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A ground‐vehicle‐mounted receiver was placed in an environment comprising N cellular CDMA towers. The states of the towers , where , were collaboratively estimated by mapping receivers in the navigating receiver’s vicinity. The mapping receivers had knowledge of their own states from GPS. The pseudoranges made by the receiver on the N cellular towers along with the estimates produced by the mapping receivers were fed to a least‐squares estimator to produce an estimate of the receiver’s states and an associated estimation error covariance matrix P, from which the VDOP, HDOP, and GDOP were calculated and are tabulated in Table 38.6 for M GPS SVs and N cellular towers. A sky plot of the GPS SVs is shown in Figure 38.62(a). The tower locations, receiver location, and a comparison of the resulting 95th‐percentile estimation uncertainty ellipsoids of for {M, N} = {5, 0} and {5, 3} are illustrated in Figure 38.62(b). The corresponding vertical errors were 1.82 m and 0.65 m, respectively. Hence, adding three cellular towers to the navigation solution that used five GPS SVs reduced the vertical error by 64.3%.