WO2011123990A1

WO2011123990A1 - Timing in telecommunications

Info

Publication number: WO2011123990A1
Application number: PCT/CN2010/000469
Authority: WO
Inventors: Bernhard Raaf; Haiming Wang; Jing HAN
Original assignee: Nokia Siemens Networks Oy
Priority date: 2010-04-09
Filing date: 2010-04-09
Publication date: 2011-10-13

Abstract

In order to facilitate use of single transceiver relays a periodically alternating HARQ timing is used with corresponding patterns.

Description

TIMING IN TELECOMMUNICATIONS

FIELD OF THE INVENTION

The invention relates to the field of telecommunications and, particularly, to timing of an error-control method. BACKGROUND OF ART

The following description of background art may include insights, discoveries, understandings or disclosures, or associations together with disclosures not known to the relevant art prior to the present invention but provided by the invention. Some such contributions of the invention may be specifically pointed out below, whereas other such contributions of the invention will be apparent from their context. The evolvement of wireless cellular communications technologies and different services increase user needs to obtain over a wireless connection same broadband services that are obtained via a fixed connection. To fulfil both mobility requirements and increasing speed requirements, a solution called long term evolution (LTE) release 8, has been specified in 3GPP (Third Generation Partnership Project) . LTE is a packet-only wideband radio access with flat architecture that provides higher data speeds and reduced packet latency and supports various services, such as high-speed data, multimedia unicast and multimedia broadcast services. One step in the evolution path towards fourth generation (4 G) cellular systems is a further development of LTE, called LTE-Advanced (LTE-A) .

Relay nodes (RN) have been introduced to LTE-A to enhance coverage of high data rates, group mobility, temporary network deployment, a cell-edge throughput and/or to provide coverage in new areas. A relay node is an intermediate node between a base station (such as an enhanced node B, or advanced enhanced node B, i.e. eNodeB) and user equipment. A link between the relay node and the base station is a backhaul link, and a link between the relay node and the user equipment is an access link. The original idea is that a relay node may concurrently transmit or receive on both directions (uplink and downlink) of the backhaul link and the access link. However, hardware of such a relay node is rather complicated, and thereby the relay node will be rather expensive. Therefore a relay node that is able to transmit only on one band at a time and/or receive only on one band at a time has been suggested. The suggested relay node can be considered as a "low cost relay node" since its structure is less complex and thereby cheaper. The suggested relay node is called below a single transceiver relay node. The backhaul link and access link are temporarily separated at the single transceiver relay node. Since the single transceiver relay node can transmit and/or receive only on one band at a time, transmission on the backhaul link and access link cannot take place concurrently. The same applies to reception on the backhaul link and access link. In other words, at the suggested single transceiver relay only the backhaul uplink and downlink transmission can occur concurrently, and, similarly, only the access uplink and downlink transmission can occur concurrently .

One of the error-control methods used in LTE is hybrid automatic repeat request (HARQ) , and the suggested HARQ timings are every 4^th subframe, i.e. every 4 ms, or alternatively every 5^th subframe, i.e. every 5 ms . The latter one overcomes some problems caused by the every 4 ms timing at single transceiver relays. However, when the every 5 ms timing is used, the access uplink HARQ processes will collide (i.e. there will be two or more attempts to use the same resource) and all HARQ processes at the access link will be impacted.

SUMMARY OF THE INVENTION The following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an extensive overview of the invention. It is not intended to identify key/critical elements of the invention or to delineate the scope of the invention. Its sole purpose is to present some concepts of the invention in a simplified form as a prelude to the more detailed description that is presented later.

Aspects of some embodiments are to use periodically alternating timing, one of the aspects being to use successive alternating timing so that the round trip delay is constant, and other aspect being to use timing alternating between two or more values so that also the round trip delay may alternate.

