Abstract:
The present disclosure relates to an apparatus and technique for a wireless communications receiver architecture and, more particularly, to an apparatus and technique for an analog adaptive receiver architecture.

Description:
BACKGROUND  
         [0001]    1. Field  
           [0002]    The present disclosure relates to an apparatus and technique for a wireless communications receiver architecture and, more particularly, to an apparatus and technique for an analog adaptive receiver architecture.  
           [0003]    2. Background Information  
           [0004]    Typically, wireless signals are subject to interference. This interference may come from many different sources, such as, multiple-access interference (MAI) that may originate in the wireless network, other wideband interference, for example, signals from a similar wireless network using the same frequency band, or narrowband interference, for example, signals from a dissimilar wireless network using the same frequency band. These interfering signals may have a greater received power than the typical additive white noise and may be a principal source of error. In addition, a time-variant multi-path channel, or frequency band, generates detrimental inter-symbol interference and time-variant fading in a received signal. Both the multi-access interference and multipath fading may limit the performance of a wireless multi-access system. Traditionally, techniques for addressing these issues for UWB communications include a digital differential phase shift key (DPSK) demodulation or the use of a RAKE receiver.  
           [0005]    [0005]FIG. 1 is a block diagram illustrating a traditional DPSK receiver  100  that utilizes a least-means squared (LMS) filter. The traditional DPSK receiver may include an antenna  105 , a bandpass filter  110 , a low-noise amplifier  120 , an analog-to-digital converter  130  and a LMS filter  140 . The conventional implementation of a least-means squared (LMS) filter requires storage components  150 , if the observation window size in the filter is greater than one symbol duration. The delayed signals are assigned weights  160  and summed  170  before being sent to the PSK symbol detector  199 . Conventionally, the PSK symbol detector extracts information from the received and filtered signals. Often, however, the DPSK receiver does not allows the UWB signal to be sampled at the Nyquist rate at a low cost. Alternatively, the DPSK receiver may use a delay spread, or observation window, for the UWB channel of less than a one symbol duration. Also, a DPSK receiver is subject to intersymbol interference (ISI) and noise amplification.  
           [0006]    [0006]FIG. 2 is a block diagram illustrating a traditional RAKE filter receiver  200 . The traditional RAKE filter receiver may include an antenna  105 , a bandpass filter  110 , a low-noise amplifier  120 , and a PSK symbol detector  199 . The RAKE filter  230  consists of multiple correlators or matched filters  242  &amp;  248 , in which the received signal is multiplied by time-shifted versions of a locally generated code sequence. The local reference signal may be stored within the matched filters  242  &amp;  248 . The module  270  often provides timing when the switches should open and close. Module  270  may also provide channel information, such as, for example, channel gains on each path to the combining module. The RAKE filter often separates signals such that each finger only processes signals received via a single (resolvable) path. A conventional RAKE filter employs a combining module  280 , such as, for example, a maximum ratio combiner or equal gain combiner, to combine the signal energy distributed in the paths. Like the DPSK receiver of FIG. 1, the combining module  280 , of FIG. 2, is often subject to intersymbol interference (ISI) and multiple-access interference (MAI).  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]    Subject matter is particularly pointed out and distinctly claimed in the concluding portions of the specification. The claimed subject matter, however, both as to organization and the method of operation, together with objects, features and advantages thereof, may be best understood by a reference to the following detailed description when read with the accompanying drawings in which:  
         [0008]    [0008]FIG. 1 is a block diagram illustrating a traditional DPSK receiver;  
         [0009]    [0009]FIG. 2 is a block diagram illustrating a traditional RAKE filter receiver;  
         [0010]    [0010]FIG. 3 is a block diagram illustrating a multi-branched embodiment of an apparatus in accordance with the disclosed matter;  
         [0011]    [0011]FIG. 4 is a block diagram illustrating an embodiment of an apparatus in accordance with the disclosed matter utilizing down converters;  
         [0012]    [0012]FIG. 5 is a block diagram illustrating an embodiment of an apparatus in accordance with the disclosed matter utilizing RAKE filters;  
         [0013]    [0013]FIG. 6 is a block diagram illustrating an embodiment of a system in accordance with the disclosed matter; and  
         [0014]    [0014]FIG. 7 is a flowchart illustrating an embodiment of a technique in accordance with the disclosed matter.  
