GB2498927A

GB2498927A - Configuring random access channels based on an ABS pattern within the vicinity of an apparatus

Info

Publication number: GB2498927A
Application number: GB1200911.4A
Authority: GB
Inventors: Samuli Turtinen; Sami-Jukka Hakola; Timo Koskela; Tero Henttonen; Ville Vartiainen
Original assignee: Renesas Mobile Corp
Current assignee: Renesas Electronics Corp
Priority date: 2012-01-19
Filing date: 2012-01-19
Publication date: 2013-08-07
Anticipated expiration: 2032-01-19
Also published as: GB201200911D0; GB2498927B

Abstract

Systems and techniques for managing access to a random access channel. A base station (104) is informed of almost blank subframe patterns used by devices (108,110) in its vicinity, and configures its random access channels so that, for every almost blank subframe pattern in the vicinity of the base station (104), a subframe in a specified position of a random access response window of at least one random access channel will correspond to an almost blank subframe of the almost blank subframe pattern.

Description

1

METHOD, APPARATUS AND COMPUTER PROGRAM FOR CONFIGURING RANDOM ACCESS CHANNELS

Technical Field

5 The present invention relates to a method, apparatus and computer program for configuring random access channels. The exemplary and non-limiting embodiments of this invention relate generally to wireless communication systems, methods, devices and computer programs, and more specifically relate to mechanisms for enhanced inter-cell interference coordination (elCIC).

10

Background

The following abbreviations that may be found in the specification and/or the drawing figures are defined as follows:

15

ABS

almost blank subframes

CDMA

code division multiple access

CQI

channel quality indication

CSG

closed subscriber group

CSI

channel state information

20

CSI-RS

channel state information reference signal

DL

downlink

elCIC

enhanced inter-cell interference coordination

eNodeB

evolved Node B

eNB

evolved Node B

25

FDD

frequency division duplex

HARQ

hybrid automatic repeat request

HSS

home subscription server

LTE

Long Term Evolution

MTC

machine-type communications

30

OA&M

operations, administration and maintenance

PDCCH

physical downlink control channel

2

PDSCH

physical downlink shared channel

PLMN

public land mobile network

PMI

precoding matrix indicator

PRACH

physical random access channel

P-RNTI

paging radio network temporary identifier

PUCCH

physical uplink control channel

PUSCH

physical uplink shared channel

RA

random access

RACH

random access channel

RAR

random access response

RNTI

radio network temporary identifier

RRC

radio resource control

SI-RNTI

system information radio network temporary identifier

TDD

time division duplex

TTI

transmission time interval

UE

user equipment

UL

uplink

The demand for communication services has grown at an increasingly rapid 20 rate in recent years, and this trend is expected to continue. Deployment and infrastructure has increased, and many installations overlap. For example, multiple cells may occupy the same geographic area. A larger area may encompass a large area, serviced by a macro base station or macro eNB, and one or more smaller areas within the macro cell encompassing smaller cells, with such a smaller cell being 25 known, for example, as a pico cell or a femto cell served by a pico eNB or femto eNB. A pico cell or a femto cell encompassing a portion of the geographic area served by a macro cell may be dedicated to a closed subscriber group (CSG), providing access only to specified user equipment (UEs) which are identified as members of the CSG. A pico or femto eNB that supports a closed subscriber group may operate in the 30 vicinity of a UE that is served by the macro cell, but may not allow the UE to use resources provided by the pico or femto eNB because the UE is not a member of the

3

closed subscriber group. Pico eNBs and femto eNBs consume network resources such as available frequencies and channels. Therefore, unless appropriate measures are taken, UEs served by macro cells may be subject to interference presented by eNBs to which they are not allowed access.

