Abstract:
A communications system and method for exchanging spectrum usage information through a drop box ( 100 ) includes one or more central stations ( 101 ) that defines a region of operation. A central drop box ( 102 ) is associated with the central station ( 101 ) for providing a database of spectrum usage information. Stations ( 103, 105, 107 ) using the communications system may submit information regarding spectrum usage to the central drop box ( 102 ) that affects the region of operation ( 109, 115 ) for providing the most efficient and non-interfering uses of the frequency spectrum.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to the efficient utilization of radio frequency (RF) spectrum and more particularly to a regional CR database for allowing heterogeneous cognitive radio networks to submit and share information regarding sensing observations. 
     BACKGROUND 
     Cognitive radio (CR) is a paradigm for wireless communication in which either a network or a wireless node changes its transmission or reception parameters to communicate efficiently while avoiding interfering with licensed users and coexisting with other unlicensed users. This alteration of parameters is based on the active monitoring of several factors in the external and internal radio environment, such as radio frequency spectrum, user behavior and network state. In a CR network, elements of the network may be assigned sensing tasks to maximize the network&#39;s responsiveness to the presence of one or more parameters, such as higher priority users, interference, or important changes to the operation of the air interface. Generally, the individual nodes draw conclusions about the spectral occupancy of multiple channels, frequencies, and networks and submit their conclusions to a coordinating node in one or more centralized network or with neighbors in a distributed network. This information is kept within each of the networks. 
     CR networks in proximity to one another could benefit from a sharing of observations, which would act to extend the effective sensing range and/or reliability of the individual nodes and networks. This would allow networks to better utilize resources and abandon a channel or other frequency spectrum due to the presence of a higher priority user or potential interference. Networks could also discover the extent of their emissions as measured by neighboring networks, thereby allowing them to compare their emissions with expectations and adjust transmit power accordingly. 
     The prior art describes various types of spectrum sensing systems and methods; however, these systems do not describe how to process this information. For example, the publication to Visotsky et al. entitled “On Collaborative Detection of TV Transmissions in Support of Dynamic Spectrum Sharing” describes combining signal-to-noise (SNR) data for soft combining of sensing, but does not measure parameters such as raw spectrum or time domain measurements that can afford a greater opportunity for extraction of signal information. The publication to Gruenwald entitled “A Power-Aware Technique to Manage Real-Time Database Transactions in Mobile AD-Hoc Networks” describes a repository of information and a reservation system as well as nodes reporting their location information and energy level such as in battery reserves. However, the Gruenwald publication does not describe a database being used to enhance or otherwise coordinate radio operations or make spectrum choices which could improve the capacity and reliability performance of the system. The publication to Grecu et al. entitled “Detection of Anomalous Propagation Echoes in Weather Radar Data using Neural Networks” proposes limiting the examination of a propagation anomaly to an originating node. However, much more information could be gathered by a network of sensing nodes to determine the propagation. Finally, the publication to Kim et al. entitled “WRAN PHP/MAC Proposal for TDD/FDD” describes the use of a separate scanning receiver but does not describe any encrypted transmission of sensing results for protection of the database. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       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. 
         FIG. 1  is a block diagram illustrating a cognitive radio system used for exchanging spectrum sensing measurements though a drop box in accordance with an embodiment of the present invention. 
         FIG. 2  is a flowchart diagram illustrating the steps for posting and exchanging information to a drop box. 
         FIG. 3  is a flowchart diagram illustrating steps in a user request to become a remote drop box. 
         FIG. 4  is a flowchart diagram illustrating steps in a user request for pattern analysis. 
         FIG. 5  is a flowchart diagram illustrating steps in a user request posting of MAC/PHY info. 
         FIG. 6  is a flowchart diagram illustrating steps in a user request for posting its own usage statistics. 
         FIG. 7  is a flowchart diagram illustrating steps in a user request for permission to submit sensing conclusions. 
         FIG. 8  is a flowchart diagram illustrating steps in a user request for permission to submit sensing data. 
     
    
    
     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 of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention. 
     DETAILED DESCRIPTION 
     Before describing in detail embodiments that are in accordance with the present invention, it should be observed that the embodiments reside primarily in combinations of method steps and apparatus components related to a method for exchanging and processing spectrum sensing measurements through a drop box. Accordingly, the apparatus components and method steps have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein. 
