U.S. patent application number 11/593697 was filed with the patent office on 2007-03-08 for method and system for determining correct escape mechanisms and controlling interference in third generation wireless systems.
This patent application is currently assigned to InterDigital Technology Corporation. Invention is credited to Teresa Hunkeler, Eldad Zeira.
Application Number | 20070054620 11/593697 |
Document ID | / |
Family ID | 30003265 |
Filed Date | 2007-03-08 |
United States Patent
Application |
20070054620 |
Kind Code |
A1 |
Zeira; Eldad ; et
al. |
March 8, 2007 |
Method and system for determining correct escape mechanisms and
controlling interference in third generation wireless systems
Abstract
A correct escape mechanism is determined according to
interference type. Transmission is arranged so that interference
may be measured at all time slots as needed to compute a measure of
variance in interference in time slots. If the variance is above a
predetermined value, time division duplex escape mechanisms are
employed. If the variance is below a predetermined value,
appropriate escape mechanisms are employed depending on whether the
escape mechanism is being implemented during an uplink or downlink.
Interference causing FDD WTUs may be handed over to carrier bands
to control interference experienced by TDD users.
Inventors: |
Zeira; Eldad; (Huntington,
NY) ; Hunkeler; Teresa; (Montreal, 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
|
Family ID: |
30003265 |
Appl. No.: |
11/593697 |
Filed: |
November 6, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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|
10608280 |
Jun 27, 2003 |
7133673 |
|
|
11593697 |
Nov 6, 2006 |
|
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60392595 |
Jun 28, 2002 |
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60406406 |
Aug 27, 2002 |
|
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Current U.S.
Class: |
455/63.1 ;
455/436 |
Current CPC
Class: |
H04W 36/20 20130101;
H04W 16/14 20130101; H04W 36/06 20130101 |
Class at
Publication: |
455/063.1 ;
455/436 |
International
Class: |
H04B 1/00 20060101
H04B001/00; H04Q 7/20 20060101 H04Q007/20 |
Claims
1. A method for controlling interference in a wireless
communication network having overlapping time division duplex (TDD)
and frequency division duplex (FDD) coverage areas, wherein a
communication is transmitted in a time slotted channel, the method
comprising: measuring a level of interference in each time slot;
determining whether the interference is continuous or discontinuous
over a predetermined number of time slots; employing a hand over
mechanism if the interference is determined to be continuous; and
employing a TDD escape mechanism if the interference is determined
to be discontinuous.
2. The method of claim 1, wherein determining whether the
interference is continuous or discontinuous is based on the
variance of the interference level of each time slot over a certain
number of time slots.
3. The method of claim 2, wherein the time slotted channel
comprises downlink time slots, and the interference level is
determined based on interference in downlink time slots.
4. The method of claim 3, wherein the time slotted channel further
comprises uplink time slots, and the interference level is
determined based on interference in downlink and uplink time
slots.
5. The method of claim 1, wherein the TDD escape mechanism includes
slot reallocation, dynamic channel allocation, and dynamic channel
selection.
6. A method for controlling interference in a wireless
communication network having an overlapping time division duplex
(TDD) and frequency division duplex (FDD) coverage area where a
communication is transmitted in a time slotted channel, the method
comprising: determining a level of interference experienced by a
TDD wireless transmit receive unit (WTRU) operating in a TDD mode
in a TDD coverage area; locating an FDD WTRU operating in an FDD
mode in a first frequency band in the TDD coverage area; and
handing over the FDD WTRU to a second frequency band if the level
of interference is above a predetermined threshold.
7. The method of claim 6, wherein the handover procedure is
initiated only when a number of TDD WTRUs operating in a TDD mode
that are experiencing interference is above a predetermined
threshold.
8. The method of claim 6, wherein the second frequency band is not
adjacent to a frequency band for the TDD mode.
9. A system for controlling interference in a wireless
communication network having an overlapping time division duplex
(TDD) and frequency division duplex (FDD) coverage area where a
communication is transmitted in a time slotted channel, the system
comprising: a wireless transmit/receive unit comprising: a detector
for detecting an interference level of a current channel; and, a
transmitter for reporting the interference level; a radio network
controller comprising: a processor configured to determine whether
the reported interference is continuous or discontinuous over a
certain number of time slots, and to employ a hand over mechanism
if the interference is continuous or a TDD escape mechanism if the
interference is discontinuous.
