Bit interleaver for low-density parity check codeword having length of 64800 and code rate of 7/15 and quadrature phase shift keying, and bit interleaving method using same
A bit interleaver, a bit-interleaved coded modulation (BICM) device and a bit interleaving method are disclosed herein. The bit interleaver includes a first memory, a processor, and a second memory. The first memory stores a low-density parity check (LDPC) codeword having a length of 64800 and a code rate of 7/15. The processor generates an interleaved codeword by interleaving the LDPC codeword on a bit group basis. The size of the bit group corresponds to a parallel factor of the LDPC codeword. The second memory provides the interleaved codeword to a modulator for quadrature phase shift keying (QPSK) modulation.
1. An apparatus for transmitting a broadcast signal, the apparatus comprising:
a first memory configured to store a low-density parity check (LDPC) codeword having a length of 64800 and a code rate of 7/15;
a processor configured to generate an interleaved codeword by interleaving the LDPC codeword on a bit group basis, the size of the bit group corresponding to a parallel factor of the LDPC codeword;
a second memory configured to output the interleaved codeword;
a modulator configured to perform quadrature phase shift keying (QPSK) modulation corresponding to the interleaved codeword to generate a modulated signal; and
an antenna configured to broadcast a transmission signal corresponding to the modulated signal over a physical channel to a reception device, the broadcasted transmission signal being an electromagnetic signal having a radio frequency,
wherein the interleaving is performed using the following equation using permutation order:
Y j =X π(j) 0≤ j<N group
where X π(j) is a π(j) bit group, Y j is an interleaved j-th bit group, and π(j) is a permutation order for bit group-based interleaving,
wherein the permutation order corresponds to an interleaving sequence, the interleaving sequence being for the LDPC codeword having the length of 64800 and the code rate of 7/15 and being represented as follows:
={152 172 113 167 100 163 159 144 114 47 161 125 99 89 179 123 149 177 1 132 37 26 16 57 166 81 133 112 33 151 117 83 52 178 85 124 143 28 59 130 31 157 170 44 61 102 155 111 153 55 54 176 17 68 169 20 104 38 147 7 174 6 90 15 56 120 13 34 48 122 110 154 76 64 75 84 162 77 103 156 128 150 87 27 42 3 23 96 171 145 91 24 78 5 69 175 8 29 106 137 131 43 93 160 108 164 12 140 71 63 141 109 129 82 80 173 105 9 66 65 92 32 41 72 74 4 36 94 67 158 10 88 142 45 126 2 86 118 73 79 121 148 95 70 51 53 21 115 135 25 168 11 136 18 138 134 119 146 0 97 22 165 40 19 60 46 14 49 139 58 101 39 116 127 30 98 50 107 35 62}, and
wherein the interleaved codeword is interleaved by the interleaving sequence on the bit group basis before performing the quadrature phase shift keying (QPSK) modulation so as to distribute burst errors occurring in the transmission signal transmitted over the physical channel.
2. The apparatus of claim 1 , wherein the parallel factor is 360, and the bit group includes 360 bits.
3. The apparatus of claim 2 , wherein the LDPC codeword is represented by (u 0 , u 1 , . . . , u N ldpc−1 ) (where N ldpc is 64800), and is divided into 180 bit groups each including 360 bits, as in the following equation:
X j ={u k |360 ×j≤k <360×( j+ 1), 0 ≤k<N ldpc } for 0 ≤j<N group
where X j is an j-th bit group, N ldpc is 64800, and N group is 180.