NZ554191A - Communication method and apparatus - Google Patents

Abstract

Communications apparatus is disclosed which includes: a receiver for receiving RF input signals via multiple antennas. The receiver includes first and second input channels, a first phase rotator and a first signal comparator. The first input channel is associated with a first input signal received via a first antenna and the second input channel is associated with a second input signal received via a second antenna. The first signal comparator is configured to develop a first control output signal based on a phase difference between the first and second input signals, and the first phase rotator includes a first vector multiplier configured to rotate the phase of one input signal with respect to the other based on the first control output signal. The apparatus further includes a transmitter for transmitting RF output signals via multiple antennas including a first output channel associated with a first output signal and a second output channel associated with a second output signal, a second phase rotator and a second signal comparator, wherein the second signal comparator is configured to develop a second control output signal based on the phase difference between the first and second input signals, and the second phase rotator is configured to rotate the phase of one output signal with respect to the other based on the second control output signal.

Description

10053459177* ;554191 ;Our Ref: FRF001 NZ Patents Form No. 5 ;PATENTS ACT 1953 ;COMPLETE SPECIFICATION COMMUNICATION METHOD AND APPARATUS ;We, 4RF Communications Limited, a New Zealand company of 26 Glover Street, Ngauranga, Wellington, New Zealand, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: ;1 ;Intellectual Property Office of N.Z. ;i1 mar a57 RECEIVED ;2 ;COMMUNICATION METHOD AND APPARATUS FIELD OF THE INVENTION ;5 The present invention relates to a communication method and apparatus. In particular, the present invention relates to an improved communication transceiver, receiver and method of controlling RF signals using multiple antennas. ;10 BACKGROUND ;Various techniques are utilised in RF (radio frequency) transceivers in order to mitigate the effects of changes in the transmitted signal during transmission before it is received at the RF receiver. In particular, systems are known that 15 include multiple antenna arrays that are arranged to receive and transmit RF signals in order to mitigate the effects. ;Certain systems, known as retro-directive systems, are configured to determine the relative phase difference between signals received at one antenna when 20 compared with signals received at another antenna. By determining the phase difference, the system is able to identify the approximate location of the source that is transmitting the signals. By using this information, signals may be transmitted back to the source using beam forming techniques by adjusting the relative phase of each signal being transmitted from the antennas in the array. ;25 ;Diversity techniques may be implemented in order to reduce the effects of signal fading and interference. Various diversity techniques are available that allow a signal to be transmitted using different transmission characteristics over two or more communication channels. In this manner, the receiver is more likely to 30 receive at least one signal that is not affected by the negative effects of the transmission channel. ;Some such diversity techniques include: space or spatial diversity, wherein signals are received at different antennas located in different reception areas; ;35 frequency diversity, wherein signals are transmitted on different frequency carriers or spread over a large frequency bandwidth; polarisation diversity, wherein signals are transmitted using antennas with different polarisation. ;3 ;10 ;When communications apparatus utilises multiple antennas to receive the transmitted signals, the signals received via the different antennas are usually phase shifted with respect to each other due to the different transmission paths of the signals. The apparatus is configured to combine the multiple signals received in order to provide an improved signal. To overcome the phase shift in the signals and allow effective combining of the signals to occur, it is known to incorporate a mechanism for changing the phase of at least one of the signals within at least one of the reception channels in the receiver. ;One known apparatus is disclosed in US patent application, US 2006/0262013 by Shiroma et al.. A system is disclosed that incorporates a retro-directive array of antennas wherein one channel in the receiver is phase shifted relative to another channel using a phase shifter before the signal is forwarded to the receiver 15 demodulator. However, the system provided is an open loop system that is susceptible to process and temperature variations. Further, the phase shifter is only capable of tracking the phase of the received signals. ;In another known apparatus disclosed in PCT publication WO 2006/039302 by 20 Tzero Technologies Inc. a receiver uses a processing mechanism that adjusts the phase of a receiver channel by calculating and maximising the SNR (Signal to noise Ratio) of the incoming signals. However, this implementation limits the device to being used for specific types of modulation where the SNR is known. ;25 In another known apparatus, disclosed in US patent application US ;2003/0186660 by Lee, a diversity receiving apparatus is provided that uses a phase shifter for shifting the phase of a signal on one channel of a receiver. Again, in this implementation the phase shifter is only capable of tracking the phase of the received signals. Further, in the disclosed apparatus of Lee, the 30 signals are only combined at the radio frequency (RF) or intermediate frequency (IF) portions of the receiver. ;The present invention aims to overcome, or at least alleviate, some or all of the afore-mentioned problems. ;35 ;4 ;SUMMARY OF THE INVENTION ;In one aspect, the present invention provides communications apparatus including: a receiver for receiving RF input signals via multiple antennas, the 5 receiver including first and second input channels, a first phase rotator and a first signal comparator, wherein the first input channel is associated with a first input signal received via a first antenna and the second input channel is associated with a second input signal received via a second antenna, the first signal comparator is configured to develop a first control output signal based on a 10 phase difference between the first and second input signals, and the first phase rotator includes a first vector multiplier being configured to rotate the phase of one input signal with respect to the other based on the first control output signal, the apparatus further including a transmitter for transmitting RF output signals via multiple antennas including a first output channel associated with a first output 15 signal and a second output channel associated with a second output signal, a second phase rotator and a second signal comparator, wherein the second signal comparator is configured to develop a second control output signal based on the phase difference between the first and second input signals, and the second phase rotator is configured to rotate the phase of one output signal with respect 20 to the other based on the second control output signal. ;In a further aspect, the present invention provides communications apparatus including: a receiver for receiving RF input signals via multiple antennas, the receiver including first and second input channels, a first phase rotator and a first 25 signal comparator, wherein the first input channel is associated with a first input signal received via a first antenna and the second input channel is associated with a second input signal received via a second antenna, the first signal comparator is configured