U.S. patent application number 09/782817 was filed with the patent office on 2001-06-21 for sectorized cell having non-redundant broadband processing unit.
Invention is credited to Schmutz, Thomas R..
Application Number | 20010004592 09/782817 |
Document ID | / |
Family ID | 22342345 |
Filed Date | 2001-06-21 |
United States Patent
Application |
20010004592 |
Kind Code |
A1 |
Schmutz, Thomas R. |
June 21, 2001 |
Sectorized cell having non-redundant broadband processing unit
Abstract
A technique for converting a non-sectorized cell to a sectorized
cell having multiple sectors utilizing a single broadband
processing unit. The spectrum of a given frequency band is divided
into multiple bands. In the receive path, respective sub-bands are
used to convey analog RF signals from a subscriber in respective
sectors to an associated transceiver. Each of the transceivers
includes a front end for receiving incoming RF signals and an
analog-to-digital converter for converting the analog signal to a
digital data stream. The digital data streams from transceivers are
combined, and supplied to a single channelizer which, in turn,
supplies the data to a TDM bus for transmission to a PSTN network.
In the reverse path from the PSTN network, TDM digital data signals
emanating from a TDM bus are supplied to a combiner which feeds
each of the respective transceivers with appropriate data from the
combiner. The transceivers convert the digital signal to analog
form. After conversion, power amplifiers associated with the
respective sectors effect emission of radiated power in the
respective sectors.
Inventors: |
Schmutz, Thomas R.;
(Indialantic, FL) |
Correspondence
Address: |
ROBERT J. SACCO
AKERMAN, SENTERFITT & EIDSON, P.A.
222 Lakeview Avenue, 4th Floor
P. O. Box 3188
West Palm Beach
FL
33402-3188
US
|
Family ID: |
22342345 |
Appl. No.: |
09/782817 |
Filed: |
February 14, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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09782817 |
Feb 14, 2001 |
|
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09112149 |
Jul 9, 1998 |
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Current U.S.
Class: |
455/447 ;
455/446 |
Current CPC
Class: |
Y02D 70/00 20180101;
Y02D 30/70 20200801; H04W 16/28 20130101; H04W 88/08 20130101 |
Class at
Publication: |
455/422 ;
455/446; 455/447 |
International
Class: |
H04Q 007/20 |
Claims
What is claimed is:
1. A receiver apparatus in a cellular communication system,
comprising: an antenna device to sectorize a cell into a plurality
of sectors which accommodate a plurality of subchannels,
respectively, said plurality of sectors conveying a plurality of
analog RF signals, respectively; a plurality of receiver units to
receive said plurality of analog RF signals from said plurality of
sectors, respectively, to convert said plurality of analog RF
signals to a plurality of digital data streams, respectively, and a
structure to combine said plurality of digital data streams into a
single digital data stream, and a single channelizer to receive
said single digital data stream, to generate therefrom a digital
data signal associated with said plurality of subchannels of said
plurality of sectors, and to supply said digital data signal to a
bus.
2. The receiver apparatus according to claim 1, wherein said
plurality of receiver units are broadband receivers.
3. A transmitter apparatus in a cellular communication system,
comprising: an antenna device to sectorize a cell into a plurality
of sectors which accommodate a plurality of subchannels,
respectively; a single combiner to receive a digital data signal
representative of subchannel data associated with said plurality of
sectors received from a bus, and to generate therefrom a combined
digital data signal, and a plurality of transmitter units each to
receive said combined digital data signal from said single
combiner, to select from said combined digital data signal said
subchannel data associated with said respective plurality of
sectors, and to convert said subchannel data into an analog signal
for emission.
4. The transmitter according to claim 3, further comprising a
plurality of power amplifiers in said plurality of sectors,
respectively, to amplify each said analog signal for emission, said
plurality of power amplifiers in said plurality of sectors
operating at lower power levels than a power amplifier in a
non-sectorized cell.
5. The transmitter unit according to claim 3, wherein said
plurality of transmitter units each include a digital band pass
filter which receives said combined digital data signal from said
single combiner and which passes said subchannel data associated
with said respective plurality of sectors.
6. The transmitter unit according to claim 3, wherein said
plurality of transmitter units are broadband transmitters.
7. A method for receiving data in a sectorized cell, comprising the
steps of: sectorizing a cell into plurality of sectors which
accommodate a plurality of subchannels, respectively, said
plurality of sectors conveying a plurality of analog RF signals,
respectively; receiving said plurality of analog RF signals from
said plurality of sectors, respectively; converting said plurality
of analog RF signals to a plurality of digital data streams,
respectively; combining said plurality of digital data streams into
a single digital data stream, and providing said single digital
data stream to a single combiner for generating therefrom digital
data signals associated with said plurality of subchannels of said
plurality of sectors.
