U.S. patent application number 11/428457 was filed with the patent office on 2006-10-26 for assigning physical channels of a new user service in a hybrid time division multiple access/code division multiple access communication system.
This patent application is currently assigned to INTERDIGITAL TECHNOLOGY CORPORATION. Invention is credited to Eldad Zeira, Guodong Zhang.
Application Number | 20060239214 11/428457 |
Document ID | / |
Family ID | 25319411 |
Filed Date | 2006-10-26 |
United States Patent
Application |
20060239214 |
Kind Code |
A1 |
Zeira; Eldad ; et
al. |
October 26, 2006 |
ASSIGNING PHYSICAL CHANNELS OF A NEW USER SERVICE IN A HYBRID TIME
DIVISION MULTIPLE ACCESS/CODE DIVISION MULTIPLE ACCESS
COMMUNICATION SYSTEM
Abstract
A method for assigning physical channels to time slots in a
hybrid wireless time division multiple access/code division
multiple access communication system begins by providing physical
channels for assignment. A set of time slots is provided for
potential assignment. The set of time slots is arranged into a
sequence based on a quality of each of the set of time slots. The
provided physical channels are assigned to the time slots in a time
slot order of the sequence.
Inventors: |
Zeira; Eldad; (Huntington,
NY) ; Zhang; Guodong; (Farmingdale, NY) |
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
3411 Silverside Road Concord Plaza, Suite 105
Wilmington
DE
|
Family ID: |
25319411 |
Appl. No.: |
11/428457 |
Filed: |
July 3, 2006 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
09854728 |
May 14, 2001 |
7072312 |
|
|
11428457 |
Jul 3, 2006 |
|
|
|
Current U.S.
Class: |
370/280 ;
370/458 |
Current CPC
Class: |
H04W 72/00 20130101;
H04W 72/082 20130101; H04W 72/04 20130101; H04J 3/1682 20130101;
H04W 28/065 20130101; H04B 7/2618 20130101; H04J 13/00
20130101 |
Class at
Publication: |
370/280 ;
370/458 |
International
Class: |
H04J 3/00 20060101
H04J003/00 |
Claims
1. A method for assigning physical channels to time slots in a
hybrid wireless time division multiple access/code division
multiple access communication system, comprising the steps of:
providing physical channels for assignment; providing a set of time
slots for potential assignment; arranging the set of time slots
into a sequence based on a quality of each of the set of time
slots; and assigning the provided physical channels to the time
slots in a time slot order of the sequence.
2. The method of claim 1, wherein the provided physical channels
are physical channels of a user service.
3. The method of claim 1, wherein the provided physical channels
are physical channels of a coded composite transport channel.
4. The method of claim 1, wherein the quality of each time slot is
based on in part an interference measurement and an allowed number
of the provided physical channels to be assigned to that
channel.
5. The method of claim 1 for use in downlink physical channel
assignments, wherein the quality of each time slot is based on in
part a transmit power of that slot and an allowed number of the
provided physical channels to be assigned to that time slot.
6. A radio network controller (RNC) for use in a hybrid wireless
time division multiple access/code division multiple access
communication system, the RNC assigning a set of physical channels
to a set of time slots, the RNC comprising: a radio resource
management device configured to arrange the set of time slots into
a sequence based on a quality of each of the set of time slots and
configured to assign the set of physical channels to the time slots
in a time slot order of the sequence.
7. The RNC of claim 6, wherein the set of physical channels are
physical channels of a user service.
8. The RNC of claim 6, wherein the set of physical channels are
physical channels of a coded composite transport channel.
9. The RNC of claim 6, wherein the quality of each time slot is
based on in part an interference measurement and an allowed number
of the provided physical channels to be assigned to that
channel.
10. The RNC of claim 6 for use in downlink physical channel
assignments, wherein the quality of each time slot is based on in
part a transmit power of that slot and an allowed number of the
provided physical channels to be assigned to that physical
channel.
11. A radio network controller (RNC) for use in a hybrid wireless
time division multiple access/code division multiple access
communication system, the RNC assigning a set of physical channels
to a set of time slots, the RNC comprising: arranging means for
arranging the set of time slots into a sequence based on a quality
of each of the set of time slots; and assigning means for assigning
the set of physical channels to the time slots in a time slot order
of the sequence.