Various aspects of the invention comprise a method, an apparatus, a system and a computer program product as defined in the independent claims. Further embodiments of the invention are disclosed in the dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following different embodiments will be described in greater detail with reference to the attached drawings, in which

Figure 1 shows simplified architecture of a radio access network and schematic diagrams of apparatuses according to an embodiment;

Figure 2 illustrates pre-defined patterns according to an embodiment; and Figures 3 and 4 illustrate signalling examples according to embodiments . DETAILED DESCRIPTION OF SOME EMBODIMENTS

Exemplary embodiments of the present invention will now be described more fully hereinafter with reference to the ac- companying drawings, in which some, but not all embodiments of the invention are shown. Indeed, the invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Although the specification may refer to "an", "one", or "some" embodiment ( s ) in several locations, this does not necessarily mean that each such reference is to the same embodiment (s) , or that the feature only applies to a single embodiment. Single features of different embodiments may also be combined to provide other embodiments.

Embodiments of present invention are applicable to any relay node, base station, corresponding component, corresponding apparatus, and/or to any communication system or any com- bination of different communication systems supporting single transceiver relays, or corresponding apparatuses. The communication system may be a wireless communication system or a communication system utilizing both fixed networks and wireless networks. The protocols used and the specifications of communication systems, and apparatuses, especially in wireless communication, develop rapidly. Such development may require extra changes to an embodiment. Therefore, all words and expressions should be interpreted broadly and are intended to illustrate, not to restrict, the embodiment.

In the following, different embodiments will be described using, as an example of an access architecture to which the embodiments may be applied, a radio access architecture based on LTE Advanced, LTE-A, that is based on OFDMA in a downlink and a single-carrier frequency-division multiple access SC-FDMA in an uplink, without restricting the embodiments to such an architecture, however. Other examples of the radio access architecture include Wi ax and 4 G radio access network.

A general architecture of LTE-A, or more precisely a radio access network 100 implementing LTE-A, is illustrated in Figure 1. Figure 1 is a simplified architecture only showing a relay node 110 configured to be in a wireless connection on communication channels on an access link 101 with user equipment 120 and in a wireless connection on communication channels on a backhaul link 102 with a base station 130 (a so called donor base station) providing a donor cell. The access link and the backhaul link may be temporarily separated in the relay node but the links may be aligned in the relay node. The base station is further connected to an evolved packet core network (EPC) . The illustrated relay node 110 and the base station 130 have some elements and functional entities that all are logical units whose implementation may differ from what is shown. It is apparent to a person skilled in the art that the radio access of LTE-A comprises in practise many relay nodes and base stations serving many user equipment, and one user equipment may use multiple cells, and the radio access of LTE-A may comprise other apparatuses. For example, if a coordinated multi-point (CoMP) is utilized in the radio access network 100, the radio access network may comprise a management node configured to take care of the management and scheduling of radio resources. LTE-A utilizes various multiple input multiple output (MI O) technologies, such as a single user multiple input multiple output (SU-MIMO) and a multi-user multiple input multiple output (MU-MIMO) .

The relay node 110 is an intermediate node relaying communications, and not being an endpoint of a communication it relays. The relay node may be a single antenna or multi-antenna relay node. Depending on how the user equipment is aware of the relay node, it may be a transparent or non-transparent relay node. Depending on the relaying strategy, the relay node may control its own cell or be part of the donor cell. With respect to the usage of spectrum, the relay node may be an outband relay node operating having different carrier frequencies for backhaul and access links, or an inband relay node sharing the same carrier frequencies with backhaul and access links. Further, the relay node may be a coordination relay node or a non-coordination relay node. Based on the set of features, the relay node may be a so called Ll relay that simply forwards all received signals or a so called L2 relay that will include some processing (error correction, decoding, etc.) of the received signals before retransmitting the received signals, or a so called L3 relay, i.e. a base station having a wireless backhaul and acting as a relay node. In LTE-A the L3 relay may be of type 1, la, lb or type 2, wherein type 1 relay node is an inband relay node controlling cells, type la is an outband relay node controlling cells, type lb is an inband relay node controlling cells with adequate antenna isolation and type 2 is an inband relay node that is part of the donor cell.

