Patent Publication Number: US-2022217077-A1

Title: Star topology fixed wireless access network with lower frequency failover

Description:
RELATED APPLICATIONS 
     This application is a Continuation of U.S. patent application Ser. No. 16/380,463, filed on Apr. 10, 2019, which claims the benefit under 35 USC 119(e) of U.S. Provisional Application No. 62/655,351, filed on Apr. 10, 2018, both of which are incorporated herein by reference in their entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     Internet service providers (ISPs) have historically used a number of different technologies in their subscriber or access networks to deliver network connectivity to premises such as homes, multidwelling units, and businesses. Initially premises were connected via dial-up connections over POTS lines, or ISDN. Often businesses used T-1 to T-3 connections. 
     Nowadays, DSL, cable and optical fiber networks are common in urban and metropolitan areas to provide network access. 
     Fixed wireless network access is another option in some areas. ISPs providing the wireless network access can transmit and receive data to and from endpoint nodes usually at premises as radio waves via transmission towers. This has been typically used in rural areas where cable and optical fiber networks are not available. 
     SUMMARY OF THE INVENTION 
     The systems described herein utilize high-frequency wireless data links, typically operating in the 10 GHz to 300 GHz band for communications between aggregation nodes and one or more endpoint nodes such as fixed subscriber nodes and/or multi-dwelling unit nodes, usually in star-topology networks. Nevertheless, the technology also has application to mobile and semi-mobile applications and point-to-points links. This spectral band encompasses millimeter wavelengths (mm-wave) that are typically described as covering the 30 GHz to 300 GHz frequency band. 
     The presently disclosed systems further provide for lower frequency wireless data links, which have carrier frequencies less than high-frequency wireless data links. These lower frequency links will typically operate in the 1 GHz to 10 GHz band. They provide for auxiliary communications between aggregation nodes and one or more endpoint nodes. 
     In many of the systems, the aggregation nodes have at least one phased array antenna that divides an area of coverage into multiple subsectors for the high-frequency wireless data links. 
     Preferably, however the lower frequency wireless data links will utilize directional antennas which cover the entire portion in azimuth that is served by the aggregation node, or at least a sector of coverage of such a node. Further, the lower frequency wireless data links utilize multi-user multiple-input and multiple output (MU-MIMO) technologies supporting multiple spatial streams. Thus, the lower frequency wireless data links may not require directional antennas but can nonetheless maintain simultaneous connections with multiple endpoint nodes. 
     In operation, the aggregation nodes transmit and receive high-frequency modulated carrier signals to and from the endpoint nodes. These nodes are associated with different subsectors in a preferably azimuthal/horizontal fan pattern of the antennas. By forming beams for these subsectors and towards a specific endpoint nodes or groups of endpoint nodes, and/or simultaneously forming several beams to different endpoint nodes within different subsectors from the same antenna, the aggregation node can communicate with the endpoint nodes, with lower or without interference between nodes. 
     However, in the event that the high-frequency link between a particular aggregation node and a particular endpoint node is impaired, a low-frequency data link is utilized until the high-frequency link resumes normal operation. A typical reason for such impairment is weather, such as hail or unusually high rainfall, for example. 
     In general, according to one aspect, the invention features a wireless access system. The wireless access system comprises endpoint nodes installed at premises and an aggregation node for communicating with the endpoint nodes. The aggregation node comprises a phased array antenna system and one or more auxiliary antennas, both of which transmit information to and receive information from the endpoint nodes. The phased array antennas system utilizes high-frequency data links, whereas the auxiliary antennas utilize low-frequency data links. 
     In embodiments, the aggregation node and endpoint nodes provide wireless connectivity between user devices at the premises containing the endpoint nodes and an internet service provider by exchanging packet data. 
     The endpoint nodes comprise dual-band antenna systems for transmitting the information to and receiving the information from the aggregation node via both links. 
     The high-frequency wireless data links operate between 10 and 300 Gigahertz, while the low-frequency wireless data links operate between 1 and 10 Gigahertz. 
     During normal operation, the packet data is exchanged via the high-frequency wireless data links, and the aggregation node and the endpoint nodes exchange auxiliary communications via the low-frequency wireless data links. However, the aggregation node and the endpoint nodes switch over to exchanging the packet data via the low-frequency wireless data links in response to determining that the high-frequency wireless data links are impaired and resume exchanging the packet data via the high-frequency wireless data links in response to determining that the high-frequency wireless data links are no longer impaired. The aggregation node determines that the high-frequency wireless data links are impaired based on results of ping queries sent from the aggregation node to the endpoint nodes via the high-frequency wireless data links. 
