WO2012031389A1

WO2012031389A1 - Random access channel design in machine type communications

Info

Publication number: WO2012031389A1
Application number: PCT/CN2010/076724
Authority: WO
Inventors: Gilles Charbit; Tao Chen; Wei Zou
Original assignee: Nokia Corporation
Priority date: 2010-09-08
Filing date: 2010-09-08
Publication date: 2012-03-15

Abstract

A method for a random access channel design in machine type communications comprises: sending a contentious access request of a machine to a cellular device acting as a machine gateway, and receiving from a network node a contentious access response comprising a random access preamble sequence allocated by the network node for a non-contentious access transmission from the machine to the machine gateway. According to exemplary embodiments, the random access preamble sequence may be allocated based at least in part on a timing advance parameter of the cellular device according to a predefined rule.

Description

RANDOM ACCESS CHANNEL DESIGN IN

MACHINE TYPE COMMUNICATIONS

FIELD OF THE INVENTION

The present invention generally relates to communication networks. More specifically, the invention relates to Machine-to-Machine (M2M) communications and integration of wireless sensors and sensor networks with cellular networks.

BACKGROUND

Machine communications have become one of the major topics in recent discussions on wireless systems applications. Machine applications can be used for many purposes, for example, smart homes, smart metering, fleet management, remote healthcare, access network operation management, etc. Machine communications are now under active standardization work. In January 2009, European Telecommunications Standards Institute (ETSI) started work in a new Technical Committee (ETSI TC M2M) to specify M2M requirements and to develop an end-to-end high level architecture for machine systems. In September 2009, the 3rd Generation Partnership Project (3GPP) Technical Steering Group (TSG) Radio Access Network (RAN) decided to open a new Study Item on "RAN Improvements for Machine-type Communications".

SUMMARY

The present description involves a Random Access Channel (RACH) design in

Machine Type Communications (MTC). In general, a "non-contentious" machine to machine Gateway (GW) random access request is proposed for a MTC system, which may use the information of Timing Advance (TA) of a cellular device for the assignment of dedicated preamble sequences. According to a first aspect of the present invention, there is provided a method comprising: sending a contentious access request of a machine to a cellular device acting as a machine GW; and receiving from a network node a contentious access response comprising a random access preamble sequence allocated by the network node for a non-contentious access transmission from the machine to the machine GW; wherein the random access preamble sequence is allocated based at least in part on a TA parameter of the cellular device according to a predefined rule.

According to a second aspect of the present invention, there is provided an apparatus comprising at least one processor and at least one memory including computer program code. The at least one memory and the computer program code may be configured to, with the at least one processor, cause the apparatus to perform at least the following: sending a contentious access request to a cellular device acting as a machine GW; and receiving from a network node a contentious access response comprising a random access preamble sequence allocated by the network node for a non-contentious access transmission from the apparatus to the machine GW; wherein the random access preamble sequence is allocated based at least in part on a TA parameter of the cellular device according to a predefined rule.

According to a third aspect of the present invention, there is provided a computer program product comprising a computer-readable medium bearing computer program code embodied therein for use with a computer, the computer program code comprising: code for sending a contentious access request of a machine to a cellular device acting as a machine GW; and code for receiving from a network node a contentious access response comprising a random access preamble sequence allocated by the network node for a non-contentious access transmission from the machine to the machine GW; wherein the random access preamble sequence is allocated based at least in part on a TA parameter of the cellular device according to a predefined rule. According to a fourth aspect of the present invention, there is provided an apparatus, comprising: sending means for sending a contentious access request to a cellular device acting as a machine GW; and receiving means for receiving from a network node a contentious access response comprising a random access preamble sequence allocated by the network node for a non-contentious access transmission from the apparatus to the machine GW; wherein the random access preamble sequence is allocated based at least in part on a TA parameter of the cellular device according to a predefined rule.

According to a fifth aspect of the present invention, there is provided a method, comprising: forwarding a contentious access request of a machine to a network node from a cellular device acting as a machine GW, in response to receipt of the contentious access request; and obtaining a random access preamble sequence allocated by the network node for a non-contentious access transmission from the machine to the machine GW; wherein the random access preamble sequence is allocated based at least in part on a TA parameter of the cellular device according to a predefined rule.

According to a sixth aspect of the present invention, there is provided an apparatus, comprising at least one processor and at least one memory including computer program code. The at least one memory and the computer program code may be configured to, with the at least one processor, cause the apparatus to perform at least the following: forwarding a contentious access request of a machine to a network node from the apparatus acting as a machine GW, in response to receipt of the contentious access request; and obtaining a random access preamble sequence allocated by the network node for a non-contentious access transmission from the machine to the machine GW; wherein the random access preamble sequence is allocated based at least in part on a TA parameter of the apparatus according to a predefined rule. According to a seventh aspect of the present invention, there is provided a computer program product comprising a computer-readable medium bearing computer program code embodied therein for use with a computer, the computer program code comprising: code for forwarding a contentious access request of a machine to a network node from a cellular device acting as a machine GW, in response to receipt of the contentious access request; and code for obtaining a random access preamble sequence allocated by the network node for a non-contentious access transmission from the machine to the machine GW; wherein the random access preamble sequence is allocated based at least in part on a TA parameter of the cellular device according to a predefined rule.

According to an eighth aspect of the present invention, there is provided an apparatus, comprising: forwarding means for forwarding a contentious access request of a machine to a network node from the apparatus acting as a machine GW, in response to receipt of the contentious access request; and obtaining means for obtaining a random access preamble sequence allocated by the network node for a non-contentious access transmission from the machine to the machine GW; wherein the random access preamble sequence is allocated based at least in part on a TA parameter of the apparatus according to a predefined rule.

According to a ninth aspect of the present invention, there is provided a method, comprising: allocating, in response to receipt of a contentious access request of a machine from a cellular device acting as a machine GW, a random access preamble sequence by a network node for a non-contentious access transmission from the machine to the machine GW, based at least in part on a TA parameter of the cellular device according to a predefined rule; and sending to the machine a contentious access response comprising the random access preamble sequence.

