Abstract:
A MIMO signal receiving apparatus includes a first antenna for receiving a first RF signal; a second antenna for receiving a second RF signal; a superheterodyne receiver for receiving one or all of the first and second RF signals into at least one first analog signal; a direct conversion receiver for converting one or all of the first and second RF signals into at least one second signal; and an antenna switching module coupling the first and second antennas to the superheterodyne receiver and the direct conversion receiver for electively directing the first and second RF signals to the superheterodyne receiver and/or the direct conversion receiver, depending on an antenna switch control signal indicating a signal quality derived from the first and second analog signals.

Description:
CROSS REFERENCE 
       [0001]    The present application claims the benefits of U.S. Patent Provisional Application No. 60/816,929 filed on Jun. 27, 2006, entitled “Multiple Receiver Architecture Optimized for Performance, Cost, and Size for Use in MIMO Mobile Wireless Broadband Receiver.” 
     
     FIELD OF THE INVENTION 
       [0002]    This invention relates generally to wireless communications, and more particularly to a multiple input multiple output (MIMO) signal receiving apparatus with optimized performance. 
       BACKGROUND 
       [0003]    MIMO technology has attracted a lot of attentions in areas of telecommunications because it allows a significant increase in throughput in the same bandwidth and overall power expenditure. The MIMO technology exploits phenomena such as a multi-path propagation to increase data throughput and range, or reduce bit error rates. In general, the MIMO technology increases the spectral efficiency of a wireless telecommunications system. 
         [0004]      FIG. 1  illustrates a conventional MIMO signal receiving apparatus  100 , which includes two typical direct conversion receivers  102  and  104  coupled to two antennas  106  and  108 , respectively. The direct conversion receiver  102  is comprised partially of a radio frequency (RF) filter  110 , a low noise amplifier  112 , a RF filter  114 , a RF amplifier  116 , and an IQ demodulator  118 , which mixes outputs of the RF amplifier  116  and outputs of a RF local oscillator  119  to generate I and Q baseband signals that are forwarded to baseband low pass filters  120  and  122 , respectively. The outputs of the baseband low pass filters  120  and  122  are amplified by variable gain amplifiers  124  and  126 , respectively, to produce filtered I and Q signals for analog-to-digital converters (not shown in this figure) to convert into digital signals for further processing. The direct conversion receiver  104  has a functional structure similar to that of the receiver  102 . Thus, the detailed description of the receiver  104  is hereby omitted in order to avoid redundancy. 
         [0005]    The conventional direct-conversion type MIMO signal receiving apparatus is simple in design and has advantages of low manufacturing costs and low power consumption rates. However, it is particularly susceptible to signal interference induced by adjacent out-of-band frequencies (so called jammers). This causes serious problems when such direct-conversion type MIMO signal receiving apparatus is implemented in a mobile device. For example, if the mobile device is moved to an area where there are many high power transmitters operating at the frequencies that are very close to the receiver&#39;s desired channel, it will not function properly and will result in poor signals. 
         [0006]      FIG. 2  illustrates a conventional superheterodyne MIMO signal receiving apparatus  200 , which includes two typical superheterodyne receivers  202  and  204  coupled to two antennas  206  and  208 , respectively. The superheterodyne receiver  202  is comprised partially of a RF filter  210 , a low noise amplifier  212 , a RF filter  214 , a RF amplifier  216 , and a mixer  218 , which mixes outputs of the RF amplifier  216  and outputs of a RF local oscillator  220 . An intermediate frequency surface acoustic wave (IF SAW) filter  222  receives the mixed signal output from the mixer  218  and outputs a filtered signal to a variable gain filter  224 . An IQ demodulator  226  mixes outputs of the variable gain amplifier  224  with outputs of an IF local oscillator  228  to generate I and Q baseband signals for analog-to-digital converters (not shown in this figure) to convert into digital signals for further processing. The superheterodyne receiver  204  has a functional structure similar to that of the receiver  202 . Thus, the detailed description of the receiver  204  is hereby omitted in order to avoid redundancy. 
