1998 - Draper Laboratory

GPS Receiver Antijam Capability (dB)100908070605040302010100 kW10 kW1 kW100 W10 W1 W100 mWJAMMER ERP=10 mW010 20 30 40 50 60 70 80 90 100Range to Jammer (km)GPS Receiver Antijam Capability (dB)100908070605040302010ADVANCED RECEIVER WITH ADVANCED ANTENNAP(Y) CODE LOCK LOSS ADVANCED INTEGRATED RECEIVERP(Y) CODE LOCK LOSS CONVENTIONAL RECEIVERP(Y) CODE ACQUISITIONC/A CODE ACQUISITION100 kW10 kW1 kW100 W10 W1 W100 mWJAMMER ERP=10 mW010 20 30 40 50 60 70 80 90 100Range to Jammer (km)Figure 10. GPS jamming calculationsThe P(Y) code has more theoretical A/J protection than the C/Acode due to its ten times larger spread-spectrum bandwidth.Therefore, receivers have been developed that acquire the P(Y)code directly without having to acquire the C/A code first.However, because the P(Y) code is very long, a long time or manycorrelators are needed for a two-dimensional search over codetiming and Doppler frequency. It would be faster if satelliteephemerides and accurate code timing were available to performa “hot start.” For a GPS-aided weapon, accurate timing andsatellite position could be transferred from the aircraft to theweapon. This transfer normally requires a wide-band data bus;currently, few aircraft are so equipped.As new receiver technology with advanced algorithms andadaptive or nulling antenna technologies are incorporated into thesystem, increasing its A/J capability, A/J performance will improvesignificantly. Some possibilities are illustrated in Figure 11 (Ref.[14]). If A/J performance is increased significantly, then thejammer power must also be increased significantly. A largeFigure 11. Possible A/J capabilitiesjammer would present an inviting target to an antiradiation,homing missile. In the terminal area of flight against a target, thejammer located at the target will eventually jam the receiver andthe vehicle will have to depend on inertial-only guidance or theuse of a target sensor. Thus, it is important to ensure thataccurate guidance and navigation capability is provided to meetmilitary mission requirements against adversaries who are willingto invest in Electronic Countermeasures (ECM). This fact is truetoday and is expected to remain so in the foreseeable future.In summary, the following militarily-driven developments will beaccomplished in the near future to improve the A/J performanceof military systems:(1) Lower-cost but accurate inertial systems using newtechnologies such as micromechanical inertialinstruments and FOGs.(2) Highly integrated INS/GPS system architectures.(3) Higher-performance, lower-cost adaptive antennasusing digital beam forming and modern algorithms.INS/GPS Technology Trends for Military Systems12