     In general, according to another aspect, the invention features a method of operation of a wireless access system. An aggregation node transmits information to and receives information from endpoint nodes installed at a premises via high-frequency wireless data links using a phased array antenna system of the aggregation node. The aggregation node also exchanges the information with the endpoint nodes via low-frequency wireless data links using one or more auxiliary antennas of the aggregation node. 
     In general, according to one aspect, the invention features a wireless access system. The wireless access system comprises endpoint nodes installed at premises and an aggregation node for communicating with the endpoint nodes. The aggregation node comprises an antenna system and one or more auxiliary antennas, both of which transmit information to and receive information from the endpoint nodes. The antenna system utilizes high-frequency data links operating at a frequency of at least 20 Gigahertz (GHz), whereas the auxiliary antennas utilize low-frequency data links operating at a frequency between 1 and 10 GHz. 
     8 The above and other features of the invention including various novel details of construction and combinations of parts, and other advantages, will now be more particularly described with reference to the accompanying drawings and pointed out in the claims. It will be understood that the particular method and device embodying the invention are shown by way of illustration and not as a limitation of the invention. The principles and features of this invention may be employed in various and numerous embodiments without departing from the scope of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the accompanying drawings, reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale; emphasis has instead been placed upon illustrating the principles of the invention. Of the drawings: 
         FIG. 1  is a schematic diagram of an exemplary fixed wireless network to which the present invention is applicable; 
         FIG. 2  is schematic diagram for an exemplary aggregation node; 
         FIG. 3  is a perspective view of the dual-band antenna system according to an embodiment of the current invention; 
         FIG. 4  is a perspective view of the dual-band antenna system with a portion cut away to show feed antennas of the dual-band antenna system; 
         FIG. 5  is a perspective view of the 5 GHz feed antenna; 
         FIG. 6  is a side view of the 5 GHz feed antenna; 
         FIG. 7  shows a radiation pattern for the 5 GHz feed antenna; 
         FIG. 8  shows a radiation pattern for the 5 GHz feed antenna when operating with the reflectors of the dual-band antenna system; 
         FIG. 9  is a perspective view of the 38 GHz feed antenna; 
         FIG. 10  is a side view of the 38 GHz feed antenna; 
         FIG. 11  shows a radiation pattern for the 38 GHz feed antenna; 
         FIG. 12  shows a radiation pattern for the 38 GHz feed antenna when operating with the reflectors of the dual-band antenna system; and 
         FIG. 13  is a sequence diagram illustrating the process by which failover from a high-frequency data link to a low-frequency data link is arranged and maintained. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The invention now will be described more fully hereinafter with reference to the accompanying drawings, in which illustrative embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. 
     As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. Further, the singular forms and the articles “a”, “an” and “the” are intended to include the plural forms as well, unless expressly stated otherwise. It will be further understood that the terms: includes, comprises, including and/or comprising, when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. Further, it will be understood that when an element, including component or subsystem, is referred to and/or shown as being connected or coupled to another element, it can be directly connected or coupled to the other element or intervening elements may be present. 
     A fixed wireless network  100  illustrated in  FIG. 1  shows an aggregation node (AN)  102  and a plurality of network endpoint nodes (EN)  104 , e.g.,  104 - 1 ,  104 - 2 ,  104 - 3  and  104 - 4 . 
     In general, the aggregation node  102  distributes packet data to and from the endpoint nodes  104 , for example, to provide wireless connectivity between user devices at the premises containing the endpoint nodes  104  and an internet service provider (ISP) wired network. More specifically, the aggregation node  102  receives packet data from one or more networks connected to the fixed wireless network  100  (e.g. the internet) and routes the packet data to the appropriate endpoint nodes  104  of different subscribers. The endpoint nodes  104  then route the packet data to the user devices typically on a local area network of the subscriber. Typically, the endpoint nodes are dedicated to individual subscribers or are dedicated to multi-unit dwellings (MDUs) in which multiple subscribers live. The endpoint nodes  104  also receive the packet data from the user devices and transmit the packet data received from the user devices to the aggregation node  102 , which then routes the packet data to the connected networks to be delivered to its destination. In one example, the packet data include individual packets, which are formatted units of data carried by packet-switched networks. In general, the packets include control information and user data. The control information includes data used to route and deliver the user data across the network to the destination, including source and destination network addresses. The user data includes intended messages for the destination devices. One such example of packet data includes packets formatted and processed by networks according to the transmission control protocol (TCP), user datagram protocol, and/or internet protocol (IP), among other examples. In general, the user data is exchanged, in the form of packets, between host devices, which include user devices (e.g. at the different premises) and web and mail servers, among other examples. The user data includes application data such as hypertext transfer protocol (HTTP) request and response messages used by web applications running on the user devices to request and display web content, to name just one example. 