The relay node 110 is configured to perform one or more of relay node functionalities described below with an embodiment, and it may be configured to perform functionalities from different embodiments. For this purpose, the relay node comprises a timing unit TU 111 for an error-control method. In an embodiment, the timing unit 111 comprises hard-coded error-control timing. In another embodiment the timing unit 111 is configured to receive the timing in radio resource control messages, for example. Further, the relay node illustrated in Figure 1 is a single transceiver relay node comprising an internal structure (details not illustrated in Figure 1 since they bear no significance to the invention.) in which a receiving unit 112 and/or a sending unit 113 are configured so that transmission takes place on only one band at a time and/or reception takes place on only one band at a time. In an implementation of the single transceiver relay node both the receiving unit and the sending unit are configured so that the transmission takes place on only one band at a time, i.e. when an access link 101 is in use, the backhaul link 102 is disabled and vice versa. In another implementation of the single transceiver relay node, the receiving unit is configured so that the reception takes place on only one band at a time (i.e. receive on either the backhaul link or the access link at a time) but the transmitting unit may transmit concurrently (i.e. transmit on both the backhaul link and the access link at the same time) . In a further implementation of the single transceiver relay node, the transmitting unit is configured to that it can transmit on only one band at a time (i.e. transmit on either the backhaul link or the access link at a time) but the receiving unit may receive concurrently (i.e. receive on both the backhaul link and the access link at the same time) . The further embodiment provides a lower cost by utilizing the fact that receivers are cheaper than transmitters because of power amplifiers needed in the transmitters. When a link is in use it may be used for transmission and reception simultaneously or only for transmission or for reception.

The user equipment 120 illustrates one type of an apparatus to which resources on the air interface are allocated and assigned The user equipment 120 refers to a portable computing device that includes wireless mobile communication devices operating with or without a subscriber identification module (SIM) , including, but not limited to, the following types of devices: mobile phone, smartphone, personal digital assistant (PDA) , handset, laptop computer.

The base station, or advanced evolved node B, 130 is a computing device configured to control the radio resources, and connected to the evolved packet core network, thereby providing the user equipment 110 a connection to the communication system.

Typically, but not necessarily, the base station comprises all radio-related functionalities of the communication whereby the base station, for example, configures connection parameters and controls the user equipment measurement reporting. The base station 130 is configured to perform one or more of base station functionalities described below with an embodiment, and it may be configured to perform functionalities from different embodiments. For this purpose, the base station comprises a timing and allocation unit T&A 131 for an error-control method and/or for setting backhaul subframe patterns. In an implementation, the timing and allocation unit 131 comprises hard-coded error-control timing. Further, the base station may comprise other units, and it comprises different interfaces, such as a receiving unit 132 and a sending unit 133.

In other embodiments, for example in embodiments in which a common (more centralized) radio resource management and/or scheduling is applied, the timing and allocation unit 131 or some functionality of the timing and allocation unit may locate in another network entity/node. Examples of such a network entity/node comprise an operation and maintenance element, a self organized network (SON) element and the management node. However, in the following it is assumed that the functionalities locate in the same base station without restricting the embodiment to such a solution.

Although the apparatuses, such as the relay node and the base station, have been depicted in Figure 1 as one entity, they may be implemented in one or more physical or logical entities. Their units and functions may be software and/or software-hardware and/or firmware components (recorded indelibly on a medium such as read-only-memory or embodied in hard-wired computer circuitry) .

The relay nodes, base station and corresponding apparatuses implementing functionality or some functionality according to an embodiment may generally include a processor (not shown in Figure 1), controller, control unit, micro-controller, or the like connected to a memory and to various interfaces of the apparatus. Generally the processor is a central processing unit, but the processor may be an additional operation processor. The timing unit 111, and/or the timing and allocation unit 131 may be configured as a computer or a processor, or a microprocessor, such as a single-chip computer element, or as a chipset, including at least a memory for providing storage area used for arithmetic operation and an operation processor for executing the arithmetic operation. The timing unit 111, and/or the timing and allocation unit 131 may comprise one or more computer processors, application-specific integrated circuits (ASIC), digital signal processors (DSP) , digital signal processing devices (DSPD) , programmable logic devices (PLD),

field-programmable gate arrays (FPGA), and/or other hardware components that have been programmed in such a way to carry out one or more functions of one or more embodiments.

The receiving units and the transmitting units each provides an interface in an apparatus, the interface including a transmitter and/or a receiver or a corresponding means for receiving and/or transmitting information, such as data, content, control information, messages and performing necessary functions so that user data, content, control information, signalling and/or messages can be received and/or transmitted. The receiving and sending units may comprise a set of antennas, the number of which is not limited to any particular number.

