U.S. patent application number 15/393606 was filed with the patent office on 2017-06-22 for reconfigurable antennas and configuration selection methods for ad-hoc networks.
The applicant listed for this patent is Drexel University, Politecnico di Milano. Invention is credited to Michele D'Amico, Kapil R. Dandekar, John Kountouriotis, Prathaban Mookiah, Daniele Piazza.
Application Number | 20170179613 15/393606 |
Document ID | / |
Family ID | 44649618 |
Filed Date | 2017-06-22 |
United States Patent
Application |
20170179613 |
Kind Code |
A1 |
Piazza; Daniele ; et
al. |
June 22, 2017 |
Reconfigurable Antennas And Configuration Selection Methods For
Ad-Hoc Networks
Abstract
Reconfigurable antennas in an ad-hoc network are provided where
all nodes employ MIMO/SIMO/MISO communication techniques. Three
types of reconfigurable antennas: Reconfigurable Printed Dipole
Array (RPDA), Reconfigurable Circular Patch Antenna (RCPA) and
Two-Port Reconfigurable CRLH Leaky Wave Antennas are used. The
RPDA, RCPA and the CRLH Leaky Wave antennas have a different number
of configurations as well as different degrees of pattern diversity
between possible configurations. To effectively use these antennas
in a network, the performance of centralized and decentralized
antenna configuration selection schemes are quantified for
reconfiguration at one or both link ends. The sum capacity of the
network is used as a metric to quantify the performance of these
antennas in measured and simulated network channels.
Inventors: |
Piazza; Daniele; (Lodi,
IT) ; Kountouriotis; John; (Philadelphia, PA)
; D'Amico; Michele; (Milano, IT) ; Dandekar; Kapil
R.; (Philadelphia, PA) ; Mookiah; Prathaban;
(San Diego, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Drexel University
Politecnico di Milano |
Philadelphia
Milano |
PA |
US
IT |
|
|
Family ID: |
44649618 |
Appl. No.: |
15/393606 |
Filed: |
December 29, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13634381 |
Feb 20, 2013 |
9565717 |
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PCT/US2011/029008 |
Mar 18, 2011 |
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15393606 |
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61315148 |
Mar 18, 2010 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04B 7/04 20130101; H01Q
3/24 20130101; H04W 84/18 20130101; H01Q 9/0435 20130101; H01Q
21/08 20130101; H01Q 1/007 20130101; H01Q 9/285 20130101; H01Q
9/0407 20130101; H01Q 9/145 20130101; H01Q 21/29 20130101; H01Q
5/342 20150115; H01Q 13/203 20130101; H04W 88/06 20130101; H01Q
21/062 20130101 |
International
Class: |
H01Q 21/29 20060101
H01Q021/29; H01Q 5/342 20060101 H01Q005/342; H04B 7/04 20060101
H04B007/04; H01Q 13/20 20060101 H01Q013/20; H01Q 21/06 20060101
H01Q021/06; H01Q 3/24 20060101 H01Q003/24; H01Q 9/04 20060101
H01Q009/04 |
Goverment Interests
GOVERNMENT RIGHTS
[0002] This invention was made with government support under
research Grant Nos. #CNS-0322795, #CNS-0322797, and #ECS-0524200
awarded by the National Science Foundation. The United States
Government has certain rights in the invention.
Claims
1. An ad-hoc network system, comprising: at least one multi-element
reconfigurable transmitter and/or at least one multi-element
reconfigurable receiver, each said multi-element reconfigurable
transmitter and each said multi-element reconfigurable receiver
comprising multiple antennas where each antenna is capable of
changing a radiation pattern and/or a polarization of a radiated
field; and a processor that processes software implementing a
configuration selection method for selecting an antenna
configuration for said at least one multi-element reconfigurable
transmitter and/or receiver based on knowledge of all or part of
communication and interference channels in the ad-hoc network,
where the antenna configuration is selected based on changes in
interference in a transmission over a transmission link including
the antenna being configured, a transmission rate of at least one
transmitter, a received signal strength of at least one receiver,
an error vector magnitude of at least one receiver, a channel
matrix of at least one receiver, and/or a packet error rate of at
least one of the receivers or transmitters of the transmission
link, wherein the selected antenna configuration optimizes a sum
capacity of the ad-hoc network, a sum throughput of the ad-hoc
network, and/or an error rate of the ad-hoc network.
2. A system as in claim 1, wherein the processor changes the
antenna configuration of only a receiver in response to changes in
interference in said transmission link.
3. A system as in claim 1, wherein the processor changes the
antenna configuration of only a transmitter, wherein the antennas
of different transmission links are allowed to change only after
the interference level in said transmission link has adapted to a
new antenna configuration at the transmitter of the transmission
link.
4. A system as in claim 1, wherein the at least one multi-element
reconfigurable transmitter or receiver comprises
multiple-input-multiple-output (MIMO), single-input-multiple-output
(SIMO) or multiple-input-single-output (MISO) transceivers.
5. A system as in claim 4, wherein at least one of the MIMO
transceivers comprises a reconfigurable circular patch antenna.
6. A system as in claim 4, wherein at least one of the MIMO
transceivers comprises a two-port reconfigurable leaky wave
antenna.
7. A system as in claim 4, wherein at least one of the MIMO
transceivers comprises a reconfigurable printed dipole array.
8. An ad-hoc network system, comprising: at least one multi-element
reconfigurable transmitter and/or at least one multi-element
reconfigurable receiver, each said multi-element reconfigurable
transmitter and each said multi-element reconfigurable receiver
comprising multiple antennas where each antenna is capable of
changing a radiation pattern and/or a polarization of a radiated
field; and a processor that processes software implementing a
distributed configuration selection method for selecting an antenna
configuration for said at least one multi-element reconfigurable
transmitter and/or receiver, where the antenna configuration is
selected using link channel and interference noise plus a noise
covariance matrix, a transmission rate, a received signal strength,
an error vector magnitude, a channel matrix, and/or a packet error
rate for the transmission link including the antenna being
configured by optimizing the link capacity, link throughput, or the
link packet error rate of said transmission link.
9. A method for selecting a configuration of at least one
multi-element reconfigurable transmitter and/or at least one
multi-element reconfigurable receiver in an ad-hoc network, each
said multi-element reconfigurable transmitter and each said
multi-element reconfigurable receiver comprising multiple antennas
where each antenna is capable of changing a radiation pattern
and/or a polarization of a radiated field, comprising: a processor
selecting an antenna configuration for said at least one
multi-element reconfigurable transmitter and/or at least one
multi-element reconfigurable receiver of a transmission link in
said ad-hoc network; measuring or estimating interference, a
channel matrix, a transmission rate, a received signal strength, an
error vector magnitude, and/or an error packet rate of said
transmission link in said ad-hoc network including an antenna of
the transmitter and/or receiver to be configured; and selecting an
antenna configuration for another transmission link in said ad-hoc
network based on based on knowledge of all or part of communication
and interference channels in the ad-hoc network and said measured
or estimated interference, channel matrix, transmission rate,
received signal strength, error vector magnitude, and/or error
packet rate of said transmission link, wherein the selected antenna
configuration optimizes a sum capacity of the ad-hoc network, a sum
throughput of the ad-hoc network, and/or an error rate of the
ad-hoc network.
10. A method as in claim 9, comprising repeating the measuring or
estimating and selecting steps so as to allow transmission links in
said ad-hoc network besides said transmission link to respond to
new measured or estimated levels caused by a change in a transmit
configuration of a transmitter of said transmission link.
11. A method as in claim 9, wherein the antenna configuration is
selected only for a receiver in response to changes in the measured
or estimated levels in said transmission link.
12. A method as in claim 9, wherein the antenna configuration is
selected only for a transmitter, wherein the antennas of different
transmission links are allowed to change only after the measured or
estimated levels in said transmission link have adapted to a new
antenna configuration at the transmitter of the transmission
link.
13. A method as in claim 9, wherein the at least one multi-element
reconfigurable transmitter or receiver comprises
multiple-input-multiple-output (MIMO), single-input-multiple-output
(SIMO) or multiple-input-single-output (MISO) transceivers.
14. A method as in claim 9, wherein an antenna configuration at
only one end of said transmission link is changed and an end of
said transmission link that is not changed is restricted to use the
most radiation efficient antenna configuration at all times.
