U.S. patent application number 10/298273 was filed with the patent office on 2003-08-28 for circuit switching and packet switching efficient sharing of capacity.
Invention is credited to Schilling, Donald L..
Application Number | 20030161386 10/298273 |
Document ID | / |
Family ID | 25164927 |
Filed Date | 2003-08-28 |
United States Patent
Application |
20030161386 |
Kind Code |
A1 |
Schilling, Donald L. |
August 28, 2003 |
Circuit switching and packet switching efficient sharing of
capacity
Abstract
An improvement to a spread-spectrum,
code-division-multiple-access (CDMA) cellular system having
multiple circuit-switched (CS) remote stations, multiple
packet-switched (PS) remote stations and a base station per cell.
The CS-remote station transmits a spread-spectrum CDMA signal, with
a chip rate of f.sub.c, with a CS-symbol rate of f.sub.b, and with
a power level P.sub.CS. The PS-remote station transmits a
spread-spectrum CDMA signal with the chip rate of f.sub.c,
PS-symbol rate f.sub.p, and with a power level P.sub.PS. The power
level P.sub.PS from the PS-remote station and the power level
P.sub.CS from the CS-remote station are related by a relation of
the CS-symbol rate and the PS-symbol rate to efficiently share
system capacity.
Inventors: |
Schilling, Donald L.; (Palm
Beach Gardens, FL) |
Correspondence
Address: |
DAVID NEWMAN CHARTERED
Centennial Square
P. O. Box 2728
La Plata
MD
20646-2728
US
|
Family ID: |
25164927 |
Appl. No.: |
10/298273 |
Filed: |
November 18, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10298273 |
Nov 18, 2002 |
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09795181 |
Mar 1, 2001 |
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6512784 |
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Current U.S.
Class: |
375/141 ;
370/352; 375/E1.002 |
Current CPC
Class: |
H04W 52/16 20130101;
H04B 1/707 20130101; H04W 52/343 20130101; H04W 88/10 20130101;
H04W 48/14 20130101 |
Class at
Publication: |
375/141 ;
370/352 |
International
Class: |
H04B 001/707 |
Claims
I claim:
1. An improvement to a spread-spectrum,
code-division-multiple-access (CDMA) cellular system comprising: a
plurality of circuit-switched (CS) remote stations, each CS-remote
station for transmitting a spread-spectrum CDMA signal, with a chip
rate of f.sub.c, with a CS-symbol rate of f.sub.b, and with a
respective power level P.sub.CSi where i refers to an i.sup.th
CS-remote station in the plurality of PS-remote stations; a
plurality of packet-switched (PS) remote stations, each PS-remote
station for transmitting a spread-spectrum CDMA signal with the
chip rate of f.sub.c, with a PS-symbol rate f.sub.p, and with a
power level P.sub.PS1 where i refers to an i.sup.th PS-remote
station in the plurality of PS-remote stations; and wherein the
power level P.sub.PS1 from the i.sup.th PS-remote station and the
power level P.sub.CS1 from the i.sup.th CS-remote station are
related by a ratio P.sub.PS1/P.sub.CS1 being approximately equal to
f.sub.p/f.sub.b.
2. An improvement to a spread-spectrum,
code-division-multiple-access (CDMA) cellular system comprising: a
plurality of circuit-switched (CS) remote means, each CS-remote
means for transmitting a spread-spectrum CDMA signal, with a chip
rate of f.sub.c, with a CS-symbol rate of f.sub.b, and with a
respective power level P.sub.CS1 where i refers to an i.sup.th
CS-remote station in the plurality of PS-remote stations; a
plurality of packet-switched (PS) remote means, each PS-remote
means for transmitting a spread-spectrum CDMA signal with the chip
rate of f.sub.c, with a PS-symbol rate f.sub.p, and with a power
level P.sub.PS1 where i refers to an i.sup.th PS-remote station in
the plurality of PS-remote stations; and wherein the power level
P.sub.PS1 from the i.sup.th PS-remote means and the power level
P.sub.CSi from the i.sup.th CS-remote means are related by a ratio
P.sub.PSi/P.sub.CS1 being approximately equal to
f.sub.p/f.sub.b.
3. An improvement to a spread-spectrum,
code-division-multiple-access (CDMA) cellular method, the
improvement comprising the steps of: transmitting, from a
circuit-switched (CS) remote station, a spread-spectrum CDMA
signal, with a chip rate of f.sub.c, with a CS-symbol rate of
f.sub.b, and with a power level P.sub.CS; transmitting, from a
packet-switched (PS) remote station, a spread-spectrum CDMA signal
with the chip rate of f.sub.c, with a PS-symbol rate f.sub.p, and
with a power level P.sub.PS; and wherein the power level P.sub.CS
from the PS-remote station and the power level P.sub.CS from the
CS-remote station are related by a ratio P.sub.PS/P.sub.CS being
approximately equal to f.sub.p/f.sub.b.
4. An improvement to a spread-spectrum,
code-division-multiple-access (CDMA) cellular system having
packet-switched (PS) signals and circuit-switched (CS) signals,
comprising: a base station communicating with a plurality of
CS-remote stations; a PS-remote station for sending a PS-packet to
the base station, indicating that the PS-remote station is present
in the geographical coverage area of the base station and
requesting to send access the PS-spread-spectrum channel on the
base station; and said base station, responding to the packet, for
sending a BS-packet indicating any of PS-spread-spectrum channel
availability, power level, and capacity availability.
5. An improvement to a code-division-multiple-access (CDMA) system
having a base station, a plurality of circuit-switched (CS) remote
stations communicating with the base station having a plurality of
spread-spectrum channels including a multiplicity of CS-channels
with spread-spectrum modulation, and a packet-switched (PS) remote
station, with the plurality of CS-remote stations using all or less
than total available capacity at in the plurality of
spread-spectrum channels of said base station, comprising the steps
of: determining, at said PS-remote station, availability of a PS
channel; determining, at said PS-remote station, available capacity
in the plurality of spread-spectrum channels of said base station;
determining, at said PS-remote station, available data rate for
data transmission; determining, at said PS-remote station, a
particular chip-sequence signal to be used for the available
PS-channel; and transmitting, using radio waves, to said base
station, in response to determining the availability of a PS
channel, the available capacity, the available data rate, and the
particular chip-sequence signal, a packet having data, with the
packet transmitted on the PS channel using all or less than the
available capacity and with a particular data rate equal or less
than the available data rate, and with the packet having the
particular chip-sequence signal.
6. The improvement to the spread-spectrum, CDMA cellular method as
set forth in claim 5, with the step of determining the availability
of the PS channel including the steps of determining, at said base
station, the availability of the PS channel and transmitting, from
said base station, information including the available PS channel
to said PS-remote station.
7. The improvement to the spread-spectrum, CDMA cellular method as
set forth in claim 5, with the step of determining available
capacity including the steps of determining, at said base station,
available capacity, and transmitting, from said base station,
information including the available capacity to said PS-remote
station.
8. The improvement to the spread-spectrum, CDMA cellular method as
set forth in claim 5, with the step of determining available data
rate including the steps of determining, at said base station, the
available data rate, and transmitting, from said base station,
information including the available data rate to said PS-remote
station.
9. The improvement to the spread-spectrum, CDMA cellular method as
set forth in claim 5, with the step of determining the particular
chip-sequence signal including the steps of determining, at said
base station, the particular chip-sequence signal, and
transmitting, from said base station, information including the
particular chip-sequence signal to said PS-remote station.
10. An improvement to a spread-spectrum,
code-division-multiple-access (CDMA) cellular method having a base
station, a plurality of circuit-switched (CS) remote stations
communicating with the base station having a plurality of
spread-spectrum channels including a multiplicity of CS-channels
with spread-spectrum modulation, and a plurality of packet-switched
(PS) remote stations with a particular PS-remote station, with the
plurality of CS-remote stations using all or less than total
available capacity at in the plurality of spread-spectrum channels
of said base station, comprising the steps of: determining, at said
particular PS-remote station, availability of a PS channel;
determining, at said particular PS-remote station, available
capacity in the plurality of spread-spectrum channels of said base
station; determining, at said particular PS-remote station, a power
level for packet transmission; determining, at said particular
PS-remote station, a particular chip-sequence signal to be used for
the available PS-channel; and transmitting, using radio waves, to
said base station, in response to determining the availability of a
PS channel, the available capacity, the power level, and the
particular chip-sequence signal, a packet having data, with the
packet transmitted on the PS channel using all or less than the
available capacity and with the power level, and with the packet
having the particular chip-sequence signal.
11. The improvement to the spread-spectrum, CDMA cellular method as
set forth in claim 10, with the step of determining the
availability of the PS channel including the steps of determining,
at said base station, the availability of the PS channel and
transmitting, from said base station, information including the
available PS channel to said PS-remote station.
12. The improvement to the spread-spectrum, CDMA cellular method as
set forth in claim 10, with the step of determining available
capacity including the steps of determining, at said base station,
available capacity, and transmitting, from said base station,
information including the available capacity to said PS-remote
station.
13. The improvement to the spread-spectrum, CDMA cellular method as
set forth in claim 10, with the step of determining available data
rate including the steps of determining, at said base station, the
available data rate, and transmitting, from said base station,
information including the available data rate to said PS-remote
station.
14. The improvement to the spread-spectrum, CDMA cellular method as
set forth in claim 10, with the step of determining the particular
chip-sequence signal including the steps of determining, at said
base station, the particular chip-sequence signal, and
transmitting, from said base station, information including the
particular chip-sequence signal to said PS-remote station.
15. The improvement to the spread-spectrum, CDMA cellular system as
set forth in claim 10, with the step of determining the power level
including the steps of determining, from a channel-sounding signal
transmitted from said base station to said PS-remote station, the
power level.
