WO2000019643A1

WO2000019643A1 - A terminal unit and a method for locating a terminal unit

Info

Publication number: WO2000019643A1
Application number: PCT/US1999/020969
Authority: WO
Inventors: Steven Elliot King; Warren Reif; John Douglas Reed
Original assignee: Motorola Inc.
Priority date: 1998-09-28
Filing date: 1999-09-09
Publication date: 2000-04-06
Also published as: TW429730B

Abstract

A method for determining the optimal location of a receiver in a fixed wireless system. The method comprises choosing an initial locating (304), measuring the received signal level (306), checking if a threshold level is exceeded (308), if the signal is not above a threshold relocating (310) the receiver, and remeasuring the power level (306), if the signal is above the threshold level, measuring the ratio of pilot power to total power (312), checking if the ratio is at a maximum level (314), if not relocating the receiver (316), and starting the method again, if the ratio is at a maximum level (314), halting the process with the determination that the location is optimal.

Description

A TERMINAL UNIT AND A METHOD FOR LOCATING A TERMINAL UNIT

Field of the Invention

The present invention relates generally to wireless communication systems, and more particularly to a terminal unit and method for locating a terminal unit in a wireless communication system.

Background of the Invention

Wireless communication systems are well known. A common example of a wireless communication system is a cellular radiotelephone communication system, which is commonly viewed as being a mobile communication system. That is, a cellular communication system offers its user's great flexibility in moving about while using the system, with the user's cellular telephone being a hand-held or vehicle mounted device ("mobile station"). These systems provide communication services utilizing radio frequency transmission techniques between land based radio transceiver stations, or base stations, and mobile radio transceivers, or mobiles. Each of the base stations and the mobile stations thus include a radio transceiver for communicating voice, data, or other information utilizing a communication resource, i.e., a radio link, and a standard communication protocol. For example, several such protocols for cellular radiotelephony are the Narrowband Advanced Mobile Phone System (NAMPS), the Advanced Mobile Phone System (AMPS), the Global System for Mobile Communications (GSM), the Time Division Multiple Access (TDMA), or the Code Division Multiple Access (CDMA) protocols. A feature of certain of these protocols, and the CDMA protocol in particular, is an ability to simultaneously provide communications services to a mobile station from a number of base stations in the communication system. This feature is sometimes referred to as soft or softer handoff (" soft handoff" ) in that communication services are seemlessly provided to the mobile station as it moves through the various cells of the communication system by the mobile station being continuously linked to one or more base stations. The need for providing a soft handoff is determined based in part upon an ability of the mobile station to receive signals, subject to multi-path, fading, interference, etc., from the various base stations. Of course, these conditions are dynamic in that the mobile station is moving through the system and are thus continuously analyzed and evaluated and the soft handoff status revised. The benefits of wireless communication systems technology has not been limited to mobile applications. As wireless communication systems do not require land line wiring to each termination point, the technology offers an ability to provide communication services in remote areas without the construction of a traditional, land line telephone network infrastructure. Instead, one or more base stations are constructed in an area as required to provide wireless communication services in the area. Users then install within their homes, businesses, etc., fixed wireless terminal units ("terminal unit"), which communicate via radio frequency links with the base stations in accordance with one or more communication protocols. The terminal units typically couple to a traditional telephone, which to the user functions no differently than a traditional land line telephone. Proper positioning of the terminal unit within the structure is important to the reception of radio communication signals, and hence, to good quality communication services. An improperly positioned terminal unit may experience significantly degraded communication quality leading to dissatisfied customers and increased numbers of service calls to the system operator. The problem of properly locating the terminal unit lies with the many factors that effect the quality of the received radio signals including interference, fading, multi-path, etc.

In an attempt to ensure a terminal unit is properly located within a structure, it is known to use received signal strength indicator (RSSI) information. The RSSI information provides the installer with an indication of the strength of a particular radio frequency signal received at the terminal unit. In theory, a strong RSSI indication should yield good quality communication services. However, RSSI provides only an indication of the strength of a received signal, including any interference or noise from extraneous sources such as other base stations operating in the area that may be contained in the signal, and is therefore not a true indication of the quality of the signals received. Thus, even if the reported RSSI value is quite high, communication channels with the radio signals, such as pilot, page, sync and traffic channels in a CDMA system, may not be useable. An additional consideration, from the system operators perspective, results from the effect soft handoff conditions have on system capacity. If the location of the terminal unit causes it to be frequently, but unnecessarily, in soft handoff, the capacity of the wireless communication system as a whole is unnecessarily reduced. The RSSI information, however, does not inform the terminal unit installer whether a particular location will cause frequent soft handoff conditions.