     Additionally, the aggregation node  102  exchanges auxiliary communications with the endpoint nodes  104 , for example, to send instructions to the endpoint nodes  104 , which are executed by the endpoint nodes  104 . In contrast to the bidirectional packet data (which is associated with devices of the various subscribers), the auxiliary communication pertains, for example, to the functioning of the fixed wireless network  100  and specifically to the data links between the aggregation node  102  and the endpoint nodes  104 . For example, the ultimate sources and destinations of the auxiliary communications are the aggregation node  102  and the endpoint nodes  104  themselves, and the messages are used to administer the fixed wireless network  100 . 
     According to a preferred embodiment, the aggregation node includes a network processer  200 , multiple WiFi access point chipsets  1810 , a high-frequency antenna system  103 , and a low-frequency antenna system  105 . The network processer  200  generally directs the functionality of the aggregation node by, for example, directing network traffic to and from different endpoint nodes  104  via the WiFi chipsets  1810  and the antenna systems  103 ,  105 . The WiFi chipsets are commercially available systems of one or more chips that implement the IEEE 802.11 standard. These chipsets are capable of maintaining multiple spatial streams such as provided by the IEEE 802.11n, 802.1 lac or 802.1 lax versions and follow-on versions of the standard. Each of these WiFi chipsets produce WiFi signals, which are signals that have been encoded according to the IEEE 802.11 standard. Each of these WiFi chipsets further decode received WiFi signals. In this way, packet data connectivity is established and maintained between the ISP wired network and each of the endpoint nodes  104 . 
     On the other hand, the endpoint node  104  is a residential or business fixed wireless endpoint that distributes packet data to and from the aggregation node  102  and communicates with the aggregation node  102  via the fixed wireless network  100 . The endpoint node  104  includes an endpoint node processor  204 , a WiFi chipset  212 , and a dual-band antenna system  210 . The endpoint node processer  204  generally directs the functionality of the endpoint node by, for example, directing network traffic to and from the aggregation node  102  via the WiFi chipset  212  and the dual-band antenna system  210 . 
     Each endpoint node  104  communicates with the aggregation node  102  by means of an electronic assembly or system that provides a wireless ISP (internet service provider) handoff at the subscriber&#39;s premises or MDU where the endpoint node  104  is installed. The endpoint node  104 , in a typical residential implementation, communicates with networking devices at the premises such as a modem/router or access point over possibly a WiFi tunnel (in the 2.4 or 5 GHz bands or the WiGig tri-band in the 2.4, 5 and 60 GHz bands, or IEEE 802.11ac IEEE 802.11ad-2012) or via a wired connection (e.g., IEEE 802.3 1000BASE-T). The networking devices then maintain the local area network at the subscriber&#39;s premises. In other cases, the endpoint node  104  itself maintains the wired and/or wireless LAN at the premises. It provides typical functions associated with LAN routers, such as Network Address Translation (NAT), guest networks, Parental Controls and other Access Restrictions, VPN Server and Client Support, Port Forwarding and UPnP, and DHCP (Dynamic Host Configuration Protocol) server that automatically assigns IP addresses to network devices on the LAN. 
     During normal operation, the aggregation node  102  utilizes the high-frequency antenna system  103  to exchange packet data with the endpoint nodes  104 - 1 - 104 - 4  by establishing a high-frequency network (i.e., using high-frequency duplex communication links/radios) comprising high-frequency data links H between the aggregation node  102  and the endpoint nodes  104 . The high-frequency antenna system  103  is preferably a phased array antenna system and preferably covers an azimuthal arc of between about 90 degrees and 180 degrees; with about 120 degrees currently being used in some installations and 90 degrees being used in other installations. In some embodiments, the high-frequency network operates at a frequency between 10 and 300 GHz, or more commonly between about 20 and 60 GHz. 
