Patent Publication Number: US-2010111229-A1

Title: Method and apparatus of generating packet preamble

Description:
BACKGROUND OF THE INVENTION 
     A personal wireless area network (WPAN) is a network used for communication among computing devices (for example, personal devices such as telephones and personal digital assistants) close to one person (the devices may or may not belong to that person). The reach of a WPAN may be a few meters. WPANs may be used for interpersonal communication among personal devices themselves, or for connecting via an uplink to a higher level network, for example the Internet. 
     The IEEE 802.15.3 Task Group 3c (TG3c) was formed in March 2005. TG3c is developing a millimeter-wave (mmWave) based alternative physical layer (PHY) for the existing 802.15.3 Wireless Personal Area Network (WPAN) Standard e.g., IEEE 802.15.3-2003. This mmWave WPAN may operate in a band including the 57-64 GHz unlicensed band defined by FCC 47 CFR 15.255 and other regulatory bodies and may be referred to as “600 Hz”. The millimeter-wave WPAN may allow very high data rate (e.g., over 2 Gigabit per second (Gbps)) applications such as high speed Internet access, streaming content download (e.g., video on demand, high-definition television (HDTV), home theater, etc.), real time streaming and wireless data bus for cable replacement. 
     However, an mmWave communication link is significantly less robust than links operating at lower frequencies (e.g. 2.40 Hz and 5 GHz bands) due to the Friis transmission equation, oxygen absorption and high attenuation through obstructions. In addition, the mmWave communication link may use a directional antenna and/or antennas array to increase the communication range. The use of a directional antenna makes a link very sensitive to mobility. For example, a slight change in the orientation of the device or the movement of a nearby object and/or person may disrupt the link. 
     60 GHz communication standards tend to have both orthogonal frequency-division multiplexing (OFDM) and single carrier (SC) physical layers. In some standards only one of the OFDM or the SC is mandatory, and in some other standards neither of OFDM and SC is mandatory. In systems having both OFDM and SC most of the time different preambles are used for each type of modulations. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The subject matter regarded as the invention is particularly pointed out and distinctly claimed in the concluding portion of the specification. The invention, however, both as to organization and method of operation, together with objects, features and advantages thereof may best be understood by reference to the following detailed description when read with the accompanied drawings in which; 
         FIG. 1  is a schematic illustration of a wireless communication network according to exemplary embodiments of the present invention; 
         FIG. 2  is a schematic illustration of a packet preamble according to exemplary embodiment of the invention; and 
         FIG. 3  is a block diagram of a wireless communication device according to some embodiments of the present invention; 
         FIG. 4  is a schematic illustration of flowchart of a method of transmitting a packet preamble according to some exemplary embodiments of the invention; and 
         FIG. 5  is a block diagram of a system according to embodiments of the invention. 
     
    
    