According to a tenth aspect of the present invention, there is provided an apparatus, comprising at least one processor and at least one memory including computer program code. The at least one memory and the computer program code may be configured to, with the at least one processor, cause the apparatus to perform at least the following: allocating, in response to receipt of a contentious access request of a machine from a cellular device acting as a machine GW, a random access preamble sequence for a non-contentious access transmission from the machine to the machine GW, based at least in part on a TA parameter of the cellular device according to a predefined rule; and sending to the machine a contentious access response comprising the random access preamble sequence.

According to an eleventh aspect of the present invention, there is provided a computer program product comprising a computer-readable medium bearing computer program code embodied therein for use with a computer, the computer program code comprising: code for allocating, in response to receipt of a contentious access request of a machine from a cellular device acting as a machine GW, a random access preamble sequence by a network node for a non-contentious access transmission from the machine to the machine GW, based at least in part on a TA parameter of the cellular device according to a predefined rule; and code for sending to the machine a contentious access response comprising the random access preamble sequence.

According to a twelfth aspect of the present invention, there is provided an apparatus, comprising: allocating means for allocating, in response to receipt of a contentious access request of a machine from a cellular device acting as a machine GW, a random access preamble sequence for a non-contentious access transmission from the machine to the machine GW, based at least in part on a TA parameter of the cellular device according to a predefined rule; and sending means for sending to the machine a contentious access response comprising the random access preamble sequence.

In accordance with exemplary embodiments, the predefined rule may comprise: allocating to a cell served by the network node a set of random access preamble sequences for non-contentious access transmissions; reusing the set of random access preamble sequences for cellular devices with sufficiently different TA parameters in the cell; and assigning different random access preamble sequences from the set of random access preamble sequences to respective cellular devices with similar TA parameters in the cell. According to exemplary embodiments, the predefined rule may further comprise: allocating a different set of random access preamble sequences for non-contentious access transmissions to a different cell.

In accordance with exemplary embodiments, the predefined rule may comprise: allocating to a sector served by the network node a set of random access preamble sequences for non-contentious access transmissions; reusing the set of random access preamble sequences for cellular devices with different TA parameters in the sector; and assigning different random access preamble sequences from the set of random access preamble sequences to respective cellular devices with the same TA parameter in the sector. According to exemplary embodiments, the predefined rule may further comprise allocating a different set of random access preamble sequences for non-contentious access transmissions to a different sector.

In accordance with exemplary embodiments, the allocated random access preamble sequence may comprise a frequency- domain spreaded random access preamble sequence for code domain multiplexing of the non-contentious access transmission.

According to exemplary embodiments, if the cellular device moves within a cell served by the network node while being signaled a new TA parameter, the machine may be signaled by the network node to initiate a new contentious access to a new machine GW within the machine's transmission range. In exemplary embodiments, the new contentious access may use a sequence different from those random access preamble sequences reserved for non-contentious access transmissions. In accordance with exemplary embodiments, the contentious access request may be sent from the machine to the cellular device on specified Downlink (DL) resources, and forwarded from the cellular device to the network node on scheduled Uplink (UL) resources, and the contentious access response may be sent from the network node to the machine on scheduled DL resources.

According to exemplary embodiments, allocation of resources to the cellular device and the machine may be performed in a centralized way by the network node via a Multimedia Broadcast Single Frequency Network (MBSFN) subframe configured for transmissions from the machine to the machine GW.

In exemplary embodiments of the present invention, the provided methods, apparatus, devices and computer program products can mitigate RACH overload problems by setting a proper RACH configuration in a network to accommodate machine communications. Moreover, the solution of the present invention can simplify implementation of machines and cellular devices, save machine power, and avoid false machine detection. In addition, high reuse of common DL resources for machine access requests may be achieved due to spatial and code domains orthogonality.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention itself, the preferable mode of use and further objectives are best understood by reference to the following detailed description of the embodiments when read in conjunction with the accompanying drawings, in which:

Fig.l is a diagram exemplarily illustrating a generic framework for data uploading in M2M use cases;

Fig.2A is a flowchart illustrating a method for RACH design in MTC which may be implemented at a machine in accordance with embodiments of the present invention; Fig.2B is a flowchart illustrating a method for RACH design in MTC which may be implemented at a cellular device in accordance with embodiments of the present invention;

Fig.2C is a flowchart illustrating a method for RACH design in MTC which may be implemented at a network node in accordance with embodiments of the present invention;

Fig.3 shows schematically allocation of random access preamble sequences for a machine and a machine GW in a network in accordance with embodiments of the present invention;

Fig.4 is a diagram exemplarily illustrating a MTC system in accordance with embodiments of the present invention;

Fig.5 shows schematically a machine MBSFN subframe configuration in accordance with embodiments of the present invention;

Fig.6 is a diagram exemplarily illustrating the RACH in Uplink Pilot Transmission Sequence (UpPTS) in a Time Domain Duplexing (TDD) system in accordance with embodiments of the present invention; and

Fig.7 is a simplified block diagram of various devices which are suitable for use in practicing exemplary embodiments of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The embodiments of the present invention are described in detail with reference to the accompanying drawings. Reference throughout this specification to features, advantages, or similar language does not imply that all of the features and advantages that may be realized with the present invention should be or are in any single embodiment of the invention. Rather, language referring to the features and advantages is understood to mean that a specific feature, advantage, or characteristic described in connection with an embodiment is included in at least one embodiment of the present invention. Furthermore, the described features, advantages, and characteristics of the invention may be combined in any suitable manner in one or more embodiments. One skilled in the relevant art will recognize that the invention may be practiced without one or more of the specific features or advantages of a particular embodiment. In other instances, additional features and advantages may be recognized in certain embodiments that may not be present in all embodiments of the invention.

Fig. 1 shows a generic framework for M2M use cases, in which it seems likely for a mobile cellular device acting as the M2M GW to forward the M2M traffic. An efficient RACH design for machine communications in a cellular network is a challenge. Different with the normal cellular RACH procedure, there are several constraints and challenges for a machine access procedure.