     The operation of the high-frequency antenna system  103  then divides the antenna&#39;s area of coverage into multiple subsectors S 1 , S 2 , . . . , Sn. In the illustrated example, the subsectors are distributed in an azimuthal fan, with the subsectors adjoining and typically slightly overlapping one another. There are at least two subsectors; with some embodiments having four, eight or more subsectors. As a result, in typical implementations, each subsector covers an azimuthal arc of between possibly 8 degrees and 60 degrees. Currently, the subsector arc is between about 20 degrees and 30 degrees. 
     The aggregation node WiFi chipsets  1810   a - 1810   x  associated with the high-frequency antenna system  103  produce and decode WiFi signals as previously mentioned. For transmission, the WiFi signals are then upconverted and transmitted to the endpoint nodes  104 . In turn, the endpoint nodes transmit high-frequency signals back via the endpoint node dual-band antenna system  210 , which signals are downconverted to WiFi signals at the conventional frequencies such as 2.4 or 5 GHz. 
     These WiFi chipsets  1810   a - 1810   x  are allocated to their own, one or more, subsectors S 1 , S 2 , . . . , Sn. Further, their WiFi signals originate on different frequencies and are also preferably up and down converted to different carrier frequencies to minimize inter-chipset interference. Thus, for example, WiFi chipset  1810   a  might communicate with nodes in subsectors S 1  and S 2  at frequency F 1 , whereas WiFi chipset  1810   b  might communicate with nodes in subsectors S 3  and S 4  at frequency F 2 , with  1810   a  and  1810   b  producing two different frequency outputs. 
     The high-frequency antenna system  103  forms transmit and receive beams that correspond to each of the subsectors. In this way, the aggregation node  102  reduces interference between endpoint nodes, conserves power on the downlinks and reduces transmit power requirements by the endpoint nodes on the uplinks. 
     The endpoint nodes  104  are distributed within and thereby associated with different subsectors. In the illustrated example, endpoint node  104 - 1  is associated with subsector S 1 , endpoint node  104 - 2  is associated with subsector S 2 , endpoint node  104 - 3  is associated with subsector S 3 , and endpoint node  104 - 4  is associated with subsector S 4 . However, more than one endpoint node  104  can be in each subsector, or a particular subsector can contain no endpoint nodes  104 . 
     In some embodiments, the high-frequency antenna system  103  produces a number of beams for the endpoint node/group of endpoint nodes in each subsector S 1 , S 2 , . . . , Sn. The high-frequency antenna system  103  typically includes one or more transmit phased array antennas  103 -T for transmitting data streams to the endpoint nodes  104  and one or more receive phased array antennas  103 -R for receiving data streams from the endpoint nodes  104 . 
     In situations when normal operation is impossible or may be impaired (for example, when the high-frequency data link H between the aggregation node  102  and one or more endpoint nodes  104  is slow to respond, perhaps due to weather), an auxiliary low-frequency network, which is otherwise used to exchange auxiliary communications such as instructions between the aggregation node  102  and the endpoint nodes  104 , is then further utilized to carry the subscriber packet data (i.e., using low-frequency communication links/radios). The low-frequency network comprises low-frequency data links L between the aggregation node  102  and the endpoint nodes  104  via the low-frequency antenna system  105  and the dual-band antenna system  210 . The low-frequency antenna system  105  is preferably a 5 GHz antenna array, including omni-directional or directional antennas. The lower frequency data links L have carrier frequencies less than high-frequency wireless data links H. In some embodiments, the low-frequency network operates at a frequency in the 1 GHz to 10 GHz band. 
     According to one embodiment, the low-frequency antenna system  105  is a 2×2 single-user multiple-input and multiple output (SU-MIMO) antenna array with one of the transmit/receivers assigned to vertical polarization and the other assigned to horizontal polarization. 
     According to an alternative embodiment, the low-frequency antenna system  105  is a multi-user multiple-input multiple-output (MU-MIMO) antenna array supporting multiple spatial streams capable of maintaining simultaneous connections. This can include two half sector antennas, each assigning 1 transmitter/receiver to horizontal and one to vertical for each of the two half-sectors respectively. 
     In general, a control process  206  executing on the network processor of the aggregation node  102  directs the process of detecting whether the high-frequency data link H between the aggregation node  102  and that particular endpoint node  104  has been impaired. The control process  206  measures the round-trip time for messages (e.g. ping queries) sent and echoed back between the aggregation node  102  and the endpoint nodes  104  via both the high-frequency and low-frequency networks. If it is determined that the high-frequency data link H has been significantly impaired, the control process  206  sends instructions to a helper process  202  executing on the endpoint node processor  204  of the endpoint node  104  to direct traffic for the affected endpoint node over the low-frequency network. 