16. An improvement to a spread-spectrum,
code-division-multiple-access (CDMA) cellular system comprising: a
base station having a plurality of spread-spectrum channels
including a multiplicity of CS-channels with spread-spectrum
modulation; a plurality of circuit-switched (CS) remote stations
communicating on the multiplicity of CS-channels with the base
station, with the plurality of CS-remote stations using all or less
than total available capacity in the plurality of spread-spectrum
channels of said base station; a packet-switched (PS) remote
station for determining, availability of a PS channel, for
determining available capacity in the plurality of spread-spectrum
channels of said base station, for determining available data rate
for data transmission, and for determining a particular
chip-sequence signal to be used for the available PS-channel; and
said PS-remote station for transmitting, using radio waves, to said
base station, in response to determining the availability of a PS
channel, the available capacity, the available data rate, and the
particular chip-sequence signal, a packet having data, with the
packet transmitted on the PS channel using all or less than the
available capacity and with a particular data rate equal or less
than the available data rate, and with the packet having the
particular chip-sequence signal.
17. The improvement to the spread-spectrum, CDMA cellular system as
set forth in claim 16, with said base station for determining the
availability of the PS channel and for transmitting information
including the available PS channel to said PS-remote station.
18. The improvement to the spread-spectrum, CDMA cellular system as
set forth in claim 16, with said base station for determining
available capacity, and for transmitting information including the
available capacity to said PS-remote station.
19. The improvement to the spread-spectrum, CDMA cellular system as
set forth in claim 16, with the said base station for determining
the available data rate, and for transmitting information including
the available data rate to said PS-remote station.
20. The improvement to the spread-spectrum, CDMA cellular system as
set forth in claim 16, with said base station for assigning the
particular chip-sequence signal, and for transmitting information
including the particular chip-sequence signal to said PS-remote
station.
21. An improvement to a spread-spectrum,
code-division-multiple-access (CDMA) cellular system comprising: a
base station having a plurality of spread-spectrum channels
including a multiplicity of CS-channels with spread-spectrum
modulation; a plurality of circuit-switched (CS) remote stations
communicating on the multiplicity of CS-channels with the base
station, with the plurality of CS-remote stations using all or less
than total available capacity in the plurality of spread-spectrum
channels of said base station; a packet-switched (PS) remote
station for determining availability of a PS channel, for
determining available capacity in the plurality of spread-spectrum
channels of said base station, for determining a power level for
packet transmission, and for determining a particular chip-sequence
signal to be used for the available PS-channel; and said PS-remote
station for transmitting, using radio waves, to said base station,
in response to determining the availability of a PS channel, the
available capacity, the power level, and the particular
chip-sequence signal, a packet having data, with the packet
transmitted on the PS channel using all or less than the available
capacity and with the power level, and with the packet having the
particular chip-sequence signal.
22. The improvement to the spread-spectrum, CDMA cellular system as
set forth in claim 21, with said base station for determining the
availability of the PS channel and for transmitting information
including the available PS channel to said PS-remote station.
23. The improvement to the spread-spectrum, CDMA cellular system as
set forth in claim 21, with said base station for determining
available capacity, and for transmitting information including the
available capacity to said PS-remote station.
24. The improvement to the spread-spectrum, CDMA cellular system as
set forth in claim 21, with the said base station for determining
the available data rate, and for transmitting information including
the available data rate to said PS-remote station.
25. The improvement to the spread-spectrum, CDMA cellular system as
set forth in claim 21, with said base station for assigning the
particular chip-sequence signal, and for transmitting information
including the particular chip-sequence signal to said PS-remote
station.
26. The improvement to the spread-spectrum, CDMA cellular system as
set forth in claim 21, with said base station for transmitting, to
said PS-remote station, a channel-sounding signal, and with said
PS-remote station for determining the power level from the
channel-sounding signal.
27. An improvement to a code-division-multiple-access (CDMA) system
having a base station, a plurality of circuit-switched (CS) remote
stations communicating with the base station having a plurality of
spread-spectrum channels including a multiplicity of CS-channels
with spread-spectrum modulation, and a packet-switched (PS) remote
station, with the plurality of CS-remote stations using all or less
than total available capacity at in the plurality of
spread-spectrum channels of said base station, comprising the steps
of: determining, at said PS-remote station, available data rate for
data transmission; and transmitting, using radio waves, to said
base station, in response to determining the available data rate, a
packet having data, with the packet transmitted with a particular
data rate equal or less than the available data rate.
28. The improvement to the spread-spectrum, CDMA cellular method as
set forth in claim 27, further including the step of determining,
at said base station, the availability of a PS channel and
transmitting, from said base station, information including the
available PS channel to said PS-remote station.
29. The improvement to the spread-spectrum, CDMA cellular method as
set forth in claim 27, further including the step of determining,
at said base station, available capacity, and transmitting, from
said base station, information including the available capacity to
said PS-remote station.
30. The improvement to the spread-spectrum, CDMA cellular method as
set forth in claim 27, with the step of determining available data
rate including the steps of determining, at said base station, the
available data rate, and transmitting information including the
available data rate to said PS-remote station.
31. The improvement to the spread-spectrum, CDMA cellular method as
set forth in claim 27, further including the step of determining,
at said base station, the particular chip-sequence signal, and
transmitting, from said base station, information including the
particular chip-sequence signal to said PS-remote station.
32. An improvement to a spread-spectrum,
code-division-multiple-access (CDMA) cellular method having a base
station, a plurality of circuit-switched (CS) remote stations
communicating with the base station having a plurality of
spread-spectrum channels including a multiplicity of CS-channels
with spread-spectrum modulation, and a plurality of packet-switched
(PS) remote stations with a particular PS-remote station, with the
plurality of CS-remote stations using all or less than total
available capacity at in the plurality of spread-spectrum
determining, at said particular PS-remote station, a power level
for packet transmission; and transmitting, using radio waves, to
said base station, in response to determining the power level, a
packet having data, with the packet transmitted with the power
level.
33. The improvement to the spread-spectrum, CDMA cellular method as
set forth in claim 32, further including the steps of determining,
at said base station, an availability of a PS channel and
transmitting, from said base station, information including the
available PS channel to said PS-remote station.
34. The improvement to the spread-spectrum, CDMA cellular method as
set forth in claim 32, further including the steps of determining,
at said base station, available capacity, and transmitting, from
said base station, information including the available capacity to
said PS-remote station.
35. The improvement to the spread-spectrum, CDMA cellular method as
set forth in claim 32, with the steps of determining the power
level including the steps of determining, at said base station, the
power level, and transmitting, from said base station, information
including the power level to said PS-remote station.
36. The improvement to the spread-spectrum, CDMA cellular method as
set forth in claim 32, further including the steps of determining,
at said base station, a particular chip-sequence signal, and
transmitting, from said base station, information including the
particular chip-sequence signal to said PS-remote station.
37. The improvement to the spread-spectrum, CDMA cellular method as
set forth in claim 32, with the step of determining the power level
including the steps of determining, from a channel-sounding signal
transmitted from said base station to said PS-remote station, the
power level.
38. An improvement to a spread-spectrum,
code-division-multiple-access (CDMA) cellular system comprising: a
base station having a plurality of spread-spectrum channels
including a multiplicity of CS-channels with spread-spectrum
modulation; a plurality of circuit-switched (CS) remote stations
communicating on the multiplicity of CS-channels with the base
station, with the plurality of CS-remote stations using all or less
than total available capacity in the plurality of spread-spectrum
channels of said base station; a packet-switched (PS) remote
station for determining available data rate for data transmission;
and said PS-remote station for transmitting, using radio waves, to
said base station, in response to determining the available data
rate, a packet having data, with the packet transmitted on the PS
channel using a particular data rate equal or less than the
available data rate.
39. The improvement to the spread-spectrum, CDMA cellular system as
set forth in claim 38, further including said base station for
determining the availability of a PS channel and for transmitting,
from said base station, information including the available PS
channel to said PS-remote station.
40. The improvement to the spread-spectrum, CDMA cellular system as
set forth in claim 38, further including said base station for
determining available capacity, and for transmitting, from said
base station, information including the available capacity to said
PS-remote station.
41. The improvement to the spread-spectrum, CDMA cellular system as
set forth in claim 38, with the said base station for determining
the available data rate, and for transmitting, from said base
station, information including the available data rate to said
PS-remote station.
42. The improvement to the spread-spectrum, CDMA cellular system as
set forth in claim 38, further including said base station for
assigning a particular chip-sequence signal, and for transmitting,
from said base station, information including the particular
chip-sequence signal to said PS-remote station.
43. An improvement to a spread-spectrum,
code-division-multiple-access (CDMA) cellular m system comprising:
a base station having a plurality of spread-spectrum channels
including a multiplicity of CS-channels with spread-spectrum
modulation; a plurality of circuit-switched (CS) remote stations
communicating on the multiplicity of CS-channels with the base
station, with the plurality of CS-remote stations using all or less
than total available capacity in the plurality of spread-spectrum
channels of said base station; a packet-switched (PS) remote
station for determining a power level for packet transmission; and
said PS-remote station for transmitting, using radio waves, to said
base station, in response to determining the power level, a packet
having data, with the packet transmitted on the PS channel using
the power level.
44. The improvement to the spread-spectrum, CDMA cellular system as
set forth in claim 43, further including said base station for
determining an availability of a PS channel and for transmitting
information including the available PS channel to said PS-remote
station.
45. The improvement to the spread-spectrum, CDMA cellular system as
set forth in claim 43, further including said base station for
determining available capacity, and for transmitting information
including the available capacity to said PS-remote station.
46. The improvement to the spread-spectrum, CDMA cellular system as
set forth in claim 43, further including said base station for
determining the available data rate, and for transmitting
information including the available data rate to said PS-remote
station.
47. The improvement to the spread-spectrum, CDMA cellular system as
set forth in claim 43, further including said base station for
assigning the particular chip-sequence signal, and for transmitting
information including the particular chip-sequence signal to said
PS-remote station.
48. The improvement to the spread-spectrum, CDMA cellular system as
set forth in claim 43, with said base station for transmitting, to
said PS-remote station, a channel-sounding signal, and with said
PS-remote station for determining the power level from the
channel-sounding signal.
Description
RELATED PATENTS
[0001] This patent stems from a continuation application of U.S.
patent application Ser. No. 09/795,181, and filing date of Mar. 1,
2001, entitled EFFICIENT SHARING OF CAPACITY BY REMOTE STATIONS
USING CIRCUIT SWITCHING AND PACKET SWITCHING by inventor, DONALD L.
