Abstract:
A method and a system for low-rate bidirectional communications for establishing and maintaining a unidirectional high-rate data link, is provided, wherein orthogonal frequency division multiplexing (OFDM) with spreading is utilized on the low-rate channel. Low-rate communications in an omni-directional mode achieve similar coverage as the high-rate communications in a beamforming mode.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to wireless communication and in particular, to low-rate channel communication in wireless HD communication systems. 
       BACKGROUND OF THE INVENTION 
       [0002]    With the proliferation of high quality video, an increasing number of electronic devices (e.g., consumer electronic devices) utilize high-definition (HD) video. Conventionally, most devices compress the HD video, which can be more than several Gbps (gigabits per second) in bandwidth, to a fraction of its size to allow for transmission between devices. However, with each compression and subsequent decompression of the video, some video information can be lost and the picture quality is degraded. 
         [0003]    The High-Definition Multimedia Interface (HDMI) specification defines an interface for uncompressed HD transmission between devices through the HDMI cables (the wired links). Existing wireless local area networks (WLANs) and similar technologies do not have the bandwidth needed to carry uncompressed HD video, such as providing an air interface to transmit uncompressed video over a 60 GHz bandwidth. Further, existing networks can suffer from interference issues when several devices are connected, leading to video signal degradation. 
         [0004]    There is therefore a need for a communication method and system that can support high-rate gigabit per second wireless communications, utilizing a forward link (or data link) for wireless HD communications. There is also a need for a dedicated low-rate control signaling link to establish and to maintain the high-rate forward data link. 
       BRIEF SUMMARY OF THE INVENTION 
       [0005]    The present invention provides a wireless communication method and a system implementing a low-rate control link (channel) for maintaining a high-rate forward link for wireless HD communications. The high-rate channel is utilized for transmission of uncompressed video or high-rate data in WLANs. Although the low-rate link is mainly for communicating control signals, it can also support other type of signals such as packets of data, audio, video, etc. 
         [0006]    In one embodiment, this involves utilizing a low-rate communication model implementing orthogonal frequency division multiplexing (OFDM) with code spreading, for communication over the low-rate control signaling links. In a preferred embodiment, the low-rate communication model includes a symmetric system design, which provides symmetric bidirectional communications between two wireless devices. During a low-rate control signaling session, both devices usually require that data throughput and communication coverage is at roughly the same level. The high-rate data link can be unidirectional, in that during a high-rate data transmission session, one device may function only as the transmitter or a signal source, and the other device may function only as the receiver or signal sink. 
         [0007]    These and other features, aspects and advantages of the present invention will become understood with reference to the following description, appended claims and accompanying figures. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  shows a functional block diagram of a wireless network that implements low-rate and high-rate channel communication, according to an embodiment of the present invention. 
           [0009]      FIG. 2  shows a functional block diagram of an example wireless communication station which implements a low-rate communication model for transmission of control signaling over a low-rate channel in a communication system, according to an embodiment of the present invention. 
           [0010]      FIG. 3  shows a diagrammatical example of a symbol repetition process implemented by the wireless communication station of  FIG. 2 . 
           [0011]      FIG. 4  shows an example flowchart of the steps of a low-rate communication model transmission process, according to an embodiment of the present invention. 
           [0012]      FIG. 5  shows a functional block diagram of an example receiver on the low-rate channel, according to an embodiment of the present invention. 
           [0013]      FIG. 6  shows an example flowchart of the steps of a low-rate communication receiving process, according to an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0014]    The present invention provides a method and a system for communication of control signals and data over low-rate wireless channels and support high-rate data communications, e.g., unidirectional uncompressed video communications, on the forward link. In one embodiment, this involves utilizing a low-rate communication model implementing OFDM with spreading for communication over low-rate wireless channels. 
         [0015]    An example implementation of the present invention in conjunction with a wireless HD (WiHD) communication system is now described.  FIG. 1  shows a functional block diagram of a wireless network  10  that implements uncompressed HD video transmission between WiHD devices such as a WiHD coordinator  12  and WiHD stations  14  (e.g., Dev 1  . . . DevN). 
         [0016]    The WiHD stations  14  utilize a low-rate wireless channel  16  (shown by dashed lines in  FIG. 1 ), and may use a high-rate channel  18  (shown by heavy solid lines in  FIG. 1 ), for communication therebetween. The WiHD coordinator  12  uses a low-rate channel  16  and a high-rate wireless channel  18  for communication with the stations  14 . Each station  14  uses the low-rate channel  16  for communications with other stations  14 . The high-rate channel  18  only supports unicast transmission over directional beams established by beamforming (i.e., the high-rate channel model). In one example, the high-rate channel  18  uses a multi-GB/s bandwidth to support uncompressed HD video transmission. Typically, the high-rate channel is maintained and established by exchange of control signaling over the low-rate channel. 
         [0017]    The low-rate channel  16  can support bi-directional transmission with smaller throughput requirement, e.g. with at most 20 Mbps throughput compared to several Gbps throughput requirement on the high-rate channel. The low-rate channel  16  is used to transmit control frames such as acknowledgement (ACK) frames. The low-rate channel can also be used to transmit low-rate data such as audio and/or compressed video. 
         [0018]    In this example, the WiHD coordinator  12  is a receiver of video information (hereinafter “receiver  12 ”) on the high-rate data channel and a WiHD station  14  is a sender of the video information (hereinafter “sender  14 ”). For example, the receiver  12  can comprise a sink of video and/or audio data, such as a HDTV set in a wireless local area network (WLAN). The sender  14  can be a source of uncompressed video or audio, such as a set-top box, a DVD player, etc., in the WLAN. 
         [0019]    Each of the devices  12  and  14  in  FIG. 1  is a type of wireless communication station with full transmission and reception capability on the low-rate channel. Therefore, a wireless communication station herein can function as a transmitter/sender, and/or a receiver/responder, on the low-rate channel. 
