Abstract:
The wireless receiver of the present invention accommodates dual-carrier Evolved EDGE without significantly impacting existing receiver architectures. The inventive receiver comprises a shared local oscillator and two image-rejecting downconverters. The local oscillator generates a local oscillator frequency between two carrier frequencies of adjacent radio channels. The receiver receives a signal in each of the adjacent radio channels. In a dual-carrier mode, a first image-rejecting downconverter uses the local oscillator frequency to downconvert a first signal received in the first radio channel while rejecting a second signal received in the second radio channel. A second image-rejecting downconverter uses the local oscillator frequency to downconvert the second signal while rejecting the first signal. In a diversity mode, the first and second image-rejecting downconverters use the local oscillator frequency to downconvert the signal received in one of the radio channels while rejecting the signal received in the other radio channel.

Description:
BACKGROUND 
     The present invention relates generally to wireless receivers, and more particularly to dual-carrier wireless terminal receivers for Evolved EDGE. 
     EDGE (Enhanced Data Rates for GSM Evolution) is a wireless network protocol that provides increased capacity, data transmission rates, and/or data transmission reliability over conventional GSM networks. EDGE uses the same TDMA frame structure, logic channel, and 200 kHz carrier bandwidth as GSM. Thus, in most instances, implementing EDGE requires a simple upgrade to an existing GSM network. 
     EDGE was initially introduced in the United States in 2003, and quickly gained in popularity. As of May 2007, 223 commercial GSM/EDGE networks exist in 113 countries, out of 287 mobile network operator commitments in 142 countries (source: Global mobile Suppliers Association). While EDGE provides improved performance over conventional GSM, e.g., data speeds up to 200 kb/s, further improvements to EDGE, known as “Evolved EDGE,” are currently under development by the 3rd-Generation Partnership Project (3GPP). (For details, see 3GPP TR 45.912, “Feasibility study for evolved GSM/EDGE Radio Access Network (GERAN),” v. 7.2.0, Mar. 20, 2007, available as of the filing date of the present application at www.3gpp.org/FTP/Specs/html-info/45912.htm, hereinafter referred to as “Evolved EDGE Feasibility Study.”) With enhancements including receiver diversity, higher-order modulation, and a new dual-carrier mode, Evolved EDGE promises data rates exceeding 1 Mb/second under some circumstances. Because Evolved EDGE also uses the same TDMA frame structure, logic channels, and carrier bandwidth as GSM networks, Evolved EDGE may also easily be implemented on existing GSM networks. However, new mobile terminals must be designed to fully exploit these improvements. Currently, wireless terminal vendors are reluctant to implement dual-carrier Evolved EDGE in wireless terminals due to expected impacts on radio architecture. Thus, there remains a need for an improved wireless terminal that is compatible with not only the existing GSM and EDGE networks, but is also compatible with Evolved EDGE networks. 
     SUMMARY 
     The present invention provides a wireless receiver that accommodates dual-carrier Evolved EDGE signals in adjacent radio channels and/or dual-mode operations. The receiver includes a shared oscillator unit and two image-rejecting downconverters. By using the same local oscillator to downconvert received signals, receiver embodiments of the present invention save space and power. Further, the receiver embodiments of the present invention minimize the impact of Evolved EDGE to the receiver architecture by reusing available downconverter hardware to downconvert the received dual-carrier signals. 
     Exemplary embodiments of the invention comprise a dual-carrier EDGE receiver comprising a shared oscillator, a first image-rejecting downconverter, and a second image rejecting downconverter. The shared oscillator unit generates a local oscillator frequency between two carrier frequencies of adjacent first and second radio channels. The first image-rejecting downconverter is operatively connected to the shared oscillator unit and is configured to downconvert a first EDGE signal received in the first radio channel while rejecting a second EDGE signal received in the second radio channel. The second image-rejecting downconverter is operatively connected to the shared oscillator unit and is configured to downconvert the second EDGE signal while rejecting the first EDGE signal. 
