Abstract:
A wireless data transmitter including: a data modulator adapted to modulate a data signal based on a frequency signal; and at least one antenna adapted to wirelessly transmit the modulated data signal and the frequency signal independently.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the priority benefit of French patent application number 11/54998, filed on Jun. 8, 2011, entitled WIRELESS TRANSMISSION SYSTEM, which is hereby incorporated by reference to the maximum extent allowable by law. 
       BACKGROUND 
       [0002]    1. Technical Field 
         [0003]    The present invention relates to the field of wireless data transmission, and in particular to wireless data transmission by modulation based on a carrier frequency signal. 
         [0004]    2. Discussion of the Related Art 
         [0005]      FIG. 1  illustrates a wireless data transmission system  100  comprising a transmission side  102  and a reception side  104 . This topology is known as a homodyne or direct conversion technique. On the transmission side  102 , a local oscillator  106  (LO), usually based on a phase locked loop (PLL)  108 , generates a frequency signal f LO . The frequency signal f LO  is provided to a data modulator  110  (IQ MOD), which receives a data signal comprising I (in phase) and Q (in quadrature) components. Data modulator  110  modulates the data signal based on the frequency signal f LO . The output modulated signal S(t) is then transmitted via an antenna  112 . 
         [0006]    On the receive side  104 , a receive antenna  114  receives the modulated data signal S′(t), and provides it to a data demodulator  116  (IQ DEMOD). Demodulator  116  demodulates the data signal based on a frequency signal f′ LO  provided by local oscillator  118 , which mainly comprises a carrier recovery block. The purpose of the carrier recovery block is to synchronize the frequency signal f′ LO  with the carrier frequency of the signal S′(t) in both frequency and phase. For this, a first few data blocks of the data signals I′ and Q′, estimated based on the receive signal S′(t), are provided to an analog-to-digital converter  120  (ADC), which generates digitalized data signals I′ and Q′, in turn provided to a digital processing block  122 . Block  122  for example corresponds to a Costa loop, and outputs a correction signal on a line  124 , which is proportional to the frequency/phase difference between the signals f′ LO  and S′(t), in a similar manner to a frequency/phase locked loop. The first few blocks of the I′ and Q′ data cannot generally be correctly demodulated and only form a preamble used for synchronization. 
         [0007]    A problem with the transmission system  100  of  FIG. 1  is that a local oscillator is needed on both the transmission and the reception sides, and in order to ensure successful data transmission, the frequency signals f LO  and f′ LO  have to be well synchronized. At relatively high frequencies this is difficult, as the phase noise and frequency instability of the frequency signal f LO , increase by a squared relation to its frequency. Furthermore, the phase locked loop  108  on the transmission side, and the ADC  120  and digital decoding circuitry  122  on the to reception side add complexity, energy consumption and cost to the transmission system. 
       SUMMARY 
       [0008]    According to one embodiment, there is provided a wireless data transmitter comprising: a local oscillator adapted to generate an initial frequency signal; a signal modulator adapted to generate a frequency signal by modulating said initial frequency signal based on a code signal; a data modulator adapted to modulate a data signal based on said frequency signal; and at least one antenna adapted to wirelessly transmit said modulated data signal and said frequency signal independently. 
         [0009]    According to one embodiment, said data signal comprises I and Q quadrature components. 
         [0010]    According to another embodiment, said at least one antenna is adapted to transmit said modulated signal using a first type of polarization, and said frequency signal using a second type of polarization different to said first polarization. 
         [0011]    According to another embodiment, said first type of polarization is one of horizontal and vertical polarization, and said second type of polarization is the other of horizontal and vertical polarization. 
         [0012]    According to another embodiment, said first type of polarization is one of clockwise and anti-clockwise circular polarization, and said second type of polarization is the other of clockwise and anti-clockwise circular polarization. 
         [0013]    According to another embodiment, said at least one antenna is formed on a single antenna patch. 
