EP2195992A2 - System for transmitting and receiving signals - Google Patents

System for transmitting and receiving signals

Info

Publication number
EP2195992A2
EP2195992A2 EP08793741A EP08793741A EP2195992A2 EP 2195992 A2 EP2195992 A2 EP 2195992A2 EP 08793741 A EP08793741 A EP 08793741A EP 08793741 A EP08793741 A EP 08793741A EP 2195992 A2 EP2195992 A2 EP 2195992A2
Authority
EP
European Patent Office
Prior art keywords
pilots
symbols
pilot
index
scattered
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP08793741A
Other languages
German (de)
French (fr)
Other versions
EP2195992A4 (en
Inventor
Woo Suk Ko
Sang Chul Moon
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
LG Electronics Inc
Original Assignee
LG Electronics Inc
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by LG Electronics Inc filed Critical LG Electronics Inc
Publication of EP2195992A2 publication Critical patent/EP2195992A2/en
Publication of EP2195992A4 publication Critical patent/EP2195992A4/en
Withdrawn legal-status Critical Current

Links

Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L5/00—Arrangements affording multiple use of the transmission path
    • H04L5/0001—Arrangements for dividing the transmission path
    • H04L5/0014—Three-dimensional division
    • H04L5/0023—Time-frequency-space
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/26—Systems using multi-frequency codes
    • H04L27/2601—Multicarrier modulation systems
    • H04L27/2602—Signal structure
    • H04L27/261—Details of reference signals
    • H04L27/2613—Structure of the reference signals
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/26—Systems using multi-frequency codes
    • H04L27/2601—Multicarrier modulation systems
    • H04L27/2602—Signal structure
    • H04L27/261—Details of reference signals
    • H04L27/2613—Structure of the reference signals
    • H04L27/26134—Pilot insertion in the transmitter chain, e.g. pilot overlapping with data, insertion in time or frequency domain
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/26—Systems using multi-frequency codes
    • H04L27/2601—Multicarrier modulation systems
    • H04L27/2626—Arrangements specific to the transmitter only
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/26—Systems using multi-frequency codes
    • H04L27/2601—Multicarrier modulation systems
    • H04L27/2647—Arrangements specific to the receiver only
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L5/00—Arrangements affording multiple use of the transmission path
    • H04L5/003—Arrangements for allocating sub-channels of the transmission path
    • H04L5/0048—Allocation of pilot signals, i.e. of signals known to the receiver
    • H04L5/005—Allocation of pilot signals, i.e. of signals known to the receiver of common pilots, i.e. pilots destined for multiple users or terminals
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L25/00—Baseband systems
    • H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
    • H04L25/0202—Channel estimation
    • H04L25/022—Channel estimation of frequency response
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L25/00—Baseband systems
    • H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
    • H04L25/0202—Channel estimation
    • H04L25/0224—Channel estimation using sounding signals

