The role outdoor antennas play in MIMO links

Session One: The role antennas play in a MIMO link
Africa Radio Comms Conference Johannesburg 2014
www.poynting.co.za
1
Session One
The role antennas play in a MIMO link
Dr Andre Fourie
CEO, Poynting Antennas
Abstract (All headings - Arial 14, BOLD)
MIMO, in conjunction with SDMA, is a technology that is used in 4G networks
to increase the data throughput of a wireless network. The antennas used in
the link have a direct correlation with the performance of a MIMO link. The
antenna attributes that play the dominant performance enhancing role in MIMO
links are the radiation pattern and the polarization.
The nature of the indoor and outdoor channels is discussed and it is shown that
a MIMO link performs far better in outdoor channels; hence the use of outdoor
antenna installations is emphasized.
Introduction
One of the primary drives for contemporary wireless communication systems is
to increase the rate of throughput. MIMO, which is used in Wi-Fi (IEEE 802.11),
WiMAX (IEEE 802.16e) and 3GPP LTE, is one of the techniques used to
achieve this aim.
This tutorial describes how MIMO (in conjunction with SDMA, spacial division
multiplexing) works and the importance antennas play in enabling the
technology.
The attributes of an antenna that contribute directly to the performance of a
MIMO channel include the radiation pattern and its polarization properties.
These antenna parameters are introduced and discussed.
The properties of the channel determine the efficacy of the MIMO link. Various
possible MIMO channels are identified such as cluttered outdoor channels and
channels that terminate indoors. It is shown that channels that terminate
outdoors are far more data-throughput friendly than indoor channels and hence
the use of outdoor antennas (where possible) is stressed.
Antennas and channels
Antennas play a pivotal role in a MIMO link. The two most important
characteristics of an antenna (as far as MIMO is concerned) are the radiation
patterns and its polarization. These characteristics will be discussed in the
following sections.
Radiation patterns
From a transmission point of view, the radiation pattern of an antenna is a
graphical representation of how energy that is fed into the antenna is radiated
into space.
An example of a radiation pattern is given in Figure 1.

www.poynting.co.za
2
Figure 1: Example of a radiation pattern
The radiation pattern of antenna is the same for both reception and
transmission. When an antenna is used for reception, the radiation pattern can
be interpreted as the antennas ability to receive a radio signal from various
directions.
Polarisation
The polarisation of an antenna is defined in terms of the orientation that an
antenna radiates or receives an electric field (as opposed to the magnetic field).
This orientation is often referred to with respect to the earth.
For example, an antenna that is susceptible to electric fields that are vertically
oriented with respect to the earth is considered to be vertically polarised.
Rotate that antenna by 90° about the axis that it radiates and that same
antenna will then be horizontally polarised. In such an orientation it will no
longer receive vertically polarised electric fields. Typically, an antenna that is
mounted perpendicular to the orientation of the electric field will have a gain
about 20dB below that when the antenna is in the same orientation as the
electric field.
This property of an antenna is exploited by the MIMO technology to separate
two streams of data that are modulated onto radio waves at the same
frequency.
An electromagnetic wave can also be circularly polarised. In this case, the
electric field rotates about the axis of propagation. So, rather than being in a
fixed orientation with respect to the earth, the orientation of a circularly
polarised electric field is continuously changing. If a linearly polarised antenna
is used to receive a circularly polarised signal, the effective gain of the antenna
will be half that compared to when it is receiving a linearly polarised signal.
Expressed in decibels, the effective gain would be 3dB lower than the linear
gain.
Channels
In the communication literature, reference is often made of the concept of a
channel. A channel can be considered to be the path between a transmitter and
a receiver for a given frequency range on which data is modulated (including
the antennas at either end of the link).

www.poynting.co.za
3
An example of a channel is the free space (unobstructed channel) shown in
Figure 2.
Figure 2: The free space channel
An electromagnetic wave is generated at the transmitter and propagates
unimpeded through space to the receiver.
A more complicated channel could involve an object from which there is a
reflection.
Figure 3: A channel with a single reflection
An urban channel has multiple objects and hence many possible reflections.