10. The system of claim 9, wherein the processor is further
configured to determine a variance of the interference level of
each time slot over a certain number of time slots.
11. The system of claim 10, wherein the time slotted channel
comprises downlink time slots, and the processor is further
configured to determine the variance based on interference in
downlink time slots.
12. The system of claim 11, wherein the time slotted channel
further comprises uplink time slots, and the processor is further
configured to determine the variance based on interference in
downlink and uplink time slots.
13. The system of claim 9, wherein the processor is further
configured to implement TDD escape mechanisms that include slot
reallocation, dynamic channel allocation and dynamic channel
selection.
14. A system for controlling interference in a wireless
communication network having an overlapping time division duplex
(TDD) and frequency division duplex (FDD) coverage area where a
communication is transmitted over a time slotted channel, the
system comprising: a TDD wireless transmit/receive unit (WTRU)
operating in a TDD mode in a TDD coverage area comprising means for
measuring an interference level experienced by the TDD WTRU; a
radio network controller comprising: a processor configured to
locate an FDD WTRU operating in an FDD mode in a first frequency
band in the TDD coverage area; and to hand over the FDD WTRU to a
second frequency band if the interference level is above a
predetermined threshold.
15. A system of claim 14, wherein the processor is configured to
hand over the FDD WTRU only if a number of TDD WTRUs operating in a
TDD mode that are experiencing interference is above a
predetermined threshold.
16. The system of claim 14, wherein the processor is configured to
hand over the FDD WTRU to a second frequency band that is not
adjacent to a frequency band for the TDD mode.
17. A wireless transmit/receive unit (WTRU) for use in a wireless
communication network having interference controls and an
overlapping time division duplex (TDD) and frequency division
duplex (FDD) coverage area, the WTRU comprising: a detector for
detecting an interference level of a current channel; a transmitter
for transmitting the interference level to a radio network
controller (RNC) to enable the RNC to provide the WTRU with an
appropriate mechanism for mitigating the effect of interference on
the current channel; and a processor configured to employ an
interference control mechanism determined by the radio network
controller.
18. The WTRU of claim 17, wherein the processor is further
configured to employ a handover mechanism when the radio network
controller determines the interference to be continuous.
19. The WTRU of claim 17, wherein the processor is further
configured to employ a TDD escape mechanism when the radio network
controller determines the interference to be discontinuous.
20. The WTRU of claim 17, wherein the WTRU is configured as an FDD
WTRU.
21. The WTRU of claim 17, wherein the WTRU is configured as a TDD
WTRU.
Description
CROSS REFERENCE TO RELATED APPLICATION(S)
[0001] This application is a continuation of U.S. patent
application Ser. No. 10/608,280 filed Jun. 27, 2003, which claims
priority from U.S. Provisional Application No. 60/392,595 filed
Jun. 28, 2002, and U.S. Provisional Application No. 60/406,406
filed Aug. 27, 2002, which are incorporated by reference as if
fully set forth.
FIELD OF INVENTION
[0002] The present invention is related to communication systems
employing a time slot structure when operating in physical and
spectral vicinity to other systems that employ continuous
transmission. In particular, the invention is related to coexisting
TDD/CDMA (UMTS) and FDD/CDMA (UMTS) systems.
BACKGROUND
[0003] In third generation cellular systems (3GPP), where UMTS FDD
and UMTS-TDD spectra are both allocated, continuous (FDD) and
discontinuous (TDD) transmissions are employed. In FDD mode,
transmissions are continuous because each transmission is
associated with a particular code and frequency. In TDD mode, the
transmissions are discontinuous because each transmission is
associated with not only a particular code and frequency but also a
particular time slot. The uplink and downlink transmissions share
the same frequency which is divided into time slots, with some time
slots being used for the downlink and some time slots being used
for the uplink. In 3GPP, an uplink is defined as the frequency at
which a wireless transmit/receive unit (WTRU) transmits and a base
station (BS) receives; and the downlink is defined as the frequency
at which a BS transmits and a WTRU receives.
