Patent Description:
Self interference is a problem for wireless and other communications devices which attempt to send, e.g., transmit and receive at the same time using electrical or wireless signals. While different frequency bands may be used for sending, e.g., uplink, and receiving, e.g., downlink, some of the signal being transmitted may be received by a receiver of the device interfering with the receipt of signals being received from one or more other devices, Interference from the transmitter to the receiver of a device particularly in the case of a shared transmit and receive antenna or cable, or a transmit and receive antenna in close proximity between the transmitter and receiver which is often the case for antennas on mobile communications devices can create interference problems even when the transmit and receive frequency bands are different.

Attempts at canceling self interference by using one or more electronic circuits and filters implemented as electrical components operating in same frequency range as the signals being received and transmitted, e.g., radio frequency domain, have had limited success.

The generation of an interference cancelation signal using electrical components in the form of filters, etc., e.g., in the radio frequency domain, has several problems associated with it. For one thing the electrical circuit elements used to generate an interference cancelation signal may themselves radiate interference, particularly when dealing with signals in the RF frequency band, as wires and/or other components of a filter implemented as an electrical circuit operate as signal transmitters and receivers. Such additional self interference can be highly undesirable in a communications device which transmits and receives radio signals, e. g, using antennas, or electrical signals, e.g., using a electrical cable interface such as a coax cable, Ethernet cable or other non-optical cable. Another problem with the use of filters that operate in the RF band is that shielding within a small device to prevent the transmission of interference generated by such filters in the small device can be difficult to implement given space constraints.

Electrical filter circuits which may be used to generate an interference cancelation filter also have the disadvantage of being relatively bulky making it difficult to implement a large number of filter taps and/or separate delays in an electrical filter being used to generate an interference cancelation filter. For this reason attempts to generate an interference cancelation signal using electrical components operating in the RF frequency domain are often limited to using filters with very few taps and/or delays. Furthermore attempts to pack large numbers of RF circuits or filter taps in a small space can further complicate the problem of interference from one component leaking to another component via unintended radio frequency interaction between nearby components, e.g., with one component acting as an unintended RF transmitter and another component acting as an unintended RF receiver.

Power issues with splitting an electrical signal are also of concern as is thermal noise with electrical components that may be used to generate an interference cancelation signal using electrical components. If a weak interference signal is to be generated for one or more received signal components or frequencies the thermal noise of the electrical circuits may preclude the generation of a meaningful interference cancelation signal since the thermal noise of the electrical circuits used to generate the interference signal may, in some cases, exceed the expected interference signal to be canceled. Moreover, insertion losses in RF systems with couplers and/or microstrips can be high and should normally be impedance-matched carefully, keeping the resulting capacitance and inductances in mind, making the use of such components increasingly more challenging for higher RF frequencies.

Another problem with implementing filters as electrical circuits in the RF range is that it may be difficult to design or implement electrical circuits with the desired filter characteristics since frequency range of the filters may not be uniform in the desired frequency range that may be required to generate an appropriate interference cancelation signal.

While attempts to determine an appropriate interference cancelation signal in a digital RF domain may be attempted, to generate an accurate analog interference cancelation signal to be combined with a received signal may require digital to analog converters with a very large frequency range and resolution which can be costly and/or difficult to implement.

A paper entitled "<NPL>, discloses an optical self-interference cancellation system to realize full-duplex spectrum sensing in cognitive radios. The optical system is an analog radiofrequency front-end module, which cancels in-band self-interference, enabling a radio to simultaneously transmit and receive signals. <CIT> discloses a system and method for cancelling broadband in-band RF interference that operates in a dynamically changing multipath environment.

In view of the above discussion it should be appreciated that there is a need for improved methods and apparatus which can be used for self interference cancelation in which communicate using radio frequency signals. In particular it would be desirable if methods and/or apparatus could be developed which address, overcome or reduce one or more of the above discussed problems associated with generating interference cancelation signals using electrical circuits and/or filters operating in the radio frequency domain and/or require the conversion of a digital interference cancelation signal generated in the RF domain to an analog interference cancelation signal using a high resolution electrical digital to analog signal converter.

Optional features are defined in the dependent claims. Methods and apparatus are described which involve the use of one or more optical circuits, e.g., optical filters, to generate an analog interference cancelation signal which can be combined with a received analog signal as part of a self interference cancelation operation. The methods and apparatus are well suited for use in a wide range of communications devices which communicate in an RF frequency band. In the present application the RF frequency band is to include frequencies from <NUM> to <NUM>. Optical frequencies are above the <NUM> frequency.

The interference techniques are well suited for devices which communicate using antennas as well as those which communicate using RF frequencies over other media such as wire cables. The interference cancelation techniques can be used with wireless communications devices and/or wired communications devices. In the case of wireless communications devices a variety of antenna configurations can be used with the interference cancelation apparatus and methods. For example a single shared antenna may be used for transmitting and receiving signals, separate transmit and receive antennas may be used and/or the communications device may use one or more MIMO (multiple in multiple out) antenna configurations. Wired communications system with which the interference cancelation techniques may be used include Ethernet, coax and/or other wired communications systems where the non-optical conductors, e.g., metal, wire conductors or RF waveguides are used to communicate signals.

Communications devices may be, e.g. mobile devices such as cell phones which may communize wirelessly to other user devices or base stations, fixed devices such as stationary base stations or a wide variety of other types of communications devices which communicate, e.g., send and/or receive, RF signals.

In various embodiments, by using one or more optical filters to generate an interference cancelation signal in the optical domain, and then using an optical to electrical converter to generate an analog RF interference cancelation signal from an optical interference cancelation signal one or more of the problems associated with electrical RF filter circuits can be avoided with regard to generation of an interference cancelation signal.

In various embodiments an analog, or optionally digital, RF signal to be transmitted is converted into an optical signal. The optical signal is then filtered using one or more optical filters of an optical filter assembly. Amplitude and/or gain of one or more optical filters of the optical filter assembly are controlled taking into consideration communications channel conditions. Gain control may result in signal amplification or attenuation depending on the control value, e.g., coefficient, used to control the optical amplifier. Phase of an optical signal may also be controlled, e.g., through the use of an optical amplifier or another element. Different optical filters may and often are controlled to have different delays and/or gains. The optical filter assembly acts as and sometimes is a multi-tap filter. Different taps, e.g., parallel filters, in the optical filter assembly may be, and sometimes are, controlled to have different gains. Since the filters, e.g., taps, of the optical filter assembly are implemented in the optical domain they have several advantages over electrical filters. For example, they can be implemented without concern for radiating RF signals and interference to other components since the optical signals will not be picked up by RF signal components such as regular copper wires. Furthermore, optical filters can be implemented in a relatively small space and at a relatively low cost allowing for the use of optical filter assemblies with a relatively large number of filter taps as compared to electrical filter circuits. For example, in some embodiments the optical filter assembly used to generate an interference cancelation signal includes <NUM>, <NUM>, <NUM>, <NUM> or even more parallel optical filters working as separate controllable filter taps in a relatively small space, e.g., inside the housing of a cell phone or other mobile communications device.

Since optical filter circuits do not suffer from the same thermal noise issues of electrical filter circuits, the optical filter assembly can be used in at least some embodiments to generate reliable interference cancelation signals with relatively low power at one or more frequencies where the power level might be below that of the thermal noise floor of electrical filter components which might be used in a filter.

The use of optical filters allows for multiple taps with different gains and/or delays to be used and controlled using optical gain and delay control techniques which are easily implemented using known optical techniques and which can allow for rapid changes in filter gain and/or delay values to reflect detected changes in channel conditions.

While numerous different features and examples are described all features need not be used in all embodiments. For example, in some embodiments fixed optical filter weights and delays are used while in other embodiments filter weights and delays are changed dynamically in response to detecting changes in channel conditions. Fixed gain and delay filter embodiments are well suited for static conditions where a device may be stationary and the communications channel does not change significantly over time while dynamic control of optical gains and delays is well suited for dynamic environments where channel conditions between a receiver and transmitter of a device are likely to change, e.g., due to device movement or changes in the environment.

Given that the radio frequency is considerably lower than the optical frequencies used in generating the interference cancelation signals, reliable and generally uniform filter characteristics can be achieved by using optical filters.

In addition to one or more of the above benefits, generation of an interference cancelation signal in the optical domain and then conversion of the analog optical signal to an analog radio interference cancelation signal using an optical to electrical signal converter allows an analog RF interference cancelation signal to be generated without the need for a high resolution and potential expensive electrical digital to analog converter which might be required if a digital RF interference cancelation signal was generated and then needed to be converted to an analog RF interference signal prior to use.

An exemplary implementation allows for full duplex communications through mitigation of the self-interference. A feature of some but not all embodiments, is to reconstruct a negative copy of the interference seen at the receiver through linear and/or non-linear filtering operations performed in an optical domain on a copy of the transmitted signal. This operation is facilitated by the fact that the transceiver has knowledge of the transmit signal at various points in the transmit chain. In some but not all embodiments, channel estimation is used to determine the characteristics of the channel between the transmitter and the receiver and to control one or more optical gains and/or delays based on the channel conditions detected at a given point in time. Thus as the channel changes, the optical filter components can be and sometimes are modified in terms of gains and/or delays as part of generating the interference cancelation signal. While a negative analog version of the interference is generated in some embodiments to facilitate combining with a received signal to cancel interference, in other embodiments a positive version of the interference signal is generated for use as an interference cancelation signal and the signal is subtracted from the received signal to provide interference cancelation,.

An exemplary communications device, in accordance with some but not all embodiments, comprises: a radio frequency signal to optical signal converter having a radio frequency input configured to receive a radio frequency signal to be communicated and an optical output for outputting a first optical signal generated from said radio frequency signal to be communicated; an optical filter assembly for filtering said first optical signal; and an optical to radio frequency converter coupled to an output of said optical filter assembly, said optical to radio frequency converter for generating a radio frequency interference cancelation signal from a second optical signal output by said optical filter assembly.

