Abstract:
A networked position multiple tracking system comprises a plurality of individual units which are networked multi-tracking devices networked and their location information is shared via a data link. The individual units are organized as groups and groups are further networked to facilitate the data transfer in a large area or different geographical areas. The typical applications of the present invention include tracking of family members; tracking of cab vehicles of a taxi company; tracking of law enforcement officials pursuing criminals or suspects. In a military environment, the soldiers in a regiment can track each other during military missions by using the present invention. The pilots of aircraft in a formation can use the multi-tracking system to maintain formation flight and evade potential collision.

Description:
CROSS REFERENCE OF RELATED APPLICATION  
       [0001]    This is a regular application of a provisional application having an application No. 60/231,504 and a filing date of Sep. 9, 2000. 
     
    
     
       BACKGROUND OF THE PRESENT INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates to remote tracking processing, and more particularly to a networked position multiple tracking process, wherein all multi-tracking devices are networked and their location information is shared via a data link. Moreover, individual units are organized as groups and groups are further networked to facilitate the data transfer in a large area or different geographical areas.  
           [0004]    2. Description of Related Arts  
           [0005]    There is a demand for determining another person&#39;s or vehicle&#39;s location. There is a further demand for determining other persons&#39; or vehicles&#39; locations relative to a host. The current technology utilizes a monitoring center equipped with computers and communication links. The persons tracked send their location data via a communication resource to a monitoring center. The monitoring center is capable to display their current location on a display unit in real time.  
           [0006]    The present invention provides an innovative way to implement the networked tracking of entities without a monitoring center, where an entity can be a person or a vehicle. In the present networked position multiple tracking system, all individuals each of which is given a unique identification (ID) are equal and combined in a group. Each individual can freely leave this group. The group can also receive newcomers as members after the automatic registration process.  
         SUMMARY OF THE PRESENT INVENTION  
         [0007]    A main objective of the present invention is to provide a networked position multiple tracking process, which is a method to organize individual members or units in a hierarchical architecture. All individual units are organized in a plurality of unit groups, and the unit groups are further organized into larger groups, and so on. Accordingly, the networked position multiple tracking process of the present invention substantially saves communication resource for a communication network and provides efficient data exchanges among big amount of individuals.  
           [0008]    Another objective of the present invention is to provide a networked position multiple tracking process, which is a method to acquire the current location of objects in a networked group. The objects are defined as persons or vehicles. These objects&#39; locations are displayed on a host-display, where the host is located at a center of the display so that the host knows the profile of the relative locations of its group members. The present invention allows any person or vehicle with a display unit to display their positions and the positions of any other persons or vehicles in a networked group.  
           [0009]    It is a further objective of the present invention to provide a networked position multiple tracking process to acquire the current locations of individuals in a networked group. These individuals&#39; locations are displayed with a map as background on the acquirer&#39;s display unit. The present invention allows any person or vehicle with a display unit to display their positions and the relative positions of any other persons or vehicles in a networked group.  
           [0010]    It is a further objective of the present invention to provide a networked position multiple tracking process, in which a communication mechanism is designed to facilitate the data transmission among individuals. The data exchange package is also defined.  
           [0011]    It is a further objective of the present invention to provide a networked position multiple tracking process, in which an intra-group communication mechanism is designed to facilitate the data transmission among individual groups. The intra-group data exchange package is also defined.  
           [0012]    It is a further objective of the present invention to provide a networked position multiple tracking process, in which a self-contained miniature IMU (inertial measurement unit) is used along with a GPS (global positioning system) receiver to deliver uninterrupted positioning data for each individual.  
           [0013]    In order to accomplish the above objectives, the present invention provides a system and process for networked position multiple tracking among independent individuals without a monitoring center, where an individual is a person, a vehicle, or any other property. With such networked multiple tracking system, the individuals are networked in a group, and each individual can search and track other individuals of interest.  
           [0014]    The present networked position multiple tracking system is also capable of intra-group tracking, where each group has a group controller who is responsible for data exchange among individual groups.  
           [0015]    The individuals&#39; locations are overlaid on a digital map on the host&#39;s display unit. The host is at the center of the display, thus the relative locations of other individuals are displayed on the host&#39;s display unit. The networked individual can send messages to each other as well.  