5

Summary

According to a first aspect of the present invention, there is provided apparatus for configuring random access channels, the apparatus comprising a processing system constructed and arranged to cause the apparatus to perform actions comprising 10 at least receiving almost blank subframe information relating to almost blank subframe patterns used by devices in the vicinity of the apparatus, and configuring random access channels so that, for every almost blank subframe pattern in the vicinity of the apparatus, a subframe in a specified position of a random access response window of at least one random access channel will correspond to an almost 15 blank subframe of the almost blank subframe pattern.

According to a second aspect of the present invention, there is provided apparatus for configuring initial access to a base station, the apparatus comprising a processing system constructed and arranged to cause the apparatus to perform 20 functions comprising at least receiving almost blank subframe information relating to almost blank subframe patterns of an overlying aggressor cell in the vicinity of the apparatus, and configuring initial access to a base station so as to adjust timing of an initial access to a base station so as to select a random access channel for use in transmitting a random access preamble based on a position of a specified almost blank 25 subframe in a random access response window of the random access channel.

According to a third aspect of the present invention, there is provided a method of configuring random access channels, the method comprising receiving almost blank subframe information relating to almost blank subframe patterns used by 30 devices in the vicinity of the apparatus, and configuring random access channels so that, for every almost blank subframe pattern in the vicinity of the apparatus, a

4

subframe in a specified position of a random access response window of at least one random access channel will correspond to an almost blank subframe of the almost blank subframe pattern.

5 According to a fourth aspect of the present invention, there is provided a computer program comprising instructions execution of which by a processor configures an apparatus to perform actions comprising at least receiving almost blank subframe information relating to almost blank subframe patterns used by devices in the vicinity of the apparatus, and configuring random access channels so that, for 10 every almost blank subframe pattern in the vicinity of the apparatus, a subframe in a specified position of a random access response window of at least one random access channel will correspond to an almost blank subframe of the almost blank subframe pattern.

15 The computer program may be stored as instructions on a computer-readable medium.

The processing system may comprise memory and at least one processor, as well as a program of instructions, the program of instructions being configured to, 20 with the memory and the at least one processor, configure the apparatus to perform actions as described above.

Further features and advantages of the invention will become apparent from the following description of preferred embodiments of the invention, given by way of 25 example only, which is made with reference to the accompanying drawings.

Brief Description of the Drawings

Figure 1 shows schematically an example of a wireless network comprising one or more embodiments of the present invention;

30

5

Fig. 2 shows schematically details of an exemplary base station and user equipment according to an embodiment of the present invention;

Fig. 3 shows schematically exemplary configurations of subframes according 5 to an embodiment of the present invention; and;

Fig. 4 illustrates shows schematically an example of a process according to an embodiment of the present invention.

10 Detailed Description

Examples of embodiments of the present invention recognise that closed subscriber groups are required to operate in such a way that they do not prevent non-member UEs from receiving service from macro cells, and it is also important that this requirement be met for UEs in the radio resource control idle (RRCIDLE) mode as 15 well as for UEs in the radio resource control connected (RRC CONNECTED) mode. An eNB supporting a closed subscriber group and presenting interference to a nearby macro eNB may be referred to as an aggressor eNB. A UE that is served by a macro eNB, and that suffers interference from an aggressor eNB may be referred to as a victim UE. A macro eNB that suffers interference from an aggressor eNB may be 20 referred to as a victim eNB.

The present invention recognises that one mechanism for providing access by a UE to a victim eNB is through the use of almost blank subframes (ABS). LTE Release 10 (LTE-A) uses carrier aggregation, in which the whole system bandwidth is 25 divided into multiple component carriers. Since LTE-A contemplates many more network access nodes of various varieties (for example, conventional cells termed macro cells, pico/femto cells/home eNBs, remote radio heads and repeaters), it has also introduced a mechanism to mitigate interference among them, referred to as enhanced inter-cell interference coordination elCIC. According to this technique, one 30 cell coordinates with its neighbour cells to avoid interfering transmissions. One aspect of elCIC in LTE Release 10 is the use of almost blank subframes (ABS), in

