Patent Application
20090046674
Radio communication systems, such as a wireless data networks (e.g., Third Generation Partnership Project (3GPP) Long Term Evolution (LTE) systems, spread spectrum systems (such as Code Division Multiple Access (CDMA) networks), Time Division Multiple Access (TDMA) networks, WiMAX (Worldwide Interoperability for Microwave Access), etc.), provide users with the convenience of mobility along with a rich set of services and features. This convenience has spawned significant adoption by an ever growing number of consumers as an accepted mode of communication for business and personal uses. To promote greater adoption, the telecommunication industry, from manufacturers to service providers, has agreed at great expense and effort to develop standards for communication protocols that underlie the various services and features. One area of effort involves providing link adaptation using feedback methods to improve link performance.
Therefore, there is a need for an approach to provide more efficient feedback signaling.
According to one embodiment of the present invention, a method comprises partitioning a bandwidth into one or more resource groups corresponding to one or more resource units. The method also comprises designating one or more of the partitions for transmission of a plurality of uplink pilots that specify channel information for the corresponding resource units.
According to another embodiment of the present invention, an apparatus comprises a processor configured to partition a bandwidth into one or more resource groups corresponding to one or more resource units. The processor is further configured to designate one or more of the partitions for transmission of a plurality of uplink pilots that specify channel information for the corresponding resource units.
According to another embodiment of the present invention, a method comprises receiving one or more uplink pilots from a user equipment, wherein the uplink pilots specify channel information for a plurality of resource units. The method also comprises partitioning a channel bandwidth into a plurality of resource groups corresponding to the resource units, wherein the partitions are utilized for transmission of the uplink pilots.
According to yet another embodiment of the present invention, an apparatus comprises a transceiver configured to receive one or more uplink pilots from a user equipment, wherein the uplink pilots specify channel information for a plurality of resource units. The apparatus also comprises a processor configured to partition a channel bandwidth into a plurality of resource groups corresponding to the resource units, wherein the partitions are utilized for transmission of the uplink pilots.
Still other aspects, features, and advantages of the embodiments of the invention are readily apparent from the following detailed description, simply by illustrating a number of particular embodiments and implementations, including the best mode contemplated for carrying out the embodiments of the invention. The invention is also capable of other and different embodiments, and its several details can be modified in various obvious respects, all without departing from the spirit and scope of the invention. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as restrictive.
The embodiments of the invention are illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings and in which like reference numerals refer to similar elements and in which:
An apparatus, method, and software for providing feedback information in a multiple input multiple output (MIMO) system are described. In the following description, for the purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the invention. It is apparent, however, to one skilled in the art that the invention may be practiced without these specific details or with an equivalent arrangement. In other instances, well-known structures and devices are shown in block diagram form in order to avoid unnecessarily obscuring the invention.
Although the embodiments of the invention are discussed with respect to a wireless network compliant with the Third Generation Partnership Project (3GPP) Long Term Evolution (LTE) architecture, it is recognized by one of ordinary skill in the art that the embodiments of the inventions have applicability to any type of communication system and equivalent functional capabilities.
According to one embodiment, the system 100 is a multiple input multiple output (MIMO) system. The Node B or eNB 103 may utilize a MIMO antenna system 105 to provide increased data rates and improved coverage and capacity. That is, this arrangement supports the parallel transmission of independent data streams to achieve high data rates. The system 100 provides multiple parallel streams or layers to a single UE 101. Multi-layer transmission may be applied for downlink (DL) as well as uplink (UL) transmission.
In a wireless system, link performance can be improved by adapting the transmissions to account for current channel conditions. Schemes for conveying channel information between receiver and transmitter are called closed-loop methods. As shown, the base station 103 includes closed loop preceding and beamforming logic 107 to maximize the signal level. The UE 101 can report the channel state information back to the base station 103 to use for subsequent transmissions. In a beam-forming closed-loop MIMO system, the BS 103 utilizes the channel information to form a beam towards the UE 101 using preceding weights (e.g., a pre-coding matrix extracted from the channel matrix). The base station 103 also includes a scheduler 111, which manages the scheduling of data and control information for transmission to the user equipment 101.