www.poynting.co.za
4
Figure 4: An urban channel
Indoor environments generate channels with even more reflections because of
the close proximity of the walls, roof and floor.
The properties of the channel have a marked impact of their ability to be used
to carry data. Figure 5 graphs the signal-to-noise ratio (x-axis) required to
obtain a given quality communications channel (y-axis). For example, if an error
rate of 1 in 10000 bits is considered acceptable, then the signal-to-noise ratio
for an outdoor environment would be about 8dB whist for an indoor
environment it would be about 34dB. So the signal strength would have to be
400 times stronger (26dB) inside compared to outside to achieve a link with the
same performance.
Figure 5: Illustrating the bit error rate versus signal-to-noise ratio for an outdoor
environment (blue) and indoor environment (red)
The outdoor environment is far more forgiving. The figure illustrates a case for
using an externally mounted antenna rather than an indoor antenna when
connecting to a wireless service provider.

www.poynting.co.za
5
MIMO (multiple input – multiple output)
MIMO is an acronym that stands for multiple input – multiple output. It is a term
used to describe communications links where multiple transmitters and multiple
receivers are used at each end of a link.
The multiple transmitters and receivers can be used in a number of ways to
either improve the reliability of the link or to increase the data rate through the
link, or both.
This tutorial is going to concentrate on increasing the data rate through a
channel using a technique called SDMA (spacial division multiplexing). Often
SDMA is defined as spacial division multiple access; however multiplexing is, in
my opinion, a better description of the process.
SDMA is a technique which attempts to send multiple streams of data over a
link using the same frequency resource. To see how this could be possible,
consider the 2x2 MIMO link in Figure 6.
Figure 6: A contrived 2x2 MIMO link
Transmitter 1 makes use of an object to reflect a signal such that it is received
by receiver 1. Similarly, transmitter 2 makes use of another object to bounce a
signal to receiver 2. Both transmitter 1 and 2 can use the same frequency
spectrum. This illustrates that it is in fact possible to send two streams of data
using the same frequency band to a receiver (made up of two receiving radios),
albeit in a contrived scenario.
The scenario in Figure 6 made use of the environment to “create” two
uncorrelated (un-related) paths between the receiver and transmitter. The
transmitter and receiver are each made up of two radios which are linked by a
controller which does the required digital processing (see Figure 8).
Another method of creating two independent paths is to make use of two
differently polarised antennas on each end of the link. In Figure 7, the antenna
connected to receiver 2 is vertically polarised and the antenna connected to
receiver 1 is horizontally polarised.

www.poynting.co.za
6
Figure 7: A link with cross-polarised antennas at each end
The vertically polarised antenna is practically immune to horizontally polarised
waves and visa-versa. Thus one stream of data can be transmitted on one
polarisation and another stream on the other polarisation.
The examples considered so far are called 2x2 MIMO systems because they
make use of two transmitters and two receivers. In general, any combination of
receivers and transmitters can be used in a MIMO link; LTE release 10
supports 4x4 MIMO an 8x6 MIMO link (or any other combination) is also
possible. In this tutorial only 2x2 MIMO links will be considered.
Other acronyms similar to MIMO that are used in the literature include SISO
(single input- single output), SIMO (single input – multiple output) and MISO
(multiple input – single output).
How MIMO works
The MIMO link with cross-polarised antennas is one of the techniques used by
operators to implement a MIMO connection; however, is cannot be guaranteed
that the antenna that is supposed to be immune to one of the data streams
does not receive it to some extent. In general both receive antennas will be
exposed to both streams of data.

www.poynting.co.za
7
Figure 8: Illustrating the fact that both receive antennas are exposed to both data
streams
Receiver 1 receives a signal 𝑟1which is made up of a linear combination of 𝑠1
and 𝑠2, say 𝑟1 = 𝑎𝑠1 + 𝑏𝑠2.
Similarly receiver 2 receives a signal 𝑟2 = 𝑐𝑠2 + 𝑑𝑠2. Where (𝑎, 𝑏, 𝑐, 𝑑) are
complex numbers.
So, at the receiver, we have the following data:
𝑟1 = 𝑎𝑠1 + 𝑏𝑠2
𝑟2 = 𝑐𝑠2 + 𝑑𝑠2
or, in matrix form
[
𝑟1
𝑟2
] = [
𝑎 𝑏
𝑐 𝑑
] [
𝑠1
𝑠2
]
Solving for 𝑠1 and 𝑠2
[
𝑠1
𝑠2
] = [
𝑎 𝑏
𝑐 𝑑
]
−1
[
𝑟1
𝑟2
]
Now, if we know (𝑎, 𝑏, 𝑐, 𝑑), then 𝑠1 and 𝑠2 can be found.
[
𝑎 𝑏
𝑐 𝑑
] is a matrix whose entries depend only on the channel. The channel is
made up of the transmit antennas, the region between the antennas (including
buildings, cars etc.) and the receive antennas.
It is important to understand that the antennas on both sides on the link are an
integral part of the channel; in fact, changing the antennas changes the
characteristics of the link.
In order to estimate the parameters (𝑎, 𝑏, 𝑐, 𝑑) that define the channel, the base
station sends out known pilot (or training) sequences.
In its simplest for, this process can be viewed as follows:
𝑟1 = 𝑎𝑠1 + 𝑏𝑠2.
𝑟2 = 𝑐𝑠2 + 𝑑𝑠2.
𝑠1 𝑠2