         [0014]    According to another embodiment, said at least one antenna comprises a first antenna adapted to wirelessly transmit said modulated data signal and a second antenna adapted to wirelessly transmit said frequency signal. 
         [0015]    According to another embodiment, there is provided a wireless data receiver, comprising at least one antenna adapted to receive a modulated data signal and a frequency signal, the frequency signal corresponding to an initial frequency signal modulated based on a code signal; and a data demodulator adapted to receive said modulated data signal and said frequency signal from said at least one antenna, and to demodulate said data signal based on said frequency signal. 
         [0016]    According to another embodiment, there is provided a wireless data transmission system comprising the above receiver and data transmitter. 
         [0017]    According to another embodiment, there is provided an electronic device comprising first and second chips adapted to communicate with each other via the above data transmission system. 
         [0018]    According to another embodiment, there is provided a method of wireless data transmission comprising: generating by a local oscillator an initial frequency signal; generating by a signal modulator a frequency signal by modulating said initial frequency signal based on a code signal; modulating by a data modulator a data signal based on said frequency signal; and wirelessly transmitting said modulated data signal and said frequency signal via at least one antenna. 
         [0019]    According to another embodiment, the method further comprises, prior to modulating said data signal, generating by a local oscillator an initial frequency signal and generating by a signal modulator said frequency signal by modulating a code signal based on said initial frequency signal. 
         [0020]    According to another embodiment, there is provided a method of wireless data reception, comprising: receiving, via at least one antenna, a modulated data signal and a frequency signal, the frequency signal corresponding to an initial frequency signal modulated based on a code signal; and demodulating said modulated data signal based on said frequency signal. 
         [0021]    According to another embodiment, said at least one antenna comprises a first antenna adapted to receive said modulated data signal and a second antenna adapted to receive said frequency signal. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]    The foregoing and other purposes, features, aspects and advantages of the embodiments of the present disclosure will become apparent from the following detailed description of embodiments, given by way of illustration and not limitation with reference to the accompanying drawings, in which: 
           [0023]      FIG. 1  (described above) illustrates an embodiment of a data transmission system; 
           [0024]      FIG. 2  illustrates a data transmission system according to one embodiment; 
           [0025]      FIG. 3  illustrates a data transmission system according to another embodiment; 
           [0026]      FIG. 4  illustrates a data transmission system according to another embodiment; 
           [0027]      FIG. 5  illustrates a data transmission system according to another embodiment; 
           [0028]      FIG. 6  illustrates a data transmission system according to another embodiment; 
           [0029]      FIG. 7  illustrates an electronic device comprising transmission systems according to another embodiment; and 
           [0030]      FIGS. 8A to 8C  are graphs illustrating the frequency spectrums of transmitted frequency and data signals according to some embodiments. 
       
    
    
     DETAILED DESCRIPTION 
       [0031]      FIG. 2  illustrates a wireless data transmission system  200  comprising a transmission side  202  and a reception side  204 . 
         [0032]    The transmission side  202  comprises a local oscillator  206 . However, unlike the transmission system  100  of  FIG. 1 , there is no phase locked loop on the transmission side, the local oscillator generating a frequency signal f LO  that may vary to some extent in time. The local oscillator  206  is for example implemented by a free-running VCO (voltage controlled oscillator), and for example does not use a quartz oscillator or other type of high precision oscillator or time reference. 
         [0033]    The frequency signal f LO  is provided to a data modulator  208 . Modulator  208  modulates a data signal, which comprises I and Q components, based on the frequency signal f LO , to provide a modulated data signal S(t), which is transmitted via an antenna  210 . Furthermore, the frequency signal f LO  is provided from the local oscillator  206  to a second antenna  212 , for wireless transmission separately from the transmission of the modulated data signal. 
