Abstract:
The present invention provides a solution to improve coverage and cell edge performance in a mobile user communication system is the use of fixed relays, which are pieces of infrastructure without a wired backhaul connection. The relays transmit or “relay” downlink messages between the base station (BS) and mobile stations (MSs) through a multi-hop communication. The present invention is a method and system for supporting a multiple user mobile broadband communication network that includes relay techniques suitable for user equipment in the downlink communication to the user equipment.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is related to Provisional Patent Application Ser. No. 61/109,679 filed on Oct. 30, 2008, and priority is claimed for this earlier filing under 35 U.S.C. §119(e). The Provisional patent application is also incorporated by reference into this utility patent application. 
     
    
     TECHNICAL FIELD OF THE INVENTION 
       [0002]    This application relates to wireless communication techniques in general, and to relay techniques suitable for user equipment in downlink, in particular. 
       BACKGROUND OF THE INVENTION 
       [0003]    There is an increasing demand on mobile wireless operators to provide voice and high-speed data services, and at the same time, these operators want to support more users per base station to reduce overall network costs and make the services affordable to subscribers. As a result, wireless systems that enable higher data rates and higher capacities to the user equipment are needed. The available spectrum for wireless services is limited, however, and the prior attempts to increase traffic within a fixed bandwidth have increased interference in the system and degraded signal quality. 
         [0004]    Wireless communications networks are typically divided into cells, with each of the cells further divided into cell sectors. A base station is provided in each cell to enable wireless communications with mobile stations located within the cell. One problem existing in the prior art systems includes the situation where the transmission/reception of each user&#39;s signal becomes a source of interference to other users located in the same cell location on the network, making the overall system interference limited. 
         [0005]    An effective way to increase efficiency of bandwidth usage and reduce this type of interference is to use multiple input-multiple output (MIMO) technology that supports multiple antennas at the transmitter and receiver. For a multiple antenna broadcast channel, such as the downlink on a cellular network, transmit/receive strategies have been developed to maximize the downlink throughput by splitting up the cell into multiple sectors and using sectorized antennas to simultaneously communicate with multiple users. Such sectorized antenna technology offers a significantly improved solution to reduce interference levels and improve the system capacity. 
         [0006]    The sectorized antenna system is characterized by a centralized transmitter (cell site/tower) that simultaneously communicates with multiple receivers (user equipment, cell phone, etc.) that are involved in the communication session. With this technology, each user&#39;s signal is transmitted and received by the basestation only in the direction of that particular user. This allows the system to significantly reduce the overall interference in the system. A sectorized antenna system consists of an array of antennas that direct different transmission/reception beams toward each user in the system or different directions in the cellular network based on the user&#39;s location. 
         [0007]    To improve the performance of a sectorized cell sector, schemes have been implemented using orthogonal frequency domain multiple access (OFDMA) systems. The various components on the system may be called different names depending on the nomenclature used on any particular network configuration or communication system. For instance, “user equipment” encompasses PC&#39;s on a cabled network, as well as other types of equipment coupled by wireless connectivity directly to the cellular network as can be experienced by various makes and models of mobile terminals (“cell phones”) having various features and functionality, such as Internet access, e-mail, messaging services, and the like. 
         [0008]    Further, the words “receiver” and “transmitter” may be referred to as “access point” (AP), “basestation,” and “user” depending on which direction the communication is being transmitted and received. For example, an access point AP or a basestaion (eNodeB or eNB) is the transmitter and a user is the receiver for downlink environments, whereas an access point AP or a basestaion (eNodeB or eNB) is the receiver and a user is the transmitter for uplink environments. These terms (such as transmitter or receiver) are not meant to be restrictively defined, but could include various mobile communication units or transmission devices located on the network. 
         [0009]    One of the main challenges faced by the current system developers is providing high throughput at the cell edge. Technologies like multiple input multiple output (MIMO), orthogonal frequency division multiplexing (OFDM), and advanced error control codes enhance per-link throughput, but these technologies do not solve the detrimental effects of interference at borders with other cells or at the cell edge. 
