Abstract:
An operational mechanism enables frequency re-use techniques, including selective frequency hopping and channel aggregation, on very low-cost transceiver hardware.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application is a continuation-in-part of and claims the benefit of previously filed, co-pending U.S. patent application, Ser. No. 10/730,753, filed Dec. 8, 2003, by Brent Saunders et al, entitled: “Radio Communication System Employing Spectral Reuse Transceivers” (hereinafter referred to as the &#39;753 application), and further claims the benefit of previously filed, co-pending U.S. patent application Ser. No.: 11/532,306, filed Sep. 15, 2006 by E. Gerhardt et al., entitled: “Spectral Reuse Transceiver-based Aggregation of Disjoint, Relatively Narrow Bandwith (voice) Channel Segments of Radio Spectrum for Wideband RF Communication Applications” (herein referred to as the &#39;306 application), which incorporates by reference and claims priority to U.S. Patent Application Ser. No. 60/784,105, filed Mar. 20, 2006, by E. Gerhardt et al, entitled: “Link Utilization Mechanism for Aggregation of Disjoint Radio Bandwidth,” (herein referred to as the &#39;105 application), the disclosures of the above three applications, each being incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates in general to communication systems and subsystems thereof, and is particularly directed to an ‘cost-efficient’ embodiment that may be employed by the communications controller of a spectral reuse in transceiver (transceiver) of a communication system of the type disclosed in the above-identified &#39;753 application, to enable spectral-reuse methods in transceivers having many of the benefits of the communication system disclosed in the above identified &#39;753 applications, having minimal processor and memory capability. 
       BACKGROUND OF THE INVENTION 
       [0003]    As described in the above-identified &#39;753 application, in some radio bands, such as the 217-220 MHz VHF band, as a non-limiting example, governmental licensing agencies (e.g., the Federal Communications Commission (FCC)) customarily grant primary licensees non-exclusive use of the band for a variety of communication services, such as push-to-talk voice transmission. These primary users pay for this licensed use with an expectation that they will not encounter interference by other users. The FCC also allows secondary users to access the same band and the same channels within the band on a ‘non-interfering’ or secondary basis, whereby a channel may be used by a secondary, non-licensed, user, so long as the primary user is not using that channel. 
         [0004]    The FCC and similar agencies in foreign countries are continually looking for ways that allow expanded use of these licensed radio frequency bands, without reducing the quality of service available to the primary users. For secondary users, these bands provide a cost-free opportunity with excellent radio transmission properties for telemetry and other applications. Because secondary users must not interfere with primary users, complaints of interference from a primary user to the FCC may result in its issuing an administrative order requiring that the secondary user move to another portion of the band or leave the band entirely. Such a spectral transition is disruptive to the secondary user&#39;s service and can be expensive, especially if site visits, equipment modification, or exchange are required, in order to implement the mandated change. It will be appreciated, therefore, that there has been a need for a mechanism that allows a secondary-user to employ a licensed band on a non-interfering basis and will adapt the radio&#39;s frequency usage should new primary users appear. It should be noted that primary users always have priority over secondary users, there is no first-use channel frequency right for secondary users. 
         [0005]    Advantageously, the invention described in the above-referenced &#39;753 application successfully addresses this need by means of a monitored spectral activity-based link utilization control mechanism. Briefly reviewing this link utilization control mechanism, which may, without limitation, be used in a star-configured communication system, such as that depicted in the reduced complexity diagram of  FIG. 1 , a spectral reuse transceiver installed at a master site  10  communicates with respective spectral reuse transceivers installed at a plurality of remote sites  12 . Each spectral reuse transceiver operates with a selectively filtered form of frequency hopping for producing a sub-set of non-interfering radio channels or ‘sub-channels’. It should be noted here that other configuration or network topologies may be used consistent with the invention disclosed herein. Thus the invention may be used with radio links between transceivers in other topologies, such as point-to-point, and individual links in mesh networks, without limitation, consistent herewith. 
         [0006]    For this purpose, the master site  10  periodically initiates a clear sub-channel assessment routine, in which the master site and each of the remote sites  12  participate, in order to compile or ‘harvest’ a list of non-interfering or ‘clear’ sub-channels (such as 6.25 kHz wide sub-channels), which may be used by participants of the network for conducting communication sessions that do not ostensibly interfere with any licensed user. By transmitting on only (clear) sub-channels, a respective site&#39;s spectral reuse transceiver is ensured that it will not interfere with any primary user of the band of interest. 
