Patent Publication Number: US-2005124334-A1

Title: Wireless network and wireless mobile stations using variable fade timer value

Description:
CROSS-REFERENCE TO RELATED APPLICATION AND CLAIM OF PRIORITY  
      The present invention is related to that disclosed in U.S. Provisional Patent Application Ser. No. 60/527,129, entitled “Wireless Networks and Wireless Mobile Stations Using Variable Fade Timer Value” and filed on Dec. 5, 2003. U.S. Provisional Patent Application Ser. No. 60/527,129 is assigned to the assignee of the present application. The subject matter disclosed in U.S. Provisional Patent Application Ser. No. 60/527,129 is hereby incorporated by reference into the present disclosure as if fully set forth herein. The present invention hereby claims priority under 35 U.S.C. §119(e) to U.S. Provisional Patent Application Ser. No. 60/527,129.  
    
    
     TECHNICAL FIELD OF THE INVENTION  
      The present invention is directed, in general, to wireless networks and, more specifically, to CDMA2000 wireless network base stations and wireless mobile stations that use a variable mobile station (MS) fade timer value that varies according to the type of voice or data service.  
     BACKGROUND OF THE INVENTION  
      Businesses and consumers use a wide variety of fixed and mobile wireless terminals, including cell phones, pagers, Personal Communication Services (PCS) systems, and fixed wireless access devices (i.e., vending machine with cellular capability). Wireless service providers create new markets for wireless devices and expand existing markets by making wireless devices and services cheaper and more reliable. Wireless service providers accomplish this, in part, by implementing new services, including digital data services that provide, for example, web browsing and e-mail capabilities.  
      For many digital data services, it is essential that calls (or data sessions) be set up and broken down as quickly as possible in order to minimize the use of base station resources. The decision of when to break down a call is controlled by a fader timer value established by the base station. In a wireless network, the propagation conditions required for good quality signal communication between base stations and mobile stations cannot always be met due to the irregularities in cell coverage and rapid signal loss. As a result, base stations and mobile stations typically have fade timers that are used to set an amount of time for which the base stations and mobile stations will wait while no good quality signals are being received before declaring a call failure and dropping the call.  
      Conventional wireless networks, including code division multiple access (CDMA) wireless networks, generally have fade timers programmed to 5 seconds, while conventional base stations generally have fade timers programmed to 10 seconds. The fade timer controls the transmitters in the mobile stations and base stations. During a call, a mobile station turns off its transmitter circuitry and resets the fade timer. The receiver circuitry of the mobile station then monitors the traffic channel to see if two consecutive good frames are received before the fade timer expires.  
      If two consecutive good frames are received, the mobile station turns on the transmitter circuitry and responds, if necessary. If two consecutive good frames are not received before the 5-second fade timer expires, then the mobile station drops the call and the receiver circuitry begins monitoring the paging channel to see if a new call has been received.  
      The 5-second fade timer value used in the prior art wireless networks was designed (or selected) with conventional or legacy voice services in mind. The 5-second fade timer value was not selected with fast setup packet data and voice services in mind. As more and more data users load a wireless network, the fade timer requirement of 5 seconds may hamper the performance of the wireless network.  
      Therefore, there is a need in the art for improved wireless networks and improved wireless terminals for accessing the wireless networks. In particular, there is a need for CDMA2000 wireless network base stations and wireless mobile stations that are not hampered by the use of 5-second fade timer values.  
     SUMMARY OF THE INVENTION  
      The present invention overcomes the shortcomings of conventional wireless networks by implementing a variable mobile station (MS) fade timer value. According to the principles of the present invention, the value of the variable MS fade timer value is controlled by the base station and depends on the type of service (packet data, voice, etc.) being used by the mobile station.  
