WO2013038865A1

WO2013038865A1 - Method and device for accessing wireless communication system

Info

Publication number: WO2013038865A1
Application number: PCT/JP2012/070779
Authority: WO
Inventors: Lei Huang; Zeng YANG; Ming Ding
Original assignee: Sharp Kabushiki Kaisha
Priority date: 2011-09-13
Filing date: 2012-08-09
Publication date: 2013-03-21
Also published as: CN103002468A; AU2012309718A1

Abstract

A method for accessing a wireless communication system is provided, which comprises: detecting a Primary Synchronization Channel (PSCH) and a Secondary Synchronization Channel (SSCH) for synchronization; detecting a Cell-specific Reference Signal (CRS) on a Physical Broadcast Channel (PBCH); demodulating data transmitted on the PBCH with the detected CRS and obtaining a Cyclic Redundancy Check (CRC) mask code; and monitoring a common search space for a Physical Downlink Control Channel (PDCCH) based on a number of Base Station (BS) antenna ports indicated by the CRC mask code. Also provided is a corresponding User Equipment (UE).

Description

DESCRIPTION

TITLE OF INVENTION:

METHOD AND DEVICE FOR ACCESSING WIRELESS COMMUNICATION SYSTEM TECHNICAL FIELD

The invention relates to mobile communication technology, and more particularly, to a method and a device for accessing a wireless communication system. BACKGROUND ART

In the 3^rd Generation Partner Proj ect (3GPP) Long Term Evolution (LTE) Rel-8 / 9 / 10 system, a Base Station (BS) transmits a Cell-specific Reference signal (CRS) in each downlink data sub-frame to support data demodulation for physical downlink shared / control channel . Meanwhile, a User Equipment (UE) also uses the CRS as a reference signal for downlink channel measurement.

In LTE Rel- 10 , in addition to the use of CRS as a Demodulation Reference Signal (DMRS) , a UE-specific DMRS with pre-coding, is also introduced for a dedicated transmission mode . The use of UE-specific DMRS enables more flexible scheduling at the BS . Transmission points and UEs can be completely transparent to each other, such that multi-BS Coordinated Multi-Point (CoMP) transmission is made possible . In LTE Rel- 10, the function of the CRS has been gradually weakened and its main purpose is to be compatible with UEs of previous releases and used for data modulation for some common channels .

In the contribution R l - 1 10461 , Ericsson, Baseline Schemes and Focus of CoMP Studies, in 3GPP TSG-RAN WG 1 #63bis meeting, Dublin, Ireland, January 20 1 1 , it is pointed out that further research on enhanced Physical Downlink Control Channel (PDCCH) technique is necessary to investigate the possibility of PDCCH transmission using UE specific reference signal. Also, it is pointed out in this contribution that, if some UE specific control signals, such as PDCCH and Physical Hybrid ARQ Indicator Channel (PHICH) , are still demodulated based on CRS, their flexibility will be significantly restricted. In order to increase the capacity and coverage of these control signals while taking the introduction of UE specific demodulation reference signal into consideration, some advanced techniques, such as coordinated multi-point transmission, multi-user MIMO and beamforming, should be applied to the PDCCH / PHICH transmission . Another main function of the CRS is to measure a downlink channel. In the up-to-date LTE Rel- 10 specification, it is defined that, for a UE operating in Transmission Mode 9 and configured with a pmi-RI-Report parameter by an upper layer signaling of system, channel measurement will be carried out based on a Channel State Information Reference Signal (CSI-RS) to calculate a Channel Quality Indicator (CQI) value to be reported. On the other hand, for a UE operating in Transmission Mode 9 but not configured with a pmi-RI-Report parameter by an upper layer signaling of system or the UE operating in another modes, the channel measurement will be carried out based on CRS to calculate the CQI value to be reported. However, the introduction of either a new UE specific reference signal or a new CSI-RI will occupy the valuable radio resources in the wireless communication system, which may cause a shortage of the radio resources .