     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,” or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises 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” does not, without more constraints, preclude the existence of additional identical elements in the process, method, article, or apparatus that comprises the element. 
     It will be appreciated that embodiments of the invention described herein may be comprised of one or more conventional processors and unique stored program instructions that control the one or more processors to implement, in conjunction with certain non-processor circuits, some, most, or all of the functions of a method for exchanging and processing spectrum sensing measurements through a drop box as described herein. The non-processor circuits may include, but are not limited to, a radio receiver, a radio transmitter, signal drivers, clock circuits, power source circuits, and user input devices. As such, these functions may be interpreted as steps of a method to perform a method for exchanging and processing spectrum sensing measurements through a drop box. 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. Thus, methods and means for these functions have been described herein. 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 present invention is directed to a regional CR database or CR “Wiki” that allows heterogeneous CR networks to submit information regarding sensing observations as well as other information that could benefit heterogeneous networks. The CR environment  100  includes a central licensed station  101  working in a point-to-multipoint manner with a plurality of mobile stations  103 ,  105 ,  107 . The central station  101  and mobile stations  103 ,  105 ,  107  operate within a region of operation such as licensed protected boundary  109 . Similarly, licensed mobile stations  111 ,  113  operate in a peer-to-peer fashion at an arbitrary location which may overlap an unlicensed network boundary  115 , which in turn may operate adjacent to or within the licensed protected boundary  109 . As seen in  FIG. 1 , a portion of the unlicensed boundary  115  may extend or overlap into the licensed protected boundary. 
     In a preferred embodiment, the CR database is accessible over the Internet via wireless or wired connections. Cognitive radios  117  that do not have direct access to the Internet themselves may gain access through an unlicensed unit  119  which has an Internet connection  121 . In some cases, if the cognitive radios can configure themselves with the appropriate licensed personality, they may access the Internet through licensed networks such as cellular, personal communication services (PCS), third generation cellular systems (3G), Worldwide Interoperability for Microwave Access (WiMAX) or other licensed networks. In operation a regional CR database may be centralized at a central station  101  or can be a distributed regional real-time database that serves as a repository for information from multiple CR networks within the range of influence of the database. The centralized database may include a superset of information in a wired network, distributed in a number of wireless nodes, or both where access of the database may be over either wired or wireless channels. Several types of information would be conducive to the efficient use of unused or underused spectrum, and several examples are given here. Even if the database were distributed to a number of wireless nodes, these stations or “nodes” could all contain more information than that particular node could use. For example, if a node can operate at VHF/UHF/700/800 cognitively, but cannot operate at 2.4, 4.9, and/or 5.8 GHz because it does not have a transceiver for those frequencies, it can still contain database information for some or all of those frequency bands, so that other nodes which come within range that can work at both lower frequencies and higher frequencies can retrieve the info. 
       FIG. 2  is a flowchart diagram illustrating the steps for posting and exchanging information to a drop box as shown in  FIG. 1 . Initially, a geographic region is defined  201  by specifying a central location coordinate and a radius, location coordinates at the vertices of a polygon, or other geometric constructs, defining an area of operation for one or more network stations as well as a plurality of mobile stations. A master drop box  203  may be established with a message board which typically will be accomplished at least one of the network stations. Access is then provided to the info at the drop box  205  while the system will wait for users  207  to access this information. 
     Thereafter, a plurality of requests may then be made by the user to access and/or post various requests regarding system functionality. For example, a user may request to become a remote drop box  209 . 
       FIG. 3  is a flowchart diagram illustrating the steps in such a request to become a remote drop box. Initially, CR nodes receive a time stamped copy of the database for the remote drop box  301  and a determination is made  303  if the valid time stamp has expired. If the time stamp has not expired, this process is then repeated  303 . However, upon expiration, a determination is made if the remote drop box has info to update the master drop box  305 . If the master drop box is to be updated, the remote drop box node accesses the master drop box and relays information it has accumulated  307 . However, if the remote drop box has no master update information, or if the accumulated information has been relayed, then the remote drop box requests an update from the master  309 . This process repeats until the user request to become a remote drop box has been accomplished. 