     It will be appreciated that for simplicity and clarity of illustration, elements shown in the figures have not necessarily been drawn to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elements for clarity. Further, where considered appropriate, reference numerals may be repeated among the figures to indicate corresponding or analogous elements. 
     DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION 
     In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However it will be understood by those of ordinary skill in the art that the present invention may be practiced without these specific details. In other instances, well-known methods, procedures, components and circuits have not been described in detail so as not to obscure the present invention. 
     Some portions of the detailed description, which follow, are presented in terms of algorithms and symbolic representations of operations on data bits or binary digital signals within a computer memory. These algorithmic descriptions and representations may be the techniques used by those skilled in the data processing arts to convey the substance of their work to others skilled in the art. 
     Unless specifically stated otherwise, as apparent from the following discussions, it is appreciated that throughout the specification discussions utilizing terms such as “processing,” “computing,” “calculating,” “determining,” or the like, refer to the action and/or processes of a computer or computing system, or similar electronic computing device, that manipulates and/or transforms data represented as physical, such as electronic, quantities within the computing system&#39;s registers and/or memories into other data similarly represented as physical quantities within the computing system&#39;s memories, registers or other such information storage, or transmission devices. The terms “a” or “an”, as used herein, are defined as one, or more then one. The term plurality, as used herein, is defined as two, or more than two. The term another, as used herein is defined as at least a second or more. The terms including and/or having, as used herein, are defined as, but not limited to, comprising. The term coupled as used herein, is defined as operably connected in any desired form for example, mechanically, electronically, digitally, directly, by software, by hardware and the like. 
     It should be understood that the present invention may be used in a variety of applications. Although the present invention is not limited in this respect, the circuits and techniques disclosed herein may be used in many apparatuses such as stations of a radio system. Stations intended to be included within the scope of the present invention include, by way of example only, wireless local area network (WLAN) stations, wireless personal network (WPAN), and the like. 
     Types of WPAN stations intended to be within the scope of the present invention include, although are not limited to, mobile stations, access points, stations for receiving and transmitting spread spectrum signals such as, for example, Frequency Hopping Spread Spectrum (FHSS), Direct Sequence Spread Spectrum (DSSS), Complementary Code Keying (CCK), Orthogonal Frequency-Division Multiplexing (ODM) and the like. 
     Turning first to  FIG. 1 , a schematic illustration of a wireless communication network  100 , according to exemplary embodiments of the invention is shown. Wireless communication network  100  may include for example, a WPAN/WLAN. For example, wireless communication network  100  may operate according to the standard developed by the IEEE 802 802.11 Task Group ad (TGad). TGad is developing an Enhancements for Very High Throughput in the 60 GHz Band for WLAN 
     According to this exemplary embodiment of the invention, wireless communication network  100 , for example a WPAN, may include stations  120 ,  130  and  140 . Stations  120 ,  130   140  are depicted as devices (DEVs) e.g., DEV 1 , DEV 2  and DEV 3 , respectively. Although the scope of the present invention is not limited in this respect, stations  120 ,  130  and  140  may include a camera, a mouse, an earphone, a speaker, a display, a mobile personal device or the like. Furthermore, each of DEV 1 , DEV 2  and DEV 3  may serve at and/or be a part of another WPAN, if desired. 
     According to this exemplary embodiment of the invention, DEV 1   130  and DEV 2   120  may transmit and receive OFDM signals and/or single carrier (SC) signals via a direct link  150 , if desired. According to some embodiments of the invention a direct link may be a wireless link between two devices without the intervention of another device and/or base station and/or network controller or the like. For example, DEV 3   140  may transmit a packet preamble which includes plurality of sequences via a direct link  160  to DEV 1   160 . DEV 1   130  may transmit the preamble packet to DEV 2   120  via a direct link  150 , if desired. 
     According to at least one embodiment of the invention, the same preamble packet may be transmitted and detected by both SC devices and multiple carrier devices (e.g., OFDM), although the scope of the present invention is not limited in this respect. 
     Turning to  FIG. 2 , a schematic illustration of a packet preamble  200  according to exemplary embodiment of the invention is shown. According to embodiments of the invention packet preamble  200  may be used for both multiple carrier scheme transmissions SC scheme transmissions for example, OFDM and for SC transmissions, if desired. According to one example embodiment, packet preamble  200  may include a detection field  210 , a synchronization field (SFD)  220 , and a channel estimation field  230 . 
     According, to some exemplary embodiments of the invention, the preamble portion of the packet  200  may be used for, for example, automatic gain control (AGC), signal detection, frequency offset estimation, synchronization and channel estimation. The detection. AGC and frequency offset estimation (FOE) may be done on periodic sequences. According to some exemplary embodiments, packet  200  may be based on π/2-BPSK sequences that may be used by SC receivers. 
     For example, detection field  210  may be made up of a repetition of a sequence with good cross correlation properties. According to embodiments of the invention, a sequence with a desired cross correlation property may be defined as a sequence whose cross correlation (either periodic or a-periodic) with its sequence having a large peak and many zeros around the peak. Non-limiting examples for sequences with the desired correlation property are pseudorandom number (PN) sequences, complementary (Golay) sequences, barker codes, a Constant Amplitude Zero AutoCorrelation (CAZAC) sequences and the like. SFD  220  may include the sequence used for the detection and selection of the transmitted modulation. For example, an inversion of the sequence used for detection or modulation of group of these sequences. 
     In some other embodiments of the invention SFD  220  may be omitted and its tasks may be performed by channel estimation field  230 . Channel estimation field  230  may include sequences including either a long PN sequence or a pair of complementary (Golay) sequences, although the scope of the present invention is not limited in this respect. 
     According to exemplary embodiments of the invention, preamble packet  200  of signal sequences may be transmitted to both a single carrier wireless device and a multiple carrier wireless device. According to one example, a preamble of a packet may include a first sequence for detecting a signal (e.g., sequences of detection field  210 ), a second sequence for detecting and selecting a transmitter modulation (e.g. sequences of SFD  220 ) and a third sequence for estimating a channel (e.g., sequences of channel estimation field  230 ). The first, second mid third sequences may be modulated by 2/π Binary Phase Shift Keying (BPSK) modulation, if desired. It should be understood that other modulation schemes may be used with some other embodiments of the invention. 
     According to one exemplary embodiment of the invention, preamble packet  200  may be transmitted by an SC transmitter. In this case, the first sequence, the second sequence and the third sequence may be filtered by a pulse shaping filter. In other embodiments of the invention, preamble packet  200  may be transmitted by a multiple carrier transmitter for example, an OFDM transmitter. In this case the first, second and third sequences may be resampled by a filter known to the receiver as for example described in the following equations: 
     Firstly the first, second and third sequences may be resampled resample according to the following equation: 
     
