MIMO interference cancellation

Abstract

A multiple-input multiple-output (MIMO) antenna configuration includes a transmit hybrid circuit connected to receive a first transmit signal and a second transmit signal, output a sum of the first transmit and second transmit signals, and output a difference between the first transmit and second transmit signals; a first antenna connected to receive the sum output; a second antenna connected to receive the difference output; a receive hybrid circuit connected to receive signals from the first and second antennas, output a sum of the signals from the first and second antennas, and output a difference between the first antenna signal and the second antenna signal; a first cancellation circuit connected to receive the first transmit signal and configured to compensate for interference due to the first transmit path; and a second cancellation circuit connected to receive the second transmit signal and configured to compensate for interference due to the second transmit path, wherein the sum output of the receive hybrid circuit and the output of the first cancellation circuit are combined to generate a first receive signal, and the difference output of the receive hybrid circuit and the output of the second cancellation circuit are combined to generate a second receive signal.

Description

[Technical field]

[0001] The present invention relates to a method and apparatus for suppressing interference between receive and transmit paths in a multiple-input multiple-output (MIMO) antenna configuration, particularly, but not exclusively, to MIMO implementations in radio frequency (RF) technologies such as mobile technologies. [Background technology]

[0002] A feature of wireless communication equipment is the ability to simultaneously transmit and receive radio signals using multiple antennas, known as Multiple-Input, Multiple-Output (MIMO). MIMO is a method of increasing the capacity of a wireless link by using multiple transmit and receive antennas to take advantage of multipath propagation.

[0003] Simultaneous transmission and reception of wireless signals in a MIMO configuration creates the problem that the relatively high power signals transmitted from each transmitter can couple into each receiver, creating interfering signals that obscure the relatively low power signals that are desired to be received. Thus, a MIMO configuration that suppresses interference at or before one or more receivers is typically required to ensure successful reception even in the presence of transmissions from multiple antennas.

[0004] Referring to FIG. 1, first and second transmission signals T x1 and T x2 and a first and a second received signal R using the first and second antennas 101 and 102, respectively. x1 and R x2 An exemplary MIMO configuration is shown including two antennas for receiving a first transmit signal T. A first circulator 121 is connected to the first antenna 101 and receives a first transmit signal T x1 and receiving the first received signal R x1 The second circulator 122 is connected to the second antenna 102 and outputs a second transmission signal T x2 and receiving a second received signal R x2Output.

[0005] In this example MIMO configuration, there are four paths of interference from the transmit path through the circulator to the receive path. x1 First received signal R from the path x1 Arrows to the path 17 11 The path indicated by the first transmission signal T x1 Second received signal R from the path x2 Arrows to the path 17 12 The path indicated by the second transmission signal T x2 Second received signal R from the path x2 Arrows to the path 17 22 The path indicated by the second transmission signal T x2 First received signal R from the path x1 Arrows to the path 17 21 The path is indicated by:

[0006] To minimize this interference, a canceller may be provided. The outputs of the first circulator 121 and the second circulator 122 are respectively connected to combiners 141 and 142, which each further receive the outputs of two cancellers.

[0007] Canceller 16 11 is the first transmit signal path T x1 and the first coupler 141, and the canceller 16 12 is the first transmit signal path T x1 and the second coupler 142, and the canceller 16 22 is the second transmit signal path T x2 and the second coupler 142, and the canceller 16 21 is the second transmit signal path T x2 and the first coupler 141.

[0008] Therefore, a canceller is provided to compensate for each interference path. In general, the number of interference paths is the product of the number of transmission channels and the number of reception channels. Therefore, the number of canceller circuits required is generally equal to the product of the number of transmitters and the number of receivers. Therefore, the number of cancellers required for n-stage MIMO is n 2 become.

[0009] It is an object of the present invention to provide an improved technique for suppressing interference between receive and transmit paths in a MIMO configuration. Summary of the Invention

[0010] A multiple-input multiple-output (MIMO) antenna configuration is provided comprising a transmit hybrid circuit connected to receive a first transmit signal and a second transmit signal, and to output a sum of the first transmit signal and the second transmit signal and a difference between the first transmit signal and the second transmit signal; a first antenna connected to receive the sum output; a second antenna connected to receive the difference output; a receive hybrid circuit connected to receive signals from the first antenna and the second antenna, and to output a sum of the signals from the first antenna and the second antenna and to output a difference between the first antenna signal and the second antenna signal; a first cancellation circuit connected to receive the first transmit signal and configured to compensate for interference due to the first transmit path; and a second cancellation circuit connected to receive the second transmit signal and configured to compensate for interference due to the second transmit path, wherein the sum output of the receive hybrid circuit and an output of the first cancellation circuit are combined to generate a first receive signal, and the difference output of the receive hybrid circuit and an output of the second cancellation circuit are combined to generate a second receive signal.

[0011] The first canceller can cancel interference in the first receive path arising from the first transmit path. The second canceller can cancel interference in the second receive path arising from the second transmit path. This can be achieved if the transfer function of each canceller is the inverse of the transfer function from the first transmit path or the second transmit path to the first receive path or the second receive path. The transmit path can be an input to a transmit hybrid circuit and the receive path can be an output of the receive hybrid circuit.

[0012] Each canceller can compensate for the self-interference coupling component caused by (due to) mutual coupling of signals between two antennas.