Thus, there is a need for an improved method and apparatus for locating a terminal unit in a wireless communication system.

Brief Description of the Drawings

FIG. 1 is a block diagram of a wireless communication system which may advantageously benefit from the method and apparatus of the present invention.

FIG. 2 is a block diagram of an alternate configuration of a wireless communication system which again may benefit from the method and apparatus of the present invention. FIG. 3 is a schematic diagram of a fixed wireless terminal unit located within a structure in accordance with a preferred embodiment of the present invention.

FIG. 4 is a flow chart illustrating a method of locating a terminal unit in accordance with a preferred embodiment of the present invention.

FIG. 5 is a flow chart further illustrating the method shown in FIG. 4. FIG. 6 is schematic diagram illustrating a terminal unit location with respect to operating base stations within a wireless communication system, the terminal unit being located in accordance with the preferred embodiments of the present invention.

FIG. 7 is a chart illustrating evaluation of measured signal characteristics in accordance with a preferred embodiment of the present invention. FIG. 8 is a is a perspective illustration of a terminal unit in accordance with a preferred embodiment of the present invention.

FIG. 9 is a block diagram illustrating functional elements of a terminal unit in accordance with a preferred embodiment of the present invention. Detailed Description of the Preferred Embodiments

The present invention is described in terms of several preferred embodiments, and particularly, in terms of a wireless communication system providing service to a plurality of fixed wireless terminal units (" terminal units" ) and operating in accordance with the TIA/EIA interim Standard IS-95A, Mobile Station-Base Station Compatibility Standards or Dual-Mode Wideband Spread Spectrum Cellular Systems, Telecommunications Industry Association, Washington, D.C. July 1993 (IS-95A), and all addenda and revisions thereto, including but not limited to TIA Telecommunications Systems Bulletin: Support for 14.4 kbps Data Rate and PCS Interaction for Wideband Spread Spectrum Cellular Systems, ("the Bulletin"), February 1996, and TIA/EIA Interim Standard IS-96, (IS-96), the disclosures of each of which are hereby expressly incorporated herein by reference. Another communication system using CDMA channelization is described in TIA/EIA Interim Standard IS-99, Data Services Option Standard for Wideband Spread Spectrum Digital Cellular Systems, (IS-99). Of course, the described preferred embodiments are intended to be illustrative of principles of the present invention, and in no way should be taken as limiting of its broad application.

Referring now to FIG. 1, a typical cellular wireless communication system 10, which may benefit from the principles of the present invention, includes a plurality of base stations one shown as 12 coupled to at least one base station controller 14, which includes a mobility manager. Base station controller 14 is, in turn, coupled to a mobile switching center 16. Wireless communication 10 provides communication services to a variety of mobile communication devices such as a vehicle mounted mobile station 18 and a hand held mobile station 20. Wireless communication system 10 further provides services to a plurality of fixed communication devices generally illustrated as terminal unit 22. As shown in FIG. 1, and throughout the application, terminal unit 22 is separate from and adapted to be coupled to a traditional telephone 24, however, it will be readily appreciated that the terminal unit may be combined with a telephone without departing from the fair scope of the present invention. Each of base station 12, base station controller 14 and mobile switching center 16 operate in accordance with the IS-95A CDMA standard and are commercially available from, e.g., Motorola, Inc., Schaumburg, Illinois and other commercial sources. In FIG. 2, a wireless communication system 100 is arranged to provide dedicated service to terminal units 22. Wireless communication system 100 includes a plurality of base stations 112 coupled to a wireless access manager 114 which in turn is coupled to an end office switching center 116. Further shown coupled to manager 114 is a subscriber access manager (SAM) 118 and an operations and maintenance center - radio 120. Each of base station 112, wireless access manager 114, end office switching center 116, SAM 118 and operations and maintenance center - radio 120 operate in accordance with the IS-95A CDMA standard and are commercially available.

It is preferred to mount terminal unit 22 to a wall, at or adjacent to a window. Furthermore, the antenna may be remotely located from terminal unit 22 by a length of cable. In this embodiment, the location optimizing process involves the location and mounting of the antenna. It is also possible to have more than one antenna if diversity techniques are employed, and the optimization process would then apply to both antennas.

