Method of simultaneous radio transmission of digital data between a plurality of subscriber stations and a base station

• US 6,188,717 B1
• Filed: 11/17/1997
• Issued: 02/13/2001
• Est. Priority Date: 11/19/1996
• Status: Expired due to Term

• Current Assignee: Bayerische Motoren Werke AG
• Original Assignee: Deutsche Telekom AG
• Inventors: Kaiser, Stefan, Fazel, Khaled
• Primary Examiner(s): Chin, Stephen
• Assistant Examiner(s): McKiernan, Thomas E
• Application Number:
  US08/971,583
• Time in Patent Office: 1,184 Days
• Field of Search: 375/200, 375/130, 370/200
• US Class Current: 375/148
• CPC Class Codes: H04B 7/2628 using code-division multiple access [CDMA] or spread spectrum multiple access [SSMA] H04B7/2618 takes precedence
• CPC Class Codes: H04J 13/00 Code division multiplex systems for frequency hopping H04B1/713
• CPC Class Codes: H04L 25/0204 of multiple channels
• CPC Class Codes: H04L 25/0224 using sounding signals
• CPC Class Codes: H04L 5/0021 in which codes are applied as a frequency-domain sequences, e.g. MC-CDMA
• CPC Class Codes: H04L 5/026 using code division

Abstract

The method of the invention is based on an optimum combination of multi-carrier modulation with the spread-spectrum technique. The data of a subscriber station are spread, with the data of a subscriber station being modulated on a set of orthogonal spread sequences and superimposed. The data of a subscriber station are transmitted to a partial quantity of subcarriers in the frequency band, with the partial quantity of sub-carriers associated with the individual subscriber stations being disjunct and distributed over the entire transmission band. A channel estimation required for receiving-side data detection is performed by means of filtering in the time and/or frequency direction of reference symbols. A low-complexity maximum-likelihood sequence estimation is possible for data detection. The method of the invention is well-suited for use for both the upstream and downlinks in future cellular mobile-radio systems.

Claims

1. A method which uses a combination of the multi-carrier modulation method, a plurality of sub-carriers in a frequency band for modulation, and the spread spectrum technique, said method being for simultaneous radio transmission of digital data between a plurality of subscriber stations and a base station, said method comprising:

transmitting reference symbols for channel estimation to be performed on a receiving side, wherein on transmission side the digital data of a subscriber station are spread prior to transmission such that they are modulated with a set of orthogonal spread sequences and superimposed with them;

then transmitting the spread data of a subscriber station, in modulated form, on a partial quantity of sub-carriers in a multi-carrier frequency band, wherein the partial quantities of sub-carriers associated with the individual subscriber stations being disjunct and distributed over an entirety of the frequency band; and

inserting the reference symbols, which are known to the receiving side, into a sub-carrier data stream of each respective subscriber station associated therewith, for channel estimation;

multi-carrier demodulating and separating, on the receiving side, the received digital data with regard to the respective subscriber station sub-carrier;

extracting from the information-carrying data the reference symbols, for channel estimation for each sub-carrier to be detected and for deriving channel-state information that is necessary for later data detection and channel decoding for the respective information-carrying data;

detecting together, with a suitable de-spreading detection method, the information-carrying digital data of a subscriber station;

wherein the sub-carriers of a subscriber station are distributed over an entirety of the transmission-frequency band;

wherein spacing between adjacent sub-carriers of a subscriber station is a multiple factor of a reciprocal value of a duration of a multi-carrier modulated data symbol; and

wherein the sub-carriers are distinguished for the respective subscriber station at a particular frequency and time.

2. The method according to claim 1, including converting serial/parallel, in blocks on the transmission side, information-carrying, digital data sequences of a subscriber station, which comprises serial, complex data symbols,

multiplying data symbols of the block present in parallel form by a spread sequence of the length L (L chips), a maximum of L spread sequences being modulated with data symbols that are symbol- and thus chip-synchronized, and

superimposing per block, a maximum of L spread sequences modulated with data symbols are symbol-and thus chip-synchronously, resulting in a transmission sequence comprising L chips, which contains the information of a maximum of L data symbols.

3. The method according to claim 1, wherein on the transmission side, a channel encoder first provides the digital data with an error-protection channel code against channel disturbances.

4. The method according to claim 3, wherein the channel code includes at least one of convolution codes, turbo codes or block codes.

5. The method according to claim 3, including scrambling of code bits obtained from the channel encoder with an interleaver.

6. The method according to claim 5, wherein the scrambling is carried out in blocks.

7. The method according to claim 5, including mapping and digitally modulating the scrambled code bits into complex data symbols in a symbol mapper.

8. The method according to claim 7, including performing a digital modulation in the symbol mapper by phase shift keying including at least one of Binary Phase Shift Keying (BPSK) modulation or a Quadrature Phase Shift Keying (QPSK) modulation, wherein the complex data symbols are present in a respective modulated form at an output of the symbol mapper.

