Abstract:
The invention is directed at a hybrid modulation apparatus which combines a polar modulation circuit and a linear modulation circuit. The hybrid apparatus allows a communications device to function as a polar or a linear modulation circuit with less components as the output of the linear modulation circuit is an input of the polar modulation circuit.

Description:
FIELD OF THE INVENTION 
   The present invention relates generally to modulation. More particularly, the present invention relates to a hybrid linear and polar modulation apparatus. 
   BACKGROUND OF THE INVENTION 
   The use of modulation in the field of telecommunications is well known. Modulation is used to vary an input signal, such as a periodic waveform, so that the waveform can then be used to transmit or convey a message. After receiving the input signal, the communication device modulates the input signal to produce a transmittable signal. 
   Typically, a communication device includes components to receive an analog or digital input signal and then modulates the signal either using linear or polar modulation. Linear modulation is also known as direct or Cartesian modulation. Most devices are capable of handling only one of the two modes of modulation and therefore certain devices are restricted to predetermined communication protocols. 
   Use of a solely linear modulation circuit in a communication device, such as the one shown in  FIG. 1 , is known in the art. The linear modulation circuit  10  includes a first input  12 , denoted as I_data, and a second input  14 , denoted as Q_data. The first input  12  is connected to a multiplier  16  which multiplies the input with the value (cos ωt) with ω representing the radio frequency at which the wireless communications is performed and t representing a specific moment in time. 
   The second input  14  is connected to a multiplier  18  and multiplied with the value (sin ωt). The products, or outputs, from the multipliers  16  and  18  are then added together via a summer  20  to produce the transmittable signal. The disadvantage of this type of circuitry is that if there is any amplification or gain after the summer  20 , it has to be linear in order for the signal to be used by other device circuitry. This requires more power to be drawn for the overall linear modulation process. This is unwanted since there is a limited amount of power available within the device. 
   Use of a communication device having only polar modulation circuitry, such as that which is shown schematically in  FIG. 2 , also has its disadvantages. The polar modulation circuitry  30  comprises a pair of inputs  32  and  34  whereby the first input  32  is denoted by A(t) while the second input  34  is denoted as V(t). These values are related to the two inputs in  FIG. 1 , but in polar form whereby V(t) represents the phase information of θ(t), and A(t) is the amplitude information. 
   The second input  34  is passed through a summer  35  before being transmitted to a voltage controlled oscillator (VCO)  36 , and then combined along with the first input  32  using an amplifier  38 . The output of the amplifier  38  is then transmitted to an antenna which transmits the output to another communicating party. 
   An output of the VCO  36  is fed back to the summer  35  through a phase lock loop (PLL)  37  in order to control the phase difference between the two inputs  32  and  34  after the second input  34  passes the VCO  36 . As is known, there is a delay which is introduced into the circuitry  30  while the VCO  36  is in operation and therefore it is difficult to time the arrival of the first  32  and second  34  inputs at the amplifier  38  since both are based on time. Therefore, the PLL  37  locks the phase at time equals 0. One disadvantage is that the bandwidth of the PLL  37  can be restricted by the bandwidth of V(t). 
   It is, therefore, desirable to provide a hybrid linear and polar modulation apparatus. 
   SUMMARY OF THE INVENTION 
   It is an object of the present invention to obviate or mitigate at least one disadvantage of previous modulation circuitry. 
   The present invention is directed at apparatus for providing linear and polar modulation using a hybrid circuitry. The invention allows for both linear and polar modulation to be operational in the same radio frequency path. The hybrid nature of the apparatus also reduces the number of components required in order to allow a mobile communication device to operate in either a linear or polar modulation mode, as selected by the carrier service. 
   This allows for the selection of which architecture is best for a selected modulation type. For instance, the mobile device can operate using polar modulation for 8PSK modulation as used in the EDGE and then subsequently operate using linear modulation for 16QAM modulation. 
   In a first aspect, the present invention provides a hybrid linear and polar modulation apparatus comprising: a linear modulation circuit; and a polar modulation circuit; whereby an input of the polar modulation circuit is an output of the linear modulation circuit. 
   Other aspects and features of the present invention will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying figures. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Embodiments of the present invention will now be described, by way of example only, with reference to the attached Figures, wherein: 
       FIG. 1  is a schematic diagram of a prior art linear modulation circuit; 
       FIG. 2  is a schematic diagram of a prior art polar modulation circuit; 
       FIG. 3  is a schematic diagram of apparatus for performing modulation; 
       FIG. 4  is a schematic diagram of a hybrid linear and polar modulation apparatus; and 
       FIG. 5  is a flowchart outlining a method of modulation using a hybrid linear and polar modulation apparatus. 
   

