WO2013023834A1

WO2013023834A1 - Indicating the availability of an alternate uplink resource

Info

Publication number: WO2013023834A1
Application number: PCT/EP2012/063008
Authority: WO
Inventors: Vikas Dhingra; Shin Horng Wong
Original assignee: Alcatel Lucent
Priority date: 2011-08-12
Filing date: 2012-07-04
Publication date: 2013-02-21

Abstract

The present subject matter discloses systems and methods for allocation of uplink resources in a wireless communication system. In one implementation, a method comprising transmitting a preamble signature pertaining to an Enhanced Dedicated Channel (E-DCH) to request an E-DCH resource in a random access procedure, and receiving, in response, a fallback indication is described. In one embodiment, the fallback indication indicates availability of an alternate resource.

Description

INDICATING THE AVAILABILITY OF AN ALTERNATE UPLINK RESOURCE

FIELD OF INVENTION

[0001] The present subject matter relates to radio resource control between a user equipment (UE) and a wireless network, and, particularly, but not exclusively, to uplink resource access in CELL FACH state in a Universal Mobile Telecommunication System (UMTS) network.

BACKGROUND

[0002] A Universal Mobile Telecommunication System (UMTS) is a broadband, packet based system for the transmission of data based on Wideband Coded Division Multiple Access (W-CDMA). In a UMTS network, a Radio Resource Control (RRC) connection may be in four states such as CELL PCH, URA PCH, CELL FACH, and CELL DCH. The states CELL PCH and URA PCH, also known as the idle modes, are states in which a user equipment (UE) uses Discontinuous Reception (DRX) to monitor broadcast messages and pages. No uplink activity is possible in the CELL PCH and URA PCH states. In the CELL-DCH state, a dedicated channel is allocated to the UE in uplink and downlink to exchange data while in the CELL FACH state, no dedicated channel is allocated to the UE and, instead, common channels are used to exchange a small amount of data.

[0003] The CELL FACH state is advantageous for various applications that generate traffic that is bursty in nature since keeping the mobile phone in a fully connected state i.e. CELL DCH state while only little data is to be transferred intermittently is wasteful in terms of bandwidth and battery capacity. For example, consider a user browsing the Internet on his mobile phone. In such a situation, most of the times there would not be any activity except for the times when some content is required to be downloaded or uploaded. Accordingly, the UMTS network usually sets UEs into the CELL FACH state, once it detects that there is only little activity.

[0004] Several releases of 3rd Generation Partnership Project (3GPP) standards for

UMTS have imparted additional features to the UMTS to cater to the number of UEs in the CELL FACH state, for example due to an increase in number of internet enabled UEs, and to enhance the Quality of Service (QoS) of the UMTS. The 3 GPP release 7 introduced Enhanced CELL FACH to the UMTS. Enhanced CELL FACH allows the UEs to receive HSDPA (High Speed Downlink Packet Access) packets enabling the UE to receive large bursts of downlink data. Similarly, after the 3GPP release 8 introduced HSUPA (High Speed Uplink Packet Access) to Enhanced CELL FACH, the UEs became equipped to send a large burst of uplink data. Thus, UEs that support Enhanced CELL FACH, are capable of transmitting large amount of data in the uplink and downlink while residing in the CELL FACH state.

[0005] To start with, the UEs capable of HSUPA in Enhanced CELL FACH were to use only Enhanced Dedicated Channel (E-DCH) for uplink transmission while the UEs incapable of HSUPA in Enhanced CELL FACH continued to use Random Access Channel (RACH) i.e. the legacy uplink channel of the CELL FACH state, for uplink transmissions. Thus, even though a UE capable of HSUPA in Enhanced CELL FACH possessed the capability to use RACH for uplink transmission, it was restricted from doing so.

[0006] However, as the UMTS evolved further, in view of the ever increasing number of UEs supporting Enhanced CELL FACH, it was realized that the UEs supporting HSUPA in Enhanced CELL FACH should be allowed to use RACH to efficiently utilize the available resources of the UMTS network. Accordingly, the release 1 1 of the 3GPP provides for the UEs to use either RACH or E-DCH as an uplink resource. SUMMARY

[0007] This summary is provided to introduce concepts related to allocation of uplink resources in a wireless communication system. This summary is not intended to identify essential features of the claimed subject matter nor is it intended for use in determining or limiting the scope of the claimed subject matter.

[0008] In accordance with an embodiment of the present subject matter a method to obtain an uplink resource is described. The method comprises transmitting a preamble signature pertaining to an Enhanced Dedicated Channel (E-DCH) to request an E-DCH resource in a random access procedure, and receiving, in response, a fallback indication comprising an Acquisition Indicator (AI) and an Extended Acquisition Indicator (E-AI) to indicate an alternate resource. The alternate resource may comprise a Random Access Channel (RACH) resource. The method further comprises switching to the alternate resource based on the fallback indication received in the response. In one embodiment, subsequent to the switching, a retransmitting of a preamble signature pertaining to RACH may occur or a message having a specification pertaining to RACH may be sent further to the already transmitted preamble signature pertaining to E-DCH.

[0009] In accordance with another embodiment of the present subject matter, an uplink resource allocation method comprising receiving a preamble signature requesting an E-DCH resource in a random access procedure and sending a configuration of AI and E-AI in response to the receiving, to indicate availability of an alternate resource comprising a RACH, is described.

[0010] In yet another embodiment of the present subject matter, a Radio Network Controller (RNC) is described. The RNC comprises a RNC fallback module to determine at least one reserved preamble signature. The at least one reserved preamble signature is provided to a user equipment (UE) and one or more node B (NB) by a RNC communication module. The UE uses at least one reserved preamble signature to indicate a fallback capability of the UE to the NB while the NB uses the at least one reserved preamble signature to identify a UE having the fallback capability.

[0011] Further described is a UE according to an embodiment of the present subject matter. The UE comprises a resource access module configured to use a reserved preamble signature to request an associated NB for allocation of an E-DCH resource. The resource access module further comprises a UE fallback module configured to fallback to an alternate resource comprising a Random Access Channel (RACH) resource, based on a configuration of AI and E- AI in an AICH received in response to the request.

[0012] According to one more embodiment of the present subject matter, an NB comprising a resource allocation module and an NB fallback module is described. The resource allocation module is configured to allocate an uplink resource to UEs based on a request it receives from the UEs. The NB fallback module is configured to identify at least one UE, requesting an E-DCH resource, as having a fallback capability, based on a reserved preamble signature received from the UE. The NB module is further configured to indicate availability of an alternate resource to the at least one identified UE. The alternate resource may comprise one or more of a RACH resource, a 10ms TTI E-DCH resource, and a 2ms TTI E-DCH resource.