           [0016]    The typical applications of the present invention include tracking of family members; tracking of cab vehicles of a taxi company and tracking of law enforcement officials pursuing criminals or suspects. In a military environment, the soldiers in a regiment can track each other during military missions by utilizing the present invention. The pilots of aircraft in a formation can use the networked position multiple tracking system to maintain formation flight and evade potential collision. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]    [0017]FIG. 1 is a block diagram illustrating a portable multiple tracking unit which comprises a position producer, an intelligent display, a system processor, and a wireless communication device.  
         [0018]    [0018]FIG. 2 illustrates the communication architecture for networked position multiple tracking process, where all the individual portable multiple tracking units are equal.  
         [0019]    [0019]FIG. 3 illustrates the communication architecture for the inter-group data exchanges, where each group has a group controller.  
         [0020]    [0020]FIG. 4 illustrates the communication architecture with data link relay for the inter-group data exchanging, where each group has a group controller.  
         [0021]    [0021]FIG. 5 illustrates a hierarchical structure of the individual units and individual groups, where individual units are organized as small groups and small groups are organized as bigger groups, and so on.  
         [0022]    [0022]FIG. 6 is a block diagram illustrating a communication mechanism in a group.  
         [0023]    [0023]FIG. 7 is a block diagram illustrating the processing of a networked position multiple tracking unit.  
         [0024]    [0024]FIG. 8 is a block diagram illustrating the operation flow of the portable multi-tracking system.  
         [0025]    [0025]FIG. 9 is a block diagram illustrating the communication mechanism among groups.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0026]    Referring to FIGS.  1  to  9 , a system of networked position multiple tracking is illustrated, wherein the networked position multiple tracking system is processed via a data link, where the data link is responsible for location and command data exchanges between individuals among a networked group. According to the networked position multiple tracking system of the present invention, the individuals are networked in a group that each individual can search and track other individuals.  
         [0027]    The networked position multiple tracking system comprises a plurality of individual units each of which is carried by an individual carrier, which can be a person, a vehicle, or any other property. The individual units are organized as intra-groups and a predetermined number of unit groups are further networked into link-groups to facilitate the data transfer in a large area or different geographical areas.  
         [0028]    The networked position multiple tracking system further comprises a communication mechanism in each unit-group of individual units which is designed to facilitate the data transmission among the individual units, wherein a data exchange package is also defined.  
         [0029]    The networked position multiple tracking system further comprises an intra-group communication mechanism in each intra-group of unit-groups, which is designed to facilitate the data transmission among the unit-groups, wherein an intra-group data exchange package is also defined.  
         [0030]    The networked position multiple tracking system further comprises a self-contained miniature IMU (inertial measurement unit) which is used along with a GPS (global positioning system) receiver to deliver uninterrupted positioning data for each individual unit.  
         [0031]    Equipped with a powerful small size IMU (Inertial Measurement Unit) device, such as the micro IMU invented by the American GNC Corporation, the network position multiple tracking system of the present invention is self-contained and capable of tracking personnel inside a building, where the IMU device provides continuous carrier&#39;s position information. In the open area a GPS (Global Positioning System) unit is activated to provide precision absolute location data which can be blended with the self-contained IMU data to improve the accuracy and robustness of the positioning services. Thus, the present invention provides excellent position tracking outside a building.  
         [0032]    The IMU/GPS integrated device, in general, is costly and big in size. Weight, and large size lead to an infeasible deployment in a car or for being carried by a single individual. With the emergence of the MEMS (MicroElectronicMechanical System) technology, a miniature IMU based on MEMS technology becomes an embraceable reality.  
         [0033]    American GNC Corporation, Simi Valley, Calif., invented MEMS angular rate sensors and MEMS IMUs (Inertial Measurement Units), referring to U.S. patents pending, “MicroElectroMechanical System for Measuring Angular Rate”, serial No. 60/154,700; “Processing Method for Motion Measurement”, Ser. No. 09/399,980; “Angular Rate Producer with MicroElectroMechanical System Technology”, Ser. No. 09/442,596; “Micro Inertial Measurement Unit”, Ser. No. 09/477,151. American GNC Corporation invented the coremicro™ IMU, which is currently “The world&#39;s smallest” IMU, based on the combination of solid state MicroElectroMechanical Systems (MEMS) inertial sensors and Application Specific Integrated Circuits (ASIC) implementation. The coremicro™ IMU is a fully self-contained motion-sensing unit. It provides angle increments, velocity increments, a time base (sync) in three axes and is capable of withstanding high vibration and acceleration. The coremicro™ IMU is opening versatile commercial applications, in which conventional IMUs can not be applied, including land navigation, automobile navigation, personal hand held navigators, robotics, marine vehicles and unmanned air vehicles, various communication, instrumentation, guidance, navigation, and control applications.  