Turning now to FIG. 3, a terminal unit 22 is shown located, in accordance with the preferred embodiments of the present invention, within a structure 200. Terminal unit is coupled to a source of electrical power 202, such as 120 volt 60 Hz ac as may be typically found in a residence. Terminal unit 22 is further coupled to a telephone 24. Terminal unit 22 is in communication with either of wireless communication system 10 or wireless communication system 100, as the case may be, via radio communication signals for providing wireless communication services.

A preferred method 300 for locating terminal unit 22 within structure 200 is shown in FIGs. 4 and 5, and will now be described. The method begins at step 302 and at step 304, the installer locates terminal unit 22 within structure 200 in a desired location. With terminal unit 22 so located, in a first installation mode, mode 0, a RSSI measurement is made, step 306, and at step 308, the measured RSSI is evaluated to determine if it is within a desired range of a target RSSI level. If it is not, terminal unit 22 is relocated, step 310. Steps 306, 308 and 310 are repeated until a desired RSSI level or a maximum available RSSI level is achieved. It will be appreciated that the RSSI value is selected and optimized for each particular system type, and will therefore vary based upon a particular system type. Once a suitable RSSI value is obtained, the method proceeds to step 312. At step 312, in a second installation mode, mode 1, the CDMA value Ec/Io is measured, where Ec is the pilot energy received per pseudo-noise (PN) chip period from a base station of the wireless communication system and Io is the total received energy within its nominal channel bandwidth at terminal unit 22. In this regard, Ec/Io is a specialized form of signal-to-noise ratio and is measured in decibels. Since the power of a pilot signal will always be less than the total energy received, Ec/Io is a negative decibel value. It will be appreciated that other signal characteristics indicative of a quality of the radio communication signals received at terminal unit 22 may be measured in addition to Ec/Io or in place thereof. For example, a frame erasure rate (FER) measurement also provides an indication of the quality of the received radio communication signals.

At step 314 a determination is made whether the measured Ec/Io value is within a desired range of a target value. Again, the target value is selected and optimized depending on the system type. If the measured Ec/Io is not sufficiently high, terminal unit 22 is relocated until the target value is achieved or a maximum available value is achieved. Relocating terminal unit 22 at this point requires first repeating steps 306, 308 and 310 to ensure a suitable RSSI value is obtained and then repeating steps 312, 314 and 316 until a satisfactory Ec/Io value is obtained.

It is possible to stop at this point of the installation as it has been sufficiently determined that terminal unit 22 is at a location within structure 200 to ensure good quality wireless communication with the servicing wireless communication system. However, the selected location may not be optimal from a soft handoff perspective and/or from other system perspectives. For example, if terminal unit 22 is located where it will be frequently, but unnecessarily, in soft handoff, system capacity is unnecessarily reduced. Thus, in accordance with additional preferred embodiments of the present invention, in a third installation mode, mode 2, further evaluation of the location of terminal unit 22 is undertaken to ensure a truly optimal location has been selected.

With reference then to FIG. 5, method 300 continues at step 318 where the Ec/Io values for pilot signals of neighboring base stations are measured. At step 320, these Ec/Io values are evaluated to determine if any are sufficient to sustain a soft handoff condition. If not, the installation is complete, step 322. It should be noted that if a location of terminal unit 22 which provides good quality communication services without requiring a soft handoff condition may be ascertained, this is a preferred location. Soft handoff effects overall system capacity, and therefore, it is desirable to avoid such conditions when possible.

If there are pilot signals that are capable of supporting soft handoff, step 320, the Ec/Io values are organized, binned, based upon a window value into preferably three bins, X, Y and Z, step 324. The X bin gathers pilot signals with window values where soft handoff will be likely, the Z bin gathers pilot signals with window values where soft handoff is unlikely and the Y bin gathers pilot signals with window values falling somewhere in between. The window values may be more fully understood with reference to FIGs. 6 and 7. As seen in FIG. 6, a base station 401 services a coverage area 402 while a base station 403 services a coverage area 404. A terminal unit, shown as 405, is located in a region where coverage area 402 overlaps coverage area 404. The pilot signal of base station 401 has a pseudo-noise sequence time offset of "A" and the pilot signal of base station 403 has pseudo-noise sequence time offset of "B" . Referring to FIG. 7, the values of Ec/Io for the pilot signal of each base station as received by terminal unit 405 are depicted on the chart. At 406 is represented a window value between the base station 401 pilot signal and the base station 403 pilot signal measured in decibels. The window value represented by 407 is exemplary of a threshold window value indicating a location with low potential for greater than 1 way soft handoff, i.e., where the terminal unit will not be in communication with more than one base station. Of course the threshold window value will be determined and optimized for the particular system.

