U.S. patent number RE44,010 [Application Number 12/023,611] was granted by the patent office on 2013-02-19 for modular base station with variable communication capacity.
This patent grant is currently assigned to InterDigital Technology Corporation. The grantee listed for this patent is Stephen G. Dick, Leonid Kazakevich, Fatih M. Ozluturk, Jeffrey S. Polan, Robert T. Regis, Richard Turner. Invention is credited to Stephen G. Dick, Leonid Kazakevich, Fatih M. Ozluturk, Jeffrey S. Polan, Robert T. Regis, Richard Turner.
United States Patent |
RE44,010 |
Polan , et al. |
February 19, 2013 |
Modular base station with variable communication capacity
Abstract
The present invention provides a base station architecture that
is modular in configuration, lowering the initial cost of
implementing a new CDMA telecommunication system for a defined
geographical region while allowing for future capacity. The
scalable architecture is assembled from a digital base station unit
that is configured to support a plurality of simultaneous wireless
calls connecting to a conventional public switched telephone
network. For initial startup, two base station units are deployed
for redundancy in case of a single failure. Additional base station
units may be added when the need arises for extra traffic capacity.
If sectorization is required, the base station units may be
directionally oriented. Coupled to and remote from each base
station unit are two amplified antenna modules that contain an
omni-directional or an external directional antenna, a high power
RF amplifier for transmitted frequencies and a low noise amplifier
for received frequencies. A separate power supply module capable of
supporting two base station units provides continued service in the
event of a mains power outage.
Inventors: |
Polan; Jeffrey S. (New Hope,
PA), Dick; Stephen G. (Nesconset, NY), Kazakevich;
Leonid (Plainview, NY), Ozluturk; Fatih M. (Port
Washington, NY), Regis; Robert T. (Huntington, NY),
Turner; Richard (Oakdale, NY) |
Applicant: |
Name |
City |
State |
Country |
Type |
Polan; Jeffrey S.
Dick; Stephen G.
Kazakevich; Leonid
Ozluturk; Fatih M.
Regis; Robert T.
Turner; Richard |
New Hope
Nesconset
Plainview
Port Washington
Huntington
Oakdale |
PA
NY
NY
NY
NY
NY |
US
US
US
US
US
US |
|
|
Assignee: |
InterDigital Technology
Corporation (Wilmington, DE)
|
Family
ID: |
35694903 |
Appl.
No.: |
12/023,611 |
Filed: |
March 17, 1999 |
PCT
Filed: |
March 17, 1999 |
PCT No.: |
PCT/US99/05776 |
371(c)(1),(2),(4) Date: |
April 23, 2001 |
PCT
Pub. No.: |
WO99/48228 |
PCT
Pub. Date: |
September 23, 1999 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
Reissue of: |
09646371 |
Apr 23, 2001 |
6993001 |
Jan 31, 2006 |
|
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Current U.S.
Class: |
370/335; 375/130;
455/524 |
Current CPC
Class: |
H04W
72/005 (20130101); H04B 17/318 (20150115); H04W
16/12 (20130101); H04B 17/382 (20150115); H04W
52/322 (20130101); H04W 52/325 (20130101) |
Current International
Class: |
H04B
7/216 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Behague et al., Modularity and Flexibility: The Keys to Base
Station System Configuration for the GSM Network, Nov. 13, 1991,
pp. 161-168. cited by applicant.
|
Primary Examiner: Sam; Phirin
Attorney, Agent or Firm: Volpe and Koenig, P.C.
Claims
What is claimed is:
1. A bidirectional communication system using a CDMA air interface
between a plurality of subscriber units communicating with a base
station, the system comprising: a scalable base station configured
from up to a select maximum number n of modular colocated base
station units for supporting incremental communication capacity
based on the number of modular base station units, each base
station unit for communicating with a predefined number of
subscriber units; each base station unit transmitting a unique CDMA
global pilot channel signal at a full power level for a discrete
limited time interval which time interval is distinct from the time
intervals of all other base station units in the scalable base
station configuration; and a plurality of subscriber units for CDMA
communication with the scalable base station, each subscriber unit
having means for selectively receiving global pilot channel signals
from up to n modular base station units, such that reception of
each global pilot channel signal is in a discrete time interval
synchronized with the full power level transmission time interval
of the respective global pilot channel signal which time interval
is distinct from the reception of all other transmission time
intervals of the global pilot channel signals.
2. The communication system according to claim 1 where n is
calculated based upon a maximum desired communication capacity
divided by the capacity of a single base station unit.
3. The communication system according to claim 1 wherein the
scalable modular base station is configured from a selected number
m of modular base station units where m<n.