         [0010]    Cell edge performance is becoming more important as cellular systems employ higher bandwidths with the same amount of transmit power, and the systems use higher carrier frequencies with infrastructure designed for lower carrier frequencies. New standards are needed for mobile broadband access that will meet the throughput and coverage requirements of a fourth generation cellular technology. 
       SUMMARY OF THE INVENTION 
       [0011]    The present invention provides a solution to improve coverage and cell edge performance in a mobile user communication system is the use of fixed relays, which are pieces of infrastructure without a wired backhaul connection. The relays transmit or “relay” downlink messages between the base station (BS) and mobile stations (MSs) through a multi-hop communication. The present invention is a method and system for supporting a multiple user mobile broadband communication network that includes relay techniques suitable for user equipment in the downlink communication to the user equipment. Several specific relay techniques are addressed with respect to the specific embodiments shown in the accompanying drawing figures. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    Embodiments of the present application will now be described, by way of example only, with reference to the accompanying drawing figures, wherein: 
           [0013]      FIG. 1  is a block diagram of a cellular communication system; 
           [0014]      FIG. 2  is a block diagram of an example base station that might be used to implement some embodiments of the present 5 application; 
           [0015]      FIG. 3  is a block diagram of an example wireless terminal that might be used to implement some embodiments of the present application; 
           [0016]      FIG. 4  is a block diagram of an example relay station that might be used to implement some embodiments of the present application; 
           [0017]      FIG. 5  is a block diagram of a logical breakdown of an example OFDM transmitter architecture that might be used to implement some embodiments of the present application; and 
           [0018]      FIG. 6  is a block diagram of a logical breakdown of an example OFDM receiver architecture that might be used to implement some embodiments of the present application; 
           [0019]      FIG. 7  is a block diagram of an SC-FDMA transmitter  7 ( a ) and receiver  7 ( b ) used to implement some embodiments of the present application; 
           [0020]      FIG. 8(   a ) are packet diagrams used in the invention; 
           [0021]      FIG. 8(   b ) are packet diagrams used in the invention; 
           [0022]      FIG. 9(   a ) are packet diagrams used in the invention; 
           [0023]      FIG. 9(   b ) are packet diagrams used in the invention; 
       
    
    
       [0024]    Like reference numerals are used in different figures to denote similar elements. 
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0025]    Referring to the drawings,  FIG. 1  shows a base station controller (BSC)  10  which controls wireless communications within multiple cells  12 , which cells are served by corresponding basestations (BS)  14 . In some configurations, each cell is further divided into multiple sectors  13  or zones (not shown). In general, each base station  14  facilitates communications using OFDM with mobile and/or wireless terminals  16 , which are within the cell  12  associated with the corresponding base station  14 . The movement of the mobile terminals  16  in relation to the base stations  14  results in significant fluctuation in channel conditions. 
         [0026]    As illustrated, the base stations  14  and mobile terminals  16  may include multiple antennas to provide spatial diversity for communications. In some configurations, relay stations  15  may assist in communications between base stations  14  and wireless terminals  16 . Wireless terminals  16  can be handed from any cell  12 , sector  13  zone, base station  14  or relay  15  to another cell  12 , sector  13  zone, base station  14  or relay  15 . In some configurations, base stations  14  communicate with each and with another network (such as a core network or the internet, both not shown) over a backhaul network  11 . In some configurations, a base station controller  10  is not needed. 
         [0027]    With reference to  FIG. 2 , an example of a base station  14  is illustrated. The base station  14  generally includes a control system  20 , a baseband processor  22 , transmit circuitry  24 , receive circuitry  26 , multiple antennas  28 , and a network interface  30 . The receive circuitry  26  receives radio frequency signals bearing information from one or more remote transmitters provided by mobile terminals  16  (illustrated in  FIG. 3 ) and relay stations  15  (illustrated in  FIG. 4 ). In addition to the components shown in  FIG. 2 , a low noise amplifier and a filter may cooperate to amplify and remove broadband interference from the signal for processing. Further, downconversion and digitization circuitry will then downconvert the filtered, received signal to an intermediate or baseband frequency signal, which is then digitized into one or more digital streams. 