to develop a first control output signal based on a phase difference between the first and second input signals, the first phase 30 rotator configured to rotate the phase of one input signal with respect to the other based on the first control output signal, and the first phase rotator and first signal comparator are configured to form a phase locked loop, the apparatus further including a transmitter for transmitting RF signals via multiple antennas including a first output channel associated with a first output signal and a second output 35 channel associated with a second output signal, a second phase rotator and a second signal comparator, wherein the second signal comparator is configured to ;5 ;develop a second control output signal based on the phase difference between the first and second input signals, and the second phase rotator is configured to rotate the phase of one output signal with respect to the other based on the second control output signal. ;5 ;In yet a further aspect, the present invention provides a method of controlling signals received via multiple antennas including the steps of: receiving on a first input channel a first input signal via a first antenna, receiving on a second input channel a second input signal via a second antenna, detecting the phase 10 difference between the first and second input signals, phase rotating one input signal with respect to the other based on the detected phase difference using a phase locked loop, summing the phase rotated input signal with the other input signal, providing a first output signal on a first output channel, providing a second output signal on a second output channel, and phase rotating one output signal 15 with respect to the other based on the detected phase difference. ;In yet a further aspect, the present invention provides a method of controlling signals received via multiple antennas including the steps of: receiving on a first input channel a first input signal via a first antenna, receiving on a second input 20 channel a second input signal via a second antenna, detecting the phase difference between the first and second input signals, phase rotating one input signal with respect to the other based on the detected phase difference using a vector multiplier, summing the phase rotated input signal with the other input signal, providing a first output signal on a first output channel, providing a second 25 output signal on a second output channel, and phase rotating one output signal with respect to the other based on the detected phase difference. ;In yet a further aspect, the present invention provides communications apparatus including: a receiver for receiving RF input signals via multiple antennas, the 30 receiver including first and second input channels, a first phase rotator and a first signal comparator, wherein the first input channel is associated with a first input signal received via a first antenna and the second input channel is associated with a second input signal received via a second antenna, the first signal comparator is configured to develop a first control output based on the phase 35 difference between the first and second input signals, and the first phase rotator ;6 ;includes a first vector multiplier being configured to rotate the phase of one input signal with respect to the other based on the first control output. ;BRIEF DESCRIPTION OF THE DRAWINGS ;5 ;Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: ;Figure 1 shows an analogue transceiver according to an embodiment of the 10 present invention; ;Figure 2 shows an analogue phase rotator according to an embodiment of the present invention; ;Figure 3 shows an analogue signal controller according to an embodiment of the present invention; ;15 Figure 4 shows a digital transceiver according to an embodiment of the present invention; ;Figure 5 shows a digital phase rotator and signal controller according to an embodiment of the present invention; ;Figure 6 shows a digital vector rotator according to an embodiment of the 20 present invention; ;Figure 7A shows a circuit configuration according to an embodiment of the present invention; ;Figure 7B shows another circuit configuration according to an embodiment of the present invention; ;25 Figure 7C shows another circuit configuration according to an embodiment of the present invention; ;Figure 7D shows another circuit configuration according to an embodiment of the present invention; ;Figure 7E shows another circuit configuration according to an embodiment of the 30 present invention; ;DETAILED DESCRIPTION OF THE INVENTION ;First Embodiment ;35 ;Figure 1 shows communication apparatus according to this first embodiment in the form of an analogue transceiver. ;7 ;This transceiver system is used in conjunction with an antenna array that includes two or more antennas. In this embodiment only two antennas and their associated circuitry are shown. However, it will be understood that any number 5 of antennas may be used by reproducing and interconnecting the below described functionality. ;A receiver portion of the transceiver includes a first antenna 101 arranged to detect a first RF input signal that has been transmitted by a source (not shown). 10 This first RF input signal is processed using a first input channel with the following components: an RF band-pass filter 103; an RF amplifier 105; a local oscillator 107; a mixer 109; an IF band-pass filter 111, an IF amplifier 113. ;The first input channel is split after the IF amplifier 113, with one portion of the 15 channel being provided as a first input to a phase detector 115 and a second portion of the channel being provided as a first input to a summer 117. ;A second antenna 119 is arranged to detect a second RF input signal that has also been transmitted from the same source. The second RF input signal is 20 processed using a second input channel with the following components: an RF band-pass filter 121; an RF amplifier 123; the same local oscillator 107 as in the first RF input channel; a mixer 125; an IF band-pass filter 127, an IF amplifier 129; a phase rotator 131; a signal controller 133. ;25 The second input channel is split after the phase rotator 131, with one portion of the channel being provided as a second input to the phase detector 115, while a second portion of the channel is provided as a second input to the summer 117. ;The output of the phase detector 115 is connected to an input of the signal 30 controller 133. The output of the signal controller 133 is connected to an input of the phase rotator 131. ;The signal processing carried out by the receiver will now be described. ;8 ;Referring to the first input channel, the first RF input signal detected by the first antenna 101 is band pass filtered using the RF band pass filter 103. The filtered signal is then amplified using the RF amplifier 105. ;10 ;The local oscillator 107 is arranged to operate at a frequency of the radio frequency (RF) minus the intermediate frequency (IF), i.e. the local oscillator frequency = RF-IF. It will be understood that the local oscillator may be run at other suitable frequencies. For example, the local oscillator frequency may be set to run at a frequency equal to the sum of the RF and IF. ;The output signal of the local oscillator 107 is applied to a first input of the mixer 109, while the amplified RF signal from the RF amplifier 105 is applied to the second input of the mixer 109. The combination of the local oscillator 107 and mixer 109 down converts the received signal from RF to IF. In this embodiment, 15 the IF used is 70MHz. However, it will be understood that any other suitable frequencies may be used. ;The IF output of the mixer 109 is fed into an IF band-pass filter 111. The filtered output is fed into an IF amplifier 113. The output of the IF amplifier 113 is split, 20 with a first portion being provided as a first input to the phase detector 115, while the second portion is provided as a first input to the summer 117. ;Referring to the second input channel, the second RF input signal detected by the second antenna 119 is band pass filtered using the RF band pass filter 121. 