Method of handoff control in an enterprise code division multiple access wireless system

A wireless office communication system including a wireless internet base station (WIBS) encompassing a base station controller (BSC), a mobile switch controller (MSC), and an ethernet interface module for coupling the wireless internet base station (WIBS) to an existing internet protocol (IP) based network. A wireless office communication system can also be based on the conventional architecture comprising the base station transceiver subsystem BTS, BSC, and MSC. The WIBS or BTS is attached to a number of antennas via different and identifiable delay elements for the purpose of determining the serving antennas of mobile communication units. A location determination logic enables the system to handle handoffs between a WIBS or BTS and the external public communication system in an optimum manner. Handling handoff requests in this manner prevents unnecessary ping-ponging of hand off and can also increase the percentage of successful handoff by frequency monitoring of the quality of the mobile communication units located in the handoff transition area, particularly to the public communication system.

CROSS-REFERENCE TO RELATED APPLICATION

This is related to Joo et al., co-filed U.S. patent application Ser. No. 09/655,102, entitled “HANDOFF CONTROL IN A CODE DIVISION MULTIPLE ACCESS WIRELESS SYSTEM.” To the extent not repeated herein, the contents of Joo et al. are incorporated by reference.

FIELD OF THE INVENTION

The present claimed invention relates generally to the field of wireless communication systems. More particularly, the present claimed invention relates to a method of handoff control between code division multiple access communication systems within an indoor enterprise system and with the public system.

BACKGROUND ART

Communication systems that utilize coded communication signals are well known in the art. One such system is a code division multiple access (CDMA) cellular communication system such as set forth in the Telecommunications Industry Association/Electronic Industries Association International Standard (TIA/EIA IS-95), hereinafter referred to as IS-95. In accordance with the IS-95, the coded communication signals used in CDMA systems comprise CDMA signals that are transmitted in a common 1.25 MHz bandwidth to base stations of the system from mobile or wireless communication units, such as cell phones or portable wireless computers or wireless handheld devices, that are communicating in a specific coverage area of the base station. In conventional CDMA systems, a base station transceiver subsystem (BTS) communicates with a base station controller (BSC) which allows the communication unit to communicate with other communication units within the same coverage area. Each CDMA signal includes a pseudo-noise (PN) sequence associated with a particular base station and an identification number of a communicating communication unit.

Typically, the BSC is connected to a mobile switching controller (MSC) which allows a BTS to connect with other BTS outside its coverage area in order to allow a communicating communication unit communicate with other units outside its coverage area.

FIG. 1illustrates a conventional CDMA communication system100including a first base station110, a second base station120, and one or more communication units105,106. The communication system100illustrated inFIG. 1is an exemplary CDMA system which includes a direct sequence CDMA cellular communication system, such as that set forth in TIA/EIA IS-95.

In the system shown inFIG. 1, base stations110and120are connected to base station controller130and mobile switching controller140which is in turn are connected to public switched telephone network (PSTN)150using known techniques.

The system shown inFIG. 1further connects to the public land mobile network (PLMN) and PSTN to allow mobile communication units to travel from one network (roaming) to another network while maintaining a subscriber profile information. A detailed illustration of the PLMN is shown inFIG. 1B. In the system shown inFIG. 1B, a conventional cellular (or PCS) wireless communication network is shown. In the network shown inFIG. 1B, a network subscriber's profile information is typically stored and maintained in a home location register (HLR) and a visitor location register (VLR).

Still referring toFIG. 1, when a communication unit initiates a call sequence to either one of base stations110and120within a coverage area, an end-to-end connection is established between the respective base station and base station controller130and MSC140using known CDMA call setup techniques. Base stations110and120typically communicate with BSC130and MSC140via communication links, such as a T1connection. Base stations110and120typically have antennas to define the coverage area within which either base stations primary accommodate the communication units.

In the system shown inFIG. 1, when a communicating communication unit initiates a call sequence (uplink) to the nearest base station, the call is assigned to the target communication unit via BSC130and MSC140within a prescribed bandwidth (e.g. 1.25 MHz for IS-95).

