TECHNICAL FIELD

The invention relates to a high frequency (HF) radio including an adjustable-bandwidth tunable bandpass filter for improved detection of incoming calls and methods for processing incoming calls.

BACKGROUND

High frequency (HF) radio stations are configured to perform long-distance ionospheric radio communications at frequencies within the HF band. However, a range of frequencies over which a HF radio station can perform ionospheric radio communications varies over time due to changes over time in ionospheric propagation conditions and interfering HF communications. In view of the foregoing, a HF radio station cannot listen for calls at a fixed, unchanging frequency, but rather must listen for calls at varying frequencies (i.e., channels) within the HF band.

An approach for listening for calls by a HF radio station is known as Automatic Link Establishment (ALE). Under this approach, a plurality of ALE channels that are known to be suitable for ionospheric radio communications are assigned to HF radio stations in a HF radio network for linking between the HF radio stations in the network. However, only a subset of the assigned ALE channels are suitable for linking at any given time, due to changes over time in ionospheric propagation conditions and interfering HF communications.

One technique for ensuring that HF radio stations can detect incoming calls at all times is known as scanning ALE. Using this technique, each HF radio station in a HF radio network continuously scans through assigned ALE channels until it detects a possibility of an incoming call from a calling HF radio station. A drawback of this technique is the delay in link establishment between a calling HF radio station and a called HF radio station, since the called HF radio station generally is not monitoring the ALE channel along which the calling HF radio station wishes to transmit, and since the calling HF radio station is generally not aware if the ALE channel along which it wishes to transmit is occupied. This is problematic when HF radio communications are used in environments in which link establishment time is critical.

A technique for significantly reducing the time required for link establishment is known as staring ALE. According to this technique, each HF radio station in a staring ALE network has a plurality of parallel receivers configured to continuously monitor a plurality of ALE channels within the HF band for calling signals, the plurality of ALE channels being assigned to the respective HF radio station. The problem with this approach is that the HF radio stations are exposed to strong interfering HF signals throughout the HF band that make it difficult for the HF radio stations to detect faint calls, thereby complicating or preventing the detection of at least some calling signals.

There is thus a need in the art for a HF radio station in a staring ALE network with an improved capability for detecting calling signals, while maintaining the fast link establishment that characterizes the staring ALE technique.

References considered to be relevant as background to the presently disclosed subject matter are listed below. Acknowledgement of the references herein is not to be inferred as meaning that these are in any way relevant to the patentability of the presently disclosed subject matter.

Eric E. Johnson, “Staring Link Establishment for High-Frequency Radio”, MILCOM 2015-2015 IEEE Military Communications Conference, pages 1433-1438, investigates the possibility and advantages of using various non-scanning ALE techniques with a new wideband ALE (WALE) to improve spectrum awareness and linking speed.

Andree Bengtsson, “Instantaneous Channel Access for 3G-ALE Systems”, published on Aug. 31, 2014, discloses removing a need for a scanning mechanism for radio systems that use a 3G-ALE standard while retaining the capability to handle multiple channels, thereby decreasing latency. This can be accomplished by using a parallel receiver that receives on all the channels in the channel group.

Chinese Patent Application Publication No. 101567674A, published on Oct. 28, 2009, discloses a tunable bandpass filter, which adopts a method of the combination of left-handed and right-handed non-linear transmission lines, wherein the left-handed non-linear transmission line consists of a series varactor and a shunt inductor, and has high-pass characteristic; and the right-handed non-linear transmission line consists of a series inductor and parallel varactor, and has low-pass characteristic. The capacitances of the varactors are changed by controlling the bias voltages of the varactors of the left-handed and right-handed non-linear transmission lines so as to adjust lower and upper side frequencies of the bandpass filter respectively.

Saha et al., “Tunable Band-Pass Filter Using RF MEMS Capacitance and Transmission Line, Progress In Electromagnetics Research C, Vol. 23, pages 233-247, 2011, presents the design and fabrication of an RF MEMS tunable band-pass filter. The band-pass filter design uses both distributed transmission lines and RF MEMS capacitances together to replace the lumped elements. The use of RF MEMS variable capacitances gives the flexibility of tuning both the centre frequency and the band-width of the band-pass filter. A prototype of the tunable band-pass filter is realized using parallel plate capacitances. The variable shunt and series capacitances are formed by a combination of parallel plate RF MEMS shunt bridges and series cantilevers. The filter operates at C-X band. The measurement results agree well with the simulation results.