6

which a network node transmits nothing except the common reference signals used for measurements (and in some cases also essential control information such as synchronisation, paging, or system information) but never any unicast DL user data. In general, an eNB transmits its ABSs according to a known pattern and the 5 transmission of the eNB during the ABSs should cause little if any interference to transmissions of neighbouring eNBs. The elCIC concept is used for both macro and pico/femto eNBs. A femto eNB may coordinate its transmissions with the overlay macro eNB in order to allow macro user devices close to the femto eNB to experience less interference during the femto eNB's ABS transmissions. Or a macro eNB 10 coordinates its own ABS transmissions with a nearby pico eNB so that the smaller interference from the macro eNB's ABSs allows user devices within a larger area to find and connect to the pico eNB.

A UE in an RRC IDLE mode initiates a connection to an eNB through a 15 random access request. For an eNB to be able to send a random access response to a UE using almost blank subframes, the UE's random access response window should include almost blank subframes, and the eNB should be able to identify the victim UE's random access attempts.

20 The sending of random access response (RAR) messages in almost blank subframes in every case, whether or not directed towards a response from a victim UE, is likely to degrade performance of the macro eNB, affecting characteristics such as random access capacity and latency performance. Always sending an RAR message in an almost blank subframe (ABS) can cause unnecessary latency in random 25 access, even for UEs that are not affected by interference from an interfering cell. If the RAR message is always sent in an almost blank subframe, the RAR message cannot be sent without a wait for an almost blank subframe in an RA Response window.

30 For example, in a pattern of 1 ABS per 8 subframes, an RA response window should be at least 8 subframes wide to ensure that it covers at least one ABS

7

subframe. An RAR message would likely not be sent out in the first subframe in the ABS response window, but might instead be subject to a delay of 7 ms. Such an added delay would be incurred even by a UE that is unaffected by interference from a neighbouring cell, and that would not need to rely on an ABS to receive an RAR 5 message.

A common search space may also be used by physical downlink control channel (PDCCH) messages with P-RNTI. The common search space is also used by PDCCH messages with SI-RNTI. If all four PDCCH in the common search space are 10 used for RAR messages, no PDCCH will be available for paging or system information updates. Sending all RAR messages only in ABS will also impose additional pressure on the availability of PDCCH resources to schedule physical downlink shared channel (PDSCH). Because an interfered UE can only be served in an ABS, the overall effectiveness of the range expansion, including user throughput 15 and cell edge throughput, will be adversely impacted.

If the ABS density is large, the delay and performance issues may be less severe, but this is at the expense of taking resources away from the interfering cell and reserving them as ABS for the interfered cell. This may impose negative impact on 20 the overall system throughput. Therefore, it is not feasible to send all the RAR messages in the protected subframes.

To reduce the impact of a high ABS density on the performance of interfering cells, operators may configure several low overhead ABS patterns for different cells. 25 For example, a configuration may include a cell 1 exhibiting the pattern (1/8, 1, ABS) with subframe configuration 10000000, a cell 2 with the same pattern and with subframe configuration 00010000, and a cell 3 the same pattern with configuration 00000100. Such an approach increases ABS density from the macro cell point of view to be 3/8 subframes, but from the point of view of the interfering cell, the ABS 30 density is still 1/8 subframes. Therefore, the macro cell experiences the lower interference associated with a higher ABS density, but the interfering cell does not

8

suffer the additional burden associated with a higher ABS density. However, implementing such a scenario presents difficulties in the identification of a particular victim UE with a macro cell, or the assignment of an ABS pattern to an eNB.