Also, in the conventional CDMA system shown inFIG. 1, communication between a communicating communication unit and the base station requires a dedicated end-to-end connection between the base station, the BSC and the MSC. Such dedicated end-to-end connection can also be very expensive and time-consuming.

In the exemplary CDMA system shown inFIG. 1, each base station transmits a pilot signal having a common PN spreading code that is offset in code phase from the pilot signal of other base stations within the system. During system operation, the mobile communication unit is provided a list of code phase offsets corresponding to neighboring base stations surrounding the base station through which communication is established. The mobile unit is equipped with a searching function which allows the mobile unit to track the signal strength of the pilot signal from a group of base stations including the neighboring base stations.

Various methods exist for switching the mobile communication unit from one base station to another (typically known as “handoff”). One such method is termed a “soft” handoff, in which communication between the mobile unit and the end user is uninterrupted by the eventual handoff from an original base station to a subsequent base station. This method is considered a soft handoff in that communication with the subsequent base station is established before terminating communication with the original base station. When the mobile unit is communicating with two base stations, a single signal for the end user is created from the signals from each base station by a communication system controller.

Mobile unit assisted soft handoff operates based on the pilot signal strength of several sets of base stations as measured by the communication unit. An active set is the set of base stations through which active communication is established. A neighbor set is a set of base stations surrounding an active base station comprising base stations that have a high probability of having a pilot signal strength of sufficient level to establish communication.

When communications are initially established, the communication unit communicates through a first base station, and the unit monitors the pilot signal strength of the base station in the active set and the neighbor set. When a pilot signal of a base station in the neighbor set exceeds a predetermined threshold level, the base station is added to the candidate set and removed from the neighbor set at the communication unit.

The communication unit communicates a message identifying the new base station. The BSC decides whether to establish communication between a new base station and the communication unit. Should the BSC decide to do so, the BSC sends a message to the new base station with identifying information about the communication unit and a command to establish communications.

When the communication unit is communicating with multiple base stations, it continues to monitor the signal strength of base stations to determine which base station to connect to in the event of a signal strength degradation.

Each base station has a coverage area that has two handoff boundaries. A handoff boundary is defined as the physical location between two base stations where the link would perform the same regardless of whether the mobile unit were communicating with the first base station or the second base station. Each base station has a forward link handoff boundary and a reverse link handoff boundary.

The forward link handoff boundary is defined as the location where the mobile unit's receiver would perform the same regardless of which base station it was receiving. The reverse link handoff boundary is defined as the location of the mobile unit where two base station receivers would perform the same with respect to that mobile unit. Ideally these boundaries should be balanced, meaning that they have the same physical location, with respect to the base station. If they are not balanced, system capacity may be reduced as the power control process is disturbed or the handoff region unreasonably expands.

In any of these conventional systems, the soft handoff between base stations still require the active base station to maintain contact with the BSC as it hands off communication to a neighboring base station or a candidate base station. Upon handing over communication, the new base station (now active base station) resumes communication with the mobile unit via the BSC. The conventional system described inFIG. 1orFIG. 2does not allow each base station to communicate with the other during a handoff since all communication has to go through the BSC. This takes time and in a data traffic transmission can be costly.

With the introduction of enterprise in building wireless communication services, the problem of handoff is even more accentuated within the enterprise system.FIG. 3is a prior art illustration of an enterprise communication system. In the system ofFIG. 3, the enterprise system may comprise of multiple BTS subsystems which may be located at the lower floor of a multi-floor building or campus networks.

The enterprise system ofFIG. 3needs to co-exist with the wide-area public system in terms of frequency reuse, interference control and to provide seamless services via handoff. However, in the system ofFIG. 3, a common problem occurs when a mobile user enters a location that is near a border between two cell sites within the enterprise system. In this situation the signal level of the mobile unit tends to fluctuate at both cell sites. This signal level fluctuation results in a ping-pong situation in which repeated requests are made to handle calls back and forth between the two cell sites. Furthermore, the ping-pong situation raises the possibility that the call will be discontinued if it is unnecessarily transferred to a cell in which all channels are in use and thus unavailable for accepting the handoff.

