Multiplex communications – Duplex – Communication over free space
Reexamination Certificate
1999-08-25
2001-05-01
Chin, Wellington (Department: 2664)
Multiplex communications
Duplex
Communication over free space
C455S080000
Reexamination Certificate
active
06226275
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to wireless communication systems. More particularly, the present invention relates to a linear transceiver antenna switching circuit for use in high power time division duplex (TDD) wireless communication base station systems.
BACKGROUND OF THE INVENTION
Wireless communication systems include paging systems, trunk group communication systems, cordless telecommunication systems, and cellular mobile communication systems. Current important research topics in wireless communication systems focus on increasing system subscriber capacity and spectrum utilization rate, while reducing systems costs. State of the art wireless systems must provide a variety of features including voice communication, paging, message transmission, group dispatch communication, locating position features, and data communication.
Wireless communications systems, such as cellular and personal communications systems, operate over limited spectral bandwidths and must make highly efficient use of the scarce bandwidth resource for providing quality service to a large population of users. Code Division Multiple Access (CDMA) protocol is commonly used for wireless communications systems for making efficiently use of limited bandwidths.
The use of wide-band multi-carrier RF technology and Time Division Duplex (TDD) technology in wireless communication systems provides a variety of advantages including increased spectrum utilization rates, low cost RF components, and simplified RF circuit structures. The use of wide-band multi-carrier RF and TDD technologies in wireless communication systems has also allowed for improved locating position features for determining the positions of subscriber terminals. Furthermore, wide-band multi-carrier RF and TDD technologies have allowed for efficient use of digital beam forming (DBF) based on a smart antenna for the purposes of reducing multi-path fading, raising coverage ranges, improving the accuracy of locating positions, and reducing the transmit power required for subscriber terminals.
The of multi-carrier RF transceiver systems reduces the complexity and costs of TDD base stations. Time division duplex (TDD) radio transceiver systems are used for providing duplex radio communications by alternately transmitting and receiving on a time division basis. In such systems, a transmitter and a receiver operate in time division duplex to transmit and receive respectively in different time slots. Therefore, a single antenna needs to be connected at any instant to either the transmitter or receiver but not to both simultaneously.
For wide-band multi-carrier TDD radio transceiver systems, it is important to optimize the linearity of multi-carrier RF circuits used therein. For example, a multi-carrier RF transceiver must be linear enough to ensure that the 3rd-order intermodulation distortion (IM3) of the transmitter amplifier is less than some value. For example, it is desirable that the intermodulation distortion of the transmitter amplifier have a value of −60 dBc while the transmitter provides an output power of +40 dBm. Conventional antenna switching circuits used in wide-band multi-carrier TDD radio transceiver systems do not meet this criteria. Therefore, the development of TDD wireless communications system has been limited.
Some antenna switching circuits have been designed for lower transmitting power wireless communication systems (e.g., CT2, PHS). However, these antenna switching circuits are not easily adapted to provide higher output power if it is desired.
FIG. 1
shows a schematic circuit diagram at
10
of a typical prior art full duplex transceiver having time division duplex (TDD) features. The transceiver
10
includes: a digital signal processor (DSP)
12
having a first port
14
, and a second port
16
; a transmitter subsystem
18
having a first port
20
coupled for communication with port
14
of the DSP, and a second port
22
for providing a transmission signal; a receiver subsystem
24
having a first port
26
coupled for communication with port
16
of the DSP, and a second port
28
; and an antenna switching circuit
36
having a port
37
coupled to port
22
of the transmitter subsystem via a cable
35
, and a port
38
coupled to provide a received RF signal to port
28
of the receiver subsystem
24
via a cable
39
.
The antenna switching circuit
36
includes: an RF circulator
40
formed by a three-port transfer device having a first port
42
, a second port
44
coupled to receive the transmission signal from port
22
of the transmitter subsystem, and a third port
46
; a band pass filter
48
having a first port
50
coupled with the first port
42
of the RF circulator
40
, and a second port
52
coupled with an antenna
54
; a switch
56
having a first port
58
coupled with port
46
of the circulator, a second port
60
, and a third port
62
coupled with port
28
of the receiver subsystem
24
via port
38
of the antenna switching circuit; and a load impedance
64
having an impedance value RL, and having a first terminal connected to the second port
60
of the circulator, and a second terminal connected to ground.
The transmitter subsystem
18
includes: a transmitter signal processing unit
70
coupled for communication with port
14
of the DSP via port
20
of the transmitter subsystem; a modulator unit
72
having a first port coupled to receive a base band signal from unit
70
via a path
74
; a transmitter
76
having a first port coupled for communication with modulator
72
having a first port coupled to receive a base band signal from unit
70
via a path
78
; and a power amplifier
30
having an input
32
coupled to receive a signal from transmitter
76
, and an output
34
providing the transmission signal at port
22
of the transmitter subsystem. The receiver subsystem
24
includes: a receiver signal processing unit
80
coupled for communication with port
16
of the DSP via port
26
of the receiver subsystem; a demodulator unit
82
coupled to unit
80
via a path
84
; and a receiver
86
having a first port coupled for communication with demodulator
82
via a path
88
, and a second port coupled for communication with the third port
62
of switch
56
of the antenna switching circuit via the cable
39
.
The circulator
40
facilitates signal transfer in an upstream direction, and minimizes signal transfer in a downstream direction. For signals propagating in the downstream direction (from port
44
to port
42
, from port
42
to port
46
, and from port
46
to port
44
), insertion loss is approximately 0.7 dB. For signals propagating in the upstream direction (from port
42
to port
44
, from port
44
to port
46
, and from port
46
to port
42
), insertion loss is approximately 30 to 40 dB. The band pass filter
48
attenuates unnecessary radio waves in both the transmitting mode and the receiving mode. In a TDD mode, the transmitting frequency is substantially equal to the receiving frequency.
In a transmit mode of operation of the depicted transceiver
10
, switch
56
of the antenna switching circuit is controlled so that its first port
58
is connected to its second port
60
. In a receive mode, switch
56
of the antenna switching circuit is controlled so that its first port
58
is connected to its third port
62
.
In the transmit mode, a base-band signal is generated by unit
70
, modulated by modulator
72
, transmitted by the transmitter
76
, and amplified by amplifier
30
to generate the transmission signal at port
22
of the transmitter subsystem. The circulator
40
of the antenna switching circuit is operative to circulate the transmission signal received at its second port
44
to its first port
42
which is connected to the antenna
54
via the band pass filter
48
. The generation of the transmission signal by the transmitter subsystem
18
and the switched path of the transmission signal by the switching circuit
36
operating in the transmit mode is illustrated by a transmission path
90
.
A reflection p
Gu Yucong
Li Shiping
Yang Zhang Ping
Boyce Justin
Chin Wellington
Hamrick Claude A. S.
Nguyen Steven
Oppenheimer Wolff & Donnelly LLP
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