[0013] The transfer function of each cancellation path may have the inverse transfer function of the self-interference path, including compensation for mutual coupling of the antennas. Compensation may be provided with adjustable circuitry in each canceller.

[0014] Each of the first and second canceller circuits may include a phase inverter, and the first and second combiners combine the respective outputs of the receive hybrid circuit with inverted outputs of the canceller circuits.

[0015] Each of the first and second canceller circuits may include a sub-canceller circuit for matching an impedance of the respective first and second antennas, respectively.

[0016] The MIMO antenna configuration may further include a first transmit filter connected between a sum output of the transmit hybrid circuit and the first antenna, a second transmit filter connected between a differential output of the transmit hybrid circuit and the second antenna, a first receive filter connected between the first antenna and the receive hybrid circuit, and a second receive filter connected between the second antenna and the receive hybrid circuit.

[0017] The transmit hybrid circuit may include a first transmit filter for filtering a sum output of the transmit hybrid circuit and a second transmit filter for filtering a differential output of the transmit hybrid circuit, and the receive hybrid circuit may include a first receive filter for filtering the first antenna signal and a second receive filter for filtering the second antenna signal.

[0018] The first and second transmit filters and the first and second receive filters may be tunable filters.

[0019] The first cancellation circuit may include a first cancellation receive filter connected to receive the first transmit signal, and a first cancellation transmit filter connected to receive the signal from the first cancellation receive filter.

[0020] The second cancellation circuit may include a second cancellation receive filter connected to receive the first transmit signal, and a second cancellation transmit filter connected to receive a signal from the second cancellation receive filter.

[0021] The first cancellation circuit may comprise a 180° phase shift circuit. The second cancellation circuit may include a 180° phase shift circuit.

[0022] The first and second cancellation transmit filters and the first and second cancellation receive filters may be variable filters.

[0023] The first transmit filter may match the first canceling transmit filter, the second transmit filter may match the second canceling transmit filter, the first receive filter may match the first canceling receive filter, and the second receive filter may match the second canceling receive filter.

[0024] Each cancellation circuit may include a subcanceller connected between a respective cancellation transmit filter and a respective cancellation receive filter. Each subcanceller circuit may be a variable impedance circuit. The subcanceller circuit may be adjustable to match an impedance of a respective first antenna or a respective second antenna. Each subcanceller circuit may be adjustable to compensate for interference in a respective transmit path.

[0025] The MIMO antenna configuration may further comprise a first circulator connecting the first antenna, the sum output of the transmit hybrid circuit, and the input to the receive hybrid circuit, and a second circulator connecting the second antenna, the differential output of the transmit hybrid circuit, and the input to the receive hybrid circuit.

[0026] The MIMO antenna arrangement may further comprise a first power amplifier for providing the first transmit signal, and a second power amplifier for providing the second transmit signal.

[0027] The MIMO antenna configuration may further comprise a first low noise amplifier for receiving the first receive signal, and a second low noise amplifier for receiving the second receive signal.

[0028] A method of transmitting and receiving in a multiple-input multiple-output (MIMO) antenna configuration is provided, the method including receiving a first transmit signal and a second transmit signal, outputting a sum of the first transmit signal and the second transmit signal to a first antenna, outputting a difference of the first transmit signal and the second transmit signal to a second antenna, receiving the first signal and the second signal from the first antenna and the second antenna on a first receive path and a second receive path, outputting a sum of the received signals from the first antenna and the second antenna, and outputting a difference of the received signals from the first antenna signal and the second antenna signal. determining interference on a first receive path due to the first transmit signal; determining interference on a second receive path due to the second transmit signal; combining a sum power of signals received from the first antenna and the second antenna and an inverse of the determined interference on the first receive path due to the first transmit signal to generate a first receive signal; and combining a difference power of signals received from the first antenna and the second antenna and an inverse of the determined interference on the second receive path due to the second transmit signal to generate a second receive signal.

[0029] Determining interference in the first and second receive paths due to the respective first and second transmit signals may include matching impedances of the respective first and second antennas, respectively.

[0030] The method may further include filtering the sum output before the first antenna in a first filtering step, filtering the difference output before the second antenna in a second filtering step, filtering the signal received from the first antenna in a second filtering step, and filtering the signal received from the second antenna in a fourth filtering step.

[0031] Determining the interference in the first receive path due to the first transmit signal may include applying filtering steps equivalent to a first filtering step and a third filtering step to the first transmit signal, and determining the interference in the second receive path due to the second transmit signal may include applying filtering steps equivalent to a second filtering step and a fourth filtering step to the second transmit signal.

[0032] The method may further include providing a 180° phase shift circuit for each of the determined interferences in the first receive path due to the first transmit signal and in the second receive path due to the second transmit signal, or for each of the signals in the receive paths.

[0033] A method for providing a circuit, or any portion of a circuit, may be provided.

[0034] A method for controlling any portion of the circuit may be provided.

[0035] A computer program may be provided which, when executed on a processor, performs any part of the method.

[0036] A computer program product may be provided that stores such code. The computer program product may be a non-transitory product. [Brief description of the drawings]

[0037] The present invention will now be described with reference to the accompanying drawings.