         [0028]    The baseband processor  22  processes the digitized received signal to extract the information or data bits conveyed in the received signal. This processing typically comprises demodulation, decoding, and error correction operations. As such, the baseband processor  22  is generally implemented in one or more digital signal processors (DSPs) or application-specific integrated circuits (ASICs). The received information is then sent across a wireless network via the network interface  30  or transmitted to another mobile terminal  16  serviced by the base station  14 , either directly or with the assistance of a relay  15 . 
         [0029]    On the transmit side, the baseband processor  22  receives digitized data, which may represent voice, data, or control information, from the network interface  30  under the control of control system  20 , and encodes the data for transmission. The encoded data is output to the transmit circuitry  24 , where it is modulated by one or more carrier signals having a desired transmit frequency or frequencies. A power amplifier (not shown) will amplify the modulated carrier signals to a level appropriate for transmission, and deliver the modulated carrier signals to the antennas  28  through a matching network (not shown). Modulation and processing details are described in greater detail below. 
         [0030]    With reference to  FIG. 3 , an example of a mobile terminal  16  is illustrated. Similar to the base station  14 , the mobile terminal  16  will include a control system  32 , a baseband processor  34 , transmit circuitry  36 , receive circuitry  38 , multiple antennas  40 , and user interface circuitry  42 . The receive circuitry  38  receives radio frequency signals bearing information from one or more base stations  14  and relays  15 . A low noise amplifier and a filter (not shown) may cooperate to amplify and remove broadband interference from the signal for processing. Downconversion and digitization circuitry (not shown) will then downconvert the filtered, received signal to an intermediate or baseband frequency signal, which is then digitized into one or more digital streams. 
         [0031]    The baseband processor  34  processes the digitized received signal to extract the information or data bits conveyed in the received signal. This processing typically comprises demodulation, decoding, and error correction operations. The baseband processor  34  is generally implemented in one or more digital signal processors (DSPs) and application specific integrated circuits (ASICs). 
         [0032]    For transmission, the baseband processor  34  receives digitized data, which may represent voice, video, data, or control information, from the control system  32 , which it encodes for transmission. The encoded data is output to the transmit circuitry  36 , where it is used by a modulator to modulate one or more signals that is at a desired transmit frequency or frequencies. A power amplifier (not shown) will amplify the modulated carrier signals to a level appropriate for transmission, and deliver the modulated carrier signal to the antennas  40  through a matching network (not shown). Various modulation and processing techniques available to those skilled in the art are used for signal transmission between the mobile terminal and the base station, either directly or via the relay station. 
         [0033]    In OFDM modulation, the transmission band is divided into multiple, orthogonal carrier waves. Each carrier wave is modulated according to the digital data to be transmitted. Because OFDM divides the transmission band into multiple carriers, the bandwidth per carrier decreases and the modulation time per carrier increases. Since the multiple carriers are transmitted in parallel, the transmission rate for the digital data, or symbols, on any given carrier is lower than when a single carrier is used. 
         [0034]    OFDM modulation utilizes the performance of an Inverse Fast Fourier Transform (IFFT) on the information to be transmitted. For demodulation, the performance of a Fast Fourier Transform (FFT) on the received signal recovers the transmitted information. In practice, the IFFT and FFT are provided by digital signal processing carrying out an Inverse Discrete Fourier Transform (IDFT) and Discrete Fourier Transform (DFT), respectively. Accordingly, the characterizing feature of OFDM modulation is that orthogonal carrier waves are generated for multiple bands within a transmission channel. The modulated signals are digital signals having a relatively low transmission rate and capable of staying within their respective bands. The individual carrier waves are not modulated directly by the digital signals. Instead, all carrier waves are modulated at once by IFFT processing. 
         [0035]    In operation, OFDM is preferably used for at least downlink transmission from the base stations  14  to the mobile terminals  16 . Each base station  14  is equipped with “n” transmit antennas  28  (n&gt;=1), and each mobile terminal  16  is equipped with “m” receive antennas  40  (m&gt;=1). Notably, the respective antennas can be used for reception and transmission using appropriate duplexers or switches and are so labeled only for clarity. When relay stations  15  are used, OFDM is preferably used for downlink transmission from the base stations  14  to the relays  15  and from relay stations  15  to the mobile terminals  16 . 