       FIG. 2  illustrates an exemplary schematic for the aggregation node  102  that utilizes the high-frequency antenna system (e.g. phased array antenna system)  103 T,  103 R to communicate with multiple subscriber nodes  104 , where the phased array antenna system  103  divides an area of coverage into multiple subsectors. 
     The embodiment leverages MU-MIMO WiFi chipsets that implement the IEEE 802.1 lac version of the standard and follow-on versions. MU-MIMO relies on spatially distributed transmission resources. In particular, MU-MIMO WiFi chipsets encode information into and decode information from multi spatial stream WiFi signals associated with multiple subscribers or users. 
     Considering the transmission side/path, data to be transmitted (e.g., data from a fiber coaxial backhaul of the ISP network) is provided to two 4-port mu-MIMO WiFi access point chipsets  1810   a ,  1810   b.    
     The WiFi chipsets  1810   a ,  1810   b  produce eight 5 to 6 GHz WiFi signals that are output on two signal paths Tx 1 , Tx 2  (i.e., 4 WiFi signals on Tx 1  and other 4 WiFi signals on Tx 2 ). The WiFi signals are provided to two transmit diplexers  1812   a ,  1812   b.    
     Each of the two transmit diplexers  1812   a ,  1812   b  uses fixed local oscillator signals (IFLO 1 , IFLO 2 , IFLO 3 , IFLO 4 ) to down-convert the 5 to 6 GHz WiFi signals to intermediate frequency (IF) signals (IF 1 , IF 2 , IF 3 , IF 4 ) in a range of 2 to 3 GHz. In some implementations, the IFLO signals are in the range of 7.8-8.2 GHz. 
     At each transmit diplexer, IF 1  and IF 2  signals are combined (summed/added) to form one IF signal, and IF 3  and IF 4  signals are combined to form another IF signal. In this way, the WiFi signal are multiplexed into IF signals. Preferably the IF signals are offset by over 100 MHz, such as by 700 MHz. 
     These combined IF signals from the two diplexers  1812   a ,  1812   b  are provided to four block up convertors (BUCs)  1814   a ,  1814   b ,  1814   c ,  1814   d.    
     The BUCs  1814   a ,  1814   b ,  1814   c ,  1814   d  upconvert the combined IF signals to high-frequency signals. The upconverted IF signals are provided as inputs to a phase control device that includes one or more 8-port Rotman lens  1816   a ,  1816   b , in this specific implementation. The phase control device is configured to feed the transmit phased array antenna system  103 T (e.g., transmit antenna arrays  1820   a ,  1820   b  of the phased array antenna system) via a set of feedlines  1819   a ,  1819   b . In particular, Rotman lens  1816   a  feeds a horizontal polarization transmit antenna array  1820   a  and Rotman lens  1816   b  feeds a vertical polarization transmit antenna array  1820   b . In some implementations, the upconverted IF signals are combined at a combiner associated with each Rotman lens  1816   a ,  1816   b.    
     The Rotman lens  1816   a ,  1816   b  vary phases of the upconverted high-frequency signals to, in combination with the transmit antenna arrays  1820   a ,  1820   b , steer the high-frequency signals towards one or more subsectors in the area of coverage. Specifically, the upconverted signals are directed to different ports of the Rotman lens  1816   a ,  1816   b . The Rotman lens  1816   a ,  1816   b  control phases of the upconverted signals to be fed to an amplifier system and then to the transmit antenna arrays  1820   a ,  1820   b . The amplifier system includes power amplifiers  1818   a ,  1818   b  provided at output ports of the Rotman lens  1816   a ,  1816   b . The amplifier system amplifies the feeds on the feedlines  1819   a ,  1819   b  to the transmit antenna arrays  1820   a ,  1820   b.    
     The BUCs  1814   a ,  1814   b ,  1814   c ,  1814   d  use a first frequency local oscillator signal RFLO 1  or a second frequency local oscillator signal RFLO 2  that are frequency shifted from each other by 380 MHz. These local oscillator signals are utilized to convert the IF signals received from the diplexers  1812   a ,  1812   b  to the high-frequency signals for transmission. The center frequencies of the high-frequency signals, however, are shifted with respect to each other. 