[0038] [Figure 1] FIG. 1 shows a conventional exemplary implementation of a two-antenna MIMO configuration that includes circuitry for canceling interference between a transmitter and a receiver. [Diagram 2] FIG. 2 shows an exemplary implementation of a two-antenna MIMO configuration. [Diagram 3] FIG. 3 illustrates the implementation of FIG. 2 in a schematic manner to illustrate the presence of interference that is addressed by the exemplary implementation of FIG. [Figure 4] FIG. 4 shows an example implementation of an improved two-antenna MIMO configuration that includes circuitry for canceling interference between a transmitter and a receiver. [Diagram 5] FIG. 5 illustrates an alternative exemplary implementation of an improved two-antenna MIMO configuration that includes circuitry for canceling interference between a transmitter and a receiver. [Figure 6] FIG. 6 shows an alternative exemplary embodiment of an improved two-antenna MIMO configuration, including an embodiment of a circuit for canceling interference between a transmitter and a receiver. [Figure 7] FIG. 7 shows an alternative exemplary embodiment of an improved two-antenna MIMO configuration, including an embodiment of a circuit for canceling interference between a transmitter and a receiver. [Figure 8] FIG. 8 illustrates an exemplary filter / hybrid network that can be used in the configuration of FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0039] The present invention will now be described with reference to examples and embodiments.

[0040] An example of a two-stage MIMO configuration with two antennas is shown. In general, the described techniques are applicable to n-stage MIMO configurations with n antennas.

[0041] An exemplary, but non-limiting implementation of the described apparatus is in the front-end of an RF device, such as a mobile RF device, such as a mobile phone.

[0042] 2, there is shown a MIMO configuration including a first antenna 101 and a second antenna 102. The first antenna 101 and the second antenna 102 each transmit signals to each antenna via a transmit path and receive signals from each antenna via a receive path.

[0043] 2 further includes, on the transmit side, a first power amplifier 201 in a first transmit path and a second power amplifier 202 in a second transmit path, each connected to receive a respective signal to be transmitted and generate a respective transmit signal Tx1 and Tx2 at an input of the 180° transmit hybrid circuit 22. Thus, each transmit signal on the transmit paths is provided as an input to a single 180° hybrid circuit.

[0044] The 180° transmit hybrid circuit has a sum output 23 and a differential output 25. The sum output 23 is connected to an input of a first transmit filter 241, which has an output connected to the first antenna 101. The differential output 25 is connected to an input of a second transmit filter 242, which has an output connected to the second antenna 102.

[0045] The signal at the sum output 23 of the hybrid circuit 22 is the sum of the two signals received from the two transmit paths. The signal at the difference output 25 of the hybrid circuit 22 is the difference of the two signals received from the two transmit paths.

[0046] 2 further includes a first receive filter 261 and a second receive filter 262 on the receive side, each connected to receive signals from the first antenna 101 and the second antenna 102, respectively. Each receive filter 261 and 262 is connected to provide a received signal from the respective antenna 101 and 102 to a 180° receive hybrid circuit 28. Thus, each signal received at an antenna is provided as an input to a single 180° receive hybrid circuit.

[0047] The 180° receive hybrid circuit 28 has a sum output 29 and a difference output 31. The sum output 29 is connected to the signal R x1 is fed to the input of the first low noise amplifier 301. The differential output 31 provides the signal R x2 to the input of the second low noise amplifier 302.

[0048] The signal at the sum output 29 of the hybrid circuit 28 is the sum of the two signals received from the two antennas. The signal at the difference output 31 of the hybrid circuit 28 is the difference of the two signals received from the two antennas.

[0049] Each low noise amplifier provides a signal to a respective receive path.

[0050] Typically, both transmit filters are tuned to the same (transmit) frequency, and both transmit signals (T x1 and T x2 ) are of the same frequency. Typically, both receive filters are tuned to the same (receive) frequency, and both receive signals (R x1 and R x2 ) are received at the same frequency. Antennas 101 and 102 have an operating bandwidth that covers both the transmit and receive bands.

[0051] Although power amplifiers and low noise amplifiers are not required to implement a MIMO configuration for interference cancellation, they are included in current common MIMO implementations.

[0052] The hybrid circuits 22 and 28 can be implemented using any known circuit for generating sum and difference signals, such as a hybrid transformer or a rat race coupler. The phase shift applied by the hybrid circuits 22 and 28 is implementation dependent. For example, - In some implementations, the sum is T x1 (90°)+T x2 (90°), the difference is T x1 (90°)+T x2 (270°). - In some implementations, the sum is T x1 (0°)+T x2 (0°), and the difference is T x1 (0°)+T x2 (180°).

[0053] In practice, arbitrary phase may be added due to transmission line lengths, etc. This does not affect the scheme, provided that it is equal between the two parts so that the sum and difference relationship is maintained.

[0054] The MIMO configuration of FIG. 2 achieves this interference cancellation without the canceller circuitry requirements of the conventional implementation of FIG.

[0055] The interference that occurs in the example arrangement of Figure 2 is described below with reference to Figure 3. Where elements of Figure 3 correspond to elements of Figure 2, like reference numerals are used.

[0056] 3, the first transmit filter 241 and the second transmit filter 242 are denoted by A and C, respectively, and the first receive filter 261 and the second receive filter 262 are denoted by B and D, respectively. The notations A, B, C, and D indicate the filter transfer functions of the respective filters.