8. A method for transmitting data in a sectorized cell, comprising
the steps of: sectorizing a cell into plurality of sectors which
accommodate a plurality of subchannels, respectively; receiving
digital data signals representative of subchannel data associated
with said plurality of sectors; providing said digital data signals
to a single combiner for generating therefrom a single combined
digital data signal; selecting from said combined digital data
signal said subchannel data associated with said respective
plurality of sectors; converting said subchannel data into a
plurality of analog signals, and amplifying said plurality of
analog signals for emission.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation application of and claims
the priority from U.S. application Ser. No. 09/112,149, entitled
"SECTORIZED CELL HAVING NON-REDUNDANT BROADBAND PROCESSING UNIT",
filed Jul. 9, 1998, the entirety of which is incorporated herein by
reference.
BACKGROUND
[0002] 1. Field of the Invention
[0003] The present invention relates to wireless communication
systems, but more particularly, to a method and system for
attaining sectorization in a cellular communication system
utilizing a single broadband processing unit.
[0004] 2. Discussion of the Prior Art
[0005] In order to provide multi-channel voice and data
communications over a broad geographical area, wireless
communication providers currently install base station transceivers
in protected and maintainable structures, known as cell sites. A
cell site encompasses an antenna, a tower or building upon which
the antenna is mounted, high-power amplifiers, duplexers,
transmitters, receivers and broadband processing equipment. The
broadband processing equipment channelizes and combines digital
signals on multiple channels that are associated with respective
subscribers. The digital signals, however, are communicated over
the air with subscribers in the analog domain. Thus, the base
station equipment further includes analog-to-digital and
digital-to-analog converters, depending on the direction of
information flow, as described in commonly owned U.S. Pat. Nos.
5,535,240 and 5,592,480 which issued Jul. 9, 1996 and Jan. 7, 1997,
respectively, to Ronald R. Carney, et al., incorporated herein by
reference.
[0006] The cell itself is an area on the ground that is generally
depicted as a hexagon. This is the simplest way to illustrate the
cellular idea, but in reality, the actual shape of the cell and the
coverage provided by the radiated signal from the cell site is
rarely as regular, uniform and clearly defined. The actual shape of
the cell depends upon the contours and the condition of the terrain
surrounding the cell site. Factors such as the size and number of
trees and/or the degree of urbanization determine how large an area
one cell can cover. The cell may itself be sectorized wherein it is
provided with an antenna designed to concentrate energy in an arc
of 120 degrees rather than the usual 360 degrees. Different
frequencies may be used for each sector, and these frequencies may
be repeated among cells. Using the sectorization, the cell site is
able to accommodate communication for a greater number of
subscribers. The instant application is directed to sectorization
which is sometimes referred to as cell-splitting.
[0007] Each sector is configured to provide two-way (duplex)
multi-channel communication capability for only a limited portion
of the frequency spectrum that is allotted to the wireless
communication service provider. A typical cellular communication
channel consists of a pair of frequencies, one for each direction
of transmission, used for full-duplex operation. A typical
transceiver consists of multiple sets of discrete receiver and
transmitter signal processing components in order to service a
particular portion of the frequency spectrum, usually 400 30 Khz
channels within a 12 MHZ bandwidth. The receiver section of a
typical transceiver includes a dedicated set of signal processing
components, including a front end, an intermediate frequency (IF)
section and a baseband section.
[0008] A primary limitation in current cellular communication
systems is that a service provider is only allocated a fixed number
of frequencies with which to handle subscriber calls. Typically,
there must be a 35 mile separation between cells using the same
frequency set, so that subscribers communicating on the same
frequencies do not interfere with one another. Frequency reuse
allows subscribers to use the same frequencies in adjoining cells
without interference, thereby allowing a service provider to
accommodate more subscribers.
[0009] Whenever a base station employs sectorization, however, each
sector requires its own broadband processing unit to perform
digital combining and channelizing. Unfortunately, such replication
of digital processing equipment increases the complexity and
expense of the base station.
SUMMARY OF THE INVENTION
[0010] It is a general objective of the present invention to
increase the channel capacity of a cell using existing broadband
processing equipment.
[0011] It is a more specific objective of the invention to provide
a scheme for sectorizing a cell without replication of broadband
processor units.