SCHILLING. The benefit of the earlier filing date of the parent
patent application is claimed for common subject matter pursuant to
35 U.S.C. .sctn. 120.
BACKGROUND OF THE INVENTION
[0002] This invention relates to spread-spectrum cellular and
non-cellular communications, and more particularly to the 3.sup.rd
generation (3G) system or 4.sup.th generation (4G) system wherein a
remote station may use the 3G or 4G system as either a
circuit-switched network or as a packet-switch network.
DESCRIPTION OF THE RELEVANT ART
[0003] The 3.sup.rd generation system employs circuit-switched (CS)
remote stations which transmit voice, or data, as continuous data,
and packet-switched (PS) remote stations which transmit packets of
data in an irregular, bursty manner. The PS-remote stations, for
example, might be accessing the Internet, with irregular packets of
data. The PS-remote station and the CS-remote station may reside in
a common transceiver, or
[0004] If too many CS-remote stations used a particular base
station, then the PS-remote stations are blocked from the base
station because of lack of available capacity in the
spread-spectrum channels assigned to the base station. When a
PS-remote station enters the cell, this PS-remote station initially
may transmit too much power and jam the transmissions from the
CS-remote stations. If a power ramp-up procedure were used by the
PS-remote station in order to avoid jamming the CS-remote stations,
then the header portion of a packet from the PS-remote station
typically is sent several times until a link is established, which
increases the duration of the packet and significantly reduces the
efficiency of a packet-switched system.
SUMMARY OF THE INVENTION
[0005] A general object of the invention is efficient sharing of
system capacity of a 3G system cell, or a 4G system cell, between
CS-remote stations and PS-remote stations.
[0006] Another object of the invention is to allow the PS-remote
station to be located within the system so that calls to the
PS-remote station go to the correct base station for transmission
to the mobile PS-remote station.
[0007] According to the present invention, as embodied and broadly
described herein, an improvement to a spread-spectrum,
code-division-multiple-access (CDMA) system is provided, comprising
one or more cells, with each cell containing multiple
circuit-switched (CS) remote stations, and multiple packet-switched
(PS) remote stations and a base station capable of transmitting
circuit-switched signals and packet-switched signals. A CS-remote
station transmits a spread-spectrum CDMA signal, with a chip rate
f.sub.c, with a CS-symbol rate of f.sub.b, and with a power level
P.sub.CS. A PS-remote station transmits a spread-spectrum CDMA
signal with the chip rate of f.sub.c, with a PS-symbol rate
f.sub.p, and with a power level P.sub.PS.
[0008] Assume that a plurality of CS-remote stations communicates
with a particular base station. A PS-remote station can communicate
with the base station provided that (1) a packet channel is
available, (2) there is available capacity in the spread-spectrum
channels at the base station, (3) the required data rate is
available, (4) the base station provides the PS-remote station a
chip-sequence signal for communicating with the base station, and
(5) the base station provides the PS-remote station a power level
for the PS-remote station to transmit to the base station. For
efficient sharing of system capacity in the spread-spectrum
channels at the base station, between the CS-remote station and the
PS-remote station, the power level P.sub.PS from the PS-remote
station and the power level P.sub.CS from the CS-remote station are
related by: E=P.sub.PS/f.sub.p=P.sub.CS/f.sub.b, in which the
energies E are the same, or P.sub.PS/f.sub.p=kP.sub.CS/f.sub.b, in
which the energies E differ by a factor k. If k.noteq.1, then the
error rates in the circuit switched system will differ from the
error rates in the packet switched system.
[0009] Additional objects and advantages of the invention are set
forth in part in the description which follows, and in part are
obvious from the description, or may be learned by practice of the
invention. The objects and advantages of the invention also may be
realized and attained by means of the instrumentalities and
combinations particularly pointed out in the appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] The accompanying drawings, which are incorporated in and
constitute a part of the specification, illustrate preferred
embodiments of the invention, and together with the description
serve to explain the principles of the invention.
[0011] FIG. 1 illustrates a base station communicating with several
circuit-switched remote stations and a packet-switched remote
station in a star network;
[0012] FIG. 2 illustrates several base stations communicating with
several circuit-switched remote stations and packet-switched remote
stations in a distributed network, spread-spectrum system;
[0013] FIG. 3 illustrates several base stations communicating with
several circuit-switched remote stations and packet-switched remote
stations in a distributed network, spread-spectrum system, with
several nodes communicating with a central office;
[0014] FIG. 4 is a block diagram illustrating key elements of a
base station with a central office communicating with a set of a
plurality of nodes;
[0015] FIG. 5 is an alternative block diagram illustrating key
elements of a base station;
[0016] FIG. 6 shows a representative example of a packet;
[0017] FIG. 7 illustrates a remote station communicating with a
base station, with channel sounding;
[0018] FIG. 8 is a block diagram illustrating a base station signal
with channel sounding added to a base station spread-spectrum
transmitter;
[0019] FIG. 9 is a block diagram illustrating the improvement to
the remote station spread-spectrum receiver for the
BS-channel-sounding signal;
[0020] FIG. 10 is a block diagram illustrating the improvement to
the remote station spread-spectrum transmitter;
[0021] FIG. 11 is a block diagram showing an interference-reduction
subsystem at a front end to a base station spread-spectrum
receiver;
[0022] FIG. 12 is a timing diagram of how several base stations
might transmit the BS-channel-sounding signal; and
[0023] FIG. 13 depicts available capacity at a base station, versus
number of users.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0024] Reference now is made in detail to the present preferred
embodiments of the invention, examples of which are illustrated in
the accompanying drawings, wherein like reference numerals indicate
like elements throughout the several views.
[0025] The present invention provides an improvement to a
spread-spectrum, code-division-multiple-access (CDMA) system,
having one or more cells, with each cell including a plurality of
circuit-switched (CS) remote stations and a plurality of
packet-switched (PS) remote stations communicating with a base
station. The base station is in a conventional star network, or a
distributed network, communicating with a central office. Each
CS-remote station communicates with the base station using a
spread-spectrum CDMA signal, and transmits a spread-spectrum CDMA
signal with power P.sub.CS. The power P.sub.CS is proportional to
transmitted data rate of the CS-remote station. The PS-remote
station transmits in a packet mode, and is assumed to transmit a
spread-spectrum CDMA packet signal, so that power P.sub.PS is
sufficient to ensure that the energy per symbol is
E.sub.P=P.sub.PS/f.sub.P.
[0026] More particularly, the present invention pertains to a
cellular structure or environment with each cell containing a base
station communicating with a plurality of CS-remote stations and
PS-remote stations, using spread-spectrum modulation. The present
invention preferably is for packet data, with data being sent
between a CS-remote station or a PS-remote station, and a base
station, as packet signals. A CS-remote station might be a
hand-held unit or telephone or computer, or other device which may
be stationery or in motion. A PS-remote station might be a
connection to a hand-held unit or telephone or a computer or other
modem, or other device which may be stationery or in motion.
[0027] A spread-spectrum signal, as used herein, typically includes
a data signal, multiplied by a chip-sequence signal, and multiplied
by a carrier signal. The data signal represents a sequence of data
bits. The chip-sequence signal represents a sequence of chips, as
normally used in a direct sequence, spread-spectrum signal. The
carrier signal is at a carrier frequency, and raises the product of
the data signal and the chip-sequence signal, to the carrier
frequency. For synchronization, the data signal typically is a
constant value, for example, a series of "one" bits, or has very
slowly time-varying data. For a PS-remote station, the
spread-spectrum signal is a packet, with a header followed by data.
For a CS-remote station, the spread-spectrum signal may be a
packet, with a header followed by data, or a plurality of
spread-spectrum channels, with one of the spread-spectrum channels
used for synchronization.
[0028] A particular spread-spectrum channel is defined by a
particular chip-sequence signal, as is well known in the art. For
the case of the packet, synchronization is performed on the header,
as is well-known in the art. For a dedicated spread-spectrum
channel for synchronization, synchronization is performed using the
dedicated channel.
[0029] The base station is assumed to transmit to the plurality of
remote stations at a first frequency f.sub.1, also known as a
carrier frequency of the base station transmitter. The plurality of
remote stations is assumed to transmit to the base station at a
second frequency f.sub.2, also know as the carrier frequency of the
remote station transmitters. For frequency division duplex
operation, the second frequency f.sub.2 is different from the first
frequency f.sub.1, and typically outside the correlation bandwidth
of the first frequency f.sub.1. For time division duplex (TDD)
operation, the second frequency f.sub.2 is the same as the first
frequency f.sub.1. The present invention works with either a FDD
CDMA system or a TDD CDMA system.
[0030] A particular channel from the base station to a remote
station is defined or determined by a particular chip-sequence
signal, as is well known in the art for direct-sequence (DS)
code-division-multiple access (CDMA) systems. A particular channel
from a particular remote station to the base station is defined or
determined by a particular chip-sequence signal, as is well known
in CDMA systems.
[0031] CDMA Network Architecture
[0032] The improvement to a method and system of the instant
invention provides efficient sharing of capacity in the
spread-spectrum channels between CS-remote stations and PS-remote
stations in a spread-spectrum CDMA network. The spread-spectrum,
CDMA network may be a star network or a distributed network.
[0033] As illustratively shown in FIG. 1, a star network, as
presently employed for cellular networks, is used to communicate
data between a central office 50 and a plurality of remote stations
(RS). The plurality of remote stations include a plurality of
CS-remote stations and a plurality of PS-remote stations. The term
remote station, as used herein, refers in general to a remote
station which may be a CS-remote station or a PS-remote station. A
particular remote station may include both, a CS-remote station and
a PS-remote station. The CS-remote station and the PS-remote
station may share common transmitter and common receiver subsystems
or components. The prefixes CS and PS are added to the term remote
station, when specifically referring to a circuit-switched remote
station and a packet-switched remote station, respectively.
[0034] A plurality of base stations 20, 30, 40, communicate
directly with the central office 50. A first base station 20
communicates data to and from a first plurality of remote stations
11, 22, 23, 24. A second base station 30 communicates data to and
from a second plurality of remote stations 31, 32, 33, 34, 35, 36.
A third base station 40 communicates data to and from a third
plurality of remote stations 41, 42, 43, 44, 45.
