Abstract:
Radio resource allocation is carried out on the basis of a radio environment map. The radio environment map is constructed based on received reports of signal quality and/or strength. Using history and triangulation, estimates of station positions can be determined, and expectations can be determined for interference between stations and between stations and access points. Resource requests can then be fulfilled on the basis of separate treatment of requests which have little potential for causing interference, and those which have potential to cause interference.

Description:
FIELD 
       [0001]    Embodiments described herein relate to radio resource allocation in wireless communications networks. 
       BACKGROUND 
       [0002]    Radio resource allocation is a process which is employed to manage finite radio resource in an environment in which a wireless communications network is established. In a cellular paradigm, radio resource allocation aims to take account of likely interference impact of adjacent cells, when allocating radio resource. In opportunistic or ad hoc paradigms, gathering information to enable effective radio resource allocation is equally if not more important. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0003]      FIG. 1  is a schematic representation of a wireless communications network; 
           [0004]      FIG. 2  is a schematic representation of an access point in accordance with a described embodiment; 
           [0005]      FIG. 3  is a graphical representation of a resource block of a communications channel defined in the network; 
           [0006]      FIG. 4  is a schematic representation of a resource allocation coordination manager of the access point of  FIG. 3 ; 
           [0007]      FIGS. 5 a  and 5 b    are schematic geometrical representations of station position examples to aid in understanding of operation of the described embodiment; 
           [0008]      FIG. 6  is a process flow diagram for a list update process of the described embodiment; 
           [0009]      FIG. 7  is an example list of stations produced by the list update process; 
           [0010]      FIG. 8  is a resource allocation process of the described embodiment; 
           [0011]      FIG. 9  is a normal allocation sub-process called by the resource allocation process of  FIG. 8 ; 
           [0012]      FIG. 10  is an exclude allocation sub-process called by the resource allocation process of  FIG. 8 ; 
           [0013]      FIG. 11  is a list update process of an alternative embodiment; 
           [0014]      FIG. 12  is a resource allocation process of an alternative embodiment; 
           [0015]      FIG. 13  illustrates example lists produced and maintained by the list update process of  FIG. 11 ; 
           [0016]      FIG. 14  illustrates sorted allocation lists generated from the lists of  FIG. 13 ; 
           [0017]      FIG. 15  illustrates prioritised sorted allocation lists generated from the lists of  FIG. 13 ; and 
           [0018]      FIG. 16  is a schematic representation of a portion of the resource block, in the course of an allocation process. 
       
    
    