Definitions

  • the present invention relates to efficient transmitter and receiver for an OFDM
  • TFS Time Frequency Slicing
  • a single service can be transmitted through multiple RF (Radio Frequency) channels on a two-dimensional time-frequency space.
  • RF Radio Frequency
  • OFDM Orthogonal Frequency Division Multiplexing
  • FDM frequency-division multiplexing
  • a large number of closely-spaced orthogonal sub-carriers are used to carry data.
  • the data are divided into several parallel data streams or channels, one for each sub-carrier.
  • Each sub-carrier is modulated with a conventional modulation scheme (such as quadrature amplitude modulation or phase shift keying) at a low symbol rate, maintaining total data rates similar to conventional single-carrier modulation schemes in the same bandwidth.
  • a conventional modulation scheme such as quadrature amplitude modulation or phase shift keying
  • OFDM has developed into a popular scheme for wideband digital communication, whether wireless or over copper wires, used in applications such as digital television and audio broadcasting, wireless networking and broadband internet access.
  • OFDM frequency diversity gain and statistical multiplexing gain can be obtained, thus, resources can be efficiently utilized.
  • a specific frequency is used for a specific service as opposed to a multi- frequency network where multiple frequencies can be used for a same service.
  • the present invention provides efficient transmitter and receiver for an OFDM (Orthogonal Frequency Division Multiplexing) system including TFS (Time-Frequency Slicing). More specifically, the present invention provides a pilot structure for an efficient channel estimation in an SFN (Single Frequency Network) environment and for reducing an overhead by pilots. In addition, if a pilot is assigned for each transmitter in an SFN environment, transmission channel can be efficiently estimated and overhead by pilots can be reduced.
  • a method of transmitting signals for OFDM system including TFS in an SFN environment comprising: encoding frames made of bitstreams; transforming the encoded frames into symbols; inserting pilots into the symbols to exhibit a scattered pilot pattern, wherein each pilot of the scattered pilot pattern corresponds to an index of each transmitter among a predetermined number of transmitters; and encoding the pilots inserted symbols into a multiple or a single signal.
  • a receiver for OFDM system including TFS in an SFN environment comprising: a demodulator configured to perform echo estimations based on scattered pilots (SP) and scattered adjacent pilots (SAPs) on received symbols, wherein the SAPs comprise a plurality of pilot groups having an identical index of a transmitter among a predetermined number of transmitters structured in the symbols exhibiting a scattered pattern in a frequency domain; a decoder configured to transform the symbols into multiple data; and a frame parser configured to transform the multiple data into bitstreams.
  • SP scattered pilots
  • SAPs scattered adjacent pilots
  • a method of receiving signals for OFDM system including TFS in an SFN environment comprising: performing echo estimations based on scattered pilots (SP) and scattered adjacent pilots (SAPs) on received symbols, wherein the SAPs comprise a plurality of pilot groups having an identical index of a transmitter among a predetermined number of transmitters structured in the symbols exhibiting a scattered pattern in a frequency domain; transforming the symbols into multiple data; and transforming the multiple data into bitstreams.
  • SP scattered pilots
  • SAPs scattered adjacent pilots
  • Fig. 1 is a block diagram of an example of a TFS (Time Frequency Slicing)-OFDM
  • FIG. 2 is a block diagram of an example of the input processor shown in the Fig. 1.
  • FIG. 3 is a block diagram of an example of the BICM (Bit-Interleaved Coding and
  • FIG. 4 is a block diagram of an example of the Frame Builder shown in Fig. 1.
  • Fig. 5 is a first example of a scattered pilot structure for an SFN (Single Frequency
  • Fig. 6 is a second example of a scattered pilot structure for an SFN environment.
  • Fig. 7 is a third example of a scattered pilot structure for an SFN environment.
  • Fig. 8 is a first example of a scattered adjacent pilot structure for an SFN environment.
  • Fig. 9 is a second example of a scattered adjacent pilot structure for an SFN environment.
  • Fig. 10 is a third example of a scattered adjacent pilot structure for an SFN environment.
  • Fig. 11 is a fourth example of a scattered adjacent pilot structure for an SFN environment.
  • Fig. 12 is a fith example of a scattered adjacent pilot structure for an SFN environment.
  • Fig. 13 is a sixth example of a scattered adjacent pilot structure for an SFN environment.
  • Fig. 14 is a block diagram of an example of the MIMO/MISO decoder shown in
  • Fig. 15 is a block diagram of an example of the modulator, specifically an example of an OFDM modulator.
  • FIG. 16 is a block diagram of an example of the analog processor shown in Fig. 1.
  • Fig. 17 is a block diagram of an example of a TFS-OFDM receiver.
  • Fig. 18 is a block diagram of an example of the AFE (Analog Front End) shown in Fig. 17.
  • Fig. 19 is a block diagram of an example of the demodulator, specifically an OFDM demodulator.
  • Fig. 20 is a block diagram of an example of a channel estimation.
  • Fig. 21 is a block diagram of an example of the MIMO/MISO decoder shown in
  • Fig. 22 is a block diagram of an example of the frame parser shown in Fig. 17.
