WO2014097267A1

WO2014097267A1 - Single channel full duplex wireless communication with enhanced baseband processing

Info

Publication number: WO2014097267A1
Application number: PCT/IB2013/061232
Authority: WO
Inventors: Octavian Sarca
Original assignee: Redline Communications Inc
Current assignee: Redline Communications Inc
Priority date: 2012-12-21
Filing date: 2013-12-20
Publication date: 2014-06-26
Anticipated expiration: 2015-06-21

Abstract

A single-channel full-duplex wireless communication system includes a baseband processor, a transmitter, a receiver. Part of the transmission signal from the transmitter leaks. The transmitter and the receiver utilize one channel, at the same time, to transmit and receive wireless signals with no separation between frequencies used for the transmitting and the receiving. The output of the receiver includes self-interference caused by the leakage from the transmission signal. The processor estimates a transfer function whose input includes the transmission signal fed to the input of the transmission path, and whose output is fed to an input of a secondary transmission path to produce an intermediate signal at an output of the secondary transmission path. A cancellation signal is generated based upon the intermediate signal and is subsequently combined with the received signal in the receiver's combining element to reduce the self-interference in the output signal from the receiver.

Description

SINGLE CHANNEL FULL DUPLEX WIRELESS COMMUNICATION WITH

ENHANCED BASEBAND PROCESSING

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Application No.

61/740,679 filed December 21, 2012, entitled "Single Channel Full Duplex Wireless Communication" and this application is related to the Patent Application No. 13,713,443, filed December 13, 2012, now Patent No. 8,576,752 and to U.S. Provisional Application No. 61/570,357, filed December 14, 2011, and the contents of each are incorporated entirely herein by reference.

FIELD OF THE INVENTION

[0002] The present disclosure relates to duplex wireless communication, and more particularly, to systems and methods providing single channel full duplex wireless communication.

BACKGROUND OF THE INVENTION

[0003] Duplex communication systems are methods of transmitting signals that allow two people or two parts to communicate with one another in opposite directions. Duplex communication systems are widely used in the area of telecommunications and especially in telephony and computer networking. Existing duplex wireless communication systems include half-duplex and full duplex types.

[0004] Existing half-duplex wireless communication systems provide for communication in two directions, but only in one direction at a time. Thus, while the transmitter is transmitting, the receiver must wait until the transmitter stops before transmitting. Such systems require significant latency periods.

[0005] Full-duplex (also known as double-duplex) systems are capable of transmitting and receiving data-carrying signals simultaneously. Such systems still require that the transmissions be separated in some way to enable the receivers to receive signals at the same time as transmissions are being made. Such separation may be achieved by two well-known methods: frequency separation using frequency division duplex (FDD) and time separation using time division duplex (TDD).

[0006] FDD systems include a transmission antenna and a reception antenna and operate using two independent, non-overlapping channels, one for transmitting and one for receiving. This method requires implementation of complex filters to separate the very weak received signal from the very strong transmission signal and to enable the receiver not to be unduly affected by the transmitter signal.

[0007] TDD systems are capable of transmitting in two directions, but use a single channel that alternates between transmitting and receiving. Thus the transmitter and receiver operate on the same frequency, but only in one direction at a time. TDD systems do not require two channels and frequency selective filters to separate the received signal from the transmission system. However, TDD systems require a guard interval that includes (1) the time required for the transmission to travel from the transmitter to the receiver and (2) the time required for the receiver to change from receive to transmit mode. Thus, TDD systems tend to introduce more overhead and more latency than protocols used with full-duplex operations and are not generally suitable for use over long distances.

[0008] Frequency spectrum is becoming an increasingly scarce resource, while technological progress, particularly in the area of 3G and 4G telecommunication systems and wireless internet services, has greatly increased the demand for wireless broadband. Both full-duplex and half-duplex wireless communication systems utilize the wireless channel(s) in only one direction at any given moment of time, therefore wasting spectrum. There is a growing need to optimize the use of available spectrum and to provide a method and apparatus that can achieve satisfactory performance for short, medium, and long distance communications and allows a full-duplex wireless system to operate on a single channel, i.e., to utilize the wireless channel in both directions at the same time, therefore doubling the spectral efficiency.

[0009] Different solutions have been proposed to solve this problem. However, these solutions either involve the use of extra radio frequency components such as antennas or other radio frequency processing components, which add complexity and cost while lacking the precision necessary to achieve proper performance.