12. The RNC of claim 11, wherein the set of physical channels are
physical channels of a user service.
13. The RNC of claim 11, wherein the set of physical channels are
physical channels of a coded composite transport channel.
14. The RNC of claim 11, wherein the quality of each time slot is
based on in part an interference measurement and an allowed number
of the provided physical channels to be assigned to that
channel.
15. The RNC of claim 11 for use in downlink physical channel
assignments, wherein the quality of each time slot is based on in
part a transmit power of that slot and an allowed number of the
provided physical channels to be assigned to that time slot.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation of U.S. patent
application Ser. No. 09/854,728, filed May 14, 2001, which is
incorporated by reference as if fully set forth herein.
BACKGROUND
[0002] The invention generally relates to wireless hybrid time
division multiple access/code division multiple access
communication systems. In particular, the invention relates to
resource management in such systems.
[0003] FIG. 1 depicts a physical layout of a wireless communication
system. The system has a plurality of base stations 20. Each base
station 20 communicates with user equipments (UEs) 22 in its
operating area or cell 23. Communications transmitted from the base
stations 20 to the UEs 22 are referred to as downlink
communications and communications transmitted from the UEs 22 to
the base stations 20 are referred to as uplink communications.
[0004] A network perspective of a wireless communication system is
shown in FIG. 2. Each node-B 24 within the system wirelessly
communicates with associated UEs 22 or users. Each node-B 24 has a
single site controller (SC) 34 associated with either a single or
multiple base stations 20. A group of node-Bs 24 is connected to a
radio network controller (RNC) 28.sub.1. To transfer communications
between RNCs 28, an interface between the RNCs (IUR) 26 is
utilized. Each RNC 28 is connected to a mobile switching center
(MSC) 30 which in turn is connected to the core network 32.
[0005] In code division multiple access (CDMA) communication
systems, multiple communications can be sent over the same spectrum
simultaneously. The multiple communications are distinguished by
their codes. In hybrid time division multiple access (TDMA)/CDMA
communication systems, such as time division duplex (TDD) using
CDMA (TDD/CDMA) communication systems, the spectrum is time divided
into repeating frames having time slots, such as fifteen time
slots. In such systems, communications are sent in selected time
slots using selected codes. A physical channel is defined as one
code in one time slot. The use of a single code in a single time
slot with a spreading factor of sixteen is referred to as a
resource unit. Based on the type of service being provided to a
user (UE 22) in the system, one or multiple physical channels may
be assigned to support the users uplink and downlink
communications.
[0006] The assignment of physical channels to users in such a
system is a complex problem. Each physical channel used in a time
slot creates interference with respect to other channels used in
that time slot. Accordingly, it is desirable to choose time slots
as to minimize interference.
[0007] However, there are drawbacks to choosing time slots solely
based on interference. A UE 22 communicating using less time slots
typically will have a lower power consumption. By stacking codes in
a smaller number of time slots, other time slots are left open for
new users. Additionally, some UEs 22 may be only able to use a few
time slots, such as one or two.
[0008] Accordingly, it is desirable to have effective resource
management in hybrid TDMA/CDMA communication systems.
SUMMARY
[0009] Physical channels of a new user service are to be assigned
to a set of time slots in a hybrid time division multiple
access/code division multiple access wireless communication system.
The new user service physical channels are ordered based on a
desired reception quality of each of the new user service physical
channels. The new user service physical channels are assigned to
the set of time slots based on the order and the time slot
sequence.
[0010] A method for assigning physical channels to time slots in a
hybrid wireless time division multiple access/code division
multiple access communication system begins by providing physical
channels for assignment. A set of time slots is provided for
potential assignment. The set of time slots is arranged into a
sequence based on a quality of each of the set of time slots. The
provided physical channels are assigned to the time slots in a time
slot order of the sequence.
[0011] A radio network controller (RNC) for use in a hybrid
wireless time division multiple access/code division multiple
access communication system, the RNC assigning a set of physical
channels to a set of time slots, the RNC including a radio resource
management device configured to arrange the set of time slots into
a sequence based on a quality of each of the set of time slots and
configured to assign the set of physical channels to the time slots
in a time slot order of the sequence.
