U.S. patent application number 12/731841 was filed with the patent office on 2010-07-15 for reverse link rate and stability control.
This patent application is currently assigned to Airvana, Inc., a Massachusetts corporation. Invention is credited to Satish Ananthaiyer, Sae-Young Chung, Sepehr Mehrabanzad.
Application Number | 20100177731 12/731841 |
Document ID | / |
Family ID | 36683773 |
Filed Date | 2010-07-15 |
United States Patent
Application |
20100177731 |
Kind Code |
A1 |
Ananthaiyer; Satish ; et
al. |
July 15, 2010 |
REVERSE LINK RATE AND STABILITY CONTROL
Abstract
In a radio access network, the reverse link rate of an access
terminal is controlled and stabilized by determining a number of
connections in one or more sectors in which the access terminal has
a connection and setting a rate limit based on at least one of the
determined number of connections. The number of connections can be
determined for each sector in which the access terminal has a
connection or for some subset of these sectors. If the number of
connections is determined for more than one sector, the radio
access network may limit the reverse link rate based on the sector
having the greatest number of connections.
Inventors: |
Ananthaiyer; Satish;
(Tewksbury, MA) ; Chung; Sae-Young; (Tewksbury,
MA) ; Mehrabanzad; Sepehr; (Southborough,
MA) |
Correspondence
Address: |
FISH & RICHARDSON PC
P.O. BOX 1022
MINNEAPOLIS
MN
55440-1022
US
|
Assignee: |
Airvana, Inc., a Massachusetts
corporation
|
Family ID: |
36683773 |
Appl. No.: |
12/731841 |
Filed: |
March 25, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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11037515 |
Jan 18, 2005 |
7729243 |
|
|
12731841 |
|
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Current U.S.
Class: |
370/329 |
Current CPC
Class: |
H04W 28/22 20130101 |
Class at
Publication: |
370/329 |
International
Class: |
H04W 72/04 20090101
H04W072/04 |
Claims
1-35. (canceled)
36. A method for controlling a rate of transmission of an access
terminal in a sector of a radio access network, the method
comprising: determining an effective number of connections for the
sector, wherein the effective number of connections for the sector
is less than a number of reverse link connections for the sector;
comparing the effective number of connections with one or more
ranges of values; and setting a rate limit for the access terminal
based on the comparing.
37. The method of claim 36 wherein the sector comprises a first
sector and the effective number of connections comprises a first
effective number of connections, and wherein the method further
comprises: determining a second effective number of connections for
a second sector of the radio access network serviced by a common
radio node.
38. The method of claim 36 wherein setting the rate limit
comprises: accessing a maximum rate limit table; and setting the
rate limit based on the maximum rate limit table.
39. The method of claim 36 wherein the sector comprises a first
sector and the effective number of connections comprises a first
effective number of connections and wherein setting the rate limit
comprises: setting the rate limit for the access terminal based on
a second effective number of connections for a second sector of the
radio access network, wherein the second effective number of
connections is equal to or greater than a third effective number of
connections for a third sector of the radio access network.
40. The method of claim 36 further comprising: performing a rise
over thermal measurement for the sector; and transmitting a signal
to the access terminal indicating that the sector is becoming
overloaded if the rise over thermal measurement (ROT) exceeds a
predetermined amount.
41. The method of claim 40 further comprising: performing a post
automatic gain control ROT estimation for the sector; and
transmitting a signal to the access terminal indicating that the
sector is becoming overloaded if the post automatic gain control
ROT estimation exceeds a predetermined amount.
42. The method of claim 41 wherein setting the rate limit
comprises: using a first rate limit scheme when the ROT is
performed for the sector; and using a second rate limit scheme when
the post automatic gain control ROT estimate is performed for the
sector.
43. The method of claim 36 wherein the radio access network
comprises a evolution data-only compliant network.
44. The method of claim 36 further comprising: transmitting the
rate limit to the access terminal.
45. The method of claim 44 wherein transmitting the rate limit
comprises: broadcasting a rate limit message to the access terminal
in at least one sector in which the access terminal has the
connection.
