GB2583067A

GB2583067A - Receiving apparatus

Info

Publication number: GB2583067A
Application number: GB1902686.3A
Authority: GB
Inventors: Bookham David; Mallett Malcolm
Original assignee: Individual
Current assignee: Individual
Priority date: 2019-02-28
Filing date: 2019-02-28
Publication date: 2020-10-21
Also published as: GB201902686D0

Abstract

A spaced antennae signal receiver apparatus or method comprises a pair of spaced antennae receiving the same signal A, B where the signal of one antenna B is phase shifted by an amount giving a minimum difference value between the signals A, B received by the antennae and to align the phases of the antennae signals and where the in-phase signals are then combined in a summed signal 26 to provide a maximised received signal. The antennae signals A, B are received and corresponding sum 26 and difference 29 signals are derived. The received signals and the sum and difference signals are stored in a memory 32 for different applied phase shifts, where the phase shift with the minimum difference signal 29 is selected. An electronically variable phase shifter 24, a fixed phase shifter 27, summer circuits 25, 28, a digital signal processor 30 and a local oscillator generating a modulating carrier wave, may be used. The apparatus and method may be used on moving vehicles such as cars, trains or ships. An iterative process may be used in repeating the method to combine signals from multiple antennae pairs. A dynamic phase shift change may be applied in real time. A model may be created from historical values stored in a memory and used in a predicted phase correction.

Description

RECEIVING APPARATUS

This disclosure relates to receiver apparatus mounted on a vehicle to receive a signal from a remote transmitter such as a satellite, and to methods associated therewith.

Phase shifting technology is well known within the satellite communication industry, and the technology dates back to the invention of the radio. Today we see phase shifters used in a multitude of satellite technologies, such as signal tracking.

One such field of use is in phased array antennas, where phase shifters have been used as a means for collimating the radio beam. Most of the phase shifters are static and are only updated for calibration needs.

Active antennae also use phase shifters. Active antennae are usually made of several sub-modules, and synchronised by static phase shifters to amplify signals. Again, the phase shift is only updated for calibration purposes. There are phase shifters that are considered more dynamic, where phase shifts are updated at regular intervals, but are not continually updated in real time.

Phase shifters have also been employed in electronic scanning antennae, that is, antennae that do not mechanically scan an area, but rather use phase shifters to scan certain areas without mechanical movement of the antennae. Yet again, the phase shifters are only updated in order to calibrate the signal.

Examples of prior disclosures relating to the above include: US2003/0122709, 20 US2013/018168, US4278978, US20180317186, CN108092001, and CN207504175 The conventional practice in communication systems for vehicles such as ships is to mount a pair of spaced antennae on the vessel for navigation by receiving signals from remote transmitters such as a satellite. In such systems, at any one time, one of the two antennae is redundant. The systems operate by choosing the antenna with the greater signal at any one time and ignoring the other. The reason for this is that one, but not both antennae at the same time, may be at least partially blocked, for example by superstructure of the ship, and may not have a clear uninterrupted view of the signal source.

The present disclosure arises from Applicant's work seeking to improve the signal-to-noise ratio for such vehicle mounted systems. As explained in detail hereinbelow, it applies phase shift technology in a novel and inventive manner to such dual antennae systems, and utilises signals received by both antennae, contrary to the accepted practice.

In accordance with one aspect of this disclosure, receiver apparatus is mounted on a moving vehicle, preferably a ship, the apparatus comprising a pair of spaced antennae adapted to receive the same signal from a remote transmitter such as a satellite, in which a maximised signal is derived from first and second received signals received by respective first and second antennae of said pair by circuitry that receives the first and second received signals and derives a sum signal therefrom after applying a predetermined phase change to one of the two received signals to bring it into phase with the other received signal; the circuitry including a memory for storing the amplitudes of the first and second received signals, and sum and difference circuits respectively deriving values for the sum and difference between the amplitudes of the stored first and second received signals after applying different values of applied phase change, and the circuitry selecting that applied phase change at which the difference is a minimum as the predetermined phase change.