[0012] A RNC for use in a hybrid wireless time division multiple
access/code division multiple access communication system, the RNC
assigning a set of physical channels to a set of time slots, the
RNC including arranging means and assigning means. The arranging
means arranges the set of time slots into a sequence based on a
quality of each of the set of time slots. The assigning means
assigns the set of physical channels to the time slots in a time
slot order of the sequence.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is an illustration of a physical layout of a wireless
communication system.
[0014] FIG. 2 is an illustration of a network layout of a wireless
communication system.
[0015] FIG. 3 is a simplified radio network controller using radio
resource management.
[0016] FIG. 4 is a simplified node-B using radio resource
management.
[0017] FIG. 5 is a simplified user equipment using radio resource
management.
[0018] FIG. 6 is a flow chart of channel assignment/reassignment
using a fragmentation parameter.
[0019] FIGS. 7-7D are flow charts of channel
assignment/reassignment.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0020] Radio resource management (RRM) is a continuous process of
allocating physical resources to users (UEs 22) in an acceptable
resource allocation. RRM is used to find an efficient solution in
view of the aggregate demand for resource units by all users.
[0021] FIG. 3 is a simplified RNC 28 for use in RRM. The RNC 28 has
a RRM device 36 and a measurement collection device 38. The
measurement collection device 38 collects various measurements from
other components of the network, such as the node-Bs 24 and the UEs
22. These measurements include transmission power levels (both
uplink and downlink), pathloss information and other information.
The RRM device 36 uses the measurements in determining efficient
assignment of resources which is sent to the other components.
[0022] FIG. 4 is a simplified node-B 24 for use in RRM. An antenna
40 receives radio frequency signals over a radio channel from the
UEs 22. The received signals are passed through an isolator 42 to a
receiver 46 and a measurement device 48. A channel assignment
device 44, which receives channel assignments from the RNC 28,
identifies the physical channels and time slots to allow the
receiver 46 to detect the transmitted data. The receiver 46 may be
a multiuser detection device (MUD), a RAKE or a different type of
receiver. The receiver 46 also recovers signaled information from
the UE 22, such as measurement information, which is relayed to the
RNC 28.
[0023] A measurement device 48 takes various measurements at the
node-B 24, such as interference levels and reception power levels.
These measurements are also relayed to the RNC 28. A transmitter 50
sends data and signaled information, such as channel assignments
and a transmission power level of the node-B transmitter 24, to the
UEs 22. The channel assignment device 44 determines a transmission
power level for the node-B transmitter 50. Although the following
discussion usually refers to an open loop power control algorithm,
other power control algorithms, such as closed loop, outer loop or
a combination, may be used. A transmit power controller 54 controls
the gain of an amplifier 52 to control the transmission power
level. The transmitted signals pass through the isolator 42 and are
radiated by the antenna 40.
[0024] FIG. 5 is a simplified UE 22 for use in RRM. An antenna 56
receives radio frequency signals over a radio channel from the
node-B 24. The received signals are passed through an isolator 58
to a receiver 66 and a measurement device 68. A channel assignment
detection device 64 recovers the signaled information concerning
the UE's channel assignments for both uplink and downlink. The
receiver 66 may be a multiuser detection device (MUD), a RAKE or a
different type of receiver.
[0025] A measurement device 68 takes various measurements at the UE
22, such as interference levels and reception power levels. These
measurements are also relayed to the RNC 28 by being transmitted to
the node-B 24. A transmitter 70 sends data and signaled
information, such as measurements, pathloss information and a
transmission power level of the UE transmitter 70, to the node-B
24. A transmit power controller (TPC) 60 determines a transmission
power level for the UE transmitter 70. The TPC 60 controls the gain
of an amplifier 62 to control the transmission power level. The
transmitted signals pass through the isolator 58 and are radiated
by the antenna 56.
[0026] One procedure for assigning resource units in a TDMA/CDMA
system, such as a TDD/CDMA system, uses fast dynamic channel
allocation (F-DCA). F-DCA is the process of assigning the resource
units to the users. F-DCA is typically invoked when a new or
modified service is required, a handover of a user occurs or a
change in interference levels occurs. Prior to F-DCA, an initial
determination is made which slots are allowed for assignment. The
allowed time slots may be based on interference measurements, such
as measured by interference signal code power (ISCP), or other
factors.