   DETAILED DESCRIPTION 
   Generally, the present invention provides a method and system for a hybrid linear and polar modulation apparatus. 
   In transmission theory, there is a correlation between linear and polar coordinates. In linear coordinates, a linear signal is represented by I and Q values where:
 
the linear signal= I* cos ω t+Q *sin ω t  
         where ω represents the carrier frequency and t represents time       

   In polar coordinates, a polar signal is represented by R and θ values where: 
   
     
       
         
           
             
               
                 
                   the 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   polar 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   signal 
                 
                 = 
                 
                   
                     R 
                     ⁡ 
                     
                       ( 
                       t 
                       ) 
                     
                   
                   * 
                   
                     sin 
                     ⁡ 
                     
                       ( 
                       
                         
                           ω 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           t 
                         
                         + 
                         
                           θ 
                           ⁡ 
                           
                             ( 
                             t 
                             ) 
                           
                         
                       
                       ) 
                     
                   
                 
               
             
           
           
             
               
                 = 
                 
                   
                     
                       R 
                       ⁡ 
                       
                         ( 
                         t 
                         ) 
                       
                     
                     * 
                     cos 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     
                       θ 
                       ⁡ 
                       
                         ( 
                         t 
                         ) 
                       
                     
                     * 
                     sin 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     ω 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     t 
                   
                   + 
                   
                     
                       R 
                       ⁡ 
                       
                         ( 
                         t 
                         ) 
                       
                     
                     * 
                     sin 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     
                       θ 
                       ⁡ 
                       
                         ( 
                         t 
                         ) 
                       
                     
                     * 
                     cos 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     ω 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     t 
                   
                 
               
             
           
         
       
     
       
       
         
           where R equals the amplitude of the waveform signal and θ represents the angle in polar coordinates. 
         
       
     