         [0007]    Except when it is transmitting a message to the master site, each remote user site sequentially steps through and monitors a current list of clear sub-channels (that it has previously obtained from the master site), in accordance with a pseudo-random (PN) hopping sequence that is known a priori by all the users of the network, looking for a message that may be transmitted to it by the master site transceiver. During the preamble period of any message transmitted by the master site, each remote site&#39;s transceiver scans all frequency bins within a given spectrum for the presence of energy. Any bin containing energy above a prescribed threshold is marked as a non-clear sub-channel, while the remaining sub-channels are identified as clear and therefore available for reuse sub-channels. 
         [0008]    Whenever a remote site notices a change in its clear sub-channel assessment, it reports this to the master site at the first opportunity. As the master site has received clear sub-channel lists from all the remote sites, it logically combines all of the clear sub-channel lists, to produce a composite clear sub-channel list. This composite clear sub-channel list is stored in the master site&#39;s transceiver and is broadcast to all of the remote sites over a prescribed one of the clear sub-channels that is selected in accordance with a PN sequence through which clear sub-channels are selectively used among the users of the network. When the composite clear sub-channel list is received at a respective remote site it is stored in its transceiver. 
         [0009]    To ensure that all communications among the users of the network are properly synchronized (in terms of the (composite) clear sub-channel list and the order through which the units traverse, or ‘hop’ through, the clear sub-channel entries of the clear sub-channel list), the master site&#39;s transceiver transmits an initialization message on an a priori established clear sub-channel, which each of the remote units monitors. This initialization message contains the clear sub-channel list, an identification of the preamble channel, a PN sequence tap list, and a PN seed that defines the initial sub-channel and hopping sequence for the duration of an upcoming transmit burst. Once a remote site has received an initialization message, that site will transition to normal multiple access mode. 
         [0010]    For further details of the architecture and operation of the spectral reuse link control mechanism disclosed in the above-referenced &#39;753 application, attention may be directed to that document. They will not be detailed here, in order to focus the present description on the problem of a ‘cost efficient’ embodiment, whereby lower-end processors, smaller memory devices, and lower system requirements may be used, thereby lowering the cost of manufacture and deployment of a spectral reuse communication system, while preserving many of the benefits of spectral reuse. 
       SUMMARY OF THE INVENTION 
       [0011]    In accordance with the present invention, this ‘cost efficient’ goal is successfully addressed by proscribing a set of operating parameters described in the &#39;753 applications, including the number of carriers simultaneously transmitted (‘multi-carriers’), the sub-channel size (typically in kHz), hopping rate (every ‘n’ symbols, for example), the hopping pattern, the interference threshold by which the transceiver decides to hop to a new frequency set, and the clear sub-channel assessment period or trigger. 
         [0012]    A first of these parameter sets lowers the microprocessing and memory required of the transceiver, so that lower-cost components can be used. A second of these parameter sets further lowers the microprocessing and memory required of the transceiver and improves the clear sub-channel assessment. 
         [0013]    In another embodiment of the present invention, a parameter set will be chosen so that the transceiver will ‘aggregate’ and therefore provide greater re-use of said licensed channels. This embodiment uses the example of occasional-use voice channels by which the present embodiment provides data service during periods of non-voice usage. 
         [0014]    In another embodiment of the present invention, the transceiver provides increased upstream bandwidth through the use of a plurality of receiver circuits. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0015]      FIG. 1  diagrammatically illustrates the overall architecture of a communication network, with respective terminal unit transceiver sites which employ the spectral reuse transceiver of the invention disclosed in the above-referenced &#39;753 application; 
           [0016]      FIG. 2  graphically illustrates the division of usable channels into a selected subset and the remainder of the channels into an unselected subset. In one [all] embodiment(s), the transceiver will only use the selected subset of channels; 
           [0017]      FIGS. 3   a - c  illustrate an example hopping sequence through the usable channels according to the present invention, and the relationship between an interfering signal and a set of usable channels; 
           [0018]      FIG. 4   a - b  is a flowchart of a routine for implementing a sub-channel discriminator to select a hopping sequence according to an embodiment of the present invention; 
           [0019]      FIG. 5  is a flowchart of a routine for implementing a sub-channel discriminator to select a hopping sequence according to an embodiment of the present invention; 
           [0020]      FIG. 6  illustrates a transceiver with two receivers used to aggregate upstream transmissions; and 
           [0021]      FIG. 7  illustrates an example hopping sequence through the usable channels for the purpose of aggregating channels, according to an embodiment of the present invention. 
