Patent Publication Number: US-2007121561-A1

Title: Wlan mobile phone and wireless network

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
      This application claims priority to and is a continuation-in-part (CIP) of U.S. patent application Ser. No. 11/075,781 filed on Mar. 9, 2005 entitled “WIRELESS PACKET COMMUNICATIONS SYSTEM AND METHOD.” This application also claims priority to U.S. provisional patent application Ser. No. 60/739,620 filed on Nov. 23, 2005, entitled “WIFI MOBILE PHONE.” Both the Ser. No. 11/075,781 and the 60/739,620 applications are hereby incorporated by reference in their entirety. 
    
    
     FIELD  
      The claimed invention is related to a system for mobile wireless IP phones which transmit and receive IP packets, and, more particularly, to wireless phones which transmit and receive IP packets and which emulate traditional cellular phones.  
     BACKGROUND  
      Wireless local area networks (WLAN&#39;s) are being deployed in coffee shops, terminals, office buildings, campuses, homes, as well as other locations to obviate the need for a wired local area network connection for computers and other equipment that is networked. At the same time, software is being developed which can sample an analog conversation, code the conversation as a series of digital packets, and route the digital data over the internet to a recipient, where the digital data packets are uncoded and changed back into an analog signal which can be amplified for the recipient to hear. This type technology is referred to as voice-over-internet-protocol or VoIP teleology. Lately, companies have recognized the possibility that telephones can be developed with VoIP processors for coding and decoding voice data which can then be sent over the internet to a recipient while the VoIP phone user is connected to the network within a WLAN hotspot.  
      Unfortunately, the users of such VoIP telephones are limited to making their calls while staying within the relatively small WLAN hotspot, as compared to the freedom of movement afforded users of the currently more common cellular telephone. Current WLAN VoIP telephones encounter hand-off issues when moving from one coverage area or hotspot to another due to the conditions placed on the routing of IP data packets for voice. When transitioning from one WLAN coverage area to another, the currently available association process for the VoIP WLAN phones produces a noticeable void or interruption in voice conversations while the IP addressing and routing occurs.  
      This hotspot transition or hand-off issue is an even larger concern in a WLAN-based phone network, because transitions are more likely to occur. Since WLAN coverage areas are much smaller than the more conventional cellular wide area networks (WAN&#39;s) it will take many more WLAN coverage areas to create an overall coverage area to compete with the conventional cellular systems. Given this even larger number of WLAN areas, each covering a relatively small area, there exists a need for a wireless network and the related WLAN mobile phones which can utilize VoIP technology while reducing the hand-off delays when moving between hotspots so that voice conversations are not impacted by noticeable interruptions. If the current problem of noticeable WLAN hand-off interruptions can be solved, WLAN phone systems become attractive as an alternative to conventional cellular telephones, because they transmit IP data directly between the individual mobile phone, computer, or similar equipment (the client) and a base station (sometimes referred-to as an access point (AP)) while providing significantly higher data rates than conventional cellular systems available today or which will be available in the near future.  
      These problems, plus the present lack of additional features that cellular users are accustomed to and are not present in current WLAN mobile phone systems, will need to be overcome to make a commercially viable WLAN mobile phone and wireless network.  
     SUMMARY  
      A wireless network has a plurality of base stations, each configured to communicate with at least one portable device using a wireless local area network (WLAN) protocol. The wireless network also has a Voice-over-IP (VoIP) core network coupled to each of the base stations.  
      A wireless local area network (WLAN) mobile phone has an antenna and an RF section coupled to the antenna. The WLAN mobile phone also has a VoIP processor coupled to the RF section and configured to monitor a current signal strength from a current base station and an alternate signal strength from an alternate base station, wherein the VoIP processor is configured to disassociate from the current base station when an analysis of the current signal strength and the alternate signal strength indicate that it would be better to associate with the alternate base station.  
