Abstract:
A single subscriber station of a wireless metropolitan area network is shared among multiple households through a local AC power line that serves the households. The WMAN is connected to a power line network through a dual medium bridge modem located, for example, in the general proximity of a power transformer.

Description:
BACKGROUND OF INVENTION  
       [0001]     The two primary economic barriers to the development of fixed broadband wireless access (FBWA) have been the cost of the customer-premise equipment (CPE) and the cost of its installation. The cost of FBWA CPE with an outdoor mounted antenna routinely exceeds $1000. This is expensive in comparison to telephone digital subscriber loop (DSL) CPEs and cable broadband access modem CPEs which are in the range of $75. Although microelectronic circuit integration and large production runs will help lower the cost of FBWA CPE, the cost for existing products and technologies is expected to remain an economic problem for the industry. A related barrier is CPE installation which requires an expensive truck roll with a trained technician to set up the outdoor antenna and install new wires to the customer&#39;s premises. Published estimates on the overall cost to the service provider for CPE installation is on the order of $1000 per subscriber installation.  
       SUMMARY OF INVENTION  
       [0002]     The cost of providing data and voice service to customers is substantially reduced by having multiple customers share a single subscriber station (SS) of a wireless metropolitan area network (WMAN) through the use of a local area network formed using utility power lines. Typically, multiple customers share a single medium to low voltage transformer. The low voltage power lines between the houses are thus interconnected on the low voltage side of the transformer. Because the transformer blocks propagation of high frequency signals onto the medium voltage power lines, the low voltage lines extending between multiple customers can function as a shared medium for a local area network for just those customers sharing the transformer. Each electric power customer thus may use its electrical power lines to access a WMAN subscriber station using relatively low cost power line networking equipment that can be installed by the customer. Thus, the costs of a WMAN subscriber station can be distributed among more than one potential customer, and can be installed without running new wires or providing installation services for customer premise equipment.  
     
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0003]      FIG. 1  is a schematic diagram illustrating prior art use of low voltage AC power lines for home networking.  
         [0004]      FIG. 2  is a schematic diagram illustrating prior art use of encryption keys to define logical networks for power line stations that share the same low voltage power line medium.  
         [0005]      FIG. 3  is a schematic diagram illustrating an access bridge modem (ABM-WMAN-PL) that internetworks a wireless broadband access network with power line stations that share a common MV-to-LV utility power distribution transformer.  
         [0006]      FIG. 4  is a schematic diagram illustrating use of encryption keys to define logical networks for maintaining separate broadband access service for individual power line stations.  
         [0007]      FIG. 5  is a schematic diagram illustrating system architecture for bridging a fixed broadband wireless access network to a power line network, emphasizing software components, media-specific stations and network interfaces. 
     
    
     DETAILED DESCRIPTION  
       [0008]     In the following description, like numbers refer to like elements.  
         [0009]     In the following description, a dual-medium bridge modem—one medium being free space and the other medium being the low-voltage power line—is used to connect a power line network to a fixed (antenna) broadband wireless access network. “Low voltage” in this context means the voltage presented to the ultimate utility power consumer, e.g., in the United States (US) the 115 volts alternating current (AC) at household or office wall sockets. This dual-medium bridge modem will also be referred to herein as an access bridge modem (ABM) for wireless metropolitan area networks (WMAN) and power line (PL) networks, or ABM-WMAN-PL for short.  
         [0010]     A dual medium bridge for wireless metropolitan area network and a power line network has at least two physical or signaling interfaces: one for free space and one for wireline. Each interface has associated with it a media access controller (MAC) for communicating over the respective networks. The dual medium bridge modem also includes interworking logic that coordinates the exchange of data and control signals between the two networks. In an example of a preferred embodiment of an ABM-WMAN-PL described below, the two networks are a wireless metropolitan area network based on the IEEE 802.16® standard and a power line local area network (LAN) based on the HomePlugm standard.  
         [0011]     The ABM-WMAN-PL is most advantageously mounted on a pole or tall object near the utility power distribution step-down (distribution) transformer for best reception. However, it and/or its antenna may be placed elsewhere. The ABM-WMAN-PL utilizes one or more antennas to communicate through free space with one or more base stations of a fix broadband wireless access (FBWA) network. The ABM-WMAN-PL uses the low voltage power line to communicate with one or more power line stations in the one or more homes or offices that receive utility power from the distribution transformer.  
         [0012]      FIGS. 1 and 2  illustrate prior art methods of using a representative low voltage AC power line as a medium for power line network stations to establish a broadband, i.e., high data rate, local area network between data appliances, such as Ethernet routers, bridges, switches and personal computers.  
