WO2009084931A1 - Procédé d'établissement de signal de synchronisation dans un système de communications sans fil - Google Patents

Procédé d'établissement de signal de synchronisation dans un système de communications sans fil Download PDF

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Publication number
WO2009084931A1
WO2009084931A1 PCT/KR2008/007902 KR2008007902W WO2009084931A1 WO 2009084931 A1 WO2009084931 A1 WO 2009084931A1 KR 2008007902 W KR2008007902 W KR 2008007902W WO 2009084931 A1 WO2009084931 A1 WO 2009084931A1
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WIPO (PCT)
Prior art keywords
pss
band
synchronization
mbms
dedicated mbms
Prior art date
Application number
PCT/KR2008/007902
Other languages
English (en)
Inventor
Seung Hee Han
Min Seok Noh
Jin Sam Kwak
Hyun Woo Lee
Dong Cheol Kim
Sung Ho Moon
Wook Bong Lee
Yeong Hyeon Kwon
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
Priority claimed from KR1020080072848A external-priority patent/KR101417089B1/ko
Application filed by Lg Electronics Inc. filed Critical Lg Electronics Inc.
Priority to US12/811,465 priority Critical patent/US8625526B2/en
Publication of WO2009084931A1 publication Critical patent/WO2009084931A1/fr

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Classifications

    • 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
    • H04L27/2647—Arrangements specific to the receiver only
    • H04L27/2655—Synchronisation arrangements
    • 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
    • H04L27/2655—Synchronisation arrangements
    • H04L27/2657—Carrier synchronisation
    • 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
    • H04L27/2655—Synchronisation arrangements
    • H04L27/2662—Symbol synchronisation

Definitions

  • the present invention relates to wireless communications, and more particularly, to a method for obtaining a synchronization signal for a multimedia broadcast multicast service (MBMS).
  • MBMS multimedia broadcast multicast service
  • a multimedia broadcast multicast service is a service in which a plurality of base stations (BSs) transmit the same downlink signal in a single frequency network (SFN) system.
  • the MBMS can obtain an SFN combining gain between cells by performing a multicast broadcast single frequency network (MBSFN) operation.
  • the SFN combining gain denotes a diversity gain obtained in a receiving end by transmitting the same information for each cell without an extra operation.
  • the plurality of BSs transmit the same signals, the same signals transmitted from multiple cells act as self signals instead of acting as inter-cell interference. As a result, the same effect as multipath fading is produced, and thus a frequency diversity gain and a macro diversity gain can be obtained.
  • a unicast service is a service in which a user equipment (UE) accesses to a BS to transmit/receive data from/to the BS.
  • UE user equipment
  • a MBMS may be provided together with the unicast service, or only the MBMS may be provided.
  • a dedicated MBMS When only the MBMS is provided, it is called a dedicated MBMS.
  • synchronization signals are transmitted through a primary synchronization channel (P-SCH) and a secondary synchronization channel (S-SCH).
  • the UE can obtain slot synchronization by using a primary synchronization signal (PSS) transmitted through the P-SCH.
  • PSS primary synchronization signal
  • SSS secondary synchronization signal
  • System configuration information is transmitted through a physical broadcast channel (P-BCH).
  • the UE performs synchronization through the P-SCH and the S-SCH in an initial cell search procedure which is initially performed after power is on and a non-initial cell search procedure which performs handover or neighbor cell measurement.
  • the UE obtains basic system information which is broadcast through the
  • a service provided in a cell may be a unicast service or a dedicated MBMS.
  • a reference signal used in the unicast service has a different structure from that used in the dedicated MBMS.
  • the UE cannot know whether the service provided in the cell is the unicast service or the dedicated MBMS, and thus performs blind detection by estimating channels for both a unicast reference signal and a dedicated MBMS reference signal in a P-BCH decoding process. As a result, an operation time required for obtaining system information by the UE is delayed.
  • the present invention provides a method for obtaining a synchronization signal for a multimedia broadcast multicast service (MBMS).
  • MBMS multimedia broadcast multicast service
  • a method for obtaining a synchronization signal in a wireless communication system includes dividing a full frequency band into a synchronization band for transmission of the synchronization signal and a usual band for transmission of multicast broadcast multimedia service (MBMS) data, and searching for a primary synchronization signal (PSS) for a dedicated MBMS in the synchronization band, and detecting the PSS for the dedicated MBMS through the synchronization band.
