Abstract:
A method of controlling admission of a user equipment to a cell of a multi-mode base station, being a base station arranged to operate as a plurality of cells, the plurality of cells comprising at least a first cell and a second cell, and the method comprising: determining information relating to the first cell, and controlling admission of a user equipment to the second cell in dependence on the information relating to the first cell.

Description:
PRIORITY CLAIM 
       [0001]    This application is a continuation application of U.S. patent application Ser. No. 13/440,880, filed Apr. 5, 2012, entitled “MULTIMODE BASE STATION,” which claims priority to and the benefit of Great Britain Application No. 1105769.2 filed on Apr. 5, 2011. Each of these applications is incorporated herein by reference in its entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to controlling admission of user equipment to a cell of a multimode base station (such as multimode picocell, femtocell or the like) which is arranged to operate as two or more logical cells. 
       RELATED ART 
       [0003]    As will be familiar to a person skilled in the art, a base station is the unit which provides a user equipment such as a mobile phone or computer with access to a wireless cellular network such as a network operating according to both 3G and 4G standards, the base station being the first stage up from the user equipment in the cellular hierarchy, i.e. the unit with which the user equipment immediately communicates via a wireless connection (without an intermediary station). According to 3GPP terminology, a base station is sometimes referred to as a “node B”, but the more generic term “base station” will be maintained herein for convenience. 
         [0004]    A femtocell is a type of cellular base station designed to operate over a relatively short range compared to a conventional base station. Short-range dedicated base stations such as femtocells have become more viable in recent years due to reduction in the cost and size of the electronics required to implement a cellular base station. The idea is to provide a dedicated base station to cover a relatively small geographical area which is expected to experience a high density of users and/or regular usage. For example femtocells are typically intended to be deployed in a small office, shop, café or even the home. Other types of short range base stations include picocells or microcells, typically covering an intermediately sized area; although the scope of femtocells is increasing as they are encroaching on what have been traditionally called picocells and microcells, supporting large offices, shopping malls and outdoor deployments. The scope of femtocells is increasing due to increased functionality over picocells and microcells. In some wireless standards, femtocells combine the functionality of several wireless network elements, for example in UMTS a femtocell combines the functionality of a base station and radio network controller (RNC). Also, it is typical for a femtoceli to be installed by the end user, not the network operator, and extra functionality is required to support this, such as the ability to locate (sniff) neighboring base stations. This is in contrast to picocells and microcells that are installed by a network operator and only provide base station functionality. 
         [0005]    Base-stations (BS), including femtocells, contain a radio resource management (RRM) entity which includes admission control mechanisms to decide whether a new connection request from a user equipment (UE) should be admitted. This RIM entity may refuse the UE access to the BS due to it being congested and unable to support more users. This congestion can be on the air-interface, but could also be related to hardware processing resources, or back-haul congestion. When a base-station experiences congestion it has the following options: 
         [0006]    If the UE is very high priority, for example, an emergency call, it must accept this UE and release or downgrade an alternative UE. 
         [0007]    The base-station can direct the UE to an alternative base-station for service, where this base-station could be at a different frequency sub-band or a different radio access technology (RAT). 
         [0008]    The base-station can offer to service the UE with a lower quality of service (QOS) than it requested. 
         [0009]    The base-station can refuse service to the UE and not provide any alternatives. 
         [0010]    A dual-mode femtocell is a base-station operating as two cells. These cells could be operating as different RATs, or the same RATs but in different sub-bands. Each cell operates an independent RRM admission control mechanism. 
       SUMMARY 
       [0011]    If both the cells operate an independent RRM admission control mechanism then this can lead to inefficient use of base-station resources—a UE could be admitted to the least optimum cell for its QOS, or one cell could be fully loaded while the other is only lightly loaded, Improvements could be achieved by performing joint admission control for a dual-mode femtocell. These improvements can be related to the throughput and QOS achieved by the admitted UE, other UE in the same cell, or UEs in neighboring cells. 
