Tentpoles scheme to achieve reliable V2V communications

1. A communications system comprising: a transmitter that transmits a signal including user data as normal data symbols and at least one dual-use data symbol, where the at least one dual-use data symbol includes data and additional training symbols, said at least one dual-use data symbol having extra protection that is better than the normal data symbols; and a receiver that receives the signal, said receiver decoding the at least one dual-use data symbol and identifying information in the at least one dual-use data symbol that improves channel estimation accuracy, where the transmitter varies the at least one dual-use data symbol based on a channel condition, where the channel condition defines the reliability of the channel.

2. The system of claim 1 where the signal includes multiple subcarrier frequencies and where at least one of the subcarrier frequencies is a dual-use subcarrier frequency, where the dual-use subcarrier frequency includes extra protection for the data symbols that are transmitted in the dual-use subcarrier frequency.

3. The system of claim 1 where varying the at least one dual-use data symbol varies the level of extra protection on the at least one dual-use data symbol or where the at least one dual-use data symbol is a plurality of data symbols and the transmitter varies the number of dual-use data symbols by equally separating the dual-use data symbols among the normal symbols.

4. The system of claim 3 where the channel condition is monitored using a signal-to-noise ratio, a bit-error rate or a packet error rate.

5. The system of claim 1 where the extra protection uses convolution coding or low-density parity-check (LDPC) coding.

6. The system of claim 1 where the signal is compliant with an 802.11 p standard, and the data symbols are orthogonal frequency division multiplexing (OFDM) data symbols.

7. The system of claim 1 where the extra protection uses a systematic code that has information bits and checking bits.

8. The system of claim 7 where the signal is an 802.11 p signal that has tail bits, and where the checking bits are located after the tail bits.

9. The system of claim 1 where the communications system is a vehicular communications system.

10. A communications system comprising: a transmitter that transmits a signal including user data in normal subcarriers and in at least one dual-use subcarrier where the at least one dual- use subcarrier includes data and additional training symbols, said at least one dual-use subcarrier having extra protection that is better than the normal subcarriers; and a receiver that receives the signal, decodes the at least one dual-use subcarrier and uses information from decoding the subcarrier to improve an estimation accuracy of the normal subcarrier, where the transmitter varies the at least one dual-use data symbol based on a channel condition, where the channel condition defines the reliability of the channel.

11. The system of claim 10 where the subcarriers include dual-use data symbols and where a first normal subcarrier includes at least at least one, but less than all, dual-use data symbol, where the dual-use data symbols have extra protection better than a normal data symbol and where the dual-use data symbols are separated equally among the normal symbols.

12. The system of claim 10 where varying the dual-use subcarriers varies the level of extra protection on the at least one dual-use subcarrier or where the at least one dual-use subcarrier is a plurality of dual-use subcarriers and the transmitter varies the number of dual-use subcarriers.

13. The system of claim 10 where the extra protection uses convolution coding or low-density parity-check (LDPC) coding.

14. The system of claim 10 where the signal is an 802.11 p signal.

15. The system of claim 14 where the extra protection uses a systematic code with information bits and checking bits and where the 802.11 p signal has one or more sets of tail bits and the checking bits are located after one of the tail bits.

16. A vehicular communications system comprising: a transmitter transmitting a signal with user data as normal data symbols and at least one dual-use data symbol, where the at least one dual-use data symbol includes data and additional training symbols, said at least one dual- use data symbol having extra protection that is better than the normal data symbols; and a receiver that receives the signal, decodes the at least one dual- use data symbol and uses information from decoding the at least one dual-use data symbol to improve accuracy of a channel estimation, where the transmitter varies the at least one dual-use data symbol based on a channel condition, where the channel condition defines the reliability of the channel.

17. The system of claim 16 where the dual-use data symbol is a plurality of dual-use data symbols that are located at different times such that the plurality of dual-use data symbols are separated equally among the normal symbols.

18. The system of claim 16 where the dual-use data symbol is located in different frequencies.