While various embodiments have been discussed in the summary above, it should be appreciated that not necessarily all embodiments include the same features and some of the features described above are not necessary but can be desirable in some embodiments. Numerous additional features, embodiments, and benefits of various embodiments are discussed in the detailed description which follows.

Methods and apparatus for performing self interference cancellation on radio frequency or other signals are described. While the signals which are transmitted and received are radio frequency signals in at least some embodiments, radio frequency to optical frequency conversion and optical signal processing is used in some embodiments to facilitate generation of a radio frequency signal interference cancelation signal. The use of optical filters allows for a wide range of frequencies to be supported as part of generating the interference cancelation signal with an optical signal being converted to an analog RF signal without the need for generation of a digital RF version of the interference cancelation signal in at least some but not necessarily all embodiments.

Optical filters may be implemented in a cost effective manner allowing for a relatively larger number of optical filters to be used in parallel, e.g., as part of a multi-tap optical filter, in generating the interference cancelation filter. While generation of the interference cancelation signal occurs to a large extent in the optical domain, prior to combining with the received radio frequency signal the optical interference cancelation signal is converted to the radio frequency domain to facilitate interference cancelation in the RF domain.

Thus in various embodiments interference caused to a receiver of a device, by the transmissions of a signal using from the transmitter of the same device, is partially or full achieved by using knowledge of the to transmitted signal, along with multipath delay information to control multiple optical filters, to generate from the transmitted signal an interference cancelation signal which can be combined with a received signals to cancel or reduce the self interference from the received radio frequency signal.

The interference cancelation signal can be a negative copy of the received interference signal to facilitate subtraction from a received signal to reduce the interference to received signal. Alternatively the interference cancelation signal maybe a positive estimate of the received signal which is combined though a negative input of a combining circuit with the received signal to achieve the desired interference cancelation.

In case of full duplex communication, the transmit and receive chains maybe close to each other, e.g., in the same device housing and connected to the same transceiver circuit. The transmit power required to achieve successful communication, e.g., successful receipt of signals from another device is a function the amount of isolation between the transmitter and receiver of a device which can be expressed in terms of the path loss between a device's transmitter and receiver.

For example, in case of wireless local area network communication systems, the transmit power maybe about 200mW (23dBm) while the receiver maybe required to have a sensitivity of about -85dBm when the radios are operating over a bandwidth of <NUM>. This required transmit power level will affect the minimum possible distance between the transmitter and receiver dependent on the medium and the frequency of the carrier. If the transmitter and receiver are operating at the same time, in some systems the interference from transmitter to receiver maybe as high as 108dB or more if there is a direct coupling between the transmit and receiver circuit on the transceiver. In such an exemplary embodiment for a true full duplex operation, the receiver may be required to cancel the self interference by 108dB and reduce the interference below the noise floor of the receiver. Such interference cancelation will then allow for the receiver to decode the desired signal from other nodes.

Attempts to perform self-interference cancellation completely in the radio frequency domain suffer from responsiveness and difficulty in supporting a wide range of frequencies in the RF domain. Attempts at interference in the digital radio frequency domain suffer from limitations due to the dynamic range of the digital-to-analog converter (DAC) and analog-to-digital (ADC) converter used in converting radio frequency digital signals to an analog interference cancelation signal. The effective number of bits of these converters drive the maximum signal-to-noise (SNR) ratio. For example, in case where the interference power is 100dB higher than the receive noise floor, the digital domain cancellation with <NUM> effective number of bits at ADC can be limited to about 60dB. Moreover, the high power interference signal overdrives the receive chain and drives it to its non-linear region and over saturates the ADC. This requires for a multi-stage interference cancellation architecture where there is a need for a RF/analog frontend canceller that reduces the interference signal power to a range where the digital interference cancellation can cancel the remaining interference signal while preserving the desired receive signal. The present invention avoids some of the problems associated with DAC of an RF interference cancelation signal by converting an optical interference cancelation signal into an analog interference cancelation signal. The analog interference cancelation signal generated in such a manner can include a wide range of frequencies allowing for good interference cancelation.

<FIG> is a drawing of an exemplary communications device <NUM> including self-interference cancellation capability in accordance with an exemplary embodiment. Exemplary communications device <NUM> includes a transceiver circuit <NUM> a processor <NUM>, e.g., a CPU, a memory <NUM>, and an assembly of modules <NUM>, e.g., assembly of hardware modules, e.g., circuits, coupled together via a bus <NUM>, over which the various elements <NUM>, <NUM>, <NUM> may communicate data and information. Memory <NUM> includes a communications routine <NUM> configured to control communications operations for the communications device <NUM> including controlling operation of the transceiver circuit <NUM>, a control routine <NUM>, an assembly of modules <NUM>, e.g., an assembly of software modules, and data/information <NUM>. Data/information includes device information <NUM>, includes interface information including optical filter component information and antenna information, etc., and communications data/information <NUM> includes, e.g., RF frequency information, channel type information, channel conditions, determined filter coefficients, received signal information, transmitted signal information, generated radio frequency interference cancellation signal information, etc.. In some embodiments, some information stored in memory <NUM> is also stored in local memory within transceiver circuit <NUM>. In some embodiments, processor <NUM>, e.g., a CPU, executes routines including software modules included in memory <NUM> to control the communications device <NUM> to implement a method in accordance with the present invention, e.g., control the transceiver circuit <NUM> to implement a radio frequency interference cancellation method which includes the use of an optical filter assembly. In some embodiments, one or more of steps of the exemplary method are implemented alternatively by one or more hardware modules, e.g., circuits, included in assembly of modules <NUM>.

Transceiver circuit <NUM> includes a bus interface <NUM> and a communications interface <NUM>. Bus interface <NUM> couples the transceiver circuit to bus <NUM>. Communications interface <NUM> couples the transceiver circuit <NUM> to one or more or all of: an antenna assembly <NUM>, a waveguide <NUM> and a wire/cable <NUM>. In some embodiments, the antenna assembly is included as part of the communications device <NUM>. Antenna assembly <NUM> includes one or more antennas (<NUM>,. In some embodiments, antenna assembly <NUM> includes a single antenna <NUM> which is used by both the transmitter and receiver of the transceiver circuit <NUM>. In some embodiments, that antenna assembly <NUM> includes a transmit antenna <NUM> and a receive antenna <NUM>. In some embodiments, the antenna assembly includes a plurality of transmit antennas and a plurality of receive antennas. In some such embodiments, the antenna assembly <NUM> and the transceiver circuit <NUM> support MIMO operations.

<FIG> illustrates an exemplary transceiver circuit <NUM>' in accordance with an exemplary embodiment. Transceiver circuit <NUM>' includes communications interface <NUM>' and bus interface <NUM>. In some embodiments, transceiver circuit <NUM>' is transceiver circuit <NUM> of <FIG>, and communications interface <NUM>' is communications interface <NUM> of <FIG>.

<FIG> and <FIG> illustrate two exemplary variants of a wireless transceiver architecture that includes one transmit chain and one receiver chain. The realization shown in drawing <NUM> of <FIG> illustrates a two antenna approach where the transmitter chain and the receiver chain use separate antennas <NUM>, <NUM>, respectively. The coupling between transmit and receive is driven by the distance between the antennas, the antenna type and size. In case of the realization shown in drawing <NUM>' in <FIG>, , the transmit chain and the receive chain use a single antenna <NUM>. The antenna <NUM> is coupled to the transmit and receive chains using a circulator <NUM> where the circulator provides some degree of isolation between the transmit signal <NUM> and receive signal <NUM>. The high power self-interference seen at the receive chain is driven by the isolation provided by the circulator <NUM> and the reflection from the antenna <NUM> that leaks back in to the receive chain.

Drawing <NUM> of <FIG> illustrates an exemplary transceiver circuit <NUM>" in accordance with an exemplary embodiment. Transceiver circuit <NUM>" is, e.g., transceiver circuit <NUM> of <FIG> and/or transceiver circuit <NUM>' of <FIG>. Transceiver circuit <NUM>" includes communications interface <NUM>", bus interface <NUM>, transmit (TX) digital baseband (BB) circuit <NUM>, TX digital BB to analog BB circuit <NUM>, TX analog BB to radio frequency (RF) circuit <NUM>, coupler device <NUM>, signal combiner/coupler device <NUM>, RX RF to analog BB circuit <NUM>, RX analog BB to digital BB circuit <NUM>, RX digital BB circuit <NUM>, RF up-converter and interference cancellation filter circuit <NUM>, and channel estimator, filter, e.g., digital filter, and filter control circuit <NUM>, coupled together as shown in <FIG>. Signal combiner <NUM> is configured to combine a received radio frequency signal <NUM> with the radio frequency interference cancellation signal <NUM> to produce a recovered radio frequency signal <NUM>. In various embodiments, the signal combiner <NUM> is configured to subtract the radio frequency interference signal <NUM> from the received radio frequency signal <NUM> to generate the recovered radio frequency signal <NUM>.

A high level overview of the transceiver circuit <NUM>" of <FIG> will now be described. The transceiver circuit <NUM>" comprises of a transmit chain and the receive chain. In the transmit chain, the transmit digital baseband circuit <NUM> receives, via bus interface <NUM>, input data <NUM> to be transmitted in the form of bits, converts the bits into a digital baseband waveform <NUM>, which is output to the TX digital BB to analog BB circuit <NUM>. The TX digital baseband circuit <NUM> performs encoding and modulation of the received input data <NUM>. The encoding and modulation performed by TX digital baseband circuit <NUM> uses, e.g. orthogonal frequency division multiplexing, CDMA, or another encoding and modulation scheme. The TX digital BB to analog BB circuit <NUM>, e.g., a filter and digital to analog converter (DAC) assembly, converts the digital signal <NUM> into analog baseband signal <NUM>, which is output to TX analog BB to RF circuit <NUM>. Analog baseband signal <NUM> is received by TX analog BB to RF circuit <NUM> and subsequently up-converted to the operating RF frequency using a direct conversion or an intermediate frequency converter included in circuit <NUM>. The up-converted RF signal <NUM> is the output of a power amplifier included in circuit <NUM>. The up-converted RF signal <NUM> is coupled or divided using a device <NUM> where the pass-through signal <NUM> goes to the communication interface <NUM>" and the tapped signal <NUM> is fed to the RF up-converter and interference cancellation filter circuit <NUM>. The RF signal <NUM> in the communication interface <NUM>" passes through to the antenna <NUM> in case of this realization.