The apparatuses, such as the relay node and the base station, may generally include volatile and/or non- volatile memory and typically store content, data, or the like. For example, the memory may store computer program code such as software applications (for example, for the timing unit or the timing and allocation unit) or operating systems, information, data, content, or the like for the processor to perform steps associated with operation of the apparatus in accordance with embodiments. The memory may be, for example, random access memory, a hard drive, or other fixed data memory or storage device. Further, the memory, or part of it, may be removable memory detachably connected to the apparatus. It should be appreciated that the apparatuses may comprise other units used in or for error-control and other information transmission. However, they are irrelevant to the actual invention and, therefore, they need not to be discussed in more detail here.

Below different embodiments are disclosed assuming that a following scheme for resource partitioning in the

time-frequency space (i.e. TDD) at the relay node is used: - base station -> relay node and relay node -> user equipment links are time division multiplexed in a single carrier frequency (only one is active at any time)

- relay node -> base station and user equipment -> relay node links are time division multiplexed in a single carrier frequency (only one is active at any time) .

Figure 2 illustrates a set of predefined patterns that may be used as backhaul subframe patterns with respective HARQ timing, the patterns allowing creation of transmission gaps in the relay node in access downlink for the backhaul uplink and downlink transmissions. The patterns may be hard-code to relay nodes and/or base stations, or they may be predefined and stored to a memory in the corresponding apparatus or they may be sent in a higher layer signalling. The HARQ timing in the illustrated patterns is a successive alternating timing having a constant round trip delay. In the illustrated embodiment the timing that may be hard-coded to the relay node and/or to the base station alternates 4, 6, 4, 6, etc and the constant round trip relay is 10 ms, and backhaul subframes (SF) may be allocated in the following patterns:

Pattern#l : SF {1 7 11 17 21...} -» 6 4 6 4 ms

Pattern#2: SF {2 8 12 18 22...} -» 6 4 6 4 ms

Pattern#3: SF {2 6 12 16 22...} -» 4 6 4 6 ms

Pattern#4 : SF {3 7 13 17 23...} - 4 6 4 6 ms

In Figure 2, a solid line with an arrow denotes 6 ms, and a dashed line with an arrow denotes 4 ms, UL stands for uplink and DL stands for downlink. The allocated backhaul subframes are denoted by black subframes. Corresponding HARQ processes, denoted by HARQ, are illustrated with bolded numbers and bolded frames. Those subframes (SF) that cannot be configured as so called MBSFN (multicast broad single frequency network) subframes, i.e. cannot be used for backhaul information exchange at the relay node in order to provide compatibility with legacy user equipment have criss-cross lines. In other words, according LTE specifications, downlink subframes 1, 2, 3, 6, 7 and 8 are eligible for the backhaul downlink. As a consequent, the same subframes are usable for a single transceiver relay node in the backhaul uplink.

An example of illustrating the HARQ timing and patterns in Figure 2 is to perform an uplink process as follows: for pattern#l and pattern#2, the uplink grant timing (the time difference between uplink grant and corresponding uplink data transmission) is 6ms, while the uplink grant timing is 4ms for pattern#3 and pattern#4; the downlink feedback timing (the time different between uplink data transmission and downlink

ACK/NACK feedback) is 4ms for pattern#l and pattern#2, while it is 4ms for pattern#3 and pattern#4. (ACK/NACK feedback is part of HARQ method.) An advantage of the example illustrated in Figure 2 is that it allows selecting patterns in accordance with a processing time performance of a relay node and/or a donor base station. In other words, it is possible to select a pattern with a longer grant timing when the processing time in the relay node/donor base station is slower for the grant than feedback, and vice versa. This may allow reducing further implementation cost of the relay node or the donor base station.