A memory 109 stores the preceding weights that are used for beamforming. Beamforming implies that multiple antennas 105 are used to form the transmission or reception beam; in this way, the signal-to-noise ratio at the UE 101 is increased. This technique can both be used to improve coverage of a particular data rate and to increase the system spectral efficiency. Thus, beamforming can be applied to both to the downlink and the uplink.
The user equipment 101 possesses a feedback module 113 for conveying channel information, such as channel quality information (CQI) and channel state information (CSI), to the base station 103 (i.e., network). As such, a measurement module 115 provides for measuring parameters relating to state of the communication channel (e.g., downlink). This feedback mechanism provides sufficient information to enable the BS 103 to perform the closed-loop transmission on the DL—e.g., quantized channel response or quantized transmit weights). Further, a memory 117 permits storage of preceding weights, as part of the closed-loop MIMO mechanism. The user equipment 101 utilizes a scheduler 119 to schedule transmissions on the uplink. In the MIMO system 100, the UE 101 also has multiple antennas 121 for receiving and transmitting signals.
The base station 103, in an exemplary embodiment, uses OFDM (Orthogonal Frequency Divisional Multiplexing) as the downlink transmission scheme and a single-carrier transmission (e.g., SC-FDMA (Single Carrier-Frequency Division Multiple Access) with cyclic prefix for the uplink transmission scheme. SC-FDMA can be realized also using DFT-S-OFDM principle, which is detailed in 3GGP TR 25.814, entitled “Physical Layer Aspects for Evolved UTRA,” v.1.5.0, May 2006 (which is incorporated herein by reference in its entirety). SC-FDMA, also referred to as Multi-User-SC-FDMA, allows multiple users to transmit simultaneously on different sub-bands.
In an exemplary embodiment, Walsh-Hadamard spreading is used to create orthogonal codes, in which different users can transmit their control channels. Such control channels are multiplexed with the data channels. In this regard, in case of single user multi-stream (i.e., MIMO) transmission, the Walsh-Hadamard spreading is applied in the antenna domain. As a consequence, this approach can achieve transmitter diversity gain provided by the underlying Walsh-Hadamard spreading in the antenna domain. In addition, this approach, according to one embodiment, can use the same spreading in order to improve the detection reliability in case of single user MIMO transmission; such approach can arrange orthogonal control signaling for MIMO application with symbol level multiplexing between control and data channels.
Uplink control signaling, according to 3GGP TR 25.814, is divided into data-associated and data non-data-associated control signaling. Data-associated control signaling is typically transmitted with uplink data transmission. Data non-data-associated control signaling includes, for example, Channel Quality Information (CQI), and thus, can be transmitted independently of uplink data transmission.
In the exemplary scenario of
In TDD, due to the channel reciprocity of the uplink and the downlink, CSI can be conveyed to the Node B 103 by sending uplink sounding pilots (i.e., training sequences or reference symbols), according to an exemplary embodiment. This approach provides for reduced CSI delay, minimal or no quantization loss and no feedback transmission error. Also, the computation burden needed for computing the beamforming weights is placed at the base station 103, which has greater resources for handling such computations.
As mentioned, the communication system 100, according to one embodiment, is an LTE system, as next described.
The MME (Mobile Management Entity)/serving gateways 201 are connected to the eNBs 103 in a full or partial mesh configuration using tunneling over a packet transport network (not shown). Although shown as a single component, the MME and the serving gateway 201 can be implemented as separate components, as later described. Exemplary functions of the MME/Serving GW 201 include distribution of paging messages to the eNBs 103, IP header compression, termination of U-plane packets for paging reasons, and switching of U-plane for support of UE mobility. Since the MME/Serving GW 201 serve as a gateway to external networks, e.g., the Internet or private consumer networks 203, the GWs 201 include an Access, Authorization and Accounting system (AAA) 205 to securely determine the identity and privileges of a user and to track each user's activities.
As seen in
The eNB 103 communicates with the MME 201a and serving gateway 201b via an SI interface. The MME 201a provides a NAS security function 227, an Idle State Mobility Handling function 229, as well as a SAE (System Architecture Evolution) Bearer Control 229. The serving gateway 201b has a mobility anchoring function 231. The gateway 201b has connectivity to a data network 235, such as the global Internet.
In
Thus, service providers have the capability to specify topological locations of the serving gateways 249 independently from the locations of MMEs 247 to optimize network performance.