[0035] The distributed network, as illustrated in FIGS. 2 and 3,
provides an alternative architecture, for routing packet signals
between a central office, through a plurality of nodes, to a remote
station. Each of the nodes in a distributed system includes a base
station, plus additional system components for the distributed
system.
[0036] In the exemplary depictions in FIGS. 2 and 3, a distributed
network, direct-sequence, spread-spectrum,
code-division-multiple-access (CDMA) system, by way of example,
comprises a plurality of remote stations and a plurality of nodes
110, 120, 130, 140, 150, 160, 170 180, 190. The plurality of nodes
110, 120, 130, 140, 150, 160, 170 180, 190 forms the distributed
network. Each node includes a base station, as referred to in FIG.
1, plus added circuitry to operate in a distributed network. The
distributed network plus the plurality of remote stations form the
distributed system. The plurality of remote stations includes a
plurality of CS-remote stations and a plurality of PS-remote
stations, as discussed and defined for the star network. The
plurality of nodes 110, 120, 130, 140, 150, 160, 170 180, 190 of
FIG. 2, depicts, as an illustration, a first node 110, a second
node, 120, a third node 130, a fourth node 140, a fifth node 150, a
sixth node 160, a seventh node 170, an eighth node 180 and a ninth
node 190.
[0037] In the plurality of nodes 110, 120, 130, 140, 150, 160, 170
180, 190, one node, which happens to be labeled the second node
120, is a hub node, which communicates to a central telephone
office 50. There may be a plurality of hubs. In an alternative
embodiment, as shown in FIG. 3, a set of the plurality of nodes
(hubs) communicates to the central office 50. The set of the
plurality of nodes (hubs), may include the entire plurality of
nodes.
[0038] The plurality of nodes 110, 120, 130, 140, 150, 160, 170
180, 190 covers a geographic area. Each node in the plurality of
nodes 110, 120, 130, 140, 150, 160, 170 180, 190 forms a
micro-cell. A micro-cell typically has a radius much less than one
mile.
[0039] In the plurality of nodes 110, 120, 130, 140, 150, 160, 170
180, 190, the first node 110 communicates with the second node 120,
the fourth node 140 and the fifth node 150. The second node 120
communicates with the first node 110, the third node 130, the
fourth node 140, the fifth node 150 and the sixth node 160. The
third node communicates with the second node 120, the fifth node
150 and the sixth node 160. The fourth node communicates with the
first node 110, the second node 120, the fifth node 150, the
seventh node 170 and the eighth node 180. The fifth node
communicates with the first node 110, the second node 120, the
third node 130, the fourth node 140, the sixth node 160, the
seventh node 170, the eighth node 180 and the ninth node 190. The
sixth node 160 communicates with the second node 120, the third
node 130, the fifth node 150, the eighth node 180 and the ninth
node 190. The seventh node 170 communicates with the fourth node
140, the fifth node 150 and the eighth node 180. The eighth node
180 communicates with the fourth node 140, the fifth node 150, the
sixth node 160, the seventh node 170 and the ninth node 190. The
ninth node communicates with the fifth node 150, the sixth node 160
and the eighth node 180.
[0040] FIGS. 2 and 3 show the first node 110 communicating with a
first plurality of remote stations 11, 112, 113, 114. The second
node 120 communicates with a second plurality of remote stations,
with FIGS. 2 and 3 showing a first remote station 121 of the second
plurality of remote stations. The third node 130 communicates with
a third plurality of remote stations 131, 132 and the fourth node
140, the fifth node 150 and the sixth node 160 communicate with a
fourth plurality of remote stations, a fifth plurality of remote
stations, and a sixth plurality of remote stations, respectively.
FIG. 2 shows the fourth node 140 communicating with a first remote
station 141 of the fourth plurality of remote stations, the fifth
node 150 communicating with a first remote station 151 of the fifth
plurality of remote stations, and the sixth node 160 communicating
with a first remote station 161 of the sixth plurality of remote
stations. The seventh node 170 and the eighth node 180 are shown
communicating with a seventh plurality of remote stations 171, 172,
173 and an eighth plurality of remote stations 181, 182,
respectively. The ninth node 190 communicates with a ninth
plurality of remote stations, and FIG. 2 shows the ninth node 190
communicating with a first remote station 191 of the ninth
plurality of remote stations.
[0041] CDMA Base Station
[0042] FIGS. 4 and 5 illustratively show an example of what might
be at each base station in the star network of FIG. 1, or at each
base station of each node in the distributed network of FIGS. 2 and
3. For communicating between nodes, for example, in FIG. 4 shows
node transceiver 350, or equivalently, a node transmitter 351 and a
node receiver 352. The node transmitter 351 and the node receiver
352 are coupled through a node isolator 353 to a node antenna 354.
Transceiver 350 can be at microwave frequencies or connect to a
fiber optic link or any other channel capable of handling the
traffic between nodes. In the case of the star network of FIG. 1,
the node transceiver 350, or equivalently, a node transmitter 351
and a node receiver 352, would be located at a base station, and
can operate at microwave frequencies or connected to a fiber optic
link or any other channel capable of handling the communications to
and from the central office 50.
[0043] FIG. 5 shows an example of a plurality of node transceivers
350, 360 and 370, or equivalently, a plurality of node transmitters
351, 361, 371 and a plurality of node receivers 352, 362, 372. In
place of using a single antenna and an isolator, the first node
transmitter 351 is coupled to a first node-transmitter antenna 356,
and the first node receiver 352 is coupled to the first
node-receiver antenna 357. Similarly, the second node transmitter
361 is coupled to a second node-transmitter antenna 366 and the
second node receiver 362 is coupled to the second node-receiver
antenna 367, and the third node transmitter 371 is coupled to the
third node-transmitter antenna 376 and the third node receiver 372
is coupled to the third node-receiver antenna 377. The antennas
could be omnidirectional, sectored, or steerable (smart)
antennas.
[0044] With each node using the node transmitter 351 and the node
receiver 352, of FIG. 4, or the plurality of node transmitters 351,
361, 371 and the plurality of node receivers, 352, 362, 372 of FIG.
5, a node communicates with a different node having a node
transmitter and node receiver node receiver. Thus, in the plurality
of nodes 110, 120, 130, 140, 150, 160, 170 180, 190, the first node
110 communicates with the second node 120, the fourth node 140 and
the fifth node 150. The second node 120 communicates with the first
node 110, the third node 130, the fourth node 140, the fifth node
150 and the sixth node 160. The third node communicates with the
second node 120, the fifth node 150 and the sixth node 160. The
fourth node communicates with the first node 110, the second node
120, the fifth node 150, the seventh node 170 and the eighth node
180. The fifth node communicates with the first node 110, the
second node 120, the third node 130, the fourth node 140, the sixth
node 160, the seventh node 170, the eighth node 180 and the ninth
node 190. The sixth node 160 communicates with the second node 120,
the third node 130, the fifth node 150, the eighth node 180 and the
ninth node 190. The seventh node 170 communicates with the fourth
node 140, the fifth node 150 and the eighth node 180. The eighth
node 180 communicates with the fourth node 140, the fifth node 150,
the sixth node 160, the seventh node 170 and the ninth node 190.
The ninth node communicates with the fifth node 150, the sixth node
160 and the eighth node 180.
[0045] Each base station of FIG. 1, and each node of FIGS. 2 and 3,
may include a plurality of spread-spectrum transceivers 310, 320,
330, or, equivalently, a plurality of spread-spectrum transmitters
311, 321, 331 and a plurality of spread-spectrum receivers 312,
322, 332, a store-and-forward subsystem 341, and a flow-control
subsystem 340. The flow-control subsystem 340 typically would
include a processor or computer. The store-and-forward subsystem
341 typically would include memory and the memory may be part of
the computer embodying the processor for the flow-control subsystem
340. The store-and-forward subsystem 341 stores information, as
bits, received from a CS-remote station and from a PS-remote
station. The memory may be random access memory (RAM) or hard
drive, or other volatile or non-volatile memory and memory storage
device. Other devices are well-known in the art, and include hard
drives, magnetic tapes, compact disk (CD), and other laser/optical
memories and bubble memory devices. The particular flow-control
subsystem 340 and the store-and-forward subsystem 341 would be
specified by a particular system requirements and design
criteria.
[0046] Each node in the plurality of nodes 110, 120, 130, 140, 150,
160, 170 180, 190 also includes at least one node transmitter 351,
and more typically a plurality of node transmitters 351, 361, 371
and at least one node receiver 352 and more typically a plurality
of node receivers 352, 362, 372. The store-and-forward subsystem
341 is coupled to and controlled by the flow-control subsystem 340.
The plurality of spread-spectrum transmitters 311, 321, 331, are
coupled between a plurality of spread-spectrum antennas 316, 326,
336 and the flow-control subsystem 340. The plurality of
spread-spectrum receivers 312, 322, 332 are coupled between a
plurality of receiver antennas 317, 327, 337 and the flow-control
subsystem 340. FIGS. 2 and 3 show the first node 110 communicating
with a first plurality of remote stations 11, 112, 113, 114. The
second node 120 communicates with a second plurality of remote
stations, with FIGS. 2 and 3 showing a first remote station 121 of
the second plurality of remote stations. The third node 130
communicates with a third plurality of remote stations 131, 132 and
the fourth node 140, the fifth node 150 and the sixth node 160
communicate with a fourth plurality of remote stations, a fifth
plurality of remote stations, and a sixth plurality of remote
stations, respectively. FIGS. 2 and 3 show the fourth node 140
communicating with a first remote station 141 of the fourth
plurality of remote stations, the fifth node 150 communicating with
a first remote station 151 of the fifth plurality of remote
stations, and the sixth node 160 communicating with a first remote
station 161 of the sixth plurality of remote stations. The seventh
node 170 and the eighth node 180 are shown communicating with a
seventh plurality of remote stations 171, 172, 173 and an eighth
plurality of remote stations 181, 182, respectively. The ninth node
190 communicates with a ninth plurality of remote stations, and
FIGS. 2 and 3 show the ninth node 190 communicating with a first
remote station 191 of the ninth plurality of remote stations.