25 The filtered signal is then amplified using the RF amplifier 123. ;As explained above, the local oscillator 107 is arranged to operate at a frequency of RF-IF. The output signal of the local oscillator 107 is applied to a first input of the mixer 125, while the amplified RF signal from the RF amplifier 123 is applied 30 to the second input of the mixer 125. The combination of the local oscillator 107 and mixer 125 provides a down conversion of the received signal from RF to IF. ;35 ;The IF output of the mixer 125 is applied to an IF band-pass filter 127. The filtered output is applied to an IF amplifier 129. The output of the IF amplifier 129 is applied to a phase rotator 131, which is configured to rotate the phase of the IF ;9 ;signal on the second channel in order to match its phase with the IF signal on the first input channel. ;The output of the phase rotator 131 is split into two separate channels, with the 5 first split channel being provided as a second input to the phase detector 115, while the second split channel is provided as a second input to the summer 117. ;The phase detector 115 thus has two inputs, one being the IF signal on the first channel and the other being the phase adjusted IF signal on the second channel 10 The output of the phase detector 115 provides a phase error signal (0e) that corresponds to the phase difference of the signals at the two inputs of the phase detector 115. It will be understood that any suitable phase detector device can be used. ;15 The phase error signal 6e from the phase detector 115 is fed into the signal controller 133. The signal controller 133 uses the phase error signal 0e to provide a suitable control output for driving the phase rotator 131. ;In this embodiment, the control output of the receiver signal controller 133 20 includes two output signals. The first output signal = sine (0d), while the second output signal = cosine (0d). Sin (0d) and Cos (0d) are the sine and cosine values of the phase difference 0d between the two signals received at the first and second antennas. These two signals are used to drive the phase rotator, as will be explained in more detail below in relation to figures 2 and 3. ;25 ;A transmitter portion of the transceiver will now be described with reference to figure 1. ;The transmitter includes a modulator (not shown) with the output of the modulator 30 connected to a splitter 135. The splitter 135 provides a first and second output channel. ;The first output channel includes a phase rotator 137, a signal controller 139, an IF amplifier 141, and IF band-pass filter 143, a mixer 145, a local oscillator 147, 35 an RF amplifier 149, an RF band-pass filter 151 and a third antenna 153. ;10 ;The second output channel includes an IF amplifier 155, an IF band-pass filter 157, a mixer 159, the same local oscillator 147 as in the first output channel, an RF amplifier 161, an RF band-pass filter 163 and a fourth antenna 165. ;5 The signal controller 139 in the transmitter receives the same phase error signal 6e from the phase detector 115 as the signal controller 133 in the receiver. The output of the signal controller 139 is connected to an input of the phase rotator 137. ;10 The signal processing carried out by the transmitter will now be described. ;An IF modulated signal from a modulator (not shown) is provided to a splitter 135 to provide a first and second output channel. Any suitable modulation may be used. ;15 ;On a first output channel, a first modulated IF signal is phase rotated by the phase rotator 137. The phase rotator 137 receives a control output signal from the signal controller 139. In this embodiment, the control output signal of the transmitter signal controller 139 includes two output signals. The first output 20 signal = sine (-©d), while the second output signal = cosine (-9d). Therefore, the first output signal is orthogonal to the second output signal. That is, the first output signal of the transmitter signal controller 139 is the conjugate of the first output signal of the receiver signal controller 133. Further, the second output signal of transmitter signal controller 139 is the conjugate of the second output 25 signal of the receiver signal controller 133. In this manner, phase conjugate signals are provided to the receiver and transmitter such that the transmitter is arranged to transmit the signals back towards the source by utilising the phase difference (0d) between the received signals. Further details of how the signal controller produces the required control output are provided below. ;30 ;The phase rotator 137 outputs a phase rotated version of the first modulated IF signal. The amount of phase rotation is associated with the phase difference 0d between the first and second RF input signals received at the receiver. ;35 The phase rotated signal is amplified using the IF amplifier 141 and band-pass filtered using the IF band-pass filter 143. A local oscillator 147 output is mixed ;11 ;with the IF signal using the mixer 145. The output of the local oscillator 147 is set to a frequency of RF-IF such that the output of the mixer is an RF signal. It will be understood that other frequencies for the local oscillator can be used. For example, as an alternative the local oscillator 147 could be set to a frequency of 5 RF+IF if the first and second output signals are arranged to be sin(0d) and cos(0d) respectively. ;The output of the mixer 145 is amplified by the RF amplifier 149 and filtered by the RF band-pass filter 151. The output of the RF band-pass filter 151 is 10 supplied to the third antenna 153 where the signal is transmitted. ;The second modulated IF signal on the second output channel is amplified using the IF amplifier 155, and band-pass filtered using the band-pass filter 157. A mixer 159 receives as one input the local oscillator frequency signal from the 15 local oscillator 147, and as a second input the band pass filtered signal to provide an RF output signal. ;The RF output signal is amplified by the RF amplifier 161 and band-pass filtered by the RF band-pass filter 163. The output of the RF band-pass filter 163 is 20 supplied to the fourth antenna 165 where the signal is transmitted. ;Using the above described transceiver arrangement the signals on the first and second input channels are phase matched by using a phase locked loop within one of the channels. In this embodiment, the phase locked loop includes a 25 phase rotator that has a vector multiplier. The phase matched signals are then summed using the summer 117 before being demodulated. Further, one of the first and second output signals on the first or second output channel is modified with respect to the other such that their relative phase difference enables the RF transmitted signal to be directed back towards the source. ;30 ;Although the communication apparatus described uses separate antennas for the receiver and the transmitter, it will be understood that the same physical transmitters may be used for both receiving and transmitting the RF signals. For example, a duplexing arrangement could be used to enable the sharing of the 35 antennas. ;12 ;Referring to figure 2, the phase rotator 131 of the receiver will be explained in more detail. It will be understood that in this embodiment the phase rotator 131 of the receiver uses equivalent circuitry to that of the phase rotator 137 in the transmitter. ;5 ;The phase rotator 131 includes a 90° phase shifter and a vector multiplier 203. The vector multiplier 203 includes an amplifier 205 and multiplier 207 on a first processing channel, and an amplifier 209 and multiplier 211 on a second processing channel. A summer 213 is provided to sum the signals provided by 10 the first and second processing channels. An output amplifier 215 