         [0034]    On the reception side  204 , the modulated data signal S′(t) is received via an antenna  214 , and provided to a data demodulator  216 . In parallel, an antenna  218  receives the frequency signal f LO , which is also provided to the data demodulator  216 . Based on the frequency signal f LO , the modulated data signal S′(t) is demodulated to provide output data signals I and Q. Thus, for example, no local oscillator is present on the reception side. Furthermore, given that the same frequency signal f LO  is used to modulate and demodulate the data signal, the ADC  120  and digital circuitry  122  of  FIG. 1  can be omitted. 
         [0035]    The frequency signal f LO  is for example in the range of 1 to several hundred GHz, or even to several terahertz. 
         [0036]    The antenna pairs  212 / 218  and  210 / 214  use different forms of transmission, which enables their transmission paths to be relatively independent from each other. There is for example an attenuation of at least 3 dB between the wireless transmission path provided from antenna  210  to antenna  214  and the wireless transmission path that may be present between antenna  210  and antenna  218 . Similarly, there is for example an attenuation of at least 3 dB between the wireless transmission path provided from antenna  212  to antenna  218  and the wireless transmission path that may be present between antenna  212  and antenna  214 . In some cases, an attenuation of 20 dB between these transmission paths is provided, which ensures a very limited interference. 
         [0037]    Independence between the transmission paths can be achieved for example by transmitting the signals via each antenna using different polarizations. For example, the communication via antennas  210 ,  214  uses horizontal polarization, and the communication via antennas  212 ,  218  uses vertical polarization, or vice versa. Alternatively, the communication via antennas  210  and  214  uses clockwise circular polarization, and the communication via antennas  212 ,  218  uses counter-clockwise circular polarization, or vice versa. Alternatively, selectivity between the transmission channels could be achieved by a physical separation of the antennas, to limit any cross-coupling, and/or by directional control of the transmission from each antenna, in the case that the respective orientations of the transmission and reception sides are fixed. 
         [0038]      FIG. 3  illustrates the data transmission system  200  of  FIG. 2  in more detail according to one example. Like features have been labelled with like reference numerals and will not be described again in detail. 
         [0039]    In the example of  FIG. 3 , the data modulator  208  comprises a mixer  302 , which receives the frequency signal f LO  from the local oscillator  206 . Mixer  302  multiplies the I component of the data signal by the frequency signal to generate a component S I (t) of the modulated data signal S(t). The frequency signal f LO  is also provided to a mixer  304  via a quarter-period phase shifter  306 . Mixer  304  multiplies the Q component of the data signal by the shifted frequency signal, to generate a component S Q (t) of the modulated data signal S(t). The signals S I (t) and S Q (t) are summed to form the modulated data signal S(t) for transmission on the antenna  210 . 
         [0040]    On the reception side  204 , the data demodulator  216  comprises a mixer  308 , which multiplies the modulated data signal S′(t) received via antenna  214  with the frequency signal f LO  received via antenna  218 , to provide the I component of the data signal. The modulated data signal S′(t) received via antenna  214  is also provided to a mixer  310 . Mixer  310  multiples this signal by the frequency signal f LO  after a quarter-period phase shift has been applied by phase shifter  312 , to provide the Q component of the data signal. 
         [0041]      FIG. 4  illustrates a data transmission system  400 , which is similar to the transmission system  200  of  FIG. 2 , and again like features are labelled with like reference numerals and will not be described again in detail. 
         [0042]    However, in  FIG. 4 , the antennas on the transmission and reception sides  402 ,  404  are implemented by antenna patches  406  and  408  respectively. Each of the patches  406 ,  408  comprises a built-in horizontal antenna  406 A,  408 A and a built-in vertical antenna  406 B,  408 B respectively. Alternatively, rather than comprising separate antennas, the antenna patches  406 ,  408  could each comprise a single element that forms both antennas. 