As seen in
The MME 247 also provides the control plane function for mobility between LTE and 2G/3G access networks with the S3 interface terminating at the MME 247 from the SGSN (Serving GPRS Support Node) 251. The SGSN 251 is responsible for the delivery of data packets from and to the mobile stations within its geographical service area. The functions of the SGSN 251 include packet routing and transfer, mobility management, logical link management, and authentication and billing.
The S6a interface enables transfer of subscription and authentication data for authenticating/authorizing user access to the evolved system (AAA interface) between the MME 247 and a HSS (Home Subscriber Server) 253. The S10 interface between MMEs 247 provides MME relocation and MME 247 to MME 247 information transfer.
The serving gateway 249 is the node that terminates the interface towards the E-UTRAN 245 via S1-U. The S1-U interface provides a per bearer user plane tunneling between the E-UTRAN 245 and serving gateway 249. It contains support for path switching during handover between eNBs 245. The S4 interface provides the user plane with related control and mobility support between SGSN 251 and the 3GPP anchor function of the serving gateway 249. The S12 is an interface between UTRAN 243 and serving gateway 249.
A Packet Data Network (PDN) gateway 255 provides connectivity to the UE 101 to external packet data networks. The PDN gateway 255 performs policy enforcement, packet filtering for each user, charging support, lawful interception and packet screening. The PDN gateway 255 additionally serves as the anchor for mobility between 3GPP and non-3GPP technologies, such as WiMax and 3GPP2 (CDMA IX and EvDO (Evolution Data Only)). The S7 interface provides transfer of QoS policy and charging rules from PCRF (Policy and Charging Role Function) 257 to Policy and Charging Enforcement Function (PCEF) in the PDN gateway 255. The SGi interface is the interface between the PDN gateway 255 and a packet data network 259 (e.g., supporting the operator's IP services). The packet data network 259 may be an operator external public or private packet data network or an intra operator packet data network, e.g., for provision of IMS (IP Multimedia Subsystem) services. Rx+ is the interface between the PCRF and the packet data network 259.
The above LTE architecture is more described in TR 23.882, entitled “3GPP System Architecture Evolution (SAE): Report on Technical Options and Conclusions,” and 3GPP TR 25.813, entitled “E-UTRA and E-UTRAN: Radio Interface Protocol Aspects”; which are incorporated herein by reference in their entireties.
As seen in
For the DL MIMO use (shown in
In recognition of this problem, a feedback mechanism is provided, as shown in
To exploit this observation, an UL sounding pilot transmission scheme is proposed, as shown in
B
—
S=B
—
UL+B
—
CQI.
In step 403, a set of resource groups that can cover the total bandwidth (B_S) is selected (the set is denoted as G). Next, the uplink sounding pilots are transmitted, per step 405, in the bandwidth of G. According to one embodiment, the transmission of the sounding pilots is in a frequency hopping pattern, if more than one resource group G is to be sounded (as in steps 407 and 409). In each UL sub-frame the sounding pilots are transmitted in one (or more) resource group of G. By way of example, the sounding pilot occupies one of a Long Block in an UL sub-frame. It is noted that if more than one group needs to be sounded at a time, a larger repetition factor (RF) is used (as shown in
In step 411, the sounding pilots are transmitted in a distributed pattern in each resource group. If more than one UE 101 needs to transmit in the same resource group, then frequency division multiplexing (FDM) or code division multiplexing (CDM) can be utilized.
As shown in
Exemplary frame 505 provides a situation in which the B_UL and B_CQI do not overlap. The CQI is reported in a period of 10 ms, for example. As with the previous example, the best resource unit is in G3 and the second best is in G2.
In
In
In
As mentioned above, the repetition factor (RF) can be larger such that sounding can be performed in consecutive time slots if more than one resource groups are involved, as seen in
In the above examples (
For the case of LCR-TDD frame structure with only one UL subframe, if G encompasses multiple resource groups, then the sounding pilots can be transmitted in the resource group which covers the best RU if the UE 101 has only DL traffic. Alternatively, the sounding pilots can be transmitted in the resource group covering the best RU and the resource group covering the UL scheduling bandwidth if the UE 101 has both DL and UL traffic.