provides an output signal to be fed into the phase detector 115 and summer 117. ;The output signal from the IF amplifier 129 is split into two separate channels. A first channel is fed through the phase shifter 201 to provide a 90° phase shifted 15 signal, which is known as the quadrature or Q signal. A second channel provides the in-phase or I signal to the vector multiplier. ;The two output signals from the signal controller sin(0d) and cos(0d) are provided as inputs to the multiplier 207 on the first processing channel and the multiplier 20 211 on the second processing channel respectively. In this manner, the output of the first multiplier = Q.sin(0d) and the output of the second multiplier = l.cos(0d). ;The two outputs of the multipliers are summed using the summer 213 and are output from the phase rotator 131. The output = l.cos(0d) + Q.sin(0d). This 25 output signal is equivalent to a phase rotated input signal from the IF amplifier 129 that has been phase rotated by phase=0d. ;For the transmitter the two output signals provided by the signal controller 139 are sin(-0d) and cos(-0d) and the output of the phase rotator = l.cos(-0d)+Q.sin(-30 0d), which is equivalent to an IF modulated signal from the splitter 135 that has been phase rotated by phase=-0d. ;Referring to figure 3, the receiver signal controller 133 is shown in more detail and includes a microcontroller 301 and a loop filter 302. The microcontroller 301 35 is arranged to effectively operate as an NCO (numerically controlled oscillator). It ;13 ;will be understood that the transmitter signal controller 139 would have similar functionality to that of the receiver signal controller 133. ;The loop filter 302 receives a phase error signal 0e from the phase detector 115 5 and produces a frequency error signal (we). The microcontroller 301 includes an analogue to digital converter (ADC) 303, which receives as an input the frequency error signal (we) from the loop filter 302. A clock 304 provides a clock signal to the microcontroller 301, which is subsequently used to generate clock signals for processing, ADC and DAC operations. The output of the ADC 303 is 10 integrated using an integrator 305. The output of the integrator 305 is used to obtain values from a cosine look up table (LUT) 307 and a sine look up table (LUT) 311. The outputs of theses tables are converted back from digital to analogue using digital to analogue converters (DAC) 309 and 313 respectively. In this manner, two output signals sine(0d) and cosine(0d) are generated by the 15 signal controller, which represent the sine and cosine of the phase difference 0d between the two signals received at the first and second antennas. During operation, the phase error (0e) from the phase detector will approach zero, as will the frequency error (we). The output of the microcontroller 301 will approach the sine and cosine of the phase difference (0d) between the signals received via the 20 two antennas. ;It will be understood that the transmitter signal controller 139 may use different look up tables to obtain the respective values of sin(-0d) and cos(-0d). Alternative arrangements may be made whereby the values are obtained from 25 the same look up tables by decrementing the look up table when accessing the information rather than incrementing it to provide the negative phase values. ;By using a phase locked loop system, a mechanism is provided that automatically eliminates errors in the system. This is due to the system 30 constantly maintaining a zero phase error. Further, the method by which the system locks to the phase can be adjusted so that only the relevant phase information is tracked. In this system it is preferable to track relative phase between the carriers but not track the phase in the modulation. This can be achieved by selecting an appropriate loop bandwidth. Further, by efficiently 35 detecting the relative phase difference of incoming signals, various advantages ;14 ;are provided such as antenna beam forming and various forms of diversity, such as space diversity, frequency diversity and polarisation diversity. ;Further, by using a vector multiplier, the incoming signals are easily adjusted to 5 control the relative phase difference. Also, the vector multiplier enables the system to be adapted so that signals can be manipulated in other ways, such as controlling the frequency of the signal. ;Second Embodiment ;10 ;Figure 4 shows communication apparatus according to this second embodiment in the form of a digital transceiver. The same advantages as described above in the first embodiment also apply to this embodiment. Further, additional improvements are realised through the use of a digital implementation. ;15 ;As in the first embodiment, the antenna array is shown to incorporate two separate antennas for each of the receiver and transmitter portions of the transceiver. However, it will be understood that more than two antennas may be applied to each of the receiver and transmitter, and that the receiver and 20 transmitter may share the same antennas using any suitable duplexing arrangement. ;The receiver portion of the transceiver is configured as a ZIF (zero intermediate frequency) receiver. The receiver portion of the transceiver includes a first 25 antenna 401 arranged to detect a first RF input signal that has been transmitted by a source (not shown). This first RF input signal is processed using a first input channel with the following components: an RF band-pass filter 403; an RF amplifier 405; a local oscillator 407; a mixer 409; a base-band low pass filter 411, a base-band amplifier 413; analogue to digital converters (ADCs) 415. ;30 ;The first input channel is split after the ADCs 415, with one portion of the channel being provided as a first input to a phase detector 417 and a second portion of the channel being provided as a first input to a summer 419. ;35 ;A second antenna 421 is arranged to detect a second RF input signal that has also been transmitted from the same source. The second RF input signal is ;15 ;processed using a second input channel with the following components: an RF band-pass filter 423; an RF amplifier 425; the same local oscillator 407 as in the first RF input channel; a mixer 427; a base-band low pass filter 429, a base-band amplifier 431; analogue to digital converters (ADCs) 435; a phase rotator 437; a 5 signal controller 439. ;The second input channel is split after the phase rotator 437, with one portion of the channel being provided as a second input to the phase detector 417, while a second portion of the channel is provided as a second input to the summer 419. ;10 ;The output of the phase detector 417 is connected to an input of the signal controller 439. The output of the signal controller 439 is connected to an input of the phase rotator 437. ;15 The signal processing carried out by the receiver will now be described. ;20 ;Referring to the first input channel, the first RF input signal detected by the first antenna 401 is band pass filtered using the RF band pass filter 403. The filtered signal is then amplified using the RF amplifier 405. ;The local oscillator 407 is arranged to operate at a frequency of the radio frequency (RF), i.e. the local oscillator frequency = RF. The local oscillator 407 output is applied to a first input of the mixer 409, while the amplified RF signal from the RF amplifier 405 is applied to the second input of the mixer 409. The 25 combination of the local oscillator 407 and mixer 409 down converts the received signal from RF to a DC (direct current) base-band signal. The mixer 409 provides in-phase (I) and quadrature (Q) signals in the form of DC output baseband signals. These are applied to the base-band low pass filter 411. It will be understood that references to signals after the mixer 409 herein are intended to 30 include both I and Q components of the signal. ;The filtered output is applied to the base-band amplifier 413. The output of the