United States Patent (19)
`Trompower et al.
`
`54 CELLULAR COMMUNICATION SYSTEM
`WITH DYNAMICALLY MODIFIED DATA
`TRANSMISSION PARAMETERS
`
`(75) Inventors: Michael L. Trompower, Navarre,
`
`- .
`Ohio; Paul F. Struhsaker, Plano, Tex.;
`George L. Grim, III, Youngstown;
`James K. Holt, Hudson, both of Ohio;
`Victor K. Paulsen, Mineral Well, Tex.
`73 Assignee: Telxon Corporation, Akron, Ohio
`
`21 Appl. No.: 08/566,502
`22 Filed:
`Dec. 4, 1995
`
`Related U.S. Application Data
`
`63 Stinuation-in-part of application No. 08/523.942, Sep. 6,
`
`USOO595O124A
`Patent Number:
`11
`(45) Date of Patent:
`
`5,950,124
`Sep. 7, 1999
`
`5,291,516 3/1994 Dixon et al..
`5,321,721 6/1994 Yamaura et al. ........................... 375/1
`5,335,249 8/1994 Krueger et al. ............................. 375/1
`5,341,396 8/1994 Higgins et al..
`
`5,353.300 10/1994 Lee et al. - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 375/1
`
`5,363,404 11/1994 Kotzin et al. ............................... 375/1
`5,377,256 12
`2- .
`.
`.
`f1994 Franklin et al. .
`5,425,051 6/1995 Mahany.
`5,450,616 9/1995 Rom.
`5,497.505
`3/1996 Koohgoli et al. ....................... 455/452
`5,509,050 4/1996 Berland ................................... 455/557
`5,511,073
`4/1996 Padovani et al..
`5,565,982 10/1996 Lee et al..
`5,574,771 11/1996 Driessen et al. .......................... 379/57
`5,614.914 3/1997 Bolgiano et al. ....................... 342/364
`5,673.260 9/1997 Umeda et al..
`5,687,166 11/1997 Natali et al. ............................ 455/403
`5,689,524 11/1997 Takaki et al..
`5,694,417 12/1997 Andren et al..
`FOREIGN PATENT DOCUMENTS
`
`5
`6
`
`Ref
`Cited
`eferences Cite
`
`
`
`579372 1/1994 European Pat. Off..
`(51) Int. Cl. ................................................. H04B 7700
`622911 11/1994 European Pat. Off..
`52 U.S. Cl. .......................... 455/422; 455/466; 455/557;
`455/561; 455/562; 455/550; 455/551; 455/571;
`Primary Examiner Wellington Chin
`455/572; 455/403; 455/23:455/517; 455/65.
`455/126; 375/281; 342/463; 342/364; 342/362 Alist Entitles Boisselle & Skvl
`58 Field of Search ..................................... 455/422, 466,
`styley gent, Or Firm-Renner, Otto, BoISSelle
`ylar,
`455/557, 561, 562, 550, 551, 571, 572,
`u u
`ABSTRACT
`403, 23,517, 65, 126, 522; 375/281; 342/463,
`57
`364, 362
`An apparatus and proceSS for improving the performance of
`Ilul
`y
`ing di
`C
`a Cellular COmmunicatIOn SWStem uSIng direct Sequence
`Spread spectrum techniques. The apparatus and process
`enable dynamic modification of communication System
`parameters including PN code length, chipping rate and
`modulation technique for transmission of a data packet.
`Modification is based on proximity of the transmitter and
`receiver, transmitter and receiver capabilities and other
`factors. The System evaluates tradeoffs between data trans
`mission Speed and communication range to improve System
`performance.
`
`U.S. PATENT DOCUMENTS
`4,041,391 8/1977 Deerkoski ............................... 375,281
`4,665,404 5/1987 Christy et al. ...
`... 342/463
`4,672,658 6/1987 Kavehrad et al. ........................ 379/63
`4,907,224 3/1990 Scoles et al.
`4,930,140 5/1990 Cripps et al..
`SES 8.1: that
`2 - . 12
`WCIl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
`5,164,958 11/1992 Omura.
`5,177,766
`1/1993 Holland et al..
`5,204.876 4/1993 Bruckert et al. ............................ 375/1
`
`375/1
`
`46 Claims, 12 Drawing Sheets
`
`23
`
`MOBILE
`610 TERMINAL 62
`
`23
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`TEN 820
`
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`Qualcomm Incorporated
`Exhibit 1007
`Page 1 of 32
`
`