           [0022]      FIG. 8  illustrates a mobile radio with two receivers receiving signals from a plurality of base stations, according to an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION  
       [0023]    Before describing the details of the ‘cost efficient’ spectrum reuse transceiver of the present invention, it should be observed that the invention essentially involves special cases of the sub-channel hopping control mechanism executed by the communications control processor of the spectral reuse transceiver of the type disclosed in the above-referenced &#39;753 application, that involves the execution of one or more prescribed discriminators or sub-channel selection filters, so as to effectively reduce the receiving end of a transceiver link. As will be described, these filter functions are readily implemented by appropriately setting the configuration parameters used by the communications controller of the transceiver disclosed in the &#39;753 application to control the operation of the transceiver. The architecture of the transceiver of the &#39;753 application remains unchanged, except as noted. As a consequence, the present invention has been illustrated in the drawings by readily understandable diagrammatic illustrations, which include a generalized network architecture diagram, and a sub-channel sub-division diagram, that show only those details that are pertinent to the invention, so as not to obscure the disclosure with details which will be readily apparent to one skilled in the art having the benefit of the description herein. 
         [0024]    As pointed out briefly above, an essential objective of the invention is to effectively cost-reduce the transceiver selection of transceiver parameters. Non-limiting, but preferred examples of such parameters include: 1—limiting number of carriers that the transceiver can simultaneously transmit; and 2—limiting the rate of sub-channel hopping. The operation and effect of each of these and other parameters will be discussed individually below. 
         [0025]      FIG. 1 , as described earlier, graphically illustrates spectral reuse transceiver, of the type described in the above-referenced &#39;753 application, installed at a master site  10  communicates with respective spectral reuse transceivers installed at a plurality of remote sites  12 . Each spectral reuse transceiver operates with a selectively filtered form of frequency hopping for producing a sub-set of non-interfering radio channels or sub-channels. 
         [0026]    To facilitate an understanding of the functionality and effect of the first discriminator—division of available channels - attention may be directed to  FIG. 2 , which graphically illustrates an instance of a hopping sequence of the type described in the above-referenced &#39;753 application. In graph  20  of  FIG. 2 , a frequency band  25 , is comprised of unused channels  21 , that are not in the hopping sequence, and hopping channels  22 , marked with the letters a-z in the figure, that are in the present hopping sequence. In some embodiments of the present invention, described below, one of said hopping channels  22   a - z , the currently selected hopping sub-channel, the ‘operational sub-channel’, will be selected for use for transmission and reception. In another embodiment of the present invention, described herein below, an additional hopping sub-channel, ‘the receive-only sub-channel’ will be selected as a secondary receiving sub-channel. Unused channels  21  and hopping channels  22   a - z  may be of any sub-channel size, including without limitation 6.25 kHz, 12.5 kHz and 25 kHz, , i.e. or example. The hopping sequence instance illustrated in the figure is representative, and may vary in length, according to application requirements, band conditions which can, for example, include interference, and regulatory matters. The number of hopping channels  22   a - z  that may be used simultaneously may vary according to the transceiver design and application requirements, band conditions such as including interference, regulatory matters, and administrative settings of the transceiver. For example, a transceiver of the type described in the above-referenced &#39;753 application may transmit one to sixty hopping channels  22  simultaneously, in one physical embodiment thereof, as an example. The transceiver may dwell on this set of simultaneously transmitted channels for a parameterized period, and then move to another subset of the hopping channels  22 . The order in which the hopping channels  22  are used in the &#39;753 application transceiver may be determined by a parameterized, i.e. administratively determined’, fixed order or may be determined pseudo-randomly, for example, through a PN sequence circuit or software, as is well-known to one skilled in the art. The transceiver described in the &#39;753 application could also automatically modify the set of hopping channels  22   a - z  it uses to avoid interfering signals that might occur from time to time, excluding those current hopping channels  22  that presently have interfering signals thereon. 
         [0027]    For the purposes of reducing the hardware costs of the transceiver of the present invention, some or all of the operating parameters describe above may be set advantageously. For example, the number of simultaneously transmitted hopping channels  22  may be reduced to a few or one hopping sub-channel  22   a - z , and the hopping sequence may be restricted to an administratively determined fixed set of hopping channels  22   a - z , and the dwell time for transmitting on the same sub-channel may be unlimited, until, as will be shown below in the description of additional figures, when the presently used hopping sequence  22   a - z  is interfered with, in which case another hopping sub-channel in the set of hopping channels  22   a - z  will be selected. By making these advantageous selections of the operating parameters of the present invention, the processing power and memory requirements for the transceiver&#39;s one or more control processors may be significantly reduced, thereby reducing cost and reducing energy requirements. 