         [0036]    With reference to  FIG. 4 , an example of a relay station  15  is illustrated. Similarly to the base station  14 , and the mobile terminal  16 , the relay station  15  will include a control system  132 , a baseband processor  134 , transmit circuitry  136 , receive circuitry  138 , multiple antennas  130 , and relay circuitry  142 . The relay circuitry  142  enables the relay  14  to assist in communications between a base station  16  and mobile terminals  16 . The receive circuitry  138  receives radio frequency signals bearing information from one or more base stations  14  and mobile terminals  16 . A low noise amplifier and a filter (not shown) may cooperate to amplify and remove broadband interference from the signal for processing. Downconversion and digitization circuitry (not shown) will then downconvert the filtered, received signal to an intermediate or baseband frequency signal, which is then digitized into one or more digital streams. 
         [0037]    The baseband processor  134  processes the digitized received signal to extract the information or data bits conveyed in the received signal. This processing typically comprises 10 demodulation, decoding, and error correction operations. The baseband processor  134  is generally implemented in one or more digital signal processors (DSPs) and application specific integrated circuits (ASICs). 
         [0038]    For transmission, the baseband processor  134  receives digitized data, which may represent voice, video, data, or control information, from the control system  132 , which it encodes for transmission. The encoded data is output to the transmit circuitry  136 , where it is used by a modulator to modulate one or more carrier signals that is at a desired transmit frequency or frequencies. A power amplifier (not shown) will amplify the modulated carrier signals to a level appropriate for transmission, and deliver the modulated carrier signal to the antennas  130  through a matching network (not shown). Various modulation and processing techniques available to those skilled in the art are used for signal transmission between the mobile terminal and the base station, either directly or indirectly via a relay station, as described above. 
         [0039]    With reference to  FIG. 5 , a logical OFDM transmission architecture will be described. Initially, the base station controller  10  will send data to be transmitted to various mobile terminals  16  to the base station  14 , either directly or with the assistance of a relay station  15 . The base station  14  may use the channel quality indicators (CQIs) associated with the mobile terminals to schedule the data for transmission as well as select appropriate coding and modulation for transmitting the scheduled data. The CQls may be directly from the mobile terminals  16  or determined at the base station  14  based on information provided by the mobile terminals  16 . In either case, the CQI for each mobile terminal  16  is a function of the degree to which the channel amplitude (or response) varies across the OFDM frequency band. 
         [0040]    Scheduled data  44 , which is a stream of bits, is scrambled in a manner reducing the peak-to average power ratio associated with the data using data scrambling logic  46 . A cyclic redundancy check (CRC) for the scrambled data is determined and appended to the scrambled data using CRC adding logic  48 . Next, channel coding is performed using channel encoder logic  50  to effectively add redundancy to the data to facilitate recovery and error correction at the mobile terminal  16 . 
         [0041]    Again, the channel coding for a particular mobile terminal  16  is based on the CQI. In some implementations, the channel encoder logic  50  uses known Turbo encoding techniques. The encoded data is then processed by rate matching logic  52  to compensate for the data expansion associated with encoding. 
         [0042]    Bit interleaver logic  54  systematically reorders the bits in the encoded data to minimize the loss of consecutive data bits. The resultant data bits are systematically mapped into corresponding symbols depending on the chosen baseband modulation by mapping logic  56 . Preferably, Quadrature Amplitude Modulation (QAM) or Quadrature Phase Shift Key (QPSK) modulation is used. The degree of modulation is preferably chosen based on the CQI for the particular mobile terminal. The symbols may be systematically reordered to further bolster the immunity of the transmitted signal to periodic data loss caused by frequency selective fading using symbol interleaver logic  58 . 