• Machines may not be equipped with Subscriber Identity Module (SIM) card, which is necessary for the cellular physical non- synchronous RACH procedure - Layer 1 (LI) random access procedure encompasses the transmission of a random access preamble and a random access response. The remaining messages are scheduled for transmissions by the higher layer on the shared data channel.

• There could be much many more machines than cellular devices with every machine access request requiring additional RACH resources, which may already be scarce in normal cellular scenarios.

• Machines like small sensors may not be equipped with a battery sufficiently powerful to transmit RACH to a distant evolved Node B (eNB) due to small size and cost requirements.

The last point is particularly relevant as it may require a radically different approach for the RACH design. In case a nearby cellular device acting as a machine

GW is used to relay a machine access request to the eNB, the low-power short-range transmission can be assumed. However, there is a need for an efficient RACH design to allow (i) many machines making access requests to the same machine gateway; (ii) machines making access requests to different machine gateways.

In the cell edge, it is likely that a cellular device acting as a machine GW attached to an eNB in the serving cell may receive a sequence transmitted from a machine attached to another eNB in a neighbor cell. The cellular device may not know whether the machine is from the neighbor cell or the serving cell, and would forward the report to the eNB even though it may not be possible to establish the machine to machine GW communication, because the machine can not listen to the downlink signaling from the non-serving (or neighbor) eNB. This would cause wasted resources and cause unpredicted behavior of the system.

It is desirable to consider the impact of machine communications on the RACH load in a cellular network. Setting a right RACH configuration in the network to accommodate machine communications may mitigate RACH overload problems. Further, it is concluded that alternative solutions such as preamble grouping where RACH preambles are reserved for machine communications should be further studied due to drawbacks such as RACH collision with legacy terminals and inefficient use of resources. The RACH power consumption limitations of small sensors transmitting to a distant eNB are not addressed in the current study. The machines may not transmit to the eNB but instead to a machine GW to reduce impacts on network signaling and reduce power. In one possible implementation, asymmetric connections between the machine - machine GW - eNB may be configured. The machine GW may receive machine transmissions on DL resources while relaying machine transmissions to the eNB on UL resources. The RACH design for the cellular device acting as a machine GW for the machines is not covered in the current study. In particular, Release 8 RACH design seems not suited for a machine access request to the machine GW for the following reasons such as (i) the transmission range of machine to machine GW is typically a few tens of meters which may allow spatial reuse of resources; (ii) fewer machines connecting to a machine GW (compare to many Release 8 devices connecting to the same eNB) do not require machine access request configuration parameters with 5 preamble formats, 64 preambles per cell, and minimum of 4 Physical Resource Blocks (PRBs) used for RACH.

Assuming asymmetric connections between the machine - machine GW - eNB, a hybrid machine access procedure may be proposed. In particular, the machine - machine GW connection is assumed to take place on the DL to limit impacts on the UL signaling in a cellular network. Pre- contention via the busy signal transmission between machines is used to reserve the machine access channel for transmission of the machine access request message to the machine GW. This reduces the machine collision during the "contentious" machine access procedure. One aspect for further consideration is that it is probably not practical to reserve resources on DL PRBs for the machine access request. In Release 8 (R8), there is similar issue with contentious-RACH procedure due to resources being not allocated to any specific user equipments (UEs) during initial cell access (or when a UE wakes up from the idle state after some time). But in R8, the eNB always expects some non-contentious-RACH in pre-allocated resources as given by the specifications. It may be desirable to provide a design of the machine access request message (for example, machine RACH) and allocation of DL resources for the "non-contentious" machine access request.

For a channel access procedure in the ad-hoc system, typically, it has to know users beforehand by listening to the broadcast channels or user- specific beacon signals. Then they may communicate via Request To Send / Clear To Send (RTS/CTS) or busy tones with a known called user. However, in the case of machine communications, the locations of cellular devices are unknown for machines, which can not hear any beacon signal from cellular devices due to unpaired Transmit / Receive (Tx/Rx). Then it is impossible to communicate with unknown devices via RTS/CTS. Moreover, there is no any further protection on the data channel since the busy tone or RTS/CTS is assumed to provide the orthogonal channel access for simultaneous transmissions. It is noted that local communications in the ad-hoc network have been synchronized naturally due to the short distance. Thus, there is no need to send any preamble sequence once they have claimed the orthogonal data channels via busy tone or RTS/CTS.

It can be seen that for M2M communications in a cellular network and more specifically with low powered machine devices, RACH resources may be scarce due to huge amount of machine access requests to the network. Thus there is a need to set a proper RACH configuration in the network to accommodate machine communications, in order to mitigate RACH overload problems.

Fig.2A is a flowchart illustrating a method for RACH design in a MTC system which may be implemented at a machine in accordance with embodiments of the present invention. Correspondingly, Fig.2B and Fig.2C also illustrate the RACH design in a MTC system in accordance with embodiments of the present invention, which may be implemented at a cellular device and a network node, respectively. As shown in Fig.l and Fig.4, in a MTC system, a cellular device (such as a UE, a mobile device, a wireless terminal and etc.) has a capability of acting act as a M2M/Sensor GW to forward the M2M traffic, and a machine like a sensor may not transmit signals to a network node (such as eNB/BS/control center) but instead to a machine GW to reduce impact on network signaling and reduce power.

During the initial access procedure, as shown in block 202, a machine may send a contentious access request to a cellular device acting as a machine GW. For example, the machine may communicate with the cellular device on DL resources. In an exemplary embodiment, the machine may make an initial machine access using a "contentious" access request by transmitting it to the nearby machine GW on the specified DL PRBs based at least in part on system bandwidth (BW). Then the nearby machine GW may relay the machine access request to an eNB on UL resources. In block 204, the machine may receive from a network node a contentious access response comprising a random access preamble sequence allocated by this network node for a non-contentious access transmission from the machine to the machine GW. According to exemplary embodiments, the random access preamble sequence may be allocated based at least in part on a TA parameter of the cellular device according to a predefined rule. Correspondingly, for a cellular device acting as a machine GW, in response to receipt of a contentious access request of a machine (which may be sent on specified downlink resources for example), as shown in block 212, it may forward the contentious access request to a network node (for example, on scheduled uplink resources). In block 214, the cellular device may obtain a random access preamble sequence allocated by the network node for a non-contentious access transmission from the machine to the machine GW. In an exemplary embodiment, the allocated random access preamble sequence may comprise a frequency- domain spreaded random access preamble sequence for Code Domain Multiplexing (CDM) of the non-contentious access transmission. With respect to a network node, in response to receipt of a contentious access request of a machine from a cellular device acting as a machine GW, as shown in block 222, it may allocate a random access preamble sequence for a non-contentious access transmission based at least in part on a TA parameter of the cellular device according to a predefined rule, and in block 224 send a contentious access response comprising the random access preamble sequence to the machine (for example, on scheduled downlink resources). According to exemplary embodiments, the network node may perform allocation of resources to the cellular device and the machine in a centralized way via a MBSFN configured for transmissions from the machine to the machine GW.

