Telecommunications – Transmitter and receiver at same station – With transmitter-receiver switching or interaction prevention
Reexamination Certificate
1998-07-28
2001-10-30
Trost, William (Department: 2746)
Telecommunications
Transmitter and receiver at same station
With transmitter-receiver switching or interaction prevention
C455S024000, C455S063300, C455S278100, C455S284000, C455S295000, C455S296000
Reexamination Certificate
active
06311045
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to radio transceivers which operate to both transmit and receive radio signals. In particular, but not exclusively, the present invention relates to radio transceivers, which are provided with a means to isolate signals transmitted by a transmitter of the transceiver system and received by a receiver of the transceiver system.
In modem radio communications equipment it is often a requirement to both transmit and receive radio signals. Such transmitted and received radio signals may be on different frequencies separated by a guard band. As such, in order to ensure that signals transmitted from a transmit antenna of the transceiver do not corrupt and distort signals received on a receive antenna, it is necessary to provide isolation between the transmitter and receiver of the transceiver system.
In broadband Code Multiple Access systems (CDMA), the transmit and receive signals have a relatively wide bandwidth. As such, the bandwidth of the transmit and receive signals may be comparable to the guard band separating the transmit and receive frequency bands.
In known systems, a duplexing filter is provided which is coupled to the output of the transmitter and the input of the receiver in order to effect the desired frequency separation between transmitter and receiver.
The purpose of the duplexing filter is to provide isolation between the Transmit (Tx) and the Receive (Rx) ports whilst connecting the Tx and the Rx to a common antenna. This is achieved by filtering the appropriate Rx and Tx frequencies prior to combining them at the antenna port. A typical duplexing filter achieves 30 to 40 decibels (dB) isolation between the Rx and the Tx ports. Since the attenuation is provided by filtering, each duplexing filter is dedicated to a specific band of Rx/Tx frequencies.
It is well known in the art of radio transceiver systems that dual or multi-mode handsets, operating in two or more frequency bands, use a separate duplexing filter for each frequency band, with the appropriate band being selected by a switch. Since the duplexing filters are relatively large components, this approach becomes less attractive for multi-mode operation due to lack of space in the handset.
A truly multi-mode terminal must have a flexible architecture which covers arbitrary standards and frequencies. For such a terminal, a key device is a duplexer, which provides Rx/Tx isolation without the need for filtering which is dedicated to specific frequencies.
A further disadvantage with known duplexing filter based transceiver systems is that an inherent insertion loss associated with the connection of the duplexing filter to the receiver, causes a degradation in the receiver noise figure and furthermore reduces the power with which the transmitted signal may be transmitted. Another disadvantage with duplexing filters is that impairment is caused to the received and transmitted signals as a result of in-band amplitude and group delay ripple effects caused by the duplexing filter. This, in turn leads to loss of capacity in a radio system such as a CDMA system. The impairment is more significant in broadband systems such as broadband CDMA, in which the bandwidth of signals is comparable to the receiver and transmitter frequency separations.
The aforementioned disadvantages represent a technical problem which is addressed by the present invention.
SUMMARY OF THE INVENTION
The present invention relates to a transceiver which provides fully duplexed operation without Rx/Tx filtering in the frequency domain. Since the need for a duplexing filter is eliminated, the new transceiver is ideally suited for a flexible architecture terminal. Furthermore, since the receive and transmit separation is now not based on frequency selectivity, the receive and transmit frequencies can be allocated more closely, which leads to more flexible network planning.
According to the present invention there is provided a radio communications transceiver which operates to transmit radio signals via a transmit antenna and receive radio signals via a receive antenna, wherein said transmit and receive antennas are disposed to provide at least a substantial amount of radio signal isolation therebetween, wherein said radio communications transceiver further including a cancellation device comprising a first coupler coupled to the transmit antenna and arranged to extract a sample of said transmit signal, a second coupler coupled to the receiver antenna and arranged to extract a sample of said received signal, a control unit fed on first and second inputs with said transmit and said received signal samples respectively, said control unit operating to generate an error signal representative of a correlation of said transmit and received radio signals, which error signal is fed to a modulator which operates to modulate said transmit signal sample, consequent upon said error signal which modulated transmit signal sample which is fed to said radio receiver via a further coupler, and which modulated transmit signal sample serves to substantially cancel transmit signals received by said receiver antenna, said cancellation device operating in combination with said disposal of said transmit and receive antennas to effect a desired radio signal separation between said transmit and receive signals.
The transmit and receive antennas may be disposed so as to be substantially orthogonal. The transmit and receive antennas may be separated by a short distance, thereby providing said at least substantial radio signal isolation.
The control unit may comprise an adaptive control unit which operates in conjunction with a look-up table to provide control coefficients which when applied to said cancellation device provide substantial cancellation of said transmit signal received by said received antenna.
The adaptive control unit may comprise a gradient search algorithm and said controller operates in a closed loop configuration. Alternatively, the adaptive control unit may compute the value of said control coefficient based on a model of said cancellation device and said sample of said transmit and said received signal, with said control unit operating in an open loop configuration. Altematively, the adaptive control unit may pre-calculate said control coefficients in a manner so as to identify an area of the global minimum and subsequently perform a gradient search to optimise said control coefficients for a local minimum, thus operating initially in an open loop configuration and thereafter operating in a closed loop configuration.
The initial substantial amount of radio frequency isolation may be provided by means of a hybrid coupler device. Alternatively, the initial substantial amount of radio frequency isolation may be provided by means of a circulator device.
The transceiver may further include a filter which is arranged to provide a substantial level of isolation between transmit and receiver antennas.
According to a further aspect of the present invention there is provided a method of transmitting and receiving signals contemporaneously using two antennas separated by a short distance or two co-located but orthogonal antennas, comprises the steps of measuring the inherent coupling between two antennas, using a cancellation device connected between the two antennas to form a cancellation path, and a control device which operates to control the cancellation device in accordance with the measured coupling so that the cancellation path is equal in magnitude and opposite in phase of the coupling between the two antennas.
In modern radio communications equipment it is often a requirement to use wide band transmitters which are arranged to transmit radio frequency signals which occupy a substantial bandwidth, such as for example, broadband CDMA signals. Wide band transmitters suffer a problem in that generation of the wide band radio frequency signal within a predetermined frequency range using a conventional super heterodyne transmitter arrangement in which an intermediate frequency signal is formed, requires
Crowell & Moring LLP
Roke Manor Research Limited
Sobutka Philip J.
Trost William
LandOfFree
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