5 Fig. 1 shows schematically a network 100 comprising a cell 102 served by a macro eNB 104, as well as a femto eNB 106, and UEs 108 and 110. The UE 108 is served by the eNB 104 and the UE 110 is a member of a closed subscriber group and is served by the eNB 106. The eNB 106 is a possible source of interference to the eNB 104 and the UE 108. In addition, eNBs 112 and 114 also act as similar sources 10 of interference to the eNB 104 and the UE 108. The UE 108 may be configured to operate in an RRC IDLE mode until it needs service from the eNB 104, and then to attach to the eNB 104 once it needs service. When the UE 108 is in an RRC IDLE mode, it is configured to perform elCIC, and has stored, or has access to, information defining the ABS pattern of a closed system group or other interfering cell, such as 15 the eNB 106, to which the UE 108 does not have access. The eNB 106 is in close proximity to the UE 108. The UE 108 and the eNB 106 are in a coverage area of the macro eNB 104. The macro eNB 104 may suitably have stored, and in fact may have configured, all active ABS patterns in its vicinity. One mechanism by which the eNB 104 may inform others of the ABS patterns in its vicinity is through operations, 20 administration, and maintenance (OA&M.)

Fig. 2 shows schematically additional details of the eNB 104 and the UE 108. The eNB 104 suitably comprises a transmitter 202, receiver 204, radio controller 206, and antenna 208. The eNB 104 further suitably comprises a processor 210, memory 25 212, and storage 214, communicating with one another and with the radio controller 206 over a bus 216. The eNB 104 suitably further employs data 218 and programs 220, residing in storage 214.

The UE 108 suitably comprises a transmitter 242, receiver 244, radio 30 controller 246, and antenna 248. The UE 108 further suitably comprises a processor 250, memory 252, and storage 254, communicating with one another and with the

9

radio controller over a bus 256. The UE 108 also suitably employs data 258 and programs 260, residing in storage 254.

The eNB 104 and the UE 108 are adapted to allow for access by the UE 108 to 5 random access channels of the eNB 104 in such a way that the eNB 104 provides a RACH response window with an ABS subframe in a desired location for every ABS pattern used by devices in the vicinity of the eNB 104.

To take one exemplary configuration, an eNB such as the eNB 104 may 10 configure its random access channels (RACH) in such a way that an ABS subframe of every ABS pattern in the vicinity of the eNB 104 will be the first ABS subframe of an RA response window of at least one RACH in the cell of the eNB. Such configuration may be accomplished by configuration of common random access parameters, selected ones of which may be exemplified by LTE information elements 15 (IEs) such as RACH-ConfigCommon and PRACh-Config. Such information elements may, for example, be stored as part of the data 218. In such an embodiment, the eNB 104 will thus provide a victim UE with an immediate opportunity to deliver its RA response during an almost blank subframe of the aggressor cell.

20 To take another exemplary configuration, the eNB 104 may configure its common random access parameters so that an ABS subframe in the vicinity of the eNB will be in the primary position within an RA response window of at least one RACH in the cell of the eNB. An ABS subframe that is in the primary position is in the first, second, or last ABS subframe of the RA response window, relative to other 25 ABS subframes in the RA response window.

As a further alternative, the common random access parameters may be configured so that an ABS subframe of every ABS pattern in the vicinity of the eNB will be in a one position of a specified range of positions, such as in one of the 30 primary to secondary position, one position of the primary to tertiary position, and so on. In one embodiment, if the definition of the primary, secondary, tertiary position

10

and so on is not signalled in the cell, the first position within an RAR window for an ABS subframe may be used for a default primary position value.

The eNB 104 may suitably implement a cycle in within which an ABS 5 subframe of a particular ABS pattern will be in the first, or primary position, or in a secondary, tertiary, and so on, position within an RAR window of at least one RACH in the eNB. The cycle may be configurable or fixed, and may be expressed as a multiple of a subframe, radio frame, ABS pattern cycle, or other unit or parameter. For example, one cycle that may be used is the MeasSubframePattern-rlO cycle that is 10 defined in relevant LTE specifications. The cycle may suitably be defined by a variable whose attributes and value may be stored as part of the data 218. In one exemplary embodiment of the invention, the cycle may be less than a system information modification period, such as the LTE information element modificationPcriodCocfPdefaultPagingCycle. In another exemplary embodiment, 15 the cycle may be less than the default paging cycle, which may be represented, for example, by the LTE information element defaultPagingCycle.

