Adaptive time diversity and spatial diversity for OFDM
An adaptable orthogonal frequency-division multiplexing system (OFDM) that uses a multiple input multiple output (MIMO) to having OFDM signals transmitted either in accordance with time diversity to reducing signal fading or in accordance with spatial diversity to increase the data rate. Sub-carriers are classified for spatial diversity transmission or for time diversity transmission based on the result of a comparison between threshold values and at least one of three criteria. The criteria includes a calculation of a smallest eigen value of a frequency channel response matrix and a smallest element of a diagonal of the matrix and a ratio of the largest and smallest eigen values of the matrix.
1. An apparatus for transmitting data, comprising:
an orthogonal frequency division multiplexing (OFDM) encoder for loading:
a first data on a sub-carrier of an OFDM symbol associated with an antenna;
a second data on a sub-carrier of an another OFDM symbol associated with the antenna;
said first and said second data on sub-carriers of OFDM symbols associated with an another antenna according to at least one mapping rule, wherein said at least one mapping rule is a conjugate mapping rule;
said antenna transmits said first data;
said antenna transmits said second data; and
said another antenna transmits said first and said second data;
wherein
said transmission of said first data with said another antenna is transmitted subsequent to said transmission of said first data with said antenna; and
said transmission of said second data with said antenna is transmitted subsequent to said transmission of said second data with said another antenna.
2. The apparatus of claim 1 , wherein said OFDM encoder is configured to load:
said first data on said sub-carrier of said OFDM symbols associated with said another antenna according to said conjugate mapping rule; and
said second data on said sub-carrier of said OFDM symbol associated with said another antenna according to a negative conjugate mapping rule.
3. The apparatus of claim 2 , wherein
a rate of transmission of said first data with said antenna is substantially equal to a rate of transmission of said first data with said another antenna; and
a rate of transmission of said second data with said antenna is substantially equal to a rate of transmission of said second data with said another antenna.
4. An apparatus for transmitting data, comprising:
an orthogonal frequency division multiplexing (OFDM) encoder configured to load:
a first data on a sub-carrier of an OFDM symbol associated with an antenna;
a second data on a sub-carrier of an another OFDM symbol associated with the antenna; and
said first and said second data on sub-carriers of OFDM symbols associated with another antenna according to a first conjugate mapping rule and a second conjugate mapping rule, to thereby produce a first mapped data and a second mapped data;
wherein
said antenna is configured to transmit said first data;
said antenna is configured to transmit said second data;
said another antenna is configured to transmit said first mapped data;
said another antenna is configured to transmit said second mapped data; and
respective transmissions with said another antenna are subsequent to corresponding transmissions with said antenna.
5. The apparatus of claim 4 , wherein said second conjugate mapping rule is a negative conjugate mapping rule.
6. The apparatus of claim 5 , wherein
a rate of transmission of said first data with said antenna is substantially equal to a rate of transmission of said first mapped data with said another antenna; and
a rate of transmission of said second data with said antenna is substantially equal to a rate of transmission of said second mapped data with said another antenna.
7. The apparatus of claim 4 , wherein said first and second conjugate mapping rules are the same.