  • MBMS multicast broadcast multimedia service
  • a method for transmitting a synchronization signal in a wireless communication system includes transmitting a PSS through a synchronization band having a part of a bandwidth of a full frequency band, and transmitting MBMS data through a usual band excluding the synchronization band from the full frequency band, wherein a root index of the PSS is one of root indices of a plurality of Zadoff-Chu (ZC) sequences selected in an ascending order of a frequency offset sensitivity.
  • ZC Zadoff-Chu
  • a process of obtaining a synchronization signal and system information in a dedicated multimedia broadcast multicast service (MBMS) can be effectively performed, and a single frequency network (SFN) combining gain of broadcasting information received through a physical broadcast channel (P-BCH) can be obtained.
  • SFN single frequency network
  • P-BCH physical broadcast channel
  • FIG. 1 shows a wireless communication system.
  • FIG. 2 shows an exemplary frame for supporting both a unicast service and a multicast broadcast multimedia service (MBMS).
  • MBMS multicast broadcast multimedia service
  • FIG. 3 shows an exemplary structure of a radio frame.
  • FIG. 4 shows another exemplary structure of a radio frame.
  • FIG. 5 shows a radio frame for a dedicated MBMS.
  • FIG. 6 shows an exemplary structure of a reference signal in a subframe for unicast using a normal cyclic prefix (CP).
  • FIG. 7 shows an exemplary structure of a reference signal in a subframe for a dedicated MBMS.
  • FIG. 8 shows a radio frame for a dedicated MBMS according to an embodiment of the present invention.
  • FIG. 10 is a graph showing a frequency offset sensitivity of a PSS generated from a
  • FIG. 11 shows mapping of a ZC sequence according to an embodiment of the present invention.
  • FIG. 12 shows mapping of a ZC sequence according to another embodiment of the present invention.
  • FIG. 13 shows mapping of a ZC sequence according to another embodiment of the present invention.
  • FIG. 14 shows a radio frame for a dedicated MBMS according to another embodiment of the present invention.
  • FIG. 15 shows a radio frame for a dedicated MBMS according to another embodiment of the present invention.
  • FIG. 16 shows a radio frame for a dedicated MBMS according to another embodiment of the present invention.
  • FIG. 17 is a graph showing a frequency offset sensitivity of a PSS generated from a
  • FIG. 18 shows mapping of a ZC sequence according to another embodiment of the present invention.
  • FIG. 19 is a flowchart showing a method for obtaining a synchronization signal and system information according to an embodiment of the present invention.
  • FIG. 1 shows a wireless communication system.
  • the wireless communication system can be widely deployed to provide a variety of communication services, such as voices, packet data, etc.
  • the wireless communication system includes at least one user equipment (UE) 10 and a base station (BS) 20.
  • the UE 10 may be fixed or mobile, and may be referred to as another terminology, such as a mobile station (MS), a user terminal (UT), a subscriber station (SS), a wireless device, etc.
  • the BS 20 is generally a fixed station that communicates with the UE 10 and may be referred to as another terminology, such as a node-B, a base transceiver system (BTS), an access point, etc.
  • BTS base transceiver system
  • a downlink represents a communication link from the BS 20 to the UE 10
  • an uplink represents a communication link from the UE 10 to the BS 20.
  • a transmitter may be a part of the BS 20, and a receiver may be a part of the UE 10.
  • the transmitter may be a part of the UE 10, and the receiver may be a part of the BS 20.
  • the wireless communication system may be an orthogonal frequency division multiplexing (OFDM)/orthogonal frequency division multiple access (OFDMA)-based system.
  • the OFDM uses a plurality of orthogonal subcarriers. Further, the OFDM uses an orthogonality between inverse fast Fourier transform (IFFT) and fast Fourier transform (FFT).
  • IFFT inverse fast Fourier transform
  • FFT fast Fourier transform
  • the transmitter transmits data by performing IFFT.
  • the receiver restores original data by performing FFT on a received signal.
  • the transmitter uses IFFT to combine the plurality of subcarriers, and the receiver uses FFT to split the plurality of subcarriers.
  • the BS 20 can transmit downlink data in a unicast, multicast, or broadcast manner.