     In more detail, BUCs  1814   a ,  1814   c  receive RFLO 1  and BUCs  1814   b ,  1814   d  receive RFLO 2 . This arrangement results in the two WiFi chips sets operating at different center frequencies that are shifted with respect to each other in the high-frequency signals for transmission. This occurs because the 4Tx 1  signals from the first WiFi chipset  1810   a  are routed from the TX diplexer  1812   b  to BUCs  1814   b ,  1814   d . In contrast, the 4Tx 2  signals from the second WiFi chipset  1810   b  are routed from the TX diplexer  1812   a  and to BUCs  1814   a ,  1814   c.    
     A 100 megahertz signal received from GPS disciplined 100 MHz clock generator  1870  is converted to RFLO synthesizer signals (RFLO 1 , RFLO 2 ) by driving a synthesizer module  1880 . Preferably, generator module  1870  and the synthesizer module  1880  also generate the IFLO signals used by the transmit diplexers  1812   a ,  1812   b  to convert WiFi signals to IF signals. 
     The output ports of each of the two Rotman lenses  1816   a ,  1816   b  feed into eight parallel amplifiers  1818   a ,  1818   b  for each antenna array  1820   a ,  1820   b . These eight amplifiers  1818   a ,  1818   b  for each of the Rotman lenses  1816   a ,  1816   b  feed into the two 8×16 antenna arrays  1820   a  and  1820   b . However, 8×8, 8×10, 8×12, 8×18 antenna arrays might other be selected depending on the link budget requirement. 
     One of the transmit antenna arrays  1820   a  then transmits the high-frequency signals associated with Rotman lens  1816   a  with a horizontal polarization and the other transmit antenna array  1820   b  transmits the high-frequency signals associated with Rotman lens  1816   b  with a vertical polarization. The polarization diversity can be achieved by adding a polarizing sheet in front of one of the antennas to rotate its emissions. 
     On the receive side/path, two 8×16 receive antenna arrays  1840   a ,  1840   b  of the receive phased array antenna system  103 R are provided. 8×8, 8×10, 8×12, 8×18 antenna arrays might be used in the alternative, however. Antenna array  1840   a  operates at a horizontal polarization and the other antenna array  1840   b  operates at a vertical polarization. The eight output ports of each of the two antenna arrays  1840   a ,  1840   b  feed into the phase control device that includes one or more 8-port Rotman lens  1842   a ,  1842   b.    
     The Rotman lens phase control devices  1842   a ,  1842   b  receive high-frequency signals from one or more subsectors and/or different directions associated with the one or more subsectors simultaneously. In particular, Rotman lens  1842   a ,  1842   b  receives high-frequency signals at one or more of its input ports and controls the phases of the received signals to produce outputs to low noise block-down converters (LNBs)  1844   a ,  1844   b ,  1844   c ,  1844   d , in which pairs of outputs corresponds to a unique subsector of the corresponding receive antenna array  1840   a ,  1840   b . Each of the two Rotman lenses  1842   a ,  1842   b  produces two outputs that feed into two LNBs. For example, Rotman lens  1842   a  feeds into LNBs  1844   a ,  1844   b , and Rotman lens  1842   b  feeds into LNBs  1844   c ,  1844   d . Outputs from LNBs  1844   a  and  1844   c  (with different polarizations) correspond to one subsector and the outputs from LNBs  1844   b  and  1844   d  (with different polarizations) correspond to another subsector. 
     The received high-frequency signals at receive antenna arrays  1840   a ,  1840   b  are combined at a combiner associated with each Rotman lens  1842   a ,  1842   b . The combiner vectorially sums the received high-frequency signals present at the antenna ports to be presented to one LNB input, such that each LNB  1844   a ,  1844   b ,  1844   c ,  1844   d  then receives one formed beam. However, an alternative method of beamforming can be utilized where each signal is provided to the LNB and the outputs from the LNB can be summed to form a beam. 
     The LNBs  1844   a ,  1844   b ,  1844   c ,  1844   d  also use the local oscillator signals RFLO 1  and RFLO 2  generated by the synthesizer module  1880  for converting the high-frequency signals received at the antenna arrays  1840   a ,  1840   b  to IF signals. Each subsector is handled by only one of the WiFi chipsets  1810   a  or  1810   b , and also operates at a different center in the high frequencies. LNBs  1844   a  and  1844   c  receive RFLO 1 . In contrast, LNBs  1844   b  and  1844   d  receive RFLO 2 . As a result, despite the WiFi signals from two WiFi chipsets being upconverted and transmitting at different high-frequency center frequencies, they are downconverted to the same IF frequencies. 
