Patent Publication Number: US-2013242786-A1

Title: Network Controlled Throughput for Enhanced Uplink FACH

Description:
RELATED APPLICATIONS 
     This application is a continuation of Ser. No. 13/270,694, filed Oct. 11, 2011, which is a continuation application of U.S. patent application Ser. No. 13/020,869, filed Feb. 4, 2011, now abandoned, which is a continuation of U.S. patent application Ser. No. 12/337,276, filed Dec. 17, 2008, now U.S. Pat. No. 7,885,212, issued Feb. 8, 2011, which claims priority and benefit from International Application No. PCT/SE2008/050917, filed Aug. 12, 2008, which claims priority to U.S. Provisional Application No. 61/026,633, filed Feb. 6, 2008, the entire teachings of which are incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present invention relates generally to telecommunications systems, and in particular to methods and systems for controlling uplink throughput and interference in radiocommunications systems. 
     BACKGROUND 
     Radiocommunication networks were originally developed primarily to provide voice services over circuit-switched networks. The introduction of packet-switched bearers in, for example, the so-called 2.5G and 3G networks enabled network operators to provide data services as well as voice services. Eventually, network architectures will likely evolve toward all Internet Protocol (IP) networks which provide both voice and data services. However, network operators have a substantial investment in existing infrastructures and would, therefore, typically prefer to migrate gradually to all IP network architectures in order to allow them to extract sufficient value from their investment in existing infrastructures. Also, to provide the capabilities needed to support next generation radiocommunication applications, while at the same time using legacy infrastructure, network operators could deploy hybrid networks wherein a next generation radiocommunication system is overlaid onto an existing circuit-switched or packet-switched network as a first step in the transition toward an all IP-based network. 
     One example of such an evolving network structure can be seen in the evolution of wideband code division multiple access (WCDMA) systems. Specified by 3GPP TSG RAN, WCDMA systems have evolved from their initial role as a 3G mobile communication system through the addition of High Speed Downlink Packet Access (HSDPA) in Release 5 and, subsequently, Enhanced Uplink (EUL) in Release  6  (which are sometimes jointly referred to as High Speed Packet Access (HSPA)) to provide data bandwidths which support broadband mobile data applications. For example, downlink and uplink data rates of up to approximately 14 and 5.7 Mbit/s, respectively, may be supported in systems designed in accordance with Release 6 of the HSPA standards. Among other things, such data rate improvements are achieved through the use of techniques such as hybrid automatic retransmission request (HARM) with soft combining, higher order modulation, scheduling and rate control. 
     Of particular interest for the present discussion associated with the uplink is the scheduling feature of HSPA systems. The EUL in Release 6 introduces a new enhanced dedicated channel (E-DCH) which supports uplink data transmissions from a user&#39;s equipment (UE). The EUL is non-orthogonal such that uplink transmissions from different UEs interfere with one another. Thus, the shared resource on the EUL is the amount of tolerable interference in a cell, i.e., the total received power at a NodeB. Accordingly, transmissions on the E-DCH are controlled by a scheduler, located in the NodeB, which controls when and at what data rate the UE is permitted to transmit data. 
     UEs operating in WCDMA systems, including those designed in accordance with the HSPA standards, typically operate in one of three states shown in  FIG. 1  in order to balance power consumption against transmission delay/response time. Therein, state  2  represents a “sleep” mode wherein the UE only occasionally powers up its transceiver equipment to check for paging messages. In the random access (CELL_FACH) state  4 , UEs are typically able to transmit small amounts of data as part of a random access (RACH) process which leads to a transition to the active (CELL_DCH) state  6 , in which UEs transmit and receive data normally using the E-DCH and a High-Speed Downlink Shared Channel (HS-DSCH) channels, respectively. 
     In some areas, HSPA may become a replacement to asymmetric digital subscriber line (ADSL) service for connecting PCs to the Internet. This change in user behavior has a corresponding impact on traffic load and network characteristics. For example, PCs run a range of applications that communicate in the background without the need for end-user interaction. Among other things, such background traffic includes keep-alive messages, probes for software updates, and presence signaling. To efficiently support this type of traffic, the 3GPP has worked to enhance the CELL_FACH state  4  in Releases 7 and 8 of the WCDMA standards. More specifically, in Release 7, HSDPA has been activated for UEs operating in the CELL_FACH state  4 . Thus, in the downlink, UEs monitor the HSDPA control channels to detect scheduling information for their own specific identities (H-RNTI) and are able to receive data more rapidly from the network while in the random access state. 
