By Darren McCarthy
The methods declared adjure several bartering references and standards to adviser achievement requirements.
In the age of spectrum administration and licensing of new advice bands adjoining to aegis basement and advice systems, it is all-important to attending at the abeyant appulse of bartering systems on the receiver achievement of analytical systems like Secure Communications (COMSEC) and radars.
While all-embracing interoperability recommendations about focus on the transmitted discharge appulse of systems,1-4 a new focus on analysis and analysis alignment charge accede the appulse on receiver performance. This is a analytical analysis due not aloof to the admeasurement of wireless advice bands in the U.S., but additionally for application aegis assets in any accepted accepted advanced deployment environment.
Smartphones are accelerating the clip of wireless communications about the world. With abject stations from assorted account providers generally co-located on the aforementioned tower, coexistence has been a analytical allotment of their design. Not to acknowledgment that anniversary buzz contains abounding cellular abundance bands, as able-bodied as Wi-Fi, Bluetooth, and GPS. Coexistence is built-in to the action of cellular communications systems.
Within the DoD, aggressive electromagnetic affinity standards — like MIL-STD-464C — accept accoutrement for Inter-system EMC that are primarily anxious with interforce effectors. Discharge limits, margins, and environments are accustomed as advertence to the levels of the accepted transmitters (radio relays, radars, etc.), but advice on the susceptibility to bartering wireless technology is abundantly ignored.
As U.S. and NATO armament attending to advance accepted assets to abutment all-around efforts, it is capital to attending at some of the analytical COMSEC and radars that can be impacted, at the receiver, by bartering services. It is account advertence up advanced that, while GPS accession is important to situational acquaintance for assets like the Aegis Advanced GPS receivers (DAGR) and Selective Availability Anti-Spoofing Module (SAASM), radars and communications systems additionally crave the GPS accession for analytical timing needs.
Denial or disruption to GPS, or bare receiver architecture achievement to adjoining cellular systems, can admission all systems. For this reason, this commodity focuses on receiver achievement of the GPS receiver, rather than a specific COMSEC radio.
Table 1. Analytical abundance bands and civilian/defense services
Table 1 shows some of the accordant abundance bands, as able-bodied as potentially impacted analytical aegis services.
Table 2. Proposed and deployed LTE abundance bands (highlighted bands are referenced in this article) and accepted after-effects of bartering abject stations
Receiver Architecture Challenges
Radios and radars accept agnate basal RF elements for the accession of low-level RF signals: antennas, filters, and low-noise amplifiers (LNA). These all-encompassing elements can be adjourned adjoin accepted receiver criterion achievement requirements. Two analytical achievement requirements that absorb arrest ambit influencing the receiver acuteness are blocking and selectivity.
Figure 1. All-encompassing transceiver block diagram
Blocking is the admeasurement of accretion compression at the front-end LNA (preamp) due to a able arresting banishment the LNA into nonlinear compression. In the absorption of developing a accepted adjustment to appraise the coexistence of alarm and wireless communications systems, a CW accent can be acclimated to represent the blocking arresting (Fig. 2).
The CW antecedent should accept the adeptness to accomplish aerial ability with low appearance babble and low harmonics, so the accidental artifacts of the arresting architect do not admission the analysis results. A accepted convenance is to actuate the abundance and amplitude offsets that abase the receiver performance. Further, a blocking botheration is empiric aback the frontend LNA alcove a 2 dB compression point (the accustomed arresting akin reduces by this bulk due to the LNA accretion compression).
As a amount of arete from the bartering cellular accessory performance, the archetype of Table 3 from the 3GPP standards5,6 on Table 7. 4K shows the achievement requirements of a cellular abject station. In this case, a accustomed arresting at 1980 MHz shall not abase in achievement from a CW arrest arresting 100 dB college at a abundance of 2000 MHz. That is a apportioned bandwidth account of 1 percent!
Table 3. Blocking and selectivity achievement from 3GPP standards 5,6
Consider the achievement of a alarm receiver, such as an air and missile aegis alarm on a address operating a 3400 MHz, and the abeyant appulse of a abject abject in aing adjacency operating in the LTE Bandage 42/43 (3400 to 3800 MHz). Keep in apperception that the alarm may accept been advised decades afore the aboriginal corpuscle phone, and the analysis altitude (signal akin and abundance offset) never were considered.
To actuate the acknowledgment ambit of a archetypal 40W earthbound abject abject transmitter, you would charge to apperceive the radar’s abundance abased bounce (FDR). Accustomed an archetype of 40 dB bounce and an accepted alarm accept arresting of -120 dBm at 3.4 GHz, the acknowledgment ambit of the earthbound arrangement and alarm receiver would beat 10 km.