      A method of handing-off a VoIP call-in-progress from a first base station to a second base station with reduced interruption in voice communication is disclosed. A determination is made that a call association should be changed from the first base station to the second base station. Identifying information about the second base station is stored before disassociating from the first base station. The first base station is disassociated from. An IP address assignment which was active when the call-in-progress was associated with the first base station is maintained. The second base station is associated with. The second base station is communicated with using the maintained IP address assignment. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  schematically illustrates an embodiment of a wireless network.  
       FIG. 2  schematically illustrates an embodiment of a wireless network having an embodiment of a repeater.  
       FIG. 3  schematically illustrates an embodiment of a wireless network having an embodiment of a voice gateway.  
       FIG. 4  schematically illustrates an embodiment of a wireless network having an embodiment of a fixed line gateway.  
       FIG. 5  schematically illustrates an embodiment of a wireless network having different embodiments of VoIP core network couplings.  
       FIG. 6A  schematically illustrates another embodiment of a wireless network.  
       FIG. 6B  schematically illustrates an embodiment of a sector for a base station of the embodied wireless network of  FIG. 6A .  
       FIG. 6C  schematically illustrates a top view of an embodiment of a 4-sector base station of the embodied wireless network of  FIG. 6A .  
       FIG. 6D  schematically illustrates an embodiment of the structure of a multi-sectored base station with N number of sectors.  
       FIG. 6E  schematically illustrates an embodiment of a VoIP core network.  
       FIG. 7  illustrates one embodiment of a method of handing-off a VoIP call-in-progress from a first base station to a second base station with reduced interruption in voice communication.  
       FIG. 8  is a front view of an embodiment of a WLAN mobile phone.  
       FIG. 9  is a block diagram of a portion of the WLAN mobile phone embodied in  FIG. 8 .  
       FIG. 10  is a block diagram of a further portion of the WLAN mobile phone embodied in  FIG. 8 .  
       FIG. 11  illustrates one embodiment of a timing diagram of a WLAN mobile phone handoff process when the WLAN mobile phone roams from one sector connection (or base station connection) to another sector connection (or another base station connection) within a network. 
    
    
      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.  
     DETAILED DESCRIPTION  
       FIG. 1  schematically illustrates an embodiment of a wireless network  30 . A first base station  32  and a second base station  34  are coupled  36  to a VoIP core network  38 . Each base station  32 ,  34  has its own WLAN coverage area. In this embodiment, the first base station  32  has a first coverage area  40 , and the second base station  34  has a second coverage area  42 . The first and second coverage areas  40 ,  42  have an overlap coverage area  46 . The base stations  32 ,  34  are configured to communicate  48 ,  50  with at least one portable device  52  using different frequency channels within a first frequency band. One example of a suitable first frequency band is approximately 2.4 GHz-2.5 GHz, such as would be used if the WLAN base stations were employing WiFi 802.11b or 802.11g. In other embodiments, different frequency channels and/or frequency bands could be used, for example, but not limited to, the  5 . 8  GHz frequency band. Since the base stations with overlapping coverage areas are preferably communicating on different channels, a portable device  52  can be configured to tell the difference between communications from one base station  32  and another  34 .  
      Although only two base stations  32 ,  34  are illustrated in this embodiment, it should be understood that any plurality of base stations could be coupled to the VoIP core network  38 . For simplicity, each base station is illustrated as having only one sector (one coverage area), but in other embodiments, a single base station can have a plurality of sectors by having separate sector antennas and processing circuitry for each sector on the same base station. One base station with a plurality of overlapping sectors or coverage areas would operate effectively like the two base station example above, but the separate coverage areas emanate from a single base station. Therefore, a plurality of base stations for the purposes of the claimed invention can also be made-up of a single base station having a plurality of overlapping sectors. A plurality of base stations can also mean one or more base stations, or any combination thereof.  