         [0034]    The coremicro™ IMU manufactured by the American GNC Corporation can be embodied into the networked position multiple tracking system for delivering robust location data.  
         [0035]    The networked position multiple tracking system processes the following steps according to the present invention:  
         [0036]    (a) Provide a unit data link among a plurality of individual units to form a unit-group. The unit data link creation follows the defined intra-group communication mechanism.  
         [0037]    (b) Provide an intra data link among a plurality of unit-groups to form an intra-group. The intra data link creation among unit-groups follows the defined inter-group communication mechanism.  
         [0038]    (c) Receive position data from a positioning unit incorporated with each of the individual units, wherein the positioning unit can be a GPS receiver, an IMU positioning device, or an integrated GPS/IMU device. The position data is a three dimensional vector of (x, y, z) coordinates in the Earth-Centered-Earth-Fixed (ECEF) coordinate system, or of (latitude, longitude, altitude) coordinates in the Geodetic coordinate system.  
         [0039]    (d) Receive data from a wireless communication module employed in each of the individual units, where the wireless communication module creates and maintains a communication resource with other individual units. The data received from the wireless communication module includes client location data, identifications (IDs), inquiring commands, and other messages of the other individual units.  
         [0040]    (e) Process the received data, retrieve map data from a map database stored in a storage device of each of the individual units, display a host location data on the map, decode the data from other individual units, and display the client location data on the map.  
         [0041]    (f) Send the host and client location data and identifications via the wireless communication module to a network to the other individual units for the other individuals of the individual units to access these data.  
         [0042]    As shown in FIG. 1, each of the individual units is a networked position multiple tracking device which comprises a position producer  10 , an intelligent display  20 , a system processor  30 , a wireless communication device  40 , and an antenna  50 . The position producer  10  is responsible for the delivery of location data. It can be an IMU (inertial measurement unit), a GPS (global positioning system) receiver, or an IMU/GPS integrated device.  
         [0043]    The intelligent display  20  is used to show the host location and other relative client locations of to the individual units. The system processor  30  is responsible for sending and receiving data, retrieving map data, responding to commands, and numerical calculations. The wireless communication device  40  is used to receive and send location data and other messages.  
         [0044]    As shown in FIG. 2, the communication architecture of the networked multiple tracking process is designed to meet the following requirements:  
         [0045]    (1) Assignment of communication resource  60 , i.e. the unit data link, can be made to individual units (A, B,  1 C, D, E, F, and G) that occasionally approach the host.  
         [0046]    (2) Free data exchange is allowed among the individual units within a unit-group or a specific area.  
         [0047]    (3) Release of the assigned communication resource  60  can be made when an individual unit leaves the specific area.  
         [0048]    Logically, the communication resource works with the following steps:  
         [0049]    (1) ID Presetting: each individual unit in a unit-group should be assigned a unique ID.  
         [0050]    (2) Partner Querying: when a partner individual unit is assigned in a unit-group, it keeps signaling for other partner individual units.  
         [0051]    (3) ID Recognition User Registration: when a partner individual unit&#39;s ID is received, the ID will be logged to its registration table.  
         [0052]    (4) Group Negotiation for Communication Resource Assignment: each partner individual unit inside the unit-group negotiates for the communication resource assignment for the new approaching individual unit.  
         [0053]    (5) Data Exchange I: each partner individual unit in the unit-group transmits its position and other dynamic state together with its unique ID.  
         [0054]    (6) Data Exchange II: each partner individual unit in the unit-group receives the information from other partner individual units to derive their dynamic states and to determine all partner individual units existing in the unit-group.  
         [0055]    (7) Resources Recycling: when no partner individual unit in the unit-group receives any information from a specific partner individual unit, the specific partner individual unit will be deleted from the unit-group, and the communication resource  60  assigned to this specific partner individual unit will become available for other potential partner individual units.  