[0047] Each node's spread-spectrum transceiver, or equivalently
spread-spectrum transmitter and spread-spectrum receiver,
communicates, using packets having spread-spectrum modulation, over
radio waves, with the plurality of remote stations. Each packet has
a source address and a destination address, and may have header,
start of data, end of data, and other information such as
flow-control information, forward error correction, and message
data. FIG. 6 shows, by way of example, one way a packet may be
structured.
[0048] The store-and-forward subsystem 341 in the star network of
FIG. 1, stores and forward to the central office 50, one or more
packets to and from the remote station. The flow-control subsystem
340 in the star network controls the store-and-forward subsystem
341, to store each packet arriving at the base station, and to
forward the packet to the central office 50.
[0049] The store-and-forward subsystem 341 in the distributed
network of FIGS. 2 and 3, stores and forwards, to another node or
to the central office 50, one or more packets to and from the
remote station. The store-and-forward subsystem 341, in the
distributed network, for example, stores and forwards the one or
more packets to and from another node in the plurality of nodes
110, 120, 130, 140, 150, 160, 170 180, 190.
[0050] The flow-control subsystem 340 in the distributed network
controls the store-and-forward subsystem, to store each packet
arriving at the base station. In a preferred embodiment, the
flow-control subsystem 340 also is distributed throughout the
network, with a flow-control subsystem 340 resident at each node.
It is possible, of course, to have a central flow-control system.
The flow-control subsystem 340 communicates traffic information
between each of the nodes in the plurality of nodes. The traffic
information typically includes traffic density at each of the nodes
and memory availability. Using the traffic information and in
response to a packet having the destination address to the hub
node, the flow-control subsystem 340 routes the packet through
appropriate nodes to the appropriate hub node. Based on the traffic
at each node, and each packet having a destination address to
either the hub or a remote station, the flow-control subsystem 340
transmits the packet from the hub node to an appropriate node, and
routes the packet to the first recipient node. Each packet may
traverse a different route en route to the remote station.
[0051] In response to the traffic congestion and to a plurality of
packets having voice data, the flow-control subsystem routes the
plurality of packets through a path in the plurality of nodes to
ensure that the plurality of packets arrive sequentially. The flow
control procedure balances the activity in each node relative to
other nodes in the distributed network.
[0052] When an information packet arrives from a central office,
the hub node routes the information packet to an appropriate second
recipient node on the way to an intended remote station destination
address.
[0053] Spread-Spectrum Sounding Channel
[0054] The base station is assumed to transmit to the plurality of
remote stations at a first frequency f.sub.1. A particular channel
from the base station to a remote station is defined or determined
by a particular chip-sequence signal, as is well known in the art
for direct-sequence (DS) code-division-multiple access (CDMA)
systems. The plurality of remote stations are assumed to transmit
to the base station at a second carrier frequency f.sub.2. A
particular channel from a particular remote station to the base
station is defined or determined by a particular chip-sequence
signal, as is well known in CDMA systems.
[0055] The spread-spectrum sounding channel overcomes a major
problem with a plurality of remote stations transmitting to a
common base station. The plurality of remote stations may be
located at different distances, and each remote station may have a
different propagation path, to the base station. Thus, even if all
the remote stations transmitted with the same power level, then the
spread-spectrum signal from each remote station may arrive at the
base station with a different power level. A strong power level
from one remote station may cause sufficient interference to block
or inhibit reception of the spread-spectrum signal from a more
distant remote station. This power problem is commonly known as the
"near-far" problem, or power control problem: How does the
spread-spectrum system control the power transmitted from each
remote station, so that the power received at the base station from
each remote station is approximately the same? If the power
received at the base station is the same for each remote station,
then the capacity is limited by the number of remote stations
transmitting to the base station. If, however, a particular remote
station is sufficiently close to the base station, and its
transmitter power can block reception of other remote stations,
then capacity may be limited severely to only the remote station
closest to the base station.
[0056] The spread-spectrum sounding channel overcomes the power
control problem by permitting a remote station to have knowledge, a
priori to transmitting, of a proper power level to initiate
transmission. After the initial power level is used, closed-loop
power control, which is well-known in the art, can be employed.
[0057] An additional or alternative benefit from the
spread-spectrum sounding channel is more accurate frequency control
at a remote station. The carrier frequency transmitted from a
remote station may be shifted at the base station due to Doppler
shift in carrier frequency caused by motion. This spread-spectrum
sounding channel corrects or compensates for Doppler shift in
carrier frequency caused by the effective motion of the remote
station. The remote station could be at a fixed location, and the
Doppler shift in carrier frequency could be caused by time changes
in the propagation path, such as trees blowing in the wind. After
initial communications, a Costas loop or other frequency
controlling circuit may be employed to control or compensate for
frequency changes. Such devices or circuits are well-known in the
art.
[0058] The spread-spectrum sounding channel broadly provides an
improvement to a spread-spectrum system which has a base station
(BS) and a plurality of remote stations (RS). The base station has
a BS-spread-spectrum transmitter and a BS-spread-spectrum receiver.
The BS-spread-spectrum transmitter transmits, using radio waves, a
plurality of BS-spread-spectrum signals at a first frequency
f.sub.1. The BS-spread-spectrum receiver receives, at a second
frequency f.sub.2, as radio waves, a plurality of
RS-spread-spectrum signals from the plurality of remote stations.
The plurality of BS-spread-spectrum signals at the first frequency
f.sub.1 are outside the correlation bandwidth of the plurality of
RS-spread-spectrum signals at the second frequency f.sub.2. Each of
the plurality of remote stations has an RS-spread-spectrum
transmitter for transmitting, as a radio wave, an
RS-spread-spectrum signal at the second frequency f.sub.2.
[0059] At the base station, the improvement for the sounding
channel includes BS-transmitter means, and interference-reduction
means. The BS-transmitter means transmits, as a radio wave, a
BS-channel-sounding signal at the second frequency f.sub.2. The
BS-channel-sounding signal has a bandwidth which is no more than
twenty per cent of the spread-spectrum bandwidth of the plurality
of RS-spread-spectrum signals, and preferably not more than one per
cent of the spread-spectrum bandwidth.
[0060] The interference-reduction means is located at a front end
to the BS-spread-spectrum receiver. The interference-reduction
means reduces, by cancelling and notch filtering, at the second
frequency, the BS-channel-sounding signal from the plurality of
RS-spread-spectrum signals arriving at the base station.
[0061] While the BS-channel-sounding signal should have a bandwidth
of no more than one per cent of the spread-spectrum bandwidth of
the RS-spread-spectrum signal, system performance improves
significantly as the bandwidth of the BS-channel-sounding signal
decreases. Preferably, the BS-channel-sounding signal has a
bandwidth of no more than one per cent, and should not exceed
twenty per cent, of the spread-spectrum bandwidth of the
RS-spread-spectrum signal. The BS-channel-sounding signal may be a
continuous wave signal, also known as a carrier signal.
Alternatively, the BS-channel-sounding signal may be modulated with
amplitude modulation (AM), frequency modulation (FM), phase
modulation (PM), or a combination thereof. Amplitude-shift-keying
(ASK) modulation, frequency-shift-keying (FSK) modulation or
phase-shift-keying (PSK) modulation may be employed. Similarly, a
narrowband spread-spectrum signal could modulate the
BS-channel-sounding signal. A combination of these modulations also
could be employed. The modulation in the BS-channel-sounding signal
can be used for base station identification, as well as for other
information such as commercials, stock quotes, etc.
[0062] The bandwidth of the BS-channel-sounding signal is a
determinative factor, and a design choice, since increased
bandwidth will cause increased interference to the plurality of
RS-spread-spectrum signals, which are at the same frequency as the
BS-channel-sounding signal. At a one per cent bandwidth of the
plurality of RS-spread-spectrum signals, little degradation in
system performance results.
[0063] Each of the plurality of remote stations includes
RS-receiver means, RS-power means and compensating means. The
RS-receiving means receives the BS-channel-sounding signal at the
second frequency, and demodulates the BS-channel-sounding signal,
and outputs an RS-receiver signal. RS-power-level means, in
response to the received power level of the BS-channel-sounding
signal, adjusts an initial RS-power level of the RS-spread-spectrum
transmitter located at the remote station. In response to the
RS-receiver signal, the compensating means compensates the second
frequency, for Doppler shift, of the RS-spread-spectrum signal of
the RS-spread-spectrum transmitter located at the remote station.
For example, if the carrier frequency of the received
BS-channel-sounding signal had a negative Doppler shift from its
carrier frequency, as received at the remote station, then the
compensating means would impose a positive shift from the
designated carrier frequency on the transmitted RS-spread-spectrum
signal. Due to motion of the remote station or propagation path
motions in the communications channel, the RS-spread-spectrum
signal arrives at the base station at the corrected carrier
frequency, i.e., at the second frequency f.sub.2. In a preferred
embodiment, the RS-power means is employed to initially set the
transmitter power of the remote station. The compensating means may
also be used to correct the transmitter frequency of the
RS-spread-spectrum transmitter.
[0064] In the exemplary arrangement shown in FIG. 7, the base
station 12 is shown communicating, using radio waves, with a remote
station with frequency compensation. Since the BS-channel-sounding
signal is transmitted, as a radio wave, from the base station 12 at
the second frequency f.sub.2 to the remote station 11, and the
remote station 11 knows at what frequency the BS-channel-sounding
signal is suppose to be received, then remote station 11 can
determine the Doppler frequency shift f.sub.D and compensate its
transmitter frequency by a similar amount so that the
RS-spread-spectrum signal arrives at the base station 12 with a
carrier frequency at the correct second frequency f.sub.2. Thus,
the RS-spread-spectrum signal is detected at the base station at
the second frequency f.sub.2, without a Doppler shift in carrier
frequency f.sub.D. If motion of the remote station caused a
positive shift in the Doppler frequency f.sub.D, then the correct
compensation would be to subtract the Doppler shift in carrier
frequency f.sub.D and transmit at frequency f.sub.2-f.sub.D. The
remote station 11 also can measure the power level of the
BS-channel-sounding signal, and from this measurement, set its
initial power level for transmitting the RS-spread-spectrum signal
at the second frequency f.sub.2.