      The portable device  52  communicates with the at least one base station using a wireless local area network (WLAN) protocol. Examples of suitable protocols include, but are not limited to 802.11 (all variations), WiFi, and Bluetooth®. The portable device  52  and the base stations each preferably have an antenna which facilitates communication on the desired frequencies. In some embodiments, the portable device  52  can be a WLAN mobile phone, however, any mobile device which can also code and decode voice data for WLAN communication could be the portable device  52 , such as, for example, a police radio in a police car. The portable device  52  does not only have to have WLAN communications capabilities. The portable device  52  could also have wireless wide area network (WWAN) capabilities, for example cellular GSM or cellular CDMA capabilities for when a WLAN connection was not available.  
      The VoIP core network  38  coordinates the overall wireless network. In an example communication, a portable device  52  associates with a base station  32  (also referred-to as an access point or AP). The portable device  52  can then register with the VoIP core network  38  via the base station  32 . The VoIP core network  38  manages IP address assignments for each of the registered devices, tracks which base station the portable device is communicating through, and routes data to and from the portable device  52 .  
       FIG. 2  schematically illustrates another embodiment of a wireless network. In this embodiment, a repeater  54  is added to the network  30  and is also configured to communicate  56  with a portable device  52  using the first frequency band which the base stations use. Relative to the communication  56  between the repeater  54  and the portable device  52 , the repeater  54  acts just like a base station  32 ,  34  from the portable device&#39;s point of view. The repeater  54  creates at least one WLAN coverage area in the vicinity of the repeater  54 . The repeater  54 , however, is coupled to the VoIP core network  38  via a base station  34 . In this embodiment, the repeater  54  communicates  58  with the base station  34  using a second frequency band so as not to interfere with the portable device communications on the first frequency band. For example, in some embodiments, the first frequency band might be the 2.4 GHz band and the second frequency band might be the 5.8 GHz frequency band, although other frequency bands can be chosen. A repeater  54  is useful for situations where base stations have trouble providing strong enough communication signals to the portable devices, such as within a building. Although only one repeater is shown in this embodiment, other embodiments may have a plurality of repeaters, either distributed separately at different base stations an-d/or set-up such that there is more than one repeater communicating with a single base station. Preferably, the portable device  52  should not be able to tell the difference between the repeater  54  and a base station  32 . The portable device  52  can register with the VoIP core network  38  via the repeater  54  through the base station  34 .  
      The embodiments described thus far enable one portable device  52  to communicate with another portable device  52 , provided the two devices are both registered with the VoIP core network  38 . In other embodiments, it may be desirable for a portable device  52  registered with the VoIP core network  38  to be able to communicate with a network outside of the wireless VoIP network  30 .  FIG. 3  schematically illustrates another embodiment of a wireless network  30  which addresses this situation. In the embodiment of  FIG. 3 , the VoIP core network  38  has or is connected to a voice gateway  60  which is capable of coding and decoding voice data appropriately for communication with a voice network  62  that is separate from network  30 . Although only one voice network  62  is illustrated in this embodiment, other embodiments may be configured to allow the VoIP core network  38  to communicate with a plurality of other voice networks using one or more voice gateways  60 . Examples of voice networks  62  which a voice gateway  60  could connect to include, but are not limited to, a cellular communication system, such as GSM or CDMA; a private branch exchange (PBX) system; and a circuit-switched calling system such as a public switched telephone network (PSTN).  
      In other embodiments, it may be desirable to allow fixed telephone lines to communicate over the wireless network  30  without having to connect the fixed telephone lines over a separate voice network  62 .  FIG. 4  schematically illustrates an embodiment of a wireless network which addresses this situation. A fixed line gateway  64  is provided to communicate  66  with a base station  34  similar to how a portable device  52  would communicate with the base station  34  over the first frequency band. In addition to having this WLAN communication capability, the fixed line gateway  64  is also coupled to a fixed line telephone  68 . The fixed line gateway  64  can register the fixed line telephone  68  with the VoIP core network  38  for communications on the wireless network  30 . The fixed line gateway  64  also handles the coding and decoding necessary to translate between the fixed line phone  68  voice format and the VoIP packet format. Although only one fixed line gateway  64  is illustrated in the embodiment, other embodiments can have a plurality of fixed line gateways communicating with one or more base stations. Furthermore, in other embodiments, a single fixed line gateway  64  may be configured to connect more than one fixed line telephone  68  to the wireless network  30 .  
