Patent Description:
Traffic and operations management for unmanned aircraft systems (UAS; also unmanned aerial vehicles (UAV)) may be achieved by private wireless networks using specialized control and non-payload communications (CNPC) waveforms over aviation spectrum bands. For example, airborne UAS may carry onboard CNPC-based air radio systems (ARS) while ground-based control facilities maintain CNPC-based ground radio stations (GRS). A GRS may establish point-to-multipoint links to multiple ARS (e.g., multiple ARS operating within a coverage area dedicated to the GRS or within its transmission range) based on spectrum resources (e.g., bandwidth) assigned to the GRS. For example, the GRS may maintain command and control (C2) links to each ARS operating within its coverage area, via which the GRS may maintain spatial separation between ARS or prevent an ARS from entering dangerous or geofenced areas via control input submitted via the C2 link to the ARS operator or directly to the ARS itself. However, careless spectrum reuse may lead to self-interference (e.g., where a CNPC signal is interfered with by another CNPC signal from within the same C2 link system, as opposed to external interference, where a competing CNPC system may be operating on the same frequency within the same vicinity). C2 communications are disclosed in <CIT>, <CIT> and in <NPL>.

Also important to effective traffic management is how spectrum resources assigned to each GRS are shared by the ARS operating within the coverage area of that GRS. If, for example, the number of ARS operating within the coverage area at any given time is limited, the GRS will be able to manage the limited amount of traffic without congestion. As the coverage area becomes more and more crowded by operating UAS, however, a CNPC-based operating environment (which may include multiple GRS and their respective coverage areas) must be able to manage system capacity and increase capacity where needed. For example, dynamic spectrum access (DSA) may provide valuable opportunities for efficiently using and reusing operating frequencies within the CNPC operational bands. However, effective use of DSA to find spectrum use and reuse opportunities requires robust spectrum sensing capabilities throughout the CNPC operating environment.

An intuitive approach to increasing spectrum sensing capacity is to add commercial off the shelf (COTS) hardware-based sensors to every ARS and GRS. However, this approach requires hardware upgrades to the system. Further, operating UAS may operate under size, weight, and power (SWaP) restrictions that may make it impractical or otherwise not feasible to add additional hardware.

A command and control (C2) communications device is provided as defined in claim <NUM>.

In some embodiments, the C2 device is embodied in an ARS aboard a UAS, and identifies uplink slots which may be used for spectrum sensing if no preamble is acquired.

In some embodiments, the C2 device is embodied in a GRS and identifies downlink slots which may be used for spectrum sensing if no preamble is acquired.

In some embodiments, the assigned sensing frequency is assigned by a centralized spectrum arbitrator of the C2 link system. The receiver forwards the determined noise floor and mean energy level to the spectrum arbitrator for additional processing.

In some embodiments, the C2 device evaluates whether the determined interference level is tolerable or intolerable for C2 operations at the assigned sensing frequency, and forwards the evaluation to the spectrum arbitrator.

In some embodiments, the subframe includes a guard time indicating the end of the subframe; the C2 device selects N and TS such that the time window (N x TS) during which the set of spectral energy samples is collected concludes before the guard time.

In some embodiments, the C2 device further determines, by processing the collected set of N spectral energy samples, a standard deviation from the noise floor and a standard deviation from the mean energy level.

In some embodiments, the C2 device identifies an interfering signal (which may or may not be a constant-envelope signal) responsible for the determined interference level at the assigned sensing frequency.

A method for same-channel out-of-band spectrum sensing within a command and control (C2) link system is also provided as defined by claim <NUM>.

In some embodiments, the method includes forwarding the determined noise floor, mean energy level, interference level, and/or tolerance evaluation to the centralized spectrum arbitrator.

In some embodiments, the method includes configuring an air radio system (ARS) aboard an unmanned aircraft system (UAS) to scan the one or more operating frequencies, and identifying uplink slots (e.g., for ground-to-air communications with the ARS) within the subframe for spectrum sensing if no preamble is acquired.