15. A method for selecting a configuration of at least one
multi-element reconfigurable transmitter and/or at least one
multi-element reconfigurable receiver in an ad-hoc network, each
said multi-element reconfigurable transmitter and each said
multi-element reconfigurable receiver comprising multiple antennas
where each antenna is capable of changing a radiation pattern
and/or a polarization of a radiated field, comprising: a processor
selecting an antenna configuration for said at least one
multi-element reconfigurable transmitter and/or at least one
multi-element reconfigurable receiver of a transmission link in
said ad-hoc network; measuring or estimating interference, a
channel matrix, a transmission rate, a received signal strength, an
error vector magnitude, and/or an error packet rate of said
transmission link in said ad-hoc network including an antenna of
the transmitter and/or receiver to be configured; and selecting an
antenna configuration for another transmission link in said ad-hoc
network by implementing a distributed configuration selection
process that selects the antenna configuration using link channel
and interference noise plus a noise covariance matrix, a
transmission rate, a received signal strength, an error vector
magnitude, a channel matrix, and/or a packet error rate for the
transmission link including the antenna being configured by
optimizing the link capacity, link throughput, or the link packet
error rate of said transmission link.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a Continuation of U.S. patent
application Ser. No. 13/634,381 filed Feb. 20, 2013, which is the
National Stage of International Application No. PCT/US2011/029008,
filed Mar. 18, 2011, which claims benefit of Provisional
Application No. 61/315,148 filed Mar. 18, 2010, the disclosures of
which are incorporated herein by reference in their entireties.
TECHNICAL FIELD
[0003] The present invention relates generally to the field of
Ad-Hoc Networks. Specifically, the present invention relates to
reconfigurable antennas and configuration selection methods for
Ad-Hoc Networks.
BACKGROUND
[0004] Research in the area of ad-hoc networks has yielded
important advances, notably in the field of physical layer
techniques. In particular, a lot of effort has been spent in: i.)
applying smart antennas and antenna diversity techniques to ad-hoc
networks as explained in "Smart antenna system analysis,
integration and performance for mobile ad-hoc networks (MANETs),"
IEEE Transactions on Antennas and Propagation, vol. 50, no. 5, pp.
571-581, 2002 by S. Bellofiore, J. Foutz, R. Govindarajula, I.
Bahceci, C. Balanis, A. Spanias, J. Capone, and T. Duman; in "Ad
hoc networking with directional antennas: a complete system
solution," IEEE Journal on Selected Areas in Communications, vol.
23, no. 3, pp. 496-506, 2005, by R. Ramanathan, J. Redi, C.
Santivanez, D. Wiggins, and S. Polit; and in "Emerging adaptive
antenna techniques for wireless ad-hoc networks," ISCAS 2001. The
2001 IEEE International Symposium on Circuits and Systems, vol. 4,
pp. 858-861, 2001, by T. Ohira, ii.) developing medium access
control protocols suitable for Multiple Input Multiple Output
(MIMO) ad hoc networks as explained in "MIMO ad hoc networks with
spatial diversity: medium access control and saturation
throughput," vol. 3, 2004, pp. 3301-3306, 2004 43rd IEEE Conference
on Decision and Control (CDC), by M. Hu and J. Zhang; in "Improving
throughput and fairness for MIMO ad hoc networks using antenna
selection diversity," GLOBECOM '04. IEEE Global Telecommunications
Conference, vol. 5, pp. 3363-3367, 2004, by M. Park, J. Heath, R.
W., and S. Nettles; and in "A MAC protocol for mobile ad hoc
networks using directional antennas," 2000 IEEE Wireless
Communications and Networking Conference, vol. 3, pp. 1214-1219,
2000, by A. Nasipuri, S. Ye, J. You, and R. Hiromoto, and iii.)
adaptive algorithms for antenna beamforming in ad hoc networks as
described in "Noncooperative iterative MMSE beamforming algorithms
for ad hoc networks," IEEE Transactions on Communications, vol. 54,
no. 4, pp. 748-759, 2006, by R. Iltis, S. Kim, and D. Hoang; in
"Smart-antenna system for mobile communication networks part 2:
Beamforming and network throughput," IEEE Antennas and Propagation
Magazine, vol. 44, no. 4, pp. 106-114, 2002, by S. Bellofiore, J.
Foutz, C. Balanis, and A. Spanias, and in "On the performance of ad
hoc networks with beamforming antennas," Proceedings of the 2001
ACM International Symposium on Mobile Ad Hoc Networking and
Computing, pp. 95-105, 2001, by R. Ramanathan. Directional
antennas, like phased arrays and switchable parasitic elements
antennas, have been proposed as a solution to reduce the
interference of adjacent nodes, maximizing overall network
throughput in articles such as "Smart antenna system analysis,
integration and performance for mobile ad-hoc networks (MANETs),"
(citation above) "Emerging adaptive antenna techniques for wireless
ad-hoc networks," (citation above) and "Multicast communication in
ad hoc networks with directional antennas," Proceedings 12th
International Conference on Computer Communications and Networks,
pp. 385-390, 2003, by C. Jaikaeo and C. C. Shen. In order to
further increase the network spectral efficiency, MIMO spatial
multiplexing (SM) techniques and diversity techniques have been
adopted. However, directional arrays and MIMO SM/diversity
techniques cannot be integrated on compact portable devices, where
the limited space available makes mounting multiple directional
antennas difficult.
[0005] In order to overcome practical space limitations and merge
the benefits of MIMO SM/diversity techniques with those of
directional antennas, the inventors propose to adopt electrically
reconfigurable antennas as a key element of
MIMO/single-input-multiple-output
(SIMO)/multiple-input-single-output (MISO) transceivers in ad-hoc
networks. These antennas have been demonstrated to increase channel
capacity while reducing the space occupation of the antenna on the
communication device. While this previous work has focused on the
performance of reconfigurable antennas in single link
communications, there has been no published work on implementing
and field testing a system that employs reconfigurable antennas in
multi-link MIMO/SIMO/MISO ad hoc networks.
SUMMARY
[0006] The invention relates to a MIMO/SIMO/MISO ad-hoc network
comprising at least one transmitter and/or receiver having at least
one multi-element reconfigurable array of transceivers and a
processor that processes software which implements a configuration
selection method. The method is used to select an antenna
configuration for at least one of the specified multi-element
reconfigurable arrays. The antenna configuration is based on
changes in the interference in a transmission over a transmission
link including the antenna being configured, a transmission rate of
the transmitter, a received signal strength of the receiver, an
error vector magnitude of the receiver, a channel matrix of the
receiver, and/or a packet error rate of the receiver or
transmitter. The performance of the system is improved where the
processor changes the antenna configuration of only the receiver in
response to changes in the measured or estimated levels of the
measured values over the transmission link. In the alternative,
only the transmitting antenna can have its configuration changed.
In this scenario, transmitters of different transmission links are
allowed to change only after the levels of the values for the
transmission link have adapted to the new antenna configuration at
the transmitter of the transmission link. Reconfigurable circular
patch antennas, two-port reconfigurable leaky wave antennas and/or
reconfigurable printed dipole arrays can be used in MIMO/SIMO/MISO
ad-hoc networks.
[0007] The method used to select an antenna configuration of at
least one multi-element reconfigurable array of transceivers in the
ad-hoc network includes a processor which selects the antenna
configuration for at least one transmitter and/or a receiver of a
transmission link in the ad-hoc network. The processor measures or
estimates the interference, transmission rate, received signal
strength, error vector magnitude, channel matrix, and/or packet
error rate of the transmission link. Finally, an antenna
configuration is selected for the other transmission links in the
ad-hoc network based on the measured or estimated interference,
transmission rate, received signal strength, error vector
magnitude, channel matrix, and/or packet error rate using the first
selected antenna configuration. The process of measuring and
selecting is done for every transmission link in the ad-hoc network
to allow every transmitter to respond to the new levels caused by
the transmit configuration of the first transmitter in the link. On
the other hand, antenna configurations can be done for receivers
only in response to changes in measured or estimated levels in the
transmission link.