[0057] Block 21, denoted with the notation X, represents the mutual coupling channel between the two sets of transmit / receive filters. It models the effect of mutual coupling between the two antennas 101 and 102. In FIG. 4, for simplicity of illustration, the two antennas 101 and 102 are not shown, and in the following examples the signals received by the antennas are not taken into account (aimed at showing the cancellation of the transmitted signal components arriving at the receiver). Block 21 is therefore shown connected between the junction of the first transmit filter 241 and the first receive filter 261 and the junction of the second transmit filter 242 and the second receive filter 262.

[0058] The signal in the path at the sum output 23 of the transmit hybrid circuit 22 is:

number

[0059] The signal on the path at the differential output 25 of the transmit hybrid circuit 22 is as follows:

number

[0060] In the following analysis, attenuation through filters 241, 242, 261, 262 is used to show the measurement of interference paths. In general, however, the analysis may consider circuits as necessary depending on the implementation. Although the evaluation based on attenuation limits the filters to passive circuits, no general limitation applies, this is implementation specific to provide examples. Filters may be passive and / or active circuits.

[0061] Due to the attenuation A due to the first transmit filter 241, and the attenuation C due to the filter 242, and X due to the cross antenna connection, the signal in the path at the output of the first transmit filter 241 becomes:

number

[0062] Due to the attenuation C due to the second transmit filter 242, and the attenuation A due to the filter 241, and X due to the cross antenna connection, the signal in the path at the output of the second transmit filter 242 becomes:

number

[0063] Due to the attenuation B by the first receive filter 261, the signal of the path at the output of the first receive filter 261 becomes:

number

[0064] Due to the attenuation D by the second receive filter 262, the signal of the path at the output of the second receive filter 262 becomes:

number

[0065] Considering the signals entering and leaving the receiver hybrid circuit 28, the first receive signal R x1 and the second received signal R x2 The formula can be derived as follows:

[0066] For the first received signal, R x1 is expressed as follows:

number

number

[0067] By using filter tuning, A is set equal to C and B is set equal to D, so AB=AD=CB=CD. Therefore, the subtraction of BA and DC cancels each other, and the subtraction of DAX and BCX cancel each other, resulting in T x2 The term is eliminated, so we get

number

number

number

number

[0068] In the configuration example of FIG. 2, the first receive path R x1 The interference of the transmission path T x1 It depends only on the signal from the transmission path T x2It can be seen that the interference in the first receive path does not depend on the signal from the first transmit path. The reason why the interference in the first receive path depends only on the signal from the first transmit path is due to the hybrid circuit. x2 The interference from is cancelled.

[0069] Therefore, the canceller is x1 and the first receive path R x1 This canceller is implemented only during the transmission signal T x1 The canceller is configured to cancel interference in the first receive path caused by (i) = (i+i) = (i+i), thereby reducing or eliminating interference in the first receive path. This can be achieved if the transfer function of the canceller is the antiphase value of equation (1).

[0070] For the second received signal, R x2 is expressed as follows:

number

number

[0071] By using filter tuning, A is set equal to C and B is set equal to D, so AB=AD=CB=CD. Therefore, the subtraction of BA and DC cancels each other, and the subtraction of DAX and BCX cancel each other, resulting in T x1 The term is eliminated, so we get

number

number

number

number

[0072] In the configuration example of FIG. 2, the second receiving path R x2 The interference of the second transmission path T x2 The first transmission path T x1 By using a hybrid transmission circuit, the first transmission path T x1 The interference from is cancelled.

[0073] Therefore, the second canceller is x2 and the second receive path R x2 , and can only compensate for interference from the second transmit path. x2 The second canceller is configured to cancel interference in the second receive path caused by (i) = (i+i) = (i+i) , thereby reducing or eliminating the interference in the second receive path. This can be achieved if the transfer function of the second canceller is the antiphase value of equation (2).

[0074] Due to the operation of the transmit hybrid circuit 22, the signals transmitted by the antennas 101 and 102 are both transmit signals T x1 and T x2 However, the signal T x1 and T x2 By appropriately controlling , it remains possible to independently control the signals transmitted from antennas 101 and 102. For example, if signals Y and Z are transmitted on antennas 101 and 102, respectively, this can be achieved by setting

number

number

[0075] In this case, the signal in the path at the sum output 23 of the transmit hybrid circuit 22 can be expressed as:

number

[0076] Similarly,

number

number

number

[0077] Thus, despite the implementation of addition and subtraction operations in the transmit hybrid circuit 22, the signals transmitted from the antennas may still be independently controlled if required for a particular MIMO transmission. In some embodiments, this allows either one of the antennas 101 and 102 to be used for transmission while the other antenna is not transmitting. Thus, in some embodiments, a MIMO configuration may also be provided that can operate in both a single antenna mode and a MIMO mode of operation. As in the above example, the received signal R may be independently controlled if required. x1 and R x2 By processing the sums and differences, the signals received at each antenna 101 and 102 can be recovered.

[0078] Figure 4 shows an implementation of the MIMO configuration according to Figure 2 incorporating a canceller circuit to cancel interference between the antenna transmit and receive paths. Where elements of Figure 4 correspond to elements of Figure 2, similar reference numbers are used.