[0013] Also described in one more embodiment of the present subject matter is a computer- readable medium having embodied thereon a computer program for executing a method of receiving a preamble signature pertaining to an E-DCH for requesting an E-DCH resource in a random access procedure and, in response to the receiving, sending an AI set to a positive value and a predetermined value of an E-AI in an AICH to indicate availability of an alternate resource.

BRIEF DESCRIPTION OF THE FIGURES

[0014] The detailed description is described with reference to the accompanying figures. In the figures, the left-most digit(s) of a reference number identifies the figure in which the reference number first appears. The same numbers are used throughout the figures to reference like features and components. Some embodiments of system and/or methods in accordance with embodiments of the present subject matter are now described, by way of example only, and with reference to the accompanying figures, in which:

[0015] Figure 1 shows a wireless communication system having a fallback functionality, in accordance with one embodiment of the present subject matter.

[0016] Figure 2 illustrates a method to obtain an uplink resource in accordance with one embodiment of the present subject matter.

[0017] Figure 3 illustrates an uplink resource allocation method according to one embodiment of the present subject matter.

[0018] It should be appreciated by those skilled in the art that any block diagrams herein represent conceptual views of illustrative systems embodying the principles of the present subject matter. Similarly, it will be appreciated that any flow charts, flow diagrams, state transition diagrams, pseudo code, and the like represent various processes which may be substantially represented in computer readable medium and so executed by a computer or processor, whether or not such computer or processor is explicitly shown.

DETAILED DESCRIPTION

[0019] Systems and methods for uplink resource allocation are described herein. In accordance with an embodiment of the present subject matter, systems and methods to enable a Node B (NB) to assign an uplink resource, such as a Random Access Channel (RACH) and Enhanced Dedicated Channel (E-DCH) to user equipments (UEs) in a Universal Mobile Telecommunication System (UMTS) are described.

[0020] The systems and methods can be implemented in systems capable of exchanging data in accordance with the Global System for Mobile (GSM) communication standards and support evolved High Speed Packet Access (HSPA) functionality. The evolved HSPA may include the enhanced high speed downlink packet access (HSDPA) and high speed uplink packet access (HSUPA) according to the 3rd Generation Partnership Project (3GPP) release 7 and release 8. Although the description herein is with reference to UMTS, the systems and methods may be implemented in other networks, albeit with a few variations, as will be understood by a person skilled in the art.

[0021] The systems and methods can be implemented in a variety of entities, such as communication devices, and computing systems. The entities that can implement the described method(s) include, but are not limited to, desktop computers, hand-held devices, laptops or other portable computers, tablet computers, mobile phones, PDAs, smartphones, and the like. Further, the method may also be implemented by devices capable of exchanging data to provide connectivity to different communicating devices and computing systems. Such devices may include, but are not limited to, data cards, mobile adapters, wireless adapters, routers, and the like. Although the description herein is explained with reference to a communicating device such as a smartphone, the described method(s) may also be implemented in any other devices, as will be understood by those skilled in the art.

[0022] Advancements in the tele-communication technology are constantly made to meet demands of the ever increasing number of telecommunication devices, such as mobile phones, laptops, Personal Digital Assistants (PDAs), and smart phones. Wireless communication systems continue to evolve to meet user demands by efficiently utilizing the available limited resources.

[0023] UMTS is a third generation mobile cellular technology for communication networks based on the GSM standard developed by the 3 GPP (3rd Generation Partnership Project). UMTS networks utilize wideband code division multiple access (WCDMA) to increase in data transfer capabilities and better resource utilization.

[0024] Improvements and latest capabilities have been added to the UMTS, with various releases of 3GPP standards for UMTS. The 3GPP release 7 introduced Enhanced CELL FACH to the UMTS to enable the UEs to receive HSDPA (High Speed Downlink Packet Access) packets while residing in the Cell-FACH state. The 3GPP release 8 introduced HSUPA (High Speed Uplink Packet Access) allowing the UEs to send a large burst of uplink data while residing in the Cell-FACH state. [0025] Prior to the release 11 , the standards dictated the UEs capable of HSUP A in

Enhanced CELL FACH to use only E-DCH resources for uplink transmission while RACH resources i.e. the legacy uplink channel of the CELL FACH state was to be used by those UEs that are not capable of HSUPA in Enhanced CELL FACH. Thus, the standards restricted a UE capable of HSUPA in Enhanced CELL FACH and possessing the capability to use RACH for uplink transmission from using RACH as an uplink resource.

[0026] With further evolutions made in UMTS, in release 11 , the UEs supporting

HSUPA in Enhanced CELL FACH have been allowed to use RACH to efficiently utilize the available resources of the UMTS network. Accordingly, the release 1 1 of the 3GPP provides for the UEs to use either RACH or E-DCH as an uplink resource.

[0027] Subsequent to release 11 , in the initial access process that UEs perform to obtain an uplink resource for its traffic, a UE may selectively request either a RACH or E-DCH as a resource. RACH and E-DCH have also been referred to as RACH and E-DCH resources in this description hereinafter referring to one or more radio channels comprising Random Access Channels or Enhanced Dedicated Channel channels. In one typical approach, a UE may select the resource, i.e., either one of RACH or E-DCH, on the basis of the specific service requiring access to the network. For example, if the service required by the UE involves transmitting high amount of payload in the uplink, the UE may request E-DCH as a resource while on the other hand RACH may be requested if low bandwidth signals have to be transmitted to the NB.

[0028] In the initial access, the UE performs a random access procedure to obtain an uplink resource for its traffic. In the initial access, the UE is required to select either RACH or E- DCH as an uplink resource for its traffic. However, the UE is unaware of the status of the resources and their availability, and thus may request for a resource that may be unavailable while an alternate resource may still be available. If the resource requested by the UE is not available at the NB due to congestion or some other reasons, the NB denies the request. Upon denial of the resource, the UE typically backs off for a predetermined amount of time before re- attempting another initial access to request either the same resource as previously requested or the alternative one. For example, if UE has performed a random access procedure to access E- DCH and NB rejects the access, the UE starts a back-off timer. After expiry of the back-off timer, a persistence check is performed. Based on result of the persistence check, the UE may perform the random access procedure again to access RACH either in present transmission time interval or later. Therefore an incorrect selection of a resource made by an UE may result in a delay in completion of the initial access.