[0012] It is another object of the invention to provide a
sectorized communication cell using lower power transmitters for
the respective sectors.
[0013] In accordance with the invention, the improvement comprises
a technique in which a non-sectorized cell is converted to a
sectorized cell having multiple sectors. In a preferred embodiment,
the spectrum of a given frequency band having a center frequency
'.OMEGA..sub.0 is divided into multiple bands (three, for example)
having center frequencies '.OMEGA..sub.0, '.OMEGA..sub.0-.alpha.
and '.OMEGA..sub.0+.alpha. (in the case where three sectors are
employed). In the receive path, respective sub-bands are used to
convey analog RF signals in respective sectors to a transceiver.
Each of the transceivers include a front end for receiving incoming
RF signals and an analog-to-digital converter for converting the
analog signal to a digital data stream. The digital data streams
from transceivers are combined, i.e., processed by exclusive
or'ing, and supplied to a single channelizer which, in turn,
supplies the data to a TDM bus. In the reverse path, TDM digital
data signals emanating from TDM bus are supplied to a combiner
which feeds each of the respective transceivers, which select the
appropriate data from the combiner by digital filtering or
processing. The transceivers convert the digital signal to analog
form. After conversion, power amplifiers associated with the
respective sectors effect emission of radiated power in the
respective sectors.
[0014] Advantageously, amplifiers in the sectorized improvement
operate at lower power levels than the single high power amplifier
of a non-sectorized cell thereby providing substantial cost
savings. More importantly, instead of deploying multiple Carney
engines, the improved sectorized cell requires only a single Carney
engine, thereby providing further economies. The invention only
requires software modification of the Carney engine used in a
single cell site to handle information distributed in different
spectral bands associated with the sectors.
[0015] These and other objects of the invention will become
apparent upon review of the accompanying disclosure when read in
conjunction with the accompanying drawing figures, wherein like
reference numerals designate the same number of corresponding parts
throughout the several views.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 depicts a frequency reuse scheme in a cellular
communication system useful for describing the present
invention;
[0017] FIG. 2A illustrates a sectorized cell among plural cells in
a frequency reuse scheme of a cellular communication system;
[0018] FIG. 2B depicts respective transmitter and receiver paths of
a base station transceiver in which the present invention is
employed;
[0019] FIG. 3 illustrates processing of information signals in the
transmit path of the base station transceiver of FIG. 2B;
[0020] FIG. 4 illustrates processing of information signals in the
receive path of the base station transceiver of FIG. 2B;
[0021] FIG. 5 depicts a circuit block diagram of the improvement of
the present invention; and
[0022] FIG. 6 depicts a transceiver unit of the circuit diagram of
FIG. 5.
DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS
[0023] The geographic disbursements optimizes service coverage with
the entire bandwidth (e.g. 12 MHz) available to the service
provider, and ensures non-interfering coverage among dispersed cell
sites. Over a broad geographical area however, the frequency
allocation within respective cells and the separation between
adjacent cell sites may be prescribed to effectively prevent mutual
interference among any of the channels of the system. Thus,
frequency reuse is the core concept of cellular communications. A
rule of thumb in the cellular industry states that a channel can be
reused again in every seven cells. The application of this rule
varies due to the factors that determine the size of a cell and the
propagation of cellular transmissions such as the particular
terrain, the degree and density of urban growth, the expected
number of subscribers, etc. Since a system operator cannot add
channels to their system--each system is limited to 400
channels--frequency reuse schemes are often employed.
[0024] FIG. 1 depicts a typical cellular communication pattern. The
frequency assignments are fixed to seven discrete channel sets. The
frequencies used in this arrangement of cells helps prevent
interference between cells with identical frequency assignments
(i.e. co-channel cells) by separating these cells by at least two
cells of different frequency assignments. The instant sectorization
scheme allows for one cell to handle more than one frequency
set.
[0025] FIG. 2A depicts a sectorized cell resulting from
implementation of the invention. By changing the antenna design in
the cell so that radiated energy is concentrated in an arc of 120
degrees rather than the complete 360 degree circle, the number of
cells appears to increase. Using the sectorization technique, only
the antenna needs to be changed, and the additional equipment
associated with a cell site can remain the same. If each of the
seven cells shown in FIG. 2A were sectorized, the resulting system
would appear to have a total of twenty-one cells, and therefor
could accommodate twenty times more subscriber communications
simultaneously.