  • a unicast service is a service in which the UE 10 accesses to the BS 20 to transmit and receive user-specific data.
  • a multicast service is a service in which two or more UEs 10 accessed to the BS 20 are configured into a UE group to transmit UE group specific data.
  • a broadcast service is a service for transmitting data which needs to be commonly received by all UEs 10 within a cell.
  • the BS 20 can provide a multimedia broadcast multicast service
  • the MBMS is a service in which a plurality of BSs transmit the same downlink data so that the UE can obtain a single frequency network (SFN) combining gain.
  • the MBMS may be provided together with the unicast service or may be provided alone.
  • a service for providing the MBMS alone is referred to as a dedicated MBMS.
  • FIG. 2 shows an exemplary frame for supporting both a unicast service and an
  • the frame for supporting the MBMS in the unicast service includes a unicast region for the unicast service and an MBMS region for the MBMS.
  • the unicast region and the MBMS region may be multiplexed using a time division multiplexing (TDM) scheme in which the regions are divided in a time domain.
  • TDM time division multiplexing
  • FDM frequency division multiplexing
  • FIG. 3 shows an exemplary structure of a radio frame.
  • the radio frame uses a normal cyclic prefix (CP). This may be found in sections 4.1 and 6.11 in the 3GPP TS 36.211 v8.1.0 (2007-11) "Physical channel and modulation".
  • CP normal cyclic prefix
  • the radio frame may consist of 10 subframes, and one subframe may include two slots.
  • One slot may include a plurality of OFDM symbols in a time domain. The number of OFDM symbols included in one slot may be determined variously according to a CP structure.
  • one slot may include 7 OFDM symbols.
  • a primary synchronized signal is transmitted through a last OFDM symbol in each of a 0 slot and a 10 slot. The same PSS is transmitted through the two OFDM symbols.
  • the PSS is used to obtain time domain synchronization and/or frequency domain synchronization such as OFDM symbol synchronization, slot synchronization, etc.
  • a Zadoff-Chu (ZC) sequence may be used for the PSS.
  • the wireless communication system has at least one PSS.
  • a secondary synchronization signal is transmitted through an immediately previous OFDM symbol of the last OFDM symbol in each of the 0 slot and the 10 slot.
  • the SSS and the PSS may be transmitted through contiguous OFDM symbols. Different SSSs are transmitted through the two OFDM symbols.
  • the SSS is used to obtain frame synchronization and/or CP configuration of a cell, that is, usage information of a normal CP or an extended CP.
  • An m-sequence may be used for the SSS.
  • One OFDM symbol includes two m-sequences. For example, if one OFDM symbol includes 63 subcarriers, two m-sequences, each with a length of 31, are mapped to one OFDM symbol.
  • a physical-broadcast channel (P-BCH) is located in a 0 subframe in the radio frame.
  • the P-BCH starts from a 3 rd OFDM symbol (starting from a 0 th OFDM symbol) of the ⁇ ' subframe and occupies 4 OFDM symbols excluding the PSS and the SSS.
  • the P- BCH is used to obtain basic system configuration information of a corresponding BS.
  • the P-BCH may have a period of 40 ms.
  • FIG. 4 shows another exemplary structure of a radio frame.
  • the radio frame uses an extended CP.
  • a PSS is transmitted through a last OFDM symbol in each of a 0 slot and a 10 slot
  • an SSS is transmitted through an im- mediately previous OFDM symbol of the last OFDM symbol in each of the 0 slot and the 10 slot.
  • the P-BCH is located in a 0 subframe in the radio frame. The P-BCH starts from a 3 r OFDM symbol of the 0 subframe and occupies four OFDM symbols excluding the PSS and the SSS.
  • a ZC sequence may be used as the PSS.
  • An m-sequence may be used as the SSS.
  • Equation 2 shows that the ZC sequence always has a size of 1.
  • Equation 3 shows that auto-correlation of the CAZAC sequence is indicated by a Dirac-delta function. The auto-correlation is based on circular correlation.
  • Equation 4 shows that cross correlation is always constant.
  • the m-sequence is one of pseudo-noise (PN) sequences.
  • the PN sequence can be reproduced and shows a characteristic similar to a random sequence.
  • the PN sequence is characterized as follows. (I) A repetition period is sufficiently long. If a sequence has an infinitely long repetition period, the sequence is a random sequence. (2) The number of Os is close to the number of Is within one period.
