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EP-4736378-A1 - MULTIPOINT-TO-MULTIPOINT OFDMA SYNCHRONIZATION PROCESSING FOR STREAM-BASED SYSTEMS

EP4736378A1EP 4736378 A1EP4736378 A1EP 4736378A1EP-4736378-A1

Abstract

There is disclosed a communication device (20) for an OFDMA communication in particular for multipoint to multipoint communications, configured to receive and transmit OFDMA signals (512A, 512B, 512C), wherein the communication device is configured to receive a periodic synchronization signal (510) wherein the communication device is configured to derive a transmission characteristic (249, 251) on the basis of the received synchronization signal (510) and to adapt a subsequent transmission (512A, 512B, 512C) to the derived transmission characteristic.

Inventors

  • KOEPP, Matthias
  • HABEL, Kai

Assignees

  • Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V.

Dates

Publication Date
20260506
Application Date
20240701

Claims (20)

  1. 1. A communication device (20) for an OFDMA communication, configured to receive and transmit OFDMA signals (512A, 512B, 512C), wherein the communication device is configured to receive a periodic synchronization signal (510) wherein the communication device is configured to derive a transmission characteristic (249, 251) on the basis of the received synchronization signal (510) and to adapt a subsequent transmission (512A, 512B, 512C) to the derived transmission characteristic.
  2. 2. The communication device of claim 1, wherein the communication device is configured to generate the subsequent transmission as including a sequence of OFDMA symbols (512A, 512B, 512C), and configured to: generate, for each OFDMA symbol of the sequence of OFDMA symbols, an initial cyclic extension in which there are copied the last samples of the OFDMA symbol, and/or generate, for each OFDMA symbol of the sequence of OFDMA symbols, a final cyclic extension in which there are copied the first samples of the OFDMA symbol.
  3. 3. The communication device of any of the preceding claims, wherein the communication device is configured to derive a transmission characteristic on the basis of the received synchronization signal (510) and to adapt a subsequent transmission to the derived transmission characteristic.
  4. 4. The communication device of any of the preceding claims, configured to determine the transmission characteristic as comprising timing information (249).
  5. 5. The communication device of any of the preceding claims, configured to determine the transmission characteristic as comprising information (251) for resynchronizing its internal clock.
  6. 6. The communication device of any of the preceding claims, configured to determine the transmission characteristic as comprising subcarrier frequency and/or carrier frequency.
  7. 7. The communication device of any of the preceding claims, configured to determine the transmission characteristic as comprising sampling frequency.
  8. 8. The communication device of any of the preceding claims, configured to receive the synchronization signal (510) as a periodic signal.
  9. 9. The communication device of any of the preceding claims, configured to receive the synchronization signal (510) as comprising a known sequence of OFDMA symbols, and/or the communication device being configured to determine the transmission characteristic on the basis of the received known sequence of OFDMA symbols.
  10. 10. The communication device of any of the preceding claims, configured to receive the synchronization signal (510) as comprising a known sequence of samples, and/or configured to determine the transmission characteristic on the basis of the received known sequence of, e.g. OFDMA symbols.
  11. 11. The communication device of claim 10, configured to evaluate the difference between the current sample frequency and the frequency as determined from the synchronization signal (510), to thereby adapt the sample frequency by adopting a new sampling frequency compensating the difference between the current frequency and the frequency as determined from the synchronization signal.
  12. 12. The communication device of any of the preceding claims, configured to receive the synchronization signal (510) as comprising at least one carrier or subcarrier, and/or the communication device being configured to determine the transmission characteristic on the basis of the received at least one carrier or subcarrier, so as to adapt the subsequent transmission to the derived frequency or frequency offset of the received carrier or subcarrier(s).
  13. 13. The communication device of any of the preceding claims , configured to refrain from transmitting any signal during the reception of the synchronization signal (510).
  14. 14. The communication device of any of the preceding claims, configured to receive, in the synchronization signal (510), a sequence of symbols, so as to derive time difference information between the reception of symbols of the sequence of symbols and the assumed time of reception of the symbols of the sequence of symbols, thereby deriving the transmission characteristic.
  15. 15. The communication device of any of the preceding claims, configured to derive the transmission characteristic by evaluating at least one time distance between at least one symbol received in the synchronization signal and an assumed time point based on the current transmission characteristic.
  16. 16. The communication device of claim 15, configured to evaluate the at least one time distance by performing a cross correlation with at least one pre-defined sample.
  17. 17. The communication device of any of the preceding claims, configured to evaluate the difference between a current frequency and a frequency of the synchronization signal, to thereby adapt the transmission frequency of a subsequent transmission from the communication device by adopting a new frequency which compensates for the difference between the current frequency and the frequency as determined from the synchronization signal.
  18. 18. The communication device of any of the preceding claims, further configured to transmit and/or receive at least one transmission signal to include, in an initial guard time (N g ) of a ODFMA symbol (512A), a repetition of a final portion of the ODFMA symbol (512A) and/or include, in a final guard time of a ODFMA symbol, a repetition of an initial portion of the ODFMA symbol.
  19. 19. The communication device of any of the preceding claims, configured to process the received synchronization signal (510) to thereby derive the transmission characteristic (249, 251), while transmitting the subsequent transmission using at least one initial symbol (512A) based on a non-updated, previously obtained transmission characteristic, and, after having updated the transmission characteristic, to use the transmission characteristic for the remaining symbols (512B, 512C) of the same, subsequent transmission.
  20. 20. The communication device of any of the preceding claims, configured to perform: a first, rough synchronization, , so as to derive a frequency offset, and compensate for a frequency offset, and/or a second, fine synchronization, to derive the time instant to send an OFDMA symbol.