In some embodiments, the method includes configuring a ground radio system (GRS) to scan the one or more operating frequencies, and identifying downlink slots (e.g., for air-to-ground communications with the GRS) within the subframe for spectrum sensing if no preamble is acquired.

In some embodiments, the method includes identifying a standard deviation from the determined noise floor and/or a standard deviation from the determined main energy level.

In some embodiments, the method includes selecting a number N of spectral energy samples to be collected and a sample period TS for each energy sample such that that the time window (N x Ts) during which the set is collected concludes before the guard time indicating the end of the subframe.

In some embodiments, the method includes identifying an interfering signal associated with the determined interference level at the assigned sensing frequency.

Broadly speaking, embodiments of the inventive concepts disclosed herein are directed to a CNPC operating environment (e.g., command and control (C2) link system) incorporating software-based means for spectrum sensing throughout the operating environment, allowing for more robust DSA operations. For example, spectrum sensing operations may be implemented throughout the C2 link system via same-channel sensing, "same-channel" referring to the same hardware channel, e.g., using CNPC-based communications hardware of each GRS and ARS for spectrum sensing. The CNPC waveform already provides for same-channel in-band sensing (e.g., analyzing communications channel metrics to detect low signal-to-noise ratio (SNR), high bit error rate (BER), or other factors that may preclude use of an assigned frequency). Embodiments of the inventive concepts disclosed herein additionally provide for same-channel out-of-band sensing, whereby an ARS or GRS may take advantage of idle times (e.g., when the ARS/GRS is not otherwise receiving a C2 signal) to probe for other frequencies with the potential for use within a given area. Probing for additional useful frequencies may counter overly conservative spectrum reuse on the part of a centralized spectrum arbitrator, e.g., a centralized server configured for the management of spectrum resources throughout the C2 link system. Similarly, probing may enhance system capacity by reducing rippling throughout the C2 link system, e.g., when an operating frequency is found to be interfered with, and its use immediately reversed or discontinued.

Referring to <FIG>, a command and control (C2) link system <NUM> (e.g., command and non-payload communications (CNPC) operating environment) is disclosed. The C2 link system <NUM> may include air radio systems <NUM> (ARS), ground radio stations <NUM> (GRS), and, within the ARS <NUM> or GRS <NUM>, C2 radio system components including a radio modem <NUM>, CNPC transceiver <NUM>, antenna elements <NUM>, and control processors (e.g., local control processors <NUM> and centralized control processors <NUM>, the local control processors responsible for processes local to the ARS/GRS). The C2 link system <NUM> may further include a centralized spectrum arbitrator <NUM> (e.g., central server). For example, the local control processors <NUM> may include distributed controller agents of each ARS <NUM>/GRS <NUM>, the distributed controller agents in communication with a centralized controller (e.g., centralized control processors <NUM>) of the centralized spectrum arbitrator <NUM>.

In embodiments, each GRS <NUM> may be assigned a particular coverage area and allocated a sub-band or group of operating frequencies by the centralized spectrum arbitrator <NUM>. The GRS <NUM> may establish C2 links with, and thereby communicate with, ARS <NUM> operating within its coverage area by allocating an operating frequency and time slots to each ARS. While the ARS <NUM> operates within the coverage area of the GRS <NUM>, the GRS and ARS may exchange C2 communications at the allocated frequency and during the allocated timeslots, e.g., uplink communications (where the GRS transmits and the ARS received) and downlink communications (where the ARS transmits and the GRS receives).

In embodiments, the ARS <NUM> may terminate the C2 link to the GRS <NUM>, e.g., if the ARS enters the coverage area of a new GRS. Accordingly, the ARS <NUM> may, at any given time, be listening to (e.g., receiving) signals broadcast by multiple GRS <NUM>, whether or not the ARS is within sufficient range of other GRS to receive a robust signal therefrom. As noted above, the GRS <NUM> may also be listening to multiple ARS <NUM> at any given time. The centralized spectrum arbitrator <NUM> may identify frequencies not currently in use within the coverage area of the GRS <NUM> and assign one or more said identified frequencies to the ARS <NUM> or the GRS for spectrum sensing.

