|Publication number||USRE42224 E1|
|Application number||US 11/193,996|
|Publication date||Mar 15, 2011|
|Filing date||Jul 29, 2005|
|Priority date||May 24, 1999|
|Also published as||US6600914, US20020065063|
|Publication number||11193996, 193996, US RE42224 E1, US RE42224E1, US-E1-RE42224, USRE42224 E1, USRE42224E1|
|Inventors||Christopher R. Uhlik, Mitchell D. Trott, Lawrence J. Alder|
|Original Assignee||Durham Logistics Llc|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (157), Non-Patent Citations (32), Classifications (15), Legal Events (4)|
|External Links: USPTO, USPTO Assignment, Espacenet|
The present invention relates to a wireless communication system. More particularly, the present invention relates to an emergency call system which improves the grade of service (GOS) of a wireless communication system that has reached its maximum call capacity.
Wireless local loop systems are used in remote locations which typically have electricity but do not have telephone service. Instead of spending money on providing a wireline telephone service, it is typically easier to use a wireless local loop system. The wireless local loop system allows a user to operate a telephone at a remote site. The typical wireless local loop system includes at least one telephone device which is connected to an interface which in turn is connected to a radio telephone transceiver (either cellular or other wireless systems). The combination of the telephone device or devices and the remote radio telephone transceiver is referred to as the “subscriber unit.”
In a wireless local loop system, the link from the subscriber unit to the telephone system, for example, the local-exchange switch, is provided at least partially by a wireless communication channel. For example in a cellular wireless local loop (WLL) system, each subscriber unit is in a fixed location and communicates with a cellular radio base station responsible for all subscriber units within a cell. Sets of subscriber units communicate with one or more base stations which in turn are connected to the rest of the telephone network, typically a local exchange switch or other voice switching communications network router.
A caller cannot place a call in a wireless local loop system without a communication link existing between the subscriber unit and telephone system, including a wireless communication channel between the subscriber unit and the base station. In a typical wireless local loop system, there are usually more subscriber units than available wireless communication channels for audio links. Therefore in an emergency situation, a caller might not be able to make an emergency call because there are no wireless communication channels available.
In wireless telephone systems, the failure to obtain an open communication channel to place a telephone call is an “accepted evil.” However if someone is trying to place an emergency call, this accepted evil can be fatal. In an emergency, it is imperative that a caller be able to dial an emergency telephone number. An emergency telephone number can be “911” or the telephone number for the police, ambulance, fire department, poison control, or another known emergency telephone number.
A wireless local loop system subscriber unit may have a locally generated dial tone to simulate the “look and feel” of a conventional wireline telephone device when the handset is taken “off hook.” Alternatively, detecting an off hook condition on the telephone device of the subscriber unit may lead to a channel assignment request being made to a base station. Once a wireless channel is assigned, this being a channel for an audio link, a dial tone is generated by the switch and transmitted to the subscriber unit as in conventional wireline systems. The embodiments of the present invention are more suitable to this second case but may be used in both cases. The embodiments of the present invention also are suitable for use in a regular cellular system wherein the subscriber units are not necessarily fixed in location and may not necessarily be attached to a “plain old telephone set” (POTS).
In a wireless local loop system in which a dial tone is not generated until an audio-grade communication channel is assigned from the subscriber unit to the local switch, three things must occur in order to allow a caller to dial an emergency number without the presence of a dial tone: 1) the caller must be able to dial a telephone number, even without requiring a switch-generated dial tone or indeed any dial tone to be present, 2) the telephone number dialed must be recognized in some manner as an emergency call, and 3) the call must be placed if indeed it is recognized as an emergency call. Present day wireless telephone systems, whether wired or not, do not allow a call to be placed in this manner.
Therefore there is a need for a telephone system which activates an emergency call recognition system, recognizes when an emergency number is dialed and provides a communication channel for the caller to complete such a call even at maximum capacity. Such a system also would cut off or otherwise compromise the service quality of those calls that are not emergency calls when the system is operating at such maximum capacity.
One feature of the present invention is allowing for the placement (by dialing) of emergency telephone calls in a wireless system operating at capacity.
Another feature of the present invention is providing a communication channel to a caller who is placing such an emergency call in a wireless system.
Another feature of the present invention is using an emergency call recognition system which compares the dialed number (a sequence of digits) to one or more predefined digit sequences defined as emergency telephone numbers in a wireless system.
Yet another feature of the present invention is recognizing if an emergency telephone number has been dialed without requiring a dial tone in a wireless system.
Yet another feature of the present invention is providing an indicator to a caller if all of the communication channels are in use in a wireless system.
One aspect of the present invention is an emergency call recognition system which is part of a wireless system and which recognizes when a dialed number is an emergency number is dialed and which provides a wireless communication channel to the caller to complete the call when the call is determined to be an emergency call. Thus, the present invention allows emergency calls to be made at any time by ensuring allocation of a communication channel for this purpose.
In a first embodiment of the present invention, a certain number of wireless channels of the totality of communication channels licensed to a wireless system are reserved for the purpose of determining at the base station if a set of dialed digits is an emergency call when all the non-reserved channels are busy. While this reduces to some extent the maximum capacity of the system for non-emergency calls, the grade of service (GOS) for emergency calls is dramatically improved.
In a second embodiment of the channel allocation of the present invention, a number of low-bit-rate wireless communication channels is reserved for the purpose of recognizing at the base station when an emergency call is being made when all full-rate channels are busy. These low-bit-rate channels typically are not sufficient for an audio communication, for example, for voice or a facsimile. The recognition preferably is digit by digit. After emergency number determination, via a priority recognition system, the emergency call is given a full-rate (e.g., audio-grade) wireless communication channel by cutting off an existing full rate non-emergency telephone call or downgrading the bit rate of one or more non-emergency telephone calls.
In a third embodiment of the channel allocation of the present invention, the subscriber unit recognizes an emergency telephone number, preferably digit by digit. Thereafter the subscriber unit sends an emergency link request to the base station. If there are no available channels, the base station assigns a channel by disconnecting or otherwise downgrading an existing telephone call that is not an emergency call or degrading the bit rate of existing non-emergency calls, providing the freed channel to the emergency caller.
As defined herein, an emergency call is defined as a sequence of digits of a set of pre-defined emergency digit sequences (e.g., 911). Any user who dials a pre-configured emergency number using either DTMF or pulse dialing will have an improved chance of seizing a channel on a congested system. Emergency numbers can then be detected in the base station of the wireless local loop or, in another embodiment, in the subscriber unit of the present invention, for example, before channel allocation. In the preferred embodiment, emergency numbers are detected on a digit by digit basis to rapidly determine if the sequence is not an emergency number, such determining being possible before all the numbers have been dialed, thereby speeding up the determination of which telephone calls are not emergency numbers.
One aspect of the present invention is a system and method for emergency call channel allocation in a wireless system. The technology of the present invention allows emergency calls to be placed by a user in distress (or is otherwise a priority user) even when the wireless system is operating at capacity, that is, all wireless communication channels are in use. The various embodiments of the present invention are described in detail below. They share certain common characteristics however such as:
In all embodiments, a wireless local loop system having a limited number of communication channels is addressed. In a wireless local loop system, the subscriber unit establishes two way communications with a base station which in turn is linked to a master cellular-type switching center which is in turn is linked with a local telephone central switching office (the switch). A base station transceiver establishes a link with a subscriber unit transceiver by assigning a wireless communication channel between the base station and the subscriber unit. Note that the terms base station and communication station are used interchangeably herein.
In the preferred embodiment, the base station transceiver uses an array of antenna elements together with spatial processing to communicate with the subscriber unit. Such spatial processing clearly is not a necessary part of the invention. During reception, the spatial processing acts on the signals received at the antenna array and in particular transforms the antenna signals into a received signal from a particular subscriber unit. During transmission, the spatial processing transforms a to-be-transmitted signal into antenna signals to be transmitted at the antenna array elements to the subscriber unit. The spatial processing, preferably linear spatial processing is adaptively determined. Such systems are sometimes called “smart antenna” wireless communication systems. Such spatial processing of the antenna signals potentially provides several signal quality advantages, including increased cell-phone capacity in each cell. In some cases, smart antenna systems enable simultaneous communications over the same “conventional communication channel.” This is sometimes called spatial division multiple access (SDMA). A conventional communication channel is a frequency, time, or code communication channel or a combination of these. For a description of spatial processing See U.S. Pat. No. 5,592,490 to Barratt et al., incorporated herein by reference. While smart antenna systems with spatial processing allow for SDMA, that is, more than one “spatial communication channel” per conventional communication channel, many of the advantages of spatial processing are still available even with one spatial communication channel per conventional communication channel.