         [0028]    Refer now to  FIGS. 3   a  to  3   c , which graphically illustrate the relationship between an interfering signal and a hopping sequence in a spectral reuse transceiver of the present invention. In graph  30  of  FIG. 3   a , a frequency band  34  comprises unused channels  31  and hopping channels  32   a - z , where the unused channels are administratively blocked from use. The hopping channels  32   a - z  form a ‘logical band’ of ‘sub-channels’ in which the transceiver (not shown) may operate. As shown in the figure, the transceiver is transmitting one signal  33 , the operational hopping sub-channel, which happens to be in hopping sub-channel  32   b . No interfering signals are represented in the figure. The transceiver is transmitting in only one sub-channel, which is the preferred embodiment of the present invention. 
         [0029]    Graph  35  of  FIG. 3   b  is similar to graph  30  of  FIG. 3   a , except that an interfering signal  36  has appeared in  FIG. 3   b ; interfering signal  36  happens to span two hopping channels  32   b - c  and the unused sub-channel  31  therebetween. The transceiver of the present invention would detect the interfering signal  36 , as will be described in the description of subsequent figures herein, and determine that it interferes with the transceiver&#39;s single signal  33  in hopping sub-channel  32   b.    
         [0030]    Graph  38  of  FIG. 3   c  is similar to graph  35  of  FIG. 3   b . Graph  38  illustrates that the transceiver of the present invention noticed that interfering signal  36  appeared and is interfering with used channels  22   b  and  22   c ; the said transceiver therefore moves transmitting signal  33  from hopping sub-channel  32   b  to hopping sub-channel  32   d , as illustrated by arrow  39 . The transceiver did not choose any unused sub-channel  31  because they are administratively blocked from use, and did not choose hopping sub-channel  32 - c , because hopping sub-channel  32   c  also is interfered with by interfering signal  36 . The transceiver of the present invention therefore selected the next hopping sub-channel  32   a - z  in its list of hopping channels, hopping sub-channel  32   d , in this example. 
         [0031]    In another embodiment of the present invention, the transceiver (not shown) in graph  38  of  FIG. 3   c , after detecting interfering signal  36  has interfered with hopping channels  22   b  and  22   c , rather than selecting the next hopping sub-channel  32   a -z in its list, selects the best hopping sub-channel  32   a - z  in its list of hopping channels  32 , based on a comparison of measurements of signal strengths of all hopping channels  32   a - z , the measurements being made by all transceivers in the network and combined into a composite measurement by one of the transceivers, typically the base station transceiver in star networks. The said measurements, said combining of measurements, and said selection of the next hopping sub-channel  22   a - z  will be described in the descriptions of subsequent drawings herein below. 
         [0032]    A sub-channel assessment and selection mechanism, shown in the flowchart of  FIG. 4   a  and described below, involves a base station radio incrementally ‘sweeping’ the transmission frequencies, for example, from the lowest hopping sub-channel to the highest available hopping sub-channel, during a period when transceivers in the network are known not to be transmitting, thereby detecting interfering signals while avoiding falsely detecting other radios in the network as interference. After an ‘init’ initialization phase, a transmission and reception cycle begins (not shown) , during which a spectrum analysis process begins, illustrated by  FIG. 4   a . During sample spectrum period  404 , the base station transceiver scans the available sub-channels in which the transceiver is operating during a time in which no other radios in the network are operating. For example, in the non-limiting example of a polled star network, the base station can choose a said sample spectrum period  404  after a poll-response period and before the base station transceiver transmits the next poll message. In another example, the base station transceiver can transmit a signal that informs the remote stations that a no-transmit period has begun, after which a sample spectrum period  404  may begin. During the sample spectrum  404  period, the base station transceiver measures and records the signal level of each of the hopping channels. Then assessment period  406  begins during which time the base station compares the hopping sequence currently being used with the signal level measurements made in the sample spectrum  404  step described above. The transceiver determines which of the hopping channels currently in use now have interfering signals thereon, ‘new interference’). If there is any new interference, the transceiver notes that a new hopping sequence must be constructed that excludes the still active old interference and the new interference. The transceiver also determines which hopping channels not in the current hopping sequence no longer have interference thereon (‘newly interference free’) By adding the newly interference free sub-channels to the present hopping sequence and subtracting the new-interference sub-channels from the hopping sequence, a new ‘candidate’ hopping sequence may be constructed. As is well-known to one skilled in the art, the reuse of newly interference free sub-channels may be advantageously delayed by applying a minimum period of absence of interference, hysteresis, or a similar filter to prevent a sub-channel from “ping-ponging” between use and non-use due to an inconsistent or unpredictable interference signal. 
         [0033]    Once assessment period  406  is complete, the base station transceiver has a candidate new hopping sequence if a new interference pattern had emerged. In the preferred embodiment of the present invention, the candidate hopping sequence is further filtered by interference reports reported to the base station transceiver from a remote transceiver (or the far end of a point-to-point connection, for example), as indicated by the merge interference  408  step of  FIG. 4   a . In the merge interference  408  step, any interference report from a remote or far station that has been received since the last merge interference  408  period is merged with the interference data measured by the remote station. The remote or far transceiver&#39;s interference-measurement and reporting mechanism is described below in  FIG. 4   b  and the description thereof. If no new interference was detected by the base station transceiver and no new interference was detected and reported by any remote or far transceiver, then by decision block  410  and path  412 , the base station transceiver returns to the sample spectrum  404  period; otherwise, in step  416 , the base station transceiver creates a new clear sub-channel map from the merged interference data of step  408 , said clear sub-channel map comprising a list of hopping sub-channels that are interference free. The base station transceiver then creates a new sub-channel hopping sequence from the said clear sub-channel map and selects a new hopping sub-channel or sub-channels from the said clear sub-channel map, if the current hopping sub-channel is now being interfered with. The said selection being, for example, the next sub-channel or sub-channels in the said clear sub-channel map. In step  418 , the base station transceiver disseminates the new sub-channel hopping sequence and the new current hopping sub-channel or sub-channels to the remote or far transceivers, for example, by transmitting a management message to said remote or far transceivers. The base station transceiver then returns to step  404  to begin a new cycle of interference detections. Note that the base station transceiver can jump from a transmit and receiver period (not shown) via entry point  409  to Merge Interference step  408  any time a remote or far transceiver reports new interference. 
         [0034]    A sub-channel assessment and selection mechanism, shown in the flowchart of  FIG. 4   b  and described below, involves a remote or far transceiver (‘remote transceiver’) incrementally ‘sweeping’ the transmission frequencies, for example, from the lowest hopping sub-channel to the highest available hopping sub-channel, during a period when transceivers in the network are known not to be transmitting, thereby detecting interfering signals while avoiding falsely detecting other radios in the network as interference. After an ‘nit’ initialization phase, a transmission and reception cycle begins (not shown), during which a spectrum analysis process begins, illustrated by  FIG. 4   b . During sample spectrum period  444 , the remote transceiver scans the available sub-channels in which the transceiver is operating during a time in which no other radios in the network are operating. For example, in the non-limiting example of a polled star network, the base station can choose a said sample spectrum period  444  after a poll-response period and before the base station transceiver transmits the next poll message. In another example, the base station transceiver can transmit a signal that informs the remote stations that a no-transmit period has begun, after which a sample spectrum period  444  may begin. During the sample spectrum  444  period, the remote transceiver measures and records the signal level of each of the hopping sub-channel&#39;s ‘assessment data’, the present list of hopping sub-channels having been transmitted to remote transceivers by the base station transceiver. Then assessment period  446  begins during which time the remote transceiver compares the hopping sequence currently being used with the assessment data of step  444 , described above. The remote transceiver determines and notes which of the hopping sub-channels currently in use now have newly interfering signals thereon and which hoping sub-channels are newly absent of interference. 
         [0035]    Once assessment period  446  is complete, the remote transceiver begins merge interference step  448 . In step  448 , if there is new interference or new absence of interference on any hopping sub-channels, the remote transceiver will merge the assessment data of step  446  with the present system-wide hopping sub-channel interference previously provided by the base station transceiver, wherein the merged data will include an indication of newly detected interference and newly detected lack of interference. In decision block  450 , the remote transceiver will return to step  444  via path  452  if said merged data indicates that no newly detected interference and no newly detected lack of interference was found in step  448 ; otherwise, step  456  begins. In step  456 , the remote transceiver sends said merged data to the base station transceiver, for example, in a maintenance message which may, without limitation, be sent asynchronously, periodically or when polled by the base station transceiver. The remote transceiver then returns to begin a new sample spectrum period  444 . 
         [0036]    In another embodiment of the present invention, during assessment period  406  of  FIG. 4   a  and assessment period  446  of  FIG. 4   b , the base station and each of the remote transceivers detect interference in each hopping sub-channel by measuring the signal strength, typically the RSSI value for each of said hopping channels; during the assessment reporting period, the said RSSI value for each of said hopping channels is included in the assessment report. In the subsequent new clear sub-channel map period  416  of  FIG. 4   a , the base station transceiver uses the said RSSI value and a threshold parameter therefor to determine if a hopping sub-channel has an interfering signal. 
         [0037]    In another embodiment of the present invention, during the new clear sub-channel map period  416  of  FIG. 4   a , the base station transceiver selects a new hopping sub-sub-channel by choosing a hopping sub-sub-channel with the lowest RSSI value. 