SUMMARY OF THE INVENTION

[0010] An aspect of the present disclosure relates to a single channel full duplex wireless communication system. The system includes a baseband processor; a transmitter coupled to the baseband processor, the transmitter transmitting a transmission signal via a transmission path. A portion of the transmission signal is leaked. The system further includes a receiver to receive a received signal, which includes the leakage from the transmission signal. The receiver includes at least one combining element and at least one reception path. The transmitter and the receiver utilize one channel, at the same time, to transmit and receive the transmission and received signals with no separation between frequencies used for the transmitting and the receiving. The at least one combining element is coupled to an input of the receiver. The at least one reception path is coupled to an output of the receiver. The output of the receiver is coupled to the baseband processor. The receiver produces an output signal, which includes self-interference caused by the leakage from the transmission signal. The system further includes a secondary transmission path coupled to the baseband processor and to the at least one combining element. The processor estimates a first transfer function, which has an input comprising the transmission signal fed to the input of the transmission path. The output of the first transfer function is fed to an input of the secondary transmission path to produce a first intermediate signal at an output of the secondary transmission path. A first cancellation signal is generated based upon the first intermediate signal. The first cancellation signal is subsequently combined with the received signal in the at least one combining element so as to reduce the self-interference in the output signal from the receiver.

[0011] The system can further include a second cancellation signal generated by modifying a second intermediate signal using a second transfer function, which is estimated by the baseband processor. The second cancellation signal can be subsequently combined with the output signal from the receiver within the baseband processor, thereby further reducing the self-interference in the output signal from the receiver.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The present disclosure will be better understood from the following description of preferred embodiments together with reference to the accompanying drawings, in which:

[0013] FIG. 1 is an embodiment of a single channel full duplex wireless communication system.

[0014] FIG. 2 is another embodiment of a single channel full duplex wireless communication.

[0015] FIG. 3 is another embodiment of a single channel full duplex wireless communication system.

[0016] FIG. 4 is another embodiment of a single channel full duplex wireless communication system. another embodiment of a single channel full duplex wireless another embodiment of a single channel full duplex wireless another embodiment of a single channel full duplex wireless another embodiment of a single channel full duplex wireless another embodiment of a single channel full duplex wireless

FIG. 10 is another embodiment of a single channel full duplex wireless

DETAILED DESCRIPTION OF ILLUSTRATED EMBODIMENTS

[0023] Although the present disclosure will be described in connection with certain preferred embodiments, it will be understood that the present disclosure is not limited to those particular embodiments. On the contrary, the present disclosure is intended to cover all alternatives, modifications, and equivalent arrangements as may be included within the spirit and scope of the invention as defined by the appended claims.

[0024] Turning now to the drawings, FIGS. 1-10 show different embodiments of a single channel full duplex wireless communication system that is configured to operate at a wide range of frequencies and to provide sufficient cancellation such that the system may be employed for short, medium, and long-distance wireless communications. FIG. 1 shows an embodiment of a single channel full duplex wireless communication system including a baseband processor 400, a transmission path 420, a transmission splitter 415, a transmission feedback path 410, a reception path 440, a combining element 465, a secondary transmission path 460, a secondary transmission splitter 455, a secondary transmission feedback path 450, and a circulator-like device 480 that connects the transmission path 420 via the transmission splitter 415; and the reception path 440 via the combining element 465; to the antenna 490. A receiver 421 includes the combining element 465 and the reception path 440. The input to the receiver 421 is port 482 which in FIG. 1 is also an output port of a circulator-like device [0025] The transmission path 420 and the reception path 440 communicate in both the transmission and the reception direction, while using the same channel at the same time, unlike half-duplex and full-duplex systems described above. The circulator-like device 480 that connects the transmission path 420 and the reception path 440 to the antenna 490 is a circulator or an equivalent device or circuit that is configured to allow the signal entering the circulator-like device 480 through port 481 to exit through port 483 with minimal attenuation (less than approximately ldB) and with only a minor part of signal energy exiting through port 482 (approximately 1% of total transmission signal energy or 20dB). Moreover, the circulator-like device 480 is further configured to allow the signal entering the circulator-like device 480 through port 483 to exit through port 482 with minimal attenuation.

[0026] The transmission splitter 415 is a directional coupler or similar device that takes a fraction of transmitted signal power at the output of the transmission path 420 and feeds it to the transmission feedback path 410, while feeding most of the transmitted signal power to the port 481. The secondary transmission splitter 455 is a directional coupler, splitter or similar device that feeds a fraction of the signal power at the output of the secondary transmission path 460 to the secondary transmission feedback path 450 and another fraction of the power of the same signal to the combining element 465. The combining element 465 may be a combiner or a similar device that is capable of combining the signal from port 482 with the signal from the secondary transmission splitter 455 and feeding the resulting combined signal to the reception path 440.