  • Fig. 23 is a block diagram of an example of the BICM decoder shown in Fig. 17.
  • Fig. 24 is a block diagram of an example of the output processor shown in Fig. 17.
  • Fig. 1 shows an example of a proposed transmitter for an OFDM (Orthogonal
  • a multiple MPEG2-TS (Transport Stream) and a multiple Generic stream can be inputted into a TFS transmitter.
  • the input processor (101) can split the inputted streams into a multiple output signals for a multiple PLP (Physical Layer Path).
  • the BICM (Bit- Interleaved Coding and Modulation) (102) can encode and interleave the PLP individually.
  • the frame builder (103) can transform the PLP into total R of RF bands.
  • MIMO (Multiple-Input Multiple- Output)/MIS O (Multiple-Input Single- Output) (104) technique can be applied for each RF band.
  • Each RF band for each antenna can be individually modulated by the modulator (105a, b) and can be transmitted to antennas after being converted to an analog signal by the analog processor (106a, b).
  • Fig. 2 is an example of the input processor.
  • MPEG-TS Transport Stream
  • Generic streams Internet protocol
  • GSE General Stream Encapsulation
  • Each output from the TS-MUX and GSE can be split for multiple services by the service splitter (202a, b).
  • PLP is a processing of each service.
  • Each PLP can be transformed into a frame by the BB (Baseband) Frame (103a ⁇ d).
  • Fig. 3 is an example of the BICM.
  • Fig. 4 is an example of the frame builder.
  • QAM mapper (401a, b) can transform inputted bits into QAM symbols.
  • Hybrid QAM can be used.
  • Time domain interleaver (402a, b) can interleave data in time domain to make the data be robust against burst error. At this point, an effect of interleaving many RF bands can be obtained in a physical channel because the data are going to be transmitted to a multiple RF bands.
  • TFS frame builder (403) can split inputted data to form TFS frames and send the TFS frames to total R of RF bands according to a TFS scheduling.
  • Each RF band can be individually interleaved in frequency domain by frequency domain interleaver (404a, b) and can become robust against frequency selective fading.
  • Ref Reference Signals
  • PL Physical Layer
  • pilots can be inserted when the TFS frame is built by Ref/PL Signal (405).
  • Fig. 5 shows an example of an SP (Scattered Pilot) for SFN (Single Frequency
  • a single SFN receiver is receiving signals from total eight of transmitters.
  • the location of numbered sub-carrier is a location of SP.
  • Each number represents corresponding index of a transmitter.
  • SPs for transmitters of index 1 through 4 and SPs for transmitters of index 5 through 8 can be alternatively transmitted to a different OFDM symbol.
  • Signals with total four of structures can be transmitted at a period of eight OFDM symbols.
  • the distances between identical pilots are given as Dt for time domain and Df for frequency domain. Effective distances Dti and Dfi can be obtained after interpolation in each domain.
  • the above parameters are parameters that can be determined by Doppler speed and delay spread regarding system channel estimation.
  • Fig. 5 shows an example of a case where Dt is 8, Dti is 2, Df is 4*K, and Dfi is 1*K, assuming that the distance between effective pilot position in frequency domain equals k, or k sub- carriers.
  • Fig. 6 shows an example of a scattered pilot structure with different parameters. Dfi has become 2*K or doubled from Fig. 5 and Dt has become 4 or shrank in half from Fig. 5. This means limiting a channel delay spread in half but instead, allowing increasing a Doppler speed of a channel twice from Fig. 5.
  • Fig. 7 shows an example of expanding Dfi even further to 4*K or four times from Fig. 5 and reducing Dt to 2 or one fourth from Fig. 5.
  • the above SPs are pilots for estimating channel path from one transmitter to a receiver.
  • scattered adjacent pilot SAP
  • the circles shown in Fig. 8 represent SPs and the hexagons represent SAPs. Each number is an index of a transmitter.
  • SAPs can be transmitted to subcarriers adjacent to each other, thus, delay spread to a maximum symbol length can be estimated.
  • a typically used ratio of guard interval is considered, it can be seen that a relative echo delay between transmitters in SFN can be estimated without difficulty.
  • Fig. 8 shows that each SAP is transmitted in a scattered pattern in a frequency domain.
  • each Doppler speed and delay spread can be determined by distances between SAPs in time and frequency domains.
  • SAPs can be transmitted at an appropriate interval in a frequency domain while overhead by pilots and robustness of channel estimation are being considered.
  • When SAPs are transmitted in a scattered pilot structure unlike continual pilot where SAPs are transmitted with an identical subcarrier index, more robust characteristics can be realized for frequency selective channel.
  • SAPs corresponding to a group of the transmitters and SAPs corresponding to another group of the transmitters can be inserted alternatively to different symbols.
  • a distance between two SAPs having an identical index of the transmitter can be varied in a time domain, in a frequency domain, or in both domains.
  • Fig. 9 is an example which shows an improved robustness against frequency selective fading from Fig. 8. Specifically, two SAPs are interleaved into one SAP to improve robustness against frequency selective fading. As shown in the figure, if a time domain interleaving is performed, SAPs can be obtained for total eight of sub- carriers, thus, channel estimation can be improved twice.