4. The communication system according to claim 1 where n=6.
5. The communication system according to claim 1 wherein the time
interval is determined by the time of day.
6. The communication system according to claim 1 wherein the means
for selectively receiving global pilot channels includes waking up
for the discrete time interval.
7. The communication system according to claim 1 wherein each
modular base station unit further transmits a fast broadcast
channel and a slow broadcast channel.
8. The communication system according to claim 1 wherein the means
for receiving global pilot channels further includes storing a
relative global pilot channel signal strength received.
9. The communication system according to claim 7 wherein the means
for receiving global pilot channels further includes receiving the
slow broadcast channel and the fast broadcast channel and deriving
and storing that base station unit's communicating capacity from
the slow and fast broadcast channels.
10. The communication system according to claim 9 wherein a
subscriber unit initiates communication with one of the modular
base station units by choosing from storage the modular base
station unit having the strongest global pilot signal strength.
11. The communication system according to claim 10 wherein the
choosing from storage further includes the communication capacity
of that base station unit.
12. A base station for use in a bidirectional communication system
using a CDMA air interface between a plurality of subscriber units
communicating with the base station, comprising: a scalable base
station configured from up to a select maximum number n of modular
colocated base station units for supporting incremental
communication capacity based on the number of modular base station
units, each base station unit for communicating with a predefined
maximum number of subscriber units at any given time; and each base
station unit transmitting a unique CDMA global pilot channel at a
high power level for a discrete limited time interval which time
interval is distinct from the time intervals of all other base
station units in the scalable base station configuration.
13. A method of providing bidirectional communication using a CDMA
air interface between a plurality of subscriber units communicating
with a base station, the steps comprising: configuring from up to a
select maximum number n of modular colocated base station units a
scalable base station for supporting incremental communication
capacity based on the number of modular base station units, each
base station unit for communicating with a predefined number of
subscriber units; transmitting a unique CDMA global pilot channel
signal from each base station unit at a full power level for a
discrete limited time interval which time interval is distinct from
the time intervals of all other base station units in the scalable
base station configuration; and selectively receiving global pilot
channel signals from up to n modular base station units at a
plurality of subscriber units for CDMA communication with the
scalable base station, such that reception of each global pilot
channel signal is in a discrete time interval synchronized with the
full power level transmission time interval of the respective
global channel which is distinct from the reception of all others
of the global pilot channel signals.
.Iadd.14. A code division multiple access (CDMA) subscriber unit
comprising: circuitry configured to receive n synchronization
signals from a CDMA base station such that each of the n
synchronization signals are received in n discrete time intervals,
each discrete time interval for receiving a different
synchronization signal; circuitry configured to receive and recover
information from a broadcast channel; and circuitry configured to
transmit at least one code in an access procedure derived from the
recovered information from the broadcast channel..Iaddend.
.Iadd.15. The CDMA subscriber unit of claim 14 wherein each of the
n synchronization signals comprises a code..Iaddend.
.Iadd.16. The CDMA subscriber unit of claim 14 wherein each of the
n synchronization signals is a pilot signal..Iaddend.
.Iadd.17. The CDMA subscriber unit of claim 14 further comprising
circuitry configured to receive an acknowledgement from the base
station indicating that at least one of the plurality of codes was
received by the base station..Iaddend.
.Iadd.18. The CDMA subscriber unit of claim 14 wherein the
circuitry further configured to receive synchronization signals
from other CDMA base station and wherein the synchronization
signals from the other CDMA base stations are offset from each
other by a plurality of chips..Iaddend.
.Iadd.19. The CDMA subscriber unit of claim 14 comprising circuitry
configured to transmit a reverse link pilot signal..Iaddend.
.Iadd.20. A method for use by a code division multiple access
(CDMA) subscriber unit comprising: receiving n synchronization
signals from a CDMA base station by the CDMA subscriber unit such
that each of the n synchronization signals are received in n
discrete time intervals, each discrete time interval for receiving
a different synchronization signal..Iaddend.
.Iadd.21. The method of claim 20 wherein each of the n
synchronization signals comprises a code..Iaddend.
.Iadd.22. The method of claim 20 wherein each of the n
synchronization signals is a pilot signal..Iaddend.
.Iadd.23. The method of claim 20 comprising: receiving and
recovering information from a broadcast channel; and transmitting a
plurality of codes in an access procedure derived from the
recovered information from the broadcast channel..Iaddend.
.Iadd.24. The method of claim 23 comprising receiving an
acknowledgement from the base station indicating that at least one
of the plurality of codes was received by the base
station..Iaddend.
.Iadd.25. The method of claim 20 comprising receiving
synchronization signals from other CDMA base station and wherein
the synchronization signals from the other CDMA base stations are
offset from each other by a plurality of chips..Iaddend.