46. The method of claim 44 wherein the sector comprises a first
sector and wherein transmitting the rate limit comprises:
unicasting a rate limit message to the access terminal in a second
sector of the radio access network in which the access terminal has
a traffic channel established.
47. The method of claim 36 wherein the sector comprises a first
sector and the connection comprises a first connection, the method
further comprising: transmitting, to the access terminal, a rate
limit message immediately upon the access terminal establishing a
second connection in a second sector of the one or more
sectors.
48. A radio node configured to transmit radio signals to, and to
receive radio signals from, an access terminal in a sector of a
radio access network, the radio node comprising: one or more
processing devices; and memory for storing instructions that are
executed by the one or more processing devices to: determine an
effective number of connections for the sector, wherein the
effective number of connections for the sector is less than a
number of reverse link connections for the sector; compare the
effective number of connections with one or more ranges of values;
and set a rate limit for the access terminal based on the
compare.
49. The radio node of claim 48 wherein the sector comprises a first
sector and the effective number of connections comprises a first
effective number of connections and wherein the instructions
further cause the one or more processing devices to: set the rate
limit for the access terminal based on a second effective number of
connections for a second sector of the radio access network,
wherein the second effective number of connections is equal to or
greater than a third effective number of connections for a third
sector of the one or more sectors.
50. The radio node of claim 48 wherein the sector comprises a first
sector and the effective number of connections comprises a first
effective number of connections and wherein the radio node is
further configured to: receive a second effective number of
connections for a second sector of the radio access network.
51. The radio node of claim 50 wherein the radio node comprises a
first radio node and wherein the second effective number of
connections is received from a second radio node.
52. The radio node of claim 50 wherein the second effective number
of connections for the second sector is received from a radio
network controller.
53. The radio node of claim 48 wherein the instructions cause the
one or more processing devices to set the rate limit by: accessing
a maximum rate limit table; and setting the rate limit based on the
maximum rate limit table.
54. The radio node of claim 48 wherein the memory also stores
instructions that cause the one or more processing devices to:
transmit the rate limit to the access terminal.
55. The radio node of claim 54 wherein the instructions cause the
one or more processing devices to transmit the rate limit to the
access terminal via a unicast message.
56. The radio node of claim 54 wherein the instructions cause the
one or more processing devices to transmit the rate limit to the
access terminal via a broadcast message.
Description
FIELD
[0001] This disclosure relates to control of reverse link rate and
stability in a multi-user wireless communication system.
BACKGROUND
[0002] In a radio access network, such as a cellular network, it is
often important to ensure that sectors in the network do not become
overloaded. One way in which a sector can become overloaded is if
many access terminals (e.g., cellular devices) in a sector transmit
at high data rates, which increases the transmission power. In a
first Evolution Data-Only (1.times.EV-DO) network, the
1.times.EV-DO protocol provides mechanisms for measuring sector
load (referred to as a "rise-over thermal (ROT)" measurement) and
reducing the transmission rates of ATs in the sector by
transmitting a bit (referred to as the "reverse activity bit") to
ATs in a sector that is becoming overloaded. However, ROT
measurement may not always be not available, and, in these cases, a
radio access network may fail to detect and mitigate overloading of
a sector.
SUMMARY
[0003] In one aspect, the invention features a method for
controlling the rate of transmission of an access terminal in a
radio access network (e.g., a 1.times.EV-DO network) that includes,
for one or more sectors in which the access terminal has a
connection, determining a number of connections for the sector, and
setting a rate limit for the access terminal based on one or more
of the determined number of connections.
[0004] Implementations may include one or more of the following
features. The method may include determining a number of
connections for each sector in which the access terminal has a
connection (e.g., sectors in which an AT is in soft or softer
handoff). The method may also include determining a number of
connections for a subset of sectors in which the access terminal
has a connection (e.g., only those sectors in which the access
terminal has a connection serviced by a common radio node).
[0005] Determination of a number of connections may include
determining an effective number of connections for a sector.
Determining an effective number of connections for a sector may
include, for each connection in a sector, applying a weight to one
or more characteristics of the connection to determine a weighted
connection, and summing the weighed connections.
