U.S. patent application number 11/409130 was filed with the patent office on 2006-08-24 for system for efficiently providing coverage of a sectorized cell for common and dedicated channels utilizing beam forming and sweeping.
This patent application is currently assigned to InterDigital Technology Corporation. Invention is credited to Angelo Cuffaro.
Application Number | 20060189355 11/409130 |
Document ID | / |
Family ID | 27739131 |
Filed Date | 2006-08-24 |
United States Patent
Application |
20060189355 |
Kind Code |
A1 |
Cuffaro; Angelo |
August 24, 2006 |
System for efficiently providing coverage of a sectorized cell for
common and dedicated channels utilizing beam forming and
sweeping
Abstract
A communication system transmits and receives communications
within a sectorized cell between at least one primary station and
at least one secondary station. The communication system includes a
unit for generating and shaping a beam; an antenna for transmitting
and receiving signals within said beam; and a unit for directing
the beam. The shaped beam is directed at a plurality of
predetermined directions; either continuously or discretely.
Inventors: |
Cuffaro; Angelo; (Laval,
CA) |
Correspondence
Address: |
VOLPE AND KOENIG, P.C.;DEPT. ICC
UNITED PLAZA, SUITE 1600
30 SOUTH 17TH STREET
PHILADELPHIA
PA
19103
US
|
Assignee: |
InterDigital Technology
Corporation
Wilmington
DE
19810
|
Family ID: |
27739131 |
Appl. No.: |
11/409130 |
Filed: |
April 21, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10329886 |
Dec 26, 2002 |
7043274 |
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11409130 |
Apr 21, 2006 |
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60392597 |
Jun 28, 2002 |
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60420355 |
Oct 21, 2002 |
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Current U.S.
Class: |
455/562.1 |
Current CPC
Class: |
H04B 7/0408 20130101;
H04W 16/28 20130101; H04B 7/0491 20130101; H04B 7/04 20130101; H04W
64/00 20130101; H04B 7/0695 20130101 |
Class at
Publication: |
455/562.1 |
International
Class: |
H04M 1/00 20060101
H04M001/00 |
Claims
1. A method for transmitting and receiving communications between
at least one base station and at least one wireless
transmit/receive unit (WTRU), where the base station transmits a
plurality of common channels covering a sectorized cell using at
least one beam, the method comprising: generating at a base station
at least one shaped beam for transmitting and receiving a
communication; sweeping the shaped beam, wherein the beam is
selectively directed at a plurality of locations, each location at
a predetermined time; receiving the sweeped beam at a WTRU;
determining at said WTRU the time of receipt of the sweeped beam;
reporting from the WTRU to said base station the time of receipt of
the sweeped beam; and determining the location of said WTRU based
on the reported time of receipt of the received beam.
2. The method of claim 1, further comprising: transmitting from
said base station a dedicated channel beam based on said determined
location for communication with said WTRU.
3. The method of claim 1, wherein said base station shapes the
beams into one of a plurality of selectable widths; ranging from a
wide width to a narrow width.
4. The method of claim 3, wherein the beam width is selected so
that the number of WTRUs entering or leaving the beam is below a
predetermined threshold.
5. The method of claim 4, wherein if the number of WTRUs entering
or leaving the beam is above the predetermined threshold, the beam
width is widened.
6. The method of 1, wherein said plurality of directions coincide
with the sectors of the cell.
7. The method of claim 1, wherein the cell sectors are different
sizes and the beams are shaped to cover the cell sectors.
8. The method of claim 1, wherein the beam is sweeped to cover a
plurality of directions in a predetermined sequence.
9. The method claim 8, wherein the sequence is consecutive.
10. The method claim 8, wherein the sequence is
non-consecutive.
11. The method of claim 10, wherein the non-consecutive sequence
causes the beam to be directed toward at least one of the plurality
of directions more frequently than others of the plurality of
directions.
12. The method of claim 10, wherein the non-consecutive sequence
causes the beam to be directed toward some of the plurality of
directions for a longer duration than others of the plurality of
directions.