         [0056]    The Data Exchange Package is defined to include:  
         [0057]    (i) Unit ID Number of each Individual unit  
         [0058]    (ii) All Registered Unit IDs in a Registration Table  
         [0059]    (iii) State information, Position, Attitude, Time Stamp, etc.  
         [0060]    As shown in FIG. 3, the intra-group communication mechanism is defined to include:  
         [0061]    (i) Unit-Group Registration  
         [0062]    (ii) Gather the Information from All Available Unit-Groups  
         [0063]    (iii) Request for Specific Unit&#39;s State from a Specific Unit-Group.  
         [0064]    (iv) Offers the state of Unit to other unit-groups in respond to the request  
         [0065]    As shown in FIG. 3, another communication resource, i.e. the intra data link  70 , is responsible for delivering position data and other messages among unit-groups ( 1 A and  1 B). Each unit-group has a Group Controller ( 1 A-C or  1 B-C). This Group Controller is responsible for:  
         [0066]    Keep Transmitting the Group Registration Code, which includes Group ID  
         [0067]    Upon it been registered, it will transmit Group Information Package. The Package includes: Group ID, Group member&#39;s ID, Group communication status Info.  
         [0068]    The intra-Group Data Exchange Package is defined to include:  
         [0069]    (i) Intra-Group ID  
         [0070]    (ii) Intra-Group Controller&#39;s ID  
         [0071]    (iii) Intra-Group controller&#39;s state information (Position, Attitude, Time Stamp)  
         [0072]    (iv) Intra-Group members&#39; ID  
         [0073]    (v) Intra-Group members&#39; state information  
         [0074]    [0074]FIG. 4 illustrates a network architecture including a communication satellite  80 , which is an alternative intra data link. In this architecture the communication satellite relays data transmission among individual unit-groups or intra-groups to cover a large area.  
         [0075]    [0075]FIG. 5 illustrates a three level hierarchical structure of the organization of individual units, unit-groups and intra-groups. All individual units are organized into first level unit-groups. Each individual unit is denoted as A, B, or C, and so on. Each first level unit-group is denoted as  1 A,  1 B, or  1 C, and so on. Each small unit-group has a first level unit group controller denoted as  1 A-C for first level group  1 A,  1 B-C for first level group  1 B, and so on. All first level unit-groups are organized as a second level intra-group denoted as  2 A,  2 B, or  2 C, and so on. Each second level intra-group has a second level intra group controller denoted as  2 A-C for second level intra-group  2 A,  2 A-C for second level intra-group  2 B, and so on. All second level intra-groups are organized as a third level intra-group denoted as  3 A,  3 B, or  3 C, and so on. Each third level intra-group has a third level intra group controller denoted as  3 A-C for third level intra-group  3 A,  3 B-C for third level intra-group  3 B, and so on.  
         [0076]    As shown in FIG. 5, the first level unit group controller can be one of individual units gathered in this first level unit-group. Second level intra group controller,  2 A-C,  2 B-C, or  2 C-C in FIG. 5 can be one of the first level unit group controllers gathered in this second level intra group. It is also acceptable to have a specific or independent individual unit acting as the second level intra group controller. Third level intra group controller,  3 A-C in FIG. 5 can be one of the second level intra group controllers gathered in this third level intra-group. It is also acceptable to have a specific or independent individual unit acting as the third level intra group controller.  
         [0077]    Each individual unit in each of the first level unit-groups is assigned with a unique individual identification (IID) to distinguish from other individual units in the same first level unit-group. Each first level unit-group in a second level intra-group is assigned with a unique first level group identification (GID) to distinguish from other first level unit-groups in the same second level intra-group. Each second level intra-group in a third level intra-group is assigned a unique second level group identification (GID) to distinguish from other second level intra-groups in the same third level intra-group. This same way of identification assignment continues for even larger groups. By this way the hierarchical architecture can trace down to every individual unit with a unique combination of GID and IID. For example, the third level intra-group  3 A can be identified in FIG. 5. Then second level intra-group  2 B can be recognized and first level unit-group  1 A would be distinguished in the second level intra-group  2 B. Finally individual units in the first level unit-group  1 A can be identified. The process flow follows:  3 A→ 2 B→ 1 A→X, where the number before the letter denotes the level of group, the letter distinguishes each member in this group, and X is an individual units in the first level unit-group.  
