Patent Publication Number: US-2017374654-A1

Title: Scalable video coding over simultaneous unicast/multicast lte dl shared channel

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 61/648,235, filed May 17, 2012, titled “SCALABLE VIDEO CODING OVER SIMULTANEOUS UNICAST/MULTICAST LTE DL SHARED CHANNEL”, the entire contents of which being hereby incorporated by reference herein, for all purposes. 
    
    
     BACKGROUND 
     Scable video coding (SVC) is a standardized technique that may include the encoding of a high-quality video bitstream that may also contain one or more subset bitstreams. A subset video bitstream may be derived by dropping packets from the larger video to reduce the bandwidth required for the subset bitstream. The subset bitstream can represent a lower spatial resolution, lower temporal resolution, and/or lower quality video signal, for example. 
     Unicasting may include the transmission of messages to a single network destination that may be identified by a unique address, perhaps where privacy and/or unique network resources may be useful. 
     Multicasting may include the transmitting of a message or information to a group of destination devices simultaneously in perhaps a single transmission from a source. Multicasting may be referred to as one-to-many communication, such as over an Internet Protocol (IP) based communication network. 
     SUMMARY 
     Embodiments contemplate one or more techniques and systems for receiving unicast and multicast transmissions over a downlink shared channel in parallel. For example, hybrid automatic repeat request (HARQ) entities may be configured to perform retransmissions of the multicast and/or unicast messages. Common and/or dedicated (e.g., separate) HARQ entities may be utilized for retransmission. The multicast downlink shared channels may be activated and/or deactivated on demand. The activation and/or deactivation may be performed using radio resource control (RRC) signaling and/or Medium Access Control (MAC) signaling. The multicast and/or unicast downlink shared channel data may include scalable video coding (SVC) data of varying priority. 
     Embodiments contemplate one or more techniques for a wireless transmit receive unit (WTRU) to receive data. One or more techniques may include receiving a configuration at the WTRU for a first downlink shared channel (first DL-SCH) for one or more unicast transmissions. Techniques may also include receiving a configuration at the WTRU for a second downlink shared channel (second DL-SCH) for one or more multicast transmissions. Techniques may also include receiving at the WTRU at least one multicast transmission over the second DL-SCH in parallel with at least one unicast transmission over the first DL-SCH. 
     Embodiments contemplate a wireless transmit/receive unit (WTRU) that may comprise a processor configured at least in part to receive a configuration for a first downlink shared channel (first DL-SCH) for one or more unicast transmissions. The processor may also be configured to receive a configuration for a second downlink shared channel (second DL-SCH) for one or more multicast transmissions. The processor may also be configured to receive at least one multicast transmission over the second DL-SCH in parallel with at least one unicast transmission over the first DL-SCH. 
     Embodiments contemplate an evolved node-B (eNB) that may comprise a processor that may be configured, at least in part to provide a configuration for a first downlink shared channel (first DL-SCH) for one or more unicast transmissions. The processor may also be configured to provide a configuration for a second downlink shared channel (second DL-SCH) for one or more multicast transmissions. The processor may also be configured to initiate the sending of at least one multicast transmission over the second DL-SCH in parallel with at least one unicast transmission over the first DL-SCH. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more detailed understanding may be had from the following description, given by way of example in conjunction with the accompanying drawings wherein: 
         FIG. 1A  is a system diagram of an example communications system in which one or more disclosed embodiments may be implemented. 
         FIG. 1B  is a system diagram of an example wireless transmit/receive unit (WTRU) that may be used within the communications system illustrated in  FIG. 1A . 
         FIG. 1C  is a system diagram of an example radio access network and an example core network that may be used within the communications system illustrated in  FIG. 1A . 
         FIG. 1D  is a system diagram of another example radio access network and an example core network that may be used within the communications system illustrated in  FIG. 1A . 
         FIG. 1E  is a system diagram of another example radio access network and an example core network that may be used within the communications system illustrated in  FIG. 1A . 
         FIG. 2  illustrates an example video conferencing architecture with simultaneous unicast/multicast shared channel operation consistent with embodiments. 
         FIG. 3  illustrates an example Layer 2 structure for the downlink with a separate HARQ unit for a multicast channel consistent with embodiments. 
         FIG. 4  illustrates an example Layer 2 structure for simultaneous unicast/multicast with common a HARQ unit consistent with embodiments. 
         FIG. 5  illustrates an example architecture for a Layer 2 structure for the downlink with a spate HARQ unit for a multicast channel with a multicast/unicast switching capability consistent with embodiments. 
         FIG. 6  illustrates an example Layer 2 structure for the downlink that may implement techniques for utilizing the existing LTE Layer 2 structure to support simultaneous multicast/unicast consistent with embodiments. 
         FIG. 7  illustrates an example of HARQ process timing for separate HARQ units consistent with embodiments. 
         FIG. 8  illustrates the HARQ processes timing when an example common HARQ unit is utilized consistent with embodiments. 
         FIG. 9  illustrates an example of conflicts if one or more, or each, of the retransmissions is sent on the unicast channel consistent with embodiments. 
         FIG. 10  illustrates an example graph showing of the probability for retransmission as a function of the number of users in the group consistent with embodiments. 
         FIG. 11  illustrates an example graph showing of the probability for retransmission as a function of the number of users in the group when the first retransmission is offloaded to a unicast channel consistent with embodiments. 
         FIG. 12  illustrates an example messaging sequence for a WTRU to indicate to the network that it may desire to join an existing UEgroup consistent with embodiments. 
         FIG. 13  illustrates an example of mapping a fresh point to multipoint downlink logical channel to a transport channel consistent with embodiments. 
         FIG. 14  illustrates an example mapping of transport channels to physical channels consistent with embodiments. 
         FIG. 15  illustrates an example MAC structure for a WTRU receiver with a dedicated HARQ unit consistent with embodiments. 
         FIG. 16  illustrates an example MAC structure for a WTRU receiver with a common HARQ unit consistent with embodiments. 
         FIG. 17  illustrates an example Activation/Deactivation MAC control element that may be utilized in order to activate and/or deactivate one or more unicast and/or multicast channels consistent with embodiments. 
         FIG. 18  is a flowchart of an example technique of transmitting SVC formatted packets consistent with embodiments. 
         FIG. 19  is a flowchart of an example technique utilizing an ACKed-broadcast consistent with embodiments. 
     
    
    
     DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS 
     A detailed description of illustrative embodiments will now be described with reference to the various Figures. Although this description provides a detailed example of possible implementations, it should be noted that the details are intended to be exemplary and in no way limit the scope of the application. 
       FIG. 1A  is a diagram of an example communications system  100  in which one or more disclosed embodiments may be implemented. The communications system  100  may be a multiple access system that provides content, such as voice, data, video, messaging, broadcast, etc., to multiple wireless users. The communications system  100  may enable multiple wireless users to access such content through the sharing of system resources, including wireless bandwidth. For example, the communications systems  100  may employ one or more channel access methods, such as code division multiple access (CDMA), time division multiple access (TDMA), frequency division multiple access (FDMA), orthogonal FDMA (OFDMA), single-carrier FDMA (SC-FDMA), and the like. 
     As shown in  FIG. 1A , the communications system  100  may include wireless transmit/receive units (WTRUs)  102   a,    102   b,    102   c,  and/or  102   d  (which generally or collectively may be referred to as WTRU  102 ), a radio access network (RAN)  103 / 104 / 105 , a core network  106 / 107 / 109 , a public switched telephone network (PSTN)  108 , the Internet  110 , and other networks  112 , though it will be appreciated that the disclosed embodiments contemplate any number of WTRUs, base stations, networks, and/or network elements. Each of the WTRUs  102   a,    102   b,    102   c,    102   d  may be any type of device configured to operate and/or communicate in a wireless environment. By way of example, the WTRUs  102   a,    102   b,    102   c,    102   d  may be configured to transmit and/or receive wireless signals and may include user equipment (UE), a mobile station, a fixed or mobile subscriber unit, a pager, a cellular telephone, a personal digital assistant (PDA), a smartphone, a laptop, a netbook, a personal computer, a wireless sensor, consumer electronics, and the like. 
     The communications systems  100  may also include a base station  114   a  and a base station  114   b.  Each of the base stations  114   a,    114   b  may be any type of device configured to wirelessly interface with at least one of the WTRUs  102   a,    102   b,    102   c,    102   d  to facilitate access to one or more communication networks, such as the core network  106 / 107 / 109 , the Internet  110 , and/or the networks  112 . By way of example, the base stations  114   a,    114   b  may be a base transceiver station (BTS), a Node-B, an eNode B, a Home Node B, a Home eNode B, a site controller, an access point (AP), a wireless router, and the like. While the base stations  114   a ,  114   b  are each depicted as a single element, it will be appreciated that the base stations  114   a ,  114   b  may include any number of interconnected base stations and/or network elements. 
     The base station  114   a  may be part of the RAN  103 / 104 / 105 , which may also include other base stations and/or network elements (not shown), such as a base station controller (BSC), a radio network controller (RNC), relay nodes, etc. The base station  114   a  and/or the base station  114   b  may be configured to transmit and/or receive wireless signals within a particular geographic region, which may be referred to as a cell (not shown). The cell may further be divided into cell sectors. For example, the cell associated with the base station  114   a  may be divided into three sectors. Thus, in one embodiment, the base station  114   a  may include three transceivers, i.e., one for each sector of the cell. In another embodiment, the base station  114   a  may employ multiple-input multiple output (MIMO) technology and, therefore, may utilize multiple transceivers for each sector of the cell. 
     The base stations  114   a,    114   b  may communicate with one or more of the WTRUs  102   a,    102   b,    102   c,    102   d  over an air interface  115 / 116 / 117 , which may be any suitable wireless communication link (e.g., radio frequency (RF), microwave, infrared (IR), ultraviolet (UV), visible light, etc.). The air interface  115 / 116 / 117  may be established using any suitable radio access technology (RAT). 
     More specifically, as noted above, the communications system  100  may be a multiple access system and may employ one or more channel access schemes, such as CDMA, TDMA, FDMA, OFDMA, SC-FDMA, and the like. For example, the base station  114   a  in the RAN  103 / 104 / 105  and the WTRUs  102   a,    102   b,    102   c  may implement a radio technology such as Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access (UTRA), which may establish the air interface  115 / 116 / 117  using wideband CDMA (WCDMA). WCDMA may include communication protocols such as High-Speed Packet Access (HSPA) and/or Evolved HSPA (HSPA+). HSPA may include High-Speed Downlink Packet Access (HSDPA) and/or High-Speed Uplink Packet Access (HSUPA). 
     In another embodiment, the base station  114   a  and the WTRUs  102   a,    102   b,    102   c  may implement a radio technology such as Evolved UMTS Terrestrial Radio Access (E-UTRA), which may establish the air interface  115 / 116 / 117  using Long Term Evolution (LTE) and/or LTE-Advanced (LTE-A). 
     In other embodiments, the base station  114   a  and the WTRUs  102   a,    102   b,    102   c  may implement radio technologies such as IEEE 802.16 (i.e., Worldwide Interoperability for Microwave Access (WiMAX)), CDMA2000, CDMA2000 1x, CDMA2000 EV-DO, Interim Standard 2000 (IS-2000), Interim Standard 95 (IS-95), Interim Standard 856 (IS-856), Global System for Mobile communications (GSM), Enhanced Data rates for GSM Evolution (EDGE), GSM EDGE (GERAN), and the like. 
     The base station  114   b  in  FIG. 1A  may be a wireless router, Home Node B, Home eNode B, or access point, for example, and may utilize any suitable RAT for facilitating wireless connectivity in a localized area, such as a place of business, a home, a vehicle, a campus, and the like. In one embodiment, the base station  114   b  and the WTRUs  102   c,    102   d  may implement a radio technology such as IEEE 802.11 to establish a wireless local area network (WLAN). In another embodiment, the base station  114   b  and the WTRUs  102   c,    102   d  may implement a radio technology such as IEEE 802.15 to establish a wireless personal area network (WPAN). In yet another embodiment, the base station  114   b  and the WTRUs  102   c,    102   d  may utilize a cellular-based RAT (e.g., WCDMA, CDMA2000, GSM, LTE, LTE-A, etc.) to establish a picocell or femtocell. As shown in  FIG. 1A , the base station  114   b  may have a direct connection to the Internet  110 . Thus, the base station  114   b  may not be required to access the Internet  110  via the core network  106 / 107 / 109 . 
     The RAN  103 / 104 / 105  may be in communication with the core network  106 / 107 / 109 , which may be any type of network configured to provide voice, data, applications, and/or voice over internet protocol (VoIP) services to one or more of the WTRUs  102   a,    102   b ,  102   c,    102   d.  For example, the core network  106 / 107 / 109  may provide call control, billing services, mobile location-based services, pre-paid calling, Internet connectivity, video distribution, etc., and/or perform high-level security functions, such as user authentication. Although not shown in  FIG. 1A , it will be appreciated that the RAN  103 / 104 / 105  and/or the core network  106 / 107 / 109  may be in direct or indirect communication with other RANs that employ the same RAT as the RAN  103 / 104 / 105  or a different RAT. For example, in addition to being connected to the RAN  103 / 104 / 105 , which may be utilizing an E-UTRA radio technology, the core network  106 / 107 / 109  may also be in communication with another RAN (not shown) employing a GSM radio technology. 
     The core network  106 / 107 / 109  may also serve as a gateway for the WTRUs  102   a ,  102   b,    102   c,    102   d  to access the PSTN  108 , the Internet  110 , and/or other networks  112 . The PSTN  108  may include circuit-switched telephone networks that provide plain old telephone service (POTS). The Internet  110  may include a global system of interconnected computer networks and devices that use common communication protocols, such as the transmission control protocol (TCP), user datagram protocol (UDP) and the internet protocol (IP) in the TCP/IP internet protocol suite. The networks  112  may include wired or wireless communications networks owned and/or operated by other service providers. For example, the networks  112  may include another core network connected to one or more RANs, which may employ the same RAT as the RAN  103 / 104 / 105  or a different RAT. 
     Some or all of the WTRUs  102   a,    102   b,    102   c,    102   d  in the communications system  100  may include multi-mode capabilities, i.e., the WTRUs  102   a,    102   b,    102   c,    102   d  may include multiple transceivers for communicating with different wireless networks over different wireless links. For example, the WTRU  102   c  shown in  FIG. 1A  may be configured to communicate with the base station  114   a,  which may employ a cellular-based radio technology, and with the base station  114   b,  which may employ an IEEE 802 radio technology. 
       FIG. 1B  is a system diagram of an example WTRU  102 . As shown in  FIG. 1B , the WTRU  102  may include a processor  118 , a transceiver  120 , a transmit/receive element  122 , a speaker/microphone  124 , a keypad  126 , a display/touchpad  128 , non-removable memory  130 , removable memory  132 , a power source  134 , a global positioning system (GPS) chipset  136 , and other peripherals  138 . It will be appreciated that the WTRU  102  may include any sub-combination of the foregoing elements while remaining consistent with an embodiment. Also, embodiments contemplate that the base stations  114   a  and  114   b,  and/or the nodes that base stations  114   a  and  114   b  may represent, such as but not limited to transceiver station (BTS), a Node-B, a site controller, an access point (AP), a home node-B, an evolved home node-B (eNodeB), a home evolved node-B (HeNB), a home evolved node-B gateway, and proxy nodes, among others, may include some or all of the elements depicted in  FIG. 1B  and described herein. 
     The processor  118  may be a general purpose processor, a special purpose processor, a conventional processor, a digital signal processor (DSP), a plurality of microprocessors, one or more microprocessors in association with a DSP core, a controller, a microcontroller, Application Specific Integrated Circuits (ASICs), Field Programmable Gate Array (FPGAs) circuits, any other type of integrated circuit (IC), a state machine, and the like. The processor  118  may perform signal coding, data processing, power control, input/output processing, and/or any other functionality that enables the WTRU  102  to operate in a wireless environment. The processor  118  may be coupled to the transceiver  120 , which may be coupled to the transmit/receive element  122 . While  FIG. 1B  depicts the processor  118  and the transceiver  120  as separate components, it will be appreciated that the processor  118  and the transceiver  120  may be integrated together in an electronic package or chip. 
     The transmit/receive element  122  may be configured to transmit signals to, or receive signals from, a base station (e.g., the base station  114   a ) over the air interface  115 / 116 / 117 . For example, in one embodiment, the transmit/receive element  122  may be an antenna configured to transmit and/or receive RF signals. In another embodiment, the transmit/receive element  122  may be an emitter/detector configured to transmit and/or receive IR, UV, or visible light signals, for example. In yet another embodiment, the transmit/receive element  122  may be configured to transmit and receive both RF and light signals. It will be appreciated that the transmit/receive element  122  may be configured to transmit and/or receive any combination of wireless signals. 