As mentioned before, the random access preamble sequence may be allocated based at least in part on a TA parameter of the cellular device according to a predefined rule. According to exemplary embodiments, the predefined rule may comprise: allocating to a cell served by the network node a set of random access preamble sequences for non-contentious access transmissions; reusing the set of random access preamble sequences for cellular devices with sufficiently different TA parameters (for example, in case that a difference between TA values is larger than or equal to a predetermined threshold) in the cell; and assigning different random access preamble sequences from the set of random access preamble sequences to respective cellular devices with similar TA parameters (for example, in case that a difference between TA values is smaller than the predetermined threshold) in the cell. In an exemplary embodiment, the proposed resource allocation for non-contentious access transmissions can be extended across neighboring cells, and thus the predefined rule may further comprise allocating a different set of random access preamble sequences for non-contentious access transmissions to a different cell.

In an exemplary embodiment, to allow a "non-contentious" machine access request, an eNB may allocate machine GW common DL PRBs for the access request with some periodicity via higher-layer signaling to the machine and the machine GW. This may include pairing of a machine and a machine GW with a machine identity (ID) and a machine GW ID. The machine access request are "non-contentious" for the machines paired with the same machine GW, but may still involve high contention in case there are many machines paired with other machine GWs in the same cell or across different cells within a typical machine transmission range. According to an exemplary embodiment, if the cellular device moves within a cell served by the network node while being signaled a new TA parameter, the machine may be signaled by the network node to initiate a new contentious access to a new machine GW within the machine's transmission range. The new contentious access may use a sequence different from those random access preamble sequences reserved for non-contentious access transmissions. The various blocks shown in Figs.2A-2C may be viewed as method steps, and/or as operations that result from operation of computer program code, and/or as a plurality of coupled logic circuit elements constructed to carry out the associated function(s). The schematic flowchart diagrams described above are generally set forth as logical flowchart diagrams. As such, the depicted order and labeled steps are indicative of specific embodiments of the presented methods. Other steps and methods may be conceived that are equivalent in function, logic, or effect to one or more steps, or portions thereof, of the illustrated methods. Additionally, the order in which a particular method occurs may or may not strictly adhere to the order of the corresponding steps shown.

An example of the RACH design in MTC is described with reference to Fig.3 which shows schematically allocation of random access preamble sequences for a machine and a machine GW in a network in accordance with embodiments of the present invention. To optimize resource allocation for a "non-contentious" access request, the TA information of cellular devices acting as machine GWs may be used by an eNB as follows.

a). Cellular devices with different TA in same sector may be allocated common DL PRB resources with same frequency- domain spreaded machine random access preamble sequences Sj for CDM of a machine access request, where i=l,2, N, and N is the number of frequency- domain spreaded machine random access preamble sequences which may be used in this sector. For the example illustrated by Fig.3, N=3 and there are three different TA values as denoted by TAi, TA₂ and TA₃. For example, devices D₂, D₆, D₉ may be assigned the same CDM sequence S₂. Cellular devices with different TA parameters are assumed to be distant and hence machine transmissions to machine GWs are sufficiently spatially separated to allow reuse of the CDM sequence. It is noted that N=3 in the example of Fig.3 because there are three cellular devices in each group of cellular devices with same TA, however, if the numbers of cellular devices in respective groups of cellular devices with same TA are different, the value of N may be dimensioned for the worst case. For example, if the number (N of cellular devices with TAi differs from the number (N₂) of cellular devices with TA₂, then the value of N may be determined as N=max(N₁, N₂) with some margin as the number of cellular devices with similar/same TA may vary depending on traffic loads and their locations. In an exemplary embodiment, a larger set of sequences with size N could be specified, which would in most practical scenarios allow to assign enough sequences.

b). Cellular devices with same TA in same sector may be allocated common DL PRB resources with different frequency- domain spreaded machine random access preamble sequence Si for CDM of a machine access request to allow orthogonal sequence- separated machine transmissions. In the example shown in Fig.3, each device with the same TA value (as shown by a circle in dashes) is assigned its own CDM sequence, for example, devices D₄, D₅, D₆ with TA₂ value may be assigned CDM sequences Si, S₃, S₂ respectively. In practical scenario, the assignment of CDM sequences to the devices with same TA in same sector is likely to be somewhat random as new machines need sequences while a machine moving out of the machine GW coverage may free a sequence. For example, a simple rule would be that the eNB may randomly pick one sequence in available sequences (not yet assigned) for a new machine. Alternatively, another way would be that the eNB may pick available sequences in an ascending order. For example, if Si and S₃ are available and S₂ already assigned, then the eNB may assign Si to a new machine and then S₃ to the next new machine.

In the proposed invention, the machine may get the frequency- domain spreaded machine random access preamble sequence used for machine - machine GW from an eNB in a contentious machine RACH response message. According to exemplary embodiments, to extend the proposed way across sectors, a different set of frequency-domain spreaded machine random access preamble sequences, for example {S_j } with j=7, 8, 9, are available to cellular devices on a different sector. Cellular devices with different TA on the different sector may be allocated common DL PRB resources with same frequency- domain spreaded machine random access preamble sequences S_j for CDM of a machine access request. Further, cellular devices with same TA on different sectors may be allocated common DL PRB resources with different frequency-domain spreaded machine random access preamble sequence S_j in similar ways as outlined above. Sectors are not shown on Fig.3 to improve clarity. Similarly, to extend the proposed way across neighboring cells, cellular devices on different cells may be allocated common DL PRB resources with a different set of frequency- domain spreaded machine random access preamble sequences, for example {Sj with k=4, 5, 6 as shown by Fig.3.