[0027] The main challenge in a full-duplex communication system and especially in a single channel full duplex system is the self-interference, i.e., the interference caused by the transmission signal on the received signal. Signal strength diminishes quickly over distance; thus the strength of the received signal is much weaker than that of the transmission signal. Simultaneously decoding the weak signal while transmitting the strong transmission signal has been a challenge. Particularly, sufficient attenuation of the self-interference has been a major obstacle to implementation of single channel full duplex systems.

[0028] The circulator-like device 480 that connects the transmitter 422 and receiver

421 to the antenna via the transmission splitter 415 and the combining element 465 respectively provides some isolation between the transmitter 422 and the receiver 421, but the isolation is not sufficient to achieve decent/acceptable receiver performance. Since the same channel is used for the transmission and reception direction, there is no frequency separation between the operation of the transmitter and the receiver. This prevents the use of frequency selective filtering, such as duplexers or diplexers used in existing full-duplex FDD wireless communication systems to enhance the isolation between the transmission path 420 and reception path 440. Some transmission signal strength gets reflected at the interface between the circulator-like device 480 and the antenna 490, or over the air. There is no known device such as the circulator-like device 480 that would be capable of properly attenuating these reflections of the transmission signal.

[0029] A practical circulator-like device 480 is generally capable of offering isolation in the range of 20dB for an implementation using passive components or 50dB for an implementation using passive and active components e.g., for active interference canceling techniques. Active interference canceling at radio frequencies are implemented using analog components and therefore cannot offer enough the precision necessary to reduce the self- interference to a level by that enables the single channel full duplex operation. Assuming the transmission signal is 20dBm, the power of the leaked transmission signal at the input of the receiver 421 (port 482) would be around OdBm or -30dBm, respectively. If the received signal is -90dBm, the signal-to-interference ratio caused by self-interference would be -90dB or -60dB, respectively. Thus, signal-to-interference ratio would be not only negative, but it would also be such that the leaked transmitted signal (the one causing self-interference) would cause distortion in the reception path 440 to a level that nothing could be done in the baseband processor to recover the received signal with an acceptable signal-to-interference ratio. No cancelation method that is implemented only in the baseband can achieve acceptable signal-to-interference ratio to enable signal channel full duplex operation.

[0030] For the receiver 421 to operate properly it is necessary to provide a method for reducing the power of the transmitted signal leaked to the input of the receiver 421 (port 482) to a level that does not cause distortions in the reception path 440, and to provide a method to further improve the signal-to-interference ratio in the baseband processor 400.

[0031] To reduce the power of the transmitted signal leaked to the input of the receiver (port 482), the baseband processor 400 feeds a secondary transmission path 460 with a signal adjusted in such a way that it cancels the transmission signal leaked to the port 482. To do this, the baseband processor 400:

[0032] (1) estimates the transfer function H_Tx(x) from the input of the transmission path 420 to the input of the reception path 440;

[0033] (2) estimates the transfer function Hs_x(x) from the input of the secondary transmission path 460 to the input of the reception path 440; [0034] (3) then calculates the transfer function H_D(x) 401 that has the property that

HS_X(H_D(X))+H_Tx(X)=0. The processor 400 then passes the signal at the input of the transmission path 420 through the H_D(x) transfer function 401 and applies it to the input of the secondary transmission path 460 to cancel or reduce the transmission signal leaked to the port 482.

[0035] If all transfer functions are linear then ¾_χ(Η₀(χ)) = ¾_χ(χ)Ή₀(χ)) and H_D(x) can be computed as H_D(x) = - H_Tx(x)/ ¾_χ(χ). Further to this, if transfer functions are represented in the analog-domain the variable x is commonly denoted as s and if represented in digital-domain variable x is commonly denoted as z. Most practical implementations will use digital-domain representation of transfer functions. However, the present disclosure is neither limited to digital-domain representation nor to linear transfer functions.

[0036] In one embodiment, the baseband processor 400 measures the transfer function H_TxRx(X)=H_Rx(H_TX(X)) from the input of the transmission path 420 to the output of the reception path 440 and the transfer function HS_XRX(X)=H_RX(HS_X(X)) from the input of the secondary transmission path 460 to the output of the reception path 440, where H_Rx(x) is the transfer function of the reception path 440, i.e., from the input of the reception path 440 to its output. The baseband processor 400 will calculate the transfer function H_D(x) 401 for which HS_XRx(H_D(X))+H_TxRx(X)=0. This guarantees that ¾_χ(Η_ο(χ))+Η_Τχ(χ)=0 at least for the frequencies of interest, i.e. frequencies for which H_Rx(x) is not null.