     
    
     DETAILED DESCRIPTION  
       [0015]    In the following detailed description, numerous details are set forth in order to provide a thorough understanding of the present disclosed subject matter. However, it will be understood by those skilled in the art that the disclosed subject matter may be practiced without these specific details. In other instances, well-known methods, procedures, components, and circuits have not been described in detail so as to not obscure the disclosed subject matter.  
         [0016]    [0016]FIG. 3 is a block diagram illustrating a multi-branched embodiment of an apparatus  300  in accordance with the disclosed matter. It is contemplated that other embodiments of the disclosed subject matter may exist that do not utilize a multi-branched filter. The apparatus may receive a UWB signal  366  via antenna  305 . The signal may be isolated (isolated signal  364 ) and amplified by an amplification unit  315 . The amplification unit may produce a received signal  367 . The received signal may be filtered by an analog adaptive front end  330 . The analog adaptive front end may attempt to, at least in part, suppress interference in the received UWB signal. It is contemplated that such interference may include, for example, multiple-access interference or intersymbol interference; however, other forms of interference may be suppressed. In one embodiment, the analog adaptive front end may perform adaptive filtering using a modified least means squared (LMS) function however, it is contemplated that other embodiments may utilize other filtering techniques. The analog adaptive front end may produce at least one symbol signal  365 ,  365 ′ &amp;  365 ″. The symbol signal(s) may be processed by PSK symbol detector  399  that may extract information from the symbol signal.  
         [0017]    The amplification unit  315  may include a bandpass filter  310  to isolate the UWB signal  366  and a low noise amplifier (LNA)  320  to amplify the isolated signal  364 . It is contemplated that other components may be used to isolate and amplify the UWB signal.  
         [0018]    The analog adaptive front end  330  may include a number of branches  390 ,  380  &amp;  370 . It is contemplated that one branch may exist for each observed symbol within an observation window. Accordingly, in this example embodiment, FIG. 3 illustrates an observation window of three symbols, and therefore, three branches. However, it is contemplated that any number, greater than one, of symbols may be observed. In one embodiment, if the observation window is only one symbol in duration, only one branch, e.g. the top circuit  390 , may be required. By adding more branches, e.g., branches  380  &amp;  370 , the observation window may be expanded.  
         [0019]    In this embodiment, each branch  390 ,  380  &amp;  370  may include a delay component  392 ,  382  &amp;  372 , a multiplier  394 ,  384  &amp;  374 , and an integrator  396 ,  386 , &amp;  376 , respectively. The delay component may delay an analog feedback signal  368 . This feedback signal may be generated by a feedback path circuit. This feedback circuit may include an adder  397  to compare a processed version of the received signal with the output of the PSK symbol detector  399 , and further include an amplifier  398 . In one embodiment, the amplifier may include a variable gain amplifier; however, other embodiments may utilize other amplification techniques.  
         [0020]    In one embodiment, the adder  397  may compute the difference between the training signal, or the feedback signal, i.e. s(iL+1), and the output of the integrator  396 . The difference in sign information, illustrated in FIG. 3, may, in one embodiment, be used to control the positive or negative gain of the variable gain amplifier  398 . It is contemplated that other forms of feedback amplification may be used, including, but not limited to, a multiplier, such as, for example multiplier  394 . In the embodiment illustrated by FIG. 3, the feedback path is integrated with the first branch  390 ; however, it is contemplated that the feedback path may be a discrete component.  
         [0021]    The multipliers  372 ,  382 , &amp;  392  substantially filter the received UWB signal utilizing the filter, or feedback, signal. The feedback signals stay within the circuit and thus no digital storage components are needed in this embodiment. The integrators  376 ,  386 , &amp;  396  produce a symbol signal utilizing the output of the multiplier. The PSK symbol detector  399  may then extract information from the symbol signal(s) received from the branches.  