13. A wireless communication system for transmitting and receiving
communications between at least one base station and at least one
wireless transmit/receive unit (WTRU), where the base station
transmits a plurality of common channels covering a sectorized cell
using at least one beam, the system comprising: at least one base
station comprising: a beam generator for generating at least one
shaped beam for transmitting and receiving a communication; a beam
sweeper for sweeping the shaped beam, wherein the beam is
selectively directed at a plurality of locations, each location at
a predetermined time; and a processor configured for determining
the location of said WTRU based on a reported time of receipt of a
received beam; and at least one wireless transmit/receive unit
(WTRU) comprising: a transceiver for receiving a shaped beam from
said base station; and a processor configured for determining the
time of receipt of the sweeped beam; wherein the WTRU reports the
time of receipt of the sweeped beam to said base station.
14. The system of claim 13, wherein the base station transmits a
dedicated channel beam based on said determined location for
communication with said WTRU.
15. The system of claim 13, wherein said base station shapes the
beams into one of a plurality of selectable widths; ranging from a
wide width to a narrow width.
16. The system of claim 15, wherein the beam width is selected so
that the number of WTRUs entering or leaving the beam is below a
predetermined threshold.
17. The system of claim 16, wherein if the number of WTRUs entering
or leaving the beam is above the predetermined threshold, the beam
width is widened.
18. The system of claim 13, wherein said plurality of directions
coincide with the sectors of the cell.
19. The system of claim 13, wherein the cell sectors are different
sizes and the beams are shaped to cover the cell sectors.
20. The system of claim 13, wherein the beam is sweeped to cover a
plurality of directions in a predetermined sequence.
21. The system claim 20, wherein the sequence is consecutive.
22. The system claim 20, wherein the sequence is
non-consecutive.
23. The system of claim 22, wherein the non-consecutive sequence
causes the beam to be directed toward at least one of the plurality
of directions more frequently than others of the plurality of
directions.
24. The system of claim 22, wherein the non-consecutive sequence
causes the beam to be directed toward some of the plurality of
directions for a longer duration than others of the plurality of
directions.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application claims priority from U.S. patent
application Ser. No. 10/329,886 filed Dec. 26, 2002 which in turn
claims the benefit of Provisional Patent Application Nos.
60/420,355, filed Oct. 21, 2002, and 60/392,597, filed Jun. 28,
2002, which are incorporated by reference as if fully set forth
herein.
BACKGROUND
[0002] Sectoring is a well known technique for providing distinct
coverage areas within individual cell sites and can be achieved
with "smart antenna" technology. Smart antenna methods dynamically
change the radiation pattern of an antenna to form a "beam," which
specifically focuses the antenna's transmitted and received energy
and provides a desired topographical coverage. Beam forming is an
enhancement on sectoring in that the sectors can be adjusted in
direction and width. Both techniques are employed to: 1) reduce
interference between cells and the wireless transmit/receive units
(WTRUs) deployed within the cells; 2) increase the permissible
range between a receiver and a transmitter; and 3) locate the
geographic position of a WRTU. These techniques are usually applied
to the dedicated channels of the WRTUs once their general location
is known.
[0003] Prior to knowing the location of a WTRU, the common channels
broadcast information that all WTRUs may receive. While this
information may be sent in static sectors, it is not sent in
variable beams. There are inherent inefficiencies in this approach
in that extra steps are required to determine the appropriate beam
to use for the dedicated data exchanges. Additionally, the beams
must be generally large enough to provide a broad coverage area,
which in turn means their power with distance from the transmitter
is lower. In such cases, they must use higher power, have longer
symbol times and/or more robust encoding schemes to cover the same
range.
[0004] The common channel coverage found in the prior art shown in
FIG. 1 has four overlapping wide beams. This provides
omni-directional coverage, while giving a degree of reuse to the
cell site. It also provides a coarse degree of directivity to the
WTRUs (WTRU1, WTRU2) detecting one of the transmissions, by having
each sector transmit a unique identifier.
[0005] Referring to FIG. 2, downlink dedicated beams between a
primary station (P) and several WTRUs (WTRU3, WTRU4) are shown.