     In one exemplary dual-carrier EDGE receiver, the first image-rejecting downconverter comprises a summing combiner to output the downconverted first EDGE signal while rejecting the second EDGE signal, and the second image-rejecting downconverter comprises a subtracting combiner to output the downconverted second EDGE signal while rejecting the first EDGE signal. 
     In one exemplary dual-carrier EDGE receiver, the first EDGE signal comprises an EDGE signal received in an upper radio channel relative to the local oscillator frequency, and the second EDGE signal comprises an EDGE signal received in a lower radio channel relative to the local oscillator frequency. 
     The exemplary dual-carrier EDGE receiver may further comprise a single antenna connected to an input of both the first and second image-rejecting downconverters. 
     The exemplary dual-carrier EDGE receiver may further comprise a first antenna connected to an input of the first image-rejecting downconverter and a separate second antenna connected to an input of the second image-rejecting downconverter. 
     Exemplary embodiments of the present invention also include a method for processing received signals. One exemplary method comprises generating a shared local oscillator frequency between two carrier frequencies of adjacent first and second radio channels; downconverting a first signal received in the first radio channel while rejecting a second signal received in the second radio channel using the shared local oscillator frequency in a first image-rejecting downconverter; and downconverting the second received signal while rejecting the first received signal using the shared local oscillator frequency in a second image-rejecting downconverter. 
     In one exemplary method, downconverting the first signal comprises using a summing combiner in the first image-rejecting downconverter to output the downconverted first signal while rejecting the second signal, and downconverting the second signal comprises using a subtracting combiner in the second image-rejecting downconverter to output the downconverted second signal while rejecting the first signal. 
     In one exemplary method, using the summing and subtracting combiners in the respective first and second image-rejecting downconverters comprises using the summing and subtracting combiners in the respective first and second image-rejecting downconverters during a first mode, and wherein during a second mode the method may further comprise using a summing combiner or a subtracting combiner in both the first and second image-rejecting downconverters to output the downconverted first signal from both image-rejecting downconverters while rejecting the second signal. 
     In one exemplary method, the first mode comprises a dual-carrier mode and the second mode comprises a diversity mode. 
     The exemplary method may further comprise connecting the first and second image-rejecting down converters to a single antenna during the first mode and connecting the first and second image-rejecting down converters to different antennas during the second mode. 
     The exemplary method may further comprise connecting the first and second image-rejecting downconverters to different antennas during the first and second modes. 
     In one exemplary method, the first signal comprises an EDGE signal received in an upper radio channel relative to the local oscillator frequency, and the second signal comprises an EDGE signal received in a lower radio channel relative to the local oscillator frequency. 
     Exemplary embodiments of the invention also comprise a dual-mode receiver comprising a shared oscillator, a processor, a first image-rejecting downconverter, and a second image rejecting downconverter. The shared oscillator unit generates a local oscillator frequency offset from one or both carrier frequencies of adjacent first and second radio channels. The processor configures the receiver to operate in a first mode or a second mode. The first image-rejecting downconverter is operatively connected to the shared oscillator unit and is configured to downconvert a first signal received in the first radio channel while rejecting a second signal received in the second radio channel when the receiver is configured to operate in either the first or second modes. The second image-rejecting downconverter is operatively connected to the shared oscillator unit, and is configured to downconvert the second signal while rejecting the first signal when the receiver is configured to operate in the first mode and downconvert the first signal while rejecting the second signal when the receiver is configured to operate in the second mode. 
     During operation in the first mode of one exemplary dual-mode receiver, the first image-rejecting downconverter comprises a summing combiner to output the downconverted first signal while rejecting the second signal, and the second image-rejecting downconverter comprises a subtracting combiner to output the downconverted second signal while rejecting the first signal. 
     During operation in the second mode of one exemplary dual-mode receiver, the first and second image-rejecting downconverters both comprise either a summing combiner or a subtracting combiner. 
