EE 589
Project Report
SMART ANTENNA SYSTEMS
by Çiğdem Aksu- 2007706060
submitted to Prof. Dr. Emin Anarım
29.12.2008
Introduction:
Smart antennas are considered to be promising technology for increasing the performance of
wireless communication systems. A smart antenna consists of several antenna elements, whose
signals are processed adaptively in order to exploit the spatial domain of the mobile radio channel
[1]. Usually, the signals received at the different antenna elements are multiplied with complex
weights w, and then summed up; the weights are chosen adaptively. Not the antenna itself, but
the whole antenna system including the signal processing is called "adaptive" [2]. Only the
antenna is not smart, the antenna system which contains also antenna elements is called smart.
Early smart antennas were designed for governmental use in military applications, which used
directed beams to hide transmissions from an enemy. Implementation required very large antenna
structures and time-intensive processing and calculation. Today, smart antennas have been widely
deployed in many of the top wireless networks worldwide to address wireless network capacity
and performance challenges [3]. Smart antennas can be used to achieve different benefits. The
most important is higher network capacity, i.e. the ability to serve more users per base station,
thus increasing revenues of network operators, and giving customers less probability of blocked
or dropped calls. Also, the transmission quality can be improved by increasing desired signal
power and reducing interference [4].
The following report is an introduction to the essential concepts of smart antenna systems and the
important advantages of smart antenna system design over conventional omnidirectional
approaches. The discussion also differentiates between the various and often dissimilar
technologies broadly characterized today as smart antennas. These range from simple diversity
antennas to fully adaptive antenna array systems.
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1. ANTENNAS AND ANTENNA SYSTEMS [5]
Antennas
Radio antennas couple electromagnetic energy from one medium (space) to another (e.g., wire,
coaxial cable, or waveguide). Physical designs can vary greatly.
Omnidirectional Antennas
Since the early days of wireless communications, there has been the simple dipole antenna, which
radiates and receives equally well in all directions. To find its users, this single-element design
broadcasts omnidirectionally in a pattern resembling ripples radiating outward in a pool of water.
While adequate for simple RF environments where no specific knowledge of the users'
whereabouts is available, this unfocused approach scatters signals, reaching desired users with
only a small percentage of the overall energy sent out into the environment.
Figure 1.1: Omnidirectional Antenna and Coverage Patterns
Given this limitation, omnidirectional strategies attempt to overcome environmental challenges
by simply boosting the power level of the signals broadcast. In a setting of numerous users (and
interferers), this makes a bad situation worse in that the signals that miss the intended user
become interference for those in the same or adjoining cells.
In uplink applications (user to base station), omnidirectional antennas offer no preferential gain
for the signals of served users. In other words, users have to shout over competing signal energy.
Also, this single-element approach cannot selectively reject signals interfering with those of
served users and has no spatial multipath mitigation or equalization capabilities.
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Omnidirectional strategies directly and adversely impact spectral efficiency, limiting frequency
reuse. These limitations force system designers and network planners to devise increasingly
sophisticated and costly remedies. In recent years, the limitations of broadcast antenna
technology on the quality, capacity, and coverage of wireless systems have prompted an
evolution in the fundamental design and role of the antenna in a wireless system.
Directional Antennas
A single antenna can also be constructed to have certain fixed preferential transmission and
reception directions. As an alternative to the brute force method of adding new transmitter sites,
many conventional antenna towers today split, or sectorize cells. A 360° area is often split into
three 120° subdivisions, each of which is covered by a slightly less broadcast method of
transmission. All else being equal, sector antennas provide increased gain over a restricted range
of azimuths as compared to an omnidirectional antenna. This is commonly referred to as antenna
element gain and should not be confused with the processing gains associated with smart antenna
systems. While sectorized antennas multiply the use of channels, they do not overcome the major
disadvantages of standard omnidirectional antenna broadcast such as cochannel interference.
