Patent Publication Number: US-2011051655-A1

Title: Relay System and Method in a Wireless Communications system

Description:
This application claims the benefit of U.S. Provisional Application No. 61/236,765, filed on Aug. 25, 2009, entitled “Relay System and Method in a Wireless Communications System,” which application is hereby incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present invention relates generally to wireless communications and, more particularly, to a relay system and method in a wireless communications system. 
     BACKGROUND 
     In wireless communication networks, a Relay Node (RN) may be used as a tool to improve, e.g., the coverage of high data rates, group mobility, temporary network deployment, cell-edge throughput, and/or to provide coverage in new areas. The RN may be wirelessly connected to a wireless communications network via a donor cell (also referred to as a donor enhanced Node B (donor eNB or D-eNB)). The RN may serve as an eNB to one or more pieces of User Equipment (UE). To the UE that is being served by the RN, the RN may appear identical to an eNB, scheduling uplink (UL) and downlink (DL) transmissions to the UE over a connection between the RN and the UE, also known as an access link. When a UE is served by more than one RN, Cooperative Multipoint Transmission/Reception (CoMP) may be made by the multiple RNs which may help to provide cooperative gain and improve the performance of the UE. 
     However, the RN may not be able to relay communications at all times. For example, if the RN is a mobile RN, it will move in and out the coverage area of the D-eNB, and may experience loss of service, thereby causing loss of service to the subservient UE as well. Furthermore, because the UE may remain in communication with the RN, the UE may not realize that the RN has experienced any problem, thereby preventing the UE from attempting to solve the communication loss by itself. 
     SUMMARY OF THE INVENTION 
     Technical advantages are generally achieved, by embodiments of a system and method for access link resource allocation in a wireless communications system. 
     In accordance with an embodiment of the present invention, a method for transmitting data to a first piece of user equipment comprises wirelessly transmitting a first data packet from a relay node, the relay node being in a first state. The relay node enters a second state different from the first state, wherein the relay node is not accessible in the second state. 
     In accordance with yet another embodiment of the present invention, a method for receiving data from a relay node comprises receiving a first data packet from the relay node, the receiving being performed wirelessly, and receiving a notification message from, the notification message comprising a notice of unavailability. 
     In accordance with yet another embodiment of the present invention, a system for transmitting data comprises a relay node, wherein the relay node is configured to enter into a second mode from a first mode, and a wireless transmitter coupled to the relay node, the transmitter configured to transmit a message comprising information regarding the relay node entering the second mode. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the embodiments, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  illustrates a wireless communications system in accordance with an embodiment of the present invention; 
         FIG. 2  illustrates uplink (UL) and downlink (DL) paths that may occur in a transmission in accordance with an embodiment of the present invention; 
         FIG. 3  illustrates three separate states into which a piece of user equipment may operate in accordance with an embodiment of the present invention; and 
         FIG. 4  illustrates three separate states into which a relay node may operate in accordance with an embodiment of the present invention. 
     
    
    
     Corresponding numerals and symbols in the different figures generally refer to corresponding parts unless otherwise indicated. The figures are drawn to clearly illustrate the relevant aspects of the preferred embodiments and are not necessarily drawn to scale. 
     DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS 
     The making and using of the embodiments are discussed in detail below. It should be appreciated, however, that the present invention provides many applicable inventive concepts that can be embodied in a wide variety of specific contexts. The specific embodiments discussed are merely illustrative of specific ways to make and use the invention, and do not limit the scope of the invention. 
       FIG. 1  illustrates a wireless communications system  100  that may include a base station  105 , a first relay node (RN)  110 , a second RN  111 , a first piece of user equipment (UE)  115  and a second UE  116 . The base station  105  may be, e.g., a donor enhanced Node B (donor eNB or D-eNB), an access network, an access point, or the like. The base station  105  may have a corresponding coverage area  101 , wherein a UE, such as the first UE  115 , that is within the coverage area  101  may communicate directly with the base station  105  (as indicated in  FIG. 1  by line  103 ). 
     The first RN  110  may wirelessly communicate with the base station  105  through, for example, a backhaul connection (represented in  FIG. 1  by line  107 ), and may be used to relay data from the base station  105  to, e.g., the first UE  115  or the second UE  116  (both of which are described further below) which may be located within a second coverage area  102  of the first RN  110 . Such a relay of data may occur through a transmission associated with the first RN  110  and may help to extend the effective range of the base station  105  as it allows a piece of user equipment (such as the second UE  116 ) to be located outside of the first coverage area  101  but remain within the second coverage area  102  of the first RN  110 . 