     The four low noise block-down converters  1844   a ,  1844   b ,  1844   c ,  1844   d  feed into two receive diplexers  1846   a ,  1846   b . The inputs to the diplexers  1846   a ,  1846   b  are the IF signals of 2 to 3 GHz. The diplexer demultiplexes the two offset signals in each IF signal. Specifically, receive diplexer  1846   a  produces four Rx2 WiFi signals that will be processed by the second mu-MIMO WiFi chipset  1810   b . In contrast, receive diplexer  1846   b  produces four Rx1 WiFi signals that will be processed by the first mu-MIMO WiFi chipset  1810   a.    
     On the other hand, for the low-frequency antenna system  105 , data to be transmitted is provided to a 4-port mu-MIMO WiFi chipset  1810   z , which is implemented on the modem board at the SH modem block  1702 . The WiFi chipset  1810   z  produces four 5 to 6 GHz WiFi signals, which are output by four antennas of the low-frequency transmission antenna system  105 -T. At the same time, four antennas of the low-frequency receiving antenna system  105 -R receive WiFi signals that will be processed by the WiFi chipset  1810   z.    
       FIG. 3  is a perspective view of the dual-band antenna system  210  of the endpoint nodes  104  according to one embodiment. This design is of the dual-band antenna system  210  is a dual feed Cassegrain antenna. 
     A convex sub reflector  403  is secured in a position suspended above a parabolic main reflector  402  by three struts  404 - 1 ,  404 - 2 ,  404 - 3  at the focal point of the main reflector  402 . 
       FIG. 4  is a perspective view of the dual-band antenna system  210  with a portion cut away to show a 5 GHz feed antenna  406  and a 38 GHz feed antenna  408 . 
     In general, beams emanating from the feed antennas  406 ,  408  illuminate the sub-reflector  403  which then reflects to the main reflector  402  which forms the desired antenna pattern and gain. 
     The 38 GHz feed antenna  408  and 5 GHz feed antenna  406  are on different planes, with the 5 GHz feed antenna  406  positioned between the 38 GHz feed antenna  408  and the sub reflector  403 . The 5 GHz feed antenna  406  includes an opening  412  that provides a path for the 38 GHz beam between the 38 GHz feed antenna  408  and the sub reflector  403 . 
     Both feed antennas  406 ,  408  use dual polarized aperture coupled patch antenna technology on various substrate material. The feed antennas  406 ,  408  are dual polarized so that they have two ports, one for transmitting and receiving vertical polarization only and one for transmitting and receiving horizontal polarization only. As a result, each feed antenna  406 ,  408  has two Tx and two Rx streams. 
     The 38 GHz feed antenna  408  is configured as a 2×2 array to be able to effectively illuminate the sub reflector  403  and can be a standalone board or integrated into a main radio board of the dual-band antenna system  210 . 
     The 5 GHz feed antenna  406  is configured as a 2×1 array. The phase center of the 5 GHz feed antenna  406  is positioned in the center of the antenna board where a square opening  412  allows the 38 GHz beam to penetrate through to or from the 38 GHz feed. antenna  408 . 
       FIG. 5  is a perspective view of the 5 GHz feed antenna  406 , showing the square opening  412  between two 5 GHz antenna patches  410 , the patches being arranged in a 2×1 array. 
       FIG. 6  is a side view of the 5 GHz feed antenna  406 , showing the 5 GHz antenna patches  410 , an upper substrate layer  602 , an air layer  604 , a ground layer  606 , a lower substrate layer  608 , and a feed network layer  610 . The 5 GHz antenna patches  410  are embedded in the upper substrate layer  602 , which is separated from the ground layer  606  by the air layer  604  to increase the antenna bandwidth. The ground layer  606  is separated from the feed network layer  610  by a lower substrate layer  608 . 
       FIG. 7  shows a radiation pattern for the 5 GHz feed antenna  406 . 
       FIG. 8  shows a radiation pattern for the 5 GHz feed antenna  406  when operating with the reflectors  402 ,  403  of the dual-band antenna system  210 . 
       FIG. 9  is a perspective view of the 38 GHz feed antenna  408 , showing four 38 GHz antenna patches  414  arranged in a 2×2 array. 
       FIG. 10  is a side view of the 38 GHz feed antenna  408 , showing the 38 GHz antenna patches  414 , an upper substrate layer  800 , a ground layer  802 , a lower substrate layer  804 , and a feed network layer  808 . The 38 GHz antenna patches  414  are embedded in the upper substrate layer  800 , which separates the patches from the ground layer  802 . Similarly, the ground layer  802  is separated from the feed network layer  808  by a lower substrate layer  808 . 
