The present disclosure generally relates to wireless communication systems, and more particularly to wireless multicast/broadcast communication systems using a plurality of transmission towers.
In traditional terrestrial broadcast systems, backhaul data is delivered from a broadcast gateway to broadcast transmitters via studio-to-transmitter links (STL). The STL links are usually implemented using wired connections or dedicated microwave links, both suffering from issues with availability and cost. For the legacy high-power-high-tower (HPHT) deployments, where a single tower covers an entire city, these solutions are affordable.
However, new generation terrestrial broadcasting systems, such as the Advanced Television Systems Committee (ATSC) 3.0, single-frequency-network (SFN) with multiple lower-power transmitters become more attractive in comparison to the traditional single-transmitter HPHT system, in order to deliver mobile services to portable/handheld and indoor receivers, and to support higher service quality. With the number of transmitters increasing, the existing STL solutions quickly become unaffordable. To address this challenge, a one-way wireless in-band backhaul technology to feed broadcast SFN transmitters has been described in U.S. Pat. No. 10,771,208, which is incorporated herein by reference for all purposes.
US Patent Publication 2022/0159650, which is incorporated herein in its entirety, discloses a broadcast communication system including a plurality of transmitter tower stations (TTS) configured to exchange inter-tower communication (ITC) signals to support a wireless ITC network (ITCN). Several ITCN-integrating broadcast systems operating in the same or different frequency band may be interconnected to support an integrated inter-tower wireless communication network. Each TTS includes a transmitter (Tx) antenna, at least one receiver (Rx) antenna, and an ITCN server configured to form outgoing ITC signals for transmitting with the Tx antenna and to process incoming ITC signals received with at least one Rx antenna. Each of the TTSs is configured to multiplex outgoing ITC signals with broadcast services signals prior to the transmitting and to detect the incoming ITC signals in a wireless signal received with at least one Rx antenna.
Embodiments disclosed herein will be described in greater detail with reference to the accompanying drawings, which are not to scale, in which like elements are indicated with like reference numerals, and wherein:
The following acronyms may be used herein:
Embodiments described herein relate to terrestrial single-frequency broadcast systems that include a plurality of broadcast stations equipped with wireless receivers to support station to station communications using in-band signaling. The broadcast stations are typically provided on transmission towers and are therefore referred to herein as transmitter tower stations (TTSs). However, the term “TTS” as used herein encompasses broadcast stations with broadcast antennas located at dedicated transmission towers as well as other suitably tall structures, e.g., on the roofs of high-rise buildings in a city environment. Some of the examples described herein may refer to ATSC 3.0 standards to deliver broadcast TV services; however, embodiments described herein are not limited to ATSC 3.0 compliant systems, but generally relate to wireless RF transceivers configured for in-band reception of wireless RF signals, such as e.g. inter-tower communication (ITC) signals. The embodiments further relate to techniques for at least partially overcoming detrimental effects of self-interference in such transceivers on reception quality using frequency-domain filtering guided by transmitter-provided reference signals, and time-domain windowing of filter weights adapted to a delay profile of the self-interference channel. Some of the embodiments may use an iterative process to update the filter coefficients based on a received signal estimate obtained by re-encoding and/or re-modulating an output signal of a decoder and/or a demodulator of a signal processing chain of the receiver.
An aspect of the present disclosure provides an apparatus comprising: a digital processor for a wireless transceiver comprising a transmitter and a receiver. The digital processor is configured for filtering a frequency-domain spectrum R(k) of a transmitter-provided reference signal R(t) to estimate an interference spectrum SI(k), and estimating a spectrum E(k) of a remotely-transmitted signal at the receiver based on the estimated interference spectrum SI(k) and a spectrum Y(k) of a received signal Y(t), wherein in operation the received signal Y(t) is received by the receiver from a receiver antenna. The filtering comprises estimating filter weights W(k) based, at least, on the frequency-domain spectra R(k) and Y(k), and applying a de-noising filter to the estimated filter weights.