.Iadd.26. The method of claim 20 comprising transmitting a reverse
link pilot signal..Iaddend.
.Iadd.27. A code division multiple access (CDMA) base station
comprising: circuitry configured to transmit n synchronization
signals such that each of the n synchronization signals are
transmitted in n discrete time intervals, each discrete time
interval for transmitting a different synchronization signal; and
circuitry configured to transmit information on a broadcast
channel..Iaddend.
.Iadd.28. The CDMA base station of claim 27 wherein each of the n
synchronization signals comprises a code..Iaddend.
.Iadd.29. The CDMA base station of claim 27 wherein each of the n
synchronization signals is a pilot signal..Iaddend.
.Iadd.30. A method for use by a code division multiple access
(CDMA) base station comprising: transmitting n synchronization
signals such that each of the n synchronization signals are
transmitted in n discrete time intervals, each discrete time
interval for transmitting a different synchronization
signal..Iaddend.
.Iadd.31. The method of claim 30 wherein each of the n
synchronization signals comprises a code..Iaddend.
.Iadd.32. The method of claim 30 wherein each of the n
synchronization signals is a pilot signal..Iaddend.
.Iadd.33. A code division multiple access (CDMA) subscriber unit
comprising: circuitry configured to receive n synchronization
signals from a CDMA base station such that each of the n
synchronization signals are received in n discrete time intervals,
each discrete time interval for receiving a different
synchronization signal; and circuitry configured to receive and
recover information from a broadcast channel; wherein the receive
and recover information circuitry is synchronized based on at least
one of the synchronization signals..Iaddend.
.Iadd.34. The CDMA subscriber unit of claim 33 wherein each of the
n synchronization signals comprises a code..Iaddend.
.Iadd.35. The CDMA subscriber unit of claim 33 wherein each of the
n synchronization signals is a pilot signal..Iaddend.
.Iadd.36. The CDMA subscriber unit of claim 33 comprising:
circuitry configured to transmit a plurality of codes in an access
procedure derived from the recovered information from the broadcast
channel..Iaddend.
.Iadd.37. The CDMA subscriber unit of claim 36 further comprising
circuitry configured to receive an acknowledgement from the base
station indicating that at least one of the plurality of codes was
received by the base station..Iaddend.
.Iadd.38. The CDMA subscriber unit of claim 33 wherein the
circuitry further configured to receive synchronization signals
from other CDMA base station and wherein the synchronization
signals from the other CDMA base stations are offset from each
other by a plurality of chips..Iaddend.
.Iadd.39. The CDMA subscriber unit of claim 33 comprising circuitry
configured to transmit a reverse link pilot signal..Iaddend.
.Iadd.40. A method for use by a code division multiple access
(CDMA) subscriber unit comprising: receiving n synchronization
signals from a CDMA base station by the CDMA subscriber unit such
that each of the n synchronization signals are received in n
discrete time intervals, each discrete time interval for receiving
a different synchronization signal; and receiving and recovering
information from a broadcast channel; wherein the receiving
information is synchronized based on at least one of the
synchronization signals..Iaddend.
.Iadd.41. The method of claim 40 wherein each of the n
synchronization signals comprises a code..Iaddend.
.Iadd.42. The method of claim 40 wherein each of the n
synchronization signals is a pilot signal..Iaddend.
.Iadd.43. The method of claim 40 comprising: transmitting a
plurality of codes in an access procedure derived from the
recovered information from the broadcast channel..Iaddend.
.Iadd.44. The method of claim 43 comprising receiving an
acknowledgement from the base station indicating that at least one
of the plurality of codes was received by the base
station..Iaddend.
.Iadd.45. The method of claim 40 comprising receiving
synchronization signals from other CDMA base station and wherein
the synchronization signals from the other CDMA base stations are
offset from each other by a plurality of chips..Iaddend.
.Iadd.46. The method of claim 40 comprising transmitting a reverse
link pilot signal..Iaddend.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to communication systems. More
specifically, the invention relates to a communication system using
a code division multiple access air interface between a plurality
of individual subscribers distributed within a cellular community
and a plurality of small capacity base stations, some colocated per
cell to increase operational economy in proportion to the number of
subscribers.
2. Description of the Prior Art
Advanced cellular communication makes use of a state of the art
technique known as code division multiplexing, or more commonly, as
code divisional multiple access or CDMA. An example prior art
communication system is shown in FIG. 1.