The calculation of the cycle may be associated with a system frame number (SFN), and may, in one embodiment of the invention, be the result of a modulo 20 operation on a system frame number, such as SFN mod X, with the value of X being any suitable positive integer. Information defining the cycle may suitably be defined in appropriate groups of information elements, such as the LTE system information block 2, and specifically in the RACH-ConfigCommon information element in the system information block 2. Alternatively or in addition, indices of the primary, 25 secondary, and so on positions of the RACH RAR may be carried in the system information block 2, and specifically in the RACH-ConfigCommon information element in the system information block 2. As a further alternative, such information may be carried in a system information block specifically dedicated to carrying information for elCIC UEs.

30

11

Each position within an RAR window may correspond to groups of RA preambles used by devices implementing elCIC, such as the UE 108. The eNB 104 may configure the number of preambles that may belong to each group, and the number of preambles within each group may be different. The eNB 104 may be 5 configured so that all of the RA preambles used by the eNB 104 are elCIC preambles.

In one embodiment of the invention, a UE such as the UE 108 may be configured so as to adjust the timing of its transmission of the RA preamble according to the position of the ABS subframe of the ABS pattern of overlying aggressor cells 10 within an RAR window as compared with other ABS subframes of other ABS patterns. The UE 108 may therefore have access to information relating to the RAR windows of the various RACH channels used by the eNB 104. Such information may, for example, be stored as part of the data 258, or may be otherwise made accessible to the UE 108. The UE 108 may also store or have available information 15 defining the locations of ABS subframes of aggressor cells. The UE 108 may use cycle information from the eNB 104, or similar to that used by the eNB 104 in making such adjustments.

Fig. 3 shows schematically exemplary configurations of subframes used by 20 various devices according to one or more embodiments of the present invention. Frame configurations 302 and 304 representing frame structures that may be used by the eNB 104 are illustrated. The frame configurations 302 and 304 illustrate all three ABS pattern configurations discussed above, as well as the response windows 306 and 308 representing the RA response windows implemented by the eNB 104 for the 25 random access channels 318 and 320. The configuration 310 is the RA resource/channel configuration, and the remaining configurations are the ABS patterns 312, 314, and 316 used by the eNBs 106, 112, and 114, respectively.

In the configurations 302 and 304, the eNB 104 has configured the primary 30 and secondary positions and groups of elCIC RA preambles for use for initial access by devices such as the UEs 108 and 110. In the present exemplary embodiment, the

12

primary position is the first occurrence of an ABS subframe in an RAR window and the secondary position corresponds to the last occurrence. Suppose, then, that the UE 108 is applying the ABS pattern 312 and uses its random access signal. The random access preamble transmission is initially configured to correspond to the first random 5 access channel available to a UE after the UE needs to initiate a random access procedure. This random access channel is illustrated here as the RACH channel of subframe #1 of the first radio frame, which is defined here as RA instant #1,318. The ABS subframe of the ABS pattern 312 is in the second or next to last subframe in the RAR window 306.

10

Desired relative positions of the ABS subframe pattern 312 are either the first or the last occurrence in the RAR window. Therefore, the UE 108 adjusts the timing of the random access preamble transmission to the next possible RACH subframe, which is subframe 3 of ABS pattern 312, shown here as 320. With this adjustment, 15 the position of the ABS subframe of the pattern 312 with respect to other ABS subframes in the patterns 314 and 316 is the first position in the RAR window 308.