Assuming the same power from the primary station P for FIGS. 1 and
2 and all other attributes being equal, the WTRUs (WTRU3 and WTRU4)
shown in FIG. 2 can be further away from the primary station P than
the WTRUs (WTRU1, WTRU2) shown in FIG. 1. Alternatively, the
coverage areas can be made approximately the same by decreasing the
symbol rate or increasing the error correction coding. Either of
these approaches decreases the data delivery rate. This also
applies to the receiver uplink beam patterns of the primary station
P; and the same comments about coverage and options apply for data
from the WTRUs to the primary station P.
[0006] In the prior art, the range of a primary station P or a WTRU
is generally increased by combinations of higher power, lower
symbol rates, error correction coding and diversity in time,
frequency or space. However, these methods yield results that fall
short of optimized operation. Additionally, there is a mismatch
between the common and dedicated communications channels in the
ways that coverage is aligned.
[0007] The downlink dedicated channels may be transmitted in a beam
having a narrower width by a smart antenna. The narrower beam
serves a narrower area. The benefit in narrowing the beam is the
reduced interference to WTRUs in other areas of the cell, which has
a positive impact on the system efficiency. However, dedicated
channels are still susceptible to interference generated by the
common channels. The common channels have to be available to all
mobiles in the entire coverage area. FIG. 3 shows the radiation
pattern for the current deployment of a cellular system using a
smart antenna system emitting a beam with a narrow width over a
small coverage area 10 for the dedicated channel coverage and an
omni-directional antenna emitting an omni-directional pattern over
a wide coverage area 12 for the common channel coverage. Since the
common channel is transmitted at a high output power to ensure
complete cell coverage, a WTRU's reception of the dedicated channel
may be interfered with as the WTRU's location becomes closer to the
high powered common channel transmitter.
[0008] It is therefore desirable to provide a method of providing
equitable coverage for both common and dedicated channels in
wireless communication systems without the disadvantages of prior
art.
SUMMARY
[0009] A communication system for transmitting and receiving common
channel and dedicated channel communications between at least one
primary station and at least one secondary station in a sectorized
cell uses at least one beam comprising an antenna. The system
includes a device for generating and shaping the beam; and a device
for sweeping the shaped beam. The sweeping device selectively
directs the shaped beam at a plurality of directions.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 is a prior art common channel coverage scheme between
a primary station and several WTRUs with four overlapping wide
beams.
[0011] FIG. 2 is a prior art scheme of downlink dedicated beams
between a primary station and several WTRUs using dedicated
beams.
[0012] FIG. 3 is a prior art of the radiation pattern for a
cellular system using a narrow-width beam over a small coverage
area for dedicated channel coverage and an omni-directional pattern
over a wide coverage area for common channel coverage.
[0013] FIG. 4 is a rotating common channel beam emanating from a
primary station.
[0014] FIG. 4A is a flow diagram illustrating sweeping of the
common beacon channel.
[0015] FIG. 5 is a beam configuration for known uneven distribution
of WTRUs.
[0016] FIG. 6 is a beam configuration having the beam width
adjusted for traffic type.
[0017] FIG. 7 is a beam configuration having equivalent coverage
areas for both dedicated and common channels.
[0018] FIG. 8 is a beam configuration having equivalent coverage
areas for both dedicated and common channels.
[0019] FIG. 9 is a flow diagram of an embodiment in which the
common beacon channel is swept.
[0020] FIG. 10 is a flow diagram of an embodiment in which the
unique common beacon channels are transmitted to different
positions of a cell.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0021] The present invention will be described with reference to
the drawing figures where like numerals represent like elements
throughout. The foregoing statements about beam forming are
applicable to both transmission of the signal and its reception.
For example, narrower transmission beams cause less interference to
those devices outside the beam. Conversely, a narrower reception
beam decreases interference from signals outside the beam. The
foregoing description of the invention is applicable to both the
reception and transmission of signals. The context of a particular
part of the description will sometimes explicitly refer to
reception or transmission when this is not case.