In a second and alternative aspect of this disclosure, there is described a method for deriving a maximised signal from a pair of spaced antennae mounted on a vehicle, and consisting of a first antenna and a second antenna, receiving the same signal from a remote transmitter; the method comprising forming a sum of respective first and second signals received by the respective first and second antennae after applying a predetermined phase change to one said received signal, the predetermined phase change being determined by storing the amplitudes of the first and second received signals, and deriving values for the sum and difference between the amplitudes of the stored first and second received signals after applying different values of applied phase change, and selecting that applied phase change at which the difference is a minimum as the predetermined phase change.

In an alternative arrangement, the receiving apparatus comprises 2" antennae in which a maximised signal is derived by an iterative process in which the signals at respective pairs of antennae in said 2" antennae are summed after applying a predetermined phase shift to one signal of said pair, the phase shift being derived by storing the amplitudes of the respective signals and deriving values for the sum and difference between of the amplitudes of the stored signals after applying different values of applied phase change, and selecting that applied phase change at which the difference is a minimum as the predetermined phase change, thereby resulting in 2'1 combined signals; and repeating this process by combining the combined signals in pairs with a predetermined phase shift in the same fashion as many times as necessary to result in a single combined signal.

Reference should now he made by way of example only to the accompanying drawings, in which: Fig. 1 is a schematic plan view showing a receiving apparatus comprising two antennae mounted on a ship where both antennae have an open channel to the transmitting satellite, as shown at the left in the Figure, and where one antenna is blocked by the ship's superstructure as shown at the right of the Figure; Fig. 2 is a schematic plan view showing a receiving apparatus comprising two antennae mounted on a train, where one antenna is blocked by a bridge; Fig. 3 is a schematic circuit diagram for circuitry linking a pair of antennae; Fig. 4 is a schematic view showing how signals may be combined from 2" antennae mounted on a vehicle, here a train, the Figure illustrating this for n=2; Fig. 5 shows a schematic circuit diagram for deriving a maximised signal from a pair of spaced antennae mounted on a vehicle; Fig. 6 shows a graph comparing the sum and difference in the power of two signals combined with different phase changes applied to one of them; Fig. 7 shows a portion of Fig. 6 at increased scale on the abscissa; and Fig. 8 is similar to Fig. 7 in a situation where the received signal falls below the detection threshold of the receiver.

Turning first to Fig. 1, the drawing shows on the left a ship I with a pair of antennae 2, 3 mounted on either side of the vessel's superstructure 4. With the bearing shown, both antennae 2, 3 have a clear, un-blocked, path to a transmitting satellite 5. In the conventional practice for navigation, there is deliberate redundancy in the system, with only the signal from one antenna being utilised at any one time, namely the larger of the two detected signals. The reason for this will be obvious when considering the right hand portion of Fig. 1 which shows the same vessel on a different bearing. As can be seen, the path from satellite 5 to one antenna 3 is blocked by the superstructure 4.

Similarly in Fig. 2, which shows a pair of antennae 6, 7 mounted on a train 8 travelling along a track 9 passing through a schematically indicated tunnel 10 or under a schematically indicated bridge 10, the signal to one antenna is blocked by the terrain or bridge. Again, only the larger of the two signals, or in the case of a train with multiple antennae mounted on successive cars, the largest detected signal, will be utilised at any one time, the signals from other antennae being redundant.

The present Inventors have appreciated that, contrary to the above described accepted practice in communication systems, a maximised signal with enhanced signal-to-noise ratio could be obtained from the same antennae if the signals are appropriately combined rather than (apart from the largest signal at any one time) being rejected as redundant. Fig. 3 illustrates circuitry for achieving this. Respective received signals 11 and 12 from antennae such as 2 and 3 or 6 and 7 are combined with a carrier wave from a local oscillator at mixers 13 and 14 to provide modulated received signals 15 and 16.