     DETAILED DESCRIPTION 
       [0019]    A wireless communications network is illustrated in  FIG. 1 . 
         [0020]    In general terms, the embodiment employs a Radio Environment Map (REM), to proactively estimate interference in dense small cell deployments. Embodiments described herein achieve full frequency reuse, i.e. a factor of 1. Embodiments described herein could also exploit white space spectrum opportunities. 
         [0021]    The REM approach, as described in relation to the embodiments, uses a measurement based prediction model of the radio environment in order to estimate the interference to neighbours. 
         [0022]    Conceptually, REM is based on collecting radio related measurements in order to build a statistical map for making radio environment predictions. Dynamic REM (DREM) is considered to be a REM that can perform predictions in short time periods (i.e. at seconds or sub-second resolutions). The DREM approach, used by embodiments described herein, involves an access point performing estimation of interference signal levels, assuming no prior knowledge of the locations of stations capable of communicating with that access point, or locations of other access points. 
         [0023]    The approach then uses these estimates in order to make predictions of the interference levels caused to neighbouring devices. In order to do this, the embodiments make use of received signal power measurements received from participating stations. For example, if the technology specified in the LTE standard is employed, an access point (HeNB) could employ the Reference Signal Received Power (RSRP) measurements reported by UEs. Locations of neighbouring access points are estimated using several accumulated received signal power measurements taken at different positions. 
         [0024]    The described approach does not need prior knowledge of the locations of devices that are deployed. That is, the approach does not rely on position information which could, for instance, be gathered from GPS facilities integrated into devices. While many devices now have such facilities, users may deactivate such facilities for privacy or power consumption reasons, or the facilities may not be available in certain environment (such as indoors). 
         [0025]    Instead, the approach employed by embodiments described herein relies on the collection of measurements made at devices, and makes SIR predictions based on those measurements. The examples disclosed herein make REM predictions of SIR based on RSRP and/or MDT reports, in the context of an LTE based implementation. 
         [0026]    The measurements are accumulated to determine the radio environment. These predictions are used in a constraint policy to determine conflicts. The conflicts are avoided by “excluding” them in a process of assigning radio resource blocks to particular stations in the network. 
         [0027]    Operationally, a characteristic of embodiments described herein is the manner in which the REM is used to collect the measurements in order to make predictions without using location information. Another characteristic is the way in which excluded resource assignments are applied, using the “conflicts” detected by REM SIR estimation. Exclusion is achieved using a sequential “order” of resource block selection. The following description of embodiments will set out an example of a way in which the “order” can be deduced (using the information from REM) and then used to avoid interference. 
         [0028]    The coordinated scheduling scheme of the described embodiments uses the REM predictions of the UE and HeNB SIR (in the context of an LTE implementation) to coordinate RB allocation that attempts to avoid interference. In this approach, interference avoidance is achieved by allocating RBs sequentially as well as avoiding conflicting RB allocations. A SIR threshold (SIRT) is applied to the predicted SIR levels in order to determine whether unacceptable interference may occur. It is also assumed that retransmissions and DL traffic take priority. 
         [0029]    In this scheduling approach the REM user obtains SIR estimates and uses this for restricting the RB scheduling through a constraint policy which identifies the excluded RBs based on these SIR predictions. 
         [0030]    The result of the constraint policy, as laid out in the described embodiments, is the identification of conflicts, which are then assigned resources using the EXCLUDE order in an opposite sequential direction to the normal order, with the direction determined by the respective indices, for instance, with i&lt;j ascending and i&gt;j descending. 
         [0031]    Accordingly,  FIG. 1  illustrates a typical wireless communications network  10 , including an access point  110  and numerous wireless communications devices  120 . A neighbouring access point  110 ′ is also illustrated. 
         [0032]    Expected lines of communication are indicated by solid arrows. The access points  110 ,  110 ′ provide connection facilities to a wider network (typically referred to as “backhaul”), for example to access communications facilities such as the internet. This can be by, for instance, a physically wired network, such as telephone networks or cable networks, power line communication or fibre optics, or by wireless communications media. 
         [0033]    The present example is concerned with the manner in which the access point  110  manages the allocation of radio resource in establishing communication with the wireless devices  120 . 