  • a portion having a run length of 1 is 1/2, a portion having a run length of 2 is 1/4, a portion having a run length of 3 is 1/8, and so on.
  • the run length is defined as the number of contiguous identical symbols.
  • a cross-correlation between sequences within one period is significantly small.
  • a whole sequence cannot be reproduced by using small sequence pieces.
  • Reproducing is possible by using a proper reproducing algorithm.
  • a PN sequence includes an m-sequence, a gold sequence, a Kasami sequence, etc.
  • the m-sequence has an additional characteristic in which a side lobe of a periodic auto-correlation is -1.
  • the PSS and the SSS are used to obtain physical-layer cell identities (IDs).
  • the physical-layer cell ID can be expressed by 168 physical-layer ID groups and 3 physical-layer IDs belonging to each physical-layer ID group. That is, a total number of physical-layer cell IDs is 504, and the physical-layer cell IDs are expressed by a physical-layer ID group in the range of 0 to 167 and physical-layer IDs included in each physical-layer cell ID and having a range of 0 to 2.
  • the PSS may use 3 ZC sequence root indices indicating the physical-layer IDs.
  • the SSS may use 168 m- sequence indices indicating the physical-layer cell ID groups.
  • a root index u indicating a physical-layer ID of a physical-layer cell ID group is as shown in Table 1.
  • Table 1 [Table 1] [Table ]
  • a BS selects one of the 3 PSSs and transmits the selected PSS by carrying it on a last OFDM symbol in each of a 0 slot and a 10 slot.
  • a sequence for the SSS can be generated by Equation 6. [65] Math Figure 6 [Math.6] c o (n) in slot 0 c o (n) in slot 10 in) in slot 0 , (n) in slot 10
  • s (m) (n) denotes the SSS
  • c (n) denotes a PSS based-scrambling code
  • z z
  • (m) (n) denotes a segment based scrambling code.
  • the SSS is scrambled into two scrambling codes.
  • Equation 7 shows a generating polynomial of an m-sequence for generating the SSS and PSS-based scrambling code and the segment based scrambling code.
  • the SSS and PSS-based scrambling code and the segment based scrambling code use a cyclic shift version of a sequence generated from the generating polynomial of the m- sequence.
  • the MBMS cannot be supported in a 0 subframe and a 5 subframe which are assigned with the PSS, the SSS, and the P-BCH and in which a unicast UE performs initial cell search and non-initial cell search procedures and obtains broadcast information.
  • the PSS, the SSS, and the P-BCH are channels used by the UE to perform initial synchronization acquisition, cell search, and broadcast information acquisition and must be transmitted within 1.4 MHz that is a minimum unit of measurable bands.
  • 73 subcarriers including the DC subcarrier are included in a range of 1.4 MHz.
  • FIG. 5 shows a radio frame for a dedicated MBMS.
  • the dedicated MBMS is a service for providing only the MBMS and can obtain a single frequency network (SFN) combining gain by transmitting the same information in all cells.
  • the SFN combining gain denotes a diversity gain obtained by a UE by transmitting the same information for each cell without an extra operation.
  • information obtained through a P-BCH is equally transmitted in all cells, and thus the SFN combining gain can be obtained.
  • the radio frame of FIG. 3 and FIG. 4 can be referred to as a radio frame for unicast.
  • the radio frame for the dedicated MBMS has a different structure from the radio frame for unicast so as to obtain the SFN combining gain.
  • the radio frame for the dedicated MBMS may consist of 10 subframes.
  • One subframe may include two slots.
  • One slot may include three OFDM symbols.
  • a subcarrier has a spacing of
  • a CP size may be 1024 Ts, that is, double of an extended CP size. Therefore, in the radio frame of 10 ms for the dedicated MBMS, one slot includes 3 OFDM symbols.
  • reference signals may be arranged with an interval of one OFDM symbol. For example, the reference signals may be arranged in 1 st , 3 r , and 5 OFDM symbols (starting from a 0 OFDM symbol) within a subframe of 1 ms.
  • the structure of the aforementioned radio frame that is, the radio frame using the normal CP or the radio frame using the extended CP or the radio frame for the dedicated MBMS is for exemplary purposes only, and thus the number of subframes included in the radio frame and the number of slots included in the subframe may change variously.
