16k mode interleaver in a digital video broadcasting (DVB) standard
A data processing apparatus maps input symbols to be communicated onto a predetermined number of sub-carrier signals of an Orthogonal Frequency Division Multiplexed (OFDM) symbol. The data processor includes an interleaver memory which reads-in the predetermined number of data symbols for mapping onto the OFDM sub-carrier signals. The interleaver memory reads-out the data symbols on to the OFDM sub-carriers to effect the mapping, the read-out being in a different order than the read-in, the order being determined from a set of addresses, with the effect that the data symbols are interleaved on to the sub-carrier signals. The set of addresses are generated from an address generator which comprises a linear feedback shift register and a permutation circuit.
1. A data processing apparatus configured to map input symbols to be communicated onto a predetermined number of sub-carrier signals of an Orthogonal Frequency Division Multiplexed (OFDM) symbol, the data processing apparatus comprising:
an interleaver configured to read-into a memory the predetermined number of data symbols for mapping onto the OFDM sub-carrier signals, and to read-out of the memory the data symbols for the OFDM sub-carriers to effect the mapping, the read-out being in a different order than the read-in, the order being determined from a set of addresses, with the effect that the data symbols are interleaved on the sub-carrier signals, and
an address generator configured to generate the set of addresses, an address being generated for each of the input symbols to indicate one of the sub-carrier signals onto which the data symbol is to be mapped, the address generator comprising:
a linear feedback shift register including a predetermined number of register stages and being configured to generate a pseudo-random bit sequence in accordance with a generator polynomial,
a permutation circuit configured to receive the content of the shift register stages and to permute the bits present in the register stages in accordance with a permutation order to form an address of one of the OFDM sub-carriers, and
a control unit configured in combination with an address check circuit to re-generate an address when a generated address exceeds a predetermined maximum valid address, wherein
the predetermined maximum valid address is approximately sixteen thousand,
the linear feedback shift register has thirteen register stages with a generator polynomial for the linear feedback shift register of R i ′[ 12 ]=R i-1 ′[ 0 ]⊕ R i-1 ′[ 1 ]⊕ R i-1 ′[ 4 ]⊕ R i-1 ′[ 5 ]⊕ R i-1 ′[ 9 ]⊕ R i-1 ′[ 11 ], and the permutation order forms, with an additional bit, a fourteen bit address R i [n] for the i-th data symbol from the bit present in the n-th register stage R i ′[n] in accordance with a code defined by the table:
R′ i bit positions
12
11
10
9
8
7
6
5
4
3
2
1
0
R i bit
8
4
3
2
0
11
1
5
12
10
6
7
9
positions.
2. The data processing apparatus as claimed in claim 1 , wherein the predetermined maximum valid address is a value substantially between twelve thousand and sixteen thousand three hundred and eighty four.
3. The data processing apparatus as claimed in claim 1 , wherein the OFDM symbol includes pilot sub-carriers, which are arranged to carry known symbols, and the predetermined maximum valid address depends on a number of the pilot sub-carrier symbols present in the OFDM symbol.
4. The data processing apparatus as claimed in claim 1 , wherein the interleaver memory is configured to effect the mapping of the input data symbols onto the sub-carrier signals for even OFDM symbols by reading in the data symbols according to the set of addresses generated by the address generator and reading out in a sequential order, and for odd OFDM symbols by reading in the symbols into the memory in a sequential order and reading out the data symbols from the memory in accordance with the set of addresses generated by the address generator.
5. The data processing apparatus as claimed claim 1 , wherein the permutation circuit is configured to change the permutation code, which permutes the order of the bits of the register stages to form the addresses from one OFDM symbol to another.
6. The data processing apparatus as claimed in claim 5 , wherein the permutation circuit is configured to cycle through a sequence of different permutation codes for successive OFDM symbols.
7. The data processing apparatus as claimed in claim 6 , wherein the sequence of permutation codes comprises two permutation codes, which are
R′ i bit positions
12
11
10
9
8
7
6
5
4
3
2
1
0
R i bit
8
4
3
2
0
11
1
5
12
10
6
7
9
positions
and
R′ i bit positions
12
11
10
9
8
7
6
5
4
3
2
1
0
R i bit
7
9
5
3
11
1
4
0
2
12
10
8
6
positions.