When the round trip delay is 10 ms, the advantages obtained by the 5 ms timing are obtained. One of the advantages is an allocation having a 10 ms or 20 ms repetition that is compatible with the eligible subframes. When this is combined with the use of the alternating timing, collisions of HARQ processes on the access link are much more rare compared to the every 5 ms timing. A further advantage of the embodiment is that since half of the timing uses 4 ms, which is the uplink grant timing of LTE Release 8 user equipment, and typically used also with LTE user equipment of later releases, there is less impact on the scheduling of the LTE user equipment and on the scheduling implementation of a base station. In further embodiments, the periodically alternating timing is implemented so that a first time interval is used for predetermined times and then alternated to a second time interval used for the same predetermined times or other predetermined times and then alternated back to the first time interval. In the embodiments, also the round trip delay alternates. For example, if timing 4, 4, 6, 6, 4, 4, 6, 6 is used, the round trip delay alternates 8, 10, 12, 10, 8, 10 ms, etc. Other examples with corresponding patterns include the following: PatternX: SF { 3 7 11 13 17 21 23...} -^ 4 4 2 4 4 2 ms

PatternY: SF { 3 7 11 18 22 26 33...} -> 4 4 7 4 4 7 ms

It should be appreciated that also other timings can be used, and it is possible to use more than two different time intervals, such as 4, 6, 4, 4, 2, 4, 6, 4, 4, 2, etc timing. For example, in case the network architecture allows all subframes to be allocated for backhaul and if the processing capabilities allow, it is also possible to use alternating 3, 7, 3, 7 etc timing or 2, 8, 2, 8, etc timing or 1, 9, 1, 9, etc timing, and to have the 10 ms round trip delay.

Figure 3 illustrates an example of how a higher layer signalling, such as a radio resource control (RRC) signalling, is used to control the patterns a relay node uses. In point 3-1 a base station BS, or more precisely the timing and allocation unit in the base station, detects a need to allocate/configure or reallocate/reconfigure a backhaul link between the base station and a relay node RN. In the example, depending on the load and how balanced the load is, the base station selects a most suitable pattern or pattern combination to the relay node and sends in message 3-2 an indication of the pattern or pattern combination to the relay node. In response to receiving message 3-2, the relay node, or more precisely, the timing unit in the relay node, starts to follow, after point 3-3, the indicated patterns using the hard-coded timing for each pattern.

In an embodiment, in which the timing is not hard-coded, message 3-2 contains the pattern with corresponding timing.

Figure 4 illustrates another example of how a higher layer signalling, such as a radio resource control (RRC) signalling, is used to control the patterns a relay node uses. In the illustrated example it is assumed that the patterns illustrated with Figure 2 are used and that the base station is configured to use pattern#l for three relay nodes whenever it is possible without restricting the embodiments to such a solution. It should be appreciated that in addition to illustrated signalling other signalling takes place but, for the sake of clarity, it is not shown in Figure 4 neither discussed below. The example in Figure 4 starts in a situation in which no relay node is active in a donor cell of a base station. Then, in point 4-1 the base station BS, or more precisely the timing and allocation unit in the base station, detects that there is an active relay node RNl, allocates a backhaul link between the base station and a relay node RNl, and selects pattern#l to be used on this link. Then the base station sends an indication of the pattern#l to the relay node RNl in message 4-2. In response to receiving message 4-2, the relay node RNl, or more precisely, the timing unit in the relay node RNl, starts to follow, after point 4-3, the pattern#l using the hard-coded timing for the pattern#l.

Then, in point 4-4 the base station BS detects that there are two new active relay nodes RN2 and RN3, allocates a backhaul link between the base station and the relay node RN2 and a backhaul link between the base station and the relay node RN3, and selects pattern#l to be used on the links since pattern#l can provide enough resources for three relay nodes. Then the base station sends an indication of the pattern to the relay nodes RN2 and RN3 in messages 4-2. In response to receiving message 4-2, the relay nodes RN2 and RN3, or more precisely, the timing unit in the corresponding relay node, start to follow, after point 4-3, the pattern#l using the hard-coded timing for the pattern#l.

Then, in point 4-5, the base station BS detects a further active relay node RN4, allocates a backhaul link between the base station and the relay node RN4, notices than pattern#l cannot accommodate more than three relay nodes and therefore selects, in point 4-5, pattern#3 to be used on the backhaul link between the base station and relay node RN4. Then the base station sends an indication of the pattern#3 to the relay node RN4 in message 4-2'. In response to receiving message 4-2' , the relay node RN4 , or more precisely, the timing unit in the relay node RN4, starts to follow, after point 4-3' , the pattern#3 using the hard-coded timing for the pattern#3.