[0008] In exemplary embodiments of the invention the software
processed by the processor may implement a centralized
configuration selection process that has knowledge of part or all
communication and interference channels in the ad-hoc network and
selects the antenna configuration that optimizes the sum capacity
of the ad-hoc network, the sum throughput of the ad-hoc network,
and/or the error rate of the ad-hoc network or a distributed
configuration selection process that selects the antenna
configuration using link channel and interference noise plus a
noise covariance matrix, a transmission rate, a received signal
strength, an error vector magnitude, a channel matrix, and/or a
packet error rate for the transmission link including the antenna
being configured by optimizing the link capacity, link throughput,
or the link packet error rate of the transmission link. Also, an
antenna configuration at only one end of the transmission link may
be changed and an end of the transmission link that is not changed
is restricted to use the most radiation efficient antenna
configuration at all times.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] The foregoing and other beneficial features and advantages
of the invention will become apparent from the following detailed
description in connection with the attached figures, of which:
[0010] FIG. 1 illustrates a schematic of the Reconfigurable Printed
Dipole Array in accordance with the invention.
[0011] FIG. 2 illustrates a radiation pattern (in dB) in the
azimuthal plane of the two printed dipoles separated by in all the
configurations for an operation frequency of 2:48 GHz: (a) antenna
1 "short", antenna 2 "short"; (b) antenna 1 "long", antenna 2
"short"; (c) antenna 1 "short", antenna 2 "long"; (d) antenna 1
"long", antenna 2 "long".
[0012] FIG. 3 illustrates a schematic of a Reconfigurable Circular
Patch Antenna (RCPA).
[0013] FIG. 4 illustrates a pattern (in dB) in the azimuthal plane
at the two ports of the RCPA in all its configurations for an
operation frequency of 2:48 GHz: (a) port 1 "Mode 3", port 2 "Mode
3"; (b) port 1 "Mode 4", port 2 "Mode 4".
[0014] FIG. 5 illustrates a measured topology using the illustrated
arrays.
[0015] FIG. 6 illustrates a CDF of Sum Capacity for RCPA with Equal
Power Allocation-Centralized Configuration Selection
(Measurements).
[0016] FIG. 7 illustrates a CDF of Sum Capacity for RCPA with Equal
Power Allocation-Centralized Configuration Selection
(Simulation).
[0017] FIG. 8 illustrates a CDF of Sum Capacity for RCPA with Equal
Power Allocation-Distributed Configuration Selection
(Measurements).
[0018] FIG. 9 illustrates a CDF of Sum Capacity for RCPA with Equal
Power Allocation-Distributed Configuration Selection
(Simulation).
[0019] FIG. 10 illustrates a CDF of Sum Capacity for RPDA with
Equal Power Allocation-Centralized Configuration Selection
(Measurements).
[0020] FIG. 11 illustrates a CDF of Sum Capacity for RPDA with
Equal Power Allocation-Centralized Configuration Selection
(Simulation).
[0021] FIG. 12 illustrates a CDF of Sum Capacity for RPDA with
Equal Power Allocation-Distributed Configuration Selection
(Measurements).
[0022] FIG. 13 illustrates a CDF of Sum Capacity for RPDA with
Equal Power Allocation-Distributed Configuration Selection
(Simulation).
[0023] FIG. 14 illustrates a block diagram representing a general
purpose computer system in which aspects of the present invention
may be incorporated.
DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS
[0024] The present invention may be understood more readily by
reference to the following detailed description taken in connection
with the accompanying figures and examples, which form a part of
this disclosure. It is to be understood that this invention is not
limited to the specific products, methods, conditions or parameters
described and/or shown herein, and that the terminology used herein
is for the purpose of describing particular embodiments by way of
example only and is not intended to be limiting of any claimed
invention. Similarly, any description as to a possible mechanism or
mode of action or reason for improvement is meant to be
illustrative only, and the invention herein is not to be
constrained by the correctness or incorrectness of any such
suggested mechanism or mode of action or reason for improvement.
Throughout this text, it is recognized that the descriptions refer
both to methods and software for implementing such methods.
[0025] A detailed description of illustrative embodiments of the
present invention will now be described with reference to FIGS.
1-14. Although this description provides a detailed example of
possible implementations of the present invention, it should be
noted that these details are intended to be exemplary and in no way
delimit the scope of the invention.
[0026] The description below quantifies the benefits achievable
with reconfigurable antennas in MIMO/SIMO/MISO ad-hoc networks,
while also investigating antenna configuration selection schemes at
each node. In an exemplary embodiment, the antenna configuration
selection schemes are implemented in software implemented on one or
more network processors. In a network scenario, the antenna
configuration selection algorithm for a single link not only seeks
the configuration combination (i.e., the configuration at the
receiver and the configuration at the transmitter) that will
provide a "rich" channel between the receiver and the transmitter,
but will also aim to mitigate the interference that the link is
suffering from. This configuration selection process is made more
complex by the fact that when the antenna configuration at a
transmitter is modified, it changes the interference seen by the
other links in the network. While directional antennas can perform
interference mitigation by estimating the direction of the incoming
signals at the receiver, it may be shown that reconfigurable
MIMO/SIMO/MISO antennas can achieve a similar result, with lower
system complexity, by only estimating the channel matrix.
[0027] In order to maximize network sum capacity without a
centralized controller, a distributed selection algorithm is
described below that can be used to efficiently select the antenna
configuration at each node. The performance of this distributed
selection scheme is compared to that of an ideal centralized
approach that uses an exhaustive search process to assign the
optimal antenna configuration to every node. It is assumed for both
centralized and distributed antenna configuration control that all
transmitters make use of the equal power allocation scheme proposed
which requires no channel feedback from the receiver to the
transmitter.
[0028] The sum network capacity that can be achieved with
MIMO/SIMO/MISO reconfigurable antennas for different network
topologies through channel measurements and electromagnetic ray
tracing simulations conducted in an indoor environment are
determined. In an exemplary embodiment, two prototype electrically
reconfigurable antenna architectures in a 2.times.2 MIMO system
employing SM are considered: i.) a Reconfigurable Printed Dipole
Array (RPDA) that makes use of two reconfigurable length dipole
antennas and ii.) a Reconfigurable Circular Patch Antenna (RCPA)
that makes use of a single variable-radius circular patch antenna
with two feedpoints. As explained below, parameters like the number
of antenna configurations, the spatial orthogonality between the
array elements, and the level of antenna radiation efficiency can
be used to predict the achievable performance with a particular
reconfigurable antenna in an ad-hoc network.
I. RECONFIGURABLE ANTENNA ARCHITECTURES
[0029] Two different compact pattern reconfigurable antennas,
intended to be used as a building block of MIMO/SIMO/MISO systems
in ad hoc networks, are presented. The following antennas were all
designed to operate in the 2:4-2:5 GHz frequency band typical of an
802:11-like MIMO network. The performance of each multi-element
reconfigurable array of transceivers is quantified using radiation
patterns, radiation pattern spatial correlation, and radiation
efficiency.
[0030] The level of diversity between the patterns generated at the
two ports of the array, as well as between the patterns generated
at the same port for different configurations of the array, is
estimated through the spatial correlation coefficient value.
Assuming a rich scattering environment, the spatial correlation
coefficient, .rho..sub.j,k,l,m, is defined as:
.rho. j , k , l , m = .intg. 4 .pi. E j , k ( .OMEGA. ) E l , m **
( .OMEGA. ) d .OMEGA. [ .intg. 4 .pi. E j , k ( .OMEGA. ) 2 d
.intg. 4 .pi. E l , m ( .OMEGA. ) 2 d .OMEGA. ] 1 / 2 ( 1 )
##EQU00001##
where j and l define the array port and k and m the antenna
configuration at the port j and l respectively. E.sub.j,k(.OMEGA.)
is the radiation pattern of the configuration k at port j over the
solid angle .OMEGA.=(.phi.,.theta.) and <*> is the transpose
operator.
[0031] Radiation pattern spatial correlation coefficients can be
used as a first estimate of the performance of the reconfigurable
antenna designs. In particular, the spatial correlation between
radiation patterns excited at two different ports of the antenna
array gives an indication of how much decorrelated are the signals
collected at the two multi-element reconfigurable array elements. A
lower correlation coefficient between the two ports will lead to
lower correlation between the communication channels from these
ports, resulting in higher capacity. Similarly, spatial correlation
coefficients relative to radiation patterns generated at the same
port for different configurations give an indication of the
increment in system diversity achievable using reconfigurable
antennas with respect to standard non reconfigurable antenna
systems. The higher the diversity between different configurations,
the higher the overall system diversity and the higher the
achievable channel capacity.
[0032] Radiation efficiency is also an important performance
measure for reconfigurable antennas. In particular, for a fixed
transmitter power, the higher the radiation efficiency, the greater
the received signal power and channel capacity.
[0033] Reconfigurable Printed Dipole Array
[0034] The Reconfigurable Printed Dipole Array (RPDA) consists of
two microstrip dipoles separated by a distance of a quarter
wavelength. The active elements in the multi-element reconfigurable
array can be electrically reconfigured in length using PIN diode
switches. Two configurations are defined for each dipole: one in
which both switches are activated ("long" configuration) and
another in which they are deactivated ("short" configuration).
Thus, four different configurations can be defined for the RPDA:
both antennas "long" (l-l), both antennas "short" (s-s), one
antenna "short" and the other "long" (s-l) and vice versa (l-s). A
schematic of the structure of the RPDA is depicted in FIG. 1.
[0035] The setting of the switches results in different geometries
of the antenna and, consequently, in different levels of
inter-element mutual coupling and far-field radiation patterns.
Four different pairs of radiation patterns can then be produced.
FIG. 2 shows these radiation patterns in the azimuthal plane.
[0036] Table I(A) shows the values of spatial correlation between
the measured azimuthal patterns generated at the two ports of the
RPDA, while Table I(C) shows the values of correlation between the
measured azimuthal patterns generated at the same port for all the
array configurations. Table I(A) shows that the correlation values
between radiation patterns at the two ports of the array are small
enough for all the configurations (.ltoreq.0:7) to provide
significant diversity gain. In contrast, Table I(C) shows that the
level of diversity between the different configurations is not as
high (.rho..sub.1,k,1,m>0.8) and is much less than that of the
RCPA discussed below.
[0037] The measured radiation efficiency for each array
configuration is given in Table I(B). It should be noted from this
table that there is an imbalance in the radiation efficiency for
the different configurations: "short-short" is the most efficient
antenna configuration while "long-long" is the least efficient.
TABLE-US-00001 TABLE 1 (A) SPATIAL CORRELATION BETWEEN PATTERNS
GENERATED AT TWO DIFFERENT PORTS OF THE RPDA, (B) MEASURED
RADIATION EFFICIENCY OF THE RPDA AND (C) SPATIAL CORRELATION
BETWEEN PATTERNS GENERATED AT THE SAME PORT OF THE RPDA (A)
short-short long-short short-long long-long 0.43 0.28 0.28 0.31 (B)
Antenna 1 Antenna 2 short-short 84% 84% short-long 77% 48%
long-short 48% 77% long-long 52% 52% (C) E.sub.1,s-s E.sub.1,s-l
E.sub.1,l-s E.sub.1,s-l E.sub.1,s-s 1 0.87 0.94 0.9 E.sub.1,s-l
0.87 1 0.9 0.93 E.sub.1,l-s 0.94 0.9 1 0.93 E.sub.1,s-l 0.9 0.93
0.93 1
[0038] Reconfigurable Circular Patch Antenna
[0039] The Reconfigurable Circular Patch Antenna (RCPA), consists
of a circular patch whose radius can be electrically varied by
turning all the switches on and off simultaneously. Thus, the RCPA
has two configurations: one in which all the switches are turned
off and the electromagnetic mode TM.sub.31 is excited ("Mode 3"
configuration) and another in which they are turned on and the
electromagnetic mode TM.sub.41 is excited ("Mode 4" configuration).
The structure of the RCPA is shown in FIG. 3. The antenna is fed
through two ports placed on the antenna structure such that: i.)
the radiation patterns excited simultaneously at the two ports are
spatially orthogonal to each other and ii.) the port isolation is
higher than 20 dB. The design is ideal for compact MIMO systems in
that two channels can be achieved using a single physical
antenna.
[0040] The measured radiation patterns of the RCPA are shown in
FIG. 4 for both configurations in the azimuthal plane. FIG. 4 shows
that the radiation patterns excited by "Mode 3" and "Mode 4"
configurations are significantly different, resulting in a large
amount of pattern diversity.
[0041] The spatial correlation coefficient value between azimuthal
patterns generated at two antenna ports, and between azimuthal
patterns of different configurations generated at the same port,
are calculated according to (1) and reported in Tables II(A) and
II(C) respectively. From Table II(A) it can be seen that the
patterns generated at the two ports of the RCPA are spatially
orthogonal for both configurations. Moreover Table II(C) shows the
very high level of diversity (.rho..sub.1,k,1,m=0.2) existing
between the two configurations of the RCPA.
[0042] The measured antenna radiation efficiencies are reported in
Table II(B). This antenna suffers of low radiation efficiency
because higher order modes are excited on a lossy substrate (FR4
with tan .delta.=0.02). "Mode 3" exhibits higher radiation
efficiency than "mode 4" configuration because lower order modes
are more efficient than higher order modes and because no power is
lost in the switches when "mode 3" is active.
TABLE-US-00002 TABLE II (A) SPATIAL CORRELATION BETWEEN PATTERNS
GENERATED AT TWO DIFFERENT PORTS OF THE RCPA, (B) MEASURED
RADIATION EFFICIENCY OF THE RCPA AND (C) SPATIAL CORRELATION
BETWEEN PATTERNS GENERATED AT THE SAME PORT OF THE RCPA (A) Mode3
Mode4 0.06 0.18 (B) Port1 Port2 Mode3 21% 17% Mode4 6% 5% (C)
E.sub.1,mode3 E.sub.1,mode4 E.sub.1,mode3 1 0.2 E.sub.1,mode4 0.2
1
[0043] Comparison of RCPA with RPDA
[0044] A comparison between the RPDA and the RCPA shows that, based
on the results of Tables I(A), I(C), II(A), and II(C), in a rich
scattered environment, the RCPA provides a higher degree of
diversity for all its configurations (and among the different
configurations) with respect to the RPDA. Therefore the RCPA allows
for higher decorrelation between signals at the receiver and it
provides higher system diversity. In contrast, the RPDA allows for
switching between double the number of radiation patterns offered
by the RCPA. Thus, the RPDA and RCPA can be viewed as representing
two different "philosophies" for using reconfigurable antennas in
wireless communications systems: i.) substantial changes in
radiation pattern (e.g., RCPA), and ii.) a large number of
radiation pattern states (e.g., RPDA).
[0045] Both antenna designs allow for full radiation coverage in
the azimuth plane. Therefore, a good signal reception is guaranteed
independently from the relative orientation of the transmitter and
the receiver.
[0046] Finally, the RPDA is characterized by higher radiation
efficiency than the RCPA. Thus the RPDA is expected to collect a
stronger signal than the RCPA. This could lead to higher values of
channel capacity because of a stronger received SNR, but it could
also lead to stronger co-channel interference.
II. SYSTEM MODEL AND NOTATION
[0047] It is assumed that the ad-hoc network consists of L
co-located links which interfere with each other. All links are
single hop (i.e., no node is used for relaying) and all
transmit-receive pairs are pre-determined. The following notation
will be used hereafter. H.sub.t.sub.rc.sub.,j.sub.tc denotes the
channel between the receiver of link i and the transmitter of link
j, which is a function of the receive configuration of link
i(i.sub.rc) and the transmit configuration of link j(j.sub.tc). In
the case of the RPDA, l.sub.rc,l.sub.tc.epsilon.[1, 4], and for the
RCPA, l.sub.rc; l.sub.rc,l.sub.tc.epsilon.[1, 2]. x.sub.i is the
signal vector of link i, which results in the power covariance
matrix of link i, Q.sub.1 as Q.sub.t=E{x.sub.ix.sub.i.sup.H}.