In some implementations, the processor may be configured to divide the spectrum Y(k) of the received signal Y(t) by the spectrum R(k) of the reference signal to estimate the filter weights W(k). In some implementations, the processor may be configured to subtract, from the received signal, an estimate of a contribution therein of the remotely-transmitted signal prior to the dividing to estimate the filter weights W(k).
In any of the above implementations, the processor may be configured to subtract the estimated interference spectrum SI(k) from the spectrum Y(k) of the received signal Y(t) to estimate the spectrum E(k) of the remotely-transmitted signal.
In any of the above implementations, the processor may be further configured to: a) estimate a transmission channel response for the remotely-transmitted signal based on the estimated spectrum E(k), and b) compute an estimate of the remotely-transmitted signal based on the transmission channel response. In some implementations, the processor may be further configured to: c) estimate a contribution of the remotely transmitted signal into the received signal based on the estimated transmission channel response and the estimate of the remotely-transmitted signal; d) subtract the estimated contribution of the remotely transmitted signal from the received signal to update the filter weights W(k); and, e) modify the estimated interference spectrum SI(k) based on the updated filter weights to update the estimates of the transmission channel response and the remotely transmitted signal. In some implementations, the apparatus may be further configured to iteratively repeat the operations (a) to (e) until a stopping criterion is reached.
In any of the above implementations, applying the de-noising filter may comprise applying one or more time-domain windows to a time-domain representation of the filter weights. In some of such implementations, the one or more time-domain windows may comprise a low-pass window. In some of such implementations, the one or more time-domain windows may comprise a plurality of non-overlapping time-domain windows. In some implementations, the one or more time-domain windows may be selected based on an estimate of a time-delay profile of an interference channel from the transmitter to the receiver. In some implementations, the time-domain windowing may comprise DFT and inverse-DFT processing. In some implementations, the de-noising filter may comprise a Wiener filter.
In any of the above implementations, the processor may be configured to update a current set of the filter weights W(k) based on one or more earlier-generated sets of the filter weights.
In any of the above implementations the apparatus may comprise a communication channel from the transmitter to the receiver for providing the reference signal. In some of such implementations the communication channel comprises a wired connection from an output of the transmitter to an input of the receiver. In some of such implementations the communication channel may comprise an additional receiving antenna. The apparatus may comprise a broadcast antenna configured to transmit signals generated by the transmitter, and the additional receiving antenna may be a directional receiving antenna aimed at the broadcast antenna.
A related aspect of the present disclosure provides a transceiver for a wireless broadcast station, the transceiver comprising: a transmitter for connecting to a transmitting antenna to broadcast a signal; and, a receiver for connecting to a receiving antenna to receive a remotely-transmitted signal. The receiver comprises a digital processor for cancelling an interference signal from the transmitter. The processor is configured to perform the acts of: filtering a frequency-domain spectrum R(k) of a transmitter-provided reference signal R(t) to estimate an interference spectrum SI(k); and subtracting the estimated interference spectrum SI(k) from a spectrum Y(k) of a received signal Y(t) to estimate a spectrum E(k) of the remotely-transmitted signal, the received signal Y(t) being received from the receiving antenna. The filtering comprises: estimating filter weights W(k) based, at least, on the frequency-domain spectra R(k) and Y(k), and applying a de-noising filter to estimated filter weights.
A related aspect of the present disclosure provides a method for receiving remotely-transmitted signals by a transceiver of a wireless broadcast station, the transceiver comprising a transmitter connected to a transmit antenna and a receiver connected to a receive antenna. The method comprises filtering a frequency-domain spectrum R(k) of a transmitter-provided reference signal R(t) to estimate an interference spectrum SI(k) at the receiver, and subtracting the estimated interference spectrum SI(k) from a spectrum Y(k) of a received signal Y(t) to estimate a spectrum E(k) of the remotely-transmitted signal, the received signal being provided from the receive antenna. The filtering comprises: estimating filter weights W(k) based, at least, on the frequency-domain spectrum R(k) and the spectrum Y(k) of the received signal Y(t), and time-domain windowing of the filter weights.