The present invention, however, is not restricted to using smart antenna wireless communications systems.
The interface preferably comprises a power supply (not shown), a circuit for detecting whether the telephone device is in an on-hook or off hook state 101, a telephone number converter 103, and a digital signal processor (DSP) 108 having storage for programs 110. These include programs to provide a priority communication channel request, and, in some embodiments, for performing emergency call recognition based upon emergency call number sequences stored in a memory 112 of the DSP 108. In the preferred implementation, the DSP 108 and memory 112 are both part of the subscriber unit transceiver 104, and also perform other functions such as signal modulation and demodulation. All non-DSP implemented parts of the transceiver, such as the receiving and transmitting RF components, the digital to analog and analog to digital converters, are shown in block 105. The interface power supply is the same as the power supply that supplies power to the rest of the subscriber unit, for example the subscriber unit transceiver.
Note that because it is anticipated that DSP functionality, including DSP programs, may in the future be incorporated into special purpose hardware, for example as part of an application specific integrated circuit (ASIC) or part of a very large scale integrated circuit (VLSI), and because DSP functionality may also be met by other processors, for example a general purpose microprocessor, the term digital signal processor as used herein includes these equivalent alternatives.
In those embodiments wherein the emergency call recognition program is in the subscriber unit DSP, the telephone number converter 103 converts individual standard DTMF (touch-tone) or pulse dialing signals from the telephone device into digital signals. The subscriber unit DSP-based recognition program has at least one predefined sequence of digits, representing an emergency number which a user dials using telephone device 100. The sequences are shown as Emer. #1, . . . , Emer. #12 stored in memory 112 of DSP 108.
The emergency call recognition program is a series of instructions for performing digit-by-digit comparison of dialed digits to stored digits representing an emergency number and is programmed to recognize at least one emergency telephone number. The emergency telephone numbers can include the telephone numbers for the police, ambulance, fire department, poison control, 911, or any other emergency telephone number, however this list is not meant as a limitation. It is anticipated as within the scope of the present invention to have emergency numbers to be programmable by a technician in the factory or in the field.
As each digital signal is generated it is compared to a digit of an emergency number. The emergency call recognition program of the DSP recognizes if the dialed telephone number is an emergency telephone number by using digit comparison. Emergency number recognition program compares the converted digital signals to at least one predefined sequence for an emergency telephone number in digital form. The at least one predefined sequence of emergency telephone number in digital form is stored in the memory 112 of the DSP 108.
The emergency call recognition system is initiated as soon as an off-hook state is determined at the subscriber unit. The emergency call recognition system does not require the presence of a dial tone. Some implementations may include locally generating (i.e., “faking”) a dial tone, while others may include, upon an off hook condition being obtained, opening a non-audio wireless channel to convey dial-tone status from the switch. Alternatively, upon off-hook, after the subscriber unit fails to obtain a channel, a special “dialing in progress” tone (which might simply be silence) is provided to the telephone device during the dialing.
Digit by digit dialing analysis comprises a method for discriminating between a potential emergency sequence and a non-emergency sequence. For example, if 9-1-1 was the only valid emergency number, means would be included for distinguishing digit-by-digit between the following three, possibly partial, digit sequence cases:
In the preferred embodiment, this digit-by-digit number analysis allows non-emergency call determination as early as possible during congested situations where non-emergency calls are being dialed. While this early detection of non-emergency call numbers feature may optimally allocate call resources, the present invention, however, is not restricted to such careful implementations.
In yet another alternate embodiment, the emergency call recognition program recognizes the dialed telephone number by using audio (DTMF) comparison. Methods for recognizing, i.e., discriminating between a set of audio patterns are well known in the art. For example, methods using hidden Markov models are widely used in speech recognition and may easily be adapted for this application. The emergency call recognition program compares the DTMF audio signals to at least one predefined audio sequence for an emergency telephone number. Predefined audio sequences may also be stored in the memory of the DSP. The at least one predefined audio sequence for an emergency telephone number in digital form is located in memory 112 of DSP 108.
Storing the different sequences of emergency numbers in the memory of the DSP can be accomplished in a variety of ways. In one embodiment, a technician stores the emergency telephone numbers in the DSP memory 112. This can be done at the store or during the installation of the telephone system. In another embodiment, the users are able to store their own emergency telephone numbers in the DSP memory 112. In another embodiment, the manufacturer stores the emergency telephone numbers for a specific geographic area in the DSP memory 112.
In yet another embodiment, the emergency telephone numbers are entered automatically once the subscriber unit 102 is initialized with the rest of the system for the first time. In this embodiment, once the subscriber unit 102 is initialized, the subscriber unit makes a wireless connection to a base station which downloads the emergency numbers for the given area. In addition, the subscriber unit 102 can periodically make wireless connections to the base station to update the emergency numbers for a given area.
Several formats for storing the numbers are possible within the scope of the invention. One form is a table enumerating all possible emergency call phone numbers. Alternatively, compressed forms such as regular expressions may be used. A regular expressions is an expression in a syntax for specifying strings, typically for matching operations. See J. E. F. Friedl, Mastering Regular Expressions: Powerful Techniques for Perl and Other Tools, Sebastopol, Calif.: O'Reilly & Associates, 1997. (ISBN: 1565922573). Alternatively, the numbers may be stored as a set of rules, for example matching rules suitable for rule-based-analyses. Other well known storage schemes suitable for matching also may be used. For example, if 7 digit numbers beginning with 123 are emergency numbers, then this could be stored as a table enumerating 10,000 possibilities or, more compactly, as the rule “1-2-3 followed by any four digits” or as a regular expression like “123 ? ? ?”. Of course combinations of these techniques are also anticipated such as lists of regular expressions. Each of the storage methods would be accompanied by a corresponding method for discriminating between an emergency and a non-emergency sequence.
If the DSP recognizes an emergency number, the DSP sends an emergency (i.e., priority) communication channel request to its base station in the WLL system. The request for a priority communication channel assignment is transmitted by subscriber unit transceiver 104 to the base station. The base station responds to the request for a priority communication channel assignment by providing a communication channel to the emergency caller. The base station disconnects a non-emergency call to provide the emergency caller a communication channel in the case that no other communication channels are available.
The storage of the emergency calls and the emergency call recognition program is as described above for the case where the call recognition program is in the subscriber unit DSP 108. In this case, the at least one predefined sequence of digits, representing an emergency number, are shown as Emer. #1, . . . , Emer. #12 stored in memory 132 of DSP 128.
Subscriber Unit Detection of Emergency Numbers
If there are no communication channels available, then the telephone device is provided with an indicator that a channel is not available, i.e., a “try-later” signal such as a “fast busy” signal, and the subscriber unit begins to listen for DTMF tones 212 generated by the user dialing the emergency number. Once a DTMF tone is detected by the DSP, the “fast busy” signal is terminated 214. The DTMF tones are then converted to digital signals in a sequence and sent to the DSP 216. An emergency call recognition program then compares the digital signals, digit by digit, to at least one predefined emergency telephone number 218. If any one digit of the sequence of digital signals fails to match the predefined stored emergency telephone number 220 when that digit is dialed, then the call is disconnected 221.
If the sequence of digital signals dialed matches a predefined stored emergency telephone number 220, then an emergency (i.e., priority) communication channel request is sent to the base station 222. The base station then disconnects an existing call 226, and assigns this channel to the user. The Call Disconnect procedure is described below. The base station then assigns a channel to the user, thus opening a path to the telephone device from the switch and passing the switch-generated dial tone to the telephone device 228. Upon detection of the dial tone by the DSP, the DSP dials the pre-configured emergency number stored in the memory of the DSP 230 that was recognized by the DSP and which the caller previously dialed. Once the DSP completes dialing the entered emergency number, the call proceeds as a normal call 210.
Subscriber Unit-based Discrimination: Some Variations
The subscriber unit typically contains the following elements: a circuit for detecting whether or not the telephone set is “off-hook, i.e., activated or deactivated, a circuit for converting the telephone set audio-band analog signals into digital signals, a signal processing mechanism capable of recognizing emergency telephone numbers by comparing digit sequences to a pre-stored emergency phone number description, the description being of one or more pre-defined emergency number sequences and stored using table enumeration, regular expression, procedural description, or rule-based description, a channel requesting mechanism, a mechanism capable of notifying the base-station that the requested call is of an emergency or priority nature, and a processing mechanism capable of continuing or discontinuing call progress based on digit sequence detected or upon request of a base-station.