Unless the transmitter is directly ahead, as shown at the left in Fig. 1, there will be a phase difference between received signals 11 and 12 which will be carried over into the modulated received signals 15, 16. To get maximum power and maximum signal-to-noise ratio, a corrective phase change must be applied to one of the two signals to correct for the phase difference between the received signals. This applied phase change can be applied at 17 directly to the received signal or at 18 to the modulated signal. The respective signals are then combined at summer 19. Only the noise is non-coherent, so that there is an improvement in the signal-to-noise ratio and increased data download speeds.

As can be seen from Fig. 4, the receiving apparatus is capable of combining multiple pairs of antennae by an iterative process in a 2" sequence, with n being an integer greater than 1, the system being illustrated for n=2. As can be seen the signals 20 from successive pairs of antennae are combined using circuitry 21, as shown in Fig. 3. Thus, for each pair of antennae, a phased shifted signal is combined with the signal from the other antenna of the pair. Repeating this for successive pairs, will result in 2'1 combined signals 22. These combined signals 22 are then combined in pairs a similar way with a phase shift applied to one combined signal of the pair. The result will be 2'2 recombined signals. The process is continued until there are only two remaining signals to be combined in the same way to result in a final single signal. As shown for the train 8 shown in Fig. 4 which has four cars, the second iterative step results in a final combined signal.

The key to this system working correctly lies in identification of the phase shift to be applied to one signal of a pair to be combined. Since the bearing of vessel to the satellite or the instant direction of the train track will change as time passes, we employ a dynamic adaptive applied phase change in real time. Fig. 5 illustrates how this can be achieved. Incoming signals are received in paths A and B, and split into two streams, a first one of which passes straight to an output switch 23, while, of the respective second streams, a phase change is applied to the signal from path B by an electronically variable phase shifter 24. The phase shifted signal from path B is summed with the signal from path A in summer 25 to provide a sum signal 26. A lin fixed shift is applied to the signal from path A at fixed phase shifter 27 and combined with the phase shifted signal from path B in summer 28 to create a difference signal 29. The sum and difference signals 26, 29 are received at output switch 23, and as inputs to a digital signal processor 30. As the phase shift applied by phase shifter 24 is varied, the sum and difference signals recorded at the processor 30 will change, as illustrated in Fig. 6. At different phase shifts a sharper null value is apparent in the difference signal than the maximum value in the sum signal. That value for the phase difference which achieves the null value in the difference signal is chosen as the phase shift to be applied by a control signal 31 to phase shifter 24, and the maximised sum signal at that phase shift will usually be the optimum signal present at output switch 23, which is designed to select the optimum signal present on its four inputs at any one time.

It will be appreciated that when the total phase shift applied approaches Mr, the designation of signals as "sum" and "difference" signals breaks down, and their functions are reversed. Accordingly, the channel on which a sharp null signal is detected is taken as the difference channel at any time.

In maritime or rail application the vehicle will often travel at a reasonably constant velocity, and change course relatively infrequently. The system described will continually optimise phase combining by comparing the sum and difference paths storing the data in a memory 32 associated with processor 30. When a change in velocity is detected, the system updates a predictive model, using data from memory 32, which will be used to compute the required phase shift for the accompanying change in velocity. At the same time, in the event of loss of signal in either path A or B, output switch 23 selects the optimum remaining signal.

By storing the signals in memory 32, and using the historical values to determine the phase shift to be applied at any instant, as described above, a model is created and stored in memory 32 so that if the received signal falls below the detection threshold of the receiver as shown in Fig. 8, a predicted phase correction can still be produced using the model.