The TTS 110A is further provided with a transceiver 120 including a transmitter 122 and a receiver 124. The transmitter 122 is coupled to the Tx antenna 112 for transmitting at least the broadcast signal 101 provided by the transmitter 122. In some embodiments, the Tx antenna 112 may also transmit the ITC signals 103 sharing a same frequency band with the broadcast signal 101, e.g. for spectral efficiency (“in-band transmission”). In various embodiments, the transmitter 122 may be configured to combine the broadcast signal 101 and the ITC signal 103 using a time-division multiplexing (TDM), layer-division multiplexing (LDM), or some combination thereof, and to provide the multiplexed signal to the Tx antenna 112.
The receiver 124 is coupled to the Rx antenna 114 to receive wireless signals 116 generated by a transmitter of the second TTS 110B (“remote transmitter”, not shown). The wireless signals 116 may include the broadcast signal 101 and a second ITC signal 105 directed to the first TTS 110A, and the receiver 124 includes a processor 126 configured for detecting said second ITC signal 105 to extract ITC data contained therein. The ITC signals 103 and 105 and the broadcast signal 101 may be transmitted by the first and second TTS 110A, 110B in overlapping radio-frequency (RF) bands; such “in-band” transmission of the broadcast and ITC signals, being spectrally efficient, can however make the operation of the receiver 124 vulnerable to transmitter-receiver interference (“self-interference”).
The Rx antenna 114 is typically a high-gain directional antenna aimed at a “partner” TTS, e.g. the second TTS 110B. However, the Rx antenna 114, being typically located in a vicinity of the Tx antenna 112, may capture a stray portion 117 of the wireless signals 113 transmitted by the Tx antenna 112. When overlapped in time and frequency with the wireless signals 116 from the “partner” TTS carrying the second ITC signal 105, the captured portion 117 interferes with the detection of the second ITC signal 105 in the signal received by the processor 126 from the Rx antenna 114 (“self-interference”). According to an aspect of the present disclosure, the digital processor 126 is configured to at least partially reduce, or approximately cancel, this self-interference, e.g. as described below with reference to example embodiments.
The following terms and notations may be used herein with reference to operation of a digital processor of an RF receiver (“Rx processor”), such as the digital processor 126 of the receiver 124 of the TTS 110A. The signal received by the Rx processor from the Rx antenna that is aimed at a remote TTS (e.g. Rx antenna 114 aimed at TTS 110B) will be referred to as the received signal or the antenna signal and denoted “Y”, with a time-domain representation thereof denoted as Y(t), and a frequency-domain representation denoted as Y(k). The signal generated by the transmitter of a remote TTS (“remote transmitter”), e.g. the transmitter of the second TTS 110B, will be referred to as the remotely-transmitted signal and denoted “S”, with a time-domain representations thereof denoted as S(t), and a frequency-domain representation denoted as S(k). A reference signal provided to the Rx processor from an output of the co-located transmitter, as described below, is referred to as the RF reference signal, or RFRS, and denoted R, with the time-domain and frequency-domain representations thereof denoted R(t) and R(k), respectively. Here and in the following, “t” denotes sampling time at the receiver, and k=1, . . . , N is an integer indicating a DFT or, more specifically, FFT frequency bin, with N indicating the size of the DFT or FFT operation to convert the time-domain signals Y(t), S(t), and R(t) into the frequency domain signals Y(k), S(k), and R(k), respectively. The propagation from the remote transmitter to the Rx processor, which modifies the remotely transmitted signal S, may be described as propagation via a transmission channel having a transmission channel response denoted “F”, or F(k) in the frequency domain. The transmission channel from the remote transmitter to the Rx processor may be referred to as the forward channel (“FwCh”) and the transmission channel response “F” referred to as the forward channel response. The propagation-modified version of the remotely-transmitted signal S that is contained in the received signal Y may be referred to as the received remote signal and denoted “SRX”, with the frequency domain representation thereof SRX(k)≅F(k)·S(k). The received signal Y further includes an interference signal from a co-located transmitter as described above (e.g. the stray signal 117,
The receiver 230 is coupled to an Rx antenna 214 and includes a digital Rx processor 240. The Rx processor 240 may be an embodiment of the Rx processor 126 of
According to an aspect of the present disclosure, the digital Rx processor 240 is configured to perform the SI cancellation (SIC) based on a transmitter-provided RFRS 223, using a frequency-domain filtering of the RFRS 223 for SI estimation. The RFRS 233 is an RF signal tapped off from an output signal of the transmitter 220. In the context of this specification, “RF” refers to the broadcast frequencies of a corresponding broadcast transmitter, e.g. between 100 MHz and 10 GHz typically.