[0037] In one embodiment, each of the H_TxRx(x) and HS_XRX(X) is estimated using an adaptive filter. An adaptive filter is adjusted to estimate the transfer function that, when applied to given input signal produces an output that resembles a given desired output signal with a minimum error. For H_TxRx(x) the input of the adaptive filter is the input of the transmission path 420 and the desired output is the output of the reception path 440. For HsxRx(x) the input of the adaptive filter is the input of the secondary transmission path 460 and the desired output is the output of the reception path 440. Once H_TxRx(x) and HS_XRX(X) are estimated, H_D(x) can then be computed using well known mathematical algorithms. In case of linear transfer function, H_D(x) = - H_TxRx(x)/ HS_XRX(X).

[0038] For linear transfer functions, the most common adaptive filters are Wiener and the Least Mean Square (LMS) filter. In both cases, the transfer functions are adapted by adjusting filter coefficients to minimize the mean square error (MSE) between the desired output and the actual output of the filter when applied to the supplied input. The main difference between Wiener and LMS filters is how the coefficients are adapted. With the Wiener filter, the filter coefficients are adapted only once. More precisely, the input and desired output statistical data is first collected and then the filter coefficients are calculated from the collected data. With LMS filter, the filter coefficients are adapted after every data sample is taken.

[0039] In practical implementations it may be required to use non-linear transfer functions, at the very least for H_TxRx(x) and H_D(x), if not also for HS_XRx(X). This is especially true when the transmission path is operated closer to its maximum transmission power case in which it introduces non-linear distortions which in turn creates in-band intermodulation products. One solution is to extend the Wiener or LMS filter to allow implementation of non-linear transfer functions. In digital domain both the Wiener and the LMS filters are Finite Impulse Response (FIR) filters. The output of an FIR is a weighted sum of terms that are derived from the input signal by adding delays:

v(n) = ho-u(n) + h_ru(n-l) + h₂ u(n-2) + ...

where u(n) is the input, v(n) is the output and H(z) = h₀+ hrz^"1 + h₂ z^"2 + ... is the filter transfer function whose coefficients h₀, hi, h₂, ... are adapted. The nonlinear extension of an FIR is a weighted sum of terms that are derived from the input signal by adding delays and applying a Taylor series expansion. In the most general form, the nonlinear filter is:

v(n) = hio-u(n) + hn u(n-l) + hi₂ u(n-2) + ... + h₂₀₀ u(n)² + h_2iru(n-l)² + h₂₂₂ u(n-2)² + ...+ 2 h₂₀ru(n) u(n-l) + 2 h₂₀₂ u(n) u(n-2) + 2 h₂i₂ u(n-l) u(n-2) + ... + h₃₀oo u(n)³ + h _m u(n- l) + h₃₂₂₂ u(n-2)³ + ... + 3 h₃₀oi u(n)² u(n-l) + ....

and the coefficients can be adapted using the same algorithms as those used for the Wiener or LMS filters in the linear case. In most practical scenarios there is no need to include all higher order terms. For communications systems where the bandwidth is significantly smaller than the center frequency, the even order intermodulation products are located outside of the bandwidth of existing circuits and are filtered out, which means there is no need to include even powers in the filter terms. Furthermore, power decreases with the order of the intermodulation products. For example, the 5^th order intermodulation products have much lower power that the 3 order intermodulation products and may not need cancellation. Then, in order to perform the necessary processing, only 1^st and 3^rd power terms are considered, that is:

v(n) = hio u(n) + hn u(n-l) + h_i2 u(n-2) + ... + h ₀oo u(n)³ + h _m u(n-l)³ + h ₂₂₂ u(n-2)³ + ... + 3 h ₀oru(n)² u(n-l) + ... [0040] Due to limited precision, noise, and various imperfections, the secondary transmission path 460 is generally not adapted to provide a desired amount of cancellation. The transmission path 460 can typically improve signal-to-interference ratio by an amount in the range of 60dB, which is generally not sufficient to provide a satisfactory signal-to- interference ratio. Thus, in one embodiment, the baseband processor 400 is further adapted to provide additional cancellation.

[0041] In the preferred embodiment, the baseband processor 400 uses the transmission feedback path 410 and the secondary transmission feedback path 450 to acquire the signals at the output of the transmission path 420 and the secondary transmission path 460 (including the noise, the linear and the non-linear distortions). The baseband processor 400 the transmission signal, the output of the transmission feedback path 410 and the output of the secondary transmission feedback path 450 to further reduce the self-interference. In one embodiment, shown in FIG. 1 the baseband processor 400 estimates the transfer functions H_TF(X) 402 and HS_F(X) 403 that need to be applied to the signal at the outputs of the transmission feedback path 410 and the secondary transmission feedback path 450, respectively, so that, when added to the received signal present at the output of the reception path 440, the remaining self-interference is completely cancelled or significantly reduced. In one embodiment the H_TF(x) and HS_F(X) are adaptive filters with the desired output being the output of the reception path multiplied by -1. In other words, they will adapt to subtract any transmit signal, noise and distortion left after the cancelation done at the input to the reception path. In another embodiment one of the adaptive filters H_TF(x) and HS_F(X) is trained with the desired output being the output of the reception path multiplied by -1 while the other is trained with the desired output being the result of adding the output of the other filter to the output of the reception path, everything multiplied by -1. In other words, in the embodiment the two cancelers are cascaded instead of working in parallel.