Receive antenna <NUM> receives a wireless RF signal and outputs received signal <NUM> into in to interface <NUM>" toward the receive chain. On the receive side of the transceiver circuit <NUM>", the receive signal <NUM> from the communication interface <NUM>" feeds in to a coupler or combiner <NUM> which is <NUM> port device. Coupler or combiner <NUM> is responsible for combining input signal <NUM>, which is an output of the RF-up converter and interference cancellation filter circuit <NUM>, and input signal <NUM>, which is the signal received via receive antenna <NUM>, to generate output RF signal <NUM>. The output RF signal <NUM> is fed into the RX RF to analog BB circuit, <NUM>, which is an RF down-converter, that down-converts the RF signal <NUM> into a baseband analog signal <NUM>. This baseband analog signal <NUM> is received, filtered and sampled by RX analog BB to digital BB circuit <NUM>, which generates and outputs sampled output signal <NUM>. The sampled output signal <NUM> is fed into the RX digital BB circuit <NUM> including a digital receive processor that is responsible for demodulation and decoding.

RF Signal <NUM>, a copy of the transmit signal <NUM> is fed into the RF up-converter and interference cancellation filter circuit <NUM>. T RF Up-converter and interference cancellation filter circuit <NUM> produces signal <NUM> which is a negative copy or near negative copy of the interference signal received as a component of receive signal <NUM>, said interference signal being an effect of transmission of signal <NUM>. The combining of the negative copy <NUM> with the received signal <NUM> using a combiner/coupler device <NUM> results in cancellation of interference that is caused by the transmitter of transceiver circuit <NUM>" at the receiver of transceiver circuit <NUM>".

Channel estimator, filter and filter control circuit <NUM> interfaces with the digital processing block of transmit digital baseband circuit <NUM> and with the digital processing block of receive digital baseband circuit <NUM>. The channel estimator, filter, and filter control circuit <NUM> is responsible for reconstruction of the residual interference signal that is observed at the sampled signal <NUM> in the RX digital baseband circuit <NUM>. The channel estimator, filter and filter control circuit <NUM> is responsible for the measurement and training of a digital filter included in circuit <NUM> and the RF cancellation filter included in circuit <NUM>. Channel estimator, filter, and filter control circuit <NUM> uses input signal <NUM>, a copy of the digital transmit signal, and received sampled signal <NUM> to determine the effect of the transceiver circuit <NUM>" and antennas (<NUM>, <NUM>), determine the channel that causes interference, and determine the appropriate coefficients to be programmed to the RF interference cancellation filter included in circuit <NUM>. The determined appropriate coefficients are communicated in signal <NUM> from channel estimator, filter and filter control circuit <NUM> to RF up-converter and interference cancellation filter circuit <NUM>. Channel estimator, filter and filter control circuit <NUM> also recreates a negative copy <NUM> of the interference signal, which it sends to RX digital BB circuit <NUM> to be subtracted from the received signal <NUM>. RX digital BB circuit <NUM> receives the recreated negative copy <NUM> of the interference signal and subtracts the recreated negative copy <NUM> of the interference signal from received signal <NUM>, as part of its processing. Circuit <NUM> further generates digital data out signal <NUM> and outputs digital data out signal via interface <NUM>.

Drawing <NUM>' of <FIG> illustrates exemplary transceiver circuit <NUM>‴ which implements a transceiver architecture where the communications interface <NUM>"' includes a <NUM>-port circulator device <NUM>. The circulator <NUM> is responsible for the creation of isolation between the ports in one direction. This created isolation prevents the transmit RF signal <NUM> leaking to the receive RF signal <NUM>. The circulator based design facilitates simultaneous transmission and reception using a single antenna <NUM>.

Drawing <NUM>' of <FIG> illustrates exemplary transceiver circuit <NUM>‴ in accordance with an exemplary embodiment. Transceiver circuit <NUM>"' is, e.g., transceiver circuit <NUM> of <FIG> and/or transceiver circuit <NUM>' of <FIG>. Transceiver circuit <NUM>"' includes communications interface <NUM>"' which includes circulator <NUM>, bus interface <NUM>, transmit (TX) digital baseband (BB) circuit <NUM>, TX digital BB to analog BB circuit <NUM>, TX analog BB to radio frequency (RF) circuit <NUM>, coupler device <NUM>, combiner/coupler device <NUM>, RX RF to analog BB circuit <NUM>, RX analog BB to digital BB circuit <NUM>, RX digital BB circuit <NUM>, RF up-converter and interference cancellation filter circuit <NUM>, and channel estimator, filter, e.g., digital filter, and filter control circuit <NUM>, coupled together as shown in <FIG>. Signal combiner <NUM> is for combining a received radio frequency signal <NUM> with the radio frequency interference cancellation signal <NUM> to produce a recovered radio frequency signal <NUM>. In various embodiments, the signal combiner <NUM> is configured to subtract the radio frequency interference signal <NUM> from the received radio frequency signal <NUM> to generate the recovered radio frequency signal <NUM>.

A high level overview of the transceiver circuit <NUM>"' of <FIG> will now be described. The transceiver circuit <NUM>"' comprises of a transmit chain and the receive chain. In the transmit chain, the transmit digital baseband circuit <NUM> receives, via bus interface <NUM>, input data <NUM> to be transmitted in the form of bits, converts the bits into a digital baseband waveform <NUM>, which is output to the TX digital BB to analog BB circuit <NUM>. The TX digital baseband circuit <NUM> performs encoding and modulation of the received input data <NUM>. The encoding and modulation performed by TX digital baseband circuit <NUM> uses, e.g. orthogonal frequency division multiplexing, CDMA, or another encoding and modulation scheme. The TX digital BB to analog BB circuit <NUM>, e.g., a filter and digital to analog converter (DAC), converts the digital signal <NUM> into analog baseband signal <NUM>, which is output to the transmit analog baseband to RF (TX analog BB to RF) circuit <NUM>. Analog baseband signal <NUM> is received by the TX analog BB to RF circuit <NUM> and subsequently up-converted to the operating RF frequency using a direct conversion or an intermediate frequency converter included in circuit <NUM>. The up-converted RF signal <NUM> is the output of a power amplifier included in circuit <NUM>. The up-converted RF signal <NUM> is coupled or divided using a device <NUM> where the pass-through signal <NUM> goes to the communication interface <NUM>‴ and the tapped signal <NUM> is fed to the RF up-converter and interference cancellation filter circuit <NUM>. The RF signal <NUM> in the communication interface <NUM>‴ passes through circulator <NUM> to the antenna <NUM> in case of this realization.

Antenna <NUM> receives a wireless RF signal and outputs received signal into circulator <NUM> of interface <NUM>", which sends the received signal <NUM> toward the receive chain. On the receive side of the transceiver circuit <NUM>"', the receive signal <NUM> from the communication interface <NUM>‴ feeds into a coupler or combiner <NUM> which is <NUM> port device. Coupler or combiner <NUM> is responsible for combining input signal <NUM>, which is an output of the RF-up converter and interference cancellation filter circuit <NUM>, and input signal <NUM>, which is the signal received via antenna <NUM>, to generate output RF signal <NUM>. The output RF signal <NUM> is fed into the RX RF to analog BB circuit <NUM>, which is an RF down-converter, that down-converts the RF signal <NUM> into a baseband analog signal <NUM>. This baseband analog signal <NUM> is received, filtered and sampled by RX analog BB to digital BB circuit <NUM>, which generates and outputs sampled output signal <NUM>. The sampled output signal <NUM> is fed into the RX digital BB circuit <NUM> including a digital receive processor that is responsible for demodulation and decoding.

RF Signal <NUM>, a copy of the transmit signal <NUM> is fed into the RF up-converter and interference cancellation filter circuit <NUM>. RF Up-converter and interference cancellation filter circuit <NUM> produces signal <NUM> which is a negative copy or near negative copy of the interference signal received as a component of receive signal <NUM>, said interference signal being an effect of transmission of signal <NUM>. The combining of the negative copy <NUM> with the received signal <NUM> using a combiner/coupler device <NUM> results in cancellation of interference that is caused by the transmitter of transceiver circuit <NUM>‴ at the receiver of transceiver circuit <NUM>"'.

Channel estimator, filter and filter control circuit <NUM> interfaces with the digital processing block of transmit digital baseband circuit <NUM> and with the digital processing block of receive digital baseband circuit <NUM>. The channel estimator, filter, and filter control circuit <NUM> is responsible for reconstruction of the residual interference signal that is observed at the sampled signal <NUM> in the RX digital baseband circuit <NUM>. The channel estimator, filter and filter control circuit <NUM> is responsible for the measurement and training of a digital filter included circuit <NUM> and the RF cancellation filter included in circuit <NUM>. Channel estimator, filter, and filter control circuit <NUM> uses input signal <NUM>, a copy of the digital transmit signal, and received sampled signal <NUM> to determine the effect of the transceiver circuit <NUM>"' and antenna <NUM>, determine the channel that causes interference, and determine the appropriate coefficients to be programmed to the RF interference cancellation filter included in circuit <NUM>. The determined appropriate coefficients are communicated in signal <NUM> from channel estimator, filter and filter control circuit <NUM> to RF up-converter and interference cancellation filter circuit <NUM>. Channel estimator, filter and filter control circuit <NUM> also recreates a negative copy <NUM> of the interference signal, which it sends to RX digital BB circuit <NUM> to be subtracted from the received signal <NUM>. RX digital BB circuit <NUM> receives the recreated negative copy <NUM> of the interference signal and subtracts the recreated negative copy <NUM> of the interference signal from received signal <NUM>, as part of its processing. Circuit <NUM> further generates digital data out signal <NUM> and outputs digital data out signal via interface <NUM>.