      To address the above-discussed deficiencies of the prior art, it is a primary object of the present invention to provide a base station for use in a wireless network capable of communicating with a plurality of mobile stations in a coverage area of the wireless network. According to an advantageous embodiment of the present, the base station is capable of transmitting a variable fade timer value to a first mobile station, wherein the variable fade timer value may be modified according to a service being used by the mobile station.  
      According to one embodiment of the present invention, the base station comprises a fade timer controller capable of determining whether the service being used by mobile station is one of i) a voice service and ii) a data service.  
      According to another embodiment of the present invention, the fade timer controller, in response to a determination that the mobile station is using a data service, causes the base station to transmit to the mobile station a variable fade timer value that is shorter than a fade timer value associated with a voice service.  
      According to still another embodiment of the present invention, the base station transmits the variable fade timer value to the mobile station in a forward control channel message.  
      According to yet another embodiment of the present invention, the forward control channel message is a special-purpose message.  
      According to a further embodiment of the present invention, the wireless network comprises a CDMA2000 network and the forward control channel message is one of an Extended Channel Assignment message, a Universal Hand-off Direction message, or a Service Connect message.  
      It is another primary object of the present invention to provide a mobile station capable of accessing a wireless network comprising a plurality of base stations that communicate with mobile stations in a coverage area of the wireless network. The mobile station comprises a programmable fade timer and the mobile station is capable of receiving from a first one of the plurality of base stations a variable fade timer value for use by the programmable fade timer.  
      Before undertaking the DETAILED DESCRIPTION OF THE INVENTION below, it may be advantageous to set forth definitions of certain words and phrases used throughout this patent document: the terms “include” and “comprise,” as well as derivatives thereof, mean inclusion without limitation; the term “or,” is inclusive, meaning and/or; the phrases “associated with” and “associated therewith,” as well as derivatives thereof, may mean to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, or the like; and the term “controller” means any device, system or part thereof that controls at least one operation, such a device may be implemented in hardware, firmware or software, or some combination of at least two of the same. It should be noted that the functionality associated with any particular controller may be centralized or distributed, whether locally or remotely. Definitions for certain words and phrases are provided throughout this patent document, those of ordinary skill in the art should understand that in many, if not most instances, such definitions apply to prior, as well as future uses of such defined words and phrases.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      For a more complete understanding of the present invention and its advantages, reference is now made to the following description taken in conjunction with the accompanying drawings, in which like reference numerals represent like parts:  
       FIG. 1  illustrates an exemplary wireless network, which uses a variable mobile station (MS) fade timer value according to the principles of the present invention;  
       FIG. 2  illustrates in greater detail an exemplary base station that controls a variable MS fade timer value according to the principles of the present invention; and  
       FIG. 3  illustrates in greater detail an exemplary wireless mobile station that uses a variable MS fade timer value according to the principles of the present invention.  
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
       FIGS. 1 through 3 , discussed below, and the various embodiments used to describe the principles of the present invention in this patent document are by way of illustration only and should not be construed in any way to limit the scope of the invention. Those skilled in the art will understand that the principles of the present invention may be implemented in any suitably arranged wireless network.  
       FIG. 1  illustrates exemplary wireless network  100 , which uses a variable mobile station (MS) fade timer value according to the principles of the present invention. Wireless network  100  comprises a plurality of cell sites  121 - 123 , each containing one of the base stations, BS  101 , BS  102 , or BS  103 . Base stations  101 - 103  communicate with a plurality of mobile stations (MS)  111 - 114  over code division multiple access (CDMA) channels according to, for example, the IS-2000 standard (i.e., CDMA2000). In an advantageous embodiment of the present invention, mobile stations  111 - 114  are capable of receiving data traffic and/or voice traffic on two or more CDMA channels simultaneously. Mobile stations  111 - 114  may be any suitable wireless devices (e.g., conventional cell phones, PCS handsets, personal digital assistant (PDA) handsets, portable computers, telemetry devices) that are capable of communicating with base stations  101 - 103  via wireless links.  