9. The method according to claim 2, including use of orthogonal Walsh-Hadamard sequences, of which L orthogonal spread sequences of a length L (L chips) exist, as spread sequences.

10. The method according to claim 2, including superimposing less than L spread sequences having a length L, the spread sequences having been modulated with data symbols.

11. The method according to claim 2, including scrambling the chips of a plurality of transmission sequences in frequency and time direction, with a frequency and time interleaver using a plurality of multi-carrier-modulated data symbols.

12. The method according to claim 11, wherein the scrambling is carried out in blocks.

13. The method according to claim 2, including:

spreading and sequence superimposing or scrambling in the frequency and time interleaving;

wherein

a number M of sub-carriers of a subscriber station may not be a multiple of the spread-code length L.

14. The method according to claim 13, wherein the sub-carriers of a subscriber station are distributed over an entirety of the transmission-frequency band.

15. The method according to claim 14, wherein spacing between adjacent sub-carriers of a subscriber station is equidistant.

16. The method according to claim 14, wherein spacing between adjacent sub-carriers of a subscriber station is pseudo-random.

17. The method according to claim 1, including use of Orthogonal Frequency-Division Method (OFDM) for transmission-side multi-carrier modulation.

18. The method according to claim 17, wherein the orthogonal frequency-division method is realized with an Inverse Fast Fourier Transformation (IFFT) and a Fast Fourier Transformation (FFT).

19. The method according to claim 2, wherein the multi-carrier-modulated data symbols are extended by a cyclic prefix on the tramission side, the cyclic prefix being a copy of last samples of the multi-carrier modulated signal.

20. The method according to claim 2, including:

multi-carrier-demodulating and frequency-demapping the data symbols on the receiving side, specifically to the subscriber station following an analog/digital conversion of the received data streams and an elimination of the possibly-present guard interval;

extracting the reference symbols necessary for the channel estimation from the information-carrying data; and

then parallel/serial converting the information carrying data.

21. The method according to claim 20, including filtering the received reference symbols in the channel estimation for each sub-carrier to be detected over time, and determining therefrom the channel-state information necessary for data detection and channel decoding for the information-carrying data.

22. The method according to claim 20, wherein, when the sub-carriers associated with one of the subscriber stations are not distributed over an entirety of the transmission-frequency bandwidth on the transmission side, and when at least one group of adjacent sub-carriers is formed in a transmission-frequency band, then, during the channel estimation in the receiver, the receiver reference symbols for each sub-carrier to be detected are frequency-domain filtered in a frequency direction within the multi-carrier symbol over the subcarriers and in a time direction over several multi-carrier symbols and the channel-state information required for data detection and channel decoding is determined therefrom for the information-carrying data.

23. The method according to claim 21, including use of a Wiener filter for filtering in the channel estimation.

24. The method according to claim 20, including providing corresponding scrambling on the transmission side and including at least one of detection in the receiver of the received information-carrying data following multi-carrier demodulation and subscriber station-specific frequency demapping after unscrambling in a frequency and time de-interleaver.

25. The method according to claim 24, including using a maximum-likelihood sequence estimation, the maximum-likelihood sequence estimation determining most probable sequences of all possible transmitted sequences and providing the associated data as soft decisions, for data detection.

26. The method according to claim 25, wherein the maximum-likelihood sequence estimation is performed separately in the I and Q signal components in a presence of QPSK-modulated data symbols.

27. The method according to claim 24, including use, for data detection, of a conventional detection method detecting all data symbols of a subscriber station after a equalization by means of a de-spreading, and providing of a soft decisions.

28. The method according to claim 27, including iterative use of the conventional data-detection method to attain a reduction in interference in the superimposed spread sequences.

29. The method according to one of claim 24, including deriving in the receiver the digital, information-carrying data from the detected data symbols of a subscriber station after at least one of a data-symbol mapping, a code-bit unscrambling in a de-interleaver, or a channel decoding, if corresponding measures are provided on the transmission side.

30. The method according to claim 1, including

selecting system parameters to provide substantially more data per transmission channel than is necessary for pure voice transmission (9.6 kbit/s), and

accommodating a plurality of voice channels in a transmission channel per transmission channel the via a Time-Division Multiple-Access (TDMA) method.

31. The method according to claim 1, including flexibly allocating the number of sub-carriers to a mobile subscriber station depending on an available capacity thereof, regardless of the selected spread-code length.

32. The method according to claim 1, including using said method for both the uplink from the subscriber station to the base station and the downlink from the base station to the subscriber station.

33. The method according to claim 1, including using said method in a field of mobile radio.

34. The method according to claim 33, wherein said field of mobile radio includes cellular mobile radio.

35. The method according to claim 1, including using said method in a field of cordless telephone (CT).

36. The method according to claim 5, wherein the scrambling is carried out pseudo-randomly.

37. The method according to claim 5, wherein the scrambling is carried out pseudo-randomly.