Telecommunications – Transmitter and receiver at same station – Radiotelephone equipment detail
Reexamination Certificate
1999-05-24
2003-03-18
Chin, Vivian (Department: 2682)
Telecommunications
Transmitter and receiver at same station
Radiotelephone equipment detail
C455S078000
Reexamination Certificate
active
06535748
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a transceiver for use in wireless communication. In particular, but not exclusively, the present invention relates to a transceiver that has a dual mode of operation where in the first mode of operation the signals received and the signals transmitted by the transceiver are in different frequency ranges and in the second mode of operation the received and transmitted signals are in the same frequency range.
BACKGROUND TO THE INVENTION
In most cellular telecommunication networks, mobile stations in a cell associated with a base transceiver station use a first frequency range to transmit signals to the base transceiver station. The base transceiver station uses a second, different, frequency range to transmit signals to the mobile stations in the cell associated with that base transceiver station. This is known as the frequency division duplex (FDD) mode of operation and has been used in analogue cellular telecommunication systems as well as in the current digital cellular telecommunications systems such as GSM.
Reference is made to
FIG. 10
a
which illustrates the principle of FDD operation in a frequency division multiple access system. The first frequency range F
1
is used to transmit signals from the mobile stations to the base station and the second frequency range F
2
is used to transmit signals from the base station to the mobile stations. In practice each of the frequency ranges F
1
and F
2
are divided into a plurality of smaller frequency ranges f
1
and f
2
respectively. Thus a mobile station in a particular cell will be allocated one of the smaller frequency ranges f
1
to communicate with the base station associated with the cell in which the mobile station is located. Likewise, the base station will be allocated one of the smaller frequency ranges f
2
to communicate with the mobile station.
In a system such as the GSM system which uses time division multiple access (TDMA), each smaller frequency range is divided into a plurality of frames
100
, one of which is shown in
FIG. 10
d
. Each frame
100
comprises a plurality of time slots
102
. The base station will be allocated a particular time slot
102
in successive frames to communicate with a given mobile station in one of the smaller frequency ranges f
2
. Likewise the mobile station will be allocated a particular time slot in successive frames to communicate with the base station in one of the smaller frequency ranges f
1
.
It has also been proposed that in some systems the base transceiver station can also use the same frequency range to communicate with a mobile station as the mobile station uses to communicate with the base station. This is known as the time division duplex (TDD) mode and is for example used in the DECT system. The frame and slot structure illustrated in
FIG. 10
d
is also used. Thus in the TDD mode certain of the time slots in each frame will be allocated for use by the mobile stations to transmit signals to the base transceiver station. The remaining slots in each frame will be used by the base transceiver station to send signals to the mobile stations.
It has been proposed to have dual mode mobile stations which, for example can use both GSM and DECT modes of operation.
In the systems described hereinbefore which use time division multiple access|, a mobile station will not receive and transmit signals at the same time. Accordingly, no consideration needs to be given to the isolation of the signals received and transmitted by the mobile station.
Another wireless communication access method is the code division multiple access (CDMA) method that also uses a first frequency range F
1
for signals transmitted from mobile stations to the base transceiver station and a second frequency range F
2
for signals transmitted from the base transceiver station to the mobile stations. The CDMA system like the above described FDMA/TDMA system in that, as shown in
FIG. 10
b,
has the first and second frequency ranges divided into smaller frequency ranges. However the same frame and time slot structure is not used. Instead each signal is transmitted in one of the smaller frequency ranges and signals in the same smaller frequency range are distinguished by the spreading codes applied to the signals. In the CDMA method, the mobile station may receive and transmit signals at the same time. Accordingly, mobile stations which use the CDMA method have a duplex filter connected to the antenna. The duplex filter needs to have sufficient isolation to prevent the received signal from interfering with the signal to be transmitted and vice versa.
Three different transceivers have been considered by the inventors for implementation of a mobile station which can operate in a FDD mode and a TDD mode and which can receive and transmit signals at the same time in the FDD mode of operation. In both modes of operation CDMA, TDMA or any other appropriate HIS method is used. It should be noted that these three transceivers, which are shown in
FIGS. 1
to
3
, do not constitute part of the state of the art.
A first one of these transceivers is shown in FIG.
1
and is now described in detail. An antenna
2
is arranged to receive signals and also to transmit signals. The antenna
2
is arranged to transmit signals in the frequency range F
1
and to receive signals in the frequency ranges F
2
and F
1
. The antenna
2
is connected to a switch
4
which selectively connects either a duplex filter
6
or a bandpass filter
8
to the antenna
2
. The position of the switch
4
is dependent on the mode of operation and will be discussed in more detail hereinafter. The duplex filter
6
comprises a receive filter portion
6
a
which is tuned to frequency range F
2
and a transmit filter portion
6
b
which is tuned to frequency range F
1
. The bandpass filter
8
is tuned to frequency F
1
. A switch
10
selectively connects the filter
8
or the receive filter portion
6
a
of the duplex filter
6
to a low noise amplifier
12
. The output of the low noise amplifier
12
is connected to a mixer
14
which mixes the received signal with a signal from a high frequency synthesizer
16
. The high frequency synthesizer
16
acts as a local oscillator. The output of the mixer
14
is at an intermediate frequency which is usually lower than the frequency of the signal which is received by the antenna
2
. Other parts of the transceiver are known to those skilled in the art and will not be described.
In a similar manner, a signal to be transmitted is input at an intermediate frequency to a second mixer
18
. The second mixer
18
also has an input from a second high frequency synthesizer
20
which again acts as a local oscillator. The output of the second mixer
18
represents the signal to be transmitted at the radio frequency and is in the frequency range F
1
. The radio frequency is the frequency at which the signal is transmitted across the channel to the base transceiver station. The output of the second mixer
18
is input to a power amplifier
22
which amplifies the signal. The output of the power amplifier
22
is received by the transmit portion
6
b
of the duplex filter
6
where the signal is filtered to remove undesired signal components and noise outside the frequency range F
1
.
The transceiver shown in
FIG. 1
has two modes of operation. In the FDD mode of operation, the switch
4
connects the antenna
2
to the receive filter portion
6
a
of the duplex filter
6
. The antenna
2
is not connected to the filter
8
. The second switch
10
connects the receive portion
6
a
of the duplex filter
6
to the low noise amplifier
12
. Thus, the signals received by the antenna
2
pass through the receive filter portion
6
a
of the duplex filter
6
to the low noise amplifier
12
. From the low noise amplifier
12
the received signals are passed to the mixer
14
.
In the FDD mode, the signals to be transmitted pass from the second mixer
18
to the power amplifier
22
. The signals to be transmitted are then filtered by the transmit portion
6
b
Lilja Harri
Vuorio Juha
Chin Vivian
Moore James K
Nokia Mobile Phones Ltd.
Perman & Green LLP
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