[0029] In one conventional approach implemented to reduce the delay due to back-off timer, the UE does not start its back-off timer and, after the first rejection, immediately proceeds to request the alternate resource. For example, a UE may first attempt to access E-DCH, and failing its allocation, the UE may immediately attempt to access RACH. However, as evident, this approach relies on receiving a first rejection from the NB by the UE to re-attempt for the alternate resource which slows down the initial access due to the rejection and re-attempt. Furthermore, by the time the first rejection from the NB is received and the UE makes another attempt for the alternate resource, the availability of resource at the NB may have changed. For example, E-DCH may be congested and a request by UE to select E-DCH in its first attempt may be rejected. In the UE's second attempt, the UE may select to use RACH instead. However, during this time, RACH may have become congested whilst E-DCH may have been relieved of congestion. Such a possibility is likely owing to the fact that every UE that may have been denied E-DCH in the previous attempt, would request for RACH access in the subsequent attempt.

[0030] The above described approach facilitating multiple attempts may result in severe congestion, specifically in cells having a large number of UEs. If a resource is congested, the large number of UEs will all make reattempts, resulting in further congestion and even higher interference.

[0031] Also, approaches allowing a UE to make attempts to acquire a resource without waiting for a back-off timer to expire may cause further congestions. This is because both RACH and E-DCH may be congested at the same time. In such a scenario, UEs, after their first failed attempt, if allowed to immediately proceed to try the alternate resource type, may cause the network to choke. Accordingly, UEs may have to back-off for some random time before retrying. Doing so may however, as discussed above, result in delay.

[0032] Uplink resources, such as RACH and E-DCH are managed by the NB and while the NB is aware of the availability of these resources, the NB is configured only to grant or deny the resource requested by the UE and not allocate an alternate resource based on its knowledge of availability of the resources. Conventionally, there exists no mechanism for the NB to allocate an alternate available resource, other than the resource that has been requested by the UE. Also, there is no mechanism that may enable the NB to indicate to the UE that a particular resource is available so that the UE may select the available resource over the alternate one.

[0033] In accordance with an embodiment of the present subject matter, systems and methods to enable an NB to allocate the uplink resource to a UE for its initial access in a UMTS network are described. The UE may select an unlink resource, such as RACH or E-DCH in a random access procedure and request the NB for allocation of the selected resource. In one embodiment, in response to the random access procedure initiated by the UE, the NB may selectively assign to the UE, an alternate resource i.e. an uplink resource that may not have been requested by the UE, based on the availability of the resource.

[0034] To enable dynamic allocation of an uplink resource by the NB based on the availability, the UE and the NB are imparted a fallback functionality. Embodiments of the UE and the NB having the fallback functionality have been described to explain certain aspects of the fallback functionality. Such embodiments are provided only for the purposes of explanation and should not be considered as the only possible embodiments. Various other embodiments and modifications thereof will be apparent to one skilled in the art in the light of such embodiments.

[0035] In one embodiment, the fallback functionality enables the NB to indicate to a UE that a particular resource is available so that the UE may select the available resource over the requested one.

[0036] A UE performs a random access procedure to access any of the uplink resources, such as the RACH or the E-DCH. The random access procedure is completed in two stages. The first stage is referred to as the preamble stage where a preamble signature specifying the requested resource, such as the RACH and the E-DCH, is transmitted, whereas the second stage is the data transmission stage where the actual message is transmitted. As known conventionally, uplink resources, such as E-DCH and RACH have their own set of preamble signatures. Thus, a UE requesting E-DCH, for example, uses a preamble signature associated with the E-DCH to indicate to the NB that the UE has selected E-DCH for its initial access.

[0037] Typically, after sending the preamble the UE waits for an acknowledgement in the Acquisition Indicator Channel (AICH) from the NB before transmitting the message part. The transmit power for the message part is already determined from the preamble since the preamble is transmitted at a power where the NB can decode the preamble signature. [0038] The data transmitted in the AICH by the NB generally consists of an Acquisition

Indicator (AI), and an Extended Acquisition Indicator (E-AI). Various coding schemes of AI and E-AI are used to indicate to the UEs, the resource that may have been allocated to the UEs by the NB. Thus, AI and E-AI let a UE know whether a resource requested by the UE and indicated to the NB in the preamble signature has been allocated or not.

[0039] Presently, in case a UE sends a preamble signature corresponding to a RACH resource, an AI set to +1 represents a positive acknowledgement and indicates that a RACH resource has been assigned and the UE may transmit the actual message on the allocated RACH resource. Similarly, an AI set to -1 represents a negative acknowledgement following which the UE may repeat the random access procedure.

[0040] If a UE sends a preamble signature corresponding to a request for allocation of E-

DCH, the response provided to the request for allocation may depend on E-AI in addition to AI. If AI is set to +1 , it represents a positive acknowledgement and a default E-DCH resource configuration is allocated to the UE. However, if AI is set to -1 , the UE checks for the E-AI configuration. If the E-AI is configured, then the UE detects which one of the Extended Acquisition Indicator signatures is present. Likewise, if the EAI is not configured, the UE is not allocated any of the E-DCH resources and the UE may repeat the random access procedure to obtain an uplink resource.

[0041] In accordance with an embodiment of the present subject matter, the fact that the E-AI is unutilized when AI is set to +1 is exploited by the NB to indicate to a UE whether the resource requested by the UE is available for allocation, or whether the UE should fallback to an alternate resource.

[0042] Consider an example where a UE selects E-DCH and sends a preamble signature corresponding to an E-DCH resource. In this situation, in accordance with an embodiment of the present subject matter, to indicate to the UE that a default common E-DCH is allocated, NB uses E-AI along with AI set to + 1 . Thus, the combination of AI as +1 together with a first predetermined value of E-AI may be used for indicating to the UE that a default common E- DCH is allocated while another combination of AI as +1 along with a second predetermined value of E-AI may indicate to the UE that a fallback needs to be performed. Thus, if a default common E-DCH is allocated, AI is set to +1 and EAI is given a first predetermined value, for example +1 , and if a fallback needs to be performed, AI is set to +1 and EAI is set to a second predetermined value, for example -1.