      The VoIP core network  38  may be coupled to the base stations in a variety of ways.  FIG. 5  schematically illustrates an embodiment of a wireless network  30  which illustrates some of the possible couplings. In this embodiment, three separate base stations  70 ,  72 ,  74  are provided for WLAN communication with portable devices  52 . Base station  70  is coupled to the VoIP core network  38  via a wide area network (WAN)  76 . An example of a suitable WAN  76  includes the internet. As an alternate, base station  72  is coupled to the VoIP core network  38  via a local area network (LAN), such as a wireless LAN  78 . As a further alternate, base station  74  is coupled to the VoIP core network  38  via a wired connection  80 . The wired connection can be either electrically conductive wires or one or more fiber optic wires. Although only one base station is shown connecting to the VoIP core network  38  for each example coupling method in the embodiment of  FIG. 5 , in other embodiments there can be multiple base stations connecting via similar coupling methods.  
      The embodiments of wireless networks in  FIGS. 1-5 , and their equivalents, can be combined in various ways to create different configurations of wireless networks.  FIG. 6A  schematically illustrates one embodiment of such a combination. Like the previous embodiments, this embodiment enables VoIP services similar to existing cellular technologies, but with the much higher data rates WLAN-based access provides, while reducing the interruptions in the voice communication which occur when switching from one antenna coverage area to another. The system of this embodiment combines a portable, cellular-style phone with a WLAN wireless radio network operating on the 2.4 gigahertz open frequency band and using the 802.11b/g protocols. As mentioned earlier, other embodiments may use other frequency bands and other WLAN protocols.  
      The wireless network  82  has WLAN base stations  84 ,  86 , and  88  operating on the 2.4 gigahertz open frequency band and using the 802.11b/g protocols. The base stations may be installed on house/building rooftops, on towers, on poles, on trees, etc. in accordance with an area&#39;s layout, in order to allow optimal reception for defined areas. The wireless network also has repeaters  90 ,  92  which can be used to cover areas where wireless coverage is not sufficient, such as inside buildings. The repeaters  90 ,  92  may be connected via wires or wirelessly to a base station.  
      This embodiment provides two types of end-user devices which allow a user to hold a phone conversation. One end-user device is a unique wireless phone  94  which operates on the 2.4 gigahertz open frequency and uses the 802.11b/g protocols, on SIP standard. Another type of end-user device is the combination of a fixed line VoIP gateway  96  plus a fixed-line phone  98 . In this embodiment, the fixed line VoIP gateway  96  uses 802.11b/g protocols, on SIP standard to provide fixed line VoIP for a standard fixed-line phone  98 .  
      This embodiment also has a VoIP Core Network unit  100  which provides VoIP services and which is coupled to a PSTN  102  of a national telephone system.  
      The base stations  84 ,  86 ,  88  may be used to transmit and receive to and from the end-units  94 ,  98 . In this embodiment, each base station is a modular unit of up to 4 sectors made possible with one or more sector antennas. For example, base station  84  has two sectors  104  and  106 . The number of sectors for each base station is determined in concordance with the coverage needs of a given area. In other embodiments, the one or more sectors can be of any desired size and coverage shape by changing the characteristics of the sector antenna. In this embodiment, the sector antennas are modular, and each sector arbitrarily covers a 90 degree area. Therefore, in this embodiment, a four sector base station is used for 360 degree coverage. The transmission range of each sector can reach up to two kilometers in an open spaced area and five hundred to seven hundred and fifty meters in a built up area.  
