Abstract:
A dual mode mobile handset provides a single set of RF circuit elements which interface with a single set of analog circuit elements thereby reducing redundancy in the system. A DSP connected to the analog circuit elements modulates and demodulates both modes of transmission signals with software elements and pre and post processes the standard signals employing embedded softward. A single control CPU provides data to and receives data from the DSP for selected processing as the first standard transmission signal or the second standard transmission signal.

Description:
FIELD OF THE INVENTION  
       [0001]     This invention relates generally to the field of mobile phone handsets and, more particularly, to mobile phones employing a single set of RF, analog and other hardware components with pre and post processing to implement two wireless communication standards.  
       BACKGROUND OF THE INVENTION  
       [0002]     Mobile phones have been developed based on numerous standards including both analog and digital communications capability. Most current cellular phones operate with digital capability; however, multiple standards have proliferated for digital mobile phone system technology including GSM and CDMA. PHS technology for telecommunications systems is gaining in popularity in emerging markets for primary infrastructure development. However, to avoid carrying multiple mobile phones to also have capability to communicate with current cellular phone standards, it is desirable for a PHS user to have a single mobile handset that also includes standard cellular mobile communications technology such as GSM or CDMA.  
         [0003]     Current handsets accommodate this requirement by providing dedicated hardware circuitry for both the PHS and cellular standards. This requires significant duplication of hardware elements and is a costly and complex solution.  
         [0004]     It is therefore desirable to have a mobile phone system that employs one set of RF, analog and other hardware components to support both PHS and a cellular mobile phone standard.  
         [0005]     It is also desirable to provide software elements of the system which can be modified to accommodate differing cellular mobile standards.  
       SUMMARY OF THE INVENTION  
       [0006]     A dual mode mobile handset as defined by the present invention employs a single set of RF circuit elements which interface with a single set of analog circuit elements thereby reducing redundancy in the system. A DSP is connected to the analog circuit elements and has first system software elements for modulating and demodulating a first standard transmission signal and software for pre-processing data for modulation as the first standard transmission signal and post-processing data demodulated from the first standard transmission signal. The DSP has second system software elements for modulating and demodulating a second standard transmission signal and software for pre-processing data for modulation as the second standard transmission signal and post-processing data demodulated from the second standard transmission signal. A single control CPU provides data to and receives data from the DSP for selected processing as the first standard transmission signal or the second standard transmission signal. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]     These and other features and advantages of the present invention will be better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:  
         [0008]      FIG. 1  is a block diagram of the hardware elements of a handset employing the present invention;  
         [0009]      FIG. 2  is a timeline demonstrating GSM and PHS communication windows; and  
         [0010]      FIG. 3  is a block diagram of the functional elements of the handset.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0011]     Referring to the drawings, a handset employing a GSM hardware chipset is disclosed. As shown in  FIG. 1 , a single RF transmission system is employed with a common antenna  10  and RF components  12  which are interconnected to an Analog Front End (AFE)  14 . The AFE provides an interface to peripheral devices on the handset such as the liquid crystal display (LCD), keypad, buzzer, battery charger, speaker, microphone, camera and other standard features, generally identified jointly as  16 . A single crystal oscillator  18  provides clocking for the system as will be described in greater detail subsequently. A digital baseband processing system  20  provides numerical processing capability for rate conversion operations for both transmit and receive operations, timing generation for GSM and PHS signal standards, and equalization, etc.  
         [0012]     The RF components in an exemplary embodiment comprise a Low Noise Amplifier (LNA), Mixer, Amplifier, RF Signal Generator, and Filters. The RF components for the embodiment are comparable to a GSM EDGE system, with the addition of one frequency band for the necessary PHS frequencies. The functions of the RF components are to convert the base band signals into RF signal and to convert RF signal into baseband signals. For the transmission path, the RF components can convert almost any baseband signal into a RF signal. For the recevie path, the RF components can receive any signal with similar bandwidth and the same frequency.  
         [0013]     When the dual mode (GSM/PHS) mobile phone system is receiving and transmitting in GSM mode, a normal GSM signal path can be applied.  
         [0014]     Signal modulation for the GSM standard employs two modes; GMSK and 8 PSK. The modulation scheme for PHS is p/4 DQPSK. 8 PSK and p/4 DQPSK have very similar characteristics with both having amplitude and phase changes. However, the coefficients of raising cosine shaping filter for PHS are quite different from the requirements for a GSM filter. Also, the symbol rates are 192 KHz and 270.8333 KHz for PHS and GSM, respectively. To maximize the similarities, a GSM chipset with 8 PSK capability is therefore employed in the embodiment shown and accommodation for the varying symbol rates is made by the digital signal processor as described subsequently.  