         [0043]    At this point, groups of bits have been mapped into symbols representing locations in an amplitude and phase constellation. When spatial diversity is desired, blocks of symbols are then processed by space-time block code (STC) encoder logic  60 , which modifies the symbols in a fashion making the transmitted signals more resistant to interference and more readily decoded at a mobile terminal  16 . The STC encoder logic  60  will process the incoming symbols and provide “n” outputs corresponding to the number of transmit antennas  28  for the base station  14 . The control system  20  and/or baseband processor  22  as described above with respect to  FIG. 5  will provide a mapping control signal to control STC encoding. At this point, assume the symbols for the “n” outputs are representative of the data to be transmitted and capable of being recovered by the mobile terminal  16 . 
         [0044]    For the present example, assume the base station  14  has two antennas  28  (n=2) and the STC encoder logic  60  provides two output streams of symbols. Accordingly, each of the symbol streams output by the STC encoder logic  60  is sent to a corresponding IFFT processor  62 , illustrated separately for ease of understanding. Those skilled in the art will recognize that one or more processors may be used to provide such digital signal processing, alone or in combination with other processing described herein. The IFFT processors  62  will preferably operate on the respective symbols to provide an inverse Fourier Transform. 
         [0045]    The output of the IFFT processors  62  provides symbols in the time domain. The time domain symbols are grouped into frames, which are associated with a prefix by prefix insertion logic  64 . Each of the resultant signals is up-converted in the digital domain to an intermediate frequency and converted to an analog signal via the corresponding digital up-conversion (DUC) and digital-to-analog (D/A) conversion circuitry  66 . The resultant (analog) signals are then simultaneously modulated at the desired RF frequency, amplified, and transmitted via the RF circuitry  68  and antennas  28 . Notably, pilot signals known by the intended mobile terminal  16  are scattered among the sub-carriers. The mobile terminal  16 , which is discussed in detail below, will use the pilot signals for channel estimation. 
         [0046]    Reference is now made to  FIG. 6  to illustrate reception of the transmitted signals by a mobile terminal  16 , either directly from base station  14  or with the assistance of relay  15 . Upon arrival of the transmitted signals at each of the antennas  40  of the mobile terminal  16 , the respective signals are demodulated and amplified by corresponding RF circuitry  70 . For the sake of conciseness and clarity, only one of the two receive paths is described and illustrated in detail. Analog-to-digital (A/D) converter and down-conversion circuitry  72  digitizes and downconverts the analog signal for digital processing. The resultant digitized signal may be used by automatic gain control circuitry (AGe)  74  to control the gain of the amplifiers in the RF circuitry  70  based on the received signal level. 
         [0047]    Initially, the digitized signal is provided to synchronization logic  76 , which includes coarse synchronization logic  78 , which buffers several OFDM symbols and calculates an auto-correlation between the two successive OFDM symbols. A resultant time index corresponding to the maximum of the correlation result determines a fine synchronization search window, which is used by fine synchronization logic  80  to determine a precise framing starting position based on the headers. The output of the fine synchronization logic  80  facilitates frame acquisition by frame alignment logic  84 . 
         [0048]    Proper framing alignment is important so that subsequent FFT processing provides an accurate conversion from the time domain to the frequency domain. The fine synchronization algorithm is based on the correlation between the received pilot signals carried by the headers and a local copy of the known pilot data. Once frame alignment acquisition occurs, the prefix of the OFDM symbol is removed with prefix removal logic  86  and resultant samples are sent to frequency offset correction logic  88 , which compensates for the system frequency offset caused by the unmatched local oscillators in the transmitter and the receiver. Preferably, the synchronization logic  76  includes frequency offset and clock estimation logic  82 , which is based on the headers to help estimate such effects on the transmitted signal and provide those estimations to the correction logic  88  to properly process OFDM symbols. 
         [0049]    At this point, the OFDM symbols in the time domain are ready for conversion to the frequency domain using FFT processing logic  90 . The results are frequency domain symbols, which are sent to processing logic  92 . The processing logic  92  extracts the scattered pilot signal using scattered pilot extraction logic  94 , determines a channel estimate based on the extracted pilot signal using channel estimation logic  96 , and provides channel responses for all sub-carriers using channel reconstruction logic  98 . In order to determine a channel response for each of the sub-carriers, the pilot signal is essentially multiple pilot symbols that are scattered among the data symbols throughout the OFDM sub-carriers in a known pattern in both time and frequency. 