In the system illustrated inFIG. 3, a user located in a higher floor in a multi-floor building may experience unnecessary ping-pong handoffs as a result of the mobile unit trying to communicate with the BTS internal to the enterprise system and the external cell sites which may be transmitting stronger signals than the internal BTS serving the mobile unit. This is because the signal strength of the wide-area public system is stronger, especially at locations “Loc A” and “Loc B” than the signal strength from the BTS located on the ground floor of the building.

Such unnecessary ping-pong of handoffs increases the mobile unit incorrectly hearing handoff commands or failure in hearing commands. Furthermore, the ping-pong situation raises the possibility that a call will be discontinued. This can be very costly and time-consuming for a mobile user communicating with any other mobile user within the enterprise system. Unnecessary ping-ponging handoffs also make it costly for the enterprise system accounting to reconcile calls within the enterprise system and those made to external cell sites.

Therefore, it is desirable to have a robust method for handing-off CDMA calls including voice and data over a communication pathway within an enterprise wireless communication system. It is further desirable to have a CDMA call handling method that handles the transmission of calls, especially data calls, without the inherent costly call ping-pong effect of the prior art. A need further exists for an improved and less costly system which improves the efficiency and the transmission rate and time of calls between a mobile unit and a base station and between base stations and a base station controller and between adjacent base stations within an enterprise wireless communication system.

SUMMARY OF INVENTION

The present invention is directed to a system and a method for providing an enterprise in-building or campus-wide IP based code division multiple access (CDMA) wireless system. The present invention is capable of handling both voice and data transmission within the CDMA system without the inherent delays and signal quality degradation encountered during call handoffs by conventional CDMA systems. The present invention further provides a system which controls handoffs between an enterprise CDMA communication system and macro systems external to the enterprise system by keeping users on the enterprise premise to the enterprise system. This therefore provides a less costly and a timely way of handling handoffs between the enterprise system and external macro systems without unnecessary ping-ponging between the two systems.

In the enterprise CDMA system of the present invention, a handoff technique is implemented which permits a mobile unit within the enterprise system to initiate a handoff. The mobile unit is permitted to determine the best new cell site to which communications are to be transferred to and from an old cell site. The invention further permits a cell base station to identify the location of the mobile unit requesting a handoff in order to determine the most efficient way to handle the handoff requests.

The invention further includes an integrated wireless internet base station (WIBS) which is connected to the Internet and an existing networking infrastructure within an office building or campus. The WIBS utilizes known ethernet transmission protocols to transmit data over an ethernet back bone to various wireless communication devices within a building. The WIBS further includes a call processing module which is capable of determining whether a call originating from or received by the base station to and from a communication unit is either a voice call or a data call. The WIBS also integrates the BCS functions of the prior art to reduce call setups between a communication unit and the WIBS, and call handoffs between multiple WIBS.

The invention further includes location based handoff control logic for handling communication diversity signal handoffs between various communication units and base stations within the enterprise system. The location based handoff control logic determines a particular base station, within the enterprise system, serving a particular user and hands off the user based on the signal delays inserted in the communication path between the user and the base station.

In one embodiment of the present invention, the hand off control logic hands off a mobile user to macro cell sites external to the enterprise system from a predetermined designated location within the enterprise system in order to avoid signal degradation and the cost of reconciling when mobile units within the enterprise system are communicating with the external cell sites.

The designated transition locations within the enterprise system are covered by extended antenna units which are directly or remotely connected to base stations located within the enterprise system. In a multi-floor enterprise system configuration, the extended antenna units may be distributed on various floors of a multi-floor building in order to provide the requisite coverage for the mobile units within the enterprise system.

The invention further includes communication signal delay elements which are inserted into the signal paths between the mobile units and the base stations in order to ensure that the enterprise base stations can only handoff communications with mobile units to the external macro cell site within the designated transition areas.