SUMMARY OF INVENTION

In order to save radio resources in a wireless communication system, a method for accessing a wireless communication system is provided , capable of greatly reducing the number of CRSs used or even eliminating the need for CRS .

According to an aspect of the present invention, a method for accessing a wireless communication system is provided, which comprises : detecting a Primary Synchronization Channel (PSCH) and a Secondary Synchronization Channel (SSCH) for synchronization; detecting a Cell-specific Reference Signal (CRS) on a Physical Broadcast Channel (PBCH) ; demodulating data transmitted on the PBCH with the detected CRS and obtaining a Cyclic Redundancy Check (CRC) mask code ; and monitoring a common search space for a Physical Downlink Control Channel (PDCCH) based on a number of Base Station (BS) antenna ports indicated by the CRC mask code . Preferably, the CRS is adjacent to a symbol at which the

PBCH is located.

Preferably, if the CRC mask code indicates that the number of BS antenna ports is 0 , the CRS is detected on a predetermined Resource Block (RB) or Resource Element (RE) and the PDCCH transmitted on the predetermined RB or RE is blindly decoded with the CRS .

Preferably, the predetermined RB or RE comprises an integer number of RBs reserved at fixed positions in system bandwidth.

Preferably, the predetermined RB or RE comprises REs distributed over both sides of entire system bandwidth. Preferably, the predetermined RB or RE comprises REs reserved on each RB in system bandwidth .

According to another aspect of the present invention, a User Equipment (UE) is provided, which comprises: a synchronization unit configured to detect a Primary Synchronization Channel (PSCH) and a Secondary Synchronization Channel (SSCH) for synchronization; a detection unit configured to detect a Cell- specific Reference Signal (CRS) on a Physical Broadcast Channel (PBCH) ; a demodulation unit configured to demodulate data transmitted on the PBCH with the detected CRS and obtain a Cyclic Redundancy Check (CRC) mask code; and a monitor unit configured to monitor a common search space for a Physical Downlink Control Channel (PDCCH) based on a number of Base Station (BS) antenna ports indicated by the CRC mask code .

Preferably, the detection unit is configured to detect the CRS adj acent to a symbol at which the PBCH is located .

Preferably, the monitor unit is configured to detect, if the CRC mask code indicates that the number of BS antenna ports is 0, the CRS on a predetermined Resource Block (RB) or Resource Element (RE) and blindly decode the PDCCH transmitted on the predetermined RB or RE based on the CRS . Preferably, the monitor unit is configured to detect the CRS on an integer number of RBs reserved at fixed positions in system bandwidth.

Preferably, the monitor unit is configured to detect the CRS on REs distributed over both sides of entire system bandwidth . Preferably, the monitor unit is configured to detect the

CRS on REs reserved on each RB in system bandwidth .

In the access method according to the present invention , the BS only transmits a limited number of CRS s, thereby saving a large amount of radio resources. Additionally, by re-designing the necessary CRSs, the demodulation of the necessary common channel data in the access procedure will not be affected . With the method of the present invention, the design requirements for the current and LTE-Advanced systems as well as the evolution thereof can be satisfied without significantly modifying the systems themselves.

BRIEF DESCRIPTION OF DRAWINGS

The above and other features of the present invention will become more apparent from the following detailed description with reference to the figures, in which:

Fig. 1 is a flow chart illustrating the access method according to an embodiment of the present invention;

Fig. 2 is a schematic diagram of the PBCH position in the LTE Rel- 10 system;

Fig. 3 is a schematic diagram showing the CRSs reserved on the RBs at which the PBCH is located in the existing LTE Rel- 10 system;

Fig. 4 is a schematic diagram showing the CRSs reserved on the RBs at which the PBCH is located according to an embodiment of the present invention;

Fig. 5 is a schematic diagram showing the RBs reserved as the PDCCH common search space according to an embodiment of the present invention;

Fig. 6 is a schematic diagram showing the CRSs mapped on the RBs in the PDCCH common search space according to another embodiment of the present invention;

Fig. 7 is a schematic diagram showing the RBs reserved on both sides of the system bandwidth as the PDCCH common search space according to another embodiment of the present invention;

Fig. 8 is a schematic diagram showing some of REs in a RB reserved as the PDCCH common search space according to another embodiment of the present invention; and

Fig. 9 is a block diagram of the UE according to an embodiment of the present invention.

DESCRIPTION OF EMBODIMENTS

The principles and implementations of the present invention will become more apparent from the following description of the particular embodiments of the present invention with reference to the drawings. It should be noted that the present invention is not limited to the particular embodiments given below. Further, in the following description, details of well-known techniques unnecessary to the present invention are omitted so as not to obscure the concept of the invention.

The embodiments of the present invention will be described below in the application scenario of the LTE Rel- 1 1 mobile communication system and its future evolutions . The mobile communication system according to the embodiments of the present invention transmits a smaller amount of CRSs than the communication systems in the prior art. Herein, it is to be noted that the present invention is not limited to the application scenario exemplified in the embodiments . Rather, it is also applicable to other communication systems, such as the future 5G cellular communication system. Fig. 1 is a flow chart illustrating the access method according to an embodiment of the present invention . The method starts with step S I 10.

At step 1 20 , the UE detects a Primary Synchronization Channel (PSCH) and a Secondary Synchronization Channel (SSCH) and performs Orthogonal Frequency Division Multiplexing (OFDM) symbol synchronization and frame synchronization, respectively. The UE only needs to monitor the synchronization symbols on the system sub-frames #0 and #5 for synchronization, without processing any reference signals . Thus , this step can be implemented using e .g. , a corresponding procedure in the LTE Rel- 10 system.

At step 130 , the UE detects Cell-specific Reference Signal (CRS) on Resource Blocks (RBs) at which the Physical Broadcast Channel (PBCH) is located, demodulates data transmitted on the PBCH with the detected CRS and obtains a corresponding Cyclic Redundancy Check (CRC) mask code . In the existing LTE Rel- 1 0 mobile communication system, the CRS needs to be transmitted in each sub-frame of each frame . In contrast, according to an embodiment of the present invention, the CRS only needs to be transmitted on the first sub-frame of each frame . In the following, the operation in step S 130 will be further detailed with reference to Figs . 2 -4. Fig. 2 is a schematic diagram of the PBCH position in the LTE Rel- 10 system. Since some common system information is transmitted on the PBCH , the demodulation of the data transmitted on the PBCH is dependent on the CRS . As shown in Fig. 2 , in an embodiment, the BS can configure the PBCH onto the 72 sub-carriers (i. e . , 6 RBs)in the middle of the 8^th, 9^th, 10^th and 1 1 ^th symbols in each sub-frame #0 (the first sub-frame) . In order to successfully demodulate the data transmitted on these 6 RBs, a certain number of CRSs are transmitted on these RBs . According to the specification for the LTE Rel- 10 system, the desired system information transmitted on the PBCH can be correctly demodulated by reserving one antenna port for the CRS . Fig. 3 is a schematic diagram showing the CRSs reserved on the RBs at which the PBCH is located in the existing LTE Rel- 10 system. As shown in Fig. 3 , the CRS corresponding to the antenna port 0 as defined in the LTE Rel- 10 is transmitted on the 6 RBs on the PBCH . That is, the CRS is transmitted on the 1 ^st, 5^th, 8^th and 12^th symbols (8 REs in total) of each RB .

It can be seen from the schematic diagram of CRS as shown in Fig. 3, the 1 ^st and the 5^th symbols are distant from the symbols at which the PBCH is located. During the actual demodulation procedure, the symbols distant from the symbols at which the PBCH is located have very limited use . Thus, in order to further save the limited radio resources, only the CRS closest to the symbols at which the PBCH is located can be used for data demodulation . That is, the non-precoded CRS is transmitted on the 8^th and 12^th symbols only, as shown in Fig. 4.

Next, the UE detects the CRS transmitted at the respective positions on the RBs at which the PBCH is located, and demodulates the data transmitted on the PBCH based on the CRS . In the LTE-Rel- 10 standard , the CRC mask codes corresponding to different numbers of the BS antenna ports are defined as follows :

Table 1 - CRC Mask Codes for PBCH

Table 1 shows three different configurations corresponding to the situations in which the CRS is transmitted using one single antenna, two antennas and four antennas, respectively. The UE performs CRC check on the demodulated PBCH data using different CRC mask codes . By using the CRC mask code for the correct CRC check, the number of the transmission antenna ports of the current BS can be obtained . In order to ensure the compatibility of the system such that the UE can access both the conventional LTE Rel- 10 system and the system transmitting limited CRS according to this embodiment, a new PBCH CRC mask code is introduced for discriminating whether the UE accesses the system according to this embodiment or not, as shown in the table below:

Table 2 - CRC Mask Codes for PBCH

As shown in Table 2 , a set of new 16-bit binary code is introduced to represent the situation in which the number of BS antenna ports is 0. It means that the BS only transmits the limited CRS at specific positions for transmitting the CRS . As shown in Table 2 , the newly added 16-bit binary code has the shortest vector distance to the other 16-bit binary codes and is thus preferable. However, it can be understood that another value can be used for this newly added 16-bit binary code . A unique correct CRC mask code can be obtained by subj ecting the data on the PBCH to demodulation and CRC check.

Referring back to Fig. 1 , at step S 140, the UE determines the number of transmission antenna ports at the BS side based on the obtained CRC mask code, so as to determine whether the number of BS antenna ports is 0. Since the unique correct CRC mask code has been obtained at step S 130 , it is possible to obtain the number of BS antenna ports by looking up Table 2. If the UE determines that the number of BS antenna ports is 1 , 2 or 4 , it means that the UE is accessing a conventional LTE Rel- 10 system. Thus, at step S 160, the UE can perform the subsequent operations as defined in the LTE Rel- 10 system. The procedure then ends at step S 170.

On the other hand, if the UE determines at step S 140 that the number of BS antenna ports is 0 , it means that the UE is accessing the system transmitting the limited CRS according to the present embodiment. In this case, the procedure proceeds with step S 1 50 in which the UE detects the CRS on predetermined RB or RE and blindly decodes the common PDCCH transmitted on the predetermined RB or RE with the CRS , in order to obtain the corresponding resource allocation information .

In particular, after correctly obtaining the data transmitted on the PBCH , the UE needs to further monitor the common search space for PDCCH , so as to obtain more system information or random access information . The common search space for PDCCH is a common resource which is monitored by all UEs, thus they need the CRS for data demodulation. In the existing system, the common search space for PDCCH is the first 16 Control Channel Elements (CCEs) which are mapped onto the first few symbols of each sub-frame in the entire system bandwidth. In order to reduce unnecessary overhead for the CRS, according to an embodiment of the present invention, the BS can re-configure the PDCCH common search space . In the following, the configuration of the PDCC H common search space according to the present invention will be detailed with reference to Figs . 5-8.

First Configuration

Fig. 5 is a schematic diagram showing the RBs reserved as the PDCCH common search space according to an embodiment of the present invention. As shown in Fig. 5, an integer number of RBs at fixed positions in the system bandwidth are specifically reserved as the PDCCH common search space . The CRS for one antenna port is provided on the reserved RB for demodulation of the data transmitted on the reserved RB .

Further, taking the robustness of the PDCCH transmission into account, in order to improve the performance of the common PDCCH transmission, a certain number of reference signal resources can be increased to optimize their mapping positions. Fig. 6 is a schematic diagram showing the CRSs mapped on the RBs in the PDCCH common search space according to another embodiment of the present invention. As shown in Fig. 6, by modifying the positions on which the reference signal REs of the antenna port 5 are mapped, on the antenna port 0 , the number of REs for transmitting the CRS in each RB is extended from 8 to 12. By applying such extension, the reliability of the common PDCCH data demodulation can be improved to some extent.

Second Configuration Taking the frequency diversity gain of the PDCCH common search space in to account, it is possible to use an approach similar to that for the resource mapping of Physical Uplink Control Channel (PUCCH) to distribute the RB s reserved for the PDCCH common search space over both sides of the entire system bandwidth. Fig. 7 is a schematic diagram showing the RBs reserved on both sides of the system bandwidth as the PDCCH common search space according to another embodiment of the present invention. As shown in Fig. 7 , according to the specification of LTE Rel-8, the PDCCH common search space consists of successively numbered CCEs each being mapped onto 36 physical REs. The CCEs having odd numbers and the CCEs having even numbers are mapped onto RBs at two sides of the system bandwidth, respectively. In transmission of the corresponding common control information, the B S maps the common control information onto successively CCEs, e. g. , eight CCEs CCE0 - CCE7. Since CCE0 -CCE7 are mapped onto two sides of the physical transmission bandwidth, respectively, such mapping can obtain a certain frequency diversity gain, thereby improving the robustness of common control information transmission .

It is to be noted that Fig. 7 only gives an example configuration for the PDCCH common search space. In this example, the CCEs are mapped onto the corresponding RBs in a first- frequency -domain-then-time-domain manner, However, the CCEs can be mapped onto the corresponding RBs in a first- frequency -domain-then-time-domain manner, as an alternative . Further, in order to improve the robustness of transmission of the common PDCCH , the mapping of the CRS as shown in Fig. 6 can be applied to Fig. 7.

Third Configuration

Fig. 8 is a schematic diagram showing some of REs in a RB reserved as the PDCCH common search space according to another embodiment of the present invention . As shown in Fig. 8, some REs are reserved on each RB in the system bandwidth and a certain amount of CRSs are inserted into these REs for data demodulation of the reserved PDCCH REs. In the example shown in Fig. 8 , seven successive REs in the first symbol of each RE are reserved. Two of the seven REs are transmitted as CRSs for demodulation of the data transmitted on the other five REs. With such mapping scheme, a common PDCCH can be mapped onto a number of RBs and thus distributed over a number of segments of frequency domain resources. In this way, it is possible to achieve better frequency diversity gain and improve the performance of PDCCH transmission .

At step S 150 , the UE blindly decodes the common PDCCH transmitted on the predetermined RB or RE with the previously detected CRS (e. g. , the configurations of PDCCH common search space as described above with reference to Figs. 5-8) , so as to obtain the corresponding resource allocation information .

Finally, the method ends at step S 170.

With the access method according to the present invention, the BS only transmits a limited number of CRSs, thereby saving a large amount of radio resources . Additionally, by re-designing the necessary CRSs, the demodulation of the necessary common channel data in the access procedure will not be affected. With the method of the present invention, the design requirements for the current and LTE Rel- 1 1 systems as well as the evolution thereof can be satisfied without significantly modifying the systems themselves.

Fig. 9 is a block diagram of the UE 90 according to an embodiment of the present invention. As shown in Fig. 9 , the UE 90 includes a synchronization unit 9 10 , a detection unit 920, a demodulation unit 930 and a monitor unit 940.

The synchronization unit 9 10 detects a Primary Synchronization Channel (PSCH) and a Secondary Synchronization Channel (SSCH) and performs OFDM symbol synchronization and frame synchronization, respectively. Since the synchronization operation only needs to be performed on the synchronization symbols on the system sub-frames #0 and #5 , no processing on the reference signals is required. Thus, the synchronization unit 9 10 can operates according to the corresponding procedure in the LTE Rel- 10 system.

The detection unit 920 detects a Cell-specific Reference Signal (CRS) on a Resource Block (RB) at which a Physical Broadcast Channel (PBCH) is located . Then, the demodulation unit 930 demodulates data transmitted on the PBCH with the detected CRS and obtains a corresponding Cyclic Redundancy Check (CRC) mask code . As explained above, according to an embodiment of the present invention, the CRS only needs to be transmitted on the six RBs in the middle of the first sub-frame of each frame. Thus, the detection unit 920 only detects the CRS on the middle six RBs in the first sub-frame of each frame .

The monitor unit 940 determines the number of transmission antenna ports at the BS side based on the obtained CRC mask code, so as to determine whether the number of BS antenna ports is 0. The monitor unit 940 monitors a common search space for a PDCCH based on the number of BS antenna ports indicated by the CRC mask code . For example, it is possible to obtain the number of BS antenna ports by looking up Table 2 as given above . If the monitor unit 940 determines that the number of BS antenna ports is 1 , 2 or 4 , it means that the UE is accessing a conventional LTE Rel- 10 system. Thus, the monitor unit 940 can perform the subsequent operations as defined in the LTE Rel- 10 system. On the other hand, if the monitor unit 940 determines that the number of B S antenna ports is 0 , it means that the UE is accessing the system transmitting the limited CRS according to the present embodiment. In this case, the monitor unit 940 detects the CRS on predetermined RB or RE and blindly decodes the common PDCCH transmitted on the predetermined RB or RE with the CRS , in order to obtain the corresponding resource allocation information .

The present invention has been described above with reference to the preferred embodiments thereof. It should be understood that various modifications, alternations and additions can be made by those skilled in the art without departing from the spirits and scope of the present invention. Therefore, the scope of the present invention is not limited to the above particular embodiments but only defined by the claims as attached and the equivalents thereof.

Claims

1 . A method for accessing a wireless communication system, comprising:

-detecting a Primary Synchronization Channel (PSCH) and a Secondary Synchronization Channel (SSCH) for synchronization;

-detecting a Cell- specific Reference Signal (CRS) on a Physical Broadcast Channel (PBCH) ;

-demodulating data transmitted on the PBCH with the detected CRS and obtaining a Cyclic Redundancy Check (CRC) mask code; and

-monitoring a common search space for a Physical Downlink Control Channel (PDCCH) based on a number of Base Station (BS) antenna ports indicated by the CRC mask code .

2. The method of claim 1 , wherein the CRS is adjacent to a symbol at which the PBCH is located .

3. The method of claim 1 , wherein, if the CRC mask code indicates that the number of BS antenna ports is 0, the CRS is detected on a predetermined Resource Block (RB) or Resource Element (RE) and the PDCCH transmitted on the predetermined RB or RE is blindly decoded with the CRS .

4. The method of claim 3, wherein the predetermined RB or RE comprises an integer number of RBs reserved at fixed positions in system bandwidth .

5. The method of claim 3 , wherein the predetermined RB or RE comprises REs distributed over both sides of entire system bandwidth.

6. The method of claim 3 , wherein the predetermined RB or RE comprises REs reserved on each RB in system bandwidth .

7. A User Equipment (UE) , comprising:

-a synchronization unit configured to detect a Primary Synchronization Channel (PSCH) and a Secondary Synchronization Channel (SSCH) for synchronization;

-a detection unit configured to detect a Cell-specific Reference Signal (CRS) on a Physical Broadcast Channel (PBCH) ;

-a demodulation unit configured to demodulate data transmitted on the PBCH with the detected CRS and obtain a Cyclic Redundancy Check (CRC) mask code ; and

-a monitor unit configured to monitor a common search space for a Physical Downlink Control Channel (PDCCH) based on a number of Base Station (BS) antenna ports indicated by the CRC mask code .

8. The UE of claim 7, wherein the detection unit is configured to detect the CRS adjacent to a symbol at which the PBCH is located.

9. The UE of claim 7, wherein the monitor unit is configured to detect, if the CRC mask code indicates that the number of BS antenna ports is 0 , the CRS is detected on a predetermined Resource Block (RB) or Resource Element (RE) and the PDCCH transmitted on the predetermined RB or RE is blindly decoded with the CRS .

10. The UE of claim 9 , wherein the monitor unit is configured to detect the CRS on an integer number of RBs reserved at fixed positions in system bandwidth.

1 1 . The UE of claim 9 , wherein the monitor unit is configured to detect the CRS on REs distributed over both sides of entire system bandwidth.

12. The UE of claim 9 , wherein the monitor unit is configured to detect the CRS on REs reserved on each RB in system bandwidth .