[0027] F-DCA has three primary roles. First, F-DCA is used to
determine the resource units for initial allocation, handover or a
user resource unit reconfiguration. A reconfiguration may occur as
a result of another user or user service being dropped to allow for
more efficient resource allocation. Second, F-DCA is an escape
mechanism for a user or user service experiencing high interference
or not capable of meeting a desired quality of service (QOS).
Third, F-DCA is used as a tool to keep UE and system resource usage
at reasonable levels at all times. There are two competing
interests in efficient allocation of resource units: interference
minimization and fragmentation. It is desirable to minimize the
interference levels seen by the users. Minimum interference
increases system capacity. Driving the interference levels down may
spread the resource units over the most available time slots,
reducing the number of resource units in each time slot.
[0028] However, it is also desirable to reduce the fragmentation of
a user's resource units over multiple time slots. Using less time
slots reduces a UE's power consumption and, accordingly, increases
a UE's battery life. Reduced fragmentation also leaves slots
available for new users. Some UEs 22 may be only capable of
handling communications in a limited number of time slots, such as
1 or 2 time slots. For these UEs 22, reduced fragmentation is
essential.
[0029] FIG. 6 is a flow chart of channel assignment using a
fragmentation parameter. A UE 22 requires resource units for
admittance, a new service or a change in units for reassignment
(72). The RRM device 36 needs to assign resource units to the UE 22
to support the new service. The assignment of resource units may be
limited by a maximum number of slots or physical channels per slot
associated with that service's code composite transport channel
(CCTrCH), such as three (3) time slots and three (3) physical
channels per slot. In assigning resource units for this CCTrCH, the
RRM device 36 utilizes the available time slots and their
respective interference measurements. Based on this information,
the RRM device 36 has a tendency to fragment the resource units
over many time slots to reduce interference in all the time
slots.
[0030] To reduce this tendency, a fragmentation parameter, P.sub.j,
is introduced to adjust the RRM device's resource unit assignment.
Although the fragmentation parameter is preferably set so that a
low value indicates a preference for and a high value indicates a
strong preference against assigning the channel to that time slot,
other parameter values may be used. P.sub.j represents the penalty
for assigning a CCTrCH to j time slots (74). To illustrate, CCTrCH
assigned to one time slot has a fragmentation parameter of P.sub.1.
P.sub.1 represents zero or a low fragmentation penalty. A CCTrCH
assigned to two time slots has a penalty P.sub.2. P.sub.2
represents the fragmentation penalty for using a second time slot
and may be the same as P.sub.1 indicating a non-penalty, slightly
higher indicating a moderate penalty, or an "infinite" penalty
indicating assignment to a second slot is not permitted. Further
time slots used for a CCTrCH result in fragmentation penalties of
P.sub.3 . . . P.sub.n.
[0031] The fragmentation parameter values, typically, are set by an
operator or by a mechanical device. The selection of fragmentation
parameters is based on various factors, such as over-all
interference levels and capacity. Examples of fragmentation
penalties for a CCTrCH which can only support three (3) time slots
and three (3) channels per slot is shown in Tables 1 and 2.
TABLE-US-00001 TABLE 1 P.sub.1 = 0 P.sub.2 = 10 P.sub.3 = 10
P.sub.4 to P.sub.n = .infin.
[0032] TABLE-US-00002 TABLE 2 P.sub.1 = 0 P.sub.2 = 0 P.sub.3 = 10
P.sub.4 to P.sub.n = .infin.
[0033] The value zero represents no penalty for fragmentation. The
value 10 indicates a high penalty, such as 10 dB. The value .infin.
indicates an "infinite" penalty, which prevents further
fragmentation. The "infinite" penalty is a prohibitively high
number. The values in table 1 represent a strong preference for
using one time slot. The values in table 2 represent a strong
preference for using one or two time slots. Using more than three
slots is prohibited.
[0034] An alternate assignment scheme is per Equation 1. P j = { p
j , where .times. .times. j .ltoreq. C UE .infin. , where .times.