         [0034]    As shown in  FIG. 2 , the access point  110  is a relatively generic computing device, configured by specific software to implement the described embodiment. To that end, the access point  110  comprises a processor  130  operable to execute computer executable instructions presented to it. A working memory  132  (which would normally comprise volatile and non-volatile memory components) stores program components, such as administrator applications  134  for use by an administrator of the access point and other operating programs, in particular, a communications controller  136  configuring the access point  120  in accordance with the described embodiment. 
         [0035]    A mass storage unit  140  provides bulk data and program storage facilities—normally, mass storage comprises a high volume storage medium which may have relatively slow access speed, certainly in relation to the working memory  132 , and the processor  130  will access data and code stored in the mass storage unit  140  as required, usually storing the same in the working memory  132  for rapid access for convenience. 
         [0036]    A bus  142  provides access by the processor  130  to other components of the access point  120 . In particular, a wireless communications unit  150  is effective to establish radio frequency communication with other devices, in a predetermined band of frequencies specified by a technical standard. In this example, the LTE standard is employed, but the reader will appreciate that this is not essential to an appreciation for the present disclosure. 
         [0037]    A USB port  152  enables connection of the access point  120  to another device, such as a PC based computer, such as to enable wired connection to the services offered by the access point  120  or to enable configuration and control thereof. 
         [0038]    A backhaul interface unit  154  enables connection of the access point to a backhaul facility, such as a cable modem or a telephone line, so that the access point  120  can access facilities offered on such a backhaul installation, for example internet based services. 
         [0039]      FIG. 3  is a representation of the LTE radio frame illustrating resource block structure in TDD (time division duplex) mode. It illustrates the resource available for allocation by the access point. 
         [0040]    As illustrated, each radio frame is a two-dimensional array of resource blocks defined by ten subframes (denoted TRB#), numbered from 0 to 9, covering twelve frequency subcarriers (FRB#) numbered from 0 to 11. 
         [0041]    Within the radio frame, resource blocks in subframes TRB 0  and TRB 5  are reserved for downlink (denoted ‘D’), while resource blocks in subframes TRB 1  and TRB 6  are reserved for synchronisation (denoted ‘S’). 
         [0042]    Each frame is composed of ten subframes, each of which comprise two slots. A resource block is denoted by reference to a slot of a subframe TRB#, carried across the 12 subcarriers FRB#. Within a resource block, resource elements are defined, within which symbols can be transmitted. 
         [0043]    Allocation of these resource blocks as uplink or downlink (except for the reserved resource blocks, as detailed above) is the responsibility of the access point. This allocation is established by way of a process whose architecture is illustrated in  FIG. 4 . 
         [0044]    In the embodiment illustrated in  FIG. 4 , a resource allocation coordination manager  200  is implemented, for example by firmware or software, including a network information acquisition and storage facility  204  able to gather and store report from stations  130  in the network. Then, an REM manager  202  is operable to process the acquired and stored information, to obtain a radio environment map (REM). The estimated SIR is then passed to a resource block scheduler  206  which generates resource block allocation messages back to the stations  130 . 
         [0045]    Each station  130  reports to the access point  120  on received signals attributable to other stations and access points in the network. For example, in LTE, each station  130  reports Reference Signal Received Power (RSRP) measurements. From this information, candidates can be determined for predictions of signal to interference ratios for signals received around the network.  FIG. 5 a    illustrates a simple example of this, for a situation where a station (with index i) is positioned at a position with coordinates (x i. , y i ) and another (with index j) at (x j. , y j ) can be in receipt of signals from two access points (with indices 1 and 2 respectively). The two access points are positioned with coordinates (−c,0) and (c,0), respectively, on a nominal two dimensional reference frame. The reader will appreciate that a two dimensional reference frame is used here, but that this analysis would be extendable to a three dimensional reference frame without difficulty. 
         [0046]    As shown in  FIG. 5 a   , b i , and d i  represent distance between the station at (x i. , y i ) and the respective access points. RSRP levels are collected by the station for signals received from the two access points, these levels are denoted z 1,i  and z 2,i  respectively. The quantity c is the separation between the access points and a midway reference point (0,0). 
         [0047]    A working assumption in this analysis is that this midway point is that point where the same RSRP would be received from each access point (assuming equal transmit power). The validity of this assumption could be tested with accumulation of data over time. 
         [0048]    Thus, the location of the station can be computed as follows: 
         [0000]        b   i =√{square root over ( y   i   2 +( c+x   i ) 2 )} and  d   i =√{square root over ( y   i   2 +( c−x   i ) 2 )}
 