[0006] Setting a rate limit for the access terminal based on one or
more of the determined number of connections may include using a
rate-limit table to set a rate limit. A rate limit table may, for
example, assign a first rate limit if a number of connections
determined for the access terminal is within a first range of
values, and a second rate limit if a number of connections
determined for the access terminal is within a second range of
values. If a number of connections is determined for multiple
sectors in which an AT has a connection, the method may set a rate
based on an determined number of connections for a sector having a
value equal to or greater than any other effective number of
connections determined for other sectors.
[0007] The method may including changing the way in which a number
of connections is determined for a sector (e.g., applying different
weights to connections in a sector) and/or a rate limit table used
to set rate limitations based on the way in which the radio access
network performs its RA bit estimation. If it uses ROT measurement
to set or clear RA bits for ATs, the method may use one rate limit
scheme, whereas if ROT measurement is not available (and the system
uses, for example, post-automatic gain control-ROT estimation),
then the method may use a different rate limit scheme. The method
may include transmitting a rate limit message via a broadcast
message or a unicast message to the access terminal. The method may
also include transmitting to the access terminal a rate limit
message immediately upon the access terminal establishing a
connection in a sector.
[0008] In another aspect, the invention features a radio node
configured to transmit radio signals to and receive radio signals
from an access terminal having one or more connections in a group
of one or more sectors of a radio access network. The radio node
includes a processor and a medium bearing instructions to cause the
processor to determine a number of connections for one or more
sectors in which the access terminal has a connection and set a
rate limit for the access terminal based on at least one of the
determined number of connections.
[0009] Implementations may include one or more of the following
features. The radio node may be configured to determine a number of
connections for each of sector in the group of sectors in which the
access terminal has a connection. If the radio node determines
multiple numbers of connections for sectors in which the access
terminal has a connection, the radio node may be configured to base
a rate limit on the greatest determined number of connections.
[0010] The radio node may be configured to receive (e.g., from
another radio node or from an radio network controller) an
effective number of connections for other sectors in the radio
access network in which the access terminal has a connection but is
not in the group of sectors serviced by the radio node.
[0011] The radio node may be configured to determine an effective
number of connections by, for example, weighting characteristics of
each connection in a sector and summing the weighed connections.
The radio node may be configured to set a rate limit based on a
rate limit table that, for example, specifies a first rate limit if
a number of effective connections determined for the access
terminal is within a first range of values and specifies a second
rate limit if a number of effective connections determined for the
access terminal is within a second range of values. The radio node
may also be configured to transmit a rate limit to the access
terminal (e.g., via a broadcast or unicast message).
[0012] In another aspect, the invention features a system for
controlling the rate of transmission of an access terminal in a
radio access network that includes a processor and a medium bearing
instructions to cause the processor to determine an effective
number of connections for one or more sectors in which the access
terminal has a connection and set a rate limit for the access
terminal based on at least one determined effective number of
connections.
[0013] In one specific implementation, the processor of the system
may be part of a radio network controller. In cases where the
processor is part of a radio network controller, the instructions
may be written to cause the processor to determine a number of
connections for each of sector in which the access terminal has a
connection. If the access terminal has connections in multiple
sectors, the radio network controller may set a rate limit based on
the sector with the greatest number of connections.
[0014] In another particular implementation, the processor of the
system may be part of a radio node that services a group of
sectors. The instructions may be written to determine a number of
connections for each of the sectors in the group of sectors in
which the AT has a connection. The radio node may be configured to
set a rate limit based only on this determination. The radio node
may also be configured to receive information (e.g., from an RNC or
from other RNs) on numbers of connections in sectors other than the
group of sectors with which the AT has a connection and may be
configured to set a rate limit based also on these numbers of
connections. The system may also include a radio network controller
that is configured to determine a number of connections for sectors
outside the RN's group of sectors with which the AT has a
connection. The radio network controller may be configured to also
send the AT a rate limit message based on these numbers.
DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 is a diagram of a radio access network.
[0016] FIG. 2 is a diagram of several cells and sectors in a radio
access network.
[0017] FIG. 3 is a diagram of a radio node.
[0018] FIGS. 4-7 are diagrams of radio access networks.