`

`U.S. Patent
`
`Sep. 7, 1999
`
`Sheet 1 of 12
`
`5,950,124
`
`
`
`110 -A
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`ORIGINAL
`DATA
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`ORIGINAL
`DATA
`BITS
`
`101
`
`Page 2 of 32
`
`

`

`U.S. Patent
`
`Sep. 7, 1999
`
`Sheet 2 of 12
`
`5,950,124
`
`290
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`TERMINAL
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`Page 3 of 32
`
`

`

`U.S. Patent
`
`Sep. 7, 1999
`
`Sheet 3 of 12
`
`5,950,124
`
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`Page 4 of 32
`
`

`

`U.S. Patent
`
`Sep. 7, 1999
`
`Sheet 4 of 12
`
`5,950,124
`
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`Page 5 of 32
`
`

`

`U.S. Patent
`US. Patent
`
`Sep. 7, 1999
`Sep. 7, 1999
`
`Sheet 5 of 12
`Sheet 5 0f 12
`
`5,950,124
`5,950,124
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`Page 6 of 32
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`Page 6 of 32
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`
`
`
`
`
`
`

`

`U.S. Patent
`
`Sep. 7, 1999
`
`Sheet 6 of 12
`
`5,950,124
`
`
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`
`Page 7 of 32
`
`

`

`U.S. Patent
`
`Sep. 7, 1999
`
`Sheet 7 of 12
`
`5,950,124
`
`SET MOBILE
`PARAMETERS-1510
`
`TRANSMIT
`PACKET
`
`SIGNA
`RECEIVED FROM
`BASE
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`
`Page 8 of 32
`
`

`

`U.S. Patent
`US. Patent
`
`Sep. 7, 1999
`Sep. 7, 1999
`
`Sheet 8 of 12
`Sheet 8 0f 12
`
`5,950,124
`5,950,124
`
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`Page 9 of 32
`
`Page 9 of 32
`
`
`
`
`
`

`

`U.S. Patent
`
`Sep. 7, 1999
`
`Sheet 9 of 12
`
`5,950,124
`
`
`
`g9 °61-I
`
`ÅRH_LITTONIO
`
`O
`
`S H
`
`Page 10 of 32
`
`

`

`U.S. Patent
`
`Sep. 7, 1999
`
`Sheet 10 of 12
`
`5,950,124
`
`NON-CONTROLLABLE
`TRANSMITTER
`
`
`
`
`
`
`
`610 -
`
`
`
`610 y : 710a
`NON-CONTROLLABLE
`TRANSMITTER
`
`Z 710b
`CONTROLLABLE
`TRANSMITTER
`
`Page 11 of 32
`
`

`

`U.S. Patent
`
`Sep. 7, 1999
`
`Sheet 11 of 12
`
`5,950,124
`
`PN CODE
`SELECTION
`SIGNAL
`
`
`
`
`
`
`
`
`710a Y
`713
`STATIC
`PN CODE
`SEOUENCER
`
`DATA
`
`Fig. 7D
`DATA
`
`PN CODE
`SELECTION
`SIGNAL
`
`
`
`710b -
`72
`ADJUSTABLE
`PN CODE
`SECUENCER
`
`
`
`62O Y
`
`MODULATED
`PN CODED
`SIGNAL
`
`MODULATED
`PN CODED
`SIGNAL
`
`Page 12 of 32
`
`

`

`U.S. Patent
`
`Sep. 7, 1999
`
`Sheet 12 of 12
`
`5,950,124
`
`620 Y
`
`MODULATED
`PN CODED
`SIGNAL
`
`
`
`
`
`810a .
`
`
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`
`
`STATIC
`PN CODE
`817. MSEQUENCER
`Fig . 8D
`
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`SIGNAL
`
`
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`814
`DEMODULATOR
`
`816
`FILTER
`
`819
`CORRELATOR
`
`
`
`ADJUSTABLE
`PN CODE
`SEOUENCER
`
`Page 13 of 32
`
`

