U.S. patent application number 11/965788 was filed with the patent office on 2009-07-02 for probabilistic interference mitigation for wireless cellular networks.
Invention is credited to Nageen Himayat, Guowang Miao, Shilpa Talwar.
Application Number | 20090170497 11/965788 |
Document ID | / |
Family ID | 40799114 |
Filed Date | 2009-07-02 |
United States Patent
Application |
20090170497 |
Kind Code |
A1 |
Miao; Guowang ; et
al. |
July 2, 2009 |
PROBABILISTIC INTERFERENCE MITIGATION FOR WIRELESS CELLULAR
NETWORKS
Abstract
An interference mitigation system randomizes transmissions to
cell-edge users by carefully controlling the probability of
transmission to these users, thereby creating a virtual fractional
frequency system that does not require extensive frequency
management and coordination across the network. In some
embodiments, the interference mitigation system identifies severely
interfered links and reduces the probability of transmission on
these links, with the result being a reduced probability of
interference.
Inventors: |
Miao; Guowang; (Atlanta,
GA) ; Himayat; Nageen; (Freemont, CA) ;
Talwar; Shilpa; (Santa Clara, CA) |
Correspondence
Address: |
CARRIE A. BOONE, P.C.
2450 Louisiana, Suite # 400-711
HOUSTON
TX
77006
US
|
Family ID: |
40799114 |
Appl. No.: |
11/965788 |
Filed: |
December 28, 2007 |
Current U.S.
Class: |
455/422.1 |
Current CPC
Class: |
H04W 72/082
20130101 |
Class at
Publication: |
455/422.1 |
International
Class: |
H04Q 7/20 20060101
H04Q007/20 |
Claims
1. A system, comprising: a base station comprising a medium access
controller, the medium access controller comprising transmission
randomization capability; a subscriber station comprising
co-channel interference avoidance, the subscriber to notify the
base station when interference exceeds a threshold; wherein
transmissions to the subscriber station are randomized based on a
channel threshold for the subscriber station.
2. The system of claim 1, further comprising: a second base station
comprising a second medium access controller the second medium
access controller comprising transmission randomization capability,
the base station to notify the second base station when
interference exceeds the threshold; wherein transmissions by the
second base station to the subscriber station are randomized based
on the channel threshold.
3. The system of claim 2, wherein the transmissions to the
subscriber station are randomized after receiving notification from
both base stations.
4. The system of claim 2, the base station and the second base
station further comprising physical layer optimization, wherein the
base stations determine power allocation and rate parameters for a
link between the base station and the subscriber station.
5. The system of claim 4, wherein the power allocation is given by:
if P m < P _ 1 - F ( H _ ( i , j ) k * ) , P ( i , j ) k * ( h )
= P m for h .gtoreq. H _ ( i , j ) k * , otherwise , P ( i , j ) k
* ( h ) = { P m .upsilon. * < R ( hP m n o W ) h n o W 0
.upsilon. * .gtoreq. R ( hP m n o W ) h n o W , R ' - 1 ( .upsilon.
* n o W h ) n o W h otherwise ##EQU00008## where h.gtoreq.
H.sub.(i,j).sub.k*. R'.sup.-1( ) is an inverse function of R'( ),
and .upsilon.*.gtoreq.0 is uniquely given by .intg. H _ ( i , k ) k
.infin. P ( i , j ) k * ( h ) f ( h ) h = P _ . ##EQU00009##
6. The system of claim 1, wherein the threshold is determined using
an optimization equation: H _ * = arg max X _ .A-inverted. ( i , j
) k ln ( p ( i , j ) k l .di-elect cons. N j ( 1 - p l ) ) ,
##EQU00010## where (i,j).sub.k is the link between the i.sup.th
base station and the j.sup.th subscriber on the k.sup.th channel,
and p(i,j).sub.k is the probability of transmission on link
(i,j).sub.k, and p.sub.l is the probability of transmission by the
l.sup.th interfering base station.
7. A method, comprising: determining a channel threshold for a link
between a base station and a subscriber; and setting a probability
of transmission for the link based on the channel threshold.
8. The method of claim 7, further comprising: receiving an
indication of interference from the subscriber by the base station;
wherein the subscriber interference indication causes the base
station to determine the channel threshold.
9. The method of claim 7, further comprising: determining a
location of the subscriber; wherein the base station determines the
channel threshold when the location exceeds a predetermined
distance from a cell center in which the base station resides.