         [0038]    In another embodiment of the present invention, during new clear sub-channel map period  416  of  FIG. 4   a , the base station transceiver selects a new hopping sub-channel by choosing a hopping sub-channel with the lowest RSSI value below a threshold parameter therefor. If there is no hopping sub-channel with a said lowest RSSI value below a said threshold parameter, then, according to a policy configured, for example, in the base station transceiver software, the base station transceiver may select a hopping sub-channel with a said lowest RSSI value, or cease transmitting until an interference-free hopping sub-channel becomes available, or lower its transmit power, or lower its throughput rate, or a combination thereof, or similar policies well-known to one skilled in the art. 
         [0039]    In another embodiment of the present invention, during new clear sub-channel map period  416  of  FIG. 4   a , the base station transceiver avoids selecting a new hopping sub-channel that is adjacent to the current hopping sub-channel. 
         [0040]    In another embodiment of the present invention, during sample spectrum period  404  of FIG.  4   a , the base station transceiver avoids selecting a new hopping sub-channel that is adjacent to the current hopping sub-channel. 
         [0041]    In another embodiment of the present invention, the base station transceiver is a full-duplex radio and selects a pair of interference-free channels rather than a single sub-channel (for half-duplex communications.) In another embodiment of the present invention, the media access protocol is not poll-response, but is aloha, slotted-aloha, TDD, TDMA, or another media access protocol well-known to one skilled in the art. 
         [0042]    A sub-channel assessment and selection mechanism, shown in the flowchart of  FIG. 5   a  and described below, involves a base station radio incrementally ‘sweeping’ the transmission frequencies—for example, from the lowest hopping sub-channel to the highest available hopping sub-channel, during a period when transceivers in the network are known not to be transmitting, thereby detecting interfering signals while avoiding falsely detecting other radios in the network as interference. After an ‘init’ initialization phase, a remote transmit and receive period  51  begins. The base station transceiver begins a poll-response period with the remote transceivers, in the non-limiting example of a polled star network. After the conclusion of the remote transmit and receive period  51 , the base station sends a message to all remotes, thereby starting an assessment period  52  during which time no remote or base station transceiver is transmitting. During this assessment period  52 , each remote and the base station measures the signal level of each of the hopping channels. At the end of assessment period  52 , the base station begins assessment reporting period  53  by polling each remote for its ‘assessment report’, sent via one or more assessment report messages. Each remote reports any hopping channels whose signal level is above a threshold parameter (‘discriminator’) via a said assessment report message. After receiving all said assessment report messages, the base station begins assessment report assembly period  54 , combining all said assessment reports into a single ‘combined interference report’ which shows which hopping channels currently have interference thereon. The base station then performs the current sub-channel interference decision  57 . If the said combined interference report indicates that the operational hopping sub-channel has no interference thereon, then by branch  58  the base station returns to its remote transmit and receive period  51 ; otherwise, the base station performs the new sub-channel select function  59 . In the new sub-channel select function  59 , the base station selects a new operational hopping sub-channel for which the said combined interference report indicates no interference was found thereon. In one embodiment of the present invention, the next interference-free hopping sub-channel in the hopping sub-channel list is selected. The base station then sends a ‘change hopping sub-channel’ message to all remotes which instructs said remotes to move to the said new operational hopping sub-channel. The base station changes its present operational hopping sub-channel to the new operational hopping sub-channel and returns to remote transmit and receive period  51 . Since interference had been found on the old operational hopping sub-channel, the said change hopping sub-channel message might not be received by one or more of the remotes. Those remotes not receiving the said change hopping sub-channel message will detect that they no longer see the base station&#39;s periodic transmission ‘signature,’ described as a “preamble” in the above-referenced &#39;753 application, and rejoin the network thereat by first searching all the hopping channels until the said base station&#39;s transmission signature is found and, in the preferred embodiment, waiting for the next remote transmit and receive period  51  to begin, said period indicated by the receipt of base station poll messages. 
         [0043]    In another embodiment of the present invention, during assessment period  52 , the base station and each of the remote stations detect interference in each hopping sub-channel by measuring the signal strength, typically the RSSI value for each of said hopping channels; during the assessment reporting period, the said RSSI value for each of said hopping channels is included in the assessment report. In the subsequent new sub-channel select period  59 , the base station uses the RSSI value and a threshold parameter therefor to determine if a hopping sub-channel has an interfering signal. 
         [0044]    In another embodiment of the present invention, during the new channel select period  59 , the base station selects a new hopping sub-channel by choosing a hopping sub-channel with the lowest RSSI value. 