         [0050]    Continuing with  FIG. 6 , the processing logic compares the received pilot symbols with the pilot symbols that are expected in certain sub-carriers at certain times to determine a channel response for the sub-carriers in which pilot symbols were transmitted. The results are interpolated to estimate a channel response for most, if not all, of the remaining sub-carriers for which pilot symbols were not provided. The actual and interpolated channel responses are used to estimate an overall channel response, which includes the channel responses for most, if not all, of the sub-carriers in the OFDM channel. 
         [0051]    The frequency domain symbols and channel reconstruction information, which are derived from the channel responses for each receive path are provided to an STC decoder  100 , which provides STC decoding on both received paths to recover the transmitted symbols. The channel reconstruction information provides equalization information to the STC decoder  100  sufficient to remove the effects of the transmission channel when processing the respective frequency domain symbols. 
         [0052]    The recovered symbols are placed back in order using symbol deinterleaver logic  102 , which corresponds to the symbol interleaver logic  58  of the transmitter. The de-interleaved symbols are then demodulated or de-mapped to a corresponding bitstream using de-mapping logic  104 . The bits are then de-interleaved using bit de-interleaver logic  106 , which corresponds to the bit interleaver logic  54  of the transmitter architecture. The de-interleaved bits are then processed by rate de-matching logic  108  and presented to channel decoder logic  110  to recover the initially scrambled data and the CRC checksum. Accordingly, CRC logic  112  removes the CRC checksum, checks the scrambled data in traditional fashion, and provides it to the de-scrambling logic  114  for de-scrambling using the known base station de-scrambling code to recover the originally transmitted data  116 . 
         [0053]    In parallel to recovering the data  116 , a CQI, or at least information sufficient to create a CQI at the base station  14 , is determined and transmitted to the base station  14 . As noted above, the CQI may be a function of the carrier-to-interference ratio (CR), as well as the degree to which the channel response varies across the various sub-carriers in the OFDM frequency band. For this embodiment, the channel gain for each sub-carrier in the OFDM frequency band being used to transmit information is compared relative to one another to determine the degree to which the channel gain varies across the OFDM frequency band. Although numerous techniques are available to measure the degree of variation, one technique is to calculate the standard deviation of the channel gain for each sub-carrier throughout the OFDM frequency band being used to transmit data. 
         [0054]    Referring to  FIG. 7 , an example SC-FDMA transmitter  7 ( a ) and receiver  7 ( b ) for single-in single-out (SISO) configuration is illustrated provided in accordance with one embodiment of the present application. In SISO, mobile stations transmit on one antenna and base stations and/or relay stations receive on one antenna.  FIG. 7  illustrates the basic signal processing steps needed at the transmitter and receiver for the LTE SC-FDMA uplink. 
         [0055]    In some embodiments, SC-FDMA (Single-Carrier Frequency Division Multiple Access) is used. SC-FDMA is a modulation and multiple access scheme introduced for the uplink of 3GPP Long Term Evolution (LTE) broadband wireless fourth generation (4G) air interface standards, and the like. SC-FDMA can be viewed as a DFT pre-coded OFDMA scheme, or, it can be viewed as a single carrier (SC) multiple access scheme. There are several similarities in the overall transceiver processing of SC-FDMA and OFDMA. Those common aspects between OFDMA and SC-FDMA are illustrated in the OFDMA TRANSMIT CIRCUITRY and OFDMA RECEIVE CIRCUITRY, as they would be obvious to a person having ordinary skill in the art in view of the present specification. SC-FDMA is distinctly different from OFDMA because of the DFT pre-coding of the modulated symbols, and the corresponding IDFT of the demodulated symbols. Because of this pre-coding, the SC-FDMA sub-carriers are not independently modulated as in the case of the OFDMA sub-carriers. As a result, PAPR of SCFDMA signal is lower than the PAPR of OFDMA signal. Lower PAPR greatly benefits the mobile terminal in terms of transmit power efficiency. 