As mentioned previously, there may be likely scenario where the machine GW may be moving significantly within the serving cell. If the machine GW moves within the cell while being signaled a new TA parameter as part of the Release 8 UL timing alignment procedure (3GPP TS 36.321), the eNB may signal to the machine to initiate a new "contentious" machine RACH to connect to a different machine GW within its machine transmission range. To avoid confusing for the machine GW, the "contentious" machine RACH may use other sequences than the ones reserved for "non-contentious" machine RACH (which are TA based sequences). So the machine GW can clearly differentiate between the new machines and the connected machines.

Fig.4 is a schematic diagram illustrating a MTC system in accordance with an embodiment of the present invention. Although the MTC system shown in Fig.4 only comprises one eNB, one cellular device and two machines/sensor nodes, those skilled in the art would realize that more eNBs may be located in the MTC system, and each eNB may serve more cellular devices and machines/sensor nodes.

As shown in Fig.4, the machines such as sensor nodes may not transmit signals to the eNB but instead to a machine GW (such as a cellular device like a UE, a mobile terminal, a wireless device and etc.) to reduce impacts on network signaling and reduce power. According to an exemplary embodiment, the eNB may operate using cellular DL and UL channels in Frequency Domain Duplexing (FDD) mode. For example, the eNB may send signals to both machines and cellular devices (M2M GWs) in DL carrier, and only receive signals from cellular devices in UL carrier. For the cellular device which has capability to acting as a M2M/Sensor GW, it may operate using cellular UL and DL channels in FDD mode. For example, the cellular device may send signals to the eNB in UL carrier, and receive signals from both machines and eNB in DL carrier. For the machine device, it may operate using cellular DL channel resources in TDD mode. For example, the machine may send signals to cellular devices and optionally to other machines in DL carrier, and receive signals from the eNB and optionally from other machines in DL carrier.

In an exemplary embodiment, the TA parameter resolution may be 16*T_s=0.52us which corresponds to the round trip propagation delay between the eNB and the cellular device or an eNB-device distance about 75m as specified in 3GPP TS 36.331, v8.2.0. This means two cellular devices with different TA can be assumed to be 75m away from each other if in a Line of Sight (LOS) to the eNB, or longer if not in a LOS to the eNB.

An example of eNB signaling for the machine to machine GW connection is described here. During initial "contentious" RACH access, the machine may send a "contentious" machine RACH to the machine GW on specified PRBs on the DL as indicated by System Information Block (SIB). The machine may select a machine RACH preamble as part of a machine RACH preamble group similarly as specified in R8. On reception of the "contentious" machine RACH, the machine GW forwards it to the eNB on the scheduled UL resources. In case the machine GW has no scheduled UL resources, it may first initiate a schedule request using a "non-contentious" RACH procedure if in active state or initiate a "contentious" RACH procedure otherwise. The machine may subsequently get the CDM sequence used for machine - machine GW in the contentious machine RACH response message from the eNB on DL resources Physical Downlink Shared Channel (PDSCH) as scheduled by the eNB Media Access Control (MAC) layer via Physical Downlink Control Channel (PDCCH) similarly to a R8 cellular device. For example, the PDSCH may be sent in the data region, while the PDCCH is sent in the control region in a normal subframe. It is noted that this is different from the MBSFN subframe configured for machine to machine GW transmissions as described hereafter. According to exemplary embodiments, the machine needs not to know the machine GW TA parameters for the machine to machine GW transmission on DL PRBs, as it is assumed that (i) a machine and a machine GW are DL synchronized to the same eNB; (ii) a machine and a machine GW are typically within a few tens of meters.

Now the discussion is made with respect to the synchronization of machines. According to exemplary embodiments, a machine may get its downlink synchronization from the eNB and transmit to a nearby cellular device acting as a machine GW on DL resources. Hence, the machine needs not perform random access to the eNB including a timing- advance measurement problem, as the UL timing alignment is not needed for the machine to machine GW transmission. The machine may only require a machine access request to the machine GW. This simplifies the implementation of machines and cellular devices as only Orthogonal Frequency Domain Multiplexing (OFDM) modulation is needed for a MTC connection. It saves machine power as the machine may only send a relatively short machine access request via a machine RACH in a OFDM PRB to a nearby cellular device acting as a machine GW (instead of a longer cellular RACH with high transmission power to reach a typically distant eNB as specified in R8).

A novel machine MBSFN subframe configuration for machine - machine GW communications is also proposed here. According to exemplary embodiments, the allocation of resources to a machine and a cellular device acting as a machine GW may be done in a centralized way by an eNB via this machine (M2M) MBSFN subframe configuration to limit the inter-machine interference and interferences to the cellular devices (normal cellular devices or cellular devices acting as machine GWs). An example of the machine MBSFN subframe configuration in accordance with embodiments of the present invention is illustrated in Fig.5. During the cellular device R8 control region (for example, first 2 Orthogonal Sequences (OS) in Fig.5), the eNB can transmit R8 control signaling to the cellular device, such as Physical Control Format Indicator Channel (PCFIC), PDCCH and Physical Hybrid-ARQ Indicator Channel (PHICH). The eNB may also transmit control signaling to the machines there. Then, the 3rd OS may be used for switching from a cellular mode to a machine mode in the cellular device (for example, HW parameters are different due to much lower M2M transmission power). The remaining of the MBSFN subframe can be used for machine transmissions to the cellular device. There is no DL interference to the cellular device there as they do not get DL grant on the PDCCH and thus do not receive anything in these symbols.