      As mentioned earlier, a base station can have one or more sectors.  FIG. 6B  schematically illustrates an embodiment of a sector  108 . The sector  108  has a wireless access point  110 , for example a Cisco wireless access point (model AIR-BR-1310G) with a 100 mw transmission capacity. FCC: LDK102052P approval. The wireless access point  110  sends and receives data packets. An RF amplifier and channel filter  112  is coupled to the wireless access point  110 . An example of a suitable RF amplifier and channel filter  112  is manufactured by RF-LINX with volumes of between 125 mw and 1 watt, together with a filter channel which allows for changing channel selection from channel  1  through channel  11 . An antenna  114  is coupled to the RF amplifier and channel filter  112 . Those skilled in the art can select a variety of antenna designs which will fulfill a desired sector pattern. One example of a suitable antenna  114  is a multi-polarized antenna with 9.2 dBi transmission intensity and −97 dB reception sensitivity. The sector  108  also has lightning protection  116 .  
      In this embodiment, in order to help increase performance and avoid interference, each sector is allocated with one of three non-over lapping channels  1 ,  6 , and  11 . At a four sector base station, identical channels will be placed in opposite directions. For example,  FIG. 6C  schematically illustrates a top view of an embodiment of a 4-sector base station  118 , having sectors  120 A,  120 B,  120 C, and  120 D. In this embodiment, opposite sectors  120 A and  120 C are set to channel  1  since these sectors  120 A and  120 C are positioned not to interfere with each other. Intervening sectors  120 B and  120 D are set to channels  11  and  6  respectively. Other embodiments may use other channel choices, different numbers of sectors, and/or different sector antenna patterns. While constructing a wireless network with multiple base stations, it is desirable to avoid a situation where identical channels will overlap, in order to decrease the possibility of mutual disturbances.  
       FIG. 6D  schematically illustrates the structure of a multi-sectored base station with N number of sectors. Each sector has an antenna  122  with lighting protection  124  coupled to an RF amplifier and channel filter  126  coupled to a wireless access point  128  coupled to an access point injector  130 . The access point injectors  130 - 1  to  130 -N are then coupled to an IP switch  132  which helps direct traffic to/from the base station.  
      As described already with regard to  FIG. 6A , the wireless network  82  has at least one repeater  90 ,  92 . The repeater is intended to assist coverage in areas where base station transmission and reception is insufficient (mainly inside buildings). In this embodiment, each repeater has an access point, and two antennas, one for communication  134  (See  FIG. 6A ) with the end-use equipment  94 , and one for communication  136  with the adjacent base station  88 . One embodiment of a suitable repeater can include a wireless access point unit, model WX-7800A by Spark Lan with FCC RYK—7800A approval. The two antennas can suitably be, for example, two multi-directional antennas, each with  8  dBi transmission intensity, Model No. OAN-2080, by Level One. In this embodiment, each repeater  90 ,  92  has the following characteristics: a transmission capacity of 100 mw (mw200 EIRP), using a protocol of 802.11a/b/g, with a data transfer rate of up to 54 Mbps.  
      The end-user handset  94  in this embodiment is an 802.11b/g protocol mobile phone that operates in much the same way that a cellular phone would from the user&#39;s point of view. The handset  94 , however is communicating using VoIP, using the SIP standard in this embodiment. The phone handset  94  is designed to work through a provider&#39;s network of base stations in addition to WiFi “hot spots”. In a preferred embodiment, the WLAN mobile phone  94  has a maximum transmission strength capable of reaching up to mw600 (EIRP), although other transmission strengths may be used in other embodiments. In some embodiments, the phone  94  sets the transmission strength automatically, according to the local wireless network&#39;s reception strength in order to help conserve the handset&#39;s battery when possible. In this embodiment, the WLAN mobile phone has a reception sensitivity of −97 dB.  
