Fig. 1. H matrix and the corresponding tanner graph of (6,4) LDPC code.

Fig. 2. Schematic diagram of base matrix expansion.

Fig. 3. Performance of constructed LDPC codes with $R=22/68$, $Z=64\backslash 96\backslash 128\backslash 192\backslash 256\backslash 384$. Code length $=4325\backslash 6528\backslash 8704\backslash 13,056\backslash 17,408\backslash 26,612$ bits, binary phase-shift keying (BPSK) modulation, max iteration $\mathrm{n}\mathrm{u}\mathrm{m}=50$.

Fig. 4. performance of constructed LDPC codes with $R=10/52$, $Z=80\backslash 128\backslash 160\backslash 256\backslash 320\backslash 384$. Code length $=4160\backslash 6656\backslash 8320\backslash \mathrm{13,312}\backslash \mathrm{16,640}\backslash \mathrm{19,968}$ bits, binary phase-shift keying (BPSK) modulation, max iteration $\mathrm{n}\mathrm{u}\mathrm{m}=50$.

Fig. 5. Experimental setup of CVQKD scheme based on GG02 protocol. CW laser, continuous-wave laser; BS, beam splitter; AM, amplitude modulator; PM, phase modulator; ATT, attenuator.

Fig. 6. (a) FER values of constructed QC-LDPC codes with rates 1/4 and 10/52. (b) FER values of constructed QC-LDPC codes with rates 1/3 and 22/68. Both (a) and (b) are binary phase-shift keying (BPSK) modulation, max iteration $\mathrm{n}\mathrm{u}\mathrm{m}=500$, frame $\mathrm{n}\mathrm{u}\mathrm{m}=10,000$. (c) Reconciliation efficiency of the QC-LDPC codes for FERs of 0.5, 0.1, 0.01, and 0.001.

Fig. 7. Secret key rate as a function of distance for a CVQKD system with a homodyne detector, excess noise $ϵ=0.01$, detection efficiency $\eta =0.6$, electronic noise $V_{el}=0.01$, and the attenuation factor $\alpha$ of the quantum channel set to be 0.2 dB/km. Pinkish-red dashed curve and blue dashed curve show the QC-LDPC codes (length 62,800, rates 1/4 and 1/3) in the DVB-S2 protocol, respectively. Red solid curve shows the QC-LDPC code (length 68,000, rate 22/68) in the 5G protocol.

Table 1. Two Types of BGs Given in the 5G Protocol

Table 2. Sets of LDPC Lifting Size Z