CA2218546A1 - Mobile radio communications system with moving base station - Google Patents
Mobile radio communications system with moving base station Download PDFInfo
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- CA2218546A1 CA2218546A1 CA002218546A CA2218546A CA2218546A1 CA 2218546 A1 CA2218546 A1 CA 2218546A1 CA 002218546 A CA002218546 A CA 002218546A CA 2218546 A CA2218546 A CA 2218546A CA 2218546 A1 CA2218546 A1 CA 2218546A1
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W88/00—Devices specially adapted for wireless communication networks, e.g. terminals, base stations or access point devices
- H04W88/08—Access point devices
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B7/00—Radio transmission systems, i.e. using radiation field
- H04B7/24—Radio transmission systems, i.e. using radiation field for communication between two or more posts
- H04B7/26—Radio transmission systems, i.e. using radiation field for communication between two or more posts at least one of which is mobile
- H04B7/2603—Arrangements for wireless physical layer control
- H04B7/2609—Arrangements for range control, e.g. by using remote antennas
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- Computer Networks & Wireless Communication (AREA)
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- Mobile Radio Communication Systems (AREA)
Abstract
A mobile communication system employs moving base stations moving in the direction of flow of traffic moving along a roadway. The moving base station communicates with fixed radio ports connected to a gateway office. A plurality of moving base stations are spaced apart on a closed loop and move with the flow of traffic along one roadway on one leg of the loop and with a flow of traffic on another roadway in another leg of the loop. The moving base stations communicate with a plurality of fixed radio ports connected by a signal transmission link to a gateway office which, in turn, is connected to the wire line network. The moving base stations are each provided with a pair of directional antennas with one antenna directed toward the flow of traffic and another antenna directed to the fixed radio ports.
Description
CA 02218~46 1997-11-06 W ~96/39002 PCTnUS95J07037 Mobile Radio Com~unications System with Moving Base Station BACKGROU~D OF THE INVENTION
Field of the Invention The invention relates to cellular telephone systerns in which a mobile unit co~ icates by wireless co------l--~ication to a base station connected to the wire telephone network and more particularly to ce~ r telephone systems adapted for use with fast-moving mobile units.
R~~ d Art In a typical cellular telephone system, an area is divided into a 10 plurality of cells with each cell having a centrally located cell site. A mobile unit moving in such a cellular network coll."lullicates by radio with a nearest cell site. The cell sites are each connected by cable or point-to-point microwave to a telephone network interface. The network interface typically provides co-lll"ll"ication among cell sites and between the cell sites and the so-called lS wire line telephone network. The functions of a typical network interface aredescribed in The Bell System Technical Journal, January 1979, Volume 58, No.
1. One of the functions to be performed by the telephone network interface is the so-called "handoff" function. As a mobile unit moves through a cellular network, it will move away from one cell site and toward another cell site. Each20 cell site monitors signal quality of the signal received from the mobile unit and passes information to the telephone network interface and deter~nines when a call in progress is to be transferred from one cell site to another. This procedure is known as "handoff". The handoff process involves several operations inch-~ling selecting a cell site trunk between the MTSO and the new 25 cell site, sending a mec~ e to the mobile unit transmitter/rece*er to tune from its present voice channel to a voice channel in the new cell site corresponding to the newly selected trunk, setting up a talking path in the MTSO from the cell site trunk to the trunk of the telephone network presently in use in the call, and idling the talking path in the switching network in the MTSO between the old 30 cell trunk and the telephone network trunk assigned to the call.
CA 02218~46 1997-11-06 W 096/39002 PCTrUS95/07037 A problem with I~Yi~ting mobile telephone systems is the considerable time required in h~n-loffc. This becom~os a particular problem in urban areas which are highly congeste~l A basic principle of cellular telephone systems is the concept of frequency reuse. It can be shown that traffic capacity5 of a cell~ r system is increased by a factor N2 as the size of the cell, i.e., its meter, is decreased by a factor of N. This is due to the fact that, at least in principle, all frequencies in the mobile telephone spectrum are available for use in each independent cell. Thus, as the number of cells is increased, the total number of calls that can con~ulle,ltly exist in an area is increased. A drawback, 10 however, to decreasing the size of the cells is that a mobile unit tends to cross cell boundaries more often, requiring a larger number of handoffs which will tend to overload the mobile telephone switching office (MTSO) to the point where existing calls may be interrupted or dropped.
Personal co.. l--.. ic~tion service (PCS) functions in subst~nti~lly 15 the same manner as the mobile cellular system. In PCS, the user may be in a building or walking in a street or riding a vehicle and using a handset which collllllullicates with a base station in the same manner that the mobile unit collJ.l-ullicates with the base station or cell site in the cellular network. It is envisioned that PCS, by implementing very small cells, could provide service to 20 a very large number of users, for example in a densely populated urban area.
The difficulty with PCS is the same as in the cellular system in that handoffs become the bottleneck.
Modern cellular systems use what is known as code division multiple access (CDMA) spread-spectrum co.. --l~ications. In direct-sequence 25 coding CDMA (DS-CDMA), the energy of the user signal is distributed ullifollllly over the system bandwidth through the spreading process providing separation between users of the same frequency in adjacent cells. A
requirement of DS-CDMA is that no interfering signal received may be significantly stronger than the desired signal since it would jam the weaker 30 signal. This type of coding is used in what is sometimes referred to as hierarchal cell structures. The most commonly referenced hierarchal structure isa macro/umbrella cell overlaying a number of micro cells. A fast-moving CA 02218~46 1997-11-06 W O 96/3~002 PCTnUS95107037 mobile unit, for example, may be served by the macro cell to avoid an extreme number of handovers. Slow-moving users are allocated to micro cells to save c~p~ y for the macro cells. Using the DS-CDMA concept, micro cells and macro cells share the same frequency. To avoid strong intelferellce at a micro 5 cell from mobile unit in co~ ication with a macro base station, the output power of the mobile unit in the micro cell is increased to ovc;~uwe~ the interfering signal. The use of hierarchal cell structure to provide high-qualityspeech, data co-.--..----ication at rates up to 2 megabits per second and video co...... ,.~-ication with mobile units travelling at rates in excess of 100 miles per 10 hour and accommodating PCS are seen as needed to meet future mobile teleco.. ....ication demands.
In the hierarchal cell structure, the low tier, small cells, e.g., on the order of 100 feet in diameter, accommodate low speeds. The low speed is mostly pedestrian traffic and other traffic moving at speeds below 30 miles per 15 hour. The advantages of small cells is low power, simple, inexpensive and light-weight termin~lc. What is desirable is an infra structure which allows use of such terminals in all applications, whether in the home or office as a cordless phone, on streets, in shopping malls, airports, etc., and in cars on expressways at highway speeds. Additionally, high-spectrum reuse is needed to provide low-20 cost, high-quality service which requires a large bandwidth for each subscriber.
To provide wire line toll, quality-voice service, a 32-kilobit per second bit rate is required with ADPCM coders. As wireless data services emerge, even more spectrum bandwidth will be required. In the future, it may be possible to utilize the spectrum in the 60 gigahertz range providing very large 2$ amounts of bandwidth. However, the radio wave characteristics at that frequency dictate a very short range, line of site propagation, requiring very small cells. However, as noted, small cells and fast-moving mobile units are incompatible due to the time required for handof~
SUMMARY OF THE INVENTION
These and other problems of the prior art are overcome in accordance with this invention by means of a moving base station which is CA 02218~46 1997-11-06 W 096/39002 PCTrUS95/07037 interposed between a moving mobile telephone unit and a fixed base station. In accordance with this invention, a movable base station moves with the traffic ata rate of speed which is co~ alable to the speed of the traffic and co,.,.,.",-icates with a moving mobile telephone unit via st~n-l~rd mobile radio5 l,~ ion The movable base station further co~ ..icates by radio signals with a plurality of fixed ~ntenn~ spaced along the path of travel of the mobile base station. The several fixed antennas are connected to a telephone wire line network via a telephone gateway office in a st~ntl~rd fashion. In accordance with this invention, the fixed radio ports are synchlol,i;ced and the interface 10 between the moving base station and the fixed radio ports is a time division multiplexed ( lDM) - direct-sequence, spread-spectrum CDM~
In one particular embodiment, a number of fixed base stations are provided in addition to moving base stations allowing slower moving traffic, such as pedestrian traffic or rush hour mobile traffic to collllllullicate via the fixed 15 base stations.
In a specific embodiment of the invention, the moving base stations are provided with highly directional antennas directed to moving traffic and highly directional antennas directed to the radio ports. Communications from the fixed radio ports to the movable base stations are at a relatively low 20 power level and from the movable base stations to the mobile units are at a relatively higher power level. Due to the characteristics of the direct-sequence, spread-spectrum CDMA, ~he higher power level signal will overpower the lower level signal such that the mobile unit does not receive collJlllu,lications from the fixed radio port but only from the movable base station. In the reverse 25 direction, a low level of signal is transmitted from the mobile units to the movable base station and a high-level signal is transmitted from the base station to the fixed radio ports, thereby elimin~ting any direct communication from the mobile unit to the fixed radio port.
In one embodiment of the invention, the movable base stations 30 are supported on a series of closed loops and ends of adjacent loops overlap to f~cilit~te transfer of telephone cells between adjacent loops.
CA 02218546 1997-11-06 p C W ~ 95 /~ 0 ~4/~ ~
BRIEF DESCRIPTION OF THE DRAWING
A ~ref~ d embodiment of the invention is described below with reference to the drawing in which:
FIG. 1 is a block diagram representation of a roadway structure 5 with fixed base stations, moving base stations, and fixed radio ports;
FIG. 2 is a block diagram representation of a fixed radio port of FIG. l;
FIG. 3 is a block diagram representation of a fixed base station of FIG. l;
FIG. 4 is a block diagram representation of a moving base station of FIG. l;
FIG. 5 is a block diagram representation of a g~l~wa~ telephone office shown in FIG. l;
FIG. 6 is a tabular representation of ch~nnel allocation;
FIG. 7 is a representation of selected channels of FIG. 6;
FIG. 8 illustrates signal tr~ncmi.csion among various of the system entities; and FIG. 9 is a block diagram representation of moving base stations operating in separate loops.
AMCN~ED SHEET
CA 02218~46 1997-11-06 W O 96/39002 PCTnUS95107~37 DETAILED DESCRIPIION
FIG. 1 is a diagr~mm~tic representation of a mobile ., telecc,.. -;cation system incorporating principles of the invention. FIG. 1 represents, for example, a divided highway with mobile units 20 traveling on a S first roadway 10 in one direction and a plurality of mobile units 25 travelingalong a second roadway 15, in the opposite direction. A plurality of moving base stations 30 are disposed along one side of the roadway 10. The base stations are spaced apart by a selected distance equivalent to the diameter of the cell served by the moving base station. The moving base stations 30 may be 10 moved by means of a rail 35, or other suitable collvt;yil-g device which may in~hlde an automotive vehicle travelling on the roadway, in the same direction as the traffic flow on the roadway 10, as in~ te~l by the arrow 12. In a similarfashion, a plurality of moving base stations 40 are disposed ~ cent the roadway 15 moving in the direction of the traffic as indicated by the arrow 17. The 15 moving base stations 40 are moved along a rail 45. The moving base stations 30, 40 may be supported on any suitable collvt;ying device such as rails 35, 45.The conveying device may be at ground level or overhead, depending on the terrain and available space for the device. The moving base stations are ~ferelably disposed for Op~illlUlll radio collllll~nlication with the mobile units on 20 the roadways.
Disposed between the moving base stations moving along the rails 35, 45 are a plurality of fixed radio ports 50 which are connected by means of afiber optic ring 55 or a similar signal transmitting device to a telephone office connected to the wire line telephone network and referred to as a gateway 25 office. The gateway office 60 forrns the interface between the mobile teleco--...-..-.ication system and the wire line telephone network. The gateway office is a well-known equipment. It is part of the telephone network and is ~ responsible for call processing in conjunction with the base stations. As described further later herein, the gateway office will in~ de certain processor30 hardware and software to detect a best signal quality indication and to selectively transmit information with a best signal quality indicator to the telephone network. A plurality of fixed base stations 70 are disposed in the CA 02218~46 1997-11-06 W 096/39002 PCT~US95/07037 vicinity of the roadway 10 and are connected to the gateway office 60 by means of a fiber optic ring 75 or similar signal tr~n~mi~sion device.