Figure1.2: Directional Antenna and Coverage Pattern
Antenna Systems
How can an antenna be made more intelligent? First, its physical design can be modified by
adding more elements. Second, the antenna can become an antenna system that can be designed
to shift signals before transmission at each of the successive elements so that the antenna has a
composite effect. This basic hardware and software concept is known as the phased array
antenna. The following summarizes antenna developments in order of increasing benefits and
intelligence.
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1-Sectorized Systems
Sectorized antenna systems take a traditional cellular area and subdivide it into sectors that are
covered using directional antennas looking out from the same base station location.
Operationally, each sector is treated as a different cell, the range of which is greater than in the
omnidirectional case. Sector antennas increase the possible reuse of a frequency channel in such
cellular systems by reducing potential interference across the original cell, and they are widely
used for this purpose. As many as six sectors per cell have been used in practical service. When
combining more than one of these directional antennas, the base station can cover all directions.
Figure 3. Sectorized Antenna and Coverage Patterns
2-Diversity Systems
In the next step toward smart antennas, the diversity system incorporates two antenna elements at
the base station, the slight physical separation (space diversity) of which has been used
historically to improve reception by counteracting the negative effects of multipath.
Diversity offers an improvement in the effective strength of the received signal by using one of
the following two methods:
• switched diversity: Assuming that at least one antenna will be in a favorable location at
a given moment, this system continually switches between antennas (connects each of the
receiving channels to the best serving antenna) so as always to use the element with the
largest output. While reducing the negative effects of signal fading, they do not increase
gain since only one antenna is used at a time.
• diversity combining: This approach corrects the phase error in two multipath signals
and effectively combines the power of both signals to produce gain. Other diversity
systems, such as maximal ratio combining systems, combine the outputs of all the
antennas to maximize the ratio of combined received signal energy to noise.
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Because macrocell type base stations historically put out far more power on the downlink (base
station to user) than mobile terminals can generate on the reverse path, most diversity antenna
systems have evolved only to perform in uplink (user to base station).
Figure 4. Switched Diversity Coverage with Fading and
Switched Diversity
Figure 5. Combined Diversity Effective Coverage Pattern with
Single Element and Combined Diversity
Diversity antennas merely switch operation from one working element to another. Although this
approach mitigates severe multipath fading, its use of one element at a time offers no uplink gain
improvement over any other single element approach. In high-interference environments, the
simple strategy of locking onto the strongest signal or extracting maximum signal power from the
antennas is clearly inappropriate and can result in crystal-clear reception of an interferer rather
than the desired signal. The need to transmit to numerous users more efficiently without
compounding the interference problem led to the next step of the evolution antenna systems that
intelligently integrate the simultaneous operation of diversity antenna elements.
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2. WHAT IS A SMART ANTENNA?
A smart antenna system is defined by the IEEE as, an antenna system that has circuit elements
associated with its radiating elements such that one or more of the antenna properties are
controlled by the received signal. [6]
Generally co-located with a base station, a smart antenna system combines an antenna array with
a digital signal processing capability to transmit and receive in an adaptive, spatially sensitive
manner. In other words, such a system can automatically change the directionality of its patterns
in response to its signal environment. [5]
Figure 2.2: A beam-forming smart-antennas system [7]
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3. CLASSIFICATION OF SMART ANTENNA SYSTEMS
Figure 3.1: Classification of Smart Antenna Systems [8]
There are basically two types of smart antennas: Switched beam systems and adaptive array
systems.
3.1 Switched beam systems
BEAMFORMER
SIGNAL
BEAM
SELECT
Figure 3.2: Switched beam systems [9]
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SIGNAL
OUTPUT
Switched beam antenna systems multiple fixed beams with heightened sensitivity in particular
directions. These antenna systems detect signal strength, choose from one of several
predetermined, fixed beams, one switch from one beam to another as the mobile moves through
the sector. [5] In other words, the system scans the outputs of each beam and selects the beam
with the largest output power.
Figure 3.3 Reused Frequencies [10]
The black cells in Figure 3.3 reuse the frequencies currently assigned to the mobile, so they are
potential sources of interference. The use of a narrow beam reduces the number of interfering
sources 'seen' at the base station. As the mobile moves, the smart antenna system continuously
monitors the signal quality to determine when a particular beam should be selected.