         [0049]    Assuming b i /c=r i  and d i /c=s i ; 
         [0000]    then 
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         [0000]    where r i  and s i  are defined as relative distances from the respective access points to the station, as a ratio to half the access point separation c, which is estimated by determining the midway reference point (0,0), where the measured signal levels are z 0,i . 
         [0050]    This is useful, as the evaluation of r i  and s i  does not require absolute measurements, but rather as ratios, respectively, of z 1,i  and z 2,i  to z 0,i . Further, if the measured signal levels are reported on a logarithmic scale, then ratios are re-expressed as differences, and the computational effort required to derive r i  and s i  is further eased, so: 
         [0000]      10α log( r   i )= z   1,i   −z   0,i  and
 
         [0000]      10α log( s   i )= z   2,i   −z   0,i  
 
         [0051]    In each of these cases, no knowledge is required of the transmit powers of the access points. α is a path loss exponent. This can be estimated by numerical methods as more data is collected, although it may also be possible to start with a working assumption based on past experience. 
         [0052]    From this analysis, it therefore follows that the download Signal to Interference Ratio (SIR), at any station (UEi) for a signal from one access point (AP1) interfered by a signal from another access point (AP2), is given by: 
         [0000]        HeNB SIR   1,2 =10α log( b   i   /d   i )=10α log( r   i   /s   i )= z   1,i   −z   2,i  
 
         [0000]    and evidently vice versa by: 
         [0000]        HeNB SIR   2,1 =10α log( d   i   /b   i )=10α log( s   i   /r   i )= z   2,i   −z   1,i  
 
         [0000]    where i denotes the index of the station (UE). 
         [0053]    Likewise for any two selected UE locations (i.e. denoted by index 1 and 2 associated with AP1 and AP2 respectively), as shown in  FIG. 5 b   , the expression for the uplink SIR resulting from the signal from one UE (UE2) on the signal from another (UE1) is given by: 
         [0000]        UL SIR   1,2 =10α log( d   2   /d   1 )=10α log( s   2   /s   1 )= z   2,2   −z   2,1  
 
         [0000]      and evidently vice versa by: 
         [0000]        UL SIR   2,1 =10α log( b   1   /b   2 )=10α log( r   1   /r   2 )= z   1,1   −z   1,2  
 
         [0054]    Further, for time division duplex (TDD) communications, it is also important to consider the effect of interference when the uplink and downlink are not aligned. For example, an arrangement could be contemplated where two stations are associated with respective access points and use resource blocks at the same time as the access points. The stations are positioned at points (x 1 , y 1 ) and (x 2 , y 2 ) denoted by UE1 and UE2 respectively. Indexing the distances between the stations and the access points in the same way as is illustrated in  FIG. 5 b   , the SIR for a signal, received at a location UE1 (associated with the AP1), with respect to interference from UE2, is: 
         [0000]    
       
         
           
             
               
                 
                   
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         [0055]    Likewise for the SIR for a signal, received at a location UE2 (associated with the AP2), with respect to interference from UE1 is: 
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         [0056]    Using the equal power assumption, therefore, the reference distance c can be cancelled, implying that the actual positions of access points is not required for this analysis. 
         [0057]    The reader will note that the geometric analysis as laid out above can give rise to plural results, because of the dual solutions to quadratic problems, as represented by the use of the ±operator above. 
         [0058]    However, this can be resolved over time. It will be appreciated that, in many cases, stations would be expected to move over time, but not so quickly that they cannot be tracked between one measurement opportunity and the next. Using successive reports, the acquisition of information can lead to certain candidate solutions being rejected, as being inconsistent, and for other candidate solutions to be retained in favour. Thus, as time progresses, the resultant radio environment map (REM) will resolve into SIR and station position information with high degrees of confidence associated therewith. 
         [0059]      FIG. 6  then illustrates a process by which this information, built into a REM, can be harnessed to allocate resource in the wireless communications system  100  in which resource blocks are defined in time and frequency. 
         [0060]    Reports are received from time to time from stations  120 . In this process, it is assumed that reports are received periodically, but other arrangements may be provided depending on the implementation. In the first step S 1 - 2  of the process, therefore, reports are acquired from each station associated with an access point. These reports, containing signal measurement vectors z (or relative values), are then used, in step S 1 - 4 , to update the REM. REM computes the SIR estimates using the data collected from all of the stations  120 . 
         [0061]    Each access point  110  pair and each station pair  120  is then tested against a rule in step S 1 - 6  and is designated as belonging to one or more EXCLUDE groups on the basis of that test. In this embodiment, a typical rule for each node (denoted i and j) is: 
         [0000]    IF {HeNB SIR i,j &lt;SIR T } THEN EXCLUDE j
 
Likewise for each UE  120  pair, denoted (i,j) the typical rule is:
 
IF {UL SIR i,j &lt;SIR T } OR {UE SIR i,j &lt;SIR T } THEN EXCLUDE i,j
 
Alternative rules are:
 
IF {UL SIR i,j &lt;SIR T } OR {UE SIR i,j &lt;SIR T } THEN EXCLUDE j
 
IF {UL SIR i,j &lt;SIR T } OR {UE SIR i,j &lt;SIR T } THEN EXCLUDE i
 
where the SIRT threshold margin is a constant selected according to the desired target. In one example, SIRT could be 10 dB.
 