In operation, the moving base stations 30 may move in the direction of the flow of the traffic at a rate of, for example, 60 miles per hour, 5 which may be faster than some traf~lc and slower than other traffic. The moving base station ~lefelably handles telecommull~cations with mobile units which travel at a rate of not more than 30 miles per hour faster or slower than the moving base station. For example, the moving base stations 30, 40 may be traveling at the rate of 60 miles per hour to accommodate traffic moving in the 10 range of 30 to 90 miles per hour. In the arrangement of FIG. 1, fixed base stations 70 would accommodate conm,ullications with mobile units traveling at a speed of less than 30 miles per hour in~ in~ pedestrian traffic and stationary units. It will be readily apparent that instead of having fixed and moving base stations as depicted in FIG. 1, slowly moving and rapidly moving units may be 15 used as well. A particular moving base station is effective when the mobile units are moving in the same direction as a base station. FIG. 1 shows two roadways traveling in opposite directions with the moving base stations disposedbetween moving in the direction of the traffic. The base stations may also be placed on opposite sides of the same roadway with two-way traffic with the 20 moving base stations moving in opposite directions on the opposite sides of the roadway.
In the typical cellular telephone system, the base station, also referred to as a cell site, forms an interface between the mobile unit and the gateway office. As such, the base stations may perform a number of functions, 25 inrh1tling functions such as locating a particular mobile unit, as well as voice processing and functions associated with call setup, call supervision, and call termination. Additionally, the base stations perform the function of h~n~ling off and receiving an existing call involving a mobile unit which has moved into or out of the normal service area of a base station. All of these are well-known 30 base station functions. In some proposed mobile telephone systems, the base stations are primarily only radio interface units and a base station controller,connected to a plurality of base stations performs call-h~n~lling functions for the CA 02218~46 1997-11-06 W ~ 96/39002 PCTnUS95~07037 plurality of base stations. The system in accordance with the invention differs from ~he prior art primarily in that the base stations 30, 40 are moving with the traffic and co.. l.icate with the gateway office 60 via fixed radio ports 50.Furthermore, the various call-h~ntlling functions, inclll-ling h~ndoff, are S performed by the moving base st~tion- Advantageously, because of movement of the base station in the same direction as the traveling mobile unit, the number of h~ns~off.c is greatly redllced Each of the moving base stations 30, 40 is provided with antennas 100, 101. The antennas 100, 101, preferably high gain, directional antennas for 10 use in mobile co...~ ..ication, are well know and commercially available. Thefixed base stations 70 are provided with four separate ~ntenn~c 110 extending infour dir~rellt directions. The ~ntenn~c 100 on the base stations 30, 40 are usedto co-.. l.. -icate with the mobile units 20, 25 whereas the antennas 101 on the moving base stations 30, 40 are used to collllllullicate with the fixed radio ports 15 50. The fixed base stations 70 are preferably each provided with four antennas 102-105. Fewer than four antennas may also be used. In that case, at least one omni-directional antenna is used. Xn the config,uration of FIG. 1, the antennas 102 are arranged to colllnlullicate with the mobile units 20 and the antennas 103-105 are arranged to co"""-~"icate with other mobile telephone 20 collllllullications from slow moving traffic or stationary subscribers. The fixed radio ports 50, in the configuration of FIG. 1, are each provided with a pair ofdirectional antennas 110, 111 of the same general type as the directional antennas 100-105. As the moving base stations 30, 40 move relative to the fixed radio ports S0, data representing voice signals and call related inforInation is25 tr~ncmitted between the ~ntenn~c 101 on the moving base stations 30, 40 and the antennas 110, 111 on the fixed radio ports 50.
FIG. 2 is a diagr~mm~tic representation of the fixed radio ports 50. The unit includes a standard microprocessor 150 as well as a radio interfacecircuit 154 providing an interface between the radio signals received on the 30 antennas 110, 111 and the processor 150. The circuits are of a type typicallyused in fixed base stations and are well known in the art. Additionally, each radio port S0 includes a processor 150 connected to an add/drop multiplexer CA 02218~46 1997-11-06 W 096/39002 PCTrUS95/07037 (ADM) 152. The ADM 152 interfaces with the fiber optic cable 55 and is able to add data from the processor 150 to the data stream on the ~lber optic cable 55. Additionally, the ADM 152 recognizes a data stream accompanied by an address idell~iryillg the processor 150 and transfers such data from the data stream of the fiber optic cable 55 to the processor 150. As will be described further later herein, the processor 150 colllpules a signal quality indicator for the il~ollllation received from the radio interface circuits 154, based primarily on radio signal strength intensity, in a well-known fashion. Processor 150 controls the transfer information between the fiber optic cable 55 and the various moving base stations via the antennas 110, 111.
FIG. 3 is a block diagram representation of one of the fixed base stations 70. The fixed base stations 70 perform the functions of a standard prior art fixed base station. The base stations 70 are connected to the fiber optic ring 75 and include an add/drop multiplexer (ADM) 162 which provides an interface between the processor 160 and the ~lber optic ring 75.
As mentioned earlier, both the optical ring 55 and optical ring 75 are connected to the gateway office 60. The primary function of the gateway office is to provide the interface to a wired telephone network. It distributes the teleco~ .ullications traffic between the network and the moving base stations via the fixed radio ports. The fiber optic rings 55, 75 are preferably continuous rings with an add/drop multiplexer for each ring in the gateway office. Data tr~ ion on the fiber optic rings 55, 75 is preferably in accordance with one of the well-known SONET or synchronous digital hierarchy (SDH) tr~n~mic~ion protocols.
The directional antennas 100-105, 110, 111 may be of a sectorized architecture or may be phased array antennas with highly directional radio frequency beams. Such antennas are preferably used to decrease interference between the mobile base stations and the fixed radio ports, allowing greater spectrum reuse. Antenna diversity can be provided with two spatially separated radio beams separated in time with a predefined time-delay offset for easier separation at reception. Various techniques for obtaining high antenna diversity , CA 02218~46 1997-11-06 W O 96/39002 PCTnUS95107037 g are well known in the art and antennas employing such techniques are commercially available.
FIG. 4 is a block diagram representation of the moving base station 30. The station 30 in~ es a processor 130 connecte~l via radio 5 interfaces 132, 134 to the ~ntçnn~c 100, 101, respectively. The processor 130 may be a st~n-l~rd microprocessor and the radio interface circuits 132 may be st~n~l~rd radio interface circuits. The rnicroprocessor is ~lefeldbly programmedto handle the call proceccin~ functions performed in a prior art system by a call site or by a shared base station controller. In this manner, the moving base 10 station has greater autonomy and requires less colll-llul~ications with a shared base station controller or the like. The circuits 132, like the radio interface circuits 154 in the fixed radio port 50 and the radio interface circuits 164 in the fixed base station 70, are well known and commercially available circuits.
The radio interface between the mobile units 20, 25 and the 15 moving base stations 30, 40 and the fixed base station 70 is a standard radiointerface, well known in the art. The radio interface between the moving base stations 30, 40 and the fixed radio ports 50 is preferably a time division multiplexed, direct-sequence, spread-spectrum, code-division multiple-access interface (TDM/CDMA). Multiple channels between the base station and the 20 fixed radio ports are time division multiplexed as time slots in a data stream.
The data stream is spread with a pseudo-random code over the allocated spectrum. A pilot sequence is inserted in the transmitted signal for ease of synchronization in a well-known manner. The interface between the movable base station and the fixed radio port is preferably transparent to the overall 25 system in spectrum use.
Frequency division or time division may be used for duplex co-,----l..-ications. In the frequency division duplex (FDD) mode, data is simultaneously tr~ncmitte~i in both directions, each in a different spectrum band.
In a typical system in the FDD mode, the TDM frame tr~ncmiccion duration 30 will be a~ oxi...~tely 500 microseconds mzlking the interface substantially transparent to overall system delay.
CA 02218~46 1997-11-06 W 096/39002 PCTrUS95/07037 The interface between the mobile unit and the movable base may be the st~nd~rd IS-95-based PCS air interface st~nd~rd. The channel capacity for the so-called ".oYten-led mode" (2.5 mhz) has been determined to be seven ~nnel~ at 32 kilobits per second. The FCC allocated licensed spectrum for S personal co.. ~ ;cations services (PCS) inrlllcles 10-rnhz licenses and 30-mhz licenses. Each 1~mhz license provides two separated 5-mhz bands and each 30-rnhz license provides two separated 15-rnhz bands, for two-way co~ -ic~tions.
Two 5-mhz bands can support 14 duplex channels at 32 kilobits per second and two 15-mhz bands can ~U~JOl l 42 duplex channels at 32 kilobits per second.
Voice signals between a mobile unit and the gateway office are encoded in a standard fashion using ADPCM voice encoding with a Illil~illllllll bit rate of 32 kilobits per second in each channel. The interface between the moving base station and the fLxed radio port is adapted to carry up to 19 channels of 32 kilobits per second each at 16 bits per time slot. The frame 15 structure includes 16 bearer channels of 32 kilobits per second at 16 bits per time slot. The time division multiplexed frame rate between the movable base station and the fixed radio port is 608 kilobits per second. To achieve a procec~ing gain of 9 decibels, the frame rate is multiplied by a factor of 8, yielding 4,864 kilobits per second, which fit into a single 5-mhz band. FIG. 6 is 20 a tabular representation of the channel allocation showing 16 bearer channels plus 3 channels for sign~lling, control, and error code. FIG. 7 is a representation of ch~nnel~ 18 and 19 of FIG. 6.
The moving base stations are addressed using predefined code sequences derived in a known manner by the use of Walsh functions. U.S. Pat.
25 5,103,349 entitled "System and Method for Generating Signal Wave Forms in CDMA Cellular Telephone System" describes the use of Walsh functions for code generation. U.S. Pat. 5,103,349 is incorporated by reference herein. As described in that patent, by choosing a Walsh function of order 8 provides 8 orthagonal codes in the present embodiment using spread spectrum CDMA uses 30 the all 0 Walsh sequence as a pilot carrier with the other 7 sequences available for moving base station communications. The code sequences may be repeated as ABCDEFG; ABCDEFG; . . . Although fewer codes could be used, CA 02218~46 1997-11-06 W 096/39002 PCTnUS95107037 preferably no less than 3 are used. Bec~llse of dir~lhlg propagation times for signals between a particular moving base station and two or more different fixedradio ports, it is not possible to satisfy the condition of time ~lignm~nt required for Walsh function orthagonality for 2 or more fixed radio ports at one time.
5 For this purpose, two outer pseudonoise codes are used to provide ~lie.-. ;...i..z~tion between signals arriving at the moving base station from .lirreren fixed radio ports. The pselldonoice code rate is ~refelably 4,864 kilobits per second. The sequence length for the ll~ ed carrier signal is preferably 32,768 chips, as described in U.S. Pat. 5,103,459. The outer pseudonoise codes modulate the signal in quadrature phase shift keying.
The pilot signal will be tr~n~mitted in both directions, from the moving base stations to the fixed radio ports and vice, versa. This is made possible by the line of site fading characterized as Rician.
The pilot sequence will be long enough that a number of different sequences can be generated by shifts in the basic sequence. The separation will be great enough to ensure that there is no interference between pilot ~ign~lc.
Each moving base stations will use a different offset from a neighboring moving base station to provide signal separation. Similarly, each fixed radio port willuse a different offset from a neighboring fixed radio port.