CDMA is a communication technique in which data is transmitted with
a broadened band (spread spectrum) by modulating the data to be
transmitted with a pseudo-noise signal. The data signal to be
transmitted may have a bandwidth of only a few thousand Hertz
distributed over a frequency band that may be several million Hertz
wide. The communication channel is being used simultaneously by m
independent subchannels. For each subchannel, all other subchannels
appear as noise.
As shown, a single subchannel of a given bandwidth is mixed with a
unique spreading code which repeats a predetermined pattern
generated by a wide bandwidth, pseudonoise (pn) sequence generator.
These unique user spreading codes are typically orthogonal to one
another such that the cross-correlation between the spreading codes
is approximately zero. The data signal is modulated with the pn
sequence producing a digital spread spectrum signal. A carrier
signal is then modulated with the digital spread spectrum signal
establishing a forward-link and transmitted. A receiver demodulates
the transmission extracting the digital spread spectrum signal. The
transmitted data is reproduced after correlation with the matching
pn sequence. When the spreading codes are orthogonal to one
another, the received signal can be correlated with a particular
user signal related to the particular spreading code such that only
the desired user signal related to the particular spreading code is
enhanced while the other signals for all other users are not
enhanced. The same process is repeated to establish a
reverse-link.
If a coherent modulation technique such as phase shift keying or
PSK is used for a plurality of subscribers, whether stationary or
mobile, a global pilot is continuously transmitted by the base
station for synchronizing with the subscribers. The subscriber
units are synchronizing with the base station at all times and use
the pilot signal information to estimate channel phase and
magnitude parameters. For the reverse-link, a common pilot signal
is not feasible. Typically, only non-coherent detection techniques
are suitable to establish reverse-link communications. For initial
acquisition by the base station to establish a reverse-link, a
subscriber transmits a random access packet over a predetermined
random access channel (RACH).
Most prior art CDMA communications systems employed to date,
whether communicating with fixed or mobile subscribers that include
personal communication services (PCS), have been designed for
immediate large scale traffic considerations. A communication
system specification proposed by a service provider establishes a
required number of base stations which determine the region of
communication coverage. The specification geographically locates
each cell and establishes a traffic capacity that determines the
number of anticipated subscribers per cell including fixed and
mobile. The maximum capacity of communication traffic in each cell
is typically fixed by this design.
Prior art CDMA communication systems have been designed and sized
to immediately handle many simultaneous communications and are
therefore costly start-up installations for the service provider.
These systems have not addressed the need for a flexible base
station architecture that permits a cost effective, small scale
initial installation that can accommodate future subscriber
growth.
Accordingly, the object of the present invention is to decrease the
initial installation cost of a CDMA communication system while
allowing future expansion when the need arises.
SUMMARY OF THE INVENTION
The present invention provides a base station architecture that is
modular in configuration, lowering the initial cost of implementing
a new CDMA telecommunication system for a defined geographical
region while allowing for future capacity. The scalable
architecture is assembled from a digital base station unit that is
configured to support a plurality of simultaneous wireless calls
connecting to a conventional public switched telephone network. For
initial startup, two base station units are deployed for redundancy
in case of a single failure. Additional base station units may be
added when the need arises for extra traffic capacity. If
sectorization is required, the base station units may be
directionally oriented. Coupled to and remote from each base
station unit are two amplified antenna modules that contain an
omni-directional or an external directional antenna, a high power
RF amplifier for transmitted frequencies and a low noise amplifier
for received frequencies. A separate power supply module capable of
supporting two base station units provides continued service in the
event of a mains power outage.
The present invention supports both small and large size sectors or
omni-cells with an architecture that allows for easy growth to
support expanding traffic capacity without incurring a large
initial fixed cost.
Accordingly, it is an object of the present invention to allow for
easy expansion when subscriber communication traffic increases.
Other advantages may become apparent to those skilled in the art
after reading the detailed description of the preferred
embodiment.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a simplified block diagram of a typical, prior art, CDMA
communication system.
FIG. 2 is a communication network embodiment of the present
invention.
FIG. 3 is a physical installation of a scalable modular base
station.
FIG. 4 is a block diagram of a power supply for the scalable
modular base station.
FIG. 5 is a block diagram of a base station unit.
FIG. 6 is a block diagram of two base station units.
FIG. 7A is a block diagram of two amplified antenna modules and
radio frequency control modules for the first base station as shown
in FIG. 6.
FIG. 7B is a block diagram of a baseband transceiver module and six
air interface modules for the first base station unit as shown in
FIG. 6.
FIG. 7C is a block diagram of two amplified antenna modules and
radio frequency control modules for the second base station unit as
shown in FIG. 6.
FIG. 7D is a block diagram of a baseband transceiver module and six
air interface modules for the second base station unit as shown in
FIG. 6.
