問91
頻出度★★☆
IoT 機器やスマートフォンなどの端末に搭載されている GPS 機能を利用して, この端末が自らの位置情報を得る仕組みとして, 適切なものはどれか。
令和2年度 ITパスポート試験 問91
ストラテジ系ビジネスインダストリ › ビジネスシステム
This question's explanation and your answers so far.
解説
問 91
Incorrectア
A GPS receiver is a receive-only mechanism that does not transmit radio waves itself. The two-way communication of “sending a location-information notification request to an artificial satellite and receiving a response” differs from the principle of GPS, so it is wrong.
Incorrectイ
A method in which the terminal sends a request to a ground-based radio base station and gets a response is close to positioning that uses base stations (base-station positioning) and is not GPS in the first place. It contradicts the question's premise of “using the GPS function”, and since GPS involves no transmission, it is wrong.
- ウ
正解 GPS (Global Positioning System) is a mechanism in which multiple GPS satellites orbiting the Earth continuously transmit radio waves that include a transmission time, and the receiver on the terminal side merely receives them. The terminal calculates the distance to each satellite from the difference between the transmission time and the reception time of the radio waves, and once the distances to three or more satellites are known, it can pinpoint a single point on the ground (its own position) by the principle of trilateration. Therefore, option “ウ”, in which the terminal does not transmit radio waves but receives radio waves from three or more artificial satellites and derives its position from the time differences, is correct.
Incorrectエ
The point about receiving radio waves and deriving the position from the time difference is correct, but the source of the radio waves is given as a “ground-based radio base station”. Because GPS uses radio waves from artificial satellites, treating base stations as the source is wrong.
ここがポイント
- GPS is a mechanism that receives, in a receive-only manner, the radio waves transmitted by multiple artificial satellites and derives the distance to each satellite from the difference between the transmission time and the reception time (the terminal does not transmit radio waves).
- It pinpoints the terminal's own position by trilateration using the distances to three or more satellites.
用語