[0022] This invention generally relates to considerations of
coverage in a wireless communication system utilizing smart
antennas to emit both common and dedicated channels, and to
providing similar coverage for common and dedicated channels. The
common channels are utilized, as their name implies, by all
devices. The system and method of the present invention formats
these common channels in a fashion that provides useful information
to the system and the WTRU for eventual establishment of the
dedicated channels.
[0023] Referring to FIG. 4, the dashed outlines represent possible
positions P.sub.1-P.sub.n for a common channel beam B emanating
from a primary station (PS). At a particular time period, the beam
B exists only in one of the positions P.sub.1 as illustrated by the
solid outline. The arrow shows the time sequencing of the beam B.
In this illustration, the beam B sequentially moves from one
clockwise position P.sub.1 to another P.sub.2-P.sub.n, although a
clockwise rotation is not necessary.
[0024] The system provides for identifying the beam B at each of
the positions P.sub.1-P.sub.n. FIG. 4A is a flow diagram of a
method 40 in accordance with the embodiment of the invention shown
in FIG. 4. The transmitted identifying beam B, which includes a
unique identifier while the beam B is in each position P.sub.1-Pn,
is swept around the cell (step 41). For example, at a first
position P.sub.1 a first identifier I.sub.1 will be transmitted, at
a second position P.sub.2 a second identifier I.sub.2 will be
generated, and so on for each of the positions P.sub.1-P.sub.n. If
the beam B is swept continuously, a different identifier
I.sub.1-I.sub.m may be generated for each degree, (or preset number
of degrees), of rotation.
[0025] When a WRTU successfully acquires the beacon common channel
(step 42), it reports the identifier number of the common channel
it acquires to the PS (step 44). This information is used by the
system to determine the WTRUs location (step 46). The PS then
assigns a dedicated channel in the proper direction of the WTRU
(step 48). Since the common channels are only in one sector for a
short period of time, the overall interference caused by the common
channels to the dedicated channels is substantially reduced. A
minor disadvantage may be an extended acquisition time, but the
disadvantage could be alleviated by increasing the data rate of the
common channels.
[0026] A second embodiment for identifying the position
P.sub.1-P.sub.n of the beam B is to use a time mark as a type of
identifier, which the WTRU returns to the PS. Returning either the
time mark or the identifier to the PS informs the PS which beam B
was detected by the WTRU. For that time period, the PS now knows
the position P.sub.1-P.sub.n of the beam B that was able to
communicate with the WTRU. However, it should be noted that due to
possible reflections, this is not necessarily the direction of the
WTRU from the PS.
[0027] A third embodiment for identifying the position
P.sub.1-P.sub.n of the beam B is to use time-synchronization. The
beam B is positioned and correlated with a known time mark. One way
of achieving this is for both the WTRUs and the PS to have access
to the same time reference, such as the global positioning system
(GPS), National Institute of Standards and Technology internet time
or radio time broadcasts (WWV) or local clocks with adequate
synchronization maintained.
[0028] A fourth embodiment for identifying the position
P.sub.1-P.sub.n of the beam B is for the WTRUs and the PS to
synchronize to timing marks coming from the infrastructure
transmissions. The WTRUs can detect beam transmissions identifying
the PS, but not necessarily the individual beam B positions
P.sub.1-P.sub.n. By the WTRU reporting back to the PS the time
factor when it detected the beam B, the PS can determine which beam
B the WTRU is referencing. The benefit of this embodiment is that
the common channel transmission does not have to be burdened with
extra data to identify the position P.sub.1-P.sub.n of the beam
B.
[0029] A fifth embodiment for identifying the position of the beam
B is to incorporate a GPS receiver within the WTRU. The WTRU then
determines its geographical location by latitude and longitude and
reports this information to the PS. The PS can then use this
information to precisely generate the direction of the beam B, beam
width and power. Another advantage of this embodiment is the
precise location obtained of the WTRU, which will allow users to
locate the WTRU if the need arises.