         [0043]    On the transmission side  402 , the modulated data signal S(t) is provided to the horizontal antenna  406 A of patch  406  via an amplifier  410 , while the frequency signal f LO  is provided to the vertical antenna  406 B of the patch  406  via an amplifier  412 . 
         [0044]    Similarly, on the reception side  404 , the modulated data signal S′(t) is provided to the data demodulator  216  from the horizontal antenna  408 A of patch  408  and via an amplifier  414 , while the frequency signal f LO  is provided to the data demodulator  216  from the vertical antenna  408 B and via an amplifier  416 . 
         [0045]    In alternative embodiments, the modulated data signal could be transmitted and received via the vertical antennas of patches  406 ,  408 , and the frequency signal could be transmitted and received via the horizontal antennas of patches  406 ,  408 . 
         [0046]      FIG. 5  illustrates another embodiment of a data transmission system  500 , which is similar to the system  200  of  FIG. 2 , and like features are labelled with like reference numerals and will not be described again in detail. 
         [0047]    With respect the system  200  of  FIG. 3 , the system  500  additionally comprises, on the transmission side  502 , a second local oscillator  506  and a pair of mixers  508 ,  510 , and on the reception side, a second local oscillator  512  and a pair of mixers  514  and  516 . In  FIG. 5 , the frequency signal generated by local oscillator  206  on the transmission side and received by the to demodulator  216  on the reception side is labelled f LO1 . 
         [0048]    On the transmission side, oscillator  506  generates a frequency signal f L02 , which is provided to the mixers  508  and  510 . Mixer  508  multiplies the signal f LO2  by the signal f LO1  generated by local oscillator  206 , and provides the output to the antenna  212 . Mixer  510  multiplies the signal f LO2  by the output of the modulator  208 , to provide the signal S(t) for transmission via antenna  210 . 
         [0049]    On the reception side  504 , oscillator  512  generates a frequency signal f LO2 ′, which is provided to mixers  514  and  516 . Mixer  514  multiples signal f L02 ′ by the signal received via antenna  218 , to retrieve the frequency signal f L01 , which is provided to demodulator  216 . Mixer  516  multiples the signal f L02 ′ by the signal S′(t) received via antenna  214  to retrieve the modulated data signal, which is also provided to the demodulator  216 . 
         [0050]    The mixers  508 ,  510  provide an additional up conversion of the frequency and data signals prior to transmission, while the mixers  514  and  516  provide corresponding down conversion on the reception side. This allows a greater transmission distance between the reception and transmission sides. The local oscillators  506  and  512  may be selected to provide frequency signals of the same frequency. However, they are, for example, implemented by a free-running VCO (voltage controlled oscillator), and can be permitted to have relatively poor frequency stability and/or noise characteristics, meaning that the frequencies of the signals may vary to some extent over time. 
         [0051]      FIG. 6  illustrates a further embodiment of a data transmission system  600 , which is again similar to the system  200  of  FIG. 2 , and like features have been labelled with like reference numerals and will not be described again in detail. 
         [0052]    The transmission system  600  comprises a transmission side  602  and a reception side  604 . The transmission side  602  comprises a mixer  606 , which receives a code signal C, and multiplies this signal by frequency signal f LO  from the local oscillator  206  to generate a frequency signal f C . The code signal C for example comprises a random code, that enables the frequency spectrum of the carrier frequency signal to be spread out. For example, the code signal modulates the phase of the frequency signal f LO  provided by the local oscillator  206 . The code signal is for example a random signal synchronized with the data signals I and Q and having the same data rate as the signals I and Q. The data rate of the code signal C is for example substantially equal to that of the data signal I,Q, such that the modulation speed of the to frequency signal f C  is for example substantially equal to that of the modulated data signal. 
         [0053]    The modified frequency signal f C  is then used by the data modulator  202  to modulate the data signals I and Q, and provide the modulated signal S(t). Furthermore, it is the modified frequency signal f C  that is transmitted via the antenna  212 . 