      The handset  94  is configured to allow users to conduct conversations within the network, while on the move between sectors and between base stations without disturbances and disconnections. This will be discussed in greater detail later with regard to  FIG. 7 . Although the handset specifications in other embodiments may vary, the handset specifications in this embodiment are as follows:  
                                      Conversation Protocol   SIP, SIP 2       Wireless Transmission Protocol   802.11b/g       Encoding   WEP-64/128, WPA-PSK, WPA, WPA2       Frequency   2.4 GHz       Antenna   2.5 dBi       Quality of Service   802.11e Protocol       Encryptor   Encryption code G711-A G711H G729       Battery   4 Hours talk time, 100 Standby Hours       Operating System   Linux       Transmission Capacity (EIRP)   100 mW to 600 mW       Reception Sensitivity   −97 dB       Capacity Management   PMU system for transmission capacity           management                  
 
      The VoIP core network  100  in this embodiment has a voice gateway which allows for a connection between the base station and a standard phone line, for example on a PSTN  102 , and for conversion from a regular vocal signal from the PSTN  102  to a digital signal and visa versa. The VoIP core network  100  takes care of all phone call related issues and connections with other operators.  FIG. 6E  schematically illustrates one embodiment of a VoIP core network  100 . In this embodiment, the VoIP core network  100  has a voice gateway  138  for coupling to an external telephone network, such as a public switched telephone network (PSTN). The voice gateway  138  is coupled to a SIP proxy server  140  for managing the IP registration and packet sessions. A firewall  142  is coupled to the SIP proxy  140 , followed by a management switch  144 , router  146 , and firewall  148 , all of which help the VoIP core network  100  communicate with specific base stations. The VoIP core network  100  is coupled to the base stations by a variety of different methods which have been discussed above with regard to other embodiments.  
      Referring again to the embodiment of  FIG. 6A , when the end-user turns on the wireless handset  94  within the network&#39;s coverage area, the phone  94  executes an identification and connection process, and registers with the VoIP core network  100 . After the identification, connection, and registration are completed successfully, the phone  94  is ready for action.  
      The wireless phone  94  scans the coverage area for existing networks within range. Although not illustrated, there may be competing VoIP networks with their own base stations and separate VoIP core network within range of an end-user&#39;s phone  94 . In this embodiment, the phone is associated with a default preference for a VoIP wireless network. If the default network is not found, the phone will connect to another network in accordance with a user-defined preferred network list. If defined networks are not found the user can manually initiate a network search and connect to any other available and compatible networks.  
      At the end of the network search, the phone displays the name of the chosen network, and executes a connection and registration with the core network using the IP address embedded within the phone as defined by the phone provider. Phone numbers, user names and passwords may be registered with the VoIP core network  100  for identification purposes. When the phone  94  is connected to the VoIP core network  100  a phone number associated with the phone  94  can be displayed on the handset screen.  
      When the user desires to make a call, the user dials the desired number or, alternatively, accesses his phone&#39;s stored numbers and sends a “call” request. The request containing the phone number goes through to the VoIP core network  100  and from there to the national telephony system  102  or internal network system  100  while the voice data is converted from an analog signal to a digital signal or visa versa as needed.  
      The embodied wireless VoIP networks discussed herein are more than just a plurality of single WLAN networks which are capable of communicating VoIP data. The VoIP core network and the portable devices connecting to the base stations are configured to allow a VoIP call-in-progress to be handed-off from a first base station or sector to a second base station or sector with a reduced interruption in the voice communication, where ideally, the end-user is not even aware of the transition. In some embodiments, a reduced interruption in the voice communication may even mean an eliminated interruption in the voice communication.  
       FIG. 7  illustrates one embodiment of a method for handing off a VoIP call-in-progress from a first base station to a second base station with reduced interruption in the voice communication. It should be understood from the preceding discussion of base stations and sectors, that the method which applies to transitions from one base station to another base station is also intended to apply to transitions between different sectors of the same base station. Such sector transitions are effectively transitions between different base stations.  
      The starting situation where the method of  FIG. 7  applies is after a VoIP call has been initiated via a first base station. As part of the call initiation, an access point (AP) association and an AP authentication are made via the communication channel of the first base station. The phone transmits and receives via a first channel, and a SIP call initiation and an IP address assignment are made with the VoIP core network. At this point, the VoIP call is in progress. According to the embodied method of  FIG. 7 , while the call is in progress, a determination  150  is made that a call association should be changed from a first base station to a second base station. The phone is configured to monitor other channels beyond the channel currently in use. In doing so, the signal strengths of various available channels can be compared. In some embodiments, these signal strengths can be used to make the determination  150  that the call association should be changed, for example by comparing the first and current signal strength to a second and alternate signal strength to see if the second signal strength exceeds the first signal strength by a threshold. A suitable threshold for some embodiments may be 3 dB. Other thresholds and/or comparison methods may be used in other embodiments.  