[0079] In the MIMO configuration of FIG. 4, a canceller circuit is introduced that cancels interference in accordance with the interference determination described with reference to FIG.

[0080] Comparing FIG. 4 with FIG. 2, a first canceller circuit 381 and a second canceller circuit 382 are added, and a first coupler 401 and a second coupler 402 are added.

[0081] The first canceller circuit 381 cancels the transmission signal T x1 The first combiner 401 is connected to receive the sum output 29 of the 180° receive hybrid circuit 28 and combines the sum output 29 with the output of the canceller circuit 381 to provide a receive signal R x1 to provide.

[0082] The second canceller circuit 382 cancels the transmit signal T x2 A second combiner 402 is added to connect the differential output 31 of the 180° receive hybrid circuit 28 and combines the differential output 31 with the output of the canceller circuit 382 to provide the receive signal R x2 to provide.

[0083] Comparing the configuration of Figure 4 with the configuration of Figure 1, it can be seen that the MIMO configuration requires one canceller circuit for each antenna, and the number of canceller circuits required maps to the number of antennas, unlike the configuration of Figure 1 where the number of canceller circuits required is the square of the number of antennas.

[0084] In general, each canceller circuit 381 and 382 inserts the inverse of the interference into the respective path and into the output of the hybrid circuit 28. Canceller 381 implements the inverse of equation (1) and canceller 382 implements the inverse of equation (2).

[0085] In some embodiments, the canceller circuits 381 and 382 may be passive circuit networks with adjustable and / or fixed circuit components (e.g., resistors, capacitors, inductors, transformers, transmission lines, other components, etc.) that can adjust the frequency response (i.e., transfer function) of the network such that a cancellation signal that is an anti-phase copy of the self-interference signal at each of the outputs 29 and 31 of the receive hybrid 28 is generated across a frequency band of interest (e.g., the transmit and / or receive frequency bands). Adjustable components within each canceller 381 and 382 allow the transfer function of the canceller to be adjusted and / or tuned such that interference from each transmit path at each receive path is canceled at each combiner 401 and 402.

[0086] Although additional circuitry is required (specifically 180° hybrid circuits 22 and 28), the overall circuitry required is less than that required in a configuration such as FIG.

[0087] Figure 5 shows an alternative implementation of the MIMO configuration with interference cancellation technique of Figure 4. Where elements of Figure 5 correspond to elements of Figure 4, like reference numerals are used.

[0088] As shown in FIG. 5, the first transmit filter 241 and the second transmit filter 242 and the first receive filter 261 and the second receive filter 262 are replaced with a first circulator 501 and a second circulator 502.

[0089] The first circulator 501 is connected to the antenna 101, receives the sum output of the 180° transmit hybrid circuit 22, and provides an input to the 180° receive hybrid circuit .

[0090] The second circulator 502 is connected to the antenna 102 , receives the differential output of the 180° transmit hybrid circuit 22 , and provides an input to the 180° receive hybrid circuit 28 .

[0091] The canceller circuits 381 and 382 in FIG. 5 can perform the same functions through the same means as described with reference to FIG.

[0092] As shown in Figure 2, the transmit filters are tuned to the same transmit frequency and the receive filters are tuned to the same receive frequency. In the configuration of Figure 5, the circulators are replaced by transmit and receive filters, so that each circulator can be used to transmit and receive simultaneously at the same frequency.

[0093] Referring to Figure 6, there is shown an example implementation of the canceller of Figure 4. Where elements of Figure 6 correspond to elements of Figure 4, like reference numbers are used.

[0094] The implementation of the canceller shown in FIG. 6 is based on implementing the requirements of equations (1) and (2) as described above.

[0095] In the implementation of FIG. 6, the first combiner 401 and the second combiner 402 are simply implemented as connection points 701 and 702 of three signals to / from the respective combiners 401 and 402 .

[0096] The first and second transmit filters 241 and 242 and the first and second receive filters 261 and 262 are preferably implemented as tunable filters. They may be implemented as tunable filters in any implementation.

[0097] The canceller 381 comprises a first canceller receive filter 601 having an input connected to the output of the first power amplifier 201, a first canceller transmit filter 621 having an input connected to the output of the first canceller receive filter 601, a 180° phase shifter 641 connected between the output of the first canceller receive filter 621 and the combiner connection point 701, and a sub-canceller circuit 661 connected between the first canceller receive filter 601 and the first canceller transmit filter 621.

[0098] The canceller 382 comprises a second canceller receive filter 602 having an input connected to the output of the second power amplifier 202, a second canceller transmit filter 622 having an input connected to the output of the second canceller receive filter 602, a 180° phase shifter 642 connected between the output of the second canceller receive filter 621 and the combiner connection point 702, and a sub-canceller circuit 662 connected between the second canceller receive filter 602 and the second canceller transmit filter 622.

[0099] In some embodiments, the sub-canceller circuits 661 and 662 may be passive networks with adjustable and / or fixed circuit components such that the frequency response of the network can be adjusted, together with adjustable filters included within the cancellers 381 and 382, ​​such that a cancellation signal is produced at the canceller output that is an anti-phase copy of the self-interference signal at the outputs 29 and 31, respectively, of the receive hybrid 28 across a frequency band of interest (such as the transmit frequency band and / or the receive frequency band). The cancellers 381 and 382 preferably compensate for a self-interference coupling component (denoted by the notation X in the above equations) resulting from mutual coupling of signals between the antennas 101 and 102.

