Patent Application
20130265034
The present invention generally relates to signal detection, and more particularly to fast spectral survey to determine signal presence.
In a cognitive radio system of the type considered for use by IEEE 802.22, a cognitive secondary radio system will utilize spectrum assigned to a primary system using an opportunistic approach. With this approach, the secondary radio system will share the spectrum with primary incumbents as well as those operating under authorization on a secondary basis. Under these conditions, it is imperative that any user in the cognitive radio system not interfere with primary users.
Having spectrum awareness is an essential tool for agile cognitive radios where they may access unlicensed spectrum opportunistically, when other primary or secondary systems are not using it. For a robust and efficient wide-band spectral usage, especially when channel's instantaneous as well as long run occupancy varies over time, fast and reliable sensing of vast spectrum that will result in an accurate time-varying statistical channel characterization is a must. Therefore, a need exists for a method and apparatus for a dynamic fast spectral survey to determine signal presence.
The accompanying figures where like reference numerals refer to identical or functionally similar elements throughout the separate views, and which together with the detailed description below are incorporated in and form part of the specification, serve to further illustrate various embodiments and to explain various principles and advantages all in accordance with the present invention.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions and/or relative positioning of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the present invention. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are often not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention. It will further be appreciated that certain actions and/or steps may be described or depicted in a particular order of occurrence while those skilled in the art will understand that such specificity with respect to sequence is not actually required.
In order to address the above-mentioned need, a method and apparatus for a multi-resolution, multi-bandwidth spectral survey to determine signal presence is provided herein. During operation, a plurality of detectors is provided to determine if an input signal is above a predetermined threshold. The input signal comprises a first frequency range having a first bandwidth. If it is determined that the input signal of the first bandwidth is above a first predetermined threshold, then the same plurality of detectors are used to further analyze sub-bands of the first frequency range, each sub-band having a second bandwidth less than the first bandwidth. The further analysis determines if an input signal to a detector is above a second predetermined threshold.
This above-described method and apparatus allows for fast and reliable low to high resolution spectral occupancy updates. Furthermore, the ability of the above method and apparatus to adaptively change the band being analyzed, the frequency resolution, and the threshold or amplitude resolution, lends itself for fast detection and classification of signals in a large amount of spectrum.
The following description describes a receiver used to rapidly detect energy throughout a vast spectrum to determine channel occupancy. The receiver comprises a down-converting frequency mixer with an agile local oscillator (LO synthesizer) frequency source, a channel filter followed by a vector-magnitude level detector with its threshold set above the channel noise floor for acceptable falsing-rate statistics whose output signals occupancy, a LO synthesizer dwell timer controlling the LO synthesizer source's frequency such that the LO synthesizer dwells for the channel filter's minimum required time to allow the detector to trip if energy stronger than noise exists (i.e. minimum time is the filter's group delay), a channelization scheme to either rapidly step through frequency spectrum sequentially (sequential processing) or rapidly sweep through frequency spectrum simultaneously (parallel processing).
A plurality of level detectors is combined in order to trade-off level resolution versus frequency resolution and detection speed. A multiplexor can be switched such that one channel filter is connected to all level detectors with the level detector thresholds scaled for multi-bit level detection (high resolution). Furthermore, the operation allows for one or fewer level detectors be distributed in different bands for multiband low resolution detection.
The method and apparatus provide a parallel processing signal acquisition system that utilizes a multi-filter (Multi Bandwidth), multi-detector & multi-resolution time varying approach. The system can acquire large sections of bandwidth at low resolution in several orders of magnitude less time and then quickly reconfigure to a more traditional higher resolution signal acquisition and demodulation system.
The method and apparatus enables a means to rapidly acquire time dependent information and classification of a large frequency band for further analysis, classification, tracking, utilization, occupancy and/or demodulation. Detectors and filters can be quickly re-configured for trading off low resolution/low latency for high resolution/high latency. These detectors and filters can process distinct spectrums and signals concurrently and independently.