       FIG. 11  shows a radiation pattern for the 38 GHz feed antenna  408 . 
       FIG. 12  shows a radiation pattern for the 38 GHz feed antenna  408  when operating with the reflectors  402 ,  403  of the dual-band antenna system  210 . 
       FIG. 13  is a sequence diagram illustrating the process by which the failover from the high-frequency data link H to the low-frequency data link L is arranged and maintained. In the illustrated example, two endpoint nodes  104 - 1  and  104 - 2  exchange packet data and communicate with one aggregation node  102 . 
     In general, in order for the low frequency link L to perform the routing relatively quickly, the low frequency link L must be kept alive. Then, in general, the control process  206  executing on the network processor  200  of the aggregation node  102  detects that the high frequency link H has been impaired and makes a decision to redirect traffic through the low frequency link L. It then bridges its inputs to the low frequency links L. 
     In step  302 , the aggregation node  102  and the endpoint nodes  104  establish high-frequency data links H between the high frequency antenna system  103  of the aggregation node  102  and the dual-band antenna systems  210  of the endpoint nodes  104 . During normal operation of the fixed access network  100 , the nodes exchange packet data associated with the different subscribers via the high-frequency data link H. 
     In step  303 , the aggregation node  102  and the endpoint nodes  104  establish low-frequency data links L between the low frequency antenna system  105  of the aggregation node  102  and the dual-band antenna systems  210  of the endpoint nodes. During normal operation, the nodes exchange auxiliary communications such as instructions via the low-frequency data links L, which are executed by the endpoint nodes  104 , for example. 
     In step  304 , the aggregation node  102  periodically sends ping queries to the endpoint nodes  104  over the high-frequency data links H. More specifically, the aggregation node  102  sends a query message to each of the endpoint nodes  104 , each of which echoes the received query message back to the aggregation node  102  by sending a query response message to the aggregation node  102  in response to receiving the query message. The aggregation node  102  measures the round-trip time for each of the query messages, the round-trip time indicating, for example, the amount of time elapsed between sending the query message and receiving a corresponding query response message. 
     In general, the aggregation node  102  determines whether the high-frequency data link H is impaired based on the results of the ping queries. 
     For example, in step  306 , the aggregation node  102  determines that the ping query results (e.g. round trip time) for the second endpoint node  104 - 2  were below a predetermined time threshold and thus the high-frequency data link H is functioning normally. Therefore, in step  308 , the aggregation node  102  and the second endpoint node  104 - 2  continue exchanging packet data via the high-frequency data link H. 
     On the other hand, in step  310 , the aggregation node  102  determines that the ping query results (e.g. round trip time) for the first endpoint node  104 - 1  were above a predetermined time threshold and thus the high-frequency data link H is impaired (for example, the data link is running too slowly or has been interrupted entirely). Therefore, in step  312 , the aggregation node  102  sends a second ping query to the first endpoint node  104 - 1  over the low-frequency data link L and, in step  314 , compares the results of both ping queries to determine which was shorter. In the illustrated example, the aggregation node  102  determines that the ping results for the low-frequency data link L were shorter. As a result, in step  316 , the aggregation node  102  sends instructions to the first endpoint node  104 - 1  to discontinue subscriber or user traffic for that node over the high-frequency data link H and instead direct the packet data to the low-frequency data link L, which the first endpoint node  104 - 1  does in step  318 . 
     In step  320 , the aggregation node  102  and the first endpoint node  104 - 1  exchange subscriber packet data over the low-frequency data link L. 
     In step  322 , the aggregation node  102  periodically sends ping queries to the first endpoint node  104 - 1  over both the low- and high-frequency data links L, H. In step  326 , the aggregation node  102  determines that the ping query results for the high-frequency data link H were below the predetermined time threshold (and thus the high-frequency data link H has resumed functioning normally). As a result, in step  328 , the aggregation node  102  sends instructions via the low-frequency data link L to the first endpoint node  104 - 1  to discontinue traffic on the low-frequency data link L and direct the packet data instead to the high-frequency data link H, which the first endpoint node  104 - 1  does in step  330 . 
     Finally, in step  332 , the aggregation node  102  and the first endpoint node  104 - 1  resume exchanging packet data over the high-frequency data link H. 
     While this invention has been particularly shown and described with references to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims.