Abstract:
An access point in a wireless packet communication system is disclosed. The access point has an antenna for receiving IP data encoded according to a wireless IP communication protocol. The access point also has a combiner having an input coupled to said antenna and having first and second outputs. The access point further has a first decoder for receiving encoded IP data on a first channel at a first output of said combiner. The access point also has a second decoder for receiving encoded IP data on a second channel at a second output of said combiner. The access point further has a router for receiving unencoded IP data from said first decoder at a first input, and receiving unencoded IP data from said second decoder at a second input, said router having a single output for passing unencoded IP data from said first decoder and said second decoder.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 11/075,781, entitled, “WIRELESS PACKET COMMUNICATIONS SYSTEM AND METHOD” which was filed on Mar. 9, 2005. The parent Ser. No. 11/075,781 application and this application also claim the benefit of U.S. Provisional Application Ser. No. 60/570,561, filed May 13, 2004. 
    
    
     TECHNICAL FIELD 
     The present invention is related to wireless voice and data transmission systems, and, more particularly, to wireless transmission systems which transmit internet protocol IP data. 
     BACKGROUND OF THE INVENTION 
     Voice over IP (VoIP) systems are being used to, among other things, replace conventional PBX&#39;s in offices. Wireless fidelity (Wi-Fi) systems, which transmit IP data, are being deployed in office buildings and on campuses to obviate the need for a wired LAN connection for computers and other equipment that is networked, and to provide wireless telephone service (wireless VoIP) as an alternative to conventional cellular systems such as TDMA, CDMA, GSM, and 3G. At present the conventional cellular systems&#39; coverage area is much greater than the total area covered by wireless VoIP systems for several reasons, a main reason being the relative newness of the wireless VoIP system. However, there are other problems deploying wireless VoIP systems such as battery capacity and tolerance to RF disturbances. On the other hand, Wi-Fi systems, because they transmit IP data directly between the individual computer or similar equipment (the client) and an access point (AP) provide significantly higher data rates than conventional cellular systems available today or will be available in the near future. 
     Mobile wireless VoIP telephones require more intensive data processing than conventional cellular telephones and therefore require more battery power and consequently more frequent battery charging or larger capacity (and heavier) batteries than conventional cellular telephones. A method to reduce the battery drain is to reduce the RF transmission signal level from the telephone. This results in smaller areas of coverage for each access point (AP)/base station than for each base station in a conventional cellular system, and consequently more base stations are required than conventional cellular base stations for a particular area. Therefore, the cost of purchasing and installing each base station is more of a critical factor in wireless VoIP systems. 
     While the conventional cellular systems were initially designed for roaming from one cell to another without a disturbance in the voice communication, the Wi-Fi system was initially designed for electronic equipment which can tolerate gaps in the data flow to the equipment. The most common protocol for wireless IP communication is the IEEE 802.11 standard. This standard requires termination of a first connection between a user and an AP before connection to the new AP, then reauthentication usually including encryption coordination and establishment of a new connection. This process produces gaps in the voice transmission which are noticeable to a Wi-Fi telephone user. 
     Therefore, it can be appreciated that a Wi-Fi system for mobile users over a wide area such as a metropolitan area that is relatively inexpensive to build, and that provides virtually uninterrupted voice transmission when a mobile telephone user is changing connections from one AP to another is highly desirable. 
     It is an object of the present invention to provide an AP configuration that is relatively inexpensive to build and install. 
     It is a further object of the invention to provide a Wi-Fi system that does not create disturbances for mobile telephone user. 
     It is a still further object of the invention to provide a Wi-Fi system that can be used for both voice and computer data without degrading the voice communications and that is not significantly more expensive than a voice only system. 
     SUMMARY OF THE INVENTION 
     Briefly described, a wireless packet data communication system that provides communication to a mobile communication device includes a plurality of access points. Each sector has an antenna that transmits and receives wireless communication with the mobile communication device. Coupled to the antenna is a frame encoder and decoder that encodes and decodes frames of data passing through the antenna. 
     Preferably, a SIP wireless connection with a mobile communication device is transferred from a first access point antenna to a second access point antenna by storing an IP address of the mobile communication device used during the SIP wireless connection, then disassociating the mobile communication device from the first access point antenna and associating and authenticating the mobile communication device with the second access point including reassigning the same IP address to the mobile communication device and continuing the SIP session from the connection with the first access point antenna. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features and advantages of the invention will be more fully understood and appreciated from the following description of certain exemplary embodiments of the invention taken together with the accompanying drawings, in which: 
         FIG. 1  is a conceptual perspective diagram of a wireless packet communication system according to the present invention; 
         FIG. 2  is a block diagram of some of the base stations shown in  FIG. 1 ; 
         FIG. 3  is a block diagram of some of the base stations shown in  FIG. 1  and not shown in  FIG. 2 ; 
         FIG. 4  is a block diagram of the wireless packet communication system shown in  FIG. 1 ; 
         FIG. 5  is a conceptual physical depiction of a base station shown in  FIG. 1 ; 
         FIG. 6  is a block diagram a portion of a base station shown in  FIG. 1 ; 
         FIG. 7  is a timing diagram of the handoff of a mobile user moving and switching from one sector to another; and 
         FIG. 8  is a block diagram of a wired packet communication system where the functions of the national office shown in  FIG. 4  have been shifted to the regional point-of-presence. 
     
    
    
     It will be appreciated that for purposes of clarity and where deemed appropriate, reference numerals have often been repeated in the figures to indicate corresponding features, and that the various elements in the drawings have not necessarily been drawn to scale in order to better show the features of the invention. 
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Turning now to the drawings,  FIG. 1  is a conceptual diagram of a packet communications system  20  according to the present invention. The packet communications system  20  includes a Wireless-Fidelity (Wi-Fi) section that is shown in  FIG. 1  as three regional areas (RAs) RA 1 , RA 2 , and RA 3 , and a mobile communication device  22 . Each of the RAs has a plurality of base stations, however, for simplicity base stations are only illustrated in RA 1 .  FIG. 1  shows seven base stations  24 ,  26 ,  28 ,  30 ,  32 ,  34 ,  36 ,  38  and  40  in RA 1  which communicate with the mobile wireless communication device  22  at 2.4 GHz. It will be appreciated that the number of RAs can vary depending on the geographical area covered, and that the number of base stations in each RA can vary depending upon various factors including the size of the geographical area of the RA, the obstructions to RF communication within the RA, the anticipated number of simultaneous mobile wireless connections to each base station, and the cost of each base station. 
     The areas covered by each of the base stations  24 - 40  overlap so that there is complete coverage in RA 1 , and RA 1 , RA 2 , and RA 3  overlap such that there are no gaps in coverage between the RAs. The number of RAs, and therefore the region covered by the system, is virtually unlimited, the larger area requiring more base stations and larger bandwidth connections through the internet  50 . 
     Also shown in  FIG. 1  are three regional points of presence (RegPOP)  42 ,  44 , and  46 . The RegPOPs process the Wi-Fi traffic to and from each Base Station in RA 1 , RA 2 , and RA 3  generally over a 5.8 GHz RF link, although a wired connection can be used instead. A core network site or national office  48  is connected to each of the RegPOPs  42 ,  44 , and  46  by the internet  50 . 
     Intermediate 5.8 GHz relay points, referred to herein as RPOPs, can be used where a direct 5.8 GHz connection between a base station and a RegPOP is not feasible. These RPOPs can also be a base station such as base stations  28  and  36 . The RPOP at base station  28  relays 5.8 GHz communications between base stations  24 ,  30  and RegPOP  42 , while the RPOP at base station relays 5.8 GHz communications between base stations  32 ,  34  and RegPOP  42 . Alternatively, the RPOPs  28  and  36  can be connected to the RegPOP  42  by wired connections  51  and  52 , respectively rather than the 5.8 GHz RF connections. 
     Each of the base stations has four or six 2.4 GHz antennas for RF communication with the mobile communication device  22 . The base stations with four 2.4 GHz antennas have their beams directed at 90 degree rotational offsets in the horizontal plane as shown in diagram  53 . Similarly, the base stations with six 2.4 GHz antennas have their beams directed at 60 degree rotational offsets in the horizontal plane as shown in diagram  54 . 
     The 2.4 GHz communication between the base stations and mobile communication device  22  conforms to the IEEE 802.11 standard; more specifically, the 802.11 b and 802.11 g standards. The 802.11 b standard has a 11 Mbps data rate while the 802.11 g standard has a 54 Mbps data rate, but the 802.11 b standard is able to communicate over longer distances than the 802.11 g standard. With wireless mobile audio communication devices  22  which can operate under both 802.11 b and 802.11 g, the base stations  24 - 40  detect the signal strength of the transmission from the wireless mobile audio communication device  22 , and if it is high enough, the wireless mobile audio communication device  22  and the base stations  24 - 40  communicate using the 802.11 g standard to take advantage of the higher data rate which allows more simultaneous connections to one of the 2.4 GHz antennas without degrading the transmissions. If the signal strength isn&#39;t high enough for the 802.11 g standard, but is high enough for the 802.11 b standard, then the 802.11 b standard is used. In practice only about five percent of the 11 Mbps and 54 Mbps data rate can be used to provide a high quality audio transmission. The system in the preferred embodiment of the present invention uses a VoIP CODEC, which requires a voice bandwidth of about 40 Kbps. Thus an antenna on base stations  24 - 40  transmitting and receiving signals using the 802.11 b standard can provide simultaneous transmissions with about 10 to 14 wireless communication devices  22 , while an antenna transmitting and receiving signals using the 802.11 g standard can provide simultaneous transmissions with about 65 to 70 wireless audio communication devices  22 . A wireless audio mobile communication device  22 , when roaming into an AP area, may necessitate using the 802.11 b standard, but as the audio mobile communication device  22  continues to move in the AP area, the signal strength may improve such that the 802.11 g standard can be used. 
     Although 802.11 b and g provide 13 channels, the system of the present invention uses only channels  1 ,  6  and  11  for voice to minimize disturbances in the RF transmissions. The channel assignments of each antenna for the four antenna base station and the six antenna base station are shown in diagrams  53  and  54 , respectively. 
     Installing a base station having four or six antennas as well as selecting the number and placement of the base station is determined mainly by the maximum number of anticipated simultaneous communications at each base station, the RF disturbances present in the base station area, the RF disturbances along the 5.8 GHz path from the base station to the RPOP or RegPOP, and the costs of the four antenna and six antenna base stations. 
     Also shown in  FIG. 1  is a router  64  and a plurality of wired connections  66  to each of the base stations  24 - 40 , RPOPs  28  and  38  and the RegPOP  42 . The router  64  and wired connections  66  are part of an out-of-band (OOB) network which monitors the wireless system and provides operating commands to the various elements of the system. The router  64  is connected through the RegPOP  42  and through the internet  50  to a server and operator interface to the OOB network in the national office  48 . In the preferred embodiment the wired connections  66  are fast network connections. 
       FIG. 2  is a block diagram of base stations  24 ,  28 ,  30 ,  32 ,  34 , and  36 . Shown in  FIG. 2  are three sections  70 ,  72 , and  74  that are the electronics exclusive to the 2.4 GHz 802.11 sectors  1 ,  2 , and  4  or  6 , respectively. A fourth section  76  shows the 5.8 GHz 802.11 electronics for the base stations  24 ,  28 ,  30 ,  32 ,  34 , and  38 . The sections  70 ,  72 ,  74 , and  76  have electrical connections to an switch  78 . The sector electronics comprise a 2.4 GHz antenna  80  connected through a lightning protector  82  to a channel filter  84  that, in turn, is connected to a 1 watt amplifier  86 . The 1 watt amplifier  86  is connected by a low loss cable  88  to another lightning protector  90  that is also connected to an AP 2.4 GHz 802.11 interface  94  by an amp injector  92 . The AP 2.4 GHz 802.11 interface  94  is connected to an AP injector  96 , that is also connected to the switch  78 . 
     Section  76  includes a narrow band 5.8 GHz antenna  98  connected through a lightning protector  82  to a 5.8 GHz 802.11 interface or radio  100 . The 5.8 GHz radio  100  is connected to a radio injector  102  that, in turn, is connected to the switch  78 . In some cases a wired connection to RegPOP  42  or to a RPOP is made through a cable  103 . In those cases, section  76  would not be used since the cable  103  would provide a direct IP connection obviating the need for the 5.8 GHz 802.11 link. 
     In the preferred embodiment, the antennas  80  are multipolarized. 