FIG. 8 is block diagram of a scalable base station using two base
station units.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The present invention is described with reference to the drawing
figures where like numerals represent like elements throughout.
A system diagram illustrating a CDMA communication system 15
employing scalable modular base stations is shown in FIG. 2. Four
cells 17, 19, 21, 23 of a multi-cellular telecommunication system
are shown with respect to their base station transceivers 17N',
19N', 21', 23'. One subscriber unit 25 is shown within one cell. A
plurality of individual forward and reverse signals are transmitted
in respective regions of the common CDMA frequency bandwidth
between the base station 17' and subscriber unit 25.
The base station units or BSUs employed in the scalable modular
base station enable a scalable configuration proportional to the
number of subscribers 25. As an example, 150 subscribers whose
average utilization during busy period is less than 10 percent,
would require a base station unit with 16 modems supporting up to
15 simultaneous calls. For redundancy in case of a single failure,
the scalable modular base station requires two colocated BSUs
(having twice the minimum capacity) to serve the same communicating
population to provide limited service in the event that one BSU
failed.
The colocated modular approach supports additional growth,
expanding beyond the two BSUs as the need arises. Each BSU is
omnidirectional or may be configured with a directional antenna for
sectoring. Likewise, as growth in a particular area of the cell
arises, BSUs favoring a specified direction would be deployed to
service the higher density sector. Each BSU connects to the public
switched telephone network or PSTN via any one of several standard
or proprietary terrestrial interfaces.
To support fault tolerance, it is necessary that each subscriber
unit 25 be capable of communicating with a minimum of two BSUs. If
1 to n BSUs share coverage of a given cell area or sector, each
subscriber unit 25 can communicate with any one of the n BSUs. In a
presently preferred embodiment, n=6. Each subscriber unit 25 with
the cell selects the BSU having the smallest path loss.
The scalable modular base station for a CDMA air interface requires
a set of global channels to support operation. The global pilot
supports initial acquisition by the subscriber and provides channel
estimation for coherent processing. One or more global broadcast
channels provide signaling information. Each BSU requires its own
set of global channels. However, global channels use air capacity
and is therefore costly to assign a set of full strength global
channels for each BSU.
The scalable modular base station supports subscriber operation on
battery standby during power outages. To do so requires a sleep
mode where the subscriber unit 25 wakes up briefly, for example,
once per second, to check for paging messages indicating an
incoming call. However, when a subscriber's waking period is short,
a base station's global pilot must be strong. The pilot strength
must be greater than the level needed to simply provide a reference
signal for coherent demodulation and channel estimation.
Each subscriber unit 25 is assigned to a set of colocated BSUs and
alternately acquires each one in sequence, once per wake up period.
The subscriber unit 25 acquires a first BSU on even seconds and a
second BSU on odd seconds. If more than two BSUs are deployed, the
subscriber acquires each BSU in sequence returning to the first for
the next interval. In direct correspondence, each BSU transmits its
pilot at alternating high and low power levels in dependence upon
how many BSUs are deployed in the particular cell. Only one BSU
transmits a high power global pilot at a given time. The BSUs are
preprogrammed to specify which BSU is selected to send its pilot at
high power and which is selected to send its pilot at low
power.
All colocated BSUs of the same group are preprogrammed to store two
indices; Igroup, which designates the identity of the group and
Iunit, which designates the identity of the BSU within the group.
Each subscriber unit 25 is assigned to a group, designated by
Igroup. For fixed wireless access, this can be designated and
entered during registration. For mobile subscribers, this can be
derived by the subscriber unit 25 testing the relative strengths of
BSU pilots and selecting the strongest as is used for roaming and
handoff.
Once a subscriber unit 25 is associated with an Igroup, when
synchronizing it accesses each member BSU of the group; Igroup,
Iunit. Each time a subscriber unit 25 wakes up, it re-synchronizes
with the pilot signal of the BSU (Iunit) transmitting the pilot at
full power. The subscriber unit 25 derives the identity of the BSU
based on time of day. Other subscriber units 25 associated with
Igroup use the same method to specify which BSU is transmitting the
strong pilot and broadcast channels. The effect is that all
subscriber units 25 wake up and listen to the pilot and broadcast
channels of the respective BSU transmitting at full power.
Each subscriber unit 25 receives the time of day from the PSTN.
Network Operations and Maintenance functions provide messages which
contain the time of day accurate to within 2 milliseconds. The
messages are sent over the terrestrial link from the O&M
function to each base station location and on to each BSU. Each BSU
sends the time of day once over a slow broadcast channel. The
subscriber unit 25 uses the message to synchronize its internal
clock.