         [0056]      FIGS. 1 to 7  provide one specific example of a communication system that could be used to implement embodiments of the application. It is to be understood that embodiments of the application can be implemented with communications systems having architectures that are different than the specific example, but that operate in a manner consistent with the implementation of the embodiments as described herein. 
         [0057]    Two alternative embodiments are disclosed in accordance to relay techniques suitable for user equipment in downlink. Both embodiments are particularly suitable for LTE Rel-8 system in downlink, and are described in that context in an exemplary fashion only as others skilled in the art may be able to apply the teachings of this disclosure to other standards in view of the present disclosure. 
       First Preferred Embodiment 
       [0058]    For this embodiment, a new type of sub frame should be introduced in Rel-8 spec, which could be signalled to UE by a semi-static higher layer signalling. The location and periodicity of such sub frames can be configured through higher-layer signalling. In such sub frames, control region is referred as the first one or two OFDM symbols and data region is referred as the rest symbols in the sub frame. 
         [0059]    Control signals for UEs served directly by eNB could be transmitted in the control region in such sub frames. eNB to relay node (RN) transmission can be scheduled together with PDSCH channels for UEs directly served by eNB and transmitted in data region of such sub frames. 
         [0060]    Dedicated resource block (RB) could be reserved to convey control information for eNB to RN transmission. No new control channel is needed for eNB to RN transmission. Resource allocation for control information for RN can be statically or dynamically signaled to the RN, together with the configuration of the new sub frame, e.g., offset and periodicity. 
         [0061]    Common reference signal (RS) and dedicated RS could be used for decoding eNB to RN transmission. RN transmits control signal and RS in control region of such sub frames to the UE it serves, for it to conduct channel measurement and estimation. RN receives and decodes eNB to RN transmission in data region of such sub frames. UE served by RN should not expect to decode and conduct channel measurement/estimation in data regions of such sub frames. 
         [0062]    One radio is needed at RN for downlink. It transmits in the control region and receives in the data region in such sub frames. 
       Second Preferred Embodiment 
       [0063]    In this second embodiment, there is no need to introduce new type of sub frame in Rel-8 spec. RN is treated as a UE and can be scheduled together with UE directly served by eNB. A high layer signal could be needed to inform the UE about the sub frames containing transmission from eNB to RN. However, that doesn&#39;t bring impact to Rel-8 UE. 
         [0064]    For example, the location and periodicity of such sub frames can be configured through higher-layer signalling. Similar to an UE, RN may also decode PDCCH to locate the data transmitted from eNB to RN, which may consists of some control information for the RN and the data to be relayed to the UE. 
         [0065]    In sub frames when eNB transmits to RN, RN transmits control signal, along with RS in both control and data regions to the UE it serves using one radio transmitter, while simultaneously decode eNB to RN transmission in both control and data regions using a separate radio receiver. 
         [0066]    In such sub frames when eNB transmits to RN, UE served by RN will not be scheduled for receiving data, but it could still conduct channel measurement/estimation based on RS transmitted from RN in both control and data regions. 
         [0067]    No impact on Rel-8 standard with respect to UE behavior. Two radios are needed at RN for downlink, one for transmitting control signal, and RS throughout the sub frame, one for receiving transmission from the eNB. These two radios need good separations to reduce self-interference. 
         [0068]    The solutions are trying to solve the problem that LTE Rel-8 UE be supported by the relay system specifically and other UE generically. The disclosure teaches how to enhance the performance for LTE system with the help of relay while minimizing the impact to the LTE spec and Rel-8 terminal. Some solutions to introduce relay for Rel-8 UE have also been proposed as follows. 
       Solution 1: Introducing Blank Subframes in Rel-8 Spec 
       [0069]    Blank sub frames will be used for eNB and relay node (RN) transmission. UE won&#39;t decode these sub frames. Such blank sub frames could be signalled to UE through high layer signals like SIB. Such proposal would make the introduction of relays such as L2 relay to Rel-8 UE more easily in the future. 