     In operation the mobile communication device  22  establishes an 802.11 compliant communication with the AP 2.4 GHz 802.11 interfaces  94  through a signal path that includes the antenna  80 , lightning protector  82 , channel filter  84 , 1 watt amplifier  86 , low impedance connection  88 , lightning protector  90 , and amplifier injector  92 . The IP data to and from the AP 2.4 GHz 802.11 interfaces  94  after the 802.11 frame structure is passed through the AP injector  96  to and from the switch  78 . In base stations  24 ,  26 ,  30 ,  32 ,  34 , and  38  the data is passed through the radio injector  102  and to and from the 5.8 GHz radio  100  which communicates with an RPOP  28  or  36  or AP  40  using the 802.11 communication interface. 
       FIG. 3  is a block diagram of base stations  28  and  36 . The block diagram for base stations  28  and  36  is the same as the block diagram of  FIG. 2  but with the addition of another section  104  which is the same as section  76  except that the narrow beam 5.8 GHz antenna  98  is replaced by a broad beam 5.8 GHz antenna  106 . The broad beam 5.8 GHz antenna  106  communicates with the narrow band 5.8 GHz antennas  98  of the base stations  24 ,  30 ,  32 , and  34 . 
     Base station  40  has the same block diagram as  FIG. 3  except that section  76  is missing since the connection between the base station  40  and the RegPOP  42  is through cable  103 . Base station  40  could also be configured without the 2.4 GHz sections  70 - 74  and thus consist of a section  104  and switch  78  with the cable connection  103  to the RegPOP  42 . 
     The base stations  24 - 38  can operate without a special IP cable which reduces the cost of installation and operating fees for the base stations. 
       FIG. 4  is a block diagram that includes RA 1 , RPOPs  28  and  36 , RegPOP  42  and the national office  48 . The block diagrams for the base station  24 - 40  have been described above. The RegPOP  42  transfers IP data with the base station in router/switch  110  and transfers the data through a firewall  112  that is connected with a router  113  that, in turn, is connected to the internet  50 . Voice data is passed between the RegPOP  42  and the national office  48  through a virtual private network in the internet  50 . Computer IP data (i.e., data for another computer or an IP network) is transferred to and from the public portion of the internet  50  at each of the RegPOPs  42 ,  44 , and  46  which have their own separate internet addresses. Connected to the internet  50  in the national office  48  is a router  114  that has a connection to a firewall  116  that, in turn, is connected to a switch  118 . The switch  118  is also connected to a session border controller  120  that in turn is connected to a SIP proxy  122 . The SIP proxy  122  is connected to a voice gateway  124  that interfaces the public switched telephone network (PSTN)  126  to complete the connection between a voice mobile communication device  22  and a caller using the PSTN  126 . 
     The router  114  has another connection that is to another firewall  128  that, in turn, is connected through a switch  130  to a RADIUS/LDAP server  132  that stores information on the mobile communications devices  22 . The RADIUS/LDAP server  132  is also connected to a value added services module  134  that includes VMS (voice mail system), SMS (short message service), INFO, and IN (intelligent network). 
       FIG. 5  is a conceptual representation  140  of a base station according to the present invention. Shown in  FIG. 5  is a tower having a cable  88  through the tower from a lower electronics enclosure  144  to an upper electronics enclosure  146 . Attached to the top of the tower  142  are four or six 2.4 GHz antennas  80 . Shown below the 2.4 GHz antennas  80  are the two 5.8 GHz antennas  98  and  106 . The upper electronics enclosure  146  holds the electronic blocks within the dashed lined rectangles  146  shown in  FIGS. 2 and 3 . The rest of the electronics at the base station are located in the lower enclosure  144 . The lower enclosure has a first cable passing through a wall of the enclosure that is one of the OOB cables  66  shown in  FIG. 1 , and the lower enclosure  144  may also have a second cable  103  passing through the wall of the enclosure. Cable  103  is shown in  FIGS. 2 ,  3 , and  4 . It will be appreciated that a tower is not required for a base station. A base station can be mounted on the side or top of a building, for example. Also, since the coverage area for each base station is smaller than the coverage area for a conventional cellular phone base station, the height needed for the cellular base station antenna is not necessarily required for a base station antenna. 