8. The data processing apparatus as claimed in claim 5 , wherein for both odd OFDM symbols and even OFDM symbols the interleaver is configured to read-into the memory the predetermined number of data symbols for mapping onto the OFDM sub-carrier signals in a sequential order, and to read-out of the memory the data symbols for the OFDM sub-carriers to effect the mapping according to the set of addresses generated by the address generator.
9. A transmitter for transmitting data using Orthogonal Frequency Division Multiplexing (OFDM), the transmitter including the data processing apparatus according to claim 1 .
10. The transmitter as claimed in claim 9 , wherein the transmitter is configured to transmit data in accordance with a Digital Video Broadcasting standard such as including the Digital Video Broadcasting-Terrestrial standard, the Digital Video Broadcasting-Handheld standard, or the Digital Video Broadcasting-Terrestrial2 standard.
11. A method of mapping input symbols to be communicated onto a predetermined number of sub-carrier signals of an Orthogonal Frequency Division Multiplexed (OFDM) symbol, the method comprising;
reading-into a memory the predetermined number of data symbols for mapping onto the OFDM sub-carrier signals,
reading-out of the memory the data symbols for the OFDM sub-carriers to effect the mapping, the read-out being in a different order than the read-in, the order being determined from a set of addresses, with the effect that the data symbols are interleaved on the sub-carrier signals, and
generating the set of addresses, an address being generated for each of the input symbols to indicate one of the sub-carrier signals onto which the data symbol is to be mapped, the generating the set of addresses comprising:
using a linear feedback shift register including a predetermined number of register stages to generate a pseudo-random bit sequence in accordance with a generator polynomial,
using a permutation circuit configured to receive the content of the shift register stages to permute the bits present in the register stages in accordance with a permutation order to form an address, and
re-generating an address when a generated address exceeds a predetermined maximum valid address, wherein
the predetermined maximum valid address is approximately sixteen thousand,
the linear feedback shift register has thirteen register stages with a generator polynomial for the linear feedback shift register of R i ′[ 12 ]=R i-1 ′[ 0 ]⊕ R i-1 ′[ 1 ]⊕ R i-1 ′[ 4 ]⊕ R i-1 ′[ 5 ]⊕ R i-1 ′[ 9 ]⊕ R i-1 ′[ 11 ], and the permutation order forms, with an additional bit, a fourteen bit address R i [n] for the i-th data symbol from the bit present in the n-th register stage R i ′[n] in accordance with a code defined by the table:
R′ i bit positions
12
11
10
9
8
7
6
5
4
3
2
1
0
R i bit
8
4
3
2
0
11
1
5
12
10
6
7
9
positions.
12. The method as claimed in claim 11 , wherein the predetermined maximum valid address is a value substantially between twelve thousand and sixteen thousand three hundred and eighty four.
13. The method as claimed in claim 11 , wherein the OFDM symbol includes pilot sub-carriers, which are arranged to carry known symbols, and the predetermined maximum valid address depends on a number of the pilot sub-carrier symbols present in the OFDM symbol.
14. The method as claimed in claim 11 , wherein the using a permutation circuit to receive the content of the shift register stages and permuting the bits present in the register stages in accordance with a permutation code to form an address, includes changing the permutation code, which permutes the order of the bits of the register stages to form the addresses, from one OFDM symbol to another.
15. The method as claimed in claim 14 , wherein the changing the permutation code, which permutes the order of the bits of the register stages to form the addresses, from one OFDM symbol to another includes cycling through a sequence of different permutation codes for successive OFDM symbols.
16. The method as claimed in claim 15 , wherein the sequence of permutation codes comprises two permutation codes, which are
R′ i bit positions
12
11
10
9
8
7
6
5
4
3
2
1
0
R i bit
8
4
3
2
0
11
1
5
12
10
6
7
9
positions
and
R′ i bit positions
12
11
10
9
8
7
6
5
4
3
2
1
0
R i bit
7
9
5
3
11
1
4
0
2
12
10
8
6
positions.