     The first RN  110  may comprise a fixed node, which does not move its position in relation to the base station  105 . Alternatively, the first RN  110  may comprise a mobile node. For example, the first RN  110  may be located on a movable station, such as a bus or train, such that the first RN  110  may move into and out of communication range of the base station  105 . 
     Additionally, the first RN  110  may be a regenerative type RN, wherein the received signal is decoded and then forwarded. Once received and decoded, the signal may be scheduled for forwarding towards the destination using a suitable radio resource management strategy. Alternatively, the first RN  110  may be a non-regenerative RN, wherein the signal is merely amplified by the first RN  110  and simply forwarded to the next station, such as the base station  105 . 
     The second RN  111  may be similar to the first RN  110 , but is not necessarily the same as the first RN  110 . As such, the second RN  111  may be a fixed or mobile RN that may utilize either a regenerative or non-regenerative type of transmission. The second RN  111  may have a third coverage area  104  which may overlap a portion of the second coverage area  102  and the first coverage area  101 . 
     The first UE  115  may comprise any device that desires to communicate, either directly or indirectly, with the base station  105 . The first UE  115  may change its location within the wireless communications system  100 . The first UE  115  may include mobile phones, personal data assistants (PDAs), notebook computers, other computers that have a wireless connection with the base station  105 , or the like, and any suitable device that may be used to transfer data between itself and the base station  105  (through, e.g., a transceiver) may be used as the first UE  115 . 
     The first UE  115  preferably utilizes release  10  of the 3GPP wireless communication specification (3GPP Rel-10) or later versions of the 3GPP wireless communication specification. However, the present embodiments are not limited to only this wireless communication specification. For example, the Worldwide Interoperability for Microwave Access (WiMAX), Evolution-Data Optimized EV-DO, or Universal Mobile Telecommunications System (UMTS) communication standards may alternatively be utilized. These standards and all other suitable standards are fully intended to be included within the scope of the present embodiments. Additionally, the present embodiments may be modified as described more fully below to be backwards compatible with previous versions of the 3GPP specification. 
     Additionally, the first UE  115  may be currently located within the first coverage area  101  of the base station  105 . As such, the first UE  115  may communicate directly with the base station  105  if desired. Such communications may be performed in order to maintain, e.g., a control channel with no data traffic or else to receive data packets from both the base station  105  and the first RN  110  or second RN  111  in order to increase the traffic flow to the first UE  115 . 
     The first UE  115  may also be located within an overlapping region of the second coverage area  102  and the third coverage area  104 , wherein it may be capable of receiving transmissions from both the first RN  110  and the second RN  111  through, for example, a wireless connection such as an access link. In this location, the performance of the first UE  115  may be improved by transmitting multiple instances of the same data and utilizing, e.g., Cooperative Multipoint Transmission/Reception (CoMP) to achieve cooperative gain, to the first UE  115 . 
     The second UE  116  may be similar to the first UE  115 , but does not necessarily need to be the same. As such, the second UE  116  may include mobile phones, personal data assistants (PDAs), notebook computers, other computers that desire to communicate, either directly or indirectly, with the base station  105 , and any suitable device that may be used to transfer data from itself to the base station  105  may be used as the second UE  116 . All such devices are fully intended to be included within the scope of the present embodiments. 
     Additionally, the second UE  116  may be located outside of the coverage area  101  of the base station  105 . However, by remaining with either the second coverage area  102  of the first RN  110  or the third coverage area  104  of the second RN  111 , the second UE  116  may communicate with the base station  105  by relaying its transmissions through either the first RN  110  or the second RN  111 . In other words, communications between the second UE  116  and the base station  105  may be relayed through the first RN  110  or the second RN  111 . 
     The wireless communication system  100  may utilize a communication standard such as the 3GPP LTE-Advanced standard in order to standardize the communications such as described in 3GPP TS 36.331 V8.5.0 (2009-03), Evolved Universal Terrestrial Radio Access (E-UTRA); Radio Resource Control (RRC); Protocol specification, and 3GPP TR 36.814 V1.2.1 (2009-06), “Further Advancements for E-UTRA; Physical Layer Aspects; (Release 9),” both of which are hereby incorporated herein by reference. The 3GPP LTE-Advanced standard with relaying helps to improve the wireless network by improving the coverage of high data rates, group mobility, temporary network deployment, the cell-edge throughput and/or to provide coverage in new areas 
     However, as one of ordinary skill in the art will recognize, the 3GPP LTE-Advanced standard is merely an exemplary standard that may be utilized and is not meant to limit the present embodiments in any fashion. Other standards, such as Worldwide Interoperability for Microwave Access (WiMAX) or Universal Mobile Telecommunications System (UMTS), may alternatively be utilized while remaining within the scope of the present embodiments. All of these standards and any other suitable standard may be utilized, and all such standards are fully intended to be included within the scope of the present embodiments. 