www.poynting.co.za
8
Figure 9: Illustrating the transmission of a pilot signal from transmitter 1
Transmitter 1 sends out a pilot signal 𝑡1 which is known to both the transmitters
and receivers. Both receivers receive this known data and can deduce how the
signal was changed over the channel. In this manner the parameters (𝑎, 𝑏) can
be found:
𝑎 =
𝑟1
𝑡1
𝑏 =
𝑟2
𝑡1
Similarly, the channel coefficients (𝑐, 𝑑) can be deduced by sending out a pilot
signal from transmitter 2.
Figure 10: Illustrating the transmission of a pilot signal from transmitter 2
Given this data, the signals 𝑠1 and 𝑠2 can be found from the received data 𝑟1
and 𝑟2 by solving the equation:
[
𝑠1
𝑠2
] = [
𝑎 𝑏
𝑐 𝑑
]
−1
[
𝑟1
𝑟2
]
𝑡1
𝑟1 = 𝑎𝑡1
𝑟2 = 𝑏𝑡1
𝑡2
𝑟1 = 𝑐𝑡2
𝑟2 = 𝑑𝑡2

www.poynting.co.za
9
These coefficients can be used to determine the transmitted signals as long as
the channel does not change too much between the event of measuring the
channel and sending the data.
Earlier it was mentioned that the outdoor environment was far more data-
throughput friendly that the indoor environment. One of the reasons is that the
indoor environment changes very rapidly with time whereas the outdoor
environment is more stable. This is another motivating factor for using outdoor
antennas for wireless links.
The above procedure roughly describes the manner in which the MIMO
technology is able to send multiple streams of data over a given frequency
band at the same time.
There are, however, circumstances where this technique fails. One example is
where both receivers receive the same combination of 𝑠1and 𝑠2.
Figure 11: Illustrating the reception of two copies of the same data
𝑟1 = 𝑎𝑠1 + 𝑏𝑠2
𝑟2 = 𝑎𝑠2 + 𝑏𝑠2
In this event, the controller at the receiver end of the link has two copies of the
same data and there is no way of solving for 𝑠1and 𝑠2. This is a situation where
the two channels are poorly de-correlated and poorly de-correlated signals are
bad for MIMO.
Testing the MIMO concept
Practical tests have been conducted to substantiate the claim that outdoor
antennas result in far better performing wireless links than indoor antennas and
that good de-correlation is essential to get the most out of a MIMO link. These
tests are reported in this section.
The first test involved comparing the performance of various LTE modems
when connected to internal antennas, a single outdoor antenna and two
outdoor antennas.
𝑟1 = 𝑎𝑠1 + 𝑏𝑠2
𝑟2 = 𝑎𝑠1 + 𝑏𝑠2
𝑠1
𝑠2

www.poynting.co.za
10
Consider the case of the internal antennas being substituted with a single
outdoor antenna. The download speedup of between 2.5 and 3.5 times is due
to the fact that the signal quality is better and hence a more efficient modulation
scheme is used.
The almost doubling of the downlink speed through the use of two external
antennas rather than just one is due to the action of MIMO.
Another test investigated the effect of using two omni-directional antennas
compared to the use of two directional external antennas. Both external
antenna configurations far out perform the internal antennas.
A test devised to illustrate the importance of having well de-correlated antennas
involved making use of two vertically polarised to connect to an LTE base
station. The two antennas were incrementally spaced apart in order to increase
the de-correlation between them. At each separation, speed tests were done to
assess the link improvement.