Turning now to the drawings, wherein like numerals designate like components,
In combination, LO 102 and modulator 101 are capable of providing an output from modulator 101 having a particular bandwidth and frequency range. Low-pass or band-pass filters 103 (only one labeled) are provided to filter a particular frequency band output from modulator 101. Multiplexer 104 combines the outputs of the filters 103. The combined output is provided to a plurality of detectors 105 (only one labeled).
In one embodiment detectors 105 comprise simple one-bit detectors that serve to simply indicate (via a 0 or a 1) if an input is above a particular threshold level (LEVth). The threshold level 106 is output to/from logic circuitry 107. Logic circuitry 107 comprises a digital signal processor (DSP), general purpose microprocessor, a programmable logic device, or application specific integrated circuit (ASIC) and is utilized to access and control apparatus 100. As shown, logic circuitry 107 serves as dwell timer 108 that controls the timing of frequency sweeps and the particular frequency bands output by modulator 101, as well to control and change bandwidths output from multiplexer 104 to any particular detector 105. Additionally logic circuitry 107 modifies thresholds utilized by detectors 105.
During operation LO 102 is tuned to output a first bandwidth within a first frequency range from modulator 101. A first threshold level 106 (LEVth<0>) for a first detector 105 set to an acceptable level above a receive noise floor. LO 102 dwell timer set to the minimum time required to trip a detection by detector 105 (this criteria speeds up the detection process since we are only interested in a binary result as to whether energy is present and not interested in waiting the extra time required to allow the energy to grow to its full magnitude). The dwell time is inversely proportional to channel bandwidth, i.e. smaller bandwidth longer dwell time and vice versa.
The first bandwidth, within the first frequency range (referred to from here on as a first wideband signal) enters a single first detector 105. If the input signal amplitude to the single first detector 105 is above a predetermined threshold, multiple detectors 105 (including the single first detector 105) are utilized to further analyze the first wideband signal. Logic circuitry 107 continuously monitors the outputs of all detectors 105. More specifically, if the first single detector detects a signal within the first wideband signal, logic circuitry 107 then instructs multiple detectors 105 to analyze narrowband portions of the first wideband signal. This is accomplished by inputting a narrowband portion of the first wideband signal into each detector 105, covering the frequency range. This is illustrated in
As shown in
The above process can be run in parallel for multiple wideband signals by simultaneously passing a wideband signal to one of the plurality of detectors 105 and then narrowing the bandwidth until the complete bandwidth of interest has been analyzed. For each wideband signal, LO 102 and modulator 101 can be stepped through N sub-channels using threshold levels set above a receive noise floor and dwell timer set to corresponding minimum time for detection. As energy is detected logic circuitry 107 arranges the resultant bits to create a time-frequency spectrogram bitmap (this will be described below).
Although the process of
However, if at step 405 logic circuitry 107 detects energy on a given channel, the data is stored (step 407), and that channel is scanned at a narrower bandwidth (step 409). More particularly, LO 102 and modulator 101 are set to pass N narrowband channels within the previous wideband channel. The threshold detector level 106 is also adjusted accordingly, and detectors 105 determine if any narrowband channels have energy above a threshold. At step 415 logic circuitry 107 determines if all narrowband channels have been scanned. If so, the data is stored (step 417) and the logic flow continues to step 419 where the necessary parameters are set again to scan the first channel (CH#0). If, however, at step 415 it is determined that all narrowband channels have not been scanned, then the logic flow returns to step 413.
The process described in
It should be noted that all of the detectors described in
Arranging Resultant Bits into a Time-Frequency Spectrogram Bitmap
As a first step, spectral occupancy information is needed. This is provided as described above. More particularly, the spectral updates come in the form of binary occupancy data for the different frequencies (1 bit data representation), which implies that the energy detection is already performed in the sensing process. These data are passed from detectors 105 to DSP 107 where they can be combined to describe the occupancy and classification of a channelized spectrum (uniform or variable BWs per channel) as in
In the foregoing specification, specific embodiments have been described. However, one of ordinary skill in the art appreciates that various modifications and changes can be made without departing from the scope of the invention as set forth in the claims below. Accordingly, the specification and figures are to be regarded in an illustrative rather than a restrictive sense, and all such modifications are intended to be included within the scope of present teachings.
