Abstract:
The present disclosure discloses a pilot signal configuration method in a wireless communication system and an associated wireless network node. The method comprises allocating a dedicated pilot signal to a User Equipment (UE) within a combined cell. The method further comprises selecting, from all Transmit-Receive Points (TRPs) within the combined cell, at least one TRP in the proximity of the UE for transmission of the dedicated pilot signal to the UE. The present disclosure further provides a pilot-signal-based reception method in a wireless communication network and an associated UE.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application claims priority from PCT application No. PCT/CN2012/084573 filed on Nov. 14, 2012 and titled “PILOT SIGNAL CONFIGURATION METHOD, ASSOCIATED WIRELESS NETWORK NODE, PILOT-SIGNAL-BASED RECEPTION METHOD AND ASSOCIATED USER EQUIPMENT”, the contents of which are hereby incorporated by reference in its entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    The present disclosure generally relates to configuration and use of pilot signal, and particularly, to pilot signal configuration method, an associated wireless network node, a pilot-signal-based reception method, and an associated user equipment (UE). 
       BACKGROUND 
       [0003]    The number of smart phones, wireless-enabled tablets and laptop computers in the Universal Mobile Telecommunications System (UMTS) networks is growing rapidly. It is important for network operators to evolve their networks in terms of capacity and coverage so that positive user experience can be sustained. 
         [0004]    Deployment of low-power nodes (LPNs) is seen as a powerful tool to achieve the goal. A network consisting of traditional macro NodeBs and LPNs is referred to as a heterogeneous network. Two use-cases for heterogeneous network deployment that may be envisioned are coverage holes ad localized traffic hotspots. Deployment of LPNs as a complement to a macro network then aims at improving coverage and capacity, respectively. 
         [0005]    In the heterogeneous network deployment, an LPN can either form a separate cell (such as, a pico cell or a micro cell) by itself or be one of the spatially separated Transmit-Receive Points (TRPs) in one logical cell. The former case is referred to as separated-cell scenario, while the latter case is referred to as combined-cell (or shared-cell) scenario. 
         [0006]    As compared with the separated-cell scenario, signalling reception and interference handling for the combined-cell scenario are much easier. Moreover, for the combined-cell scenario, no handover is needed between the different TRPs in the same combined cell, ensuring a more smooth mobility procedure and easing the Radio Network Controller (RNC) load. 
         [0007]    However, according to the prior-art transmission scheme for the combined-cell scenario, all TRPs within a combined-cell transmit the same physical channel. This adversely limits the system capacity of the combined cell. 
         [0008]    At Technical Specification Group-Radio Access Network (TSG-RAN) meeting #56, a study item (SI) was initiated on Universal Mobile Telecommunications System (UMTS) Heterogeneous Networks for 3 rd  Partnership Project (3GPP) Rel-12 [1]. There exist more opportunities for 3GPP Rel-12 to include value-added features to further improving the performance of Heterogeneous Networks. 
       SUMMARY 
       [0009]    An object of the present embodiments is to facilitate simultaneous transmissions to more than one UEs from selected TRPs in the proximity of the UEs within the same combined cell by providing a novel pilot signal configuration method, an associated wireless network node, a pilot-signal-based reception method and an associated UE. 
         [0010]    To achieve the object, according to a first aspect of the embodiments, there is provided a pilot signal configuration method performed by a wireless network node in wireless communication system. The method comprises allocating a dedicated pilot signal to a UE within a combined cell. The method also comprises selecting, from all TRPs within the combined cell, at least one TRP in the proximity of the UE for transmission of the dedicated pilot signal to the UE. 
         [0011]    According to a second aspect of the embodiments, there is provided a wireless network node. The wireless network node comprises a pilot allocation unit configured to allocate a dedicated pilot signal to a UE within a combined cell. The wireless network node also comprises a TP selection unit configured to select, from all TRPs within the combined cell, at least one TRP in the proximity of the UE for transmission of the dedicated pilot signal to the UE. 
         [0012]    According to a third aspect of the embodiments, there is provided a pilot-signal-based reception method performed by a UE in a wireless communication system. The method comprises receiving a dedicated pilot signal from at least one TRP in the proximity of a UE. The method also comprises performing channel estimation and/or demodulation based on the received dedicated pilot signal. 
         [0013]    According to a fourth aspect of the embodiments, there is provided a UE. The UE comprises a pilot receiving unit, a channel estimation unit and a demodulation unit. The pilot receiving unit is configured to receive dedicated pilot signal from at least one TRP in the proximity of the UE. The channel estimation unit is configured to perform channel estimation based on the received dedicated pilot signal. The demodulation unit is configured to perform demodulation based on the received dedicated pilot signal. 