DETAILED DESCRIPTION
[0019] Referring to FIG. 1, a radio access network (RAN) 20 uses
the first evolution data-only (1.times. EV-DO) protocol to transmit
data packets between an AT, such as laptop 24 and personal data
assistant (PDA) 26, and an external network such as the Internet
40. The 1.times.EV-DO protocol has been standardized by the
Telecommunication Industry Association (TIA) as TIA/EIA/IS-856,
"CDMA2000 High Rate Packet Data Air Interface Specification", 3GPP2
C.S0024-0, Version 4.0, Oct. 25, 2002, which is incorporated herein
by reference.
[0020] The radio access network 20, which may cover a large service
area, includes one or more Access Sub-Networks (ASN's), e.g., ASN
22, each anchored by a Radio Network Controller (RNC) 34
communicating with several Radio Nodes (RN's) 10, 12, 14 using a
private or public IP backhaul network 32. Each RN may support
multiple sectors, such as the three sectors shown in FIG. 1, with
each sector covering a certain cell area around the RN.
[0021] ASN 22 is connected over a public or private IP network 36
to one or more Packet Data Serving Node's (PDSN's), e.g., PDSN 38.
The PDSN, in turn, receives and transmits data packets (e.g., voice
over IP packets) to a server 42 via the Internet 40. In some
implementations, the functions of a PDSN and an RNC are combined
into a single device.
[0022] Each AT is in communication with a radio node, e.g., RN 10,
via an air link 28a, 28b. An air link comprises a forward link,
which carries data transmitted from an RN to an AT, and a reverse
link, which carries data transmitted from the AT to the RN. As an
AT moves from one sector to another sector serviced by the same RN,
it undergoes a "softer handoff" between the sectors. Similarly,
when an AT moves from one sector to another sector serviced by
different RNs, it undergoes a "soft handoff" between the RNs. When
an AT is in soft or softer handoff, it will have connections in
multiple sectors.
[0023] As shown in FIG. 2, a geographic area covered by radio
access network 20 (shown in FIG. 1) is divided into multiple cells
1, 2, and 3, which are each further divided into three sectors A,
B, and C. Each cell includes a radio node (RN) 10, 12, 14 that
communicates with access terminals (e.g., cellular telephones) (not
shown) located within each RN's cell. Each radio node uses a
directional antenna (not shown) appropriately positioned in each
sector to send data to and receive data from ATs located in the
sectors.
[0024] As shown in FIG. 3, each radio node, e.g., RN 10, includes a
radio interface 11 and modem 15 for transmitting radio signals to
and receiving radio signals from ATs in a sector. A set of
digital-to-analog and analog-to-digital converters 13, 17 converts
the data exchanged between the radio interface 11 and the modem 15.
The radio node also includes network interface 19 for exchanging
digital data between the RN and an RNC, e.g., RNC 34, via a
backhaul network (e.g., backhaul network 32 shown in FIG. 1).
[0025] The pole capacity is the theoretical capacity of access
terminals supported by a radio node. The pole capacity of an RN is
a function of the signal-to-noise ratio (SNR) necessary to achieve
a certain aggregate data rate with a certain aggregate error rate
within a cell. Pole capacity is a theoretical maximum capacity of a
cell and it is often advisable to design radio access networks in
which the number of active ATs within a cell is limited to some
percentage of the pole capacity, e.g., 50% to 75% of the pole
capacity, which corresponds to an Rise-Over-Thermal (ROT) of 3 or 6
dB respectively.
[0026] A radio node, such as RN 10 shown in FIGS. 1-3, can
determine whether one of its sectors is becoming overloaded by
measuring the rise over thermal (ROT) value of the sector. The
radio node can determine the ROT of a sector by measuring the
thermal noise at the radio receiver in the sector when all ATs in
the sector are silent. (IS-856 provides a mechanism in which a
radio node and ATs in a sector served by the radio node can set up
a time and duration during which ATs in the sector will remain
silent.)
