At present, technologies using RFID in the research of positioning are divided into four categories: time of arrival (TOA), time difference of arrival (TDOA), received signal strength
(RSS), and angle of arrival (AOA).
Activities of turtles between sequential signal strength
recordings (collected at 1 min intervals) were categorized as: no movement = turtle in same orientation and location between automated telemetry recordings, small movement = turtle orientation changed less than 45[degrees] and location changed less than 0.5 body lengths, and large movement = turtle orientation changed more than 45[degrees] or location changed more than 0.5 body lengths.
The effects of the soil water content on the received signal strength
and error rate were measured at three carrier frequencies, 240 MHz, 433 MHz, and 868 MHz, respectively.
After integrating the measurement results from these fifty-eight test locations, the WiMAX received signal strengths
in its coverage range have a distribution as shown in Figure 2.
However, in the real world, the signal strength
is highly dynamic and affected by multiple factors in the environment.
The signal strength
can therefore rise or fall in response to the flare, both effects being clearly seen in this chart.
It said later it had discovered a software glitch that overstates signal strength
, though it did not directly address concerns about the antenna with that admission.
However, in a letter addressed to iPhone 4 users, Apple said its own investigation revealed the "simple and surprising" cause was the formula, by which it calculated signal strength
, has always been "totally wrong".
Apple admitted its signal strength
miscalculation dates back to its original 2007 iPhone.
Apple said that's the reason behind widespread complaints from users that the latest model, iPhone 4, can show a sudden plunge in signal strength
when they hold it in a way that covers a small black strip on one edge of the phone.
Apple has decided to adopt a formula recently recommended by telecoms group AT&T Inc (NYSE:T) for calculating how many bars to display for a given signal strength
. The actual signal strength
will remain the same but the iPhone's bars will report it far more accurately, giving users a better indication of the reception they will get in a given area.
As the approaching pig transmitter's signal strength
increases, a "Geiger Counter" (modulating) piercing audio and visual display informs the operator of the pig's approach and passage.