The RFRS 303 is filtered in the frequency domain by a frequency-domain filter (FDF) 310 using filter weights W(k), where k=1, . . . , N denote the frequency bins of an N-point digital Fourier transform (DFT) operation, e.g. an N-point fast Fourier transform (FFT). The FDF 310 outputs an estimate of a SI spectrum 305, denoted SI(k), approximately in accordance with equation (1):
S
I(k)=R(k)·W(k) (1)
where the frequency-domain amplitudes R(k), k=1, . . . , N, are an output of the N-point DFT operation on the time-domain RF reference signal R(t). In an example embodiment, the filter weights W(k) are estimated in RF, without the down-conversion of the signals Y(t) and R(t) to the baseband. E.g. FWE 340 may compute a set {W} of N filter weights W(k) based at least on the received signal Y(t) 301 and the RFRS R(t) 303. The filter weights W(k) may be computed in the frequency domain based on the spectra Y(k) and R(k) of the respective time-domain signals Y(t) and R(t), where the frequency-domain amplitudes Y(k), k=1, . . . , N, are an output of the N-point DFT operation on the time-domain received signal Y(t).
In some embodiments, the FWE 340 may generate a first estimate of the weights W(k), using element-by-element division of the received signal spectrum Y(k) by the reference signal spectrum R(k), e.g. in accordance with equation (2):
W(k)=Y(k)/R(k) (2)
The weights W(k) may then be filtered by the dNF 330 to reduce noise, e.g. to lessen a contribution into the weights W(k) of time delays outside of an estimated delay spread of the self-interference signal from the co-located transmitter. When the SI signal from the co-located transmitter is dominant in the received signal Y(t), the set {W} of the weights W(k) provided by equation (2) approximates a frequency-domain channel transmission function for the SI signal (“loop-back channel”), from the transmitter 220 to the Rx processor of the co-located receiver, e.g. processor 240 of the receiver 230. Equation (2) may provide a least-square (LS) estimate of the loop-back SI channel if the contribution into the received signal Y(t) of all other signals may be approximated by Gaussian noise, including that from the remotely-transmitted signal S(t) (“intrinsic noise”). In some embodiments the FWE 340 may use, in a next iteration, a re-modulated feedback signal 309 from a downstream demodulator or decoder (not shown) to reduce the “intrinsic noise” in the weight estimates, as further described below.
The transmitter 410 includes a modulator/encoder unit 416, followed by a digital to analog converter (DAC) 414. In an embodiment, the modulator/encoder 416 may be configured to encode the broadcast signal 101 and the ITC signal 103, e.g. using any suitable encoding techniques known in the art, multiplex the encoded broadcast and ITC signals using, e.g. TDM and/or LDM, and then modulate the combined signal onto a carrier or a plurality of carriers using a suitable modulation format, e.g. an orthogonal frequency domain multiplexing (OFDM). The modulator/encoder 416 may also perform other functions, such as e.g. time and frequency domain interleaving, adding of one or more pilot signals, preambles, guard intervals, etc., as will be known to those skilled in the art. The DAC 414 is configured to convert the output of the modulator/encoder 416 to an analog RF signal, which is then suitably amplified by the power amplifier 412 for transmitting, e.g. broadcasting, with the Tx antenna 401.