         [0078]    The position producer  10  outputs the host location data, i.e. the location data of the unit group controller or intra group controller, to the system processor  30 . The system processor combines the host location data with the host&#39;s ID, i.e. the IID or GID, and sends them to the wireless communication device  40 . The wireless communication device  40  is a combination of hardware and software and is responsible to send these data onto the network so that other individual units can access these data. The data stream sent from the unit group controller or intra group controller has an order as follows (in words):  
         [0079]    (1) Time Tag in milliseconds: 1 word.  
         [0080]    (2) ID: 1 word, when necessary it can be extended into 2 words to encompass more mobile users.  
         [0081]    (3) Three dimensional location in the Geodetic coordinate system, including Latitude in radians, Longitude in radians, height above sea level in meters. Each location component occupies 1 word.  
         [0082]    (4) Three dimensional location in an earth-centered inertial coordinate system (ECIZ). Each location component occupies 1 word.  
         [0083]    (5) Three dimensional velocity in an earth-centered inertial coordinate system (ECIZ). Each velocity component occupies 1 word.  
         [0084]    The above motion parameters are sufficient for characterizing a ground vehicle to realize multi-tracking. When used for aircraft tracking, the message will be enhanced by adding the following information:  
         [0085]    (6) Three dimensional acceleration in an earth-centered inertial coordinate system (ECIZ). Each acceleration component occupies 1 word.  
         [0086]    (7) Rotation matrix from the earth-centered inertial coordinate system to the body coordinate system (BC).  
         [0087]    (8) Three dimensional angular velocity in radians/second when the observer is in an earth-centered inertial coordinate system and the resolution is in the body coordinate system.  
         [0088]    (9) Three dimensional angular acceleration in radians/second 2  when the observer is in the earth-centered inertial coordinate system and the resolution is in the body coordinate system.  
         [0089]    In order to simplify the following description regarding both the communication resources, i.e. the unit data link  60  and intra data link  70 , the following term “group” represents both the “unit-group” and “intra-group” and the following term “member” represents the “individual unit” of a unit-group, the “unit group controller” of a unit-group within an intra-group, and the “intra group controller” of an intra-group within a higher level intra-group.  
         [0090]    [0090]FIG. 6 illustrates the processing of creating and maintaining a communication network among individual units, which comprises a plurality of modules of identification number assignment  31 , communication resource assignment  32 , and communication resource recycling  33 .  
         [0091]    The identification number assignment module  31  assigns the unique identification number (IID or GID) to each member involved in the networked position multiple tracking processing. Each member can be recognized by the assigned IID or GID.  
         [0092]    The communication resource assignment module  32  assigns communication resource to each member in a group, where communication resource is an opportunity for a networked position multiple tracking device to send data onto the network. For a time-division-multi-address (TDMA) configuration, the communication resource is a piece of time slot assigned to a specific individual during which this individual can send data out. For a frequency-division-multi-address (FDMA) configuration, the communication resource is a radio frequency which the member uses to transmit data. For a code-division-multi-address (CDMA) configuration, the communication resource is a random pseudo number sequence used to identify member in a networked group.  
         [0093]    The communication resource recycling module  33  releases communication resource assigned to a specific individual unit when this member leaves the networked group. This step is very important in that the communication resource can be reused by other potential member after one member leaves the group.  
         [0094]    The communication resource management is a very important issue in the present invention. The above three steps represent a very competitive group communication mechanism with communication resource assignment and releasing operations. In a TDMA communication network, each member is assigned a piece of time for data transmission. For instance, the required position update rate for each member is once per second (1 Hertz) and required time period for a member to transmit position data is 100 milliseconds. The number of maximum allowed members in a group with this TDMA configuration is 10. When there are less than 10 members in this group, the position transmission rate would be higher. If there are more than 10 members in this group, the position transmission rate would be lower than 1 Hz.  