[0004] In FDD mode, transmissions may occur in A-bands and B-bands.
The FDD A-band uplink range is 1920 to 1980 MHz while the downlink
range is 2110 to 2170 MHz. The B-band uplink range is 1850 to 1910
MHz while the downlink range is 1930 to 1990 MHz. In TDD mode,
transmissions may occur in A-, B-, and C-bands. The TDD A-band is
1900 to 1920 MHz and 2010 to 2025 MHz. The B-band is 1850 to 1910
MHz and 1930 to 1990 MHz. The C-band spans 1910 to 1930 MHz. It
should be noted that the particular bands and frequencies
identified in this paragraph may vary according to system
deployment and are mentioned purely for example to illustrate that
FDD and TDD bands may be adjacent to each other in certain
cases.
[0005] Since the uplink bands of the FDD spectrum may be adjacent
to TDD bands, TDD WTRUs and TDD BSs may experience not only
discontinuous interference from the discontinuous transmissions of
other TDD WTRUs and BSs but also continuous interference from the
continuous transmissions of FDD WTRUs and BSs. The interference
usually causes loss of signal strength resulting invariably in poor
performance to the TDD user that is subject to the
interference.
[0006] It would therefore be desirable to determine appropriate
escape mechanisms and control interference in coexisting TDD/CDMA
(UMTS) and FDD/CDMA (UMTS) systems.
SUMMARY
[0007] The present invention is a method and system for determining
appropriate escape mechanisms based on interference type and for
controlling continuous interference created by an FDD WTRU and/or
BS that impacts TDD users. The method and system evaluates
interference and, based thereon, determines appropriate escape
mechanisms. In a preferred embodiment, continuous interference from
a FDD WTRU is controlled by handing over the interference-causing
FDD WTRU to another carrier band.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1 is a diagram of two TDD frames associated with
particular carriers.
[0009] FIG. 2 is a diagram of neighboring cells in a wireless
system.
[0010] FIG. 3 is a wireless system in accordance with the present
invention.
[0011] FIG. 4 is a flow diagram of a method for determining
interference type in the downlink and employing appropriate escape
mechanisms.
[0012] FIG. 5 is a diagram of adjacent and alternate carrier bands
in accordance with the present invention.
[0013] FIG. 6 is a diagram of coexisting TDD/CDMA (UMTS) and
FDD/CDMA (UMTS) systems.
[0014] FIG. 7 is a flow diagram of a method for controlling
interference created by FDD WTRUs in joint FDD TDD systems.
[0015] FIG. 8 is a flow diagram of a method for determining
interference type in the uplink and employing appropriate escape
mechanisms.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)
[0016] By way of introduction, a wireless transmit/receive unit
(WTRU) as used herein includes, but is not limited to, a user
equipment (UE), mobile station, fixed or mobile subscriber unit,
pager, or any other type of client device capable of operating in
any type of wireless environment. Exemplary types of wireless
environments include, but are not limited to wireless local area
networks (WLANs) and public land mobile networks (PLMNs). The WTRUs
described herein are preferably capable of operating in both a
time-slotted mode or a frequency divided mode, such as TDD and FDD,
respectively. When referred to hereafter, a base station (BS)
includes, but is not limited to a Node-B, site controller, access
point or other type of interfacing device in a wireless
environment.
[0017] Referring now to FIGS. 1 and 2, in TDD systems carriers are
associated with a series of repeating time frames. For example, in
FIG. 1 frame 10 may belong to a group of repeating time frames
associated with a first carrier. Similarly, frame 20 may belong to
a group of repeating time frames associated with a second
carrier.
[0018] Each frame is broken down into a plurality of time slots.
For example, as shown in FIG. 1, 3GPP frames are divided into 15
time slots wherein each time slot may be allocated uplink or
downlink. Although each time slot may be allocated uplink or
downlink, it is preferable, that neighboring cells synchronize
their uplink and downlink transmissions so that the neighboring
cells use the same time slots for either uplink or downlink.
[0019] For example, referring to FIG. 2, it is preferable for
neighboring cells 30, 32, 34 to each use time slots 0 through 6 of
frame 10 for downlink and time slots 7 through 14 of frame 10 for
uplink. Such synchronization eliminates situations where
interference is created because, for example, cell 30 is using time
slot 0 for downlink and cell 32 is using time slot 0 for uplink.