Operation (.)H denotes the conjugate transpose. Using this notation
and assuming a flat fading channel, the input-output relationship
for link l can be written as:
y t = H lrc , ltc x t + t .di-elect cons. L \ l H l rc , l tc x i +
n t .di-elect cons. L \ l H l rc , l tc x i + n ( 2 )
##EQU00002##
is the interference plus noise, which results in an interference
plus noise covariance matrix for link l:
R l = .sigma. 2 I + t .di-elect cons. L \ l H l rc , l tc Q t H l
rc , l tc H ##EQU00003##
For the above equation, the assumption was made that the noise has
power .sigma..sup.2 and is independent across receive elements.
Vector c is an 1.times.2L vector that contains the configurations
for all links, (i.e., c=[1.sub.rc, 1.sub.tc, 2.sub.rc, 2.sub.tc, .
. . , L.sub.rc, L.sub.tc]). Notice also that the interference plus
noise covariance matrix is a function of the receive configuration
of the link and the transmit configurations used in the network. It
is also assumed that the single type of reconfigurable antenna,
RCPA or RPDA, is used by all nodes in the network.
[0048] The power allocation strategy considered herein is the Equal
Power Allocation technique. Although the Equal Power Allocation
technique was used in the following example other power allocation
strategies would work also. It is the simplest MIMO transmission
strategy, proved to be optimal in the case where there is no
channel feedback to the transmitter. This strategy consists of
splitting the total available power in a node equally among the
transmit antenna elements and assigning each element an independent
symbol to transmit. In this case, x has N.sub.T non-zero elements,
while Q is always a diagonal matrix with diagonal elements equal
to
P T N T ##EQU00004##
each. For the Equal Power Allocation technique, the capacity of
link l becomes:
C l = log ( det ( I + P T .sigma. 2 N T H l rc l tc H l rc l tc H R
l - 1 ) ) where R l = I + t .di-elect cons. L \ l P T .sigma. 2 N T
H l rc , l tc H l rc , l tc H ( 3 ) ##EQU00005##
is the interference plus noise covariance matrix.
[0049] To quantify the performance of the different types of
reconfigurable antennas in an ad-hoc network, the sum capacity of
the network is used:
C = l .di-elect cons. L log 2 ( det ( I + P T .sigma. 2 N T H l rc
, l tc H l rc , l tc H R l - 1 ) ) ( 4 ) ##EQU00006##
[0050] Closed loop MIMO power allocation algorithms that make use
of channel feedback information from the receiver to the
transmitter could also be implemented to improve link and network
capacity. However, these algorithms become more complex when
reconfigurable antennas are used. In particular, channel feedback
information would have to be provided for all the different antenna
configurations used by the transmitter and receiver. Closed loop
algorithms become even more challenging in a network using
reconfigurable antennas because knowledge of the interference state
of the network would be needed. This interference also depends on
the specific antenna configurations used by all the transmitters in
the network so it would be difficult to keep all channel and
interference estimates current.
III. ANTENNA CONFIGURATION SELECTION METHODS
[0051] Consider three different cases for using reconfigurable
antennas in the network. In the first case, called Double-Side
Reconfigurable Antennas (DSRA), both the receiver and the
transmitter of any given link can adapt its configuration. For the
other two cases, either the link receiver or the link transmitter
alone is allowed to switch its configuration. These situations are
referred to as Receiver-Side Reconfigurable Array (RXRA) and
Transmitter-Side Reconfigurable Array (TXRA), respectively. The
side of the link that is not allowed to change configuration is
restricted to use the most efficient configuration at all times
(i.e., the short-short configuration for the RPDA case, and mode 2
for RCPA). For these three different cases, consider centralized
and a distributed configuration selection schemes using circular
patch antennas, two-port reconfigurable leaky wave antennas, and
printed dipole antennas, as discussed below.
[0052] Centralized Configuration Selection Technique
[0053] To provide an upper bound on the performance of
reconfigurable antennas in ad-hoc networks, consider the use of a
powerful centralized controller that has instantaneous knowledge of
part or all communication and interference channels (e.g.,
H.sub.l.sub.rc.sub.,l.sub.tc, .A-inverted.l,i.epsilon.L). This
controller is allowed to control the state of all reconfigurable
antennas in the network to optimize the sum capacity given in the
prior equation. Specifically, the central controller solves the
following optimization problem:
max c ( l .di-elect cons. L log 2 ( det ( I + P T .sigma. 2 N T H l
rc , l tc H l rc , l tc H R l - 1 ) ) ) ( 5 ) ##EQU00007##
where c is an 1.times.2L is a vector that contains the
configurations for each node. To solve this optimization problem,
the centralized controller conducts an exhaustive search over all
possible antenna configurations in all network nodes. The central
controller also may optimize the sum throughput and/or the error
rate of the ad-hoc network.
[0054] Distributed Configuration Selection Technique
[0055] For a more practical approach to configuration selection in
MIMO ad-hoc networks making use of reconfigurable antennas, a
distributed configuration technique is also considered. In this
technique, each link makes its own configuration selection using
only the link channel (H.sub.l.sub.rc.sub.,l.sub.tc) and
interference plus noise covariance matrix R.sub.l. The assumption
of such locally available channel information is commonly used in
ad-hoc networks. Since each link does not have information about
other channels in the network, the antenna configuration decision
cannot be geared towards maximizing network sum capacity. Instead,
each transmitter performs configuration selection to optimize
individual link capacity, link throughput, or the link packet error
rate of the transmission link. Mathematically, link l solves the
following optimization problem:
max rc , tc ( log 2 ( det ( I + P T .sigma. 2 N T H l rc , l tc H l
rc , l tc H R l - 1 ) ) ) ( 6 ) ##EQU00008##
where R.sub.l continues to depend on the transmit configuration of
all the other links and the receive configuration of link l.
However, a change in transmit configuration for a particular link
leads to a different amount of interference encountered by the
other links. These other links, in turn, will have to respond to
this change in interference levels by choosing their antenna
configurations to maximize their own capacity. Thus, the
Distributed technique is an iterative procedure where each link
continually updates its configuration selection in response to
changes in the interference. The procedure is very similar to the
Iterative Waterfilling algorithm, but instead of using different
power allocation matrices to respond to changes in the
interference, the nodes will use different antenna configuration
combinations. The distributed configuration selection process may
also select the antenna configuration using transmission rate,
received signal strength, error vector magnitude, channel matrix,
and/or error packet rate for the transmission link including the
antenna being configured.
[0056] Single Side Reconfigurable Antennas
[0057] As mentioned previously, the inventors individually
considered situations with reconfigurable antennas at both ends of
the link (DSRA), at the transmitter only (TXRA), and at the
receiver only (RXRA). Looking at Equation 3, it is apparent that a
link's capacity is a function of receive and transmit
configurations of it, as well as the transmit configurations of the
other links (through the interference plus noise covariance matrix
R) that co-exist in the network. In other words, when a link
changes its receive configuration, it affects only its own
capacity, while when a link changes its transmit configuration it
does not only affect its own capacity but the capacities of all the
other links as well. So, in the case of distributed antenna
configuration selection, when a link is allowed to change its
transmit configuration there is the need for an iterative
procedure, so as to allow for the other links to respond to the new
interference levels caused by the change in the transmit
configuration of one of them. But when only the receive
configurations are allowed to change, a change of the configuration
in one link will only affect this link and thus it is no longer
needed to have iterations.
[0058] Apart from the inherit iterative nature of the configuration
selection schemes which also involve changing the transmit
configuration, allowing configuration changes in the receive side
only has another positive merit: it removes the requirement of
having to implement a feed-back loop needed for the receiver to
notify the transmitter on which configuration it should be using.
These two properties of the configuration selection scheme at the
receiver only (not iterative and no need for feed-back) make the
RXRA scheme much more appealing for a practical implementation due
to its simplicity and its much less overhead.
[0059] The RXRA technique is also desirable in that the Distributed
and Centralized schemes become equivalent; when a link maximizes
its own capacity by changing reconfigurable antennas only at the
receiver, it also maximizes network sum capacity. This is again
true via the fact that a change in the receive configuration of a
link will only affect the capacity of this link, while leaving the
capacities of the rest of the links in the network the same.
Distributed and Centralized schemes are not necessarily equivalent
when reconfigurable antennas are used at the transmitters of ad-hoc
network links as the "selfish" choice that each node makes to
maximize its own capacity in the distributed schemes, is no longer
guaranteed to have a positive impact on the overall network sum
capacity, as it is achieved with the centralized schemes.