GENERAL DESCRIPTION

In accordance with a first aspect of the presently disclosed subject matter, there is provided a high frequency (HF) radio configured to process an incoming call from another HF radio, the HF radio comprising: a plurality of receivers configured to simultaneously monitor a corresponding plurality of assigned Automatic Link Establishment (ALE) channels within a staring frequency band for one or more digital calling signals that are indicative of incoming calls, wherein the staring frequency band is a subset of a HF band, and wherein a bandwidth of the staring frequency band is adjustable; an adjustable-bandwidth tunable bandpass filter configured to obtain, from at least one antenna, first HF signals within a HF band, and to provide only second HF signals within the staring frequency band, the second HF signals including one or more analog calling signals that are indicative of the incoming calls; a first receive path connected to an output of the adjustable-bandwidth tunable bandpass filter and configured to convert the analog calling signals to the digital calling signals; and a controller configured to: establish a communication link between the HF radio and the another HF radio, in response to a given receiver of the receivers decoding a given digital calling signal of the digital calling signals that is indicative of the incoming call from the another HF radio, the given digital calling signal being communicated from the another HF radio over a given assigned ALE channel of the assigned ALE channels; and select the staring frequency band and the assigned ALE channels.

In some cases, the adjustable-bandwidth tunable bandpass filter comprises an adjustable high pass filter (HPF) and an adjustable low pass filter (LPF) connected in series, and wherein the controller is configured to select the staring frequency band by independently adjusting a first cut-off frequency of the HPF and a second cut-off frequency of the LPF.

In some cases, the controller is configured to select the staring frequency band and the assigned ALE channels, based on values of parameters that are indicative of ionospheric propagation conditions at a given time.

In some cases, the given time is a current time. In some cases, the parameters include one or more of: a calendar date, a time of day at a geographical location of the HF radio, a time of day at a geographical location of the another HF radio, a geographical location of the HF radio, a geographical location of the another HF radio, or a distance between the HF radio and the another HF radio.

In some cases, the controller is configured to select the staring frequency band and the assigned ALE channels based on an analysis of a quality of signal reception over ALE channels at a plurality of times in the past, the analysis being indicative of a relationship between the parameters and the ionospheric propagation conditions.

In some cases, the controller is configured to select the staring frequency band and the assigned ALE channels to prevent one or more expected interfering HF signals from being included within the staring frequency band.

In some cases, the controller is configured to select the staring frequency band and the assigned ALE channels based on an analysis of a quality of signal reception over ALE channels at a plurality of times in the past, the analysis being indicative of the expected interfering HF signals.

In some cases, the controller is configured to narrow the staring frequency band to prevent one or more actual interfering HF signals from being included within the staring frequency band.

In some cases, the first receive path comprises: a first amplification circuit coupled to an output of the adjustable-bandwidth tunable bandpass filter and configured to generate amplified calling signals based on the analog calling signals; and a first analog-to-digital converter (ADC) connected to an output of the first amplification circuit and configured to convert the amplified calling signals to the digital calling signals.

In some cases, the first receive path further comprises: a low-noise amplifier (LNA) connected to an output of the adjustable-bandwidth tunable bandpass filter and configured to amplify the analog calling signals to generate modified calling signals; wherein the first amplification circuit is coupled to an output of the LNA and is configured to generate the amplified calling signals based on the modified calling signals.

In some cases, the first receive path further comprises: a radio frequency (RF) splitter coupled to an output of the adjustable-bandwidth tunable bandpass filter and configured to generate split calling signals based on the analog calling signals; wherein the first amplification circuit is connected to an output of the RF splitter and is configured to amplify the split calling signals to generate the amplified calling signals.

In some cases, upon establishment of the communication link between the HF radio and the another HF radio, the adjustable-bandwidth tunable bandpass filter is configured to obtain one or more analog data traffic signals from the another HF radio over the given assigned ALE channel.

In some cases, the HF radio further comprises: a second receive path connected to an output of the adjustable-bandwidth tunable bandpass filter and configured to obtain the analog data traffic signals therefrom, the second receive path being further configured to convert the analog data traffic signals to digital data traffic signals; wherein the plurality of receivers are connected to the second receive path; and wherein the given receiver is configured to decode the digital data traffic signals.