10. The method of claim 7, further comprising: identifying
interference by the subscriber, the subscriber being part of a
wireless neighborhood comprising base stations and subscribers.
11. The method of claim 10, further comprising: comparing an
interference-to-carrier ratio of the link to a threshold; and not
reporting interference to the base station if the threshold is not
exceeded.
12. The method of claim 11, further comprising: reporting the
interference to the base station if the threshold is exceeded.
13. The method of claim 12, further comprising: reporting the
interference to other base stations in the wireless neighborhood;
wherein each base station communicates with the subscriber
according to the probability of transmission.
14. The method of claim 13, further comprising: obtaining the
threshold using an optimization equation.
15. The method of claim 14, obtaining the threshold using an
optimization equation further comprising: using optimization
equation H _ * = arg max H _ .A-inverted. ( i , j ) k ln ( p ( i ,
j ) k l .di-elect cons. N j ( 1 - p l ) ) , ##EQU00011## where
(i,j).sub.k is the link between the i.sup.th base station and the
j.sup.th subscriber on the k.sup.th channel, and p(i,j).sub.k is
the probability of transmission on link (i,j).sub.k, and p.sub.l is
the probability of transmission by the l.sup.th interfering base
station.
16. A method, comprising: identifying interference by a subscriber,
the subscriber being part of a wireless neighborhood comprising
base stations and subscribers, wherein the subscriber reports the
interference to a base station; determining a channel threshold for
a link between the base station and the subscriber; and setting a
probability of transmission for the link based on the channel
threshold.
17. The method of claim 16, further comprising: comparing an
interference-to-carrier ratio of the link to a threshold; and not
reporting interference to the base station if the threshold is not
exceeded.
18. The method of claim 17, further comprising: reporting the
interference to the base station if the threshold is exceeded.
19. The method of claim 18, further comprising: using optimization
equation H _ * = arg max H _ .A-inverted. ( i , j ) k ln ( p ( i ,
j ) k l .di-elect cons. N j ( 1 - p l ) ) , ##EQU00012## where
(i,j).sub.k is the link between the i.sup.th base station and the
j.sup.th subscriber on the k.sup.th channel, and p(i,j).sub.k is
the probability of transmission on link (i,j).sub.k, and p.sub.l is
the probability of transmission by the l.sup.th interfering base
station.
Description
TECHNICAL FIELD
[0001] This application relates to wireless cellular systems and,
more particularly, to mitigation of co-channel interference in a
wireless neighborhood.
BACKGROUND
[0002] The performance of wireless cellular systems is
significantly limited due to co-channel interference from
neighboring base stations, especially as these systems move towards
aggressive frequency reuse scenarios. While the overall spectral
efficiency of the cellular system may improve with aggressive
frequency reuse, the performance of cell-edge users degrades
substantially. Recent research is focused on a variety of
interference management techniques, ranging from the design of
fractional frequency reuse (FFR) mechanisms for cell-edge users, to
coordinated transmit beam-forming techniques, to receiver
interference cancellation using multiple antennas.
[0003] One simple approach to reducing interference for the cell
edge users is to reserve a set of frequencies used for transmission
to only cell-edge users in a fashion such that adjacent cells use
different sets of frequencies. This may be achieved through a
fractional frequency reuse (FFR) mechanism wherein a lower
frequency reuse is specified for users at the cell edge,
cell-center users enjoy full frequency reuse. This improves the
throughput performance of cell-edge users since they experience
lower levels of interference.
[0004] FIG. 1 shows an exemplary network deployment 50 with
fractional frequency reuse. Such a deployment enables most of the
frequencies (`white`) to be reused over a significant portion of
each cell, and only a fraction of frequencies to be set aside for
cell-edges (`dotted`, `vertical striped`, `diagonal striped`).
While initial deployments with FFR may use a static sub-division of
cell-edge and cell-center frequencies, it is expected that the
frequency reuse patterns be dynamically adjustable through
coordination across the network, since the traffic load and user
distribution may not be uniform across the network.
BRIEF DESCRIPTION OF THE DRAWINGS
[0005] The foregoing aspects and many of the attendant advantages
of this document will become more readily appreciated as the same
becomes better understood by reference to the following detailed
description, when taken in conjunction with the accompanying
drawings, wherein like reference numerals refer to like parts
throughout the various views, unless otherwise specified.