[0042] FIG. 2 shows an embodiment of a single channel full duplex wireless communication system, where a transmission antenna 491 is connected, via the transmission splitter 415, to the transmission path 420, and a receiver antenna 492 is connected, via the combining element 465, to the reception path 440. The receiver 421 still comprises combining element 465 and reception path 440, and the input to the receiver is port 482. The crosstalk between the two antennas, transmitter antenna 491 and receiver antenna 492, plus the over-the-air reflections cause transmission signal to leak into the input of the receiver (port 482). In other words, the signal received by the combining element 465 from the receiver antenna 492 experiences self-interference due to the leaked transmission signal. Such self-interference needs to be cancelled or reduced in order to achieve desired wireless system performance.

[0043] The transmission signal leak is addressed by the processor 400 estimating and applying a transfer function H_D(x) 401 that has the property that

The processor 400 then passes the signal at the input of the transmission path 420 through the transfer function H_D(x) 401 and applies it to the input of the secondary transmission path 460 to cancel or significantly reduce the transmission signal leaked into the input of the receiver (the port 482) at the input of the reception path 440.

[0044] Moreover, this embodiment also provides additional cancellation in the baseband processor 400 via transmission feedback path 410 and the secondary transmission feedback path 450 as described above in relation to FIG. 1.

[0045] FIG. 3 shows an embodiment of a single channel full duplex wireless communication system where the secondary transmission feedback path 420 of FIG. 1 is not used and the secondary transmission path 460 is connected to the combining element 465. This solution is adapted for systems where the noise of the secondary transmission path 460 is low enough that its cancellation in baseband processor 400 is not required. FIG. 5 is a variation of the embodiment shown in FIG. 3 in which the transmission path 420 is connected, via the transmissions splitter 415, to the transmission antenna 491 and the reception path 440 is connected, via the combining element 465, to the receiver antenna 492. In both FIG. 3 and FIG. 5, the input to the receiver 421 is port 482, which is also an output port of a circulator-like device 480.