[0030] Referring to FIG. 5, the beam pattern may be tailored as
desired by the system administrator. In this manner, the PS may
position the beam B in a pattern consistent with the expected
density of WTRUs in a particular area. For example, a wide beam
W.sub.1, W.sub.2, W.sub.3 may be cast in positions P.sub.1,
P.sub.2, P.sub.3, respectively with few WTRUs, and more narrow
beams N.sub.4, N.sub.5, N.sub.6 cast in positions P.sub.4, P.sub.5,
P.sub.6, respectively with many WTRUs. This facilitates the
creation of narrower dedicated beams B in the denser areas and also
increases the capacity for the uplink and downlink use of the
common channels to establish initial communications.
[0031] The beam width manipulation is preferably performed in real
time. However, the conditions of communication and the nature of
the application determine the suitability of the number of beam
positions P.sub.1-P.sub.n and their associated beam width patterns.
The beam patterns formed should be sufficiently wide such that the
number of WTRUs entering and leaving the beam can be handled
without excessive handoff to other beams. A static device can be
serviced by a narrow beam. Swiftly moving cars for example, could
not be serviced effectively by a narrow beam perpendicular to the
flow of traffic, but could be serviced by a narrow beam parallel to
the direction of travel. A narrow perpendicular beam would only be
adequate for short message services, not for voice services such as
phone calls.
[0032] Another advantage to using different beam widths is the
nature of the movement of WTRUs within a region. Referring to FIG.
6, a building BL is shown (representing an area having primarily
slower moving pedestrian-speed devices WTRU.sub.s), and a highway H
is shown (representing an area having primarily faster-moving
devices WTRU.sub.f). The slower speed devices WTRU.sub.s can be
served by narrow beams N.sub.1-N.sub.3 that are likely to be
traversed during a communication time period. Alternatively, the
faster moving devices WTRU.sub.f require wider beams
W.sub.1-W.sub.3 to support a communication.
[0033] Beam width shaping also decreases the frequency of handover
of WTRUs from one beam B to another. Handover requires the use of
more system resources than a typical communication since two
independent communication links are maintained while the handover
is occurring. Handover of beams also should be avoided because
voice communications are less able to tolerate the latency period
often associated with handover.
[0034] Data services are packet size and volume dependent. Although
a few small packets may be transmitted without problems, a large
packet requiring a significant number of handovers may utilize
excessive bandwidth. This would occur when links are attempted to
be reestablished after a handover. Bandwidth would also be used up
when multiple transmissions of the same data is sent in an attempt
to perform a reliable transfer.
[0035] Downlink common channel communication will often be followed
by uplink transmissions. By knowing the transmission pattern of the
PS, the WTRU can determine the appropriate time to send its uplink
transmission. To perform the necessary timing, a known fixed or
broadcast time relationship is utilized. In the case of a fixed
relationship, the WTRU uses a common timing clock. The WTRU waits
until a time in which the PS has formed a beam over the WTRU's
sector before transmitting. In the case of a broadcast time
relationship, the PS informs the WTRU when to send its uplink
signal. The uplink and downlink beam forming may or may not
overlap. It is often an advantage to avoid overlap, so that a
device responding to a transmission can respond in less time than
would be required to wait an entire antenna beam forming timing
cycle for the same time slot to occur.
[0036] It should be noted that CMDA and other RF protocols utilize
some form of time division. When responding to these types of
temporal infrastructures, both beam sectoring and the time slots of
the protocol would be of concern. Other non-time dependent RF
protocols, such as slotted Aloha would only involve sectoring.
[0037] The embodiment described hereinbefore was directed to
"sweeping" the beam B around a PS in a sequential manner. In many
instances this will typically be the most convenient way to
implement the invention. There are, however, alternative ways to
assume the various positions. For instance, it may be desirable to
have more instances of coverage in certain areas. This could be
done generating the beam in a sequence of timed positions. For
instance, if there are 7 positions, (numbered 1 through 7), a
sequence of (1, 2, 3, 4, 2, 5, 6, 2, 7, 1) could be used. This
would have the area covered by beam position number 2 more often
than other positions, but with the same dwell time. It might also
be desirable to have a longer dwell time in a region. The sequence
(1, 2, 3, 4, 4, 5, 6, 7, 1) for instance would have beam position
number 4 remain constant for two time periods. Any suitable
sequencing could be utilized and modified as analysis of the
situation warranted.