[0065] In FIG. 8, the improvement to the BS-spread-spectrum
transmitter is shown. The signal source 829 generates the
BS-channel-sounding signal. The BS-channel-sounding signal is
combined in combiner 824 with the BS-spread-spectrum signal. The
BS-spread-spectrum signal may be generated, as is well known in the
art, by a plurality of product devices 816, 817, 818, which
multiply a plurality of data signals d.sub.1(t), d.sub.2(t), . . .
d.sub.k(t), by a plurality of chip-sequence signals g.sub.1(t),
g.sub.2(t), . . . g.sub.k(t). The outputs from the plurality of
product devices 816, 817, 818 is a plurality of spread-data
signals. Typically, the plurality of spread-data signals is
combined linearly by a combiner 821, to generate a
combined-spread-data signal. The combined-spread-data signal is
multiplied by in-phase product device 822 by a cosine signal at the
first frequency f.sub.1, and by a quadrature-phase product device
823 by a sine signal at the first frequency f.sub.1, to generate
in-phase and quadrature-phase components of the BS-spread-spectrum
signal. The in-phase component of the BS-spread-spectrum signal and
the quadrature-phase component of the BS-spread-spectrum signal are
then combined to make the BS-spread-spectrum signal which is
transmitted from the base station 12 at the first frequency
f.sub.1, by antenna 825. Techniques for generating spread-spectrum
signals are well known in the art, and the technique shown in FIG.
8 is only representative.
[0066] The design of spread-spectrum transmitters is well-known in
the art. Typically, the BS-spread-spectrum transmitter would be
implemented in a digital signature processor (DSP) or application
specific integrated circuit (ASIC). Alternative techniques for
building a spread-spectrum transmitter include using a
surface-acoustic-wave (SAW) device, with the SAW device having an
impulse response matched to the specific chip-sequence signal
desired for a spread-spectrum channel. Further, the plurality of
chip-sequence signals can be stored in a memory, and each time a
particular digital signal is applied to a memory address, and
particular chip-sequence signal is outputted to the combiner 821.
All these techniques, and others, are well known in the art for
generating spread-spectrum signals.
[0067] The signal source 829 generates the BS-channel-sounding
signal, which may be a simple continuous wave signal, or a signal
modulated with AM modulation, FM modulation, PM modulation, ASK
modulation, FSK modulation, PSK modulation or spread-spectrum
modulation. With modulation, the BS-channel-sounding signal can
carry data, such as signaling data or order wire data.
Alternatively, the BS-channel-sounding signal can broadcast to the
plurality of remote stations general information such as timing,
advertisements or commercials, and other information to update the
remote station from the base station.
[0068] FIG. 9 illustratively shows the improvement to the remote
station receiver. The RS-spread-spectrum receiver includes the
spread-spectrum receiver 931, the RF filter 932, and the low noise
amplifier (LNA) 930, coupled to the antenna 933. The RF filter 932
is coupled between the spread-spectrum receiver 921 and the low
noise amplifier 930. The components for the RS-spread-spectrum
receiver are well known in the art. For example, the
RS-spread-spectrum receiver may be embodied as a plurality of
product devices and a chip-signal generator, with output lowpass or
bandpass filters. The operation of multiplying a received
spread-spectrum signal by a plurality of chip-sequence signals is
well known, and can be found in many textbooks on the subject.
Alternatively, the RS-spread-spectrum receiver may be embodied as a
plurality of matched filters, which have a plurality of impulse
responses matched to the plurality of chip-sequence signals
embedded in the received BS-spread-spectrum signal. The
RS-spread-spectrum receiver may be implemented as an integrated
circuit, ASIC, SAW device, and may operate at baseband,
intermediate frequency or other processing frequency.
[0069] The sounding channel improvement includes RS-receiver means,
which is embodied as demodulator 935. The demodulator 935 is
coupled to low noise amplifier 930, for receiving the
BS-channel-sounding signal at the second frequency f.sub.2, or at
the second frequency f.sub.2 plus or minus a Doppler shift f.sub.d
in carrier frequency from the second frequency f.sub.2. The
demodulator 935 may include a tracking filter, phase-locked-loop
(PLL) circuit, FM or PM discriminator, spread-spectrum receiver, or
other circuitry for demodulating the BS-channel-sounding signal.
The demodulator 35 demodulates the BS-channel-sounding signal, and
outputs an RS-receiver signal. The RS-receiver signal is a
demodulated version of the received BS-channel-sounding signal, and
may include a power level proportional to a received power level of
the BS-channel-sounding signal, and a frequency representation or
shift, of the received BS-channel-sounding signal.
[0070] The compensating means is embodied as a frequency-adjust
circuit 934, coupled to the RS demodulator 935. In response to the
RS-receiver signal, the frequency-adjust circuit 934 compensates to
the first frequency f.sub.1 the RS-spread-spectrum signal of the
RS-spread-spectrum transmitter located at the remote station. The
frequency-adjust circuit 934 also can provide Doppler information,
including Doppler shift in carrier frequency f.sub.D, by way of a
Doppler signal to the spread-spectrum receiver 931. The
frequency-adjust circuit 934 might include a local oscillator or
other signal source, and a comparator circuit. The local oscillator
or signal source from the RS-spread-spectrum transmitter generates
a local signal at the second frequency f.sub.2. The comparator
compares the local signal with the received BS-channel-sounding
signal, or the RS-receiver signal, to determine Doppler shift in
carrier frequency f.sub.D. A signal with the Doppler shift in
carrier frequency can be used to adjust the transmitter frequency
of the RS-spread-spectrum signal. Electronic circuits for the
comparator and frequency-adjust circuit 934, are well known in the
art. The spread-spectrum receiver can adjust its oscillator
circuit, or the frequency-adjust circuit 934 can adjust the
frequency of the oscillator for the spread-spectrum receiver 931,
thereby compensating for Doppler shift in carrier frequency f.sub.D
due to motion.
[0071] The RS-power means may be embodied as a power-adjust circuit
936, which is coupled to the output of the demodulator 935. As
shown in FIG. 10, the power-adjust circuit 936 couples to a
variable power amplifier 940 of the RS-spread-spectrum transmitter.
Depending on the power level from the BS-channel-sounding signal,
or RS-receiver signal, the power-adjust circuit 936 can adjust the
output power of the variable power amplifier 940 to a desired
level. An equivalent circuit for the variable power amplifier 940
would be a variable attenuator, which attenuates in response to a
power-adjust signal.
[0072] Similarly, the frequency-adjust circuit 934 may couple to
the signal source 939 of the RS-spread-spectrum transmitter. The
frequency-adjust circuit 934 can offset the transmitter frequency
by the Doppler frequency f.sub.D, so that the RS-spread-spectrum
signal arrives at the base station 12 at the correct second
frequency f.sub.2. By subtracting the Doppler frequency f.sub.D
from the second frequency f.sub.2, the transmitter frequency of the
RS-spread-spectrum signal shifts back to the second frequency
f.sub.2 due to the Doppler frequency f.sub.D added to the carrier
frequency of the RS-spread-spectrum signal, due to motion of the
remote station.
[0073] In FIG. 10, the RS-spread-spectrum transmitter includes a
product device 937 for multiplying a chip-sequence signal by data
to generate a spread-data signal. For a positive Doppler shift in
carrier frequency of the BS-channel-sounding signal, the
spread-data signal is shifted to a carrier frequency of
f.sub.2-f.sub.D, by product device 938, to generate the
RS-spread-spectrum signal. For a negative Doppler shift in carrier
frequency of the BS-channel-sounding signal, the spread-data signal
is shifted to a carrier frequency of f.sub.2+f.sub.D, by product
device 938, to generate the RS-spread-spectrum signal. The
RS-spread-spectrum signal is amplified by amplifier 940 and
radiated by antenna 941.
[0074] FIG. 11 shows the improvement to the BS receiver. The BS
transmitter 824 is connected to a coupler 949, such as a
circulator, which connects to the antenna 825. The antenna 825 is
used in FIG. 11 for transmitting and receiving at the second
frequency f.sub.2. The RS-spread-spectrum signals received from the
remote stations pass through the coupler 949, through the bandpass
filter 947 and in to the interference canceller 951. The
BS-channel-sounding signal from the signal source 829 passes in to
the phase-shift attenuator 950. An output of the interference
canceller 951 is coupled to an input of the phase-shift attenuator
950. The signal from the interference canceller 51 adjusts the
phase-shift attenuator 950 so as to minimize the
BS-channel-sounding signal level fed in to the base station
spread-spectrum receiver 946.
[0075] As an option, a notch filter 948 may be coupled between the
interference canceller 951 and the base station spread-spectrum
receiver 946. The notch filter 948 notch filters the interference
from the BS-channel-sounding signal. An interference canceller 951
with a phase-shift attenuator 950 for reducing interference, in
general, is well known in the art. The interference canceller 951
and the phase-shift attenuator 950 operate in a feedback loop so as
to minimize the effect of a received signal at the second frequency
f.sub.2 by effectively feeding a signal from signal source at the
second frequency f.sub.2, 180.degree. out of phase with the
received signal.
[0076] The present invention may be used in a cellular architecture
having a plurality of base stations. The BS-channel-sounding signal
may be modulated to identify a particular base station. Thus, a
remote station knows with which cell it is in communication by the
modulation on the BS-channel-sounding signal. An alternative may
have a plurality of base stations, which cover a large geographic
area, transmit their respective BS-channel-sounding signal in a
respective time slot, as shown in FIG. 12. During a particular time
slot, a packet may be transmitted by the respective base station.
The packet may include no information, or identifying information.
From the packet, a remote station can determine relative power, and
Doppler shift in carrier frequency f.sub.D, of the particular base
station to the remote unit.