In the embodiment in which the dialed digit detection and phone number analysis for the purpose of emergency/non-emergency call discrimination occurs in the subscriber unit, several variations are possible as to what happens once an off-hook state is detected at the subscriber unit. For example, upon off-hook, the subscriber unit can immediately fake a dial tone. At that point, the subscriber unit can immediately attempt to open an audio channel, or can postpone attempting to open an audio-grade channel until a complete phone number has been dialed, or can postpone attempting to open an audio channel until the called party answers, since sometimes the party may not answer. In another variation, upon off-hook, a non-voice channel to the base station is obtained and then used to convey dial-tone status from the switch. Again, the subscriber unit can immediately attempt to open an audio channel, or can postpone attempting to open an audio-grade channel until either a complete phone number has been dialed, or until the called party answers.
In the preferred subscriber unit-detection embodiment, upon off-hook, the subscriber unit tries to establish an audio channel, and on failure, provides an audio signal (typically a tone or possibly even silence) to the user during which digit collection continues regardless of the type of tone. Thus, in one version, the audio signal is null (silence), but the subscriber unit continues processing digits, while in another version, the audio signal is a substantially dial-tone-like “fake dial tone”, and in yet another version, the audio signal sounds different from dial-tone, for example a “fast busy.”
In the preferred embodiment, once the call is determined to be an emergency call, it is tagged as emergency for the purpose of enhancing its reliability for the remainder of the call duration. A call so tagged will not be allowed to be dropped or otherwise degraded in response to other emergency call attempts.
In this embodiment, the subscriber unit decides whether or not the phone number is an emergency call. The subscriber unit unilaterally takes the decision to discontinue the call when it is determined that the call is a non-emergency call. In an alternate embodiment, the subscriber unit simply provides the emergency/non-emergency status of the call to the communication-station using one of the control channels normally used for status and channel assignment in the wireless communication system. The base station then uses this information, including the phone number (or partial number) that was dialed. This phone number is provided by the subscriber unit to the communication-station's channel allocation means which subsequently uses the phone number information to decide which calls may be dropped. In yet another alternate, if and when the subscriber unit can be sure the call is not an emergency call, the subscriber unit tells the communication-station immediately that the call is not an emergency. The communication-station can then perform a system capacity/load check to decide if the call should be allowed to continue. In such a case, the communication-station can temporarily store the emergency determination status to use when deciding which calls to drop (or degrade) if and when such dropping or degrading becomes necessary.
Base Station Detection of Emergency Numbers
A WLL system is licensed to have a certain number of channels. One aspect of the emergency call communication channel allocation feature of the present invention allows a certain number of those full rate channels to be reserved (reserve channels) for detecting emergency calls. While this scheme reduces the maximum capacity of the system for non-emergency calls, the grade of service for emergency calls is dramatically improved.
If the system has reached its maximum capacity, the base station determines if the channel request being placed is for an outgoing call 306, that is, whether the channel is request is not one for maintenance but for the purpose of placing a call beyond the base station. If the request being made is not for an outgoing call and the system capacity is at its maximum, the call is disconnected 308 and the user must try again later. If the request is for an outgoing call, the base station checks to see if the call is the lowest priority of all active calls on the system 310. If there are lower priority calls on the system, calls of a lower priority are singled out to be disconnected 312. Thereafter the lower priority call selected is disconnected 314 so that the higher priority call can be connected 316.
If there are no lower priority calls on the system, the call is marked as an emergency call 318 and the base station performs further analysis on the call 320. At his juncture the caller is provided with a full rate communication channel which is one of the several full rate communication channels of the system that are reserved for emergency call use.
If the caller does dial a digit within a time limit, i.e., five (5) seconds 322, then the system determines if the dialed digit matches the correspondingly positioned digit of any of a predefined sequence of numbers representing an emergency number 332. The system then determines if all the digits dialed so far match any of a predefined sequence of numbers representing an emergency telephone number 334. If dialed digits do not yet match a predefined sequence of numbers representing an emergency telephone number, then the system determines if the caller is done dialing 336. This is accomplished by known dialing rules, for example, if the first digit a caller dials is a one (1), then the caller must dial ten (10) more digits to complete the call. If the caller is not done dialing, then the system goes back to step 322 for the next digit. That is, the system checks if the caller has dialed another digit within a time limit, i.e., five (5) seconds 322, and so forth as described above. Otherwise, if the maximum number of digits has been dialed, and in step 334 a match to an emergency telephone number is found, then the system determines in step 338 if another caller must be disconnected in order for there to be maintained a full rate communication channel for another potential emergency call. If the system has reached maximum capacity 338, then the system chooses a call to disconnect 342 and disconnects the caller 344 and maintains the connection for the emergency caller 340 and reserves a full rate channel for future emergency calls. In alternate embodiments that allow for multiple rate calls, such as half rate voice calls, or twice full rate data transfer calls, rather than disconnect a call, one or more calls are downgraded (for example from full rate 32 kbps to half rate 16 kbps, or from a 2-channel 64 kbps link used for data to a slower 32 kbps link) in order to provide the necessary free full-rate channel for the emergency call. If the system has not reached maximum capacity, then the system maintains the connection 340.
Communication Channel Allocation (Less Than Full Rate)
A low rate communication channel is a communication channel which operates at a lower speed than a full rate communication channel. In one embodiment, the low rate communication channel operates at 250 bps which is 1/128 of a full rate communication channel. The full rate communication channels operate at 32 kbps. In order to use a low bit-rate communication channel, the telephone device uses compression using a special vocoder. The special vocoder is capable of working with two (2) discrete sine waves. The special vocoder in is stored in a DSP located in either the telephone device, or interface as described in the earlier embodiments. The two simultaneous tones are adequate to pass DTMF, dial tone, busy signal, fast busy, etc., including all standard audio band signaling mechanisms used in telephone systems today. Thus when all of the full rate communication channels for a wireless local loop telephone system are in use, a caller can still receive dial-tone from the switch and dial a telephone number using a low rate communication channel. Note that in this embodiment, the audio signal compressor in the subscriber unit does not explicitly “recognize” the digits. It only finds discontinuities of tones and signals the frequency and amplitude of the tonal components as they appear. It is up to the base-station to turn this tone sequence encoding into digit sequences and then, perhaps, do emergency call discrimination.
Many methods are known for providing low-rate channels in a manner compatible with a given air interface standard. The preferred embodiment uses the Personal HandyPhone system (PHS) standard described, for example in the Association of Radio Industries and Businesses (ARIB, Japan) Preliminary Standard, Version 2, RCR STD-28 and Technical Standards of the PHS Memorandum of Understanding Group (PHS MoU—see http://www.phsmou.or.jp). In time-division (i.e., slotted) air-interface standards such as PHS, ½-rate (16 kbps) and ¼-rate (8 kbps) connections are supported by providing rate handshaking between the subscriber unit and the base station at the start of the low-rate connection, and then transmitting only on every other (for ½-rate) or every fourth (for ¼-rate) communication slot that would normally be used by a full-rate connection. While not directly supported in the PHS standard, this method may be extended in an obvious manner to support any fractional rate, such as the preferred rate of 1/256. Similar fractional-rate methods may be applied to other air-interface standards. Alternatively, low-rate connections may be carried out using any of a variety of well-known random access technique. The random access uplink technique used in PHS for link channel requests can be easily modified to carry low-rate compressed audio traffic on a different dedicated channel. With this method, uplink messages are sent on a shared random access channel and the base station positively acknowledges each message it receives. If a subscriber unit does not receive an acknowledgement, it waits a proscribed amount of time and retransmits. In this way many low-rate uplink users may share a common channel. On the downlink, the base station sends messages (e.g., compressed audio signals) on a common downlink channel, using a messaging protocol analogous to that used for the downlink PHS downlink link channel assignment messages. Each message contains both a payload and a subscriber unit address field. The address field enables the targeted subscriber to identify and extract those messages it is intended to receive.