[0060] Configuration adaptation at a single side of the link also
provides a smaller search space for the Centralized technique and
less channel training for the Distributed technique. For example,
in the case of RPDAs where there are four configurations available,
a link has 16 different configuration combinations to choose from
with DSRA. However, this number decreases to four configuration
combinations for TXRA and RXRA. This difference in the number of
available configurations, while reducing the degrees of freedom the
network has, would also require less training. Less channel
training may have a positive impact on the performance when the
channel estimation errors are taken into account, depending on the
total number of configuration combinations that need to be
considered.
[0061] When assuming configuration adaptation at only one side of
the link, it is still assumed that the other link end uses a
reconfigurable antenna, since in an ad-hoc network any node can be
either a receiver or a transmitter. However, the side that is not
allowed to switch its configuration is restricted to use the most
radiation efficient configuration at all times.
IV. DATA COLLECTION
[0062] The performance that can be achieved, in terms of sum
network capacity, combining reconfigurable antennas and the
techniques described above, was investigated through field
measurements and electromagnetic ray tracing simulations in an
indoor environment.
[0063] Measurement Setup
[0064] The network topology where measurements were made is shown
in FIG. 5. For the measurements the HYDRA Software Defined Radio
platform was used. This platform was also used for the evaluation
of reconfigurable antennas in single link scenarios. The platform
is a 2.times.2 MIMO platform that operates in the 2.4 GHz band
using OFDM with 64 subcarriers (52 are carrying data).
[0065] In FIG. 5, three nodes (RX1 to RX3) with two receive
elements each acted as receivers and three nodes (TX1 to TX3) with
two transmit elements each acted as transmitters, so as to create 6
different network topologies, by perturbating the intended
receiver/transmitter pairs. To capture small scale fading effects,
the receive elements were placed on a robotic antenna positioner
and were moved at 40 different positions at displacements of
.lamda./10 along the y-axis for RX1 and RX2 and along the x-axis
for RX3. At each position, 100 noisy channel estimates were
captured and averaged for each subcarrier, so as to get the channel
response between each receiver-transmitter pair. Based on these
estimated channels for each of the positions, the sum network
capacity was calculated as discussed above. In this way, 240
samples were acquired (6 network topologies with 40 samples each)
of sum network capacities per subcarrier for each of the employed
antennas and each configuration selection scheme. The response at
each subcarrier was treated as an independent narrow band channel
and for each location, the sum network capacity was averaged over
these 52 subcarriers.
[0066] The acquired channels were normalized with a common
parameter, so that
max l , t .di-elect cons. L rc , tc E ( s = 1 52 H l rc , l tc s F
2 ) = 4 .smallcircle. 52 , ##EQU00009##
with the expectation over the 40 positions and subcarrier index, s.
With this normalization procedure, it was possible to remove path
loss effects from the strongest channel, while maintaining the
relative strength of the channels between the different
configurations and between different receiver-transmitter pairs.
This normalization was performed on a per reconfigurable antenna
basis (i.e., one normalization parameter for the RCPA and one for
the RPDA) because of the large difference in radiation efficiency
between the two antenna architectures.
[0067] Simulation Setup
[0068] The simulated channels were acquired via numerical
computation using an electromagnetic ray tracer, FASANT. FASANT is
a deterministic ray tracing program based on geometric optics and
the uniform theory of diffraction. A 3D model of the hallway of the
3rd floor of the Bossone Research building on Drexel University
campus was simulated as the geometry input of FASANT.
[0069] The 3D radiation patterns of the three antennas presented
above were used in the ray tracing simulation both at the receiver
and at the transmitter in a 2.times.2 MIMO ad-hoc network. These
patterns were acquired by measurements in an anechoic chamber. Note
that the orientation of the reconfigurable antennas was selected
such that the maximum degree of pattern diversity between the
patterns of different antenna configurations was in the azimuthal
plane.
[0070] The simulations were conducted by transmitting a single tone
at 2:484 GHz to obtain the values of the entries of the channel
matrices, H, for all channel and interference matrices. The
extracted channel matrices were then used to calculate the sum
network capacity for each of the methods discussed above.
[0071] The simulated channels, as in the measurement case, were
normalized with a common parameter, so that
max l , t .di-elect cons. L rc , tc E { s = 1 52 H l rc , l tc s F
2 } = 4 , ##EQU00010##
with the expectation over the 40 positions. Again, like
measurements, one normalization factor was used for the RPDA and
another normalization factor was used for the RCPA.
V. RESULTS
[0072] For the following results, it was assumed that
P T .sigma. 2 = 100 ##EQU00011##
for all the nodes. The maximum number of iterations allowed for the
Distributed TXRA and DSRA techniques was 10. If convergence was
still not achieved after 10 iterations, the sum capacity achieved
at the 10.sup.th iteration was used in forming the CDFs that appear
below. However, when the Distributed TXRA and DSRA techniques did
not converge, the iteration count was not included in the
calculation of the average number of iterations discussed further
below.
[0073] Results for the Reconfigurable Circular Patch Array
[0074] 1) Sum Capacity Results: In FIGS. 6 and 7, the CDFs of the
network sum capacity using the Centralized configuration selection
methods are plotted for the measured and simulated results
respectively. The CDFs of sum capacity resulting from the
Distributed configuration selection schemes appear in FIG. 8 for
the measurement results and in FIG. 9 for the simulation results.
Both the simulation and measurement CDFs show that the increases in
sum capacity, as compared to the case where all nodes are equipped
with non-reconfigurable Mode 3 circular patch antennas, are
considerable. For easier comparison, the expected sum capacity
resulting from these CDFs along with the capacity percentage
increase of using reconfigurable antennas, are summarized in Table
III. From these tables, the measured sum capacity increases are
greater than those predicted from the simulations. In particular,
for the Centralized DSRA scheme, simulations show an increase of
around 50% when using reconfigurable antennas, whereas for the
measurements the percentage increase is around 75%. Note that both
simulations and measurements show that relatively large sum
capacity increases can be expected--the minimum increase is 8:70%
for the measured Distributed TXRA case, while for the more
appealing Distributed RXRA technique, the percentage increase is
14% for the simulations and 31% for the measurements. The trends in
selection technique performance are generally the same for both
measured and simulated results. However, in the Distributed RXRA
and TXRA techniques, the trends are reversed: in the measurements
Distributed RXRA outperforms Distributed TXRA, while in simulations
the reverse is true.
TABLE-US-00003 TABLE III RCPA MEAN SUM NETWORK CAPACITY Simulations
Mean Sum % Increase vs. Selection Technique Capacity (bps/Hz)
Non-Reconfigurable DSRA-Distributed 6.40 30.77 RXRA-Distributed
5.60 14.42 TXRA-Distributed 5.91 20.93 DSRA-Centralized 7.33 49.90
RXRA-Centralized 5.60 14.42 TXRA-Centralized 6.79 38.80
Non-Reconfigurable 4.89 0 Measurements DSRA-Distributed 6.84 35.51
RXRA-Distributed 6.60 30.81 TXRA-Distributed 5.49 8.70
DSRA-Centralized 8.87 75.68 RXRA-Centralized 6.60 30.81
TXRA-Centralized 7.83 55.11 Non-Reconfigurable 5.05 0
[0075] 2) Convergence Properties: Table V shows the average number
of iterations required before convergence for the iterative
Distributed DSRA and Distributed TXRA techniques. From the table it
can be seen that convergence is achieved quickly, even in the DSRA
case, where both transmitter and receiver were adapting their
antenna configurations. It is noted that scenarios in which there
was no convergence after 10 iterations were not included in the
average shown in Table V. However, in both measurements and
simulations more than 99% of the scenarios reached convergence
before the 10th iteration.