[0100] In some embodiments, the transmit filters 241, 242, 621, and 622 may be circuits of the same design and may be tuned to have the same center frequency and transfer function, and the receive filters 261, 262, 601, and 602 may be circuits of the same design and may be tuned to have the same center frequency and transfer function. In such embodiments, the overall transfer function of the cancellation circuit 381 between the output of the power amplifier 201 and the node 701 may be equal in magnitude and opposite in phase compared to the overall transfer function of the circuit including the hybrid circuit 22, the filter 241, the antenna 101, the filter 261, and the hybrid 29 between the output of the power amplifier 201 and the node 701.

[0101] Assuming that filters 621 and 241 have identical transfer functions denoted by notation A, and filters 601 and 261 have identical transfer functions denoted by notation B (using the same notation as used in FIG. 3), and taking into account the signal inversion due to the 180° phase shift, the overall transfer function of canceller 381 can be denoted as −BLA, where the notation L denotes the transfer function of subcanceller circuit 661. If subcanceller circuit 661 is tuned such that L=(1+X), then the transfer function of canceller 381 becomes −BA(1+X), which is the inverse of equation (1), thereby providing cancellation at node 701.

[0102] Similarly, if filters 622 and 242 have identical transfer functions denoted by notation A, and filters 602 and 262 have identical transfer functions denoted by notation B, and take into account signal inversion due to a 180° phase shift, then the overall transfer function of canceller 382 can be denoted as −BPA, with the notation P denoting the transfer function of subcanceller circuit 662. If subcanceller circuit 662 is tuned such that P=(1−X), then the transfer function of canceller 382 becomes −BA(1−X), which is the inverse of equation (2), thereby providing cancellation at node 702.

[0103] In other embodiments, filters 622 and 242 may have different designs and / or transfer functions, and filters 602 and 262 may have different designs and / or transfer functions. Additionally, in some embodiments, due to manufacturing imperfections, additional loss and / or phase shift may be applied by hybrid junctions 22 and 28. However, in such embodiments, the filters and / or subcancellers that make up cancellers 381 and 382 may be adjusted so that the transfer functions of cancellers 381 and 382, ​​respectively, are adjusted to be equal to or greater than T x1 and R x1 Between and T x2 and R x2 By making the self-interference coupling channel between the two equalizers inverse, self-interference cancellation can be achieved.

[0104] The order of the transmit and receive filters is preferably swapped in the canceller path. Since this is a linear system, the overall transfer function is the same. The filters are preferably swapped so that the canceller does not load the transmit and receive ports. For example, considering the output of the power amplifiers 201 and 202, at this point in the circuit it is desirable (for transmitter energy efficiency) for most of the power at the transmit frequency to be sent to the hybrid circuit (and transmitted out of the antenna) and for minimal transmit power to be sent to the cancellation circuit. In this example design, this occurs because the receive filter passes only minimal energy at the transmit frequency (which is within the stop band of the receive filter). Similarly, the output of the receive hybrid 28 is connected to a low noise amplifier and canceller, where it is desirable for all energy at the receive frequency to be sent to the low noise amplifier and not the canceller output. This is achieved by placing a transmit filter here that passes minimal energy at the receive frequency.

[0105] In this example, it is assumed that the transfer functions of the filters 621, 622, 241, and 242 have the same transfer function, that the filters 601, 602, 261, and 262 have the same transfer function, and that the sub-canceller networks 661 and 662 are tuned to compensate for the mutual coupling of the antennas. In other embodiments, the filters 601, 602 may exhibit a different transfer function than the filters 261 and 262, and the filters 621, 622 may exhibit a different transfer function than the filters 241 and 242, and the sub-canceller circuits 621, 622 may also be tuned to provide the different transfer functions required to cancel the self-interference signal at the respective signal junctions 701 and 702. In general, the desired requirement is that the cancellation path has an inverse transfer function compared to the self-interference path, including compensation for the mutual coupling of the antennas if necessary. Such compensation may occur with any tunable circuit that comprises the respective cancellers 381 and 382.

[0106] Note that this is an example implementation. In a configuration such as that shown in Figure 5, there are no transmit and receive filters. Typically, a canceller circuit is provided in combination with each signal received from the antenna in the receive path to cancel the interference from the corresponding transmit path.

[0107] In the exemplary configuration of FIG. 7, the cancellers 381 and 382 are shown as including 180° phase shift circuits 641 and 642, respectively. This phase shift circuit may be considered as part of the respective canceller circuit as shown in the figure, or may be provided as a circuit separate from the canceller circuit but located in the cancellation path. Alternatively, this 180° phase shift may be provided in the receive path, for example in the sum or difference output of the hybrid circuit 28. Alternatively, this 180° phase shift may be provided elsewhere in the system. Those skilled in the art will recognize that all that is required is that the respective cancellation signals be combined in anti-phase with the respective interfering signals in the respective receive paths, and that there are numerous locations in the circuit where a phase shift can be provided to achieve this.

[0108] Referring to Figure 7, there is shown an example implementation of the MIMO of Figure 6. Where elements of Figure 7 correspond to elements of Figure 6, like reference numerals are used.