The receiver 420 includes an analog-to-digital (ADC) converter 422 coupled to a digital processor 430. The digital processor 430, which may be an embodiment of the Rx processor 240 of
E(k)=[Y(k)−SI(k)]=[Y(k)−W(k)·R(k)] (3)
The N-point FFT processors 811, 812 operate on blocks of consecutive time samples of the digital signals R(t) and Y(t), converting them into consecutive N-point FFT blocks {Ri(k)} and {Yi(k)}, with i being an integer block counter. In embodiments using OFDM, the FFT blocks {Ri(k)} and {Yi(k)} may be referred to as the OFDM blocks or the OFDM symbols. The AWE 835 may generate a set {Wi} of N weights Wi(k) for each of the FFT blocks {Ri(k)} and {Yi(k)}. In an embodiment, the weight update unit 837 may be configured to compute an updated set of weights Wu(k) based on M>1 weight sets {Wi} for M consecutive FFT blocks. The updated weight set {Wu} may then be applied by the AWE unit 835 to each of the M FFT blocks {Ri(k)}, or to a current FFT block {R(k)}, to compute the SI spectrum estimate SI(k) and the output spectrum E(k), e.g. according to equations (1) and (3) respectively.
In some embodiments, the weight update unit 837 may be configured to use a known adaptive filtering method to update the filter weights based on the SI-reduced output spectrum E(k) and the reference signal spectrum R(k), as indicated in
In some embodiments, the updated set of weight {Wu(k)} may be computed by averaging the sets of weights for the M consecutive FFT blocks, e.g. using a moving average. In some embodiments the averaging may be according to equation (4a):
In some embodiments, the weight update may be using Wiener filtering for noise reduction, e.g. according to equation (4b):
W
u(k)=Σi=1MaiWi(k), (4b)
where {ai} are coefficients of the Wiener filter.
The delay unit 839 may be a delay network configured to timely communicate the filter weight sets {Wi(k)} to the weight update unit 837 according to a chosen averaging method, so that the weight update unit receives the filter weight sets of the multiple FFT blocks. In some embodiments, e.g. wherein the averaging is over (M−1) previous blocks and a current block, the averaging may be performed block by block. In some embodiment units 835, 837, and 839 may co-operate to implement a “moving average” approach wherein the updated set of weights {Wu(k)} for a current FFT block is computed by averaging over a size-M window including L previous FFT blocks and L FFT blocks following the current FFT block, where L=(M−1)/2 is an integer.
In some embodiments, the SIC circuit 830 may be configured to compute the sets of filter weights W(k) iteratively, using an estimated spectrum {tilde over (S)}(k) of the remotely-transmitted signal and the transmission channel estimate {tilde over (F)}(k) as feedback at each subsequent iteration, with the {tilde over (S)}(k) and {tilde over (F)}(k) obtained from downstream signal processing in the Rx processor. The AWE unit 835 may upconvert the estimated spectrum {tilde over (S)}(k) and {tilde over (F)}(k) to the RF frequency. At a first iteration, the AWE unit 835 may compute the sets of filter weights W(k) for each FFT block based on the spectra R(k) and Y(k), e.g. as described above with reference to
where the product {tilde over (F)}(k)·{tilde over (S)}(k) is an estimate of the remotely transmitted signal at the input to the SIC module 800. The set of weighs computed according to equation (5) is then used first to update the output spectrum estimate E(k), e.g. in accordance with equation (3), and then update the estimates {tilde over (F)}(k) and {tilde over (S)}(k) based on the updated output signal spectrum E(k). The iterations may continue, e.g., a set number of times or until a specified termination condition is met. In some embodiments, the iteratively-computed weights W(k) may then be averaged over two or more consecutive FFT blocks, e.g. as described above with reference to the weight update unit 837 and the delay unit 839.