         [0062]    That is, for any acquired SIR statistic or estimate then, if the SIR of that signal pair is lower than the threshold, the corresponding stations are designated within one of the EXCLUDE groups. 
         [0063]    Thus, for any access point, its associated terminal stations (UE) may be designated within the EXCLUDE groups. These are expressed, in this embodiment, as lists as set out in  FIG. 7 . This designation determines the way in which resources are subsequently allocated. 
         [0064]    In step S 1 - 8 , a routine is called to update, store and if necessary distribute the corresponding station lists designated as EXCLUDE using the above rule. This depends on where the lists are generated, which can be centrally or locally within each access point (REM manager,  202 ). 
         [0065]    The aforementioned lists in step S 1 - 10  are used in the resource allocation process of each access point, in an independent manner, as illustrated in  FIG. 8 . In this routine, an initialisation step S 2 - 2  starts the normal round robin processing of resource requests, starting with the downlink (DL). If the selected station is on the excluded list, as determined in step S 2 - 4 , the exclude allocation sub process is performed in step S 2 - 8  (according to  FIG. 10 ), otherwise the normal allocation sub process is performed in step S 2 - 6  (according to  FIG. 9 ). 
         [0066]    The normal allocation sub process, in step S 3 - 2 , initialises corresponding TRB and FRB pointers to the start of the subframe, in time, and at a midway point in frequency respectively. For instance, when there are multiple subframes per frame in time TRB is set to the beginning of the first subframe and resource blocks allocated, in S 3 - 8 , in accordance with the requests, in step S 3 - 4 , providing the sufficient resources are available, as determined in step S 3 - 6 . 
         [0067]    Likewise, if the request under consideration, in step S 2 - 2 , corresponds to a station on the EXCLUDE list, the allocation process called is set out in  FIG. 10 . In this case, by contrast, the starting point for allocation of resource requests, in step S 4 - 2 , is half a frame (i.e. a subframe) and half the frequency bandwidth distant to that in S 3 - 2 . This offers improvement of separation of the potential interferers which are contained in the EXCLUDE list. An initialisation step S 4 - 2  implements this on the start of each frame allocation process. 
         [0068]    Then, similar to the earlier described procedure, step S 4 - 4  establishes an allocation process by selecting a resource request corresponding to the station on the EXCLUDE list. This resource request is then tested in step S 4 - 6  to determine if it can be fulfilled. If it can, then in step S 4 - 8  the resource is allocated, and the pointers for next allocation are updated. Step S 4 - 10  acts to remove the resource requests once allocated. 
         [0069]    Step S 4 - 12  is a check to determine if there are more pending resource requests. If there are, the routine returns to step S 4 - 4  otherwise it terminates. 
         [0070]    Following this, and returning to  FIG. 8 , a step S 2 - 10  determines if the resource blocks are fully allocated or if all resource requests have been dealt with, returning to step S 2 - 2  if this is not the case, or moves to the uplink phase. If the uplink phase has not already been completed, as determined in step S 2 - 11 , the process proceeds to the uplink (UL) allocation phase, which is initialised in step S 2 - 12  and thence to step S 2 - 2  as before. Once the uplink phase is complete, the process terminates for that frame. 
         [0071]    The reader will appreciate that the resource allocation process laid out above is but one example. The guiding principle, in general terms, is to identify potential interferers using the REM. Then, the EXCLUDE designated resource requests are distinguished, in the resource allocation process to separate, as far as possible, the allocated resource blocks that could cause interference, thereby reducing the possibility of interference. 
         [0072]    In the example above, requests are handled in a round robin manner. This may be desirable in some circumstances, but not in others. Therefore, modifications to the above processes may offer different approaches which provide different prioritisation, while also accommodating the above general principle, which remains unchanged. 
