Abstract:
A communication protocol divides the data payload ( 206 ) into segments ( 402, 404 ) with each of the payload segments ( 402, 404 ) providing a short synch word ( 406 ) which allows for an equalizer ( 104 ) to be retrained. This provides for improved performance during bursty interference conditions. The segmentation of the data also reduces the chances that the complete data in the payload has to be retransmitted due to bursty interference signals.

Description:
TECHNICAL FIELD  
         [0001]    This invention relates in general to the field of radio communications and more specifically to a communication protocol and method for providing short training sequences.  
         BACKGROUND  
         [0002]    In wireless communication protocols such as Bluetooth (including the yet to be finalized Bluetooth 2.0 standard) or the Institute of Electrical and Electronic Engineers (IEEE) 802.15.3 standard, the data packets that are transmitted are broken down into smaller segments for robustness against interference. Each segment is succeeded by a Cyclic Redundancy Checksum (CRC) at the end. No training is included in the beginning of each segment under the assumption that the channel may not change significantly when the interference occurs. This however ignores the effect of residual frequency error. Even with a residual frequency error of only +/−1 kHz (+/−0.4 parts-per-million accuracy) the phase drift during a 625 microsecond Bluetooth interference packet is +/−225 degrees. In the presence of decision feedback equalization, exact phase reference in the segments is required, which is not provided by current designs.  
           [0003]    Although a proposed solution to the above noted problem is the introduction of differential encoding, it however is not enough to overcome an interference signal when decision feedback equalization has to be performed at the receiver. In the absence of an equalizer, in the currently proposed Bluetooth 2.0 standard, performance degrades in the presence of a delay spread and has a coverage of less than 90% in a 10 meter radius around a Bluetooth 2.0 device. Additional coding in the system, such as Reed-Solomon coding, etc. does not help solve the above problem. A need thus exists for a solution to the above-mentioned problem. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0004]    The features of the present invention, which are believed to be novel, are set forth with particularity in the appended claims. The invention, may best be understood by reference to the following description, taken in conjunction with the accompanying drawings, in the several figures of which like reference numerals identify like elements, and in which:  
         [0005]    [0005]FIG. 1 is a block diagram of a receiver in accordance with the invention.  
         [0006]    [0006]FIG. 2 shows a packet structure for use in a wireless system in accordance with the invention.  
         [0007]    [0007]FIG. 3 illustrates a time-division-duplex (TDD) system using the packets of FIG. 2 in a Bluetooth system in accordance with the invention.  
         [0008]    [0008]FIG. 4 shows a payload segment including using a sync field in each of the payload segments in accordance with the invention.  
         [0009]    [0009]FIG. 5 shows a synchronization field as used in association with the packet in accordance with the present invention.  
         [0010]    [0010]FIG. 6 illustrates a communication system in accordance with the invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0011]    While the specification concludes with claims defining the features of the invention that are regarded as novel, it is believed that the invention will be better understood from a consideration of the following description in conjunction with the drawing figures.  
         [0012]    In FIG. 1 there is shown a receiver  100  in accordance with the invention. The receiver  100  in the preferred embodiment is designed to operate in a Bluetooth system. The receiver  100  includes a sync (synchronization) word acquisition and estimation block that is used to synchronize the receiver using the segmented payload sync words described further below. An equalizer  104  is used which uses the periodic synch words ( 406  in FIG. 4) for retraining. The equalizer  104  does away with the need of using diversity antenna systems in order to combat busty jamming causes by interfering signals. The equalizer is retrained through out a single packet (see  200  in FIG. 2) since the payload is broken up into multiple segments each having a sync word.  
         [0013]    Referring now to FIG. 2, there is shown a packet structure  200  in accordance with the invention. Packet  200  includes a Sync (synchronization) field  202 , an Automatic Repeat reQuest (ARQ) field  204  and a segmented payload (data) field  206 . The Sync field  202  starts with a preamble  208  that aids in the initial symbol timing acquisition, carrier frequency offset estimation and channel estimation by the receiver in a wireless system like a Bluetooth system. An illustration of a Sync field  202  is shown in FIG. 2. Points used in the preamble are (1+j) PN and PN=[−1 −1 −1 −1 1 −1 −1 1 −1 1 1 −1 −1 1 1 1 1 1 −1 −1 −1 1 1 −1 1 1 1 −1 1 −1 1]. The ARQ field  204  follows the header  210 , which contains link layer information. The header  210  and ARQ field  204  can either be repeated at a predetermined code rate (i.e., ⅕) or an alternate solution would be to repeat the header a predetermined number of times (i.e., 5 times). The header  210  provides such things as receive (RX) and transmit (TX) flow control information, modulation and coding information, etc. between a master and slave unit, information on the number of payload segments, etc. in a Bluetooth system. In the preferred embodiment the ARQ field  204  includes a bitmap field of between 1 and 63 bits, a Fill field of between 15 and 77 bits, and a CRC field of 32 bits. This provides for a total of 110 ARQ bits before coding.  
