Transceiver with hybrid adaptive self-interference canceller for removing transmitter generated noise to prevent modem jamming

A self-interference canceller (SIC) is incorporated into a transceiver to reduce or eliminate modem jamming when a transmitter in the transceiver transmits at high power levels. The SIC is configured to receive at a first input a transmitter noise reference signal including a self-interfering signal component generated by the transmitter, to receive at a second input a corrupted signal including the self-interfering signal component and a desired signal component generated by the transmitter, and to output a correction signal that resembles the self-interfering signal component. The correction signal is subtracted from the corrupted signal to generate a processed signal that is input to the modem. The SIC may be disabled when the output power of the transmitter is at a level below a predetermined threshold. The invention may be applied to a multi-radio access technology (RAT) transceiver.

FIELD OF INVENTION

The invention is related to wireless communication systems.

BACKGROUND

Current mobile technology trends integrate multiple radio access technologies (RATs) into a single wireless transmit/receive unit (WTRU) that transmits and receives via respective individual antennas, or via a common antenna that is shared through a duplexer filter. Particular specifications for RAT air interfaces are derived based on typical deployment scenarios. In the case of multiple RATs integrated into the same WTRU, self-interference can be significant, which results in receiver desensitization.

FIG. 1shows an example of a problem that occurs in a conventional transceiver100including a transmitter105, a power amplifier (PA)110and a modulator/demodulator (modem)140, whereby noise generated by the transmitter105and the PA110causes the modem140to jam. The transceiver100may also include a duplexer115, an antenna120, a low noise amplifier (LNA)125, a receiver130and an analog-to-digital converter (ADC)135. The duplexer115may include a transmit filter115A and a receive filter115B. The transmitter105outputs a signal that is amplified by the PA110and is routed to the antenna120via the transmit filter115A of the duplexer115. Signals received by the antenna120are routed to the modem140via the receive filter115B of the duplexer115, the LNA125, the receiver130and the ADC135. The LNA125amplifies the received signals, the receiver down-converts the received signals to baseband signals, and the ADC135converts the baseband signals to digital signals that are input to the modem140.

In the example shown inFIG. 1, the output noise density of the PA115is −120 dBm/Hz (@+24 dBm output in receive bands) and the duplexer115may provide about 40 dB of isolation to suppress the transmitter band noise. Thus, self-interference noise power from the transmitter105is −160 dBm/Hz, which is 7 dB above the noise floor of the receiver −167 dBm/Hz (−174 dBm/Hz, which is 50 Ohm noise density, plus 7 dB, which is the noise figure of a typical receiver)

It would be desirable to suppress the transmitter noise to the level, when the total combined noise of the receiver and the transmitter generated noise in receive band will not degrade the total noise figure (NF) by more than 1 dB. In the example ofFIG. 1, It would be expected to see a combined noise at −166 dBm/Hz, which will limit the transmitter generated noise to:

-166⁢⁢dBm⁢/⁢Hz-(-167⁢⁢dBm⁢/⁢Hz)⁢=2.5⁢⁢e-17⁢mW⁢/⁢Hz-2⁢e-17⁢⁢mW⁢/⁢Hz⁢=0.5⁢⁢e-17⁢mW⁢/⁢Hz⁢=-173⁢⁢dBm⁢/⁢Hz.
Thus, it would be desirable to reduce the noise generated by the transmitter105by −160 dBm/Hz−(−173 dBm/Hz)=13 dB.

SUMMARY

A self-interference canceller (SIC) is incorporated into a transceiver to reduce or eliminate modem jamming when a transmitter in the transceiver transmits at high power levels. The SIC is configured to receive at a first input a transmitter noise reference signal including a self-interfering signal component generated by the transmitter, to receive at a second input a corrupted signal including the self-interfering signal component and a desired signal component generated by the transmitter, and to output a correction signal that resembles the self-interfering signal component. The correction signal is subtracted from the corrupted signal to generate a processed signal that is input to the modem. The SIC may be disabled when the output power of the transmitter is at a level below a predetermined threshold. The invention may be applied to a multi-RAT transceiver.

DETAILED DESCRIPTION

Hereafter, a wireless transmit/receive unit (WTRU) includes but is not limited to a user equipment (UE), mobile station, fixed or mobile subscriber unit, pager, or any other type of device capable of operating in a wireless environment. When referred to hereafter, a base station includes but is not limited to a Node-B, site controller, access point or any other type of interfacing device in a wireless environment.