      The present invention is not limited to mobile devices. The present invention also encompasses other types of wireless access terminals, including fixed wireless terminals. For the sake of simplicity, only mobile stations are shown and discussed hereafter. However, it should be understood that the use of the term “mobile station” in the claims and in the description below is intended to encompass both truly mobile devices (e.g., cell phones, wireless laptops) and stationary wireless terminals (e.g., a machine monitor with wireless capability).  
      Dotted lines show the approximate boundaries of cell sites  121 - 123  in which base stations  101 - 103  are located. The cell sites are shown approximately circular for the purposes of illustration and explanation only. It should be clearly understood that the cell sites may have other irregular shapes, depending on the cell configuration selected and natural and man-made obstructions.  
      As is well known in the art, each of cell sites  121 - 123  is comprised of a plurality of sectors, where a directional antenna coupled to the base station illuminates each sector. The embodiment of  FIG. 1  illustrates the base station in the center of the cell. Alternate embodiments may position the directional antennas in corners of the sectors. The system of the present invention is not limited to any particular cell site configuration.  
      In one embodiment of the present invention, each of BS  101 , BS  102  and BS  103  comprises a base station controller (BSC) and one or more base transceiver subsystem(s) (BTS). Base station controllers and base transceiver subsystems are well known to those skilled in the art. A base station controller is a device that manages wireless communications resources, including the base transceiver subsystems, for specified cells within a wireless communications network. A base transceiver subsystem comprises the RF transceivers, antennas, and other electrical equipment located in each cell site. This equipment may include air conditioning units, heating units, electrical supplies, telephone line interfaces and RF transmitters and RF receivers. For the purpose of simplicity and clarity in explaining the operation of the present invention, the base transceiver subsystems in each of cells  121 ,  122  and  123  and the base station controller associated with each base transceiver subsystem are collectively represented by BS  101 , BS  102  and BS  103 , respectively.  
      BS  101 , BS  102  and BS  103  transfer voice and data signals between each other and the public switched telephone network (PSTN) (not shown) via communication line  131  and mobile switching center (MSC)  140 . BS  101 , BS  102  and BS  103  also transfer data signals, such as packet data, with the Internet (not shown) via communication line  131  and packet data server node (PDSN)  150 . Packet control function (PCF) unit  190  controls the flow of data packets between base stations  101 - 103  and PDSN  150 . PCF unit  190  may be implemented as part of PDSN  150 , as part of MSC  140 , or as a stand-alone device that communicates with PDSN  150 , as shown in  FIG. 1 . Line  131  also provides the connection path for control signals transmitted between MSC  140  and BS  101 , BS  102  and BS  103  that establish connections for voice and data circuits between MSC  140  and BS  101 , BS  102  and BS  103 .  
      Communication line  131  may be any suitable connection means, including a T1 line, a T3 line, a fiber optic link, a network packet data backbone connection, or any other type of data connection. Line  131  links each vocoder in the BSC with switch elements in MSC  140 . The connections on line  131  may transmit analog voice signals or digital voice signals in pulse code modulated (PCM) format, Internet Protocol (IP) format, asynchronous transfer mode (ATM) format, or the like.  
      MSC  140  is a switching device that provides services and coordination between the subscribers in a wireless network and external networks, such as the PSTN or Internet. MSC  140  is well known to those skilled in the art. In some embodiments of the present invention, communications line  131  may be several different data links where each data link couples one of BS  101 , BS  102 , or BS  103  to MSC  140 .  
      In the exemplary wireless network  100 , MS  111  is located in cell site  121  and is in communication with BS  101 . MS  113  is located in cell site  122  and is in communication with BS  102 . MS  114  is located in cell site  123  and is in communication with BS  103 . MS  112  is also located close to the edge of cell site  123  and is moving in the direction of cell site  123 , as indicated by the direction arrow proximate MS  112 . At some point, as MS  112  moves into cell site  123  and out of cell site  121 , a hand-off will occur.  
