Channel randomization and time diversity for MIMO system
A method is provided for creating an artificial a fast fading channel in a MIMO communication system. The method includes encoding a series of source data to generate a first plurality of encoded output signals and multiplying the first plurality of encoded output signals by a plurality of random complex numbers to generate a second plurality of encoded output signals, and transmitting the second plurality of encoded output signals via the corresponding plurality of antennas. The transmitted signals vary in time and frequency independent of the channel conditions.
1. A method comprising:
at a multiple-input multiple-output (MIMO) communication device having a plurality of antennas and configured to send MIMO transmissions over a wireless channel, encoding a series of source data using a MIMO channel encoder to generate a plurality of encoded output signals;
generating a plurality of pseudo-random complex numbers that are independent of conditions of the wireless channel and that are configured to vary over time faster than a channel characteristic of the wireless channel in order to produce an artificial fast fading wireless channel;
multiplying corresponding ones of the plurality of encoded output signals by corresponding ones of the plurality of pseudo-random complex numbers to generate a plurality of transmit signals for transmission via a corresponding antenna of the plurality of antennas, wherein the plurality of pseudo-random complex numbers are configured to vary the amplitude and phase of the plurality of encoded output signals so as to form the artificial fast-fading wireless channel when transmitted via the plurality of antennas; and
transmitting the plurality of transmit signals via the plurality of antennas.
2. The method of claim 1 , wherein generating comprises generating the plurality of pseudo-random complex numbers that are configured to randomize the transmit signals and to provide time diversity to the wireless channel when the wireless channel has relatively static channel conditions.
3. The method of claim 1 , further comprising modulating the plurality of encoded output signals before multiplying by the plurality of pseudo-random complex numbers.
4. The method of claim 3 , further comprising modulating the plurality of encoded output signals using Phase Shift Keying (PSK), Quadrature Amplitude Modulation (QAM) or Orthogonal Frequency Division Multiplexing (OFDM) modulation techniques.
5. The method of claim 1 , wherein generating comprises generating the plurality of pseudo-random complex numbers at each transmission time.
6. The method of claim 5 , wherein generating comprises generating the plurality of pseudo-random complex numbers that are configured to provide a fast time-varying channel condition.
7. The method of claim 1 , further comprising embedding information representing the plurality of pseudo-random complex numbers within the transmit signals.
8. The method of claim 1 , wherein generating comprises generating the plurality of pseudo-random complex numbers such that the output power of the transmit signals conforms to a transmit power level constraint.
9. A method comprising:
at a multiple-input multiple-output (MIMO) communication device having a plurality of antennas and configured to send MIMO transmissions over a wireless channel, encoding a series of source data using a MIMO channel encoder to generate a plurality of encoded output signals;
modulating the plurality of encoded output signals to generate a first plurality of orthogonal frequency division multiplexed (OFDM) modulated signals; generating a plurality of pseudo-random complex numbers that are independent of conditions of the wireless channel and that are configured to vary over time faster than a channel characteristic of the wireless channel in order to produce an artificial fast fading wireless channel;
multiplying corresponding ones of the first plurality of OFDM modulated signals by corresponding ones of the plurality of pseudo-random complex numbers to generate a second plurality of OFDM modulated signals for transmission via a corresponding antenna of the plurality of antennas, wherein the plurality pseudo-random complex numbers are configured to vary the amplitude and phase of the first plurality of OFDM modulated signals so as to form the artificial fast-fading wireless channel when transmitted via the plurality of antennas; and
transmitting the second plurality of OFDM modulated signals via the plurality of antennas.
10. The method of claim 9 , wherein generating comprises generating the plurality of pseudo-random complex numbers that are configured to randomize the second plurality of OFDM modulated signals and to provide time diversity to the wireless channel when the wireless channel has relatively static channel conditions.
11. The method of claim 9 , wherein generating comprises generating the plurality of pseudo-random complex numbers at each transmission time.
12. A method comprising:
at a multiple-input multiple-output (MIMO) communication device having a plurality of antennas and configured to send MIMO transmissions over a wireless channel, encoding a series of source data using a MIMO channel encoder to generate a first plurality of encoded output signals;
generating a plurality of complex vectors comprising pseudo-random complex numbers such that the complex vectors are independent of conditions of the wireless channel and that are configured to vary over time faster than a channel characteristic of the wireless channel in order to produce an artificial fast fading wireless channel, wherein each complex vector comprises a plurality of pseudo-random complex numbers up to a number of subcarriers used when modulating the source data;
multiplying corresponding ones of the first plurality of encoded output signals by corresponding ones of the plurality of complex vectors to generate a second plurality of encoded output signals for transmission via a corresponding antenna of the plurality of antennas, wherein the plurality of complex vectors are configured to vary the amplitude and phase of the first plurality of encoded output signals so as to form the artificial small-scale multipath fading wireless channel when transmitted via a plurality of antennas in order to provide time diversity to the wireless channel;
modulating the second plurality of encoded output signals to provide a plurality of modulated signals; and
transmitting the second plurality of modulated signals via the plurality of antennas.
13. The method of claim 12 , wherein generating comprises generating the plurality of pseudo-random complex numbers that are configured to randomize the second plurality of encoded output signals.
14. The method of claim 12 , wherein modulating comprises modulating the second plurality of encoded output signals using Phase Shift Keying (PSK), Quadrature Amplitude Modulation (QAM) or Orthogonal Frequency Division Multiplexing (OFDM) modulation techniques.
15. The method of claim 12 , wherein generating comprises generating the plurality of random complex numbers at each transmission time.
16. The method of claim 15 , wherein generating comprises generating the plurality of pseudo-random complex numbers that are configured to provide a fast time-varying channel condition.
17. The method of claim 12 , further comprising:
generating a number of pilot signals corresponding to a number of the plurality of antennas; and
multiplying corresponding ones of the pilot signals by corresponding ones of the plurality of complex vectors to generate a third plurality of encoded output signals for transmission via corresponding ones of the plurality of antennas.