The time of day (tod) is converted to the identity of one BSU by
using modular arithmetic Iunit=tod mod(n) Equation 1 where n is the
stored value of the number of BSUs within Igroup. Both the BSU and
all subscribers of Igroup know which BSU will be broadcasting at a
specific time. When awakened, the subscriber unit 25 synchronizes
time, reads the messages in its assigned time slot and measures the
strength of the received pilot signal from the transmitting BSU.
The subscriber unit 25 also measures the activity of the
transmitting BSU.
The BSUs indicate the amount of capacity over the slow or fast
broadcast channels. The slow broadcast channel indicates the amount
of activity. The fast broadcast channel indicates activity through
the use of traffic lights. Each traffic channel has an indicator
called a traffic light resident on the fast broadcast channel which
tells the subscriber unit 25 availability. Using the traffic lights
as capacity indication, the subscriber unit 25 can derive which of
the BSUs is least busy. All BSUs send paging messages. Upon
identifying a page, the subscriber unit 25 will select the optimal
BSU to connect with. The choice is determined on information such
as level of usage and signal strength. The subscriber unit 25 will
select the BSU which is associated with the strongest received
pilot level unless that BSU is near maximum capacity determined by
the traffic lights and/or the level of activity.
Since a BSU pilot is always programmed to be strong when a
subscriber unit 25 wakes-up, the wake up time can be minimized. The
strong pilot is required to simplify reacquisition by a subscriber
unit 25 after wake-up. Thereafter, the subscriber unit 25 returns
to low duty cycle and low battery consumption. The lower level
pilot, with a signal power level approximately 1/2 of a normal
traffic channel is transmitted at all times. Since each BSU is
transmitting a global pilot at a lower power level when not
supporting the wake-up process, each BSU supports coherent
demodulation of established traffic channels at all times with a
negligible affect on total air capacity.
For each wake-up cycle, the subscriber units 25 derive the BSU of
choice from the Igroup, based on the time of day, and load the pn
spreading codes corresponding to the global pilot and broadcast
channels of the BSU chosen. The subscriber unit 25 then measures
the relative strength of the received pilot signal, once per
wake-up cycle and stores the relative level and performs an average
of the most recent set of measurements for each of the candidate
BSUs.
The subscriber unit 25 reads the amount of traffic currently
supported by the given BSU if that information is transmitted on
the slow broadcast channel or, observes and stores the number of
red traffic lights on each BSU maintaining a short term
average.
The subscriber unit 25 performs a selection process to identify a
favored BSU. When a subscriber unit 25 requests an access channel,
the preferred BSU is selected loading the appropriate codes and
initiating a normal ramp-up process.
The BSUs maintain a time of day clock, reading the time at either
once per millisecond or once per subepoch. The time of day is used
to identify its global channel transmit period. Thereafter, its
respective global channels are allocated and the transmit power is
set to the desired level. Traffic messages and signals normally
sent by the BSU over its broadcast channels proceed. When
synchronization between the subscriber unit 25 and a BSU is
complete, the subscriber unit 25 transmits symbol length short code
while gradually increasing the transmit power level. The subscriber
unit 25 monitors the BSU for an acknowledgment signal, which acts
as a traffic light to determine if the BSU receives and
acknowledges the short code.
The subscriber unit 25 process for BSU selection includes keeping a
data base in memory with the following information: .cndot.
RelPower(Iunit); where Iunit=1 to n where RelPower is the relative
power of BSU (Iunit) and there are n units total. .cndot.
Activity(Iunit); where Iunit=1 to n For each wake up cycle: .cndot.
RelPower(Iunit) is maintained as a low pass filtered estimate of
the received measured pilot power: .cndot.
RelPower(Iunit)=RelPower(Iunit)+.A-inverted.(measured pilot
power-RelPower) Equation 2 .cndot. Activity(Iunit)=level of traffic
as sent on broadcast channel, or .cndot. Activity(Iunit)=number of
red traffic lights counted on current wake up cycle for the BSU
When a subscriber unit 25 attempts an access request, the BSU
assignment is determined as a function of relative received pilot
power level and relative activity. For example, the subscriber unit
25 can select the BSU with the strongest received pilot provided
its activity is below a threshold. As one skilled in this art would
recognize, other performance criteria could be used.
The architecture and physical implementation for an example
scalable modular base station 61 is shown in FIGS. 3, 4 and 5. The
physical configuration for a base station 61 includes four separate
enclosures: 1) a digital base station cabinet (DBC) 63; 2) a base
station power supply module (BSPM) 65; and 3&4) two amplified
antenna modules (AAM) 67.sub.1, 67.sub.2.
The base station cabinet 63 is an environmental enclosure which
supports indoor or outdoor installation. The DBC 63 houses BSUs 69.