The processor 900 includes a forward signal path 910 and a feedback signal path 920. The forward signal path 910 includes a CES module 914 and a demodulator/decoder 916, which are connected in series downstream of an RF-SIC module 912. The feedback signal path 920 includes a re-encoder/re-modulator 922, and a forward signal canceller 926. The CES module 914 and the demodulator/decoder 916 may be embodiments of the CES module 426 and the demodulator/decoder 428 of
{tilde over (Y)}(k)=Y(k)−{tilde over (F)}(k)·{tilde over (S)}(k) (6)
The estimate 925 is then provided to the RF SIC module 912 to update the filter weights W(k) e.g. according to equation (5). The updated weights are then filtered in the time domain as described above with reference to
Principles of the RF SIC described above may be extended to MIMO receivers and transmitters. The corresponding signal processing, referred to as MIMO-RFSIC, may be conveniently described in matrix form. In one embodiment, for a L×L MIMO, where L≥2 is an integer number of corresponding antennas, the reference signal and the received signal from a corresponding Rx antenna at k-th FFT bin, may be described by L×L matrices R[k] and Y[k], respectively. Weight elements may be estimated, e.g. at least in a first iteration, based on the reference and signal vectors R[k] and Y[k], and described by an L×L matrix WL[k], e.g., according to equation (7):
W
L
[k]=Y[k]·R
−1
[k] (7)
The estimates WL[k] for all k may be collected into a 3-dimensional (3D) array and processed with a DFT-windowing process for de-noising, similarly to the time-domain windowing process that is described above with reference to
Referring to
The FWE units 1120 may be configured to iteratively compute the filter weights W11(k) and W12(k) as follows. The filter weights are first initialized, e.g. W110(k)=W120(k)=0. At an i-th iteration, the filter weight estimates may be updated according to equations (8A) and (8B):
Ŵ
11
i+1
[k]=(Y1[k]−W12i[k]·R2[k])/R1[k] (8A)
Ŵ
12
i+1
[k]=(Y1[k]−W11i[k]·R1[k])/R2[k] (8B)
A DFT windowing process may then be applied to a vector formed of Ŵ11i+1 [k] at all subcarriers k to obtain the refined filter weight Ŵ11i+1[k] for the (i+1)th iteration. Simulation results show that 3-4 iteration may be enough to obtain the filter weights with good accuracy. Outputs of the FWE units may then be subject to the DFT windowing, as described above, to obtain two sets of the filter weights W11(k) and W12(k). Finally, the SI-reduced output signal is then obtained as, e.g., in accordance with equation (6).
E
1
[k]=Y
1
[k]−W
11
i+1
[k]·R
1
[k]−W
12
i+1
[k]·R
2
[k] (9)
Example embodiments described above provide an RF transceiver (e.g. the RF transceivers 120 of
Advantageously, the technique described above with reference to the example embodiments and
The above-described exemplary embodiments are intended to be illustrative in all respects, rather than restrictive, of the present invention. Indeed, various other embodiments and modifications to the present disclosure, in addition to those described herein, will be apparent to those of ordinary skill in the art from the foregoing description and accompanying drawings.
Furthermore, each of the example embodiments described hereinabove may include features described with reference to other embodiments. For example, the de-noising filter 330 in
Furthermore, in the description above, for purposes of explanation and not limitation, specific details are set forth such as particular architectures, interfaces, techniques, etc. in order to provide a thorough understanding of the present invention. In some instances, detailed descriptions of well-known devices, circuits, and methods are omitted so as not to obscure the description of the present invention with unnecessary detail. Thus, for example, it will be appreciated by those skilled in the art that block diagrams herein can represent conceptual views of illustrative circuitry embodying the principles of the technology. All statements herein reciting principles, aspects, and embodiments of the invention, as well as specific examples thereof, are intended to encompass both structural and functional equivalents thereof.
This application claims priority from the U.S. Provisional Patent Application No. 63/350,619, filed on Jun. 9, 2022, entitled “Self-Interference Cancellation in RF Transceiver” which is incorporated herein by reference in their entirety.
Number | Date | Country | |
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63350619 | Jun 2022 | US |