How one may achieve compression for use in the low-rate channel is now described in more detail. Many methods for reducing downlink bandwidth may be used. For example, if the switch is able to generate only a small number of distinct audio signals during call connection, e.g., dial tone or fast busy, then these audio signals may be broadcast to all subscriber units using a single broadcast channel, switching between the audio signals in a cyclic fashion. A very low-rate downlink signaling channel is then used to individually instruct a subscriber unit to either play back a particular received broadcast audio signal to the telephone device, to play back silence to the telephone device, or to enter normal audio processing mode. Alternate compression schemes may be used to pass the signaling information. Methods for compressing audio signals are known in the art. Compression methods take as input a sampled digital version of an audio signal and produce a digital sequence that represents the salient audio features of the signal in compact form. Compressing audio signals that consist of a mixture of tones is a particularly straightforward problem; compression methods that work well for speech signals will also work well for mixtures of tones, such as occurs in DTMF signals, as mixtures of tones may be viewed as a special case of audio signals, and indeed many compression methods used for telephony applications are designed specifically to pass DTMF tones and other signaling tones with minimal distortion. Any standard low-rate speech compression method may therefore be used in the invention, provided that the method preserves the frequency of signaling tones.
Preferably, however, a method with much lower computational complexity is used. Many methods exist for counting the number and determining the frequency of tones in a signal that consists of a mixture of tones. The preferred method divides the quantized audio sequence into blocks of duration 10 millisecond, applies a computationally efficient tone estimation method such as ESPRIT (see, for example, U.S. Pat. No. 4,965,732 to Roy, III, et al., entitled METHODS AND ARRANGEMENTS FOR SIGNAL RECEPTION AND PARAMETER ESTIMATION), and outputs a sequence of values for each 10 millisecond block representing the number, frequency, and intensity of those tones (up to a maximum of two tones) whose intensity exceeds a proscribed minimum sensitivity value for DTMF detection. If no significant tones are present then a silence indicator is produced for the block. The compressed sequence that results from the processing of the 10 millisecond blocks is then subject to run-length coding to further collapse tones sustained over multiple 10 millisecond blocks into a single frequency/intensity/duration indicator. Other compression methods more efficient than run-length coding may also be used.
An alternate embodiment of the present invention which uses a low rate link to the base station where detection of the emergency number sequence is made is illustrated in FIG. 4A and FIG. 4B. The subscriber unit goes off-hook 400. The subscriber unit requests a communication channel 402. At this point, a dial tone is not present. The base station determines if there is an open full rate communication channel which can be assigned to the caller 404. If an open full rate communication channel is available, the open full rate communication channel is assigned to the caller 406. The system then provides a dial tone to the caller 408. The call proceeds as a normal call 410.
If there are no open full rate communication channels available, then the subscriber unit is provided with a low bit-rate communication channel 412. A low bit-rate communication channel is a communication channel which operates at a lower bit-rate than a full rate communication channel. In one embodiment, the low rate communication channel operates at 250 bps which is 1/128 of a full rate communication channel. The full rate communication channels operate at 32 kbps. In order to use a low rate communication channel, the telephone device uses compression using a special vocoder. The special vocoder is capable of working with two (2) discrete sine waves. The special vocoder in is stored in a DSP located in either the telephone device or interface as described in the earlier embodiments. Such a compression allows DTMF tones and possibly one or more signals to be transmitted to the base station. Such a low rate vocoder is also capable of transmitting the dial tone, busy signal, and other call progress signals to the subscriber unit in the downlink direction.
The base station provides a dial tone to the caller and a DSP at the base station (base station DSP) listens for the codes for DTMF tones 414 which have been passed from the subscriber unit to the base station on the low bit-rate channel. Referring now to
If the caller does dial a digit within a time limit, i.e., five (5) seconds 422, then the base station determines if the dialed digit matches the correspondingly positioned digit of any of a predefined sequence of numbers representing an emergency number 432. The system at the base station then determines if all the digits dialed so far match any of a predefined sequence of numbers representing an emergency telephone number 434. If dialed digits do not yet match a predefined sequence of numbers representing an emergency telephone number, then the system determines if the caller is done dialing 436. This is accomplished by known dialing rules, for example, if the first digit a caller dials is a one (1), then the caller must dial ten (10) more digits to complete the call. If the caller is not done dialing, then the system goes back to step 422 for the next digit. That is, the system checks if the caller has dialed another digit within a time limit, i.e., five (5) seconds 422, and so forth as described above. Otherwise, if the maximum number of digits has been dialed, and in step 434 a match to an emergency telephone number is found, then the system determines in step 438 if another caller must be disconnected in order for there to be maintained a full rate communication channel for another potential emergency call. If the system has reached maximum capacity 438, then the system chooses a call to disconnect 442 and disconnects the caller 444 (or chooses one or more calls to downgrade and so downgrades these calls) and assigns the new full-rate channel for the emergency caller 440, including dialing the number dialed. Similarly, if the system has not reached maximum capacity, then the system assigns a new full-rate channel for the emergency caller 440, including dialing the number dialed.
In alternate embodiments that allow for multiple rate calls, such as half rate voice calls, or twice full rate data transfer calls, rather than disconnect a call, one or more calls are downgraded (for example from full rate 32 kbps to half rate 16 kbps, or from a 2-channel 64 kbps link used for data to a slower 32 kbps link) in order to provide the necessary free full-rate channel for the emergency call.
Call Disconnect Procedure
The WLL system of the preferred embodiment of the present invention provides six levels of caller priority which can be assigned to different customer classes. High priority outgoing calls have an improved chance of connecting in a system that has reached maximum call capacity. The priority level of each subscriber unit is assigned by the base station when the subscriber unit is brought on line. When the system is operating at maximum capacity and a call is attempted, the priority of the new call's subscriber unit is compared to the priority of existing calls on the system. A new call may preempt any call that has a lower priority level than itself. A lower priority call is be disconnected so the new call can be assigned its resources. If the call is from a multi-rate subscriber unit, one or more than one call resource is be disconnected so that the multi-rate call can be accommodated at the higher rate. For example, double-rate calls use two channels and are supported. Similarly, half rate calls use half a channel. The method of selecting which call(s) to disconnect is performed as follows:
In short, any user of a WLL system who dials a recognizable emergency call using either a DTMF or pulse telephone will have an increased chance of the emergency call going through, even if the system is operating at its maximum capacity.
In alternate embodiments that allow for multiple rate calls, such as half rate voice calls, or twice full rate data transfer calls, rather than disconnect a call, one or more calls are downgraded (for example from full rate 32 kbps to half rate 16 kbps, or from a 2-channel 64 kbps link used for data to a slower 32 kbps link) in order to provide the necessary free full-rate channel.
In order for the system of the present invention to not be overcrowded with repeated erroneous calls, a time out program is resident in the DSP of the base station. This program allows a user selectable certain number of non-emergency calls to be attempted during times of peak use from a given subscriber unit. When a subscriber unit exceeds the number of allotted call attempts during a peak period, the base station denies further access to that subscriber unit for a set period of time. After the expiration of that time, the subscriber unit is again permitted to attempt phone calls. In this manner, the system is kept from being overcrowded in the processing of those calls that are potentially emergency in nature.
Base Station-Based Discrimination: Some Variations
The preferred embodiment for base-station based phone number analysis for the purpose of emergency/non-emergency call discrimination also includes base-station dialed digit detection. As described above, in one version, low-rate channels are used during the call setup phase to carry the dial tone, DTMF digits, pulse-dial-events, and other low-information-bit-rate call setup signaling. In another version, a certain number of full-rate reserve channel is made available. Calls in their startup phase can occupy a full-rate reserved channel. When a non-emergency call is confirmed in the reserved channel, the call is moved into the non-reserved channel set. If this cannot be accomplished, the call is discontinued.
In the low-rate channel scheme, in one version, the low-rate channel is preserved until connect. When it is confirmed that the wireless system is at full load and the non-emergency status is confirmed, the call is discontinued. When, on the other hand, the wireless system is not at full capacity, the call is promoted to a full rate (i.e., voice-capable) channel if and when the call connects. When it is confirmed that the wireless system is at full voice channel capacity and that the call is an emergency call, another call is dropped (or one or more calls are degraded in data-rate) to make room for the emergency call. Preferably, in such a case, the emergency status is remembered by the base-station for use in call dropping decisions.
