First network node and a method therein for generation and transmission of a binary phase shift keying (BPSK) signal
A first network node (NN) and a method therein for generation and transmission of a Binary Phase Shift Keying (BPSK) signal to a second NN. The first and second NNs are operating in a communications network. The first NN generates a third bit stream x(n) from a first bit stream d(n) of data for transmission, wherein each output bit comprised in the third bit stream depends on a transition in bit values between two input bits from the first bit stream. Further, the first NN generates a fourth bit stream y(n) from the third bit stream by expanding the third bit stream by a predetermined factor M. By means of a CPM signal generating module, the first NN generates a BPSK signal based on the fourth bit stream. Furthermore, the first NN transmits the BPSK signal to an OFDM signal receiving module of the second NN.
1. A method performed by a first network node for generation and transmission of a Binary Phase Shift Keying, BPSK, signal to a second network node, wherein the first and second network nodes are operating in a communications network, and wherein the method comprises:
generating a third bit stream x(n) from a first bit stream d(n) of data for transmission, wherein each output bit comprised in the third bit stream x(n) depends on a transition in bit values between two input bits from the first bit stream d(n);
generating a fourth bit stream y(n) from the third bit stream x(n) by expanding the third bit stream x(n) by a predetermined factor M,
wherein the predetermined factor M is a non-zero positive integer;
by means of a Continuous Phase Modulation, CPM, signal generating circuit comprised in the first network node, generating a BPSK signal based on the fourth bit stream y(n); and
transmitting the BPSK signal to an Orthogonal Frequency Division Multiplexing, OFDM, signal receiving circuit of the second network node.
2. The method of claim 1 , wherein the generating of the third bit stream x(n) from the first bit stream d(n) comprises:
assigning an output bit of the third bit stream x(n) a first value when there is no transition in bit values between a first input bit and a second input bit from the first bit stream d(n), and
assigning the output bit of the third bit stream x(n) a second value when there is a transition in bit values between the first input bit and the second input bit, wherein the first and second input bits are consecutive input bits, and wherein one of the first and second values is 1 and the other one of the first and second values is 0.
3. The method of claim 1 , wherein the generating of the third bit stream x(n) from the first bit stream d(n) comprises:
differentially encoding the first bit stream d(n) to generate the third bit stream x(n).
4. The method of claim 1 , wherein the generating of the fourth bit stream y(n) from the third bit stream x(n) by expanding the third bit stream x(n) by the predetermined factor M comprises:
generating the fourth bit stream y(n) to comprise all bit values of the third bit stream x(n); and
inserting M−1 bits equal to 0 after each bit value from the third bit stream x(n).
5. The method of claim 1 , further comprising:
selecting a first centre frequency of the first network node to be separated by a predetermined number of frequency units from a second centre frequency of a subcarrier in of one of the OFDM subcarriers used by the second network node.
6. The method of claim 5 , wherein the predetermined number of frequency units results in a frequency separation between the first and second centre frequencies that is equal to a maximum frequency deviation of signals generated by the CPM signal generating circuit.
7. The method of claim 6 , wherein the maximum frequency deviation of the BPSK signal is equal to a frequency spacing between two OFDM signals.
8. The method of claim 1 , wherein the generating of the fourth bit stream y(n) from the third bit stream x(n) by expanding the third bit stream x(n) by the predetermined factor M comprises:
generating the fourth bit stream y(n) from the third bit stream x(n) in dependence of a second bit stream b(n) of data for transmission and by expanding the third bit stream x(n) by the predetermined factor M; and
wherein the BPSK signal generated based on the fourth bit stream y(n) is a BPSK and Frequency Shift Keying, FSK, signal.
9. The method of claim 8 , wherein the generating of fourth bit stream y(n) from the third bit stream x(n) in dependence of the second bit stream b(n) of data for transmission and by expanding the third bit stream x(n) by the predetermined factor M comprises:
generating the fourth bit stream y(n) to comprise all bit values of the third bit stream x(n);
inserting M−1 bits equal to 0 after each bit value from the third bit stream x(n) when the bit value of the second bit stream b(n) is 0; and
inserting M−1 bits equal to 1 after each bit value from the third bit stream x(n) when the bit value of the second bit stream b(n) is 1.