  • the position or number of OFDM symbols in which the PSS and the SSS are arranged on a slot is for exemplary purposes only, and thus may change variously according to a system.
  • FIG. 6 shows an exemplary structure of a reference signal in a subframe for unicast using a normal CP.
  • FIG. 7 shows an exemplary structure of a reference signal in a subframe for a dedicated MBMS.
  • a resource element is defined with one OFDM symbol and one subcarrier.
  • reference signals are arranged with an interval of 3 resource elements in a time domain and with an interval of 2 resource elements in a frequency domain.
  • the reference signals are arranged with an interval of 2 resource elements in the time domain and with an interval of 2 resource elements in the frequency domain. It can be seen that the unicast reference signal has a different structure from the dedicated MBMS reference signal.
  • a UE In a process of obtaining a synchronization signal by using a PSS and an SSS and in a process of receiving system information through a P-BCH, a UE cannot know whether a unicast type or a dedicated MBMS type is used as a transmission type of a cell. Therefore, in a decoding process of the P-BCH, the UE has to perform blind detection for the two service types by performing channel estimation on both the unicast reference signal and the dedicated MBMS reference signal. As a result, a process of obtaining initial control information (e.g., a synchronization signal and system information) may be delayed, and system complexity may be increased.
  • initial control information e.g., a synchronization signal and system information
  • a synchronization band denotes a frequency band used for the PSS, the SSS, and the P- BCH
  • a usual band denotes a frequency band used to transmit unicast data and/or dedicated MBMS data.
  • the synchronization band may use an intermediate frequency band in a full frequency band.
  • the usual band may use a frequency band excluding the synchronization band in the full frequency band.
  • the synchronization band may have a range of 1.4 MHz around a center frequency of the full frequency band.
  • the position of the synchronization band in the full frequency band is not limited thereto, and thus the synchronization band may use any band in the full frequency band and may use two or more frequency bands.
  • FIG. 8 shows a radio frame for a dedicated MBMS according to an embodiment of the present invention.
  • the radio frame for the dedicated MBMS is divided into a usual band and a synchronization band in a frequency domain.
  • the usual band is used to transmit MBMS data.
  • the synchronization band is used for a PSS, an SSS, and a P- BCH.
  • the usual band and the synchronization band have the same structure in a time domain.
  • the usual band and the synchronization band are multiplexed using a frequency division multiplexing (FDM) scheme.
  • FDM frequency division multiplexing
  • the PSS and the SSS of the synchronization band may have the same definition as in the radio frame supporting unicast. That is, the PSS is mapped to a last OFDM symbol in each of a ⁇ ' slot and a 10 slot, and the SSS is mapped to an immediately previous OFDM symbol in the last OFDM symbol in each of the 0 slot and the 10 slot.
  • the PSS the same sequence is transmitted through two OFDM symbols.
  • the SSS different sequences are transmitted through two OFDM symbols.
  • the number of OFDM symbols in use may be regulated according to information transmitted at the synchronization band.
  • the P- BCH may be determined to start at a 0 OFDM symbol of a 0 subframe and to occupy two OFDM symbols excluding the PSS and the SSS.
  • Reference signals may be arranged in 1 st , 3 r , and 5 OFDM symbols (starting from a ⁇ ' OFDM symbol).
  • the reference signals may be arranged as shown in FIG. 7. Since the usual band and the synchronization band have the same structure in the time domain, the reference signals may be arranged in the SSS and the P-BCH. Symbols of the SSS are mapped by being punctured in a resource element to which the reference signal is arranged. In the P-BCH, symbols of system information are mapped by avoiding a resource element to which the reference signal is arranged. That is, the symbols of the system information are not punctured in the P-BCH.
  • the P-BCH uses 72 subcarriers
  • the P-BCH may use 144 subcarriers (herein, a subcarrier spacing of the dedicated MBMS is half of a subcarrier spacing of unicast) within 1.4 MHz and 288 resource elements in a range of 2 OFDM symbols. That is, in the radio frame for unicast and the radio frame for the dedicated MBMS, the P-BCH can use the same number of resource elements.
  • an index of a PSS for the dedicated MBMS is defined, wherein the PSS for the dedicated MBMS has a different length from a PSS for unicast.