In the low-rate channel scheme, in another version, the low-rate channel is used only until emergency status can be confirmed or denied. When it is confirmed that the wireless system is at full load and the non-emergency status is confirmed, the call is discontinued. When, on the other hand, the wireless system is not at full capacity, the call is promoted to a full rate (i.e., voice-capable) channel if and when the call connects. When it is confirmed that the wireless system is at full voice channel capacity and that the call is an emergency call, another call is dropped (or one or more calls are degraded in data-rate) to make room for the emergency call. Preferably, in such a case, the emergency status is remembered by the base-station for use in call dropping decisions.
In the reserve full-rate channel scheme, in one version, when a call made on one of the reserved channels is confirmed to be an emergency call, a non-emergency call is dropped to restore a channel to the reserved channel pool. In the preferred version, calls that have not (yet) been confirmed as emergency calls that are occupying one of the reserved channels, have a inter-digit dialing time imposed to limit time occupying a reserved channel. In yet another version, any call that has not (yet) been confirmed as an emergency call, and that is occupying a reserved channel, has a maximum total dialing time imposed to limit the time any call can occupying a reserved channel.
General System Requirements
The system of the present invention is a TDMA system that operates under the personal Handiphone Standard (PHS) and includes a plurality of subscriber units. Generally each subscriber unit has three Motorola ® M56303 digital signal processors (DSP), whose characteristics are incorporated herein by reference in their entirety, one for transmission, one for reception, and one for audio signal coding and decoding. These DSPs are not meant as a limitation. Other DSPs having the capabilities of these specific DSPs are considered within the scope of the invention. Further, it is anticipated that future DSPs will be available having similar or more powerful characteristics, and would find use in the present invention. Further, it is anticipated that many of the functions now implemented by DSP programs may in the future be incorporated into special purpose hardware, for example as part of an application specific integrated circuit (ASIC) or part of a very large scale integrated circuit (VLSI). As would be clear to those of ordinary skill in the art, a general purpose microprocessor may also be used instead of a DSP device.
The base station comprises several Motorola ® M56303 DSPs, whose characteristics are incorporated herein by reference in its entirety. The number of DSPs depends on the number of antennas in the antenna array and the number of network connections available for the base station. In general, there is one for each time slot on the receive side and one for eight slots on the transmit side (the PHS system has four receive and four transmit time slots in each frequency band), although this DSP is not meant as a limitation. Several PowerPC microprocessors (Motorola®/IBM®) control the DSPs. The Motorola ® DSP56303 is a 24-bit processor of the family of processors of the designation DSP56300. Other processors of this family would be suitable substitutes as would other DSPs or DSP ASIC cores from other manufacturers, or microprocessors, or special purpose hardware or other processing means as would be clear to those in the art.
Although the present invention has been described in detail for purpose of illustration, it is understood that such detail is solely for that purpose, and variations can be made therein by those skilled in the art without departing from the scope of the invention as described. The present invention is defined by the following claims:
|Cited Patent||Filing date||Publication date||Applicant||Title|
|US3704465||Aug 28, 1970||Nov 28, 1972||Hazeltine Corp||Angular position determining system compensated for doppler|
|US3774209||Nov 18, 1970||Nov 20, 1973||Air Land Systems Co||Radio communication system|
|US3798645||Aug 28, 1970||Mar 19, 1974||Hazeltine Corp||Angular position determining systems using time scanned arrays|
|US3852749||Jan 24, 1973||Dec 3, 1974||Int Standard Electric Corp||Radiolocation system|
|US3946385||Jan 20, 1975||Mar 23, 1976||The United States Of America As Represented By The Secretary Of The Department Of Transportation||Interferometric navigation and guidance system|
|US4005379||Nov 4, 1975||Jan 25, 1977||Lockheed Electronics Co., Inc.||R.F. power distribution network for phased antenna array|
|US4035746||Sep 7, 1976||Jul 12, 1977||The Bendix Corporation||Concentric broadband power combiner or divider|
|US4085319||Feb 1, 1977||Apr 18, 1978||The United States Of America As Represented By The Secretary Of The Army||Spatial-multiplex, spatial-diversity optical communication scheme|
|US4128740||Feb 14, 1977||Dec 5, 1978||Motorola, Inc.||Antenna array for a cellular RF communications system|
|US4263568||Mar 12, 1979||Apr 21, 1981||International Telephone And Telegraph Corporation||Large scale low-loss combiner and divider|
|US4316191||Apr 14, 1980||Feb 16, 1982||The Bendix Corporation||Low angle radar processing means|
|US4375622||Apr 20, 1981||Mar 1, 1983||Motorola, Inc.||Multiport radio frequency signal combiner|
|US4434505||Dec 1, 1982||Feb 28, 1984||The United States Of America As Represented By The Secretary Of The Army||Interference cancelling system for a mobile subscriber access communications system|
|US4475010||May 5, 1983||Oct 2, 1984||At&T Bell Laboratories||High density cellular mobile radio communications|
|US4639732||Feb 22, 1985||Jan 27, 1987||Allied Corporation||Integral monitor system for circular phased array antenna|
|US4639914||Dec 6, 1984||Jan 27, 1987||At&T Bell Laboratories||Wireless PBX/LAN system with optimum combining|
|US4646859||May 17, 1985||Mar 3, 1987||Malvern Scale Company||Scale|
|US4658096||Sep 18, 1984||Apr 14, 1987||Metrofone, Inc.||System for interfacing a standard telephone set with a radio transceiver|
|US4737794||Dec 9, 1985||Apr 12, 1988||Mcdonnell Douglas Corporation||Method and apparatus for determining remote object orientation and position|
|US4737975||Dec 30, 1986||Apr 12, 1988||Metrofone, Inc.||Programmable system for interfacing a standard telephone set with a radio transceiver|
|US4742356||Dec 9, 1985||May 3, 1988||Mcdonnell Douglas Corporation||Method and apparatus for determining remote object orientation and position|
|US4750147||Nov 6, 1985||Jun 7, 1988||Stanford University||Method for estimating signal source locations and signal parameters using an array of signal sensor pairs|
|US4775997||Apr 8, 1987||Oct 4, 1988||Metrofone, Inc.||System for interfacing a standard telephone set with a radio transceiver|
|US4796291||Mar 7, 1986||Jan 3, 1989||Nec Corporation||Mobile radio communications system|
|US4827395||Apr 6, 1987||May 2, 1989||Intelli-Tech Corporation||Manufacturing monitoring and control systems|
|US4829554||Jan 31, 1985||May 9, 1989||Harris Corporation||Cellular mobile telephone system and method|
|US4837800||Mar 18, 1988||Jun 6, 1989||Motorola, Inc.||Cellular data telephone system and cellular data telephone therefor|
|US4855748||Mar 18, 1988||Aug 8, 1989||Allied-Signal Inc.||TCAS bearing estimation receiver using a 4 element antenna|
|US4910794||Aug 4, 1988||Mar 20, 1990||Norand Corporation||Mobile radio data communication system and method|
|US4922517||Sep 15, 1988||May 1, 1990||Metrofone, Inc.||System for interfacing a standard telephone set with a radio transceiver|
|US4926186||Mar 20, 1989||May 15, 1990||Allied-Signal Inc.||FFT-based aperture monitor for scanning phased arrays|