         [0095]    To illustrate the advantage of the efficient communication resource management of the present invention, a more detailed example is provided. In a TDMA configuration communication network, there are 5 members. The required position update rate for each member is still once per second (1 Hertz). The time period for a member to transmit position data is 100 milliseconds. The total time period for all the five members to transmit their position data is 0.5 seconds and meets the position update rate requirement. The communication network capacity can allow another five members to join in. The communication network can not handle more 10 members and meets the 1 Hz position update rate. If we do not have communication resource releasing operation, the communication network can only allow another five members to join in even when one or more members leave this group. With the communication resource releasing operation of the present invention, the communication network can allow another 5+N members to join in when N (N&lt;=5) members leave this group.  
         [0096]    As shown in FIG. 7, the data processing in the networked position multiple tracking system is carried by functional modules of data transmission  301 , data reception  302 , partner querying  303 , new partner checking  304 , absent partner checking  305 , partner ID reception  306 , partner ID logging  307 , negotiation for communication resource assignment  308 , and communication resource recycling  309 . The data processing comprises the steps of:  
         [0097]    (a) Transmit position data and other messages along with ID onto the network. This step is to inform other members the existence of the host, i.e. the unit group controller or the intra group controller, in the networked group and its position information.  
         [0098]    (b) Receive data from network. This step is to capture other members&#39; information including position data and IDs. Steps (1) and (2) finish the data exchange among members.  
         [0099]    (c) Query partners. This step is to search for new partner members and to check absent partner members. The new partner members are defined as new individual units, unit group controllers or intra group controllers coming into this network. On the host there is a partner ID registration Table on which all members among a group are listed. Searching for new partner members can be finished by comparing received IDs (IID or GID) with IDs (IID or GID) on the partner ID registration Table. The absent partner members are defined as individual units, unit group controllers or intra group controllers who left the network. Checking absent partner members can be performed by checking the time period for which an ID (IID or GID) corresponding to a specific member has not been received.  
         [0100]    When new partner members are found, the following additional steps are included:  
         [0101]    (i) Receiving new partner IDs.  
         [0102]    (ii) Logging the new partner IDs onto the partner ID registration Table.  
         [0103]    (iii) Negotiating for communication resource assignment.  
         [0104]    When absent partner member or members are found, the following additional step is included:  
         [0105]    (iv) Releasing communication resources assigned to the absent partner member or members.  
         [0106]    [0106]FIG. 8 shows the networked multi-tracking mechanism in accordance with the present invention. It comprises a start module  311 , an initialization module  312 , a data reception module  313 , a data processing module  314 , a data transmission module  315 , a program termination module  316 , and an end module  317 .  
         [0107]    [0107]FIG. 9 illustrates the processing of creating and maintaining a communication network among unit-groups and intra-groups, which comprises of functional modules of group registration  34 , group information gathering  35 , requesting for specific unit information  36 , and offering unit information  37 . The processing comprises the following steps:  
         [0108]    (1) Perform group registration. Each unit-group or intra-group involved in the network is assigned a group registration code and a unique group ID (GID). As mentioned above, each unit-group has a unit group controller and each intra-group has a intra group controller.  
         [0109]    (2) Gather information from all involved unit-groups or intra-group by unit group controllers in each unit-group or intra group controllers in each intra-group.  
         [0110]    (3) Request information for a specific individual unit from a specific unit-group by a unit group controller, a specific unit group controller by an intra group controller, or a specific intra group controller by another intra group controller in a higher level intra-group.  
         [0111]    (4) Keep transmitting group information package, including group ID, group registration code, each member&#39;s ID in a group, group controller&#39;s information, and group communication status.  
         [0112]    (5) Send the position data and other messages associated with a specific individual unit to other unit-group from a unit group controller upon requested from other unit-groups or a specific unit group controller to other unit group controller from an intra group controller upon requested from other intra-groups.  
         [0113]    The unit-group and intra-group communication mechanisms can be built on several wireless communication specifications that offer wireless connectivity in various ways. Data rate transfers and range are among the most salient characteristics among wireless products. Several of the wireless solutions are briefly outlined below.  
         [0114]    Infrared Data Association (IrDA): This communication system is created through a web of infrared light. It can only be used in open spaces since it is unable to penetrate walls or any other solid surface.  
         [0115]    Digital Enhanced Cordless Telecommunications (DECT): Characterized by a “handover” process that uses two radio links during each connection and selects the best of the two for the communication process. If the portable device moves out of range of the base station, the handover process allows for the range to be increased by allowing the portable device to use another nearby range station.  