base-band amplifier 413 is applied to the ADCs 415, such that one ADC converts the in-phase component of the signal, and another ADC converts the quadrature 35 component of the signal from analogue to digital. ;16 ;The first input channel after the ADCs 415 is split so that the output of the ADCs 415 is provided as a first input to the phase detector 417 and is also provided as a first input to the summer 419. ;5 ;Referring to the second input channel, the second RF input signal detected by the second antenna 421 is band pass filtered using the RF band pass filter 423. The filtered signal is then amplified using the RF amplifier 425. ;10 As explained above, the local oscillator 407 is arranged to operate at a frequency of RF. The local oscillator 407 output is applied to a first input of the mixer 427, while the amplified RF signal from the RF amplifier 425 is applied to the second input of the mixer 427. The combination of the local oscillator 407 and mixer 427 provides a down conversion of the received signal from RF to DC (base-band 15 signal). As in the first input channel, I and Q signals are produced by the mixer 427. ;The base-band output of the mixer 427 is applied to the base-band low pass filter 429. The filtered output is applied to the base-band amplifier 431. The output of 20 the base-band amplifier 431 is applied to the ADCs 435. ;The output from the ADCs 435 is fed into the phase rotator 437, which is configured to rotate the phase of the base-band signal on the second input channel with respect to the base-band signal on the first input channel in order to 25 phase match the base-band signals. ;The output of the phase rotator 437 is split into two separate channels, with the first split channel being provided as a second input to the phase detector 417, while the second split channel is provided as a second input to the summer 419. ;30 ;The phase detector 417 thus has two inputs, one being the base-band signal on the first channel and the other being the phase adjusted base-band signal on the second channel. The output of the phase detector 417 provides a phase error signal (0e) that corresponds to the phase difference (0d) of the signals at the two 35 inputs of the phase detector. ;17 ;The phase difference is measured between the two input signals of the phase detector as follows, in order to produce a phase error signal (0e). ;The phase difference of two signals A and B may be derived from the formula: ;5 ;0=ATAN( (IB.Qa-IA-QB) / (IA.IB+QA-QB) ) ;Where 9 = phase difference between two signals A and B lA = In-phase component of signal A 10 lB = In-phase component of signal B Qa = Quadrature component of signal A Qb = Quadrature component of signal B ATAN = Inverse tangent, or arc tangent ;15 However, as the phase error signal becomes quite small in value when the PLL is locked, the inverse tangent (ATAN) value at about zero is almost linear. Therefore, there is no requirement for the circuit to calculate the inverse tangent value, but instead the phase difference value can be calculated using the following approximation; ;20 ;0= (Ib.Qa-Ia-Qb)/ (Ia-Ib+Qa-Qb) ;There is a phase ambiguity in this expression which can be resolved by the following logic. ;25 ;That is, if IBQA - IAQB > 0 and IAIB + QAQB < 0 then phase = phase + pi. If IBQA - IAQB < 0 and IAIB + QAQB < 0 then phase = phase - pi. ;Otherwise, phase = phase. ;30 With this approximation a field programmable gate array (FPGA) or an application specific integrated circuit (ASIC) may be configured using known techniques to provide the necessary phase signal output. The FPGA or ASIC can be used to implement all the digital processing required. ;18 ;The phase error signal (0e) from the phase detector 417 is fed into the signal controller 439. The signal controller uses the phase error signal to provide a suitable control output for driving the phase rotator 437. ;5 In this embodiment, the control output of the receiver signal controller 439 ;includes two output signals. The first output signal = sine (0d), while the second output signal = cosine (0d). Sin (0d) and cos (0d) are the sine and cosine values of the phase difference 0d between the two signals received at the first and second antennas. These two signals are used to drive the phase rotator 437, as 10 will be explained in more detail below in relation to figure 5. ;A transmitter portion of the transceiver will now be described with reference to figure 4. ;15 The transmitter includes a modulator (not shown) with an output connected to a splitter 441. The splitter 441 provides a first and second output channel. ;The first output channel includes a phase rotator 443, a signal controller 445, DACs 447, a base-band amplifier 449, and base-band low pass filter 451, a mixer 20 453, a local oscillator 455, an RF amplifier 457, an RF band-pass filter 459 and a third antenna 461. ;The second output channel includes DACs 462, a base-band amplifier 465, a base-band low pass filter 467, a mixer 469, the same local oscillator 455 as in the 25 first output channel, an RF amplifier 471, an RF band-pass filter 473 and a fourth antenna 475. ;The signal controller 445 in the transmitter receives the same phase error signal (0e) from the phase detector 417 as the signal controller 437 in the receiver. The 30 output of the signal controller 445 is connected to an input of the phase rotator 443. ;The signal processing carried out by the transmitter will now be described. ;19 ;A base-band modulated signal from a modulator (not shown) is provided to the splitter 441 to provide a first and second output channel. Any suitable modulation may be used. ;5 On the first output channel, a first modulated base-band signal is phase rotated using the phase rotator 443. The phase rotator 443 receives a control output signal from the signal controller 445. In this embodiment, the control output signal of the transmitter signal controller 445 includes two output signals. The first output signal = sine (-0d), while the second output signal = cosine (-0d). 10 Therefore, the first output signal is orthogonal to the second output signal. That is, the first output signal of the transmitter signal controller 445 is the conjugate of the first output signal of the receiver signal controller 439. Further, the second output signal of transmitter signal controller 445 is the conjugate of the second output signal of the receiver signal controller 439. In this manner, phase 15 conjugate signals are provided to the receiver and transmitter such that the transmitter is arranged to transmit the signals back towards the source by utilising the phase difference (0d) between the signals received at the antennas. Further details of how the signal controller produces the required control output are provided below. ;20 ;25 ;The phase rotator 443 outputs a phase rotated version of the base-band signal on the first output channel. The amount of phase rotation is based on the phase difference 0d associated with the first and second RF input signals received at the receiver. ;The phase rotated base-band signal is converted from a digital to analogue signal using the DACs 447. ;The analogue base-band signal is amplified using the base-band amplifier 449 30 and low pass filtered using the base-band low pass filter 451. A local oscillator 455 output is mixed with the base-band signal using the mixer 453. The output of the local oscillator 455 is set to RF such that the output of the mixer is an RF signal. ;20 ;The output of the mixer 453 is amplified by the RF amplifier 457 and filtered by the RF band-pass filter 459. The output of the RF band-pass filter 459 is supplied to the third antenna 461 where the signal is transmitted. ;5 The second modulated base-band signal on the second output channel is converted from a digital signal to an analogue signal using the DACs 463. ;The analogue base-band signal is amplified using the base-band amplifier 465, and low pass filtered using the base-band