www.poynting.co.za
11
Figure 12: The setup used to test the requirement for good de-correlation between
antennas
A figure of merit defining the de-correlation between the antennas was
computed from the radiation patterns of the two antennas (see appendix 1 for
details). The results of this calculation are shown in Figure 13.
Figure 13: The computed de-correlation between the antennas (0 indicates good de-
correlation and 1 indicates poor de-correlation).

www.poynting.co.za
12
Each line in the graph indicates the de-correlation between antennas for a
given antenna separation (varying from 10mm to 100mm). The red vertical line
indicates the frequency of the LTE signal and the red dots on this line show the
MIMO speedup. The MIMO speedup shows the speed improvement when
using two antennas compared to using a single antenna (in other words, a
measure of the effect of using MIMO).
So, when the antennas were spaced 10mm apart, it made little difference
whether one or two antennas were used – using two antennas resulted in
download speeds that were 1.04 times faster than using a single antenna.
As the antennas were spaced further apart, so the de-correlation improved and
also the speedup.
It is seen that no improvement was made once the de-correlation of 0.5 was
reached.
Conclusion
MIMO incorporating SDMA is a technology that is used in LTE, WiMax and Wi-
Fi. A brief description of how SDMA with works with MIMO was given.
It was emphasised that making use of external antennas, even in a non-MIMO
technology (such as 3G), makes a massive difference to the data throughput. If
MIMO is used and the two antennas are well de-correlated then the data
throughput can be doubled (when compared to using a single external
antenna).

www.poynting.co.za
13
Appendix 1: PREDICTING THE LTE PERFORMANCE OF AN ANTENNA BY
MEANS OF RADIATION PATTERN ANALYSIS
Introduction
The performance of a MIMO system is dependent on the propagation
characteristics of the environment and the characteristics of the antennas. The
environment could vary between an indoor scenario where the angular spread
of scattered field is large, to an outdoor uncluttered environment where the
angular spread is more confined. In both cases the ideal antenna (for good
diversity performance) should have radiation patterns with low correlation over
the possible angles of arrival of multipath components.
The envelope correlation between two radiation patterns 𝐹1(𝐸 𝜃, 𝐸 𝜙) and
𝐹2(𝐸 𝜃, 𝐸 𝜙) is given by:
𝜌 𝑒 =
[∫ (
𝑋
1 + 𝑋
𝐸1𝜃 𝐸2𝜃
∗
𝑃𝜃 +
1
1 + 𝑋
𝐸1𝜙 𝐸2𝜙
∗
𝑃 𝜙) 𝑑ΩΩ
]
2
∫ (
𝑋
1 + 𝑋
𝐸1𝜃 𝐸1𝜃
∗
𝑃𝜃 +
1
1 + 𝑋
𝐸1𝜙 𝐸1𝜙
∗
𝑃 𝜙) 𝑑ΩΩ
× ∫ (
𝑋
1 + 𝑋
𝐸2𝜃 𝐸2𝜃
∗
𝑃𝜃 +
1
1 + 𝑋
𝐸2𝜙 𝐸2𝜙
∗
𝑃 𝜙) 𝑑ΩΩ
Where:
Ω(𝜃, 𝜙) represents the spatial angle
E1θ, E2θ, E1ϕ, E2ϕare the complex envelopes of the components of the
field patterns for each port of the antenna
𝑃𝜃, 𝑃 𝜙 are the probability distributions of the power incident on the
antenna in the two polarisations.
𝑋 is the cross polarisation power ratio, which is defined as the mean
received power in the vertical to the horizontal polarisation.
In an indoor environment there are many objects from which the signal may
scatter; hence the signals impinge upon the antenna isotropically. In such a
scenario, Pθ and Pϕ are equal to 1
4𝜋⁄ indicating that there is an equal probability
of a signal arriving from any angle (when compared to any other angle).
In an outdoor environment the range of angles from which a signal is likely to
come is limited to the antenna azimuth plane over a smallish range of elevation
angles. In this case suitable functions for Pθ and Pϕ have to be chosen to
represent such a distribution. Knudsen [2] found that an elliptical distribution
function for Pθ and Pϕ fits experimental data reasonably well.
Vaughan [ 1] has derived a rule-of-thumb that states that good diversity
operation is possible when the envelope correlation of the patterns of an
antenna is less than 0.5.
Computing the envelope correlation for a prospective LTE antenna will enable
a figure of merit to be assigned to the antenna indicating its efficacy in an LTE
link.
Canonical case studies
Matlab code was written to evaluate the expression for the radiation pattern
envelope correlation. In order to ensure that the function was correctly coded
canonical studies taken from the literature were repeated.