The AAMs 67.sub.1, 67.sub.2 are mounted remote from the BSU 69, at
a high elevation 71. Each BSU 69 requires two AAMs 67.
The BSPM 65 is shown in FIG. 4 and includes storage batteries 73,
an ac/dc rectifier/inverter 75 and active voltage regulation 77.
The BSPM 65 receives external power 79 from a 120/220 Vac mains
power supply (not shown) and provides an isolated filtered output
81 to a DBC 63. Operation is similar to an uninterruptable power
supply commonly known in the electronic arts. The batteries 73
provide up to four hours of continuous operation for one DBC 63
(two BSUs 69) configured for maximum capacity upon a mains power
supply fault. Power is coupled via an umbilical to the respective
BSU(s) 69. Since a DBC 63 may be located outdoors, the BPSM 65 is
remote and environmentally sealed as well.
As shown in FIG. 5, the BSU 69 is a card rack 83 assembly having a
common communication backplane 85 using a high speed parallel data
bus 87 and a power distribution bus 89. The removable card
complement for a base station 61 requires: 1) one system control
module (SCM) 91; 2) one baseband transceiver module (BTM) 93; 3)
one power supply module (PSM) 95; 4) two radio frequency control
modules (RFC) 97; and 5) up to six air interface modules (AIM) 99
each having 16 transmit/receive modems (not shown). The PSM 95
couples the external BSPM 65 with a BSU 69 via male/female
connectors (not shown) and provides local power supply regulation
and filtering.
The SCM 91 contains a systems level microprocessor with collateral
memory for controlling transmit/receive modem selection and
coordinating component failure with another colocated BSU 69. Each
SCM 91 includes a communication bus port 105 to allow communication
over a data transport such as Ethernet.RTM. E1 line between
colocated BSUs 69. The communication bus also allows external
interrogation of each SCM 91 for up-loading or down-loading
operational software or operation parameters. SCM 91 identification
is accomplished via DIP switches or the like. External connections
to the modular base station are made via F-ports 109 on this module
and can support copper HDLC lines or fiber optic lines for
receiving a POTS E1 line 111 which may carry up to 60 EDPCM
calls.
The BTM 93 coordinates transmission by combining the analog
baseband signals from active transmit AIMs 99 and distributes
received communication signals to active receive AIMs 99. If the
required capacity of an installation requires two BSUs 69, each BTM
93 per BSU 69 is coupled with each other.
The RFC 97 accepts the signal from a BTM 93 and upconverts 113 for
transmission L.sub.0, L.sub.1. Likewise, the RFC 97 downconverts
115 received signals A, B for the BTM 93. Digital to analog
conversion along with transmit 117 and receive 119 selectable
digital delays take place in the RFC 97.
The AAM 67 encloses an omnidirectional printed circuit antenna 121
for transmission L.sub.0, L.sub.1 and reception A, B of
communication signals. A directional antenna may be employed if
cell sectorization is a design requirement. A directional antenna
may be configured to support three and six sector operation. High
125 and low 127 power duplexers separate the transmitting L.sub.0,
L.sub.1 and receiving A, B frequencies with separate amplifiers
129, 131 located in between for each respective frequency
direction. Remote location of the transmitting 129 and receiving
131 amplifiers allow the use of low cost coaxial cable 133 between
an RFC 97 and an AAM 67. A dc potential is impressed by the BTM 93
on the coaxial cable to power both amplifiers 129, 131.
Each AIM 99 includes up to 16 individual modems (not shown) for
either transmission L.sub.0, L.sub.1 or reception A, B depending on
assignment. A BSU 69 can be configured with a minimum of one up to
a complement of six AIMs 99. Each AIM 99 contains 16 modems (15
simultaneous calls plus one broadcast modem). Depending upon
traffic need, a maximum of six AIMs 99 can support up to 98 PCM or
180 LD-CELP calls.
The modular architecture 61 can support both small and large size
sectors in a cell or an omni cell. Each BSU 69 is initially
configured to support the number of calls and the specific type of
service required depending upon the number of modems 135 (AIMs 99)
installed. A minimum of two colocated BSUs 69 are required for
redundant operation at a designated cell location. Since each BSU
69 has no internal redundancy if a single failure occurs,
redundancy is achieved by allowing any fixed or mobile subscriber
unit 25 to communicate with a colocated BSU 69 at the cell base
station site. Redundancy is achieved by allowing any subscriber 25
to associate with any BSU 69 in a sector. If a BSU 69 should fail,
capacity is lost, but a subscriber 25 can access another colocated
BSU 69. A BSU 69 in a sector can be configured with excess capacity
thereby providing a cushion in the unlikely event of a failure in
that sector.