     In addition, although the transmit/receive element  122  is depicted in  FIG. 1B  as a single element, the WTRU  102  may include any number of transmit/receive elements  122 . More specifically, the WTRU  102  may employ MIMO technology. Thus, in one embodiment, the WTRU  102  may include two or more transmit/receive elements  122  (e.g., multiple antennas) for transmitting and receiving wireless signals over the air interface  115 / 116 / 117 . 
     The transceiver  120  may be configured to modulate the signals that are to be transmitted by the transmit/receive element  122  and to demodulate the signals that are received by the transmit/receive element  122 . As noted above, the WTRU  102  may have multi-mode capabilities. Thus, the transceiver  120  may include multiple transceivers for enabling the WTRU  102  to communicate via multiple RATs, such as UTRA and IEEE 802.11, for example. 
     The processor  118  of the WTRU  102  may be coupled to, and may receive user input data from, the speaker/microphone  124 , the keypad  126 , and/or the display/touchpad  128  (e.g., a liquid crystal display (LCD) display unit or organic light-emitting diode (OLED) display unit). The processor  118  may also output user data to the speaker/microphone  124 , the keypad  126 , and/or the display/touchpad  128 . In addition, the processor  118  may access information from, and store data in, any type of suitable memory, such as the non-removable memory  130  and/or the removable memory  132 . The non-removable memory  130  may include random-access memory (RAM), read-only memory (ROM), a hard disk, or any other type of memory storage device. The removable memory  132  may include a subscriber identity module (SIM) card, a memory stick, a secure digital (SD) memory card, and the like. In other embodiments, the processor  118  may access information from, and store data in, memory that is not physically located on the WTRU  102 , such as on a server or a home computer (not shown). 
     The processor  118  may receive power from the power source  134 , and may be configured to distribute and/or control the power to the other components in the WTRU  102 . The power source  134  may be any suitable device for powering the WTRU  102 . For example, the power source  134  may include one or more dry cell batteries (e.g., nickel-cadmium (NiCd), nickel-zinc (NiZn), nickel metal hydride (NiMH), lithium-ion (Li-ion), etc.), solar cells, fuel cells, and the like. 
     The processor  118  may also be coupled to the GPS chipset  136 , which may be configured to provide location information (e.g., longitude and latitude) regarding the current location of the WTRU  102 . In addition to, or in lieu of, the information from the GPS chipset  136 , the WTRU  102  may receive location information over the air interface  115 / 116 / 117  from a base station (e.g., base stations  114   a,    114   b ) and/or determine its location based on the timing of the signals being received from two or more nearby base stations. It will be appreciated that the WTRU  102  may acquire location information by way of any suitable location-determination method while remaining consistent with an embodiment. 
     The processor  118  may further be coupled to other peripherals  138 , which may include one or more software and/or hardware modules that provide additional features, functionality and/or wired or wireless connectivity. For example, the peripherals  138  may include an accelerometer, an e-compass, a satellite transceiver, a digital camera (for photographs or video), a universal serial bus (USB) port, a vibration device, a television transceiver, a hands free headset, a Bluetooth® module, a frequency modulated (FM) radio unit, a digital music player, a media player, a video game player module, an Internet browser, and the like. 
       FIG. 1C  is a system diagram of the RAN  103  and the core network  106  according to an embodiment. As noted above, the RAN  103  may employ a UTRA radio technology to communicate with the WTRUs  102   a,    102   b,    102   c  over the air interface  115 . The RAN  103  may also be in communication with the core network  106 . As shown in  FIG. 1C , the RAN  103  may include Node-Bs  140   a,    140   b,    140   c,  which may each include one or more transceivers for communicating with the WTRUs  102   a,    102   b,    102   c  over the air interface  115 . The Node-Bs  140   a,    140   b,    140   c  may each be associated with a particular cell (not shown) within the RAN  103 . The RAN  103  may also include RNCs  142   a,    142   b.  It will be appreciated that the RAN  103  may include any number of Node-Bs and RNCs while remaining consistent with an embodiment. 
     As shown in  FIG. 1C , the Node-Bs  140   a,    140   b  may be in communication with the RNC  142   a.  Additionally, the Node-B  140   c  may be in communication with the RNC 142   b.  The Node-Bs  140   a,    140   b,    140   c  may communicate with the respective RNCs  142   a,    142   b  via an Iub interface. The RNCs  142   a,    142   b  may be in communication with one another via an Iur interface. Each of the RNCs  142   a,    142   b  may be configured to control the respective Node-Bs  140   a,    140   b ,  140   c  to which it is connected. In addition, each of the RNCs  142   a,    142   b  may be configured to carry out or support other functionality, such as outer loop power control, load control, admission control, packet scheduling, handover control, macrodiversity, security functions, data encryption, and the like. 
     The core network  106  shown in  FIG. 1C  may include a media gateway (MGW)  144 , a mobile switching center (MSC)  146 , a serving GPRS support node (SGSN)  148 , and/or a gateway GPRS support node (GGSN)  150 . While each of the foregoing elements are depicted as part of the core network  106 , it will be appreciated that any one of these elements may be owned and/or operated by an entity other than the core network operator. 
     The RNC  142   a  in the RAN  103  may be connected to the MSC  146  in the core network  106  via an IuCS interface. The MSC  146  may be connected to the MGW  144 . The MSC  146  and the MGW  144  may provide the WTRUs  102   a,    102   b,    102   c  with access to circuit-switched networks, such as the PSTN  108 , to facilitate communications between the WTRUs  102   a,    102   b,    102   c  and traditional land-line communications devices. 
     The RNC  142   a  in the RAN  103  may also be connected to the SGSN  148  in the core network  106  via an IuPS interface. The SGSN  148  may be connected to the GGSN  150 . The SGSN  148  and the GGSN  150  may provide the WTRUs  102   a,    102   b,    102   c  with access to packet-switched networks, such as the Internet  110 , to facilitate communications between and the WTRUs  102   a,    102   b,    102   c  and IP-enabled devices. 
     As noted above, the core network  106  may also be connected to the networks  112 , which may include other wired or wireless networks that are owned and/or operated by other service providers. 
       FIG. 1D  is a system diagram of the RAN  104  and the core network  107  according to an embodiment. As noted above, the RAN  104  may employ an E-UTRA radio technology to communicate with the WTRUs  102   a,    102   b,    102   c  over the air interface  116 . The RAN  104  may also be in communication with the core network  107 . 
     The RAN  104  may include eNode-Bs  160   a,    160   b,    160   c,  though it will be appreciated that the RAN  104  may include any number of eNode-Bs while remaining consistent with an embodiment. The eNode-Bs  160   a,    160   b,    160   c  may each include one or more transceivers for communicating with the WTRUs  102   a,    102   b,    102   c  over the air interface  116 . In one embodiment, the eNode-Bs  160   a,    160   b,    160   c  may implement MIMO technology. Thus, the eNode-B  160   a,  for example, may use multiple antennas to transmit wireless signals to, and receive wireless signals from, the WTRU  102   a.    
     Each of the eNode-Bs  160   a,    160   b,    160   c  may be associated with a particular cell (not shown) and may be configured to handle radio resource management decisions, handover decisions, scheduling of users in the uplink and/or downlink, and the like. As shown in  FIG. 1D , the eNode-Bs  160   a,    160   b,    160   c  may communicate with one another over an X2 interface. 
     The core network  107  shown in  FIG. 1D  may include a mobility management gateway (MME)  162 , a serving gateway  164 , and a packet data network (PDN) gateway  166 . While each of the foregoing elements are depicted as part of the core network  107 , it will be appreciated that any one of these elements may be owned and/or operated by an entity other than the core network operator. 
     The MME  162  may be connected to each of the eNode-Bs  160   a,    160   b,    160   c  in the RAN  104  via an S1 interface and may serve as a control node. For example, the MME  162  may be responsible for authenticating users of the WTRUs  102   a,    102   b,    102   c,  bearer activation/deactivation, selecting a particular serving gateway during an initial attach of the WTRUs  102   a,    102   b,    102   c,  and the like. The MME  162  may also provide a control plane function for switching between the RAN  104  and other RANs (not shown) that employ other radio technologies, such as GSM or WCDMA. 
     The serving gateway  164  may be connected to each of the eNode-Bs  160   a,    160   b ,  160   c  in the RAN  104  via the S1 interface. The serving gateway  164  may generally route and forward user data packets to/from the WTRUs  102   a,    102   b,    102   c.  The serving gateway  164  may also perform other functions, such as anchoring user planes during inter-eNode B handovers, triggering paging when downlink data is available for the WTRUs  102   a,    102   b,    102   c,  managing and storing contexts of the WTRUs  102   a,    102   b,    102   c,  and the like. 
     The serving gateway  164  may also be connected to the PDN gateway  166 , which may provide the WTRUs  102   a,    102   b,    102   c  with access to packet-switched networks, such as the Internet  110 , to facilitate communications between the WTRUs  102   a,    102   b,    102   c  and IP-enabled devices. 
     The core network  107  may facilitate communications with other networks. For example, the core network  107  may provide the WTRUs  102   a,    102   b,    102   c  with access to circuit-switched networks, such as the PSTN  108 , to facilitate communications between the WTRUs  102   a,    102   b,    102   c  and traditional land-line communications devices. For example, the core network  107  may include, or may communicate with, an IP gateway (e.g., an IP multimedia subsystem (IMS) server) that serves as an interface between the core network  107  and the PSTN  108 . In addition, the core network  107  may provide the WTRUs  102   a,    102   b,    102   c  with access to the networks  112 , which may include other wired or wireless networks that are owned and/or operated by other service providers. 
       FIG. 1E  is a system diagram of the RAN  105  and the core network  109  according to an embodiment. The RAN  105  may be an access service network (ASN) that employs IEEE 802.16 radio technology to communicate with the WTRUs  102   a,    102   b,    102   c  over the air interface  117 . As will be further discussed below, the communication links between the different functional entities of the WTRUs  102   a,    102   b,    102   c,  the RAN  105 , and the core network  109  may be defined as reference points. 