         [0020]      FIG. 2  shows an example functional block diagram of a wireless communication station  20  implementing a low-rate communication model according to the present invention. The example station  20  can work in both beamforming mode as well as in omni-directional mode. When transmitting control signals such as beacons, the station  20  can work in omni-directional transmission mode, providing low-rate signaling, in all directions. When transmitting audio signals or data signals, the station  20  can function in a beamforming mode, providing relatively high-rate data in certain directions only. An omni-directional low-rate transmission from the station  20  has the same coverage (in terms of coverage radius) as a high-rate beamformed transmission. 
         [0021]    The station  20  includes a scrambling module  22 , a forward error correction (FEC) encoding module  24 , an interleaving module  26 , a modulation module  28 , a symbol repetition module  30 , an IFFT (inverse Fast Fourier transform)/GI (guard interval) module  32  and a beamforming and RF module  34  for transmissions over a wireless channel to a receiver station. Although the station  20  includes the beamforming and RF module  34  for high-rate transmissions, the beamforming function of the module  34  is not required for the low-rate sessions according to the present invention. 
         [0022]    The scrambling module  22  scrambles incoming bits and the FEC module  24  provides FEC encoding. The encoded bits are then processed in the interleaving module  26  which reshuffles the encoded bits to improve diversity and robustness against excessive channel noise. The modulation module  28  then maps interleaved bits onto constellation symbols that can be transmitted. 
         [0023]    The low-rate communication model further provides OFDM modulation in the IFFT/GI module  32 , with spreading by the symbol repetition module  30 . The IFFT/GI module  32  applies IFFT and guard interval GI window insertion. The symbol repetition module  30  provides symbol repetition using M data sub-carriers and N-times repetition, to explore frequency diversity and spreading gain. This leads to improved physical layer performance that extends the coverage radius of the low-rate communications to be comparable to the coverage radius of the high-rate communications, which implements beamforming techniques. 
         [0024]    For high-rate communication over the high-rate channel, the beamforming and RF modulation module  34  performs beamforming steering of data using a beam steering vector. The module  34  then performs necessary radio frequency (RF) operations for wireless transmission. 
         [0025]      FIG. 3  shows a diagrammatical example of a symbol repetition process  30  implemented by the symbol repetition module  30 , using M=4 data sub-carriers and N=5 times repetition. Input data  32  to the symbol repetition module  30  includes data units (symbols) A, B, C, and D as represented by corresponding vertical bars in the upper part of  FIG. 3 . Each input data unit is repeated 5 times in the output data  34  from the symbol repetition module  30 , as shown in the lower part of  FIG. 3 . Each copy of the same data unit in the input data  32  is evenly distributed across the entire frequency band in the output data  34  for maximum frequency diversity gain. As such, the symbol repetition module  30  repeats each data unit multiple times over the frequency domain. The N-times repetition itself may provide up to 10×log 10(N) dB gain when the receiver provides an essentially optimal combination of the repeated information data. For example, when N=5, a gain of approximately 7 dB may be achieved, depending on the physical environment. 
         [0026]    In order to further extend the coverage and to improve the reliability of the low-rate communications, in addition to symbol repetition, a highly reliable modulation scheme (e.g., binary phase shift keying (BPSK)) for the modulation module  28 , as well as a highly reliable FEC for the FEC module  24 , may be specified, according to further embodiments of the present invention. 
         [0027]      FIG. 4  shows an example flowchart of the steps of a low-rate communication model process  40 , according to an embodiment of the present invention, including the steps
       Step  42 : The scrambling module  22  scrambles incoming bits.   Step  44 : The FEC module  24  provides FEC encoding.   Step  46 : The encoded bits are then processed in the interleaving module  26  which reshuffles the encoded bits to improve diversity and robustness against excessive channel noise and deep fading.   Step  48 : The modulation module  28  then maps the interleaved bits to constellation symbols that can be transmitted.   Step  50 : The symbol repetition module  30  provides symbol repetition using M data sub-carriers and N-times (multiple) repetition, to explore frequency diversity and spreading gain.   Step  52 : The IFFT/GI module  32  applies IFFT and GI window insertion.   Step  54 : The symbol repetition module  30  then performs RF conversion on the data for transmission over a low-rate wireless channel to a receiver.         
         [0035]    At the receiver front end, the received signal is first converted from a RF signal to a baseband signal and from analog to digital, to allow for faster digital processing.  FIG. 5  shows a functional block diagram of an example receiver  60  for the low-rate channel, according to an embodiment of the present invention. A receiver beamforming module  62  may be used for receiving on the low-rate channel. A remove GI &amp; FFT module  64  removes the guard interval in the baseband signal and performs FFT processing on data symbols. A repetition combiner  66  then combines the FFT-processed data symbols in the time domain, so that different repetitions of the same symbol are accumulated together to form a sufficient statistics for optimal processing. A demodulator  68  (e.g., BPSK demodulator) then demaps the combined symbols from constellation symbols to information bits. A deinterleaver  70  then deinterleaves the demapped information bits and a FEC decoder  72  then decodes the deinterleaved information bits. A data descrambler  74  then descrambles the decoded information bits to recover the original information data at the receiver. 
         [0036]      FIG. 6  shows an example process  80  for receiving data on a low-rate communication channel, according to an embodiment of the present invention, which includes the following steps:
       Step  82 : Optimally combine the signals from a low-rate channel received on different antennas by receive beamforming.   Step  84 : Remove Guard Intervals from the received symbols.   Step  86 : Perform FFT on the received symbols.   Step  88 : The FFT-processed data symbols are then combined in the time domain to derive sufficient statistics for optimum processing.   Step  90 : Demodulate the combined symbols by demapping them into information bits (either hard bits or soft bits).   Step  92 : Deinterleave the demapped bits to correct bit positions.   Step  94 : Decode the deinterleaved bits by FEC decoding.   Step  96 : Descramble the decoded bits from scrambling mask to recover the original information.         
         [0045]    Table 1 below provides an example of the design parameters for a bi-directional low-rate channel wireless communication model according to the present invention. 
         [0000]    
       