The communication interface, e.g., communications interface (<NUM>, <NUM>', <NUM>", <NUM>‴‴) of a transceiver circuit (<NUM>, <NUM>' ,<NUM>", <NUM>"') can take many forms to realize coupling into a wireless channel or into a cable plant in case of a wired system.

The RF up-converter and interference cancellation filter circuit <NUM> and the channel estimator, filter, e.g., digital cancellation filter, and filter control circuit <NUM>, described with respect to <FIG> and <FIG>, are shown to cancel the interference from one transmit chain to one receive chain. However, same principle regarding interface can be, and in some embodiments is, used to cancel interference from many transmit chain to many receive chain. Thus in some embodiments, the transceiver circuit, e.g., transceiver circuit <NUM> includes a plurality of transmit chains and a plurality of receive chains. In some such embodiments, RF Up-converter and interference cancellation filter circuit <NUM> and channel estimator filter, and filter control circuit <NUM> perform are used to cancel interference from the plurality of transmit chains to the plurality of receive chains.

<FIG> includes diagram <NUM> which illustrates an exemplary delay profile of an exemplary received self interference signal. The dely profile shows the contribution of <NUM> reflections of the original transmitted signal but <NUM>, <NUM> or even more reflections may be received potentially with different delays from the original transmit time. For this reason the ability to support a larger number of filter taps and/or delays can be desirable. As should be appreciated, the multipath of a transmitted signal will be perceived at the receiver not as a single interference signal but as multiple different interference signals received with varying delays from the original transmit time and different received amplitudes since different paths may have different amounts of loss.

The vertical axis in <FIG> represents the amplitude of a received interfering copy of a transmitted signal while the horizontal axis represents time. The larger the time value the longer the delay in time from the point in time at which the interfering signal was transmitted by the device receiving the interfering version, e.g., reflection, of the transmitted signal. Each reflection maybe considered a copy of the original signal.

In the <FIG> example is can be seen that copies of a transmitted signal will be received at a delay (T1) from the original transmission. Another copy will be received at time (T2), another copy received at T3 and so on through time period T8. The amplitude shows the relative strength of each received signal with each received signal being a fraction of the overall initial transmit power. The interference profile affecting the received signal may and often does depend on objects in the environment and their motion in the environment which can affect signal reflections. The delay profile can at least be partially predicted based on channel information. since the delays are a function of the channel between a device's transmitter and receiver. Thus, channel information and channel estimates can be used to determine the delay profile which will be encountered. Channel estimation information can and in some embodiments is used in determining filter coefficients used to control one or more filters responsible for generating an interference cancelation signal.

By knowing the delay profile shown in <FIG> it is possible to predict how much signal energy of a transmitted signal will be received at a time period following the known transmission time period.

By using channel information, e.g. which can be used to determine when and how much a signal transmitted by a device will be received by the receiver of the device, it is possible to generate a composite waveform representing the excepted contribution at a particular receive time of the interference from the previously transmitted signals given that the transmitted waveforms, transmit power levels and interference delay profile associated with a device can be known and/or estimated based on a channel estimate generated by the device suffering from the self interference.

Using the transmitted signal information including transmitted waveform and power level information along with channel estimation information, in accordance with the invention, gain and delay filter coefficients are determined which can and are used to control one or more optical filters to generate interference cancelation waveforms which can be converted from an optical signal to an analog RF signal. The analog RF interference cancelation signal is then combined with a received signal to cancel some or all of the self interference.

Various exemplary circuits and devices, at least some of which use optical filters, for implementing self interference cancelation will be discussed further below.

In various embodiments, RF photonics, is used in a hybrid RF/optical approach that processes RF signals in an optical domain and then coverts the optical signals to the RF domain to generate an interference cancelation signal that is well suited for combining with a received RF signal. In the RF photonics system, an analog RF signal defines the envelope of an optical carrier wave, typically around <NUM> THz. Therefore, even multi-GHz ultra-wideband signals occupy a fractional bandwidth of less than <NUM>-<NUM>. Similarly, millimeter-wave baseband frequencies are far smaller than the typical bandwidth of optical components. Therefore, RF photonics is a powerful approach that is transparent to the RF baseband frequency, provided that a broadband modulator is used. Space-wise, optical delay lines in the form of optical fibers can be, and in some embodiments are, coiled into centimeter loops, and multiple delay lines can be, and in some embodiments are, stacked together vertically, and packed into a footprint that is <NUM> to <NUM> times smaller than microwave delay lines for a <NUM>-tap cancellation filter. Unlike the microwave filter, increasing the tap number from <NUM> to <NUM> in a RF-photonic filter only increases the height of the system, and allows for much better analog cancellation without increasing system footprint. Another important feature of RF photonic link is its fundamentally unidirectional nature, i.e. the signal path is fixed from the optical modulator (RF-to-optics) towards the optical detector (optics-to-RF), since neither device operates in a reversible fashion. Besides these technical advantages, RF-photonic approach has also benefited economically from the tremendous progress with investments in long-haul telecommunication industry, in terms of performance improvement and cost reduction. Besides addressing the challenges directly related to full-duplex transceiver, RF photonic systems also enjoy several additional advantages unique to its hybrid architecture. First, at high power, laser source provides an overall gain to the RF transfer function, which can be, and in some embodiments are, adjusted on demand. Secondly, using coherent RF photonic systems, full complex-valued filter coefficients can be, and in some embodiments are, realized by adjusting the optical phase, which only requires sub-micron displacement and can be realized with time constants less than <NUM>. More recently, on-chip optical signal processing has been realized via opto-mechanical effects: a mm long chip can provide the sample processing power which previously required <NUM> meters of optical fibers.

Active analog cancellation currently provides an additional <NUM>-35dB cancellation through an adaptive RF filter controlled by algorithms running on a processor which subtracts a reproduced copy of the remaining interference from the received signal. This RF filter typically includes an array of programmable delay lines followed by programmable attenuators, with the digital control loop running on a processor that tunes the delay and attenuation coefficients to minimize residual interference. Since these coefficients mimic the effect of all scattering paths between the transmitter and receiver, in some embodiments, the received signal is monitored, e.g., continuously monitored, and these coefficients are tuned, e.g., continuously tuned, to adapt with the changing environment. The active analog cancellation using a novel RF-photonic filter, in accordance with various embodiments, of the present invention, is expected to provide more than 50dB of cancellation over a flexible bandwidth from <NUM> to <NUM>.

The <NUM>+dB cancellation, a much improved performance from state-of-art active analog cancellation filter allows the potential elimination of RF circulators and the use of simpler and broadband RF isolator instead. The superior cancellation performance is realized by an IIR RF-photonic filter, using a configuration shown in an exemplary embodiment of <FIG>. A <NUM>-tap IIR filter, producing the numerator of the IIR response, is made possible by the inherent space-efficiency of optical delay lines. This filter also provides far greater frequency resolution than that of state-of-art active cancellation filters. In some embodiments, variable optical attenuators are used to adjust the attenuation coefficients, and negative coefficients are generated through a balanced photo-detector. In addition, in some embodiments, a 4th-order fiber-optic ring resonator, also with adjustable attenuation coefficients, is used to realize the denominator response of the IIR filter. The added feedback provides additional cancellation beneficial to multi-echo interference between strong scatterer and antennas. Bandwidths of the optical delay lines and attenuators exceed 10THz, thus the RF filter bandwidth is largely determined by the bandwidth of the electro-optical modulator and the photo-detector, which is been demonstrated to be more than <NUM>. Such large bandwidth not only allows the RF photonic analog cancellation filter to operate in a carrier frequency agnostic fashion, but also enables it to be readily extended towards higher carrier frequencies and ultra-wide bandwidth, beyond the <NUM> limit of current ferrite technology.

Various features of the present invention and the proposed approach are good with regard to: <NUM>) Delay bandwidth: the optical bandwidth over which a certain delay can be achieved; <NUM>) Maximum delay: the maximum achievable delay value; <NUM>) Fractional delay: the absolute delay value divided by the pulse width or bit time. This is important to the delay/storage capacity; <NUM>) Delay range: the tuning range that the delay can be achieved (from minimum value to maximum achievable value); <NUM>) Delay resolution: the minimum incremental delay tuning step; <NUM>) Delay accuracy: the precision percentage of the actual delay to that of the desired delay value; <NUM>) Delay reconfiguration time: the amount of time it takes to switch a delay from one state to another steady state; <NUM>) Loss over delay: The amount of loss incurred per unit delay. Lower loss per unit delay is desired.

<FIG> illustrates an exemplary RF-up converter and interference cancellation filter circuit <NUM>' in accordance with an exemplary embodiment, which is one exemplary realization of the RF filter <NUM> included in an exemplary transceiver circuit <NUM>, <NUM>' <NUM>" or <NUM>"'.

RF up-converter and interference cancellation filter circuit <NUM>' includes a laser <NUM>, a radio frequency (RF) to optical signal converter <NUM>, an optical filter assembly <NUM> and an optical to radio frequency (RF) converter <NUM> coupled together as shown in <FIG>. In some embodiments, laser <NUM> and RF to optical converter <NUM> are replaced by directly modulated laser <NUM>.

Radio frequency signal to optical signal converter <NUM> has a radio frequency input <NUM> configured to receive a radio frequency signal, e.g. RF signal <NUM>, and an optical output <NUM> for outputting a first optical signal <NUM> generated from said radio frequency signal, e.g., RF signal <NUM>, to be communicated. Optical filter assembly <NUM> is for filtering the first optical signal <NUM>. Optical to radio frequency converter <NUM> is coupled to an output <NUM> of the optical filter assembly <NUM>, said optical to radio frequency converter <NUM> for generating a radio frequency interference cancellation signal <NUM> from a second optical signal <NUM> output by the optical filter assembly <NUM>.