In some cases, the second receive path comprises: a radio frequency (RF) splitter coupled to an output of the adjustable-bandwidth tunable bandpass filter and configured to generate split data traffic signals based on the analog data traffic signals; a second amplification circuit coupled to an output of the RF splitter and configured to amplify the split data traffic signals to generate amplified data traffic signals; and a second ADC connected to an output of the second amplification circuit and configured to convert the amplified data traffic signals to the digital data traffic signals.

In some cases, the first amplification circuit has a lower gain and signal-to-noise ratio than the second amplification circuit and a higher selectivity than the second amplification circuit.

In some cases, the plurality of receivers are configured to decode the digital calling signals concurrently with the given receiver decoding the digital data traffic signals.

In some cases, the controller is configured to narrow the staring frequency band, in response to the given receiver decoding the given digital calling signal.

In some cases, the staring frequency band is narrowed such that a first passband of the staring frequency band is identical to a second passband of the given assigned ALE channel.

In some cases, the first receive path is configured to obtain the analog data traffic signals from the adjustable-bandwidth tunable bandpass filter, and to convert the analog data traffic signals into digital data traffic signals; wherein the given receiver is configured to decode the digital data traffic signals.

In some cases, the first receive path further comprises: a low-noise amplifier (LNA) connected to an output of the adjustable-bandwidth tunable bandpass filter and configured to amplify the analog data traffic signals to generate modified data traffic signals; wherein the first amplification circuit is connected to an output of the LNA and is configured to amplify the modified data traffic signals to generate amplified data traffic signals; and wherein the first ADC is configured to convert the amplified data traffic signals to the digital data traffic signals.

In accordance with a second aspect of the presently disclosed subject matter, there is provided a method for a high frequency (HF) radio to process an incoming call from another HF radio, the method comprising: selecting a staring frequency band and a plurality of assigned Automatic Link Establishment (ALE) channels within the staring frequency band; obtaining, at an adjustable-bandwidth tunable bandpass filter, from at least one antenna, first HF signals within a HF band; providing, by the adjustable-bandwidth tunable bandpass filter, only second HF signals within the staring frequency band, the second HF signals including one or more analog calling signals that are indicative of incoming calls, wherein the staring frequency band is a subset of the HF band, and wherein a bandwidth of the staring frequency band is adjustable; converting the analog calling signals to one or more digital calling signals that are indicative of the incoming calls, by a first receive path connected to an output of the adjustable-bandwidth tunable bandpass filter; monitoring, by a plurality of receivers, the ALE channels, each receiver of the receivers being configured to monitor a different assigned ALE channel of the assigned ALE channels for the digital calling signals; and establishing a communication link between the HF radio and the another HF radio, in response to a given receiver of the receivers decoding a given digital calling signal of the digital calling signals that is indicative of the incoming call from the another HF radio, the given digital calling signal being communicated from the another HF radio over a given assigned ALE channel of the assigned ALE channels.

In some cases, the adjustable-bandwidth tunable bandpass filter comprises an adjustable high pass filter (HPF) and an adjustable low pass filter (LPF) connected in series, and selecting the staring frequency band comprises: independently adjusting a first cut-off frequency of the HPF and a second cut-off frequency of the LPF.

In some cases, the staring frequency band and the assigned ALE channels are selected based on values of parameters that are indicative of ionospheric propagation conditions at a given time.

In some cases, the given time is a current time. In some cases, the parameters include one or more of: a calendar date, a time of day at a geographical location of the HF radio, a time of day at a geographical location of the another HF radio, a geographical location of the HF radio, a geographical location of the another HF radio, or a distance between the HF radio and the another HF radio.

In some cases, the staring frequency band and the assigned ALE channels are selected based on an analysis of a quality of signal reception over ALE channels at a plurality of times in the past, the analysis being indicative of a relationship between the parameters and the ionospheric propagation conditions.

In some cases, the staring frequency band and the assigned ALE channels are selected to prevent one or more expected interfering HF signals from being included within the staring frequency band.

In some cases, the staring frequency band and the assigned ALE channels are selected based on an analysis of a quality of signal reception over ALE channels at a plurality of times in the past, the analysis being indicative of the expected interfering HF signals.

In some cases, the method further comprises: narrowing the staring frequency band to prevent one or more actual interfering HF signals from being included within the staring frequency band.