[0077] The present invention also includes a method for improving a
spread-spectrum system. The spread-spectrum system has at least one
base station and a plurality of remote stations (RS). The base
station (BS) has a BS-spread-spectrum transmitter for transmitting,
as radio waves, a plurality of BS-spread-spectrum signals at a
first frequency f.sub.1. The base station also has a
BS-spread-spectrum receiver for receiving, at a second frequency
f.sub.2, a plurality of RS-spread-spectrum signals from the
plurality of remote stations. The plurality of BS-spread-spectrum
signals are assumed to be at the first frequency f.sub.1 outside a
correlation bandwidth of the plurality of RS-spread-spectrum
signals at the second frequency f.sub.2. Each of the plurality of
remote stations has an RS-spread-spectrum transmitter for
transmitting an RS-spread-spectrum signal at the second frequency
f.sub.2. The method comprises the steps of transmitting, from a BS
transmitter, located at the base station, a BS-channel-sounding
signal at the second frequency f.sub.2. The BS-channel-sounding
signal has a bandwidth no more than twenty per cent of the
spread-spectrum bandwidth of the plurality of RS-spread-spectrum
signals, and preferably less than one percent of the
spread-spectrum bandwidth of the plurality of RS-spread-spectrum
signals. The method includes receiving, at each of the plurality of
remote stations with an RS receiver, the BS-channel-sounding signal
at the second frequency f.sub.2, and receiving, at each of the
plurality of remote stations with an RS demodulator, a the
BS-channel-sounding signal. The RS demodulator outputs an
RS-receiver signal. The method further includes the step of
compensating, in response to the RS-receiver signal, a
frequency-adjust circuit to the first frequency f.sub.1 the
RS-spread-spectrum signal of the RS-spread-spectrum transmitter
located at the remote station. The method may adjust, in response
to the RS-receiver signal, an initial RS-power level of the
RS-spread-spectrum transmitter located at the remote station. At
the base station, the method includes the step of reducing, at the
second frequency f.sub.2, the BS-channel-sounding signal from the
RS-spread-spectrum signal arriving at the base station.
[0078] The method optionally may further include the step of
compensating, in response to RS-receiver signal, to the first
frequency f.sub.1 the RS-spread-spectrum signal of the
RS-spread-spectrum transmitter located at the remote station.
[0079] Sharing of Capacity between CS and PS Remote Stations
[0080] The current third generation (3G) system operates in a star
network, as illustratively shown in FIG. 1, with CS-remote
stations, but with one dedicated channel for packet-switched mode
available for PS-remote stations. The dedicated channel for
PS-remote stations uses a PS-chip-sequence signal for
spread-spectrum processing data from the PS-remote station. For one
dedicated channel, the PS-chip-sequence signal is used by all of
the PS-remote stations. Only one PS-remote station, however,
accesses the base station at a time.
[0081] More than one channel can be allocated for PS-remote
stations. For example, two or more dedicated channels may be
allocated for PS-remote stations. For two dedicated channels for
packet-switched signals, the system would have two different
chip-sequence signals, one each allocated to each of the dedicated
packet-switched channels.
[0082] The plurality of CS-remote stations and the plurality of
PS-remote stations all operate at the same frequency, and within
the same bandwidth, and preferably with the same chip rate f.sub.c.
A particular communications channel for a particular CS-remote
station or a PS-remote station is set by a particular chip-sequence
signal assigned for the respective CS-remote station or PS-remote
station. Communications channels defined by chip-sequence signals
is well-known in the art.
[0083] In the plurality of CS-remote stations, the various
CS-remote stations, while operating at the same chip rate f.sub.c,
can operate at different data rates. Typically, when a CS-remote
station initiates communications with a particular base station,
the CS-remote station requests a communications channel with a data
rate and error rate. The CS-remote station receives the
chip-sequence signal appropriate to the allocated data rate, from
the base station. This allocation is made to avoid exceeding system
capacity.
[0084] After establishing a communications channel, a CS-remote
station maintains communications with that particular base station
until finished, or until the CS-remote station makes handoff with
another base station. In the plurality of CS-remote stations, the
various CS-remote stations communicating with a base station may
operate at different data rates and error rates, and transmit with
different power levels. Data received from the CS-remote station
communicating with the base station, are stored in the
store-and-forward subsystem 341 of FIGS. 4 and 5, and then
forwarded to the central office 50 in a star network of FIG. 1, or
forwarded to a neighboring nodes and to central office 50 for the
distributed network of FIGS. 2 and 3.
[0085] For packet-switched communications, with only one dedicated
communications channel for packet-switched signals, only one
PS-remote station communicates with a base station, at a time. Each
PS-remote station uses the same PS-chip-sequence signal. Several
strategies exist in the literature, if several PS-remote stations
desired to communicate with the base station. One strategy requires
a polling of each PS-remote station that has indicated, by a
separate short transmission, its desire to transmit a packet. Such
a system works well when a large number of PS-remote stations want
to transmit simultaneously. Alternatively, a base station transmits
a busy signal when no or insufficient capacity exists. When
capacity exists, the base station transmits or assigns the
chip-sequence signal and data rate to all PS-remote stations. A
PS-remote station reads the message from the base station, and
transmits using the chip-sequence signal and data rate assigned
from the base station. This latter operation is similar to ALOHA
system and the Ethernet system.
[0086] The PS-remote station functions essentially in a
store-and-forward operation, since a particular PS-remote station
stores a packet, and only forwards the packet to the base station
when permitted to do so.
[0087] The base station also functions in a store-and-forward
operation. Data received from the PS-remote station communicating
with the base station, are stored in the store-and-forward
subsystem 341 of FIGS. 4 and 5, and then forwarded to the central
office 50 in a star network of FIG. 1, or forwarded to a
neighboring nodes and to central office 50 for the distributed
network of FIGS. 2 and 3.
[0088] A PS-remote station transmits the packet quickly, and then
ceases transmitting.
[0089] The star network typically has more users for a base station
than in a distributed network, as shown in FIG. 2, because the base
stations in the star network are far apart, while in the
distributed network, there are many base stations close
together.
[0090] In a typical operation of either a star network or
distributed network, multiple CS-remote stations communicate with
the base station, by transmitting and receiving information to and
from the base station. The multiple CS-remote stations want to
communicate with a base station continuously, and each CS-remote
station maintains a channel connection, until a "hang-up" occurs.
On the other hand, a PS-remote station wants to send a packet of
data to the base station, and then immediately break
communications. The circuit-switched system CS-remote stations
operate at the same time, each using some of the total capacity in
the spread-spectrum channels of the base station. Packet-switched
system users operate one-at-a time, and only use the capacity which
is still available in the spread-spectrum channels from the base
station, since the circuit-switched remote stations may not always
use all of the capacity available in the spread-spectrum channels
from the base station.
[0091] With many CS-remote stations communicating with a base
station, a problem can arise such that a PS-remote station cannot
communicate with the base station. The available capacity in the
spread-spectrum channels at a base station changes dynamically with
time, since CS-remote stations can stop communicating with the base
station, and new CS-remote stations can initiate communications
with a base station. When a first CS-remote station stops
communicating with a base station, another, labeled second
CS-remote station, can take the available spread-spectrum channel
relinquished by the first CS-remote station, and available capacity
in the spread-spectrum channels at the base station, made available
by the first CS-remote station. Alternatively, a PS-remote station
can take the space, or available capacity, in the spread-spectrum
channels with the base station, which became available with the
first CS-remote station ceasing communications with the base
station. The PS-remote station, however, only requires the
packet-switched channel in which to send and receive data to and
from the base station, for a short time.
[0092] If a PS-remote station wants access to a base station, and
to communicate with a base station, then the PS-remote station is
told, by the flow-control subsystem 340 of the base station: (1)
packet-switched channel availability, (2) available capacity in the
spread-spectrum channels at the bass station, (3) data rate
available for data transmission, (4) and chip-sequence signal to be
used by the PS-remote station for the particular available channel.
Additionally, the PS-remote station needs to know at which power
level to transmit to the base station, to avoid ramping up through
a series of power levels until an acceptable power level is
reached, and to avoid jamming or causing interference to the
CS-remote stations. Normally, only one PS-remote station
communicates at a time with a base station, while multiple
CS-remote stations simultaneously communicate with the base
station.
[0093] If there are too many PS-remote stations communicating with
the base station, then a PS-remote station requesting the
packet-switched channel is told either a packet-switched channel is
available, or to wait until the packet-switched channel becomes
available.
[0094] Available capacity at the base station is the ability of the
base station to receive and transmit, in the spread-spectrum
channels assigned to the base station, store, all incoming
CS-packet signals form CS-remote stations, and PS-packet signals
from PS-remote stations. Referring to FIG. 13, a chart illustrates
available capacity versus number of users. The maximum capacity
C.sub.MAX is the maximum amount of information, or the total data
rate, bits per second (bps), packets, that the spread-spectrum
channels of the base station can handle. Typically, the capacity
would be for uplink communications paths, from CS-remote stations
and PS-remote stations to the base station. The amount of
information from a CS-remote station can vary, based on data rate.
Maximum capacity is available with no users. As the number of users
increases, the available capacity decreases. If several CS-remote
stations simultaneously send at high data rates, then the total
number of users who can access the bases stations decreases.
[0095] The data rate from a PS-remote station also factors into
whether a base station can accept a PS-remote station. If the
CS-remote stations already are using the capacity in the
spread-spectrum channels of the base station, then there may be no
data rate which can be assigned to a PS-remote station.
[0096] A problem with using either the star network or the
distributed network, is that, if a CS-remote station, or multiple
CS-remote stations, required high capacity in the spread-spectrum
channels, while communicating with a base station, then that
particular CS-remote station, or multiple CS-remote stations, may
require all the capacity in the spread-spectrum channels of the
base station. Under these conditions, a PS-remote station would not
be able to communicate with the base station.
[0097] Capacity of a base station is the ability of the base
station to receive a spread-spectrum CDMA signals, in the
spread-spectrum channels. The capacity is limited by bandwidth.
[0098] If a base station had all of its available capacity taken
for a given time period, then the flow-control subsystem 340 in
that base station sends effectively a busy signal to other
subscribers, indicating the there is no available capacity. As soon
as a CS-remote station finished transmitting to the base station,
then the flow-control subsystem 340 of the base station can send a
signal indicating how much capacity in the store-and-forward
subsystem 341 is available. At this time, another CS-remote station
or PS-remote station can access the base station. Thus, if all the
capacity in the spread-spectrum channels at a base station is used,
then a CS-remote station must stop transmitting to the base
station, before a new CS-remote station can access the base
station.