Although synchronization is preferred, it is quite common to have
interference resulting from a lack of synchronization (i.e.
un-synchronized interference.)
[0020] Referring to FIG. 3, a wireless system 35 in accordance with
the present invention is shown. The system 35 includes at least one
radio network controller 36 which may service base stations and
WTRUs using time-slotted or non-time-slotted transmissions. The
system 35 also includes a plurality of base stations 37, 38 and a
plurality of WTRUs 39, 33. There may be any number of base stations
37, 38 and any number of WTRUs 39, 33. Further the base stations
37, 38 and WTRUs 39, 33 may be adapted for use in time-slotted
wireless environments (e.g. TDD) or non-time-slotted wireless
environments (e.g. FDD). The base stations 37, 38 and WTRUs 39, 33
include circuits 31 for performing various interference
measurements and computations as explained herein. The RNC 36 is
similarly adapted and may also coordinate with base stations 37, 38
and WTRUs 39, 33 to perform appropriate handovers to address
interference in wireless systems as explained below.
[0021] Referring now to FIG. 4, a method 40 for determining
interference type in the downlink and employing appropriate escape
mechanisms in accordance with the present invention is shown. The
method 40 begins in step 43 with obtaining a sampling of
interference in the active downlink time slots. A WTRU will take
interference measurements in, for example, two (2) or three (3)
active downlink time slots. Although two (2) or three (3) active
time slots is mentioned by way of example, any number of active
time slots may be measured in order to obtain a sampling of the
interference in the active downlink time slots of a particular
frame. The determination of how many active time slots to measure
is preferably based on operator preference and experience.
[0022] In step 44, the interference measurements taken in step 43
are evaluated to determine whether the interference in the measured
downlink time slots is below a predetermined value. When making
this determination, the measurements may be averaged or evaluated
individually, as desired. If the interference is below a
predetermined value, no further action to mitigate the effects of
interference is necessary and the method 40 ends. If the
interference is equal to or above the predetermined value, method
40 proceeds to step 45.
[0023] In step 45, it is determined whether there are enough
downlink time slots to compute a meaningful variance if an
interference measurement is done for all of the downlink time
slots. The determination of whether there are enough downlink time
slots to compute a meaningful variance is subjective and may be
determined according to operator preference. For example, a time
frame having five (5) downlink time slots may be considered as
being not enough whereas a frame having ten (10) downlink time
slots may be considered as being sufficient.
[0024] If it is determined that there are enough downlink time
slots in step 45, the method proceeds to step 46. In step 46, the
interference is measured in all of the downlink time slots. This
may be accomplished, for example, by having a radio network
controller (RNC) instruct a WTRU to regularly schedule interference
measurements in all downlink time slots including those used for
active downlink reception. If it is determined in step 45 that
there are not enough downlink time slots, the method 40 proceeds to
step 47. In step 47, the interference is measured in all of the
time slots (i.e. all of the downlink time slots and all of the
uplink time slots) to compensate for the lack of downlink time
slots.
[0025] Measuring interference in uplink time slots is possible by
appropriately scheduling the uplink transmission. The network
operator preferably schedules uplink transmissions such that a
sufficient number of uplink time slots are reserved every "X"
amount of frames, as desired. For example, a predetermined number
of uplink time slots may be reserved every other, or every third,
frame for measuring interference in the uplink time slots. The
reserved uplink time slots provide additional time slots (i.e. in
addition to the downlink time slots) in which an WTRU may measure
interference in a particular frame so as to obtain enough
measurements, as needed, to compute a meaningful variance (i.e.
whenever it is determined in step 45 that there are not enough
downlink time slots). Of course, the frequency with which uplink
time slots are reserved depends purely on operator preference and
may be adjusted as desired.
[0026] When measuring interference there are many different types
of interference measurements that may be made. For example, in TDD
systems, the wide bandwith interference (formerly RSSI) measuring
technique and the interference signal code power (ISCP) measuring
technique may be used. The wide bandwidth interference measuring
technique does not distinguish between inter cell interference
(i.e. interference from outside a cell) and intra-cell interference
(i.e. interference from inside a cell). Both measurements may be
used although one may have certain performance advantages to the
other as is evident to those skilled in the art. Other interference
measurements may also be used as desired.