`

`5,950,124
`
`1
`CELLULAR COMMUNICATION SYSTEM
`WITH DYNAMICALLY MODIFIED DATA
`TRANSMISSION PARAMETERS
`
`CROSS-REFERENCE TO RELATED
`APPLICATION
`This application is a Continuation-In-Part of Ser. No.
`08/523,942, filed Sep. 6, 1995, entitled CELLULAR COM
`MUNICATION SYSTEM WITH DYNAMICALLY MODI
`FIED DATA TRANSMISSION PARAMETERS, the
`entirety of which is incorporated herein by reference.
`
`TECHNICAL FIELD
`This invention relates generally to the field of wireless
`data communication Systems and, in particular, to a direct
`Sequence spread Spectrum cellular communication System
`which dynamically modifies data transmission parameters to
`enhance System performance.
`
`15
`
`2
`where no signals can pass. Further, the cell size may be
`decreased by machinery located in the vicinity of the base
`Station which generates excessive noise levels that degrade
`a signal transmitted by the base Station. Undesirable signals
`that interfere with the transmission and reception of a
`transmitted Signal are collectively referred to as noise Sig
`nals. A useful quantitative measure of relative noise in a
`communication System is the Signal-to-noise ratio (SNR).
`The SNR is the ratio of the amplitude of a desired signal at
`any given time to the amplitude of noise signals at that same
`time.
`Generally, when a mobile terminal is powered up, it
`“registers” with a base station through which the mobile
`terminal can maintain wireleSS communication with the
`network. In order to register, the mobile terminal must be
`within the cell range of the base Station and the base Station
`must likewise be situated within the effective cell range of
`the mobile terminal. It is generally not possible to have one
`base Station Service a large area by itself. This is due to
`transmission power restrictions governed by the FCC and
`the fact that the extra hardware needed to provide a mobile
`terminal with Such a large cell range would add significantly
`to the size and weight of the mobile terminal thereby making
`it leSS desirable to use. Thus, cellular communication Sys
`tems generally have Several base Stations Spaced apart Such
`that the collective cell area coverage of the base Stations is
`Sufficient to cover the entire area in which a mobile terminal
`may roam. AS the location of the mobile terminal changes,
`the base station with which the mobile terminal was origi
`nally registered may fall outside of the geographic cell range
`of the mobile terminal. Therefore, the mobile terminal may
`"deregister with the base Station it was originally registered
`to and register with another base station which is within its
`communication range.
`When designing a cellular communication System for a
`region, an appropriate number of base Stations must be
`Selected and their locations determined to assure cell cov
`erage for the region. Each additional base Station increases
`the cost of the communication System by the incremental
`cost of the base station itself and installation fees. Both the
`cost of the base Station and the installation costs are often
`great. When hardwiring a new base Station to the network,
`both a data line and a power line must be provided. The data
`line allows the base Station to transmit and receive infor
`mation from the system backbone while the power line
`provides continual power to Support the operations of the
`base Station. Although wireleSS base Stations do not require
`data lines Since all data is communicated wirelessly, they do
`require power. However, providing power lines to wireleSS
`base stations can often be difficult. This is especially true in
`the common situation where a wireleSS base Station is
