Systems and methods for decreasing latency in a digital transmission system
View Patent ↗Disclosed herein are various embodiments of methods, systems, and apparatus for encoding OFDM packets in a digital communication system. In one exemplary method embodiment, LDPC codewords in an IEEE 802.11 wireless transmission are shortened, decreasing the iterations necessary to insure accurate communications. The codewords are shortened by adding known bits in predetermined locations in the last data symbol of a packet.
1. A method, comprising:
receiving payload data;
dividing the payload data into a plurality of data blocks comprising a last data block;
encoding each of the plurality of data blocks into a code word, wherein the code word associated with the last data block is a shortened code word encoded by:
inserting predefined bits into the last data block at predefined bit locations,
generating an intermediate code word by determining low density parity check (LDPC) bits from the last data block with inserted predefined bits, and
generating the shortened code word by removing all of the predefined bits from the intermediate code word;
reducing decoding latency by encoding the plurality of code words other than the shortened code word such that each code word other than the shortened code word is decodable with at least a first number of iterations to achieve a desired bit error rate (BER), and the shortened code word is encoded such that the shortened code word is decodable using a second number of iterations to achieve the desired BER, and wherein the second number of iterations is less than the first number of iterations; and
transmitting each code word as a string of OFDM symbols such that each code word fits into an integral number of OFDM symbols.
2. The method of claim 1 , wherein encoding the shortened code words further comprises aggregating code words with a maximum effective rate into bundles, the aggregating performed in a MAC.
3. The method of claim 1 , further comprising determining a modulation mode and stream configuration.
4. The method of claim 3 , wherein generating shortened code words comprises generating shortened code words whose sizes correspond to the modulation mode and stream configuration.
5. The method of claim 1 , further comprising:
composing a packet based on the string of OFDM symbols; and
transmitting the packet.
6. The method of claim 5 , further comprising:
determining a transmission rate, and wherein composing the packet comprises composing the packet based on the determined transmission rate.
7. The method of claim 6 , wherein composing the packet based on the determined transmission rate comprises:
determining a number of OFDM symbols required to transmit the packet at the determined transmission rate;
determining a frame size for the packet; and
composing the packet based on the number of OFDM symbols and the frame size.
8. The method of claim 7 , wherein a number of the predefined bits is determined based on the frame size.
9. The method of claim 8 , wherein composing the packet comprises determining a number of fill bits.
10. The method of claim 7 , wherein determining the frame size of the packet comprises determining a minimum frame size for transmission of the packet.
11. The method of claim 1 , wherein generating shortened code words comprises selecting shortened code block structures for at least a last code block of a packet.
12. The method of claim 11 , wherein the code block structures are selected with predefined information bits and a minimum number of pad bits for at least the last code block of the packet as to require fewer iterations to decode the at least the last code block of the packet.