Unit-II
1. Discuss the key enabling technologies for 5G mm Wave.
mm Wave in 5G is emerging as a key technology for next-generation
in the mobile industry which significantly increasing network capacity, and
user experiences. mm Wave bands have been utilized for large bandwidth
30–300 GHz (1–10 mm wavelength) which supports Gigabit wireless
services such as ultra-high-definition TV also very high-speed internet
access. The mm-Wave suffers from more path loss compared to
microwaves i.e., due to an increase in frequency, the received power is
reduced to low. because of the rain and atmosphere, the mm-Wave signal
suffers from high absorption losses.
These are suited for line-of-sight communication and if there are
large obstacles in their path, mm waves are highly vulnerable to blockages.
To handle narrow beams effectively, mm-Wave systems contain high
directional antennas in a large number of arrays which also appropriate for
shortrange communication. 5G systems use both mm-Wave spectrum and
microwave due to limited spatial coverage of mm-Wave. Therefore, to
handle mm-Wave and microwave base stations and user equipment uses
separate signal processing components.
mm Wave signals are used in cellular access if the base stations are
densely installed which enables the highest data rates. The need for a high
cost of transmitter and receivers and very high path loss is practically
limited. In 5G, many small cells are overlaid on macrocells and each cell
contains its base station interconnecting each with fiber cable becomes
much expensive. Hence, the network can be organized with mm-Wave
which will be cost-effective, mm-Wave is used for high-speed WLAN,
WPAN indoor services in macrocells.
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2. What are the distinguishing features of the 5G mm Wave technology?
Features Description
Data rate 10 Gbps or higher.
10 subcarriers of 100 MHz each will be able
to provide 1GHz bandwidth due to carrier
Bandwidths aggregation sub 40 GHz frequency. 500
MHz to 2 GHz bandwidth can be achieved
without carrier aggregation.
Frequency The bands are split into “less than 40 GHz”
Bands and “40GHz to 100 GHz” frequency ranges.
Modulation
CP-OFDMA < 40GHz SC > 40GHz
types
Distance
2 meters (indoor) to 300 meters (outdoor).
coverage
Frame
TDD
topology
Latency About 1 ms
Massive MIMO is supported. Antennas are
MIMO type small; hence, approximately 16 antenna
arrays will be available in 1 square inch.
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3. Discuss the challenges in designing and deploying the 5G networks.
With so many options to choose from, simply deciding which fifth
generation approach to take is the first of many inherent deployment
challenges. Breakthrough 5G wireless technology platforms are pushing
the envelope of design, manufacturing, and testing capabilities. Network
Function Virtualization (NFV) is a prerequisite for core network slicing,
intelligence at the edge, and other essential 5G signal features. These
technologies power the delivery of IoT and AI based services.
Standardization, security, and the requisite CPU horsepower to drive
virtual functions are some of the many obstacles being tackled by NFV
developers.
The mm wave is another essential fifth generation ingredient that
can present technological and logistical challenges. Due to the limited
range and inability to transmit through solid objects, the sheer volume of
antennae required introduces hurdles that can only be addressed through
methodical, incremental deployment. Spectral efficiency, measured in
(bit/s)/Hz, is currently gated by the Shannon Limit which defines the
maximum rate that data can be sent over any medium with zero error. This
theoretical ceiling is much less than what is expected and required for 5G
deployment. Only Massive MIMO and beamforming, utilizing large
antenna arrays, enables 5G to effectively circumvent this natural limit of
faster speeds.
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4. What are the different formats for the basis of Massive MIMO?
There is a number of different MIMO configurations or formats that
can be used. These are termed SISO, SIMO, MISO and MIMO. These
different MIMO formats offer different advantages and disadvantages -
these can be balanced to provide the optimum solution for any given
application.The different MIMO formats - SISO, SIMO, MISO and MIMO
require different numbers of antennas as well as having different levels of
complexity. Also dependent upon the format, processing may be needed at
one end of the link or the other - this can have an impact on any decisions
made.
The different forms of antenna technology refer to single or multiple
inputs and outputs. These are related to the radio link. In this way the input
is the transmitter as it transmits into the link or signal path, and the output
is the receiver. It is at the output of the wireless link. therefore, the different
forms of single / multiple antenna links are defined as below:
1. SISO - Single Input Single Output
2. SIMO - Single Input Multiple output
3. MISO - Multiple Input Single Output
4. MIMO - Multiple Input multiple Output
SISO - Single Input Single Output –
The simplest form of radio link can be defined in MIMO terms as SISO
- Single Input Single Output. This is effectively a standard radio channel - this
transmitter operates with one antenna as does the receiver. There is no
diversity and no additional processing required.
The advantage of a SIS system is its simplicity. SISO requires no
processing in terms of the various forms of diversity that may be used.
However the SISO channel is limited in its performance. Interference and
fading will impact the system more than a MIMO system using some form
of diversity, and the channel bandwidth is limited by Shannon's law - the
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throughput being dependent upon the channel bandwidth and the signal to
noise ratio.
SIMO - Single Input Multiple Output –
The SIMO or Single Input Multiple Output version of MIMO occurs
where the transmitter has a single antenna and the receiver has multiple
antennas. This is also known as receive diversity. It is often used to enable
a receiver system that receives signals from a number of independent
sources to combat the effects of fading. It has been used for many years
with short wave listening / receiving stations to combat the effects of
ionospheric fading and interference.