     For example, as discussed in “Further Advancements for E-UTRA; Physical Layer Aspects; (Release 9), some resources in the time-frequency space may be set aside in order to allow for inband backhauling of the relay traffic between, e.g., the first RN  110  and the base station  105  (which may be a eNodeB in one embodiment). 
     For inband relaying, the backhaul link between the base station  105  and, e.g., the first RN  110 , may operate in the same frequency spectrum as the access link between the first RN  110  and, e.g., the first UE  115 . Due to the first RN&#39;s  110  transmitter causing interference to its own receiver, additional isolation may be warranted for simultaneous transmissions from both the base station  105  to the first RN  110  and also from the first RN  110  to the first UE  115  on the same frequency resource. Such isolation may be provided, e.g., by means of specific, well separated and well insolated antenna structures. Similarly, at the first RN  110  it may not be possible to receive UE transmissions simultaneously with the first RN  110  transmitting to the base station  105 . 
     Such an interference problem may be handled by operating the first RN  110  such that the first RN  110  is not transmitting to, e.g., the first UE  115  when it is supposed to receive data from the base station  105 . In other words, “gaps” may be created in the first RN  110 -to-first UE  115  transmission. These “gaps,” during which terminals (including Rel-10 and Rel-8 terminals) are not supposed to expect any relay transmission, may be created by configuring multicast/broadcast single frequency network (MBSFN) subframes. Base station  105 -to-first RN  110  transmissions can be facilitated by not allowing any normal relay-to-terminal transmissions in some subframes. 
       FIG. 2  illustrates uplink (UL) and downlink (DL) paths that may occur in transmissions between the base station  105  and a directly connected UE (e.g., the first UE  115  and the base station  105 ), and transmissions between the base station  105  and a UE indirectly connected to it via a relay node (e.g., the second UE  116 , the first RN  110 , and the base station  105 ) In this embodiment, the DL paths are transmitted along a first frequency band (F 1 ) and the UL paths are transmitted along a second frequency band (F 2 ). 
     As shown in  FIG. 2 , the first RN  110  may be an intermediary node between the base station  105  and the second UE  116 . As such, the first RN  110  may behave in a different mode towards the base station  105  than it does towards the second UE  116 . For example, the first RN  110  may operate in a UE mode towards the base station  105  while operating in a base station mode towards the second UE  116 . Since the first RN  110  is not a dedicated base station, the first RN  110  may provide additional information such as its buffer size, the fact that it is wirelessly connected to a base station, or the state of its wireless backhaul, to the second UE  116  in order to notify the second UE  116  on top of the information a dedicated base station  105  (such as an eNodeB) sends to its UEs. 
       FIG. 3  illustrates three separate states into which a UE, such as the first UE  115 , may operate when it is attached and communicating with the base station  105  in, e.g., the LTE-Advanced communications standard. The first UE  115  may be in an “LTE DETACHED” state  301  during a power up and start up of the first UE  115 . In the “LTE DETACHED” state  301  the first UE  115  may not have an assigned address and the position of the first UE  115  may not be known to either the first UE  115  or the base station  105 . The “LTE DETACHED” state  301  may be a transitory state in which the first UE  115  is powered-on but is in the process of searching and registering with the network. 
     Once the first UE  115  communicates with the base station  105 , is assigned an address, such as an IP address, and is attached to the base station  105  for receiving and transmitting, the first UE  115  may operate in an “LTE ACTIVE” state  303 . In the “LTE ACTIVE” state  303 , the first UE  115  may actively receive and transmit data packets from and to the base station  105 . In the “LTE ACTIVE” state  303 , the first UE  115  is registered with the network and has a radio resource control (RRC) connection with the base station  105 . In the “LTE ACTIVE” state  303 , the network knows the cell to which the first UE  115  belongs and can transmit/receive data from the first UE  115 . If the first UE  115  is in synchronization with the base station  105 , the first UE  115  may receive DL transmissions while also transmitting UL transmissions. If the first UE  115  is out of synchronization with the base station  105 , the first UE  115  may receive DL transmissions from the base station  105 . 