  • a subcarrier spacing is 15 kHz in the radio frame for unicast whereas a subcarrier spacing is 7.5 kHz in the radio frame for the dedicated MBMS.
  • a ZC sequence having a PSS with a length two times higher than the PSS for unicast is used as the PSS for the dedicated MBMS.
  • a length N of the ZC sequence used as the PSS for the dedicated MBMS may be
  • a ZC sequence having a low frequency offset sensitivity may be used as the PSS for the dedicated MBMS.
  • FIG. 9 is a graph showing a frequency offset sensitivity of a PSS generated from a
  • a ZC sequence corresponding to a root index selected from Table 2 or Table 3 may be used as the PSS for the dedicated MBMS.
  • the root index may be used as an MBMS indicator indicating that the dedicated MBMS is served.
  • the PSS for the dedicated MBMS is mapped to a resource element of the frequency domain.
  • a PSS is transmitted through 0 and 10 slots.
  • the PSS is mapped to a resource element in each of the 0 and 10 slots.
  • Equation 9 shows mapping of a ZC sequence d(n) onto the resource element.
  • a ,1 denotes a value of the resource element (k,l).
  • ⁇ y sc denotes a frequency-domain size of the resource element and is expressed by the number of subcarriers (in case of the dedicated MBMS, the number of subcarriers is
  • ⁇ N * D sy L mb indicates the number of OFDM symbols of a downlink slot, and may be 3 in case of the dedicated MBMS.
  • the resource element of Equation 10 is reserved instead of being used to transmit the PSS.
  • the ZC sequence is sequentially mapped from a subcarrier having a frequency index of -62, with the DC subcarrier being located in the center. No data is mapped to the DC subcarrier. A null value is inserted in the DC subcarrier.
  • the ZC sequence is sequentially mapped from a subcarrier having a frequency index of -63, with the DC subcarrier being located in the center. No data is mapped to the DC subcarrier. A null value is inserted in the DC subcarrier.
  • a value n of d(n) is continuously mapped to the DC subcarrier. This is equivalent to puncturing a symbol of the DC subcarrier after continuously mapping the ZC sequence in a frequency domain.
  • the ZC sequence is sequentially mapped from a subcarrier having a frequency index -62 with an interval two times higher than a subcarrier spacing of 7.5 kHz. No data is mapped to the DC subcarrier. A null value is inserted in the DC subcarrier and in a subcarrier to which the ZC sequence is not mapped.
  • the ZC sequence may be repeated two times in a time domain.
  • a correlation output for u and u can be calculated with one-time computation.
  • the correlation output for u and u2 has a computation amount similar to a correlation output for u alone.
  • the correlation output for u and u for time synchronization can be calculated with one-time computation.
  • the root index for the dedicated MBMS can be used as an MBMS indicator indicating whether the dedicated MBMS is served or not.
  • a time-continuous signal S (p) (t) of an antenna port p is defined by Equation 12 where 0 ⁇ t ⁇ (N + N) x T .
  • N denotes a length of a downlink cyclic prefix (CP) for the OFDM symbol.
  • CP downlink cyclic prefix
  • FIG. 14 shows a radio frame for a dedicated MBMS according to another embodiment of the present invention.
  • the radio frame for the dedicated MBMS is divided in a frequency domain into a usual band used to transmit MBMS data and a synchronization band used for a PSS, an SSS, and a P-BCH.
  • the synchronization band uses an OFDM symbol for the PSS and the SSS by decreasing by half a size of an OFDM symbol of the dedicated MBMS.
  • a CP size of the dedicated MBMS is also decreased by half and is then attached to each of the OFDM symbol of the PSS and the SSS.
  • an OFDM symbol size of the dedicated MBMS is 4096 Ts
  • an OFDM symbol size of each of the PSS and the SSS is 2048 Ts.
  • a CP size of the dedicated MBMS is 1024 Ts
  • the CP size of each of the PSS and the SSS is 512 Ts.
  • the usual band consists of a CP and an OFDM symbol of the dedicated MBMS.
  • all OFDM symbols have a size of 4096 Ts that is an OFDM symbol size of the dedicated MBMS, and a CP has a size of 1024 Ts that is a CP size of the dedicated MBMS.
  • all OFDM symbols have a size of a subcarrier spacing of 7.5 kHz for the dedicated MBMS.