.times. j > C UE } Equation .times. .times. 1 ##EQU1## C.sub.UE
is the maximum number of allowed time slots for the CCTrCH. p is an
incremental penalty value, such as 3 dB. To illustrate for a p=3 dB
and a C.sub.UE=3, the resulting fragmentation parameters are
P.sub.1=0 dB, P.sub.2=3 dB, P.sub.3=6 dB and P.sub.4 . . .
P.sub.N=.infin.. The RRM device 36 uses the fragmentation parameter
and the interference measurements to assign the time slots
(76).
[0035] One role of F-DCA is to determine resource units at link
setup. FIG. 7 is a flow chart for assigning resource units for a
new UE 22 or new UE service. Physical channels are to be assigned
to a CCTrCH (78). An estimation of the quality of each time slot
with respect to interference and fragmentation is determined. The
time slots are arranged in sequences of decreasing quality (80).
One time slot quality measurement is a figure of merit, which is
defined such as per Equation 2.
F.sub.i=-.alpha..DELTA.I.sub.i+.beta.f(C.sub.i) Equation 2 F.sub.i
is the figure of merit for the i.sup.th time slot. .DELTA.I.sub.i
is a difference between a measured interference level, such as
using ISCP, at the receiver for the time slot and a minimum
measured interference for all of the time slots. As a result, the
time slot having the minimum measured interference has a
.DELTA.I.sub.i of zero. f(C.sub.i) is the allowed number of
physical channels for the CCTrCH in the i.sup.th time slot. .alpha.
and .beta. are weighting factors.
[0036] To assign the physical channels, different sequences of time
slots are derived. One approach varies the weights given to
interference and fragmentation, such as by varying weights of the
figure of merit. Sequences ordering the available time slots are
determined based on altering the weights in the figure of merit and
arranging the time slots in order of decreasing figure of merit.
One scheme is as follows. k+m+1 sequences are derived by altering
.alpha. and .beta. such as per Table 3. TABLE-US-00003 TABLE 3
Favor low fragmentation: .alpha. = 1, .beta. = 2.sup.0 (Sequence 1)
.alpha. = 1, .beta. = 2.sup.1 (Sequence 2) .alpha. = 1, .beta. =
2.sup.2 (Sequence 3) . . . .alpha. = 1, .beta. = 2.sup.K (Sequence
k) Favor low interference .alpha. = 2.sup.1, .beta. = 1 (Sequence k
+ 1) .alpha. = 2.sup.2, .beta. = 1 (Sequence k + 2) .alpha. =
2.sup.3, .beta. = 1 (Sequence k + 3) . . . .alpha. = 2.sup.m,
.beta. = 1 (Sequence k + m + 1)
k is the number of low fragmentation sequences that are tried. k is
typically an empirical value, such as 4, 5 or 6. m is the number of
low interference sequences tried. m is also typically an empirical
value, such as 4, 5 or 6. To reduce computational requirements,
redundant determined sequences may be eliminated.
[0037] The channels for assignment are ordered by their desired
reception quality (78 and 92 of FIG. 7A), such as by a signal to
interference ratio (SIR). To illustrate using SIR, all the physical
channels for assignment are arranged in decreasing order of their
required SIR. For each sequence, the physical channels are assigned
to the slots based on their order in the sequence. For each of the
above k+m+1 sequences, starting with the first slot in the
sequence, the first physical channel is tentatively added to that
time slot, if there is at least one channel available for that UE
22. If the channel cannot be assigned to that time slot, the next
time slot is tried and so on until the first channel is assigned to
a time slot.
[0038] After assigning the first code to a time slot, the noise
rise and required transmit power levels for the CCTrCH in this time
slot is estimated. Based on the noise rise and required transmit
power levels, a determination of whether this channel can be
supported in this time slot is made. To illustrate, if any
transmitter exceeds or is too close to its transmit power level
capacity or noise rise exceeds a threshold, that channel cannot be
added.
