Abstract:
A method and apparatus of processing multiple adjacent radio frequency (RF) channels simultaneously are disclosed. The apparatus includes an analog front end, a local oscillator (LO), a mixer, a filter, an analog-to-digital converter (ADC) and a Hilbert transformer. Received RF signals including a plurality of channels adjacent to each other in frequency are processed by the analog front end. The received RF signals are mixed with the LO signals by the mixer to generate down-converted signals. A frequency of the LO signals is tuned such that at least two channels in the down-converted signals overlap each other. The down-converted signals are filtered and digitized by the ADC. The digitized signals are then processed by the Hilbert transformer for recovering signals on each of the RF channels.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
       [0001]     This application claims the benefit of U.S. Provisional Application No. 60/702,199 filed Jul. 25, 2005, which is incorporated by reference as if fully set forth. 
     
    
     FIELD OF INVENTION  
       [0002]     The present invention is related to a wireless communication system. More particularly, the present invention is related to a method and apparatus for processing multiple adjacent radio frequency (RF) channels simultaneously.  
       BACKGROUND  
       [0003]     Currently, most wireless transmit/receive units (WTRUs) typically utilize a multi-band, direct down-conversion to convert received RF signals to baseband signals. A plurality of analog components, such as switches, multiplexers and filters, are used in the analog front end of a receiver to select a desired bandwidth of the signals. In order to select the desired bandwidth, a frequency synthesizer is programmed to generate a local oscillator (LO) signal at a frequency in the middle of the desired channel. After implementing the appropriate lowpass filtering, the down-converted baseband signal is then converted to a digital signal by an analog-to-digital converter (ADC). A lowpass filter selects desired signals and rejects all other down-converted baseband signals.  
         [0004]     A conventional receive chain in a receiver only processes one channel of interest at a time. In order to process multiple channels simultaneously, multiple receive chains should be provided. Therefore, it is desirable to provide a method and apparatus capable of processing multiple adjacent channels simultaneously with one receive chain.  
       SUMMARY  
       [0005]     The present invention is related to a method and apparatus for processing multiple adjacent RF channels simultaneously. The apparatus includes an analog front end, an LO, a mixer, a filter, an ADC and a Hilbert transformer. Received RF signals, including a plurality of channels adjacent to each other in frequency, are processed by the analog front end. The received RF signals are mixed with the LO signals by the mixer to generate down-converted signals. A frequency of the LO signals is tuned such that at least two channels in the down-converted signals overlap each other. The down-converted signals are filtered by the filter and digitized by the ADC. The digitized signals are then processed by the Hilbert transformer for recovering signals on each of the RF channels.  
         [0006]     The LO and the filter may be software configurable, such that the apparatus may selectively process the received signals in a single channel mode or a dual channel mode by configuring a frequency of the LO signals and the bandwidth of the filter. The down-converted signals may be alternating current (AC)-coupled to the ADC or may be selectively either direct current (DC)-coupled or AC-coupled. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]     A more detailed understanding of the invention may be had from the following description of a preferred embodiment, given by way of example and to be understood in conjunction with the accompanying drawing wherein:  
         [0008]      FIG. 1  is a block diagram of a receiver for processing two adjacent channels simultaneously in accordance with the present invention;  
         [0009]      FIG. 2A  shows an RF spectrum of two adjacent channels;  
         [0010]      FIG. 2B  shows a down-converted baseband spectrum of two adjacent channels;  
         [0011]      FIG. 3A  shows baseband filtering requirements in a dual channel mode; and  
         [0012]      FIG. 3B  shows baseband filtering requirements in a single channel mode. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0013]     The present invention will be described with reference to the drawing figures wherein like numerals represent like elements throughout.  
         [0014]     The present invention is applicable to a WTRU and a base station. The terminology “WTRU” includes but is not limited to a user equipment (UE), a mobile station, a fixed or mobile subscriber unit, a pager, or any other type of device capable of operating in a wireless environment. The terminology “base station” includes but is not limited to a Node-B, a site controller, an access point or any other type of interfacing device in a wireless environment.  
         [0015]     The features of the present invention may be incorporated into an integrated circuit (IC) or be configured in a circuit comprising a multitude of interconnecting components.  
         [0016]      FIG. 1  is a block diagram of an exemplary receiver  100  for processing two adjacent channels simultaneously in accordance with the present invention. Hereinafter, the present invention will be explained with reference to a receiver configured to process two adjacent channels (dual channel mode). However, it should be noted that the present invention is also applicable to process only one channel (single channel mode) or more than two adjacent channels simultaneously, and the processing may be selectively switched between the single channel mode and the dual channel mode, which will be explained in detail hereinafter.  
         [0017]     The receiver  100  comprises an analog front end  102 , (including a first filter  104 , a second filter  108  and a low noise amplifier (LNA)  106 ), mixers  110   a ,  110   b , a third filter  112   a , a fourth filter  112   b , variable gain amplifiers (VGAs)  114   a ,  114   b , coupling networks  116   a ,  116   b , ADCs  118   a ,  118   b , a Hilbert transformer  120  and a LO  130 . It should be understood to be obvious to those of skill in the art that more or less components than those shown in  FIG. 1  may be used.  