         [0014]    In FIG. 4, there is shown an illustration of the payload  206  section, which in order to reduce the effect of interferers, is segmented in multiple payload segments  402 ,  404 . Preferably in the payload, except for the sync word  406 , which employs BPSK modulation, any of the 6 modulation and coding schemes used in Bluetooth can be used. The modulation and coding is the same over the whole payload packet. The payload  206 , is divided into payload segments  402 ,  404 , which are each protected with a 32-bit cyclic Redundancy Code (CRC) independently. The Turbo coding is applied over each segment. The sync field  406  is not protected by CRC.  
         [0015]    The Sync field  406  is preferably 28 bits long, and is transmitted using antipodal Quadrature Phase Shift Keying (QPSK) modulation and is used for recovering from bursty interference. In the preferred embodiment, the sync field  406  is derived from PN  15  and is defined as follows: 
         (1+j)*[−1 −1 −1 1 1 1 1 −1 1 −1 1 1 −1 −1 1 −1 −1 −1 1 1 1 1 −1 1 −1 1 1 −1]. 
         [0016]    The sync field  406  found in the payload segments  402 ,  404  is preferably shorter in length than the sync field  202 . The segment also includes a logical link ID (L_CH) field  408  of 4 bits, a 2-bit Frag field  410 , which provides information for Logical Link Control and Adaptation Protocol (L2CAP) reassembly. A 10-bit Segment sequence Number field (SN)  412  for use in reassembly and ARQ, with the sequence numbers being independent for each logical link, including the control link. A 9-bit length field  414  informs the receiving unit of how many data bytes in the segment. A 1-bit flush field  416  provides the transmitter of the receiving device with information to indicate that the payload segments below the sequence number associated up to the currently received segment will not be transmitted. The flushing is done separately for all the logical links. A 4-bit field  418  is reserved for future features. The Data is carried in a Data field  420  that can range in size from 0-2080 bits. The final portion of the Segment  402  is a 2-bit tail field  422  that is used by the Turbo decoder in the receiver.  
         [0017]    When using high data rates of transmission, as those proposed in the second release of Bluetooth (e.g., above 4 Mega-bits-per-second (Mbps)) with high delay spreads using an equalizer  104  improves the gain. At higher data rates 10 Mbps and above, the equalizer  104  using the sync word  406  retraining combined with segmenting the data as proposed by the present invention provides for much improved coexistence in the face of severe bursty interference.  
         [0018]    In FIG. 3, there is shown a TDD timeline showing communications between a master and a slave using the packets according to the invention. Section  302  shows communications from a Bluetooth master to a slave, and in section  304  communications from a slave to a master is shown. In FIG. 6 there is shown a communication system such as a Bluetooth piconet  602 , which uses the segmented and synchronized payload of the present invention. The piconet  602  includes one master unit  604  and two slave units  606  and  608 . Using the present invention&#39;s protocol, the devices can reduce the overhead effects caused by interference.  
         [0019]    The present invention provides improved system performance in bursty interference conditions as when used in a Bluetooth system. The invention avoids large chunks of data from being lost even when faced with severe interference. Thereby reducing any throughput degradation caused by the interference. Rather than losing complete packets of data, using the payload segments  402  and  404  with include sync words  406  of the invention, helps to minimize degradation with minimal realization complexity. The periodic sync words  406  allow the equalizer  104  to be retrained with minimal protocol overhead, and vastly improving performance.  
         [0020]    While the preferred embodiments of the invention have been illustrated and described, it will be clear that the invention is not so limited. Numerous modifications, changes, variations, substitutions and equivalents will occur to those skilled in the art without departing from the spirit and scope of the present invention as defined by the appended claims. For example, although the present invention has been discussed in association with either a Bluetooth or IEEE 802.15.3 communication system, the present invention can be used in other communication systems that require the protection of data against interferers.