      Identifying information is stored  152 , in the portable wireless device, about the second base station before disassociating from the first base station so that after the determination  150  is made to change association from a first base station to a second base station, the phone will know how to contact the second base station. An example of suitable information to be stored  152  about the second base station is a MAC address of the second base station. Next, the phone disassociates  154  from the first base station. Despite the disassociation, the IP address assignment which was active when the call-in-progress was associated with the first base station is maintained  156 . The VoIP core network can be configured to maintain this address assignment for a desired delay time to allow the phone to associate  158  with the second base station. This is a major improvement beyond previous VoIP phone systems, since in previous systems the IP address would have to be re-assigned as a result of the 802.11 protocols running in separate WLAN&#39;s without coordination. The delay in these previous systems from the IP address re-assignment is noticeable to the end-user as a gap in the conversation. By associating  158  with the second base station while the IP address is maintained  156 , the time delay for the AP disassociation from the first base station combined with the time delay for the AP association and AP authentication to the second base station can be short enough to be imperceptible to the end-user. After associating  158  with the second base station, the phone continues communicating  160  with the second base station using the maintained IP address. In some embodiments, as part of maintaining the IP address assignment, the peer-to-peer connection which was active when the call in progress was associated with the first base station is also maintained. This peer-to-peer connection can be a SIP call in some embodiments. In other embodiments the method can also include a remembering action, where a last encryption key used with the first base station is remembered  162  so that encrypted communications may more quickly be reestablished when associating with the second base station.  
       FIG. 8  is a front view of one embodiment of a WLAN mobile phone  164  which could be used with the embodied wireless networks described herein, and their equivalents. The WLAN mobile phone  164  includes a key pad  166 , a display  168 , and a radome  170 . As mentioned previously, from the end-user&#39;s point of view, the WLAN mobile phone  164  operates in a manner that emulates a cellular phone. That is, a user with knowledge of how to use a cellular phone would operate the WLAN mobile phone  164  in essentially the same manner.  
       FIG. 9  is a block diagram of a portion of the embodied WLAN mobile phone  164  shown in  FIG. 8 . The antenna  172  is coupled through a low pass filter  174  to a transmit/receive (T/R) switch  176 . Received signals from the T/R switch  176  are amplified in a low noise amplifier (LNA)  178 , the output of which is coupled through a balun  180  to the RX terminal of a transceiver  182 , which may be a BCM4318E manufactured by the Broadcom Corp. of Irvine, Calif.  
      The RF output of the transceiver  182  at terminal TX is coupled through a driver amplifier  184 , the output of which is amplified by a power amplifier  186  to provide the transmit signal into the T/R switch  176 . IP packets are transferred between the transceiver  182  and a mobile VoIP processor  188 , which may be a BCM1161, also manufactured by Broadcom Corp.  
      In operation the received signal is amplified by the LNA  178  before it passes to the RX input of the transceiver  182 . This additional amplification can provide the WLAN mobile phone  164  with a reception sensitivity of at least −97 dB, and down to about −100 dB. In a preferred embodiment the transceiver  182  is programmed to provide a signal at the terminal TX that has a variable output power. As a result, the power amplifier  186  provides a transmission signal output power range of between  14  and at least 25 dB, and up to about 28 dB. In an alternative embodiment the output power is kept constant rather than varying.  
      In the preferred embodiment the variable output power is automatically set to the lowest power that will provide a Quality of Service (QoS) for the WLAN mobile phone  164  that is commensurate with that of cellular phones. The power level can be determined by at least one of the characteristics commonly used in the art to evaluate the quality of the received signal. The use of the variable gain transmitting power both optimizes the life of the phone&#39;s battery and minimizes the RF interference generated by the WLAN mobile phone  164  to other users of the applicable frequency band.  