[0039] If a time slot cannot accept a physical channel, that time
slot is eliminated from further consideration. That time slot
sequence is updated not to include that time slot. Assignment of
that channel to the next time slot in the sequence is attempted. If
no time slots are found for the channel, this sequence fails and it
is discarded (86). If the channel meets the users' transmit power
requirements, the fragmentation penalty for the UE 22 is used to
determine whether it is acceptable to assign that channel to this
time slot. For example, a UE 22 is only capable of using 3 time
slots. If this code assignment would involve a fourth time slot
(P.sub.4=.infin.), this assignment is not acceptable and the
sequence fails and is discarded (86). If the time slot is
acceptable, the process continues with the next channel being added
to the same time slot. When no channels are left, a potential
assignment solution is found and recorded (84, 88).
[0040] For each potential solution, the highest quality solution,
such as a total predicted interference measurement adjusted for
fragmentation for the physical channels, is determined (90). The
weighted interference estimate for the CCTrCH is the summation of
each physical channel's interference plus the fragmentation penalty
for the whole CCTrCH. The recorded solution with the lowest
fragmentation adjusted interference level is used to assign the
physical channels to the service.
[0041] Another role of F-DCA is reassigning physical channels to
either reduce interference or decrease fragmentation (pack slots),
referred to as the "background operation." The desire to reassign
may be due to a UE 22 ceasing a session and freeing up resources.
It may also result from a suboptimal overall initial assignment or
changes due to mobility or external causes.
[0042] A different approach is used for the uplink and downlink
time slots. In other systems, uplink and downlink time slots may be
assigned to the same slots. The following discussion is based on
separate uplink and downlink time slots. However, for a system
sending uplink and downlink transmissions in the same slot, an
approach similar to that described for the downlink is used for all
slots.
[0043] For reassigning downlink physical channels, a quality
estimate, such as figure of merit, is determined for each downlink
physical channel (78 and 94 of FIG. 7B). One approach to determine
a figure of merit is per Equation 3.
F.sub.i=-.tau..DELTA.I.sub.i-.delta.FR Equation 3
[0044] F.sub.i is the figure of merit for the i.sup.th channel.
.DELTA.Ii is the difference between the measured interference, such
as ISCP, with respect to the i.sup.th channel in its time slot and
the measured interference for the channel having the lowest
measured interference. FR is a gauge of the fragmentation of the
physical channel. One equation to determine FR is per Equation 4.
FR = Total .times. .times. slots .times. .times. assigned .times.
.times. to the .times. .times. channel ' .times. s .times. .times.
CCTrCH Number .times. .times. of .times. .times. physical .times.
.times. channels .times. .times. in .times. .times. that .times.
.times. channel ' .times. s .times. .times. slot .times. .times.
for .times. .times. that .times. .times. CCTrCH Equation .times.
.times. 4 ##EQU2## .tau. and .delta. are weighting factors.
[0045] The channels for potential reassignment are ordered by their
quality into sequence of increasing quality. Using the figure of
merit, the channels are ordered in increasing figure of merit. One
approach to reduce the complexity of the reassignment is to only
consider a threshold number of codes with the lowest figures of
merit (first ones in the sequences). Alternately, a threshold value
can be used. Only physical channels with a figure of merit below
the threshold value are considered. Each physical channel for
reassignment is treated differently. If no time slot has a lower
interference measurement then a channel's current time slot, that
channel cannot be reassigned. Any attempts to reassign that channel
will only increase the interference in higher interference time
slots.
[0046] After determining the physical channels for reassignment
(78), the available time slots are ordered into sequences based on
their quality adjusted for various weighting of interference and
fragmentation, such as by altering the weights of the figure of
merit. The sequences order the time slots by decreasing quality,
such as by decreasing figure of merit.
[0047] One approach to determine the figure of merits is as
follows. For the uplink, the figure of merit for each slot i is per
Equation 5.
F.sub.i=-.alpha..sub.UL.DELTA.I.sub.i+.beta..sub.ULf(C.sub.i)
Equation 5
[0048] .alpha..sub.UL and .beta..sub.UL are weighting factors. For
the downlink, the figure of merit for each slot i is defined as per
Equation 6.
F.sub.i=-.alpha..sub.DL.DELTA.T.sub.i+.beta..sub.DLf(C.sub.i)
Equation 6 where .DELTA.T.sub.i is defined as T.sub.i-T.sub.min.