     In Release 8 of WCDMA, the uplink has also been improved by activating E-DCH for UEs operating in the CELL_FACH. Transmission begins by the UE ramping up power on the transmission of random preamble sequences (as is done in Rel-99 of WCDMA) to establish contact with a serving NodeB, i.e., until an acknowledge with resource allocation message (ACK) or a not acknowledged message (NACK), is received by the UE. After having detected the preamble, the Node-B which is associated with a serving cell assigns the UE to a common E-DCH configuration (managed by that Node-B). The UE may then start transmitting data on the common E-DCH with contention being resolved by means of UE identities in the E-DCH transmissions. By enabling the UE to use the E-DCH for uplink transmissions while in the CELL_FACH state  4 , a UE can then be efficiently moved to the CELL_DCH state  6  for continuous transmission. This enhancement significantly improves user perception of performance compared with systems built in accordance with Release 6 of the WCDMA standards. 
     However, by enabling UEs in the CELL_FACH state  4  to transmit and receive at higher data rates, there also comes the corresponding challenge of dealing appropriately with their increased contributions to the interference situation, e.g., intercell interference. It should be noted that the intercell interference situation is potentially more severe in CELL_FACH state  4  than in CELL_DCH state  6  due to the lack of soft handover, i.e. lack of transmit power control commands from non-serving cells and relative scheduling grants from non-serving cells. 
     SUMMARY 
     The following exemplary embodiments address issues associated with uplink interference associated with UEs operating on the EUL by enabling the network, e.g., a radio network controller (RNC), to control one or more parameters associated with uplink throughput. For example, an RNC may place limitations on UE uplink transmissions while in a random access state, e.g., the CELL_FACH state. 
     According to one exemplary embodiment, a method includes the steps of determining, at an RNC, at least one throughput parameter associated with transmissions by user equipment on an uplink channel, and transmitting, from the RNC, the at least one throughput parameter toward another network node. This provides, among other advantages, a mechanism for controlling intercell interference associated with such transmissions. 
     According to another exemplary embodiment, a radio network controller (RNC) includes a processor for controlling one or more network nodes by determining at least one throughput parameter associated with transmissions by user equipment on an uplink channel and by transmitting the at least one throughput parameter toward the one or more network nodes. This provides, among other advantages, a mechanism for controlling intercell interference associated with such transmissions. 
     According to still another exemplary embodiment, a network node includes a wireline interface for sending and receiving signals, including receiving a signal which indicates at least one throughput parameter associated with transmissions by user equipment on an uplink channel when the user equipment is operating in a random access state, a transceiver for sending and receiving signals over an air interface toward and from the user equipment, a processor, connected to the transceiver, for processing the at least one throughput parameter and for generating a serving grant signal based on the at least one throughput parameter, wherein the transceiver transmits the serving grant signal toward the user equipment. This provides, among other advantages, a mechanism for controlling intercell interference associated with such transmissions. 
     According to another exemplary embodiment, a method includes the steps of: receiving a signal which indicates at least one throughput parameter associated with transmissions by user equipment on an uplink channel when the user equipment is operating in a random access state, generating a serving grant signal based on the at least one throughput parameter, and transmitting the serving grant signal toward the user equipment. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings illustrate exemplary embodiments, wherein: 
         FIG. 1  depicts operating states of a conventional radiocommunication system; 
         FIG. 2  depicts elements of a radiocommunication system in which exemplary embodiments can operate; 
         FIG. 3  illustrates elements of the radiocommunication system of  FIG. 2  with scheduling signaling; 
         FIG. 4  shows an E-TFC selection function; 
         FIG. 5  depicts signaling associated with an exemplary embodiment; 
         FIG. 6  shows a radio network controller (RNC) in which exemplary embodiments may be implemented; 
         FIG. 7  shows a NodeB in which exemplary embodiments may be implemented; 
         FIG. 8  is a flowchart illustrating a method for communicating according to an exemplary embodiment; and 
         FIG. 9  is a flowchart illustrating another method for communicating according to an exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     The following detailed description of the exemplary embodiments refers to the accompanying drawings. The same reference numbers in different drawings identify the same or similar elements. Also, the following detailed description does not limit the invention. Instead, the scope of the invention is defined by the appended claims. The following embodiments are discussed, for simplicity, with regard to the terminology and structure of WCDMA systems. However, the embodiments to be discussed next are not limited to WCDMA systems but may be applied to other telecommunications systems. 
     Reference throughout the specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with an embodiment is included in at least one embodiment of the present invention. Thus, the appearance of the phrases “in one embodiment” or “in an embodiment” in various places throughout the specification are not necessarily all referring to the same embodiment. Further, the particular features, structures or characteristics may be combined in any suitable manner in one or more embodiments. 