Figure 3.4 The functional block diagram of a switched-beam antenna [11]
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Figure 3.5 Switched Beam Systems
Switched beam systems can be further divided into two groups: single beam and multi beam
directional antennas. In single beam directional antenna systems, only one beam is active at a
given time. No simultaneous transmissions are allowed, because in this system there is only one
transceiver as shown in Fig.3.5 (a). On the other hand, multiple beam directional antenna system
is an example of Spatial Division Multiple Access (SDMA) system. Here, each directional
antenna can be used and transmissions are allowed at the same time and frequency. The number
of beams is equal to the number of transceivers as shown in Fig.3.5 (b).
In a sense, a switched-beam is an extension of the conventional sector beam antenna in that it
divides a sector into several microsectors. Therefore, employing switched-beam antenna system
is the easiest to upgrade the existing systems that employ 120° sector antennas and dual diversity
per sector. However, switched-beam antennas also have drawbacks. They do not exploit
multipath. In addition, the signal power from the mobile terminal drops greatly when the mobile
terminal moves into the margin of a beam or the area between two beams. Furthermore, owing to
the inability to distinguish a desired user from interferers, switched-beam antennas are not
effective in combating against CCI (Co-channel interference). If a strong interfering signal is at
the center of a selected beam and the desired user is away from the center of that beam, the
interfering signal can be enhanced far more than the desired signal. [10]
Despite these disadvantages, switched beam systems are popular for several reasons. They
provide some of the range extension benefits obtained from more elaborate systems. Depending
on the propagation environment, switched beam systems offer some reduction in delay spread,
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which provides the capability to deploy low tier PCS systems in high-antenna height, high
subscriber speed environments. Switched beam systems require only moderate interaction with
the base station receiver, compared with adaptive antenna systems. Since this is a relatively low
technology approach, the engineering costs associated with implementing these systems may be
much lower than those associated with more complicated systems. [12]
3.2 Adaptive Array Systems
SIGNAL
SIGNAL
OUTPUT
INTERFERENCE
BEAMFORMER
WEIGHTS
INTERFERENCE
Figure 3.6 Adaptive array systems [8]
Adaptive antenna represents the most advanced antenna approach to date.
At this technique, Direction of Arrival (DoA) algorithm is used to locate the direction of the
signal received from the user. By this way, continuous tracking of users can be achieved. Also,
the detection of the interferers can be added to these systems, so that interference is cancelled by
adjusting the radiation pattern nulls to increase the Signal to Interference Ratio (SIR).
Clearly, adaptive beam forming is more complex than switched beam systems. Both systems
attempt to increase the gain according to the location of the user; however, only the adaptive
systems provides optimal gain while simultaneously identifying, tracking and minimizing
interfering signals. [5]
There are two kinds of adaptive beam forming: In single user beam forming, the antenna beam is
adjusted to track a user and cancel interferers. In this case, a single transceiver is sufficient where
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only one user is active at a given time as shown in Fig.3.7 (a). In multi user beam forming, there
are different beam patterns, and each beam tracks one user. Therefore, simultaneous
transmissions are allowed and SDMA is achieved. As shown in Fig.3.7 (b), there is more than
one transceiver-beam pair in multi user beam forming. [7]
Figure 3.7 Adaptive Array Smart Antennas [8]
Figure 3.8 Switched Beam Systems Coverage Patterns [5]
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Figure 3.9 Adaptive Array Coverage Pattern: A Representative Depiction of a Main Lobe Extending Toward a User
with a Null Directed Toward a Co-channel Interferer [5]
3.3 Relative Benefits/Tradeoffs of Switched Beam and Adaptive Array Systems
(Comparison)

Integration—Switched beam systems are traditionally designed to retrofit widely
deployed cellular systems. It has been commonly implemented as an add-on or appliqué
technology that intelligently addresses the needs of mature networks. In comparison,
adaptive array systems have been deployed with a more fully integrated approach that
offers less hardware redundancy than switched beam systems but requires new build-out.