The invention further includes handoff implementation logic which allows handoffs within the enterprise system only to mobile units in the designated handoff transition areas.

The present invention further provides an implementation advantage over the prior art by allowing inter-network communication between the wireless office communication system of the present invention and other mobile networks on the PLMN. The inter-networking communication of the present invention is implemented over an ANSI-41D using the ethernet transport protocol of UDP/IP or TCP/IP transport protocol via an ethernet interface to the ethernet back bone of the system. The use of the ethernet interface is less costly than the prior art and further allows easy and flexible connectivity to existing in-office, building or campus networks.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to the preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. While the invention will be described in conjunction with the preferred embodiments, it will be understood that they are not intended to limit the invention to these embodiments.

The invention is directed to a system, an architecture, subsystem and method to manage mobile communication handoff requests in an enterprise wireless communication system in a way superior to the prior art.

In the following detailed description of the present invention, a system and method for a wireless internet protocol based communication system is described. Numerous specific details are not set forth in order to provide a thorough understanding of the present invention. However, it will be recognized by one skilled in the art that the present invention may be practiced without these specific details or with equivalents thereof.

Generally, an aspect of the invention encompasses providing an integrated wireless enterprise system which may be an in-building or campus wide CDMA communication system which provides a wide range of voice, data, video and other services in conjunction with a private branch exchange interfaced to the public switched telephone network (PSTN) and the Internet. A wireless office communication system including a wireless internet base station (WIBS) encompassing a base station controller (BSC), a mobile switch controller (MSC) and an ethernet interface module for coupling the WIBS to an existing internet protocol (IP) based network. A wireless office communication system can also be based on the conventional architecture comprising the BTS, BSC and MSC. The WIBS or BTS is attached to a number of antennas via different and identifiable delay elements for the purpose of determining the serving antennas of mobile communication units. A location determination logic enables the system to handle handoffs between a WIBS or BTS and the external public communication system in an optimum manner. Handling handoff requests in this manner prevents unnecessary ping-ponging of handoff and can also increase the percentage of successful handoff by frequency monitoring of the quality of the mobile communication units located in the handoff transition area, particularly to the public communication system. The invention is generally adpatable to conventional CDMA communication systems and generally applies to frequency to frequency hard handoffs. The invention can be more fully described with reference toFIGS. 4 through 7.

FIGS. 4–7illustrates systems and methods for determining user location within an enterprise wireless communication system in accordance to the preferred embodiments of the present invention. The location based handoff system and method illustrated inFIGS. 4–7are each preferably implemented as part of a cellular telephone system that uses the CDMA techniques for communicating within a cellular telephone system.

Referring now toFIG. 4, a functional illustration of the enterprise wireless communication system (EWCS)400of the present invention is shown. EWCS400comprises extended antenna units (EAUs)410–415, signal distribution concentration unit (DCU)420, wireless base stations (BTS)425–430, communication pathway401, IP based gateway440and base station controller450.

EAUs410–415are preferably adapted to receive incoming communication signals from mobile communication units within EWCS400. EAUs410–415can be passive or active with amplifying devices. EAUs410–415collect transmitted signals from mobile communication units within EWCS400and provides the signals to DCU420. In one embodiment of the present invention, EAUs410–415include signal delay elements to resolve call multi-signals and to increase call diversity within the EWCS400. The operation of the EAUs within the EWCS400depend on the deployment, transmission power and the in-door environment. For example, EAUs410–415may operationally cover an area of about 10–20 meters in an embodiment of EWCS400.

DCU420is coupled to EAUs410–415to receive and transmit signals from the EAUs to base stations425and430. In one embodiment of the present invention, DCU420includes signal delay element unit421to enable DCU420delay signal transmits to base stations425and430.

Still referring toFIG. 4, BTS425–430are coupled to receive and transmit call signals from and to DCU420. BTS425-430preferably is an IP based system which enables EWCS400to take advantage of existing networking infrastructure in an office building or a similar environment to communicate wireless calls from the mobile units to other wireless devices on the network, Internet, or to the PSTN. BTS425–430includes switching functions to process traffic from various sources such as voice and data for delivery over the ethernet back bone.