[0043] In one embodiment, the fallback may be understood as switching from E-DCH to

RACH. For example, a UE may send a preamble signature corresponding an E-DCH resource. Realizing that the UE has requested an E-DCH resource, the NB would attempt to allocate the E- DCH resource. Based on the availability, if the NB decides to allocate a common default E-DCH resource, the NB sets the AI as +1 and EAI as +1. However, if NB is unable to allocate any E- DCH resource because of the unavailability of the same, NB may set AI as +1 and EAI as -1. This notifies to the UE that the E-DCH resource is congested and a RACH may be requested. As apparent to one skilled in the art, the allocation of other E-DCH resource apart from the common default E-DCH resource, i.e. the common E-DCH resource, is determined by the UE based on the configuration of E-AI when AI is set to -1.

[0044] Accordingly, when the UE determines that the NB has set AI as +1 and E-AI as -1 it may fallback to RACH. In said embodiment, the UE may either retransmit a preamble signature corresponding to a RACH resource or, upon being indicated by the NB to fallback to RACH, proceed to transmit only the message part corresponding to RACH. Thus, in said embodiment, a UE having transmitted a preamble signature corresponding to an E-DCH resource may fallback to RACH and send only the message part corresponding to RACH without having to resend the preamble signature, thereby saving resource acquisition time. In said embodiment, the UE may be configured to transmit the message part of RACH using conventional methods and parameters as specified by 3GPP standards. In a corresponding embodiment of the NB, once the NB indicated a UE to fallback to RACH, the NB may be configured to receive the actual message in a format pertaining to RACH without expecting a RACH preamble signature to precede the actual message in RACH format.

[0045] In one embodiment, a RNC may enable the fallback functionality in a cell. In said embodiment, from amongst all the preamble signatures and preamble scrambling codes available for the cell, the RNC may reserve certain preamble signatures and preamble scrambling codes to be used by UEs implementing the fallback functionality. The RNC may send system information broadcast signals to all the UE and provide them a list of such preamble signatures and preamble scrambling codes to be used by for implementing the fallback functionality. In a similar embodiment, a UE enabled with the fallback functionality may be configured to decipher such system information broadcast signals. At the same time, the RNC may make the list of such preamble signatures and preamble scrambling codes available to the all the NBs in the cell, for example, by using Node B Application Part (NBAP) signaling protocol. Thus, when a NB in the cell receives any of the preamble signatures present in list, the NB knows that the UE is enabled to fallback to RACH. Accordingly, upon realizing that E-DCH is congested, the NB may set AI to +1 and EAI to -1 to facilitate the UE to fallback to RACH. In a corresponding embodiment, the UE is configured to read the fallback indication to perform a fallback operation.

[0046] In the above examples, a fallback has been explained as a switch over from E-

DCH to RACH. However, it will be appreciated by one skilled in the art that the concept explained in context of the fallback from E-DCH to RACH may also be extended to other uplink resources. In one embodiment, uplink resources such as a 10ms TTI E-DCH or 2ms TTI E-DCH may also be available for allocation and fallback. Accordingly, it may be understood that alternate resources comprise available uplink resources, such as RACH, 2ms or 10ms TTI E- DCH. Also, the term fallback may be understood as switching from a resource previously requested in a random access procedure to one of the alternate resources with or without retransmission of a preamble signature transmitted in the previous random access procedure.

[0047] It is also evident that although the above example specifies that the NB may set

AI as +1 and EAI as -1 to notify the UE to fallback to RACH, EAI may also be set to +1 in various other examples. Further, various other indicators indication of resource allocation may be used in any combination to implement the fallback functionality.

[0048] The above methods and system are further described in conjunction with the following figures. It should be noted that the description and figures merely illustrate the principles of the present subject matter. It will thus be appreciated that those skilled in the art will be able to devise various arrangements that, although not explicitly described or shown herein, embody the principles of the present subject matter and are included within its spirit and scope. Furthermore, all examples recited herein are principally intended expressly to be only for pedagogical purposes to aid the reader in understanding the principles of the present subject matter and the concepts contributed by the inventor(s) to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions. Moreover, all statements herein reciting principles, aspects, and embodiments of the present subject matter, as well as specific examples thereof, are intended to encompass equivalents thereof.

[0049] It will also be appreciated by those skilled in the art that the words during, while, and when as used herein are not exact terms that mean an action takes place instantly upon an initiating action but that there may be some small but reasonable delay, such as a propagation delay, between the initial action and the reaction that is initiated by the initial action. Additionally, the word "connected" is used throughout for clarity of the description and can include either a direct connection or an indirect connection.

[0050] The manner in which the systems and methods for sharing uplink resource in a UMTS is implemented shall be explained in details with respect to the Figures 1-3. While aspects of described systems and methods for sharing uplink resources can be implemented in any number of different computing systems, environments, and/or configurations, the embodiments are described in the context of the following exemplary system(s).

[0051] Figure 1 shows a wireless communication system 100 to enable a fallback functionality in a cell, in accordance with an embodiment of the present subject matter. In one implementation, the wireless communication system 100 may be a 3^rd Generation Wireless Mobile Communication system, also referred to as a 3G system or a UMTS. The wireless communication system 100 includes a core UMTS network, one or more RNCs, one or more NBs and multiple UEs. The RNCs and the NBs make up the UMTS radio access network and are collectively termed as Universal Terrestrial Radio Access Network (UTRAN) (not shown).

[0052] While there may be several in number, Figure 1 depicts a RNC 102, an NB 104 and a UE 106 to maintain simplicity. For ease of explanation, the RNC 102, the NB 104 and the UE 106 may be considered to form a cell (not shown) wherein, in accordance with 3 GPP, the term "cell" can refer to the smallest coverage area of the NB 104.

[0053] The wireless communication system 100, as will be understood by those skilled in the art, is controlled by the RNC 102. The RNC 102 may be implemented as a network server, a server, a workstation, a mainframe computer, and the like. The RNC 102 is configured to control the NB 104 for managing resources of the communication system 100 and coordinating data transfer through the NB 104. The RNC 102 provides system information that is used to maintain radio connection between the UE 106 and the UTRAN and also to control the overall operation of the UTRAN. For example, the RNC 102 broadcasts the system information to UE 106, providing the UE 106 with data, such as radio path indication, radio measurement criterion, and paging path indication required by the UE to communicate with the UTRA . In one example, the RNC 102 may utilize point to multi-point broadcasting to keep the UE 106 in touch with the UTRAN and may use NBAP signals for controlling the NB 104.