low pass filter 467. A mixer 469 10 receives as one input the local oscillator frequency signal from the local oscillator 455, and as a second input the low pass filtered signal to provide an RF output signal. ;The RF output signal is amplified by the RF amplifier 471 and band-pass filtered 15 by the RF band-pass filter 473. The output of the RF band-pass filter 473 is supplied to the fourth antenna 475 where the signal is transmitted. ;Using the above described arrangement, the signals on the first and second input channels are phase matched by using a phase locked loop within one of the 20 channels. In this embodiment, the phase locked loop includes a phase rotator that is a digital vector multiplier. The phase matched signals are then summed using the summer 419 before being demodulated. Further, one of the first and second output signals on the first or second output channel is modified such that their relative phase difference enables the RF transmitted signal to be directed 25 back towards the source. ;Although the communication apparatus described uses separate antennas for the receiver and the transmitter, it will be understood that the same physical transmitters may be used for both receiving and transmitting the RF signals. For 30 example, a duplexing arrangement could be used to enable the sharing of the antennas. ;Referring to figure 5, the phase rotator 437 and signal controller 439 of the receiver will be explained in more detail. It will be understood that in this 35 embodiment the phase rotator 437 and signal controller 439 of the receiver use ;21 ;equivalent circuitry to that of the phase rotator 443 and signal controller 445 in the transmitter. ;The phase rotator 437 includes a digital vector rotator 507 (vector multiplier), 5 which will be described in more detail below. ;The signal controller 439 includes a loop filter 501 and a numerically controlled oscillator (NCO) 503. ;10 The loop filter 501 of the signal controller 439 receives the phase error signal 0e from the phase detector 417. The loop filter 501 filters and integrates the phase error signal. The output of the loop filter 501 is applied to the NCO 503, where the values of sin(6d) and cos(6d) are calculated and provided as outputs to the digital vector rotator 507. ;15 ;The vector rotator 507 provides in-phase (I) 509 and quadrature (Q) 511 outputs that are phase rotated by the phase difference (0d). These outputs are fed to the DAC 447 for further processing as described above. ;20 Referring to figure 6, the digital vector rotator 507 will be described in more detail. ;The digital vector rotator 507 includes a first, second, third and fourth multiplier (601, 603, 605, 607) a first and second summer (609, 615) and a first and second Q scaler (611, 617). ;25 ;The I input, which came from the ADCs 435, is applied to a first input of the first and second multiplier (601, 603). The Q input, which came from the ADCs 435, is applied to a first input of the third and fourth multiplier (605, 607). The cos(0d) input, which came from the NCO 503, is applied to a second input of the first 30 multiplier 601 and a second input of the fourth multiplier 607. The sin(0d) input, which came from the NCO 503, is applied to a second input of the second multiplier 603 and a second input of the third multiplier 605. ;35 ;The output of the first multiplier 601 is applied as a positive input to the first summer 609. The output of the second multiplier 603 is applied as a positive input to the second summer 615. The output of the third multiplier 605 is applied ;22 ;as a negative input to the first summer 609. The output of the fourth multiplier 607 is applied as a positive input to the second summer 615. ;The output of the first summer 609 is scaled by the first scaler 611 to provide an 5 in-phase (I) output. ;The output of the second summer 615 is scaled by the second scaler 617 to provide a quadrature (Q) output. ;10 The I and Q outputs are then output to the phase detector 417 for further processing as described above. Further, the I and Q outputs are fed to the summer 419 to be combined with the I and Q components of the input signal on the first input channel. The combined signal is fed to the demodulator circuitry (not shown). ;15 ;The above described circuit is able to operate on base-band data. Current digital circuits are not in general able to function efficiently on modulated signals operating at an IF of around 70MHz. Further, current ADCs are also inefficient when operating at such frequencies. The described circuit may however operate 20 at higher frequencies and is only limited by the processing speed of the hardware. ;Further Embodiments ;25 It will be understood that the embodiments of the present invention described herein are by way of example only, and that various changes and modifications may be made without departing from the scope of invention. ;Referring to figures 7A to 7E various different configurations may be realised. ;30 ;Figure 7A shows a portion of the transceiver that includes a receiver phase rotator 701, a signal comparator 703 and a transmitter phase rotator 705. In this embodiment, the signal comparator 703 includes a phase detector and signal controller to provide two control outputs. One control output is fed to the receiver 35 phase rotator 701, while a second control output is fed to the transmitter phase rotator 705. ;23 ;10 ;Figure 7B shows a portion of the transceiver that includes a receiver phase rotator 709, a first signal comparator 711, a second signal comparator 713 and a transmitter phase rotator 715. In this embodiment, separate circuits are used to supply the output signals to the receiver and transmitter phase rotators respectively. That is, the first signal comparator 711 provides a control output signal to the receiver phase rotator 709, while the second signal comparator, using the same two input signals, provides a separate control output signal to the transmitter phase rotator 715. ;Figure 7C shows a further embodiment by developing the circuit shown in Figure 7A. In this embodiment, the signal comparator 703 includes a single phase detector 719 and a single signal controller 721. The signal controller is arranged to provide two control output signals, one to drive the receiver phase rotator 701 15 and the other to drive the transmitter phase rotator 705. ;Figure 7D shows a further embodiment by developing the circuit shown in Figure 7A. In this embodiment, the signal comparator 703 includes a single phase detector 719, a first signal controller 723 and a second signal controller 725. The 20 first signal controller 723 is arranged to provide control output signals to drive the receiver phase rotator 701, while the second signal controller is arranged to provide control output signals to drive the transmitter phase rotator 705. ;Figure 7E shows a further embodiment by developing the circuit shown in figure 25 7B. In this embodiment, the first signal comparator 711 includes a first phase detector 727 and a first signal controller 729. The second signal comparator 713 includes a second phase detector 731 and a second signal controller 733. The first and second phase detectors (727, 731) receive the same two input signals. The output of the first signal controller 729 is used to drive the receiver phase 30 rotator 709. The output of the second signal controller 733 is used to drive the transmitter phase rotator 715. ;It will be understood that the configurations described above in relation to figures 7A to 7E may be realised using analogue or digital circuits, and that 35 configurations other than those specifically described may be used to implement the invention as described. ;24 ;It will be understood that the invention is not limited to the specific circuits described herein, and that various components within may be moved, changed removed from the circuits whilst still providing the advantages of the invention described herein. ;25 *