The FCC has allocated a 20 mhz of unlicensed spectrum, including a 10 mhz band for voice products and a 10-mhz band for data products. Thus, one co"Lh,uous 10-megahertz channel is available and time division multiplex ...iccion is preferably used. The bit rate for both directions of tr~ncmiccion will be twice the frequency division duplex rate, introducing an overall delay of 25 500 microseconds and a processing gain of 9 decibels. In the time division duplex mode, the l~ ",ission times and direction, forward and reverse between the mobile unit and the moving base station and between the moving base station and the fixed radio ports, are aligned. In one half of the time division, duplex cycle signals are llall~ ed from the mobile unit to the moving base 30 station and, from there, to the fixed radio port. In the other half-cycle, signals are transmitted from the fixed radio port to the moving base station and then tothe mobile unit.
CA 02218~46 1997-11-06 W 096/39002 PCTrUS95/07037 The two 15-mhz licensed spectrum bands (30 mhz) are preferably divided into three 5-megahertz channels in each direction, lltili7ing the same architectllre as described earlier herein with respect to the 5-megahertz licensed SpC~ ulll. In the 15-mhz licensed spectrum, each of the 5-megahertz ch~nn~l~
5 will support 14 traffic ch~nnel~, for a total of 42 traffic channels in each 15-mhz band. The air interface between the moving base station and the fixed radio port, as well as the signal structure, can be modified and adapted to a variety of allocations of spectrum and air interface st~nd~rds.
In the present embodiment, as described earlier herein, 7 10 orthogonals codes are available for co~l~llullication between the fixed radioports 50 and the moving base stations 30, 40. As described earlier herein and depicted in FIGS. 6 and 7, one 16 bit co~ llunication ch~nnel, channel 19, is set aside for control and identification bits. As depicted in FIG. 7, channel 19 maycolllplise 7 control bits and 9 identification bits. The 9 identification bits 15 provide 512 unique identification numbers. Using 7 orthagonal codes and 512 identification numbers, 3,854 moving base stations can be uniquely identified.
When the moving base stations are separated by a spacing of 200 feet, the total distance of coverage using the 3,854 moving base stations is apploxi...~tely 135miles. FIG. 1 shows a portion of the system with moving base st~tion~ moving 20 in opposite directions along oppositely directed roadways and fixed radio ports with dual antennas. Vehicular traffic moving in opposite directions on the same roadway are preferably served by moving base stations on opposite sides of the roadway. Where each roadway has only one-way traffic, the system is preferably disposed between the roadways. In one embodiment of the invention, depicted 25 in FIG. 9, two separate loops 200, 205 are disposed between two separate roadways 206, 208 with the traffic on the roadways indicated by the arrows 207 and 209. The loops 200 and 205 comprise moving base stations 210 and 250, respectively. The base stations, in this embodiment, are moving in the directionindicated by the arrows 201 and 202. Since, as a practical matter, the loops 200, 30 205 are not of indefinite length, a plurality of loops may be required to cover a desired area. To avoid interruption in communications, the ends of the loops are preferably sufficiently close together, or overlapping, to provide an CA 02218~46 1997-11-06 W O g6/390~2 PCTnUS95JO7037 overlapping area of coverage for mobile units traveling in the area of the loop ends. This will allow one of the mobile stations nearing the end of the loop of which it is a part to hand off the call to a mobile station of the adjacent loop.
Each loop preferably has a single gateway for conn~ction to the S wire telephone network. One advantage of that ~lallg~lllent is that it e.limin~tes the need for registration of moving base st~tion.c, which is required where a moving base station moves between gateways. FIG. 9 shows a pair of gateways 215 associated with the loop 200 and a pair of gateways 255 associated with the loop 205. The two gateways of a loop are both connected to the fixed radio ports of the loop at all times and may be operated in a load sharing mode with each capable of h~n~lling the total teleco~ ication~s traffic for the loop in the event of a failure in one of the gateways.
To avoid intellu~ g co.lll-lu--ications with a mobile unit traveling along the roadway in the area where two adjacent loops end, any existing calls are handed off from the moving base station near the terminzlting end of its loop to a moving base station of the next loop. The h~nfloff process is essentially the same as a handoff between moving base stations on the sarne loop, except that the handed off call will be routed to the wire network to a different gateway. This procedure is equivalent to a handoff between cell sites of different cells in the eYi~ting cellular network in a manner which is well known in the art. The loops 200 and 205 may physically overlap to assure proper overlap of communications between moving base stations of the two loops and to avoid loss of comm-lnication with a mobile unit handed off from one loop to another.
The timing and synchlo,.~;Gation between the moving base station and a fixed radio port with which the moving base station communicates is phase-locked to the pilot signals received from the fixed radio port with which the moving base station comml-nicates. For synchronization purposes, the moving base station vill receive a Global Positioning Satellite (GPS) Coordinated Universal Time (UCT) timing signal once each second.
CDMA Technology is well-known for sensitivity to power control.
Specifically, the more powerful signals tend to "mask out" less powerful signals =
CA 022l8~46 l997-ll-06 W 096/39002 PCTrUS95/07037 at the receiver. Typically, elaborate power control schemes are implemented to ensure that all signals arrive at the receiver at the same level. In accordance with the system of this invention, hu..~ r, the sensiLivilr to power level of CDMA is used to advantage. The principles of signal ~ .,-icsion employed in 5 the system of the invention is illustrated in FIG. 8. Two power levels of radio tr~ ...ic!~ion, high (H) and low (L), are definP~l Referring to FIG. 1, high-power level signals are tr~n~mitte~l from the moving base station 30 to the mobile unit 20 and from the base station 30 to the fixed radio port 50. Low power level signals are l~ le-l from the fixed radio port 50 to the moving 10 base station 30. Similarly, low power signals are transmitted from the mobileunit 20 to the moving base station 30. Since the moving base station receives a low power level signal from the fixed radio port and ~ a high level power signal toward terminals, the high power level received at the mobile unit 20 will mask out any signals of the low power signal ll~ns"~ ed from the fixed 15 radio port to the moving base station. In a similar fashion, any low signal ~a~ litLed from the mobile unit 20 re~ ing the fixed radio port 50 will be m~cked by the high power level signal transmitted from the moving base station to the fixed radio port. As stated earlier, the antennas 100-105, 110, 111 are ~rerelably highly directional antennas with very little feedback from the transmit 20 signal to the receive signal. Feedback due to reflections and other extraneous sources can be readily elimin~ted at the moving base station using well-known noise c~nçell~tion techniques.
When a mobile unit set is first powered up or first enters a service area, the mobile unit must register in the manner described earlier, by 25 tr~n~mitting its unique address in the new service area. The address will be received by the closest moving base station 30 and transmitted via a fixed radioport and the gateway switch 60 to the telephone network. This registration procedure is required so that an incoming call for the mobile unit can be appl Opl iately directed.
The spacing of mobile based stations 20 and the fixed radio ports 50 of FIG. 1, together with the strength of the signal transmitted between the moving base stations and the fixed radio ports, determines the number of fixed CA 02218~46 1997-11-06 wo 96139002 PCTIUS95l07037 radio ports with which a moving base station can co~ icate at any point in time. The spacing and signal strength is preferably such that each fixed radio port receives signals from three moving base st~tionc When a fixed radio port r~ceives data, acco...~ .;ed by the identification number of the moving base S station, the processor 150 (FIG. 2) co~l,putes a signal quality indication on the received signal. The signal quality in~ tion is a figure of merit plefelably col~ ed as a function of signal strength and signal-to-noise ratio. It is added to the received data and added to the fiber optic ring 55 via the ADM 152. The gateway 60 preferably receives the same data from several different ones of the 10 fixed radio ports 50 and stores the data in an internal memory in the gateway 60 in association with the moving base station identification number and Walsh function spreading code. The address of the fixed radio port from which the data has been received is stored in the memory of processor 64 as well.
Accordhlgly, multiple copies of the same data tr~n~mitted by a single moving 15 base staation are stored in the memory of the processor 64 in the gateway. The signal quality indications colllpuled by the processors 150 in each of several fixed radio ports are compared to a predefined signal quality indication threshold, and the data corresponding to a signal quality indication below the threshold value is discarded. Otherwise, the data is retained. A cyclic 20 red-lnd~ncy code transmitted with the data is used to detect any TDM frame errors. The best data, i.e., associated with the best signal quality indication is transferred from the gateway 60 to the telephone network. Data received from the telephone network at the gateway 60 and intended for a registered mobile unit is stored in the memory of the processor 150 in a register particularly 25 associated with the moving base station currently serving the mobile unit. This data will be sent via the optical ring 55 to all fixed radio ports that are identified in the memory of the processor 65 as fixed radio ports with an acceptable signal quality indication. The received data will be transmitted fromeach of the fixed radio ports which received the data together with the 30 identification code and Walsh function code of the moving base station to which the data is directed. The tr~n~mi~ion of data from different fixed radio ports will be staggered, delayed by different amounts, so that they can be received and CA 022l8~46 l997-ll-06 W 096/39002 PCTrUS95/07037 separated at the moving base stations. The delays can be precisely controlled bymeans of synchronous distribution via the optical ring 55, in the SONET or SDH format. The receiving moving base station, by means of its processor 130, comr~res the multiple copies of the received data ~i~n~lc, aligns them and 5 combines them for the best reception.
Each of the moving base st~tion~ will have one of N ~c~igned codes, where N may be any number, but })r~fe~ably is at least 3 or more. Seven Walsh function codes are preferably used. The codes may be repeated in sequence, as for example, ABCDEFGABCDEFG. The codes are assigned in 10 sequence to the various moving base stations so that two moving base stationshaving the same code will be physically separated by a sufficient distance to venl interference in the co"~,.,-lllications between fixed radio ports and moving base stations having the same identity code. The operation of the fixed base stations 70 is essentially the same as that of a standard fixed base station.
15 In congested traffic areas, a mobile unit which is stopped or slowly moving, e.g., less than 30 miles per hour, will preferably be serviced by one of the fixed base stations 70. As the speed of travel of the mobile unit 20 increases, a handoff will occur between the fixed base station and a moving base station. The procedures for detellllinillg whether a mobile unit is to be served by a fixed 20 base station or a moving base station are the same procedures as described earlier herein in determining which moving base station is selected to serve a mobile unit, i.e., based on signal strength and error rate. Thus, when a call involving a mobile unit is initiated or when it is determined that a handoff should occur, the mobile unit may be h~nde(l from a moving station to a fixed 25 station, or vice versa. Each mobile unit monitors pilot signals from fixed and moving base stations and synchronizes to the base station providing the best signal. The mobile unit may "connect" with three fixed or moving base stations while searching for a fourth in what is known as the "soft" hand-off mode. As the speed of the vehicle increases, fixed or slow moving base stations will be 30 dropped. In more congested areas where traffic speed will vary between 0 and 60 miles per hour, base stations speed may, for example, be set to move at 30 WO 96/39002 PCTnUS95)D7D37 mph. The moving base station should then be able to ~commodate all traffic in the 0-60 mph range.
It will be understood that the above-described arrangement is merely illustrative of the application of the principles of the invention and that S other arr~em~-nt~ may be devised by those skilled in the art without departing from the scope of the invention as defined by the appended claims.
Field of the Invention The invention relates to cellular telephone systerns in which a mobile unit co~ icates by wireless co------l--~ication to a base station connected to the wire telephone network and more particularly to ce~ r telephone systems adapted for use with fast-moving mobile units.
R~~ d Art In a typical cellular telephone system, an area is divided into a 10 plurality of cells with each cell having a centrally located cell site. A mobile unit moving in such a cellular network coll."lullicates by radio with a nearest cell site. The cell sites are each connected by cable or point-to-point microwave to a telephone network interface. The network interface typically provides co-lll"ll"ication among cell sites and between the cell sites and the so-called lS wire line telephone network. The functions of a typical network interface aredescribed in The Bell System Technical Journal, January 1979, Volume 58, No.