[0054] Further, the NB 104 controls and communicates with the UE 106, largely to manage the radio transmission and/or reception of the UE 106. Radio channels of the NB 104 may be accessed by the UE 106 for uplink and/or downlink of data packets, and hence may be referred to as uplink and downlink resources. The allocation of an uplink and downlink resource to the UE 106 is performed by the NB 104. The NB 104 may be a fixed station that communicates with the UEs 106 and may also be referred to as an evolved Node B (eNB), a base station, an access point, etc.

[0055] Examples of the UE 106 may include, but are not limited to, desktop computers, hand-held devices, laptops or other portable computers, tablet computers, mobile phones, PDAs, smartphones, and the like. Further, the UE 106 may include devices capable of exchanging data to provide connectivity to different communicating devices and computing systems. Such devices may include, but are not limited to, data cards, mobile adapters, wireless (WiFi™) adapters, routers, a wireless modem, a wireless communication device, a cordless phone, a wireless local loop (WLL) station, and the like. The UE 106 may be stationary or mobile and may also be referred to as a mobile station, a terminal, an access terminal, a subscriber unit, a station, etc.

[0056] In one implementation, the RNC 102, NB 104 and the UE 106 each include a processor that may be referred to as a RNC processor 108-1 , an NB processor 108-1 and a UE processor 108-3, respectively. The processors 108-1 , 108-2 and 108-3 are collectively referred to as the processors 108 hereinafter.

[0057] The processors) 108 may include microprocessors, microcomputers, microcontrollers, digital signal processors, central processing units, state machines, logic circuitries and/or any other devices that manipulate signals and data based on operational instructions. The processors) 108 can be a single processing unit or a number of units, all of which could also include multiple computing units. Among other capabilities, the processors) 108 are configured to fetch and execute computer- readable instructions stored in one or more computer readable mediums. [0058] Functions of the various elements shown in the figure, including any functional blocks labeled as "processor(s)", may be provided through the use of dedicated hardware as well as hardware capable of executing software in association with appropriate software. When provided by a processor, the functions may be provided by a single dedicated processor, by a single shared processor, or by a plurality of individual processors, some of which may be shared. Moreover, explicit use of the term "processor" should not be construed to refer exclusively to hardware capable of executing software, and may implicitly include, without limitation, digital signal processor (DSP) hardware, network processor, application specific integrated circuit (ASIC), field programmable gate array (FPGA), read only memory (ROM) for storing software, random access memory (RAM), and non volatile storage. Other hardware, conventional and/or custom, may also be included.

[0059] The computer readable medium may include any computer-readable medium known in the art including, for example, volatile memory, such as random access memory (RAM) and/or non-volatile memory, such as flash.

[0060] The RNC 102, NB 104 and the UE 106 further include one or more memory components, referred to as memory 110-1 , 1 10-2 and 1 10-3, respectively. The memory 1 10-1 , 110-2 and 110-3 are collectively referred to as memories 110 hereinafter. The memories 110 may include any computer-readable medium known in the art including, for example, volatile memory such as static random access memory (SRAM) and dynamic random access memory (DRAM), and/or non-volatile memory, such as read only memory (ROM), erasable programmable ROM, flash memories, hard disks, optical disks, and magnetic tapes.

[0061] In one implementation, the RNC 102, NB 104 and the UE 106 also include a

RNC communication module 112-1 , a NB communication module 112-2 and UE communication module 1 12-3, respectively. The RNC communication module 112-1 , the NB communication module 112-2 and the UE communication module 1 12-3, collectively referred to as communication module 112 may be understood as any conventional module, such as a transreceiver that enables communication between the RNC 102, NB 104 and the UE 106.

[0062] The RNC 102 further includes, amongst other things, various modules, and in accordance with one embodiment of the subject matter, the RNC 102 includes a RNC fallback module 1 14 and other RNC modules 116. In a similar manner, NB 104 further includes, according to one embodiment, a resource allocation module 118 that comprises an NB fallback module 120 and other NB modules 122. Similarly, in one embodiment, the UE 106 further comprises resource access module 124 that comprises a UE fallback module 126 and other UE modules 128. The other modules 116, 122 and 128 may include programs or coded instructions that supplement various functions of the RNC 102, the NB 104 and the UE 106.

[0063] The various modules described herein may be implemented or performed with a general-purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. Further the functionalities of various modules may be embodied directly in hardware, in a software module executed by a processor, or in a combination of the two.

[0064] In one embodiment, the RNC 102 may enable the fallback functionality i.e. dynamic allocation of an uplink resource by the NB 104, in the cell by providing an indication of availability of an alternate resource to the UE 106. As mentioned previously, in one embodiment, alternate resources comprise uplink resources, such as RACH, 2ms or 10ms TTI E-DCH. To enable the fallback functionality in the cell, from amongst all the preamble signatures and preamble scrambling codes available for the cell, the RNC fallback module 114 of the RNC 102 may be configured to reserve certain preamble signatures and preamble scrambling codes. The reserved preamble signatures and preamble scrambling codes are hereinafter collectively referred to as reserved preamble signatures. In one example, the RNC fallback module 114 may be indicated the reserved preamble signatures by an operator of the wireless communication system 100. The reserved preamble signatures may be understood as preamble signatures that may be used to access a predetermined number of E-DCH resources.

[0065] Further, the RNC fallback module 114 communicates information relating to the reserved preamble signatures to the UE 106 through the RNC communication module 112-1. The RNC communication module 112-1 may provide the reserved preamble signatures to the UE 106 as system information in a system information broadcast. The system information broadcast is received by the UE communication module 112-3 of the UE 106. As apparent, in the present embodiment, the UE 106 is enabled with the fallback functionality and is configured to read such system information broadcast to extract the information pertaining to the reserved preamble signatures. [0066] In addition to providing the reserved preamble signatures to the UE 106, the RNC communication module 112-1 provides the reserved preamble signatures to the NB 104. In one example, the RNC communication module 112-1 may send the information pertaining to the reserved preamble signatures to the NB communication module 112-2 using the NBAP signaling protocol.

[0067] Thus, the NB 104 and the UE 106 are made aware of the reserved preamble signatures that have been reserved for the purposes of implementation of the fallback functionality from amongst all the preamble signatures available in the cell. As explained previously in the description, the reserved preamble signatures pertain to E-DCH and are used in the random access procedure to request an E-DCH resource. For the sake of simplicity, the other available preamble signatures that have not been set aside for the fallback functionality are referred to as non-reserved preamble signatures. Accordingly, non-reserved preamble signatures may correspond to all resources available for allocation in the cell, for example, RACH resources and those E-DCH resources that do not relate to the reserved preamble signature.