       
         
           
             
               
                 
                   
                     
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     Thirdly, decimation may be performed on the first, second and third sequences by a factor of 2, taking every second sample as depicted in the following equation: 
     
       
         
           
             
               
                 
                   
                     
                       
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     In digital signal processing art the term “decimation” and its derivative may be defined as a technique for reducing the number of samples in a discrete-time signal and/or sequence. Decimation may include low-pass anti-aliasing filtering and downsampling of the signal, although the scope of the present invention is not limited in this respect. 
     According to this example, it is assumed that the OFDM (nominal) sampling rate is 1½, the chip rate of the SC for providing guard bands around the OFDM data subcarriers. The above is also applicable for other ratios between the OFDM sample rate and SC chip rate. In the receiver, detection can be done by a combination of autocorrelation and cross correlation. Efficient algorithms for correlation exist for m-sequences (PN-sequences) and complementary (Golay) sequences, if desired. 
     Although the scope of the present invention is not limited in this respect, receiving said preamble packet may be done either in a single carrier receiving scheme or in a multiple carrier receiving scheme, if desired. A receiver able to operate in both SC and OFDM may receive the preamble packet and decode the first, second and third sequences. 
     Turning to  FIG. 3  a block diagram of a wireless communication device according to some embodiments of the present invention is shown. According to this exemplary embodiment, wireless communication device  300  may include a sequence generator  310 , a digital signal processor (DSP)  320 , a shape filter  330 , a modulator  340 , a receiver (RX)  360 , a transmitter (TX)  370  and a plurality of antennas  380 ,  390 . 
     According to exemplary embodiment of the invention, RX  360  and TX  370  may be a part of Multiple-Input-Multiple-Output (MIMO) transmitters-receivers system (not shown). According to this example RX  360  and/or TX  370  may include two or more receivers and two or more transmitters, respectively and antennas  380  and  390  may include plurality of antennas and may be operably coupled to the MIMO transmitters-receivers systems, although the scope of the present invention is not limited in this respect. According to some exemplary embodiments of the invention antennas  380  and/or  390  may include one or more antennas. For example, antennas  380  and/or  390  may include directional antennas, an antenna array, a dipole antenna or the like. 
     According to some embodiments of the invention, wireless communication device  300  may operate in a millimeter-wave WPAN as both, SC device and/or OFDM device, if desired. For example, wireless communication device may operate as follows. Sequence generator  310  may generate signal sequences for a preamble packet, for example preamble packet  200 . Sequence generator  310  may generate the first sequence from repetition of a cross correlated sequence for example, pseudorandom number (PN) sequences, Golay sequences, barker codes and the like. Sequence generator  310  may generate the second sequence by an inversion of the first sequence and may generate the third sequence from a pair of complementary Golay sequences, if desired. Modulator  340  may modulate the first, second and third sequences by 2/π Binary Phase Shift Keying (BPSK) modulation, if desired 
     TX  370  may transmit the same preamble packet of signal sequences to both a single carrier wireless device and/or a multiple carrier wireless device. The preamble packet e.g., preamble packet  200 , may include detection field. SFD field and a channel estimation field. The detection field may include the first sequence which may be used by RX  360  for detecting a signal or for a frequency offset estimation. The SFD field may include the second sequence that may be used by RX  360  for detecting and selecting a transmitter modulation, if desired. The channel estimation field may include the third sequence which may be used by RX  360  for estimating the channel, although the scope of the present invention is not limited to this example. 
     According to one exemplary embodiment of the invention, a preamble packet which is intended to be transmitted to an SC device may be filtered by shape filter  330 . For example, shape filter  330  may filter an at least one of the first sequence, the second sequence and the third sequence. Modulator  340  may modulate the preamble packet which filtered by shape filter  320  able to modulate the preamble packet according to a single carrier modulation scheme. 