Fig. 4 shows schematically the steps of an example of a process 400 according to an embodiment of the present invention. At step 402, a base station, such as a 20 macro eNB, suitably receives almost blank subframe information identifying all almost blank subframes used by devices in its vicinity, such as neighbour base stations, such as eNBs, and UEs, such as UEs configured for elCIC. At step 404, the base station configures its random access channels based on the almost blank subframe information so that for every almost blank subframe pattern in the vicinity 25 of the base station, at least one random access channel will have a random access response window with a primary subframe position corresponding to an almost blank subframe in the pattern. The primary position of a response window may be the first, second, or last ABS subframe of the response window.

13

In one embodiment of the invention, the base station may configure its random access channels such that the subframe position corresponding to an almost blank subframe in the pattern is the first subframe position in the response window.

5 The configuration may be accomplished according to one or more of the mechanisms described above, such as defining a cycle exhibiting one or more of the characteristics described above. The configuration may also be accomplished in such a way that each of the configured positions corresponds to one or more groups of elCIC random access preambles, as described above, and may be accomplished in 10 such a way that elCIC random access preambles are all random access preambles of the eNB. In one or more embodiments of the invention, the elCIC preambles may be selected from among the preambles reserved by the eNB for contention free access. Such an approach ensures that the elCIC preambles thus selected will be outside the range of legacy contention based random access preambles to be used by a UE. In 15 one or more further embodiments of the invention, the elCIC random access preambles may be chosen to be within all the random access preambles of the eNB.

At step 406, a user equipment receives almost blank subframe information relating to an almost blank subframe of an aggressor cell. At step 408, the user 20 equipment adjusts timing of an initial access signal so as to send a random access preamble according to the position of the almost blank subframe pattern of the aggressor cell. The adjustment may suitably be performed so that an ABS subframe of the overlying aggressor cell is in a first or a primary position within a random access response window. The adjustment may suitably use cycle information similar 25 to that described above in making its adjustments.

The above embodiments are to be understood as illustrative examples of the invention. Further embodiments of the invention are envisaged. It is to be understood that any feature described in relation to any one embodiment may be used alone, or in 30 combination with other features described, and may also be used in combination with one or more features of any other of the embodiments, or any combination of any

14

other of the embodiments. Furthermore, equivalents and modifications not described above may also be employed without departing from the scope of the invention, which is defined in the accompanying claims.

15

Claims

1. Apparatus for configuring random access channels, the apparatus comprising a processing system constructed and arranged to cause the apparatus to perform actions

5 comprising at least:

configuring almost blank subframe information relating to almost blank subframe patterns to be used by devices in the vicinity of the apparatus; and configuring random access channels so that, for every almost blank subframe pattern in the vicinity of the apparatus, a subframe in a specified position of a random 10 access response window of at least one random access channel will correspond to an almost blank subframe of the almost blank subframe pattern.

2. Apparatus according to claim 1, wherein the specified position is the first almost blank subframe.

15

3. Apparatus according to claim 1, wherein the specified position is a primary position, wherein a primary position comprises one of the first almost blank subframe position, the second almost blank subframe position, or the last almost blank subframe position.

20

4. Apparatus according to claim 1, wherein each almost blank subframe of all the almost blank subframe patterns lies in one of a primary, secondary, or tertiary position of the random access response window.

25 5. Apparatus according to any of claims 1 to 4, wherein configuring random access channels comprises configuring RACH-ConfigCommon and PRACh-Config information elements.

6. Apparatus according to any of claims 1 to 5, wherein configuring random 30 access channels comprises defining at least one cycle within which an almost blank subframe of an almost blank subframe pattern is to be in a specified position.

16

7. Apparatus according to any of claims 1 to 6, wherein configuring random access channels comprises allocating one or more preambles from among at least one contention free random access preamble configured by the apparatus.

5

8. Apparatus for configuring initial access to a base station, the apparatus comprising a processing system constructed and arranged to cause the apparatus to perform actions comprising at least:

receiving almost blank subframe information relating to almost blank 10 subframe patterns of an overlying aggressor cell in the vicinity of the apparatus; and configuring initial access to a base station so as to adjust timing for sending a random access preamble to a base station so as to select a random access channel for use in transmitting a random access preamble based on a position of a specified almost blank subframe in a random access response window of the random access 15 channel.