[0026] FIG. 2B shows a non-sectorized cellular transceiver site
over which the present invention is an improvement. In the
non-sectorized site, digital data signals from a PSTN (or other
data network) via time division multiplex (TDM) bus 10 are conveyed
to and from subscriber units via antennas 12 and 14. In a receive
path, a receiver 16 receives broadband RF signals from subscribers
via antennas 12 and 14. Duplexer 13 isolates the respective
transmit and receive paths. Receiver 16 converts the broadband
analog signals to a digital data stream which is supplied to a
channelizer 18 associated with antenna 12. The channelizer 18
separates, in a manner described in U.S. Pat. No. 5,592,480, the
digital data stream into multiple data channels associated with
respective subscribers and supplies the same to TDM bus 10. An
antenna 14 operating at a different frequency at another cell or
sector receives signals for processing by a tandem channelizer 19
operating at a co-located or distant cell site. Multiple receive
antennas and channelizers may be employed, although only two are
illustrated. The combination of the channelizer and combiner is
called a Carney engine.
[0027] On the transmit side, signals from multiple data channels
originating from TDM bus 10 are supplied to a combiner 20. Combiner
20 supplies serial bit streams along respective outputs 22 and 24
to a transmitter unit 26 which converts the digital data on
respective paths to analog signal. Analog signals from the
transmitter 26 drive a high power amplifier 28 to produce an RF
signal for transmission to subscribers via duplexer 13 and antenna
12.
[0028] FIG. 3 depicts the basic transmitter section 100 used with
the instant invention. A receiver section 200 is discussed with
reference to FIG. 4. The transmitter section 100, along with the
receiver section 200 comprise a transceiver. The transmitter
section 100 comprises a transmitter unit 110, an FFT based bandpass
sampling signal combiner 130, a reverse In-Phase/Quadrature (I/Q)
translator 107, a digital-to-analog (D-A) converter 140, and a
plurality of digital signal processor (DSP) units 120-1 . . .
120-n, one DSP unit per channel. The transmitter section couples an
antenna 90 for communicating over channels offered by the cellular
communications service provider. The DSP units are coupled to
receive respective ones of a plurality of digitized voice/data
communication signals which are to be transmitted over respective
frequency channels, 1 . . . N.
[0029] The DSP units 120-1 . . . 120-n modulate and perform
pre-transmission error correction on respective ones of the
plurality of incoming communication signals, and supply processed
ones of the narrowband communication channels at respective ports.
From the ports the modulated communication signals are supplied via
channel links 121-1 . . . 121-n to respective ports of the bandpass
sampling signal combiner unit 130, which outputs a combined signal.
The combined signal represents the contents of a wideband signal
which is a composite of respective narrowband signal channels input
to the digital transmitter signal processor unit 120. One bandpass
sampling signal combiner 130 is installed at each cell site,
thereby allowing the transmitted channels to be combined with
minimum insertion loss and maximum signal isolation between
channels.
[0030] The bandpass sampling signal combiner 130 of the present
invention is adapted for use an Advanced Mobile Phone Service
(AMPS) 400 channel/30 KHz system, as well as a European 50
channel/200 KHz Global System for Mobile Radio (GSM) cellular
standard.
[0031] For 30 KHz channels, a sample rate of 50 KHz is assumed. For
200 KHz, a 300 KHz sample rate is assumed. The combiner 130
receives channelized data as baseband signals from the DSP units
120-1 . . . 120-n, via channel links 121-1 . . . 121-n. The output
of the combiner 130 is coupled to the I/Q translator unit 107. The
reverse I/Q unit 107 receives respective in-phase and quadrature
(I/Q) signal components from the combiner 130 via (I/Q) links 171,
172, respectively, and provides a combined output signal to the
digital-to-analog (D/A) converter 140.
[0032] The output of the D/A converter 140 connects with the
wideband multichannel transmitter 110. An amplified output of the
transmitter 110 is then supplied to the antenna 90 for transmission
over the air.
[0033] FIG. 4 depicts the basic receiver section 200 of the
transceiver used with the present invention. The receiver section
200 includes a wideband receiver 210, a high speed
analog-to-digital (A/D) converter 230, a forward
in-phase/quadrature (I/Q) translator 270, an FFT based channelizer
220, a bandpass filter, a lowpass filter, and digital signal
processing (DSP) units 241-1 . . . 241-n, one DSP unit per channel.
The receiver section 200 couples with the antenna 90 for receiving
cellular communication signals.