     As shown in  FIG. 1E , the RAN  105  may include base stations  180   a,    180   b,    180   c , and an ASN gateway  182 , though it will be appreciated that the RAN  105  may include any number of base stations and ASN gateways while remaining consistent with an embodiment. The base stations  180   a,    180   b,    180   c  may each be associated with a particular cell (not shown) in the RAN  105  and may each include one or more transceivers for communicating with the WTRUs  102   a,    102   b,    102   c  over the air interface  117 . In one embodiment, the base stations  180   a ,  180   b,    180   c  may implement MIMO technology. Thus, the base station  180   a,  for example, may use multiple antennas to transmit wireless signals to, and receive wireless signals from, the WTRU  102   a.  The base stations  180   a,    180   b,    180   c  may also provide mobility management functions, such as handoff triggering, tunnel establishment, radio resource management, traffic classification, quality of service (QoS) policy enforcement, and the like. The ASN gateway  182  may serve as a traffic aggregation point and may be responsible for paging, caching of subscriber profiles, routing to the core network  109 , and the like. 
     The air interface  117  between the WTRUs  102   a,    102   b,    102   c  and the RAN  105  may be defined as an R1 reference point that implements the IEEE 802.16 specification. In addition, each of the WTRUs  102   a,    102   b,    102   c  may establish a logical interface (not shown) with the core network  109 . The logical interface between the WTRUs  102   a,    102   b,    102   c  and the core network  109  may be defined as an R2 reference point, which may be used for authentication, authorization, IP host configuration management, and/or mobility management. 
     The communication link between each of the base stations  180   a,    180   b,    180   c  may be defined as an R8 reference point that includes protocols for facilitating WTRU handovers and the transfer of data between base stations. The communication link between the base stations  180   a,    180   b,    180   c  and the ASN gateway  182  may be defined as an R6 reference point. The R6 reference point may include protocols for facilitating mobility management based on mobility events associated with each of the WTRUs  102   a,    102   b,    102   c.    
     As shown in  FIG. 1E , the RAN  105  may be connected to the core network  109 . The communication link between the RAN  105  and the core network  109  may defined as an R3 reference point that includes protocols for facilitating data transfer and mobility management capabilities, for example. The core network  109  may include a mobile IP home agent (MIP-HA)  184 , an authentication, authorization, accounting (AAA) server  186 , and a gateway  188 . While each of the foregoing elements are depicted as part of the core network  109 , it will be appreciated that any one of these elements may be owned and/or operated by an entity other than the core network operator. 
     The MIP-HA may be responsible for IP address management, and may enable the WTRUs  102   a,    102   b,    102   c  to roam between different ASNs and/or different core networks. The MIP-HA  184  may provide the WTRUs  102   a,    102   b,    102   c  with access to packet-switched networks, such as the Internet  110 , to facilitate communications between the WTRUs  102   a ,  102   b,    102   c  and IP-enabled devices. The AAA server  186  may be responsible for user authentication and for supporting user services. The gateway  188  may facilitate interworking with other networks. For example, the gateway  188  may provide the WTRUs  102   a,    102   b,    102   c  with access to circuit-switched networks, such as the PSTN  108 , to facilitate communications between the WTRUs  102   a,    102   b,    102   c  and traditional land-line communications devices. In addition, the gateway  188  may provide the WTRUs  102   a,    102   b,    102   c  with access to the networks  112 , which may include other wired or wireless networks that are owned and/or operated by other service providers. 
     Although not shown in  FIG. 1E , it will be appreciated that the RAN  105  may be connected to other ASNs and the core network  109  may be connected to other core networks. The communication link between the RAN  105  the other ASNs may be defined as an R4 reference point, which may include protocols for coordinating the mobility of the WTRUs  102   a ,  102   b,    102   c  between the RAN  105  and the other ASNs. The communication link between the core network  109  and the other core networks may be defined as an R5 reference, which may include protocols for facilitating interworking between home core networks and visited core networks. 
     Embodiments recognize that with the accelerated adoption of smart phones capable of generating and displaying video, efficiently and effectively transporting video across advanced communication systems may continue to grow. Transporting video data may result in intensive use of network resources, may be intolerance of certain loss of data, and may have (e.g., in the case of video conferencing) stringent latency requirements. In some applications (e.g., in the case of video conferencing) the same video data may be delivered to multiple wireless transmit/receive units (WTRUs). 
     Embodiments contemplate that in a limited resource wireless communication system, perhaps where the same video content may be delivered to multiple users, among other scenarios, broadcasting or multicasting point to multi point (PTM or ptm) may be an efficient way of delivering the video with minimal resource allocation. For example, the video content may have been transmitted over a single resource allocation and might not be replicated for one or more, or each, user. For example, the video data may be sent once using point to multi point transmission via the wireless DL group SCH using a UEgroup (e.g., WTRUgroup). Perhaps in order to maintain at least a minimum video quality for one or more, or each, of the WTRUs, among other reasons, the data transmission over the point to multipoint DL SCH may be enforced using common hybrid automatic repeat request (HARQ) unit over point to multipoint or point to point DL-SCH. 
     Embodiments recognize that a difficulty when using wireless multicasting ptm may be that within the cell region the different users may experience different signal quality, perhaps due to their different distance from the base station and/or different wireless channel. LTE wireless systems may use raptor codes in higher layers to improve the broadcast experience for the users within the call region. However, such a technique may lead to a large latency introduced by the raptor codes. In wireless communication systems, HARQ may be utilized to correct errors and/or to accommodate the fast changing wireless channel conditions in order to maintain a desired QoS with less (e.g., relatively very small) additional latency. Using HARQ with multicasting ptm transmission may raise an issue of inefficiency. For example when one or more of the users experience low performance and request retransmission, the entire broadcast band allocation of the broadcast users may be used for the retransmission. 
     Scalable video coding (SVC) may be a video coding technique that may be utilized to produce a compressed bit stream. The compressed bit stream may include a number of sub-bit streams with a reduced spatial and/or temporal resolution. For example, the SVC design may provide scalability at a bit-stream level. In some embodiments, bit-streams for a reduced spatial and/or temporal resolution may be obtained by discarding network abstraction layer (NAL) units (e.g., or network packets) from a global SVC bit-stream that might not be used for decoding the target resolution. NAL units of progressive refinement (PR) slices may be truncated, perhaps in order to further reduce the bit-rate and/or the associated reconstruction quality, among other reasons. 
     In some embodiments, perhaps using SVC coding technique, the video server may generate a set of bits streams, and one or more of the bit streams may correspond to different SVC layers. The SVC layers may be assigned to a different Evolved Packet System (EPS) barrier to be delivered via the LTE system with one or more different quality of service (QoS) class priority levels. The SVC layers (e.g., layer 1—base layer, layer 2—enhanced layer 1, layer 3—enhanced layer 2 . . . ) may be assigned into EPS barriers, perhaps in some embodiments with decreasing QoS priority order. 
     The differentiation of the SVC layers with different importance (e.g., QoS) priorities may be performed within a unicast channel that may deliver a part of the layers, for example according to the transmission rate that may be allowed by the wireless channel and/or multi users scheduling. In some embodiments, the differentiation of the SVC layers with different importance (e.g., QoS) priorities may be performed using multicast point to multipoint transmission, for example where the multicast shared channel may include multiple logical channels delivering the different layers of SVC assigned with different priorities to multiple users with different performance levels. In multicast mode, users with a low signal-to-noise ratio (SNR) may dictate the throughput of the multicast channel, which in some embodiments may be the throughput that one or more, or every, UE may achieve (e.g., a UE or UEs that may be relatively more difficult to reach than other UEs—such as a UE that may have the least favorable channel condition(s) or a “least common denominator UE”, etc.). In some embodiments, one of the UEs in the multicast group may be chosen as a reference UE that may be used for deciding the amount of information to be sent on the multicast channel, among other scenarios. The choice of the reference UE may be based on one or more factors, such as but not limited to: the signal quality reported by the UEs (e.g., RSRP, RSRQ, CQI); the uplink channel quality measured for the UEs; the location of the UE; a heuristic (for e.g., average) measurements received from one or more UEs in the multicast group; a heuristic (for e.g., average) of uplink measurements of a set of UEs; and/or the number of retransmissions requested by UEs in the set. 
     In some embodiments, packets assigned to high priority QoS (e.g., SVC base layer) may be protected using HARQ and/or may consume most of the allowed delay. In an example, low priority logical channels may be discarded due to delivery timeout. 
     In some embodiments, the SVC layers may be differentiated using a simultaneous (e.g. parallel and/or substantially simultaneously) unicast/multicast shared channel, where the SVC base layer may be sent over the multicast channel and/or enhanced layers may be sent over the unicast channel. The unicast and multicast shared channels may be transmitted to a WTRU in the same transmission time interval (TTI), for example using a concept similar to carrier aggregation where multiple transport blocks (e.g., two transport blocks (TBs)) may be generated in the MAC layer and/or may be allocated by the eNB scheduler to different frequencies in a single TTI. The logical channels may correspond to SVC layers with different priorities and/or may be mapped by the scheduler to the different TBs and/or transmitted via the unicast or multicast shared channel. For example,  FIG. 2  illustrates an example video conferencing architecture with simultaneous (e.g. parallel) unicast/multicast shared channel operation. 
     One or more embodiments contemplate an LTE Layer 2 structure that may be configured to be utilized for simultaneous (e.g. parallel) unicast/multicast. In LTE, in the uplink and/or the downlink a transport block (e.g., a single transport block) per user may be generated per TTI in the absence of spatial multiplexing. Perhaps in order to achieve simultaneous (e.g. parallel) operation of unicast and multicast, among other reasons, for example in the same TTI, the Layer 2 structure may be changed. For example, the Layer 2 structure may be changed to accommodate support for additional multiplexing of UEgroups and/or HARQ for UEgroups.  FIG. 3  illustrates an example Layer 2 structure for the downlink with a separate HARQ unit for a multicast channel. The shaded elements may correspond to a HARQ entity for HARQ for a UE group. 