     According to one other exemplary embodiment of the invention, a preamble packet is which intended to be transmitted to OFDM device may be processed by DSP  320 . For example, DSP  320  may use a three step process, if desired. The first step may be processing the first, second and third sequences of the preamble packet by adding two zeros between two samples and interpolating the first, second and third sequences by three. The second step may be filtering the first, second and third sequences by a decimation filter and the third step may be sampling the first, second and third sequences every one second and decimating the samples by two. Modulator  340  may modulate the preamble packet which is processed by DSP  320  according to a multiple carriers modulation scheme although the scope of this present invention is not limited in this respect. 
     Furthermore, the preamble packet may be spreaded by spreader  350  and may be transmitted by TX  370  and antenna  390 , if desired. In the receiving device, antenna  380  and RX  360  may receive the sequences of the preamble packet either by a single carrier receiving scheme or by a multiple carriers receiving scheme. Decoder  340  may decode the first, second and third sequences, if desired. After decoding the sequences, synchronization may be done by correlation. Channel estimation may be done either by correlation in the time domain or in the frequency domain by dividing the transmitted sequence frequency response. It should be understood that the same preamble packet is used for both SC and OFDM and the preamble may be defined by resampling the π/2 BPSK sequences using a filter known to the receiver. 
     Turning to  FIG. 4  a schematic illustration of flowchart of a method of transmitting a packet preamble according to some exemplary embodiments of the invention is shovel. Although the scope of the present invention is not limited to this respect the method may start by generating fields of preamble sequences that suitable to be received by both a signal carrier receiver and a multiple carrier receiver e.g., an OFDM receiver and/or by a device having both a SC receiver and an OFDM receiver. 
     According to this example, the method may start by generating a first sequence for detecting a signal (text block  400 ), generating a second sequence for estimating a channel (text box  410 ) and generating a third sequence for detecting and selecting a transmitter modulation scheme (text block  420 ). 
     According to this exemplary embodiment, the first sequence may be generated by repetition of a sequence having a desired cross correlation properties for example, pseudo random sequences Baker codes and the like. The third sequence may inversion of the first sequence, although the scope of the present invention is not limited to this example. 
     The method may continue with modulating the first, second and third sequences by for example π/2 Binary Phase Shift Keying (BPSK) modulation (text block  440 ) and filtering an at least one of the first sequence, the second sequence and the third sequence by a pulse shaping filter (text block  440 ). 
     In the case that the packet preamble is intendment to be received by a multiple carrier receiver, the packet preamble may be further processed by adding for example two zeros between two samples, filtering the first and second sequences by a decimation filter and sampling the first and second sequences every second and decimating the samples by two, if desired (text block  450 ). The packet preamble of signal sequences may be transmit to both a single carrier wireless device and a multiple carrier wireless device (text block  460 ). The packet preamble may be received by either in a single carrier receiving scheme or in a multiple carriers receiving scheme (text block  470 ). The first, second and third sequences may be decoded at the receiver, although the scope of the present invention is not limited to this example. 
     Turning to  FIG. 5  a block diagram, of a system article according to embodiments of the invention is shown. Although the embodiments of the present invention are not limited to this respect, system  500  may include a computer  510  and storage medium such as a memory  520 . According to exemplary embodiments of the invention system  500  may include a wireless communication device, a transmitter, a receiver and/or the like. Computer  510  may include a DSP, a processor, a controller or the like that operably coupled to memory  520 . Memory  520  may be a processor readable medium, and/or a computer or processor storage medium, such as for example a memory, a disk drive, or a USB flash memory, encoding, including or storing instructions. 
     According to embodiments of the invention computer  510  may execute instructions store in memory  520 . The instructions when executed may carry out methods disclosed herein. 
     While certain features of the invention have been illustrated and described herein, many modifications, substitutions changes, and equivalents will now occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.