In embodiments, the radio modem <NUM> is configured for tuning the frequency of the CNPC transceiver <NUM>. The CNPC transceiver <NUM> is switched between one or more operating frequencies, e.g., depending on which ARS <NUM> or GRS <NUM> is being listened to or scanned for a particular subframe or timeslot. When an idle timeslot is detected, and the ARS <NUM> or GRS <NUM> commences same-channel out-of-band spectrum sensing as described below, the radio modem <NUM> tunes the CNPC transceiver <NUM> to the sensing frequency assigned by the centralized spectrum arbitrator <NUM>. When spectrum sensing operations conclude, the radio modem <NUM> retunes the CNPC transceiver <NUM> to its next regularly scheduled operating frequency before the beginning of the next subframe or slot.

Referring also to <FIG>, the CNPC frame <NUM> is disclosed. The CNPC frame <NUM> may include subframes <NUM>, uplink portions <NUM>, downlink portions <NUM>, uplink slots 208a-c (e.g., timeslots), and downlink slots 210a-c.

In embodiments, the CNPC frame <NUM> (e.g., framing structure) corresponds to a time interval divided into subframes, e.g., a one-second interval divided into <NUM> subframes <NUM> of <NUM> msec each. Each subframe <NUM> is in turn evenly divided into an uplink portion <NUM> and a downlink portion <NUM>, each <NUM> msec. The uplink portion <NUM> and the downlink portion <NUM> are similarly divided into individual uplink slots 208a-c and downlink slots 210a-c respectively, the uplink slots reserved for C2 transmissions by the GRS (<NUM>, <FIG>) and received by the ARS (<NUM>, <FIG>) and the downlink slots reserved for C2 transmissions by the ARS and received by the GRS. Accordingly, the GRS may perform scanning operations during the downlink slots 210a-c, and the ARS may perform scanning operations during the uplink slots 208a-c.

In embodiments, an uplink slot 208a may include a C2 signal transmitted by the GRS <NUM>, or the uplink slot may be an idle slot. For example, an idle slot may indicate that the ARS <NUM> may be listening to a given GRS (e.g., other than the GRS <NUM> with which the ARS is currently linked) but may not be within sufficient range of the GRS to receive a robust signal. Similarly, the GRS <NUM> may listen to ARS <NUM> outside its effective range, resulting in idle downlink slots 210a-c.

In embodiments, the ARS <NUM> and GRS <NUM> scan each subframe <NUM> ( respectively the uplink portion <NUM> and the downlink portion <NUM>) to identify the start of a subframe or the start of, respectively, an uplink slot 208a-c or downlink slot 210a-c. Similarly, the end of a subframe <NUM> (e.g., the end of the uplink portion <NUM> or downlink portion <NUM> thereof) is indicated by a short period of guard time <NUM>.

The uplink slot 208a includes a preamble <NUM>, e.g., a short segment (e.g., <NUM> symbols for an uplink preamble, <NUM> symbols for a downlink preamble 214a) indicating the presence of C2 message content within the subsequent data segment <NUM>. In the case of downlink slots 210b-c, the lack of a preamble indicates that the current slot is idle. In embodiments, if the ARS <NUM> acquires a preamble <NUM>, the ARS may perform normal functions associated with receiving the C2 message content within the subsequent data segment <NUM>. If, however, the ARS <NUM> does not acquire a preamble for the uplink slot 210a, the ARS commences same-channel out-of-band sensing (at the frequency assigned by the centralized spectrum arbitrator <NUM>). Similarly, the GRS <NUM> scans downlink slots 210a-c, if the downlink preamble 214a is detected, the GRS <NUM> may receive normally. If no downlink preamble 214a is required, however, the GRS <NUM> performs same-channel out-of-band sensing ( during the idle downlink slots 210b-c).