         [0054]    On the reception side  604 , the modified frequency signal f C  is received via antenna  218  and is used by the data demodulator  216  to demodulate the received modulated data signal S′(t). 
         [0055]    An advantage of the embodiment of  FIG. 6  is that the modified frequency signal f C  has an energy that is dispersed across a relatively broad frequency bandwidth. Advantageously, the power spectral density of the resulting carrier frequency signal is then similar to that of the modulated data signal S(t), as will now be explained with reference to the graphs of  FIGS. 8A to 8C . 
         [0056]      FIG. 8A  illustrates the frequency spectrum of the frequency signal f LO  as transmitted according to the embodiment of  FIG. 2 , which has a peak at the frequency f a  of the frequency signal f LO . 
         [0057]      FIG. 8B  illustrates the frequency spectrum of the data signal, having a relatively broad spectrum, based on the data. 
         [0058]      FIG. 8C  illustrates the frequency spectrum of the frequency signal f LO1  after mixing by mixer  508  according to the embodiment of  FIG. 5 . As illustrated, due to the random nature of the code C, and the fact that a similar data rate to the I and Q data signals is chosen, the frequency spectrum is very similar to that of the data as shown in  FIG. 8B . Furthermore, the power spectral density of the frequency signal is modified by the code signal. 
         [0059]      FIG. 7  illustrates an electronic device  700  according to one embodiment in which wireless data transmission systems as described herein are incorporated. In particular, the device  700  comprises a first circuit board  702 , comprising chips  704  and  706 . The chips  704  and  706  in this example communicate by wireless interfaces. In particular, one wireless data transmission system is provided by a transmission side  708  on chip  704  and a reception side  710  on chip  706 . Another wireless data transmission system is provided by a transmission side  712  on chip  706 , and reception side  714  on chip  704 . The transmission sides  708 ,  712  and the reception sides  710 ,  714  may be provided by those of any of the embodiments of  FIGS. 2 to 6  described above. 
         [0060]    The device  700  also comprises a circuit board  716  stacked below the circuit board  702 , and in this example comprising chips  718  and  720 . Chip  718  is for example positioned below chip  704 , and transmits data to it from a transmission side  724  on chip  718  to a corresponding reception side (not illustrated) on chip  704 . The chip  706  for example transmits data to the chip  720  from a transmission side (not illustrated) on chip  706  to reception side  722  on chip  720 . Again, these transmission and reception sides may be provided by those of any of the embodiments of  FIGS. 2 to 6  described above. 
         [0061]    The device  700  is for example a PC (personal computer), laptop computer, video decoder or other electronic device in which wireless data interfaces between chips may be implemented. Alternatively, the embodiments described herein could be used for wireless data transmission between chips of separate electronics devices, which may or may not be mobile devices. 
         [0062]    An advantage of the embodiments described herein is that the transmission circuitry and reception circuitry of the wireless data transmission system are of relatively low complexity, and furthermore data transmission of relatively low error rate is possible. Indeed, the transmission of a preamble for synchronization may be avoided, and the ADC  120  and digital circuitry  122  of  FIG. 1  may be omitted. 
         [0063]    Having thus described at least one illustrative embodiment, various alterations, modifications and improvements will readily occur to those skilled in the art. 
         [0064]    For example, it will be apparent to those skilled in the art that the various features described in relation with each of the embodiments could be combined in alternative embodiments in any combination. 
         [0065]    Furthermore, it will be apparent that, while a number of examples of types of antenna and data transmission have been described, in alternative embodiments other types would be possible. 
         [0066]    Having thus described at least one illustrative embodiment of the invention, various alterations, modifications, and improvements will readily occur to those skilled in the art. Such alterations, modifications, and improvements are intended to be within the spirit and scope of the invention. Accordingly, the foregoing description is by way of example only and is not intended as limiting. The invention is limited only as defined in the following claims and the equivalents thereto.