[0068] In one embodiment, the resource access module 124 of the UE 106 performs the random access procedure to request the NB 104 for an E-DCH resource using a reserved preamble signature. It may be noted that the UE 106 may also choose to perform the random access procedure to access any of the uplink resources, such as a RACH resource, available for allocation in the cell, using the non-reserved preamble signatures in a conventionally known manner, for example, based on the nature of data the UE 106 wishes to send to the NB 106.

[0069] In accordance with one aspect of the present subject matter, the UE 106 may request the NB 104 for an E-DCH resource using a reserved preamble signature at every instance a request for allocation of an uplink resource is to be made. As known to one skilled in the art, a request for allocation of an uplink resource may be made even after a previously allocated uplink resource is released and the UE 106 wants to send uplink data in a CELL PCH, URA PCH, and CELL FACH.

[0070] When the resource allocation module 1 18 of the NB 104 receives the request for an E-DCH resource, made using a reserved preamble signature, from the UE 106, the NB 104 recognizes that the UE 106 is fallback functionality enabled or possesses a fallback capability. Allocation of an uplink resource, in response to the request for E-DCH resources made using reserved preamble signatures may be handled by the NB fallback module 120 present in the resource allocation module 118 of the NB 104. The NB fallback module 120 is configured to provide a fallback indication to the UE 106 in response to the request for an E-DCH resource in situations where no E-DCH resource may be available for allocation. The fallback indication is indicative of availability of an alternate resource, such as a RACH resource, to the UE 106.

[0071] As apparent from the previous description, to provide the fallback indication, the

NB fallback module 120 may be configured to transmit a predetermined value of EAI along with a positive value of AI in the AICH. In one example, the positive value of AI along with a first predetermined value of E-AI is indicative of allocation of the E-DCH resource while a positive value of the AI along with a second predetermined value of E-AI is a fallback indication. The first predetermined value and the second predetermined value may be +1 and -1 , respectively, or -1 and +1 , respectively.

[0072] The UE communication module 112-3 may receive the fallback indication and provide the same to the resource access module 124. In one implementation, the UE fallback module 126 of the resource access module 124 is configured to comprehend the fallback indication and initiate a fallback operation i.e. switching to the alternate resource, such as a RACH resource. However, in other implementations, the UE fallback module 126 may be configured to switch to other alternate resources, such as a 2ms TTI E-DCH or a 10ms TTI E- DCH, if indicated by the NB 104 to do so, based on the availability of such resources in the UTRAN. In one implementation, various different configurations of AI and E-AI may be used for the purpose of indicating, to the UE fallback module 126 a resource from amongst the available alternate resources, to which the UE 106 may fallback.

[0073] In one embodiment, the fallback operation may allow the UE 106 to fallback to

RACH or, in other word, to access a RACH resource. The fallback operation comprises continuation of transmission to the NB 104 using the RACH resource. Notably, in requesting the NB 104 for the uplink resource using the reserved preamble signature, the UE 106 has sent a preamble signature pertaining to an E-DCH resource. Accordingly, for the continuation of transmission the UE 106 may transmit only the message part in RACH format without having to resend a preamble signature pertaining to a RACH resource. Thus, UE 106 may be configured to transmit the message part of RACH using conventional methods and parameters as specified by 3 GPP standards. [0074] In one embodiment, when the NB fallback module 120 provides a fallback indication to the UE 106 to facilitate the UE 106 to switch to the alternate resource, such as a RACH resource, the NB fallback module 120 may be configured to receive the message in a format pertaining to RACH without expecting a RACH preamble signature to precede the message.

[0075] Thus, in the wireless communication system 100 where the fallback functionality is supported, in cases where E-DCH is unavailable, the NB 104 indicates the availability of the alternate resource, such as RACH, to the UE 106 thus allowing the UE 106 to request for the alternate resource. Thus, uplink resources, such as RACH and E-DCH in the wireless communication system 100 are managed such that an available resource is utilized to relieve a high demand resource of congestion. Further, since the UE 106 proceeds to perform a fallback operation, upon receiving the fallback indication, without waiting for the expiry of a backoff timer, the resource acquisition time is reduced.

[0076] In an eventuality where both E-DCH and alternate resources, such as RACH resources are congested, and the NB 104 provides a negative acquisition to the UE 106 in response to the request for allocation of an uplink resource, in one embodiment, in addition to a negative acquisition in the AICH, the NB 106 also indicates to the UE 106 a resource that the UE 106 may request after a backoff. For example, if E-DCH resources are congested and RACH resources are also unavailable for fallback, the UE 106 may be indicated to use a non-reserved preamble signature. As will be appreciated by one skilled in the art, the number of reserved preamble signatures may be limited and in a situation where both RACH and E-DCH resources are congested, the UE 106 may be allowed to use a non-reserved preamble signature to access other uplink resources available in the cell. Accordingly, if the UE 106 receives a negative acquisition in the AICH, the UE 106 may perform another random access procedure using a non- reserved preamble signature to access other resources available for allocation in the cell, such as RACH and those E-DCH resources that do not relate to the reserved preamble signature. In said embodiment, several random access procedures may be performed by the UE 106 in an attempt to acquire an uplink resource, each time with or without waiting for expiry of a backoff timer.

[0077] The techniques described herein may be used for various wireless communication systems such as Code Division Multiple Access (CDMA), Time Division Multiple Access (TDMA), Frequency Division Multiple Access (FDMA), Orthogonal Frequency-Division Multiple Access (OFDMA), Single Carrier Frequency Division Multiple Access (SC-FDMA) and other systems. A CDMA system may implement a radio technology such as Universal Terrestrial Radio Access (UTRA), cdma2000, etc. UTRA includes Wideband CDMA (WCDMA) and other variants of CDMA. cdma2000 covers IS-2000, IS-95 and IS-856 standards. A TDMA system may implement a radio technology such as Global System for Mobile Communications (GSM). An OFDMA system may implement a radio technology such as Evolved UTRA (E-UTRA), Ultra Mobile Broadband (UMB), IEEE 802.20, IEEE 802.16 (WiMAX), 802.11 (WiFi™), Flash-OFDM^®, etc. UTRA and E-UTRA are part of Universal Mobile Telecommunication System (UMTS). 3GPP Long Term Evolution (LTE) is an upcoming release of UMTS that uses E-UTRA. UTRA, E-UTRA, UMTS, LTE and GSM are described in documents from an organization "3rd Generation Partnership Project" (3GPP). cdma2000 and UMB are described in documents from an organization named "3rd Generation Partnership Project 2" (3GPP2). For clarity, certain aspects of the techniques are described below for WCDMA, and 3GPP terminology is used in much of the description below.