Each BSU 69 communicates independently with an assigned subscriber.
As previously described, to accomplish this function each BSU 69
must have unique global channels for the global pilot, the fast
broadcast channel and the slow broadcast channel.
The unique global pilot allows each subscriber 25 to synchronize
with an individual BSU 69. The fast broadcast channel provides a
traffic light function to the subscriber 25 informing him on BSU 69
availability and power ramp-up status from the respective BSU 69.
The slow broadcast channel transports activity and paging
information from the BSU 69 to the subscriber 25 for personal
communication services (PCS).
As discussed above, if each BSU 69 global pilot signal is
transmitted as in the prior art, sector or cell capacity
availability would be severely affected due to the effect on air
capacity. Unlike the prior art, each BSU 69 continuously transmits
a weak global pilot signal approximately one half of the signal
strength of a standard 32 kbps POTS traffic channel.
Each colocated BSU 69 recognizes and handshakes with other
colocated BSUs 69 via the external system communication E1 line,
coupling each BSU 69 BTM 93/SCM 91 with each other to coordinate
the transmitting of the global pilot signals from one base station
location. The E1 line interrogates each of the colocated BSUs 69 to
coordinate the transmission of each of their unique global pilot
signals. Each BSU 69 increases its global pilot signal level to a
normal traffic channel level for a finite period of time. Each
other BSU 69 continues transmitting their respective global pilot
signals but at the weaker power level. This method insures that
only one BSU 69 is transmitting its respective global pilot signal
at a high power level.
The fast and slow broadcast channels are transmitted from each BSU
69 at a nominal power level. If many BSUs 69 are colocated, the
total air capacity overhead required to transmit the fast and slow
broadcast channels, global pilot signals and one strong global
pilot signal 137 is increased when compared to one base station.
However, the maximum capacity of 98 PCM calls per sector or cell is
not affected since the overhead occurs only in the forward-link.
The reverse-link is more problematic because of the assigned pilots
from each subscriber limiting air capacity.
The power modulation of each pilot signal from a BSU 69 benefits
the acquisition of subscribers 25. Since each BSU 69 broadcasts its
pilot signal at the normal power level for a finite period of time,
a subscriber 25 will most likely acquire the strongest pilot
signal. If the BSU 69 at maximum power has all of its modems active
(either transmitting or receiving), the subscriber unit 25 will
pass over and attempt to acquire the next consecutive full power
pilot signal.
Each BSU 69 requires unique codes to transmit the unique global
pilot signals. A common seed is provided to all BSUs 69 for the
each pilot signal, but unique identities are manufactured by
offsetting the code by z-thousand chips to effectively produce a
unique code for each BSU 69. From a single, common global pilot
seed, a plurality of unique codes will be produced for each BSU
69.
Referring to FIGS. 6 and 7A through 7D, a scalable modular base
station 61 installation includes at least one, two (as-shown), or a
plurality of BSUs if required.
The adjustable receive delay units 119 associated with each AAM 67
shift the time-of-arrival for the received signals A, B, C, D. A
single BSU 69 installation processes two adjustable time of
arrivals 119 where each is summed 145 yielding a signal 147 that
will have 2 copies of the received signal with different time
delays.
A modular base station 61 that is sectorized or is configured for a
large number of subscribers 25 will have a plurality of BSUs 69.
All AAMs 67 associated with this installation will share their
received signals with each BSU 69. The individual antenna 121
output are coupled to summers 145, 149 located on each respective
BTM 93 of a BSU 69.
All adjustable 119 time of arrivals are summed and input into each
BSU 69 yielding a signal that will have y copies of the received
signal with different time delays where y is an integer. Each AAM
67 receive delay unit 119 has a different predetermined delay.
Preferably, each delay unit 119 imparts a delay of at least two
chips which enables further processing to achieve a net increase in
signal strength.
Each CDMA communication is associated with a unique code. The AIM
99 modems allow simultaneous processing of multiple CDMA
communications, each processing a communication associated with a
different CDMA code. Combining x signals with a known distortion
enables the lowering of the transmit power required, increasing the
number of subscribers 25 (the number of simultaneous
communications) with a given base station.
A cellular base station with the maximum number of BSUs in a two
trunk configuration is shown in FIG. 8. A standby relationship is
formed between the BSUs inside the DBCs 63 in the event of a single
failure. From a radio distribution unit (RDU) 153, a single E1 line
111 carrying up to 68 PCM calls is coupled to the BSUs. The
topology also eliminates single mode failures while increasing
signal throughput between modules.
While the present invention has been described in terms of the
preferred embodiment, other variations which are within the scope
of the invention as outlined in the claims below will be apparent
to those skilled in the art.
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