[0027] When a radio node is able to measure sector load using ROT,
it can control load on the sector by setting (or clearing) the
reverse activity (RA) bit in the reverse activity channel on the
forward link. More particularly, the radio node compares the ROT
value with a predetermined threshold, which is referred to as the
RA bit threshold. The RA bit threshold corresponds to some
percentage of nominal sector loading (typical values are about 50
to 60% of nominal sector loading). If the ROT value is above the RA
bit threshold, then the radio node sets the RA bit, otherwise the
radio node clears the bit.
[0028] The RN transmits an RA bit every RAB length slots over the
RA medium access control (MAC) channel (which is a component
channel of the reverse activity channel). When an AT receives data
on an MAC channel with the RA bit set, the AT becomes aware that
the loaded and executes a "coin-flip" algorithm to determine
whether to freeze or reduce its transmit rate. If the coin-flip has
a first outcome, the AT freezes its transmit rate, if the coin-flip
has a second outcome, the AT decreases its rate from its current
rate to the next lowest rate defined by IS-856. By reducing the
rate at which ATs transmit on the reverse link, ATs transmit at
less power and cause less interference in the sector, which
decreases the ATs usage of the sector's capacity.
[0029] In some cases, the RN's radio interface is not available,
and, as a result, sector load cannot be measured using ROT. In this
situation, sector load is measured by the RN's modem using
post-Automatic Gain Control (AGC)-ROT estimation. A post-AGC-ROT
estimate is not as accurate as a ROT measure because it typically
does not account for interference from ATs that do not have active
connections on that sector (interference generated by other
sectors). Because of post-AGC-ROT estimation may be inaccurate, the
RA bit may not get set when a sector is becoming overloaded. If the
RA bit is not properly set, ATs in the sector are free to transmit
at higher rates (and thus also higher powers), which may eventually
lead to an overpowering of the reverse link. As the number of
active ATs in the sector grow, the problem is exacerbated because
as the number of active connections grows, the effective SNR of all
ATs denigrates until eventually the ATs in the sector lose the
reverse link.
[0030] To prevent overloading when ROT measurement is not
available, RAN 20 (shown in FIG. 1) also employs a reverse rate and
stability control algorithm that allows it to variably control the
data rate of the reverse link of ATs in a sector. The reverse rate
and stability control algorithm includes two basic components: (i)
a generalized rate-weighting algorithm by which a RAN determines
the "effective number of connections" in one or more sectors with
which an AT has a connection, and (ii) a maximum rate limit table
(MRLT), which dictates a rate limit for an AT based on the
determined effective number of connections. In some
implementations, the RAN sets a rate limit for an AT having
connections in multiple sectors based on the sector with the
largest effective number of connections. For example, if an AT has
a connection in sector "A" having an effective number of
connections equaling 10 and sector "B" having an effective number
of connections equaling 20, the RAN sets a rate limit for that AT
based on an effective number of connections of 20.
[0031] The generalized rate-weighting algorithm assigns weights to
connections in a sector to determine an effective number of
connections in the sector. If an AT is in softer handoff and has
connections in two or more sectors serviced by the same RN, the
generalized rate-weighting algorithm is applied to each of the
sectors with which the AT has a connection. In some
implementations, if the AT is in soft handoff and has connection in
two or more sectors serviced by different RNs, the generalized
rate-weighting algorithm is applied to each of the sectors with
which the AT has a connection. As mentioned above, if an AT has
connections in multiple sectors, the RAN may base the ATs rate
limit on the largest effective number of connections of the sectors
with which the AT has a connection.
[0032] The generalized rate-weighting algorithm provides systems
engineers the ability to weight the following characteristics of
connections in a sector: [0033] a. whether a connection has data to
send; [0034] b. the location of the AT associated with the
connection in the sector using the earliest pseudo-random noise
offset (EPNO) measurement during network access (for example, an AT
that is close to a sector boundary may be weighted more that ATs
not close to a boundary since it is more likely to cause more
interference to the neighboring sectors); [0035] c. the
connection's requested downlink rate (for example, an AT requesting
higher downlink rate may be weighted less since it is close to the
radio node and less likely to cause interference to neighboring
sectors); [0036] d. a soft/softer handoff factor assigned to ATs
that are in soft/softer handoff (for example, an ATs in soft/softer
handoff are weighted more than one not in handoff since an ATs in
soft/softer handoff are at the cell edge and could potentially
cause interference to neighboring sectors); and [0037] e. the
strength of the connection's signal(s) reported in the route update
message (for example, the weight of a connection may be lessened if
the connection reports a weak pilot signal strength for the sector
in question, which indicates that the AT is only just able to
observe the specific sector pilot).