         [0045]    In another embodiment of the present invention, during the new channel select period  59 , the base station selects a new hopping sub-channel by choosing a hopping sub-channel with the lowest RSSI value below a threshold parameter therefor. If there is no hopping sub-channel with a said lowest RSSI value below a said threshold parameter, then, according to a policy configured in the transceiver software, the transceiver may select a hopping sub-channel with a said lowest RSSI value, or cease transmitting until an interference-free hopping sub-channel becomes available, or lower its transmit power, or lower its throughput rate, or a combination thereof, or similar policies well-known to one skilled in the art. 
         [0046]    In another embodiment of the present invention, the base station transceiver is a full-duplex radio and selects a pair of interference-free channels rather than a single sub-channel (for half-duplex communications.) In another embodiment of the present invention, the media access protocol is not poll-response, but is aloha, slotted-aloha, TDD, TDMA, or another media access protocol well-known to one skilled in the art. 
         [0047]    Referring now to  FIG. 6 , transceiver  60  has one transmitter  61  and two receivers, receiver A  62  and receiver B  63 . Transmitter  61  and receivers  62 - 63  can communicate with processor unit  65  via bus  64 . The block diagram of transceiver  60  is simple so as not to obscure the details of the present invention. Transceiver  60  is similar to the transceivers described in the descriptions of  FIGS. 1-5  herein, except that it has two receivers  62 - 63  rather than one receiver. Processor  65  can configure receiver A  62  and receiver B  63  independently so that, for example, transmitter  61  and receiver A  62  are tuned to ‘sub-channel  2 ’ and receiver B  63  is tuned to ‘sub-channel  3 ’, wherein ‘sub-channel  2 ’ and sub-channel  3 ′ represent any two channels at frequencies within the band or bands in which transceiver  60  operates. 
         [0048]    According to one embodiment of the present invention, transceiver  60  uses transmitter  61  and one of said receivers  62 - 63 , for user traffic, and uses the other of said receivers  62 - 63  for scanning hopping channels for interference. This arrangement allows transceiver  60  to scan for interference on the hopping channels even while receiving or transmitting on the operational hopping sub-channel. In one embodiment of the present invention, transceiver  60  scans all hopping channels except the operational hopping sub-channel at any or all times during the periods  51 - 59  of  FIG. 5  and scans the operational hopping sub-channel during the assessment period  52  of  FIG. 5 . Thus scanning for interference occurs more frequently by use of the second receiver, thereby reducing detection time for interference. 
         [0049]    In another embodiment of the present invention, transceiver  60  of  FIG. 6  performs scanning of all hopping channels except the current operational hopping sub-channel and hopping channels adjacent to the current operational hopping at any or all times during the periods  51 - 59  of  FIG. 5  and scans the current operational hopping and hopping channels adjacent to the current operational hopping sub-channel during the assessment period  52  of  FIG. 5 . If the said scanning detects interference on said current operational sub-channel or said channels adjacent to the said current operational sub-channel, then during the new sub-channel select period  59  of  FIG. 5 , a new operational hopping sub-channel selection will be made, said selection excluding said current operational hopping sub-channel and said channels adjacent to the said current operational sub-channel. Thus scanning for interference occurs more frequently by use of the second receiver and therefore reducing the effect of any “bleeding” of energy from the operational sub-channel into the adjacent channels. 
         [0050]    In another embodiment of the present invention, transceiver  60  of  FIG. 6  increases throughput upstream (from remote stations towards hub) in a point-to-multipoint network by using the two receivers  62  and  63  simultaneously for receiving user data. Transmitter  61  of a  FIG. 6 , for example, polls two remote transceivers simultaneously with a polling message that assigns Receiver A&#39;s  62  upstream sub-channel frequency to one of said two remote transceivers, and Receiver B&#39;s  63  upstream sub-channel frequency to the other one of said two remote transceivers; subsequently, the two said remote transceivers simultaneously transmit a poll response to said poll message. Similarly, two upstream sub-channels may be assigned respectively to the two Receivers  62 - 63 , the channels used for aloha transmissions, where half the remote transceivers are assigned to the aloha sub-channel of Receiver  62  and the other half of the remote transceivers are assigned to the aloha sub-channel of Receiver  63  (or the remote transceivers can pseudo-randomly select one of the two aloha channels). Various ways to use or assign the two upstream channels of Receivers  62 - 63  will be apparent to one skilled in the art and are anticipated herein. In another embodiment of the present invention, transceiver  60  may use the second receiver  63  increasing upstream throughput and scanning hopping channels for interference, as described above. 