     Additionally, the first UE  115  may have the “LTE IDLE” state  305  which may be a power-conservation state for the first UE  115 , where the first UE  115  may not be transmitting or receiving packets. In the “LTE IDLE” state  305 , no context about the first UE  115  is stored in the base station  105 . In this state, the location of the first UE  115  may only be known at the mobility management entity (MME) and only at the granularity of a tracking area (TA) that consists of multiple base stations  105 . The MME knows the TA in which the first UE  115  last registered and paging may be used to locate the first UE  115  to a cell. For example, there may be periods when the first UE  115  receives discontinuous DL transmissions (DL DRX) from the base station  301 . With these discontinuous transmissions the base station  105  may only partially know the position of the first UE  115  while the first UE  115  may still have the IP address assigned to it, and may not fully receive transmissions sent to the first UE  115 . During the “LTE IDLE” state  305  the first UE  115  idles itself until it re-establishes communication with either the base station  105  to which it had been attached or else can establish communication with another base station (not shown), for example in a handoff situation. Once a connection has been re-established, the first UE  115  may exit the “LTE IDLE” state  305 . 
     Also shown in  FIG. 3  are the possible movements of the first UE  115  between the different states. As illustrated, the first UE  115  may move between any of the states to any of the other states. For example, the first UE  115  may move from the “LTE ACTIVE” state  303  to either the “LTE IDLE” state  305  or the “LTE DETACHED” state  301 , depending upon, e.g., the transmitting and receiving characteristics at the time of the transfer. For example, the first UE  115  may enter into the “LTE IDLE” state  305  from the “LTE DETACHED” state  301  when a connection is lost between the first UE  115  and the base station  105 . Additionally, the first UE  115  may transfer from the “LTE Detached” state to the “LTE IDLE” state if conditions warrant. 
       FIG. 4  illustrates states that the first RN  110  may enter as the first RN  110  is behaving like a UE in its communications between the first RN  110  and the base station  105 . In particular, the first RN  110  may have three states similar to the first UE  115  (described above with respect to  FIG. 3 ) in order to power on, attach to the base station  105 , perform cell searches, perform measurements, or the like. For example, the first RN  110  may have an “RN DETACHED” state  401 , an “RN ACTIVE” state  403 , and an “RN IDLE” state  405 . 
     Similar to the “LTE DETACHED” state  301  (see  FIG. 3  above), the “RN DETACHED” state  401  may be utilized during power up and start up of the first RN  110 . In the “RN DETACHED” state  401  the first RN  110  may have no assigned address and the position of the first RN  110  may not be known to the base station  105 . As such, the first UE  115  may be “detached” from the base station  105  and may not be visible to the first UE  115  or the second UE  116 . 
     Once the first RN  110  communicates with the base station  105 , is assigned an address, such as an IP address, and is connected to the base station  105  for receiving and transmitting, the first RN  110  may enter into and operate in the “RN ACTIVE” state  403 . In the “RN ACTIVE” state  403 , the first RN  110  may be actively receiving and transmitting data packets from and to the base station  105  and is also accessible to the UEs connected to it (e.g., first UE  115  and second UE  116 ), actively receiving and transmitting data packets from and to the UEs connected to it (e.g., first UE  115  and second UE  116 ), and relaying data packets from the base station  105  to the UEs connected to it. Furthermore, if the first RN  110  is in synchronization with the base station  105 , the first RN  110  may receive DL backhaul transmissions while also transmitting over the UL backhaul link. If the first RN  110  is out of synchronization with the base station  105 , the first RN  110  may receive DL transmissions from the base station  105 . 
     Additionally, the first RN  110  may have the “RN IDLE” state  405  during which the first RN  110  may not be transmitting or receiving packets. In the “RN IDLE” state  405 , no context about the first RN  110  is stored in the base station  105 . During the “RN IDLE” state  405 , the base station  105  may partially lose the position of the first RN  110  while the first RN  110  still has the IP address assigned to it. During the “RN IDLE” state  405 , the first RN  110  idles itself until it can re-establish communication with either the base station  105  to which it had been attached or else can establish communication with another base station (not shown), for example in a handoff situation. During this “RN IDLE” state  405  the first RN  110  is not accessible to the first UE  115 . 
     Also shown in  FIG. 4  is the movement of the first RN  110  between the different states. As illustrated, the first RN  110  may move between any of the states to any of the other states. For example, the first RN  110  may move from the “RN ACTIVE” state  403  to either the “RN IDLE” state  405  or the “RN DETACHED” state  401 , depending upon, e.g., the transmitting and receiving characteristics, such as when the first RN  110  experience a radio link failure (RLF). Additionally, the first RN  110  may transfer from the “RN DETACHED”  401  state to the “RN IDLE” state if conditions warrant, or may transfer from the “RN IDLE” state  405  to the “RN DETACHED” state  401  if, e.g., the first RN  110  attempts to recover but the establishing fails. 