     In order to provide some context for the following discussion, consider the exemplary WCDMA radiocommunication system illustrated in  FIG. 2 . Therein, two NodeBs  10  and one UE  14  are shown, although it will be appreciated that actual implementations will typically have more of both. The UE  14  uses uplink and downlink channels  16  to communicate wirelessly with one or more of the NodeBs  10 , e.g., the E-DCH and HS-DSCH channels described above, over an air interface. The two NodeBs  10  are linked to corresponding Radio Network Controllers (RNC)  18 , e.g., via wireline or wirelessly, via which links signals can be transmitted between these entities using the standardized Iub (or Iur/Iub) interface. One RNC  18  may control more than one NodeB  10 . The RNCs  18  are connected to a Core Network  20 . Each NodeB  10  transmits signals to, and receives signals from, UEs  14  within a particular geographic area or cell  22  and  24 , respectively. A UE  14  will typically be connected to one serving NodeB  10  or cell  22 , but may also receive signals from one or more neighboring NodeB  10  or cell  24 . Depending upon its distance from its serving NodeB, a UE  14  can be characterized as being a “cell edge” user, e.g., if it is close to a point where it would be handed off to a neighbor. The NodeB  10  can categorize each UE  14  which is connected thereto as being a cell edge user (or not) based upon information which it receives from either the UE  14  or the RNC  18 , e.g., channel quality information (CQI), UE transmit power headroom (UPH), transmit power commands (TPC), round trip time (RTT), etc., which is indicative of its distance from the NodeB  10 . For example, the NodeB  10  could estimate that a UE  14  with a relatively small CQI, a relatively small UPH and/or a relatively large RTT has a relatively high probability of being relatively far away from the NodeB  10  (i.e., is likely to be a cell edge UE  14 ) and hence has a relatively high probability of causing intercell interference towards another NodeB  10 . 
     For the EUL, the scheduler (not shown in  FIG. 2 ) is located in the NodeB  10 , to control the activity of various UEs  14  within its cell  22 . In order to determine appropriate resource allocation for uplink transmissions on the E-DCH (whether in CELL_FACH state  4  or CELL_DCH state  6 ), the scheduler should be provided with information about the UE  14 &#39;s buffer status (e.g., how much data does it need to transmit) and power availability information (e.g., can a given UE increase its transmit power given its own, inherent transmit capabilities). In order to enable scheduling of uplink transmissions, a NodeB  10  transmits scheduling grant messages to UEs  14  and receives scheduling request messages from the UEs  14  as shown in  FIG. 3 . The scheduling grant messages inform the UEs  14  of the upper limit on their E-DCH data rates, but permit the UEs  14  to select an E-DCH transport format combination (E-TFC) for usage in performing uplink transmissions on the E-DCH within the constraints placed upon them by the scheduler. If needed, a UE  14  may send a scheduling request to ask for a higher data rate limit than that indicated in its received grant message. 
     The UE  14  uses its received scheduling grant to select one of a number of different E-TFC combinations for transmission on the uplink E-DCH. For example, as shown in  FIG. 4 , the UE  14 &#39;s selection function  40  can consider the available data in its data storage buffers, the serving grant limitation, and its available transmit power to select one of a plurality of different E-TFCs. Each candidate E-TFC has associated therewith a transport block size (TBS) and associated E-DPDCH-to-DPCCH power offset ((β value) as shown in table 42. 
     As mentioned above, recent additions to the WCDMA standards enable UEs  14  in the CELL_FACH state  4  to transmit and receive at higher data rates using, on the uplink, a shared E-DCH channel. Given that the limiting, shared resource on the uplink is interference at the NodeB  10 , it is desirable according to these exemplary embodiments to consider, monitor and control the uplink interference contributions which will be added to such systems by users in the CELL_FACH state  4 . According to an exemplary embodiment of the present invention, signaling support is provided which enables the RNC  18  to signal a maximum TBS to the NodeB  10  for CELL_FACH users or UEs  14  which are using the Enhanced Uplink, e.g., especially users located on or near the cell edge. The introduction of this new signalling of, among other things described below, a maximum TBS value for all users operating in the CELL_FACH state  4  or, alternatively, only for cell edge users operating in the CELL_FACH state  4  allows, for example, the RNC  18  to control the intercell interference associated with such transmissions. 