         [0018]     Signals  101  received by the receiver  100  include two adjacent channels of interest, for example channel  1  and channel  2 .  FIG. 2A  shows an RF spectrum of the received signals  101  including the channel  1  and the channel  2  and adjacent channel interferers. The RF bandwidth (RFBW) of the channel  1  and channel  2 , (including guard bands of the channel  1  and channel  2 ), are adjacent to each other as shown in  FIG. 2 . Referring to  FIG. 1 , the received signals  101  are filtered by the first filter  104  and amplified by the LNA  106  to generate an amplified signal  107 , which is filtered again by the second filter  108  to generate a filtered signal  109 . The filtered signal  109  is then input to the mixers  110   a ,  110   b , which mix the filtered signals  109  with LO signals  131  generated by the LO  130  to generate down-converted signals  111   a ,  111   b . The down-conversion may be performed by more than one step, which should be obvious to those of skill in the art. The mixer  110   a  is used to recover in-phase (I) channel signals and the mixer  110   b  is used to recover Quadrature (Q) channel signals. The I channel and Q channel signals are processed separately and simultaneously thereafter.  
         [0019]     In accordance with the present invention, in a dual channel mode, the frequency of the LO signals  131  is tuned to the middle of channel  1  and channel  2 . As shown in  FIG. 2A , channel  1  and channel  2  are separated by 2Δf1 and the LO frequency is tuned to the center of the two center frequencies of the channels. Therefore, after down-conversion, the down-converted signals  111   a ,  111   b  of the two channels overlap each other, as shown in  FIG. 2B .  
         [0020]     Referring back to  FIG. 1 , after down-conversion, the down-converted signals  111   a ,  111   b  are filtered by the filters  112   a ,  112   b , respectively, to remove all other image frequencies and noises. The bandwidth of the filters  112   a ,  112   b  are preferably adjustable in accordance with a bandwidth selection signal  134 , which will be explained in detail hereinafter.  
         [0021]     The filtered signals  113   a ,  113   b  are then amplified by VGAs  114   a ,  114   b  and fed to the ADCs  118   a ,  118   b  via the coupling networks  116   a ,  116   b , respectively. Since the LO frequency is tuned to the center of the two center frequencies of the channels in a dual channel mode, the filtered signals  113   a ,  113   b  may be AC-coupled to the ADCs  118   a ,  118   b  through the coupling networks  116   a ,  116   b , respectively. There are many benefits of AC-coupling of the analog baseband signals including, but not limited to, an increase of the second order intercept point (IP2), a rejection of 1/f noise, or the like  
         [0022]     The coupling networks  116   a ,  116   b  include an AC-coupling and preferably a DC-coupling as well. The DC-coupling via the coupling network  116   a ,  116   b  is selectively switched on and off in accordance with the control signal  132  to either selectively DC-couple or AC-couple the filtered signals  113   a ,  113   b  to the ADCs  118   a ,  118   b , respectively.  
         [0023]     For example, the coupling network  116   a ,  116   b  includes a capacitor  122   a ,  122   b  coupled in series and a switch  124   a ,  124   b  coupled in parallel. The filtered signal  113   a ,  113   b  may be AC-coupled to the ADCs  118   a ,  118   b  through the capacitors  122   a ,  122   b , respectively. The switch  124   a ,  124   b  may be turned on and off in accordance with the control signal  132  to selectively DC-couple the filtered signals  113   a ,  113   b  to the ADCs  118   a ,  118   b , respectively.  
         [0024]     The ADCs  118   a ,  118   b  output digitized values  119   a ,  119   b  of the input signals. Since channel  1  and channel  2  overlap, the output  119   a  of the ADC  118   a  is the digitized values of the mixture of I components, (i.e., I 1  and I 2 ), of the received signals and the output  119   b  of the ADC  118   b  is the digitized values of the mixture of Q components, (i.e., Q 1  and Q 2 ) of the received signals.  
         [0025]     The Hilbert transformer  120  separates the I 1  and I 2  values from the output  119   a  and the Q 1  and Q 2  values from the output  119   b . The Hilbert transformer  120  is well known in the art and will not be explained in detail herein. The recovered I 1 , I 2 , Q 1  and Q 2  values are then forwarded to downstream processors (not shown).  
         [0026]     As stated above, the receiver  100  may operate either a single channel mode or a dual channel mode (or multi-channel mode). In the dual channel mode, the receiver  100  processes two channels simultaneously. In the single channel mode, the receiver  100  processed only one channel. For the single channel mode, the following is implemented: 1) the LO frequency is adjusted to the center of the channel of interest; 2) the bandwidths of the third filter  112   a  and the fourth filter  112   b  are adjusted in accordance with the bandwidth selection signal  134 ; 3) the coupling network  116   a ,  116   b  may be configured to DC-couple the down-converted signals  111   a ,  111   b  if necessary; and 4) the Hilbert transformer  120  is bypassed.  
         [0027]     As shown in  FIGS. 3A and 3B , the filtering requirements of the filters  112   a ,  112   b  for the dual channel mode and the single channel mode are different. The transition bands for both modes may be the same. However, since the LO frequency in the dual channel mode is tuned to the center of the center frequencies of the two adjacent channels but the LO frequency in the single channel mode is tuned to the center of the channel of interest, the pass band of the dual channel mode is twice as wide as the single channel mode. Therefore, a more complex filter is needed for filters  112   a ,  112   b  in the dual channel mode.  
         [0028]     Additionally, the ADCs  118   a ,  118   b  may be configured to operate with extra bits, (e.g., 2 or 3 bits), compared to conventional ADCs to accommodate the possible difference in received signal strengths of the two adjacent channels.  
         [0029]     The present invention is an enhancement to a conventional direct conversion single channel receiver with minimal additional analog and digital back end processing. In accordance with the present invention, the reception of two or more adjacent channels is facilitated and the receive processing is more flexible since the receiver is software configurable.  
         [0030]     Although the features and elements of the present invention are described in the preferred embodiments in particular combinations, each feature or element can be used alone without the other features and elements of the preferred embodiments or in various combinations with or without other features and elements of the present invention.