In some cases, converting the analog calling signals to the digital calling signals comprises: generating amplified calling signals, by a first amplification circuit coupled to an output of the adjustable-bandwidth tunable bandpass filter, based on the analog calling signals; and converting the amplified calling signals to the digital calling signals, by a first analog-to-digital converter (ADC) connected to an output of the first amplification circuit.

In some cases, generating the amplified calling signals comprises: amplifying the analog calling signals, by a low-noise amplifier (LNA) connected to an output of the adjustable-bandwidth tunable bandpass filter, to generate modified calling signals; and generating the amplified calling signals based on the modified calling signals.

In some cases, generating the amplified calling signals comprises: generating split calling signals based on the analog calling signals, by a radio frequency (RF) splitter coupled to an output of the adjustable-bandwidth tunable bandpass filter; and amplifying the split calling signals, by the first amplification circuit, to generate the amplified calling signals.

In some cases, upon establishment of the communication link between the HF radio and the another HF radio, the obtaining includes obtaining one or more analog data traffic signals from the another HF radio, the analog data traffic signals being communicated from the another HF radio over the given assigned ALE channel.

In some cases, the method further comprises: obtaining the analog data traffic signals at a second receive path, being connected to an output of the adjustable-bandwidth tunable bandpass filter; converting the analog data traffic signals to digital data traffic signals, by the second receive path; and decoding the digital data traffic signals, by the given receiver.

In some cases, converting the analog data traffic signals to digital data traffic signals comprises: generating split data traffic signals, by a radio frequency (RF) splitter coupled to an output of the adjustable-bandwidth tunable bandpass filter, based on the analog data traffic signals; amplifying the split data traffic signals, by a second amplification circuit coupled to an output of the RF splitter, to generate amplified data traffic signals; and converting the amplified data traffic signals to the digital data traffic signals, by a second ADC connected to the second amplification circuit.

In some cases, the first amplification circuit has a lower gain and signal-to-noise ratio than the second amplification circuit and a higher selectivity than the second amplification circuit.

In some cases, the method further comprises: decoding the digital calling signals, by the receivers, concurrently with the decoding of the digital data traffic signals.

In some cases, the method further comprises: narrowing the staring frequency band, in response to the decoding of the given digital calling signal.

In some cases, the staring frequency band is narrowed such that a first passband of the staring frequency band is identical to a second passband of the given assigned ALE channel.

In some cases, the method further comprises: obtaining the analog data traffic signals at the first receive path; converting the analog data traffic signals to digital data traffic signals, by the first receive path; and decoding the digital data traffic signals, by the given receiver.

In some cases, converting the analog data traffic signals to digital data traffic signals comprises: amplifying the analog data traffic signals, by a low-noise amplifier (LNA) connected to an output of the adjustable-bandwidth tunable bandpass filter, to generate modified data traffic signals; amplifying the modified data traffic signals, by the first amplification circuit, to generate amplified data traffic signals; and converting the amplified data traffic signals to the digital data traffic signals, by the first ADC.

In accordance with a third aspect of the presently disclosed subject matter, there is provided a non-transitory computer readable storage medium having computer readable program code embodied therewith, the computer readable program code, executable by at least one processor of a computer to perform a method for a high frequency (HF) radio to process an incoming call from another HF radio, the method comprising: selecting a staring frequency band and a plurality of assigned Automatic Link Establishment (ALE) channels within the staring frequency band; obtaining, at an adjustable-bandwidth tunable bandpass filter, from at least one antenna, first HF signals within a HF band; providing, by the adjustable-bandwidth tunable bandpass filter, only second HF signals within the staring frequency band, the second HF signals including one or more analog calling signals that are indicative of incoming calls, wherein the staring frequency band is a subset of the HF band, and wherein a bandwidth of the staring frequency band is adjustable; converting the analog calling signals to one or more digital calling signals that are indicative of the incoming calls, by a first receive path connected to an output of the adjustable-bandwidth tunable bandpass filter; monitoring, by a plurality of receivers, the ALE channels, each receiver of the receivers being configured to monitor a different assigned ALE channel of the assigned ALE channels for the digital calling signals; and establishing a communication link between the HF radio and the another HF radio, in response to a given receiver of the receivers decoding a given digital calling signal of the digital calling signals that is indicative of the incoming call from the another HF radio, the given digital calling signal being communicated from the another HF radio over a given assigned ALE channel of the assigned ALE channels.