10. The method of claim 8 , further comprising:
selecting a first centre frequency of the first network node to coincide with a second centre frequency of a subcarrier in of one of the OFDM subcarriers used by the second network node.
11. The method of claim 1 , further comprising:
selecting a bit period T CPM such that the predetermined factor M multiplied with the bit period T CPM is equal to a time duration of one OFDM symbol T OFDM plus a time duration of a cyclic prefix T CP .
12. The method of claim 1 , wherein the first network node is configured to generate the CPM signal with a modulation index h=0.5.
13. A first network node for generation and transmission of a Binary Phase Shift Keying, BPSK, signal to a second network node, wherein the first and second network nodes are configured to operate in a communications network, and wherein the first network node is configured to:
generate a third bit stream x(n) from a first bit stream d(n) of data for transmission, wherein each output bit comprised in the third bit stream x(n) depends on a transition in bit values between two input bits from the first bit stream d(n);
generate a fourth bit stream y(n) from the third bit stream x(n) by expanding the third bit stream x(n) by a predetermined factor M,
wherein the predetermined factor M is a non-zero positive integer;
by means of a Continuous Phase Modulation, CPM, signal generating circuit comprised in the first network node, generate a BPSK signal based on the fourth bit stream y(n); and
transmit the BPSK signal to an Orthogonal Frequency Division Multiplexing, OFDM, signal receiving circuit of the second network node.
14. The first network node of claim 13 , wherein the first network node is configured to generate the third bit stream x(n) from the first bit stream x(n) by being configured to:
assign an output bit of the third bit stream x(n) a first value when there is no transition in bit values between a first input bit and a second input bit from the first bit stream d(n), and
assign the output bit of the third bit stream x(n) a second value when there is a transition in bit values between the first input bit and the second input bit, wherein the first and second input bits are consecutive input bits, and wherein one of the first and second values is 1 and the other one of the first and second values is 0.
15. The first network node of claim 13 , wherein the first network node is configured to generate the third bit stream x(n) from the first bit stream d(n) by being configured to:
differentially encode the first bit stream d(n) to generate the third bit stream x(n).
16. The first network node of claim 13 , wherein the first network node is configured to generate the fourth bit stream y(n) from the third bit stream x(n) by expanding the third bit stream x(n) by the predetermined factor M by being configured to:
generate the fourth bit stream y(n) to comprise all bit values of the third bit stream x(n); and
insert M−1 bits equal to 0 after each bit value from the third bit stream x(n).
17. The first network node of claim 13 , further being configured to:
select a first centre frequency of the first network node to be separated by a predetermined number of frequency units from a second centre frequency of a subcarrier in of one of the OFDM subcarriers used by the second network node.
18. The first network node of claim 17 , wherein the predetermined number of frequency units results in a frequency separation between the first and second centre frequencies that is equal to a maximum frequency deviation of signals generated by the CPM signal generating circuit, wherein the maximum frequency deviation of the BPSK signal is equal to a frequency spacing between two OFDM signals.
19. The first network node of claim 13 , wherein the first network node is configured to generate the fourth bit stream y(n) from the third bit stream x(n) by expanding the third bit stream x(n) by the predetermined factor M by being configured to:
generate the fourth bit stream y(n) from the third bit stream x(n) in dependence of a second bit stream b(n) of data for transmission and by expanding the third bit stream x(n) by the predetermined factor M; and
wherein the BPSK signal generated based on the fourth bit stream y(n) is a BPSK and FSK signal.
20. The first network node of claim 19 , wherein the first network node is configured to generate the fourth bit stream y(n) from the third bit stream x(n) in dependence of the second bit stream b(n) of data for transmission and by expanding the third bit stream x(n) by the predetermined factor M by being configured to:
generate the fourth bit stream y(n) to comprise all bit values of the third bit stream x(n);
insert M−1 bits equal to 0 after each bit value from the third bit stream x(n) when the bit value of the second bit stream b(n) is 0; and
insert M−1 bits equal to 1 after each bit value from the third bit stream x(n) when the bit value of the second bit stream b(n) is 1.