1. One of the functions to be performed by the telephone network interface is the so-called "handoff" function. As a mobile unit moves through a cellular network, it will move away from one cell site and toward another cell site. Each20 cell site monitors signal quality of the signal received from the mobile unit and passes information to the telephone network interface and deter~nines when a call in progress is to be transferred from one cell site to another. This procedure is known as "handoff". The handoff process involves several operations inch-~ling selecting a cell site trunk between the MTSO and the new 25 cell site, sending a mec~ e to the mobile unit transmitter/rece*er to tune from its present voice channel to a voice channel in the new cell site corresponding to the newly selected trunk, setting up a talking path in the MTSO from the cell site trunk to the trunk of the telephone network presently in use in the call, and idling the talking path in the switching network in the MTSO between the old 30 cell trunk and the telephone network trunk assigned to the call.
CA 02218~46 1997-11-06 W 096/39002 PCTrUS95/07037 A problem with I~Yi~ting mobile telephone systems is the considerable time required in h~n-loffc. This becom~os a particular problem in urban areas which are highly congeste~l A basic principle of cellular telephone systems is the concept of frequency reuse. It can be shown that traffic capacity5 of a cell~ r system is increased by a factor N2 as the size of the cell, i.e., its meter, is decreased by a factor of N. This is due to the fact that, at least in principle, all frequencies in the mobile telephone spectrum are available for use in each independent cell. Thus, as the number of cells is increased, the total number of calls that can con~ulle,ltly exist in an area is increased. A drawback, 10 however, to decreasing the size of the cells is that a mobile unit tends to cross cell boundaries more often, requiring a larger number of handoffs which will tend to overload the mobile telephone switching office (MTSO) to the point where existing calls may be interrupted or dropped.
Personal co.. l--.. ic~tion service (PCS) functions in subst~nti~lly 15 the same manner as the mobile cellular system. In PCS, the user may be in a building or walking in a street or riding a vehicle and using a handset which collllllullicates with a base station in the same manner that the mobile unit collJ.l-ullicates with the base station or cell site in the cellular network. It is envisioned that PCS, by implementing very small cells, could provide service to 20 a very large number of users, for example in a densely populated urban area.
The difficulty with PCS is the same as in the cellular system in that handoffs become the bottleneck.
Modern cellular systems use what is known as code division multiple access (CDMA) spread-spectrum co.. --l~ications. In direct-sequence 25 coding CDMA (DS-CDMA), the energy of the user signal is distributed ullifollllly over the system bandwidth through the spreading process providing separation between users of the same frequency in adjacent cells. A
requirement of DS-CDMA is that no interfering signal received may be significantly stronger than the desired signal since it would jam the weaker 30 signal. This type of coding is used in what is sometimes referred to as hierarchal cell structures. The most commonly referenced hierarchal structure isa macro/umbrella cell overlaying a number of micro cells. A fast-moving CA 02218~46 1997-11-06 W O 96/3~002 PCTnUS95107037 mobile unit, for example, may be served by the macro cell to avoid an extreme number of handovers. Slow-moving users are allocated to micro cells to save c~p~ y for the macro cells. Using the DS-CDMA concept, micro cells and macro cells share the same frequency. To avoid strong intelferellce at a micro 5 cell from mobile unit in co~ ication with a macro base station, the output power of the mobile unit in the micro cell is increased to ovc;~uwe~ the interfering signal. The use of hierarchal cell structure to provide high-qualityspeech, data co-.--..----ication at rates up to 2 megabits per second and video co...... ,.~-ication with mobile units travelling at rates in excess of 100 miles per 10 hour and accommodating PCS are seen as needed to meet future mobile teleco.. ....ication demands.
In the hierarchal cell structure, the low tier, small cells, e.g., on the order of 100 feet in diameter, accommodate low speeds. The low speed is mostly pedestrian traffic and other traffic moving at speeds below 30 miles per 15 hour. The advantages of small cells is low power, simple, inexpensive and light-weight termin~lc. What is desirable is an infra structure which allows use of such terminals in all applications, whether in the home or office as a cordless phone, on streets, in shopping malls, airports, etc., and in cars on expressways at highway speeds. Additionally, high-spectrum reuse is needed to provide low-20 cost, high-quality service which requires a large bandwidth for each subscriber.
To provide wire line toll, quality-voice service, a 32-kilobit per second bit rate is required with ADPCM coders. As wireless data services emerge, even more spectrum bandwidth will be required. In the future, it may be possible to utilize the spectrum in the 60 gigahertz range providing very large 2$ amounts of bandwidth. However, the radio wave characteristics at that frequency dictate a very short range, line of site propagation, requiring very small cells. However, as noted, small cells and fast-moving mobile units are incompatible due to the time required for handof~
SUMMARY OF THE INVENTION
These and other problems of the prior art are overcome in accordance with this invention by means of a moving base station which is CA 02218~46 1997-11-06 W 096/39002 PCTrUS95/07037 interposed between a moving mobile telephone unit and a fixed base station. In accordance with this invention, a movable base station moves with the traffic ata rate of speed which is co~ alable to the speed of the traffic and co,.,.,.",-icates with a moving mobile telephone unit via st~n-l~rd mobile radio5 l,~ ion The movable base station further co~ ..icates by radio signals with a plurality of fixed ~ntenn~ spaced along the path of travel of the mobile base station. The several fixed antennas are connected to a telephone wire line network via a telephone gateway office in a st~ntl~rd fashion. In accordance with this invention, the fixed radio ports are synchlol,i;ced and the interface 10 between the moving base station and the fixed radio ports is a time division multiplexed ( lDM) - direct-sequence, spread-spectrum CDM~
In one particular embodiment, a number of fixed base stations are provided in addition to moving base stations allowing slower moving traffic, such as pedestrian traffic or rush hour mobile traffic to collllllullicate via the fixed 15 base stations.
In a specific embodiment of the invention, the moving base stations are provided with highly directional antennas directed to moving traffic and highly directional antennas directed to the radio ports. Communications from the fixed radio ports to the movable base stations are at a relatively low 20 power level and from the movable base stations to the mobile units are at a relatively higher power level. Due to the characteristics of the direct-sequence, spread-spectrum CDMA, ~he higher power level signal will overpower the lower level signal such that the mobile unit does not receive collJlllu,lications from the fixed radio port but only from the movable base station. In the reverse 25 direction, a low level of signal is transmitted from the mobile units to the movable base station and a high-level signal is transmitted from the base station to the fixed radio ports, thereby elimin~ting any direct communication from the mobile unit to the fixed radio port.
In one embodiment of the invention, the movable base stations 30 are supported on a series of closed loops and ends of adjacent loops overlap to f~cilit~te transfer of telephone cells between adjacent loops.
CA 02218546 1997-11-06 p C W ~ 95 /~ 0 ~4/~ ~
BRIEF DESCRIPTION OF THE DRAWING
A ~ref~ d embodiment of the invention is described below with reference to the drawing in which:
FIG. 1 is a block diagram representation of a roadway structure 5 with fixed base stations, moving base stations, and fixed radio ports;
FIG. 2 is a block diagram representation of a fixed radio port of FIG. l;
FIG. 3 is a block diagram representation of a fixed base station of FIG. l;
FIG. 4 is a block diagram representation of a moving base station of FIG. l;
FIG. 5 is a block diagram representation of a g~l~wa~ telephone office shown in FIG. l;
FIG. 6 is a tabular representation of ch~nnel allocation;
FIG. 7 is a representation of selected channels of FIG. 6;
FIG. 8 illustrates signal tr~ncmi.csion among various of the system entities; and FIG. 9 is a block diagram representation of moving base stations operating in separate loops.
AMCN~ED SHEET
CA 02218~46 1997-11-06 W O 96/39002 PCTnUS95107~37 DETAILED DESCRIPIION
FIG. 1 is a diagr~mm~tic representation of a mobile ., telecc,.. -;cation system incorporating principles of the invention. FIG. 1 represents, for example, a divided highway with mobile units 20 traveling on a S first roadway 10 in one direction and a plurality of mobile units 25 travelingalong a second roadway 15, in the opposite direction. A plurality of moving base stations 30 are disposed along one side of the roadway 10. The base stations are spaced apart by a selected distance equivalent to the diameter of the cell served by the moving base station. The moving base stations 30 may be 10 moved by means of a rail 35, or other suitable collvt;yil-g device which may in~hlde an automotive vehicle travelling on the roadway, in the same direction as the traffic flow on the roadway 10, as in~ te~l by the arrow 12. In a similarfashion, a plurality of moving base stations 40 are disposed ~ cent the roadway 15 moving in the direction of the traffic as indicated by the arrow 17. The 15 moving base stations 40 are moved along a rail 45. The moving base stations 30, 40 may be supported on any suitable collvt;ying device such as rails 35, 45.The conveying device may be at ground level or overhead, depending on the terrain and available space for the device. The moving base stations are ~ferelably disposed for Op~illlUlll radio collllll~nlication with the mobile units on 20 the roadways.
Disposed between the moving base stations moving along the rails 35, 45 are a plurality of fixed radio ports 50 which are connected by means of afiber optic ring 55 or a similar signal transmitting device to a telephone office connected to the wire line telephone network and referred to as a gateway 25 office. The gateway office 60 forrns the interface between the mobile teleco--...-..-.ication system and the wire line telephone network. The gateway office is a well-known equipment. It is part of the telephone network and is ~ responsible for call processing in conjunction with the base stations. As described further later herein, the gateway office will in~ de certain processor30 hardware and software to detect a best signal quality indication and to selectively transmit information with a best signal quality indicator to the telephone network. A plurality of fixed base stations 70 are disposed in the CA 02218~46 1997-11-06 W 096/39002 PCT~US95/07037 vicinity of the roadway 10 and are connected to the gateway office 60 by means of a fiber optic ring 75 or similar signal tr~n~mi~sion device.
In operation, the moving base stations 30 may move in the direction of the flow of the traffic at a rate of, for example, 60 miles per hour, 5 which may be faster than some traf~lc and slower than other traffic. The moving base station ~lefelably handles telecommull~cations with mobile units which travel at a rate of not more than 30 miles per hour faster or slower than the moving base station. For example, the moving base stations 30, 40 may be traveling at the rate of 60 miles per hour to accommodate traffic moving in the 10 range of 30 to 90 miles per hour. In the arrangement of FIG. 1, fixed base stations 70 would accommodate conm,ullications with mobile units traveling at a speed of less than 30 miles per hour in~ in~ pedestrian traffic and stationary units. It will be readily apparent that instead of having fixed and moving base stations as depicted in FIG. 1, slowly moving and rapidly moving units may be 15 used as well. A particular moving base station is effective when the mobile units are moving in the same direction as a base station. FIG. 1 shows two roadways traveling in opposite directions with the moving base stations disposedbetween moving in the direction of the traffic. The base stations may also be placed on opposite sides of the same roadway with two-way traffic with the 20 moving base stations moving in opposite directions on the opposite sides of the roadway.
In the typical cellular telephone system, the base station, also referred to as a cell site, forms an interface between the mobile unit and the gateway office. As such, the base stations may perform a number of functions, 25 inrh1tling functions such as locating a particular mobile unit, as well as voice processing and functions associated with call setup, call supervision, and call termination. Additionally, the base stations perform the function of h~n~ling off and receiving an existing call involving a mobile unit which has moved into or out of the normal service area of a base station. All of these are well-known 30 base station functions. In some proposed mobile telephone systems, the base stations are primarily only radio interface units and a base station controller,connected to a plurality of base stations performs call-h~n~lling functions for the CA 02218~46 1997-11-06 W ~ 96/39002 PCTnUS95~07037 plurality of base stations. The system in accordance with the invention differs from ~he prior art primarily in that the base stations 30, 40 are moving with the traffic and co.. l.icate with the gateway office 60 via fixed radio ports 50.Furthermore, the various call-h~ntlling functions, inclll-ling h~ndoff, are S performed by the moving base st~tion- Advantageously, because of movement of the base station in the same direction as the traveling mobile unit, the number of h~ns~off.c is greatly redllced Each of the moving base stations 30, 40 is provided with antennas 100, 101. The antennas 100, 101, preferably high gain, directional antennas for 10 use in mobile co...~ ..ication, are well know and commercially available. Thefixed base stations 70 are provided with four separate ~ntenn~c 110 extending infour dir~rellt directions. The ~ntenn~c 100 on the base stations 30, 40 are usedto co-.. l.. -icate with the mobile units 20, 25 whereas the antennas 101 on the moving base stations 30, 40 are used to collllllullicate with the fixed radio ports 15 50. The fixed base stations 70 are preferably each provided with four antennas 102-105. Fewer than four antennas may also be used. In that case, at least one omni-directional antenna is used. Xn the config,uration of FIG. 1, the antennas 102 are arranged to colllnlullicate with the mobile units 20 and the antennas 103-105 are arranged to co"""-~"icate with other mobile telephone 20 collllllullications from slow moving traffic or stationary subscribers. The fixed radio ports 50, in the configuration of FIG. 1, are each provided with a pair ofdirectional antennas 110, 111 of the same general type as the directional antennas 100-105. As the moving base stations 30, 40 move relative to the fixed radio ports S0, data representing voice signals and call related inforInation is25 tr~ncmitted between the ~ntenn~c 101 on the moving base stations 30, 40 and the antennas 110, 111 on the fixed radio ports 50.