     In one exemplary dual-mode receiver, the processor connects the first and second image-rejecting downconverters to a single antenna when the receiver operates in the first mode, and the processor connects the first and second image-rejecting downconverters to different antennas when the receiver operates in the second mode. 
     In one exemplary dual-mode receiver, the first signal comprises an EDGE signal received in an upper radio channel relative to the local oscillator frequency and the second signal comprises an EDGE signal received in a lower radio channel relative to the local oscillator frequency when the receiver operates in the first mode. 
     In one exemplary dual-mode receiver, the processor controls the shared oscillator unit to generate the local oscillator frequency between the carrier frequencies of the adjacent first and second radio channels during operation in the first mode, and the processor controls the shared oscillator unit to generate the local oscillator frequency offset from one of the carrier frequencies of the first and second radio channels during operation in the second mode. 
     In one exemplary dual-mode receiver, the processor connects the first and second image-rejecting downconverters to different antennas when the receiver operates in either the first or second modes. 
     In one exemplary dual-mode receiver, the first mode comprises a dual-carrier mode, and wherein the second mode comprises a diversity mode. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows an exemplary dual-carrier receiver according to one embodiment of the present invention. 
         FIG. 2  shows a frequency plot of adjacent frequency bands and the corresponding local oscillator frequency. 
         FIG. 3  shows an exemplary dual-mode receiver according to one embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Current wireless receiver architectures may be adapted according to the present invention to accommodate dual-carrier Evolved EDGE signals. For the present invention, the dual-carrier Evolved EDGE signals are associated with two carrier frequencies in adjacent radio channels. 
       FIG. 1  shows an exemplary dual-carrier receiver  100  according to one embodiment of the present invention. Receiver  100  comprises an oscillator unit  110  shared by two image-rejecting downconverters  120 ,  130 , both of which also connect to a single antenna  140 . It will be appreciated that the downconverters  120 ,  130  may alternatively connect to different antennas. 
     Oscillator unit  110  comprises a local oscillator  112  that generates a local oscillator frequency f lo . The oscillator unit  110  further includes a phase shifter  114  to generate a phase shifted version of the local oscillator frequency f lo . For dual-carrier operation, image-rejecting downconverters  120 ,  130  downconvert signals received in adjacent radio channels using the shared local oscillator frequency output by the oscillator unit  110  to generate an output signal, at an intermediate frequency (IF) or baseband frequency, for each of the upper and lower EDGE signals. One downconverter, e.g. downconverter  120 , downconverts an upper channel signal (UCS) while rejecting a lower channel signal (LCS). The other downconverter, e.g. downconverter  130 , downconverts the lower channel signal while rejecting the upper channel signal. 
     The oscillator unit  110  is configured to generate a local oscillator frequency f lo  between two carrier frequencies of adjacent radio channels. By setting the local oscillator frequency to a frequency offset from both carrier frequencies by an equal amount related to the bandwidth of a downconverter filter, e.g., 100 kHz, the local oscillator frequency f lo  lies midway between the adjacent carrier frequencies of the upper and lower radio channels, as shown in  FIG. 2 . Using such a local oscillator frequency f lo  with downconverters  120 ,  130  causes the downconverter to output signals at an IF or baseband frequency that correspond to the signals received in the upper and lower radio channels. 
     The downconverters  120 ,  130  of receiver  100  take advantage of this frequency relationship to downconvert signals received in adjacent upper and lower radio channels. More particularly, image-rejecting downconverter  120  downconverts a signal received in the upper radio channel using the shared local oscillator frequency f lo  to output a downconverted upper channel signal while rejecting the lower channel signals. Similarly, image-rejecting downconverter  130  downconverts a signal received in the lower channel using the shared local oscillator frequency f lo  to output a downconverted lower channel signal while rejecting the upper channel signals. 
