The foregoing and other advantages of the invention will become apparent upon reading the following detailed description and upon reference to the drawings in which:
The mobile units 102, generally, are adapted to roam between different RF coverage areas, sometimes referred to as “cells” (not shown) served by base stations 104 (two shown). The mobile units 102 communicate with the base stations 104 via RF resources 106 which may comprise narrowband frequency modulated channels, wideband modulated signals, broadband modulated signals, time division modulated slots, carrier frequencies, frequency pairs or generally any medium for communicating control or payload information to and from the mobile units. The RF resources may implement air interface technologies including but not limited to, CDMA, TDMA, GSM, UMTS or IEEE 802.11.
The mobile units 102 are linked via network 108 with one or more connected devices 110 (one shown) such as other mobile units or wireline devices residing within the wireless communication system 100 or within external communication systems. The network 108 may be implemented using any appropriate transmission, switching and routing technologies, as are known in the art, including but not limited to Internet Protocol (IP) and Asynchronous Transfer Mode (ATM) technologies.
Wireless calls between and among the mobile units 102 and connected devices 110 are controlled by one or more telecommunication switching systems, exchanges or the equivalent (one shown), hereinafter termed a mobile switching center (MSC) 112. The MSC 112 may comprise, for example, an AUTOPLEX™ switching system, available from Lucent Technologies, Inc. The MSC 112 includes memory and processors (not shown), for storing and executing software routines for processing and switching calls, for providing various call features to calling parties and for providing access to the network 108. The MSC 112 may be configured for operation with generally any suitable circuit, cell, or packet switching technology.
The MSC 112 is connected to the base stations 104 by links 114, which may comprise, without limitation, Asynchronous Transfer Mode (ATM) links, ISDN lines, Ethernet LAN, wireless links, and the like. Links 116 carry control and payload information between the MSC 112 and the network 108 and, as shown, between the MSC 112 and a database 118 (e.g., a subscriber database). Although the links 116 are depicted with singular lines, the links 116 are logical links that may be physically realized by multiple physical lines or wireless links.
In the exemplary embodiment of
As noted previously, the level of impairment produced by wireless signal interference due to jamming or other sources can vary depending on the strength and duration of the interference, and may or may not result in service interruptions (e.g., dropped calls). Thus, in the exemplary embodiment of
Generally, a mobile unit is in the IDLE state 202 when it is not presently engaged in a call involving other connected units. That is, a mobile unit in the IDLE state does not presently require a bearer channel (e.g., voice channel) to support a call. Nevertheless, in the IDLE state, the mobile unit may communicate control messages with a serving MSC for mobility management purposes and the like.
A mobile unit enters the CONNECTED state 204 from the IDLE state 202 when it initiates or receives a call and a bearer channel is established to support the call. Typically, the mobile unit remains in the CONNECTED state for so long as it continues to participate in the call. If the mobile unit voluntarily ends its participation in the call, the call state moves from the CONNECTED to the IDLE state. If the bearer channel or control channel is impaired during the call but the impairment does not cause the mobile unit to lose RF coverage (as might occur, for example, during inadvertent signal interference or a relatively low-power or low-duration jamming transmission), the call state moves from the CONNECTED to the COMPROMISED state 206.
While in the COMPROMISED state, the mobile unit is still able to participate in the call (albeit at an impaired level due to signal interference) and other connected parties still have bearer channels connected to the call (i.e., remaining in the CONNECTED state). As will be described in greater detail in relation to
If the bearer channel to the mobile unit is interrupted during the call (i.e., the mobile unit loses RF communication with its base station), the call state moves from the CONNECTED or COMPROMISED state to the SUSPENDED state 208. While in the SUSPENDED state, the mobile unit has lost (at least temporarily) the ability to participate in the call; and the network or the user may initiate a reconnect attempt. If a reconnect is attempted, the call state moves from the SUSPENDED state to the RECONNECTING state 210 and an attempt is made to reconnect the mobile to the suspended session. As will be described in greater detail in relation to
At step 302, jamming or other wireless signal interference is detected on a wireless channel (e.g., carrier/band) supporting an active call. That is, the jamming or other interference has a frequency, intensity or other physical characteristic that creates channel impairments so as to compromise RF communications between a mobile unit and base station on the assigned wireless channel. In one embodiment, the signal interference is detected, initially, by base station(s) of the cell/sector(s) in which affected mobile units are registered (e.g., upon RF loading exceeding a system-defined threshold) and the incident is reported to the serving MSC. At such time, the MSC and base station will consider mobile unit(s) using the compromised channel to be in the COMPROMISED state. The jamming or other signal interference may or may not result in loss of RF communication between the mobile unit and base station, and indeed the base station may not know (at least initially) whether the signal interference causes a loss of RF communication with the mobile unit.