     For example, as shown in  FIG. 3 , a WTRU may be assigned a specific UEi transport channel and/or a UEgroup transport channel (e.g., the shaded elements). One or more, or each WTRU may possess a cell radio network temporary identifier (C-RNTI), which may be a unique identification used for identifying RRC Connection and/or scheduling information. In an example, the WTRU may also be identified by the group-RNTI (G-RNTI) that may be assigned to the UEgroup. The MAC layer functionality may include multiplexing of MAC service data units (SDUs) belonging to one or more logical channels into transport blocks (TB) that may be delivered to the physical layer on transport channels for transmission to the group of WTRUs identified by UEgroup. In one or more embodiments as described herein, a wireless transmit/receive unit (WTRU) may be a user equipment (UE), or vice versa. 
     One or more embodiments contemplate an LTE Layer 2 structure that may be configured to use a common HARQ unit. For example, the HARQ unit of a unicast assigned to an individual UEi may be shared with the HARQ unit assigned to a UEgroup. For example, the common HARQ unit may be configured to schedule retransmissions of TBs that may include a detected error that may be received on at least one of the transport channels to a different transport channel for the retransmission. For example, a TB with a detected error may be originally transmitted via a UEgroup transport channel and/or may be retransmitted via UEi transport channel (e.g., and vice versa). Changing the transport channel used for retransmission may be used for common HARQ between unicast and multicast transport channels. Embodiments recognize that since a TB that may be transmitted via the multicast channel may fail to be received by a single WTRU (e.g., while other WTRUs may receive the transmission correctly), it may be inefficient in terms of system capacity to perform the retransmission over the multicast channel. In some embodiments, perhaps if a certain WTRU may have been scheduled to receive TBs from a UEi (e.g., an unicast message) and/or UEg (e.g., a multicast message) but might have been unable to correctly receive the transmission sent on a transport channel from the UEgroup, among other scenarios, the WTRU may be scheduled for retransmission of the TB (e.g., using the common UEi/UEg HARQ unit). The retransmission may be sent via the UEi transport channel (e.g., rather than and/or in addition to using the original UEg transport channel).  FIG. 4  illustrates an example Layer 2 structure for simultaneous (e.g., parallel) Unicast/multicast with common a HARQ unit. 
     In some embodiments, perhaps in order to implement the common HARQ unit, among other reasons, the number of supported HARQ processes may be doubled (e.g., from 8 to 16), for example to allow retransmission of a TB originated on one or both transport channels that may belong to the common HARQ. In some embodiments, the common HARQ unit may be allowed to retransmit from a transport channel (e.g., a single transport channel, perhaps either UEi or UEgroup). In some embodiments, allowing retransmission for a single transport channel may provide simplified common HARQ unit operation that may be particularly suitable for the case where the two transport channels assigned to UEj and UEgroup may be used to carry information with different priority level. For example, such a scheme may be applied in scenarios of SVC, where the transport channel that may be assigned to a UEgroup may carry the base layer packets while the transport channel assigned to UEj may be carrying the enhance layers SVC. Perhaps when UEj may fail to receive the transport block assigned to UEgroup and/or the transport block assign to UEj, among other scenarios, the retransmission of the combined HARQ unit (e.g., assigned to UEj and UEgroup) may retransmit the transport block from UEgroup since it may carry the base layer SVC with higher importance over the enhance layer TB generated by the transport channel assigned to UEj. 
     One or more embodiments contemplate an LTE Layer 2 structure with separate HARQ units that may be configured to perform multicast/unicast switching. For example, perhaps to simplify the operation of common HARQ, among other reasons, separate HARQ units may be used for unicast (e.g., UEi) and multicast (e.g., UEgroup). Switching the MAC PDU between transport multicast (e.g., UEgroup) and unicast (e.g., UEi) may be performed, for example using a Switching UEi, UEgroup block. The switching block may direct the MAC PDU generated from UEg multiplexer to UEi HARQ unit to be transmitted on the UEi transport channel. When the MAC PDU may be switched from UEgroup to UEi (or vice versa), the new (e.g., fresh or updated) transmission indicator may be toggled and may be included in a PDCCH transmission to indicate a new (e.g., fresh or updated) TB transmission. The WTRU that may receive the transport block after switching from multicast transport channel to unicast transport channel may handle the corresponding transport block as a new (e.g., fresh or updated) transmission, for example disregarding the previous transmissions. Generating a new (e.g., fresh or updated) transmission indicator one or more times, or every time, or nearly every time, switching may occur between multicast to unicast may allow the network to maintain the current definition of the HARQ units without modification.  FIG. 5  illustrates an example architecture for a Layer 2 structure for the downlink with a separate HARQ unit for a multicast channel with a multicast/unicast switching capability (e.g., a multicast/unicast switching function or entity). 
     Embodiments contemplate one or more techniques for utilizing the existing LTE Layer 2 structure to support simultaneous (e.g., parallel) multicast/unicast. In some embodiments, the existing Layer 2 structure may be configured to allocate a single downlink shared channel (DL-SCH) transport channel for one or more, or each WTRU. In some embodiments, perhaps in order to support simultaneous (e.g., parallel) multicast/unicast within the DL-SCH transport channels, among other reasons, a single transport channel may be allocated for DL-SCH multicast and other DL-SCH transport channels may be allocated as unicast serving, for example to serve connected WTRUs. 
     In some embodiments, the selection of the DL-SCH UEi transport channel to be allocated for multicasting may be performed by the eNB scheduler. The selection may be based on criteria such as, but not limited to, locating the WTRU with the relatively best/highest multicast channel performance among the WTRUs participating in the group. Perhaps once the DL-SCH UEi has been selected, among other scenarios, the eNB may notify one or more WTRUs that may be participating in a group of the C-RNTI of the WTRU selected for multicasting. The other WTRUs may use the C-RNTI to decode the multicast control channel, perhaps in order to identify resource allocations for the multicast transport channel and/or to detect the TB received over that transport channel. In some embodiments, the multicast transmission over the selected transport channel for multicasting may be similar to any other unicast transmission. In some embodiments, the multicast UEi with its C-RNTI allocated to it may be unaware that the transmission is multicast to other WTRUs as well. 
     In some embodiments, perhaps while the wireless channel may be changing, among other scenarios, the reallocation of the multicast channel may be performed, for example by notifying the WTRUs in the group that a new C-RNTI (e.g., that may belong to another WTRU from the group) may be used as the multicast channel. In an example, the WTRU selected for multicasting may be prevented from operating in dual transport channel mode (e.g., both unicast and multicast), receiving the multicast channel on its C-RNTI. 
     In some embodiments, perhaps for SVC delivery, among other scenarios, utilizing a C-RNTI of one of the WTRUs in the group as a de facto multicast channel may allow the SVC base layer to be transmitted over the multicast channel to a plurality of WTRUs with a relatively higher priority while the SVC enhance layers may be transmitted via the unicast channels with a relatively lower priority. In some embodiments, the lower priority unicast channel may be unavailable for the WTRU whose C-RNTi may be utilized to perform transmission of the multicast transport channel. 
     Some embodiments recognize that utilizing a C-RNTI of one of the WTRUs of the group for multicast messaging might or might not support common HARQ as described if the LTE structure is to be maintained. Switching the WTRU that may be used to carry the multicast information (e.g., via its C-RNTI) may be implemented using RRC layer signaling and/or full synchronization between the RRC messaging. In some embodiments, data allocation into different logical channels may also be utilized.  FIG. 6  illustrates an example Layer 2 structure for the downlink that may implement techniques for utilizing the existing LTE Layer 2 structure to support simultaneous (e.g., parallel) multicast/unicast. 
     Embodiments contemplate one or more techniques for HARQ handling different scenarios for simultaneous (e.g., parallel) unicast multicast messaging. In some embodiments, for the example where separate HARQ units may be utilized for multicast/unicast, HARQ handling of errors and/or retransmissions may be modified as compared to the standard LTE MAC sub layer definition. In some embodiments, for common HARQ unit handling procedures (e.g., a common HARQ entity handling unicast and multicast), HARQ handling of errors and/or retransmissions may be modified, for example to support the simultaneous (e.g., parallel) multicast/unicast.  FIG. 7  illustrates an example of HARQ process timing for separate HARQ units. As illustrated in the example shown in  FIG. 7 , in some embodiments, the multicast channel may be overloaded with retransmissions due to serving multiple users. 
       FIG. 8  illustrates, for the same or similar error behavior as in  FIG. 7 , the HARQ processes timing when an example common HARQ unit may be utilized. As illustrated in the example shown in  FIG. 8 , the multicast channel may offload the first and/or the third retransmissions to the unicast channel. In this example, the second retransmission may still be performed over the multicast channel. Such scenarios may increase the throughput of the multicast channel that may serve multiple users simultaneously (e.g., in parallel). In some embodiments, offloading the second retransmission to the unicast channel in addition to the first and/or third retransmissions may generate a conflict between the second and the first retransmissions.  FIG. 9  illustrates how a conflict may arise if one or more, or each, of the retransmissions may be sent on the unicast channel. 
     In some embodiments, the use of the dedicated (e.g., separate) HARQ unit for UEg transport channel (e.g., the multicast transport channel) may facilitate design simplification and/or maintenance, perhaps based on the principle that a HARQ unit (e.g., a single HARQ unit) may be utilized per transport channel in LTE. The probability of retransmission over the shared group transport channel allocated to UEg (e.g., UEgroup) may be determined. For example, in some embodiments, it may be assumed that N users may be assigned to the UEgroup, and one or more, or each, user i may have a probability of block error of Pbler(i) for the original transmission. In such scenarios, the probability of first retransmission over the shared channel transmitted to the group UEgroup (e.g., Pg retran ) may be expressed as: 
     