FIG. 2 is a diagr~mm~tic representation of the fixed radio ports 50. The unit includes a standard microprocessor 150 as well as a radio interfacecircuit 154 providing an interface between the radio signals received on the 30 antennas 110, 111 and the processor 150. The circuits are of a type typicallyused in fixed base stations and are well known in the art. Additionally, each radio port S0 includes a processor 150 connected to an add/drop multiplexer CA 02218~46 1997-11-06 W 096/39002 PCTrUS95/07037 (ADM) 152. The ADM 152 interfaces with the fiber optic cable 55 and is able to add data from the processor 150 to the data stream on the ~lber optic cable 55. Additionally, the ADM 152 recognizes a data stream accompanied by an address idell~iryillg the processor 150 and transfers such data from the data stream of the fiber optic cable 55 to the processor 150. As will be described further later herein, the processor 150 colllpules a signal quality indicator for the il~ollllation received from the radio interface circuits 154, based primarily on radio signal strength intensity, in a well-known fashion. Processor 150 controls the transfer information between the fiber optic cable 55 and the various moving base stations via the antennas 110, 111.
FIG. 3 is a block diagram representation of one of the fixed base stations 70. The fixed base stations 70 perform the functions of a standard prior art fixed base station. The base stations 70 are connected to the fiber optic ring 75 and include an add/drop multiplexer (ADM) 162 which provides an interface between the processor 160 and the ~lber optic ring 75.
As mentioned earlier, both the optical ring 55 and optical ring 75 are connected to the gateway office 60. The primary function of the gateway office is to provide the interface to a wired telephone network. It distributes the teleco~ .ullications traffic between the network and the moving base stations via the fixed radio ports. The fiber optic rings 55, 75 are preferably continuous rings with an add/drop multiplexer for each ring in the gateway office. Data tr~ ion on the fiber optic rings 55, 75 is preferably in accordance with one of the well-known SONET or synchronous digital hierarchy (SDH) tr~n~mic~ion protocols.
The directional antennas 100-105, 110, 111 may be of a sectorized architecture or may be phased array antennas with highly directional radio frequency beams. Such antennas are preferably used to decrease interference between the mobile base stations and the fixed radio ports, allowing greater spectrum reuse. Antenna diversity can be provided with two spatially separated radio beams separated in time with a predefined time-delay offset for easier separation at reception. Various techniques for obtaining high antenna diversity , CA 02218~46 1997-11-06 W O 96/39002 PCTnUS95107037 g are well known in the art and antennas employing such techniques are commercially available.
FIG. 4 is a block diagram representation of the moving base station 30. The station 30 in~ es a processor 130 connecte~l via radio 5 interfaces 132, 134 to the ~ntçnn~c 100, 101, respectively. The processor 130 may be a st~n-l~rd microprocessor and the radio interface circuits 132 may be st~n~l~rd radio interface circuits. The rnicroprocessor is ~lefeldbly programmedto handle the call proceccin~ functions performed in a prior art system by a call site or by a shared base station controller. In this manner, the moving base 10 station has greater autonomy and requires less colll-llul~ications with a shared base station controller or the like. The circuits 132, like the radio interface circuits 154 in the fixed radio port 50 and the radio interface circuits 164 in the fixed base station 70, are well known and commercially available circuits.
The radio interface between the mobile units 20, 25 and the 15 moving base stations 30, 40 and the fixed base station 70 is a standard radiointerface, well known in the art. The radio interface between the moving base stations 30, 40 and the fixed radio ports 50 is preferably a time division multiplexed, direct-sequence, spread-spectrum, code-division multiple-access interface (TDM/CDMA). Multiple channels between the base station and the 20 fixed radio ports are time division multiplexed as time slots in a data stream.
The data stream is spread with a pseudo-random code over the allocated spectrum. A pilot sequence is inserted in the transmitted signal for ease of synchronization in a well-known manner. The interface between the movable base station and the fixed radio port is preferably transparent to the overall 25 system in spectrum use.
Frequency division or time division may be used for duplex co-,----l..-ications. In the frequency division duplex (FDD) mode, data is simultaneously tr~ncmitte~i in both directions, each in a different spectrum band.
In a typical system in the FDD mode, the TDM frame tr~ncmiccion duration 30 will be a~ oxi...~tely 500 microseconds mzlking the interface substantially transparent to overall system delay.
CA 02218~46 1997-11-06 W 096/39002 PCTrUS95/07037 The interface between the mobile unit and the movable base may be the st~nd~rd IS-95-based PCS air interface st~nd~rd. The channel capacity for the so-called ".oYten-led mode" (2.5 mhz) has been determined to be seven ~nnel~ at 32 kilobits per second. The FCC allocated licensed spectrum for S personal co.. ~ ;cations services (PCS) inrlllcles 10-rnhz licenses and 30-mhz licenses. Each 1~mhz license provides two separated 5-mhz bands and each 30-rnhz license provides two separated 15-rnhz bands, for two-way co~ -ic~tions.
Two 5-mhz bands can support 14 duplex channels at 32 kilobits per second and two 15-mhz bands can ~U~JOl l 42 duplex channels at 32 kilobits per second.
Voice signals between a mobile unit and the gateway office are encoded in a standard fashion using ADPCM voice encoding with a Illil~illllllll bit rate of 32 kilobits per second in each channel. The interface between the moving base station and the fLxed radio port is adapted to carry up to 19 channels of 32 kilobits per second each at 16 bits per time slot. The frame 15 structure includes 16 bearer channels of 32 kilobits per second at 16 bits per time slot. The time division multiplexed frame rate between the movable base station and the fixed radio port is 608 kilobits per second. To achieve a procec~ing gain of 9 decibels, the frame rate is multiplied by a factor of 8, yielding 4,864 kilobits per second, which fit into a single 5-mhz band. FIG. 6 is 20 a tabular representation of the channel allocation showing 16 bearer channels plus 3 channels for sign~lling, control, and error code. FIG. 7 is a representation of ch~nnel~ 18 and 19 of FIG. 6.
The moving base stations are addressed using predefined code sequences derived in a known manner by the use of Walsh functions. U.S. Pat.
25 5,103,349 entitled "System and Method for Generating Signal Wave Forms in CDMA Cellular Telephone System" describes the use of Walsh functions for code generation. U.S. Pat. 5,103,349 is incorporated by reference herein. As described in that patent, by choosing a Walsh function of order 8 provides 8 orthagonal codes in the present embodiment using spread spectrum CDMA uses 30 the all 0 Walsh sequence as a pilot carrier with the other 7 sequences available for moving base station communications. The code sequences may be repeated as ABCDEFG; ABCDEFG; . . . Although fewer codes could be used, CA 02218~46 1997-11-06 W 096/39002 PCTnUS95107037 preferably no less than 3 are used. Bec~llse of dir~lhlg propagation times for signals between a particular moving base station and two or more different fixedradio ports, it is not possible to satisfy the condition of time ~lignm~nt required for Walsh function orthagonality for 2 or more fixed radio ports at one time.
5 For this purpose, two outer pseudonoise codes are used to provide ~lie.-. ;...i..z~tion between signals arriving at the moving base station from .lirreren fixed radio ports. The pselldonoice code rate is ~refelably 4,864 kilobits per second. The sequence length for the ll~ ed carrier signal is preferably 32,768 chips, as described in U.S. Pat. 5,103,459. The outer pseudonoise codes modulate the signal in quadrature phase shift keying.
The pilot signal will be tr~n~mitted in both directions, from the moving base stations to the fixed radio ports and vice, versa. This is made possible by the line of site fading characterized as Rician.
The pilot sequence will be long enough that a number of different sequences can be generated by shifts in the basic sequence. The separation will be great enough to ensure that there is no interference between pilot ~ign~lc.
Each moving base stations will use a different offset from a neighboring moving base station to provide signal separation. Similarly, each fixed radio port willuse a different offset from a neighboring fixed radio port.
The FCC has allocated a 20 mhz of unlicensed spectrum, including a 10 mhz band for voice products and a 10-mhz band for data products. Thus, one co"Lh,uous 10-megahertz channel is available and time division multiplex ...iccion is preferably used. The bit rate for both directions of tr~ncmiccion will be twice the frequency division duplex rate, introducing an overall delay of 25 500 microseconds and a processing gain of 9 decibels. In the time division duplex mode, the l~ ",ission times and direction, forward and reverse between the mobile unit and the moving base station and between the moving base station and the fixed radio ports, are aligned. In one half of the time division, duplex cycle signals are llall~ ed from the mobile unit to the moving base 30 station and, from there, to the fixed radio port. In the other half-cycle, signals are transmitted from the fixed radio port to the moving base station and then tothe mobile unit.
CA 02218~46 1997-11-06 W 096/39002 PCTrUS95/07037 The two 15-mhz licensed spectrum bands (30 mhz) are preferably divided into three 5-megahertz channels in each direction, lltili7ing the same architectllre as described earlier herein with respect to the 5-megahertz licensed SpC~ ulll. In the 15-mhz licensed spectrum, each of the 5-megahertz ch~nn~l~
5 will support 14 traffic ch~nnel~, for a total of 42 traffic channels in each 15-mhz band. The air interface between the moving base station and the fixed radio port, as well as the signal structure, can be modified and adapted to a variety of allocations of spectrum and air interface st~nd~rds.
In the present embodiment, as described earlier herein, 7 10 orthogonals codes are available for co~l~llullication between the fixed radioports 50 and the moving base stations 30, 40. As described earlier herein and depicted in FIGS. 6 and 7, one 16 bit co~ llunication ch~nnel, channel 19, is set aside for control and identification bits. As depicted in FIG. 7, channel 19 maycolllplise 7 control bits and 9 identification bits. The 9 identification bits 15 provide 512 unique identification numbers. Using 7 orthagonal codes and 512 identification numbers, 3,854 moving base stations can be uniquely identified.
When the moving base stations are separated by a spacing of 200 feet, the total distance of coverage using the 3,854 moving base stations is apploxi...~tely 135miles. FIG. 1 shows a portion of the system with moving base st~tion~ moving 20 in opposite directions along oppositely directed roadways and fixed radio ports with dual antennas. Vehicular traffic moving in opposite directions on the same roadway are preferably served by moving base stations on opposite sides of the roadway. Where each roadway has only one-way traffic, the system is preferably disposed between the roadways. In one embodiment of the invention, depicted 25 in FIG. 9, two separate loops 200, 205 are disposed between two separate roadways 206, 208 with the traffic on the roadways indicated by the arrows 207 and 209. The loops 200 and 205 comprise moving base stations 210 and 250, respectively. The base stations, in this embodiment, are moving in the directionindicated by the arrows 201 and 202. Since, as a practical matter, the loops 200, 30 205 are not of indefinite length, a plurality of loops may be required to cover a desired area. To avoid interruption in communications, the ends of the loops are preferably sufficiently close together, or overlapping, to provide an CA 02218~46 1997-11-06 W O g6/390~2 PCTnUS95JO7037 overlapping area of coverage for mobile units traveling in the area of the loop ends. This will allow one of the mobile stations nearing the end of the loop of which it is a part to hand off the call to a mobile station of the adjacent loop.