As mentioned above, many advantageous may be achieved by employing a proper machine RACH design for machine transmissions. It is benefit to develop a CDM signal structure. According to exemplary embodiments, a machine GW may identify machine transmissions based at least in part on their CDM sequences to avoid false machine detection from machines in neighboring cells. The R8 RACH design is not efficient for the machine to machine GW access as this may typically be done over a short distance of a few tens of meters. In R8 specification, the shortest RACH transmission occurs during the random access on the UpPTS in a TDD system. The random access begins 4832xT_s seconds, where T_s=l/(15000x2048), before the end of the UpPTS with a duration of 4544xT_s seconds. This leaves a guard period of

288xT_s seconds which allows for a maximum supported cell size of approximately 1.4 km. This is illustrated in Fig.6 which exemplarily shows the RACH in UpPTS in a TDD system.

However, similar mechanisms as in R8 RACH design could be used for the machine to machine GW "non-contentious" random access, for example, cell-specific groups of RACH preambles. In an exemplary embodiment, a set of machine RACH preambles {S with i=l, 2, .., N could be used in a cell, with one single sequence Si assigned to a machine GW. The size of the set, N, may depend on how many machine GWs with similar TA commands as given by an eNB there could be in a practical system. The set of machine RACH preambles, {Si}, may be reused for those machine GWs with sufficiently different TA commands based at least in part on the TA parameter resolution and machine transmission power. A different set of machine RACH preambles, {Sj with k=l, 2, ... , N and k≠ i , may be used in a neighboring cell. The size of the Cyclic Prefix (CP), T_cp, and the preamble sequence, T_SEQ, may depend on the machine-to-machine GW transmission range and detection probability at the machine GW.

In an exemplary embodiment, assuming common DL PRBs are scheduled for the "non-contentious" machine to machine GW random access, some inter-machine RACH interference may be experienced between machine transmissions to nearby machine GWs. However, the impact of such interference could be mitigated as the "non-contentious" machine RACH transmissions may be preamble separated by code domain multiplexing. This may also be a difference with R8 RACH, as the R8 RACH preambles are not actually used for code domain multiplexing of RACH transmissions, but rather used for high RACH detection probability and ranging (such as estimation of the propagation delay between a R8 UE and an eNB). In the machine to machine GW random access, more efficient use of common DL PRB resources could be achieved by code domain multiplexing. For example, this can be done by using frequency-domain spreading of a short machine RA preamble as follows: ^i-^i,0> · ·> ^i,L- ^i,L> ^i,L+b ··? ^i,2*L-b · · ·^■> ^i,(M-l)*L> ^i,(M-l)*L+b ··? ^i,M*L-l where L is the spreading factor and M is the machine RACH preamble length, and T=M*L is the frequency-domain spreaded machine RACH preamble length. There may be a set of N frequency- domain spreaded machine RACH preamble sequences, wherein N is smaller or equal to M depending on the machine RACH preamble sequence design in use. In case of initial "contentious", the machine to machine GW random access may be machine RACH preamble based without code domain multiplexing, which is closer to R8 RACH mechanisms.

The exemplary embodiments described herein propose a "non-contentious" machine to machine GW random access request, which may use the information of TA of a cellular device for the assignment of dedicated preamble sequences. The proposed solution may have significant benefits such as simplified implementation of machines and cellular devices as only OFDM modulation is needed for the MTC connection, and machine power saving since machine may only send a relatively efficient machine RACH in an OFDM PRB with low power to a machine GW (instead of R8 cellular RACH with high transmission power to reach a typically distant eNB as specified in R8). Another advantage of the proposed solution is in that a machine GW may identify machine transmissions based at least in part on their frequency-domain spreaded machine random access preamble sequences to avoid false machine detection from machines in neighboring cells. In addition, high reuse of common DL PRBs for machine access requests may be achieved due to spatial and code domains orthogonality.

Now reference is made to Fig.7 illustrating a simplified block diagram of various devices which are suitable for use in practicing exemplary embodiments of the present invention. In Fig.7, a network node 710 such as an eNB/BS/control center may be adapted for communicating with one or more cellular devices (denoted as cellular device 720 in general) in DL and UL resources, and adapted for communicating with one or more machines (denoted as machine 730 in general) only in DL resources. In an exemplary embodiment, the network node 710 may comprise a data processor (DP) 71 OA, a memory (MEM) 71 OB that stores a program (PROG) 7 IOC, and a suitable radio frequency (RF) transceiver 710D for transmitting/receiving signals to/from a cellular device (such as cellular device 720) and for transmitting signals to a machine (such as machine 730) via one or more antennas. For example, the transceiver 710D in the network node 710 may be an integrated component for transmitting and/or receiving signals and messages. Alternatively, the transceiver 710D may comprise separate components to support transmitting and receiving signals/messages, respectively. The DP 71 OA may be used for processing these signals and messages. Alternatively or additionally, the network node 710 may comprise various means and/or components for implementing functions of the foregoing steps and method described in connection with Fig.2C.

According to an exemplary embodiment, the cellular device 720 may also comprise a DP 720A, a MEM 720B that stores a PROG 720C, and a suitable RF transceiver 720D. The transceiver 720D in the cellular device 720 can be used for transmitting/receiving signals to/from a network node (such as the network node 710) and for receiving signals from a machine (such as the machine 730) when the cellular device 720 acts as a machine GW. For example, the transceiver 720D may be an integrated component for transmitting and/or receiving signals and messages. Alternatively, the transceiver 720D may comprise separate components to support transmitting and receiving signals/messages, respectively. The DP 720A may be used for processing these signals and messages. According to another exemplary embodiment, the cellular device 720, such as a mobile device, a wireless terminal, a UE or the like, may comprise various means and/or components for implementing functions of the foregoing steps and method described in connection with Fig.2B.

Fig.7 also shows a simplified block diagram of a machine 730 in accordance with exemplary embodiments. The machine 730 may comprise a DP 730 A, a MEM 730B storing a PROG 730C, and a suitable transceiver 730D. The transceiver 730D may be used for transmitting signals to a machine GW (such as the cellular device 720) and for receiving signals from a network node (such as the network node 710). For example, the transceiver 730D may be an integrated component for transmitting and/or receiving signals and messages. Alternatively, the transceiver 730D may comprise separate components to support transmitting and receiving signals/messages, respectively. The DP 730A may be used for processing these signals and messages. According to another exemplary embodiment, the machine 730 such as a sensor node or the like may comprise various means and/or components for implementing functions of the foregoing steps and method described in connection with Fig.2A.