     According to one exemplary embodiment, the RNC  18  decides the maximum TBS value in a cell  22  and signals this value to the NodeB  10  via the Iub interface using, for example, Node B Application Part (NBAP) signaling e.g., Cell Setup and Cell Reconfiguration procedures (CELL SETUP REQUEST and CELL RECONFIGURATION REQUEST messages) or Iur/Iub interface(s) using, for example, Radio Network Subsystem Application Part (RNSAP) and Node B Application Part (NBAP) signaling, e.g., Radio Link Setup, Radio Link Addition, Synchronised Radio Link Reconfiguration Preparation and Unsynchronised Radio Link Reconfiguration procedures. In order to generate a maximum TBS value, the RNC  18  makes use of information about the conditions in neighboring cells that is available from existing NodeB measurements and indicators, e.g., by utilizing Received Scheduled EDCH Power Share (RSEPS) measurements, Received Total Wideband Power (RTWP), Reference Received Total Wideband Power (Reference RTWP), etc. Thus, the RNC  18  can determine appropriate maximum TBS values for the various NodeBs  10  and then transmit them to the NodeBs  10  which are under its supervision. If the NodeB  10  measurements indicate that a cell  22  is experiencing high intercell interference, e.g., through an RTWP measurement result that significantly exceeds the Reference RTWP, the RNC  18  can try to improve the intercell interference situation towards that cell by indicating a conservative MAX TBS value to be used in neighboring cells or neighboring NodeBs. Alternatively, there could be other ways to estimate that a cell  22  has an interference problem, e.g., if the RNC  18  notices that UEs  14  in the cell have difficulty maintaining quality in terms of bit error rate, block error rate, average number of retransmissions or SIR error (i.e., SIR minus SIR target). 
     Exemplary signaling for such maximum TBS values, or more generally throughput parameters, is shown generically in the signaling diagram of  FIG. 5 . However, it will be appreciated that the MAX TBS value may be conveyed as an information element (IE) of another signal, e.g., the CELL SETUP REQUEST and/or the CELL RECONFIGURATION REQUEST messages mentioned above. The NodeB  10  uses this maximum TBS information to determine one (or more) appropriate Serving Grants which are then transmitted to the UEs  14  in this cell  22 . For example, the Serving Grants shown in  FIG. 5  may be formulated by the NodeB  10  in such a way that they place a limit on the E-TFC (or E-TFCI) selected by the UE  14 , which limit corresponds to the MAX TBS value received from the RNC  18 . The maximum TBS value which is conveyed by the Serving Grant to a UE  14  at the cell edge may be the same as, or different than, a maximum TBS value which is transmitted to a UE  14  which is not at the cell edge, as will be described below. 
     According to one exemplary embodiment, the NodeB  10 &#39;s scheduler strictly follows its received TBS limitation, i.e., the NodeB  10  will not permit the UEs  14  to transmit transport blocks on the E-DCH which exceed the maximum TBS indicated by the RNC  18 . However, according to another exemplary embodiment, the NodeB  10 &#39;s scheduler considers the signaled maximum TBS as a recommendation rather than as an absolute requirement and uses this information in the scheduling process to determine appropriate serving grants for the UEs  14 . The maximum TBS value can be updated by the RNC  18  when needed and this updating can be performed done via appropriate NBAP or RNSAP/NBAP signaling procedure(s) via the Iub or Iur/Iub interfaces. The signaling load on Iub/Iur for this updating procedure is anticipated to be relatively low since the adjustment of the TBS value is expected to occur rather infrequently. 
     Maximum TBS values can be established in a variety of different ways relative to the users or UEs  14  in a given cell  22  according to these exemplary embodiments including, but not limited to: 
     (1) the RNC  18  setting and transmitting one maximum TBS value per NodeB  10  to limit all EUL in CELL_FACH users/UEs  14  to transmitting transport blocks which are no greater than the maximum TBS value; 
     (2) the RNC  18  setting and transmitting one maximum TBS value per NodeB  10  to limit all EUL in CELL_FACH users/UEs  14  at the cell edge to transmitting transport blocks which are no greater than the maximum TBS value (i.e., according to this exemplary embodiment, non-cell edge users/UEs  14  will not be limited by the maximum TBS value transmitted from the RNC, although they may still have some TBS limit based upon the E-TFC selection process described above with respect to  FIG. 4 ); and/or 
     (3) the RNC  18  setting and transmitting two maximum TBS values per NodeB  10  to limit all EUL in CELL_FACH non-cell edge users/UEs  14  (a first value) and all EUL in CELL_FACH users/UEs  14  at the cell edge (a second value which is different than the first value). The maximum TBS values for different NodeBs  10  may be different from one another or the same. Additionally, an RNC  18  may establish a group of maximum TBS values for sets of cells  22  or NodeBs  10 . 