         [0007]      FIG. 3  illustrates another conventional superheterodyne MIMO signal receiving apparatus  300 , which includes two typical superheterodyne receivers  302  and  304  coupled to two antennas  306  and  308 , respectively. The superheterodyne MIMO signal receiving apparatus  300  is similar to the superheterodyne MIMO receiving apparatus  200  (shown in  FIG. 2 ) in their functional structures, except that the apparatus  300  has two stages of RF-to-IF conversion, whereas the apparatus  200  has only one stage. 
         [0008]    The above-mentioned conventional superheterodyne MIMO signal receiving apparatuses are superior to the direct-conversion type MIMO signal receiving apparatus  100  in terms of rejecting the out-of-band jammers, and therefore is able to receive signals with good quality in an area where there are many high power transmitters operating at the frequencies that are very close to the receiver&#39;s desired channel. However, the superheterodyne MIMO signal receiving apparatus  200  has disadvantages, such as high manufacturing costs, high power consumption rates, and a large equipment size, due to its additional devices that are needed for down converting RF signals received from the antennas into IF signals. 
         [0009]    As such, what is needed is a MIMO signal receiving apparatus that has a superior performance in rejecting out-of-band jammers, low manufacturing costs, low power consumption rates, and small in size. 
       SUMMARY 
       [0010]    The present invention discloses a MIMO signal receiving apparatus, which, in one embodiment, includes a first antenna for receiving a first RF signal; a second antenna for receiving a second RF signal; a superheterodyne receiver for receiving one or all of the first and second RF signals into at least one first analog signal; a direct conversion receiver for converting one or all of the first and second RF signals into at least one second signal; and an antenna switching module coupling the first and second antennas to the superheterodyne receiver and the direct conversion receiver for electively directing the first and second RF signals to the superheterodyne receiver and/or the direct conversion receiver, depending on an antenna switch control signal indicating a signal quality derived from the first and second analog signals. 
         [0011]    The construction and method of operation of the invention, however, together with additional objectives and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  illustrates a conventional direct conversion MIMO signal receiving apparatus. 
           [0013]      FIG. 2  illustrates a conventional one-stage superheterodyne MIMO signal receiving apparatus. 
           [0014]      FIG. 3  illustrates a conventional two-stage superheterodyne MIMO signal receiving apparatus. 
           [0015]      FIG. 4  illustrates a proposed MIMO signal receiving apparatus in accordance with one embodiment of the present invention. 
           [0016]      FIG. 5  illustrates a proposed MIMO signal receiving apparatus operating in a MIMO mode where both a superheterodyne receiver and a direct conversion receiver are enabled, in accordance with one embodiment of the present invention. 
           [0017]      FIG. 6  illustrates a proposed MIMO signal receiving apparatus operating in a single input single output (SISO) mode where a superheterodyne receiver is enabled and a direct conversion receiver is disabled, in accordance with one embodiment of the present invention. 
           [0018]      FIG. 7  illustrates a proposed MIMO signal receiving apparatus operating in a SISO mode where a superheterodyne receiver is disabled and a direct conversion receiver is enabled, in accordance with one embodiment of the present invention. 
           [0019]      FIG. 8  illustrates a flowchart for explaining how the proposed MIMO signal receiving apparatus operates in accordance with one embodiment of the present invention. 
       
    
    
     DESCRIPTION 
       [0020]    This invention describes a MIMO signal receiving apparatus with optimized performance. The following merely illustrates various embodiments of the present invention for purposes of explaining the principles thereof. It is understood that those skilled in the art of telecommunications will be able to devise various equivalents that, although not explicitly described herein, embody the principles of this invention. 
         [0021]      FIG. 4  illustrates a proposed MIMO signal receiving apparatus  400  in accordance with one embodiment of the present invention. The apparatus  400  includes a first antenna  402  and a second antenna  404  coupled to an antenna switch module  406 , which is further coupled to a superheterodyne receiver  408  and a direct conversion receiver  410 . The antenna switch module  406  selectively directs a first RF signal received from the first antenna  402  and a second RF signal received from the second antenna  404  and a second RF signal received from the second antenna  404  to the superheterodyne receiver  408  and/or the direct conversion receiver  410 . Analog outputs of the superheterodyne receiver  408  and the direct conversion receiver  410  are converted into a first digital signal and a second digital signal by a first analog-to-digital converter  412  and a second analog-to-digital converter  414 , respectively. A signal processing module  416  receives and processes the first and second digital signals output from the first and second analog-to-digital converters  412  and  414  to generate an antenna switch control signal for controlling the antenna switch module, and receiver control signals for enabling or disabling the superheterodyne receiver  408  and the direct conversion receiver  410 . 