Optical filter assembly <NUM> includes an optical IIR filter assembly <NUM>, an optical FIR filter assembly <NUM>, a filter controller <NUM>, an optical input coupler <NUM>, and an optical output coupler <NUM>, coupled together as shown in <FIG>. Optical IIR Filter assembly <NUM> includes a plurality of optical IR filters (optical IIR filter <NUM><NUM>,. , optical IIR filter M <NUM>"). Optical FIR filter assembly <NUM> includes a plurality of optical FIR filters (optical FIR filter <NUM><NUM>,. , optical FIR filter N <NUM>").

Each optical IIR filter (optical IIR filter <NUM><NUM>,. , optical IIR filter M <NUM>") includes a fixed optical delay element (fiber ring resonator <NUM>,. , fiber ring resonator <NUM>") and a gain control element, e.g., a controllable gain control element (controllable gain control element A1 <NUM>,. , controllable gain control element <NUM>"), respectively.

Each optical FIR filter (optical FIR filter <NUM><NUM>,. , optical FIR filter N <NUM>") includes a controllable optical delay element (controllable optical delay device (DD) <NUM>,. , controllable optical delay device <NUM>"), and an optical amplifier with a controllable gain (optical amplifier <NUM> with a controllable gain,. , optical amplifier <NUM>" with a controllable gain).

Laser <NUM> generates optical signal <NUM> which is input optical signal to RF to optical converter <NUM>. The RF to optical converter <NUM> receives input RF signal <NUM> on radio frequency input <NUM> and generates output optical signal <NUM>, which is output on optical output <NUM>. Alternatively, directly modulated laser <NUM> receives input RF signal <NUM> on radio frequency input <NUM>" and generates output optical signal <NUM>, which is output on optical output <NUM>". Optical signal <NUM> is an input to optical filter assembly <NUM>. Optical signal <NUM> is received by optical input coupler <NUM> which outputs optical signals (<NUM>',. , <NUM>"') to each of the optical IIR filters (optical IIR filter <NUM><NUM>,. , optical IIR filter M <NUM>"). In some embodiment, optical signals (<NUM>',. <NUM>"') are copies of optical signal <NUM>.

Filter controller <NUM> receives input signal <NUM> and generates, based on the received input signal <NUM>,: (i) controls signals (<NUM>,. , <NUM>") for controlling the controllable gain elements (A1 <NUM>,. AM <NUM>"), respectively, (ii) control signals (<NUM>,. , <NUM>") for controlling the controllable optical delay elements (optical delay device <NUM>,. , optical delay device <NUM>"), respectively, and (iii) control signals (<NUM>,. , <NUM>") for controlling the optical amplifiers with controllable gain (OA <NUM>,. , OA <NUM>"). Thus filter controller <NUM> supplies independent gain control signals (<NUM>,. , <NUM>") to each of the gain control elements (<NUM>,. <NUM>" of the optical IIR filter assembly <NUM>. Filter controller <NUM>' further controls the amount of delay implemented by controllable optical delay elements (<NUM>,. <NUM>") and the gain for the optical amplifiers (<NUM>,.

Optical signal <NUM>' is input to optical IIR filter <NUM><NUM> including FRR <NUM>, processed and output from IIR filter <NUM><NUM> as optical signal <NUM>, with input optical signal <NUM>' being subjected to a fixed delay corresponding to FFR <NUM> and a controllable gain from delay element A1 <NUM>. Optical signal <NUM> is input to optical delay device <NUM>, delayed in accordance with the controlled delay of device <NUM>, and output as optical signal <NUM>. Optical signal <NUM> is input to controllable optical amplifier <NUM>, amplified in accordance with the controlled amplification setting of amplifier <NUM> and output as optical signal <NUM>'.

Optical signal <NUM>" is input to optical IIR filter M <NUM>" including FRR <NUM>", processed and output from IIR filter M <NUM>" as optical signal <NUM>", with input optical signal <NUM>‴ being subjected to a fixed delay corresponding to FFR <NUM>" and a controllable gain from delay element AM <NUM>". Optical signal <NUM>" is input to optical delay device <NUM>", delayed in accordance with the controlled delay of device <NUM>", and output as optical signal <NUM>". Optical signal <NUM>" is input to controllable optical amplifier <NUM>", amplified in accordance with the controlled amplification setting of amplifier <NUM>" and output as optical signal <NUM>"'.

The output optical signal (<NUM>',. , <NUM>"') from each of the FIR filters (<NUM>,. , <NUM>") are input into optical coupler/combiner <NUM>. The output of optical output coupler <NUM> is an optical output of optical filter assembly <NUM>, which outputs optical signal <NUM>, which is a combined optical signals from signals (<NUM>',. , <NUM>"'). Optical to RF converter <NUM> receives optical signal <NUM> and generates RF signal <NUM> which is output from the RF up converted and interference cancellation filter circuit <NUM>'.

The main architecture for RF signal processing using the RF-up converter and interference cancellation filter circuit <NUM>' is to up-convert the RF signal <NUM> using an optical carrier. The up-conversion is carried using a RF to optical converter <NUM>. The up-conversion process is realized using either an externally modulated laser <NUM> where the laser output signal <NUM> is modulated externally by RF to optical converter <NUM> or a directly modulated laser (DML) <NUM> where the laser <NUM> and RF to optical converter <NUM> are realized using one element, DML <NUM>. The output of the RF converted to optical signal <NUM> is input to the optical filter assembly <NUM>. The optical filter <NUM> assembly includes an optical infinite impulse response (IIR) filter assembly <NUM> and an optical finite impulse response (FIR) assembly <NUM>. The optical filter assembly subjects the input optical signal <NUM> to optical filtering and outputs optical signal <NUM>. The output optical signal <NUM> of the optical filter assembly <NUM> is input to optical to RF converter <NUM>. The optical to RF converter <NUM> converts the optical signal <NUM> back to RF, generating and outputting RF signal <NUM>.

The exemplary IIR filter assembly <NUM> described in <FIG> is realized using fiber ring resonators (<NUM>,. , <NUM>") and controllable gain elements (A1 <NUM>,. , AM <NUM>". ) The FIR filter assembly <NUM> is realized using controllable optical delay devices (DD <NUM>,. , DD <NUM>") and controllable optical amplifiers (OA <NUM>,. , OA <NUM>").

Optical IIR filter <NUM><NUM> includes Fiber ring resonator <NUM>, e.g., a fixed delay device, which delays the input optical signal <NUM>' and combines the delayed optical signal with the incoming optical signal <NUM>', thus FRR <NUM> control the delay. Optical IIR filter <NUM><NUM> further includes a controllable gain element A1 <NUM> which controls the amplitude based on the control signal <NUM> received from controller <NUM>.

Optical IIR filter M <NUM>" includes Fiber ring resonator <NUM>", e.g., a fixed delay device, which delays the input optical signal <NUM>' and combines the delayed optical signal with the incoming optical signal <NUM>', thus FRR <NUM>" control the delay. Optical IIR filter M <NUM>" further includes a controllable gain element AM <NUM>" which controls the amplitude based on the control signal <NUM>" received from controller <NUM>.

In this exemplary embodiment shown in <FIG>, each IIR filter has a fixed delay and a variable gain. In some embodiments, each IIR filter has a fixed gain and fixed delay. In some embodiments, each IIR filter has a variable gain and a variable delay. In some embodiments, at least one IIR filter has a fixed delay and a variable gain. In some embodiments, at least one IIR filter has a fixed gain and fixed delay. In some embodiments, at least one IIR filter has a variable gain and a variable delay.

Thus, in some embodiments, the optical IIR filter assembly <NUM> is implemented with fixed gain and fixed delay and/or with variable gain and variable delay. In some embodiments, the IIR filter assembly is implemented where a plurality of these IIR filters (<NUM>,. <NUM>") operate on signal <NUM>. In this realization, the optical signal <NUM> can be, and sometimes is, power divided/split in to multiple optical signals (<NUM>',. , <NUM>"') that feed in to multiple optical IIR filter blocks (<NUM>,. The output of these optical IIR filter blocks (<NUM>,. <NUM>") then can be combined using an optical combiner.

Optical FIR filter assembly <NUM><NUM> described in <FIG> is implemented using a controllable delay element <NUM> and controllable optical amplifier <NUM>, e.g., a controllable optical attenuator. Optical FIR filter assembly N <NUM>" described in <FIG> is implemented using a controllable delay element <NUM>" and controllable optical amplifier <NUM>", e.g., a controllable gain device which can be controlled for optical gain greater than <NUM> and for optical gain less than <NUM>, e.g., optical attenuation.

In some embodiments, the control of delay and control of gain, e.g., amplification greater than <NUM> or attenuation, is performed using a programmable current or programmable voltage supply. In some embodiments, delay is controlled via current and gain is controlled via voltage.

<FIG> is a drawing <NUM> illustrating the optical filter assembly <NUM> of <FIG> and further illustrating components and signals corresponding to a second optical IIR filter, optical IIR filter <NUM><NUM>' and a second optical FIR filter, optical FIR filter <NUM><NUM>'. Optical IIR filter <NUM><NUM>' includes fixed delay element FFR <NUM>' and controllable gain element A2 <NUM>'. Optical FIR filter <NUM><NUM>' includes controllable optical delay element DD <NUM>' and controllable optical gain element OA <NUM>'. Filter controller <NUM> generates: control signal <NUM>' to control gain element A2 <NUM>', control signal <NUM>' to control DD <NUM>', and control signal <NUM>' to control optical amplifier <NUM>'. Optical signal <NUM>' output from coupler <NUM> is an input to optical IIR filter <NUM><NUM>', and optical signal <NUM>' is an output optical signal from optical IIR filter <NUM>. Optical signal <NUM>' is input to optical DD <NUM>' of Optical FIR filter <NUM><NUM>'; optical signal <NUM>' is an output form DD <NUM>' and an input to OA <NUM>' of optical FIR filter <NUM><NUM>'. Optical signal <NUM>" is an output of OA <NUM>' and an input to coupler/combiner <NUM>.