[0038] In addition to variably weighting characteristics of
connections in a sector, the generalized rate-weighting algorithm
can be programmed to weight connections differently based on their
transmit rate. Thus, for example, the soft/softer handoff factor of
a connection transmitting at one rate can be weighted differently
than the soft/softer handoff factor of another connection
transmitting at a different rate.
[0039] After weighting the connections in a sector, the weighted
connections in the sector are summed to obtain the effective number
of connections in the sector. For example, in some implementations
the generalized weight-rating algorithm is programmed according to
Table I.
TABLE-US-00001 TABLE I Pilot Weights Strength Wi = sum[(1/6)(P1, .
. . , P6)] Connection from 1xEVDO such that Soft/Softer Effective
Has Data Route RL Rate 0 <= EPNO DRC Handoff RL Rate to send
Update (Kbps) sum[(1/6)(P1, . . . , P6)] <= 1 (P1) (P2) Count
(P3) (P4) (P5) (P6) 153.6 W5 0 0 0 0 6 0 76.8 W4 0 0 0 0 6 0 38.4
W3 0 0 0 0 6 0 19.2 W2 0 0 0 0 6 0 9.6 W1 0 0 0 0 0 0
[0040] As shown, the generalized rate-weighting algorithm has been
programmed only to consider whether a connection has data to send
and ignores other characteristics of a connection. In addition, the
generalized rate-weighting algorithm ignores connections that are
transmitting at the lowest 1.times.EV-DO rate of 9.6 Kbps. Thus, if
a sector has 10 connections and 4 of the 10 connections have data
to send and of these 4 connections, one is transmitting at 9.6
Kbps, the generalized rate-weighting algorithm (as programmed
according to Table I) will determine that there are 3 effective
number of connections in the sector.
[0041] The RAN then sets a maximum rate limit for ATs in the sector
based on the effective number of connections. If an AT has multiple
connections for which an effective number of connections has been
determined, the RAN may set the rate limit based on the largest
effective number of connections of the sector with which the AT has
a connection. In some implementations, the RAN uses the maximum
rate limit table shown in Table II to set a maximum rate limit for
the sector.
TABLE-US-00002 TABLE II Effective Number Maximum Rate Limit of
Connections (C) (Kbps) 1 <= C <= 7 153.6 8 <= C <= 59
76.8
[0042] Thus, if the effective number of connections determined by
the generalized rate-weighting algorithm is between 1 and 7, the
RAN permits the ATs to transmit at the maximum 1.times.EV-DO rate
of 153.6 Kbps. If the effective number of connections is between 8
and 59, the RAN limits the ATs in the sector to transmit at the
second-highest 1.times.EV-DO rate of 76.8 Kbps. The current
iteration of 1.times.EV-DO limits the number of connection in a
sector to 59, which is why the table does not account for
situations where the effective number of connections is over 59.
However, future iterations of 1.times.EV-DO may increase the
maximum number of connections in a sector, in which case, the rate
limit table would be extended. Additionally, some implementations
may use other rate limit tables to limit transmit rates of ATs
based on characteristics of a sector (e.g., the hardware
capabilities of a sector, the presence of objects like buildings
that cause interference in a sector, etc.).
[0043] Some implementations may use any one or a combination of the
connection characteristics described above to determine an
effective number of connections. In addition, weighting of
connection characteristics can vary depending on the transmit rate
of the connection.
[0044] The RAN can be configured to transmit rate limit messages by
way of unicast or broadcast messaging. For broadcast messaging, the
RAN transmits a rate limit message to all ATs in a sector over the
control channel on the forward link. For unicast messaging, the RAN
transmits a rate limit message sent to individual ATs over the
forward traffic channel on the forward link.