       
         
           
             
               
                 
                   
                     Pg 
                     retran 
                   
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                     1 
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                           i 
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                         N 
                       
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                         ( 
                         
                           1 
                           - 
                           
                             
                               P 
                               bler 
                             
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                               i 
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                   Equation 
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     In LTE, the typical probability of error per transport block on the shared channel may be approximately 0.1. In the example wherein the same transmission may be sent to one or more, or each, of the users that are members of the group, to assume same typical block error rate (BLER) the scheduler may assign a modulation and coding scheme (MCS) value for TBg transmission(s) that may result in a BLER of 0.1 of the worst user. The other users may have a lower or equal BLER. Such a scheme may be implemented by tracking one or more, or each, user feedback CQI and/or selecting the worst one to set the MCS for the entire group. In this case looking at the value of Pg retran  as function of Pble(i), assuming Pble(i)&lt;=0.1, the worst case scenario for Pg retran  may occur when one or more, or each, of the users of the group may have the same (or substantially similar) probability of block error (e.g., Pble(i)=C=0.1 for i=1:N). In such scenarios, the probability of first retransmission over the shared channel transmitted to the group UEgroup (e.g., Pg retran ) may be expressed as: 
         Pg   retran =1−(1 −C ) N   Equation (2)
 
       FIG. 10  illustrates an example graph showing the probability for retransmission (e.g., Pg retran ) as a function of the number of users in the group (e.g., N). As illustrated in the example of  FIG. 10 , the probability of retransmission over the shared group transport channel may increase with an increased number of users in the group (e.g., N). In some embodiments, a worst case situation in terms of Pg retran  may occur when the probability of block error rate of one or more, or each, of the group users may be equal and/or N may be (relatively) large. In some embodiments, the system may be busy performing retransmission a majority of the time. Some embodiments contemplate that such a scheme may reduce the efficiency of the transport channel. 
     In some embodiments, using a common HARQ structure as described herein may offload the first retransmission from the multicast channel to the unicast channel. Offloading the first retransmission may reduce the probability Pg retran  as illustrated in  FIG. 11 . For example, offloading the first retransmission may result in a Pg retran =0.095 for N=10. Such a result may be obtained by assuming one or more, or each, of the users of the group may have a second retransmission probability of 0.01 on the multicast channel. 
     In some embodiments, perhaps in order to improve the retransmission probability, among other reasons, the scheduler in the eNB may be permitted to optimize the probability of Pg retran , for example based on the scheduler&#39;s knowledge of SNR(i)-&gt;Pble(i) for one or more of the potential users in the group. For example, in order to reduce the retransmissions on the multicast channel, rather than (or in addition to) adjusting the MCS to achieve Pble=0.1 for the worst user over the shared transmission intended to the group, the MCS may be adjusted in order to satisfy certain desired Pg retran . 
     In some embodiments, the scheduler may order the potential users in the group according to their SINR(i) (and/or SNR) in descending order, for example. For example, the user with a relative lowest SINR may be first and the user with a relative highest SINR may be last. The scheduler may select an MCS according to a user with lowest SINR in order to achieve Pble(1)˜0.1. The scheduler may calculate the BLER for other potential group users. The scheduler may determine  Pg     retran   , for example according to Equation (1). If Pg retran &gt;Pg retran   _   target  (e.g., where Pg retran   _   target  may be a target probability), the scheduler may change the MCS to achieve Pg retran ˜Pg retran   _   target  and/or reduce the number of users to (e.g., from N to M) to achieve Pg retran ˜Pg retran   _   target . In some embodiments, the scheduler may use a less robust MCS, for example Pg retran &lt;Pg retran   _   target , the scheduler may change MCS to achieve Pg retran ˜Pg retran   _   target . 
     In some embodiments, the eNB may send the identity of group channels that may be in progress using different techniques including, but not limited to, one or more of system information, RRC dedicated messaging, MAC control element messaging, and/or the like. 
     In some embodiments, the WTRU may indicate to the network its preference to join an existing group channel. The indication may trigger the eNB to configure the corresponding logical channel for the WTRU. The WTRU may indicate to the network its interest in a specific service or a group of services using a notification. The notification may be a contemplated message and/or a modification of an existing message. The notification may be an RRC message, a non-access stratum (NAS) message, and/or the like.  FIG. 12  illustrates an example messaging sequence for the WTRU to indicate to the network that it may desire to join an existing UEgroup. In the example shown in  FIG. 12 , the group channels may be configured through a logical entity referred to as a Session Management Entity (SME). The SME may initiate group sessions. In some embodiments, the SME may be collocated and/or interfaced to the multimedia broadcast multicast service (MBMS) coordination entity (MCE), for example as a correlated decision entity. In some embodiments, the group session may be initiated through MBMS and/or a cell-based multicast mechanism as described herein. The group session may be initiated based on factors including, but not limited to, one or more of operator input, radio link conditions, network capabilities, scope of service area, and/or the like. 
     In some embodiments, a WTRU configured for cell-multicast may receive a list/menu of available channels over existing broadcast mechanisms. For example, a WTRU configured for cell-multicast may receive a list/menu of available channels over one or more SIBs, dedicated messaging including paging, short message service (SMS), RRC/NAS dedicated signaling, and/or the like. 
     In some embodiments, common scheduling information may be signaled to each of the WTRUs that may be subscribed to a group. In some embodiments, one or more, or each, WTRU in the group may receive and/or be configured with a common group RNTI. In some embodiments, the eNB may maintain a list of C-RNTI(s) assigned to the WTRUs that may be subscribed to a particular group and/or may send common DCI information to one or more, or each, of the group members. In some embodiments, the common DCI information may be signaled to the group members individually using individual C-RNTIs. 
     In some embodiments, the WTRU may indicate an interest in a service class/group in a connection request message. For example, indicating the interest in a group in a connection request message may allow the network to configure the associated logical channel in the initial RRC configuration message. 
     In some embodiments, a particular service may be initiated as a unicast transmission in a cell. The eNB may maintain a count of WTRUs that may be interested in a particular service. In some embodiments, perhaps when the count of number of WTRUs may exceed a predetermined threshold, among other scenarios, the eNB may delete/remove the unicast logical channel and/or initiate a group based transmission. For example, the eNB may re-establish a removed unicast logical channel for multicast service. 
     Some embodiments recognize that traffic flow mapping configuration updates using RRC messages may be relatively a slow mechanism in terms of informing a WTRU/eNB of a configuration change. Perhaps in order to achieve more relatively rapid reconfigurations, one or more embodiments contemplate the definition of one or more MAC control element(s) (CEs). For example, a MAC CE may indicate the mapping of logical channel to group transport channel and/or unicast transport channel. 
     In some embodiments, the logical channel associated with the group radio bearer may be radio link control (RLC unacknowledged mode (UM)). For example, the group radio bearer may be mapped to a new (e.g., fresh or contemplated) point to multipoint downlink logical channel (e.g., Group-TCH) as illustrated in  FIG. 13 . The mapping from the transport channel to physical channel may remain the same, perhaps despite a change in the mapping of logical channels to transport channels to support cell multicast service.  FIG. 14  illustrates a mapping of transport channels to physical channels. 
     In some embodiments, the configuration of cell multicast radio bearer(s) may be defined using RRC configuration, for example using the information element (IE) DRB-ToAddMod. The logical channel configuration may include parameters to configure the group logical channel. If a group RNTI may be used, in an example the group RNTI may be included in the configuration. An example of the DRB-ToAddMod IE is shown below in Table 1. 
     