[0046] FIG. 4 shows an embodiment of a single channel full duplex wireless communication system where the secondary transmission path 460 is connected directly to the combining element 465 and where the transmission path 420 is connected directly to the circulator-like device 480. Both the transmission feedback path 410 and secondary transmission feedback path 450 of FIG. 1 are not used. This solution is adapted for systems where the noise of both the transmission path 420 and the secondary transmission path 460 is low enough that cancellation in baseband processor 400 is not required. FIG. 6 is a variation of the embodiment shown in FIG. 4 in which the transmission path 420 is directly connected to the transmission antenna 491 and the reception path 440 is connected, via the combining element 465, to the receiver antenna 492. [0047] FIG. 7 shows another embodiment, which is a further modification of the embodiment of FIG. 1. In FIG. 7, a copy of the transmission signal is directed to block 41 1 where it is modified by transfer function H_TFsc(x)- The output from block 41 1 is then negated and summed with the output from the transmission feedback path 410 in block 412. The transfer function H_TFsc(x) is adjusted so that its output matches the output of the transmission feedback path 410 as closely as possible, therefore canceling most of the transmission signal present at the output of the transmission feedback path at the output of the block 412. The signal left at the output of the block 412 contains components that cannot be canceled, more specifically the noise and distortions introduced by the transmission path 420. The output from block 412 is then fed to block 413, where it is modified by transfer function H_TFNc(x)- The transfer function H_TFNC(X) is adjusted so that when output of block 413 is added to the output of the reception path 440 in block 406, it cancels the noise and distortion introduced by the transmission path 420 that are leaked into the received signal. In one embodiment the transfer function H_TFNc(x) is adjusted so that its output matches the negative of the output of the reception path 440 as closely as possible (that is, (- 1) ^χ the output of the reception path 440), and therefore the output from H_TFNc(x) cancels the noise and distortion introduced by the transmission path 420 that are leaked into the received signal when added to the output of the reception path 440 in block 406. Similarly, a copy of the transmission signal is directed to block 451 where it is modified by transfer function Hs_Fsc(x)- The output from block 451 is then negated and summed with the output from the transmission feedback path 450 in block 452. The transfer function Hs_Fsc(x) is adjusted so that its output matches the output of the secondary transmission feedback path 450 as closely as possible, therefore cancelling most of the transmission signal present at the output of the secondary transmission feedback path 450 at the output of block 452. The signal left at the output of the block 452 contains components that cannot be canceled, more specifically the noise and the distortions introduced by the secondary transmission path 460. The output from block 452 is then fed to block 453, where it is modified by transfer function HS_FNC(X)- The transfer function HS_FNC(X) is adjusted so that when output of block 453 is added to the received signal in block 406, it cancels the noise and distortion introduced by the secondary transmission path 460 that are added into the received signal through the secondary transmission splitter 455 and the combining element 465. In one embodiment the transfer function HS_FNC(X) is adjusted so that its output matches the negative of the output of the reception path 440 (that is, (- 1) ^χ the output of the reception path 440) as closely as possible, and therefore its output cancels the noise and distortion introduced by the secondary transmission path 460 that are added into the received signal through the secondary transmission splitter 455 and the combining element 465. Another copy of the transmission signal is directed to block 405 where it is modified by transfer function H_Tsc(x)- The transfer function H_Tsc(x) is adjusted so that when the output of the block 405 is added to the received signal in block 406, it cancels any remaining portion of the transmission signal leaked into the receiving signal that was not canceled by the previous stages. In one embodiment, the transfer function H_Tsc(x) is adjusted so that its output matches as close as possible the negative of the output of the reception path 440, and therefore its output cancels the transmission signal present at the output of the reception path 440. In another embodiment, the transfer function H_Tsc(x) is adjusted so that its output matches as close as possible the negative of the sum of the output of the reception path 440, the output of block 413 and the output of block 453 (that is, (-1) ^χ (the output of the reception path 440 + the output of block 413 + the output of block 453)), and therefore its output cancels any portion of the transmission signal present at the output of the reception path 440, the output of block 413 and the output of block 453. The output of blocks 413, 405 and 453 are then summed with the output from reception path 440 in block 406 so as to reduce any self- interference in the output from reception path 440.

[0048] FIG. 8 is an alternative embodiment of FIG. 7, except that FIG. 8 has a transmit antenna 491 and a receive antenna 492; whereas FIG. 7 has a single antenna 490 connected to a circulator-like device 480 in the same fashion as in FIG. 1.

[0049] In an alternative embodiment of FIG. 7 and FIG. 8, the input to the block 451 uses a copy of the output of the transfer function H_D(x) 401 instead of a copy of the transmit signal.

[0050] In one embodiment H_TFsc(x), H_TFNC(X), H_SFSC(X) , H_SFNC(X) and H_SF(x) in FIG.

7 and FIG. 8 are adaptive filters such as Wiener and LMS filters, and therefore these transfer functions are adjusted so that the mean square error between each of the outputs from these filters and a target corresponding to each of the outputs are minimized as much as possible.

[0051] FIG. 9 shows another embodiment, which is a further modification of the embodiment of FIG. 3. In FIG. 9, a copy of the transmission signal is directed to block 411 where it is modified by transfer function H_TFsc(x)- The output from block 411 is then negated and summed with the output from the transmission feedback path 410 in block 412. The output from block 412 is then fed to block 413, where it is modified by transfer function H_TFNC(X)- The transfer function H_TFsc(x) is adjusted so that its output matches the output of the transmission feedback path 410 as closely as possible, therefore canceling most of the transmission signal present at the output of the transmission feedback path at the output of the block 412. The signal left at the output of the block 412 contains components that cannot be canceled, more specifically the noise and distortions introduced by the transmission path 420. The output from block 412 is then fed to block 413, where it is modified by transfer function H_TFNC(X)- The transfer function H_TFNC(X) is adjusted so that when output of block 413 is added to the output of the reception path 440 in block 406, it cancels the noise and distortion introduced by the transmission path 420 that are leaked into the received signal. In one embodiment the transfer function H_TFNC(X) is adjusted so that its output matches the negative of the output of the reception path 440 (that is, (-1) ^χ the output of the reception path 440) as closely as possible, and therefore the output from H_TFNC(X) cancels the noise and distortion introduced by the transmission path 420 that are leaked into the received signal when added to the output of the reception path 440 in block 406. Another copy of the transmission signal is directed to block 405 where it is modified by transfer function HS_F(X). The transfer function H_TSC(X) is adjusted so that when the output of the block 405 is added to the received signal in block 406, it cancels any remaining portion of the transmission signal leaked into the receiving signal that was not canceled by the previous stages. In one embodiment, the transfer function H_Tsc(x) is adjusted so that its output matches the negative of the output of the reception path 440 (that is, (-1) ^x the output of the reception path 440) as closely as possible, and therefore its output cancels the transmission signal present at the output of the reception path 440. In another embodiment, the transfer function H_Tsc(x) is adjusted so that its output matches the negative of the sum of the output of the reception path 440 and the output of block 413 (that is, (-1) ^χ (the output of the reception path 440 + the output of block 413)) as closely as possible, and therefore its output cancels any portion of the transmission signal present at the output of the reception path 440 and the output of block 413. The output of blocks 413 and 405 are then summed with the output from reception path 440 in block 406 so as to reduce any self-interference in the output from reception path 440.