Claims

Claims 1. Receiver apparatus for mounting on a moving vehicle, the apparatus comprising a pair of spaced antennae adapted to receive the same signal from a remote transmitter such as a satellite, in which a maximised signal is derived from first and second received signals received by respective first and second antennae of said pair by circuitry that receives the first and second received signals and derives a sum signal therefrom after applying a predetermined phase change to one of the two received signals to bring it into phase with the other received signal; the circuitry including a memory for storing the amplitudes of the first and second received signals, and sum and difference circuits respectively deriving values for the sum and difference between the amplitudes of the stored first and second received signals after applying different values of applied phase change, and the circuitry selecting that applied phase change at which the difference is a minimum as the predetermined phase change. C\ICDCO
2. Apparatus according to Claim I, wherein the circuitry comprises a first summer, a second summer, an electronically variable phase shifter, a lhr fixed phase shifter, and a digital signal processor linked to said memory; wherein the first summer is coupled to receive (i) the first received signal or a modulated first signal consisting of the first signal combined with a carrier wave from a local oscillator and (ii) the second received signal or a modulated second signal consisting of the second received signal combined with said carrier wave, in either case phase shifted by application of a phase change from said electronically variable phase shifter, thereby producing a first summed signal; and wherein the second summer is coupled to receive (iii) the first received signal or a modulated first signal consisting of the first received signal combined with said carrier wave, in either case phase shifted by application of a 1/7c fixed phase change from said 1/7c fixed phase shifter, and (ii) the second received signal or a modulated second signal consisting of the second received signal combined with said carrier wave, in either case phase shifted by application of a phase change from said electronically variable phase shifter, thereby producing a second summed signal; and wherein the digital signal processor is coupled to receive the first and second summed signal and to compare the said signals to select the one of the first and second summed signals that has the sharpest detected null signal as the phase varies as the difference signal and the other of said first and second summed signals as the sum signal, and wherein the digital processor is coupled to the electronically variable phase shifter to apply that phase at which the difference signal is at a minimum to the electronically variable phase shifter and to derive the sum signal at said that phase as the maximised signal.
A vehicle mounting receiver apparatus according to Claim 1 or Claim 2.
4. A vehicle according to Claim 3, consisting of a ship on which the antennae are mounted at spaced positions on the ship's superstructure.
5. A vehicle according to Claim 3, consisting of a railway train on which the antennae are mounted on different cars.
6. A method for deriving a maximised signal from a pair of spaced antennae mounted on a vehicle, and consisting of a first antenna and a second antenna, receiving the same signal from a remote transmitter; the method comprising forming a sum of respective first and second signals received by the respective first and second antennae after applying a predetermined phase change to one said received signal, the predetermined phase change C\I being determined by storing the amplitudes of the first and second received signals, and N 15 deriving values for the sum and difference between the amplitudes of the stored first andCDsecond received signals after applying different values of applied phase change, and CO selecting that applied phase change at which the difference is a minimum as the predetermined phase change.
7. A method according to Claim 6, wherein the respective first and second signals are combined with a carrier wave from a local oscillator to provide first and second modulated received signals, and wherein the applied phase change is applied either to the second received signal or to the second modulated received signal.
8. A method for deriving a maximised signal from receiving apparatus mounted on a moving vehicle and comprising 211 spaced antennae, where n>1, in which a maximised signal is derived by an iterative process in which: in a first step, the signals at respective pairs of antennae in said 2n antennae are summed after applying a predetermined phase shift to one signal of said pair, the phase shift being derived by storing the amplitudes of the respective signals at said pair of antennae and deriving values for the sum and difference between the amplitudes of the stored signals after applying different values of applied phase change, and selecting that applied phase change at which the difference is a minimum as the predetermined phase change, thereby resulting in 2'1 combined signals; and repeating this process in a further step by combining the combined signals in pairs with a phase shift pre-determined in the same fashion as many times as necessary to result in a single combined signal.
9. A method according to any of Claims 6 to 8, wherein the method is continuously repeated, whereby a dynamic adaptive applied phase change is applied in real time.
10. A vehicle according to Claim 3, wherein the receiver apparatus comprises 2' antennae, the respective antennae being mounted on 2n successive cars of the train, where n>1; and wherein the circuitry is adapted to perform a method according to Claim 8 or 10 Claim 9. O C\IO CO