Each loop preferably has a single gateway for conn~ction to the S wire telephone network. One advantage of that ~lallg~lllent is that it e.limin~tes the need for registration of moving base st~tion.c, which is required where a moving base station moves between gateways. FIG. 9 shows a pair of gateways 215 associated with the loop 200 and a pair of gateways 255 associated with the loop 205. The two gateways of a loop are both connected to the fixed radio ports of the loop at all times and may be operated in a load sharing mode with each capable of h~n~lling the total teleco~ ication~s traffic for the loop in the event of a failure in one of the gateways.
To avoid intellu~ g co.lll-lu--ications with a mobile unit traveling along the roadway in the area where two adjacent loops end, any existing calls are handed off from the moving base station near the terminzlting end of its loop to a moving base station of the next loop. The h~nfloff process is essentially the same as a handoff between moving base stations on the sarne loop, except that the handed off call will be routed to the wire network to a different gateway. This procedure is equivalent to a handoff between cell sites of different cells in the eYi~ting cellular network in a manner which is well known in the art. The loops 200 and 205 may physically overlap to assure proper overlap of communications between moving base stations of the two loops and to avoid loss of comm-lnication with a mobile unit handed off from one loop to another.
The timing and synchlo,.~;Gation between the moving base station and a fixed radio port with which the moving base station communicates is phase-locked to the pilot signals received from the fixed radio port with which the moving base station comml-nicates. For synchronization purposes, the moving base station vill receive a Global Positioning Satellite (GPS) Coordinated Universal Time (UCT) timing signal once each second.
CDMA Technology is well-known for sensitivity to power control.
Specifically, the more powerful signals tend to "mask out" less powerful signals =
CA 022l8~46 l997-ll-06 W 096/39002 PCTrUS95/07037 at the receiver. Typically, elaborate power control schemes are implemented to ensure that all signals arrive at the receiver at the same level. In accordance with the system of this invention, hu..~ r, the sensiLivilr to power level of CDMA is used to advantage. The principles of signal ~ .,-icsion employed in 5 the system of the invention is illustrated in FIG. 8. Two power levels of radio tr~ ...ic!~ion, high (H) and low (L), are definP~l Referring to FIG. 1, high-power level signals are tr~n~mitte~l from the moving base station 30 to the mobile unit 20 and from the base station 30 to the fixed radio port 50. Low power level signals are l~ le-l from the fixed radio port 50 to the moving 10 base station 30. Similarly, low power signals are transmitted from the mobileunit 20 to the moving base station 30. Since the moving base station receives a low power level signal from the fixed radio port and ~ a high level power signal toward terminals, the high power level received at the mobile unit 20 will mask out any signals of the low power signal ll~ns"~ ed from the fixed 15 radio port to the moving base station. In a similar fashion, any low signal ~a~ litLed from the mobile unit 20 re~ ing the fixed radio port 50 will be m~cked by the high power level signal transmitted from the moving base station to the fixed radio port. As stated earlier, the antennas 100-105, 110, 111 are ~rerelably highly directional antennas with very little feedback from the transmit 20 signal to the receive signal. Feedback due to reflections and other extraneous sources can be readily elimin~ted at the moving base station using well-known noise c~nçell~tion techniques.
When a mobile unit set is first powered up or first enters a service area, the mobile unit must register in the manner described earlier, by 25 tr~n~mitting its unique address in the new service area. The address will be received by the closest moving base station 30 and transmitted via a fixed radioport and the gateway switch 60 to the telephone network. This registration procedure is required so that an incoming call for the mobile unit can be appl Opl iately directed.
The spacing of mobile based stations 20 and the fixed radio ports 50 of FIG. 1, together with the strength of the signal transmitted between the moving base stations and the fixed radio ports, determines the number of fixed CA 02218~46 1997-11-06 wo 96139002 PCTIUS95l07037 radio ports with which a moving base station can co~ icate at any point in time. The spacing and signal strength is preferably such that each fixed radio port receives signals from three moving base st~tionc When a fixed radio port r~ceives data, acco...~ .;ed by the identification number of the moving base S station, the processor 150 (FIG. 2) co~l,putes a signal quality indication on the received signal. The signal quality in~ tion is a figure of merit plefelably col~ ed as a function of signal strength and signal-to-noise ratio. It is added to the received data and added to the fiber optic ring 55 via the ADM 152. The gateway 60 preferably receives the same data from several different ones of the 10 fixed radio ports 50 and stores the data in an internal memory in the gateway 60 in association with the moving base station identification number and Walsh function spreading code. The address of the fixed radio port from which the data has been received is stored in the memory of processor 64 as well.
Accordhlgly, multiple copies of the same data tr~n~mitted by a single moving 15 base staation are stored in the memory of the processor 64 in the gateway. The signal quality indications colllpuled by the processors 150 in each of several fixed radio ports are compared to a predefined signal quality indication threshold, and the data corresponding to a signal quality indication below the threshold value is discarded. Otherwise, the data is retained. A cyclic 20 red-lnd~ncy code transmitted with the data is used to detect any TDM frame errors. The best data, i.e., associated with the best signal quality indication is transferred from the gateway 60 to the telephone network. Data received from the telephone network at the gateway 60 and intended for a registered mobile unit is stored in the memory of the processor 150 in a register particularly 25 associated with the moving base station currently serving the mobile unit. This data will be sent via the optical ring 55 to all fixed radio ports that are identified in the memory of the processor 65 as fixed radio ports with an acceptable signal quality indication. The received data will be transmitted fromeach of the fixed radio ports which received the data together with the 30 identification code and Walsh function code of the moving base station to which the data is directed. The tr~n~mi~ion of data from different fixed radio ports will be staggered, delayed by different amounts, so that they can be received and CA 022l8~46 l997-ll-06 W 096/39002 PCTrUS95/07037 separated at the moving base stations. The delays can be precisely controlled bymeans of synchronous distribution via the optical ring 55, in the SONET or SDH format. The receiving moving base station, by means of its processor 130, comr~res the multiple copies of the received data ~i~n~lc, aligns them and 5 combines them for the best reception.
Each of the moving base st~tion~ will have one of N ~c~igned codes, where N may be any number, but })r~fe~ably is at least 3 or more. Seven Walsh function codes are preferably used. The codes may be repeated in sequence, as for example, ABCDEFGABCDEFG. The codes are assigned in 10 sequence to the various moving base stations so that two moving base stationshaving the same code will be physically separated by a sufficient distance to venl interference in the co"~,.,-lllications between fixed radio ports and moving base stations having the same identity code. The operation of the fixed base stations 70 is essentially the same as that of a standard fixed base station.
15 In congested traffic areas, a mobile unit which is stopped or slowly moving, e.g., less than 30 miles per hour, will preferably be serviced by one of the fixed base stations 70. As the speed of travel of the mobile unit 20 increases, a handoff will occur between the fixed base station and a moving base station. The procedures for detellllinillg whether a mobile unit is to be served by a fixed 20 base station or a moving base station are the same procedures as described earlier herein in determining which moving base station is selected to serve a mobile unit, i.e., based on signal strength and error rate. Thus, when a call involving a mobile unit is initiated or when it is determined that a handoff should occur, the mobile unit may be h~nde(l from a moving station to a fixed 25 station, or vice versa. Each mobile unit monitors pilot signals from fixed and moving base stations and synchronizes to the base station providing the best signal. The mobile unit may "connect" with three fixed or moving base stations while searching for a fourth in what is known as the "soft" hand-off mode. As the speed of the vehicle increases, fixed or slow moving base stations will be 30 dropped. In more congested areas where traffic speed will vary between 0 and 60 miles per hour, base stations speed may, for example, be set to move at 30 WO 96/39002 PCTnUS95)D7D37 mph. The moving base station should then be able to ~commodate all traffic in the 0-60 mph range.
It will be understood that the above-described arrangement is merely illustrative of the application of the principles of the invention and that S other arr~em~-nt~ may be devised by those skilled in the art without departing from the scope of the invention as defined by the appended claims.
Claims
WHAT WE CLAIM IS:
1. Interface apparatus for establishing signal connections between a telephone office connected to a telephone network and mobile telephone units transmitting radio signals and moving in a specified direction, the interface apparatus comprising:
a stationary interface unit connected to the telephone office via a signal transmission connection;
a plurality of spaced apart movable base stations, each of the movable base stations uniquely associated with the telephone office and supported on a conveying device for limited movement in the specified direction independent of movement of the mobile telephone units and within an area defined relative to the stationary interface, the movable base stations each having an associated geographical service area defined relative to the stationary interface and operative to perform a plurality of call handling functions relative to mobile units in the associated geographical service area, the movable base stations each responsive to radio signals transmitted by the mobile telephone units to transmit corresponding radio signals to the stationary interface unit and the stationary interface unitresponsive to the radio signals transmitted from the movable base stations to transmit signals corresponding to the signals transmitted from the movable base stations to the telephone office via the signal transmission connection.
2. The interface apparatus in accordance with claim 1 wherein the mobile telephone units move along a roadbed and the conveying device extends parallel to the roadbed.
3. The interface apparatus in accordance with claim 2 wherein the conveying device comprises a rail movably supporting the movable base stations.
4. The interface apparatus in accordance with claim 2 wherein the stationary interface unit is disposed on one side of the conveying device opposite the roadbed.
5. The interface apparatus in accordance with claim 1 wherein the movable base stations each comprise signal processing circuitry and a first radio antenna directed toward the mobile telephone unit and a second radio antenna directed toward the stationary interface unit and wherein the stationary interface unit comprises signal processing circuitry and a radio antenna directed toward the movable interface unit, the movable interface unit responsive to radio signals received at the first antenna to transmit corresponding radio signals via the second antenna to the stationary interface unit and the stationary interface unit responsive to radio signals received via the radio antenna of the stationary interface unit to transmit corresponding signals to the telephone office via the signal transmission connection.
6. Interface apparatus for establishing signal connections between a telephone office and a plurality of mobile telephone units transmitting radio signals, certain of the mobile telephone units moving in a specified direction, the interface apparatus comprising:
a plurality of movable interface units uniquely associated with the telephone office; and a plurality of stationary interface units connected to the telephone office via a signal transmission connection;
the movable interface units moving at a predefined speed in the specified direction and along an interface unit path within a limited area defined relative to the stationary interface units and the movable interface units responsive to radio signals transmitted by a mobile telephone unit to transmit corresponding radio signals in the direction of the stationary interface units, each of the stationary interface units responsive to radio signals transmitted from an adjacent movable unit to transmit signals corresponding to the signals transmitted from the adjacent movable unit to the telephone office via the signal transmission connection.
7. The interface apparatus in accordance with claim 6 wherein:
the movable interface units are movable along an interface unit path extending in a direction parallel to the predefined path and having a first sideadjacent the predefined path;
the stationary interface units are spaced apart and disposed on a second side of the interface unit path opposite the first side of the interface unit path;
each of the movable interface units comprises signal processing circuitry and an associated first radio antenna directed toward the first side and an associated second radio antenna directed toward the second side;
each of the stationary interface units comprises signal processing circuitry and an associated radio antenna directed toward the interface unit path;
each of the movable interface units is responsive to radio signals received at the associated first antenna to transmit radio signals via the associated second antenna to the stationary interface unit; and each of the stationary interface units is responsive to radio signals received via the associated radio antenna to transmit corresponding signals to the telephone office via the signal transmission connection.
9. The interface apparatus in accordance with claim 6 wherein the predefined speed is a function of an average speed of the plurality of mobile telephone units.
10. The interface apparatus in accordance with claim 6 and further comprising a plurality of mobile telephone units moving along another path in anopposite direction opposite the specified direction and a plurality of movable interface units movable in the opposite direction and wherein:
the plurality of mobile telephone units moving in the specified direction move along a first roadbed and the plurality of mobile telephone unitsmoving in the opposite direction move along a second roadbed spaced apart from the first roadbed;
the plurality of movable interface units movable in the specified direction are disposed along one side of the first roadbed adjacent the second roadbed;
the plurality of movable interface units movable in the opposite direction are disposed along one side of the second roadbed adjacent the first roadbed; and the plurality of stationary interface units are disposed between the plurality of movable interface units movable in the specified direction and the plurality of movable interface units movable in the opposite direction.