  
   In relation to the linear signal, I=R(t)*sin θ(t) and Q=R(t)*cos θ(t) 
   Turning to  FIG. 3 , a schematic diagram of apparatus for modulating signals in a telecommunications environment is shown. The apparatus  100  is typically located within a mobile communication device  102  and includes a converter  104  for receiving inputs  105  from other components in the mobile communication device  102 . The inputs to the converter represent data which is to be transmitted. The converter  104  is preferably capable of converting IQ (linear) signals to Rθ (polar) signals and vice versa and has three outputs  120   a ,  122   a  and  124   a  which serve as inputs  120   b ,  122   b  and  124   b  to a hybrid modulation apparatus  106 . An output  110  (the transmittable signal) of the hybrid modulation apparatus  106  is then transmitted to an antenna  112  which then transmits the signal to another communication party. Although not shown, other hardware, such as filters or switches, can be placed between the output  110  of the hybrid modulation circuitry  106  and the antenna  112 . It will be understood by those of ordinary skill in the art that well-known methods, procedures and components have not been described in detail so as not to obscure the embodiments described herein. 
   When the inputs  105 , or data in the form of linear or polar signals, is received by the converter  104 , this data is then converted to either linear or “polar-like” values and then output to the hybrid modulation circuitry  106 . The “polar-like” values are R(t), sin θ and cos θ and the linear values are I and Q where I=R(t)sin θ(t) &amp; Q=R(t)cos θ(t). 
   If the converter  104  converts the data to linear values, one of the outputs  120   a  is not used or is a constant value with respect to time. When the mobile communication device  102  is in a linear modulation, or transmittal, mode and the inputs to the converter  104  are polar values (i.e. R(t), θ (t)), the other two outputs  122   a  and  124   a  of the converter  104  are Q &amp; I, respectively. 
   If the mobile communication device  102  is in a polar modulation, or transmittal, mode and the inputs to the converter  104  are linear signals (i.e., I &amp; Q), the outputs  120   a ,  122   a  and  124   a  of the converter  104  are R(t), cos θ(t) &amp; sin θ(t). 
   In alternative embodiments, if the mobile communication device  102  is operating in linear modulation mode and the data input to the converter  104  is linear, there is no need to convert the data. Similarly if the mobile communication device  102  is operating in polar modulation mode and the data input to the converter  104  is polar, there is no need to convert the data. 
   If necessary, the outputs from the converter  104  are passed through a set of digital to analog converters (DACs)  108  before being input to the hybrid modulation circuitry  106 . The DACs  108  are required if the outputs from the converter  104  are in a digital format in order to convert the digital signals to analog equivalents. As will be understood, the converter  104  preferably operates in the digital domain and therefore, the signals need to be converted to the analog domain prior to being modulated. If the converter  104  is operating in the analog domain, the outputs of the converter  104  can be transmitted directly to the hybrid modulation circuit  106  which also operates in the analog domain. In an alternative embodiment, the hybrid modulation circuit  106  can be implemented digitally whereby the DACs  108  are not required if the converter  104  is also operating in a digital domain. 
   Turning to  FIG. 4 , a schematic diagram of an embodiment of the hybrid linear and polar modulation apparatus, or circuitry,  106  is shown. 
   As shown, the circuitry  106  includes a first input  120   b , a second input  122   b  and a third input  124   b , corresponding to the outputs  120   a ,  122   a  and  124   a  of the converter  104 . 
   In the linear modulation mode, the second input  122   b  is denoted as Q and the third input  124   b  is denoted as I. In the polar modulation mode, the first input  120   b  is denoted as R(t), the second input  122   b  is denoted as cos θ(t) and the third input  124   b  is denoted as sin θ(t). 
   The hybrid circuitry  106  includes a polar modulation circuit  126  and a linear modulation circuit  128  whereby an input of the polar modulation circuit  126  is an output of the linear modulation circuit  128 . The polar modulation circuit  126  further includes an amplifier  121  and is connected to the input  120   b.    
   The linear modulation circuit  128  is connected to the second input  122   b  and the third input  124   b  and comprises a pair of multipliers  130   a  and  130   b  and a summer  132 . The second input  122   b  and the third input  124   b  are multiplied, using the multipliers  130   a  and  130   b , by (sin ωt) and (cos ωt), respectively. As described above, ω represents the radio frequency at which the mobile communication device is operating and t is a specific moment in time. 
   The products are then added together via the summer  132  to produce an output  140 . The output  140  is then transmitted to the amplifier  121  of the polar modulation circuit  126  where it is combined with the first input  120   b  to produce output  110  which is then transmitted to the antenna  112 . 
   In operation, as shown in the flowchart of  FIG. 5 , an indicator signal is provided to the mobile communication device  102  to indicate whether the apparatus  100  is to operate in a linear or a polar modulation mode (step  200 ). After determining the mode, data, in the form of input signals  105 , is received by the signal converter  104  (step  202 ) which then converts the data to either linear or polar values, in accordance with the modulation mode that been selected (step  204 ). 
   If the apparatus is operating in a linear modulation mode and the data is in linear form, the converter  104  passes the values through without conversion. Similarly, if the apparatus  100  is operating in a polar modulation mode and the data is in polar form, the converter  104  does not convert the data. 
   If the apparatus is operating in a linear modulation mode and the data is in polar form (R(t), θ(t)), the second  122   a  and third outputs  124   a  of the converter  104  are Q and I, where I=R(t)*sin θ(t) and Q=R(t)*cos θ(t). If the apparatus is operating in a polar modulation mode and the data is in linear form (I, Q), the outputs  120   a ,  122   a  and  124   a  of the converter  104  are R(t), sin θ(t) and cos θ(t). 
   As will be understood, by having two equations (I=R(t)*sin θ(t) and Q=R(t)*cos θ(t)) and two unknowns, the two unknowns can be easily determined, or calculated, through various calculation methods. A processor within the converter performs these calculations. 
   After the converter  104  converts the data, the outputs  120   a ,  122   a  and  124   a  are transmitted to the hybrid modulation circuitry  106  (step  206 ). In one embodiment, the inputs  120   a ,  122   a  and  124   a  are transmitted to the DACs  108  which convert the digital values to analog equivalents. These analog equivalents are then transmitted to the hybrid modulation circuitry  106  to serve as inputs  120   b ,  122   b  and  124   b  to the hybrid modulation circuitry  106 . Alternatively, the outputs  120   a ,  122   a  and  124   a  can be directly transmitted to the circuitry  106 . 