9. Apparatus according to claim 8, wherein the position is a first almost blank subframe position of the random access response window.

20 10. Apparatus according to claim 8, wherein the position is a second almost blank subframe position of the random access response window.

11. Apparatus according to any of claims 8 to 10, wherein the adjustment is based on cycle information relating to the base station.

25

12. Apparatus according to claim 11, wherein the cycle is less than a system modification period.

30

13. Apparatus according to claim 11 or claim 12, wherein the cycle information is defined by information carried in a System Information Block dedicated to carrying information for enhanced inter-cell interference coordination of user equipment.

17

14. Apparatus according to any of claims 11 to 13, wherein the cycle information defines a cycle that is less than a default paging cycle.

5 15. Apparatus according to any of claims 8 to 14, wherein the actions comprise transmitting information relating to the preambles and specified positions used for enhanced inter-cell interference coordination using a System Information Block.

16. A method of configuring random access channels, the method comprising:

10 receiving almost blank subframe information relating to almost blank subframe patterns used by devices in the vicinity of an apparatus; and configuring random access channels so that, for every almost blank subframe pattern in the vicinity of the apparatus, a subframe in a specified position of a random access response window of at least one random access channel will correspond to an 15 almost blank subframe of the almost blank subframe pattern.

17. A method according to claim 16, wherein the specified position is the first subframe.

20 18. A method according to claim 16, wherein the specified position is a primary position, wherein a primary position comprises one of the first position, the second position, or the last position.

19. A method according to claim 16, wherein the specified position is one of a 25 primary, secondary, or tertiary position.

20. A method according to any of claims 16 to 19, wherein configuring random access channels comprises configuring specified information elements.

18

21. A method according to any of claims 16 to 20, wherein configuring random access channels comprises configuring RACH-ConfigCommon and PRACh-Config information elements.

5 22. A method according to any of claims 16 to 21, wherein configuring random access channels comprises configuring information elements in a system information block specifically dedicated to carrying information elements for enhanced inter-cell interference coordination of user equipment.

10 23. A method according to any of claims 16 to 22, wherein configuring random access channels comprises allocating one or more preambles from among at least one contention free random access preamble configured by the apparatus.

24. A computer program comprising instructions execution of which by a 15 processor configures an apparatus to perform actions comprising at least:

receiving almost blank subframe information relating to almost blank subframe patterns used by devices in the vicinity of the apparatus; and configuring random access channels so that, for every almost blank subframe pattern in the vicinity of the apparatus, a subframe in a specified position of a random 20 access response window of at least one random access channel will correspond to an almost blank subframe of the almost blank subframe pattern.

25. A computer program according to claim 24, wherein the specified position is the first subframe.

25

26. A computer program according to claim 24, wherein the specified position is a primary position, wherein a primary position comprises one of the first position, the second position, or the last position.

30 27. A computer program according to claim 24, wherein the specified position is one of a primary, secondary, or tertiary position.

19

28. A computer program according to any of claims 24 to 27, wherein configuring random access channels comprises configuring specified information elements.

5 29. A computer program according to any of claims 24 to 28, wherein configuring random access channels comprises configuring RACH-ConfigCommon and PRACh-Config information elements.

30. A computer program according to any of claims 24 to 29, wherein configuring 10 random access channels comprises configuring information elements in a system information block specifically dedicated to carrying information elements for enhanced inter-cell interference coordination of user equipment.

31. A computer program according to any of claims 24 to 30, wherein configuring 15 random access channels comprises allocating one or more preambles from among at least one contention free random access preamble configured by the apparatus.

32. Apparatus for configuring random access channels, substantially in accordance with any of the examples as described herein with reference to the accompanying

20 drawings.

33. A method of configuring random access channels, substantially in accordance with any of the examples as described herein with reference to the accompanying drawings.

25