       
         
           
               
             
               
                 TABLE 1 
               
               
                   
               
               
                 Example Information Element 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                 DRB-ToAddMod ::= SEQUENCE { 
                   
                   
                   
               
               
                   eps-BearerIdentity 
                 INTEGER (0..15) 
                 OPTIONAL, 
                 -- Cond DRB-Setup 
               
               
                   drb-Identity 
                 DRB-Identity, 
               
               
                   pdcp-Config 
                 PDCP-Config 
                 OPTIONAL, 
                 -- Cond PDCP 
               
               
                   rlc-Config 
                 RLC-Config 
                 OPTIONAL, 
                 -- Cond Setup 
               
               
                   logicalChannelIdentity 
                 INTEGER (3..10) 
                 OPTIONAL, 
                 -- Cond DRB-Setup 
               
               
                   logicalChannelConfig 
                 LogicalChannelConfig 
                 OPTIONAL, 
                 -- Cond Setup 
               
               
                   group-RNTI 
                 Group-RNTI 
                 OPTIONAL, 
                 -- Group-RNTI 
               
               
                 } 
               
               
                   
               
            
           
         
       
     
     Perhaps in order to support shared channel multicast with dedicated (e.g., separate) HARQ, among other reasons, one or more of the techniques described herein may be utilized.  FIG. 15  illustrates an example MAC structure for a WTRU receiver with a dedicated (e.g., separate) HARQ unit. 
     In some embodiments, an eNB (and/or a WTRU) may add a MAC layer shared channel dedicated HARQ unit for group/multicast transmission. For example, the HARQ unit of the eNB may send HARQ information including a New Data Indicator (NDI), Transport Block (TB) size, HARQ process ID, and/or Redundancy Version (RV). In case of spatial multiplexing on DL-SCH, the HARQ information may include a set of NDI and/or TB size(s) for one or more, or each, transport block. In some embodiments, an eNB (and/or a WTRU) may add a group UE ID in addition to the dedicated UE ID. For example, in an RRC connection within the cell, one or more, or each, user may be identified by a C-RNTI. Perhaps in order to support multicasting transmission, among other reasons, a group-RNTI (G-RNTI) may be added in order to identify a group of users in an RRC connected cell. Perhaps, when a LTE network may establish a connection to the group of WTRUs over the DL SCH, among other scenarios, the eNB may assign to them the G-RNTI. Example RNTI values including the G-RNTI are shown in Table 2. Example RNTI values, their use, and their associated Transport Channels/Logical Channels are presented in Table 2. 
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 Example RNTIs 
               
            
           
           
               
               
               
               
            
               
                   
                   
                 Transport 
                   
               
               
                 RNTI 
                 Usage 
                 Channel 
                 Logical Channel 
               
               
                   
               
               
                 P-RNTI 
                 Paging and System Information 
                 PCH 
                 PCCH 
               
               
                   
                 change notification 
               
               
                 SI-RNTI 
                 Broadcast of System Information 
                 DL-SCH 
                 BCCH 
               
               
                 M-RNTI 
                 MCCH Information change 
                 N/A 
                 N/A 
               
               
                   
                 notification 
               
               
                 RA-RNTI 
                 Random Access Response 
                 DL-SCH 
                 N/A 
               
               
                 Temporary C- 
                 Contention Resolution 
                 DL-SCH 
                 CCCH 
               
               
                 RNTI 
                 (when no valid C-RNTI is available) 
               
               
                 Temporary C- 
                 Msg3 transmission 
                 UL-SCH 
                 CCCH, DCCH, 
               
               
                 RNTI 
                   
                   
                 DTCH 
               
               
                 C-RNTI 
                 Dynamically scheduled unicast 
                 UL-SCH 
                 DCCH, DTCH 
               
               
                   
                 transmission 
               
               
                 C-RNTI 
                 Dynamically scheduled unicast 
                 DL-SCH 
                 CCCH, DCCH, 
               
               
                   
                 transmission 
                   
                 DTCH 
               
               
                 G-RNTI 
                 Dynamically scheduled multicast 
                 DL-SCH 
                 DCCH, DTCH 
               
               
                   
                 transmission 
               
               
                 C-RNTI 
                 Triggering of PDCCH ordered 
                 N/A 
                 N/A 
               
               
                   
                 random access 
               
               
                 Semi-Persistent 
                 Semi-Persistently scheduled unicast 
                 DL-SCH, UL- 
                 DCCH, DTCH 
               
               
                 Scheduling C- 
                 transmission 
                 SCH 
               
               
                 RNTI 
                 (activation, reactivation and 
               
               
                   
                 retransmission) 
               
               
                 Semi-Persistent 
                 Semi-Persistently scheduled unicast 
                 N/A 
                 N/A 
               
               
                 Scheduling C- 
                 transmission 
               
               
                 RNTI 
                 (deactivation) 
               
               
                 TPC-PUCCH- 
                 Physical layer Uplink power control 
                 N/A 
                 N/A 
               
               
                 RNTI 
               
               
                 TPC-PUSCH- 
                 Physical layer Uplink power control 
                 N/A 
                 N/A 
               
               
                 RNTI 
               
               
                   
               
            
           
         
       
     