Optionally, at step 304, the base station may boost its transmitted power on compromised wireless channels to increase the likelihood that RF communication can be maintained with mobile units that are in the COMPROMISED state. It is possible, however, that RF communication can be maintained between the base station and affected mobile units without boosting power on the compromised wireless channels.
At step 306, the base station instructs mobile units on any impaired wireless channels to retune/handoff to an alternate wireless channel (e.g., unimpaired carrier/band); and at step 308, the base station starts a wait timer to await responses from the mobile units. The period of the wait timer may be predetermined or dynamically determined for different types or levels of RF signal interference. The wait timer allows for the base station to determine, based on the presence (or absence) of responses from the mobile units during a given time threshold, which mobile units have maintained RF communication with the base station during the interference.
Mobile units having successfully received the retune/handoff instruction will request a retune/handoff to an alternate wireless channel (e.g., carrier/band). If the base station receives the retune/handoff requests before expiration of the wait timer (determined at step 312), the base station at step 310 will service the retune/handoff requests by effecting a hard handoff to an alternate wireless channel (e.g., setting up a speech path to an unimpaired carrier/band and then tearing down the speech path to the comprised carrier/band) during the active call. The mobile units having successfully retuned during the active call are now returned to the CONNECTED call state. Mobile units not responding before expiration of the wait timer are considered to have lost RF communication. At step 314, the base station will end or suspend calls to mobile units not responding before expiration of the wait timer; and the call state of the mobile units may move to the SUSPENDED or IDLE state accordingly.
At step 316, the base station will direct any reconnect requests (i.e., for mobile units in the SUSPENDED state), as well as any new call originations or terminations (i.e., for mobile units in the IDLE state) to unimpaired wireless channels.
The method presumes at step 402, one or more incidents of jamming or other wireless signal interference is detected on an available wireless channel (e.g., carrier/band). Generally, detection of jamming or other interference at step 402 can mean that a channel impairment either exists or prospectively exists on a particular channel. The available wireless channel defines, for example, a carrier/band that is either supporting an active call or that will prospectively be assigned to support an active call. In one embodiment, the signal interference is detected by base station(s) of various cell/sector(s) in geographic proximity to source(s) of the interference (e.g., upon RF loading exceeding a system-defined threshold) and reports the incident to its MSC.
In one embodiment, the base station, MSC or other network element (not shown) maintains a record associated with various wireless channels to facilitate channel assignments for reconnections, new originations/terminations or hand-offs. Upon detection of the jamming or other wireless signal interference on a particular wireless channel (e.g., carrier/band) at step 402, the wireless channel is considered to be unstable and the record is modified, accordingly, to indicate instability or unavailability of that channel for new reconnections, new originations/terminations or hand-offs until such time as sufficient time has elapsed without any further incidents of jamming on that channel.
At step 404, the base station starts or resets a stability timer, to count-down a minimum waiting period following incidents of interference before affected channel(s) may be assigned for reconnections, new originations/terminations or hand-offs. The period of the stability timer may be predetermined or dynamically determined for different types or levels of RF signal interference.
Until such time as the stability timer elapses, determined at step 410, the base station at step 406 will direct reconnections, new originations/terminations or hand-offs to stable channels (e.g., carrier/bands that have not experienced incidents of jamming or other wireless signal interference or for which sufficient time has elapsed following an incident of signal interference to be assignable). If further incidents of jamming or other signal interference is detected during count-down of the stability timer, determined at step 408, the process returns to step 404 to reset the stability timer.
If and when the stability timer elapses (i.e, sufficient time has elapsed without further incidents of jamming or other interference), the affected wireless channel is considered to be stable and at step 412, the record is modified, accordingly, to indicate availability of that channel for new reconnections, new originations/terminations or hand-offs.
The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes that come within the meaning and range of equivalency of the claims are to be embraced within their scope.