www.poynting.co.za
14
First, the envelope correlation was computed for two uncoupled half-wave
dipoles as the separation distance between them was increased.
Figure 14: Illustrating the geometry of the first canonical problem (taken from [ 3])
Clarke [ 4] showed that the theoretical envelope correlation between two half-
wave dipoles, which are parallel, z-oriented and horizontally separated by a
distance, d, is given by:
𝜌𝑐 = [𝐽0 (
2𝜋𝑑
𝜆
)]
2
This expression assumes that the dipoles are uncoupled and that the incident
field is uniformly distributed about the azimuth of the antennas.
Khaleghi [ 3] computed the envelope correlation for the same geometry, also
assuming uncoupled dipoles, but assuming that the incident field was uniformly
distributed in all directions.
The published results are shown in Figure 15.

www.poynting.co.za
15
Figure 15: Illustrating the published results for the envelope correlation giving both the
Clarke function and the second case mentioned above
SuperNEC was used to compute the uncoupled radiation patterns of such
geometry and the patterns were fed into the envelope correlation function. Two
incident field distributions were considered, namely, uniform distribution about
the azimuth (corresponding to the Clarke function) and uniform distribution from
all angles (corresponding to Khaleghi’s computation, red curve in Figure 15).
There is good agreement between the two sets of curves.
Figure 16: Using the Matlab function to compute the envelope correlation
The second canonical study involved the same geometry, but this time the
coupling between the dipoles was taken into consideration.
Khaleghi’s [ 3] computed result is shown by the dotted blue curve in Figure 17.

www.poynting.co.za
16
Figure 17: The dotted blue line give the envelope correlation between two dipoles when
including mutual coupling
The blue curve in Figure 18 shows the corresponding curve computed using
the Matlab function and SuperNEC.
Figure 18: The solid blue curve represents the envelope correlation between two
coupled dipoles
Again, excellent agreement is found between the two curves. This small study
shows an interesting result. Half-wave dipoles spaced a tenth of a wave-length
apart has a low envelope correlation. This is due to the ‘beneficial’ coupling
between the elements. As always, one never gets a benefit without some
disadvantage. The low correlation is traded off by a decrease in the antenna

www.poynting.co.za
17
radiation efficiency as power transmitted from one antenna is absorbed by the
other!
Illustrating the importance of low envelope correlation
It was mentioned in the introduction that Vaughan [ 1] derived a rule-of-thumb
that states that good diversity operation (and hence good LTE performance) is
possible when the envelope correlation of the patterns of an antenna is less
than 0.5. In order to investigate this statement an experiment was conducted
using an adjustable antenna and Vodacom’s LTE service.
Figure 19: Illustrating the experimental antenna (left), its envelope correlation as a
function of antenna spacing and the download speed improvement.
The adjustable antenna is shown on the left-hand side of Figure 19. It consists
of two vertically polarised 8 dBi patches that operated from 1700-2000 MHz.
The distance between the two patches can be varied thereby varying the
envelope correlation of the two antennas. The antenna spacing was adjusted
such that the distance between the nearest edges of the antennas varied from
10mm to 100mm in 10mm increments. For each increment, the envelope
correlation was computed. These envelope correlation figures are shown in the
graph on the right-hand side of Figure 19.
The frequency band of the Vodacom LTE service lies between 1861.3-
1867.3 MHz. This frequency band is illustrated by the vertical red line in Figure
19. The LTE performance was measured at 4 distinct antenna spacing, vis., 10,
25, 50 and 100mm. These points are marked as red circles on the vertical red
line.
At each of these four points, 10 download speed readings were taken with both
antennas connected to the LTE radio and 10 download speed readings were
taken with only one of the two antennas connected (the other was open
circuited). The download speeds for the two antenna scenarios were averaged
and the ratio of the two averages computed. This figure gives a relative speed
increase when using two antennas (making full use of LTE) compared to using
a single antenna (where diversity cannot be used). For a two antenna system,
the maximum speed up possible is 2 (assuming the signal strength (and hence
modulation scheme) is similar for both antenna scenarios). The speed-up
figures are shown to the left of the blue circles.
The following observations can be deduced from this experiment:

www.poynting.co.za
18
Envelope
correlation
Speed-
up
Comment
0.67 1.04 The patterns of the two antennas are so well
correlated that LTE hardly gives any improvement in
performance
0.48 1.47 The patterns have some de-correlation and a 50%
improvement in performance is recorded.
0.40 1.91 Here the LTE performance is close to the theoretical
maximum performance that one can expect. This
performance corresponds to an envelope correlation
of 0.4 which agrees reasonably with rule-of-thumb
given by Vaughan.
0.11 1.9 No additional improvement in LTE performance was
achieved with an envelope correlation of 0.11.
Table 1: Summarising the results of the adjustable antenna experiment
Envelope correlation of the Poynting products
The envelope correlation function was computed for various cross-polarised
MIMO antennas manufactured by Poynting; namely the, XPOL-A0001, XPOL-
A0002 and XPOL-A0004 antennas. In addition, two LPDA-A0092 antennas
were combined to form a dual polarised highly directional antenna. In each
graph the ‘rule-of-thumb’ line for good diversity performance is depicted (if the
correlation is below this line, then good diversity performance can be
expected).
XPOL-A0001 is an antenna that consists of two broadband crossed dipoles and
has a gain of about 2dBi. The envelope correlation for the two ports of this
antenna is shown in Figure 20.
Figure 20: Envelope correlation for XPOL-A0001

www.poynting.co.za
19
XPOL-A0002 is a triplexed set of dual polarised patch antennas. The gain of
the antenna is about 8 dBi. Figure 21 shows the envelope correlation which is
extremely low over all 3 frequency bands.
XPOL-A0004 is also a pair of crossed dipoles; however this antenna has been
designed to have a VSWR of better than 1.5:1 across its operating bands and
hence the dipoles are of a different construction compared to those of XPOL-
A0001. The patterns of the XPOL-A0004 dipoles are not quite as well
controlled as those of XPOL-A0001 (primarily because of the large size of the
XPOL-A0004 dipoles) and this difference is evident in the envelope correlation.
Clearly; however, the antenna will still give good diversity performance.
The LPDA-A0092 is a high gain (11 dBi), very wide band log periodic dipole
array. Two of these antennas were used to create a dual polarised antenna by
vertically spacing one antenna 0.5m above; both antennas in different

www.poynting.co.za
20
polarisations. The envelope correlation of such an antenna is extremely low as
can be seen in Figure 23. Note the scale on the graph; the vertical axis goes
from 0 to 0.001: the perfect antenna combination for a MIMO application.
Figure 23: Envelope correlation for two, oppositely polarised LPDA-A0092 antennas
(NOTE THE SCALE!)
Conclusion
Vaughan [ 1] gave a rule-of-thumb stating that if the pattern envelope
correlation of a pair of antennas is lower than 0.5, then reasonable diversity
performance can be expected.
This figure was verified by conducting an experiment where the LTE
performance as a function of envelope correlation was measured. This
experiment showed that a pair of antennas with an envelope correlation of
between 0.4 and 0.48 gives an LTE performance close to the maximum
performance expected; thus verifying Vaughan’s rule-of-thumb.
The envelope correlation for the Poynting range of antennas was computed
and all antennas have an envelope correlation well below the required 0.5.
The Poynting’s antennas are therefore the ideal antennas for any LTE
application.
References
[ 1] Vaughan, R,. “Spaced directive antennas for mobile communications by the Fourier
transform method”, IEEE Trans. On Antennas and Propagation, Vol. 48, Issue 7,
pp. 1025-1032, July 2000.
[ 2] Knudsen, M., “Antenna system for handsets”, ATV-industrial PhD projects EF-755,
Aalborg university, 2001

www.poynting.co.za
21
[ 3] Khaleghi, A., “Diversity techniques with parallel dipole antennas: radiation pattern
analysis”, Progress in electromagnetic research, PIER 64, 23-42, 2006
[ 4] Clarke, R., “A statistical theory of mobile radio reception”, Bell Syst. Tech. J., Vol.,
47, pp., 957-1000, 1969

The role outdoor antennas play in MIMO links

Recomendados

Recomendados

Más contenido relacionado

La actualidad más candente

La actualidad más candente (20)

Similar a The role outdoor antennas play in MIMO links

Similar a The role outdoor antennas play in MIMO links (20)

Más de Andre Fourie

Más de Andre Fourie (15)

Último

Último (20)

The role outdoor antennas play in MIMO links