     In some embodiments, a WTRU (and/or an eNB) may add a second DL shared transport channel with dedicated HARQ unit for group/multicast reception. For example, the HARQ unit at the WTRU may receive HARQ information. The HARQ unit may perform soft combining with a saved previous transmission, for example based on the HARQ process ID and/or the Redundancy Version (RV). 
     In some embodiments, the WTRU (and/or eNB) may add uplink ack/nack feedback for the shared multicast HARQ unit. For example, one or more, or each WTRU identified within the group may send feedback ack/nack via the physical uplink shared channel (PUCCH) to an eNB to acknowledge reception of the TB that may be sent via the multicast shared channel. The HARQ feedback, perhaps in response to downlink data transmission, among other reasons, may include a single ack/nack bit per transport block. In case of simultaneous (e.g., parallel) transmission on both unicast shared channel and multicast shared channel, multiple ack/nack bits may be sent (e.g., a single ack/nack bit for each transport block). 
     In some embodiments, the WTRU (and/or eNB) may add feedback for shared multicast channel quality indication (CQI) information for one or more, or each, WTRU, for example in additional to the unicast CQI. The CQI may be sent from the WTRU to eNB to inform the eNB of operational performance. Perhaps when the WTRU may be allocated PUSCH resources in a subframe where a CQI report may be configured to be sent, among other scenarios, the CQI report may be transmitted together with uplink data on the PUSCH. 
     In some embodiments, perhaps in order to support shared channel multicast with common HARQ, among other reasons, one or more of the techniques described herein may be utilized.  FIG. 16  illustrates an example MAC structure for a WTRU receiver with a common (e.g., shared) HARQ unit. 
     In some embodiments, an eNB (and/or a WTRU) may add a MAC layer shared channel dedicated HARQ unit for group/multicast transmission. For example, the HARQ unit of the eNB may send HARQ information including a New Data Indicator (NDI), Transport Block (TB) size, HARQ process ID, and/or Redundancy Version (RV). Perhaps in case of spatial multiplexing on DL-SCH, among other scenarios, the HARQ information may include a set of NDI and/or TB size(s) for one or more, or each, transport block. 
     In some embodiments, the eNB (and/or WTRU) may be configured to utilize a common HARQ unit, for example to direct unicast and/or multicast shared channels retransmissions via the unicast DL SCH transport channel. In an example, the common HARQ unit may include 16 HARQ processes rather than the 8 HARQ processes used in a dedicated e.g. separate) HARQ unit. Perhaps when one of the received transport channels (e.g., other than the worst WTRU multicast transport channel) may have an error, among other scenarios, the retransmission may take place on the unicast channel. In some embodiments, perhaps wherein the error may appear on both unicast and multicast shared channels, among other scenarios, the retransmissions may take place on one or more, or each of the unicast and multicast shared channels. 
     In some embodiments, perhaps when one of the received transport channels (e.g., other than the worst WTRU multicast transport channel) has an error, among other scenarios, the retransmission may take place on the unicast channel. In case the error may appear on both unicast and multicast shared channels, the retransmissions of the multicast channel may be performed over the multicast channel, and/or the unicast retransmission may be discarded. In some embodiments, such a decision to discard the unicast retransmission may be based on the fact that logical channels connected to unicast transmission may include enhanced layer SVC that may be less crucial for the video transmission. 
     In some embodiments, a WTRU (and/or an eNB) may add a second DL shared transport channel with a common HARQ unit for group/multicast reception. In some embodiments, the HARQ unit may receive HARQ information and/or may perform soft combining with its saved previous transmission(s), for example based on HARQ process ID and/or Redundancy Version (RV). The original transmission and/or retransmission may be allocated on different transport channels. The eNB may indicate the original transmission (e.g., the channel used for the original transmission) as part of the HARQ process ID. 
     In some embodiments, a WTRU (and/or an eNB) may add uplink ack/nack feedback for the shared multicast HARQ unit. For example, one or more, or each, WTRU identified within the group may send feedback ack/nack via the PUCCH to eNB, perhaps in order to acknowledge reception of the TB that may be sent via the multicast shared channel, among other reasons. The HARQ feedback in response to downlink data transmission may include a single ack/nack bit per transport block. Perhaps in case of simultaneous (e.g., parallel) transmission on both the unicast shared channel and the multicast shared channel, among other scenarios, multiple ack/nack bits may be sent to acknowledge each of the received transport blocks. 
     In some embodiments, a WTRU (and/or an eNB) may add feedback for shared multicast CQI information for each WTRU in additional to the unicast CQI. The CQI may be sent from WTRU to eNB to inform the eNB of its operating performance. Perhaps when the WTRU may be allocated PUSCH resources in a subframe where a CQI report may be configured to be sent, among other scenarios, the CQI report may be transmitted together with uplink data on the PUSCH. 
     In some embodiments, perhaps for multicast over the DL-SCH, among other scenarios, a subset of multiple input multiple output (MIMO) modes may be supported. For example, in multicast a single transmission may be directed to one or more, or each, of the users in the group. In such scenarios, one or more MIMO modes that may be applicable for transmission to a specific user might not be applicable. 
     In some embodiments, MIMO modes that might not utilize feedback may be supported, but MIMO modes which utilize feedback might not be supported. In some embodiments, the MIMO modes that may be supported for the multicast channel may include one or more of single antenna port, transmit diversity, and/or open loop spatial multiplexing. In some embodiments, the WTRU and/or eNB may refrain from utilizing other MIMO modes that may utilize feedback. 
     Perhaps in order to optimize multicast performance, one or more embodiments contemplate a mechanism to enable/disable user participation in the multicast group. In some embodiments, perhaps since the group WTRUs may be performing simultaneous (e.g., parallel) unicast/multicast, among other scenarios, an activation/deactivation MAC CE may be utilized in order to activate and/or deactivate one or more unicast and/or multicast channels.  FIG. 17  illustrates an example Activation/Deactivation MAC control element that may be utilized in order to activate and/or deactivate one or more unicast and/or multicast channels, among other reasons. In the example shown in  FIG. 17 , Bit  0  of the MAC control element (e.g., C 0 ) may be used for the activation/deactivation status of a WTRU participating in group multicast. Bit  1  of the MAC CE (e.g., C 1 ) may be used to activate/deactivate the WTRU&#39;s participation in a second group multicast channel, etc. The MAC control element may be sent via the unicast transport channel to indicate to UEj that it may activate/deactivate one or more multicast transport channel receivers. 
     In some embodiments, perhaps when an eNB determines to transition a WTRU from unicast to multicast or vice versa, among other scenarios, the logical channel may be reassigned from UEj to UEg. This may be accomplished by assigning the logical channel to both unicast and multicast. When multicast is active, the logical channel that includes the SVC may be served by the MAC multicast unit. While multicast is not activated, the logical channel may be served by the MAC unicast unit. In some embodiments, the logical channel may be configured as common between a multicast MAC unit and a unicast MAC unit. 
     In some embodiments, perhaps when simultaneous (e.g., parallel) unicast/multicast may be utilized over DL-SCH, among other scenarios, HARQ-ACK bits from unicast and/or multicast transmissions for one or more, or each WTRU may be fed back to eNB. The HARQ-ACK bit generated as response for multicast transmission(s) may be concatenated to the HARQ-ACK response for unicast transmission(s) from the same WTRU. In such scenarios, the number of scheduled PUCCH messages may be reduced. 
     One or more embodiments contemplate scalable video coding transmission over WiFi/802.11. Some embodiments contemplate transmitting SVC video traffic over WiFi/802.11, such as but not limited to live lecture broadcasts in enterprise and/or campus networks. In such scenarios, perhaps if one network may be considered (e.g., perhaps only one network), the hidden-terminal problem may not be a concern, perhaps because one or more, or all, non-access point (AP) stations (STAs) may hear the transmissions from the AP (e.g., which may be the broadcast transmitter). 
     In WiFi/802.11, embodiments recognize that broadcast (multicast) may be achieved by putting the broadcast address (e.g., a multicast address) in the MAC PDU (MPDU) header and transmitting the MPDU. Embodiments recognize performance issues that may be related to the use of broadcast/multicast over WiFi (e.g., as may be defined in the applicable standards). For example, embodiments recognize that the broadcast transmitter may not retransmit and may not back off in the event of collision, perhaps because there may be no ACK defined for broadcast to indicate successful transmission (e.g., which may also be the case for LTE/LTE-A). Embodiments also recognize that in the case of LTE/LTE-A, medium access may be based on scheduling by the eNB, and there may be no collision. Embodiments further recognize that the lack of collision detection and/or backoff in broadcast in WiFi may create unreliable broadcast and/or unfairness for unicast transmitters. Embodiments recognize the use of pseudo-broadcast and/or the selection of the receiver for pseudo-broadcast to address one or more of these performance issues. 
     Embodiments recognize that in pseudo-broadcast a MPDU may be addressed to a particular STA (e.g., that may be called a target client) and may be transmitted as a unicast packet. Other STAs may be in the promiscuous mode, which may allow a STA to process the overheard packets, perhaps even if the packets are not addressed to that STA. The target client may reply to the transmitter with an ACK if it successfully receives that MPDU. Embodiments recognize that pseudo-broadcast may implement wireless broadcast while perhaps being able to obtain an ACK from a target client. Embodiments recognize that such schemes may, at least partially, address the unreliability and/or unfairness issue resulting from the broadcast mechanism defined in the WiFi/802.11 standards. 
     Embodiments also recognize that when pseudo-broadcast may be used, perhaps if the target client may have a good channel (e.g., which may be indicated by the RSSI or CSI defined in the applicable standard(s), or by other technique), the STAs that may have (relatively) worse channels might not be able to successfully receive the unicast packet. Embodiments recognize that a choice of the STA with the worst channel as the target client may address such issues. In such scenarios, perhaps in the absence of hidden-terminal problems, if the target client may successfully receive the MPDU, one or more, or all, other STAs may also successfully receive the MPDU (in promiscuous mode). 
     One or more embodiments contemplate that broadcast/multicast may be used to transmit the packets from the SVC base layer. One or more embodiments also contemplate that unicast may be used to transmit the packets from SVC enhancement layers.  FIG. 18  illustrates a flowchart of an example technique that may be executed in some embodiments, perhaps if the video traffic generated from the traffic source may already be in SVC format, among other scenarios. In  FIG. 18 , at  1802 , the MAC layer may separate SVC packets into at least two categories: those from the base layer (e.g., PKT_BASE), and those from the enhancement layers (e.g., PKT_NON_BASE). In some embodiments, this can be done, for example, by using different port numbers for the connections that may carry PKT_BASE packets and the connections that may carry PKT_NON_BASE packets, and/or by using deep packet inspection. 
     At  1804 , the AP may perform one or more procedures for target client selection (e.g., known procedures). At  1806 , perhaps if the MAC at the AP my receive a PKT_BASE packet, it may transmit the packet using pseudo-broadcast. That is, the PKT_BASE packet may be addressed to the target client as a standard unicast packet. In some embodiments, other STAs may listen in promiscuous mode. In such scenarios, the broadcast of the PKT_BASE packet may be implemented perhaps while getting an ACK from the target client, which may ensure fairness for other unicast transmitters. In some embodiments, perhaps if the MAC at the AP may receive a PKT_NON_BASE packet, among other reasons, it may transmit the packet using standard unicast. In such scenarios, the PKT_NON_BASE packet may be sent to one or more, or all, the STAs individually using unicast. 
     In some embodiments, alternatively or additionally to the example technique described with respect to  FIG. 18 , perhaps if the video traffic generated from the traffic source might not be SVC, among other scenarios, a transcoder can be used at the AP to transcode the video traffic into SVC format. The bit rate for the base layer can be set to match the data rate of the link between the AP and the target client. As the link quality between the AP and the target client may change, the bit rate for the base layer can also change. Although some embodiments contemplate that SVC might be less efficient than advanced video coding (AVC), some embodiments also contemplate that the utilization of broadcast may provide a savings in radio resources (e.g., a relatively significant savings), and/or may facilitate an improvement of the overall video quality to one or more, or all, users. 
     One or more embodiments contemplate the successful delivery of one or more, or each, MPDU that may carry a base layer packet, perhaps while taking advantage of the broadcast nature of the wireless medium for improved efficiency.  FIG. 19  illustrates an example technique utilizing an ACKed-broadcast contemplated by one or more embodiments. At  1902 , a transmitter may maintain a variable Si for one or more, or each broadcast packet, which may be the set of STAs that might have not yet successfully received the broadcast packet i. At  1904 , the transmitter may choose a target client from Si, perhaps according to the same criteria that may be used in a pseudo-broadcast, which may be that the STA with the worst channel may be selected as the target client. The MCS used for constructing the broadcast packet may be determined to match the channel of the target client. A sequence number may be used in the broadcast packet to identify different broadcast packets, for example. 
     At  1906 , one or more, or each, STA may send an ACK if it might not have seen this broadcast packet before. In the ACK, it may be indicated which broadcast packet is being acknowledged. At  1908 , the transmitter may remove from the set Si those STAs from which it may have successfully received an ACK. At  1910 , a determination may be made regarding whether the set Si may be empty. One or more of the elements of the example technique may be repeated, perhaps until the set Si may become empty. 
     In some embodiments, perhaps as one or more, or each, time the MCS may be determined by the channel of the target client, the probability of a STA in the set Si that might not successfully receive the broadcast packet may be relatively small (e.g., relative very small). In such scenarios, the algorithm may converge relatively quickly. 
     Although features and elements are described above in particular combinations, one of ordinary skill in the art will appreciate that each feature or element can be used alone or in any combination with the other features and elements. In addition, the methods described herein may be implemented in a computer program, software, or firmware incorporated in a computer-readable medium for execution by a computer or processor. Examples of computer-readable media include electronic signals (transmitted over wired or wireless connections) and computer-readable storage media. Examples of computer-readable storage media include, but are not limited to, a read only memory (ROM), a random access memory (RAM), a register, cache memory, semiconductor memory devices, magnetic media such as internal hard disks and removable disks, magneto-optical media, and optical media such as CD-ROM disks, and digital versatile disks (DVDs). A processor in association with software may be used to implement a radio frequency transceiver for use in a WTRU, WTRU, terminal, base station, RNC, or any host computer.