      According to the principles of the present invention, wireless network  100  and the mobile stations accessing wireless network  100  implement variable mobile station (MS) fade timer values that are controlled by the base station. The selected fade timer value depends on the type of service (packet data, voice, etc.) being used by the mobile station. Hence, for data services, a base station specifies the value the base station wants to use for the mobile station (MS) fade timer. Generally, the MS fade timer value for data services is expected to be less than the conventional 5 second value used for voice services.  
       FIG. 2  illustrates in greater detail exemplary base station (BS)  101 , which controls a variable MS fade timer value according to the principles of the present invention. Base station  101  comprises base station controller (BSC)  210  and base transceiver station (BTS)  220 . Base station controllers and base transceiver stations were described previously in connection with  FIG. 1 . BSC  210  manages the resources in cell site  121 , including BTS  220 . BTS  120  comprises BTS controller  225 , channel controller  235  (which contains representative channel element  240 ), transceiver interface (IF)  245 , RF transceiver unit  250 , antenna array  255 , and fade timer controller  260 .  
      BTS controller  225  comprises processing circuitry and memory capable of executing an operating program that controls the overall operation of BTS  220  and communicates with BSC  210 . Under normal conditions, BTS controller  225  directs the operation of channel controller  235 , which contains a number of channel elements, including channel element  240 , that perform bi-directional communications in the forward channel and the reverse channel. A “forward” channel refers to outbound signals from the base station to the mobile station and a “reverse” channel refers to inbound signals from the mobile station to the base station. Transceiver IF  245  transfers the bi-directional channel signals between channel controller  240  and RF transceiver unit  250 .  
      Antenna array  255  transmits forward channel signals received from RF transceiver unit  250  to mobile stations in the coverage area of BS  101 . Antenna array  255  also sends to transceiver  250  reverse channel signals received from mobile stations in the coverage area of BS  101 . In a preferred embodiment of the present invention, antenna array  255  is multi-sector antenna, such as a three-sector antenna in which each antenna sector is responsible for transmitting and receiving in a 120° arc of coverage area. Additionally, transceiver  250  may contain an antenna selection unit to select among different antennas in antenna array  255  during both transmit and receive operations.  
      According to the principles of the present invention, fade timer controller  260  is capable of adjusting the fade timer value used by the mobile station (e.g., MS  111 ) depending on the type of service (packet data, voice, etc.) being used by the mobile station. For data services, fade timer controller  260  specifies a value for the mobile station (MS) fade timer. Fade timer controller  260  may set (or reset) the variable fade timer value at the start of a data session or during the data session as data traffic levels change, as a result of a handoff, or if the mobile station invokes a new data service.  
      According to the principles of the present invention, fade timer controller  260  may assign a variable MS fade timer value to a mobile station using, for example, one or more of the Extended Channel Assignment message (ECAM), the Universal Handoff Direction message (UHDM), and the Service Connect message (SCM). Alternatively, fade timer controller  260  may assign a variable MS fade timer value to a mobile station using a special-purpose forward channel message. If fade timer controller  260  does not specify a variable MS fade timer value in any one of the ECAM, UDHM or SCM, then the mobile station may use the default timer value of 5 seconds.  
       FIG. 3  illustrates in greater detail exemplary wireless mobile station  111 , which uses a variable MS fade timer value according to the principles of the present invention. Wireless mobile station  111  comprises antenna  305 , radio frequency (RF) transceiver  310 , transmit (TX) processing circuitry  315 , microphone  320 , and receive (RX) processing circuitry  325 . MS  111  also comprises speaker  330 , main processor  340 , input/output (I/O) interface (IF)  345 , keypad  350 , display  355 , memory  360 , and programmable fade timer  370 . Memory  360  stores basic operating system (OS) program  361  and Fade Timer Value  362 .  
