Communication node and method for generating modulated signals by backscattering
A wireless communication node ( 500 ) and method therein for generating and transmitting a modulated radio frequency (RF) signal by means of backscattering are disclosed. The wireless communication node ( 500 ) comprises an antenna ( 510 ) configured to receive a illuminating RF signal, a switch ( 520 ) that has M states, a set of impedances ( 530 ) comprising Mimpedances (Z1, Z2 . . . ZM). The antenna ( 510 ) is coupled to the set of impedances ( 530 ) by the switch ( 520 ). The wireless communication node ( 500 ) further comprises a modulating value generator ( 540 ) configured to generate modulating values based on data to be transmitted and a frequency offset and a switch controller ( 550 ) configured to switch the state of the switch ( 520 ) based on the generated modulating values such that the antenna ( 510 ) is connected to a selected impedance among the M impedances. The received illuminating RF signal at the antenna ( 510 ) is modulated by the generated modulating values and reflected by the antenna ( 510 ) to generate and transmit the modulated RF signal. The switching rate is an integer multiple of the data rate, the integer is greater than 1 and the center frequency of the modulated RF signal has the frequency offset with respect to the center frequency of the received illuminating RF signal.
1. A wireless communication node for generating and transmitting a modulated radio frequency (RF) signal by means of backscattering in a wireless communication system, the wireless communication node comprising:
an antenna configured to receive an illuminating RF signal;
a switch that has M states;
a set of impedances comprising M impedances, and wherein the antenna is coupled to the set of impedances by the switch;
a modulating value generator configured to generate modulating values based on data to be transmitted and a frequency offset; and
a switch controller configured to switch the state of the switch based on the generated modulating values such that the antenna is connected to a selected impedance among the M impedances, and thereby the received illuminating RF signal at the antenna is modulated by the generated modulating values and reflected by the antenna to generate and transmit the modulated RF signal, wherein the switching rate is an integer multiple of the data rate, the integer is greater than 1 and the center frequency of the modulated RF signal has the frequency offset with respect to the center frequency of the RF signal.
2. The wireless communication node of claim 1 , wherein the frequency offset is dependent on the duration of the data symbol to be transmitted.
3. The wireless communication node of claim 2 , wherein the frequency offset is an integer multiple of the reciprocal of the data symbol duration.
4. The wireless communication node of claim 1 , wherein the modulating value generator is configured to quantize the modulating values calculated based on the data to be transmitted, modulation index, phase pulse with memory and frequency offset Af, and store the modulating values in a look-up table.
5. The wireless communication node of claim 4 , wherein the switch controller is configured to control the state of the switch by reading the modulating values from the look-up table.
6. The wireless communication node of claim 1 , wherein the modulating values are phase modulating values.
7. The wireless communication node of claim 1 , wherein the modulated RF signal is an On-Off Keying, (OOK) modulated signal, and during on-periods of the OOK signal, the switch controller is configured to switch the state of the switch based on the generated modulating values such that the antenna is connected to selected impedances among the set of impedances.
8. The wireless communication node of claim 7 , further comprising an additional impedance, and wherein during off-periods of the OOK signal, the switch connects the antenna to the additional impedance.
9. The wireless communication node of claim 7 , wherein during off-periods of the OOK signal, the switch is set at a fixed position by connecting the antenna to one of the impedances in the set of impedances such that a signal with a center frequency equal to the center of frequency of the received illuminating RF signal is generated and transmitted.
10. The wireless communication node of claim 7 , wherein during off-periods of the OOK signal, the switch controller is configured to switch the state of the switch based on the generated modulating values in an opposite order compared to during the on-periods such that a second OOK signal with a negative frequency offset with respect to the center frequency of the received illuminating RF signal is generated and transmitted.
11. The wireless communication node of claim 1 , wherein the modulated RF signal is a Frequency Shift Keying (FSK) modulated signal.
12. The wireless communication node of claim 11 , wherein the FSK is a Gaussian FSK modulated signal.
13. The wireless communication node of claim 1 comprising any one of a semi-passive or passive internet of things device.
14. A method for generating and transmitting a modulated radio frequency (RF) signal by means of backscattering in a wireless communication node in a wireless communication network, wherein the wireless communication node comprises an antenna, a switch, a set of impedances, a modulating value generator and switch controller, the method comprising:
receiving an illuminating RF signal by the antenna;
generating modulating values based on data to be transmitted and a frequency offset by the modulating value generator;
modulating the received illuminating RF signal by switching the state of the switch by the switch controller based on the generated modulating values such that the antenna is connected to a selected impedance among the set of impedances, wherein the switching rate is an integer multiple of the data rate, the integer is greater than 1 and the center frequency of the modulated RF signal has the frequency offset with respect to the center frequency of the received illuminating RF signal; and
transmitting the modulated RF signal by reflecting the modulated RF signal at the antenna.