At least one of the PROGs 710C, 720C and 730C is assumed to comprise program instructions that, when executed by the associated DP, enable the electronic device to operate in accordance with the exemplary embodiments, as discussed above. That is, the exemplary embodiments of the present invention may be implemented at least in part by computer software executable by the DP 71 OA of the network node 710, the DP 720A of the cellular device 720 and the DP 730A of the machine 730, or by hardware, or by a combination of software and hardware. The basic structure and operation of the network node 710, the cellular device 720 and the machine 730 are known to one skilled in the art.

The MEMs 710B, 720B and 730B may be of any type suitable to the local technical environment and may be implemented using any suitable data storage technology, such as semiconductor based memory devices, flash memory, magnetic memory devices and systems, optical memory devices and systems, fixed memory and removable memory. The DPs 71 OA, 720A and 730 A may be of any type suitable to the local technical environment, and may comprise one or more of general purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs) and processors based on multi-core processor architectures, as non-limiting examples.

In general, the various exemplary embodiments may be implemented in hardware or special purpose circuits, software, logic or any combination thereof. For example, some aspects may be implemented in hardware, while other aspects may be implemented in firmware or software which may be executed by a controller, microprocessor or other computing device, although the invention is not limited thereto. While various aspects of the exemplary embodiments of this invention may be illustrated and described as block diagrams, flowcharts, or using some other pictorial representation, it is well understood that these blocks, apparatus, systems, techniques or methods described herein may be implemented in, as non-limiting examples, hardware, software, firmware, special purpose circuits or logic, general purpose hardware or controller or other computing devices, or some combination thereof.

It will be appreciated that at least some aspects of the exemplary embodiments of the inventions may be embodied in computer-executable instructions, such as in one or more program modules, executed by one or more computers or other devices. Generally, program modules include routines, programs, objects, components, data structures, etc. that perform particular tasks or implement particular abstract data types when executed by a processor in a computer or other device. The computer executable instructions may be stored on a computer readable medium such as a hard disk, optical disk, removable storage media, solid state memory, random access memory (RAM), and etc. As will be realized by one of skill in the art, the functionality of the program modules may be combined or distributed as desired in various embodiments. In addition, the functionality may be embodied in whole or in part in firmware or hardware equivalents such as integrated circuits, field programmable gate arrays (FPGA), and the like. Although specific embodiments of the invention have been disclosed, those having ordinary skill in the art will understand that changes can be made to the specific embodiments without departing from the spirit and scope of the invention. The scope of the invention is not to be restricted therefore to the specific embodiments, and it is intended that the appended claims cover any and all such applications, modifications, and embodiments within the scope of the present invention.

Claims

CLAIMS What is claimed is:

1. A method, comprising:

sending a contentious access request of a machine to a cellular device acting as a machine gateway; and

receiving from a network node a contentious access response comprising a random access preamble sequence allocated by the network node for a non-contentious access transmission from the machine to the machine gateway;

wherein the random access preamble sequence is allocated based at least in part on a timing advance parameter of the cellular device according to a predefined rule.

2. The method according to claim 1, wherein the predefined rule comprises:

allocating to a cell served by the network node a set of random access preamble sequences for non-contentious access transmissions;

reusing the set of random access preamble sequences for cellular devices with sufficiently different timing advance parameters in the cell; and

assigning different random access preamble sequences from the set of random access preamble sequences to respective cellular devices with similar timing advance parameters in the cell.

3. The method according to claim 2, wherein the predefined rule further comprises: allocating a different set of random access preamble sequences for non-contentious access transmissions to a different cell.

4. The method according to any of claims 1 to 3, wherein the allocated random access preamble sequence comprises a frequency- domain spreaded random access preamble sequence for code domain multiplexing of the non-contentious access transmission.

5. The method according to any of claims 1 to 4, wherein if the cellular device moves within a cell served by the network node while being signaled a new timing advance parameter, the machine is signaled by the network node to initiate a new contentious access to a new machine gateway within the machine's transmission range, and wherein the new contentious access uses a sequence different from random access preamble sequences reserved for non-contentious access transmissions.

6. The method according to any of claims 1 to 5, wherein the contentious access request is sent from the machine to the cellular device on specified downlink resources, and forwarded from the cellular device to the network node on scheduled uplink resources, and wherein the contentious access response is sent from the network node to the machine on scheduled downlink resources.

7. The method according to any of claims 1 to 6, wherein allocation of resources to the cellular device and the machine is performed in a centralized way by the network node via a multimedia broadcast single frequency network subframe configured for transmissions from the machine to the machine gateway.

8. An apparatus, comprising:

at least one processor; and

at least one memory including computer program code,

the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus to perform at least the following: sending a contentious access request to a cellular device acting as a machine gateway; and

receiving from a network node a contentious access response comprising a random access preamble sequence allocated by the network node for a non-contentious access transmission from the apparatus to the machine gateway; wherein the random access preamble sequence is allocated based at least in part on a timing advance parameter of the cellular device according to a predefined rule.

9. The apparatus according to claim 8, wherein the predefined rule comprises:

10. The apparatus according to claim 9, wherein the predefined rule further comprises: allocating a different set of random access preamble sequences for non-contentious access transmissions to a different cell.

11. The apparatus according to any of claims 8 to 10, wherein the allocated random access preamble sequence comprises a frequency- domain spreaded random access preamble sequence for code domain multiplexing of the non-contentious access transmission.

12. The apparatus according to any of claims 8 to 11, wherein allocation of resources to the cellular device and the apparatus is performed in a centralized way by the network node via a multimedia broadcast single frequency network subframe configured for transmissions from the apparatus to the machine gateway.

13. A computer program product comprising a computer-readable medium bearing computer program code embodied therein for use with a computer, the computer program code comprising:

code for sending a contentious access request of a machine to a cellular device acting as a machine gateway; and

code for receiving from a network node a contentious access response comprising a random access preamble sequence allocated by the network node for a non-contentious access transmission from the machine to the machine gateway;

14. A method, comprising:

forwarding a contentious access request of a machine to a network node from a cellular device acting as a machine gateway, in response to receipt of the contentious access request; and

obtaining a random access preamble sequence allocated by the network node for a non-contentious access transmission from the machine to the machine gateway; wherein the random access preamble sequence is allocated based at least in part on a timing advance parameter of the cellular device according to a predefined rule.