BTS425–430further provides interface between a CDMA PCS or a cellular mobile communication system and BTS425–430to enhance mobility within a wireless office environment covering hot spots or dead spots traditional public cellular or PCS networks such as on-campus, or the load could not address.

BTS425–430are coupled to the ethernet back bone401preferably through a 10/100 base-T interface and related software stack to handle data burst on the LAN that traditional CDMA system could not handle. BTS425–430receives and sends data to and from cellular regions within EWCS400to other subscribing mobile units in the EWCS400.

The BTS425–430has forward and reverse link boundary similar to the prior art. The forward link is defined as the location where the mobile communication unit's receiver would perform the same regardless of which BTS it was receiving. The reverse link handoff boundary is defined as the location of the mobile communication unit where two BTS receivers would perform the same with respect to that mobile unit.

In the EWCS400of the present invention, a user location identification logic (not shown) is integrated into the base stations to identify mobile communications within the enterprise system. The identification logic further includes a handoff call request logic which allows the base station to optimize the control of mobile unit handoffs only within designated handoff transition regions within the enterprise system. Controlling handoff requests within the designated handoff region prevents unnecessary ping-ponging of handoffs between the mobile communication units and the external public system (e.g. PSTN).

Referring now toFIG. 5, a functional block diagram illustrating one embodiment of the DCU420is shown. As shown inFIG. 5, DCU420preferably comprises transmit distribution subsystem (TDS)500, receive concentration subsystem (RCS)510and other signal control logic (not shown).

DCU420is coupled to EAUs410–415to receive and transmit signals from the EAUs to base stations425and430. In one embodiment of the present invention, DCU420includes signal delay element unit421to enable DCU420delay signal transmits to base stations425and430. DCU420receives divided transmit signals from base stations420–425delays the divided transmit signal, and transmits the signals to the EAUs. DCU420further includes control logic capable of generating control messages such as cell diversity mode requests and cell site communication termination commands. The control processing logic is responsive to the data received from the EAUs and base stations in making decisions relative to handoffs and diversity combining. DCU400further receives multiple delayed transmit signals from the EAUs combines the signals and transmits the combined signals to base stations425–430.

Still referring toFIG. 5, TDS500comprises a signal divider501coupled to a plurality of delay elements502–504. In the present invention, TDS500receives a CDMA signal from base stations located within EWCS400. The CDMA signal from the base stations are transmitted via multiple antennas distributed within the EWCS space for the purpose of each antenna covering part of an area to be covered by the base stations. The CDMA signal transmitted by the base stations are received by TDS500, divided in divider501and distributed to the antenna via delay elements502–504. Delay elements502–504have delay times large enough to be distinguishable by the base stations are inserted in the CDMA signal transmit paths to the antennas.

RCS510is coupled to receive CDMA signals transmitted by the various antennas within the EWCS400for transmission to the base stations. RCS510includes a combiner511and a plurality of delay elements512–514. Like the delay elements in TDS500, the delay elements in RCS510have time delays large enough to be distinguishable by the base stations. CDMA signals from mobile communication units within EWCS400are received via multiple antennas distributed within EWCS400and combined in combiner511. The combined signal is connected to the base station receiver. The location determination logic in the base station determines the antenna unit serving a given mobile communication unit, and thus its location, by detection of the delay time of the received signal via signal RX.

Although the embodiment of the DCU shown inFIG. 5shows delay elements inserted in the signal paths to the TDS and RCS, the delay elements do not necessarily have to be inserted in both the transmit and receive paths. For example, in one embodiment of the present invention, delay elements may be inserted in the transmit path and not in the receive. Alternatively, delay elements may be inserted into the receive path and not the transmit path.