[0006] FIG. 1 is an exemplary network deployment with fractional
frequency reuse, according to the prior art;
[0007] FIG. 2 is a block diagram of a interference mitigation
system, according to some embodiments;
[0008] FIG. 3 is a diagram of a wireless neighborhood using the
interference mitigation system of FIG. 2, according to some
embodiments;
[0009] FIG. 4 is a flow diagram showing the co-channel interference
avoidance of the interference mitigation system of FIG. 2,
according to some embodiments;
[0010] FIG. 5 is a flow diagram the transmission randomization of
the interference mitigation system of FIG. 2, according to some
embodiments;
[0011] FIG. 6 is a graph of a co-channel interference avoidance
trigger threshold, according to some embodiments;
[0012] FIG. 7 is a graph of comparing the CIA MAC of FIG. 2 with a
legacy MAC, according to some embodiments;
[0013] FIG. 8 is a graph showing interference to carrier ratio
versus distance, according to some embodiments; and
[0014] FIG. 9 is a graph showing the spectral efficiency
improvement using the CIA MAC of FIG. 2, according to some
embodiments;
DETAILED DESCRIPTION
[0015] In accordance with the embodiments described herein, a
system and method for reducing interference in a network, or
interference mitigation system and method, are disclosed. The
interference mitigation system includes a co-channel interference
avoidance (CIA) medium access controller (MAC) in both a base
station and a subscriber station of a wireless neighborhood. The
interference mitigation method randomizes transmissions to
cell-edge users by carefully controlling the probability of
transmission to these users, thereby creating a virtual fractional
frequency system that does not require extensive frequency
management and coordination across the network. In some
embodiments, the interference mitigation method identifies severely
interfered links and reduces the probability of transmission on
these links, with the result being a reduced probability of
interference.
[0016] An interference mitigation system 100 is depicted in FIG. 2,
according to some embodiments. The interference mitigation system
100 includes a serving base station 20 and a subscriber station 30.
The serving base station is typically selected by the subscriber
30, based on the relative strength of the base station signal
received by the subscriber. The system 100 may include one or more
other base stations, denoted as base station 24, base station 26,
and base station 28. The serving base station 20 has a medium
access controller (MAC) 20 and the subscriber station 30 has a MAC
32. The MACs 22 and 32 include functional and structural components
not described herein, which are well-known to those of ordinary
skill in the art. These functional and structural components, which
are common to all base stations in the wireless region, are known
herein as legacy MAC operations.
[0017] In some embodiments, the MACs 22 and 32 each include novel
components suitable for co-channel interference avoidance (CIA),
known as the CIA MAC 40. Because the MACs 22 and 32 continue to
support other MAC functions not described herein, both the serving
base station 20 and the subscriber station 30 have both legacy MAC
and CIA MAC 40 functionality.
[0018] The CIA MAC 40 includes co-channel interference avoidance
200, transmission randomization 300, and physical layer
optimization 400, in some embodiments. As shown in FIG. 2,
co-channel avoidance 200 is performed by the subscriber station 30
while transmission randomization 300 and physical layer
optimization 400 are performed by the base stations 20, 24, 26, 28.
Co-channel avoidance 200 is described in the flow diagram of FIG.
3; transmission randomization 300 is described in the flow diagram
of FIG. 4.
[0019] A wireless neighborhood 60 is depicted in FIG. 3, to
facilitate understanding the system 100 of FIG. 2, according to
some embodiments. The wireless neighborhood 60 includes seven cells
62, each of which has a base station, BS.sub.1-BS.sub.7
(collectively, base stations BS). Subscribers, depicted as mobile
devices, denoted M.sub.1, M.sub.2, . . . M.sub.9, are employed
throughout the wireless neighborhood 60 (collectively, subscribers
M). The number of subscribers M may vary over time. Lines c.sub.1
show the desired links between mobile subscribers and base
stations. For mobile subscriber M.sub.1, there exists a desired
link, c.sub.1, to the base station, BS.sub.1. Because the base
stations are transmitting on channel 1 (c.sub.1) using the same
frequency, such transmission may cause interference to mobile
stations in other cells. For example, in FIG. 3, interferences on
the same channel are occurring from base stations, BS.sub.4 and
BS.sub.2, indicated as i.sub.c1 in both cases.