`Situated in a large Outdoor Storage facility having a concrete
`foundation, Such as areas near a Shipyard or loading dock.
`Typically, electrical outlets are not readily accessible in Such
`areas and therefore power lines must be Supplied to the
`wireless base station from the network or elsewhere. Power
`lines could be located on the Surface of the concrete
`foundation, however, this provides an undesirable obstacle
`that must be avoided by heavy loading vehicles typically
`found operating at Such facilities. Consequently, a trench is
`often created through the concrete in order to house the
`power lines. Unfortunately, providing Such a trench adds a
`Significant amount of extra time and cost to the installation
`process. Another method of Supplying power to wireleSS
`base Stations could involve Suspending power lines from
`power poles. However, this method has been found implau
`sible given the difficulty involved with erecting such power
`
`BACKGROUND
`In recent years, the use of cellular communication SyS
`tems having mobile terminals which communicate with a
`hardwired network, Such as a local area network (LAN) and
`25
`a wide area network (WAN), has become widespread. Retail
`Stores and warehouses, for example, may use cellular com
`munications Systems to track inventory and replenish Stock.
`The transportation industry may use Such Systems at large
`outdoor Storage facilities to keep an accurate account of
`incoming and outgoing Shipments. In manufacturing
`facilities, Such Systems are useful for tracking parts, com
`pleted products and defects.
`A typical cellular communication System includes a num
`ber of fixed base Stations interconnected by a cable medium
`35
`to form a hardwired network. The hardwired network is
`often referred to as a System backbone. Also included in
`many cellular communication Systems are intermediate base
`Stations which are not directly connected to the hardwired
`network.
`Intermediate base Stations, often referred to as wireleSS
`base Stations, increase the area within which base Stations
`connected to the hardwired network can communicate with
`mobile terminals. Unless otherwise indicated, the term “base
`station' will hereinafter refer to both base stations hardwired
`to the network and wireleSS base Stations.
`ASSociated with each base Station is a geographic cell. A
`cell is a geographic area in which a base Station has Sufficient
`Signal Strength to transmit data to and receive data from a
`mobile terminal with an acceptable error rate. The error rate
`for transmitted data is defined as the ratio of the number of
`transmitted data bits received in error to the total number of
`bits transmitted. It is economically inefficient to design a
`communications System with a “Zero’ error rate. Rather,
`depending on the requirements of users of the System, an
`acceptable error rate is determined. For example, an accept
`able error rate may be set at a maximum error correcting rate
`capability of an error correcting code utilized by the System.
`The shape of each cell is primarily determined by the type
`of antenna associated with a given base Station. For instance,
`base Stations which communicate with mobile terminals
`often have omnidirectional type antennas which provide for
`generally circular shaped cells and allow for a wide area of
`coverage. In many instances, however, the cell of a base
`Station is not completely Symmetrical because physical
`Structures within the cell may partially block data Signals
`emanating from the base Station or create “dead Spots”
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`Page 14 of 32
`
`