SIMO has the advantage that it is relatively easy to implement
although it does have some disadvantages in that the processing is required
in the receiver. The use of SIMO may be quite acceptable in many
applications, but where the receiver is located in a mobile device such as a
cellphone handset, the levels of processing may be limited by size, cost and
battery drain.
There are two forms of SIMO that can be used:
• Switched diversity SIMO: This form of SIMO looks for the strongest
signal and switches to that antenna.
• Maximum ratio combining SIMO: This form of SIMO takes both
signals and sums them to give the a combination. In this way, the signals
from both antennas contribute to the overall signal.
MISO - Multiple Input Single Output –
MISO is also termed transmit diversity. In this case, the same data is
transmitted redundantly from the two transmitter antennas. The receiver is
then able to receive the optimum signal which it can then use to receive
extract the required data.
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The advantage of using MISO is that the multiple antennas and the
redundancy coding / processing is moved from the receiver to the
transmitter. In instances such as cell phone UEs, this can be a significant
advantage in terms of space for the antennas and reducing the level of
processing required in the receiver for the redundancy coding. This has a
positive impact on size, cost and battery life as the lower level of
processing requires less battery consumption.
MIMO - Multiple Input Multiple Output –
Where there are more than one antenna at either end of the radio
link, this is termed MIMO - Multiple Input Multiple Output. MIMO can be
used to provide improvements in both channel robustness as well as
channel throughput.
In order to be able to benefit from MIMO fully it is necessary to be
able to utilise coding on the channels to separate the data from the different
paths. This requires processing, but provides additional channel robustness
/ data throughput capacity.
There are many formats of MIMO that can be used from SISO,
through SIMO and MISO to the full MIMO systems. These are all able to
provide significant improvements of performance, but generally at the cost
of additional processing and the number of antennas used.
One of the key advantages of MIMO spatial multiplexing is the fact
that it is able to provide additional data capacity. MIMO spatial
multiplexing achieves this by utilising the multiple paths and effectively
using them as additional "channels" to carry data.
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5. Explain the 3 basic techniques used in MIMO communication.
MIMO communication takes advantage of multipath propagation in
complex radio communication environments. When this occurs, transmitted
information bounces off of walls, ceilings, etc. as it propagates to the receiving
antenna. Consequently, signals carrying the sent information are received at
varying angles in different timeframes. Multipath propagation can create
interference and due to temporal dispersion. For example, a single transmit signal
can be received multiple times at a single receiver due to multipath propagation.
In addition to a single signal being received at a single antenna multiple
times, a single antenna could transmit to multiple antennas in the same time
window, as shown below. In an antenna array, if all antennas were broadcasting
simultaneously, then all user antennas within the broadcast range could receive
the transmit signal from all transmitting antennas.
MIMO exploits the situation shown above to increase data throughput and
range. Many different MIMO approaches have been developed for a wide range
of networks and available channel states. Three basic techniques used in MIMO
communication are:
• Spatial diversity
• Spatial multiplexing
• Beamforming
These techniques are often used in combination to achieve maximum
throughput and scalability.
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Spatial Diversity –
In spatial diversity, multiple antennas separated at the ends of a
communication system (by at least 1/2 wavelength) can give the requisite
diversity gain. Transmit diversity and receiver diversity are both
categorized under the umbrella of spatial diversity:
• Transmit diversity involves sending identical data streams to each Tx
antenna. This provides redundancy in the system that reduces fading and
increases signal-to-noise ratio (SNR) at the receiver.
• Receive diversity applies the reciprocal idea at the receive end of a
channel, providing the same type of redundancy found in transmit
diversity.
Spatial Multiplexing –
Spatial multiplexing involves sending multiple spatial streams
through multiple antennas, and these streams are separated at the receiver
through spatial processing. Since the receiver decodes the transmitted
streams individually, data throughput can be increased for a fixed channel
bandwidth. MIMO spatial multiplexing has the ability to boost spectral
efficiency without significantly diminishing the link's robustness.
However, diversity gain is lost in this technique.
Beamforming -
The use of beamforming in MIMO communications involves
focusing a signal in a particular direction so that the greatest possible gain
is achieved at the receiving end. There are three beamforming techniques:
• Analog, which would be performed with a phased array
• Digital, which uses precoding with modulated data streams to construct
a beam pattern
• Hybrid, where analog and digital are combined and multiplexed
spatially/temporally
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Different beamforming methods used with spatial
multiplexing/diversity will require different signal processing
methodologies to precode and decode signals. This would need to be
implemented with a specialty chipset or an FPGA.
6. What are the advantages and disadvantages of the Massive MIMO
technology?
Advantages –
• High spectrum efficiency due to large multiplexing gain as well as
antenna array gain.
• High energy efficiency due to concentration of radiated energy on
MS/UE.
• High reliability due to large diversity gain.
• Weak inter-user interference and enhanced physical security due to
orthogonal MS channels and extremely narrower beam.
• Simple scheduling scheme.
• Robustness to individual element failure due to large number of antenna
array elements.
• Massive MIMO can be developed using low power and in-expensive
components.
• It enables large reduction in latency on air interface.
Disadvantages –
• Pilot contamination due to limited orthogonal pilot subcarriers as of
bounded coherent interval and bandwidth.
• High signal processing complexity due to utilization of large number of
antennas and multiplexing of UEs (or Mobile subscribers).
• Sensitive to beam alignment, as extremely narrower beam is used which
is sensitive to movement of MS or swaying of antenna array.
• Channel reciprocity assumption is used in TDD mode of Massive MIMO.