         [0014]    According to a fifth aspect of the embodiments, there is provided a wireless network node. The wireless network node comprises a memory which has machine-readable program code stored therein and a processor which executes the stored program code to control the wireless network node to perform the method according to the first aspect of the embodiments. 
         [0015]    According to a sixth aspect of the embodiments, there is provided a UE. The UE comprises a memory which has machine-readable program code stored therein and a processor which executes the stored program code to control the UE to perform the method according to the third aspect of the embodiments. 
         [0016]    According to a seventh aspect of the embodiments, there is provided a computer readable medium storing therein a program for a wireless network node or a UE. The program causes the wireless network node or the UE to perform a method according to the first and third aspects of the embodiments, respectively. 
         [0017]    As a dedicated pilot signal is transmitted from one or more selected TRPs in the proximity of a UE and received by that UE, the methods and devices according to the above aspects of the embodiments facilitate simultaneous transmissions to more than one UEs from selected TRPs in the proximity of the UEs within the same combined cell, which in turn allows for an increased system capacity of the combined cell. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]    The above and other objects, features, and advantages of the present disclosure will become apparent from the following descriptions on embodiments of the present disclosure with reference to the drawings, in which: 
           [0019]      FIG. 1  is a diagram schematically illustrating a pilot transmission scheme according to the prior art; 
           [0020]      FIG. 2  is a diagram schematically illustrating a pilot transmission scheme according to the present disclosure; 
           [0021]      FIG. 3  is a flowchart schematically illustrating a pilot signal configuration method according to an embodiment of the present disclosure; 
           [0022]      FIG. 4  is a flowchart schematically illustrating a pilot-signal-based reception method according to an embodiment of the present disclosure; 
           [0023]      FIG. 5  is a block diagram schematically illustrating an example of a structure of a wireless network node according to the present disclosure; and 
           [0024]      FIG. 6  is a block diagram schematically illustrating an example of a structure of a UE according to the present disclosure. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0025]    Hereinafter, the present disclosure is described with reference to embodiments shown in the attached drawings. However, it is to be understood that those descriptions are just provided for illustrative purpose, rather than limiting the present disclosure. Further, in the following, descriptions of known structures and techniques are omitted so as not to unnecessarily obscure the concept of the present disclosure. 
         [0026]      FIG. 1  schematically illustrates a pilot transmission scheme according to the prior art. As illustrated in  FIG. 1 , four TRPs  101 - 104  are distributed in a combined cell  100 . Although a UE  201  is geographically closest to the TRP  104 , all TRPs  101 - 104  transmit the same Common Pilot Channel (CPICH) to the UE  201 . In this case, the UE  201  cannot estimate the single channel from the TRP  104  to itself, and thus cannot perform data reception via this channel. 
         [0027]    For comparison,  FIG. 2  schematically illustrates a pilot transmission scheme according to the present disclosure. Note that CPICH is still transmitted from all TRPs within the combined-cell  100 , although it is not expressly shown for the sake of simplicity. As illustrated in  FIG. 2 , dedicated pilots are newly introduced in the combined cell  100 . In contrast with the CPICH transmitted from all TRPs within the combined-cell, a dedicated pilot is transmitted from one or more selected TRPs in the proximity of the UE. As exemplified in  FIG. 2 , a dedicated pilot  1  is transmitted from TRP  104  to UE  201 , and the same dedicated pilot  2  is transmitted from TRPs  102  and  103  to UE  202 . In this case, based on the received dedicated pilot  1 , the UE  201  can estimate the single channel from the TRP  104  to itself, so that the UE  201  can perform data transmission and reception with only one TRP (TRP  104 , in this example) in its proximity within the combined cell  100 . Likewise, based on the received dedicated pilot  2 , the UE  202  can estimate the channels from the TRPs  102  and  103  to itself, so that the UE  202  can perform data transmission and reception with more than one TRP (TRPs  102  and  103 , in this example) in its proximity within the combined cell  100 . That is, a spatial reuse scheme (i.e., simultaneous transmissions to more than one UEs from selected TRPs in the proximity of the UEs) can be implemented for the UE  201  and the UE  202  within the combined cell  100 , and a SFN or a (distributed) MIMO transmission scheme (i.e., transmission from more than one selected TRPs to a UE) can be implemented for the UE  202  within the combined cell  100 . 
         [0028]    Remarkably, the SFN transmission scheme facilitated by the dedicated pilot is superior to the conventional SFN transmission scheme facilitated by the CPICH in that it avoids transmissions from remote TRPs, which make negligible contribution to the useful signal but make considerable contribution to the interference. 
         [0029]    As known to those skilled in the art, the expression “a TRP is in the proximity of a UE” means that the distance from the TRP to the UE is lower than a certain length. Therefore, a straightforward manner for determining whether a TRP is in the proximity of a UE is to acquire the position of the UE (for example, by requesting the UE&#39;s Global Positioning System (GPS) position from the UE), calculate the distance between the TRP and the UE based on the known position of the TRP and the acquired position of the UE, and compare the calculated distance with a prescribed length. 
         [0030]    To determine their proximity to a UE for TRPs within a combined cell in the above manner, the same length or different lengths may be prescribed for the TRPs. In the former case, to ensure that at least one TRP may be selected to serve the UE, the length may be prescribed as the maximum of service area radii of all TRPs in the combined cell. In the latter case, various lengths may be prescribed by the network operator for different TRPs. 
         [0031]    As an alternative to the straightforward manner described above, instantaneous or time-average strengths of uplink control signals received at the TRPs from the UE may be employed to determine which TRP(s) within the combined cell is (are) in the proximity of the UE. Specifically, in the beginning, the TRP receiving one of the uplink control signals with the highest signal strength is determined as the optimal TRP, which is of course considered to be in the proximity of the UE. Then, it is determined whether any other TRP receives a uplink control signal with a signal strength not lower than the highest signal strength by a threshold (which is typically between 3-5 dB in logarithmic scale). If so, the TRP is able to provide the UE with a significantly improved link quality when operating in combination with the optimal TRP, and therefore may also be determined to be in the proximity of the UE. Otherwise, only the optimal TRP is determined to be in the proximity of the UE. 
         [0032]      FIG. 3  is a flowchart schematically illustrating a pilot signal configuration method according to an embodiment of the present disclosure. As illustrated, after a start of the proposed method, a dedicated pilot signal is allocated to a UE within a combined cell (S 310 ). The allocation of dedicated pilot signal can be implemented in a wireless network node, such as a RNC (Radio Network Controller), a BS (Base Station), and/or the like. The UE can be informed of the allocated pilot signal, for example, via RRC signalling. Then, at least one TRP in the proximity of the UE is selected from all TRPs within the combined cell, for transmission of the dedicated pilot signal to the UE (S 320 ). The selection of TRP can be implemented in the same wireless network node. After that, the proposed method ends. 
         [0033]    As a feasible manner to implement step S 310 , once the UE enters the combined cell, a dedicated pilot signal is allocated to the UE and exclusively used by the UE. This implies that the dedicated pilot signal is UE specific and will not change when the UE moves between TRPs within the combined cell. 
         [0034]    Accordingly, there should be (channel code) resource dedicatedly reserved for that pilot signal. That is, when one channel code is used by a dedicated pilot, this code cannot be used for any other purpose within the same combined cell. To save channel code resource, it is preferable for each UE to transmit its dedicated pilot by using a specific scrambling code. 
         [0035]    In this case, the Downlink (DL) transmission becomes very similar to the Uplink (UL) transmission in the following aspects:
       The channel code for the dedicated pilot can be predefined, as in the case with Dedicated Physical Control Channel (DPCCH) in UL.   Signalling dedicated to the UE (e.g. High Speed-Shared Control Channel (HS-SCCH) order) can be transmitted on the UE-specific scrambling code.   The UE-specific scrambling code also does not change when the UE moves between TRPs within the same combined cell.       
 
         [0039]    One major advantage with the UE-specific dedicated pilot scheme is that the transmission/mobility handling can be transparent to the UE within one combined cell (as in UL). 
         [0040]    Another feasible manner to implement step S 310  is to determine which UE group the UE belongs to and allocate a dedicated pilot signal shared by UEs in the UE group to the UE. In this regard, the dedicated pilot signal is group specific. To be specific, if a UE transfers from group A to group B, it cannot use the dedicated pilot signal specific to group A anymore; instead, the dedicated pilot signal specific to group B shall be used. 
         [0041]    By way of example, a UE may be determined as belonging to a SFN group or a non-SFN group, according to whether the UE applies the SFN transmission scheme or not applies the SFN transmission scheme. 
         [0042]    It should be understood by those skilled in the art that various other criteria could be applied to group UEs, without departing from claimed subject matter. 
         [0043]    For example, UEs may be grouped according to one or more of their capability, speed or the like, in addition to or instead of whether the SFN transmission scheme is applied. Specifically, in addition to or instead of whether it applies the SFN transmission scheme or not, a UE may be grouped according to whether or not it is MIMO-capable and/or which speed range its moving speed falls into. 
         [0044]    In this manner, UEs using the same transmission scheme and/or having the same capability and/or similar moving speeds may be grouped together. 
         [0045]    An alternative manner to implement step S 320  is to determine which area the UE is located in and allocate a dedicated pilot signal shared by UEs located in that area to the UE. In this regard, the dedicated pilot signal is area specific. To be specific, if a UE moves from area A to area B, it cannot use the dedicated pilot signal specific to area A anymore; instead, the dedicated pilot signal specific to area B shall be used. 
         [0046]    By way of example and not limitation, an area may be covered by one TRP within a combined-cell or geographically adjacent TRPs within a combined-cell, and a UE may be determined as located in that area if it is served by any of the TRPs covering the area. The area may vary in shape and/or in size, according to which TRP(s) covers it. 
         [0047]    It is also possible to determine which area a UE is located in according to which area the geographical position of the UE falls into. The geographical position of the UE may be acquired by requesting the GPS position from the UE directly or by measuring the strength of the uplink control signal from the UE and estimating the UE&#39;s position based on the measured signal strength indirectly. 
         [0048]    As those skilled in the art would appreciate, the area where a UE is located may also be considered as a factor for grouping UEs. By way of example, UEs located in the same area and using the same transmission scheme and/or having the same capability and/or similar moving speeds may be grouped together. 
         [0049]    For both the group-specific and the area-specific dedicated pilot schemes, explicit signalling is needed to inform the UE of the change of group/area. 
         [0050]    As in the UE-specific dedicated pilot scheme, different group/area-specific dedicated pilots can be either carried on the same scrambling code or on different scrambling codes. When carried on the same scrambling code, different dedicated pilots are differentiated by channel codes. The channel codes can be either predefined or allocated dynamically. In the former case, there is no need to inform the UE of the channel codes used for the pilots, but the signalling informing the UE of the change of group/area is still required. When different group/area-specific dedicated pilots are carried on different scrambling codes, it is preferable to have pre-defined channel codes for the pilots. 
         [0051]    Note that SFN transmission occupies much more channel codes than spatial reuse. It is preferable to allocate scrambling codes respectively for spatial reuse UEs and SFN UEs, so that the channel codes occupied by SFN transmission can be freed. 
         [0052]    Besides, TRPs close to each other may use the same scrambling code to avoid too much inter-scrambling code interference, while TRPs far apart from each other may use different scrambling code to have more usable channel codes. In this way, a balance between channel code and power resources can be achieved. 
         [0053]    One major advantage with the group/area-specific dedicated pilot scheme is that the code and power consumption is relatively small. 
         [0054]    The above dedicated pilot schemes can be applied separately or in any combination. For example, UE-specific dedicated pilots can be adopted for high speed UEs and/or high data rate UEs (which account for only a small fraction of all UEs in a cell and will not consume excessive resources), while group/area specific pilots can be adopted for low speed UEs with low data rate. In this regard, UE-specific and group/area-specific pilots may be adaptively used for a UE, and the UE-specific pilot, the group/area-specific pilot and the existing CPICH may co-exist in the same combined-cell. For legacy UEs, only the existing CPICH will be used. 
         [0055]    As known to those skilled in the art, the term “high speed” refers to a speed higher than or equal to 120 km/h. “High data rate” means that the amount of radio resources consumed by data transmission is much more than (e.g. ten times more than) the amount of radio resources consumed by control information transmission, that is, the radio resource overhead due to control information transmission is only a small fraction (e.g. low than 10%) of the total radio resource consumption. 
         [0056]    Moreover, one common scrambling code can be adopted if the system traffic load is low (i.e., if the system is not code limited yet), while multiple different scrambling codes can be adopted if the system becomes code limited. The code limited scenario may happen, if, for example, there are many active LPNs and many spatial reuse and SFN UEs in one combined cell. 
         [0057]    Preferably, when the ratio of legacy UEs that do not support the dedicated pilots is very high, dedicated pilots may be turned off. The ratio of legacy UEs can be calculated per TRP. 
         [0058]      FIG. 4  schematically illustrates a pilot-signal-based reception method according to the present disclosure. This method corresponds to the above-described pilot signal configuration method and is implemented at a UE. As illustrated, after a start of the proposed method, a dedicated pilot signal is received by the UE from at least one TRP in the proximity of the UE (S 410 ). Then, channel estimation and/or demodulation are performed based on the received dedicated pilot signal (S 420 ). After that, the proposed method ends. 
         [0059]    In the following, the functional module architectures of a wireless network node  500  and a UE  600  according to the present disclosure will be given with reference to  FIGS. 5 and 6 , respectively. 
         [0060]    As shown in  FIG. 5 , the wireless network node  500  comprises a pilot allocation unit  510  and a TRP selection unit  520 . The pilot allocation unit  510  is configured to allocate a dedicated pilot signal to a UE within a combined cell. The TRP selection unit  520  is configured to select, from all TRPs within the combined cell, at least one TRP in the proximity of the UE for transmission of the dedicated pilot signal to the UE. 
         [0061]    In one implementation, the dedicated pilot signal allocated by the pilot allocation unit  510  may be exclusively used by the UE. 
         [0062]    In another implementation, the pilot allocation unit  510  may comprise a determination unit  511 . The determination unit  511  may be configured to determine a UE group to which the UE belongs. A pilot signal shared by UEs in the UE group is allocated by the pilot allocation unit  510  to the UE as the dedicated pilot signal. 
         [0063]    In a further implementation, the determination unit  511  may be configured to determine an area in which the UE is located, the area being served by one or more TRPs. A pilot signal shared by UEs located in the area is allocated by the pilot allocation unit  510  to the UE as the dedicated pilot signal. 
         [0064]    As those skilled in the art will appreciate, the pilot allocation unit  510  and the TRP selection unit  520  may be implemented separately as suitable dedicated circuits. Nevertheless, the above-described units can also be implemented using any number of dedicated circuits through functional combination or separation. In some embodiments, the above-described units may be even combined in a single application specific integrated circuit (ASIC). 
         [0065]    As an alternative software-based implementation, there may be provided a wireless network node comprising a memory and a processor (including but not limited to a microprocessor, a microcontroller or a Digital Signal Processor (DSP), etc.) The memory stores machine-readable program code executable by the processor to control the wireless network node to perform the method as described above with reference to  FIG. 3 . As a non-limiting example, the processor may be operable to perform the functions of the pilot allocation unit  510 , the determination unit  511  and the TRP selection unit  520  mentioned above. 
         [0066]    As shown in  FIG. 6 , the UE  600  according to the present disclosure comprises a pilot receiving unit  610 , a channel estimation unit  620  and a demodulation unit  630 . The pilot receiving  610  is configured to receive dedicated pilot signal from at least one TRP in the proximity of a UE. The channel estimation unit  620  is configured to perform channel estimation based on the received dedicated pilot signal. The demodulation unit  630  is configured to perform demodulation based on the received dedicated pilot signal. 
         [0067]    Likewise, as those skilled in the art will appreciate, the pilot receiving unit  610 , the channel estimation unit  620  and the demodulation unit  630  may be implemented separately as suitable dedicated circuits. Nevertheless, the above-described units can also be implemented using any number of dedicated circuits through functional combination or separation. In some embodiments, the above-described units may be even combined in a single application specific integrated circuit (ASIC). 
         [0068]    As an alternative software-based implementation, there may be provided a UE comprising a memory and a processor (including but not limited to a microprocessor, a microcontroller or a Digital Signal Processor (DSP), etc.) The memory stores machine-readable program code executable by the processor to control the UE to perform the method as described above with respect to  FIG. 4 . As a non-limiting example, the processor may be operable to perform the functions of the pilot receiving unit  610 , the channel estimation unit  620  and the demodulation unit  630  mentioned above. 
         [0069]    Further, the present disclosure concerns a computer readable medium storing therein a program for a wireless network node or a UE. The program causes the wireless network node or the UE to perform the pilot signal configuration method or the pilot-signal-based reception method described above. The computer readable medium may be of any type including but not limited to a hard disk drive, a Compact Disc (CD), a Digital Video Disk (DVD), a digital tape, memory, etc. 
         [0070]    The present disclosure is described above with reference to the embodiments thereof. However, those embodiments are provided just for illustrative purpose, rather than limiting the present disclosure. The scope of the disclosure is defined by the attached claims as well as equivalents thereof. Those skilled in the art can make various alternations and modifications without departing from the scope of the disclosure, which all fall into the scope of the disclosure. 
       REFERENCE 
       [0071]    [1] RP-121436 Study on UMTS Heterogeneous Networks