[0020] The interference mitigation system 100 commences with the
subscriber station 30. The subscriber station 30 notifies the
serving base station 20 of interference from some other base
station in the wireless neighborhood 50. In FIG. 2, a feedback link
34 is shown pointing from the subscriber station 30 to the serving
base station 20 to indicate this step. Then, the serving base
station 20 shares the interference report(s) with the other base
stations in the wireless neighborhood 50 that there has been a
report of interference. Interference reporting links 36 are shown
in FIG. 2 between the serving base station 20 and each of the base
stations 24, 26, and 28 in the system 100. Once all base stations
in the wireless neighborhood 50 are aware of the interference, the
base stations determine whether to perform transmission
randomization 300, in some embodiments. Like other transmissions,
randomized transmissions occur according to parameters obtained
through physical layer optimization 400.
[0021] Co-channel interference avoidance 200 operates according to
the flow diagram of FIG. 4, in some embodiments. The operations are
performed by the subscriber 30 (or one of the subscribers M in the
wireless neighborhood 50), although the operations may be performed
simultaneously by multiple subscribers. The subscriber 30
identifies the base station 20 (or stations) causing the most
interference to transmissions on its link to the serving
base-station (block 202). The subscriber 30 then makes a
determination whether to notify its serving base station 20 of the
interference by comparing the interference-to-carrier ratios (ICR)
to a threshold (.GAMMA.) (block 204).
[0022] If the threshold is not exceeded (block 206), the
interference is not sufficient to trigger the notification by the
subscriber 30. Otherwise, the subscriber 30 submits the identity of
the base-station(s) causing the most interference to its serving
base station, 20 (block 208). In some embodiments, the submission
operation constitutes one or more exchanges of the CIA MAC trigger
information between the subscriber station 30 and the serving base
station 20. As used herein "CIA MAC trigger" means events that lead
the subscriber station 30 or the serving base station 20 to invoke
the CIA MAC 40 of their respective MACs 22, 32. In other words, the
CIA MAC trigger is when the subscriber station 30 determines that
the interference exceeds the threshold.
[0023] The serving base station 20 communicates the information
reported by the subscriber 30 to other base stations in the
wireless neighborhood 50 (block 210). At this point, each base
station knows the links in which interference has been reported,
which are the links in which transmissions may optimally be
randomized (block 212). In some embodiments, the CIA MAC trigger
may be based on average SINR conditions, determined by system
geometry and location of subscribers. In these embodiments, the CIA
MAC trigger is updated and coordinated among other base stations in
the wireless neighborhood periodically.
[0024] Once the CIA MAC 40 is triggered, the transmission
randomization 300 of the MAC 22 in the serving base station 20 is
initiated. The other base stations in the wireless neighborhood
likewise initiate transmission randomization to the subscriber
station 30. FIG. 5 is a flow diagram showing operations performed
to randomize transmissions in the wireless neighborhood 50,
according to some embodiments. The operations in FIG. 5 may be
performed by all base stations BS in the wireless neighborhood 50,
but, for simplification, only one base station is indicated in the
flow diagram.
[0025] The base station identifies the link to be analyzed (block
302), which is the link between the serving base station 20 and the
subscriber 30 that reported the interference. The base station
determines a channel threshold for the CIA MAC link (block 304). If
the channel gain on the link does not exceed a "channel threshold",
H (block 306), no transmission to the subscriber 30 occurs (block
308). Otherwise, the base station 20 transmits to the subscriber 30
with optimized physical layer parameters (block 310). Hence, in
some embodiments, the transmission probability is proportional to
the probability of exceeding the "channel threshold".
[0026] The CIA MAC 40 also includes physical layer optimization
400. In some embodiments, the power and modulation on each link is
optimized separately. The components of the CIA MAC 40 shown in
FIG. 2 may be realized in different ways.
[0027] In some embodiments, once a decision to trigger the CIA MAC
40 on a given link is reached, the system 100 determines the
transmission threshold H, the power allocation, and the modulation
selection policy through optimization of the following criterion.
This criterion is based on a proportional fair approach of
maximizing the product of the goodput of all users. The
transmission threshold, power allocation, and modulation parameters
may also be derived through alternative optimization criteria.