         [0013]     Referring to  FIG. 1 , houses  1  to N share the same medium voltage (MV) to low voltage (LV) distribution transformer  110 . The MV power lines  106  and  108  attach to the primary winding  112  of the MV to LV step down, distribution transformer  110 . The transformer&#39;s secondary winding  114  provides three outputs, also called phases: neutral (N), line  1  (L 1 ) and line  2  (L 2 ). The center or neutral tap is connected to earth ground  116 . Lines coming from these outputs are labeled  118  (L 1 ),  120  (line N), and  122  (L 2 ). They are collectively referred to as low voltage alternating current (AC) power line(s) and provide utility power to the houses  1  to n. In the United States, the number of houses n is typically 4 to 6 but may be up to 12, for example. Inside the houses the LV AC power lines encounter loads, which are indicated schematically in  FIG. 1  by resistor symbols. Loads  134  are across the AC voltage of from L 1  to L 2 , e.g., 230 volts (US). Loads  136  are across lines  118  or  122  and a local neutral line, e.g., line  120  or earth ground line  135 , and are 115 volts (US).  
         [0014]     Power line networking stations, indicated in the various figures by boxes labeled with “S”, are always connected to line L 1  or L 2  line and line N. For this reason, the communications path between any two power line stations within a house depends on whether the two stations happen to be on the same or different phase lines (L 1  or L 2 ). If the two stations, such as stations  138  and  140 , are on the same line (L 1 ), the power line distance between them is considerably less than if they are on different lines, such as stations  138  and  142 . The power line path from an L 1  station  138  to an L 2  station  142 , includes the L 1  path  118  to the MV-LV transformer  110 , the path through the secondary winding  114 , and the L 2  path back to the L 2  station  142 . Indeed, the prior art in the development of the power line stations for home networking requires that the L 1 -L 2  communications (via the distribution transformer) be adequate for high speed data transfers. As a consequence, by design all of the power line stations in any of the n houses attached to the same MV-LV transformer  110  can communicate with each other.  
         [0015]      FIG. 2  illustrates the use of encryption keys to define logical networks in the power line network stations, e.g. HomePlug™ standard compliant adaptors, bridges, routers and gateways, for home networking and other LAN applications. Although the power line stations of two different houses or offices share the same physical communications medium, namely the LV AC power lines  144 , and can therefore receive each other&#39;s signals, the stations of the two houses are assigned different encryption keys to establish separate logical networks. The power line network stations  146 ,  148 , and  150  of house  152  are logically connected to form a LAN by the mechanism of having a common encryption key. Power line station  154  of a neighboring house  156  is isolated from this LAN since it&#39;s encryption key does not match.  
         [0016]      FIG. 3  shows a schematic diagram of the same, representative utility power distribution network shown in  FIG. 1 , with the addition of placement of an ABM-WMAN-PL  200  near MV-to-LV distribution transformer  110 . The distribution transformer  110  is often elevated by attachment near the top of a utility pole  204 , from which the MV power lines  106  and  108  are also attached. In this case, the placement of ABM-WMAN-PL  200  near the top of utility pole  204  and near distribution transformer  110  is especially advantageous. This allows the ABM-WMAN-PL  200  to be close to or integrated with antenna  202 , which is preferably mounted on top of the utility pole  204 . Such a mounting provides a good antenna height for receiving and transmitting the WMAN radio frequency (RF) signals. Being next to the distribution transformer  110  is desirable for the ABM-WMAN-PL since, as discussed above, the distribution transformer is a required communications path for all power line stations in all houses or offices that receive utility power from the distribution transformer. A power line station that resides in the ABM-WMAN-PL (not shown in this view) is then conveniently connected by means of wires  218 ,  220  and  222  to the L 1 , L 2  and N lines that exit the distribution transformer  110 . This placement assures that ABM-WMAN-PL unit  200  has uniformly good communication with all power line stations S connected to the distribution transformer&#39;s LV AC network. In the case of ground level MV-to-LV distribution transformers, antenna  202  can be elevated by attachment to a standalone pole or any available structure.  
         [0017]      FIG. 4  illustrates how ABM-WMAN-PL unit  200  uses the encryption keys of the power line stations to maintain separate subscriber connections to the WMAN broadband access system. The ABM-WMAN-PL unit continuously maintains an active RF link with the WMAN base station  250  via their respective antennas  202  and  252 . The WMAN base station  250  in turn communicates with one or more data or integrated services networks  254 , which can be, for example, an Internet Protocol (IP) network, or other types of networks such as the Public Switched Telephone Network (PSTN)  256  for traditional voice services. The ABM-WMAN-PL unit  200  contains a power line station that is capable of supporting multiple encryption keys, one for each set of WMAN system services provisioned to clients served by the power line network. A house that subscribes to the WMAN broadband access service may be provisioned with one or more sets of services (voice, data, fax, etc.), depending on the service contract. A unique encryption key is used to establish s logical, local area network labeled in the figure as SVC-1 that provides, for example, broadband access to a personal computer  324  via the appropriate network interface cable  322  connecting it to power line network station  320 . Similarly, a second logical local area network, labeled SVC-2, is established using a second unique encryption key and provide broadband access to, for example, home network gateway  334  via the appropriate network interface cable  332  connecting it to power line station  330 . The use of encryption keys to set up logical local area networks permits different services sets to be delivered to different households, and even to different power line network stations within the same household, if desired, by setting up different stations with different encryption keys. Thus, for example, power line network stations  310  and  340  may be use the same power line medium without any access to the ABM-WMAN-PL unit  200 , because they are not setup to share an encryption key, i.e. they have not been provisioned with an authorized service set.  