The invention provides mitigation of self-interference caused by out-of-band transmitter noise leaking into the receive pass-band in a transceiver, such as a WTRU or a base station. The invention implements a reference receiver to sample the transmitter RF signal in the receiver band of interest. Digital baseband processing is used to adaptively subtract the self-interfering signal from the receive signal path prior to baseband modem processing.

The invention reduces the self-interfering signal that leaks into the receiver pass-band of a transceiver via the finite physical isolation of the duplexer, and parasitic paths or spatially through antennas, if more than one antenna is used on a device. A sample of the transmitted signal is used as a reference to a hybrid adaptive SIC. The receive path consists of a desired signal component s(t) and a coherent self-interfering signal component I(t). The SIC adaptively updates an equalizer weight vector to reduce the interference level at the input of the modem of the transceiver to ensure minimum receiver desensitization.

FIG. 2shows an example of a transceiver200that prevents the jamming of a modem240caused by a transmitter205and PA210in the transmit path of the transceiver200. Noise generated by the transmitter205and PA210is reduced such that the noise does not jam a desired low power signal when it is close to the receiver noise floor. The transceiver200may be incorporated into a WTRU or a base station. Besides the transmitter205and the modem240, the transceiver200may include a PA210, a duplexer215, an antenna220, an LNA225, a receiver230, a first ADC235, a coupler245, a bandpass filter248, a reference receiver250, a second ADC255, a hybrid adaptive SIC260, and an adder265. The adder may be incorporated into the hybrid adaptive SIC260, or may be a separate component that is external to the hybrid adaptive SIC260.

Referring toFIG. 2, the transmitter205outputs a signal that is amplified by the PA210and is routed to the antenna220via the coupler245and the transmit filter215A of the duplexer215. Signals received by the antenna120are amplified by the LNA225, down-converted to a baseband signal via the receiver230, converted to a digital signal275via the first ADC235. An equalizer output signal, (i.e., correction signal),285is output by the hybrid adaptive SIC260and is subtracted from the digital signal275before being outputted to a modem240. The noise in receive band at the PA210output is sampled by the coupler245, filtered by the bandpass filter248, down-converted to a baseband signal by the reference receiver250, converted to a digital signal280via the second ADC255and then input to the hybrid adaptive SIC260. The bandpass filter248rejects (i.e., attenuates) signals in the transmit band, and allows signals in the receive band to pass through with minimal loss.

The transceiver200ofFIG. 2may implement a hybrid least mean squared (LMS) correlation technique using the hybrid adaptive SIC260. The transceiver200is capable of reducing the self-interfering signal component I(t) by 6 dB or more below the noise floor of the receiver230, resulting in only a 1 dB of receiver desensitization that enables improved receiver performance, (e.g., an increased data rate). The hybrid adaptive SIC260prevents noise generated by the transmitter205from jamming the modem240by correlating a self-interfering signal component I(t) of the digital signal280with the digital signal275, which includes a desired signal component s(t) that is corrupted by the self-interfering signal component I(t), (i.e., s(t)+I(t)). The adder265removes the self-interfering signal component I(t) from the digital signal275by subtracting an equalizer output signal, (i.e., correction signal),285, which is generated by the hybrid adaptive SIC260to closely resemble the self-interfering signal component I(t), from the digital signal275, resulting in a processed digital signal270that is output by the adder265to a modem240.

Jamming of the modem240due to noise generated by the transmitter205only occurs at high power levels. Thus, there is no need for the hybrid adaptive SIC260to cancel noise generated by the transmitter205at low levels, because the noise is substantially below the noise floor of the receiver230. For example, when the output power of the transmitter205is reduced, (e.g. by 15 dB), the sensitivity degradation of the receiver230becomes negligible and the hybrid adaptive SIC260may be disabled by a transmit power control (TPC) signal290.

FIG. 3shows an example of a configuration of the hybrid adaptive SIC260used in the transceiver200ofFIG. 2. The hybrid adaptive SIC260may include a first correlator305, a maximum (max) LMS algorithm unit310, an equalizer315, a minimum (min) LMS algorithm unit320, a second correlator325, an LMS algorithm selection unit330and a delay unit335.

As shown in the example ofFIG. 3, the digital signal280, which includes the self-interfering signal component I(t), is delayed by the delay unit335in order to time-align with the digital signal275, which includes a desired signal component s(t) that is corrupted by the self-interfering signal component I(t), (i.e., s(t)+I(t)). A delayed digital noise sample signal340output by the delay335is fed into the equalizer315, the first correlator305the second correlator325.