The base station is also configured, in response to a new pattern being selected, to balance a load among subframes. Therefore the base station reallocates, in point 4-6, pattern#3 to be used on the backhaul link between the base station and the relay node RN3. Then the base station sends an indication of the pattern#3 to the relay node RN3 in message 4-3. In response to receiving message 4-3, the relay node RN3 updates its information and starts to follow, after point 4-7, the pattern#3 using the hard-coded timing for the pattern#3.

In point 4-8 the base station detects that relay node RN2 is not anymore active, and that there are only three active relay nodes. Therefore the base station reallocates, in point 4-8, pattern#l to be used on all backhaul links, and sends messages 4-2 to the relay nodes RN3 and RN4, messages 4-2 containing an indication of the pattern#l. In response to receiving message 4-2, the relay nodes RN3 and RN4 update their information and start to follow, after point 4-7, the pattern#l using the hard-coded timing for the pattern#l.

In an embodiment only one pattern is used at a time in the relay node and the indication in the message may then be a 2-bit pattern index for a solution implementing the timing and patterns illustrated in Figure 2. An example of such a pattern index is illustrated in table 1.

Table 1

In another embodiment the relay nodes, or some of the relay nodes, and the base station support multiple patterns and the indication in the message may then be a 4 bit bitmap for a solution implementing the timing and patterns illustrated in Figure 2. An example of such a bitmap is illustrated in table 2. The example allows allocation of any combination of the four patterns .

Table 2

In further embodiments only specific combinations of patterns can be allocated, and the indication may also then be an index. Examples of such embodiments for a solution implementing the timing and patterns illustrated in Figure 2 are given in tables 3 and 4.

Table 3

The embodiment illustrated in table 3 has the advantage that it enables to allocate 1, 2, 3 or 4 patterns by using only 2 bits. The patterns are allocated to make sure that no subframe is double loaded when only one or two patterns are allocated (and only odd HARQ processes are affected) . It should be appreciated that also other pattern combinations with similar properties are possible and can be easily derived.

Table 4

The embodiment illustrated in table 4 allows more flexibility for the pattern allocation, in particular for the allocation of two concurrent patterns, at the expense of more signalling. Although in the embodiment illustrated in table 4 some combinations may look like being disadvantageous at first sight, that is not, however, the case. For example, in index 1 patternl# is combined with pattern#3 with the effect that subframe 7 is carrying double load for backhaul because in total only three subframes per 10ms are allocated. However, if there is not too much backhaul traffic these three subframes may be sufficient and then the advantage of allocating only three subframes is that more subframes are available for access at the relay node.

When one or two patterns are allocated, double loading of a subframe may be avoided. For example, using the example illustrated in Figure 1, if one or two of the patterns are allocated, only odd HARQ processes are affected.

It should be appreciated that timing on different relay nodes may also be offset relative to each other so that each relay node can use the same pattern, such as pattern#l in Figure 2, and still the patterns don't overlap at the base station. In this way it is possible to use each subframe for backhaul for some of the relay nodes and no subframe is double loaded. Such an offset can be achieved by offsetting the subframe numbering on different relays.

The above pattern combinations and their indications are examples and targeted to illustrate different implementations without restricting embodiments to them. It should be appreciated that there are no restrictions for different pattern combinations and their allocations.

In one implementation scenario, single transceiver relay nodes are configured to implement one of the embodiments and "normal" relay nodes not, and the base stations are configured to detect whether a relay node is a single transceiver relay node or not, and act accordingly. In another implementation scenario, both the single transceiver relay nodes and the normal relay nodes are configured to implement one of the embodiments, as much as possible .

An example illustrating how easy it is to combine the normal relay nodes and the single transceiver relay node is as follows; when normal relay node is using downlink subframes 2, 6 and uplink subframes 6, 0, the single transceiver relay node should have in downlink subframes 2 and 6 and, naturally, in uplink subframes 2 and 6. In such case, the normal relay node may have 4 ms uplink grant timing still to maximize scheduling commonality with legacy user equipment in uplink. By accommodating both relay node types, subframes 2 and 6 may maximize trunking gain on a reverse packet data control channel (R-PDCCH) , and particularly for uplink grants.