In embodiments, the ARS <NUM> (e.g., or GRS <NUM>) commences same-channel out-of-band spectrum sensing by first tuning its CNPC transceiver (<NUM>, <FIG>) to the sensing frequency assigned by the centralized spectrum arbitrator (<NUM>, <FIG>) via the radio modem (<NUM>, <FIG>). The CNPC transceiver <NUM>, tuned to the assigned frequency, collects spectral energy samples at the assigned frequency over the antenna elements <NUM>. Each spectral energy sample may comprise an integration of spectral energy at the assigned frequency over the antenna elements <NUM> through a sample period Ts (e.g., on the order of hundreds of microseconds).

In embodiments, the CNPC transceiver <NUM> collects a series of N spectral energy samples of sample period Ts. For example, the control processors <NUM>, <NUM> may select N and Ts such that the collection of spectral energy samples is completed, and the CNPC transceiver <NUM> retuned to the proper operating frequency by the radio modem <NUM>, before the start of the end-of-subframe guard time <NUM>. For example, N and Ts may be chosen (e.g., larger N and shorter Ts; smaller N and longer Ts) based on other factors, e.g., waveform characteristics and the particular hardware of the ARS <NUM> or GRS <NUM>. For example, a larger N may be chosen to ensure the law of large numbers smooths out ambient noise spikes or other anomalies. A longer Ts; however, may increase the value of energy detection by providing a larger area under the integration curve of energy level over time, but may limit the number N of spectral energy samples that may be collected before the end of the subframe (<NUM>, <FIG>). The collected spectral energy samples may be stored (<NUM>) for processing. In some embodiments, the spectral energy samples may be collected in dBm and normalized to dB by the control processors <NUM>, <NUM>.

In embodiments, processing of the collected spectral energy samples is triggered by the retuning ( by the radio modem <NUM>) of the CNPC transceiver <NUM> to the appropriate operating frequency (e.g., scanning frequency) so that the ARS <NUM> or GRS <NUM> resumes CNPC scanning operations. For example, the collected spectral energy samples may be processed to calculate the following:.

In embodiments, the minimum energy level Emin may be indicative of a sensed frequency unencumbered by interfering signals. Similarly, a mean energy level Emean close to Emin may indicate the absence of an interfering signal at the sensed frequency. Increased deviation in the collected energy samples, however, may be associated with an interfering signal also using the sensed frequency (e.g., the stronger the signal energy, the larger the observed deviation).

In embodiments, the ARS <NUM> or GRS <NUM> may forward the collected energy samples and calculated energy levels (and deviations therefrom) to the centralized spectrum arbitrator <NUM> for detailed analysis via server fusion. The centralized spectrum arbitrator <NUM> may conduct a more detailed analysis of the collected spectrum energy samples as disclosed in concurrently filed application 127920US01. However, the control processors <NUM>, <NUM> of the ARS <NUM>/GRS <NUM> may perform a limited amount of server-side fusion operations, fusing the collected energy samples to calculate mean/minimum energy levels as described above and thereby create a binary hypothesis as to the tolerability or intolerability of the interference level detected at the sensed frequency. For example, the spectral energy sensing process may inevitably result in a certain amount of energy detected over the antenna elements <NUM> due to, e.g., ambient noise.

Referring now to <FIG>, the probability distribution function <NUM> (PDF) correlates the interference levels identified by processing of the collected energy samples to determine whether the interference is due to acceptable noise or associated with an interfering signal. For example, in the former case the control processors (<NUM>/<NUM>, <FIG>) may hypothesize that the sensed frequency is usable due to a tolerable level of detected interference; in the latter case, the interfering signal may render the interference level intolerable and the sensed frequency unusable within the region or area corresponding to the sensing ARS <NUM>/GRS <NUM>.

In embodiments, the PDF <NUM> may plot detected the energy level of collected spectral energy samples (y-axis <NUM>) normalized to dB (x-axis <NUM>), as noted above. (It should be noted that the dB range reflected by the x-axis <NUM> may vary according to the CNPC waveform, and are not limited to the {-<NUM> dB, <NUM> dB} range shown by <FIG>. ) For example, the CNPC waveforms used by the CNPC transceiver <NUM> may incorporate constant-envelope modulation; accordingly, any symbols transmitted via CNPC waveform may be associated with a constant energy level. A distribution of energy levels <NUM> grouped around a lower energy level may be associated with a tolerable noise-plus-interference energy level (e.g., normal ambient noise plus a tolerable level of interference energy), while a distribution of energy levels <NUM> encroaching upon the CNPC constant envelope energy range may clearly indicate an interfering CNPC signal precluding current use of the sensed frequency in the vicinity of the sensing ARS <NUM>/GRS <NUM>.