[0109] In the implementation of FIG. 7, the 180° transmit hybrid circuit 22 is replaced with a 180° transmit hybrid circuit 72 and the 180° receive hybrid circuit 28 is replaced with a 180° receive hybrid circuit 78.

[0110] In the implementation of Figure 7, the first transmit filter 241 and the second transmit filter 242 of Figure 6 are not provided as separate filters, and the 180° transmit hybrid circuit 72 is an integrated filter and hybrid network, where the functions of the first transmit filter 241 and the second transmit filter 242 of Figure 6 are integrated into the 180° transmit hybrid circuit 72. The integrated transmit filter is preferably tunable.

[0111] In the implementation of Figure 7, the first receive filter 241 and the second receive filter 242 of Figure 6 are not provided as separate filters, and the 180° receive hybrid circuit 72 is an integrated filter and hybrid network, with the functions of the first transmit filter 261 and the second transmit filter 262 of Figure 6 being integrated into the 180° receive hybrid circuit 78. The integrated receive filter is preferably tunable.

[0112] A first antenna 101 is connected to the sum output of the 180° hybrid circuit 72 and to the input of the 180° hybrid circuit 78. A second antenna 102 is connected to the differential output of the 180° hybrid circuit 72 and to the input of the 180° hybrid circuit 78.

[0113] Also shown in FIG. 7 are implementation examples of the subcanceller circuits 661 and 662. These implementation examples are not limited to the implementation of the hybrid circuits 72 and 78. In this example, the subcanceller circuits 661 and 662 are implemented as variable impedance circuits 671 and 672, respectively, with one node connected between the canceller receive filter and the canceller transmit filter and one node connected to ground. Such variable impedance circuits may comprise a network of one or more fixed and / or adjustable circuit elements. In some embodiments, if the filters 621, 622, 241, and 242 have identical transfer functions, the filters 601, 602, 261, and 262 have identical transfer functions, and there is no mutual coupling between the antennas, it may be preferable to tune the impedance circuits 671 and 672 to provide the same impedance as the antennas 101 and 102, respectively. If there is mutual coupling of signals between the antennas 101 and 102, it may be preferable to further tune the impedance of the adjustable impedance circuits 671 and 672 to cancel the mutual coupling between the antennas. In general, the variable impedance circuits 671 and 672 may be adjusted to increase the level of cancellation provided at the respective signal junctions 701 and 702 in a frequency band of interest (eg, a transmit and / or receive frequency band).

[0114] Referring to FIG. 8, an example implementation of the integrated filter and hybrid network as shown in FIG. 7 is shown.

[0115] In this example, the integrated filter and hybrid network is a four-port network, having two input ports 821 and 824 and two output ports 822 and 823. Filter 802 is connected between ports 821 and 822, filter 802 is connected between ports 822 and 823, filter 803 is connected between ports 823 and 824, and filter 804 and a 180° phase shifter are connected in series between ports 821 and 824. Filters 801, 802, 803, and / or 804 may be tunable.

[0116] In this network, the signal entering port 821 is filtered and coupled with a 0° phase shift to port 822 and filtered and coupled with a 180° phase shift to port 824. The signal entering port 823 is filtered and coupled with a 0° phase shift to ports 824 and 822. Thus, the signal leaving port 824 is the difference between the filtered signal entering port 823 and port 821, and the signal leaving port 822 is the sum of the filtered signal entering port 821 and port 823.

[0117] Either the integrated tunable filter / hybrid network 72 or 78 may be implemented according to the configuration of FIG. 8. Other implementations may be used. Various examples and embodiments have been shown as circuits or devices. The invention is not limited to circuits or devices. The invention may be embodied by a method or process. The method or process may be implemented, at least in part, using computer processing techniques. Computer program code may be provided that, when executed on a processor, such as the processors shown in the examples above, is capable of performing, at least in part, any method or process. A computer program product may be provided having such computer program code stored thereon.

[0118] Various examples and embodiments are provided to illustrate the invention, and aspects of the examples and embodiments may be combined.

[0119] The present invention has been described with reference to various embodiments and implementations. The invention is not limited to the details of any of the examples. The scope of protection afforded by the present invention is defined by the appended claims.

Claims

1. A multiple-input multiple-output (MIMO) antenna configuration, a transmit hybrid circuit connected to receive a first transmit signal and a second transmit signal, and to output a sum of the first transmit signal and the second transmit signal, and to output a difference of the first transmit signal and the second transmit signal; a first antenna connected to receive the sum of the outputs; a second antenna connected to receive the output difference; a receiver hybrid circuit connected to receive a first antenna signal from the first antenna and a second antenna signal from the second antenna, and to output a sum of the first antenna signal and the second antenna signal and a difference of the first antenna signal and the second antenna signal; a first cancellation circuit connected to receive the first transmit signal and configured to compensate for interference due to a first transmit path; a second cancellation circuit connected to receive the second transmit signal and configured to compensate for interference due to a second transmit path; Equipped with a sum output of the receive hybrid circuit and an output of the first cancellation circuit are combined to generate a first receive signal; a differential output of the receive hybrid circuit and an output of the second cancellation circuit are combined to generate a second receive signal; MIMO antenna configuration.

2. 2. The MIMO antenna configuration of claim 1, wherein the first cancellation circuit and the second cancellation circuit each include a phase inversion circuit, and the first combiner and the second combiner combine the respective outputs of the receive hybrid circuits with inverted outputs of the cancellation circuits.