17. The method as claimed in claim 14 , wherein the reading-into the memory the predetermined number of data symbols from the OFDM sub-carrier signals, includes for both odd OFDM symbols and even OFDM symbols reading in the data symbols into the memory the predetermined number of data symbols for mapping onto the OFDM sub-carrier signals in a sequential order, and the reading-out of the memory the data symbols for the OFDM sub-carriers, includes for both odd OFDM symbols and even OFDM symbols reading-out of the memory the data symbols for the OFDM sub-carriers to effect the mapping according to addresses generated by the address generator.
18. A method of transmitting data symbols via a predetermined number of sub-carrier signals of an Orthogonal Frequency Division Multiplexed (OFDM) symbol, the method comprising;
receiving a predetermined number of data symbols for mapping onto the predetermined number of sub-carrier signals,
reading-into a memory the predetermined number of data symbols for mapping onto the OFDM sub-carrier signals,
reading-out of the memory the data symbols for the OFDM sub-carriers to effect the mapping, the read-out being in a different order than the read-in, the order being determined from a set of addresses, with the effect that the data symbols are interleaved on the sub-carrier signals, and
generating the set of addresses, an address being generated for each of the input symbols to indicate one of the sub-carrier signals onto which the data symbol is to be mapped, the generating the set of addresses comprising:
using a linear feedback shift register including a predetermined number of register stages to generate a pseudo-random bit sequence in accordance with a generator polynomial,
using a permutation circuit configured to receive the content of the shift register stages to permute the bits present in the register stages in accordance with a permutation order to form an address, and
re-generating an address when a generated address exceeds a predetermined maximum valid address, wherein
the predetermined maximum valid address is approximately sixteen thousand,
the linear feedback shift register has thirteen register stages with a generator polynomial for the linear feedback shift register of R i ′[ 12 ]=R i-1 ′[ 0 ]⊕ R i-1 ′[ 1 ]⊕ R i-1 ′[ 4 ]⊕ R i-1 ′[ 5 ]⊕ R i-1 ′[ 9 ]⊕ R i-1 ′[ 11 ], and the permutation order forms, with an additional bit, a fourteen bit address R i [n] for the i-th data symbol from the bit present in the n-th register stage R i ′[n] in accordance with a code defined by the table:
R′ i bit positions
12
11
10
9
8
7
6
5
4
3
2
1
0
R i bit
8
4
3
2
0
11
1
5
12
10
6
7
9
positions.
19. An address generator for use with transmission of data symbols interleaved onto sub-carriers of an Orthogonal Frequency Division Multiplexed symbol, the address generator being configured to generate a set of addresses, each address being generated for each of the data symbols to indicate one of the sub-carrier signals onto which the data symbol is to be mapped, the address generator comprising:
a linear feedback shift register including a predetermined number of register stages and being configured to generate a pseudo-random bit sequence in accordance with a generator polynomial,
a permutation circuit configured to receive the content of the shift register stages and to permute the bits present in the register stages in accordance with a permutation order to form an address, and
a control unit configured in combination with an address check circuit to re-generate an address when a generated address exceeds a predetermined maximum valid address, wherein
the predetermined maximum valid address is approximately sixteen thousand,
the linear feedback shift register has thirteen register stages with a generator polynomial for the linear feedback shift register of R i ′[ 12 ]=R i-1 ′[ 0 ]⊕ R i-1 ′[ 1 ]⊕ R i-1 ′[ 4 ]⊕ R i-1 ′[ 5 ]⊕ R i-1 ′[ 9 ]⊕ R i-1 ′[ 11 ], and the permutation order forms, with an additional bit, a fourteen bit address R i [n] for the i-th data symbol from the bit present in the n-th register stage R i ′[n] in accordance with the table:
R′ i bit positions
12
11
10
9
8
7
6
5
4
3
2
1
0
R i bit
8
4
3
2
0
11
1
5
12
10
6
7
9
positions.