         [0022]    [0022]FIG. 4 is a block diagram illustrating an embodiment of an apparatus  400  in accordance with the disclosed matter utilizing down converters. It is contemplated that other embodiments of the disclosed subject matter may exist that do not utilize down convertors. The apparatus may receive a UWB signal  366  via antenna  305 . The signal may be isolated (isolated signal  364 ) and amplified by an amplification unit  315 . The amplification unit may produce a received signal  367 . The received signal may be filtered by an adaptive front end  430 . The adaptive front end may attempt to suppress, at least in part, interference in the received UWB signal. It is contemplated that such interference may include interference, such as, for example, multiple-access interference or intersymbol interference; however, other forms of interference may be suppressed. In one embodiment, the analog front end may perform adaptive filtering using a modified least means squared algorithm; however, it is contemplated that other embodiments may utilize other filtering techniques. It is also contemplated that the adaptive front end may include analog components, digital components, or a mixture thereof. The adaptive front end may produce at least one symbol signal  395 . The symbol signal(s) may be processed by PSK Symbol Detector  399  that may extract information from the symbol signal.  
         [0023]    The adaptive front end  430  may include three stages: down converters  432  &amp;  434 , integrators  442  &amp;  444 , and an adaptive filtration stage  450 . A received signal  367  is first bandpass filtered  310  and amplified  320 . In one embodiment, the amplified signal may be a carrierless signal, i.e., a signal that does not use a carrier wave. The signal may include frequency components from f i  to f u , where f i  and f u  are the low and high end cut-off frequencies of the UWB signal.  
         [0024]    In one embodiment, the carrierless signal may be down converted using down converters  434  &amp;  432 . The down converters convert the carrierless signal of f bandwidth into two signals  363  &amp;  363 ′ of f/2 bandwidth. In one embodiment, down converter  432  may generate a down converted signal  363  by multiplying the carrierless signal with a cosine wave signal. Down converter  434  may generate a down converted signal  363 ′ by multiplying the carrierless signal with a negative sine wave signal. It is contemplated that other embodiments may utilize a different down conversion technique. This down conversion may reduce the Nyquist sampling rate of the produced two signals.  
         [0025]    The integrators  442  &amp;  444  may further reduce the required sampling rate of the respective down converted signals  363  &amp;  363 ′. Traditionally, low or band pass filters are utilized after a down conversion stage. By utilizing integrators, the multipath energy, or energy of the two down converted signals, falls within the integration interval and results in a reduction of the required sampling rate.  
         [0026]    The adaptive filtration stage  450 , may attempt to suppress, at least in part, the multiple-access interference (MAI) and intersymbol interference (ISI) in the two down converted signals. In one embodiment, the adaptive filtration stage  450  may include digital components, such as, analog-to-digital converters  452  &amp;  454  and a digital adaptive filter  460 . One embodiment may include a digital least-means squared (LMS) filter as illustrated in FIG. 1. It is noted that the reduced required sampling rate resulting from the down converters and integration would greatly reduce the complexity of the digital adaptive filter. In another embodiment the analog adaptive filter  330  illustrated in FIG. 3, that includes a training stage and a decision-directed stage, may be used. However, the disclosed subject matter is not limited to the two illustrative examples.  
         [0027]    [0027]FIG. 5 is a block diagram illustrating an embodiment of an apparatus  500  in accordance with the disclosed matter utilizing RAKE filters. It is contemplated that other embodiments of the disclosed subject matter may exist that do not utilize down converters. The apparatus may receive a UWB signal  366  via antenna  305 . The signal may be isolated and amplified by an amplification unit  315 . The amplification unit may produce a received signal  367 . The received signal may be filtered by an adaptive front end  530 . The adaptive front end may attempt to suppress, at least in part, interference in the received UWB signal. It is contemplated that such interference may include, for example, multiple-access interference or intersymbol interference; however, other forms of interference may be suppressed. In one embodiment, the analog front end may perform adaptive filtering using a modified least means squared algorithm; however, it is contemplated that other embodiments may utilize other filtering techniques. The analog front end may produce at least one symbol signal  365 . The symbol signal(s) may be processed by PSK Symbol Detector  399  that may extract information from the symbol signal.  