3. 2. The MIMO antenna configuration of claim 1, wherein each of the first cancellation circuit and the second cancellation circuit includes a sub-canceller circuit that matches the impedance of the respective first antenna and second antenna.

4. a first transmit filter connected between the sum output of the transmit hybrid circuit and the first antenna; a second transmit filter connected between the differential output of the transmit hybrid circuit and the second antenna; a first receive filter connected between the first antenna and the receive hybrid circuit; a second receive filter connected between the second antenna and the receive hybrid circuit; 4. The MIMO antenna arrangement of claim 1, further comprising:

5. The transmitting hybrid circuit includes: a first transmit filter for filtering the sum output of the transmit hybrid circuit; a second transmit filter for filtering the differential output of the transmit hybrid circuit; Including, The receiving hybrid circuit includes: a first receive filter for filtering the first antenna signal; a second receive filter for filtering the second antenna signal; 4. A MIMO antenna arrangement according to claim 1, comprising:

6. The MIMO antenna configuration of claim 4 , wherein the first and second transmit filters and the first and second receive filters are tunable filters.

7. The first cancellation circuit a first canceling receive filter connected to receive the first transmit signal; a first canceling transmit filter connected to receive the signal from the first canceling receive filter; Including, The second cancellation circuit a second canceling receive filter connected to receive the first transmit signal; a second canceling transmit filter connected to receive the signal from the second canceling receive filter; 5. The MIMO antenna arrangement of claim 4, comprising:

8. 8. The MIMO antenna configuration of claim 7, wherein the first cancellation circuit comprises a 180° phase shift circuit and the second cancellation circuit includes a 180° phase shift circuit.

9. The MIMO antenna configuration according to claim 7 , wherein the first and second cancellation transmit filters and the first and second cancellation receive filters are tunable filters.

10. 8. The MIMO antenna configuration of claim 7, wherein the first transmit filter matches the first canceling transmit filter, the second transmit filter matches the second canceling transmit filter, the first receive filter matches the first canceling receive filter, and the second receive filter matches the second canceling receive filter.

11. 8. The MIMO antenna arrangement of claim 7, wherein each cancellation circuit includes a sub-canceller circuit connected between the respective cancellation transmit filter and cancellation receive filter.

12. 12. The MIMO antenna configuration of claim 11, wherein each subcanceller circuit is a variable impedance network.

13. 12. The MIMO antenna configuration of claim 11, wherein the subcanceller circuit is tunable to match the impedance of the respective first antenna or second antenna.

14. 12. The MIMO antenna arrangement of claim 11, wherein each subcanceller circuit is tunable to compensate for interference in a respective receive path from a respective transmit path.

15. a first circulator connecting the first antenna, the sum output of the transmit hybrid circuit, and an input to the receive hybrid circuit; a second circulator connecting the second antenna, the differential output of the transmit hybrid circuit, and the input to the receive hybrid circuit; 4. The MIMO antenna arrangement of claim 1, further comprising:

16. a first power amplifier for providing the first transmit signal; a second power amplifier for providing the second transmit signal; 10. The MIMO antenna configuration of claim 1, further comprising:

17. a first low noise amplifier for receiving the first received signal; a second low noise amplifier for receiving the second received signal; 10. The MIMO antenna configuration of claim 1, further comprising:

18. 1. A method for transmitting and receiving in a multiple-input multiple-output (MIMO) antenna configuration, comprising: receiving a first transmission signal and a second transmission signal; outputting the sum of the first transmission signal and the second transmission signal to a first antenna; outputting a difference between the first transmission signal and the second transmission signal to a second antenna; receiving first and second antenna signals from the first and second antennas on first and second receive paths; outputting a sum of the first antenna signal and the second antenna signal; outputting a difference between the first antenna signal and the second antenna signal; determining interference in the first receive path due to the first transmit signal; determining interference in the second receive path due to the second transmit signal; combining a sum of the first and second antenna signals received from the first and second antennas with an inverse of the determined interference in the first receive path due to the first transmit signal to generate a first receive signal; combining a differential output of the first and second antenna signals received from the first and second antennas with an inverse of the determined interference in the second receive path due to the second transmit signal to generate a second receive signal; A method comprising:

19. 20. The method of claim 18, wherein determining interference in the first receive path and the second receive path due to the respective first transmit signal and the second transmit signal comprises matching impedances of the respective first antenna and the second antenna, respectively.

20. 20. The method of claim 18 or 19, further comprising filtering the sum output before the first antenna in a first filtering step, filtering the difference output before the second antenna in a second filtering step, filtering the first antenna signal received from the first antenna in a third filtering step, and filtering the second antenna signal received from the second antenna in a fourth filtering step.

21. 21. The method of claim 20, wherein determining interference in the first receive path due to the first transmit signal comprises applying filtering steps equivalent to the first filtering step and the third filtering step to the first transmit signal, and determining interference in the second receive path due to the second transmit signal comprises applying filtering steps equivalent to the second filtering step and the fourth filtering step to the second transmit signal.

22. 20. The method of claim 18, further comprising: a 180° phase shift circuit for each of the determined interference in the first receive path due to the first transmit signal and in the second receive path due to the second transmit signal, or for each of the signals in the receive paths.

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