|US4940963||Mar 10, 1989||Jul 10, 1990||Motorola Inc.||Paging system with improved acknowledge-back capabilities|
|US4947452||Jan 11, 1989||Aug 7, 1990||The Tokyo Electric Power Company, Ltd.||Mobile communication system|
|US4955082||Jan 11, 1989||Sep 4, 1990||The Tokyo Electric Power Company Ltd.||Mobile communication system|
|US4965732||Nov 2, 1987||Oct 23, 1990||The Board Of Trustees Of The Leland Stanford Junior University||Methods and arrangements for signal reception and parameter estimation|
|US4965849||Sep 6, 1989||Oct 23, 1990||Sony Corporation||Cordless telephone|
|US4965850||Jan 23, 1989||Oct 23, 1990||Schloemer Jerry R||System for and method of assigning frequencies in a communications system with no central control of frequency allocation|
|US4972151||Oct 1, 1985||Nov 20, 1990||Hughes Aircraft Company||Steered-beam satellite communication system|
|US4989204||Feb 9, 1989||Jan 29, 1991||Nec Corporation||High throughput communication method and system for a digital mobile station when crossing a zone boundary during a session|
|US5041833||Jun 4, 1990||Aug 20, 1991||Stanford Telecommunications, Inc.||Precise satellite ranging and timing system using pseudo-noise bandwidth synthesis|
|US5052799||Jul 17, 1989||Oct 1, 1991||Thurman Sasser||Object orienting systems and systems and processes relating thereto|
|US5093924||Sep 19, 1990||Mar 3, 1992||Nippon Telegraph And Telephone Corporation||Channel assigning method in a mobile communication system|
|US5103459||Jun 25, 1990||Apr 7, 1992||Qualcomm Incorporated||System and method for generating signal waveforms in a cdma cellular telephone system|
|US5109535||Jun 14, 1989||Apr 28, 1992||Fujitsu Limited||Apparatus for transmission-reception simulation test for microwave communication|
|US5124697||Oct 16, 1989||Jun 23, 1992||Motorola, Inc.||Acknowledge-back pager|
|US5142253||May 2, 1990||Aug 25, 1992||Raytheon Company||Spatial field power combiner having offset coaxial to planar transmission line transitions|
|US5159593||Jul 2, 1990||Oct 27, 1992||Motorola, Inc.||Channel acquistion and handoff method and apparatus for a TDMA communication system|
|US5255210||Aug 3, 1992||Oct 19, 1993||The Regents Of The University Of California||Self-coherence restoring signal extraction apparatus and method|
|US5260968||Jun 23, 1992||Nov 9, 1993||The Regents Of The University Of California||Method and apparatus for multiplexing communications signals through blind adaptive spatial filtering|
|US5262789||Apr 30, 1992||Nov 16, 1993||General Electric Company||Source identification system for closely separated spatial sources|
|US5274844||May 11, 1992||Dec 28, 1993||Motorola, Inc.||Beam pattern equalization method for an adaptive array|
|US5276907||Jan 7, 1991||Jan 4, 1994||Motorola Inc.||Method and apparatus for dynamic distribution of a communication channel load in a cellular radio communication system|
|US5283540||Jul 27, 1992||Feb 1, 1994||At&T Bell Laboratories||Compact signal isolating microwave splitters/combiners|
|US5299148||May 22, 1990||Mar 29, 1994||The Regents Of The University Of California||Self-coherence restoring signal extraction and estimation of signal direction of arrival|
|US5335249||Jul 29, 1993||Aug 2, 1994||Seattle Silicon Corporation||Method and apparatus for spread spectrum communications|
|US5345596||May 26, 1993||Sep 6, 1994||Motorola, Inc.||Method and apparatus for establishing a communication link|
|US5361303||Apr 1, 1993||Nov 1, 1994||Noise Cancellation Technologies, Inc.||Frequency domain adaptive control system|
|US5367559||May 11, 1992||Nov 22, 1994||Hughes Aircraft Company||Sequential power estimation for cellular system handoff|
|US5379320||Mar 11, 1993||Jan 3, 1995||Southern California Edison Company||Hitless ultra small aperture terminal satellite communication network|
|US5387915||Nov 16, 1993||Feb 7, 1995||B. F. Goodrich Flightsystems, Inc.||Method and apparatus for detecting and decoding transponder reply signals|
|US5423072||Jul 12, 1993||Jun 6, 1995||Nec Corporation||Testing transmitter-receiver apparatus for sector cell base station|
|US5430760||Apr 4, 1994||Jul 4, 1995||Ericsson Ge Mobile Communications Inc.||Random access in mobile radio telephone systems|
|US5440281||Sep 7, 1993||Aug 8, 1995||Allen Telecom Group, Inc.||Multichannel transmitter combiners employing cavities having low output impedance|
|US5448621||Aug 2, 1993||Sep 5, 1995||Motorola, Inc.||Dynamic reallocation of spectral capacity in cellular communication systems|
|US5457812||Dec 12, 1991||Oct 10, 1995||Nokia Telecommunications Oy||Radio test loop having common combiner cable connecting transmitters, spaced at nλ/2 therealong, with receivers, via frequency converter|
|US5465399||Sep 16, 1994||Nov 7, 1995||The Boeing Company||Apparatus and method for controlling transmitted power in a radio network|
|US5471647||Apr 14, 1993||Nov 28, 1995||The Leland Stanford Junior University||Method for minimizing cross-talk in adaptive transmission antennas|
|US5475864||Jul 19, 1994||Dec 12, 1995||Nec Corporation||High-cross correlation dynamic channel assignment for sectorized cells|
|US5475868||Aug 3, 1993||Dec 12, 1995||U.S. Philips Corporation||Cellular radio system having channel evaluation and optimal channel selection via trial use of non-assigned channels|
|US5497505||Dec 17, 1993||Mar 5, 1996||Northern Telecom Limited||Call set-up and spectrum sharing in radio communication on systems with dynamic channel allocation|
|US5515378||Dec 12, 1991||May 7, 1996||Arraycomm, Inc.||Spatial division multiple access wireless communication systems|
|US5530449||Nov 18, 1994||Jun 25, 1996||Hughes Electronics||Phased array antenna management system and calibration method|
|US5530917||May 17, 1994||Jun 25, 1996||Telefonaktiebolaget Lm Ericsson||Method and a device for the utilization of channels in a radio communications system|
|US5532706||Dec 5, 1994||Jul 2, 1996||Hughes Electronics||Antenna array of radiators with plural orthogonal ports|
|US5537438||Mar 2, 1994||Jul 16, 1996||Alcatel N.V.||Method of equalizing a receive data block in a time-division multiple access communication system and receiver utilizing this method|
|US5543801||Jun 27, 1994||Aug 6, 1996||Matra Marconi Space Uk Limited||Digitally controlled beam former for a spacecraft|
|US5546090||Apr 28, 1994||Aug 13, 1996||Arraycomm, Inc.||Method and apparatus for calibrating antenna arrays|
|US5548813||Mar 24, 1994||Aug 20, 1996||Ericsson Inc.||Phased array cellular base station and associated methods for enhanced power efficiency|
|US5553074||Mar 4, 1994||Sep 3, 1996||Trustees Of Columbia University In The City Of New York||Transmission format in packet based communications|
|US5555445||Jul 15, 1994||Sep 10, 1996||Northern Telecom Limited||Method of intra-cell and inter-cell handover in a mobile communications system|
|US5557657||Sep 9, 1993||Sep 17, 1996||Hughes Aircraft Company||Handoff between overlay and underlay cells|
|US5565873||May 16, 1995||Oct 15, 1996||Northern Telecom Limited||Base station antenna arrangement|
|US5566209||Feb 10, 1994||Oct 15, 1996||Telefonaktiebolaget Lm Ericsson||Transceiver algorithms of antenna arrays|
|US5574977 *||Apr 17, 1995||Nov 12, 1996||Telefonaktiebolaget Lm Ericsson||System and method for providing priority access and channel assignment in a cellular telecommunication system|
|US5576717||May 16, 1995||Nov 19, 1996||Northern Telecom Limited||Base station antenna arrangement|
|US5592490||Jan 20, 1995||Jan 7, 1997||Arraycomm, Inc.||Spectrally efficient high capacity wireless communication systems|
|US5596625||Sep 28, 1994||Jan 21, 1997||U S West Technologies, Inc.||Method for routing emergency calls during busy interface channel conditions|
|US5603082||Dec 27, 1994||Feb 11, 1997||Nec Corporation||Channel allocation system for communication systems and an apparatus thereof|
|US5603089||Sep 21, 1995||Feb 11, 1997||Searle; Jeffrey G.||Base station antenna arrangement|
