GPS World, February 2014

SIGNAL PROCESSING Ubiquitous Positioning MUSTER Search space Frequency search space Code search space 1 ms correlation engine Initialization of relative states Approximate knowledge of relative navigation states Adjustment search space Adjustment No Additional Signal Accumulation 20 ms Initialization of relative ranges and Doppler shifts Energy based search Estimates of relative ranges and Doppler shifts RF front end Down sampled GPS signal Relative nav states are initialized Yes Adjustment Additional Signal Accumulation 20 ms Estimation of signal parameters 1 ms signal function No Multi platform signal accumulation Relative range correction algorithm Communication Relative Doppler correction algorithm Biased code carrier estimates Multi platform signal accumulation Noisy unbiased code carrier estimates Kalman filter Code carrier smoothing Code carrier estimates Propagation of relative range and Doppler over time Navigation solution data link 1 ms signal function 1 ms signal function 1 ms signal function Relative nav states are initialized Yes FIGURE 3 MUSTER signal tracking approach for cases of unknown relative states where relative states are coarsely known but this knowledge is LQVXI FLHQW WR GLUHFWO FRPELQH PXOWL SODWIRUP VLJQDOV 7KH FRPSOHWH DGMXVWPHQW VHDUFK LV SRVVLEOH RZHYHU LW LV H WUHPHO FKDOOHQJLQJ IRU DFWXDO LPSOHPHQWDWLRQV GXH WR ERWK ODUJH FRPSXWDWLRQDO ORDG DQG D GDWD Supplemental receiver 1 Supplemental receiver 2 Supplemental receiver 3 H FKDQJH UDWH DVVRFLDWHG ZLWK LW 7R H HPSOLI 1 codex 1 Doppler versions of WKH PXOWL SODWIRUP IXQFWLRQ KDYH WR EH FRPSXWHG IRU WKH FDVH ZKHUH 1 code FRGH SKDVH DQG 1 Doppler Doppler VKLIW DGMXVWPHQW VHDUFK ELQV DUH XVHG DQG RXWSXWV IURP WZR UHFHLYHUV DUH FRPELQHG QRQ FRKHUHQWO FRPSOHWH VHDUFK FRGH ELQV DQG IUHTXHQF ELQV UHTXLUHV FRPSXWDWLRQ RI IXQFWLRQV 7KLV QXPEHU LQFUHDVHV WR 2 RU LI WKH WKLUG UHFHLYHU LV DGGHG Q DGGLWLRQ UHFHLYHUV PXVW H FKDQJH WKHLU FRPSOHWH SUH correlated signal functions which puts a considerable burden on the FRPSXWDWLRQDO GDWD OLQN RU LQVWDQFH WKH H FKDQJH RI FRPSOHWH PV IXQFWLRQV ZLWK WKH ELW UHVROXWLRQ RI VDPSOHV UHTXLUHG WR WUDFN WKH carrier phase results in the 45 0ELW V GDWD UDWH IRU RQO D UHFHLYHU QHWZRUN HQFH LW LV DQWLFLSDWHG WKDW for practical scenarios a reduced DGMXVWPHQW VHDUFK ZLOO EH XWLOL HG IRU cases where the accuracy of relative states does not support the direct DFFXPXODWLRQ RI PXOWL SODWIRUP VLJQDOV IRU H DPSOH ZKHQ WKH distance between users in the network H FHHGV PHWHUV Q WKLV FDVH RQO VHJPHQWV RI PV IXQFWLRQV DURXQG H SHFWHG HQHUJ SHDNV HVWLPDWHG EDVHG RQ DSSUR LPDWH QDYLJDWLRQ NQRZOHGJH DUH H FKDQJHG Phased Arrays 0XOWL SODWIRUP SKDVHG DUUD V KDYH been developed to enable interference DQG MDPPLQJ SURWHFWLRQ IRU 166 network users who cannot afford a controlled reception pattern antenna 53 GXH WR VL H ZHLJKW DQG SRZHU 6 3 DV ZHOO DV FRVW FRQVWUDLQWV 7KH PXOWL QRGH SKDVHG MUSTER TAP RF front end Computation of temporal weights Correlation engine Open loop signal image DBF Open loop estimation of signal parameters Supplemental TAP RF front end Computation of temporal weights Correlation engine Computation of spatial weights Open loop signal image FIGURE 4 Implementation of multi platform phased array with cascaded space time adaptive processing Open loop signal image 1 Carrier phase adjustment search space Open loop signal image M satellite look up constraint DBF Chose the adjustment combination that maximizes the C No in the output signal image FIGURE 5 Modified DBF for a multi node phased array with unknown relative navigation states GPS World February 2014 www gpsworld com 30