         [0022]    It is noted that the detailed circuit constructions of the superheterodyne receiver and the direct conversion receiver are well understood by people skilled in the art of telecommunications. For example,  FIG. 1  illustrates a typical direct conversion receiver,  FIG. 2  illustrates a typical one-stage superheterodyne receiver, and  FIG. 3  illustrates a typical two-stage superheterodyne receiver. These receivers with or without modifications can be implemented as the superheterodyne receiver and the direct conversion receiver in the embodiment of the present invention. 
         [0023]      FIG. 5  illustrates the proposed MIMO signal receiving apparatus  400  operating in a MIMO mode where both the superheterodyne receiver  408  and the direct conversion receiver  410  are enabled, in accordance with one embodiment of the present invention. In an initial state, the antenna switch module  406  directs the first RF signal received from the first antenna  402  and the second RF signal received from the second antenna  404  to the superheterodyne receiver  408  and the direct conversion receiver  410 , respectively. The outputs of the superheterodyne receiver  408  and the direct conversion receiver  410  are forwarded to the first and second analog-to-digital converters  412  and  414 , respectively, which further generates a first digital signal and a second digital signal to the signal processing module  416 . 
         [0024]    The signal processing module  416  processes the first digital signal generated by the first analog-to-digital converter  412  and the second digital signal generated by the second analog-to-converter  414  to determine if their corresponding signal-to-noise ratio (SNR) is higher than a predetermined threshold value. If the second digital signal generated by the analog-to-digital converter  414  is determined to have a SNR higher than the predetermined threshold value and the apparatus  400  is not operating in a power saving mode, the signal processing module  416  will generate an antenna switch control signal that controls the antenna switch module to keep directing the first and second RF signals to the superheterodyne receiver  408  and the direct conversion receiver  410 , respectively. In such case, the signal processing module  416  will also generate receiver control signals to enable both the superheterodyne receiver  408  and the direct conversion receiver  410 . This operation mode is particularly utilized when the apparatus  400  is located in a low interfered area and is not on serious power constraints. 
         [0025]    One advantage of the proposed MIMO signal receiving apparatus is that its size, manufacturing costs, and power consumption rates are lower than those of the conventional MIMO signal receiving apparatus that includes two superheterodyne receivers. As understood by people skilled in the art of telecommunications that the manufacturing costs of a superheterodyne receiver are higher than that of a direct conversion receiver. Thus, the manufacturing costs of the proposed apparatus  400  that contains one superheterodyne receiver and one direct conversion receiver would be lower than those of its conventional counterpart, which contains two superheterodyne receivers. Similarly, as understood by people skilled in the art of telecommunications that the size and power consumption rate of a superheterodyne receiver are higher than that of a direct conversion receiver. Thus, the size and power consumption rate of the proposed apparatus  400  that contains one superheterodyne receiver and one direct conversion receiver would be smaller than those of its conventional counterpart, which contains two superheterodyne receivers. 
         [0026]      FIG. 6  illustrates a proposed MIMO signal receiving apparatus  400  operating in a SISO mode where a superheterodyne receiver  408  is enabled and a direct conversion receiver  410  is disabled, in accordance with one embodiment of the present invention. In an initial state, the antenna switch module  406  directs the first RF signal received from the first antenna  402  and the second RF signal received from the second antenna  404  to the superheterodyne receiver  408  and the direct conversion receiver  410 , respectively. The outputs of the superheterodyne receiver  408  and the direct conversion receiver  410  are forwarded to the first and second analog-to-digital converters  412  and  414 , respectively, which further generate a first digital signal and a second digital signal to the signal processing module  416 . 
         [0027]    The signal processing module  416  processes the first digital signal generated by the first analog-to-digital converter  412  and the second digital signal generated by the second analog-to-converter  414  to determine if their corresponding SNR is higher than a predetermined threshold value. If the second digital signal generated by the analog-to-digital converter  414  is determined to have a SNR lower than the predetermined threshold value, the signal processing module  416  will generate an antenna switch control signal that controls the antenna switch module  406  to direct both the first and second RF signals to the superheterodyne receiver  408 . In the mean time, the signal processing module  416  will also generate a first receiver control signal to enable the superheterodyne receiver  408 , and a second receiver control signal to disable the direct conversion receiver  410 . This operation mode is utilized, for example, when the apparatus  400  is located in a high interfered area where the direct conversion receiver cannot provide quality outputs. The signal processing module  416  will keep monitoring the SNR of the second digital signal. Once it is determined to be higher than the predetermined threshold value, the signal processing module will switch the apparatus  400  back to the MIMO mode. 