[0028] In some embodiments, the system 100 uses an optimization
equation to determine the threshold and the optimal link parameters
for transmission to the subscriber 30, as follows:
C * = Arg max { H _ , P } .A-inverted. ( i , j ) k [ R ( i , j ) k
S ( 1 - FER ( i , j ) k p ( i , k ) k l .di-elect cons. N j ( 1 - p
l ) ] ##EQU00001## subject to ##EQU00001.2## .intg. H _ ( i , j ) k
.infin. f ( h ) P ( i , j ) k h .ltoreq. P _ ( Average power
constraint ) ##EQU00001.3## 0 .ltoreq. P ( i , j ) k .ltoreq. P max
( Peak power constraint ) ##EQU00001.4##
where (i,j).sub.k is the link between the i.sup.th base station and
the j.sup.th subscriber on the k.sup.th channel; R(i,j).sub.k, is
the rate on link (i,j).sub.k; FER(i,j).sub.k is the average frame
error rate on link (i,j).sub.k; p(i,j).sub.k is the probability of
transmission on link (i,j).sub.k; N.sub.j is the set of base
stations comprising severe interferers for the j.sup.th subscriber;
p.sub.l is the probability of transmission by the l.sup.th
interfering base station; H is the threshold for transmission;
P(i,j).sub.k is the average transmit power on link (i,j).sub.k;
f(h) is the probability distribution of fast fading channel with
cumulative distribution function, F; and S is the frame length.
[0029] An example approach to solving the above optimization
problem is to separate the optimization function into two distinct
parts. The separation is motivated in part by the fact that
maximization of the objective function is equivalent to maximizing
the log of the objective function. The two parts separately address
the issue of minimizing collisions and maximizing throughput.
[0030] Using the logarithm function splits the problem into two
parts. The first part is related to the transmission probabilities
of the desired and interfering base-stations. The objective, in
this case, thus reduces to finding the threshold H to minimize the
probability of collision in the network. The second part maximizes
the sum of the average throughput on all links, which can be solved
through a suitable power and rate allocation strategy per link. The
objective functions for the two problems are defined in the
following sections.
[0031] First, the probability of transmission is determined by the
system 100 as follows. In some embodiments, the threshold H is
determined through a solution to the following optimization
criterion:
H _ * = arg max H _ .A-inverted. ( i , j ) k ln ( p ( i , j ) k l
.di-elect cons. N j ( 1 - p l ) ) ##EQU00002##
[0032] It can be shown that the optimal threshold and consequently
the probability of transmission on a given link is given by:
H _ * ( i , j ) k = F - 1 ( .GAMMA. ( i , j ) k .GAMMA. ( i , j ) k
+ 1 ) and p * ( i , j ) k = 1 .GAMMA. ( i , j ) k + 1
##EQU00003##
[0033] In the above, .GAMMA.(i,j).sub.k is the number of base
stations severely interfering on channel(i,j).sub.k.
[0034] Next, the interference mitigation system 100 performs
physical layer optimization 400, in some embodiments. This part of
the CIA MAC 40 resides in all base stations in the wireless
neighborhood 50. The interference mitigation system 100 optimizes
the physical layer parameters per link. In some embodiments, the
physical power and rate parameters on the link are determined
through maximization of the throughput of all users, using the
following objective function:
P * ( i , j ) k = arg max { P ( i , j ) k } R ( i , j ) k
##EQU00004## subject to ##EQU00004.2## .intg. H _ ( i , j ) k
.infin. f ( h ) P ( i , j ) k ( h ) h .ltoreq. P _ ( average power
constraint ) ##EQU00004.3## 0 .ltoreq. P ( i , j ) k .ltoreq. P max
( Peak power constraint ) ##EQU00004.4##
[0035] Each user may vary both the transmitted power and rate to
achieve best transmission performance. The signal-to-noise ratio
(SNR) is denoted as .eta., the data rate function R'.sup.-1(.eta.)
is continuously differentiable with first order derivative positive
and strictly decreasing, i.e. concave of .eta.. The power
allocation is given by:
if P m < P _ 1 - F ( H _ ( i , j ) k * ) , P ( i , j ) k * ( h )
= P m for h .gtoreq. H _ ( i , j ) k * , otherwise , P ( i , j ) k
* ( h ) = { P m .upsilon. * < R ' ( hP m n o W ) h n o W 0
.upsilon. * .gtoreq. R ' ( hP m n o W ) h n o W , R ' - 1 (
.upsilon. * n o W h ) n o W h otherwise ##EQU00005##
for h.gtoreq. H*.sub.(i,j).sub.k. R'.sup.-1( ) is the inverse
function of R'( ). .upsilon.*.gtoreq.0 is uniquely given by
.intg. H _ ( i , j ) k .infin. P ( i , j ) k * ( h ) f ( h ) h = P
_ . ##EQU00006##
[0036] Before the transmission randomization 300 and physical layer
optimizations 400 can take place, however, the interference
mitigation system 100 determines the threshold for the CIA MAC
trigger. In some embodiments, each subscriber 30 makes a decision
to trigger the CIA MAC 40. This trigger is based on comparing the
measured interference-to-carrier-ratio (ICR) from each base-station
to a threshold, as described in FIG. 3, above. In some embodiments
the threshold is derived based on the assumption of one strong
interferer per subscriber. The extension to multiple interferers is
straightforward. In some embodiments, where there is a single
interferer, the optimal threshold is derived by comparing the
goodput of a system using the CIA MAC with that of a system having
no CIA MAC. For the optimal threshold, the goodput of CIA MAC is
greater than the good-put of a traditional MAC. The values of the
ICR thresholds are calculated as a function of the SNR, as shown in
the graph 70 of FIG. 6, according to some embodiments.