[0052] FIG. 10 is an alternative embodiment of FIG. 9, except that FIG. 10 has a transmit antenna 491 and a receive antenna 492; whereas FIG. 9 has a single antenna 490 connected to a circulator-like device 480 in the same fashion as in FIG. 3.

[0053] In an alternative embodiment of FIG. 9 and FIG. 10, the input to the block 451 uses a copy of the output of the transfer function H_D(x) 401 instead of a copy of the transmit signal. [0054] In one embodiment H_TFsc(x), H_TFNC(X) and HSF(X) in FIG. 9 and FIG. 10 are adaptive filters such as Wiener and LMS filters and therefore these transfer functions are adjusted so that the mean square error between each of the outputs from these filters and a target corresponding to each of the outputs are minimized as much as possible. Other embodiments of single channel full frequency communication systems can be provided, containing multiple secondary transmission paths 460, some of them containing their own splitters 455 and secondary feedback paths 450, feeding via different combining elements 465 into different stages of the reception path 440, wherein the transmission path 420 is connected to the port 481 of the circulator-like device 480 and the reception path 440 is connected, via one of the combining elements 465 to port 482, which as previously explained is both an input port to the receiver, and an output port of the circulator-like device 480. Every stage achieves removal of additional undesired signal leaked from the transmission path 420. This method can offer much better removal of undesired signal leaked from the transmission path 420.

[0055] Another embodiment of single channel full frequency communication systems can be provided, containing multiple secondary transmission paths 460, some of them containing their own splitters 455 and feedback paths 450, feeding via different combining elements 465 into different stages of the reception path 440, wherein the transmission path 420 is connected to the transmission antenna 491 and the reception path 440 is connected, via one of the combining elements 465, to the receiver antenna 492. Every stage achieves removal of additional undesired signal leaked from the transmission path 420. This method can offer significantly better removal of undesired signal leaked from the transmission path 420.

[0056] Another embodiment of single channel full frequency communication systems containing multiple-input and multiple-output (MIMO) may be provided wherein there are multiple transmission paths 420 and multiple reception paths 440. There will be, for example M reception paths 440 and N transmission paths 420. There will be M secondary transmission paths 460, one for each reception path 440. Such an arrangement can significantly improve communication performance. Specifically, in wireless communications, it offers significant increases in data transmission and link range without using any additional spectrum or transmit power. It achieves this by higher spectral efficiency and link reliability. There will be N transmission feedback paths 410 and M secondary transmission feedback paths 450. The baseband processor 400 feeds each secondary transmission path 460 with the necessary signal to cancel or reduce the interference from each transmission path 420 to the respective reception path 440. The baseband processor 400 supplies the signals at the input of the M secondary transmission paths 460 through an M x N matrix of transfer functions H_D(s) 401. In other words, each of the M inputs will be the sum of N transmitted signals processed through N distinct transfer functions.

[0057] Similarly, there will a matrix of M x N H_JF(X) 402 transfer functions and a matrix of MxM ¾_F(X) 403 transfer functions that need to be applied to the signal at the outputs of the transmission feedback path 410 and the secondary transmission feedback path 450, respectively, so that, when added to the received signal present at the output of the reception path 440, the remaining self-interference is completely cancelled.

[0058] The embodiments described above are implemented in a variety of ways.

Generally, the embodiments described above may be implemented using hardware, software or a combination of hardware and software elements. The hardware aspects may include combinations of operatively coupled hardware components including microprocessors, logical circuitry, communication/networking ports, digital filters, memory, or logical circuitry. The hardware may be adapted to perform operations specified by a computer- executable code, which may be stored on a computer readable medium.

[0059] The baseband processor 400 described above may be implemented in a variety of ways, using, for example, an external conventional computer or an on-board field programmable gate array (FPGA) or digital signal processor (DSP), that executes software, or stored instructions. The baseband processor 400 may be implemented using one or more networked or non-networked general purpose computer systems, microprocessors, field programmable gate arrays (FPGAs), digital signal processors (DSPs), micro-controllers, and the like, programmed according to the teachings of the exemplary embodiments of the present disclosure, as is appreciated by those skilled in the computer and software arts.