     However, as the first RN  110  moves from the “RN ACTIVE” state  403  to one of the other states, the first UE  115  may experience a service disruption. Therefore, a mechanism may be used to notify the first UE  115  on those occasions that the first RN  110  may enter the “RN IDLE” state  405  and become inactive towards the first UE  115 . Such a mechanism may include the transmission of a notification message from the first RN  110  to the UEs that the first RN  110  is servicing (such as the first UE  115  and the second UE  116  illustrated in  FIG. 1  above). 
     The notification message may be used to provide, e.g., the first UE  115 , with information related to the first RN  110 &#39;s entering and exiting the “RN IDLE” state  405 . For example, the notification message may include timing information such as when the first UE  115  will switch its status to another state (such as the “RN IDLE” state  405 ), how long the first RN  110  will remain in another state, when the first RN  110  will switch back to its current state, how often the first RN  110  needs to switch states, combinations of these, and the like. This timing information may be provided explicitly or, alternatively, may be provided implicitly such that the first UE  115  may be able to determine the information from the information contained within the notification message. 
     In one embodiment, the notification message may be included as part of a non-dedicated broadcast that is sent and received by each UE being serviced by the first RN  110 . Such a non-dedicated broadcast may be in the form of a system information block (SIB) that periodically transmits system information to the various UEs. The information relating to the movement of the first RN  110  may include such information as the periodicity and the starting system frame number (SFN) of the movement. Such an SIB may be broadcast infrequently, such as every 160 ms or more, in order to minimize any potential disruptions. 
     Alternatively, the information related to the movement of the first RN  110  may be sent by the first RN  110  in a dedicated signal to each of the individual UEs that it is servicing, such as the first UE  115  and the second UE  116  illustrated in  FIG. 1  above. This alternative method is useful when the first RN  110  is servicing a small number of UEs, such as between about 1 and about 10 UEs. If the number of UEs is small, it is possible for the first RN  110  to send the notification message to each of the individual UEs. 
     Once the UEs (such as the first UE  115 ) receive the notification message, the UEs may prepare for the transit of the first RN  110  into the “RN IDLE” state  405 . If the first RN  110  will transfer back to the “RN ACTIVE” state  403  within a short amount of time, such as between about 30 ms and about 60 ms, the UEs may take advantage of this short period of non-accessibility to measure other base stations  105  or even other radio access technologies (RAT) and report to the first RN  110  when it reenters the “RN ACTIVE” state  403 . Alternatively, the UEs may enter the “LTE IDLE” state  305  (described above with respect to  FIG. 3 ) while the first RN  110  is in the “RN IDLE” state  405 . However, if the first RN  110  will remain in the “RN IDLE” state  405  for a longer time, such as greater than about 120 ms, the UEs may search and attach to other base stations (not shown), other RNs, or even other RATs. 
     Additionally, the notification message may be modified in order to help ensure backwards compatability with previous released standards, such as Rel-8 standards. Under these earlier standards, previous versions of UEs may receive the notification message as described above, but be unaware of its significance, thereby experiencing a service interruption. Such backwards compatability may still be maintained however, by adjusting the notification message sent to these UEs. In such instances the first RN  110  may notify the earlier release UEs to perform an inter-frequency and/or inter-RAT measurement. While the earlier release UEs are busy performing this measurement, the first RN  110  may excuse itself to enter the “RN IDLE” state  405 , perform any necessary actions, and then return to the “RN ACTIVE” state  403  before the earlier release UEs finish the measurement. 
     Once the first RN  110  has transmitted the notification message to, e.g., the first UE  115 , the first RN  110  may enter the “RN IDLE” state  405 . When the first RN  110  goes into the “RN IDLE” state, the first RN  110  does not go idle as a regular UE. Rather, the first RN  110  can fallback to UE mode and perform self-serving functions, such as using contention-based random access procedure via a random access channel (RACH) to contact the base station  110  for re-establishment, any measurements that may be desired (for example, measuring a channel condition between the first RN  110  and the base stations  110  close to it so that the first RN  110  can determine the best base station  110  to attach to), other maintenance type of functions, any handoff routines, combinations of these, or the like. 
     By setting up the “RN IDLE” state  405  along with a notification message from the first RN  110  to the UEs, the first RN  110  may go idle without causing a disruption to the UEs that the first RN  110  is servicing. This may become especially important when the first RN  110  is mobile and needs to perform a handoff routine from one base station to another base station. 
     Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims. For example, many of the features and functions discussed above can be implemented in software, hardware, or firmware, or a combination thereof. 
     Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure of the present invention, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed, that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present invention. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.