|US5606729||Jun 21, 1995||Feb 25, 1997||Motorola, Inc.||Method and apparatus for implementing a received signal quality measurement in a radio communication system|
|US5615409||Sep 25, 1995||Mar 25, 1997||Telefonaktiebolaget Lm Ericsson||Method and apparatus for transmitting and receiving signals using two classes of channels|
|US5621752||Jun 23, 1994||Apr 15, 1997||Qualcomm Incorporated||Adaptive sectorization in a spread spectrum communication system|
|US5625885||Jul 18, 1994||Apr 29, 1997||Fujitsu Limited||Mobile communication system having pagers for providing two-way data communication between a base station and mobile stations|
|US5638375||Nov 30, 1988||Jun 10, 1997||Motorola, Inc.||AGC isolation of information in TDMA systems|
|US5649287||Mar 29, 1995||Jul 15, 1997||Telefonaktiebolaget Lm Ericsson||Orthogonalizing methods for antenna pattern nullfilling|
|US5673291||Sep 14, 1994||Sep 30, 1997||Ericsson Inc.||Simultaneous demodulation and decoding of a digitally modulated radio signal using known symbols|
|US5675581||Feb 14, 1996||Oct 7, 1997||Qualcomm Incorporated||Simulating user interference in a spread spectrum communication network|
|US5678188||Sep 13, 1994||Oct 14, 1997||Sony Corporation||Emergency message communication method|
|US5684836||Jun 6, 1995||Nov 4, 1997||Mitsubishi Denki Kabushiki Kaisha||Receiver with automatic frequency control|
|US5687066||Apr 6, 1995||Nov 11, 1997||Progressive Dynamics, Inc.||Power converter with overvoltage protection|
|US5689219||Jun 27, 1995||Nov 18, 1997||Nokia Telecommunications Oy||Summing network|
|US5689502||Jun 5, 1995||Nov 18, 1997||Omnipoint Corporation||Efficient frequency division duplex communication system with interleaved format and timing adjustment control|
|US5694416||Feb 24, 1995||Dec 2, 1997||Radix Technologies, Inc.||Direct sequence spread spectrum receiver and antenna array for the simultaneous formation of a beam on a signal source and a null on an interfering jammer|
|US5726978||Jun 22, 1995||Mar 10, 1998||Telefonaktiebolaget L M Ericsson Publ.||Adaptive channel allocation in a frequency division multiplexed system|
|US5732076||Oct 26, 1995||Mar 24, 1998||Omnipoint Corporation||Coexisting communication systems|
|US5742904||Jul 8, 1996||Apr 21, 1998||Motorola, Inc.||Method of providing emergency alarm support via an alternative radio communication system|
|US5745858||Nov 8, 1994||Apr 28, 1998||Nec Corporation||Base station transmitter/receiver capable of varying composite directivity of antennas|
|US5748676||May 1, 1995||May 5, 1998||Norand Corporation||Network utilizing modified preambles that support antenna diversity|
|US5752165||Sep 14, 1994||May 12, 1998||Nokia Telecommunications Oy||Method and apparatus for comparing averages of signal levels of receivers of receiver unit for automatically providing indication of a defective receiver|
|US5774461||Sep 27, 1995||Jun 30, 1998||Lucent Technologies Inc.||Medium access control and air interface subsystem for an indoor wireless ATM network|
|US5809009||Sep 13, 1996||Sep 15, 1998||Matsushita Electric Industrial Co., Ltd.||Demodulator apparatus for digital radio communication receiver providing pseudo-coherent quadrature demodulation based on periodic estimation of frequency offset|
|US5809019||Apr 25, 1996||Sep 15, 1998||Nec Corporation||Transmisson diversity system|
|US5812090||Jun 27, 1997||Sep 22, 1998||Thomson-Csf||Method and device enabling a modem to be synchronized with an RF digital data transmitter in the presence of jammers|
|US5818918||May 31, 1996||Oct 6, 1998||Nec Corporation||Personal handy phone system|
|US5819182||Nov 13, 1995||Oct 6, 1998||Pacific Communication Sciences, Inc.||Method and apparatus for improving receiver performance in a land mobile communications system|
|US5825762||Sep 24, 1996||Oct 20, 1998||Motorola, Inc.||Apparatus and methods for providing wireless communication to a sectorized coverage area|
|US5828658||Oct 23, 1996||Oct 27, 1998||Arraycomm, Inc.||Spectrally efficient high capacity wireless communication systems with spatio-temporal processing|
|US5845212||Oct 4, 1996||Dec 1, 1998||Nec Corporation||Optimum power and handover control by cellular system mobile unit|
|US5862485||Mar 26, 1997||Jan 19, 1999||Motorola, Inc.||Method and apparatus for allocating communication resources to support priority communications in a communication system|
|US5884148||Jul 8, 1996||Mar 16, 1999||Omnipoint Corporation||Wireless local loop system and method|
|US5887038||Apr 22, 1997||Mar 23, 1999||Golden; Glenn David||Adaptive antenna array processing arrangement using a combined coherent and constant-modulus reference signal|
|US5905721||Sep 26, 1996||May 18, 1999||Cwill Telecommunications, Inc.||Methods for channel estimation and signal detection of CDMA signals|
|US5909470||Oct 11, 1996||Jun 1, 1999||Arraycomm, Inc.||Method and apparatus for decision directed demodulation using antenna arrays and spatial processing|
|US5914946||Nov 8, 1996||Jun 22, 1999||Lucent Technologies Inc.||TDM-based fixed wireless loop system|
|US5930243||Oct 11, 1996||Jul 27, 1999||Arraycomm, Inc.||Method and apparatus for estimating parameters of a communication system using antenna arrays and spatial processing|
|US5933421||Feb 6, 1997||Aug 3, 1999||At&T Wireless Services Inc.||Method for frequency division duplex communications|
|US5937355||Aug 8, 1997||Aug 10, 1999||Telefonaktiebolaget Lm Ericsson (Publ)||Emergency call handling in a cellular telecommunication system|
|US5955992||Feb 12, 1998||Sep 21, 1999||Shattil; Steve J.||Frequency-shifted feedback cavity used as a phased array antenna controller and carrier interference multiple access spread-spectrum transmitter|
|US5970394||Oct 24, 1997||Oct 19, 1999||Internet Mobility Corporation||Method of detecting damaged cellular telephone facilities|
|US5973638||Jan 30, 1998||Oct 26, 1999||Micronetics Wireless, Inc.||Smart antenna channel simulator and test system|
|US5999826||May 13, 1997||Dec 7, 1999||Motorola, Inc.||Devices for transmitter path weights and methods therefor|
|US6005854||Aug 8, 1997||Dec 21, 1999||Cwill Telecommunication, Inc.||Synchronous wireless access protocol method and apparatus|
|US6009124||Sep 22, 1997||Dec 28, 1999||Intel Corporation||High data rate communications network employing an adaptive sectored antenna|
|US6018317||Nov 22, 1996||Jan 25, 2000||Trw Inc.||Cochannel signal processing system|
|US6018555||May 5, 1998||Jan 25, 2000||Intermec Ip Corp.||Network utilizing modified preambles that support antenna diversity|
|US6018643||Jun 3, 1997||Jan 25, 2000||Texas Instruments Incorporated||Apparatus and method for adaptively forming an antenna beam pattern in a wireless communication system|
|US6023203||Oct 14, 1998||Feb 8, 2000||Arraycomm, Inc.||RF test fixture for adaptive-antenna radio systems|
|US6061553||Jan 2, 1998||May 9, 2000||Kabushiki Kaisha Toshiba||Adaptive antenna|
|US6064865||Mar 1, 1999||May 16, 2000||Ford Motor Company||Proportional diversity radio receiver system with dynamic noise-controlled antenna phasers|
|US6067324||Jun 30, 1998||May 23, 2000||Motorola, Inc.||Method and system for transmitting and demodulating a communications signal using an adaptive antenna array in a wireless communication system|
|US6108323 *||Nov 26, 1997||Aug 22, 2000||Nokia Mobile Phones Limited||Method and system for operating a CDMA cellular system having beamforming antennas|
|US6108565||Sep 15, 1997||Aug 22, 2000||Adaptive Telecom, Inc.||Practical space-time radio method for CDMA communication capacity enhancement|
|US6131016||Aug 27, 1997||Oct 10, 2000||At&T Corp||Method and apparatus for enhancing communication reception at a wireless communication terminal|
|US6154661||Dec 10, 1997||Nov 28, 2000||Arraycomm, Inc.||Transmitting on the downlink using one or more weight vectors determined to achieve a desired radiation pattern|