     To that end, the downconverters  120 ,  130  each comprises a pair of mixers  122 ,  132 , a pair of filters  124 ,  134 , a phase shifter  126 ,  136 , and a combiner  128 ,  138 . A received signal is split into two paths and input to separate mixers  122   a ,  122   b ,  132   a ,  132   b . Mixers  122   a ,  132   a  mix the received signal with the local oscillator frequency, while mixers  122   b ,  132   b  mix the received signal with the phase shifted local oscillator frequency to output in-phase and quadrature representations of the received signal. Filters  124 ,  134  filter the in-phase and quadrature signals according to a predetermined bandwidth, e.g., a 200 kHz bandwidth. Phase shifter  126 ,  136  shifts the phase of either the filtered in-phase (as shown in  FIG. 1 ) or the filtered quadrature signal by 90°. The signals from the in-phase and quadrature paths are input to and combined by the combiners  128 ,  138 . By appropriately combining the phase offset signals from the in-phase and quadrature paths, combiners  128 ,  138  output downconverted upper and lower channel signals. Table 1 illustrates this by showing the nominal phases of the upper and lower channel signals as they pass through mixers  122 ,  132 , filters  124 ,  134 , and phase shifter  126 ,  136  of the respective downconverters  120 ,  130 . 
                             TABLE 1               Node   Upper Channel Signal   Lower Channel Signal                   A    0°    0°       B    0°    0°       C   −90°   +90°       D    0°    0°       E   −90°   +90°       F   −90°   −90°                    
At combiners  128 ,  138  points D and F), the upper channel signals of the in-phase and quadrature paths are in phase while the lower channel signals of the in-phase and quadrature paths are 180° out of phase. Thus, to output the desired downconverted upper and lower channel signals, combiner  128  additively combines the combiner input signals, while combiner  138  subtractively combines the combiner input signals. As a result, for the example shown in  FIG. 1 , downconverter  120  comprises an upper channel downconverter and combiner  128  comprises a summing combiner that outputs the downconverted upper channel signal and rejects the lower channel signal, while downconverter  130  comprises a lower channel combiner and combiner  138  comprises a subtracting combiner that outputs the downconverted lower channel signal and rejects the upper channel signal.
 
     The amount of signal rejection attainable by the combiners  128 ,  138  depends on the accuracy of the 90° phase shift provided by the phase shifters  126 ,  136  and on the gain balance of the combiner input signals. In practice, the combiners  128 ,  138  may attain at least 30 dB of unwanted signal rejection, which is generally sufficient for digital signals as the unwanted signals at these levels distorts the desired signals by only a few percentage points. Error correction techniques known in the art may be used to compensate for such distortion. 
     It will be appreciated that the phase shifters  126 ,  136  may be placed in either the in-phase or the quadrature paths. Those skilled in the art will also appreciate that either or both of phase shifters  126 ,  136  may be placed at different locations in the in-phase and quadrature paths to produce the same or equivalent phase relationships. The radio channel associated with the downconverted signals output by the downconverters  120 ,  130  is determined based on the polarity of the combiner  128 ,  138  and which path includes the 90° phase shift associated with the phase shifters  126 ,  136 . For example, if the phase shifters  126 ,  136  of both downconverters  120 ,  130  are connected to the output of the filters  124 ,  134  in the quadrature paths, then the upper channel combiner  128  would be implemented as a subtracting combiner while the lower channel combiner  138  would be implemented as a summing combiner. 
     The oscillator unit, mixers, filters, phase shifters, and combiners shown in  FIG. 1  are readily available in most wireless receivers. Thus, by controlling the local oscillator frequency, the combining operations, and/or the signal transmission frequencies as described above, the present invention provides a dual-carrier receiver for Evolved EDGE that reuses available receiver components. 