  • Fig. 10 shows an example of interleaving three SAP groups to improve a robustness three times against frequency selective fading.
  • Fig. 11 shows an example of interleaving four SAP groups to improve a robustness four times against frequency selective fading.
  • Fig. 12 shows an arrangement of SAPs where each SAP corresponding to a pair of transmitters (i.e., 1,2,3,4 and 5,6,7,8 transmitters) are included in a same symbol.
  • each SAP corresponding to a pair of transmitters i.e., 1,2,3,4 and 5,6,7,8 transmitters
  • at least two different kind of the SAP having interleaved pilots corresponding to different index of the transmitter can be inserted into a same symbol to exhibit a scattered pattern in a frequency domain.
  • the robustness against frequency selective fading is same as that of Fig. 11, but a Doppler speed can be improved twice because SAP can be transmitted for each symbol for all transmitters.
  • Fig. 13 shows the same robustness as in Fig. 12.
  • an estimation according to Doppler speed can be improved because an SAP can be obtained for each symbol without time interleaving.
  • at least two different kind of the SAP having interleaved pilots corresponding to different index of the transmitter can be inserted into a same symbol to exhibit a structure where the inserted pilots having identical index of the transmitter are inserted in a same subcarrier location in a time domain.
  • carrier frequency offset or common phase offset can be estimated.
  • Fig. 14 shows an example of MIMO/MISO Encoder.
  • MIMO/MISO Encoder (501) applies MIMO/MISO method to obtain an additional diversity gain or payload gain.
  • MIMO/MISO Encoder can output signals for total A of antennas.
  • MIMO encoding can be performed individually on total A of antenna signals for each RF band among total R of RF bands.
  • A is equal to or greater than 1.
  • Fig. 15 shows an example of a modulator, specifically an example of an OFDM modulator.
  • PAPR Peak- to- Average Power Ratio
  • IFFT 602
  • PAPR reduction 2 603
  • ACE Active Constellation Extension
  • a tone reservation can be used for the PAPR reduction 2 (603).
  • guard interval 604 can be inserted.
  • Fig. 16 shows an example of the analog processor. Output of each modulator can be converted to an analog-domain signal by a DAC (Digital to Analog Conversion) (701), then can be transmitted to antenna after up-conversion (702). Analog filtering (703) can be performed.
  • DAC Digital to Analog Conversion
  • 703 Analog filtering
  • Fig. 17 shows an example of a TFS-OFDM receiver.
  • AFE Analog Front End
  • demodulators 802a,b
  • MIMO/MISO Decoder 803
  • Frame parser 804
  • BICM decoder 805
  • output processor 806
  • Fig. 18 shows an example of an AFE (Analog Front End).
  • FH Frequency
  • Hopping-tuner (901) can perform a frequency hopping and tune signals according to inputted RF center frequency. After down-conversion (902), signals can be converted to digital signals by ADC (Analog to Digital Conversion) (903).
  • ADC Analog to Digital Conversion
  • Fig. 19 shows an example of a demodulator, specifically an OFDM demodulator.
  • TFS detector (1001) can detect TFS signals in a received digital signal.
  • Channel Estimation (1005) can estimate distortion in a transmission channel based on pilot signals. Based on the estimated distortion, Channel Equalization (1006) can compensate distortion in the transmission channel.
  • PL Physical Layer
  • Fig. 20 shows an example of a channel estimation.
  • SP and SAP pilot synchronization can be performed on the FFT output.
  • pilot structure is detected by Pilot Detector (A-IOOl)
  • pilot demux (A-1002) can separate signals into SPs and SAPs.
  • Natural echo estimator (A- 1003a) can estimate distance from each transmitter to a receiver based on SPs.
  • Artificial echo estimator (A- 1003b) can estimate relative distances between transmitters and a receiver based on SAPs.
  • Two estimated channel profiles can be merged into a single channel profile by channel profile merger (A- 1004).
  • Resulting data can be used for a frequency response of a channel by a channel equalizer or can be transmitted to a synchronization logic to be used for performing a time sync after channel impulse response is estimated.
  • Fig. 21 shows an example of MIMO/MISO decoder. Diversity and multiplexing gain can be obtained from data received from total B of antennas. For MIMO, B is greater than 1. For MISO, B is 1.
  • Fig. 22 shows an example of a Frame parser.
  • Total R of the inputted RF bands data can undergo frequency deinterleaving (1201a, b), then can be reconstructed into datastream by TFS frame parser for each PLP (Physical Layer Path) according to a TFS scheduling.
  • PLP Physical Layer Path
  • input data for BICM decoder can be obtained by using time domain deinterleaver (1203a, b) and QAM demapper (1204a, b).
  • hybrid QAM demapper can be used as the QAM demapper.
  • FIG. 23 shows an example of a BICM decoder.
  • Inner deinterleaver (1301) and outer deinterleaver (1303) can convert burst errors in a transmission channel into random errors.
  • Inner decoder (1302) and outer decoder (1304) can correct errors in the transmission channel.
  • Fig. 24 shows an example of an output processor.
  • BB Baseband
  • (1401a ⁇ d) can reconstruct input data into total P of PLP data.
  • Service mergers (1402a, b) can merge data into a single TS (Transport Stream) and a single GSE stream.
  • TS-demux (1403a) can reconstruct original TS.
  • GSE Decapsulation (1403b) can reconstruct generic stream.