         [0012]    Therefore according to one aspect of the present invention, there is provided a method of controlling admission of a user equipment to a cell of a multi-mode base station, being a base station arranged to operate as a plurality of cells, the plurality of cells comprising at least a first cell and a second cell, and the method comprising: determining information relating to the first cell, and controlling admission of a user equipment to the second cell in dependence on the information relating to the first cell. 
         [0013]    In embodiments the determination of the information may comprise monitoring statistics of past behavior of the user equipment when connected to the first cell, and the control of admission may be dependent on the statistics of the past behavior of the user equipment in the first cell. 
         [0014]    The method may comprise monitoring statistics relating to past behavior of the user equipment when connected to the second cell, and controlling admission of the user equipment to the second cell in dependence on the statistics relating to past behavior of the user equipment in both the first cell and the second cell. 
         [0015]    The method may comprise receiving a request from the user equipment for admission to the first cell and, in response to the request for admission to the first cell, admitting the user equipment to the second cell based on the statistics relating to past behavior of the user equipment in the first cell. 
         [0016]    The admission of the user equipment to the second cell in response to the request for admission to the first cell may be based on the statistics relating to past behavior of the user equipment in both the first cell and the second cell. 
         [0017]    The user equipment may be admitted to the second cell based on the statistics relating to past behavior before the user equipment indicates quality of service requirements to the base station. 
         [0018]    The method may comprise receiving a request from the user equipment for access to the second cell, and in response to the request admitting the user equipment to the second cell based on the statistics relating to past behavior of the user equipment in the first cell. 
         [0019]    The admission of the user equipment to the second cell may be based on the statistics relating to past behavior of the user equipment in both the first cell and the second cell. 
         [0020]    The user equipment may be admitted to the first cell based on the statistics relating to past behavior before the user equipment indicates quality of service requirements to the base station. 
         [0021]    The statistics relating to past behavior of the user equipment may comprise at least one of: a downlink throughput requested by the user equipment from the respective cell, and an uplink throughput requested by the user equipment from the respective cell. 
         [0022]    The statistics relating to past behavior of the user equipment may comprise at least one of a downlink throughput used by the user equipment in the respective cell, and an uplink throughput used by the user equipment in the respective cell. 
         [0023]    The statistics relating to past behavior of the user equipment may comprise at least one of a downlink latency requested by the user equipment from the respective cell, and an uplink latency requested by the user equipment from the respective cell. 
         [0024]    The statistics may represent a predetermined period, the method may comprise determining an average of the statistics representing the period, and the control of admission may be based on the average. 
         [0025]    The method may comprise determining a variation of the average of the statistics representing the period, and the control of admission may be based on the variation of the average. The statistics may represent a predetermined period of at least one day. The statistics may represent a predetermined period of at least one week. In further embodiments, the determination of the information may comprise determining a prediction of performance of the first cell, and the control of admission may be dependent on the prediction of performance in the first cell. 
         [0026]    The method may comprise determining a prediction of performance of the second cell, and the control of admission may be dependent on the prediction of performance for both the first cell and the second cell. 
         [0027]    The method may comprise receiving a request from the user equipment for admission to the first cell; and, in response to the request for admission to the first cell, admitting the user equipment to the second cell based on the prediction of performance of the first cell. 
         [0028]    The admission of the user equipment to the second cell in response to the request for admission to the first cell may be based on the prediction of performance of both the first cell and the second cell. 
         [0029]    The user equipment may be admitted to the second cell in response to the request for admission to the first cell without being admitted to the first cell between the request for admission to the first cell and the admission to the second cell. 
         [0030]    The method may comprise receiving a request from the user equipment for access to the second cell, and in response to the request admitting the user equipment to the second cell based on the statistics relating to past behavior of the user equipment in the first cell. 
         [0031]    The admission of the user equipment to the second cell may be based on the prediction of performance of both the first cell and the second cell. The determination of performance may comprise a measure of at least one of: downlink throughput, downlink latency, uplink throughput, and uplink latency. 
         [0032]    The measure may comprise at least one of: a maximum downlink throughput of the respective cell, a minimum downlink latency of the respective cell, a maximum uplink throughput of the respective cell, and a minimum uplink latency of the respective cell. 