[0099] Assume that a store-and-forward subsystem 341 at a base
station has ten kilobit capacity available, with the rest of the
spread-spectrum channel capacity being used by CS-remote stations.
If a first PS-remote station requiring ten kilobits now accessed
the base station, then a second PS-remote station cannot access the
base station until the first PS-remote station finishes
transmission, and capacity in the spread-spectrum becomes
available. Of course, the first PS-remote station and the second
PS-remote station may attempt to access the base station at the
same time, with a collision resulting. Most likely, one of the
first PS-remote station and the second PS-remote station would
access the base station. The successful remote station accessing
the base station would receive an acknowledgment signal, thereby
knowing the communications of the packet is complete. The
unsuccessful PS-remote station would attempt at a later time, to
access the base station, and would continue to attempt to send the
PS-packet to the base station, until receipt of an acknowledgment
signal. As an alternative embodiment, the base station could assign
a time slot for each PS-remote station wanting to send a PS-packet
to the base station. But the overhead in setting up the time slot
is believed to reduce overall communications data rate to the base
station.
[0100] If a first PS-remote station accessed the base station and
only requires two kilobits capacity in the spread-spectrum
channels, then in the spread-spectrum channels of the base station
has eight kilobits capacity available. The second PS-remote station
can access the base station, if the second PS-remote station only
required eight kilobits capacity in spread-spectrum channels. A
second chip-sequence signal is needed for the second PS-remote
station, if packets are sent simultaneously from the first
PS-remote station and the second PS-remote station.
[0101] In general, at a base station, consider N remote stations
accessing the base station. Out of N remote stations, a particular
remote, referred to as the i.sup.th remote station, also is
accessing the base station. Then the signal-to-noise ratio, at the
base station, is related by: 1 P S1 P I1 - { f c f bi } = k i
Equation 1
[0102] where P.sub.si is the power received at the base station
from the i.sup.th remote station; P.sub.I1 is the total interfering
power received at the base station, which is interfering with
receiving the power P.sub.s1, received at the base station from the
i.sup.th remote station; f.sub.c is the chip rate; f.sub.b1 is the
data rate transmitted from the i.sup.th remote station; k.sub.i is
number proportional to the error rate in data from the i.sup.th
remote station, the probability of error P.sub.e typically is
related to k.sub.1 by the complementary error function. As k.sub.1
decreases, the probability of error, P.sub.e, increases in an
exponential manner. Consider the minimum number K.sub.i which
yields the maximum error rate permissible for receiving data from
the i.sup.th remote station, then
ki.gtoreq.K.sub.1 Equation 2
[0103] The base station knows all k.sub.1 and K.sub.1 for each
remote station. When the base station is lightly loaded, that is,
relatively few remote stations are accessing the base station, then
k.sub.1 is much greater than K.sub.1, for each i.sup.th remote
station. As the number of remote stations accessing the base
station increases, the total interfering power P.sub.I1 for each
i.sup.th remote station increases. As the total interfering power
P.sub.I1 for each i.sup.th remote station increases, the ratio
k.sub.1 for each i.sup.th remote station decreases. The decreasing
ratio k.sub.1 for each i.sup.th remote station increases the error
rate, until, maximum capacity is reached. At maximum capacity, the
interfering power P.sub.Ii for each i.sup.th remote station is a
maximum, since k.sub.1 is approximately equal to K.sub.1, for at
least one particular i.
[0104] Different remote stations may require different error rates
and also operate at different data rates. Thus, the system is
limited by the most sensitive, and vulnerable, remote station.
[0105] Equation 1 can be rewritten as a ratio of the energy in the
desired i.sup.th remote station, at the base station, to the energy
in interference in the chip of the desired i.sup.th remote station,
at the base station:
(P.sub.S1/f.sub.b1)/(P.sub.I1/f.sub.c)=k.sub.i Equation 3
[0106] Assume that a first power P.sub.S1=10.sup.-7 is received at
the base station from a first remote station, and that a second
power P.sub.S2=10.sup.-8 is received at the base station from a
second remote station. Assume that the total power P.sub.T received
at the base station from all remote stations, including the first
remote station and the second remote station, is
10.sup.-6-10.sup.-8 which equals 99.times.10.sup.-8 which equals
9.9.times.10.sup.-7. Then, the interfering power P.sub.I2 for the
second remote station equals 10.sup.-6-10.sup.-7 which equals
9.times.10.sup.-7. If the first bit rate f.sub.b1 for the first
remote station equals 320 kHz, and the second bit rate f.sub.b2 for
the second remote station equals 3.2 MHz, then 2 k 1 = ( 10 - 7 /
320 kHz ) / ( 9.9 .times. 10 - 7 / 3.2 MHz ) = 10 / 9.9 1.01
[0107] (which approximately is equal to one).
[0108] While: 3 k 2 = ( 10 - 8 / 320 kHz ) / ( 9.9 .times. 10 - 7 /
3.2 MHz ) = 10 / 9 1.1
[0109] From the above, the first ratio k.sub.1 is more sensitive
than the second ratio k.sub.2. Depending on the values used in
these equations, the vulnerability to error can become more
pronounced.
[0110] Consider in a particular system that K.sub.1=4 and that
K.sub.2=1. Then remote stations can access the base station, so
long as k.sub.1 is greater than or equal to 4.
[0111] The base station tells each remote station accessing the
base station, what maximum power level and data rate is permitted.
For example, typically P.sub.S1/f.sub.b1 is a constant since
P.sub.S1/f.sub.b1 represents the symbol energy before
forward-error-correction (FEC) encoding. Thus, when the base
station is telling a remote station what the maximum symbol rate
f.sub.b1 can be sent, the base station also is telling the remote
user the maximum power level P.sub.S1 that can be received at the
base station.
[0112] From Equation 1, the power level is most important to the
base station, since if a particular remote station is attempting to
access the base station, and transmits with too much power, then
the particular remote station jams the other remote stations at the
base station. A remote station desiring to access the base station,
whether a CS-remote station or a PS-remote station, when knowing
the power limitation, also knows the data rate limitation. This can
be simplified by having the base station tell a PS-remote station
the data rate the PS-remote station is to use. From the sounding
channel, the PS-remote station knows the power level. Closed loop
power control is used to control the power receied at the base
station, from each remote station.
[0113] If a CS-system, by way of example, is designed to handle 100
CS-remote stations, at 32 kb/s, and the power received from each
remote station is P.sub.o, then P.sub.I1=99.times.P.sub.o, and
k.sub.i=(P.sub.o/99.times.P.sub.o).times.(f.sub.c/32 kb/s)
[0114] Suppose that one of the interfering remote stations is at
the wrong power level, and sends fours times the interfering remote
station's authorized power level, 4P.sub.o, or the interfering
remote station transmits with the authorized power level, but four
times the authorized power level, 4P.sub.o, arrives at the base
station due to multipath combining or other propagation effect,
then
k.sub.1=(P.sub.o/102.times.P.sub.o).times.(f.sub.c/32 kb/s)
[0115] This is not much of a change, and the system performance
degrades gracefully.
[0116] In the present invention, assume that P.sub.S1/f.sub.b1 is
constant independent of the chosen data rate. This requirement is
not necessary, but easy and may be preferred.
[0117] Assume that the base station has a sounding channel. Then
the PS-remote station listens to the base station. When the base
station tells a particular PS-remote station that the base station
has a certain data rate available (i.e. capacity is available), for
example, that 2 Mb/s can be sent, then the particular PS-remote
station, if the particular PS-remote station has a packet to send,
automatically transmits. The time for transmission from the
particular PS-remote station can at a random time from being told
that capacity is available. The random time may be controlled by a
random number generator ro other random device. Alternatively, the
time for transmission from the particular remote station need not
be random, but may be a preset time from when being told capacity
is available.
[0118] As soon as the base station receives a bit or two from the
particular PS-remote station, then the base station sends a busy
(BT) signal, equivalent to a busy tone or packet, so that other
PS-remote station do not access the channel.
[0119] Suppose that a particular CS-remote station can receive and
hears the base station, but only requires 32 kb/s, the particular
CS-remote station can use the 32 kb/s by accessing the base
station. When the particular CS-remote station accesses the base
station, the base station transmits a data rate availability, by
way of example, of 2 MB/s-32 kb/s=1,968 kb/s.
[0120] When a PS-remote station accesses the base station, the
PS-remote station uses all of the available capacity for a short
time, for example, with a 2 Mb/s capacity, the PS-remote station
can send 10 kb in five milliseconds.
[0121] The present invention is adaptive and utilizes the capacity
in the store-and-forward subsystem 341 of the base station
efficiently. When the base station is not fully occupied by one or
more CS-remote stations, then one packet from a PS-remote station
can arrive at a time, without a collision. To accomplish this, busy
signal collision avoidance is employed. Thus, as soon as the base
station detects an incoming packet, it sends out a busy signal,
analogous to a busy tone, indicating there is no available
capacity.
[0122] Packet switched transmission from multiple PS-remote
stations involves random packets, with relatively large time
durations in between the transmissions of packets. The present
invention requires each PS-remote station to start listening to a
base station as soon as the PS-remote station enters the cell of
the respective base station. Thus, a PS-remote station turns on in
a system, and has nothing to send, the PS-remote station monitors
the surrounding base stations for power and capacity. The PS-remote
station sends a short identification packet. The base station adds
its address to this packet and forwards the packet to the central
office. The central office now knows which base station the
PS-remote station is near, and where to forward a message intended
for that particular PS-remote station.
[0123] It the PS-remote station moved and another base station
becomes the preferred base station, then the PS-remote station
sends an identification signal to this second base station. The
second base station adds its address to the packet, and forwards
the packet to the central office. The central office now knows that
the second base station is being used by the PS-remote station, and
to forward a message intended for that particular PS-remote station
to the second base station. Thus, the central office always knows
the location of each PS-remote station, in its system.
[0124] It will be apparent to those skilled in the art that various
modifications can be made to the efficient sharing of capacity by
remote stations using circuit switching and packet switching of the
instant invention without departing from the scope or spirit of the
invention, and it is intended that the present invention cover
modifications and variations of the efficient sharing of capacity
by remote stations using circuit switching and packet switching,
provided they come within the scope of the appended claims and
their equivalents.
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