As mentioned, the uplink sounding pilot pattern aids the closed-loop precoding and beamforming in TDD. This approach can be applied to both Low Chip Rate (LCR) and Generic frame structures (also denoted as “TDD Frame Structure 1”) of an LTE TDD system, and can support both UL scheduling and the DL MIMO parameter selection. Additionally, this arrangement accounts for the CQI report bandwidth, thereby reducing overhead for providing channel feedback. In addition, since the transmission of the sounding pilots only in one resource group per sub-frame, the energy per subcarrier can be guaranteed to get good estimation performance. Furthermore, the transmission pattern can be distributed in each resource group, thereby enabling use of FDM and CDM for different UE's pilot transmission.
One of ordinary skill in the art would recognize that the processes for providing channel feedback may be implemented via software, hardware (e.g., general processor, Digital Signal Processing (DSP) chip, an Application Specific Integrated Circuit (ASIC), Field Programmable Gate Arrays (FPGAs), etc.), firmware, or a combination thereof. Such exemplary hardware for performing the described functions is detailed below with respect to
The computing system 700 may be coupled via the bus 701 to a display 711, such as a liquid crystal display, or active matrix display, for displaying information to a user. An input device 713, such as a keyboard including alphanumeric and other keys, may be coupled to the bus 701 for communicating information and command selections to the processor 703. The input device 713 can include a cursor control, such as a mouse, a trackball, or cursor direction keys, for communicating direction information and command selections to the processor 703 and for controlling cursor movement on the display 711.
According to various embodiments of the invention, the processes described herein can be provided by the computing system 700 in response to the processor 703 executing an arrangement of instructions contained in main memory 705. Such instructions can be read into main memory 705 from another computer-readable medium, such as the storage device 709. Execution of the arrangement of instructions contained in main memory 705 causes the processor 703 to perform the process steps described herein. One or more processors in a multi-processing arrangement may also be employed to execute the instructions contained in main memory 705. In alternative embodiments, hard-wired circuitry may be used in place of or in combination with software instructions to implement the embodiment of the invention. In another example, reconfigurable hardware such as Field Programmable Gate Arrays (FPGAs) can be used, in which the functionality and connection topology of its logic gates are customizable at run-time, typically by programming memory look up tables. Thus, embodiments of the invention are not limited to any specific combination of hardware circuitry and software.
The computing system 700 also includes at least one communication interface 715 coupled to bus 701. The communication interface 715 provides a two-way data communication coupling to a network link (not shown). The communication interface 715 sends and receives electrical, electromagnetic, or optical signals that carry digital data streams representing various types of information. Further, the communication interface 715 can include peripheral interface devices, such as a Universal Serial Bus (USB) interface, a PCMCIA (Personal Computer Memory Card International Association) interface, etc.
The processor 703 may execute the transmitted code while being received and/or store the code in the storage device 709, or other non-volatile storage for later execution. In this manner, the computing system 700 may obtain application code in the form of a carrier wave.
The term “computer-readable medium” as used herein refers to any medium that participates in providing instructions to the processor 703 for execution. Such a medium may take many forms, including but not limited to non-volatile media, volatile media, and transmission media. Non-volatile media include, for example, optical or magnetic disks, such as the storage device 709. Volatile media include dynamic memory, such as main memory 705. Transmission media include coaxial cables, copper wire and fiber optics, including the wires that comprise the bus 701. Transmission media can also take the form of acoustic, optical, or electromagnetic waves, such as those generated during radio frequency (RF) and infrared (IR) data communications. Common forms of computer-readable media include, for example, a floppy disk, a flexible disk, hard disk, magnetic tape, any other magnetic medium, a CD-ROM, CDRW, DVD, any other optical medium, punch cards, paper tape, optical mark sheets, any other physical medium with patterns of holes or other optically recognizable indicia, a RAM, a PROM, and EPROM, a FLASH-EPROM, any other memory chip or cartridge, a carrier wave, or any other medium from which a computer can read.
Various forms of computer-readable media may be involved in providing instructions to a processor for execution. For example, the instructions for carrying out at least part of the invention may initially be borne on a magnetic disk of a remote computer. In such a scenario, the remote computer loads the instructions into main memory and sends the instructions over a telephone line using a modem. A modem of a local system receives the data on the telephone line and uses an infrared transmitter to convert the data to an infrared signal and transmit the infrared signal to a portable computing device, such as a personal digital assistant (PDA) or a laptop. An infrared detector on the portable computing device receives the information and instructions borne by the infrared signal and places the data on a bus. The bus conveys the data to main memory, from which a processor retrieves and executes the instructions. The instructions received by main memory can optionally be stored on storage device either before or after execution by processor.