Claims (31)

CLAIMS:

1. Communications apparatus including: a receiver for receiving RF input signals via multiple antennas, the 5 receiver including first and second input channels, a first phase rotator and a first signal comparator, wherein the first input channel is associated with a first input signal received via a first antenna and the second input channel is associated with a second input signal received via a second antenna, 10 the first signal comparator is configured to develop a first control output signal based on a phase difference between the first and second input signals, and the first phase rotator includes a first vector multiplier being configured to rotate the phase of one input signal with respect to the other based on the first 15 control output signal, the apparatus further including a transmitter for transmitting RF output signals via multiple antennas including a first output channel associated with a first output signal and a second output channel associated with a second output signal, a second phase rotator and a second signal comparator, wherein 20 the second signal comparator is configured to develop a second control output signal based on the phase difference between the first and second input signals, and the second phase rotator is configured to rotate the phase of one output signal with respect to the other based on the second control output signal. 25

2. Communications apparatus including: a receiver for receiving RF input signals via multiple antennas, the receiver including first and second input channels, a first phase rotator and a first signal comparator, wherein 30 the first input channel is associated with a first input signal received via a first antenna and the second input channel is associated with a second input signal received via a second antenna, the first signal comparator is configured to develop a first control output signal based on a phase difference between the first and second input signals, 35 the first phase rotator configured to rotate the phase of one input signal with respect to the other based on the first control output signal, and the first 26 phase rotator and first signal comparator are configured to form a phase locked loop, the apparatus further including a transmitter for transmitting RF signals via multiple antennas including a 5 first output channel associated with a first output signal and a second output channel associated with a second output signal, a second phase rotator and a second signal comparator, wherein the second signal comparator is configured to develop a second control output signal based on the phase difference between the first and second input 10 signals, and the second phase rotator is configured to rotate the phase of one output signal with respect to the other based on the second control output signal.

3. The apparatus of claim 2, wherein the first or second phase rotator 15 includes a vector multiplier configured to rotate the phase.

4. The apparatus of claim 1, wherein the first phase rotator and first signal comparator are configured to form a phase locked loop. 20

5. The apparatus of claim 1 or 2, wherein the first and second signal comparator is one and the same signal comparator.

6. The apparatus of claim 1 or 2, wherein the second control output signal is the phase conjugate of the first control output signal. 25

7. The apparatus of claim 1 or 2, wherein the first or second control output signal includes first and second output signals that are orthogonal to each other.

8. The apparatus of claim 1 or 2, wherein the first control output signal is 30 based on the sine of the phase difference between the first and second input signals and the second control output signal is based on the cosine of the phase difference between the first and second input signals.

