 to the unlicensed band filter 19 is completed. Thus, with
the TDD-TX switch 13 closed, the receive portion of the
transreceiver is applied to both the forward channel filter 11 and
also the unlicensed filter 19. As a result, signals in both
frequency ranges F.sub.1 and F.sub.3 will be received from the
antenna 10. When TDD switch 35 is closed, path 32 is completed and
the frequency range F.sub.2 can pass through the reverse channel 12
from the antenna 10. When receiving, the portion of the received
signal in the forward frequency band F.sub.1 passes through the
forward channel filter 11 and the portion of the received signal in
the reverse frequency band F.sub.2 passes through the receive
channel through the LNA 16 and the frequency band F.sub.3 passes
through the unlicensed channel 19. Thus, with TDD switch 34 closed
and TDD switch 35 closed, signals in frequency ranges F.sub.1,
F.sub.2 and F.sub.3 will be received from the antenna 10.
[0020] In the TDD transmit mode, the TDD-Rx switch 14 will be
closed and the TDD-Tx switch 13 will be open. With TDD switch 35
closed and TDD switch 34 open, path 32 to the unlicensed band
filter 19 is completed. Thus, the output of the transreceiver is
applied to both the reverse channel filter 12 and also the
unlicensed filter 19 through the TDD switch 35. As a result,
signals in both frequency ranges F.sub.2 and F.sub.3 will be passed
to the antenna 10 with minimal loss. When TDD switch 34 is closed,
path 31 is completed and the frequency range F.sub.1 can pass
through the forward channel 11 to the antenna 10. Thus, with TDD
switch 34 and TDD switch 35 closed, signals in frequency ranges
F.sub.1, F.sub.2 and F.sub.3 will be passed to the antenna 10 with
minimal loss. In the preferred embodiment, the forward channel and
reverse channel filters have a total electrical length between
their filter outputs that is either very small (e.g. less than
.pi./20 radians) or equal to n*.pi. radians where `n` is as small
an integer as possible.
* * * * *