Range/coverage—Switched beam systems can increase base station range from 20 to 200
percent over conventional sectored cells, depending on environmental circumstances and
the hardware/software used. The added coverage can save an operator substantial
infrastructure costs and means lower prices for consumers. Also, the dynamic switching
from beam to beam conserves capacity because the system does not send all signals in all
directions. In comparison, adaptive array systems can cover a broader, more uniform area
with the same power levels as a switched beam system.

Interference suppression—Switched beam antennas suppress interference arriving from
directions away from the active beam's center. Because beam patterns are fixed, however,
actual interference rejection is often the gain of the selected communication beam pattern
in the interferer's direction. Also, they are normally used only for reception because of the
system's ambiguous perception of the location of the received signal (the consequences of
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transmitting in the wrong beam being obvious). Also, because their beams are
predetermined, sensitivity can occasionally vary as the user moves through the sector.
Switched beam solutions work best in minimal to moderate co channel interference and
have difficulty in distinguishing between a desired signal and an interferer. If the
interfering signal is at approximately the center of the selected beam and the user is away
from the center of the selected beam, the interfering signal can be enhanced far more than
the desired signal. In these cases, the quality is degraded for the user.
Adaptive array technology currently offers more comprehensive interference rejection.
Also, because it transmits an infinite, rather than finite, number of combinations, its
narrower focus creates less interference to neighboring users than a switched-beam
approach.

spatial division multiple access (SDMA)—Among the most sophisticated utilizations of
smart antenna technology is SDMA, which employs advanced processing techniques to,
in effect, locate and track fixed or mobile terminals, adaptively steering transmission
signals toward users and away from interferers. This adaptive array technology achieves
superior levels of interference suppression, making possible more efficient reuse of
frequencies than the standard fixed hexagonal reuse patterns. In essence, the scheme can
adapt the frequency allocations to where the most users are located.
Figure 3.10 Fully Adaptive Spatial Processing, Supporting Two Users on the Same Conventional
Channel Simultaneously in the Same Cell [12]
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Utilizing highly sophisticated algorithms and rapid processing hardware, spatial processing takes
the reuse advantages that result from interference suppression to a new level. In essence, spatial
processing dynamically creates a different sector for each user and conducts a frequency/channel
allocation in an ongoing manner in real time.
Adaptive spatial processing integrates a higher level of measurement and analysis of the
scattering aspects of the RF environment. Whereas traditional beam-forming and beam-steering
techniques assume one correct direction of transmission toward a user, spatial processing
maximizes the use of multiple antennas to combine signals in space in a method that transcends a
one user-one beam methodology. [5]
4. THE ARCHITECTURE OF SMART ANTENNA SYSTEMS
4.1 Uplink processing (Listening to cell)
It is assumed that a smart antenna is only employed at the base station and not at the handset or
subscriber unit. Such remote radio terminals transmit using omni directional antennas, leaving it
to the base station to separate the desired signals from interference selectively.
The received signal from the spatially distributed antenna elements is multiplied by a weight, a
complex adjustment of an amplitude and a phase. These signals are combined to yield the array
output. An adaptive algorithm controls the weights according to predefined objectives. For a
switched beam system, this may be primarily maximum gain; for an adaptive array system, other
factors may receive equal consideration. These dynamic calculations enable the system to change
its radiation pattern for optimized signal reception.
4.2 Downlink Processing (Speaking to the Users)
The task of transmitting in a spatially selective manner is the major basis for differentiating
between switched beam and adaptive array systems. Switched beam systems communicate with
users by changing between preset directional patterns, largely on the basis of signal strength. In
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comparison, adaptive arrays attempt to understand the RF environment more comprehensively
and transmit more selectively.
The type of downlink processing used depends on whether the communication system uses time
division duplex (TDD), which transmits and receives on the same frequency (e.g., PHS and
DECT) or frequency division duplex (FDD), which uses separate frequencies for transmit and
receiving (e.g., GSM). In most FDD systems, the uplink and downlink fading and other
propagation characteristics may be considered independent, whereas in TDD systems the uplink
and downlink channels can be considered reciprocal. Hence, in TDD systems uplink channel
information may be used to achieve spatially selective transmission. In FDD systems, the uplink
channel information cannot be used directly and other types of downlink processing must be
considered.
