Base station device and distance measuring method
Provided are a distance measuring device and a distance measuring method which can easily distinguish a reflected signal from a desired tag from an unnecessary wave so as to improve the distance measuring accuracy even when IR-UWB is used for measuring a distance. The method uses a reader ID indicated by a code string formed by P bits (P is a natural number) for identifying a base station and a tag ID indicated by a code string formed by Q bits (Q is a natural number) for identifying a radio terminal. The method generates a unique word containing P pulses, each of which is ON/OFF-modulated depending on whether each of P bits indicating the reader ID is 1 or 0. The method generates a frame containing 2 M unique words and a burst containing Q frames. The method further outputs a transmission signal containing a plurality of bursts. A radio terminal Amplitude Shift Keying (ASK)—modulates the transmission signal depending on whether each of the Q bits indicating the tag ID is 1 or 0. The ASK-modulated signal is sampling-received at timings of different phases by 1/M (M is an integer not smaller than 1) of the transmission clock cycle.
1. A base station apparatus in a radio distance measuring system that uses a reader ID and a tag ID, the base station apparatus comprising:
a pulse generation section configured to generate a unique word containing P pulses, each of which is on/off modulated according to whether each of P bits representing the reader ID is 1 or 0, generates a frame containing 2×M unique words, configured to generate a burst containing Q frames, and configured to output a transmission signal containing a plurality of bursts; and
a receiving section configured to perform sampling reception of a signal resulting from modulation of the transmission signal by the radio terminal based on whether each of Q bits representing the tag ID is 1 or 0 at timings with a phase difference of 1/M (where M is an integer not smaller than 1) of a transmission clock period, the transmission clock period being a time period of a length which is the same as a width of each one of the pulses, wherein:
the reader ID is represented by a code string composed of P bits (where P is a natural number) for identifying a base station apparatus, and
the tag ID is represented by a code string composed of Q bits (where Q is a natural number) for identifying a radio terminal and detecting a first traveling wave from a tag by means of correlation calculation.
2. The base station apparatus according to claim 1 , further comprising a reader ID correlation calculation section configured to perform correlation calculation between the reader ID and a received signal, and configured to generate a delay profile.
3. The base station apparatus according to claim 2 , wherein the reader ID correlation calculation section amplifies power by adding all M phase components and performs the correlation calculation.
4. The base station apparatus according to claim 3 , wherein a modulation method used by the radio terminal to create the transmission signal is Amplitude Shift Keying (ASK) modulation.
5. The base station apparatus according to claim 2 , further comprising:
a tag ID correlation calculation section configured to store the delay profile in a time-series manner, and performs correlation calculation for the stored delay profile and a tag ID of a desired tag comprising Q bits;
a first traveling wave detection section configured to detect a first traveling wave of a tag ID based on a correlation calculation result in the tag ID correlation calculation section;
a delay time measuring section configured to measure a round-trip delay time of the detected first traveling wave; and
a distance calculation section configured to calculate a distance between the tag and the reader from the measured round-trip delay time.
6. The base station apparatus according to claim 5 , wherein a modulation method used by the radio terminal to create the transmission signal is ASK modulation.
7. The base station apparatus according to claim 2 , wherein a modulation method used by the radio terminal to create the transmission signal is Amplitude Shift Keying (ASK) modulation.
8. A distance measuring method in a base station apparatus of a radio distance measuring system that uses a reader ID represented by a code string composed of P bits (where P is a natural number) for identifying the base station apparatus and a tag ID represented by a code string composed of Q bits (where Q is a natural number) for identifying a radio terminal, comprising:
generating a unique word containing P pulses, each of which is on/off modulated according to whether each of P bits representing the reader ID is 1 or 0;
generating a frame containing 2×M unique words;
generating a burst containing Q frames;
outputting a transmission signal containing a plurality of bursts; and
performing sampling reception of a signal resulting from Amplitude Shift Keying (ASK) modulation of the transmission signal by the radio terminal based on whether each of Q bits representing the tag ID is 1 or 0 at timings with a phase difference of 1/M (where M is an integer not smaller than 1) of a transmission clock period.
9. The distance measuring method according to claim 8 , wherein a modulation method used by the radio terminal to create the transmission signal is Amplitude Shift Keying (ASK) modulation.