`

`5,950,124
`
`15
`
`25
`
`3
`poles in the concrete foundation. As a result, there is a Strong
`need in the art for a manner of Supplying power to a wireleSS
`base Station that is not unduly burdensome or costly.
`WireleSS communication Systems. Such as those described
`above often involve spread spectrum (SS) technology. ASS
`communication System is one in which the transmitted
`frequency spectrum or bandwidth is much wider than abso
`lutely necessary. Wideband frequency modulation (FM) is
`an example of an analog SS communication System. With
`regard to a digital SS communication System, the transmis
`sion bandwidth required by the baseband modulation of a
`digital Signal is expanded to a wider bandwidth by using a
`much faster Switching rate than used to represent the original
`bit period. Operationally, prior to transmission, each original
`data bit to be transmitted is converted or coded to a sequence
`of “sub bits” often referred to as “chips” (having logic values
`of Zero or one) in accordance with a conversion algorithm.
`The coding algorithm is usually termed a spreading func
`tion. Depending on the spreading function, the original data
`bit may be converted to a Sequence of five, ten, or more
`chips. The rate of transmission of chips by a transmitter is
`defined as the “chipping rate'.
`ASS communication System transmits chips at a wider
`Signal bandwidth (broadband signal) and a lower signal
`amplitude than the corresponding original data would have
`been transmitted at baseband. At the receiver, a despreading
`function and a demodulator are employed to convert or
`decode the transmitted chip code Sequence back to the
`original data on baseband. The receiver, of course, must
`receive the broadband Signal at the transmitter chipping rate.
`An advantage of a SS communication System is that the
`representation and communication of an original data bit as
`a Sequence of chips over a wide bandwidth in lieu of
`transmitting the original data bit over a narrow bandwidth
`generally results in a lower error rate at the receiver. This is
`especially true in transmission environments characterized
`by noise having high amplitude and short duration, i.e.,
`“Spike' noise. The probability of a receiver extracting and
`correctly interpreting a data bit represented by a transmitted
`Sequence of chips interspersed with random, uncorrelated
`noise Spikes is greater than the probability of the receiver
`extracting and correctly interpreting a transmission of Single
`bits interspersed with Such random noise Spikes.
`In essence, a SS communication System utilizes increased
`bandwidth and a coding Scheme to reduce error rate vis-a-vis
`a conventional baseband System. The reduction in error rate
`results in an improved output SNR at the receiver. For any
`communication system, the difference between output SNR
`and input SNR is defined as the processing gain of the
`50
`System. In a SS communication System, the processing gain
`of the System is the ratio of the transmission code rate to the
`original information bit rate. For example, assume that the
`SS coding Scheme utilizes a Sequence of ten chips to
`represent one original data bit. If the ten chips are transmit
`ted at a chipping rate Such that their collective duration is
`equal to a Single bit period at baseband, then the processing
`gain of the SS System is approximately equal to ten. Com
`munication range is determined by a fully processed SNR at
`a receiver. The fully processed SNR is the processing gain
`asSociated with SS communication techniques combined
`with the received Signal Strength.
`The coding Scheme of a SS digital communication System
`utilizes a pseudo-randombinary sequence (PRSB). One type
`of a digital SS communication System is known as a direct
`sequence spread spectrum (DSSS) system. In a DSSS
`System, coding is achieved by converting each original data
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`4
`bit (Zero or one) to a predetermined repetitive pseudo noise
`(PN) code. A type of PN code is illustrated in FIG. 1. For this
`example, the digital data Signal 110 is made up of a binary
`“1” bit and a “0” bit. APN code 120 representing the digital
`data Signal 110 is comprised of a Sequence often Sub bits or
`chips, namely, “1”, “0”, “1”, “1”, “0”, “1”, “1”, “1”, “0”,
`“1”.
`The digital data signal 110 is coded or spread by modulo
`2 multiplying (e.g., via an “EXCLUSIVE NOR” (XNOR)
`function) of the digital data signal 110 with the PN code 120.
`If the data bit is a “1”, then the resulting spread data Signal
`(PN coded signal) in digital form corresponds to the PN code
`120. However, if the data bit to be coded is a “0”, then the
`Spread data Signal in digital form will correspond to a code
`130. AS can be seen, the code 130 is the inverse of PN code
`120. That is, the PN code and its inverse are used to
`represent data bits “1” and “0” respectively.
`APN code length refers to a length of the coded Sequence
`(the number of chips) for each original data bit. As noted
`above, the PN code length effects the processing gain. A
`longer PN code yields a higher processing gain which results
`in an increased communication range. The PN code chipping
`rate refers to the rate at which the chips are transmitted by
`a transmitter System. A receiver System must receive,
`demodulate and despread the PN coded chip Sequence at the
`chipping rate utilized by the transmitter System. At a higher
`chipping rate, the receiver System is allotted a Smaller
`amount of time to receive, demodulate and despread the chip
`Sequence. AS the chipping rate increases So to will the error
`rate. Thus, a higher chipping rate effectively reduces com