         [0033]    The measure may comprise a measure of an available air interface resource of the respective cell. The measure may comprise a measure of a hardware resource of the base station available for the respective cell. The measure may comprise a measure of path loss for the respective cell. The measure may comprise a power limit of the respective cell. The measure may comprise an estimate of noise and/or interference in the respective cell. In yet further embodiments, the control of admission may be based on comparison of the past behavior with the predicted performance. 
         [0034]    According to another aspect of the present invention, there is provided a multi-mode base station arranged to operate as a plurality of cells, the plurality of cells comprising at least a first cell and a second cell, and the base station comprising a radio resource manager for controlling admission of a user equipment to the cells, the radio resource manager being configured to perform operations in accordance with any of the above combinations of method features. 
         [0035]    According to another aspect of the present invention, there is provided a computer program product for controlling access to a cell of a multi-mode base station, being a base station arranged to operate as a plurality of cells, the plurality of cells comprising at least a first cell and a second cell, and the computer program product being embodied on a non-transient computer-readable medium and configured so as when executed on a processor of the base station to perform the operations of any of the above combinations of method features 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0036]    For a better understanding of the present invention and to show how it may be put into effect, reference is made by way of example to the accompanying drawings in which: 
           [0037]      FIG. 1  is an illustration of a part of a wireless cellular communication network, and 
           [0038]      FIG. 2  is a flow chart of a method of controlling access to a multi-mode base station. 
       
    
    
     DETAILED DESCRIPTION 
       [0039]      FIG. 1  is a schematic diagram showing a part of a wireless cellular communication network such as a 3G network. The network comprises a user equipment (UE)  2  in the form of a mobile terminal, such as a smart phone or other mobile phone, a tablet, or a laptop or desktop computer equipped with a wireless data card. The network further comprises a base station in the form of a femtocell  4 , and one or more further base stations  6 . Each base station  4 ,  6  provides network coverage in the form of at least one respective cell  4   a,    4   b,    6   a.    
         [0040]    Furthermore, the femtocell  4  is configured as a dual mode femtocell. A dual-mode femtocell is a base station operating as two logical cells  4   a  and  4   b.  These cells  4   a,    4   b  may be configured to operate according to different radio access technologies (RATs), i.e. different telecommunication standards. For example one of the dual cells may be arranged to operate according to a 3G standard such as a Universal Mobile Telecommunications System (UMTS) standard and the other of the dual cells may be arranged to operate according to a 4G standard such as a Long Term Evolution (LTE) standard. Alternatively, the cells  4   a,    4   b  may be arranged to operate according to the same RAT but in different frequency sub-bands. The reach of the cells  4   a,    4   b  does not necessarily extend across exactly the same geographical area. Range is highly dependent on RAT and frequency, e.g. cell  4   a  could be twice the size of cell  4   b.  The arrangement shown in  FIG. 1  is only schematic. On a point of terminology, note that “base station” or “femtocell” refers to the unit, whilst “cell” refers to the logical combination of geographical coverage area and access technology or frequency band (also note that in the context of the present application “femtocell” refers to the base station unit rather than the cell). As the two cells  4   a,    4   b  are provided by the same base station unit then they share the same cell center point, i.e. represent the same geographical node of the network, and they also share at least some of the same hardware resources. For example a dual-mode base station  4  typically shares the same processor for both cells  4   a,    4   b,  though typically not the same antenna. The dual cells  4   a,    4   b  typically also share other base-station functionality, such as configuration management, synchronization and backhaul connection (i.e. same connection to the next element up in the cellular hierarchy). 
         [0041]    The invention could apply equally to any multi-mode base station, but by way of illustration the following embodiments are described in relation to a dual-mode femtocell  4 . 
         [0042]    The user equipment  2  is arranged to be able to request admission to a particular cell, and when it does so, e.g. requesting admission to cell  4   a,  to request a particular quality of service. For example it could request to be provided with at least a certain uplink or downlink throughput, or to be provided with no more than a certain uplink or downlink latency. 