At step 326, the RSSI value is evaluated to determine if it is above a minimum value. If it is not above the minimum value there are two possibilities. A first possibility, step 328, is to employ a gain antenna with terminal unit 22 and to restart the location process at step 302. Otherwise, at step 330, the Ec/Io values are evaluated to determine if a strongest pilot signal has an Ec/Io above a threshold value. If not, at step 332, an antenna characteristic must be improved and the location process is restarted at step 302. Improving an antenna characteristic may include increasing the height of the antenna, adding or changing location diversity, adding gain, and the like. Otherwise, installation may be completed by placing terminal unit 22 with the X bin neighbor base stations targeting N-way soft handoff. Thus, in an area of relatively low RSSI but sufficiently high Ec/Io values, terminal unit 22 may be located so as to provide a soft handoff condition in order to ensure good communication quality.

If at step 326 it is determined that the RSSI value is above the minimum value, then at step 336 the Ec/Io values are evaluated again to determine if a strongest pilot signal has an Ec/Io value above a threshold value. If so, at step 346 installation may be completed by placing terminal unit 22 with the Z bin neighbor base stations targeting 1 -way soft handoff, i.e., no soft handoff. It is acceptable, however, that terminal unit 22 be placed with the Y bin neighbor base stations, still targeting 1-way soft handoff, but accepting a minimal amount of greater than 1-way soft handoff. Thus, if there is a sufficiently high RSSI indication and a strong pilot signal, Ec/Io greater than a threshold value, terminal unit 22 may be located to attempt to maintain 1-way soft handoff conditions.

If at step 336 it is determined that the strongest pilot signal does not have an Ec/Io value above the threshold value, at step 338, a gain antenna may be installed and the location process started over. Otherwise, if a strongest Ec/Io value is greater than an intermediate threshold, step 340, installation may be completed by locating terminal unit 22 with the X bin neighbor base stations targeting N-way soft handoff. Thus, if there is a sufficiently high RSSI indication and a moderately strong pilot signal, Ec/Io above an intermediate threshold, terminal unit 22 is located to attempt to provide N-way soft handoff to ensure good communication quality. If at step 340, however, no pilot signal has an Ec/Io value above the intermediate threshold, then an antenna characteristic must be improved, step 342 and the location process restarted, step 302.

Referring now to FIG. 8 a terminal unit 522 includes a power cord 526 for coupling to a source of electrical power and is further coupled to a land line telephone 524. Terminal unit 522 may also be battery-powered and/or include a battery back-up power source. As noted above, while shown separate from terminal unit 522, a telephone may be adapted to it as a single unit without departing from the fair scope of the present invention. In addition, while a single telephone 524 is shown coupled to terminal unit 522 it will be appreciated that terminal unit 522 may have capability to support one or more telephones on a single or multiple telephone lines. Terminal unit 522 is further shown to include a liquid crystal display ( LCD) display 528 and a plurality of light emitting diodes (LEDs) 530. During the installation process, the LCD display 528 and LEDs may be used to provide installation information to the installer, such as reported RSSI and Ec/Io values, instructions to relocate the terminal unit, installation unsuccessful information, installation completed information or various other process information. However, adding an LCD and/or LEDs to the terminal unit may unnecessarily add to the cost of the device. Therefore, it is contemplated to provide installation information to the installer using audio signals over telephone 524 and/or by reporting installation information to a caller ID box, 532 coupled to terminal unit 522. With reference to FIG. 9, terminal unit 522 includes a main task function 602, a non-volatile memory 604, a radio interface and radio signal processing function 606, a telephone task function 608 and a dialed digits decoding function 610. As will be appreciated, each of the above functions may be provided by a single or multiple microprocessors operating suitable code, by dedicated chip sets and/or combinations of processors and chip sets as is well known in the art. The telephone task function 608 interfaces to telephone 524 and, if coupled, to caller ID box 532. Main task function 602 is also coupled to an LCD/LED function 612 if terminal unit 22 includes LCD 528 and/or LEDs 530.