[0034] The output of the wideband receiver 210 is a downconverted,
multi-channel signal containing the contents of all of the 30 KHz
voice/data channels assigned to the service provider. The
multichannel baseband signal is forwarded to the analog-to-digital
converter 230, and then to the I/Q translator 270. The I/Q
translator provides I and Q signals to the channelizer 220 via
links 271, 272, respectively. The I/Q translator 270 processes the
signals within any of the 400 channels of the system, and then
outputs the signals via (I/Q) links 271 and 272 to the FFT
channelizer 220. The FFT channelizer 220 then extracts from the
composite digitized multichannel (I/Q) signal, respective
narrowband channel signals representative of the contents of
respective ones of the 30 KHz communication channels received by
the wideband receiver 210. From the channelizer 220, the signals
are fed to the DSP units on lines 242-1 . . . 242-n respectively.
Each of the digital receiver processor units 241-1 . . . 241-n
demodulates the signals of the respective channel and performs
associated error correction processing based upon the content of
the modulated signal. The demodulated signals derived by the DSP
units 241-1 . . . 241-n are then coupled to a carrier interface
such as a Public Switched Telephone Network (PSTN).
[0035] FIG. 5 depicts the improvement provided by the present
invention in which a non-sectorized cell is converted to a
sectorized cell having three sectors. Although three are
illustrated, the principles may be applied to any degree of
sectorization. In the illustrated example, the spectrum of a given
frequency band having a center frequency '.OMEGA..sub.0 is divided
into three equal bands having center frequencies '.OMEGA..sub.0,
'.OMEGA..sub.0-.alpha., and '.OMEGA..sub.0+.alpha.. Assuming that a
cell is allocated a bandwidth of five megahertz, each sub-band, for
example, may be designed to handle one megabit per second data
stream in a sub-band of one megahertz in bandwidth. In the receive
path, respective sub-bands are used to convey analog RF signals in
respective sectors with antennas 30, 32 and 34 through respective
duplexers 36, 38 and 40. The duplexers supply the received signals
to respective transceiver units 42, 44 and 46. Each of the
transceivers include a front end for receiving incoming RF signals
and an analog-to-digital converter for converting the analog signal
to a digital data stream. According to the present invention, the
digital data streams from transceivers 42, 44 and 46 are combined,
i.e., processed by exclusive or'ing, and supplied to a single
channelizer 48 which, like channelizers 18 and 19 (FIG. 2B)
supplies digital data signals associated with respective
subscribers to TDM bus 50.
[0036] In the reverse path, TDM digital data signals which emanate
from TDM 50 are supplied to a combiner 52 which feeds each of the
respective transceivers 42, 44 and 46. Each of the transceivers 42,
44 and 46 select the appropriate data from the combiner by
conventional means by digital filtering or processing. The
transceivers convert the digital signal to analog form. After
conversion, power amplifiers 54, 56 and 58 associated with the
respective sectors effect emission of radiated power in the
respective sectors.
[0037] Advantageously, amplifiers 54, 56 and 58 operate at lower
power levels than the single high power amplifier 28 (FIG. 2B) in a
non-sectorized cell, thereby providing substantial cost savings.
More importantly, instead of deploying three Carney engines the
improved sectorized cell requires only a single Carney engine
comprising channelizer 19 and combiner 20, thereby providing
further economies. The invention only requires software
modification of the Carney engine used in a single cell site to
handle information distributed in different spectral bands
associated with the sectors.
[0038] FIG. 6 depicts further details of the transceivers 42, 44
and 46 of FIG. 5, which perform transmultiplexing operations. The
receive path of a transceiver (FIG. 5), for example, includes a
receiver 60, an analog-to-digital converter, and an exclusive OR
gate 64. OR gate 64 receives digital samples from the OR gate of an
adjacent preceding transceiver. The output of OR gate 64 is
supplied to the OR gate of an adjacent subsequent transceiver, and
the OR gate of the last transceiver in the sequence is supplied to
the channelizer 48, as depicted by connections 66 and 68 of FIG. 5.
On the transmit side of the transceiver, digital signal samples
from the combiner 52 enter a digital band pass filter 70 which
passes signal samples associated with the respective sectors. The
digital signals samples are then converted to analog form by
digital-to-analog converter 72 and supplied to a transmitter unit
74. Transmitter unit 74 then supplies a resulting analog signal to
a respective amplifier/duplexer pair for transmission to
subscribers.
[0039] While we have shown and described several embodiments in
accordance with the present invention, it is to be understood that
the invention is not limited thereto, but is susceptible to
numerous changes and modifications as known to a person skilled in
the art, and we therefore do not wish to be limited to the details
shown and described herein, but intend to cover all such changes
and modifications as are obvious to one of ordinary skill in the
art.
* * * * *