Joint user detection apparatus
A joint user detection apparatus for a wireless communication system, such as OFDM systems, arranged to account for timing impairments experienced by CAZAC codes. The proposed apparatus brings improvements over conventional receiving apparatuses by allowing joint user channel estimation processing and joint user equalization processing while considering timing impairments of user associated information present within a symbol of a received signal. The proposed solution could be used on conventional receiving apparatuses since both joint user channel estimation processing and joint user equalization processing can be activated independently such that either one or both improvements may be activated as needed or as required by the design of the conventional receiving apparatuses. A method and a computer program are also claimed.
1. An apparatus comprising:
a receiving unit arranged to receive a signal transmitted over a channel of a wireless communication system, the received signal comprising at least one data symbol and at least one pilot symbol, each symbol of the received signal comprising user associated information which are orthogonally multiplexed in the frequency domain with a unique cyclically shifted version of a known code exhibiting constant-amplitude zero autocorrelation, CAZAC, property;
a timing offset estimation unit operably coupled to the receiving unit and arranged to:
determine a timing offset estimation data associated with timing impairment of user associated information; and,
integrate the determined timing offset estimation data with the respective CAZAC code, thereby producing an integrated CAZAC code;
a channel estimation unit operably coupled to the receiving unit and the timing offset unit, the channel estimation unit being arranged to produce in the frequency domain, a channel estimation data associated with a channel response estimation of the channel;
an equalizing unit operably coupled to the receiving unit, the timing offset unit and the channel estimation unit, the equalizing unit being arranged to produce in the frequency domain, an equalized data symbol associated with the data symbol; and,
a processing unit such as a processor, operably coupled to the channel estimation unit and the equalizing unit, the processing unit being arranged to command the channel estimation unit and/or the equalizing unit to operate based on at least one symbol of the received signal and the associated integrated CAZAC code.
2. The apparatus of claim 1 , wherein the channel estimation unit is arranged to produce the channel estimation data based on the pilot symbol, the channel estimation data corresponding to a product between:
a matrix representation of the pilot symbol; and,
the inverse of a matrix representation of the integrated CAZAC code.
3. The apparatus of claim 1 , wherein the equalizing unit is arranged to produce the equalized data symbol based on the data symbol, the equalized data symbol corresponding to a product between:
a matrix representation of the data symbol; and,
the inverse of a matrix representation of a product between the integrated CAZAC code and the channel estimation data.
4. The apparatus of claim 2 further comprising:
a plurality of receiving antennas being operably coupled the receiving unit;
a maximum ratio combining unit being operably coupled to the timing offset estimation unit and the processing unit;
the processing unit being operably coupled to the receiving unit;
wherein, when the signal is received on the plurality of antennas, the processing unit is further arranged to command:
the receiving unit to process individually the signal received on each of the plurality of receiving antennas;
the maximum ratio combining unit to perform maximum ratio combining processing based on the data symbol and associated integrated CAZAC code, associated with each of the plurality of receiving antennas, thereby producing a combined data symbol and associated combined integrated CAZAC code;
wherein the equalizing unit is arranged to produce the equalized data symbol based on the combined data symbol and associated combined integrated CAZAC code, the equalized data symbol corresponding to a product between:
a matrix representation of the combined data symbol; and,
the inverse of a matrix representation of a product between the associated combined integrated CAZAC code and the channel estimation data.
5. The apparatus of claim 2 further comprising:
a plurality of receiving antennas being operably coupled the receiving unit;
a maximum ratio combining unit being operably coupled to the equalizing unit and the processing unit;
the processing unit being operably coupled to the receiving unit;
wherein, when the signal is received on the plurality of antennas, the processing unit is further arranged to command:
the receiving unit to process individually the signal received on each of the plurality of receiving antennas;
the maximum ratio combining unit to perform maximum ratio combining processing based on the equalized data symbol, associated with each of the plurality of receiving antennas, thereby producing a combined equalized data symbol.
6. The apparatus of claim 1 , wherein the integrated CAZAC code corresponds to a Zadoff-Chu sequence.
7. The apparatus of claim 6 wherein the channel is a LTE Physical Uplink Control Channel, PUCCH.
8. A method comprising:
receiving a signal transmitted over a channel of a wireless communication system, the received signal comprising at least one data symbol and at least one pilot symbol, each symbol of the received signal comprising user associated information which are orthogonally multiplexed in the frequency domain with a unique cyclically shifted version of a known code exhibiting constant-amplitude zero autocorrelation, CAZAC, property;
determining a timing offset estimation data associated with timing impairment of user associated information;
integrating the determined timing offset estimation data with the respective CAZAC code, thereby producing an integrated CAZAC code;
producing in the frequency domain, a channel estimation data associated with a channel response estimation of the channel;
producing in the frequency domain, an equalized data symbol associated with the data symbol; and,
causing the producing of the channel estimation data and/or the an equalized data symbol to be based on at least one symbol of the received signal and the associated integrated CAZAC code.
9. The method of claim 8 , wherein producing the channel estimation data is based on the pilot symbol, the channel estimation data corresponding to a product between:
a matrix representation of the pilot symbol; and,
the inverse of a matrix representation of the integrated CAZAC code.
10. The method of claim 8 , wherein producing the equalized data symbol is based on the data symbol, the equalized data symbol corresponding to a product between:
a matrix representation of the data symbol; and,
the inverse of a matrix representation of a product between the integrated CAZAC code and the channel estimation data.
11. The method of claim 9 further comprising:
providing a plurality of receiving antennas;
wherein, when the signal is received on the plurality of antennas, the method further comprises:
processing individually the signal received on each of the plurality of receiving antennas;
perform a maximum ratio combining processing based on the data symbol and associated integrated CAZAC code, associated with each of the plurality of receiving antennas, thereby producing a combined data symbol and associated combined integrated CAZAC code;
wherein, when the producing of the equalized data symbol is based on the combined data symbol and associated combined integrated CAZAC code, the equalized data symbol corresponds to a product between:
a matrix representation of the combined data symbol; and,
the inverse of a matrix representation of a product between the associated combined integrated CAZAC code and the channel estimation data.
12. The method of claim 9 further comprising:
providing a plurality of receiving antennas;
wherein, when the signal is received on the plurality of antennas, the method further comprises:
processing individually the signal received on each of the plurality of receiving antennas;
performing a maximum ratio combining processing based on the equalized data symbol, associated with each of the plurality of receiving antennas, thereby producing a combined equalized data symbol.
13. The method of claim 8 , wherein the integrated CAZAC code corresponds to a Zadoff-Chu sequence.
14. The method of claim 13 wherein the channel is a LTE Physical Uplink Control Channel, PUCCH.
15. A computer program product stored in a tangible, non-transitory computer-readable storage medium that stores computer-executable code for joint user detection for a wireless communication system, the computer-executable process causing a processor computer to perform the method according to claim 8 .