Description

Multipoint-to-Multipoint OFDMA Synchronization Processing for Stream-based Systems Description The invention refers to techniques for OFDMA commutations, in particular for multipoint to multipoint communications Description of the usage Environment "Multipoint-to-Multipoint OFDMA" Orthogonal Frequency Division Multiplex (OFDM) and Orthogonal Frequency Multiple Access (OFDMA) enable highly efficient data transmissions compared to conventional Frequency Division Multiplex (FDM) or Frequency Divisional Multiple Access (FDMA), respectively. In OFDM and FDM systems, frequency resources are used by only one single device at a time, whereas OFDMA and FDMA enable the use of frequency resources by different devices at the same time. The use of orthogonal frequency- modulating access systems (OFDM/A or OFDMA) is already in the prior art. OFDM/A systems divide a broadband signal into numerous orthogonal narrowband signals, called subcarriers. Advantages of OFDM/A systems over classical systems without orthogonal frequency modulation are known and may, among other things, be summarized as follows: a) Spectral efficiency through modulation of signals on sub-carriers which do not require guard bands due to orthogonality and which are able to overlap while adhering to orthogonality conditions. b) Subcarriers may be equalized in the frequency domain with low effort. c) Spectral efficiency through individual selection of modulation depth and proportional transmission power per subcarrier. d) DSP resource efficiency through common demodulation of all sub-carrier channels by means of FFT as well as common modulation of all locally assigned sub-carriers by means of IFFT e) Spectral efficiency through common temporal guard intervals of all channels f) Fine-granular allocation of channel capacity proportions in OFDMA systems with the possibility to dynamically adjust them during operation. g) Dynamic rate adjustment with respect to changed channel conditions or changed transmission requirements (e.g. robustness of the transmission vs. transmission rate) during operation. These advantages are brought, among other things, by significantly higher frequency and time synchronization requirements between transmitters and receivers. Insufficient synchronicity leads to signal transmission quality losses - and therefore to a decreased spectral efficiency - which may already become significant for relatively small values [21] [22]. These should be minimized. OFDMA systems in widespread use today are point-to-multipoint (P2MP) systems (e.g. 5G mobile communications in the downstream) or multipoint-to-point (MP2P) systems (e.g. 5G mobile communications in the upstream). Inherently, all signals pass a central node (e.g. 5Gbase station, the “P” side) that either carries out synchronization tasks or supports the synchronization of the distributed system nodes (5G user terminals, the “MP” side) (The mere fact of having dedicated central receivers already supports the synchronization in today’s OFDMA systems, as will be clarified below.) Typically, the synchronization of a P2MP- and MP2P-0FDMA duplex system (e.g. 5G system) takes place independently for each duplex direction (directions: upstream and downstream) which are separated by guard bands (in Frequency Division Duplex = FDD) or guard times (in Time Division Duplex = TDD). It is not required to adhere to orthogonality conditions between these bands. An OFDMA implementation for just one duplex direction is also possible (e.g. the upstream in DOCSIS 3.1 system). Among others, [22] shows methods for these systems. Multipoint-to-multipoint (MP2MP) systems do not have a dedicated upstream and downstream: communication takes place directly between distributed devices. Pure OFDM systems allocate all orthogonal frequency resources (all usable subcarriers) at the same time to one network device (e.g. G.9960/G.9961). Synchronization information is transmitted along and is evaluated by receiving devices (e.g. in the G.9960 frame preamble). The adherence to orthogonality conditions between the frequency resources of simultaneously communicating devices is therefore inapplicable. Among others, [21] and [23] show methods for such systems. The invention enables the creation of the synchronicity required between frequency resources used by different transmitters, to be kept orthogonal in MP2MP-0FDMA systems at all possible receiver positions inside the communication channel at the same time for preserving the possibility of correct decoding. There is no MP2MP-0FDMA system marketed today, to the best of the inventors’ knowledge; the synchronization required for OFDM/A techniques is realized exclusively in MP2MP-0FDM systems, or P2MP-0FDMA or MP2P-0FDMA systems, respectively. The biggest similarity exists with respect to MP2P-0FDMA systems where the orthogonality conditions have to be adhered to only at the central node (“P”). However, the system envisaged here is to fulfill the orthogonality conditio