`munication range. Conversely, decreasing the chipping rate
`increases communication range.
`The spreading of a digital data Signal by the PN code does
`not effect overall signal Strength (or power) the data being
`transmitted or received. However, by Spreading a signal, the
`amplitude at any one point typically will be less then the
`original (non-spread) signal.
`It will be appreciated that increasing the PN code length
`or decreasing the chipping rate to achieve a longer commu
`nication range will result in a slower data transmission rate.
`Correspondingly, decreasing the PN code length or increas
`ing the chipping rate will increase data transmission rate at
`a price of reducing communication range.
`FIG. 1A schematically illustrates a transmitter system or
`assembly 100 of a DSSS system. Original data bits 101 are
`input to the transmitter system 100. The transmitter system
`includes a modulator 102, a spreading function 104 and a
`transmit filter 106. The modulator 102 modulates the data
`onto a carrier using, for example, a binary phase shift keying
`(BPSK) modulation technique. The BPSK modulation tech
`nique involves transmitting the carrier in-phase with the
`oscillations of an oscillator or 180 degrees out-of-phase with
`the oscillator depending on whether the transmitted bit is a
`“0” or a “1”. The spreading function 104 converts the
`modulated original data bits 101 into a PN coded chip
`Sequence, also referred to as Spread data. The PN coded chip
`Sequence is transmitted via an antenna So as to represent a
`transmitted PN coded sequence as shown at 108.
`FIG. 1A also illustrates a receiver System or assembly,
`shown generally at 150. The receiver system 150 includes a
`receive filter 152, a despreading function 154, a bandpass
`filter 156 and a demodulator 158. The PN coded data 108 is
`received via an antenna and is filtered by the filter 152.
`Thereafter, the PN coded data is decoded by a PN code
`despreading function 154. The decoded data is then filtered
`and demodulated by the filter 156 and the demodulator 158
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`respectively to reconstitute the original data bits 101. To
`receive the transmitted spread data, the receiver system 150
`must be tuned to the same predetermined carrier frequency
`and be set to demodulate a BPSK signal using the same
`predetermined PN code.
`More Specifically, to receive a SS transmission Signal, the
`receiver System must be tuned to the same frequency as the
`transmitter assembly to receive the data. Furthermore, the
`receiver assembly must use a demodulation technique which
`corresponds to the particular modulation technique used by
`the transmitter assembly (i.e. same PN code length, same
`chipping rate, BPSK). Because mobile terminals communi
`cate with a common base Station, each device in the cellular
`network must use the same carrier frequency and modula
`tion technique.
`A drawback associated with current cellular communica
`tion systems is that PN code parameters such as PN code
`length and chipping rate must be Selected to provide per
`formance based on average communication range and aver
`age noise conditions. The data rate/range tradeoff leads to a
`cell size/throughput tradeoff in the communication System.
`The rate that each transmission occurs will limit the size of
`each cell. Thus, it would be desirable to have a cellular
`communication System wherein PN code parameter, modu
`lation complexity and other transmitting and receiving
`parameters could be dynamically modified for each trans
`mission based on distance between the transmitter and
`receiver and noise conditions Such that an improved data
`transmission rate for that transmission could be achieved
`thereby enhancing System performance.
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`SUMMARY OF THE INVENTION
`The present invention includes an apparatus and a proceSS
`for enhancing the performance capabilities of a cellular
`communication System utilizing DSSS techniques. The cel
`lular communication System of the present invention
`includes a plurality of mobile terminals and a plurality of
`base Stations. The base Stations may be connected to a
`hardwired network backbone or serve as wireless base
`Stations. Each base Station can transmit and receive data in
`its respective cell. For a given communication between a
`mobile terminal and a base Station, the mobile terminal and
`the base station can adjust the PN code length and the
`chipping rate depending on communication conditions to
`increase the transmission rate while retaining an acceptable
`error rate. Moreover, the System also provides that System
`components can adjust between other cellular communica
`tion System transmission parameterS Such as between dif
`ferent modulation Schemes and/or different transmitter
`power levels in conjunction with PN code adjustments to
`further enhance the performance capabilities of the System.
`Each base station and mobile terminal of the cellular
`communication System or network of the present invention
`includes a transmitter System and a receiver System.
`Furthermore, each transmitter System and receiver System
`preferably is capable of, respectively, transmitting or receiv
`ing PN coded signals formed with PN codes having different
`code lengths and chipping rates. Accordingly, as conditions
`of the wireleSS communication link between the base Station
`and mobile terminal change, the present invention advanta
`geously may adjust the PN code values to obtain the best
`available data rate possible for the current range and noise
`conditions thereby optimizing the performance capabilities
`of the cellular communication System as a whole.