[0027] In step 50, the measurements taken by the WTRU in step 46 or
step 47 are reported to an RNC either periodically or upon the
crossing of some predetermined threshold. In the RNC, the
measurements from all time slots are compared (step 52). Then, in
step 58, the RNC computes a measure of variance between time slots
to determine if the interference is discontinuous (eg. from a type
of time-slotted transmission) or continuous (eg. from a type of
continuous or non-time-slotted transmission). If the source of
interference is discontinuous, then the interference level measured
in all of the time slots will vary. If the source of the
interference is continuous, then the interference level measured in
all of the time slots will be similar.
[0028] Therefore, the next step (step 60) is to evaluate the
measure of variance against a predetermined value. If the variance
between the time slots is equal to or above the predetermined
value, the interference is considered discontinuous and standard
escape mechanisms for time-slotted transmissions (i.e. slot
reallocation, dynamic channel allocation, dynamic channel
selection, etc.) are employed (step 62). In this case, for example,
the slotted nature of TDD transmissions causes the interference to
be discontinuous. As a result, it is possible to measure the
interference levels in different time slots and assign the
transmissions to time slots where interference levels are low. Once
assigned, the interference level can be continuously monitored. A
rise of the interference level in the active time slots can cause a
time slot reallocation to other time slots with lower interference
levels. This mitigates the interference effects of other TDD
systems.
[0029] If the variance is below the predetermined value, the
interference is considered continuous and the user experiencing the
interference may be handed over to another frequency or, where the
user has appropriately configured hardware, to another mode (step
64). That is, where the interference emanates from a continuous
source, such as an FDD system, slot reassignment will not reduce
the interference level because the interference in each time slot
will be the same. For these cases it may be necessary to move the
WTRU to a different carrier frequency in TDD, using an
inter-frequency handover. Where the mobile is capable of multiple
modes (such as FDD within a TDD network, or other access
technologies) then a handover to another mode may also be used.
[0030] Referring now to FIG. 5, FDD interference (i.e. continuous
interference) impacting TDD users often occurs where a FDD WTRU is
transmitting on a carrier in a carrier band 72 that is adjacent to
a carrier band 70 being used by a TDD user. This situation
typically arises where an FDD WTRU is proximate to a TDD WTRU or
BS. Accordingly, a preferred embodiment of the invention is to
refrain from handing over the TDD user, and instead handover the
interference-causing FDD WTRUs from a carrier within the adjacent
carrier band 72 to a carrier within the alternate carrier band 74.
For purposes of describing the present invention, an adjacent
carrier band 72 is defined as the FDD carrier band that is closest
to the TDD carrier band 70 and an alternate carrier band 74 is
defined as the FDD carrier band that, beside the adjacent carrier
band 72, is closest to the TDD carrier band 70.
[0031] This embodiment controls interference created by FDD WTRUs
operating in areas where there is joint FDD and TDD service. This
embodiment may be implemented in conjunction with either method 40
(FIG. 3) or method 300 (FIG. 7).
[0032] In FIG. 6, three (3) neighboring FDD cells are shown within
a network having coexisting TDD/CDMA (UMTS) and FDD/CDMA (UMTS)
systems. The cells 81, 82, 83 are adjacent to each other and
accommodate three (3) FDD BSs 85, 86, 87. For purposes of the
preferred embodiment, it is assumed that TDD coverage is provided
in localized areas inside larger FDD coverage areas. Therefore, as
shown in FIG. 5, an area 91 containing TDD "hot spots" 96 (i.e.
areas where TDD service is available) which are established by TDD
base stations 101. As can be seen, the "hot spots" 96 in area 91
overlap areas 82 and 83 (and slightly overlap area 81).
[0033] Where there is no TDD service available, FDD WTRUs (such as
WTRU 84) are preferably using the adjacent carrier band 72. Use of
the adjacent carrier band 72 by FDD WTRUs in areas where there is
no TDD service will not create interference for TDD users.