[0076] Results for the Reconfigurable Printed Dipole Array
[0077] 1) Sum Capacity Results: The network sum capacity CDFs for
the Centralized selection schemes when the nodes are equipped with
RPDAs appear in FIG. 10 for measurements and in FIG. 11 for
simulations. The corresponding sum capacity CDFs when the
configuration selection is performed in a Distributed manner appear
in FIG. 12 for the measurements and in FIG. 13(d) for the
simulations. In Table IV the expected sum capacities resulting from
these CDFs are gathered together with the percentage increase in
expected network sum capacity versus the non-reconfigurable case,
where all the nodes were equipped with dipoles in the S-S
configuration. As in the RCPA results, it can again be seen that
the simulations underestimated the performance increase that was
observed using the measurement results. However for the RPDA
results, the relative performance between the configuration
selection schemes is maintained between measurements and
simulations, with the Centralized DSRA technique performing the
best and the Distributed TXRA technique performing the worst of all
techniques using reconfigurable antennas. By comparing these
results with the RCPA results in the previous section, it can be
seen that in both simulations and measurements, RPDAs provide a
larger percentage increase in capacity than RCPAs. Furthermore, it
can be seen that the worst to be expected as a percentage increase
in sum capacity relative to non-reconfigurable antennas is 10% for
the simulated TXRA technique and 30% for the measured TXRA
technique. For the desirable Distributed RXRA scheme discussed
above, there is a simulated increase in capacity of 24% and an
increase of 31% in measured capacity relative to non-reconfigurable
antennas.
TABLE-US-00004 TABLE IV RCPA MEAN SUM NETWORK CAPACITY Simulations
Mean Sum % Increase vs. Selection Technique Capacity (bps/Hz)
Non-Reconfigurable DSRA-Distributed 6.83 30.40 RXRA-Distributed
6.51 24.38 TXRA-Distributed 5.78 10.31 DSRA-Centralized 7.91 51.04
RXRA-Centralized 6.51 24.38 TXRA-Centralized 6.85 30.79
Non-Reconfigurable 5.23 0 Measurements DSRA-Distributed 8.00 81.42
RXRA-Distributed 6.48 46.85 TXRA-Distributed 5.77 30.71
DSRA-Centralized 9.83 122.76 RXRA-Centralized 6.48 46.85
RXRA-Centralized 7.48 69.42 Non-Reconfigurable 4.41 0
TABLE-US-00005 TABLE V AVERAGE NUMBER OF ITERATIONS BEFORE
CONVERGENCE Selection Antenna Technique Simulations Measurements
RCPA DSRA-Distributed 2.1 1.9 RCPA TXRA-Distributed 1.7 1.2 RPDA
DSRA-Distributed 2.5 3.0 RPDA RXRA-Distributed 2.0 2.3
[0078] 2) Convergence Properties: The two iterative configuration
selection schemes using RPDAs needed on average more iterations
before convergence than the RCPA case, as shown in Table V. This
longer convergence time can be attributed to the fact that RPDAs
have more configurations to choose from than the RCPAs. The greater
number of configurations to choose from also increased the number
of scenarios in which there was no convergence after 10 iterations.
In particular, for the measurement data, in the Distributed DSRA
case, 26% of the scenarios did not converge before 10 iterations.
Similarly, in the Distributed TXRA case, 7% of the scenarios did
not converge before 10 iterations. While it would certainly have
been possible to continue the iterative process until convergence
was achieved, the inventors chose to limit the number of iterations
to 10 before stopping the configuration update process because a
practical system would not have an indefinite amount of time for
configuration selection before network information became
outdated.
[0079] Comparing RCPA with RPDA
[0080] A direct comparison of the performance of the RPDA and the
RCPA, when employed in an ad-hoc network shows that the performance
of the RPDA is higher--both in percentage increase relative to
non-reconfigurable architectures, and in absolute sum network
capacity values. The performance of a reconfigurable antenna array
should be a function of the following factors: i.) the number of
configurations available, ii.) the pattern diversity between
different configurations and, iii.) the relative efficiency between
the different configurations. While the relative radiation
efficiency between RPDA and RCPA is important, the normalization
process described above effectively sets the efficiency of RPDA
configuration S-S equal to RPCA configuration Mode 3. If this
normalization had not been performed, a direct comparison between
the two architectures would not have been possible, since RPDA
efficiency is much higher than that of the RCPA.
[0081] The superior performance of the RPDA, as compared to the
RCPA, can be explained by the fact that the RPDA has more
configurations available (4 configurations per array as opposed to
2 for the RCPA) and that its configurations are closer to each
other in terms of efficiency (i.e., RPDA efficiency varies from 84%
to 48% as opposed to the RCPA where the efficiency varies from 21%
to 5%). On the other hand, the RCPA does have an advantage in that
the radiation patterns of all available configurations show very
low correlation (Table II(C)).
[0082] Effect of the Number of Configurations
[0083] In order to better analyze the effects of the number of
available configurations, the sum network capacity was calculated
for the case where the RPDAs were only allowed to switch between
the S-S and the L-L configurations. In this case, the inventors
were able to gain insight into the importance of having a large
number of array configurations. In this situation, the RPDA has as
many configuration settings as the RCPA, but with radiation
patterns that are highly correlated (Table I(C)). Comparing Table
VI with Table IV it can be seen that the percentage capacity
increase relative to the non-reconfigurable case was almost halved
for both measurements and simulations when the RPDA was restricted
in switching only between the S-S and L-L configurations. These
results highlight the importance of having a large number of
antenna configurations to switch between, even if these
configurations have radiation patterns that are relatively highly
correlated.
TABLE-US-00006 TABLE VI MEAN NETWORK CAPACITY--RPDA RESULTS USING
SS AND LL CONFIGURATIONS Simulations Mean Sum % Increase vs.
Selection Technique Capacity (bps/Hz) Non-Reconfigurable
DSRA-Distributed 5.93 13.3 RXRA-Distributed 5.84 11.58
TXRA-Distributed 5.38 2.76 DSRA-Centralized 6.60 26.06
RXRA-Centralized. 5.84 11.58 TXRX-Centralized 6.04 15.31
Non-Reconfigurable 5.23 0 Measurements DSRA-Distributed 6.41 45.23
RXRA-Distributed 5.50 24.70 TXRA-Distributed 5.33 20.73
DSRA-Centralized 7.3 65.37 RXRA-Centralized 5.50 24.70
RXRA-Centralized 6.23 41.06 Non-Reconfigurable 4.41 0
[0084] The RCPA performs better, in absolute numbers, than the RPDA
when the RPDA is confined to using only 2 of the available
configurations. This result holds true even though the radiation
efficiency difference between S-S configuration and L-L
configuration is smaller than the radiation efficiency difference
between Modes 3 and 4 of the RCPA. This result is due to the
smaller correlation that exists between Mode 3 and 4 patterns in
the RCPA, as compared to the correlation between S-S and L-L
patterns in the RPDA. The effect of uncorrelated patterns will be
considered in more detail below.
[0085] Effect of Correlation Between the Patterns
[0086] A new normalization procedure is described below to isolate
the effect of correlation between the radiation patterns in
reconfigurable antennas. In particular, each antenna configuration
was normalized separately, so that the maximum expected squared
Frobenious norm between the channels with the same configuration
combination would be the same. Thus, there are four normalization
factors for the "reduced" RPDA discussed in the previous
sub-section (i.e., one for (S-S)-(S-S), another for (S-S)-(L-L),
etc). Similarly, there are four normalization factors for the RCPA
(i.e., one for Mode 3-Mode 3, another for Mode 3-Mode 4, etc.). In
this way, the effects of radiation efficiency were removed, forcing
all configuration combinations to "receive" the same power, while
keeping the relative channel strengths of the different links in
the topology. Mathematically, the normalization parameter for the
case where the receiver was using configuration rx and the
transmitter was using configuration tx was chosen such that:
max l , l E { H l r c , l t c F 2 } = 4 ##EQU00012##
for simulations and
max l , l E { s = 1 52 H l r c , l t c F 2 } = 4 .smallcircle. 52
##EQU00013##
for measurements, with the expectation taken along the 40
points.
[0087] The RPDA performance was again considered for the case where
only the S-S and the L-L configurations were used. In this way, the
performance of two reconfigurable antenna array structures were
compared, with each having 2 configurations available and with all
the configurations having the same radiation efficiency. The only
difference between the two structures is the correlation between
the available configurations. The RCPA structure exhibits almost
uncorrelated patterns (Table II(C)), while the RPDA configurations
are highly correlated (Table I(C)). The calculated expected sum
network capacities appear in Table VII.