[0038] Likewise, it is not necessary to restrict the beam positions
to a rotating pattern. The beam positions could be generated in any
sequence that serves the operation of the communication system. For
example, a pattern that distributed the beams B over time such that
each quadrant was covered by at least one beam B might be useful
for WTRUs that are closer to the PS and are likely to be covered by
more than one beam position.
[0039] It should be noted that similar to all RF transmissions, an
RF signal only stops at a physical point if there is a Faraday-type
of obstruction, (e.g. grounded metal roof). Usually the signal dies
off, and the boundary is some defined attenuation value from the
peak value of the transmission. To provide adequate coverage in the
application of this invention, it is preferable that adjacent beam
positions overlap to some degree. The overlap will tend to be more
pronounced closer to the transmission and reception antennas. Close
to an infrastructure antenna site, any WTRU is therefore likely
able to communicate via a number of differently positioned beams B.
Devices able to communicate via several beam positions could
therefore, if needed, achieve higher data rates using these
multiple positions. Devices further away, however, are more likely
to be able to communicate via only once instant of beaming, and to
obtain higher data rates would require another technique such as a
longer dwell time.
[0040] Referring to FIG. 7, which is an embodiment where the common
beacon channel is swept through a cell which is divided into n
number of P positions, designated P.sub.1 through P.sub.n. Each
position P represents a different common channel beam B. A WTRU is
located in beam position P.sub.3 and a PS is located at the center
of the cell.
[0041] Referring to FIG. 9, a procedure in accordance with the
embodiment of the present invention of FIG. 7 is shown. The
procedure 81 commences as the common beacon channel is swept around
the cell (step 91) through positions P.sub.1 to P.sub.n. Each
position P represents the physical location of the antenna's
focused energy and its an identifier of the unique common beacon
channel signal. A WTRU located in the cell's coverage area acquires
a unique common beacon channel (step 92). The WTRU then reports
back to the PS the acquired beam's identifier (step 94). The PS
receives the identifier from the WTRU and determines the WTRUs
location (step 96). The WTRU then assigns a dedicated channel to
the direction of the WTRU (step 98).
[0042] Another embodiment of the present invention, shown in FIG.
8, comprises having a common channel beam present in every sector,
without having to sweep about the cell's coverage area. Although
such an alternative slightly increases the interference in the
cell, it provides the same amount of coverage area for both the
common and dedicated channels. As shown, the PS has eight positions
P.sub.1-P.sub.8, each representing a different unique common beacon
channel signal which are not swept. A WTRU is located in position
P4.
[0043] Referring to FIG. 10, an alternative procedure 100 in
accordance with the embodiment of the invention of FIG. 8 is shown.
Eight unique common beacon channel signals are transmitted into the
cell (step 101) in positions P.sub.1 to P.sub.8. Each position P
represents the physical location of the antenna's focused energy
and an identifier of the unique common beacon channel signal. A
WTRU located in the cell's coverage area acquires one of the eight
unique common beacon channels (step 102) and the WTRU reports back
to the PS which beam it acquired by the beam's identifier (step
104). The PS receives the identifier from the WTRU and determines
the location of the WTRU (step 106). The PS then assigns a
dedicated channel to the direction of the WTRU (step 108).
[0044] In the case of a WTRU being located on or near the border of
two or more sectors, the WTRU may have difficulty identifying to
which sector to associate. When the WTRU acquires a sector, the
system deploys hysteresis in its accusation algorithm to ensure
that the WTRU has an acceptable signal quality for some definite
time before the WTRU hops to another sector.
[0045] It should be understood by those of skill in the art, that
the number of beams, or beam positions located throughout a cell as
described herein has been used by way of example. A greater or
lesser number of beams, or beam positions, may be implemented
without deporting from the spirit and scope of the present
invention.
* * * * *