  • the PSS is transmitted through a synchronization band using an OFDM symbol having a half size of the OFDM symbol of the dedicated MBMS.
  • the SSS is transmitted through a synchronization band using an OFDM symbol having a half size of the OFDM symbol of the dedicated MBMS.
  • the PSS is transmitted through a synchronization band using a subcarrier having a double size of the subcarrier spacing of the dedicated MBMS.
  • the SSS is transmitted through a syn- chronization band using a subcarrier having a double size of the subcarrier spacing of the dedicated MBMS.
  • OFDM symbol for the PSS and the SSS of the synchronization band may have a half size of the OFDM symbol of the dedicated MBMS.
  • An example of the radio frame for the dedicated MBMS is shown in FIG. 15.
  • FIG. 15 shows a radio frame for a dedicated MBMS according to another embodiment of the present invention.
  • an OFDM symbol assigned to a PSS and an SSS in a synchronization band has a half size of an OFDM symbol of the dedicated MBMS.
  • An OFDM symbol of a usual band in the same time domain as the OFDM symbol for the PSS and the SSS also has a half size of the OFDM symbol of the dedicated MBMS.
  • both the synchronization band and the usual band have a subcarrier spacing of 15 kHz which is double of a subcarrier spacing of the dedicated MBMS.
  • the PSS and the SSS may have the same definition as in the radio frame supporting unicast.
  • the PSS may be transmitted through a last OFDM symbol in each of a 0 slot and a 10 slot
  • the SSS may be transmitted through an immediately previous OFDM symbol in the last OFDM symbol in each of the 0 slot and the 10 slot.
  • the same sequence may be transmitted through two OFDM symbols.
  • Different sequences may be transmitted through two OFDM symbols.
  • the P-BCH may be determined to start at a 0 OFDM symbol of a 0 subframe and to occupy two OFDM symbols excluding the PSS and the SSS.
  • Two ZC sequences having the conjugate symmetry relation can calculate a correlation output for u and u with one-time computation.
  • the root index of the PSS can be changed variously, and even in this case, the UE can determine whether the dedicated MBMS is served, simultaneously with cell search. For example, if the root indices for unicast are 31, 29, and 34, the root index 32 may be used for the dedicated MBMS, and if the root indices for unicast are 26, 29, and 34, the root index 37 may be used for the dedicated MBMS.
  • FIG. 16 shows a radio frame for a dedicated MBMS according to another embodiment of the present invention.
  • a bandwidth of a PSS and an SSS is decreased by half in comparison with FIG. 8.
  • the radio frame for the dedicated MBMS is divided in a frequency domain into a usual band used to transmit MBMS data and a synchronization band used for a PSS, an SSS, and a P-BCH.
  • the usual band and the synchronization band have the same structure in a time domain except that a bandwidth of the PSS and the SSS has a half size of a bandwidth of the synchronization band. If the bandwidth of the synchronization band is approximately 0.96 MHz, the bandwidth of the PSS and the SSS is approximately 0.48 MHz.
  • Table 4 [Table 4] [Table ]
  • a ZC sequence corresponding to a root index selected from Table 4 may be used the PSS.
  • the PSS for the dedicated MBMS is selected from the remaining root indices.
  • the root index of the PSS for the dedicated MBMS may be used as an indicator indicating that the dedicated MBMS is served.
  • the PSS is mapped to a resource element of a frequency domain.
  • the PSS may be transmitted through ⁇ ' and 10 slots.
  • the PSS may be mapped to the resource element of the 0 and 10 slots according to Equation 9.
  • the resource element of Equation 10 is reserved instead of being used to transmit the PSS.
  • the ZC sequence is sequentially mapped from a subcarrier having a frequency index -31, with the DC subcarrier being located in the center. No data is mapped to the DC subcarrier. A null value is inserted in the DC subcarrier.
  • a value n of d(n) is continuously mapped to the DC subcarrier, which is equivalent to puncturing a symbol of the DC subcarrier after continuously mapping the ZC sequence to a frequency domain.
  • An OFDM signal of a PSS can be transmitted by being generated according to Equation 12.
  • a subcarrier spacing is decreased by half (i.e., 7.5 kHz) and an OFDM symbol duration is doubled in the dedicated MBMS radio frame.