In some embodiments, the controllable optical amplifiers (<NUM>, <NUM>',. , <NUM>") can have positive or negative gains, e.g., in dB scale. Thus, in such an embodiment, an individual optical amplifier, e.g. device <NUM>, may serve as a positive gain amplifier or as an attenuator, e.g., device <NUM> can be controlled to go either way depending upon the losses in the channel.

In some embodiments, the controllable optical amplifiers (<NUM>, <NUM>',. , <NUM>") have positive gains, in dB scale i.e. gain greater than <NUM> in real scale.

In some embodiments, the controllable optical amplifiers (<NUM>, <NUM>',. , <NUM>") have negative gains, in dB scale i.e. gain less than <NUM> in real scale.

<FIG> illustrates an exemplary RF-up converter and interference cancellation filter circuit <NUM>" in accordance with another exemplary embodiment, which is one exemplary realization of the RF filter <NUM> included in an exemplary transceiver circuit <NUM>, <NUM>' <NUM>" or <NUM>"'.

RF up-converter and interference cancellation filter circuit <NUM>" includes a laser <NUM>, an RF signal to optical signal converter <NUM>' including a Mach-Zehnder modulator (MZM) <NUM>, an optical filter assembly <NUM>' and an optical to RF converter <NUM>, e.g., a balanced photo-detector, coupled together as shown in <FIG>. In some embodiments, laser <NUM> and RF to optical converter <NUM>' are replaced by a directly modulated laser, e.g., DML <NUM> shown in <FIG>.

Radio frequency signal to optical signal converter <NUM>' has a radio frequency input <NUM>' configured to receive a radio frequency signal, e.g. RF signal <NUM>, and an optical output <NUM>' for outputting a first optical signal <NUM> generated from said radio frequency signal, e.g., RF signal <NUM>, to be communicated. Optical filter assembly <NUM>' is for filtering the first optical signal <NUM>. Optical to radio frequency converter <NUM> is coupled to an output <NUM>' of the optical filter assembly <NUM>', said optical to radio frequency converter <NUM> for generating a radio frequency interference cancellation signal <NUM> from a second optical signal <NUM> output by the optical filter assembly <NUM>'. In various embodiments, the optical to radio frequency converter <NUM> is a balanced photodetector, and the optical to radio frequency converter <NUM> generates the radio interference signal <NUM> from the second optical signal <NUM> and a third optical signal <NUM> output from the optical filter assembly <NUM>'.

Optical filter assembly <NUM>' includes an optical IIR filter assembly <NUM>, an optical FIR filter assembly <NUM>, a filter controller <NUM>', a <NUM> to <NUM> optical coupler <NUM>, two <NUM> to N optical couplers (<NUM>, <NUM>) and two N to <NUM> optical couplers (<NUM>, <NUM>) coupled together as shown in <FIG>. Optical IIR Filter assembly <NUM> includes a plurality of optical IIR filters coupled together, each optical IIR filter including a fixed delay element, which is a fiber ring resonator (FRR) and a controllable gain element. Drawing <NUM> of <FIG> illustrates individual optical IIR filters (optical IIR filter <NUM><NUM>, optical IIR filter <NUM><NUM>,. , optical IIR filter M <NUM>) included in optical IIR filter assembly <NUM>. Each optical IIR filter (optical IIR filter <NUM><NUM>,. , optical IIR filter <NUM><NUM>,. , optical IIR filter M <NUM>) includes a fixed optical delay element (fiber ring resonator (FRR) <NUM><NUM>, fiber ring resonator <NUM>,. , fiber ring resonator M <NUM>) and a gain control element, e.g., a controllable gain control element (controllable gain control element A1 <NUM>, controllable gain control element A2 <NUM>,. , controllable gain control element AM <NUM>), respectively.

Optical FIR Filter assembly <NUM> includes a plurality of optical FIR filters, each optical FIR filter including a controllable optical delay element, e.g., a delay device, and a controllable gain element. Drawing <NUM> of <FIG> illustrates individual optical FIR filters (optical FIR filter11 <NUM>, optical FIR filter21 <NUM>,. , optical FIR filterN1 <NUM>, optical FIR filter12 <NUM>, optical FIR filter22 <NUM>,. , optical FIR filterN2 <NUM>) included in optical FIR filter assembly <NUM>. Each optical FIR filter (optical FIR filter11 <NUM>, optical FIR filter <NUM><NUM>,. , optical FIR filterN1 <NUM>, optical FIR filter12 <NUM>, optical FIR filter <NUM><NUM>,. , optical FIR filterN2 <NUM> includes a controllable optical delay element (delay device D11 <NUM>, delay device D21 <NUM>,. , delay device DN1 <NUM>, delay device D12 <NUM>, delay device D22 <NUM>,. , delay device DN2 <NUM>,) and a gain control element, e.g., a controllable gain element (controllable gain element AF11 <NUM>, controllable gain element AF21 <NUM>,. , controllable gain element AFN1 <NUM>, controllable gain element AF12 <NUM>, controllable gain element AF22 <NUM>,. , controllable gain element AFN2 <NUM>), respectively.

Laser <NUM> generates and outputs optical signal <NUM>, which is sent to RF to optical converter <NUM>, which receives optical signal <NUM>. The RF to optical converter also <NUM> receives input RF signal <NUM> on radio frequency input <NUM> and generates output optical signal <NUM>, which is output on optical output <NUM>. Alternatively, directly modulated laser <NUM> receives input RF signal <NUM> on radio frequency input <NUM>" and generates output optical signal <NUM>, which is output on optical output <NUM>". Optical signal <NUM> is an input to optical filter assembly <NUM>'. Optical signal <NUM> is processed by the optical IIR filter assembly <NUM>, which generates and outputs optical signal <NUM>. The optical IIR filter assembly <NUM> subjects the input optical signal <NUM> to: delays in accordance with the fixed delays corresponding to the FRRs (<NUM>, <NUM>,. , <NUM>) and gain adjustments in accordance with the controlled gain adjustments in accordance with the controlled gain settings of gain control elements (A1 <NUM>, A2 <NUM>,. , AM <NUM>) generating an optical output signal <NUM> of the optical IIr filter assembly <NUM>. In various embodiments, the FFRs (<NUM>, <NUM>,. <NUM>) of the optical IIR filter assembly <NUM> are coupled to one another.

Filter controller <NUM>' receives input signal <NUM> and generates, based on the received input signal <NUM>,: (i) controls signals (CA1 <NUM>, CA2 <NUM>,. , CAM <NUM>) for controlling the controllable gain elements (A1 <NUM>, A2 <NUM>,. AM <NUM>), respectively, (ii) control signals (CD11 <NUM>, CD21 <NUM>,. , CDN1 <NUM>, CD12 <NUM>, CD22 <NUM>,. , CDN2 <NUM>) for controlling the controllable optical delay elements (controllable optical delay device D11 <NUM>, controllable optical delay device D21 <NUM>,. , controllable optical delay device DN1 <NUM>, controllable optical delay device D12 <NUM>, controllable optical delay device D22 <NUM>,. , controllable optical delay device DN2 <NUM>), respectively, and (iii) control signals (CAF11 <NUM>, CAF21 <NUM>,. , CAFN1 <NUM>, CAF12 <NUM>, CAF22 <NUM>,. , CAFN2 <NUM>) for controlling the controllable gain elements (AF11 <NUM>, AF21 <NUM>,. , AFN1 <NUM>, AF12 <NUM>, AF22 <NUM>,. , AFN2 <NUM>), respectively. Thus filter controller <NUM>' supplies independent gain control signals (<NUM>, <NUM>. , <NUM>) to each of the gain control elements (<NUM>, <NUM>. <NUM>) of the optical IIR filter assembly <NUM>. Filter controller <NUM>' further controls the amount of delay implemented by controllable optical delay elements (<NUM>, <NUM>, <NUM>,. , <NUM>, <NUM>,. , <NUM>) and the gain for the optical amplifiers (<NUM>, <NUM>,. , <NUM>, <NUM>, <NUM>,.

Optical signal <NUM>, which is output from the optical IIR filter assembly <NUM> is input to a coupler <NUM>, e.g., a <NUM> to <NUM> splitter, which generates optical signals <NUM> and <NUM>. Optical signal <NUM> is input to a <NUM> x N coupler <NUM> which outputs optical signals (<NUM>, <NUM>,. , <NUM>) to the input of controllable delay devices (D11 <NUM>, D21 <NUM>,. DN1 <NUM>), respectively. Optical signal <NUM> is input to a <NUM> x N coupler <NUM> which outputs optical signals (<NUM>, <NUM>,. , <NUM>) to the input of controllable delay devices (D12 <NUM>, D22 <NUM>,. DN2 <NUM>), respectively. Optical delay devices (D11 <NUM>, D21 <NUM>,. , DN1 <NUM>, D12 <NUM>, D22 <NUM>,. , DN2 <NUM>) introduce delays corresponding to the controlled delay setting based on the filter control signals (<NUM>, <NUM>,. ,<NUM>, <NUM>, <NUM>,. , <NUM>), generating optical signals (<NUM>, <NUM>,. , <NUM>, <NUM>, <NUM>,. , <NUM>), respectively.