Therefore, in this embodiment, FDD WTRUs 84 in non-TDD areas that
are operating in the alternate carrier band 74 are handed over from
the alternate carrier band 74 to the adjacent carrier band 72. This
reserves bandwidth in the alternate carrier band 74 for handing
over FDD WTRUs in TDD areas to the alternate carrier band 74.
[0034] Where TDD service is available (i.e. area 91), however, FDD
WTRUs (such as WTRU 92) preferably avoid operating in the adjacent
carrier band 72. Therefore, in this embodiment, FDD WTRUs 92 in TDD
areas that are operating in the adjacent carrier band 72 are handed
over from the adjacent carrier band 72 to the alternate carrier
band 74. This minimizes the interference experienced by TDD users
as a result of FDD WTRUs and reserves bandwidth in the adjacent
carrier band 72 for handing over FDD WTRUs in non-TDD areas to the
adjacent carrier band 72.
[0035] Therefore, as explained above, this embodiment may be
implemented by determining that a TDD WTRU 93 or BS is experiencing
interference; determining that an FDD WTRU 92 is in an TDD area
(i.e. an area such as area 91 of FIG. 5) and causing interference;
determining the location of the FDD WTRU 92, communicating the
location to a relevant RNC 95; and enabling a handover of the
carrier band for the located FDD WTRU 92 so as to minimize the
interference. It is important to note that the RNC 95 includes
circuits for not only controlling interference as explained above
and in more detail in connection with FIG. 6, but also for
evaluating interference and determining appropriate escape
mechanisms as described in method 40 (FIG. 4) and method 300 (FIG.
8).
[0036] Referring now to FIG. 7, a method 100 is shown for
implementing this embodiment wherein interference from a FDD WTRU
is controlled through the use of adjacent and alternate carrier
bands. To begin, in step 102, it is determined whether a sufficient
number of TDD users (i.e. either a TDD WTRU or a TDD BS, for
example) are experiencing interference. If not, the method 100
ends. If so, the method 100 proceeds to step 104. In step 104, it
is determined whether FDD WTRUs are located in an area with TDD and
FDD service (i.e. an area such as area 91 in FIG. 5).
[0037] Where FDD WTRUs are not located in areas with TDD and FDD
service, the method 100 ends. Where there are FDD WTRUs located in
areas with TDD and FDD service, the method 100 proceeds to step
116. In step 116, it is determined whether there are FDD WTRUs
operating in the adjacent carrier band, as previously explained in
connection with FIGS. 5 and 6.
[0038] If the determination in step 116 is positive, the FDD WTRUs
are handed over from the adjacent carrier band to the alternate
carrier band in step 120. If the determination in step 116 is
negative, the method proceeds to step 110. In step 110, it is
determined whether there are FDD WTRUs operating in the alternate
carrier band. If no, the method 100 ends. If yes, those FDD WTRUs
are handed over from the alternate band to a band that is further
away than both the adjacent band and the alternate band. This
handover may only be done where such a band exists.
[0039] It is important to note that the determination made in step
102 may be made in accordance with method 40 as shown in FIG. 4 or
by implementing prior art techniques for simply detecting the
presence of interference. Where method 40 is used for the
determination made in step 102, the method 100 may optionally (i.e.
according to operator preference) be terminated if it is confirmed
that the interference is discontinuous (i.e. from a time-slotted
transmission). This is because if the interference is determined to
be discontinuous, the interference is from a TDD WTRU or BS and
there most likely are not any interference causing FDD WTRUs in an
area with TDD and FDD service.
[0040] As previously described, FIG. 4 is a method 40 for
determining interference type in the downlink and employing
appropriate escape mechanisms based on interference type. Referring
now to FIG. 8, a similar method 300 is shown for determining
interference type in the uplink and employing appropriate escape
mechanisms again based on interference type in accordance with the
present invention.
[0041] Method 300 begins in step 303 wherein a sampling of
interference in the active uplink time slots is obtained. A BS will
take interference measurements in, for example, two (2) or three
(3) active uplink time slots. Although two (2) or three (3) active
time slots is mentioned by way of example, any number of active
time slots may be measured in order to obtain a sampling of the
interference in the active uplink time slots of a particular frame.