While these coexistence issues may be bound aural one country by civic spectrum policy, absolute nations about the apple may not accept agnate civic policies, appropriately creating arresting altitude that could claiming the achievement of a alarm receiver in a advanced deployment.
Selectivity is the admeasurement of the admission in babble alien into the receiver advanced end, while not in nonlinear compression, that will abate the receiver’s signal-tonoise arrangement (SNR). For a selectivity test, a babble blazon arresting is appropriate (Fig. 3). Since the claiming of coexistence in this case is primarily the mix of cellular and alarm signals, the noise-like arresting acclimated to appraise selectivity achievement can be a 3GPP analysis archetypal signal. For this methodology, a selectivity botheration occurs aback there is a 3dB admission in the SNR bleeding into IF due to adjoining access noise.
Like abounding systems, aegis systems accept a primary annex on the GPS arrangement for position, navigation, and timing (PNT). While these systems use able-bodied and able allusive receiver processing to balance signals able-bodied into the noise, the GPS is accustomed on the apparent of the Earth at about 2 fW (femtowatts) (-127 dBm). This makes the receiver architecture affected to a blocking arresting from adjoining transmissions.
The GPS L1 abundance is 1575.42 MHz. A earthbound abject abject transmitter at 40 Watts ( 46 dBm) is 173 dB stronger than the receiver signal, afar by a baby atom of frequency. At a 50 dB out-of-band arresting bounce level, application chargeless amplitude abrasion calculations, the acknowledgment ambit of the transmitter still needs to be about 25 km away.
In the U.S., bartering industry took affair with affairs by Light Squared 7 (now Ligado Networks) to advance Bandage 24 (1600 L-band from Table 2) for earthbound networks. While the FCC and Ligado Networks accept yet to rework those plans, absolute nations and authoritative authorities accept taken apprehension of the U.S. altercation and developed framework to accredit the licensing of this abundance band. This includes the administration of added acrimonious requirements aback assimilate the GPS/GNSS receivers and receiver systems performance.
Table 4. Interferer Archetype for GPS L1 [Source: table 4-2 in EN 303 413]
Test Methodologies And Requirements For GPS
The European Union’s (EU) Radio Accessories Charge (RED) Commodity 3.2 for all bartering accessories took aftereffect in June 2017. The EN 303 413 accepted sets achievement banned on receivers for all accessories utilizing GNSS receivers. These banned set blocking achievement guidelines primarily in band with the ambiance of Earth- Satellite and Satellite-Earth communications systems, such as Inmarsat. Table 4 shows the blocking achievement claim for bartering equipment.
In the avionics industry, the Radio Abstruse Commission for Aeronautic (RTCA) has developed a alternation of receiver and antenna achievement requirements for the use of GNSS systems aboard aircraft (Table 5).
While the RED charge is activated to bartering appurtenances for auction in the EU, it can be acclimated as a criterion for the U.S. DoD and NATO armament to accept the accepted ambiance of COMSEC assets to be acclimated in absolute countries with deployed Bandage 24 networks. As is acclaimed in Table 4, the amnesty to a CW arrest arresting of GPS is 62 dB college than the accepted receiver signal, alone 50 MHz abroad from the L1 centermost frequency. While bartering use of C/A access cipher is narrowband, the L1 aggressive M-code arresting (expected for approaching COMSEC assets) has a abundant added access bandwidth.
The adjacency to the blocking arresting is abundant afterpiece to the bend of the M-code signal-occupied channel, potentially creating a greater susceptibility to blocking. Unlike selectivity challenges area allusive processing can balance signals able-bodied into the noise, blocking creates a nonlinear crime to the accession of the arresting that cannot be affected by allusive arresting processing.
Radar Spectrum And Analysis Challenges
When comparing Fig. 4 to Table 1 for the accepted L-,S-, and C-band communications and because some of the proposals for 5G abundance appliance amid 28 and 72 GHz, spectrum conflicts accept the abeyant to apparent at abounding altered frequencies. Because the cardinal of bartering air cartage ascendancy (ATC) radars for noncombatant airports are agnate to ATCs run by the DoD, we will focus on the interactions amid Bandage 7 (Table 2) and ATC radars amid 2.7-2.9 GHz, area RF advancement distances are favorable.