       FIG. 3  shows an exemplary receiver  200  according to another embodiment of the present invention. Receiver  200  comprises a dual-mode receiver that selectively operates in either a diversity mode or a dual-carrier mode. In the diversity mode, both downconverters  120 ,  130  operate on signals in the same radio channel, while in the dual-carrier mode, the downconverters  120 ,  130  operate on signals in separate but adjacent radio channels. To that end, dual-mode receiver  200  comprises an antenna  142 , a microprocessor  210 , and an optional switch  220  in addition to the local oscillator unit  110 , downconverters  120 ,  130 , and antenna  140  described and shown in  FIG. 1 . When operating in the dual-carrier mode, microprocessor  210  configures the local oscillator unit  110  to generate a local oscillator frequency f lo  between the carrier frequencies of the adjacent radio channels, and configures one image-rejecting downconverter  120 ,  130  as an upper channel downconverter and the other image-rejecting downconverter  120 ,  130  as a lower channel downconverter, as discussed above. If switch  220  is included, the microprocessor  210  also configures the switch to either connect both downconverters  120 ,  130  to a single antenna  140  (for dual-carrier mode) or to separate antennas  140 ,  142  (for either dual-carrier mode or diversity mode). In either case, when in the dual-carrier mode, dual-mode receiver  200  generally operates as described above and shown in  FIG. 1 . 
     When operating in the diversity mode, e.g., for existing GSM or EDGE protocols, the downconverters  120 ,  130  connect to separate antennas  140 ,  142  and microprocessor  210  determines whether the signals of interest are in an upper radio channel or a lower radio channel relative to the local oscillator frequency f lo . The diversity mode may be configured to output either the downconverted upper channel signals or the downconverted lower channel signals depending on the location of the local oscillator frequency relative to the radio channel frequency of the desired signal. In this way, the image-rejecting downconverters  120 ,  130  output signals received in the same radio channel (upper or lower) to enable implementation of any known diversity combining technique. For example, if the received signals are in the upper radio channel relative to the local oscillator frequency, microprocessor  210  configures both downconverters  120 ,  130  as upper channel downconverters that output downconverted upper channel signals while rejecting the lower channel signals. If the phase shifters  126 ,  136  are both in the in-phase paths, the combiners  128 ,  138  for the downconverters  120 ,  130  in this example may both comprise summing combiners. Alternatively, if the received signals are in the lower radio channel relative to the local oscillator frequency, microprocessor  210  configures both downconverters  120 ,  130  as lower channel downconverters that output downconverted lower channel signals while rejecting the upper channel signals. If the phase shifters  126 ,  136  are both in the in-phase paths, the combiners  128 ,  138  for the downconverters  120 ,  130  in this example may both comprise subtracting combiners. 
     The dual-mode receiver  200  may be preconfigured for a particular operating mode or may allow dynamic selection of a desired operating mode. To switch from the dual-carrier mode to the diversity mode, the microprocessor  210  determines whether the desired signal for the diversity mode is associated with the upper radio channel or the lower radio channel of the dual-carrier mode, and configures the downconverters  120 ,  130  as discussed above. 
     To switch from the diversity mode to the dual-carrier mode, microprocessor  210  configures one downconverter  120 ,  130  as an upper channel downconverter and configures the other downconverter  120 ,  130  as a lower channel downconverter. For the example shown in  FIG. 3 , such a configuration would require combiner  128  to operate as a summing combiner and combiner  138  to operate as a subtracting combiner. Microprocessor  210  also determines whether the current local oscillator frequency f lo  lies between the two carrier frequencies associated with the radio channels of the dual-carrier mode. If so, microprocessor  210  leaves the local oscillator frequency f lo  at the current value. If not, the microprocessor  210  adjusts the local oscillator frequency f lo  to lie between the two carrier frequencies. The microprocessor  210  may make this determination by, for example, evaluating the radio channel frequencies of the received signals or based on frequency information received in a control signal. 
     The present invention provides wireless receivers and corresponding methods for processing Evolved EDGE dual-carrier signals in adjacent radio channels using a single shared local oscillator and reusing available receiver components. The present invention may, of course, be carried out in other ways than those specifically set forth herein without departing from essential characteristics of the invention. The present embodiments are to be considered in all respects as illustrative and not restrictive, and all changes coming within the meaning and equivalency range of the appended claims are intended to be embraced therein.