  • the PSS and the SSS can be maintained in the same manner as in the unicast radio frame without an additional overhead.
  • cell search is classified into initial cell search initially performed when the UE is powered on and non-initial cell search for performing handover or neighbor cell measurement.
  • initial cell search initially performed when the UE is powered on
  • non-initial cell search for performing handover or neighbor cell measurement.
  • the following description will focus on the initial cell search as an example.
  • the technical features of the present invention can also apply to the non-initial cell search without modification.
  • FIG. 19 is a flowchart showing a method for obtaining a synchronization signal and system information according to an embodiment of the present invention.
  • a UE searches for a PSS (step Sl 10). If a BS provides a dedicated MBMS, the UE can detect the PSS for a dedicated MBMS by searching for a synchronization channel. The UE obtains slot synchronization or symbol synchronization through the PSS. The UE can also obtain frequency synchronization through the PSS. When power is supplied to the UE, the UE performs system synchronization of an initial cell and detects a physical-layer cell ID which is unique for each cell. The initial cell is determined according to a signal-to-interference plus noise ratio (SINR) of the UE at a time when the power is supplied.
  • SINR signal-to-interference plus noise ratio
  • the initial cell denotes a cell of a BS corresponding to the greatest signal component among signal components of all BSs, wherein the signal components are included in a downlink reception signal of the UE.
  • the UE can know whether the BS supports a unicast service or the dedicated MBMS.
  • the PSS for the dedicated MBMS is received, the UE can use an MBMS according to a defined dedicated MBMS radio frame.
  • the UE searches for an SSS (step S120).
  • the UE obtains frame synchronization through the SSS.
  • the UE obtains cell ID information by using the SSS and the PSS.
  • the UE can obtain antenna configuration or other information.
  • the UE estimates a channel by using the PSS, and detects the SSS by compensating for the estimated channel.
  • the UE decodes a P-BCH (step S130).
  • the UE knows whether a type of a service provided by the BS is a dedicated MBMS type. If the BS supports a unicast service, the UE estimates a channel by using a unicast reference signal and then performs decoding of the P-BCH. If the service provided by the BS is the dedicated MBMS, the UE estimates a channel by using a dedicated MBMS reference signal, and then performs decoding of the P-BCH.
  • the UE can obtain an SFN combining gain by performing multicast broadcast single frequency network (MBSFN) combination of broadcast information through the P- BCH.
  • MBSFN combination is an operation for obtaining a frequency diversity gain and a macro diversity gain by combining downlink signals transmitted equally from a plurality of BSs into self signals.
  • a service type of a cell is a unicast type or a dedicated MBMS type can be known in a cell search procedure.
  • the UE does not have to estimate a channel for each of the unicast reference signal and the dedicated MBMS reference signal. Further, the UE does not have to perform blind detection for the two service types. Therefore, a process of obtaining an initial control signal such as a synchronization signal and system information can be effectively performed.
  • the SFN combining gain of the broadcasting information received through the P-BCH can be obtained in the dedicated MBMS.
  • Every function as described above can be performed by a processor such as a microprocessor based on software coded to perform such function, a program code, etc., a controller, a micro-controller, an ASIC (Application Specific Integrated Circuit), or the like. Planning, developing and implementing such codes may be obvious for the skilled person in the art based on the description of the present invention.
  • a processor such as a microprocessor based on software coded to perform such function, a program code, etc., a controller, a micro-controller, an ASIC (Application Specific Integrated Circuit), or the like. Planning, developing and implementing such codes may be obvious for the skilled person in the art based on the description of the present invention.

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  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Mobile Radio Communication Systems (AREA)

Abstract

L'invention concerne un procédé d'établissement de signal de synchronisation dans un système de communications sans fil qui consiste à diviser une bande de fréquences pleine en une bande de synchronisation pour la transmission du signal de synchronisation et une bande usuelle pour la transmission de données de service multimédia de diffusion multidiffusion (service MBMS), à rechercher un signal de synchronisation primaire pour un service MBMS dédié dans la bande de synchronisation, et à détecter le signal de synchronisation primaire pour ce service MBMS dédié par le biais de la bande de synchronisation.
PCT/KR2008/007902 2007-12-17 2008-12-31 Procédé d'établissement de signal de synchronisation dans un système de communications sans fil WO2009084931A1 (fr)

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