         [0015]     To compensate for filtering and symbol rate differences, the transmit signal for a PHS transmission is generated by the DSP and software/firmware rather than by the built-in circuit for the GSM modulation. The analog portion of the GSM chipset receives a compatible signal for the 13 MHz system such as 0.8125 MHz. (13 MHz/16). To avoid incurring high processing requirements, the PHS signal is generated in two steps. The first step is to manipulate the I and Q data by applying the raising cosine and up-sampling filter which is implemented by the DSP and software. The signal of 0.203125 MHz is up-sampled 4 times to 0.8125 MHz. After up-sampling, a scaling filter of a small number of taps, implemented in exemplary embodiments with a polyphase filter, is applied to convert the symbol rate to the 192 KHz of PHS signal standard frequency. After conversion of the symbol rate, a built-in and hard wired up-sampling filter such as a Cascaded Averaging Filter (CAF) is applied to convert the signal into 6.5 MHz and forwarded to the RF circuit.  
         [0016]     Upon activation of a call the receive path for an incoming PHS transmission employs a similar two-step procedure. The received signal is first up-scaled 2 times (i.e. from 270.833 KHz to 541.6 KHz). A scaling filter with 3-4 taps is applied to convert this signal to a 384 KHz signal. The other receiving operations such as equalization, slicing and de-mapper and de-scrambling are applied on the domain of n*192 KHz. (where n is an integer).  
         [0017]     In the stand-by mode, i.e. listening mode, both GSM and PHS mode can be activated and communicate with base station periodically. As shown in  FIG. 2 , the periods of such communication, T 1  and T 2 , are both long enough and communication times, T 3  and T 4 , are small enough that the probability of both GSM and PHS systems activating at the same time will be small. If a conflict occurs, as shown at time t 1  one mode is provided with higher priority creating a skip of the other mode during the interference period. This priority is preprogrammed or may be programmed alternatively based on network availability. As the result, an incoming phone call from either GSM or PHS base-station will not be missed.  
         [0018]     In the talking mode, only one mode is activated. During operation in one mode, an incoming phone call from the other system will not be connected. The base-station will consider the handset has lost wireless connection and handset will be informed of the dropped call later when the current phone call is finished.  
         [0019]     As shown in  FIG. 3 , functional operation of the system employing the present invention uses the capabilities of the programmable capabilities of the CPU in the handset and the DSP. For a transmission from the handset, the application software  22  interfaces with the LCD  24  for communication to the user based on inputs from the system control  26 . System control also defines the call type PHS or GSM and prompts the appropriate software in the DSP. For a GSM call, data is provided through the GSM pre-process  28  to the modulation elements of the GSM modulation &amp; demodulation  30  and is passed to the D/A portion of the analog circuit elements  32  and the RF circuits  34  for transmission through the antenna. For the embodiment as described above, this constitutes the standard functioning of the normal GSM signal path.  
         [0020]     For a PHS call, the system control provides the data through the PHS pre-process  36  in which filtering is performed to compensate for any distortion to the whole transmit data-path. After completion of the pre-processing, the data is provided to the PHS modulation elements  38  to convert the binary data into an IQ signal and further convert the IQ signal into an RF frequency. The data is then passed to the D/A portion of the analog circuit elements  32  for conversion prior to passing to the RF circuit  34  for transmission through the antenna.  
         [0021]     For receiving a GSM transmission, the RF circuit passes the signal to the A/D and digital filtering portions of the analog circuit elements and through the demodulation elements  42  and post processing elements  44  of the GSM software in the DSP, again operating in the standard GSM mode of the system.  
         [0022]     For receiving a PHS transmission, the RF circuit passes the signal to the A/D and digital filtering portions of the analog circuit elements and through the PHS demodulation elements  46  of the software in the DSP. The de-modulation converts the RF signal into an IQ signal and which is then converted into binary data. The demodulated signal is then passed to the PHS Post-Process  48  for equalization, slicing and de-mapper, and de-scrambling. A single clock system  40  provides clocking for the elements of both the PHS and GSM system.  
         [0023]     Having now described the invention in detail as required by the patent statutes, those skilled in the art will recognize modifications and substitutions to the specific embodiments disclosed herein. Such modifications are within the scope and intent of the present invention as defined in the following claims.