The knowledge in the location of a mobile communication unit is used in optimizing the handoff performance between the EWCS400and the public systems, as well as within the enterprise system400. For example, if the mobile communication unit is located in areas or on floors in a building where the user is not likely to transit to the coverage are of the public system, then any hand off requests to the public system are denied. If the mobile communication unit is located in the desired handoff area with the public system, then the handoff parameters and thresholds can be adjusted to improve the probability of successful handoff to the public system.

FIG. 6is a block diagram illustration of embodiments of how the location based handoff system of the present invention may be configured. InFIG. 6, configuration600illustrates a star chain configuration of the antenna system within EWCS400. In the star chain configuration, each antenna is separately coupled to the base station via separate signal paths with varying time delay elements inserted in each path. The star configuration ofFIG. 6offers a more reliable implementation of the enterprise system of the present invention since a break in the path of one antenna connection will not affect the other antennas in the system.

Another configuration of the system of the present invention is illustrated in configuration620. In configuration620, the antennas in the enterprise system are daisy chained to the base station by coupling the antennas to a single communication path to the base station. Fixed time delay elements are inserted at various locations on the communication path to accomplish the objectives of the present invention. Although the daisy chain configuration may be a less costly than the star configuration, it is not as reliable because a break in any point in the communication path affects communications between the other antennas and the base station.

Referring toFIG. 7Ais a flow diagram of the processing of calls initiated by a mobile unit to EWCS400is illustrated. As shown inFIG. 7A, a mobile call processing is initiated at step700when the EWCS receives a service request from the mobile units. At step710, a base station receives a service request from the mobile unit, determines whether the transmitting mobile unit's profile information is stored in the EWCS, and determines the location of the mobile unit at step715. At decision step720, the base determines whether an antenna request being serviced from the EAUs is in the enterprise-macro system transition area. If the mobile unit is in the enterprise-macro system transition area, processing continues at step730; otherwise the handoff parameters of the mobile unit are not changed and processing of the signal request from the mobile unit is discontinued at step725. If, on the other hand, the mobile unit is within the enterprise-macro system transition region, the handoff parameters of the mobile unit are changed to improve handoff performance at step730. Such handoff performance improvements may include making the pilot strength measurement message (PSMM) reporting interval from the mobile station smaller. Further processing of mobile unit handoff requests continues at step735.

Referring toFIG. 7B, a flow diagram of one embodiment of the user location handoff determination logic of the present invention is shown. As illustrated inFIG. 7A, determining a user location within the EWCS400begins at step700and continues through step735when a mobile communication unit is being served by the enterprise system.

Continuing at step740the mobile communication unit transmits a PSMM to the serving base station within the enterprise system. The base station monitors the PSMM from each mobile unit via the corresponding antenna unit to determine if the signal being transmitted by the mobile unit falls within a predetermined threshold. If the strength of the pilot signal is above a certain threshold, the base station adds the signal to its active set of signals to service. Since the present invention only allows handoffs between a mobile unit and the external macro system within the handoff transition region, the base station handling inter-enterprise-macro system handoffs sets the handoff parameters for a frequent reporting of PSMM for a timely hand off to the macro system.

At step745the base station determines the antenna being served by decoding the received signal delay by utilizing the location based handoff logic of the present invention. In the preferred embodiment of the present invention, each antenna coupled to the serving base station has a time delay different from other antennas within the enterprise system.

At step750the base station determines whether the serving antenna is present in the enterprise-macro system transition area. If the serving antenna is present in the transition area, processing continues at step760. If, on the other hand, the serving antenna is not present in the transition area, the handoff request is denied.

At step760, if the serving antenna is within the handoff transition area, the base station determines whether the handoff request meets the enterprise-macro hard handoff criteria. If the antenna handoff request meets the enterprise-macro handoff criteria, processing continues at step770where the enterprise base station sends the requested message to the macro base station. If the antenna handoff request does not meet the enterprise-macro handoff request, the handoff request is denied and processing of the request is terminated at step765.

At step775, if the antenna handoff request meets the enterprise-macro handoff criteria, the enterprise base station sends an extended handoff direction message to the mobile communication unit and the handoff request processing is completed.