         [0073]    For instance,  FIG. 11  illustrates a second example of a resource block allocation process. In this example, steps S 5 - 2  and S 5 - 4  are the same as steps S 1 - 2  and S 1 - 4  described above. However, in step S 5 - 6 , two EXCLUDE lists are generated. In this case, one EXCLUDE list contains station indexes (i) and the other (j), as depicted in  FIG. 13 , in which nodes i may suffer interference from nodes j. This enables resources for each pair to be further separated beyond that possible with a single EXCLUDE list. The result of this can best be seen in  FIG. 14 , which shows the two sorted EXCLUDE lists which correspond to two separate EXCLUDE resource allocation starting points. These starting points are separated further than previously achieved with a single EXCLUDE list, thus providing more certainty in avoiding interference. 
         [0074]    This approach can be illustrated schematically as two EXCLUDE lists set out in  FIG. 13 . For instance with indexes i and j, if i&lt;j it indicates that i should use a start point 1 and j start point 2. Hence, two separate sorted allocation lists are generated from the EXCLUDE lists. The resulting sorted lists are indicated in  FIG. 14 . The lists can be further sorted based on a priority order (for instance using the index as an example) as indicated in  FIG. 15  and used in the final allocation lists. 
         [0075]    Yet a further approach to this resolution of EXCLUDE lists can be understood from a routine set out in  FIG. 12 . The process commences by sorting the exclude lists into allocation lists, as in  FIG. 14  or  FIG. 15 , in step S 6 - 2 . In this routine, an initial step, S 6 - 2 , is carried out to resolve the two lists into prioritised sorted lists, as set out in  FIG. 15 . The principles governing this sort are as follows. Firstly, the priority of requests is respected as an overriding sort criterion for each starting point. For requests with equal priority, if this is possible, the prioritised sort order can be made by the unique station index i and j for the two starting points respectively. 
         [0076]    Other sort approaches would equally be possible. 
         [0077]    Then, the allocation lists are processed, by selecting each allocation list in turn, starting with the downlink in step S 6 - 4 . The first list is designated to starting point 1, and is allocated according to the rules in step S 6 - 8 . If there are still resources available and more entries in the list, as determined in step S 6 - 9 , the process is repeated. This list is designated to starting point 2, and is allocated according to the rules in step S 6 - 10 . If there are still resources available and more entries in the list, as determined in step S 6 - 12 , the process is repeated. 
         [0078]    After that, the uplink phase is started in step S 6 - 16 , if it has not been completed as determined at step S 6 - 14 , in an identical manner to the downlink phase. 
         [0079]      FIG. 16  illustrates the contrast between the NORMAL allocation rule and the EXCLUDE allocation rules with two starting points, according to the examples described above. As can be seen, there will be some pre-allocation of resource to downlink communication by the access point, as indicated by shading. Then, if the NORMAL rule is applied, allocation commences from the mid-spectrum point, and from timeslot 0, while in the one EXCLUDE allocation list the starting point is at the end of the first subframe and the lower edge in frequency, while the other starting point is at the end of the second subframe and the upper edge in frequency. 
         [0080]    In fact, as the reader will appreciate, the exact scheme of the EXCLUDE allocation rules versus the NORMAL allocation rule is immaterial. It is desirable that they are distinctive, to the extent that the resource allocation on one rule differs from the resource allocation on the other, to reduce the possibility of two resource allocations, of potentially interfering stations, being adjacent to each other. No set of rules will completely eliminate the possibility of interference, unless joint scheduling of all access points is performed, but the presently described approach provides mitigation without the need and complexity of joint scheduling. 
         [0081]    While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel methods and systems described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions, and changes in the form of the methods and systems described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.