[0045] When an AT establishes a connection with a sector, it does
so at the lowest rate, i.e., 9.6 Kbps, and will remain at this rate
until it receives a rate limit message. Because it may take some
time before the RAN transmits a rate limit message (e.g., a RAN may
be configured to periodically broadcast rate limit messages in a
sector), in some implementations the RAN is configured to send a
rate limit message at the maximum rate of 153.6 Kbps immediately
after a new connection is established to prevent an AT from
needlessly remaining at a low transmit rate while waiting for a
first rate limit message.
[0046] In some implementations determination of the effective
number of connections and rate control is determined by the RNC.
For example, as shown in FIG. 4, a RAN 50 includes an RNC 52 in
communication with two RNs 54a, 54b over a backhaul network 56. For
simplicity, it is assumed that each RN serves a single sector. Each
RN includes an RA bit estimation algorithm 60a, 60b, which performs
ROT measurements or, if not available, provides a post-AGC-ROT
estimation, to set or clear the RA bit. As described in more detail
above, the RNs transmit the RA bit 62 on the MAC channel to ATs 58
in the sector.
[0047] RNC 52 includes a reverse rate and stability control
algorithm 63, which, as described above, uses the generalized
rate-weighting algorithm to determine an effective number of
connections for an AT over ALL sectors that the AT is in handoff
with and then uses a rate limit table (e.g., Table II above) to set
rate limits for the AT.
[0048] Rate limit messages 64 can be transmitted to ATs in the
sector either via unicast or broadcast messaging. Unicast messages
are reliable, but an individual message needs to be sent to each
AT. This may increase the processing load on the RNC and signaling
traffic between the RAN and the AT. If unicast messaging is used,
the rate limit message can be transmitted either periodically or
whenever there is a change in the rate limit.
[0049] Broadcast messages are best effort (and thus not as reliable
as unicast messages). However, a broadcast rate limit message can
be a single message per sector transmitted over the control channel
of the sector. Thus, broadcasting conserves RNC processing
resources and signaling bandwidth between AN and AT. As with
unicast messaging, a broadcast rate limit message can be
transmitted either periodically or whenever there is a change in
the rate limit. It should be noted that broadcast rate limit
messages normally needs to be transmitted to the AT through its
serving sector, and there can be ambiguity in choosing the serving
sector when the AT is switching sectors. However, periodic
broadcasted rate limit messages tend to diminish this problem.
Furthermore, due to the format of a broadcasted rate limit message,
non-serving sectors sometimes have to transmit rate limit
information for the AT, and, therefore, in some implementations,
rate limit information for an AT is broadcasted from all sectors in
handoff with an AT targeted for a rate limit.
[0050] In some implementations, a reverse rate and stability
control algorithm is implemented at the radio node. For example, as
shown in FIGS. 5A-5B, each radio node 54a, 54b executes a reverse
rate and stability control algorithm 63a, 63b in addition to the RA
bit estimation algorithm 60a, 60b. In the implementation
illustrated in FIG. 5A, if an AT is in soft handoff (and therefore
has a connection with a sector outside RN 54a), the effective
number of connections for the sector(s) with which the AT has a
connection but are outside the service area of RN 54a are provided
by the RNC that services the sector(s). In the implementation
illustrated in FIG. 5B, the effective number of connections for
sector(s) with which the AT has a connection but are outside the
service area of the RN executing the reverse rate and stability
control algorithm (e.g., RN 54a) are provided directly by the
appropriate RN via inter-RN messaging. As before, an RN can
transmit rate limit messages to ATs via either broadcast or unicast
messaging.
[0051] In the implementations illustrated in FIGS. 4 and 5A-5B a
reverse rate and stability control algorithm executed for a
particular AT in all of the sectors in which the AT has a
connection. This can be considered an optimal approach. In some
implementations, however, determination of the effective number of
connections is performed only on a subset of the sectors with which
an AT has a connection. For example, an RN may determine an
effective number of connections for the sectors with an AT has a
connection AND are serviced by the RN. Thus, the RAN would not
determine an effective number of connections for sectors in which
the AT is in soft handoff. An approach that considers a subset of
the sectors with which an AT has a connection can be considered a
sub-optimal approach, but nonetheless can prevent sector overload
without having to implement inter-RN messaging or additional RNC-RN
messaging across the backhaul network. For example, as shown in
FIG. 6, each RN 54a, 54b executes a reverse rate and stability
control algorithm without receiving information about a number of
connections in other sectors that an AT, e.g., AT 58, may be in
soft handoff with. As before, rate limit messages may be
transmitted either via unicast or broadcast messaging.