[0078] The systems and methods can be implemented in a variety of entities, such as communication devices, and computing systems. The entities that can implement the described method(s) include, but are not limited to, desktop computers, hand-held devices, laptops or other portable computers, tablet computers, mobile phones, PDAs, smartphones, and the like. Further, the method may also be implemented by devices capable of exchanging data to provide connectivity to different communicating devices and computing systems. Such devices may include, but are not limited to, data cards, mobile adapters, wireless (WiFi™) adapters, routers, and the like. Although the description herein is explained with reference to a communicating device such as a smartphone, the described method(s) may also be implemented in any other devices, as will be understood by those skilled in the art.

[0079] Figure 2 illustrates a method 200 to obtain an uplink resource in accordance with one embodiment of the present subject matter while Figure 3 illustrates an uplink resource allocation method 300 according to one embodiment of the present subject matter.

[0080] The order in which the methods 200 and 300 are described is not intended to be construed as a limitation, and any number of the described method blocks can be combined in any order to implement the methods 200 and 300, or an alternative method. Additionally, individual blocks may be deleted from the methods 200 and 300 without departing from the spirit and scope of the subject matter described herein. Furthermore, the methods 200 and 300 may be implemented in any suitable hardware, software, firmware, or combination thereof.

[0081] A person skilled in the art will readily recognize that steps of the methods 200 and

300 can be performed by programmed computers. Herein, some embodiments are also intended to cover program storage devices, for example, digital data storage media, which are machine or computer readable and encode machine-executable or computer-executable programs of instructions, wherein said instructions perform some or all of the steps of the described methods 200 and 300. The program storage devices may be, for example, digital memories, magnetic storage media such as a magnetic disks and magnetic tapes, hard drives, or optically readable digital data storage media. The embodiments are also intended to cover both communication network and communication devices configured to perform said steps of the exemplary methods 200 and 300.

[0082] With reference to method 200 as depicted in Figure 2, as illustrated at block 202, a user equipment, such as the UE 106, is configured to receive information relating to the reserved preamble signatures, for example, from the RNC 102. In accordance with one aspect of the method 200 for obtaining an uplink resource, at block 204, the UE 106 performs a random access procedure using one of the reserved preamble signatures as indicated to the UE 106 at block 202 or one of the non-reserved preamble signatures preexisting with the UE 106. As mentioned previously, reserved preamble signatures relate to predetermined number of E-DCH resources while non-reserved preamble signature pertain to other available resources, such as RACH and those E-DCH resources that do not relate to the reserved preamble signature.

[0083] It will be understood that if a non-reserved preamble signature corresponding to other available resources, such as RACH is used, then AI set to +1 or -1 in AICH is received in response as known conventionally. However, if a reserved preamble signature is used, in addition to AI, E-AI may be configured in the AICH. Consequently, in accordance with one aspect of the method 200, at block 206, in response to a random access procedure performed using a reserved preamble signature, a configuration of AI and E-AI in AICH is received. This configuration of AI and E-AI is determined at block 208.

[0084] At block 210, it is determined whether AI is set to +1 or -1. If AI is set to +1 , at block 212, a value associated with E-AI is read. In one embodiment, a first predetermined value of E-AI is indicative of allocation of an E-DCH resource while a second predetermined value of E-AI indicates availability of an alternate resource. Accordingly, at block 214, the UE 106 may access the allocated E-DCH resource and, at block 216, the UE 106 may perform a fallback operation to access the fallback operation. The first predetermined value and the second predetermined value may be +1 and -1, respectively, or -1 and +1, respectively.

[0085] However, if, at block 210, it is determined that AI is set to -1 , the method 200 proceeds to block 218 to determine whether E-AI is set to +1 or -1. If E-AI is set to +1 , the UE 106 may access the allocated E-DCH resource, at block 214. However, if E-AI is set to -1 , the UE 106 is indicated that the random access procedure has failed and proceeds to block 204 to perform another random access procedure. In accordance with one embodiment, the other random access procedure may be performed using one of the reserved preamble signatures or a non-reserved preamble signature, as indicated at block 204.

[0086] Referring to the uplink resource allocation method 300 depicted in Figure 3, an

NB, such as the previously described NB 104 may receive information relating to the reserved preamble signatures, for example, from the RNC 102, at block 302. As explained earlier in the description, upon receiving the information relating to the reserved preamble signatures, the NB 104 becomes equipped to identify UEs possessing a fallback capability.

[0087] At block 304, the NB 104 may receive a request for allocation of an E-DCH resource, from example, from the UE 106. A determination whether the request for the E-DCH resource comprises a preamble signature is made at block 306. If the UE 106 has sent the request using a reserved preamble signature, 'yes' branch of block 306 is followed and a further determination is made, at block 308, to check for availability of an EDCH resource. In case an EDCH resource is available, i.e. 'yes' branch of block 308, the E-DCH resource is allocated to the UE 106 at block 310. However, if none of the EDCH resources are available for allocation, i.e. 'no' branch of block 308, a determination of availability of an alternate resource, such as a RACH resource is made at block 312. If a RACH resource is available, i.e. 'yes' branch of block 312, at block 314, the RACH resource is allocated and a corresponding indication is sent to the UE 106. However, if a RACH resource is not available, no uplink resource can be allocated in response to the UE 106. Accordingly, at block 316-1 , i.e., the 'no' branch of block 312, the UE 106 is denied the request and the method 300is directed to block 304 where the NB 104 may again receive a request for allocation of an E-DCH resource. In one embodiment, upon denying the request, at block 316-1 , the NB 104 may also indicate an alternate resource which the UE 106 may request in one or more subsequent requests. In light of the foregoing description, one would understand that in several embodiments of the present subject matter, the subsequent requests made by the UE 106 may not necessarily be corresponding to an E-DCH resource. For instance, the UE 106 may use a non-reserved preamble signature to access a RACH resource.