The determination of how many active time slots to measure is
preferably based on operator preference and experience.
[0042] In step 304, the interference measurements taken in step 303
are evaluated to determine whether the interference in the measured
uplink time slots is below a predetermined value. When making this
determination, the measurements may be averaged or evaluated
individually, as desired. If the interference is below a
predetermined value no further action to mitigate the effects of
interference is necessary and the method 300 ends. If the
interference is equal to or above the predetermined value, method
300 proceeds to step 305.
[0043] In step 305, it is determined whether there are enough
uplink time slots to compute a meaningful variance if an
interference measurement is done for all of the uplink time slots.
The determination of whether there are enough uplink time slots to
compute a meaningful variance is subjective and may be determined
according to operator preference. For example, a time frame having
five (5) uplink time slots may be considered as being not enough
whereas a frame having ten (10) uplink time slots may be considered
as being sufficient.
[0044] If it is determined that there are enough uplink time slots
in step 305, the method proceeds to step 306. In step 306, the
interference is measured in all of the uplink time slots. This may
be accomplished, for example, by having the RNC instruct a BS to
regularly schedule interference measurements in all uplink time
slots including those used for active uplink reception. If it is
determined in step 305 that there are not enough uplink time slots,
the method 300 proceeds to step 307. In step 307, the interference
is measured in all of the time slots (i.e. all of the downlink time
slots and all of the uplink time slots) to compensate for the lack
of uplink time slots.
[0045] Measuring interference in downlink time slots is possible by
appropriately scheduling downlink transmission as explained in
connection with the scheduling of uplink transmission in method 40.
In this embodiment, however, because uplink interference is being
evaluated, the network operator preferably schedules downlink
transmission so that a sufficient number of downlink time slots are
reserved every "X" amount of frames, as desired. For example, a
predetermined number of downlink time slots may be reserved every
other or every third frame for measuring interference in the
downlink time slots. The reserved downlink time slots allow a BS to
measure interference in all of the time slots (i.e. uplink and
downlink) of a particular frame as needed (i.e. whenever it is
determined in step 305 that there are not enough uplink time
slots). Of course, as with method 40, the frequency with which
downlink time slots are reserved depends purely on operator
preference and may be adjusted as desired. Further, the techniques
used by a BS for measuring interference in method 300 are the same
as used by a WTRU for measuring interference in method 40.
[0046] Next, in step 310, the measurements taken by the BS are
reported to an RNC either periodically or upon the crossing of some
predetermined threshold. In the RNC, the measurements from all time
slots are compared (step 312). Then, in step 318, the RNC computes
a measure of variance between time slots to determine if the
interference is discontinuous (i.e. from a type of time-slotted
transmission) or continuous (i.e. from a type of continuous or
non-time-slotted transmission). If the source of interference is
discontinuous, then the interference level measured in all of the
time slots will vary. If the source of the interference is
continuous, then the interference level measured in all of the time
slots will be similar.
[0047] Therefore, the next step (step 320) is to evaluate the
measure of variance against a predetermined value. If the variance
between the time slots is equal to or above the predetermined
value, the interference is considered discontinuous and standard
escape mechanisms for time-slotted transmissions (i.e. slot
reallocation, dynamic channel allocation, dynamic channel
selection, etc.) are employed (step 322), as explained in
connection with step 62 of method 40.
[0048] If the variance is below the predetermined value, the
interference is considered continuous and the cell load in all time
slots is reduced (step 324). WTRUs that are assigned to a cell
having its cell load reduced may be handed over to TDD cells in
other frequencies or to other modes.
[0049] Although the preferred embodiments are described in
conjunction with a third generation partnership program (3GPP)
wideband code division multiple access (W-CDMA) system utilizing
the time division duplex mode, the embodiments are applicable to
any hybrid code division multiple access (CDMA)/time division
multiple access (TDMA) communication system. Additionally, some
embodiments are applicable to CDMA systems, in general, using
beamforming, such as the proposed frequency division duplex (FDD)
mode of 3GPP W-CDMA.
[0050] Although the present invention has been described in detail,
it is to be understood that the invention is not limited thereto,
and that various changes can be made therein without departing from
the scope of the invention, which is defined by the attached
claims.
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