         [0028]    In addition to the cost, size, and power consumption advantages mentioned above, the proposed MIMO signal receiving apparatus is able to provide diversity gains, such that it can function in high interfered areas where its conventional counterpart, that includes only direct conversion receivers, cannot function properly. 
         [0029]      FIG. 7  illustrates a proposed MIMO signal receiving apparatus  400  operating in a SISO mode where a superheterodyne receiver  408  is disabled and a direct conversion receiver  410  is enabled, in accordance with one embodiment of the present invention. In an initial state, the antenna switch module  406  directs the first RF signal received from the first antenna  402  and the second RF signal received from the second antenna  404  to the superheterodyne receiver  408  and the direct conversion receiver  410 , respectively. The outputs of the superheterodyne receiver  412  and the direct conversion receiver  410  are forwarded to the first and second analog-to-digital converters  412  and  414 , respectively, which further generate a first digital signal and a second digital signal to the signal processing module  416 . 
         [0030]    The signal processing module  416  processes the first digital signal generated by the first analog-to-digital converter  412  and the second digital signal generated by the second analog-to-converter  414  to determine if their corresponding SNR is higher than a predetermined threshold value. If the second digital signal generated by the analog-to-digital converter  414  is determined to have a SNR higher than the predetermined threshold value, and the apparatus  400  is operating in a power saving mode, the signal processing module  416  will generate an antenna switch control signal that controls the antenna switch module  406  to direct both the first and second RF signals to the direct conversion receiver  410 . In the meantime, the signal processing module  416  will also generate a first receiver control signal to disable the superheterodyne receiver  408 , and a second receiver control signal to enable the direct conversion receiver  410 . This operation mode is utilized, for example, when the apparatus  400  is located in a low interfered area under power constraints, such as being powered by batteries. In addition to the advantages discussed above, this operation mode allows the apparatus  400  to further operate in a power-efficient mode. 
         [0031]      FIG. 8  illustrates a flowchart for explaining how the proposed MIMO signal receiving apparatus operates in accordance with one embodiment of the present invention. In step  802 , the first and second RF signals are received by the superheterodyne receiver and the direct conversion receiver, respectively. In step  804 , the outputs of the superheterodyne receiver and the direct conversion receiver are converted into the first and second digital signals. In step  806 , the signal processing module determines if the SNR of the second digital signal is higher than the predetermined threshold value. If the SNR of the second digital signal is determined to be lower than the predetermined threshold value, the process proceeds to step  808  where the direct conversion receiver is disabled, the superheterodyne receiver is enabled, and both the first and second RF signals are directed to the superheterodyne receiver. If the SNR of the second digital signal is determined to be higher than the predetermined threshold value, the process proceeds to step  810  where whether the apparatus is operating in a power saving mode is determined. If the apparatus is operating in a power saving mode, the process proceeds to step  812  where the superheterodyne receiver is disabled, the direct conversion receiver is enabled, and both the first and second RF signals are directed to the direct conversion receiver. If the apparatus is not operating in a power saving mode, the process proceeds to step  814  where both the superheterodyne receiver and the direct conversion receiver are enabled, and the first and second RF signals are directed to them, respectively. 
         [0032]    It is noted that although the above embodiments use a two-receiver MIMO signal receiving apparatus as an example to explain the principles of the invention, the number of receivers that can be implemented is by no means limited to two. More superheterodyne receivers and direct conversion receivers can be implemented in order to achieve further optimal performance. 
         [0033]    The above illustration provides many different embodiments or embodiments for implementing different features of the invention. Specific embodiments of components and processes are described to help clarify the invention. These are, of course, merely embodiments and are not intended to limit the invention from that described in the claims. 
         [0034]    Although the invention is illustrated and described herein as embodied in one or more specific examples, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the scope of the invention, as set forth in the following claims.