      Radio frequency (RF) transceiver  310  receives from antenna  305  an incoming RF signal transmitted by a base station of wireless network  100 . Radio frequency (RF) transceiver  310  down-converts the incoming RF signal to produce an intermediate frequency (IF) or a baseband signal. The IF or baseband signal is sent to receiver (RX) processing circuitry  325  that produces a processed baseband signal by filtering, decoding, and/or digitizing the baseband or IF signal. Receiver (RX) processing circuitry  325  transmits the processed baseband signal to speaker  330  (i.e., voice data) or to main processor  340  for further processing (e.g., web browsing).  
      Transmitter (TX) processing circuitry  315  receives analog or digital voice data from microphone  320  or other outgoing baseband data (e.g., web data, e-mail, interactive video game data) from main processor  340 . Transmitter (TX) processing circuitry  315  encodes, multiplexes, and/or digitizes the outgoing baseband data to produce a processed baseband or IF signal. Radio frequency (RF) transceiver  310  receives the outgoing processed baseband or IF signal from transmitter (TX) processing circuitry  315 . Radio frequency (RF) transceiver  310  up-converts the baseband or IF signal to a radio frequency (RF) signal that is transmitted via antenna  305 .  
      In an advantageous embodiment of the present invention, main processor  340  is a microprocessor or microcontroller. Memory  360  is coupled to main processor  340 . According to an advantageous embodiment of the present invention, part of memory  360  comprises a random access memory (RAM) and another part of memory  360  comprises a Flash memory, which acts as a read-only memory (ROM).  
      Main processor  340  executes basic operating system (OS) program  361  stored in memory  360  in order to control the overall operation of wireless mobile station  111 . In one such operation, main processor  340  controls the reception of forward channel signals and the transmission of reverse channel signals by radio frequency (RF) transceiver  310 , receiver (RX) processing circuitry  325 , and transmitter (TX) processing circuitry  315 , in accordance with well-known principles.  
      Main processor  340  is capable of executing other processes and programs resident in memory  360 . Main processor  340  can move data into or out of memory  360 , as required by an executing process. Main processor  340  is also coupled to I/O interface  345 . I/O interface  345  provides mobile station  111  with the ability to connect to other devices, such as laptop computers and handheld computers. I/O interface  345  is the communication path between these accessories and main controller  340 .  
      Main processor  340  is also coupled to keypad  350  and display unit  355 . The operator of mobile station  111  uses keypad  350  to enter data into mobile station  111 . Display  355  may be a liquid crystal display capable of rendering text and/or at least limited graphics from web sites. Alternate embodiments may use other types of displays.  
      Main processor  340  also controls and monitors programmable fade timer  370 . Main processor  340  receives forward control channel messages (e.g., ECAM, UDHM or SCM) transmitted by BS  101  from RX processing circuitry  325 . These control channel messages may include a variable fade timer value that main processor  340  stores in Fade Timer Value  362 . If BS  101  does not transmit a variable MS fade timer value, then main processor  360  may use a default timer value of 5 seconds.  
      Main processor  340  enables programmable fade timer  370  when MS  111  starts receiving bad frames. When MS  111  receives consecutive bad frames, main processor  340  disables the transmitter circuitry in RF transceiver  310 . The time period for which main processor  340  disables the transmitter circuitry depends on the base station-selected value stored in Fade Timer Value  370 . During handoffs, if MS  111  goes from one base station to another, the timer value changes according to the new timer value specified by the target base station in the UHDM/GHDM.  
      The present invention improves the performance of packet data calls. When the mobile station is engaged in a packet data call, using a typical fade timer value of 5 seconds has significant drawbacks. It degrades the performance of the packet data call, since the mobile station must wait 5 seconds before determining a call failure. Using the present invention, the mobile station determines a call failure in a shorter period of time and reconnects to a new traffic channel more rapidly.  
      Although the present invention has been described with an exemplary embodiment, various changes and modifications may be suggested to one skilled in the art.