5. KEY BENEFITS OF SMART ANTENNA TECHNOLOGY
5.1. Smart antennas provide enhanced coverage through range extension, hole filling, and
better building penetration
Uplink power received from a mobile unit at a base station is given by;
Pr = Pt + Gs + Gb - PL
Pr  the power received at the base station
Pt  the power transmitted by the subscriber
Gs  gain of the subscriber unit antenna
Gb  gain of the base station antenna
PL  path loss
On the uplink, if a certain received power Pr,min , is required at the base station, by increasing the
gain of the base station, Gb, the link can tolerate greater path loss, PL. We can write PL as;
PL(d )  PL(d 0 )  10 log(
d
)  X
d0
By increasing the tolerable path loss, we can increase the reception range, d, of the base station.
Since smart antennas can allow higher gain compared to conventional antennas*, smart antenna
system can provide range extension. In order to improve the range on the range on the downlink,
we can use smart antennas at the subscriber receiver or at the base station transmitter. Since smart
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antennas are not usually feasible at mobile subscriber terminals, we may consider downlink
beamforming at the base station to increase range in balanced systems. [12]
* Basic Uplink Gain Calculation
Signal s, M antennas, M receivers, with i.i.d noises ni;
SNR 
received signal
s+....+s

noise
n1 + . . . . + n M
(Ms)2
s2
Therefore uplink SNR 
M 2
M 2

=M * single antenna SNR
Adaptive antennas improve uplink SNR by factor of M! [13]
**Basic Downlink Gain Calculation
SNR 
Received Power (Adaptive Antenna) ( P/M s + ..... + P/M s)2

M
Received Power (Single Antenna)
( P s)2
Adaptive antennas improve downlink SNR by factor of M! [13]
5.2 Through range extension, initial deployment cost to install a wireless system can be
reduced
When initially deploying cellular wireless networks, systems are often designed to meet coverage
requirements. Even with only a few customers in a system, sufficient number of base stations
must be deployed to provide coverage to critical areas. As more customers are added to a cellular
network, system capacity can be increased by decreasing the coverage range of base stations and
adding new cell sites. In this latter phase, revenue from a large base of subscribers can offset the
costs of installing new base stations; however, in early deployment, to meet initial coverage
requirements, a number of base stations must be installed without the costumer revenue to
support these base stations. Smart antennas can ease this problem by allowing larger early cell
sizes. However, the additional cost of using smart antenna systems over conventional
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technologies must be taken account when calculating the economic benefit of smart antenna
systems. [12]
5.3 Smart antennas provide robustness to system perturbations and reduced sensitivity to
non-ideal behavior
Smart antennas help to isolate the uplink signals from different users, reducing the power control
requirements or mitigating the impact of imperfect power control. Smart antennas refocus
coverage patterns to deal with hot spots, areas with temporarily high subscriber densities. [12]
5.4 Link quality can be improved through multipath management
Multipath in radio channels can result fading or time dispersion. Smart antennas help to mitigate
the impact of multipath or even exploit the diversity inherent in multipath. [12]
5.5 Smart antennas can improve system capacity
Smart antennas can be used to allow the subscriber and base station to operate at the same range
as a conventional system, but at lower power. This may allow FDMA and TDMA systems to be
rechannelized to reuse frequency channels more often than systems using conventional fixed
antennas, since the carrier-to-interference ratio is much greater when smart antennas are used. In
CDMA systems, if smart antennas are used to allow subscribers to transmit less power for each
link, then the Multiple Access Interference is reduced, which increases the number of
simultaneous subscribers that can be supported in each cell. Smart antennas can also be used to
spatially separate signals, allowing different subscribers to share the same spectral resources,
provided that they are spatially-separable at the base station. This Space Division Multiple
Access (SDMA) allows multiple users to operate in the same cell, on the same frequency/time
slot provided, using the smart antenna to separate the signals. Since this approach allows more
users to be supported within a limited spectrum allocation, compared with conventional antennas,
SDMA can lead to improve capacity. [12]
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FEATURE
BENEFIT
signal gain - inputs from multiple
antennas are combined to optimize
available power
queried to
establish given level of coverage
better range/coverage - focusing
the energy sent out into the cell
increases base station range and
coverage. Lower power requirements
also enable a greater battery life and
smaller/lighter handset size.