         [0070]    However, it requires the change of Rel-8 Spec to accommodate such new blank sub frames. That could delay the completion of Rel-8 Spec. As nothing is transmitted on these blank sub frames include RS, the impact to UE in terms of channel measurement and channel estimation is also unknown at this stage. 
         [0071]    Introducing a new type of sub frame in Rel-8 spec similar as MBSFN sub frame, which is shown in  FIG. 8 . It uses up to two OFDM symbols as control region to transmit control signal to UE served directly by the eNB. 
         [0072]    The rest of the symbols in the sub frame forms the data region and are used to transmit PDSCH channels between eNB and RN, and between eNB and UEs directly served by eNB. Some dedicated RBs could be reserved to transmit control information between eNB and RN. Therefore, no need to design new control channel for eNB to RN transmission. 
         [0073]    Dedicated RS could be used for eNB to RN transmission. In this scenario, Common RS could still be transmitted from eNB for those UE directly served by eNBs to track the channel. Such new sub frames could be signalled by high layer signals using SIB, similar to that used for signalling MBSFN sub frames. 
         [0074]    At RN side, in such sub frames, RN transmits control signal and RS to the UE it serves in the control region. In the data region, RN listens to eNB and decodes the transmission from eNB to RN. No transmission from RN in this region. 
         [0075]    No UE served by the RN will be scheduled in such sub frames. UE could still conduct channel measurement and channel estimation based on RS in control region. Only one radio is needed at RN for downlink. In such new sub frames, it first transmits in control region and then receives in data region. 
         [0076]    Spec change is needed for Rel-8 to introduce such new type of sub frames in which UE does not expect to do decoding and channel measurement/estimation in data region. However, as such sub frame is quite similar to MBSFN sub frame. The impact of introducing such sub frame into Rel8 should be very small. This can be viewed as compromised solution between solutions 1 and 2 proposed herein. 
       Solution 2: Reusing MBSFN Subframes to Support Relay 
       [0077]    MBSFN sub frames could be used for transmission between eNB and RN. A new control signal could be defined to indicate that such sub frame is used for transmission between eNB and RN. New control channel and traffic channel could be defined for transmission between eNB and RN. 
         [0078]    As PDCCH are still transmitted in first several symbols in MBSFN sub frames, they could be used to serve UE directly served by eNBs. However, this solution has less impact to the current Rel-8 spec as compared with the solution I as no new type of sub frame is introduced here. 
         [0079]    For this alternative, there is no need to introduce a new type of sub frame in Rel-8 spec because RN is treated as a UE and be scheduled together with other UE served directly by eNB as shown in  FIG. 9 . No extra Ll control signal is needed for eNB to RN transmission. 
         [0080]    A dedicated RS could be used for eNB to RN transmission, and higher-layer signalling may be needed to inform RN the sub frames containing eNB to RN transmission. But that should not impact the Rel-8 UE. At RN side, in sub frames that contain transmission from eNB to RN. The RN transmits control signal, and RS in both control and data regions to the UE it serves. 
         [0081]    No UE is served by the RN will be scheduled in these sub frames. However, DE could still conduct channel measurement and channel estimation based on RS in both control and data regions. RN listens to eNB in the data region and decodes the transmission from eNB to RN. If dedicated RS is used for transmission from eNB to RN, the interference on channel estimation could be reduced. 
         [0082]    Two radios are needed at RN for downlink, one for receiving eNB to RN transmission in data region and one for transmitting control signal, along with RS in both control and data regions. Good separation is needed between these two radios to reduce self-interference. Sectorized or directional antennas could be used for each radio. This could add more implementation and deployment complexity for RN. 
         [0083]    The above-described embodiments of the present application are intended to be examples only. Those of skill in the art may effect alterations, modifications and variations to the particular embodiments without departing from the scope of the application. In the foregoing description, numerous details are set forth to provide an understanding of the present invention. However, it will be understood by those skilled in the art that the present invention may be practiced without these details. While the invention has been disclosed with respect to a limited number of embodiments, those skilled in the art will appreciate numerous modifications and variations therefrom. It is intended that the appended claims cover such modifications and variations as fall within the true spirit and scope of the invention.