[0088] It may be noted that when a determination that the request for the uplink resource comprises a reserved preamble signature, made at block 306, is in the affirmative, availability of an alternate resource, such as RACH is made prior to rejecting the request. Accordingly, in a situation where the UE 106 selects E-DCH as an uplink resource and requests the same using a reserved preamble signature, the NB 104, in accordance with an embodiment of the present subject matter, may provide a fallback indication to the UE 106 for the UE 106 to perform a fallback operation to access an alternate resource, such as a RACH resource, in case of unavailability of any E-DCH resource. The UE 106 may proceed to perform a fallback operation, upon receiving the fallback indication, without waiting for the expiry of a backoff timer thus reducing the resource acquisition time. For the purpose, the NB 104 may configure E-AI in AICH along with AI set to +1. Thus, the combination of AI as +1 together with a first predetermined value of E-AI may be used for indicating to the UE 106 that a default common E- DCH is allocated while another combination of AI as +1 along with a second predetermined value of E-AI may indicate to the UE 106 that the fallback operation may be performed.

[0089] Referring again to block 306, in a case where it is determined that the request for the uplink resource does not comprise a reserved preamble signature, i.e. the 'no' branch of block 306, the method 300 proceeds to block 318. At block 318, as in block 308, the availability of an E-DCH resource is determined. In case an E-DCH resource is available, i.e. 'yes' branch of block 318, the E-DCH resource is allocated to the UE 106 at block 310. However, if an E-DCH resource is unavailable due to congestion or any other reasons, the UE 106 is denied the request for an uplink resource at block 316-2. Further to the request being denied, the UE 106 may make another request after the expiry of the backoff timer. Accordingly, at block 320, to receive further requests for allocation of an uplink resource by the UE 106, the NB 104 waits for the expiry of the backoff timer and thereafter, at block 304, may receive such further requests from the UE 106.

[0090] It will be appreciated that when the NB 104 determines that the request for the uplink resource does not comprise a reserved preamble signature, the NB 104 may identify that the UE 106 may not support the fallback functionality and interacts with the UE 106 in a conventional manner.

[0091] Although implementations for resource allocation in a communication network have been described in language specific to structural features and/or methods, it is to be understood that the appended claims are not necessarily limited to the specific features or methods described. Rather, the specific features and methods are disclosed as exemplary implementations for data transfer in a communication network.

Claims

I/We Claim:

1. A method to obtain an uplink resource, the method comprising:

transmitting a preamble signature pertaining to an Enhanced Dedicated Channel (E-DCH) to request an E-DCH resource in a random access procedure;

receiving a fallback indication comprising an Acquisition Indicator (AI) and an Extended Acquisition Indicator (E-AI) to indicate an alternate resource, in response to the transmitting, wherein the alternate resource comprises a Random Access Channel (RACH) resource; and

switching to the alternate resource based on the fallback indication.

2. The method as claimed in claim 1 , wherein the switching comprises one of retransmitting a preamble signature pertaining to RACH and sending a message having a specification pertaining to RACH further to the transmitted preamble signature pertaining to E-DCH.

3. The method as claimed in claim 1 , wherein a positive value of AI along with a first predetermined value of E-AI is indicative of allocation of the E-DCH resource and wherein a positive value of AI along with a second predetermined value of E-AI indicates the alternate resource.

4. An uplink resource allocation method comprising:

receiving a preamble signature pertaining to an Enhanced Dedicated Channel (E- DCH) requesting an E-DCH resource in a random access procedure; and

sending a configuration of an Acquisition Indicator (AI) and an Extended Acquisition Indicator (E-AI) in an Acquisition Indicator Channel (AICH), in response to the receiving, to indicate availability of an alternate resource comprising a Random Access Channel (RACH) resource.

5. The uplink resource allocation method as claimed in claim 4 further comprising receiving a message having a specification pertaining to RACH in response to sending the configuration.

6. A Radio Network Controller (RNC) (102) comprising:

a RNC fallback module (114) to determine at least one reserved preamble signature; and

a RNC communication module (112-1) configured to provide the at least one reserved preamble signature to a user equipment (UE) (106) to enable the UE (106) to indicate a fallback capability of the UE (106) to a Node B (NB) (104) coupled to the RNC (102).

7. The RNC (102) as claimed in claim 6, wherein the RNC communication module (112-1) is further configured to indicate the at least one reserved preamble signature to the NB (104) for allowing the NB (104) to identify a UE (106) having the fallback capability.

8. A user equipment (UE) (106) comprising:

a resource access module (124) configured to use a reserved preamble signature to request an associated NB (104) for allocation of an E-DCH resource, the resource access module further comprising:

a UE fallback module (126) configured to fallback to an alternate resource comprising a Random Access Channel (RACH) resource, based on a configuration of Acquisition Indicator (AI) and an Extended Acquisition Indicator (E-AI) in an Acquisition Indicator Channel (AICH) received in response to the request.

9. The UE (106) as claimed in claim 8, wherein the resource access module (124) is further configured to use a non-reserved preamble signature, upon the request being denied by the associated NB (104).

10. The UE (106) as claimed in claim 8 further comprising a UE communication module (1 12-3) configured to receive information relating to one or more reserved preamble signatures from a RNC (102) of a cell the UE (106) is located in.

11. A Node B (NB) (104) comprising:

a resource allocation module (1 18) configured to allocate an uplink resource to user equipments (UEs) (106) based on a request received from the UEs (106); and

aNB fallback module (120) configured to:

identify at least one UE (106) having a fallback capability based on a reserved preamble signature received from the UEs (106) requesting an E-DCH resource; and

indicate availability of an alternate resource to the at least one identified UE (106).

12. The NB (104) as claimed in claim 11 , wherein the alternate resource comprises one or more of a Random Access Channel (RACH) resource, a 10ms transmission time interval (TTI) E-DCH resource, and a 2ms TTI E-DCH resource.

13. The NB (104) as claimed in claim 11 , wherein the NB fallback module (120) is configured to assign a first predetermined value to an Extended Acquisition Indicator (E- AI) when an Acquisition Indicator (AI) in a Acquisition Indicator Channel (AICH) is set to +1 to indicate the availability of the alternate resource.

14. The NB (104) as claimed in claim 11 further comprising a NB communication module (1 12-2) configured to receive an indication of one or more reserved preamble signatures from a RNC (102) controlling the NB (104).

15. A computer-readable medium having embodied thereon a computer program for executing a method comprising:

sending, in response to the receiving, an Acquisition Indicator (AI) set to a positive value and a predetermined value of an Extended Acquisition Indicator (E-AI) in an Acquisition Indicator Channel (AICH), to indicate availability of an alternate resource.