Optical signals optical signals (<NUM>, <NUM>,. , <NUM>, <NUM>, <NUM>,. , <NUM>) are input of controllable gain elements (AF11 <NUM>, AF21 <NUM>,. , AFN1 <NUM>, AF12 <NUM>, AF22 <NUM>,. , AFN2 <NUM>), respectively. The controllable gain elements (AF11 <NUM>, AF21 <NUM>,. , AFN1 <NUM>, AF12 <NUM>, AF22 <NUM>,. , AFN2 <NUM>) adjust gains corresponding to the controlled gains settings based on the filter control signals (<NUM>, <NUM>,. ,<NUM>, <NUM>, <NUM>,. , <NUM>), generating optical signals (<NUM>, <NUM>,. , <NUM>, <NUM>, <NUM>,. , <NUM>), respectively. Optical signals (<NUM>, <NUM>,. , <NUM>) are input to N x <NUM> optical coupler <NUM> which combines the signals and outputs optical signal <NUM>. Optical signals (<NUM>, <NUM>,. , <NUM>) are input to N x <NUM> optical coupler <NUM> which combines the signals and outputs optical signal <NUM>. Optical signal <NUM> is output on output <NUM>' of optical filter assembly <NUM>'. Optical signal <NUM> is output on output <NUM>" of optical filter assembly <NUM>'. Outputs (<NUM>' and <NUM>") couple the optical filter assembly <NUM>' to optical to RF converter <NUM>, e.g., a balanced photodetector. Optical to RF converter <NUM> receives optical signals (<NUM>, <NUM>) and generates and outputs RF signal <NUM>. In the <FIG> implementation, the RF up-converter and cancellation filter circuit <NUM>' includes multiple FIR filter branches which are shown. The optical signal <NUM>, which is output from the optical FIR filter assembly <NUM> is split in to multiple branches using optical couplers <NUM>, <NUM> and <NUM>. The output filtered optical signals (<NUM>, <NUM>,. , <NUM>) from optical FIR filter assembly <NUM> are combined using optical coupler <NUM>, which generates optical output signal <NUM>. The output filtered optical signals (<NUM>, <NUM>,. , <NUM>) from optical FIR filter assembly <NUM> are combined using optical coupler <NUM>, which generates optical output signal <NUM>. The optical signals <NUM>, <NUM> are then combined using a optical to RF converter <NUM>, e.g., a balanced photo-detector to generate an RF signal <NUM>.

<FIG> is a drawing of an exemplary controllable delay element <NUM>, e.g., delay device, in accordance with an exemplary embodiment. Exemplary controllable delay element is, e.g., one of the controllable delay devices (<NUM>, <NUM>'. , <NUM>") of <FIG> or <FIG> or one of the controllable delay devices (<NUM>, <NUM>,. , <NUM>, <NUM>, <NUM>,. , <NUM>) of <FIG> or <FIG>. Controllable delay element <NUM> is a switch based optical delay device including a plurality of switches switch (<NUM>, <NUM>, <NUM>, <NUM>) for altering an optical path through the first switch based optical delay device.

In this exemplary embodiment shown in <FIG>, the controllable delay element <NUM> is implemented using optical waveguides (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) and optical switches (<NUM>, <NUM>, <NUM>, <NUM>). The optical switches (<NUM>, <NUM>, <NUM>, <NUM>), based upon their settings, control the route of an input optical signal <NUM>,. For example, consider that controllable delay element <NUM> is DD <NUM> of optical FIR filter <NUM><NUM> of <FIG>, the input optical signal <NUM> is optical signal <NUM> of <FIG>. The switches (<NUM>, <NUM>, <NUM>, <NUM>) are controlled using a optical switch controller <NUM> which is capable of individually controlling these switches (<NUM>, <NUM>, <NUM>, <NUM>). The input signal <NUM> comes out as output signal <NUM> after a certain delay which depends on the settings programmed through the control signal <NUM> to the controller <NUM>. Consider that the controllable delay element <NUM> is DD <NUM> if <FIG>, input control signal <NUM> is signal <NUM> of <FIG>. The controller <NUM> receives control signal <NUM> and generates and sends switch setting control signals (<NUM>, <NUM>, <NUM>, <NUM>) to control switches (<NUM>, <NUM>, <NUM>, <NUM>) to be set to a desired position to implement a desired delay path. In the example, shown in <FIG>, the switches are set to implement a waveguide path including optical waveguides (<NUM>, <NUM>, <NUM>, <NUM>, and <NUM>). In this exemplary switch setting, optical waveguides (<NUM>, <NUM> and <NUM>) are not in use. Consider that controllable delay element <NUM> is DD <NUM> of optical FIR filter <NUM><NUM> of <FIG>, the output optical signal <NUM> is optical signal <NUM> of <FIG>.

<FIG> is a drawing <NUM> illustrating an exemplary RX digital baseband circuit <NUM>, an exemplary TX digital baseband circuit <NUM> and an exemplary channel estimator, filter, e.g., digital filter, and filter control circuit <NUM> in further detail in accordance with an exemplary embodiment. <FIG> is used to describe digital control in an exemplary transceiver circuit, e.g., <NUM>, <NUM>' <NUM>" or <NUM>"', in accordance with an exemplary embodiment.

Channel estimator, filter and filter control circuit <NUM> includes a frame start detector (FSD) <NUM>, a channel estimator (CE) <NUM> a coefficient calculator (CC) <NUM> and a FIR filter FL2 <NUM> coupled together as shown in <FIG>. TX digital baseband circuit <NUM> includes an encode and modulation assembly <NUM> including a modulator circuit <NUM> and a encode circuit <NUM>, a pre distorter (PD) <NUM> and a plurality of up-converters (<NUM>, <NUM>, <NUM>) coupled together as shown in <FIG>. RX digital baseband circuit <NUM> includes a plurality of down converters (<NUM>, <NUM>, <NUM>), a received signal strength indicator & automatic gain control (RSSI & AGC) circuit <NUM>, a combiner <NUM>, and a demodulation and decode assembly <NUM> including a demodulator circuit <NUM> and a decode circuit <NUM> coupled together as shown in <FIG>.

The channel estimator, filter, e.g., digital cancellation filter, and filter control circuit <NUM> has two main inputs (<NUM> and <NUM>) from the digital blocks <NUM> and <NUM>, respectively. Data in signal <NUM> is received by the encode and modulation assembly <NUM>. The encode circuit <NUM> encodes received data, e.g., data bits, and the modulator circuit <NUM> modulates the encoded data generating signal <NUM>. Signal <NUM> is a copy of the transmit signal in the digital domain that represents the sample waveform that undergoes up-conversion, e.g., by up converters <NUM>, <NUM>, <NUM>, to an appropriate sampling rate and subsequent conversion in the analog domain. The signal copy <NUM> is filtered using an FIR filter realization <NUM> driven by the coefficients calculated by the coefficient calculator <NUM>. The calculated coefficients represent the compensation of linear and non-linear components of the signal. The block <NUM> takes in input signal <NUM> which is the received sample signal at the digital baseband receive <NUM>. The received signal <NUM> then goes through the frame start detection process in circuit <NUM> where through correlation, the start of the frame is found out. The accurate frame timing information and the samples are passed on to the channel estimator <NUM> in signal <NUM>. The channel estimator <NUM> calculates the coefficient of channel between the digital transmitter and the digital receiver. Since the transmit signal is already known to the estimator, the channel estimator <NUM> uses that to calculate the channel behavior. The calculated channel behavior is then passed on to the channel coefficient calculator <NUM> in signal <NUM>, and the channel coefficient calculator <NUM> derives the coefficient(s) for the RF interference cancellation filter, e.g., optical filter assembly <NUM> or <NUM>', and digital filter <NUM>. In some embodiments, the RF interference cancellation filter, e.g., optical filter assembly <NUM> or <NUM>', is programmed at every milli-second time scale; however, the digital filter <NUM> is calibrated at every micro-second time scale. Coefficient calculator <NUM> generates and sends control signal <NUM> including calculated coefficient to the filter controller <NUM> or <NUM>' of optical filter assembly <NUM> or <NUM>'. Coefficient calculator generates and sends calculated coefficients in signal <NUM> to digital filter <NUM>. The coefficient calculator <NUM> is responsible for making sure that the right coefficient is picked between the photonic filter <NUM> or <NUM>' and digital interference canceller <NUM>. The recreated self-interference signal <NUM> output from filter <NUM> is subtracted by combiner <NUM> from the processed incoming received signal <NUM>, which is a downsampled version of incoming received signal <NUM>. The output of combiner <NUM> is signal <NUM>, which is an input to demodulation and decode assembly <NUM>. Signal <NUM> is subjected to demodulation by demodulator circuit <NUM> and decoding by decode circuit <NUM> generating data out signal <NUM>. The channel estimator, filter, and filter control circuit <NUM> also controls the pre distorter <NUM> in the digital baseband circuit <NUM> of the transmit chain. This pre-distorter <NUM> can, and does, shape the transmit signal such that it is easier to cancel on the receive side. This pre-distorter <NUM> is dynamically tunable and can, and does, adapt based on a change in the requirements.

<FIG> is a drawing of an exemplary coefficient calculator circuit <NUM>' in accordance with an exemplary embodiment. Exemplary coefficient calculator <NUM>' is, e.g., coefficient calculator <NUM> of <FIG>. The input to coefficient calculator <NUM>' is channel estimates <NUM> and the outputs are coefficients <NUM>, <NUM> and <NUM>. The coefficients <NUM> are used in the pre-distorter <NUM> in the TX digital baseband circuit <NUM> of the digital transmit chain to pre-distort the digital transmit signal <NUM> for more efficient self-interference cancellation. The coefficients communicated in signal <NUM> are used to program/select the attenuation/gain and delay values of various branches and/or elements of the RF up-converter and cancellation filter circuit <NUM>. The coefficients output in signal <NUM> are computed scalars programmed to the linear and non-linear filter <NUM>. The input signal <NUM> received by the block <NUM>' includes the channel estimates of the self-channel between the transmit and receive. Input signal <NUM> also includes system parameters computed by the frame start detect <NUM> and channel estimate block <NUM> such as the transmit and receive gain values, frame start timing etc. This input <NUM> is passed on to the channel estimates processing circuit <NUM> and the controller <NUM>. The channel estimates processing circuit <NUM> is responsible for computation of coefficients <NUM> that are to be programmed into the digital filter <NUM>. The channel estimate processing circuit <NUM> also calculates the coefficients <NUM> that correspond to the values for RF up-converter and cancellation filter <NUM>. The multiplexer <NUM> can, and does, select between the computed coefficients <NUM> or the average of <NUM> and <NUM> through the averaging function device <NUM>. The channel coefficient selector circuit <NUM> selects set of coefficients <NUM> that ultimately go to the storage device <NUM> and are subsequently sent to the RF up-converter and cancellation filter <NUM>. The storage device <NUM> also keeps a copy of past programmed values. The outputs <NUM> and <NUM> from the storage device <NUM> can be selected using the select signal <NUM> from the controller <NUM>. The controller <NUM> controls the storage device <NUM>, channel coefficient selector <NUM>, and multiplexer <NUM> through control signals (<NUM>, <NUM>, <NUM>), respectively. Signal <NUM> including coefficients, output from MUX <NUM> is input to the channel coefficient selector circuit <NUM> and input into the pre-distort coefficient buffer <NUM>. , from which the coefficients are communicated to the pre-distorter <NUM> in signal <NUM>.