|US6185412 *||May 20, 1999||Feb 6, 2001||Nokia Telecommunications Oy||Procedure and system for ensuring emergency communication in a wireless local loop environment|
|US6208865||Aug 7, 1998||Mar 27, 2001||Samsung Electronics Co., Ltd||Cellular telephone system which increases efficiency of reserved channel usage|
|US6292664 *||Feb 6, 1998||Sep 18, 2001||Telefon Aktiebolaget Lm Ericsson (Publ)||Channel quality in wireless communications|
|US6332073 *||Oct 19, 1998||Dec 18, 2001||Ericsson Inc.||Emergency number dialing from a fixed cellular terminal|
|EP0639035B1||Jul 21, 1994||Oct 23, 2002||Nortel Networks Limited||Base station antenna arrangement|
|EP0665665B1||Jan 13, 1995||May 16, 2001||Thomson-Csf||Method and device enabling a modem to synchronize on a transmitter of digital data via a radio channel in the presence of interferences|
|EP0713261B1||Nov 18, 1995||Feb 13, 2002||Hughes Electronics Corporation||Phased array antenna management system and calibration method|
|EP0729285B1||Feb 23, 1996||Apr 28, 2004||Alcatel||Carrier frequency allocation in a SDMA radio system|
|EP0777400A2||Aug 20, 1996||Jun 4, 1997||Trw Inc.||Personal beam cellular communication system|
|EP0786914B1||Nov 4, 1996||Mar 17, 2004||Motorola Ltd||A space division multiple access radio communication system and method for allocating channels therein|
|GB2237706A||Title not available|
|GB2295524A||Title not available|
|GB2313261B||Title not available|
|1||Acampora et al., "A New Adaptive MAC Layer Protocol for Wireless ATM Networks in Harsh Fading and Interference Environments", 1997 IEEE, pp. 410-415.|
|2||Agee, "Blind Separation and Capture of Communication Signals Using a Multitarget Constant Modulus Beamformer", Oct. 7, 1989 Proc. IEEE Military Communications Conference, vol. 2, pp. 1-12.|
|3||Aschied et al., "An All Digital Receiver Architecture for Bandwidth Efficient Transmission at High Data Rates", 1989, IEEE Transactions on Communications, vol. 37, No. 8, pp. 804-813.|
|4||Christof Farsakh et al., Channel Allocation and Downlink Beamforming in a SDMA Mobile Radio System, 1995 IEEE, pp. 687-691.|
|5||Derek Gerlach et al., Base Station Transmitter Antenna with Mobile to Base Feedback, 1993 IEEE, pp. 1432-1436, http://www.stanford.edu/.about.apaulraj/paulraj_publist.html.|
|6||Farsakh et al.,"A Real Time Downlink Channel Allocation Scheme for an SDMA Mobile Radio System," IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, vol. 3, Oct. 18, 1996, pp. 1215-1220.|
|7||Franks, Synchronization Subsystems: Analysis and Design:, 1981, Digital Communications Satellite/Earth Station Engineering, pp. 294-335.|
|8||Friedlander et al., "Direction Finding for Wideband Signals Using an Interpolated Array", 1991, IEEE Publication, pp. 583-587.|
|9||Friedlander, "Direction Finding Using an Interpolated Array", Apr. 3, 1990, International Conference on Acoustics, Speech, and Signal Processing, vol. 5, pp. 2951-2954.|
|10||Ganz et al., "A Data-Derived Reference Signal Technique for Adaptive Arrays", IEEE Transactions on Communications, vol. 37, No. 9, Sep. 1989, pp. 975-983.|
|11||Iltis et al., A digital DS Spread-Spectrum Receiver With Joint Channel and Doppler Shift Esitamation:, IEEE Transactions on Communications, vol. 39, No. 8, Aug. 1981, pp. 1255-1267.|
|12||Krishnamurthy et al., "Polling Based Media Access Protocols For Use With Smart Adaptive Array Antennas", 1998 IEEE, pp. 337-344.|
|13||Lee et al., "Decision Directed Carrier Recovery-Chapter 16: Carrier Recovery", 1994 Digital Communications, 2nd Edition Kluwer Academic Pub., pp. 725-736.|
|14||Lee et al., "Decision Directed Carrier Recovery—Chapter 16: Carrier Recovery", 1994 Digital Communications, 2nd Edition Kluwer Academic Pub., pp. 725-736.|
|15||Lee et al., "Decision Directed Carrier Recovery-Chapter 17: Timing Recovery", 1994 Digital Communications, 2nd Edition, Kluwer Academic Pub., pp. 737-764.|
|16||Lee et al., "Decision Directed Carrier Recovery—Chapter 17: Timing Recovery", 1994 Digital Communications, 2nd Edition, Kluwer Academic Pub., pp. 737-764.|
|17||Lundell et al., "Applications of the Constant Modulus Adaptive Beamformer to Constant and Non-Constant Modulus Signals,", Proceedings, 1998 Asilomar Conference on Signals, Systems, and Computers (ACSSC-1998), pp. 432-436.|
|18||Muhamed et al., "Direction of Arrival Estimation Using Antenna Arrays", 1996, The Bradley Dept. of Electrical Engineering, Mobile and Portable Radio Research Group, Section 3.8, pp. 64-71.|
|19||Otterson, B "Array Processing for wireless communications," Proc. 8th IEEE Signal Processing Workshop on Statistical Signal and ArrayProcessing, Jun. 1996, pp. 466-473.|
|20||Papadias et al., "A Space-Time Constant Modulus Algorithm for SDMA Systems", 1996, Proceedings, IEEE 46th Vehicular Technology Conference, pp. 86-90.|
|21||Rashid-Farrokhi et al."Downlink and Uplink Capacity Enhancement in Power Controlled Cellular Systems", Proceeding, 1997 IEEE 47th Vehicular Technology Conference, vol. 2, May 1997, pp. 647-651.|
|22||Rashid-Farrokhi et al.,"Downlink Power Control and Base Station Assignment", IEEE Communications Letters, vol. 1, No. 4, Jul. 1997, pp. 102-104.|
|23||Rashid-Farrokhi et al.,"Joint Power Control and Beamforming for Capacity Improvement in Wireless Networks With Antenna Array", 1996 IEEE GLOBECOM 1996, vol. 1, pp. 555-559.|
|24||Rashid-Farrokhi et al.,"Transmit Beamforming for Cellular Communications Systems", Conference on Information Sciences and Systems, CISS-97; Mar. 1997, 4 pages.|
|25||Rashid-Farrokhi et al.,"Transmit Diversity and Equalization for Power Controlled Wireless Networks", Conference Record 31st Asilomar Conference on Signals, Systems and Computers, vol. 1, Nov. 1997, pp. 620-624.|
|26||Swidlehurst et al.,"Analysis of a Decision Directed Beamformer", IEEE Transactions on Signal Processing, vol. 43, No. 12, Dec. 1995, pp. 2920-2927.|
|27||Talwar et al., "Recursive Algorithms for Estimating Multiple Co-Channel Digital Signals Received at an Antenna Array", Proc. Fifth Annual IEEE Dual Use Technologies and Applications Conference.|
|28||Talwar et al., Blind Estimation of Multiple Co-Channel Digital Signal Arriving at an Antenna Array:, 1993, Proc. 27th Asilomar Conference on Signals, Systems, and Computers, vol. 1, pp. 342-349.|
|29||USPTO; PCt Serial No. US98/25364; PCT Search Report, May 11, 1999.|
|30||Vander Veen et al., "A Constant Modulus Factorization Technique for Smart Antenna Applications in Mobile Communications", SPIE 1994 "Advanced Signal Processing Algorithms, Architectures, and Implementations V", vol. 2296, pp. 230-241.|
|31||Xu et al.,"Throughput Multiplication of Wireless LANs for Multimedia Services: SDMA Protocol Design", 1994, IEEE, pp. 1326-1332.|
|32||Zhang et al.,"Performance of a Modified Polling Strategy for Broadband Wireless LANs in a Harsh Fading Environment", 1991, GLOBECOM 1991, pp. 1141-1146.|
|U.S. Classification||455/404.1, 455/512, 455/452.1|
|International Classification||H04M9/00, H04B7/00, H04W4/22, H04W72/04|
|Cooperative Classification||H04W4/22, H04W84/14, H04W72/10, H04W76/066, H04W76/02, H04W72/04, H04W76/007|
|Feb 14, 2007||AS||Assignment|
Owner name: ARRAYCOMM, INC., CALIFORNIA
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:UHLIK, CHRISTOPHER H.;TROTTS, MITCHELL D.;ALDER, LAWRENCE J.;REEL/FRAME:018889/0054
Effective date: 19990719
Owner name: DURHAM LOGISTICS, LLC, NEVADA
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:ARRAYCOMM, INC.;REEL/FRAME:018889/0113
Effective date: 20041206
|Jul 12, 2011||CC||Certificate of correction|
|Dec 29, 2014||FPAY||Fee payment|
Year of fee payment: 12
|Oct 2, 2015||AS||Assignment|
Owner name: XYLON LLC, NEVADA
Free format text: MERGER;ASSIGNOR:DURHAM LOGISTICS LLC;REEL/FRAME:036743/0770
Effective date: 20150813