[0037] The value of the threshold at a high SNR is derived as a
function of the target probability of error P.sub.e and the number
of data symbols, L.sub.d, as
.GAMMA. = 1 P e 1 - ( 1 / 4 ) 1 / L d R - 1 SNR . ##EQU00007##
The graph 70 plots the values of the thresholds as a function of
the SNR for various numbers of data symbols.
[0038] The interference mitigation system 100 may employ alternate
methods for triggering the CIA MAC. These include but are not
limited to comparing goodput based on more than one strong
interferer, using location-based information or cooperation between
subscribers to determine severely interfered users, etc.
[0039] Observed improvements in throughput and spectral efficiency
with the use of the CIA MAC are shown in the following figures. A
graph 80 (FIG. 7) is a comparison of the CIA MAC with a traditional
MAC for a frequency reuse system. In some embodiments, the use of
the CIA MAC is triggered at a distance of 1.2 kilometers (km) from
the center of the cell 62, based on the throughput shown at
different distances. A graph 90 (FIG. 8) plots distance to call
center versus interference to carrier ratio, in some embodiments.
Again, the CIA MAC is triggered at a distance of 1.2 km to ensure
the best overall throughput at the center cell and at the cell
edge. A graph 110 (FIG. 9) plots spectrum efficiency versus
transmit power (dBm). The graph 110 shows spectral efficiency
improvement with the CIA MAC 10 for 8QAM modulation: 75% for CIA
MAC with cross-layer optimization, 34% without cross-layer
optimization (reference 43 dBm).
[0040] The above results are described for a single-carrier
scenario. However, extensions to a multi-carrier OFDM system are
achieved, in some embodiments. A simple extension is based on
determining the CIA-triggers and thresholds based on the average
interference power in the entire OFDM band. Subsequent transmission
on each OFDMA sub-channel are controlled by the average "channel
threshold" and the instantaneous channel gain on the
sub-channel.
[0041] In FIG. 2, both the base stations 20 and the subscriber
station 30 have CIA MAC functionality. In some embodiments, the
interference mitigation system 100 may operate with a legacy
subscriber station, i.e., one without CIA MAC functionality. In
such a system, the base station 20 may trigger the CIA MAC 40 when
the subscriber is located a predetermined distance from the center
of the cell 62. For example, if the legacy subscriber is 1.2 km
from its cell center, the subscriber is likely to be at the edge of
the cell 62, and thus may be more susceptible to interference by
other base stations. In this manner, the location of the subscriber
station would be the "notification of interference" to the base
station, obviating the need for the subscriber station to notify
the base station of a likely interference situation.
[0042] The interference mitigation system 100 provides a
low-complexity method for interference mitigation, which involves
limited coordination between base-stations. In some embodiments,
the interference mitigation system 100 provides for a relatively
decentralized and automatic method for controlling the degree of
frequency reuse to improve performance of cell-edge users. Complex
frequency reuse and power management schemes across a cellular
system are avoided with the interference mitigation system 100.
[0043] The interference mitigation system 100 may provide
significant benefit to cellular users severely impacted by
co-channel interference, thereby improving their
quality-of-service. The interference mitigation system 100 may be
standardized within next generation cellular standards.
[0044] The interference mitigation system 100 is novel in its use
of randomization by the base station for controlling the level of
interference in the wireless neighborhood. In particular, the
interference mitigation system 100 provides fair transmission
opportunities for users affected by co-channel interference.
Although randomization for collision avoidance is used extensively
for uplink random access channels and wireless local area network
(LAN) systems, its use by the interference mitigation system 100
for automatically controlling the level of downlink interference
per link is novel.
[0045] While the application has been described with respect to a
limited number of embodiments, those skilled in the art will
appreciate numerous modifications and variations therefrom. It is
intended that the appended claims cover all such modifications and
variations as fall within the true spirit and scope of the
invention.
* * * * *