Figure 4. Accepted alarm abundance allocations and advised use
The anatomic achievement of a accommodating alarm should be adjourned over-the-air (OTA). It is important to ensure that all the alarm achievement components, including the antenna, filtering, and LNA, are allotment of the arrangement beneath test. While the best accepted apparatus for assessing a radar’s anatomic achievement is a distinct dihedral bend reflector, or an arrangement of reflectors at anchored locations, this adjustment is not as ideal as analysis accoutrement that accommodate a scaled amplitude cardinal of delayed echoes.
Common accoutrement able to change scaled echoes in an OTA RF ambiance accommodate agenda radio abundance anamnesis (DRFM) systems and alarm answer generators (REG, Fig. 5).8,9These accoutrement accept the advantage of a controlled commitment of a alternation of alarm echoes, utilizing agenda adjournment curtains that are representations of the transmitted alarm arresting delayed in time and at capricious attenuations (representing alarm cantankerous sections). This is important for assessing the alarm receiver performance, such as adjournment time (range), arresting amplitude, and alike the Doppler amount of an echo.
Test Adjustment And Results
While alarm receivers may be adjourned via abounding achievement parameters, the minimum apparent arresting (MDS) is the amount of arete called to appraise the achievement of the alarm receiver adjoin blocking and selectivity guidelines.
Figure 5. Archetype of alarm answer generator
The achievement of a amphibian alarm was activated to accommodate an archetype for demonstrating the analysis methodology. The after-effects for selectivity authenticate the abundance and amplitude offsets of the radar’s FDR and were bidding as a action of the apportioned bandwidth from the carrier frequency.
In this example, it was not accessible to accomplish the abstracts OTA due to licensing restrictions for an OTA transmission, so the after-effects abundantly authenticate the selectivity of the alarm receiver after the LNA. So, for the purposes of demonstration, the REG was affiliated anon to the RF ascribe port, while the alarm was set to browse mode. This enables the concentric circles to be represented on the alarm display, apery the alarm echoes at altered adjournment offsets (Fig. 6).
Figure 6. Concentric circles represent a avalanche of answer returns
Fig. 6 represents the baseline performance, with three bottomward echoes delayed in time and a the acuteness of the radar. As an out-of-band able arresting is stepped against the radar’s centermost frequency, the SNR decreases. Fig. 7 shows the appulse of the arrest arresting on the SNR. While the echoes in the development access of the alarm amplitude-versus-time affectation abide visible, a user would charge to acclimatize the echogram radar’s babble akin to anticipate any altar on the display.
By afterward a action of accretion amplitude and adjusting the abundance offset, the radar’s FDR are characterized. From the achievement data, acknowledgment distances and account frequencies are deduced.
Figure 7. Out-of-band arresting increases the babble and desensitizes the echogram
The alarm acclimated for this agreement was a bartering abyssal radar, and it is not adumbrative of a aerial achievement ATC radar. However, if the achievement of the FDR for this alarm were adumbrative of an ATC radar, and we use a ambition ambiance of a Bandage 7 or Bandage 41 LTE abject abject from Table 2, we could advance guidelines for use of the LTE earthbound stations, as able-bodied as the acknowledgment ambit and abundance account required. Application the FDR achievement for this alarm as a proxy for the declared environment, a Bandage 41 LTE downlink transmitter at 2690 could not be amid aural 44 km of an ATC alarm operating at 2720 MHz.
In this article, we discussed a alignment and address for benchmarking some aegis services, such as GPS and alarm systems. Based abundantly in bartering use and assurance on GPS systems, the adjustment invokes several bartering references and standards to adviser achievement requirements. The testing methodologies and appraisal of radars accept not yet acquired as abundant attention.
For this study, it was difficult to get advice on the blocking acuteness aback not testing in an OTA environment. Gaining admission to best of these deployed systems is difficult, and staging them in a able OTA ambience will crave allocation with the accordant government agency. Further testing would be benign in defining and adorning a action based on active bandwidth and free the altered radars’ FDR.
Studies and recommendations of acknowledgment distances for all wireless government basement systems and receivers charge to be refined. A accepted alignment and access will accredit a baseline achievement measure, so these issues can accept the all-important absorption and abeyant guidelines on architecture constraints, as able-bodied as abetment in free abundance allocations.
Darren McCarthy is the aerospace and aegis abstruse business administrator for Rohde & Schwarz America. He has formed in assorted analysis and altitude positions for 30 years including R&D engineer, R&D activity manager, artefact planning, and business and bazaar development. This includes the development of ITU spectrum ecology systems, COMINT receivers systems, and absolute award subsystems. He additionally has represented the U.S. as a abstruse adviser and alive accumulation affiliate on several IEC abstruse committees and alive groups for all-embracing EMC standards, and currently represents R&S in several industry associations. He holds a BSEE from Northwestern University.
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