T.sub.i is the measured node-B slot transmit power in slot i.
T.sub.min is the lowest node-B transmit power among all the
downlink slots. In the uplink/downlink, time slots are examined one
by one in the order of increasing figure of merit.
[0049] k+m+1 sequences are derived by altering .quadrature. and
.quadrature., such as per Table 3. For each sequence, starting with
the first slot in that sequence, the potentially reassigned channel
is added to that time slot, if there is at least one channel
available for that channel's UE 22. If the channel cannot be
assigned to that time slot, the next time slot is tried and so on
until it is assigned to a time slot (82).
[0050] After assigning the channel to a time slot, the noise rise
and required transmit power level for the CCTrCH in the time slot
is estimated. Based on the noise rise and required transmit power
levels, a determination of whether this channel can be supported in
this time slot is made. To illustrate, if any transmitter exceeds
or is too close to its transmitter power capacity or the noise rise
exceeds a threshold, that channel cannot be added.
[0051] If the time slot cannot accept the channel, that time slot
is eliminated from further consideration. The sequence is updated
not to include that time slot. An attempt is made to assign this
channel to the next time slot in the sequence. If no time slots are
found for the channel, this sequence fails (86).
[0052] If the channel reassignment meets the transmit power
requirements, the fragmentation penalty is used to determine
whether it is acceptable to assign the channel to this time slot.
If this assignment is not acceptable, this sequence fails (86). If
the time slot is acceptable for this code assignment, the next
channel in that sequence is attempted to be added to that time slot
and the assignment process continues. If there are no remaining
channels (84), an assignment solution is found and recorded (88).
This process is repeated for each time slot sequence.
[0053] For each recorded solution, a weighted interference
improvement is determined (90). The weighted interference
improvement is the difference between the estimated interference of
all the time slots for the proposed reassignment adjusted for
fragmentation and the current measured interference adjusted for
fragmentation. The reassignment with the largest improvement is
compared to a reassignment margin. The reassignment margin prevents
the oscillation between two close solutions and to prevent an
unnecessary reassignment for only a minimal overall improvement. If
the most improved reassignment exceeds the margin, that
reassignment is initiated.
[0054] For the uplink time slots, since all physical channels in a
time slot experience that same interference, the criteria for
reassignment is the fragmentation gauge, FR. A high FR indicates
high fragmentation and a low FR indicates low fragmentation. The
reassignment channels are arranged from highest FR to lowest (78
and 96 of FIG. 7C). Although a reassignment analysis can be
performed on all of the channels, preferably only a threshold
number with high FRs are selected. Alternately, the channels having
their FR exceeding a threshold are selected. After ordering the
candidate channels, the reassignment procedure occurs the same as
for the downlink per FIG. 7.
[0055] One other use for the reassignment procedure is to provide
an escape mechanism for a user or user service experiencing high
interference. When a user service experiences high interference,
the RNC 28 attempts to reassign part or all of that service,
CCTrCH, to reduce the interference. Prior to attempting
reassignment, the measured interference of each potential
reassignment time slot other than those used by the CCTrCH are
checked to see if any are less than the highest measured
interference time slot of the CCTrCH. If there is no better time
slot, there is no reason to attempt reassignment.
[0056] All physical channels that belong to the "bad" CCTrCH are
examined to select which of them, including the possibility of all
of them, are to be reassigned. Reassignment is attempted in order
of slots from high interference down (98 of FIG. 7D). In each slot,
physical channels are reassigned in order of decreasing required
SIR (100 of FIG. 7D). The number of physical channels to be
reassigned is determined as follows. At each reassignment, the
interference in the new slot is computed or estimated as in the
background operation. The average interference for all physical
channels in the CCTrCH is computed. Reassignment stops when the
average interference has dropped by a certain number of decibels,
which is a design parameter.
[0057] One approach to simplify the assignment procedures is to
eliminate time slots having an average measured interference over a
threshold. After determining each time slot interference, the
interference is compared to the threshold. The threshold may differ
for uplink and downlink and from user to user. Time slots exceeding
the threshold are eliminated from potential assignment. The
threshold is set by an operator or a mechanical device, based on
interference levels and capacity considerations.
* * * * *