         [0043]    Each of the base stations comprises a radio resource manager (RRM) arranged to receive the admission request from the UE and decide whether to admit the user equipment  2  to the requested cell. Conventionally this is done in the manner described in the background section above by an independent RRM for each cell  4   a,    4   b,    6  respectively, including independent admission control for each of the dual cells  4   a,    4   b.  However, according to the present invention there is provided a joint admission control mechanism which shares information between the two or more cells  4   a,    4   b  of a multimode base station such as a dual-mode femtocell  4 , i.e. shares information relevant to service quality in the two or more cells. This allows the radio resource manager for a requested cell  4   a  to make a decision not only based on information of the requested cell  4   a  itself, but also based on information of the one or more alternative other cells  4   b  of the multimode base station  4 . 
         [0044]    At a higher level of the cellular hierarchy the network may comprise one or more higher-level controller stations, which may be arranged to perform various further management functions. However, the present invention is concerned with radio resource management at the level of a multi-mode base station. 
         [0045]    According to a first embodiment of the present invention, the process of determining the throughput and/or other QOS requirements of a UE  2  can be enhanced by storing long-term statistics of UE behavior at the RRM. This allows the RRM to use past-behavior to admit the UE to the most appropriate cell  4   a,    4   b  of a dual-mode femtocell  4 . 
         [0046]    The joint RRM can keep a history of the past connections for a specific UE  2 , and this can be used to determine the services and throughput requirements that a specific UE typically uses. The long-term parameters kept by the RRM can include the following: 
         [0047]    Requested downlink throughput 
         [0048]    Requested uplink throughput 
         [0049]    Utilized downlink throughput 
         [0050]    Utilized uplink throughput 
         [0051]    Requested downlink latency 
         [0052]    Requested uplink latency 
         [0053]    For these parameters, one or more of the following statistics can be collected: 
         [0054]    Long-term average values for the parameters, giving a measure for basic prediction 
         [0055]    Variation for the average over 24 hour periods, to find behavior patterns across each day. 
         [0056]    Variation for the average over 7 days, to find behavior patterns across each week. 
         [0057]    Short-term average values (over a few hours) to find local trends. 
         [0058]    These parameters and statistics allow the RRM to predict the throughput and/or other QOS requirements of a particular UE  2 . The RRM can then decide whether to continue admitting the UE  2  to the cell  4   a  it is requesting, or whether to immediately admit the UE  2  to an alternative, more appropriate cell  4   b.  The use of joint RRM combined with long-term statistics enables the best cell selection to happen faster, preferably before the UE  2  indicates its QOS requirements to the femtocell  4 . In addition, moving the UE  2  between cells  4   a,    4   b  at the start of the admission process requires fewer signaling messages, thus reducing the signaling load on the network. 
         [0059]    A base station  4  may be configured to operate in one of a plurality of different available modes. Closed access mode is where the cell only provides a service to a subset of UE which are all members of its closed subscriber group (CSG). Open access mode is where the cell provides a service to any UE that are entitled to a service from the network operator (i.e. this is identical mode used in macro, micro and pica cells today). Hybrid access mode is where the cell provides a service to any UE that are entitled to a service from the network operator, but it also has a list of UE in its CSG. This allows the cell to provide an improved service level to these CSG (if it wants to). 
         [0060]    Tracking UE parameters and statistics is most beneficial in a femtocell  4  operating in either closed or hybrid mode where a finite closed group of subscribers exist, which are expected to regularly access the femtocell. This regular access allows reliable predictions to be made. 
         [0061]    The long-term prediction of statistics described above can be either used standalone, or used to produce downlink throughput and latency values (Thp_DL_Req, Latency_DL_Req) and uplink throughput and latency values (Thpt_UL_Req, Latency_UL_Req) to be combined with a second embodiment of the invention, described below. 
         [0062]    According to a second embodiment of the present invention, the selection of the best cell  4   a,    4   b  of the dual mode femtocell  4  can be enhanced by predicting the throughput and latency of each cell that can be achieved. 