15. The method according to claim 14, wherein the predefined rule comprises:

reusing the set of random access preamble sequences for cellular devices with sufficiently different timing advance parameters in the cell; and assigning different random access preamble sequences from the set of random access preamble sequences to respective cellular devices with similar timing advance parameters in the cell.

16. The method according to claim 15, wherein the predefined rule further comprises: allocating a different set of random access preamble sequences for non-contentious access transmissions to a different cell.

17. The method according to any of claims 14 to 16, wherein the allocated random access preamble sequence comprises a frequency- domain spreaded random access preamble sequence for code domain multiplexing of the non-contentious access transmission.

18. The method according to any of claims 14 to 17, wherein allocation of resources to the cellular device and the machine is performed in a centralized way by the network node via a multimedia broadcast single frequency network subframe configured for transmissions from the machine to the machine gateway.

19. An apparatus, comprising:

at least one processor; and

at least one memory including computer program code,

the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus to perform at least the following:

forwarding a contentious access request of a machine to a network node from the apparatus acting as a machine gateway, in response to receipt of the contentious access request; and

obtaining a random access preamble sequence allocated by the network node for a non-contentious access transmission from the machine to the machine gateway; wherein the random access preamble sequence is allocated based at least in part on a timing advance parameter of the apparatus according to a predefined rule.

20. The apparatus according to claim 19, wherein the predefined rule comprises: allocating to a cell served by the network node a set of random access preamble sequences for non-contentious access transmissions;

21. The apparatus according to claim 20, wherein the predefined rule further comprises: allocating a different set of random access preamble sequences for non-contentious access transmissions to a different cell.

22. The apparatus according to any of claims 19 to 21, wherein the allocated random access preamble sequence comprises a frequency- domain spreaded random access preamble sequence for code domain multiplexing of the non-contentious access transmission.

23. The apparatus according to any of claims 19 to 22, wherein allocation of resources to the apparatus and the machine is performed in a centralized way by the network node via a multimedia broadcast single frequency network subframe configured for transmissions from the machine to the machine gateway.

24. A computer program product comprising a computer-readable medium bearing computer program code embodied therein for use with a computer, the computer program code comprising:

code for forwarding a contentious access request of a machine to a network node from a cellular device acting as a machine gateway, in response to receipt of the contentious access request; and

code for obtaining a random access preamble sequence allocated by the network node for a non-contentious access transmission from the machine to the machine gateway;

25. A method, comprising:

allocating, in response to receipt of a contentious access request of a machine from a cellular device acting as a machine gateway, a random access preamble sequence by a network node for a non-contentious access transmission from the machine to the machine gateway, based at least in part on a timing advance parameter of the cellular device according to a predefined rule; and

sending to the machine a contentious access response comprising the random access preamble sequence.

26. The method according to claim 25, wherein the predefined rule comprises:

27. The method according to claim 26, wherein the predefined rule further comprises: allocating a different set of random access preamble sequences for non-contentious access transmissions to a different cell.

28. The method according to claim 25, wherein the predefined rule comprises:

allocating to a sector served by the network node a set of random access preamble sequences for non-contentious access transmissions;

reusing the set of random access preamble sequences for cellular devices with different timing advance parameters in the sector; and

assigning different random access preamble sequences from the set of random access preamble sequences to respective cellular devices with the same timing advance parameter in the sector.

29. The method according to claim 28, wherein the predefined rule further comprises: allocating a different set of random access preamble sequences for non-contentious access transmissions to a different sector.

30. The method according to any of claims 25 to 29, wherein the allocated random access preamble sequence comprises a frequency- domain spreaded random access preamble sequence for code domain multiplexing of the non-contentious access transmission.

31. The method according to any of claims 25 to 30, wherein allocation of resources to the cellular device and the machine is performed in a centralized way by the network node via a multimedia broadcast single frequency network subframe configured for transmissions from the machine to the machine gateway.

32. An apparatus, comprising: at least one processor; and

at least one memory including computer program code,

allocating, in response to receipt of a contentious access request of a machine from a cellular device acting as a machine gateway, a random access preamble sequence for a non-contentious access transmission from the machine to the machine gateway, based at least in part on a timing advance parameter of the cellular device according to a predefined rule; and

33. The apparatus according to claim 32, wherein the predefined rule comprises: allocating to a cell served by the apparatus a set of random access preamble sequences for non-contentious access transmissions;

34. The apparatus according to claim 33, wherein the predefined rule further comprises: allocating a different set of random access preamble sequences for non-contentious access transmissions to a different cell.

35. The apparatus according to claim 32, wherein the predefined rule comprises: allocating to a sector served by the apparatus a set of random access preamble sequences for non-contentious access transmissions; reusing the set of random access preamble sequences for cellular devices with different timing advance parameters in the sector; and

36. The apparatus according to claim 35, wherein the predefined rule further comprises: allocating a different set of random access preamble sequences for non-contentious access transmissions to a different sector.

37. The apparatus according to any of claims 32 to 36, wherein the allocated random access preamble sequence comprises a frequency- domain spreaded random access preamble sequence for code domain multiplexing of the non-contentious access transmission.

38. The apparatus according to any of claims 32 to 37, wherein allocation of resources to the cellular device and the machine is performed in a centralized way by the apparatus via a multimedia broadcast single frequency network subframe configured for transmissions from the machine to the machine gateway.

39. A computer program product comprising a computer-readable medium bearing computer program code embodied therein for use with a computer, the computer program code comprising:

code for allocating, in response to receipt of a contentious access request of a machine from a cellular device acting as a machine gateway, a random access preamble sequence by a network node for a non-contentious access transmission from the machine to the machine gateway, based at least in part on a timing advance parameter of the cellular device according to a predefined rule; and code for sending to the machine a contentious access response comprising the random access preamble sequence.