interference rejection- antenna
pattern can be generated toward
cochannel interference sources,
improving the signal-tointerference ratio of the received
signals
increased capacity - precise control of signal nulls quality
and mitigation of interference combine to frequency reuse
reduce distance (or cluster size), improving capacity.
Certain adaptive technologies (such as space division
multiple access) support the reuse of frequencies within the
same cell
spatial diversity - composite
information from the array is
used to minimize fading and
other undesirable effects of
multipath propagation.
multipath rejection - can reduce the
effective delay spread of the channel,
allowing higher bit rates to be
supported without the use of an
equalizer
power efficiency - combines
the inputs to multiple
elements to optimize available
processing gain in the
downlink (toward the user)
reduced expense - lower amplifier
costs, power consumption, and higher
reliability will result
Table5.1 Features and Related Benefits of Smart Antennas – summary. [5]
6.RESULTS AND CONCLUSION
Summarizing, we have shown how smart antennas reduce fading and suppress interference. This
in turn allows the increase in capacity of existing or future mobile communications networks. In
TDMA/FDMA systems, we can either decrease the reuse factor with spatial filtering, or serve
several users in one cell on the same time/frequency slot. For CDMA structures, the improvement
of the SNIR directly allows the increase in the number of users in a cell.
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We then presented the different receiver structures, namely switched beam, spatial processing,
and space-time processing. The used algorithms for weight determination can be divided into
spatial-reference, temporal reference, and blind algorithms. The first use knowledge about the
geometry of the antenna array, the second use a training sequence, and the last employ
knowledge about the structural and statistical properties of the transmitted signal.
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References :
[1] Ponnekonti, S., “An Overview of Smart Antenna Technology for Heterogeneous Networks”,
IEEE Communication Surveys, 2(4): 14-23 (1999).
[2] Loadman, C., Chen, Z., Jorgensen, D. “An Overview of Adaptive Antenna Technologies for
Wireless Communications”, in: Proc. on Communication Networks and Services Research
Conference, New Brunswich, Canada. (2003).
[3] http://www.cdg.org/technology/cdma_technology/smart_antennas/index.asp
[4] Symena Software & Consulting GmbH, “Smart Antennas- A Technical Introduction”,
Vienna, Austria.
[5] http://www.iec.org/online/tutorials/acrobat/smart_ant.pdf
[6] IEEE Standard Definitions of Terms for Antennas, IEEE STD 145-1983
[7] http://www.embedded.com/columns/technicalinsights/60401726?_requestid=719985
[8]http://fens.sabanciuniv.edu/telecom/eng/software/OPNETatSabanciUniversity/OPNET_TE404
.htm
[9] Winters, J.H., 2004. Little Wireless and Smart Antennas, Intel Smart Antenna Workshop
[online], http://www.jackwinters.com/
[10] Reudink, M., Smart Antennas For Third Generation Networks, Metawave Communications
Corporation, Washington, USA, available at http://www.tdap.co.uk/uk/archive/mobile/mob
(metawave_0003).html
[11] Sun, C., Adaptive Antenna Arrays, Encyclopedia of RF and Microwave Engineering, Wiley,
available at http://www.wel.atr.jp/~sun/SmartAntennas.html#_Toc140063816
[12] Liberti, J.C., Rappaport, T.S., 1999. Smart Antennas For Wireless Communications,
Prentice Hall, New Jersey
[13] Goldburg, M., 2002. Adaptive Antennas, Spectrum Management 2002, Internet Products
Group ArrayComm, available at http://www.arraycomm.com
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