         [0063]    The downlink throughput and latency which is achievable can be determined from: 
         [0064]    The static properties of the cell, for example, minimum achievable latency and maximum achievable throughput. 
         [0065]    The available air interface resources based on the number of currently serviced UEs. For example, in LTE this would be the number of resource blocks (RB), while for UMTS this would be the number of codes available. 
         [0066]    The available hardware resources for the cell which relate to the total number of UEs supported, or the number of UEs supported each subframe (LTE) or TTI (UMTS). 
         [0067]    The pathloss to the UE for this cell, which can be very different for each cell. 
         [0068]    Any power limit applied to the cell to protect neighbors in the same frequency sub-band, This could be determined by pathloss to neighbors, downlink loading information for the victim BS, proximity information for the victim UE, and the operating mode for the femtocell (closed, hybrid, open). 
         [0069]    Estimation, via sniffing, of the noise and interference floor at the UE for this frequency sub-band 
         [0070]    Similarly, the uplink throughput and latency which is achievable can be determined from: 
         [0071]    The static properties of the cell, for example, minimum achievable latency and maximum achievable throughput. 
         [0072]    The available air interface resources based on the number of currently serviced UEs. For example, in LTE this would be the number of resource blocks (RB), while for UMTS this would be the number of codes available. 
         [0073]    The available hardware resources for the cell which relate to the total number of UEs supported, or the number of UEs supported each subframe (LTE) or (UMTS), 
         [0074]    The pathloss to the femtocell for this cell, which can be very different for each cell. 
         [0075]    Any power limit applied to the cell to protect neighbors in the same frequency sub-band. This could be determined by pathloss to neighbors and uplink loading information for the victim BS. 
         [0076]    Estimated of the noise and interference floor at the femtocell for this frequency sub-band. 
         [0077]    These parameters can be used to determine a set of uplink and downlink throughput and latency prediction for each cell, denoted by (Thpt_DL_A, Thpt_DL_B, Latency_DL_A, Latency_DL_B) and (Thpt_UL_A, Thpt_UL_B, Latency_UL_A, Latency_UL_B). 
         [0078]    The UE is assigned to the cell with the throughput and latency capabilities which most closely match the UE requirements. 
         [0079]    This prediction of achievable throughput and latency is applicable to a femtocell operating in any of the three modes closed, hybrid or open. 
         [0080]    This can be used standalone when the UE reports its QOS requirements to the base-station, or combined with the UE throughput and QOS prediction described in the first embodiment. 
         [0081]    In addition, if a cell is heavily loaded (congested), the first and second embodiments of the invention can be used together to form a prediction of throughput and latency of each of multiple UEs, in each cell. Thus the UE is able to be optimally redistributed at the dual-mode femtocell. For example, the following values would be determined: 
         [0082]    UE 1  in RATA, UE 2  in RATA 
         [0083]    UE 1  in RATA, UE 2  in RATB 
         [0084]    UE 1  in RATB, UE 1  in RATA 
         [0085]    UE 1  in RATB, UE 1  in RATB The most efficient combination of UE and RAT can then be selected. 
         [0086]    The flow chart of  FIG. 2  illustrates an example of a preferred decision making process which may be implemented in a joint RRM of a multimode base station such as a dual mode femtocell  4 . The process is preferably implemented in the form of computer program code stored on a non-volatile storage medium of the base station  4  (e.g. magnetic memory device such as a hard drive or an electronic memory device such as a flash memory) and arranged for execution on a processing apparatus of the base station (e.g. single or multi core CPU). However, an implementation involving dedicated hardware is not excluded. 
         [0087]    At step S 10  the RRM of the femtocell  4  receives a request from the UE  2  for admission to a particular cell of the dual mode femtocell  4 , e.g. cell  4   a.    