11. The interface apparatus in accordance with claim 6 and further comprising a plurality of stationary interface units connected to the telephone office via a signal transmission connection and responsive to radio signals transmitted by a mobile telephone unit to transmit corresponding signals to the telephone office.
12. The interface apparatus in accordance with claim 1 wherein the radio signals transmitted between the movable interface unit and the stationary interface unit are transmitted in accordance with a code division multiple access, direct sequence, spread spectrum transmission signalling protocol.
13. The interface apparatus in accordance with claim 12 wherein signals transmitted from the mobile telephone unit to the movable interface unit are transmitted at a first power level and signals transmitted from the movable interface unit to the stationary interface unit are transmitted at a second power level higher than the first power level.
14. The interface apparatus in accordance with claim 1 wherein the movable interface unit is responsive to radio signals received from the stationary interface unit to transmit corresponding radio signals to the mobile telephone unit and wherein signals transmitted from the stationary interface unit to the movable interface unit are transmitted at a first power level and signals transmitted from the movable interface unit to the mobile telephone unit are transmitted at a second power level higher than the first power level.
15. The interface apparatus in accordance with claim 12 wherein data transmitted between the stationary interface unit and the movable interface unit is transmitted in a time division duplex manner.
16. The interface apparatus in accordance with claim 12 wherein data transmitted between the stationary interface unit and the movable interface unit is transmitted in a frequency division duplex manner.
17. The interface apparatus in accordance with claim 12 wherein each movable interface unit is synchronized to a selected stationary unit by transmission of pilot signals to the selected unit.
18. The interface apparatus in accordance with claim 6 wherein the telephone office is connected to a telephone network and wherein a plurality of stationary interface units are responsive to radio signals transmitted by an identified one of the movable interface units and each stationary interface unit responsive to radio signals from the identified movable interface unit is operative to compute a signal quality indication for data represented by the transmitted radio signals and to transmit to the telephone office data signals corresponding to the transmitted radio signals together with a corresponding signal quality indication, the telephone office responsive to the receipt of the data signals and signal quality indication to transmit to the telephone network data received from a selected one of the stationary interface units having a preferred signal quality indication.
19. The interface apparatus in accordance with claim 6 wherein each of the stationary units is responsive to a data message received from the telephone office to transmit a corresponding radio message to selected ones of the movable interface units and wherein the telephone office is operative to transmit a predetermined data message intended for a selected one of the movable interface units to selected ones of the stationary interface units and each of the selected ones of the stationary interface units is responsive to receipt of the predetermined data message to transmit corresponding radio signals to the selected one of the movable interface units.
20. The interface apparatus in accordance with claim 19 wherein the predetermined data message is transmitted to each of the selected ones of the stationary interface units in a timed sequence and the selected ones of the stationary interface units transmits the corresponding radio signals in a corresponding timed sequence.
22. A mobile telephone system comprising:
first and second telephone offices connected to a telephone network;
first closed loop having opposite ends and a second closed loop having opposite ends, one of the opposite ends of the first loop disposed adjacent one of the opposite ends of the second loop, each of the loops movably supporting a plurality of movable interface units, a plurality of stationary interface units disposed adjacent each of the loops, each connected to one of the telephone offices;
each movable interface unit responsive to radio telephone signals transmitted by a mobile telephone unit to transmit corresponding radio signals to one of the stationary interface units;
the telephone offices operative to record position of each of the movable base stations on each loop and to transmit an alert signal via one of the stationary interface units to a movable base station approaching one of the opposite ends of a loop and a movable base station receiving the alert signal responsive to the alert signal to indicate to mobile units communicating with a movable base station receiving the alert signal to transfer connections to another base station.
23. The system in accordance with claim 22 wherein one of the opposite ends of one of the loops overlaps one of the opposite ends of another of the loops.
24. The interface apparatus in accordance with claim 1 wherein each of the movable base stations has an associated service area and each of the movable base stations is operative to hand-off and receive existing calls to mobile units in an associated service area.
25. The interface apparatus in accordance with claim 1 wherein each of the movable base stations has an associated service area and each of the movable base stations is operative to perform a plurality of functions including locating an identified mobile unit in an associated service area.
26. The interface apparatus in accordance with claim 6 wherein each of the movable base stations has an associated service area and each of the movable base stations is operative to perform hand-off and receiving functions relative to existing calls for mobile units within an associated service area.
27. The interface apparatus in accordance with claim 6 wherein each of the movable base stations has an associated service area and is operative to perform a plurality of functions, including locating an identified mobile unit in an associated service area.
28. The apparatus in accordance with claim 1 wherein the movable interface unit is further responsive to radio signals received from the telephone office via the stationary interface unit to locate an identified mobile unit and to transmit to the identified mobile unit signals corresponding to radio signals received from the telephone office.
29. The apparatus in accordance with claim 1 and comprising a plurality of stationary interface units and wherein the area is defined relative to the plurality of interface units.
30. A method of signal communication between a telephone switching office and a mobile telephone unit moving in a specified direction andtransmitting radio signals, the method comprising the steps of:
providing a fixed radio port connected to the telephone switching office;
moving a movable base station uniquely associated with the telephone switching office in the specified direction within a limited area defined relative to the fixed radio port;
receiving at the movable base station radio signals transmitted from the mobile telephone unit; and transmitting from the movable base station to the fixed radio port radio signals corresponding to the radio signals transmitted from the mobile telephone unit.
31. The method in accordance with claim 30 and further comprising the steps of receiving at the movable base station radio signals transmitted from the fixed radio port; and transmitting from the movable base station to the mobile telephone unit radio signals transmitted from the fixed radio port.
32. The method in accordance with claim 31 wherein the mobile telephone unit moves along a roadbed and wherein the step of moving the movable base station comprises the step of moving the movable base station in one direction along a path having opposite ends and extending substantially parallel to the roadbed for a limited distance and the step of reversing direction of travel of the movable base station when the movable base station reaches one end of the limited distance.
33. The method in accordance with claim 30 wherein the step of moving a movable base station comprises moving a plurality of moving base stations in the specified direction and further comprising the step of determining signal quality of received signals originating from an identified mobile telephone unit at each of the plurality of movable base stations and the step of selecting a preferred quality signal.
34. The method in accordance with claim 30 and further comprising the step of transmitting radio signals between the movable base station and the fixed radio port in accordance with a code division multiple access, direct sequence, spread spectrum transmission protocol.
35. The method in accordance with claim 31 wherein the radio signals transmitted from the mobile telephone unit to the movable base station are transmitted at a first power level and radio signals transmitted from the movable base station to the fixed radio port are transmitted at a second power level lower than the first power level.
36. The method in accordance with claim 31 wherein radio signals transmitted from the fixed radio port to the movable base station are transmitted at a first power level and wherein radio signals transmitted from the movable base station to the mobile telephone unit are transmitted at a second power level higher than the first power level.
37. The method in accordance with claim 31 wherein the radio signals transmitted between the fixed radio port and the movable base station are transmitted in a time division duplex manner.
38. The method in accordance with claim 37 and further comprising the step of synchronizing the movable base station to a selected interface unit by transmitting a pilot signal from the movable base station to the selected interface unit.
39. A method of handling telephone calls between a telephone office and a mobile telephone unit moving in a specified direction, the method comprising the steps of:
moving a plurality of movable base station in the specified direction;
establishing a telephone call between the telephone office and the mobile unit via a selected one of the movable base stations;
monitoring signal communication from the mobile telephone unit at the selected one of the base stations and controlling at the selected base station hand-off of the telephone call from the selected base station to another of the plurality of moving base stations.
1. Interface apparatus for establishing signal connections between a telephone office connected to a telephone network and mobile telephone units transmitting radio signals and moving in a specified direction, the interface apparatus comprising:
a stationary interface unit connected to the telephone office via a signal transmission connection;
a plurality of spaced apart movable base stations, each of the movable base stations uniquely associated with the telephone office and supported on a conveying device for limited movement in the specified direction independent of movement of the mobile telephone units and within an area defined relative to the stationary interface, the movable base stations each having an associated geographical service area defined relative to the stationary interface and operative to perform a plurality of call handling functions relative to mobile units in the associated geographical service area, the movable base stations each responsive to radio signals transmitted by the mobile telephone units to transmit corresponding radio signals to the stationary interface unit and the stationary interface unitresponsive to the radio signals transmitted from the movable base stations to transmit signals corresponding to the signals transmitted from the movable base stations to the telephone office via the signal transmission connection.
2. The interface apparatus in accordance with claim 1 wherein the mobile telephone units move along a roadbed and the conveying device extends parallel to the roadbed.
3. The interface apparatus in accordance with claim 2 wherein the conveying device comprises a rail movably supporting the movable base stations.
4. The interface apparatus in accordance with claim 2 wherein the stationary interface unit is disposed on one side of the conveying device opposite the roadbed.
5. The interface apparatus in accordance with claim 1 wherein the movable base stations each comprise signal processing circuitry and a first radio antenna directed toward the mobile telephone unit and a second radio antenna directed toward the stationary interface unit and wherein the stationary interface unit comprises signal processing circuitry and a radio antenna directed toward the movable interface unit, the movable interface unit responsive to radio signals received at the first antenna to transmit corresponding radio signals via the second antenna to the stationary interface unit and the stationary interface unit responsive to radio signals received via the radio antenna of the stationary interface unit to transmit corresponding signals to the telephone office via the signal transmission connection.
6. Interface apparatus for establishing signal connections between a telephone office and a plurality of mobile telephone units transmitting radio signals, certain of the mobile telephone units moving in a specified direction, the interface apparatus comprising:
a plurality of movable interface units uniquely associated with the telephone office; and a plurality of stationary interface units connected to the telephone office via a signal transmission connection;
the movable interface units moving at a predefined speed in the specified direction and along an interface unit path within a limited area defined relative to the stationary interface units and the movable interface units responsive to radio signals transmitted by a mobile telephone unit to transmit corresponding radio signals in the direction of the stationary interface units, each of the stationary interface units responsive to radio signals transmitted from an adjacent movable unit to transmit signals corresponding to the signals transmitted from the adjacent movable unit to the telephone office via the signal transmission connection.
7. The interface apparatus in accordance with claim 6 wherein:
the movable interface units are movable along an interface unit path extending in a direction parallel to the predefined path and having a first sideadjacent the predefined path;
the stationary interface units are spaced apart and disposed on a second side of the interface unit path opposite the first side of the interface unit path;
each of the movable interface units comprises signal processing circuitry and an associated first radio antenna directed toward the first side and an associated second radio antenna directed toward the second side;
each of the stationary interface units comprises signal processing circuitry and an associated radio antenna directed toward the interface unit path;
each of the movable interface units is responsive to radio signals received at the associated first antenna to transmit radio signals via the associated second antenna to the stationary interface unit; and each of the stationary interface units is responsive to radio signals received via the associated radio antenna to transmit corresponding signals to the telephone office via the signal transmission connection.
9. The interface apparatus in accordance with claim 6 wherein the predefined speed is a function of an average speed of the plurality of mobile telephone units.
10. The interface apparatus in accordance with claim 6 and further comprising a plurality of mobile telephone units moving along another path in anopposite direction opposite the specified direction and a plurality of movable interface units movable in the opposite direction and wherein:
the plurality of mobile telephone units moving in the specified direction move along a first roadbed and the plurality of mobile telephone unitsmoving in the opposite direction move along a second roadbed spaced apart from the first roadbed;
the plurality of movable interface units movable in the specified direction are disposed along one side of the first roadbed adjacent the second roadbed;
the plurality of movable interface units movable in the opposite direction are disposed along one side of the second roadbed adjacent the first roadbed; and the plurality of stationary interface units are disposed between the plurality of movable interface units movable in the specified direction and the plurality of movable interface units movable in the opposite direction.