One or more of the Electro-Optic Active Filters described herein use optical delays and processing to enable filtering at radio frequencies. Such an architecture has multiple advantages for radio frequency filtering over systems, which generate an interference cancelation signal purely using electrical components. Some of the advantages include i) a relatively Frequency agnostic nature that allows, regardless of RF center frequency, filtering of the desired RF signal from the undesired signal; ii) support for wideband communications with, given a number of filter taps, the extent of interference cancellation depending on fractional bandwidth of the system, (f2-f1)/fc. Thus the higher the center frequency, the greater the worst-case cancellation for a given filter can be. Thus, optical interference cancellation architecture as presented here presents a much deeper extent of cancellation and range of possible interference frequencies that can be canceled than might be possible using only electrical components operating in a more limited RF frequency domain. Another advantage includes: iii) support of adaptive active filtering with the filter design allowing for both changes in delays and/or filter gain coefficients. Such gain and delay can be relatively simple to implement in the optical domain as compared to in the electrical RF domain where highly accurate linear phase shifters and/or varactors might be needed for control of electrical circuits. Furthermore introducing optical delays is substantially easier than electrical circuit delays, as optical delays can be induced through changes in index of refraction and other mechanisms for slowing light through a medium. Similarly, variable attenuation/amplitude change in light is a significantly easier process to implement than is the process to implement variable attenuation/amplitude changes in electrical signals in many cases. The methods and apparatus are well suited for use in a wide range of communications devices which communicate in an RF frequency band. In the present application the RF frequency band is to include frequencies from <NUM> to <NUM>. Optical frequencies are above the <NUM> frequency.

In various embodiments an analog, or optionally digital, RF signal to be transmitted is converted into an optical signal. The optical signal is then filtered using one or more optical filters of an optical filter assembly. Amplitude and/or gain of one or more optical filters of the optical filter assembly are controlled taking into consideration communications channel conditions. Different optical filters may and often are controlled to have different delays and/or gains. The optical filter assembly acts as and sometimes is a multi-tap filter. Different taps, e.g., parallel filters, in the optical filter assembly may be, and sometimes are, controlled to have different gains. Since the filters, e.g., taps, of the optical filter assembly are implemented in the optical domain they have several advantages over electrical filters. For example, they can be implemented without concern for radiating RF signals and interference to other components since the optical signals will not be picked up by RF signal components such as regular copper wires. Furthermore, optical filters can be implemented in a relatively small space and at a relatively low cost allowing for the use of optical filter assemblies with a relatively large number of filter taps as compared to electrical filter circuits. For example, in some embodiments the optical filter assembly used to generate an interference cancelation signal includes <NUM>, <NUM>, <NUM>, <NUM> or even more parallel optical filters working as separate controllable filter taps in a relatively small space, e.g., inside the housing of a cell phone or other mobile communications device.

It should be appreciated that since optical filter circuits do not suffer from the same thermal noise issues of electrical filter circuits, the optical filter assembly can be used in at least some embodiments to generate reliable interference cancelation signals with relatively low power at one or more frequencies where the power level might be below that of the thermal noise floor of electrical filter components which might be used in a filter.

While numerous different features and examples are described all features need not be used in all embodiments. For example, in some embodiments fixed optical filter weights and delays are used, e.g., in the optical filter assemblies shown in <FIG> and <FIG>, while in other embodiments filter weights and delays are changed dynamically in response to detecting changes in channel conditions. Fixed gain and delay filter embodiments are well suited for static conditions where a device may be stationary and the communications channel does not change significantly over time while dynamic control of optical gains and delays is well suited for dynamic environments where channel conditions between a receiver and transmitter of a device are likely to change, e.g., due to device movement or changes in the environment.

In addition the use of optical filters allows for a dynamic range and linearity of the optical filter that can be significantly higher than that of RF systems which might be found in common commercial RF communications devices. Thus, the optical filter approach can avoid introducing significant new distortions into an RF signal that might be introduced by the use of electrical component based RF filters that may be less linear than desired and/or which may suffer from thermal noise and/or may generate RF interference inside a communications device.

The techniques of various embodiments may be implemented using software, hardware and/or a combination of software and hardware. Various embodiments are directed to communications devices including RF circuitry and optoelectronic circuitry. Various embodiments are directed to apparatus, e.g., communications devices, e.g., nodes such as mobile wireless terminals, base stations, and/or communications system. Various embodiments are also directed to methods, e.g., method of controlling and/or operating a communications device, e.g., a wireless terminals, base stations and/or communications systems. Various embodiments are also directed to non-transitory machine, e.g., computer, readable medium, e.g., ROM, RAM, CDs, hard discs, etc., which include machine-readable instructions for controlling a machine to implement one or more steps of a method.

It is understood that the specific order or hierarchy of steps in the processes disclosed is an example of exemplary approaches. Based upon design preferences, it is understood that the specific order or hierarchy of steps in the processes may be rearranged while remaining within the scope of the present disclosure. The accompanying method claims present elements of the various steps in a sample order and are not meant to be limited to the specific order or hierarchy presented.

In various embodiments, devices described herein are implemented using one or more modules to perform the steps corresponding to one or more methods, for example, signal generation, processing, receiving and/or transmitting steps. Thus, in some embodiments various features are implemented using modules. Such modules may be implemented using software, hardware or a combination of software and hardware. In some embodiments modules are implemented fully in hardware, e.g., as individual circuits. Many of the above described methods or method steps can be implemented using machine executable instructions, such as software, included in a machine readable medium such as a memory device, e.g., RAM, floppy disk, etc. to control a machine, e.g., general purpose computer with or without additional hardware, to implement all or portions of the above described methods, e.g., in one or more nodes. Accordingly, among other things, various embodiments are directed to a machine-readable medium e.g., a non-transitory computer readable medium, including machine executable instructions for causing a machine, e.g., processor and associated hardware, to perform one or more of the steps of the above-described method(s). Some embodiments are directed to a device, e.g., communications node, including a processor configured to implement one, multiple, or all of the steps of one or more methods of the invention.

In some embodiments, the processor or processors, e.g., CPUs, of one or more devices, e.g., communications devices such as wireless terminals (UEs), and/or access nodes, are configured to perform the steps of the methods described as being performed by the communications nodes. The configuration of the processor may be achieved by using one or more modules, e.g., software modules, to control processor configuration and/or by including hardware in the processor, e.g., hardware modules, to perform the recited steps and/or control processor configuration. Accordingly, some but not all embodiments are directed to a communications device, e.g., user equipment, with a processor which includes a module corresponding to each of the steps of the various described methods performed by the device in which the processor is included. In some but not all embodiments a communications device includes a module corresponding to each of the steps of the various described methods performed by the device in which the processor is included. The modules may be implemented purely in hardware, e.g., as circuits, or may be implemented using software and/or hardware or a combination of software and hardware.

Some embodiments are directed to a computer program product comprising a computer-readable medium comprising code for causing a computer, or multiple computers, to implement various functions, steps, acts and/or operations, e.g. one or more steps described above. Depending on the embodiment, the computer program product can, and sometimes does, include different code for each step to be performed. Thus, the computer program product may, and sometimes does, include code for each individual step of a method, e.g., a method of operating a communications device, e.g., a wireless terminal or node. The code may be in the form of machine, e.g., computer, executable instructions stored on a computer-readable medium such as a RAM (Random Access Memory), ROM (Read Only Memory) or other type of storage device. In addition to being directed to a computer program product, some embodiments are directed to a processor configured to implement one or more of the various functions, steps, acts and/or operations of one or more methods described above. Accordingly, some embodiments are directed to a processor, e.g., CPU, configured to implement some or all of the steps of the methods described herein. The processor may be for use in, e.g., a communications device or other device described in the present application.

The methods and apparatus of various embodiments are applicable to a wide range of communications systems including many cellular and/or non-cellular systems.

Claim 1:
A communications device (<NUM>) comprising:
a radio frequency signal to optical signal converter (<NUM>, <NUM>') comprising:
a radio frequency input (<NUM>, <NUM>'); and
a first optical output (<NUM>, <NUM>');
an optical filter assembly (<NUM>, <NUM>') comprising:
an optical input operably coupled to the first optical output (<NUM>, <NUM>');
an optical filter control signal input operative to receive a control signal comprising a calculated coefficient that defines an operation of the optical filter assembly (<NUM>, <NUM>'); and
a second optical output (<NUM>, <NUM>'); and
an optical to radio frequency converter (<NUM>, <NUM>) comprising:
a second optical input operably coupled to the second optical output (<NUM>, <NUM>'); and
a radio frequency output configured to provide, as output, a radio frequency interference cancellation signal (<NUM>) operative to attenuate at least a portion of a first radio frequency signal provided as input to the radio frequency input (<NUM>, <NUM>') from a second radio frequency signal (<NUM>).