         
               
             
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 Design Parameters 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Channel bandwidth 
                 1 GHz 
               
               
                   
                 Number of subcarriers 
                 512 
               
               
                   
                 Subcarrier spacing 
                 1G/512 = 1.9531 MHz 
               
               
                   
                 FFT period 
                 512 ns 
               
               
                   
                 Guard interval 
                 128 ns 
               
               
                   
                 Symbol duration 
                 512 + 128 = 640 ns 
               
               
                   
                 Number of data carriers 
                 360 
               
               
                   
                 Number of DC carriers 
                 3 
               
               
                   
                 Number of pilot carriers 
                 18 
               
               
                   
                 Number of null carriers 
                 131 
               
               
                   
                 Modulation scheme 
                 BPSK 
               
               
                   
                 Coding (convolutional) 
                 ½ 
               
               
                   
                 Repetition 
                 9 
               
               
                   
                   
               
             
          
         
       
     
         [0046]    The parameters in Table 1 are examples, and may be adjusted in different implementation. Examples include slightly smaller bandwidth, larger root mean square (rms) delay spread (DS) which results in a larger GI, etc. The general idea of using repetition (with possibly different repetition patterns) remains the same. To support different data with different priority/importance, such as control signals, multiple spreading gains can also be applied. For example, high priority control packets may be repeated more often than control packets of lower priority. 
         [0047]    The cost of specifying such symbol repetition, BPSK modulation and FEC rate increase according to embodiments of the present invention, is additional bandwidth consumption for low-rate communication model. However, such specifications enable same range coverage as provided by beamforming on the high-rate channel. 
         [0048]    As is known to those skilled in the art, the aforementioned example architectures described above, according to the present invention, can be implemented in many ways, such as program instructions for execution by a processor, as logic circuits, as an application specific integrated circuit, as firmware, etc. 
         [0049]    The present invention has been described in considerable detail with reference to certain preferred versions thereof; however, other versions are possible. Therefore, the spirit and scope of the appended claims should not be limited to the description of the preferred versions contained herein.