         [0018]     As illustrated by the forgoing example, a low voltage AC power line network, convention, commercially available power line network stations, and an ABM-WMAN-PL, in conjunction with a service provider&#39;s WMAN base station, can be used to provide broadband access to high speed (Internet) data services as well as traditional voice telephone services. This broadband service can be provisioned at a relatively low equipment cost per subscriber, using low cost customer premise equipment (the power line network stations) installed by the customer without new wires or assistance of a technician.  
         [0019]      FIG. 5  schematically illustrates preferred embodiment of the basic structures of the major architectural elements of the examples given above. These include base station/network IF  250 , ABM-WMAN-PL unit  200  and two power line CPE devices: the CPE-Data unit  350  and CPE-Voice unit  360 . Each of these major elements has its own management software and control software. The schematic diagrams of these elements emphasize software components, media-specific stations and network interfaces.  
         [0020]     The base station/network IF  250  basically contains the circuitry and software for a WMAN base station  258 . This circuitry and software handles the functions of the physical and media access control (MAC) layers required of a WMAN base station to maintain a two-way RF link with WMAN subscriber station  260  contained in ABM-WMAN-PL unit  200 . The base station/network IF element  250  may also contain network interfaces  262  and  264  to, for example, PSTN voice network  256  and the IP data network  254 , respectively. Control software  266  of the base station/network IF  250  handles interworking functions between the MAC layer of base station  258  and the MAC layers of the network interfaces  262  and  264 . Management software  268  is used to manage operation of the base station including, for example, provisioning of services.  
         [0021]     The WMAN subscriber station  260  contains elements for handling the functions of the physical and MAC layers in order to provide a WMAN subscriber station that maintains an RF link with the WMAN base stations. The ABM-WMAN-PL unit  200  also includes a power line station  272  (i.e. circuitry and software for interfacing with a power line network) that communicates with one or more power line stations attached to the LV AC power lines  301  of its associated MV-to-LV distribution transformer (not shown). Control software  272  of the ABM-WMAN-PL unit  200  handles interworking functions between the MAC layer of the WMAN subscriber station  260  and the MAC layer of the power line station  270 . Management software  274  handles operation of the ABM-WMAN-PL. The elements of the ABM-WMAN-PL are preferably integrated into the ABM-WMAN-PL unit, but need not be. They may, however, be discrete elements assembled or interconnected at the point of installation.  
         [0022]     The CPE-data device  350  is an example of customer premise equipment suitable for connecting to a data appliance  354  to a power line network. Examples of a data appliance include a personal computer, a VoIP telephone, a network router, switch, or hub, and a “Wi-Fi” network access point (a wireless LAN based on the IEEE 802.11® Standard). CPE-data devices based on the HomePlug™ Standard are commercially available from several manufactures. A typical CPE-data device would include on one side power line station or interface  351  that communicates with the power line station of the ABM-WMAN-PL unit  200 . The power line station has circuitry and software for handling physical and MAC layer functions. A typical CPE-data device also includes a network interface  352  that communicates with a network interface (NI) in data appliance  354  and control software  355  that performs interworking between the MAC layer of the power line station and the MAC layer of the network interface (NI).  
         [0023]     The CPE-voice device  360  is also representative customer premise equipment suitable for connecting a telephone, fax machine or similar “POTS” device to a power line network. It contains circuit and software of a power line station  361  that communicates with the power line station of the ABM-WMAN-PL unit  200 . The CPE-voice device  360  also contains a (code and decode) CODEC  362  and a (subscriber line interface card) SLIC  363  which provide an analog interface for a plain old telephone service (POTS) device  364 , e.g., a standard telephone, modem or a FAX machine. Control software  366  of the CPE-voice device  360  performs the interworkings between the MAC layer of the power line station and that of the CODEC and SLIC. The CPE-Voice device can conveniently plug into an AC power outlet near a telephone jack. Once any pre-existing connection between the PSTN and the premise wiring has been broken, an inexpensive phone cord can then connect the CPE-Voice to the telephone jack and all connected telephone jacks in the residence will be supported.