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  • Engineering & Computer Science (AREA)
  • Signal Processing (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Radio Transmission System (AREA)
  • Radar Systems Or Details Thereof (AREA)

Abstract

The present invention relates to methods of transmitting signals, a receiver, and methods of receiving signals. In particular, the present invention relates to methods of transmitting signals having pilots exhibiting a scattered pilot pattern, wherein each pilot of the scattered pilot pattern corresponds to an index of each transmitter among a predetermined number of transmitters. In addition, the present invention relates to a receiver performing echo estimations based on scattered pilots (SP) and scattered adjacent pilots (SAPs) inserted in received symbols, wherein the SAPs comprise a plurality of pilot groups having an identical index of a transmitter among a predetermined number of transmitters structured in the symbols exhibiting a scattered pattern in a frequency domain.

Description

Description
SYSTEM FOR TRANSMITTING AND RECEIVING SIGNALS
Technical Field
[1] The present application claims the benefit of priority under 35 U.S.C. 119 of U.S. provisional patent application No. 60/971,256 filed on Sep. 10, 2007, which is hereby expressly incorporated by reference.
[2] The present invention relates to efficient transmitter and receiver for an OFDM
(Orthogonal Frequency Division Multiplexing) system including a TFS (Time-Frequency Slicing) in an SFN (Single Frequency Network) environment. Background Art
[3] TFS (Time Frequency Slicing) technique has been introduced for broadcasting.
When a TFS is used, a single service can be transmitted through multiple RF (Radio Frequency) channels on a two-dimensional time-frequency space.
[4] OFDM (Orthogonal Frequency Division Multiplexing) is a frequency-division multiplexing (FDM) scheme utilized as a digital multi-carrier modulation method. A large number of closely-spaced orthogonal sub-carriers are used to carry data. The data are divided into several parallel data streams or channels, one for each sub-carrier. Each sub-carrier is modulated with a conventional modulation scheme (such as quadrature amplitude modulation or phase shift keying) at a low symbol rate, maintaining total data rates similar to conventional single-carrier modulation schemes in the same bandwidth.
[5] OFDM has developed into a popular scheme for wideband digital communication, whether wireless or over copper wires, used in applications such as digital television and audio broadcasting, wireless networking and broadband internet access.
[6] When TFS, which uses multiple RF bands for each transmitter is combined with
OFDM, frequency diversity gain and statistical multiplexing gain can be obtained, thus, resources can be efficiently utilized.
[7] In an SFN (Single Frequency Network), a specific frequency is used for a specific service as opposed to a multi- frequency network where multiple frequencies can be used for a same service.
Disclosure of Invention
Technical Problem
[8] It is, therefore, an object of the present invention to provide efficient transmitter and receiver for an OFDM (Orthogonal Frequency Division Multiplexing) system including TFS (Time-Frequency Slicing). More specifically, the present invention provides a pilot structure for an efficient channel estimation in an SFN (Single Frequency Network) environment and for reducing an overhead by pilots. In addition, if a pilot is assigned for each transmitter in an SFN environment, transmission channel can be efficiently estimated and overhead by pilots can be reduced. Technical Solution
[9] According to an aspect of the present invention, there is provided a method of transmitting signals for OFDM system including TFS in an SFN environment comprising: encoding frames made of bitstreams; transforming the encoded frames into symbols; inserting pilots into the symbols to exhibit a scattered pilot pattern, wherein each pilot of the scattered pilot pattern corresponds to an index of each transmitter among a predetermined number of transmitters; and encoding the pilots inserted symbols into a multiple or a single signal.
[10] According to another aspect of the present invention, there is provided a receiver for OFDM system including TFS in an SFN environment comprising: a demodulator configured to perform echo estimations based on scattered pilots (SP) and scattered adjacent pilots (SAPs) on received symbols, wherein the SAPs comprise a plurality of pilot groups having an identical index of a transmitter among a predetermined number of transmitters structured in the symbols exhibiting a scattered pattern in a frequency domain; a decoder configured to transform the symbols into multiple data; and a frame parser configured to transform the multiple data into bitstreams.
[11] According to yet another aspect of the present invention, there is provided a method of receiving signals for OFDM system including TFS in an SFN environment comprising: performing echo estimations based on scattered pilots (SP) and scattered adjacent pilots (SAPs) on received symbols, wherein the SAPs comprise a plurality of pilot groups having an identical index of a transmitter among a predetermined number of transmitters structured in the symbols exhibiting a scattered pattern in a frequency domain; transforming the symbols into multiple data; and transforming the multiple data into bitstreams.
[12] It is to be understood that both the foregoing general description and the following detailed description of the present invention are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.
[13] Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objectives and other advantages of the invention may be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
Advantageous Effects [14] According to the present invention, it is possible to provide efficient transmitter and receiver for an OFDM (Orthogonal Frequency Division Multiplexing) system including TFS (Time-Frequency Slicing). Brief Description of the Drawings
[15] The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the principle of the invention. In the drawings:
[16] Fig. 1 is a block diagram of an example of a TFS (Time Frequency Slicing)-OFDM
(Orthogonal Frequency Division Multiplexing) transmitter.
[17] Fig. 2 is a block diagram of an example of the input processor shown in the Fig. 1.
[18] Fig. 3 is a block diagram of an example of the BICM (Bit-Interleaved Coding and
Modulation) shown in Fig. 1.
[19] Fig. 4 is a block diagram of an example of the Frame Builder shown in Fig. 1.
[20] Fig. 5 is a first example of a scattered pilot structure for an SFN (Single Frequency
Network) environment.
[21] Fig. 6 is a second example of a scattered pilot structure for an SFN environment.
[22] Fig. 7 is a third example of a scattered pilot structure for an SFN environment.
[23] Fig. 8 is a first example of a scattered adjacent pilot structure for an SFN environment.
[24] Fig. 9 is a second example of a scattered adjacent pilot structure for an SFN environment.
[25] Fig. 10 is a third example of a scattered adjacent pilot structure for an SFN environment.
[26] Fig. 11 is a fourth example of a scattered adjacent pilot structure for an SFN environment.
[27] Fig. 12 is a fith example of a scattered adjacent pilot structure for an SFN environment.
[28] Fig. 13 is a sixth example of a scattered adjacent pilot structure for an SFN environment.
[29] Fig. 14 is a block diagram of an example of the MIMO/MISO decoder shown in
Fig. 1.
[30] Fig. 15 is a block diagram of an example of the modulator, specifically an example of an OFDM modulator.
[31] Fig. 16 is a block diagram of an example of the analog processor shown in Fig. 1.
[32] Fig. 17 is a block diagram of an example of a TFS-OFDM receiver.
[33] Fig. 18 is a block diagram of an example of the AFE (Analog Front End) shown in Fig. 17.
[34] Fig. 19 is a block diagram of an example of the demodulator, specifically an OFDM demodulator.
[35] Fig. 20 is a block diagram of an example of a channel estimation.
[36] Fig. 21 is a block diagram of an example of the MIMO/MISO decoder shown in
Fig. 17.
[37] Fig. 22 is a block diagram of an example of the frame parser shown in Fig. 17.
[38] Fig. 23 is a block diagram of an example of the BICM decoder shown in Fig. 17.
[39] Fig. 24 is a block diagram of an example of the output processor shown in Fig. 17.
Best Mode for Carrying Out the Invention
[40] Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.
[41] Fig. 1 shows an example of a proposed transmitter for an OFDM (Orthogonal
Frequency Division Multiplexing) including TFS (Time Frequency Slicing). A multiple MPEG2-TS (Transport Stream) and a multiple Generic stream can be inputted into a TFS transmitter. The input processor (101) can split the inputted streams into a multiple output signals for a multiple PLP (Physical Layer Path). The BICM (Bit- Interleaved Coding and Modulation) (102) can encode and interleave the PLP individually. The frame builder (103) can transform the PLP into total R of RF bands. MIMO (Multiple-Input Multiple- Output)/MIS O (Multiple-Input Single- Output) (104) technique can be applied for each RF band. Each RF band for each antenna can be individually modulated by the modulator (105a, b) and can be transmitted to antennas after being converted to an analog signal by the analog processor (106a, b). Mode for the Invention
[42] Fig. 2 is an example of the input processor. MPEG-TS (Transport Stream) can be multiplexed into a single output through TS-MUX (201a) and Generic streams (Internet protocol) can be transformed into a single output through GSE (General Stream Encapsulation) (201b). Each output from the TS-MUX and GSE can be split for multiple services by the service splitter (202a, b). PLP is a processing of each service. Each PLP can be transformed into a frame by the BB (Baseband) Frame (103a~d).
[43] Fig. 3 is an example of the BICM. The Outer encoder (301) and the inner encoder
(303) can add redundancy for error correction in a transmission channel. The outer in- terleaver (302) and the inner interleaver (304) can interleave data randomly to mitigate burst errors. [44] Fig. 4 is an example of the frame builder. QAM mapper (401a, b) can transform inputted bits into QAM symbols. Hybrid QAM can be used. Time domain interleaver (402a, b) can interleave data in time domain to make the data be robust against burst error. At this point, an effect of interleaving many RF bands can be obtained in a physical channel because the data are going to be transmitted to a multiple RF bands. TFS frame builder (403) can split inputted data to form TFS frames and send the TFS frames to total R of RF bands according to a TFS scheduling. Each RF band can be individually interleaved in frequency domain by frequency domain interleaver (404a, b) and can become robust against frequency selective fading. Ref (Reference Signals), PL (Physical Layer) signaling, and pilots can be inserted when the TFS frame is built by Ref/PL Signal (405).
[45] Fig. 5 shows an example of an SP (Scattered Pilot) for SFN (Single Frequency
Network). Here, a situation is assumed where a single SFN receiver is receiving signals from total eight of transmitters. The location of numbered sub-carrier is a location of SP. Each number represents corresponding index of a transmitter. SPs for transmitters of index 1 through 4 and SPs for transmitters of index 5 through 8 can be alternatively transmitted to a different OFDM symbol. Signals with total four of structures can be transmitted at a period of eight OFDM symbols.
[46] The distances between identical pilots are given as Dt for time domain and Df for frequency domain. Effective distances Dti and Dfi can be obtained after interpolation in each domain. The above parameters are parameters that can be determined by Doppler speed and delay spread regarding system channel estimation. Fig. 5 shows an example of a case where Dt is 8, Dti is 2, Df is 4*K, and Dfi is 1*K, assuming that the distance between effective pilot position in frequency domain equals k, or k sub- carriers.
[47] Fig. 6 shows an example of a scattered pilot structure with different parameters. Dfi has become 2*K or doubled from Fig. 5 and Dt has become 4 or shrank in half from Fig. 5. This means limiting a channel delay spread in half but instead, allowing increasing a Doppler speed of a channel twice from Fig. 5. Fig. 7 shows an example of expanding Dfi even further to 4*K or four times from Fig. 5 and reducing Dt to 2 or one fourth from Fig. 5.
[48] As shown in Figs. 5 though 7, scattered pilots corresponding to a group of the transmitters and scattered pilots corresponding to another group of the transmitters can be inserted alternatively to different symbols.
[49] The above SPs are pilots for estimating channel path from one transmitter to a receiver. For estimating a relative path differences from multiple transmitters to a receiver in SFN, scattered adjacent pilot (SAP) as shown in Fig. 8 is proposed. The circles shown in Fig. 8 represent SPs and the hexagons represent SAPs. Each number is an index of a transmitter. As shown in the figure, SAPs can be transmitted to subcarriers adjacent to each other, thus, delay spread to a maximum symbol length can be estimated. When a typically used ratio of guard interval is considered, it can be seen that a relative echo delay between transmitters in SFN can be estimated without difficulty.
[50] Fig. 8 shows that each SAP is transmitted in a scattered pattern in a frequency domain. Here, as shown in Fig. 5, each Doppler speed and delay spread can be determined by distances between SAPs in time and frequency domains. SAPs can be transmitted at an appropriate interval in a frequency domain while overhead by pilots and robustness of channel estimation are being considered. When SAPs are transmitted in a scattered pilot structure, unlike continual pilot where SAPs are transmitted with an identical subcarrier index, more robust characteristics can be realized for frequency selective channel.
[51] Analogous to SPs shown in Figs. 5 though 7, SAPs corresponding to a group of the transmitters and SAPs corresponding to another group of the transmitters can be inserted alternatively to different symbols. In addition, a distance between two SAPs having an identical index of the transmitter can be varied in a time domain, in a frequency domain, or in both domains.
[52] Fig. 9 is an example which shows an improved robustness against frequency selective fading from Fig. 8. Specifically, two SAPs are interleaved into one SAP to improve robustness against frequency selective fading. As shown in the figure, if a time domain interleaving is performed, SAPs can be obtained for total eight of sub- carriers, thus, channel estimation can be improved twice.
[53] Fig. 10 shows an example of interleaving three SAP groups to improve a robustness three times against frequency selective fading. Fig. 11 shows an example of interleaving four SAP groups to improve a robustness four times against frequency selective fading.
[54] Fig. 12 shows an arrangement of SAPs where each SAP corresponding to a pair of transmitters (i.e., 1,2,3,4 and 5,6,7,8 transmitters) are included in a same symbol. In other words, at least two different kind of the SAP having interleaved pilots corresponding to different index of the transmitter can be inserted into a same symbol to exhibit a scattered pattern in a frequency domain. In this example, the robustness against frequency selective fading is same as that of Fig. 11, but a Doppler speed can be improved twice because SAP can be transmitted for each symbol for all transmitters.
[55] Fig. 13 shows the same robustness as in Fig. 12. In this arrangement where SAPs are arranged to exhibit a continual pilot structure, not a scattered pilot structure, an estimation according to Doppler speed can be improved because an SAP can be obtained for each symbol without time interleaving. In other words, at least two different kind of the SAP having interleaved pilots corresponding to different index of the transmitter can be inserted into a same symbol to exhibit a structure where the inserted pilots having identical index of the transmitter are inserted in a same subcarrier location in a time domain. In addition, by using this continual pilot structure, carrier frequency offset or common phase offset can be estimated.
[56] Fig. 14 shows an example of MIMO/MISO Encoder. MIMO/MISO Encoder (501) applies MIMO/MISO method to obtain an additional diversity gain or payload gain. MIMO/MISO Encoder can output signals for total A of antennas. MIMO encoding can be performed individually on total A of antenna signals for each RF band among total R of RF bands. A is equal to or greater than 1.
[57] Fig. 15 shows an example of a modulator, specifically an example of an OFDM modulator. PAPR (Peak- to- Average Power Ratio) reduction 1 (601) can be performed on Antenna (m) signals of RF (n) bands. IFFT (602) can be performed for OFDM demodulation. PAPR reduction 2 (603) can be performed after the IFFT. ACE (Active Constellation Extension) and a tone reservation can be used for the PAPR reduction 2 (603). Lastly, guard interval (604) can be inserted.
[58] Fig. 16 shows an example of the analog processor. Output of each modulator can be converted to an analog-domain signal by a DAC (Digital to Analog Conversion) (701), then can be transmitted to antenna after up-conversion (702). Analog filtering (703) can be performed.
[59] Fig. 17 shows an example of a TFS-OFDM receiver. When total R of RF bands are used for TFS system, received signals by AFE (Analog Front End) (801a,b) can be demodulated by demodulators (802a,b), then can be decoded by MIMO/MISO Decoder (803) to obtain diversity gain. Frame parser (804) can restore multiple PLP signals from received TFS frame. BICM decoder (805) can correct errors in a transmission channel. Finally, output processor (806) can restore signals according to necessary format.
[60] Fig. 18 shows an example of an AFE (Analog Front End). FH (Frequency
Hopping)-tuner (901) can perform a frequency hopping and tune signals according to inputted RF center frequency. After down-conversion (902), signals can be converted to digital signals by ADC (Analog to Digital Conversion) (903).
[61] Fig. 19 shows an example of a demodulator, specifically an OFDM demodulator.
TFS detector (1001) can detect TFS signals in a received digital signal. TFS sync
(1002) can synchronize in time and frequency domains. After GI (Guard Interval)
(1003) is removed, symbols in frequency domain can be obtained by performing FFT
(1004) for OFDM demodulation. Channel Estimation (1005) can estimate distortion in a transmission channel based on pilot signals. Based on the estimated distortion, Channel Equalization (1006) can compensate distortion in the transmission channel. Finally, PL (Physical Layer) signaling information can be extracted from equalized data and can be transmitted to a system controller.
[62] Fig. 20 shows an example of a channel estimation. SP and SAP pilot synchronization can be performed on the FFT output. After pilot structure is detected by Pilot Detector (A-IOOl), pilot demux (A-1002) can separate signals into SPs and SAPs. Natural echo estimator (A- 1003a) can estimate distance from each transmitter to a receiver based on SPs. Artificial echo estimator (A- 1003b) can estimate relative distances between transmitters and a receiver based on SAPs. Two estimated channel profiles can be merged into a single channel profile by channel profile merger (A- 1004). Resulting data can be used for a frequency response of a channel by a channel equalizer or can be transmitted to a synchronization logic to be used for performing a time sync after channel impulse response is estimated.
[63] Fig. 21 shows an example of MIMO/MISO decoder. Diversity and multiplexing gain can be obtained from data received from total B of antennas. For MIMO, B is greater than 1. For MISO, B is 1.
[64] Fig. 22 shows an example of a Frame parser. Total R of the inputted RF bands data can undergo frequency deinterleaving (1201a, b), then can be reconstructed into datastream by TFS frame parser for each PLP (Physical Layer Path) according to a TFS scheduling. For each PLP, input data for BICM decoder can be obtained by using time domain deinterleaver (1203a, b) and QAM demapper (1204a, b). At this point, hybrid QAM demapper can be used as the QAM demapper.
[65] Fig. 23 shows an example of a BICM decoder. Inner deinterleaver (1301) and outer deinterleaver (1303) can convert burst errors in a transmission channel into random errors. Inner decoder (1302) and outer decoder (1304) can correct errors in the transmission channel.
[66] Fig. 24 shows an example of an output processor. BB (Baseband) frame parser
(1401a~d) can reconstruct input data into total P of PLP data. Service mergers (1402a, b) can merge data into a single TS (Transport Stream) and a single GSE stream. For TS, TS-demux (1403a) can reconstruct original TS. For GSE stream, GSE Decapsulation (1403b) can reconstruct generic stream.
[67] It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention. Thus, it is intended that the present invention covers the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.
[68]
[69]