     The user may also request a pattern analysis of sensing data  211 .  FIG. 4  is a flowchart diagram illustrating steps in the user request for a pattern analysis. These steps would include collecting sensing results of  401  at the drop box that pertain to a common source/network. The drop box then maps geo-location and time stamp information  403  from the sensing nodes that have reported sensing information. Based on a propagation model, the drop box then maps estimated locations of sensed transmitters versus time-based overlaps of circles representing a computed radius centered on the sensing node location  405 . In cases where there are too few nodes and insufficient overlap, a message may be conveyed to the user that pattern analysis of the sensing data is not possible in view of insufficient information  409 . After the estimated locations have been mapped, the process ends  411 . 
     A user may also request a posting of the media access control layer (MAC) or the physical layer protocol (PHY).  FIG. 5  is a flowchart diagram illustrating the steps in a user-request posting of the MAC/PHY info. In view of this request, the CR network posts its MAC/PHY parameter set to the drop box  501 . This works to enable radios that wish to join their network. As will be evident to those skilled in the art, these radios may utilize duplexing methods, multiple access methods, temporal parameters, such as frame/slot/symbol duration, pulse-shaping, Fast Fourier Transform (FFT) parameters, synch sequences, frame structures, control header sequences, and the like. After the MAC/PHY parameter set has been posted to the drop box, the process ends  503 . 
     A user may also request a posting of its own usage statistics  215 .  FIG. 6  is a flowchart diagram illustrating steps in a user request to post its own usage statistics. This process begins when the CR network posts or updates its usage statistics, such as excess capacity, quality of service (QoS), latency, and throughput versus time of day, time of week, and other time-based parameters  601 . This operates to inform the radios that might want to participate in the network on expected throughput and quality of the throughput they can expect if they choose to use the network. After this information is updated, this process ends  603 . 
     The user may also request permission to submit its own sensing conclusions  217 .  FIG. 7  is a flowchart diagram illustrating the steps in a user request for permission to submit sensing conclusions. This process begins by the CR network reporting its sensing conclusions  701 . These conclusions may refer to such parameters as frequency, time, and identification of a specific transmitter or transmitter type (e.g. licensed, unlicensed) to a drop box. Thereafter, the drop box compares these sensing conclusions with other reports from the area  703 . A determination is then made if the report confirms other reports in the area  705 . If other reports are confirmed, the sensing result is posted as corroborated by N other reports in the drop box  709 . These corroborations may include such parameters as channel, sensor location, estimated transmitted location (if known), coexistence requirements, and/or observed usage patterns. 
     Thereafter, this process ends  711 . However, if no report confirmation is made, a further determination is made if other reports for the same time and location conflict with the CR report  713 . Those skilled in the art will recognize that in order for this determination to be made, this determination may be made on a majority or if some other sensor had better propagation conditions. If there is a conflict with this report, the sensing result is acknowledged, but is held without generating a report  715 . Thereafter, a confirmation is requested by posting a sensing request on the drop box message board  719 . The process ends thereafter  719 . If no other reports for the same time and location conflict with the CR report, the sensing results are posted as an unverified report on the drop box message board  717 . Confirmation can then be requested by posting a sensing request  719  where the process can then end  711 . 
     Finally, a user may also request permission to submit sensing data to a drop box  219 .  FIG. 8  is a flowchart diagram illustrating the steps in a user request for permission to submit sensing data  800 . This process begins when the CR network reports its sensing data such as time samples to a drop box  801 . The drop box performs an analysis of the sensing data  803  and compares these analysis results to known signatures for identifying a sensed wave form  805 . A determination is then made if the wave form corresponds to the known licensed or unlicensed wave forms in an area  807 . If a correspondence is made, the results are posted as a known licensed or unlicensed CR system operating in the area  809 . Thereafter, the process ends  811 . However, if the wave form does not correspond to a known licensed or unlicensed wave form, the features of the wave form are extracted  813  and posted on the drop box message board along with the request for other sensors to look for future occurrences of this wave form. The drop box may optionally contact other regional drop boxes to inquire whether such a wave form has been observed  815 . Thereafter, the process ends  811 . 
     Those skilled in the art will recognize that CR networks can benefit from shared sensing versus location and time observations. For example, a network, which may be cognitive, can report detection of television (TV) signals. If the detection of the TV signal indicates an isolated coverage area and certain temporal features, this may be an indication of an anomalous propagation mode, such as ducting or sporadic-E scattering. By sharing observations of multiple networks, a larger context of the environment can be generated and conclusions can be drawn regarding the origin of the signal. 