9. The apparatus of claim 1 or 2, wherein the first signal comparator includes 35 a first phase detector being configured to develop a first phase error signal, and further includes a first signal controller configured to develop the first control 27 output signal based on the first phase error signal, and the second signal comparator includes a second phase detector being configured to develop a second phase error signal, and further includes a second signal controller configured to develop the second control output signal based on the second 5 phase error signal.

10. The apparatus of claim 9, wherein the first and second phase detector are one and the same such that the first and second phase error signals are one and the same. 0

11. The apparatus of claim 9, wherein the first and second signal controller are one and the same.

12. The apparatus of claim 9, wherein the first or second phase detector is 15 configured to detect the phase difference between two base-band signals.

13 The apparatus of claim 12, wherein the first or second phase detector is configured to detect the phase difference between a first and second base-band signal by determining: 20 a first signal value equal to the product of the quadrature component of the first base-band signal and the in-phase component of the second base-band signal, a second signal value equal to the product of the in-phase component of the first base-band signal and the quadrature component of the second base-25 band signal, a third signal value equal to the product of the in-phase component of the first base-band signal and the in-phase component of the second base-band signal, a fourth signal value equal to the product of the quadrature component of 30 the first base-band signal and the quadrature component of the second baseband signal, a fifth signal value by subtracting the second signal value from the first signal value, a sixth signal value by adding the fourth signal value to the third signal 35 value, and 28 a phase difference value by dividing the fifth signal value by the sixth signal value.

14. The apparatus of claim 1 or 2, wherein the first or second signal controller 5 further includes a microcontroller configured to convert one of the input signals from analogue to digital, integrate the signal and provide cosine and sine values associated with the signal.

15 The apparatus of claim 1 or 2, wherein the first or second signal controller 10 further includes a loop filter and a numerically controlled oscillator.

16. The apparatus of claim 1 or 2, wherein the first or second phase rotator includes cosine and sine lookup tables. 15

17. The apparatus of claim 1 or 2, wherein the first or second phase rotator includes a numerically controlled oscillator.

18. The apparatus of claim 1 or 2 further including a splitter and a ninety degree phase shifter, wherein the splitter is configured to split one of the first or 20 second input channels into a first split input channel and a second split input channel, and the ninety degree phase shifter is configured to shift the phase of a signal on the first or second split input channel by ninety degrees, and the first or second phase rotator is configured to receive the ninety degree phase shifted input signal as a first input and further configured to receive a signal on the other 25 first or second split input channel as a second input.

19. The apparatus of claim 1 or 2, wherein the phase of one input signal with respect to the other is rotated to provide one of: space diversity; frequency diversity; polarisation diversity; antenna beam forming. 30

20. A method of controlling signals received via multiple antennas including the steps of: receiving on a first input channel a first input signal via a first antenna, receiving on a second input channel a second input signal via a second 35 antenna, detecting the phase difference between the first and second input signals, 29 phase rotating one input signal with respect to the other based on the detected phase difference using a phase locked loop, summing the phase rotated input signal with the other input signal, providing a first output signal on a first output channel, 5 providing a second output signal on a second output channel, and phase rotating one output signal with respect to the other based on the detected phase difference.

21. A method of controlling signals received via multiple antennas including 10 the steps of: receiving on a first input channel a first input signal via a first antenna, receiving on a second input channel a second input signal via a second antenna, detecting the phase difference between the first and second input signals, 15 phase rotating one input signal with respect to the other based on the detected phase difference using a vector multiplier, summing the phase rotated input signal with the other input signal, providing a first output signal on a first output channel, providing a second output signal on a second output channel, and 20 phase rotating one output signal with respect to the other based on the detected phase difference.

22. The method of claim 20, wherein the phase is rotated using a vector multiplier.

23. The method of claim 21, wherein the phase is rotated using a phase locked loop.

24. The method of claim 20 or 21 further including the steps of: 30 developing a first control output signal based on the sine of the phase difference between the first and second input signals and developing a second control output signal based on the cosine of the phase difference between the first and second input signals. 35

25. The method of claim 20 or 21 further including the steps of: developing a first phase error signal, 30 developing a first control output signal based on the first phase error signal, developing a second phase error signal, and developing a second control output signal based on the second phase 5 error signal.

26. The method of claim 25, wherein the first and second phase error signals are one and the same. 10

27. The method of claim 25, wherein the first or second phase error signals are developed by detecting the phase difference between two base-band signals.

28. The method of claim 27, wherein the phase difference between a first and second base-band signal is developed by determining: 15 a first signal value equal to the product of the quadrature component of the first base-band signal and the in-phase component of the second base-band signal, a second signal value equal to the product of the in-phase component of the first base-band signal and the quadrature component of the second base-20 band signal, a third signal value equal to the product of the in-phase component of the first base-band signal and the in-phase component of the second base-band signal, a fourth signal value equal to the product of the quadrature component of 25 the first base-band signal and the quadrature component of the second baseband signal, a fifth signal value by subtracting the second signal value from the first signal value, a sixth signal value by adding the fourth signal value to the third signal 30 value, and a phase difference value by dividing the fifth signal value by the sixth signal value. 31

29. Communications apparatus including: a receiver for receiving RF input signals via multiple antennas, the receiver including first and second input channels, a first phase rotator and a first 5 signal comparator, wherein the first input channel is associated with a first input signal received via a first antenna and the second input channel is associated with a second input signal received via a second antenna, 10 signal based on the phase difference between the first and second input signals, and the first phase rotator includes a first vector multiplier being configured to rotate the phase of one input signal with respect to the other based on the first control output. 15

30. Communications apparatus substantially as hereinbefore described with reference to the accompanying drawings.

31. A method of controlling signals substantially as hereinbefore described 20 with reference to the accompanying drawings. the first signal comparator is configured to develop a first control output 4RF COMMUNICATIONS LIMITED 25