Claims

Claims
[1] A method of transmitting signals for an OFDM (Orthogonal Frequency Division
Multiplexing) system including TFS (Time Frequency Slicing) in an SFN (Single Frequency Network) environment, comprising: encoding frames made of bitstreams; transforming the encoded frames into symbols; inserting pilots into the symbols to exhibit a scattered pilot pattern, wherein each pilot of the scattered pilot pattern corresponds to an index of one of transmitters among a predetermined number of the transmitters; and encoding the pilots inserted symbols into a multiple signal or a single signal.
[2] The method according to claim 1, wherein inserting the pilots into the symbols further comprises: varying a distance between two scattered pilots having an index that corresponds to a same transmitter in a time domain and/or in a frequency domain.
[3] The method according to claim 1, wherein inserting the pilots into the symbols further comprises: forming an SAP (Scattered Adjacent Pilot) by grouping pilots having an index that corresponds to a same transmitter together and inserting a plurality of the formed pilot group into the symbols to exhibit a scattered pattern in a frequency domain.
[4] The method according to claim 3, wherein inserting the pilots into the symbols further comprises: interleaving a plurality of the SAP to form an SAP having interleaved pilots, wherein each of the interleaved pilot corresponds to an index of a transmitter that is different from that of every other interleaved pilot.
[5] The method according to claim 3, wherein inserting the pilots into the symbols further comprises: inserting at least two different kinds of the SAP having interleaved pilots corresponding to different index of the transmitter into a symbol to exhibit a structure where the inserted pilots having an index that corresponds to the same transmitter are located in a same subcarrier in a time domain.
[6] A receiver for an OFDM (Orthogonal Frequency Division Multiplexing) system including TFS (Time Frequency Slicing) in an SFN (Single Frequency Network) environment, comprising: a demodulator (802a) configured to perform echo estimations based on scattered pilots (SP) and scattered adjacent pilots (SAPs) on received symbols, wherein the SAPs comprise a plurality of pilot groups having an index that corresponds to a same transmitter among a predetermined number of the transmitters structured in the received symbols exhibiting a scattered pattern in a frequency domain; a MIMO/MISO decoder (803) configured to decode the received symbols into multiple symbolstreams or a single symbolsteam; and a frame parser (804) configured to restore the multiple symbolstreams or the single symbolsteam into service symbolstreams.
[7] The receiver according to claim 6, wherein the demodulator (802a) comprises: a pilot detector (A-IOOl) configured to detect pilots from the received symbols; and a pilot demux (A- 1002) configured to demux the detected pilots into the SPs and the SAPs for the echo estimations.
[8] The receiver according to claim 6, wherein each of the SP corresponds to an index of one of the transmitters among a predetermined number of the transmitters.
[9] The receiver according to claim 6, wherein a plurality of the SP are structured in the received symbols such that a distance between two SPs having an index that corresponds to a same transmitter is varied in a time domain and/or in a frequency domain.
[10] The receiver according to claim 6, wherein the SAP has interleaved pilots, wherein each of the interleaved pilot corresponds to an index of a transmitter that is different from that of every other interleaved pilot.
[11] A method of receiving signals for an OFDM (Orthogonal Frequency Division
Multiplexing) system including TFS (Time Frequency Slicing) in an SFN (Single
Frequency Network) environment, comprising: performing echo estimations based on scattered pilots (SP) and scattered adjacent pilots (SAPs) on received symbols, wherein the SAPs comprise a plurality of pilot groups having an index that corresponds to a same transmitter among a predetermined number of the transmitters structured in the received symbols exhibiting a scattered pattern in a frequency domain; decoding the received symbols into multiple symbolstreams or a single symbolsteam; and restoring the multiple symbolstreams or the single symbolsteam into service symbolstreams.
[12] The method according to claim 11, wherein performing the echo estimations comprises: detecting pilots from the received symbols; and demuxing the detected pilots into the SPs and the SAPs for the echo estimations.
[13] The method according to claim 11, wherein performing the echo estimations further comprises: receiving the symbols, wherein the received symbols comprise SPs, wherein each of the SP corresponds to an index of one of transmitters among a predetermined number of the transmitters.
[14] The method according to claim 11, wherein performing the echo estimations further comprises: receiving the symbols, wherein the received symbols comprise SPs, wherein a plurality of the SP are structured in the symbols such that a distance between two SPs having an index that corresponds to a same transmitter is varied in a time domain and/or in a frequency domain.
[15] The method according to claim 11, wherein performing the echo estimations further comprises: receiving the symbols, wherein the received symbols comprise SAPs, wherein the SAP has interleaved pilots, wherein each of the interleaved pilot corresponds to an index of a transmitter that is different from that of every other interleaved pilot.
EP08793741A 2007-09-10 2008-09-09 System for transmitting and receiving signals Withdrawn EP2195992A4 (en)

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