Those skilled in the art will further recognize that references to specific implementation embodiments such as “circuitry” may equally be accomplished via either on general purpose computing apparatus (e.g., CPU) or specialized processing apparatus (e.g., DSP) executing software instructions stored in non-transitory computer-readable memory. It will also be understood that the terms and expressions used herein have the ordinary technical meaning as is accorded to such terms and expressions by persons skilled in the technical field as set forth above except where different specific meanings have otherwise been set forth herein.
The benefits, advantages, solutions to problems, and any element(s) that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as a critical, required, or essential features or elements of any or all the claims. The invention is defined solely by the appended claims including any amendments made during the pendency of this application and all equivalents of those claims as issued.
Moreover in this document, relational terms such as first and second, top and bottom, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. The terms “comprises,” “comprising,” “has”, “having,” “includes”, “including,” “contains”, “containing” or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises, has, includes, contains a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. An element proceeded by “comprises . . . a”, “has . . . a”, “includes . . . a”, “contains . . . a” does not, without more constraints, preclude the existence of additional identical elements in the process, method, article, or apparatus that comprises, has, includes, contains the element. The terms “a” and “an” are defined as one or more unless explicitly stated otherwise herein. The terms “substantially”, “essentially”, “approximately”, “about” or any other version thereof, are defined as being close to as understood by one of ordinary skill in the art, and in one non-limiting embodiment the term is defined to be within 10%, in another embodiment within 5%, in another embodiment within 1% and in another embodiment within 0.5%. The term “coupled” as used herein is defined as connected, although not necessarily directly and not necessarily mechanically. A device or structure that is “configured” in a certain way is configured in at least that way, but may also be configured in ways that are not listed.
It will be appreciated that some embodiments may be comprised of one or more generic or specialized processors (or “processing devices”) such as microprocessors, digital signal processors, customized processors and field programmable gate arrays (FPGAs) and unique stored program instructions (including both software and firmware) that control the one or more processors to implement, in conjunction with certain non-processor circuits, some, most, or all of the functions of the method and/or apparatus described herein. Alternatively, some or all functions could be implemented by a state machine that has no stored program instructions, or in one or more application specific integrated circuits (ASICs), in which each function or some combinations of certain of the functions are implemented as custom logic. Of course, a combination of the two approaches could be used.
Moreover, an embodiment can be implemented as a computer-readable storage medium having computer readable code stored thereon for programming a computer (e.g., comprising a processor) to perform a method as described and claimed herein. Examples of such computer-readable storage mediums include, but are not limited to, a hard disk, a CD-ROM, an optical storage device, a magnetic storage device, a ROM (Read Only Memory), a PROM (Programmable Read Only Memory), an EPROM (Erasable Programmable Read Only Memory), an EEPROM (Electrically Erasable Programmable Read Only Memory) and a Flash memory. Further, it is expected that one of ordinary skill, notwithstanding possibly significant effort and many design choices motivated by, for example, available time, current technology, and economic considerations, when guided by the concepts and principles disclosed herein will be readily capable of generating such software instructions and programs and ICs with minimal experimentation.
The Abstract of the Disclosure is provided to allow the reader to quickly ascertain the nature of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. In addition, in the foregoing Detailed Description, it can be seen that various features are grouped together in various embodiments for the purpose of streamlining the disclosure. This method of disclosure is not to be interpreted as reflecting an intention that the claimed embodiments require more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive subject matter lies in less than all features of a single disclosed embodiment.
Thus the following claims are hereby incorporated into the Detailed Description, with each claim standing on its own as a separately claimed subject matter.