A radio section 815 amplifies power and converts frequency in order to communicate with a base station, which is included in a mobile communication system (e.g., systems of
In use, a user of mobile station 801 speaks into the microphone 811 and his or her voice along with any detected background noise is converted into an analog voltage. The analog voltage is then converted into a digital signal through the Analog to Digital Converter (ADC) 823. The control unit 803 routes the digital signal into the DSP 805 for processing therein, such as speech encoding, channel encoding, encrypting, and interleaving. In the exemplary embodiment, the processed voice signals are encoded, by units not separately shown, using the cellular transmission protocol of Code Division Multiple Access (CDMA), as described in detail in the Telecommunication Industry Association's TIA/EIA/IS-95-A Mobile Station-Base Station Compatibility Standard for Dual-Mode Wideband Spread Spectrum Cellular System; which is incorporated herein by reference in its entirety.
The encoded signals are then routed to an equalizer 825 for compensation of any frequency-dependent impairments that occur during transmission though the air such as phase and amplitude distortion. After equalizing the bit stream, the modulator 827 combines the signal with a RF signal generated in the RF interface 829. The modulator 827 generates a sine wave by way of frequency or phase modulation. In order to prepare the signal for transmission, an up-converter 831 combines the sine wave output from the modulator 827 with another sine wave generated by a synthesizer 833 to achieve the desired frequency of transmission. The signal is then sent through a PA 819 to increase the signal to an appropriate power level. In practical systems, the PA 819 acts as a variable gain amplifier whose gain is controlled by the DSP 805 from information received from a network base station. The signal is then filtered within the duplexer 821 and optionally sent to an antenna coupler 835 to match impedances to provide maximum power transfer. Finally, the signal is transmitted via antenna 817 to a local base station. An automatic gain control (AGC) can be supplied to control the gain of the final stages of the receiver. The signals may be forwarded from there to a remote telephone which may be another cellular telephone, other mobile phone or a land-line connected to a Public Switched Telephone Network (PSTN), or other telephony networks.
Voice signals transmitted to the mobile station 801 are received via antenna 817 and immediately amplified by a low noise amplifier (LNA) 837. A down-converter 839 lowers the carrier frequency while the demodulator 841 strips away the RF leaving only a digital bit stream. The signal then goes through the equalizer 825 and is processed by the DSP 805. A Digital to Analog Converter (DAC) 843 converts the signal and the resulting output is transmitted to the user through the speaker 845, all under control of a Main Control Unit (MCU) 803—which can be implemented as a Central Processing Unit (CPU) (not shown).
The MCU 803 receives various signals including input signals from the keyboard 847. The MCU 803 delivers a display command and a switch command to the display 807 and to the speech output switching controller, respectively. Further, the MCU 803 exchanges information with the DSP 805 and can access an optionally incorporated SIM card 849 and a memory 851. In addition, the MCU 803 executes various control functions required of the station. The DSP 805 may, depending upon the implementation, perform any of a variety of conventional digital processing functions on the voice signals. Additionally, DSP 805 determines the background noise level of the local environment from the signals detected by microphone 811 and sets the gain of microphone 811 to a level selected to compensate for the natural tendency of the user of the mobile station 801.
The CODEC 813 includes the ADC 823 and DAC 843. The memory 851 stores various data including call incoming tone data and is capable of storing other data including music data received via, e.g., the global Internet. The software module could reside in RAM memory, flash memory, registers, or any other form of writable storage medium known in the art. The memory device 851 may be, but not limited to, a single memory, CD, DVD, ROM, RAM, EEPROM, optical storage, or any other non-volatile storage medium capable of storing digital data.
An optionally incorporated SIM card 849 carries, for instance, important information, such as the cellular phone number, the carrier supplying service, subscription details, and security information. The SIM card 849 serves primarily to identify the mobile station 801 on a radio network. The card 849 also contains a memory for storing a personal telephone number registry, text messages, and user specific mobile station settings.
While the invention has been described in connection with a number of embodiments and implementations, the invention is not so limited but covers various obvious modifications and equivalent arrangements, which fall within the purview of the appended claims. Although features of the invention are expressed in certain combinations among the claims, it is contemplated that these features can be arranged in any combination and order.