[0052] In some implementations, a hybrid approach between the
optimal and sub-optimal approaches is taken. For example, as shown
in FIG. 7, each of the RNs 54a, 54b executes a reverse rate and
stability control algorithm over ALL sectors for connections that
are not in soft handoff, i.e., only the sectors within the radio
node (54a or 54b) are analyzed. In addition, the RNC 52 executes a
reverse rate and stability control algorithm over ALL sectors for
connections that are in soft handoff with all the sectors being
analyzed. If the connection is not in handoff or in softer handoff,
the unicast or broadcast rate limit messages are transmitted from
the radio node (54a or 54b) itself. If the connection is in soft
handoff, then the unicast or broadcast rate limit messages are
transmitted from the RNC 52.
[0053] As described above, rate limit messages can be transmitted
to affected ATs either view unicast or broadcast messaging. In some
implementations, ATs that are not in soft or softer handoff receive
rate limit messages via broadcast messaging from the radio node in
which they have a connection, whereas ATs that are in soft or
soft-softer handoff receive unicast or broadcast rate limit
messages from the RNC. For ATs in soft handoff, the RN transmits a
broadcast rate limit message corresponding to no handoff that will
be overridden by the unicast message transmitted from the RNC. For
connections in soft-softer handoff, the RN transmits a broadcast
rate limit message corresponding to softer handoff that will be
overridden by the unicast message transmitted from the RNC.
[0054] A simulation performed on an implementation using the
sub-optimal approach with a reverse rate and stability control
algorithm using a generalized rate-weighting algorithm programmed
according to Table I above and a maximum rate limit table
programmed according to Table II above. The simulation showed an
improved reverse link sector throughput while still ensuring
stability of the reverse link versus an implementation in which all
ATs were limited to a transmit rate of 38.4 Kbps. Embodiments on
existing systems select a conservative rate limit (such as 38.4
Kbps) to maintain reverse link stability. The simulations were
based on the Strawman models provided the 3GPP2 standard bodies
(3GPP2-1.times.EV-DO Evaluation Methodology (V1.3)) for wireless
network simulation. Simulation results for a heavily loaded sector
having 18 connections are shown in Table III.
TABLE-US-00003 TABLE III Implementation in which the reverse rate
and stability control algorithm use GRW Implementation in algorithm
shown which reverse in Table I and MRLT rate is limited to shown in
Table II 38.4 Kbps for all ATs Activity Factor Average Average
(fraction of Sector Average Sector Average connections with
Throughput ROT Throughput ROT data to send) [kbps] [dB] [kbps] [dB]
0.25 298.00 5.78 117.36 2.2 0.5 290.05 5.70 116.04 2.2 1.0 269.93
5.84 114.06 2.3
[0055] Note that the simulation of a RAN using a reverse rate and
stability control algorithm achieved better sector throughput while
operating at acceptable ROT than that of a RAN using which limited
the transmit rate to 38.4 Kbps for all ATs in a sector.
[0056] In a system where more than one method for ROT measurement
and/or post-AGC-ROT estimation is available, the system may use
different rate weightings in the generalized rate-weighting
algorithm may differ depending on the ROT/post-AGC-ROT estimation
method used. Similarly, the system may use different rate limit
tables (e.g., Table II above) depending on the ROT/post-AGC-ROT
estimation method used. For example, if the system uses highly
accurate RA bit estimation method (e.g., ROT measurement), the
system may employ one weight limit table, whereas if the system
uses a less accurate RA bit estimation method (e.g., a
post-AGC-estimation ROT method), it may switch to a more
conservative rate limit table.
[0057] A number of embodiments of the invention have been
described. Nevertheless, it will be understood that various
modifications may be made without departing from the spirit and
scope of the invention, and, accordingly, other embodiments are
within the scope of the following claims.
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