During operation, telephone task function 608 retrieves from non-volatile memory 604 an Ec/Io prefix which is used to determine initiation of an installation mode. Telephone task function 608 determines if the Ec/Io prefix is dialed via telephone 524 and decoding function 610 indicating initiation of the installation mode. The installation mode may be acknowledged via audio signals to telephone 524, via alpha-numeric messages via caller id box 532 (or using LCD display 528 if terminal unit 522 is so equipped) and/or by flashing of a predetermined cadence via LEDs 530. Upon receiving an installation mode enable signal from telephone task function 608, main task function 602 retrieves from memory 604 the Ec/Io and RSSI threshold values and requests Ec/Io and RSSI values via radio function 606. Main task function then performs as described in association with method 300 for accomplishing installation of terminal unit 522. At various times during the installation operation, data may be communicated to the installer via any of telephone 524, LCD 528 and LEDs 530 and caller id box 532. As will be further appreciated, main task function 602 includes appropriate flag and timer functions to ensure proper execution of the installation process and suitable fault detection and correction.

The present invention has been described in terms of several preferred embodiments. One of ordinary skill in the art will appreciate that its application extends beyond the preferred embodiments herein described. Many modification, variations and adaptations of the present invention are possible without departing from the fair scope of the invention set forth in the subjoined claims.

Claims

CLAIMSWe claim:

1. A method for locating a terminal unit in wireless communication system comprising the steps of: a) locating the terminal unit at a location within the wireless communication system; b) measuring a received signal strength providing a received signal strength indication; c) measuring at least one additional signal characteristic providing a measured characteristic; and d) evaluating each of the received signal strength indication and the measured characteristic to determine if the location is satisfactory.

2. The method of claim 1 , wherein the measured characteristic comprises one of a signal-to-noise ratio and a ratio of a pilot signal power to a total received power.

3. The method of claim 2, wherein the step of measuring a ratio of a pilot signal power to a total received power comprises one of the step of measuring pilot signal energy received per pseudo-noise chip period and the step of measuring total received power within a nominal channel bandwidth.

4. The method of claim 1, further comprising the steps of determining an existence of a soft handoff condition and relocating the terminal unit to avoid the soft handoff condition, wherein the step of determining a soft handoff condition comprises measuring a signal characteristic for each of a plurality of signals present at the terminal unit.

5. The method of claim 1, further comprising determining one of the received signal strength indication and the measured characteristic is below a respective threshold and relocating the terminal unit to create a soft handoff condition.

6. The method of claim 1 further comprising the steps of: measuring a signal characteristic for each of a plurality of signals present at the terminal unit providing a measured characteristic: for each measured characteristic determining a window value; organizing the plurality of signals based upon the associated window value; determining a soft handoff condition based upon the window values; and one of relocating the terminal unit in view of the window values to avoid the soft handoff condition when the received signal strength indication and the measured characteristics exceed a respective threshold and relocating the terminal unit in view of the window values to create a soft handoff condition when at least one of the received signal strength indication and the measured characteristics are less than a respective threshold.

7. A terminal unit arranged for use in providing communication services in a wireless communication system, the terminal unit comprising: a received signal strength detector; a signal characteristic detector; a signal processor coupled to each of the received signal strength detector and the signal characteristic detector, the signal processor arranged to provide an indication of a sufficiency of the location of the terminal unit in the wireless communication system.

8. The terminal unit of claim 7, wherein the signal characteristic detector is adapted to receive one of a signal-to-noise ratio and a ratio of a pilot signal power to a total received power, the ratio of a pilot signal power to a total received power including one of a pilot signal energy received per pseudo-noise chip period and a total received power within a nominal channel bandwidth.

9. The terminal unit of claim 7, the terminal unit adapted to couple to an indicator device, and the indication provided through the indicator device.

10. The terminal unit of claim 7, the signal processor further adapted to detect a soft handoff condition and to provide the indication based at least in part on the soft handoff condition.

11. A method for locating a terminal unit in a wireless communication system comprising the steps of: a) locating the terminal unit at a location within the wireless communication system; b) measuring at least one signal characteristic at the terminal unit; c) determining a soft handoff condition; and d) providing an indication of the sufficiency of the location based upon the at least one signal characteristic and the soft handoff condition.

12. A method for locating a terminal unit in wireless communication system comprising the steps of: a) locating the terminal unit at a location within the wireless communication system; b) measuring a ratio of pilot signal power to total received power; and c) evaluating the ratio to determine if the location is satisfactory.

13. The method of claim 12, wherein the step of measuring a ratio comprises one of the step of measuring pilot signal energy received per pseudo-noise chip period and the step of measuring total received power within a nominal channel bandwidth.