     The system of  FIG. 1  is primarily for voice communication. To also handle data communication, the base station needs to be modified as shown in  FIG. 6  by providing two parallel communication paths, a first communication path  152  and a second communication path  154  and by placing voice data and computer data on separate channels defined in the 802.11 standard. The diagram  53  of  FIG. 1  shows a top sector which can be used for both voice and computer data with the voice data on channel  6  and the computer data on channel  13 . Each of the communication paths  152  and  154  have an AP 2.4 GHz 802.11 interface, and an AP injector  96 . The AP 2.4 GHz interface  94  in communication path  152  encodes and decodes 802.11 frames in channels  1 ,  6 , and  11 , while the AP 2.4 GHz interface  156  in communication path  152  encodes and decodes 802.11 frames in other channels, such as channel  13 , that are used for computer data. A combiner  93  combines and splits the signals between the amp injector  92  and the AP 2.4 GHz 802.11 interface  94  in each of the communication paths  152  and  154 . The IP data to and from the AP injectors  96  passes through the switch  78 . When a 2.4 GHz 802.11 interface has been established and data from the mobile communications device  22  is passing through the system, the national office  48  detects if voice data or computer data is being transferred to and from the mobile communication device  22 . If the communication is voice communication, the first communication path  152  is used, and if the communication is computer data, the second communication path  154  is used. The two communication paths  152  and  154  are necessary because the computer data transmitted is much more dense than the voice data. The delays due to retries required because of the denser traffic would degrade the quality of the voice transmission, but generally can be tolerated in computer data exchanges. 
       FIG. 7  is a timing diagram  160  of a mobile communications device  22  handoff process when the mobile communications device roams from one sector connection to another sector connection. At the top of  FIG. 7  is a perspective view of a horizontal slice near a base station. A region  162  shows the area where the predominant signal strength is to and from a sector  2  and region  164  shows the area where the predominant signal strength is to and from a sector  1 . The area  166  is the crossover region between the areas  162  and  164 . In the example of  FIG. 7  a mobile communications device  22  initiates a telephone call with an AP association shown in block  168 . After the AP association, an AP authentication occurs as shown in block  170 . This initial authentication takes about 350 to 400 ms. Once the authentication is complete, normal voice transmission using sector  2  occurs as shown in block  172 . Also, after the authentication, an IP address is assigned as shown in block  174  and a SIP call initiation occurs as shown in block  176 . As shown in the bottom row of  FIG. 7 , as the mobile communication device  22  travels, the signal strengths for sector  2  and sector  1  change. The mobile communications device  22  operates in the power save mode and uses the rest time to measure the signal strength from the surrounding sectors. 
     When the mobile communications device  22  senses that another sector has a 3 dB greater signal than the sector that the mobile communication device  22  is currently communicating with, as occurs at point  178 , the mobile communications device  22  dissociates from sector  2  in this example as shown in block  180 , associates with sector  1  as shown in block  182 , authenticates with sector  1  as shown in block  184 , and resumes normal communication as shown in block  186  using sector  1  instead of sector  2 . Advantageously, the system of the present invention keeps the IP address and SIP connection alive for one or two seconds after the mobile communication device  22  disassociates so that the mobile communication device  22  can reassociate and reauthenticate in about 50 ms which does not cause a disturbance noticeable to the user of the mobile communication device  22 . The system of the present invention also remembers the key used in the last connection for a few seconds so that the authentication and WEP/WPA/WPA2 encryption can be quickly reestablished. 
       FIG. 8  is a block diagram of a wired packet communication system in which the functions of the national office  48  shown in  FIG. 4  have been shifted to the regional point-of-presence and a Multiprotocol Label Switching (MPLS) backbone ring  190  that is a network available in many countries of the world. As shown in  FIG. 8  the router/switch  113  transfers data to and from access point  40  and optionally to and from other access points such as access points  28  and  36 . The router/switch  113  is coupled to the internet  50  through the firewall  112  and router  110 . The router/switch  113  is coupled to the MPLS backbone ring  190  and to the session border controller  120  and the RADIUS/LDAP server  132 . By moving the national office  48  functions to the RegPOP, router  114 , firewalls  116  and  128 , and switches  118  and  130  have been eliminated. However, instead of having only one national office, the remaining blocks of the national office have to be duplicated at each RegPOP. In some alternative embodiments of  FIG. 8  The RADIUS/LDAP server  132  and value added services  134  can be located in a national office and the MPLS backbone ring used to provide high speed connections between the alternative RegPOP and the alternative national office. 
     While the invention has been described by reference to various specific embodiments, it should be understood that numerous changes may be made within the spirit and scope of the inventive concepts described. Accordingly, it is intended that the invention not be limited to the described embodiments, but will have full scope defined by the language of the following claims.