         [0088]    At step S 20 , the RRM consults the past statistics it has accumulated for the UE  2  when it was connected in the alternative cell  4   b  (and preferably also the past statistics it has accumulated for the UE  2  when it was connected in the requested cell  4   a  itself). Generally the past statistics can be collected from either cell or both cells. The RRM uses these statistics to produce expected downlink throughput and/or latency values (Thp_DL_Req, Latency_DL_Req), and/or to produce uplink throughput and/or latency values (Thpt_UL_Req, Latency_UL_Req). For reasons discussed above, in a particularly preferred implementation this is done before the UE  2  signals its own requested QOS requirement(s) to the femtocell  4 . The values may be calculated from the statistics in response to the request, or for faster response time may be maintained in advance of the request. 
         [0089]    At Step S 30 , the RRM consults its prediction of performance of the alternative cell  4   b  (and preferably also its prediction of performance of the requested cell  4   a ), i.e. its prediction of one or more a priori properties that are a feature of the cell itself rather than an a posteriori observed behavior of the UE  2  when connected in the cell. Generally the performance can be determined for either cell or both cells This results in a set of uplink and/or downlink throughput and/or latency prediction values for each cell, (Thpt_DL_A, Thpt_DL_B, Latency_DL_A, Latency_DL_B) and (Thpt_UL_A, Thpt_UL_B, Latency_UL_A, Latency_B). Again in a particularly preferred implementation this is done before the UE  2  signals its own requested QOS requirement(s) to the femtocell  4 ; and the values may be calculated from the statistics in response to the request, or for faster response time may be maintained in advance of the request. 
         [0090]    At Step S 40 , the RRM compares the expected QOS requirement(s) of the UE 2  (Thpt_DL_Req, Latency_DL_Req, Thpt_UL_Req, and/or Latency_UL_Req) with the predicted performance value(s) of the alternative cell  4   b  (Thpt_DL_A, Thpt_DL_B, Latency_DL_A, Latency_DL_B, Thpt_UL_A, Thpt_UL_B, Latency_UL_A, and/or Latency_UL_B), and at step S 50  determines based on the comparison whether the UE  2  should be served by the alternative cell. Preferably this involves also comparing the expected QOS requirement(s) of the UE 2  with the predicted performance value(s) of the requested cell  4   b,  and determining whether the requested cell  4   a  or the alternative cell  4   b  represents the best match to the UE&#39;s needs. 
         [0091]    If the RRM decides the UE  2  would not be better served by the alternative cell  4   b,  it proceeds to step S 60  where it admits the UE  2  to the requested cell  4   a.  If on the other hand the RRM decides the UE would be better served by the alternative cell  4   b,  it proceeds to step S 70  where it admits the UE  2  to the alternative cell  4   b.  This may involve instructing the UE  2  to connect to the alternative cell  4   b  or offering it the option of connecting to the alternative cell  4   b  (the UE  2  could attempt a connection to a cell  6   a  of a different base station  6  in response to the offer). 
         [0092]    In further embodiments, the RIM may receive requests from multiple UEs  2  and may take into account the expected QOS requirements and/or requested QOS for the multiple UEs, so as to determine an optimal set of decisions balancing the needs of all parties involved. The decision making process may also involve more than two cells of a multimode femtocell or other such multimode base station, e.g. by performing multiple instances of the above-described comparison process for multiple alternative cells and determining which comparison results in the best match. 
         [0093]    It will be appreciated that the above embodiments have been described only by way of example. 
         [0094]    For instance, the above has been described in terms of throughput and/or latency, but other information relevant to service quality could also be used in addition or as an alternative to these, e.g. error rate, loss or jitter. 
         [0095]    Whilst it is preferred that the first and second embodiments are used together, this is not necessarily the case. For example the first embodiment could be used alone by taking the UE&#39;s past experience of high throughput or low latency in an alternative one of the multiple cells  4   b  as a trigger to admit the UE to that cell  4   b  instead of the requested cell  4   a.  Or in another example the second embodiment could be used alone by comparing the predicted performance of the alternative cell  4   b  with the UE&#39;s actual requested QOS, instead of basing the comparison on the US&#39;s expected QOS as would be determined from statistics of past behavior according to the first embodiment. 
         [0096]    Other variations may become apparent to a person skilled in the art given the disclosure herein. The scope of the invention is not limited by the described embodiments but only by the claims.