In embodiments, the origins of the interfering CNPC signal, e.g., whether or not the CNPC signal is associated with the C2 link system (<NUM>, <FIG>) or with a competing C2 link system, may be determined by server fusion performed by the centralized spectrum arbitrator <NUM>. Similarly, the presence of an interfering non-constant-envelope signal may require additional fused data (e.g., minimum and mean energy levels and standard deviations therefrom) and may be left to the centralized spectrum arbitrator <NUM>.

Referring now to <FIG>, the method <NUM> may be implemented by an ARS or GRS of the C2 link system, and includes the following steps.

At a step <NUM>, a C2 radio system (e.g., either an ARS or GRS of the C2 link system) scans operating frequencies (e.g., broadcast frequencies) via which the ARS listens for uplink transmissions and the GRS listens for downlink transmissions.

At a step <NUM>, the ARS/GRS receives an assigned sensing frequency from a centralized spectrum arbitrator of the C2 link system.

At a step <NUM>, the ARS/GRS receives subframes at the operating frequency, each subframe having an uplink portion and a downlink portion.

At a step <NUM>, the ARS/GRS identifies the start of an uplink or downlink slot within the received subframe.

At a step <NUM>, the ARS/GRS attempts to acquire a preamble associated with normal reception of a C2 transmission. If the preamble is acquired, the ARS/GRS proceeds with normal reception of an incoming C2 message and continues scanning the operating frequency.

Referring also to <FIG>, at a step <NUM>, if the preamble is not acquired, the ARS/GRS tunes to the assigned sensing frequency and commences same-channel out-of-band sensing operations.

At a step <NUM>, the ARS/GRS collects N spectral energy samples at the assigned sensing frequency, each spectral energy sample over a sample period Ts.

At a step <NUM>, the ARS/GRS returns to the appropriate operating frequency once the N spectral energy samples are collected.

At a step <NUM>, the ARS/GRS processes the collected energy samples to calculate at least a noise floor Emin and a mean energy level Emean. Based on the detected noise floor and mean energy level, the ARS/GRS calculates an interference level at the assigned sensed frequency.

At a step <NUM>, the ARS/GRS designates the calculated interference level as either tolerable (e.g., acceptable noise + interference) or intolerable (e.g., due to an interfering CNPC signal).

The method <NUM> may include an additional step <NUM>. At the step <NUM>, the ARS/GRS forwards the collected energy samples, calculated energy levels, and interference level designations to the centralized spectrum arbitrator.

Claim 1:
A command and control, C2, communications device, comprising:
a radio modem (<NUM>);
a receiver operatively coupled to the radio modem, the receiver associated with at least one operating frequency and configured to:
receive (<NUM>) at least one subframe (<NUM>) transmitted by a C2 source by scanning an operating frequency of the at least one operating frequency, each subframe having an uplink portion (<NUM>) and a downlink portion (<NUM>);
identify (<NUM>) at least one slot within a received subframe;
determine (<NUM>) whether an identified slot includes an acquired preamble;
when the identified slot does not include the acquired preamble (<NUM>), direct (<NUM>) the radio modem to tune the receiver to an assigned sensing frequency for same-channel out-of-band spectrum sensing;
collect (<NUM>) a set of N energy samples corresponding to the assigned sensing frequency, each energy sample associated with a sample period Ts, where N is an integer;
and
direct (<NUM>) the radio modem to tune the receiver to an operating frequency of the at least one operating frequency upon collection of the set of N energy samples;
and
at least one processor (<NUM>) configured to:
determine (<NUM>), by processing the set of N energy samples, at least a noise floor and a mean energy level corresponding to the assigned sensing frequency;
and
identify, based on at least the noise floor and the mean energy level, an interference level corresponding to the assigned sensing frequency.