[0060] The steps of the methods described herein may be achieved via an appropriate programmable processing device, such as an external conventional computer or an on-board field programmable gate array (FPGA) or digital signal processor (DSP), which executes software, or stored instructions. In general, physical processors and/or machines employed by embodiments of the present disclosure for any processing or evaluation may include one or more networked or non-networked general purpose computer systems, microprocessors, field programmable gate arrays (FPGAs), digital signal processors (DSPs), micro-controllers, and the like, programmed according to the teachings of the exemplary embodiments of the present disclosure, as is appreciated by those skilled in the computer and software arts. Appropriate software can be readily prepared by programmers of ordinary skill based on the teachings of the exemplary embodiments, as is appreciated by those skilled in the software arts. In addition, the devices and subsystems of the exemplary embodiments can be implemented by the preparation of application-specific integrated circuits or by interconnecting an appropriate network of conventional component circuits, as is appreciated by those skilled in the electrical arts. Thus, the exemplary embodiments are not limited to any specific combination of hardware circuitry and/or software.

[0061] Stored on any one or on a combination of tangible, non-transitory computer- readable media, the exemplary embodiments of the present disclosure may include software for controlling the devices and subsystems of the exemplary embodiments, for driving the devices and subsystems of the exemplary embodiments, for processing data and signals, for enabling the devices and subsystems of the exemplary embodiments to interact with a human user, and the like. Such software can include, but is not limited to, device drivers, firmware, operating systems, development tools, applications software, and the like. Such computer- readable media further can include the computer program product of an embodiment of the present disclosure for performing all or a portion (if processing is distributed) of the processing performed in implementations. Computer code devices of the exemplary embodiments of the present disclosure can include any suitable interpretable or executable code mechanism, including but not limited to scripts, interpretable programs, dynamic link libraries (DLLs), Java classes and applets, complete executable programs, and the like. Moreover, parts of the processing of the exemplary embodiments of the present disclosure can be distributed for better performance, reliability, cost, and the like.

[0062] Common forms of computer-readable media may include, for example, a floppy disk, a flexible disk, hard disk, magnetic tape, any other suitable magnetic medium, a CD-ROM, CDRW, DVD, any other suitable optical medium, punch cards, paper tape, optical mark sheets, any other suitable physical medium with patterns of holes or other optically recognizable indicia, a RAM, a PROM, an EPROM, a FLASH-EPROM, any other suitable memory chip or cartridge, a carrier wave or any other suitable medium from which a computer can read.

[0063] While particular embodiments and applications of the present disclosure have been illustrated and described, it is to be understood that the disclosure is not limited to the precise construction and compositions disclosed herein and that various modifications, changes, and variations may be apparent from the foregoing descriptions without departing from the spirit and scope of the invention as defined in the appended claims.

Claims

What is Claimed Is:

1. A single channel full duplex wireless communication system, comprising:

a baseband processor;

a transmitter coupled to the baseband processor, the transmitter transmitting a transmission signal via a transmission path; wherein a portion of the transmission signal is leaked;

a receiver to receive a received signal, wherein the received signal includes the leakage from the transmission signal, the receiver including at least one combining element and at least one reception path,

wherein the transmitter and the receiver utilize one channel, at the same time, to transmit and receive said transmission and received signals with no separation between frequencies used for the transmitting and the receiving,

wherein the at least one combining element is coupled to an input of the receiver and wherein the at least one reception path is coupled to an output of the receiver,

further wherein the output of the receiver is coupled to the baseband processor,

wherein the receiver produces an output signal, further wherein the output signal includes self-interference caused by the leakage from the transmission signal; a secondary transmission path coupled to the baseband processor and to the at least one combining element; and

the processor estimating a first transfer function, wherein the first transfer function has an input comprising the transmission signal fed to the input of the transmission path, and wherein the output of the first transfer function is fed to an input of the secondary transmission path to produce a first intermediate signal at an output of the secondary transmission path, and

wherein a first cancellation signal is generated based upon the first intermediate signal, the first cancellation signal being subsequently combined with the received signal in the at least one combining element so as to reduce the self-interference in the output signal from the receiver.

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2. The system of claim 1, further comprising a second cancellation signal being generated by modifying a second intermediate signal using a second transfer function, the second transfer function being estimated by the baseband processor, the second cancellation signal being subsequently combined with the output signal from the receiver within the baseband processor, thereby further reducing the self-interference in the output signal from the receiver.

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