The second correlator325outputs a correlation signal345to the min LMS algorithm unit320and the LMS algorithm selection unit330that indicates a value of the correlation, (e.g., signal-to-interference ratio (SIR)), between the processed digital signal270and the delayed digital noise sample signal340. The min LMS algorithm unit320generates a weight vector350based on the processed digital signal270and the value of the correlation signal345.

The first correlator305outputs a correlation signal355to the max LMS algorithm unit320and the LMS algorithm selection unit330that indicates the correlation between the processed digital signal270and the equalizer output signal285. The max LMS algorithm unit310generates a weight vector360based on the value of the correlation signal355.

At least one of the min LMS algorithm unit320and the max LMS algorithm unit310outputs a weight vector signal350or a weight vector signal360, respectively, that adjusts, (i.e., dynamically weights), the output signal285generated by the equalizer315such that it closely resembles the self-interfering signal component I(t). The equalizer output signal285is then subtracted from the digital signal275with the goal of completely eliminating the self-interfering signal component I(t).

Based on the values of the correlation signals345and355, the LMS algorithm selection unit330sends a weight vector select signal365to the equalizer315that determines whether to use the weight vector signal360from the max LMS algorithm unit310, or the weight vector signal350from the min LMS algorithm unit320. When the TPC signal290indicates that the power of the transmitter205is below a predetermined threshold, (e.g., between −10 dB to −20 dB), that would not cause the modem240to jam, the hybrid adaptive SIC260is disabled.

The performance of this method is limited when the level of the interfering signal component I(t) approaches the level of the desired signal component s(t). As a result, the minimum operating point of the min LMS algorithm unit320will remain close to the level of the desired signal component s(t), resulting in a 3 dB degradation in the performance of the transceiver200.

The hybrid adaptive SIC260adaptively selects between different multiple cost function criteria to achieve the optimum cancellation response at both high and low SIR.FIG. 4shows a hybrid cost “error” function. The min LMS cost function is illustrated by the convex function, and the max LMS function is illustrated by the concave function. The hybrid algorithm works by performing a joint optimization of both the min and max LMS cost functions. The optimization of the cost function is found by adapting the equalizer weights to achieve a minimum error at the output of the adder in the main signal path. The equalizer taps “Wk” are adjusted based on the gradient of the error signal ∇e(t)and constant α. The min LMS algorithm is described by Equation (1), and the max LMS algorithm is described by Equation (2).
Ŵk+1=Wk−αk·∇e(t), and  Equation (1)
Ŵk+1=Wk+αk·∇e(t);  Equation (2)
where k is an index describing the kth equalizer tap.

The error prediction used to minimize each cost function is based on Equation (3) as follows:

The min LMS algorithm initially searches for the desired operating point, but is limited by the dynamic noise and therefore cannot achieve this minimum bound. When this limit is achieved, the min LMS equalizer tap coefficients are fixed and the max LMS algorithm takes over to dynamically adjust the equalizer taps to achieve the desired max LMS operating point. The result is a cancellation of the self-interfering noise signal below the receiver noise floor enabling system performance comparable to that with no self-interfering signal.

The features of the hybrid adaptive SIC260described above can be extended to interface with multiple RATs.FIG. 5shows an illustration of a multi-RAT transceiver500. A respective coupler605,610,615is used at each transmitter output to obtain an RF sample from each interfering signal. A band select signal520is used to dynamically select and receive the band of interest and set the tuning of a reference receiver525. The reference baseband signal530is digitized by an ADC535and adaptively processed in the same way as described above. The hybrid adaptive SIC540is extended to N identical implementations to support interference cancellation of N RATs (bands). In the proposed architecture, either a single interfering RAT may be processed individually, or multiple RATs may be processed via a dynamic rotation of equalization updates.

By way of example, the embodiments herein may be implemented in a WTRU, base station, wireless network controller, at the physical layer, in the form of an application specific integrated circuit (ASIC), hardware, or digital signal processor (DSP), in an orthogonal frequency division multiplexing (OFDM)/multiple-input multiple-output (MIMO), wideband code division multiple access (WCDMA), global system for mobile communications (GSM), or IEEE 802.11-based system. The invention is applicable to data cards including high-speed downlink packet access, smart antennas, cell phones, smart phones, feature phones, laptops, or any other personal communication device.