         [0028]    The adaptive front end  430  may include a number of RAKE filters  532  &amp;  534 , and an adaptive filter  560 . The RAKE filters often separates signals such that each finger only sees signals coming in over a single (resolvable) path. A conventional RAKE receiver, illustrated by FIG. 2, provides channel gain estimation and employs a combining module  280 , such as, for example, a maximum ratio combiner or equal gain combiner, to combine the signal energy distributed in the paths. In one embodiment of the disclosed subject matter, illustrated by FIG. 5, the output of the RAKE filters may not be sent to a combining module, but instead to an adaptive filter  560 . Utilizing an adaptive filter, the adaptive front end may implicitly find the channel gains and make use of them. The adaptive filter may include a training stage and a decision-directed stage. One embodiment of such an adaptive filter is illustrated by FIG. 3. In another embodiment, the adaptive filter may include analog-to-digital converters to sample the output of the RAKE filters at a time corresponding to the paths, and a digital adaptive filter. However, it is contemplated that other adaptive filters may be used.  
         [0029]    [0029]FIG. 6 is a block diagram illustrating an embodiment of a system  600  in accordance with the disclosed matter. Such a system may include: an antenna  305 , an amplification stage  315 , an analog adaptive filter  630 , a PSK symbol detector  399 , and a PSK symbol transmitter  690 . It is contemplated that the amplification stage  315 , an analog adaptive filter  630 , a PSK symbol detector  399  may receive an UWB signal  696  as described in the illustrative example embodiments above; however, the disclosed subject matter is not limited to only the illustrative examples. PSK symbol transmitter  690  may utilize antenna  305  to transmit an UWB signal  666 .  
         [0030]    [0030]FIG. 7 is a flowchart illustrating an embodiment of a technique in accordance with the disclosed matter. Block  710  illustrates that such a technique may include receiving an UWB signal. Block  720  illustrates isolating a signal using the received UWB signal. Block  730  illustrates amplifying the isolated signal to produce a received signal. Block  740  illustrates adaptively filtering the received signal. It is contemplated that adaptively filtering may include any technique described in the illustrative example embodiments above; however, the disclosed subject matter is not limited to only the illustrative examples. For example, the filtering may include a training and decision-directed stage. Wherein the training stage includes a feedback system to train the filter to correctly recognize symbols, and the decision-directed stage isolated a recognizes the symbols. Block  750  illustrates extracting information from the filtered signal.  
         [0031]    The techniques described herein are not limited to any particular hardware or software configuration; they may find applicability in any local and/or distributed computing or processing environment. The techniques may be implemented in hardware, software or a combination of the two. The techniques may be implemented in programs executing on programmable machines such as mobile or stationary computers, personal digital assistants, and similar devices that each include a processor, a storage medium readable by the processor (including volatile and non-volatile memory and/or storage elements), at least one input device, and one or more output devices. Program code is applied to the data entered using the input device to perform the functions described and to generate output information. The output information may be applied to one or more output devices.  
         [0032]    Each program may be implemented in a high level procedural or object oriented programming language to communicate with a processing system. However, programs may be implemented in assembly or machine language, if desired. In any case, the language may be compiled or interpreted.  
         [0033]    Each such program may be stored on a storage medium or device, e.g. compact read only memory (CD-ROM), digital versatile disk (DVD), hard disk, magnetic disk or similar medium or device, that is readable by a general or special purpose programmable machine for configuring and operating the machine when the storage medium or device is read by the machine to perform the procedures described herein. The system may also be considered to be implemented as a machine-readable storage medium, configured with a program, where the storage medium so configured causes a machine to operate in a specific manner. Other embodiments are within the scope of the following claims.  
         [0034]    While certain features of the disclosed subject matter have been illustrated and described herein, many modifications, substitutions, changes, and equivalents will now occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes that fall within the true spirit of the disclosed subject matter.