`In a first illustrative example, when a mobile terminal and
`a base Station are located in relatively close proximity to
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`each other, the System in accordance with the present
`invention may select and utilize a short PN code length (e.g.,
`eleven chips per original data bit) resulting in a relatively
`fast data transmission rate. The short PN code length will
`result in a relatively low processing gain and a correspond
`ing decreased communication range. However, because the
`base Station and mobile terminal are close in proximity, the
`decreased communication range does not significantly
`increase the error rate. If the mobile terminal moves away
`from the base Station Such that the terminal is outside a
`communication range or cell when communicating using the
`short PN code length, the cellular communication system of
`the present invention recognizes the changing conditions
`and the base Station and mobile terminal Suitably increase
`the PN code length (e.g., to twenty-two chips per original
`data bit) to provide for a higher processing gain and thereby
`greater communications range. The greater processing gain
`afforded by the longer PN code length reduces the data
`transmission rate. Despite the Slower transmission rate
`between the mobile Station terminal and the base Station,
`however, the overall eXchange of data between the base
`station and all other mobile terminals will not be effected
`unless this base Station is operating close to full capacity.
`Therefore, in most instances, the reduced transmission rate
`between a Specific mobile terminal and a base Station should
`have little effect on the communication System as a whole.
`On the other hand, when a mobile terminal and a base
`Station are in need of a fast data transmission rate and
`conditions otherwise permit, the mobile unit and base Station
`according to the present invention may Select a PN code
`having a relatively rapid chipping rate value (e.g. 22 MHz).
`If the spectral bandwidth needs to be decreased due to,
`among other reasons, excessive noise on closely Situated
`frequency bands, the mobile units and base Stations may
`decrease the chipping rate (e.g. to 11 MHz) to decrease the
`required transmission bandwidth. In this case, the data
`transmission rate is reduced commensurate with the nar
`rower bandwidth.
`In a Second embodiment of this invention, each base
`Station and mobile terminal of a cellular communication
`System or network may or may not be capable of varying
`their respective chipping rates and PN code lengths.
`Therefore, a cellular network is provided in which PN code
`values are dynamically modified based on the capabilities of
`the respective transmitters and receivers.
`For example, a base Station capable of dynamically vary
`ing PN code values may be communicating with a closely
`positioned mobile terminal which transmits and receives
`data only at a Single, predetermined PN code length and
`chipping rate. Although a shorter PN code length could be
`Selected based on the close range, the mobile terminal may
`be incapable of Supporting the shorter PN code length.
`Therefore, the PN code length supported by the mobile
`terminal is utilized.
`In another aspect of the present invention, additional
`System modulation parameters may be altered by System
`components to optimize the data transmission rate/range
`tradeoff for each communication. For example, in a situation
`where a high data transmission rate is required, a base
`Station may select to use a high order modulation Scheme,
`for example, 16 QAM, 32 QAM, etc. In a situation where an
`increased cell size, lower transmitter power and/or a lower
`data error rate is required, the base Station may Select a lower
`order modulation scheme (e.g., BPSK, QPSK, etc.).
`In yet another aspect of the present invention, transmis
`Sion power is also Selectable by System components. Thus,
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`7
`in a situation where a strong PN coded signal is necessitated
`because the mobile terminal is relatively distant from the
`base Station, the present invention may Select to use a high
`power level to transmit the PN coded signal. Conversely, if
`the battery of a mobile terminal is running low, the present
`invention may select a lower power level to transmit the PN
`coded signal in order to conserve the battery's energy. Also,
`where the mobile terminal is located in Very close proximity
`to the base Station, the present invention may Select to use
`an even lower power level to transmit the PN coded signals
`back and forth between the communication devices So that
`the receivers of each device are not Saturated.
`In yet a further aspect of the present invention, the System
`components may also Select to transmit and receive PN
`coded Signals using a variety of antennas having different
`gain and directivity characteristics. For example, where a
`base Station is positioned in the center of a cell, the present
`invention may select to use an omnidirectional antenna So
`that the base Station may transmit and receive Signals in all
`directions. In another example, where a base Station is to
`communicate a longer distance, the present invention may
`Select to use a yagi directional antenna So that the base
`Station may transmit a signal with a higher gain.
`According to another feature of the invention, the wireleSS
`base Stations may be Supplied power through a Solar power
`System having Solar panels, charging circuitry and a battery
`system. This obviates the need for trenching in order to bury
`power lines and/or Suspending power lines as dis