     In a similar way, localized use by higher priority local area networks can be described by a network, and other networks could determine whether they had to take action to satisfy interference constraints, such as decreasing transmitter power, altering an antenna pattern, or moving to another frequency. Those skilled in the art will further recognize that these previous networks may be cognitive but this is not required. Cooperation between participating CR networks can also include measurements of power from other network&#39;s transmissions, the time periods at which the transmissions take place, the protocol(s) used at these times, and other information, giving the CR network an indication of the extent of its emissions and operation and enabling it to more accurately adjust transmit power, transmit timing, and other factors to remedy potential interference situations. The database can also catalog spectral signatures that have been detected in the area with any information on the system, so that a CR network could contact the database with an inquiry such as “The following spectral signature was detected. Is there any information on this signature?” 
     In yet another aspect of the invention, participating networks catalog their MAC/PHY details (e.g., IEEE 802.xx, etc.). Knowledge of a neighboring network&#39;s air interface will help a CR system looking for opportunities to know whether its air interface will be a good match for sharing with that system. Not only should the MAC/PHY protocols be categorized, but also the traffic carried on these networks. For example, if all of the traffic on a particular network is low-priority, best effort data, then this network may be a good candidate for carrying high(er)-priority periodic voice traffic (given other characteristics of the network support such a service). Knowing what the protocol is as well as what is currently being transported will allow for more intelligent decisions on utilizing available channels. An intelligent implementation of the database could function as an agent to aid in identification of available spectrum or as a “marriage broker” to coordinate sharing between two systems. This could further involve pseudomonetary incentives to share such as systems using credit tokens. 
     Authenticity of such databases would be a concern. For example, a malicious participant might submit false measurement information on a channel to clear others away from it, leaving relatively pristine spectrum for the deceiver&#39;s use. Or, the malicious user&#39;s goal may simply be to disrupt the opportunity for others. As such, some authentication is desirable to ensure the veracity of the database. One method of defense would be to see if other networks can confirm the detection reported by a submission. This may not always be effective since the reported higher priority signal may be a short range signal, or the original report may be legitimate but the confirmation malicious, in this case falsifying the absence of the higher priority signal that is really present. Thus, the database would require a security component as well, such as some kind of membership code or some other means of authentication. One approach is to let falsifiers make their claims, but if the claims are later determined to be false, the MAC address of the sender could be barred from further access (either to contribute or to read). 
     Still another aspect of the invention is for nodes to report their actual sensing measurements or raw data rather than the conclusions they might otherwise have drawn from those measurements. This would allow for lower cost nodes that do not require software updates to identify new spectral signatures, and place the complexity in the central analysis node, which may be accessed directly via wireless connection from the sensors, or may be accessed via the internet or some other backbone, depending on the response times required by the spectrum incumbents. One concern is the amount of bandwidth required to report raw data from several/many nodes. Raw data is typically amounts to a great deal of information, as compared to processed data. There may need to be some mention of either (a) that the reports from each node are only sent when information changes by a certain amount, or at a given periodicity, or both, to keep it below some loading threshold, or (b) that some intermediate compression, between full raw data and fully processed results, is done in the inexpensive nodes. A third mechanism may be that they only report when polled, so that the centralized node has control over how much info gets reported. A good example in this case is if the centralized node already has recent reports from a certain geographic area, it won&#39;t poll for more info from nodes in that area, but if there has not been a report from a different geographic area for a long time period, then the centralized node can poll and/or solicit “raw” data from that area. 
     Finally, another aspect of the invention is to have a second receiver present in each node performing scanning and identification of unused channels followed by a return to the licensed user&#39;s channels to monitor their activity. Information gathered by the nodes would use a secure channel for configuration and control of the network behaviors. This secure and/or encrypted channel could be used for reporting the information back to the centralized server which maintains the sensing database, and/or could be used to send information to other radio nodes in the ad hoc network case and distributed database case. 
     Hence, the present invention is directed to a system and method for allowing heterogeneous CR networks to submit information regarding sensing observations as well as other information that could benefit heterogeneous networks by having a common repository for information from multiple regional area systems. Since all participating networks can benefit from the larger contextual picture of the environment, the invention provides a means to coordinate operations in an efficient manner to most efficiently utilize the frequency spectrum while protecting higher priority users. 
     In the foregoing specification, specific embodiments of the present invention 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 present 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 invention. 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.