       FIG. 10  is also a block diagram of a portion of the embodied WLAN mobile phone  164  shown in  FIG. 8 . The WLAN mobile phone  164  also includes the key pad  190  and a driver circuit  192  which drives the display  168 . Phone features, including, for example, speed dialing, providing a list of received and called phone numbers, short message service (SMS), MMS, email, instant messaging, web browsing, and call muting, are provided by the software in the mobile VoIP processor  188 . Many of these features are not found on currently available WLAN mobile phones.  
      The WLAN mobile phone  164  enables a user to select a list of preferred networks and the relative priority of each of the networks using the memory  194  to store the parameters for the networks. The WLAN phone user can choose any network that is available to the public. In contrast cellular phone subscribers have this feature available only when they roam on other networks if there is a pre-signed roaming agreement between the other network and their cellular service provider.  
      Moreover, the selection of a network, other than the default network, can be automatic. The user can pre-set a number of hot spot profiles to get connected automatically in places where the default network is not yet available. The pre-set profiles can be set according to the user&#39;s priority (first to search, second to search, etc.). The phone will search first for the default transceiver network. Then if this network does not exist, the phone will search for an available base station for each of the pre-set alternative networks in the order of their priority. In the case that none of the pre-set profiles is found, the phone goes to manual mode and will present the available SSIDs on the display  168 . The user is then given the option to manually choose one and to set up a WLAN connectivity. After the WLAN connectivity is completed (either to the default network or to any other SSIDs) the phone registers with the core of the default network. This core provides the switch services and the connection to other networks: PSTN, cellular, International, and value added services such as voice mail service, SMS service, MMS, email, instant messaging, and web browsing, etc.  
       FIG. 11  illustrates one embodiment of a timing diagram  196  of a WLAN mobile phone  164  handoff process when the WLAN mobile phone  164  roams from one sector connection (or base station connection) to another sector connection (or another base station connection) within a network. At the top of  FIG. 11  is a perspective view of a horizontal slice near a base station. A region  198  shows the area where the predominant signal strength is to and from a sector  1  and region  200  shows the area where the predominant signal strength is to and from a sector  2 . The area  202  is the crossover region between the areas  198  and  200 . In the example of  FIG. 11 a  WLAN mobile phone  164  initiates a telephone call with an AP association shown in block  204 . After the AP association, an AP authentication occurs as shown in block  206 . This initial authentication takes about 350 to 400 ms. Once the authentication is complete, normal voice transmission using sector  1  occurs as shown in block  208 . Also, after the authentication, an IP address is assigned as shown in block  210  and a SIP call initiation occurs as shown in block  212 . As shown in the bottom row of  FIG. 11 , as the WLAN mobile phone  164  travels, the signal strengths for sector  1  and sector  2  change. In a preferred embodiment the WLAN mobile phone  164  measures the signal strength from the surrounding sectors or base stations every two seconds, although other sampling intervals, regular or irregular, could be used in other embodiments.  
      When the WLAN mobile phone  164  senses that another sector has a signal which is greater than the current sector exceeded by a given threshold, for example 3 dB greater, as occurs at point  214 , the WLAN mobile phone  164  stores the MAC address of sector  2 , dissociates from sector  1  in this example as shown in block  216 , associates with sector  2  as shown in block  218 , authenticates with sector  2  as shown in block  220 , and resumes normal communication as shown in block  222  using sector  2  instead of sector  1 . Advantageously, the system of the related application named above keeps the IP address and SIP connection alive for one or two seconds after the WLAN mobile phone  164  disassociates so that the WLAN mobile phone  164  can re-associate and re-authenticate in about  50  ms which does not cause a disturbance noticeable to the user of the WLAN mobile phone  164 . In other embodiments, the IP address and the SIP connection may be kept alive for different time periods. In this embodiment, the system also remembers the key used in the last connection for a few seconds so that the authentication and WEP/WPA-PSK/WPA/WPA2 encryption can be quickly reestablished.  
      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.