Although the invention has been described above using HARQ as an example of an error-control method, the embodiments may be implemented with other error-control methods, such as automatic repeat request ARQ.

As can be seen from the above, an advantage of the embodiments is that they may be implemented without requiring changes to user equipment . It will be obvious to a person skilled in the art that, as the technology advances, the inventive concept can be implemented in various ways. The invention and its embodiments are not limited to the examples described above but may vary within the scope of the claims.

Claims

1. A method comprising:

utilizing an error-control method in a data transmission; and using periodically alternating timing as a timing of the error-control method.

2. A method as claimed in claim 1, further comprising predefining one or more patterns to be used with the periodically alternating timing.

3. A method as claimed in claim 2, further comprising:

associating a pattern or a combination of patterns with an indication; and

using the indication to indicate when the pattern or the combination of patterns is to be used with the periodically alternating timing.

4. A method as claimed in any one of the preceding claims, wherein the periodically alternating timing is a successively alternating timing.

5. A method as claimed in any one of the preceding claims, wherein the timing has a constant round trip relay.

6. A method as claimed in claim 4 or 5, wherein the successively alternating timing alternates between 4 ms and 6 ms .

7. A method as claimed in claim 6, wherein four patterns are predefined, one of the patterns starting the timing on 6 ms and on a subframe one, one of the patterns starting the timing on 6 ms and on a subframe two, one of the patterns starting the timing on 4 ms and on the subframe two, and one of the patterns starting the timing on 4 ms and on the subframe three.

8. A method as claimed in claim 1, wherein the periodically alternating timing is based on alternating time intervals.

9. A method as claimed in claim 8, wherein the alternating time intervals each have their own time interval repeated with predetermined times, wherein the predetermined times is determined time interval -specifically.

10. A method as claimed in any of the preceding claims, wherein the periodically alternating timing is used between a base station and a single transceiver relay node.

11. A method as claimed in any of the preceding claims, wherein the error-control method is hybrid automatic repeat request.

12. A computer program product comprising computer program code configured to perform a method as claimed in any one of the claims 1 to 11 when executed on an apparatus.

13. An apparatus comprising means for implementing a method as claimed in any of claims 1 to 11.

14. An apparatus as claimed in claim 13, wherein the timing is hard-coded to the apparatus.

15. An apparatus as claimed in claim 14, wherein the apparatus further comprises memory including one or more predetermined patterns for the timing.

16. An apparatus as claimed in claim 15, wherein the apparatus is configured to associate each pattern and each combination of the patterns the apparatus is configured to support with an indication .

17. An apparatus as claimed in claim 16, the apparatus being further configured to receive in a higher layer signalling an indication indicating which one of the patterns and combinations of the patterns to use, and to use the indicated one.

18. An apparatus as claimed in claim 13, wherein the apparatus is configured to receive the timing and a corresponding pattern in a higher layer signalling.

19. An apparatus as claimed in claim 13, 14, 15, 16, 17 or 18, wherein the apparatus is a single transceiver relay node, the single transceiver node being one of a first, second and a third type of a relay node, the first type being a relay node configured to transmit on only one band at a time and to receive on only one band at a time, the second type being a relay node configured to transmit concurrently and to receive on only one band at a time, and the third type being a relay node configured to transmit on only one band at a time and to receive concurrently.

20. An apparatus as claimed in claim 16, wherein the apparatus is configured to select a pattern or a combination of the patterns to be used by another apparatus, and send an indication to the other apparatus, the indication indicating the selected one .

21. An apparatus as claimed in claim 20, wherein the apparatus is configured to update the selection in response to load changes.

22. An apparatus as claimed in claim 13, 14, 15, 16, 20 or 21, wherein the apparatus is a base station providing a donor cell.

23. An apparatus as claimed in claim 22, wherein the apparatus is configured to detect whether or not the relay node is a single transceiver relay node, and to use the periodically alternating timing of error control in response to the relay node being a single transceiver relay node.

24. A system comprising an apparatus as claimed in claim 12, 13, 14, 15, 16, 20, 21, 22 or 23 and providing a donor cell, and an apparatus as claimed in claim 12, 13, 14, 15, 16, 17 or 18 and configured to act as a relay node.