   The inputs  120   b ,  122   b  and  124   b  are then modulated by the hybrid modulation circuitry  106  in accordance with the selected modulation mode (step  208 ) by transmitting the second and third inputs  122   b  and  124   b  through the linear modulation circuit  128  and then combining the output  140  with the first input  120   b  via the polar modulation circuit  126 . 
   In the linear modulation mode, the first input  120   a  is either not used or is a constant with respect to time so that its value does not affect the modulation circuitry  106  from operating in the linear mode. This also allows the output  140  to be passed through the amplifier  121  without being disturbed by the first input  120   b  to provide the output  110  which is then transmitted to the antenna  112 . The second input  122   b  is supplied with the value of Q, while the third input  124   b  is supplied with the value of I. 
   In the polar modulation mode, the first input  120   b  is supplied with the value R(t), the second input  122   b  is supplied with the value cos θ(t) and the third input  124   b  is supplied with the value sin θ(t). 
   After the hybrid circuitry  106  receives the inputs  120   b ,  122   b  and  124   b  from the signal converter  104 , or the DACs  108 , the inputs are transmitted through the circuitry  106  to be modulated (step  208 ). 
   In the linear modulation mode, the second input  122   b  is multiplied with the value (sin ωt) via the multiplier  130   a  while the third input  124   b  is multiplied with the value (cos ωt) via the multiplier  130   b . These values, I*cos ωt and Q*sin ωt, are then added together via the summer  132  and the sum represented by output  140 . The output  140  of the summer  132  is then transmitted to the gain control  121  where it is multiplied to the first input  120   b . As the first input  120   b  is either not used or a constant with respect to time, there is no effect on the output  140  of the summer  132  such that the hybrid modulation circuitry  106  acts as a linear modulation circuit. The output  110  of the gain control  121  is then transmitted to the antenna  112  (step  210 ). 
   In the polar modulation mode, the second input  122   b  is multiplied with the value (sin ωt) via the multiplier  130   a  while the third input  124   b  is multiplied with the value (cos ωt) via the multiplier  130   b . These values, sin θ(t)*cos ωt and cos θ(t)*sin ωt, are then added together via the summer  132  and the sum represented by output  140 . This output  140  provides a peak to average value of 0 which results in the signal having a constant envelope. 
   As will be understood, the output of cos θ(t)*sin ωt+sin θ(t)*cos ωt equals sin(ωt+θ) which is the output that is provided by the PLL and VCO combination of  FIG. 2 . However, the hybrid modulation circuitry  106  does not require a PLL &amp; VCO combination to eliminate the phase between the inputs. Therefore, there is no trade off made between the bandwidth of the PLL and the bandwidth of the signals sin θ(t) &amp; cos θ(t) which improves overall operation of the circuitry  106  and of the device  102 . 
   The output  140  is then transmitted, as an input to the polar modulation circuit  126 , through the gain block  121  along with the first input  120   b  to produce a gain block output  110  of R(t)sin θ(t)*cos ωt and R(t)cos θ(t)*sin ωt which is then transmitted to the antenna  112  (step  210 ). 
   As shown, the hybrid apparatus  106  can operate in either a linear or a polar modulation mode by using common parts and any device  102  incorporating the hybrid modulation circuitry  106  can operate in either modulation modes without the need for two separate sets of circuitry. 
   One advantage of the present invention is that, in the polar modulation mode, the hybrid modulation circuitry  106  decouples the performance of the phase lock loop from the performance of the transmitter thereby reducing the number of components required to operate in the polar modulation mode. 
   In a further embodiment, the circuitry can include an over-sampled DAC to avoid quantization errors. 
   The hybrid circuitry  106  provides an apparatus which reduces, or eliminates, the disadvantages of individual linear or polar modulation circuitry. The provision of the converter  104  which is capable of providing the inputs  120   b ,  122   b  and  124   b  for the hybrid modulation circuitry  106  allows the same circuitry to be used for either polar or linear signals. This also reduces the number of overall components required as the same circuitry can be used for either polar or linear signals. 
   Yet another advantage of the invention over is that the signal at the output  140  has a peak to average value of 0 dB in either modulation mode. For this reason, the gain block  121  does not need to be a linear amplifier; since a linear amplifier requires more power to operate than a typical gain block or amplifier. 
   In the above description, for purposes of explanation, numerous details have been set forth in order to provide a thorough understanding of the present invention. However, it will be apparent to one skilled in the art that these specific details are not required in order to practice the present invention. In other instances, well-known electrical structures and circuits are shown in block diagram form in order not to obscure the present invention. For example, specific details are not provided as to whether the embodiments of the invention described herein are implemented as a software routine, hardware circuit, firmware, or a combination thereof. 
   Embodiments of the invention may be represented as a software product stored in a machine-readable medium (also referred to as a computer-readable medium, a processor-readable medium, or a computer usable medium having a computer readable program code embodied therein). The machine-readable medium may be any suitable tangible medium, including magnetic, optical, or electrical storage medium including a diskette, compact disk read only memory (CD-ROM), memory device (volatile or non-volatile), or similar storage mechanism. The machine-readable medium may contain various sets of instructions, code sequences, configuration information, or other data, which, when executed, cause a processor to perform steps in a method according to an embodiment of the invention. Those of ordinary skill in the art will appreciate that other instructions and operations necessary to implement the described invention may also be stored on the machine-readable medium. Software running from the machine readable medium may interface with circuitry to perform the described tasks. 
   The above-described embodiments of the present invention are intended to be examples only. Alterations, modifications and variations may be effected to the particular embodiments by those of skill in the art without departing from the scope of the invention, which is defined solely by the claims appended hereto.