11. The interface apparatus in accordance with claim 6 and further comprising a plurality of stationary interface units connected to the telephone office via a signal transmission connection and responsive to radio signals transmitted by a mobile telephone unit to transmit corresponding signals to the telephone office.
12. The interface apparatus in accordance with claim 1 wherein the radio signals transmitted between the movable interface unit and the stationary interface unit are transmitted in accordance with a code division multiple access, direct sequence, spread spectrum transmission signalling protocol.
13. The interface apparatus in accordance with claim 12 wherein signals transmitted from the mobile telephone unit to the movable interface unit are transmitted at a first power level and signals transmitted from the movable interface unit to the stationary interface unit are transmitted at a second power level higher than the first power level.
14. The interface apparatus in accordance with claim 1 wherein the movable interface unit is responsive to radio signals received from the stationary interface unit to transmit corresponding radio signals to the mobile telephone unit and wherein signals transmitted from the stationary interface unit to the movable interface unit are transmitted at a first power level and signals transmitted from the movable interface unit to the mobile telephone unit are transmitted at a second power level higher than the first power level.
15. The interface apparatus in accordance with claim 12 wherein data transmitted between the stationary interface unit and the movable interface unit is transmitted in a time division duplex manner.
16. The interface apparatus in accordance with claim 12 wherein data transmitted between the stationary interface unit and the movable interface unit is transmitted in a frequency division duplex manner.
17. The interface apparatus in accordance with claim 12 wherein each movable interface unit is synchronized to a selected stationary unit by transmission of pilot signals to the selected unit.
18. The interface apparatus in accordance with claim 6 wherein the telephone office is connected to a telephone network and wherein a plurality of stationary interface units are responsive to radio signals transmitted by an identified one of the movable interface units and each stationary interface unit responsive to radio signals from the identified movable interface unit is operative to compute a signal quality indication for data represented by the transmitted radio signals and to transmit to the telephone office data signals corresponding to the transmitted radio signals together with a corresponding signal quality indication, the telephone office responsive to the receipt of the data signals and signal quality indication to transmit to the telephone network data received from a selected one of the stationary interface units having a preferred signal quality indication.
19. The interface apparatus in accordance with claim 6 wherein each of the stationary units is responsive to a data message received from the telephone office to transmit a corresponding radio message to selected ones of the movable interface units and wherein the telephone office is operative to transmit a predetermined data message intended for a selected one of the movable interface units to selected ones of the stationary interface units and each of the selected ones of the stationary interface units is responsive to receipt of the predetermined data message to transmit corresponding radio signals to the selected one of the movable interface units.
20. The interface apparatus in accordance with claim 19 wherein the predetermined data message is transmitted to each of the selected ones of the stationary interface units in a timed sequence and the selected ones of the stationary interface units transmits the corresponding radio signals in a corresponding timed sequence.
22. A mobile telephone system comprising:
first and second telephone offices connected to a telephone network;
first closed loop having opposite ends and a second closed loop having opposite ends, one of the opposite ends of the first loop disposed adjacent one of the opposite ends of the second loop, each of the loops movably supporting a plurality of movable interface units, a plurality of stationary interface units disposed adjacent each of the loops, each connected to one of the telephone offices;
each movable interface unit responsive to radio telephone signals transmitted by a mobile telephone unit to transmit corresponding radio signals to one of the stationary interface units;
the telephone offices operative to record position of each of the movable base stations on each loop and to transmit an alert signal via one of the stationary interface units to a movable base station approaching one of the opposite ends of a loop and a movable base station receiving the alert signal responsive to the alert signal to indicate to mobile units communicating with a movable base station receiving the alert signal to transfer connections to another base station.
23. The system in accordance with claim 22 wherein one of the opposite ends of one of the loops overlaps one of the opposite ends of another of the loops.
24. The interface apparatus in accordance with claim 1 wherein each of the movable base stations has an associated service area and each of the movable base stations is operative to hand-off and receive existing calls to mobile units in an associated service area.
25. The interface apparatus in accordance with claim 1 wherein each of the movable base stations has an associated service area and each of the movable base stations is operative to perform a plurality of functions including locating an identified mobile unit in an associated service area.
26. The interface apparatus in accordance with claim 6 wherein each of the movable base stations has an associated service area and each of the movable base stations is operative to perform hand-off and receiving functions relative to existing calls for mobile units within an associated service area.
27. The interface apparatus in accordance with claim 6 wherein each of the movable base stations has an associated service area and is operative to perform a plurality of functions, including locating an identified mobile unit in an associated service area.
28. The apparatus in accordance with claim 1 wherein the movable interface unit is further responsive to radio signals received from the telephone office via the stationary interface unit to locate an identified mobile unit and to transmit to the identified mobile unit signals corresponding to radio signals received from the telephone office.
29. The apparatus in accordance with claim 1 and comprising a plurality of stationary interface units and wherein the area is defined relative to the plurality of interface units.
30. A method of signal communication between a telephone switching office and a mobile telephone unit moving in a specified direction andtransmitting radio signals, the method comprising the steps of:
providing a fixed radio port connected to the telephone switching office;
moving a movable base station uniquely associated with the telephone switching office in the specified direction within a limited area defined relative to the fixed radio port;
receiving at the movable base station radio signals transmitted from the mobile telephone unit; and transmitting from the movable base station to the fixed radio port radio signals corresponding to the radio signals transmitted from the mobile telephone unit.
31. The method in accordance with claim 30 and further comprising the steps of receiving at the movable base station radio signals transmitted from the fixed radio port; and transmitting from the movable base station to the mobile telephone unit radio signals transmitted from the fixed radio port.
32. The method in accordance with claim 31 wherein the mobile telephone unit moves along a roadbed and wherein the step of moving the movable base station comprises the step of moving the movable base station in one direction along a path having opposite ends and extending substantially parallel to the roadbed for a limited distance and the step of reversing direction of travel of the movable base station when the movable base station reaches one end of the limited distance.
33. The method in accordance with claim 30 wherein the step of moving a movable base station comprises moving a plurality of moving base stations in the specified direction and further comprising the step of determining signal quality of received signals originating from an identified mobile telephone unit at each of the plurality of movable base stations and the step of selecting a preferred quality signal.
34. The method in accordance with claim 30 and further comprising the step of transmitting radio signals between the movable base station and the fixed radio port in accordance with a code division multiple access, direct sequence, spread spectrum transmission protocol.
35. The method in accordance with claim 31 wherein the radio signals transmitted from the mobile telephone unit to the movable base station are transmitted at a first power level and radio signals transmitted from the movable base station to the fixed radio port are transmitted at a second power level lower than the first power level.
36. The method in accordance with claim 31 wherein radio signals transmitted from the fixed radio port to the movable base station are transmitted at a first power level and wherein radio signals transmitted from the movable base station to the mobile telephone unit are transmitted at a second power level higher than the first power level.
37. The method in accordance with claim 31 wherein the radio signals transmitted between the fixed radio port and the movable base station are transmitted in a time division duplex manner.
38. The method in accordance with claim 37 and further comprising the step of synchronizing the movable base station to a selected interface unit by transmitting a pilot signal from the movable base station to the selected interface unit.
39. A method of handling telephone calls between a telephone office and a mobile telephone unit moving in a specified direction, the method comprising the steps of:
moving a plurality of movable base station in the specified direction;
establishing a telephone call between the telephone office and the mobile unit via a selected one of the movable base stations;
monitoring signal communication from the mobile telephone unit at the selected one of the base stations and controlling at the selected base station hand-off of the telephone call from the selected base station to another of the plurality of moving base stations.
Priority Applications (8)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| EP95922951A EP0858715A1 (en) | 1995-06-02 | 1995-06-02 | Mobile radio communications system with moving base station |
| PL95323682A PL177554B1 (en) | 1995-06-02 | 1995-06-02 | Mobile radio communication system with mobile base station |
| AU27657/95A AU704764B2 (en) | 1995-06-02 | 1995-06-02 | Mobile radio communications system with moving base station |
| PCT/US1995/007037 WO1996039002A1 (en) | 1995-06-02 | 1995-06-02 | Mobile radio communications system with moving base station |
| CA002218546A CA2218546A1 (en) | 1995-06-02 | 1995-06-02 | Mobile radio communications system with moving base station |
| IL11849296A IL118492A (en) | 1995-06-02 | 1996-05-30 | Mobile radio communication system with moving base station |
| FI974375A FI974375A (en) | 1995-06-02 | 1997-12-01 | Mobile communication systems equipped with mobile support stations |
| NO975533A NO975533L (en) | 1995-06-02 | 1997-12-01 | Mobile communication system with mobile base station |
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| PCT/US1995/007037 WO1996039002A1 (en) | 1995-06-02 | 1995-06-02 | Mobile radio communications system with moving base station |
| CA002218546A CA2218546A1 (en) | 1995-06-02 | 1995-06-02 | Mobile radio communications system with moving base station |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2218546A1 true CA2218546A1 (en) | 1996-12-05 |
Family
ID=25679737
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002218546A Abandoned CA2218546A1 (en) | 1995-06-02 | 1995-06-02 | Mobile radio communications system with moving base station |
Country Status (6)
| Country | Link |
|---|---|
| EP (1) | EP0858715A1 (en) |
| AU (1) | AU704764B2 (en) |
| CA (1) | CA2218546A1 (en) |
| FI (1) | FI974375A (en) |
| IL (1) | IL118492A (en) |
| WO (1) | WO1996039002A1 (en) |
Families Citing this family (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CA2263031A1 (en) * | 1999-02-26 | 2000-08-26 | Kasten Chase Applied Research Limited | Communications based train control |
| US7206294B2 (en) * | 2001-08-15 | 2007-04-17 | Meshnetworks, Inc. | Movable access points and repeaters for minimizing coverage and capacity constraints in a wireless communications network and a method for using the same |
| US20050174974A1 (en) * | 2003-08-19 | 2005-08-11 | Sonntag Artur H. | System and method for roaming in data -and communication- networks |
| US9585191B2 (en) | 2011-08-28 | 2017-02-28 | Redline Communications Inc. | Mobile base station |
Family Cites Families (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE3621990C2 (en) * | 1985-07-18 | 1993-12-09 | Man Technologie Gmbh | Communication device inside vehicles |
| DE3528886A1 (en) * | 1985-08-12 | 1987-02-19 | Siemens Ag | Radiotelephony system |
| FI88451C (en) * | 1991-07-02 | 1993-05-10 | Telenokia Oy | FOERFARANDE FOER ATT UTFOERA POSITIONSDATERING FRAON ETT ROERLIGT CELLRADIOTELEFONSYSTEM TILL ETT ANNAT CELLRADIOTELEFONSYSTEM |
| US5404570A (en) * | 1992-11-23 | 1995-04-04 | Telefonaktiebolaget L M Ericsson | Radio coverage in closed environments |
-
1995
- 1995-06-02 CA CA002218546A patent/CA2218546A1/en not_active Abandoned
- 1995-06-02 EP EP95922951A patent/EP0858715A1/en not_active Withdrawn
- 1995-06-02 AU AU27657/95A patent/AU704764B2/en not_active Ceased
- 1995-06-02 WO PCT/US1995/007037 patent/WO1996039002A1/en not_active Application Discontinuation
-
1996
- 1996-05-30 IL IL11849296A patent/IL118492A/en not_active IP Right Cessation
-
1997
- 1997-12-01 FI FI974375A patent/FI974375A/en unknown
Also Published As
| Publication number | Publication date |
|---|---|
| FI974375A0 (en) | 1997-12-01 |
| WO1996039002A1 (en) | 1996-12-05 |
| FI974375A (en) | 1997-12-01 |
| EP0858715A1 (en) | 1998-08-19 |
| IL118492A (en) | 1999-12-22 |
| IL118492A0 (en) | 1996-09-12 |
| AU2765795A (en) | 1996-12-18 |
| AU704764B2 (en) | 1999-05-06 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| EEER | Examination request | ||
| FZDE | Discontinued | ||
| FZDE | Discontinued |
Effective date: 20040602 |