     Although the foregoing exemplary embodiments provide examples in the context of an RNC  18  limiting TBS values to control, e.g., intercell interference, it will be appreciated that the present invention is not limited thereto. For example, according to other exemplary embodiments, the RNC  18  may instead determine, and subsequently send to its NodeBs  10 , limitation(s) associated with a property or parameter which is different than the TBS, e.g. a permissible uplink bit rate, a parameter associated with the scheduling grant, a parameter associated with E-TFC or E-TFCI selection, a parameter associated with E-DPDCH-to-DPCCH power ratio, and/or a parameter associated with the noise rise. As used herein, the phrase “throughput parameter” is intended to be generic to these exemplary properties or parameters as well as others not explicitly mentioned herein. 
       FIG. 6  shows a generic structure of an exemplary RNC  18  which can determine and transmit at least one such throughput parameter according to these exemplary embodiments. Therein, a processor  60  (or multiple processors or cores) controls one or more network nodes, e.g., NodeB  10 s, by determining at least one throughput parameter associated with transmissions by user equipment on an uplink channel when that user equipment is operating in a random access state. The RNC  18 &#39;s processor  60  transmits the at least one throughput parameter toward the one or more network nodes  10  via a communication link, e.g., fiber optic link, using a communication interface  61  associated with those nodes, e.g., using the Iub or Iur/Iub standardized protocols. The RNC  18  may include many other elements or devices therein which cooperate to perform the aforedescribed functionality, e.g., one or more memory devices  62 , and will be connected to the core network, e.g., for circuit-switched communications via a media gateway (MGW)  64  and for packet-switched communications via a serving GPRS support node (SGSN)  66  using suitable interfaces  68  as shown. 
     Similarly, a network node  10  which receives the throughput parameter from the RNC  18  is generically illustrated in  FIG. 7 . Therein, the NodeB  10  includes one or more antennas  70  connected to processor(s)  74  via transceiver(s)  72 . The processor  74  is configured to analyze and process signals received over an air interface via the antennas  70 , as well as those signals received from the RNC  18  via e.g. wireline. The processor(s)  74  may also be connected to one or more memory device(s)  76  via a bus  78 . Further units or functions, not shown, for performing various operations as encoding, decoding, modulation, demodulation, encryption, scrambling, precoding, etc. may optionally be implemented not only as electrical components but also in software or a combination of these two possibilities as would be appreciated by those skilled in the art to enable the transceiver(s)  72  and processor(s)  74  to process uplink and downlink signals. 
     Thus, according to an exemplary embodiment, a method includes the steps illustrated in the flowchart of  FIG. 8 . Therein, at step  80 , an RNC determines at least one throughput parameter associated with transmissions by user equipment on an uplink channel. Then, at step  82 , the RNC transmits the at least one throughput parameter toward another network node, e.g., a NodeB  10 . As will be appreciated by those skilled in the art, methods such as that illustrated in  FIG. 8  can be implemented completely or partially in software. Thus, systems and methods for processing data according to exemplary embodiments of the present invention can be performed by one or more processors executing sequences of instructions contained in a memory device. Such instructions may be read into the memory device  76  from other computer-readable mediums such as secondary data storage device(s), which may be fixed, removable or remote (network storage) media. Execution of the sequences of instructions contained in the memory device causes the processor to operate, for example, as described above. In alternative embodiments, hard-wire circuitry may be used in place of or in combination with software instructions to implement exemplary embodiments. 
     The flowchart of  FIG. 9  illustrates another method according to an exemplary embodiment. Therein, at step  90 , a signal is received which indicates at least one throughput parameter, e.g., a maximum TBS and/or other parameter, associated with transmissions by user equipment when the user equipment is operating in a random access state. A serving grant signal is generated, at step  92 , based on the at least one throughput parameter. This serving grant signal is transmitted, at step  94 , toward the user equipment. 
     The above-described exemplary embodiments are intended to be illustrative in all respects, rather than restrictive, of the present invention. Thus numerous variations and modifications to the above-described exemplary embodiments may be made. For example, although the foregoing exemplary embodiments illustrate the controlling node, i.e., the node which generates the at least one throughput parameter, as being the RNC  18 , the present invention is not so limited. The controlling node may, instead, be a base station, e.g., in systems such as WCDMA, LTE, IMT-Advanced, etc. All such variations and modifications are considered to be within the scope and spirit of the present invention as defined by the following claims. No element, act, or instruction used in the description of the present application should be construed as critical or essential to the invention unless explicitly described as such. Also, as used herein, the article “a” is intended to include one or more items.