         [0116]    IEEE 802.11: Uses three physical (PHY) layer specifications and one Medium Access Control (MAC) specification. The MAC works in two configurations one is the “Independent Configuration” and the second is the “Infrastructure Configuration”. The Independent Configuration is an ad-hoc network where stations communicate with one another without infrastructure support. In the Infrastructure Configuration stations communicate through access points and their communication scheme creates a wide area coverage. The MAC provides encryption and service scanning. The three PHY include “Frequency Hop Spread Spectrum”, “Direct Sequence Spread Spectrum” and “Baseband IR”. One of its biggest defaults is its very slow frequency hopping rates.  
         [0117]    IEEE 802.11b: The PHY layer is extended in this version to provide 5.5 and 11 Mb/s, in addition to the 1 and 2 Mb/s data rates.  
         [0118]    HOMERF: Strong in the home wireless networking market and based on the specifications created by the HRFWG. HOMERF deals in the market of communications between mobile devices and PC&#39;s.  
         [0119]    Shared Wireless Access Protocol (SWAP): Able to carry both voice and data traffic. Voice “re-transmission” takes place first. Data packets are transmitted on several links in the IIDdle of the transmission and finally a voice transmission is received at the end. SWAP is designed to be low cost by using more relaxed radio specifications while maintaining the same frequency-hopping scheme of Bluetooth technology. SWAP is operable as either an add-hoc network or as a managed network.  
         [0120]    High Performance Radio Local Area Network (HIPERLAN): HIPERLAN has two specifications, H1 and H2. It is said to work well in building propagation, and high-rate medium range multimedia. Both specifications are expensive to implement.  
         [0121]    Bluetooth: Bluetooth wireless technology has several key factors that make it a feasible alternative for the Advanced Personal Communicator Prototype. Some of the more pronounced traits that favor this technology are outlined below:  
         [0122]    (a) Due to the fact that Bluetooth technology operates within the world wide unlicensed 2.4 GHz spectrum, the Advanced Personal Communicator can be operated anywhere.  
         [0123]    (b) Bluetooth communications can be encrypted.  
         [0124]    (c) One of Bluetooth&#39;s main objectives is to produce a very low cost wireless communication alternative.  
         [0125]    (d) Bluetooth has a Special Interest Group (SIG) that developers can join. Members are granted a free license to use the technology.  
         [0126]    (e) Bluetooth technology is very low power since it was designed to run from batteries.  
         [0127]    (f) Although Bluetooth technology purpose is to operate at a modest range of 10 meters, a power amplifier with a range of about 100 meters can be incorporated.  
         [0128]    Applications providing Bluetooth services must do so through the Bluetooth Protocol Stack. The Bluetooth protocol stack is made up of the following layers: Radio, Baseband, Link Controller, Link Manager, Host Controller Interface (HCI), L2CAP, RFCOMM/SDP and Application layer.  
         [0129]    The Radio interface is made up of an on air channel medium and a digital baseband, which handles data sent by the LC and ensures a robust transmission over the channel. The Radio Interface also retrieves data from the channel for processing in higher protocol layers. Radio and baseband represent the Open Systems Interconnect (OSI) Physical layer.  
         [0130]    The Baseband layer is where the channel coding and decoding process takes place as well as the timing control.  
         [0131]    Link Controller (LC) performs some of the equivalent Data Link layers tasks of transmission and error suppression. The LC executes linking operations over multiple data bursts when instructed to do so by Link Manager (LM) commands.  
         [0132]    The LM and the higher end LC are responsible for the execution of the tasks that the network layer performs. The link manager is responsible for the setup and maintenance of multiple links.  
         [0133]    The Transport layer tasks are performed by the Host Controller Interface (HCI) which is responsible for faithful data transfer.  
         [0134]    Logical Link Control and Adaptation Protocol (L2CAP) and the lower end of RFCOMM/SDP are responsible for the management of data flow.  
         [0135]    RFCOMM is the equivalent of the RS-232 layer within the Bluetooth Protocol. It is predominantly responsible for data transfers.  
         [0136]    Service Discovery Protocol (SDP) allows users to browse for services or devices such as printers. The Applications layer acts as the communication manager between two application sessions.