         [0051]    Refer now to  FIG. 7 , which graphically illustrates another aspect of the present invention, whereby the transceiver described herein above may be used to aggregate a set of licensed channels to increase utilization of the licensed channels. In the figure, a frequency band  70  comprises a set of unused channels  71  and a set of available channels  72   a - z , which need not be adjacent. The transceivers of the present invention (not shown) are configured to hop only over the available channels  72   a - z . The available channels  72   a - z  may be licensed to the owner, as a non-limiting example, for push-to-talk voice communication and will use the present invention to provide data service over the voice channels  72   a - z  whenever the voice channels  72   a - z  are not busy. The transceiver of the present invention will hop over channels  72   a - z , as described in description of  FIGS. 1-6 , treating the busy voice channels as if they were “interference.” Thus, whenever there is at least one idle voice channel  72   a - z , the transceiver of the present invention will provide data service thereover. In the figure, there is, as an example, one busy sub-channel  72   b  with a voice signal  73  thereon. Therefore, the transceiver of the present invention may use any of available channels  72   a  and  72   c - z  for data service (including digital voice).  FIG. 7  was simplified so as not to obscure the present invention. For example, the channels of the present size need not be the same size as the example voice channels. The transceiver of the present invention could have, for example, 12.5 kHz channels and the voice radios could have 25 kHz channels. Therefore, there would be two channels of the present invention for each voice channel, in this non-limiting example. 
         [0052]    Referring now to  FIG. 8 , there is a mobile network  802  which, in this non-limiting example, has two cells  804 , two base stations  806  and two mobile transceivers  808 . One cell  804 , Cell- 1 , has base station BS- 1   806  and mobile transceiver  808  Rem- 1  within said base station BS- 1 &#39;s area of radio coverage, said area of coverage indicated by the dashed line of  804 . The other cell  804 , Cell- 2 , in the present example configuration, has base station BS- 2   806  and two mobile transceivers  808 , Rem- 1  and Rem- 2 . Mobile transceiver Rem- 1  happens to be in the overlapping coverage of Cell- 1  and Cell- 2  and therefore can receive signals  802  from both base stations BS- 1  and BS- 2  from Cell- 1  and Cell- 2 , respectively. Furthermore, mobile transceiver Rem- 1  is within radio range of the remote radio signals  812  from remote transceiver Rem- 2 . 
         [0053]    Mobile transceiver  808  Rem- 1  has two receivers, as described in the descriptions of  FIGS. 6 and 7  herein. In another embodiment of the present invention, mobile transceiver Rem- 1  uses one of its said two receivers for receiving data transmissions and detecting signal levels from the base station to which it is associated (BS- 1  in the present example), and the second of its said two receivers for detecting signal levels from all other base stations  806  within radio range of mobile transceiver Rem- 1 . As is understood by one skilled in the art, the detection of signal levels from a base station  808  by a mobile transceiver  808  is useful in hand-off procedures, wherein the signal levels  802  from base stations  806  are compared by mobile transceivers  808  to determine whether to dissociate from the presently associated base station  806  to another base station  806  with a stronger signal  802 . Various schemes for comparing base station signals  802  to determine the most advantage base station  806  to which to associate are known by one skilled in the art, and are not described herein. The present invention provides several advantages for mobile transceivers. Notably, data transmission time does not need to be interrupted by signal measurements of other base stations since there is a dedicated second receiver for this purpose, thereby increasing useful throughput for the end user. In addition, the media access control (MAC) layer frequently imposes restrictions on mobile transceivers&#39;  808  timing of transmission and receive periods. A mobile transceiver  808  must be listening when a base station  806  is transmitting. With a second receiver, the mobile transceiver  808  may sample base stations continuously, thereby making more timely hand-off decisions. In addition, the mobile transceiver  808  may hear transmissions from both base stations  806  and other mobile transceivers  808 . The second receiver enables the mobile transceiver  808  to decode received messages so as to discern between signal levels of base stations  806  and other mobile transceivers  808 , so that hand-off decisions are based only on signal levels of base stations  806 . In another embodiment of the present invention, base station  806  of a mobile network may use the second receiver of  FIG. 6  for increasing upstream throughput or scanning hopping channels for interference, as described above. In another embodiment of the present invention, base station  806  of a mobile network may use the second receiver of  FIG. 6  for increasing upstream throughput and scanning hopping channels for interference, as described above. 
         [0054]    While we have shown and described several embodiments in accordance with the present invention, it is to be understood that the same is not limited thereto but is susceptible to numerous changes and modifications as known to a person skilled in the art. There is no intention that the application be limited to the details shown and described herein, but it is intended that the application cover all such changes and modifications as are obvious to one of ordinary skill in the art. For example, the transceivers described in the above-identified &#39;753 application may operate in a star network. There is no intention to limit either the &#39;753 application or the instant application to such a configuration and, without limitation, radio links between transceivers in other topologies, such as point-to-point, and individual links in mesh networks, as examples, can employ the cost-reduction and other improvements of the present invention as well.