TABLE-US-00007 TABLE VII MEAN SUM CAPACITY FOR PATTERNS NORMALIZED
SEPARATELY WITH RPDA USING ONLY S-S AND L-L Simulations RPDA Mean
Sum RCPA Mean Sum Selection Technique Capacity (bps/Hz) Capacity
(bps/Hz) DSRA-Distributed 6.43 7.13 RXRA-Distributed 6.01 6.07
TXRA-Distributed 5.54 5.91 DSRA-Centralized 6.85 8.05
RXRA-Centralized 6.01 6.07 TXRA-Centralized 5.97 6.84
Non-Reconfigurable 5.23 4.89 Measurements DSRA-Distributed 6.42
8.12 RXRA-Distributed 5.51 6.80 TXRA-Distributed 5.35 6.12
DSRA-Centralized 7.31 9.17 RXRA-Centralized 5.51 6.80
TXRA-Centralized 6.23 7.52 Non-Reconfigurable 4.41 5.05
[0088] From this table, it can be seen that the less correlated
patterns that the RCPA offers significantly improves the expected
sum capacity. It can also be observed that the capacity values for
the RPDA do not change much with this new normalization, unlike the
RCPA values, whose mean sum capacity values are significantly
improved by forcing both modes to receive the same power. These
results show that uncorrelated radiation patterns, as well as the
number of configurations and relative radiation efficiency, can be
a mechanism through which reconfigurable antennas enhance ad-hoc
networks.
VI. SOFTWARE IMPLEMENTATION
[0089] FIG. 14 and the following discussion are intended to provide
a brief general description of a suitable computing environment in
which the selection algorithms described above may be implemented.
Although not required, the selection algorithms above may be
implemented as computer-executable instructions, such as program
modules, that are executed by a computer, such as a client
workstation, server or personal computer, to implement methods of
selecting antenna configurations, for example. Generally,
computer-executable instructions include routines, programs,
objects, components, data structures and the like that perform
particular tasks or implement particular abstract data types.
Moreover, it should be appreciated that the invention and/or
portions thereof may be practiced with other computer system
configurations, including hand-held devices, multi-processor
systems, microprocessor-based or programmable consumer electronics,
network PCs, minicomputers, mainframe computers and the like. The
invention may also be practiced in distributed computing
environments where tasks are performed by remote processing devices
that are linked through a communications network. In a distributed
computing environment, program modules may be located in both local
and remote memory storage devices.
[0090] FIG. 14 is a block diagram representing a general purpose
computer system in which aspects of the present invention may be
incorporated. As shown, the exemplary general purpose computing
system includes a conventional personal computer 120 or the like,
including a processing unit 121, a system memory 122, and a system
bus 123 that couples various system components including the system
memory to the processing unit 121. The system bus 123 may be any of
several types of bus structures including a memory bus or memory
controller, a peripheral bus, and a local bus using any of a
variety of bus architectures. The system memory includes read-only
memory (ROM) 124 and random access memory (RAM) 125. A basic
input/output system 126 (BIOS), containing the basic routines that
help to transfer information between elements within the personal
computer 120, such as during start-up, is stored in ROM 124.
[0091] The personal computer 120 may further include a hard disk
drive 127 for reading from and writing to a hard disk (not shown),
a magnetic disk drive 128 for reading from or writing to a
removable magnetic disk 129, and an optical disk drive 130 for
reading from or writing to a removable optical disk 131 such as a
CD-ROM or other optical media. The hard disk drive 127, magnetic
disk drive 128, and optical disk drive 130 are connected to the
system bus 123 by a hard disk drive interface 132, a magnetic disk
drive interface 133, and an optical drive interface 134,
respectively. The drives and their associated computer-readable
media provide non-volatile storage of computer readable
instructions, data structures, program modules and other data for
the personal computer 120.
[0092] Although the exemplary environment described herein employs
a hard disk, a removable magnetic disk 129, and a removable optical
disk 131, it should be appreciated that other types of computer
readable media which can store data that is accessible by a
computer may also be used in the exemplary operating environment.
Such other types of media include a magnetic cassette, a flash
memory card, a digital video or versatile disk, a Bernoulli
cartridge, a random access memory (RAM), a read-only memory (ROM),
and the like.
[0093] A number of program modules may be stored on the hard disk,
magnetic disk 129, optical disk 131, ROM 124 or RAM 125, including
an operating system 135, one or more application programs 136,
other program modules 137 and program data 138. A user may enter
commands and information into the personal computer 120 through
input devices such as a keyboard 140 and pointing device 142. Other
input devices (not shown) may include a microphone, joystick, game
pad, satellite disk, scanner, or the like. These and other input
devices are often connected to the processing unit 121 through a
serial port interface 146 that is coupled to the system bus, but
may be connected by other interfaces, such as a parallel port, game
port, or universal serial bus (USB). A monitor 147 or other type of
display device is also connected to the system bus 123 via an
interface, such as a video adapter 148. In addition to the monitor
147, a personal computer typically includes other peripheral output
devices (not shown), such as speakers and printers. The exemplary
system of FIG. 14 also includes a host adapter 155, a Small
Computer System Interface (SCSI) bus 156, and an external storage
device 162 connected to the SCSI bus 156.
[0094] The personal computer 120 may operate in a networked
environment using logical connections to one or more remote
computers, such as a remote computer 149. The remote computer 149
may be another personal computer, a server, a router, a network PC,
a peer device or other common network node, and typically includes
many or all of the elements described above relative to the
personal computer 120, although only a memory storage device 150
has been illustrated in FIG. 14. The logical connections depicted
in FIG. 14 include a local area network (LAN) 151 and a wide area
network (WAN) 152. Such networking environments are commonplace in
offices, enterprise-wide computer networks, intranets, and the
Internet.
[0095] When used in a LAN networking environment, the personal
computer 120 is connected to the LAN 151 through a network
interface or adapter 153. When used in a WAN networking
environment, the personal computer 120 typically includes a modem
154 or other means for establishing communications over the wide
area network 152, such as the Internet. The modem 154, which may be
internal or external, is connected to the system bus 123 via the
serial port interface 146. In a networked environment, program
modules depicted relative to the personal computer 120, or portions
thereof, may be stored in the remote memory storage device. It will
be appreciated that the network connections shown are exemplary and
other means of establishing a communications link between the
computers may be used.
[0096] Computer 120 typically includes a variety of computer
readable storage media. Computer readable storage media can be any
available media that can be accessed by computer 120 and includes
both volatile and nonvolatile media, removable and non-removable
media. By way of example, and not limitation, computer readable
media may comprise computer storage media including both volatile
and nonvolatile, removable and non-removable media implemented in
any method or technology for storage of information such as
computer readable instructions, data structures, program modules or
other data. Computer storage media include, but are not limited to,
RAM, ROM, EEPROM, flash memory or other memory technology, CDROM,
digital versatile disks (DVD) or other optical disk storage,
magnetic cassettes, magnetic tape, magnetic disk storage or other
magnetic storage devices, or any other medium which can be used to
store the desired information and which can be accessed by computer
120. Combinations of any of the above should also be included
within the scope of computer readable media that may be used to
store source code for implementing the selection algorithms
described above when such source code is executed by a
processor.
[0097] The invention is not intended to be limited to the
variations and examples specifically mentioned, and accordingly
reference should be made to the appended claims to assess the
spirit and scope of the invention in which exclusive rights are
claimed.
VII. CONCLUSIONS
[0098] The performance of two different reconfigurable antenna
structures have been described when employed in a MIMO/MISO/SIMO
ad-hoc network. The cases where reconfigurable antennas are
employed at both link ends, as well as at either the receiver or
transmitter have been described and the performance of these cases
has been quantified with both a Centralized and Distributed
configuration selection scheme. For all of the investigated
techniques, the great capacity increases that can be expected by
using reconfigurable antennas in a MIMO/MISO/SIMO ad-hoc network
have been quantified. Insight into the design of reconfigurable
antenna arrays has been provided by quantifying the effects of the
number of configurations available, the correlation between
different configurations, as well as the effect of radiation
efficiency differences between the different configurations. The
Distributed technique in which only the receiver is allowed to
switch configurations (i.e., RXRA) has been shown to strike a good
balance between sum network capacity increases and practical
channel feedback and network information constraints.
* * * * *